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Zhang J, Niimi M, Yang D, Liang J, Xu J, Kimura T, Mathew AV, Guo Y, Fan Y, Zhu T, Song J, Ackermann R, Koike Y, Schwendeman A, Lai L, Pennathur S, Garcia-Barrio M, Fan J, Chen YE. Deficiency of Cholesteryl Ester Transfer Protein Protects Against Atherosclerosis in Rabbits. Arterioscler Thromb Vasc Biol 2017; 37:1068-1075. [PMID: 28428219 DOI: 10.1161/atvbaha.117.309114] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Accepted: 04/05/2017] [Indexed: 11/16/2022]
Abstract
OBJECTIVE CETP (cholesteryl ester transfer protein) plays an important role in lipoprotein metabolism; however, whether inhibition of CETP activity can prevent cardiovascular disease remains controversial. APPROACH AND RESULTS We generated CETP knockout (KO) rabbits by zinc finger nuclease gene editing and compared their susceptibility to cholesterol diet-induced atherosclerosis to that of wild-type (WT) rabbits. On a chow diet, KO rabbits showed higher plasma levels of high-density lipoprotein (HDL) cholesterol than WT controls, and HDL particles of KO rabbits were essentially rich in apolipoprotein AI and apolipoprotein E contents. When challenged with a cholesterol-rich diet for 18 weeks, KO rabbits not only had higher HDL cholesterol levels but also lower total cholesterol levels than WT rabbits. Analysis of plasma lipoproteins revealed that reduced plasma total cholesterol in KO rabbits was attributable to decreased apolipoprotein B-containing particles, while HDLs remained higher than that in WT rabbits. Both aortic and coronary atherosclerosis was significantly reduced in KO rabbits compared with WT rabbits. Apolipoprotein B-depleted plasma isolated from CETP KO rabbits showed significantly higher capacity for cholesterol efflux from macrophages than that from WT rabbits. Furthermore, HDLs isolated from CETP KO rabbits suppressed tumor necrosis factor-α-induced vascular cell adhesion molecule 1 and E-selectin expression in cultured endothelial cells. CONCLUSIONS These results provide evidence that genetic ablation of CETP activity protects against cholesterol diet-induced atherosclerosis in rabbits.
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Affiliation(s)
- Jifeng Zhang
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.).
| | - Manabu Niimi
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Dongshan Yang
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Jingyan Liang
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Jie Xu
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Tokuhide Kimura
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Anna V Mathew
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Yanhong Guo
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Yanbo Fan
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Tianqing Zhu
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Jun Song
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Rose Ackermann
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Yui Koike
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Anna Schwendeman
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Liangxue Lai
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Subramaniam Pennathur
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Minerva Garcia-Barrio
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.)
| | - Jianglin Fan
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.).
| | - Y Eugene Chen
- From the Center for Advanced Models for Translational Sciences and Therapeutics, Department of Internal Medicine (J.Z., D.Y., J.L., J.X., Y.G., Y.F., T.Z., J.S., Y.K., M.G.-B., Y.E.C.), Department of Internal Medicine, Nephrology (A.V.M., S.P.), University of Michigan Medical Center, Ann Arbor; Department of Molecular Pathology, Faculty of Medicine, Graduate School of Medical Sciences, University of Yamanashi, Japan (M.N., T.K., J.F.); Department of Pharmaceutical Sciences, Biointerfaces Institute, College of Pharmacy, University of Michigan (R.A., A.S.); and Key Laboratory of Regenerative Biology, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences (L.L.).
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Qiu DN, Shang Q, Sun DY, Ding WQ, Luo ZG, Chen J, Jiang WR, Huang JP, Jiang XY. Cholestyramine alters bile acid amounts and the expression of cholesterol-related genes in rabbit intestinal and hepatic tissues. J Dig Dis 2017; 18:107-114. [PMID: 28067465 DOI: 10.1111/1751-2980.12445] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 12/20/2016] [Accepted: 01/03/2017] [Indexed: 12/11/2022]
Abstract
OBJECTIVE Cholestyramine (CHO), as a bile acid sequestering exchange resin, has been widely used to treat hypercholesterolemia. The aim of this study was to explore how CHO regulated serum cholesterol amounts and bile acid levels in animal models. METHODS New Zealand White rabbits were randomly assigned to the control (given distilled water) and CHO-treated (given CHO solution 1 g/kg per day for 2 weeks) groups. To assess bile acid pool size, bile fistulas were constructed in five rabbits in each group. Serum cholesterol levels and biliary and fecal bile outputs were determined. Liver cholesterol 7α-hydroxylase ( CYP7A1 ), small heterodimer partner ( SHP ), bile salt export pump ( BSEP ), ileal bile acid-binding protein ( IBABP ) and LDL receptor ( LDL-R ) mRNA expressions were assessed by real-time polymerase chain reaction. CYP7A1 activity was also determined. RESULTS CHO treatment decreased serum cholesterol levels by 12.1%. Although CHO did not change the bile acid pool size and biliary bile acid output, it significantly increased fecal bile acid output. Interestingly, CHO also significantly increased the expression and activity of CYP7A1, as well as IBABP and LDL-R mRNA expressions, but decreased hepatic SHP and BSEP gene expressions. CONCLUSION CHO markedly alters bile acid and cholesterol amounts in rabbit intestinal and liver tissues, downregulating genes responsible for cholesterol homeostasis.
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Affiliation(s)
- Dong Ni Qiu
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Quan Shang
- GI Lab VA Medical Center, East Orange, New Jersey, USA
| | - Da Yu Sun
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Wei Qun Ding
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Zhong Guang Luo
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Jian Chen
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Wei Ru Jiang
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Jian Ping Huang
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
| | - Xiao Yun Jiang
- Department of Gastroenterology, Huashan Hospital, Fudan University, Shanghai, China
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Miyosawa K, Watanabe Y, Murakami K, Murakami T, Shibata H, Iwashita M, Yamazaki H, Yamazaki K, Ohgiya T, Shibuya K, Mizuno K, Tanabe S, Singh SA, Aikawa M. New CETP inhibitor K-312 reduces PCSK9 expression: a potential effect on LDL cholesterol metabolism. Am J Physiol Endocrinol Metab 2015; 309:E177-90. [PMID: 26015437 DOI: 10.1152/ajpendo.00528.2014] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 05/06/2015] [Indexed: 11/22/2022]
Abstract
Despite significant reduction of cardiovascular events by statin treatment, substantial residual risk persists, driving emerging needs for the development of new therapies. We identified a novel cholesteryl ester transfer protein (CETP) inhibitor, K-312, that raises HDL and lowers LDL cholesterol levels in animals. K-312 also suppresses hepatocyte expression of proprotein convertase subtilisin/kexin 9 (PCSK9), a molecule that increases LDL cholesterol. We explored the underlying mechanism for the reduction of PCSK9 expression by K-312. K-312 inhibited in vitro human plasma CETP activity (IC50; 0.06 μM). Administration of K-312 to cholesterol-fed New Zealand White rabbits for 18 wk raised HDL cholesterol, decreased LDL cholesterol, and attenuated aortic atherosclerosis. Our search for additional beneficial characteristics of this compound revealed that K-312 decreases PCSK9 expression in human primary hepatocytes and in the human hepatoma cell line HepG2. siRNA silencing of CETP in HepG2 did not compromise the suppression of PCSK9 by K-312, suggesting a mechanism independent of CETP. In HepG2 cells, K-312 treatment decreased the active forms of sterol regulatory element-binding proteins (SREBP-1 and -2) that regulate promoter activity of PCSK9. Chromatin immunoprecipitation assays demonstrated that K-312 decreased the occupancy of SREBP-1 and SREBP-2 on the sterol regulatory element of the PCSK9 promoter. PCSK9 protein levels decreased by K-312 treatment in the circulating blood of cholesterol-fed rabbits, as determined by two independent mass spectrometry approaches, including the recently developed, highly sensitive parallel reaction monitoring method. New CETP inhibitor K-312 decreases LDL cholesterol and PCSK9 levels, serving as a new therapy for dyslipidemia and cardiovascular disease.
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Affiliation(s)
- Katsutoshi Miyosawa
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Yuichiro Watanabe
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Kentaro Murakami
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Takeshi Murakami
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Haruki Shibata
- Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Masaya Iwashita
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Hiroyuki Yamazaki
- Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Koichi Yamazaki
- Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Tadaaki Ohgiya
- Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Kimiyuki Shibuya
- Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Ken Mizuno
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Sohei Tanabe
- Tokyo New Drug Research Laboratories, Kowa Company, Ltd., Tokyo, Japan
| | - Sasha A Singh
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and
| | - Masanori Aikawa
- Center for Interdisciplinary Cardiovascular Sciences, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; and
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de Souza MO, Souza E Silva L, de Brito Magalhães CL, de Figueiredo BB, Costa DC, Silva ME, Pedrosa ML. The hypocholesterolemic activity of açaí (Euterpe oleracea Mart.) is mediated by the enhanced expression of the ATP-binding cassette, subfamily G transporters 5 and 8 and low-density lipoprotein receptor genes in the rat. Nutr Res 2012; 32:976-84. [PMID: 23244543 DOI: 10.1016/j.nutres.2012.10.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 09/28/2012] [Accepted: 10/01/2012] [Indexed: 01/01/2023]
Abstract
Previous studies have demonstrated that the ingestion of açaí pulp can improve serum lipid profile in various animal models; therefore, we hypothesized that açaí pulp (Euterpe oleracea Mart.) may modulate the expression of the genes involved in cholesterol homeostasis in the liver and increase fecal excretion, thus reducing serum cholesterol. To test this hypothesis, we analyzed the expression of 7α-hydroxylase and ATP-binding cassette, subfamily G transporters (ABCG5 and ABCG8), which are genes involved with the secretion of cholesterol in the rat. We also evaluated the expression of sterol regulatory element-binding protein 2, 3-hydroxy-3-methylglutaryl CoA reductase, low-density lipoprotein receptor (LDL-R), and apolipoprotein B100, which are involved in cholesterol biosynthesis. Female Fischer rats were divided into 4 groups: the C group, which was fed a standard AIN-93 M diet; the CA group, which was fed a standard diet supplemented with 2% açaí pulp; the H group, which was fed a hypercholesterolemic diet (25% soy oil and 1% cholesterol); and the HA group, which was fed a hypercholesterolemic diet supplemented with 2% açaí pulp. At the end of the experimental period, the rats were euthanized, and their blood and livers were collected. The HA group exhibited a significant decrease in serum total cholesterol, low-density lipoprotein cholesterol, and atherogenic index and also had increased high-density lipoprotein cholesterol and cholesterol excretion in feces compared with the H group. In addition, the expression of the LDL-R, ABCG5, and ABCG8 genes was significantly increased by the presence of açaí pulp. These results suggest that açaí pulp promotes a hypocholesterolemic effect in a rat model of dietary-induced hypercholesterolemia through an increase in the expression of ATP-binding cassette, subfamily G transporters, and LDL-R genes.
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Affiliation(s)
- Melina Oliveira de Souza
- Research Center in Biological Sciences (NUPEB), Federal University of Ouro Preto, Minas Gerais, Brazil
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Ito BR, Zhang BH, Cable EE, Song X, Fujitaki JM, MacKenna DA, Wilker CE, Chi B, van Poelje PD, Linemeyer DL, Erion MD. Thyroid hormone beta receptor activation has additive cholesterol lowering activity in combination with atorvastatin in rabbits, dogs and monkeys. Br J Pharmacol 2009; 156:454-65. [PMID: 19183199 DOI: 10.1111/j.1750-3639.2009.00038.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND AND PURPOSE Thyroid hormone receptor (TR) agonists are in clinical trials for the treatment of hypercholesterolaemia. As statins are the standard of clinical care, any new therapies must have adjunctive activity, when given in combination with statins. As already known for the statins, the cholesterol lowering effect of TR activation involves increased expression of the low-density lipoprotein receptor. Using animal models, we tested whether TR activation would have additive cholesterol lowering activity in the presence of effective doses of a statin. EXPERIMENTAL APPROACH We evaluated the activity of a liver-targeted prodrug, MB07811, of a novel TH receptor beta agonist, MB07344, as monotherapy and in combination with atorvastatin in rabbits, dogs and monkeys. KEY RESULTS In rabbits, MB07344 (i.v.) decreased total plasma cholesterol (TPC) comparable to that achieved with a maximally effective dose of atorvastatin (p.o.). The addition of MB07344 to atorvastatin resulted in a further decrease in TPC. Similarly, the addition of MB07811 (p.o.) to atorvastatin treatment decreased TPC beyond the level achieved with either agent as monotherapy. In dogs and monkeys, atorvastatin and MB07811 were administered as monotherapy or in combination. Consistent with the rabbit studies, the combination treatment caused a greater decrease in TPC than either MB07811 or atorvastatin administered as monotherapy. CONCLUSIONS AND IMPLICATIONS We conclude that the effects of MB07811 and atorvastatin in lowering cholesterol are additive in animals. These results would encourage and support the demonstration of similarly improved efficacy of combination versus monotherapy with such agents in the clinic.
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Affiliation(s)
- B R Ito
- Department of Biological Sciences, Metabasis Therapeutics, Inc., La Jolla, CA, USA.
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Lee YK, Schmidt DR, Cummins CL, Choi M, Peng L, Zhang Y, Goodwin B, Hammer RE, Mangelsdorf DJ, Kliewer SA. Liver receptor homolog-1 regulates bile acid homeostasis but is not essential for feedback regulation of bile acid synthesis. Mol Endocrinol 2008; 22:1345-56. [PMID: 18323469 PMCID: PMC2409274 DOI: 10.1210/me.2007-0565] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Liver receptor homolog 1 (LRH-1), an orphan nuclear receptor, is highly expressed in liver and intestine, where it is implicated in the regulation of cholesterol, bile acid, and steroid hormone homeostasis. Among the proposed LRH-1 target genes in liver are those encoding cholesterol 7alpha-hydroxylase (CYP7A1) and sterol 12alpha-hydroxylase (CYP8B1), which catalyze key steps in bile acid synthesis. In vitro studies suggest that LRH-1 may be involved both in stimulating basal CYP7A1 and CYP8B1 transcription and in repressing their expression as part of the nuclear bile acid receptor [farnesoid X receptor (FXR)]-small heterodimer partner signaling cascade, which culminates in small heterodimer partner binding to LRH-1 to repress gene transcription. However, in vivo analysis of LRH-1 actions has been hampered by the embryonic lethality of Lrh-1 knockout mice. To overcome this obstacle, mice were generated in which Lrh-1 was selectively disrupted in either hepatocytes or intestinal epithelium. LRH-1 deficiency in either tissue changed mRNA levels of genes involved in cholesterol and bile acid homeostasis. Surprisingly, LRH-1 deficiency in hepatocytes had no significant effect on basal Cyp7a1 expression or its repression by FXR. Whereas Cyp8b1 repression by FXR was also intact in mice deficient for LRH-1 in hepatocytes, basal CYP8B1 mRNA levels were significantly decreased, and there were corresponding changes in the composition of the bile acid pool. Taken together, these data reveal a broad role for LRH-1 in regulating bile acid homeostasis but demonstrate that LRH-1 is either not involved in the feedback regulation of bile acid synthesis or is compensated for by other factors.
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Affiliation(s)
- Youn-Kyoung Lee
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041, USA
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7
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Shang Q, Pan L, Saumoy M, Chiang JYL, Tint GS, Salen G, Xu G. An overlapping binding site in the CYP7A1 promoter allows activation of FXR to override the stimulation by LXRalpha. Am J Physiol Gastrointest Liver Physiol 2007; 293:G817-23. [PMID: 17690173 DOI: 10.1152/ajpgi.00209.2007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The aim of this study was to explore why in rabbits activation of farnesoid X receptor (FXR) is dominant over activated liver X receptor-alpha (LXRalpha) in the regulation of CYP7A1. We cloned the rabbit CYP7A1 promoter and found a fetoprotein transcription factor (FTF) binding element embedded within the LXRalpha binding site (LXRE). Gel shift assays demonstrated that FTF competes with LXRalpha for binding to LXRE. Short heterodimer partner (SHP) enhances the competitive ability of FTF. Studies in HepG2 cells showed that SHP combined with FTF had more powerful effect to offset the stimulation of CYP7A1 by LXRalpha. Gel shift and chromatin immunoprecipitation assays demonstrated that SHP with FTF diminished LXRalpha binding to the CYP7A1 promoter. In vivo studies in rabbits fed cholesterol for 10 days showed that hepatic expression of SHP but not FTF rose and LXRalpha-bound LXRE decreased. We propose that the SHP/FTF heterodimer occupies LXRE via the embedded FTF binding element and blocks LXRalpha from recruiting to LXRE. Therefore, activation of FXR, which upregulates SHP expression, will eliminate the stimulatory effect of LXRalpha on the CYP7A1 promoter because increased levels of SHP combined with FTF diminish the recruitment of LXRalpha to CYP7A1 promoter.
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Affiliation(s)
- Quan Shang
- Department of Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey, USA
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8
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Gilardi F, Mitro N, Godio C, Scotti E, Caruso D, Crestani M, De Fabiani E. The pharmacological exploitation of cholesterol 7alpha-hydroxylase, the key enzyme in bile acid synthesis: from binding resins to chromatin remodelling to reduce plasma cholesterol. Pharmacol Ther 2007; 116:449-72. [PMID: 17959250 DOI: 10.1016/j.pharmthera.2007.08.003] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2007] [Accepted: 08/16/2007] [Indexed: 01/25/2023]
Abstract
Mammals dispose of cholesterol mainly through 7alpha-hydroxylated bile acids, and the enzyme catalyzing the 7alpha-hydroxylation, cholesterol 7alpha-hydroxylase (CYP7A1), has a deep impact on cholesterol homeostasis. In this review, we present the study of regulation of CYP7A1 as a good exemplification of the extraordinary contribution of molecular biology to the advancement of our understanding of metabolic pathways that has taken place in the last 2 decades. Since the cloning of the gene from different species, experimental evidence has accumulated, indicating that the enzyme is mainly regulated at the transcriptional level and that bile acids are the most important physiological inhibitors of CYP7A1 transcription. Multiple mechanisms are involved in the control of CYP7A1 transcription and a variety of transcription factors and nuclear receptors participate in sophisticated regulatory networks. A higher order of transcriptional regulation, stemming from the so-called histone code, also applies to CYP7A1, and recent findings clearly indicate that chromatin remodelling events have profound effects on its expression. CYP7A1 also acts as a sensor of signals coming from the gut, thus representing another line of defence against the toxic effects of bile acids and a downstream target of agents acting at the intestinal level. From the pharmacological point of view, bile acid binding resins were the first primitive approach targeting the negative feed-back regulation of CYP7A1 to reduce plasma cholesterol. In recent years, new drugs have been designed based on recent discoveries of the regulatory network, thus confirming the position of CYP7A1 as a focus for innovative pharmacological intervention.
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Affiliation(s)
- Federica Gilardi
- Dipartimento di Scienze Farmacologiche, Università degli Studi di Milano, Milan, Italy
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9
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Shang Q, Pan L, Saumoy M, Chiang JYL, Tint GS, Salen G, Xu G. The stimulatory effect of LXRα is blocked by SHP despite the presence of a LXRα binding site in the rabbit CYP7A1 promoter. J Lipid Res 2006; 47:997-1004. [PMID: 16489206 DOI: 10.1194/jlr.m500449-jlr200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The transcription of the cholesterol 7alpha-hydroxylase gene (CYP7A1) is greatly decreased in cholesterol-fed rabbits. To determine whether the molecular structure of the promoter is responsible for this downregulation, we cloned the rabbit CYP7A1 promoter, identified the binding sites for alpha-fetoprotein transcription factor (FTF) and liver X receptor (LXRalpha), and studied the effects of FTF, LXRalpha, and SHP on its transcription. Adding LXRalpha/retinoid X receptor together with their ligands (L/R) to the promoter/reporter construct transfected into HepG2 cells greatly increased its activity. FTF did not increase promoter activity, nor did it enhance the stimulatory effect of L/R. Mutating the FTF binding site abolished the promoter baseline activity. Increasing amounts of SHP abolished the effect of L/R, and FTF enhanced the ability of SHP to decrease promoter activity below baseline levels. Thus, downregulation of CYP7A1 in cholesterol-fed rabbits is attributable secondarily to the activation of farnesoid X receptor, which increases SHP expression to override the positive effects of LXRalpha. Although FTF is a competent factor for maintaining baseline activity, it does not further enhance and may suppress CYP7A1 transcription.
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Affiliation(s)
- Quan Shang
- Department of Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, 07103, USA
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10
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Ando H, Tsuruoka S, Yamamoto H, Takamura T, Kaneko S, Fujimura A. Regulation of cholesterol 7alpha-hydroxylase mRNA expression in C57BL/6 mice fed an atherogenic diet. Atherosclerosis 2005; 178:265-9. [PMID: 15694933 DOI: 10.1016/j.atherosclerosis.2004.09.016] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2004] [Revised: 08/31/2004] [Accepted: 09/10/2004] [Indexed: 10/26/2022]
Abstract
The nuclear receptors liver X receptor (LXR) alpha and farnesoid X receptor (FXR) are positive and negative regulators of cholesterol 7alpha-hydroxylase (CYP7A1) transcription, respectively. To clarify their roles in the regulation of CYP7A1 in mice, we investigated mRNA expression of their target genes in the livers of C57BL/6 mice fed the following five diets for 2 weeks: a standard diet, cholic acid, cholesterol, cholesterol+high fat, or an atherogenic diet (cholic acid+cholesterol+high fat). The mRNA level of ATP-binding cassette transporter (ABC) A1 gene, one of LXRalpha target genes, significantly increased on the diets containing cholic acid and/or cholesterol+high fat, but not on the diet containing cholesterol alone. On the other hand, the mRNA levels of the FXR target genes ABCB11, ABCC2, and short heterodimer partner increased only on the diet containing cholic acid with or without cholesterol+high fat. Surprisingly, cholesterol alone or cholesterol+high fat did not affect CYP7A1 mRNA level, whereas cholic acid with or without cholesterol+high fat greatly reduced the level. Thus, in the atherogenic diet-fed mice, cholic acid component is needed for the FXR activation, and FXR dominantly regulates CYP7A1 transcription.
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Affiliation(s)
- Hitoshi Ando
- Division of Clinical Pharmacology, Department of Pharmacology, Jichi Medical School, Tochigi 329-0498, Japan
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11
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Li H, Xu G, Shang Q, Pan L, Shefer S, Batta AK, Bollineni J, Tint GS, Keller BT, Salen G. Inhibition of ileal bile acid transport lowers plasma cholesterol levels by inactivating hepatic farnesoid X receptor and stimulating cholesterol 7 alpha-hydroxylase. Metabolism 2004; 53:927-32. [PMID: 15254889 DOI: 10.1016/j.metabol.2004.01.017] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
We investigated the effect of SC-435, a competitive inhibitor of ileal apical sodium-dependent bile acid cotransporter (ASBT) on ileal bile acid absorption and the hepatic nuclear receptor FXR (farnesoid X receptor), which regulates cholesterol 7 alpha-hydroxylase (CYP7A1) activity and mRNA levels. Eighteen New Zealand White (NZW) rabbits were divided into 2 groups: controls (n = 10) and fed SC-435 125 mg/kg/d for 1 week (n = 8). In rabbits treated with SC-435, fecal bile acid outputs increased by more than 8 times, reflecting substantial bile acid malabsorption. Plasma cholesterol levels decreased 26%, while bile acid pool sizes and biliary bile acid outputs did not change after treatment. CYP7A1 activity increased 64% and mRNA rose by 4 times after treatment. The expression of FXR target genes in the liver, short heterodimer partner (SHP) and bile salt export pump (BSEP), decreased 11.6 and 2.6 times, respectively, after treatment, which indicates inactivation of hepatic FXR. However, the mRNA levels of ileal bile acid binding protein (IBABP) did not change significantly, while ileal ASBT mRNA expression increased by 2.4 times after treatment. Rabbits treated with SC-435 developed ileal bile acid malabsorption, which decreased the return of bile acids (FXR ligands) to the liver to inactivate hepatic FXR, which upregulated CYP7A1 and lowered plasma cholesterol levels. Although fecal bile acid malabsorption was substantial, increased bile acid production from hepatic cholesterol kept biliary bile acid outputs intact. Thus, a new balance was reached in the liver, where increased bile acid synthesis compensated for diminished ileal bile acid absorption to maintain the circulating enterohepatic bile acid pool.
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Affiliation(s)
- Hai Li
- Department of Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, NJ, USA
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12
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Xu G, Pan LX, Li H, Shang Q, Honda A, Shefer S, Bollineni J, Matsuzaki Y, Tint GS, Salen G. Dietary cholesterol stimulates CYP7A1 in rats because farnesoid X receptor is not activated. Am J Physiol Gastrointest Liver Physiol 2004; 286:G730-5. [PMID: 14684380 DOI: 10.1152/ajpgi.00397.2003] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cholesterol feeding upregulates CYP7A1 in rats but downregulates CYP7A1 in rabbits. To clarify the mechanism responsible for the upregulation of CYP7A1 in cholesterol-fed rats, the effects of dietary cholesterol (Ch) and cholic acid (CA) on the activation of the nuclear receptors, liver X-receptor (LXR-alpha) and farsenoid X-receptor (FXR), which positively and negatively regulate CYP7A1, were investigated in rats. Studies were carried out in four groups (n = 12/group) of male Sprague-Dawley rats fed regular chow (control), 2% Ch, 2% Ch + 1% CA, and 1% CA alone for 1 wk. Changes in mRNA expression of short heterodimer partner (SHP) and bile salt export pump (BSEP), target genes for FXR, were determined to indicate FXR activation, whereas the expression of ABCA1 and lipoprotein lipase (LPL), target genes for LXR-alpha, reflected activation. CYP7A1 mRNA and activity increased twofold and 70%, respectively, in rats fed Ch alone when the bile acid pool size was stable but decreased 43 and 49%, respectively, after CA was added to the Ch diet, which expanded the bile acid pool 3.4-fold. SHP and BSEP mRNA levels did not change after feeding Ch but increased 88 and 37% in rats fed Ch + CA. This indicated that FXR was activated by the expanded bile acid pool. When Ch or Ch + CA were fed, hepatic concentrations of oxysterols, ligands for LXR-alpha increased to activate LXR-alpha, as evidenced by increased mRNA levels of ABCA1 and LPL. Feeding CA alone enlarged the bile acid pool threefold and increased the expression of both SHP and BSEP. These results suggest that LXR-alpha was activated in rats fed both Ch or Ch + CA, whereas CYP7A1 mRNA and activity were induced only in Ch-fed rats where the bile acid pool was not enlarged such that FXR was not activated. In rats fed Ch + CA, the bile acid pool expanded, which activated FXR to offset the stimulatory effects of LXR-alpha on CYP7A1.
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Affiliation(s)
- Guorong Xu
- Gastrointestinal Lab (15A Veterans Affairs Medical Center, 385 Tremont Ave., East Orange, NJ 07018-1095, USA.
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13
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Klett EL, Lu K, Kosters A, Vink E, Lee MH, Altenburg M, Shefer S, Batta AK, Yu H, Chen J, Klein R, Looije N, Oude-Elferink R, Groen AK, Maeda N, Salen G, Patel SB. A mouse model of sitosterolemia: absence of Abcg8/sterolin-2 results in failure to secrete biliary cholesterol. BMC Med 2004; 2:5. [PMID: 15040800 PMCID: PMC394351 DOI: 10.1186/1741-7015-2-5] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2003] [Accepted: 03/24/2004] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND Mutations in either of two genes comprising the STSL locus, ATP-binding cassette (ABC)-transporters ABCG5 (encoding sterolin-1) and ABCG8 (encoding sterolin-2), result in sitosterolemia, a rare autosomal recessive disorder of sterol trafficking characterized by increased plasma plant sterol levels. Based upon the genetics of sitosterolemia, ABCG5/sterolin-1 and ABCG8/sterolin-2 are hypothesized to function as obligate heterodimers. No phenotypic difference has yet been described in humans with complete defects in either ABCG5 or ABCG8. These proteins, based upon the defects in humans, are responsible for regulating dietary sterol entry and biliary sterol secretion. METHODS In order to mimic the human disease, we created, by a targeted disruption, a mouse model of sitosterolemia resulting in Abcg8/sterolin-2 deficiency alone. Homozygous knockout mice are viable and exhibit sitosterolemia. RESULTS Mice deficient in Abcg8 have significantly increased plasma and tissue plant sterol levels (sitosterol and campesterol) consistent with sitosterolemia. Interestingly, Abcg5/sterolin-1 was expressed in both liver and intestine in Abcg8/sterolin-2 deficient mice and continued to show an apical expression. Remarkably, Abcg8 deficient mice had an impaired ability to secrete cholesterol into bile, but still maintained the ability to secrete sitosterol. We also report an intermediate phenotype in the heterozygous Abcg8+/- mice that are not sitosterolemic, but have a decreased level of biliary sterol secretion relative to wild-type mice. CONCLUSION These data indicate that Abcg8/sterolin-2 is necessary for biliary sterol secretion and that loss of Abcg8/sterolin-2 has a more profound effect upon biliary cholesterol secretion than sitosterol. Since biliary sitosterol secretion is preserved, although not elevated in the sitosterolemic mice, this observation suggests that mechanisms other than by Abcg8/sterolin-2 may be responsible for its secretion into bile.
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Affiliation(s)
- Eric L Klett
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Kangmo Lu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Astrid Kosters
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Edwin Vink
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Mi-Hye Lee
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Michael Altenburg
- Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Sarah Shefer
- Department of Medicine, UMD-New Jersey Medical School, Newark, NJ 07013, USA
| | - Ashok K Batta
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ 07019, USA
| | - Hongwei Yu
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Jianliang Chen
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Richard Klein
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
| | - Norbert Looije
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Ronald Oude-Elferink
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Albert K Groen
- Department of Experimental Hepatology, AMC Liver Center, Academic Medical Center, Amsterdam 1105 BK, The Netherlands
| | - Nobuyo Maeda
- Department of Pathology, School of Medicine, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Gerald Salen
- Department of Medicine, UMD-New Jersey Medical School, Newark, NJ 07013, USA
- Research Service and Medical Service, Department of Veterans Affairs Medical Center, East Orange, NJ 07019, USA
| | - Shailendra B Patel
- Division of Endocrinology, Diabetes and Medical Genetics, Medical University of South Carolina, Charleston, SC 29403, USA
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14
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Honda A, Yoshida T, Xu G, Matsuzaki Y, Fukushima S, Tanaka N, Doy M, Shefer S, Salen G. Significance of plasma 7alpha-hydroxy-4-cholesten-3-one and 27-hydroxycholesterol concentrations as markers for hepatic bile acid synthesis in cholesterol-fed rabbits. Metabolism 2004; 53:42-8. [PMID: 14681840 DOI: 10.1016/j.metabol.2003.07.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Plasma 7alpha-hydroxy-4-cholesten-3-one has been used as an index of hepatic bile acid synthesis. The aim of the current study was to ascertain whether the level of this oxysterol reflects hepatic cholesterol 7alpha-hydroxylase activity when plasma cholesterol concentrations are markedly changed. In addition, the relationship of hepatic sterol 27-hydroxylase activity with plasma concentrations of 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid was studied. We used New Zealand white rabbits fed 2% cholesterol for 5 or 10 days and/or constructed bile fistula. Feeding cholesterol markedly increased and bile drainage reduced plasma cholesterol concentrations. Initially, in these models there was no correlation between plasma 7alpha-hydroxy-4-cholesten-3-one concentrations and hepatic cholesterol 7alpha-hydroxylase activities (r = -0.24, n = 10). Cholesterol feeding was associated with downregulated 7alpha-hydroxylase activities, while plasma 7alpha-hydroxy-4-cholesten-3-one concentrations were elevated in the presence of increased plasma cholesterol levels. However, this discrepancy was overcome and significant correlation was observed (r = 0.73, P <.05, n = 10) by expressing 7alpha-hydroxy-4-cholesten-3-one levels relative to cholesterol. In contrast, hepatic sterol 27-hydroxylase activities were not significantly correlated with plasma absolute (r = 0.23, difference not significant [NS], n = 10) nor cholesterol-related levels of 27-hydroxycholesterol (r = -0.13, NS, n = 10), or 3beta-hydroxy-5-cholestenoic acid concentrations (r = 0.30, NS, n = 10). In conclusion, plasma 7alpha-hydroxy-4-cholesten-3-one concentrations reflected hepatic cholesterol 7alpha-hydroxylase activities when the sterol levels were adjusted to plasma cholesterol concentrations in rabbits with hypercholesterolemia. The results suggest that plasma 7alpha-hydroxy-4-cholesten-3-one relative to cholesterol is a better marker for hepatic cholesterol 7alpha-hydroxylase activity than the absolute concentration when hypercholesterolemia is present. In contrast, 27-hydroxycholesterol and 3beta-hydroxy-5-cholestenoic acid levels in plasma did not reflect hepatic sterol 27-hydroxylase activities even if the levels were adjusted to plasma cholesterol concentrations.
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Affiliation(s)
- Akira Honda
- Ibaraki Prefectural Institute of Public Health, Mito, Japan
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15
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Abstract
The synthesis and excretion of bile acids comprise the major pathway of cholesterol catabolism in mammals. Synthesis provides a direct means of converting cholesterol, which is both hydrophobic and insoluble, into a water-soluble and readily excreted molecule, the bile acid. The biosynthetic steps that accomplish this transformation also confer detergent properties to the bile acid, which are exploited by the body to facilitate the secretion of cholesterol from the liver. This role in the elimination of cholesterol is counterbalanced by the ability of bile acids to solubilize dietary cholesterol and essential nutrients and to promote their delivery to the liver. The synthesis of a full complement of bile acids requires 17 enzymes. The expression of selected enzymes in the pathway is tightly regulated by nuclear hormone receptors and other transcription factors, which ensure a constant supply of bile acids in an ever changing metabolic environment. Inherited mutations that impair bile acid synthesis cause a spectrum of human disease; this ranges from liver failure in early childhood to progressive neuropathy in adults.
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Affiliation(s)
- David W Russell
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, Texas 75390-9046, USA.
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16
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Xu G, Li H, Pan LX, Shang Q, Honda A, Ananthanarayanan M, Erickson SK, Shneider BL, Shefer S, Bollineni J, Forman BM, Matsuzaki Y, Suchy FJ, Tint GS, Salen G. FXR-mediated down-regulation of CYP7A1 dominates LXRalpha in long-term cholesterol-fed NZW rabbits. J Lipid Res 2003; 44:1956-62. [PMID: 12897188 DOI: 10.1194/jlr.m300182-jlr200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We investigated how cholesterol feeding regulates cholesterol 7alpha-hydroxylase (CYP7A1) via the nuclear receptors farnesoid X receptor (FXR) and liver X receptor alpha (LXRalpha) in New Zealand white rabbits. After 1 day of 2% cholesterol feeding, when the bile acid pool size had not expanded, mRNA levels of the FXR target genes short-heterodimer partner (SHP) and sterol 12alpha-hydroxylase (CYP8B) were unchanged, indicating that FXR activation remained constant. In contrast, the mRNA levels of the LXRalpha target genes ATP binding cassette transporter A1 (ABCA1) and cholesteryl ester transfer protein (CETP) increased 5-fold and 2.3-fold, respectively, associated with significant increases in hepatic concentrations of oxysterols. Activity and mRNA levels of CYP7A1 increased 2.4 times and 2.2 times, respectively. After 10 days of cholesterol feeding, the bile acid pool size increased nearly 2-fold. SHP mRNA levels increased 4.1-fold while CYP8B declined 64%. ABCA1 mRNA rose 8-fold and CETP mRNA remained elevated. Activity and mRNA of CYP7A1 decreased 60% and 90%, respectively. Feeding cholesterol for 1 day did not enlarge the ligand pool size or change FXR activation, while LXRalpha was activated highly secondary to increased hepatic oxysterols. As a result, CYP7A1 was up-regulated. After 10 days of cholesterol feeding, the bile acid (FXR ligand) pool size increased, which activated FXR and inhibited CYP7A1 despite continued activation of LXRalpha. Thus, in rabbits, when FXR and LXRalpha are activated simultaneously, the inhibitory effect of FXR overrides the stimulatory effect of LXRalpha to suppress CYP7A1 mRNA expression.
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Affiliation(s)
- Guorong Xu
- Medical Service, Veteran's Administration Medical Center, East Orange, NJ 07018, USA.
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17
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Montoudis A, Boileau S, Simoneau L, Lafond J. Impact of an enriched-cholesterol diet on enzymatic cholesterol metabolism during rabbit gestation. Life Sci 2003; 73:1463-77. [PMID: 12850506 DOI: 10.1016/s0024-3205(03)00436-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
An appropriate cholesterol homeostasis is vital for the maintenance and the optimal fetal development. The cholesterol is essential for the synthesis of progesterone and 17beta-estradiol, hormones that actively participate to sustain gestation. However, the administration of 0.2% enriched cholesterol diet (ECD) during rabbit gestation significantly increased the cholesterol blood profile (total-cholesterol, LDL, HDL, esterified-cholesterol and free-cholesterol) of dams and offspring, and induced a reduction of the offspring weight of 15% as compared to the control group. Enzymes involved in cholesterol metabolism (ACAT, HMG-CoA-reductase and cholesterol-7alpha-hydroxylase) are greatly influenced by cholesterol profile. We hypothesized that the administration of an ECD during rabbit gestation modifies the activity of those enzymes. Female rabbits (pregnant or not) were fed with a standard diet or an ECD. At term, livers (dams and offspring) and placentas were collected and ACAT, HMG-CoA-reductase and cholesterol-7alpha-hydroxylase activities were assayed. Our results demonstrate that gestation induced a reduction of ACAT activity (48.9%) in dam's liver and, an augmentation of HMG-CoA-reductase activity (142.4%) whereas it has no effect on cholesterol-7alpha-hydroxylase activity. The administration of the ECD has no additive effect on ACAT, but significantly reduced the HMG-CoA-reductase activity and cholesterol-7alpha-hydroxylase activity as compared with the pregnant control group. In placentas the ECD supplementation has an influence for HMG-CoA-reductase activity, where a 43% increased in observed. Any ACAT activity was detected in placenta and the ECD has no influence on the cholesterol-7alpha-hydroxylase activity. Whereas their offspring's liver present a reduction of ACAT and HMG-CoA-reductase activity. Gestation associated with ECD reduces significantly the HMG-CoA-reductase activity, decreasing the cholesterol synthesis, but placenta seems to compensate this effect by increasing its HMG-CoA-reductase activity.
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Affiliation(s)
- Alain Montoudis
- Laboratoire de Physiologie materno-foetale, Université du Québec à Montréal, Montréal, Canada H3C 3P8
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18
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Chen JY, Levy-Wilson B, Goodart S, Cooper AD. Mice expressing the human CYP7A1 gene in the mouse CYP7A1 knock-out background lack induction of CYP7A1 expression by cholesterol feeding and have increased hypercholesterolemia when fed a high fat diet. J Biol Chem 2002; 277:42588-95. [PMID: 12202481 DOI: 10.1074/jbc.m205117200] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cholesterol 7alpha-hydroxylase (CYP7A1) catalyzes the rate-limiting step in the pathway responsible for the formation of the majority of bile acids. Transcription of the gene is regulated by the size of the bile acid pool and dietary and hormonal factors. The farnesoid X receptor and the liver X receptor (LXR) are responsible for regulation by bile acids and cholesterol, respectively. To study the effects of dietary cholesterol and fat upon expression of the human CYP7A1 gene, mice were generated by crossing transgenic mice carrying the human CYP7A1 gene with mice that were homozygous knock-outs (CYP7A1(-/-)). The mice (mCYP7A1(-/-)/hCYP7A1) expressed the human gene at much higher levels than did the transgenics bred in the wild-type background. A diet containing 1% cholic acid reduced the expression of the human gene in mCYP7A1(-/-)/hCYP7A1 mice to undetectable levels. Cholestyramine (5%) increased the level of expression of the human gene and the mouse gene. Thus, farnesoid X receptor-mediated regulation was preserved. A diet containing 2% cholesterol increased expression of the mouse gene in wild-type mice, but it did not affect expression of the human gene in mCYP7A1(-/-)/hCYP7A1 mice. None of the diets altered the serum cholesterol or triglyceride levels in these mice; 1% cholic acid caused a redistribution of cholesterol from the high density lipoprotein to the low density lipoprotein density in the humanized mice but not in wild-type mice. A diet containing 30% saturated fat and 2% cholesterol caused a decrease in CYP7A1 levels in mCYP7A1(-/-)/hCYP7A1 mice. The serum cholesterol levels rose in all mice fed this diet. The increase was greater in the mCYP7A1(-/-)/hCYP7A1 mice. Together, these data suggest that the lack of an LXR element in the region from -56 to -49 of the human CYP7A1 promoter may account for some of the differences in response to diets between humans and rodents.
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Affiliation(s)
- Jean Y Chen
- Research Institute, Palo Alto Medical Foundation, Palo Alto, California 94301, USA
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19
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Pullinger CR, Eng C, Salen G, Shefer S, Batta AK, Erickson SK, Verhagen A, Rivera CR, Mulvihill SJ, Malloy MJ, Kane JP. Human cholesterol 7alpha-hydroxylase (CYP7A1) deficiency has a hypercholesterolemic phenotype. J Clin Invest 2002. [PMID: 12093894 DOI: 10.1172/jci0215387] [Citation(s) in RCA: 346] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Bile acid synthesis plays a critical role in the maintenance of mammalian cholesterol homeostasis. The CYP7A1 gene encodes the enzyme cholesterol 7alpha-hydroxylase, which catalyzes the initial step in cholesterol catabolism and bile acid synthesis. We report here a new metabolic disorder presenting with hyperlipidemia caused by a homozygous deletion mutation in CYP7A1. The mutation leads to a frameshift (L413fsX414) that results in loss of the active site and enzyme function. High levels of LDL cholesterol were seen in three homozygous subjects. Analysis of a liver biopsy and stool from one of these subjects revealed double the normal hepatic cholesterol content, a markedly deficient rate of bile acid excretion, and evidence for upregulation of the alternative bile acid pathway. Two male subjects studied had hypertriglyceridemia and premature gallstone disease, and their LDL cholesterol levels were noticeably resistant to 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. One subject also had premature coronary and peripheral vascular disease. Study of the kindred, which is of English and Celtic background, revealed that individuals heterozygous for the mutation are also hyperlipidemic, indicating that this is a codominant disorder.
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Affiliation(s)
- Clive R Pullinger
- Cardiovascular Research Institute, University of California-San Francisco, San Francisco, CA 94143-0130, USA.
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20
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Pullinger CR, Eng C, Salen G, Shefer S, Batta AK, Erickson SK, Verhagen A, Rivera CR, Mulvihill SJ, Malloy MJ, Kane JP. Human cholesterol 7alpha-hydroxylase (CYP7A1) deficiency has a hypercholesterolemic phenotype. J Clin Invest 2002; 110:109-17. [PMID: 12093894 PMCID: PMC151029 DOI: 10.1172/jci15387] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Bile acid synthesis plays a critical role in the maintenance of mammalian cholesterol homeostasis. The CYP7A1 gene encodes the enzyme cholesterol 7alpha-hydroxylase, which catalyzes the initial step in cholesterol catabolism and bile acid synthesis. We report here a new metabolic disorder presenting with hyperlipidemia caused by a homozygous deletion mutation in CYP7A1. The mutation leads to a frameshift (L413fsX414) that results in loss of the active site and enzyme function. High levels of LDL cholesterol were seen in three homozygous subjects. Analysis of a liver biopsy and stool from one of these subjects revealed double the normal hepatic cholesterol content, a markedly deficient rate of bile acid excretion, and evidence for upregulation of the alternative bile acid pathway. Two male subjects studied had hypertriglyceridemia and premature gallstone disease, and their LDL cholesterol levels were noticeably resistant to 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. One subject also had premature coronary and peripheral vascular disease. Study of the kindred, which is of English and Celtic background, revealed that individuals heterozygous for the mutation are also hyperlipidemic, indicating that this is a codominant disorder.
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Affiliation(s)
- Clive R Pullinger
- Cardiovascular Research Institute, University of California-San Francisco, San Francisco, CA 94143-0130, USA.
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21
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Removal of the bile acid pool upregulates cholesterol 7α-hydroxylase by deactivating FXR in rabbits. J Lipid Res 2002. [DOI: 10.1016/s0022-2275(20)30185-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
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22
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Johnston TP, Nguyen LB, Chu WA, Shefer S. Potency of select statin drugs in a new mouse model of hyperlipidemia and atherosclerosis. Int J Pharm 2001; 229:75-86. [PMID: 11604260 DOI: 10.1016/s0378-5173(01)00834-1] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Poloxamer-407 (P-407) is a nonionic surfactant that induces atheroma formation in the aortas of C57BL/6 mice with long-term (14 weeks) administration. The objectives of the present study were to determine the mechanism(s) responsible for the induction of hypercholesterolemia as well as to determine whether this animal model may be of potential use in rank ordering the efficacy (lipid lowering) of various statin drugs. The effect of long-term (16 weeks) administration of P-407 on the catalytic activities of rate-limiting enzymes of cholesterol biosynthesis [HMG-CoA reductase (HMGR)] and catabolism [microsomal cholesterol 7alpha-hydroxylase (C7alphaH) and mitochondrial sterol 27 hydroxylase (S27H)] was assessed in C57BL/6 mice. Effects of P-407 on these enzymes were compared in mice fed an atheroma-inducing diet (high-cholesterol, supplemented with cholic acid) and animals maintained on a basal diet and injected with saline (controls) after 16 weeks. The mean value for the activities of C7alphaH in P-407-injected mice was 24.3+/-3.8 pmol min(-1) mg(-1) and was significantly (P<0.05) less than the mean value determined for sham-injected control animals (37.0+/-14.3 pmol min(-1) mg(-1)). In contrast, the mean values for the catalytic activities of S27H and HMGR did not change with P-407 administration. Neither C7alphaH nor S27H activity in mice fed the high-cholesterol diet differed from values for control animals, whereas the mean HMGR activity was drastically reduced (-94%, P<0.05). The hypercholesterolemic effect of P-407 is not due to altered cholesterol biosynthesis, but is mediated by reduced cholesterol catabolism due to decreased activity of the rate limiting enzyme (C7alphaH) in the classic bile acid synthetic pathway. Plasma triglyceride lowering resulting from the oral administration of equal doses of various statin drugs appeared, in general, to be positively correlated with their relative aqueous solubility and paralleled the efficacy of these agents to lower low-density-lipoprotein-associated cholesterol (LDL-C) in humans. The plasma triglyceride lowering effect of the five statin drugs tested produced the following rank order; pravastatin sodium (-44%)>atorvastatin calcium (-36%)>simvastatin (-33%)>lovastatin (-25%)>fluvastatin sodium (-19%). While reductions in plasma total cholesterol following administration of the statin drugs was not as profound as that observed with triglycerides, the relative rank order or trend was preserved. The percent reduction in plasma triglycerides in the present model appears to be a useful parameter with which to predict the relative reduction in plasma LDL-C expected for these agents in humans.
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Affiliation(s)
- T P Johnston
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri, Kansas City, MO 64110-2499, USA.
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23
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Xu G, Salen G, Shneider BL, Ananthanarayanan M, Shefer S, Ma L, Batta A, Nguyen LB, Lingutla JJ, Tint GS, Pcolinsky M, Suchy FJ. Cholecystectomy prevents expansion of the bile acid pool and inhibition of cholesterol 7α-hydroxylase in rabbits fed cholesterol. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)30276-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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24
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VanPatten S, Ranginani N, Shefer S, Nguyen LB, Rossetti L, Cohen DE. Impaired biliary lipid secretion in obese Zucker rats: leptin promotes hepatic cholesterol clearance. Am J Physiol Gastrointest Liver Physiol 2001; 281:G393-404. [PMID: 11447020 DOI: 10.1152/ajpgi.2001.281.2.g393] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Human obesity is associated with elevated plasma leptin levels. Obesity is also an important risk factor for cholesterol gallstones, which form as a result of cholesterol hypersecretion into bile. Because leptin levels are correlated with gallstone prevalence, we explored the effects of acute leptin administration on biliary cholesterol secretion using lean (FA/-) and obese (fa/fa) Zucker rats. Zucker (fa/fa) rats become obese and hyperleptinemic due to homozygosity for a missense mutation in the leptin receptor, which diminishes but does not completely eliminate responsiveness to leptin. Rats were infused intravenously for 12 h with saline or pharmacological doses of recombinant murine leptin (5 microg x kg(-1) x min(-1)) sufficient to elevate plasma leptin concentrations to 500 ng/ml compared with basal levels of 3 and 70 ng/ml in lean and obese rats, respectively. Obesity was associated with a marked impairment in biliary cholesterol secretion. In biles of obese compared with lean rats, bile salt hydrophobicity was decreased whereas phosphatidylcholine hydrophobicity was increased. High-dose leptin partially normalized cholesterol secretion in obese rats without altering lipid compositions, implying that both chronic effects of obesity and relative resistance to leptin contributed to impaired biliary cholesterol elimination. In lean rats, acute leptin administration increased biliary cholesterol secretion rates. Without affecting hepatic cholesterol contents, leptin downregulated hepatic activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, upregulated activities of both sterol 27-hydroxylase and cholesterol 7alpha-hydroxylase, and lowered plasma very low-density lipoprotein cholesterol concentrations. Increased biliary cholesterol secretion in the setting of decreased cholesterol biosynthesis and increased catabolism to bile salts suggests that leptin promotes elimination of plasma cholesterol.
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Affiliation(s)
- S VanPatten
- Department of Biochemistry, Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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25
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Abstract
Growth hormone (GH) has pleiotropic effects on cholesterol and lipoprotein metabolism. Pituitary GH is important for the normal regulation of hepatic LDL receptors (LDLR), for the enzymatic activity of bile acid regulatory cholesterol 7alpha-hydroxylase (C7alphaOH), and for the maintenance of resistance to dietary cholesterol. The present study aimed to determine whether GH has beneficial effects on plasma lipids and hepatic cholesterol metabolism in mice devoid of LDLR. Compared with wild-type controls, LDLR-deficient mice had approximately 250% elevated plasma total cholesterol and approximately 50% increased hepatic cholesterol levels; hepatic HMG CoA reductase activity was reduced by 70%, whereas C7alphaOH activity was increased by 40%. In LDLR mice, GH infusion reduced plasma cholesterol and triglycerides up to 40%, whereas HMG CoA reductase and C7alphaOH activities were stimulated by approximately 50% and 110% respectively. GH also stimulated HMG CoA reductase and C7alphaOH activities in control mice, whereas hepatic LDLR and plasma lipoproteins were unchanged. The effects of cholestyramine and atorvastatin on C7alphaOH in LDLR-deficient mice were potentiated by GH, and this was associated with a further reduction in plasma cholesterol. GH treatment reduces plasma cholesterol and triglycerides and stimulates C7alphaOH activity in mice devoid of LDLR, particularly in combination with resin or statin treatment. The potential of GH therapy in patients with homozygous familial hypercholesterolemia should be evaluated.
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Affiliation(s)
- M Rudling
- Metabolism Unit, Center for Metabolism and Endocrinology, Department of Medicine, Novum, Karolinska Institute at Huddinge University Hospital, S-141 86, Stockholm, Sweden.
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26
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Cheema SK, Agellon LB. The murine and human cholesterol 7alpha-hydroxylase gene promoters are differentially responsive to regulation by fatty acids mediated via peroxisome proliferator-activated receptor alpha. J Biol Chem 2000; 275:12530-6. [PMID: 10777541 DOI: 10.1074/jbc.275.17.12530] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
We determined if fatty acids can regulate the murine Cyp7a1 and human CYP7A1 gene promoters via peroxisome proliferator-activated receptor alpha (PPARalpha)/9-cis-retinoic acid receptor alpha (RXRalpha). In transfected cells, the murine Cyp7a1 gene promoter displayed markedly lower basal activity, but greater sensitivity to fatty acid- or WY 14,643-activated PPARalpha/RXRalpha when compared with the human CYP7A1 gene promoter. PPARalpha/RXRalpha can bind to a site (Site II) located within the region at nucleotides -158 to -132 of both promoters. Mutagenesis of the human CYP7A1 Site II element abolished the response to activated PPARalpha/RXRalpha. The murine Cyp7a1 gene promoter contains an additional PPARalpha/RXRalpha-binding site (Site I) located within nucleotides -72 to -57. Replacement of a single residue in human CYP7A1 Site I with that found in the murine Cyp7a1 Site I sequence enabled PPARalpha/RXRalpha binding, and this mutation resulted in reduced basal activity, but substantially improved the response to activated PPARalpha/RXRalpha in transfected cells. We conclude that fatty acids can regulate the cyp7a gene promoter via PPARalpha/RXRalpha. The differential response of the murine Cyp7a1 and human CYP7A1 gene promoters to PPARalpha activators is attributable to the additional PPARalpha/RXRalpha-binding site in the murine Cyp7a1 gene promoter.
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Affiliation(s)
- S K Cheema
- Medical Research Council Group on Molecular and Cell Biology of Lipids and the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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27
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Regulation of 25- and 27-hydroxylation side chain cleavage pathways for cholic acid biosynthesis in humans, rabbits, and mice: assay of enzyme activities by high-resolution gas chromatography–mass spectrometry. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)34483-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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28
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Ileal bile acid transport regulates bile acid pool, synthesis, and plasma cholesterol levels differently in cholesterol-fed rats and rabbits. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)32064-2] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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29
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Abstract
Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.
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Affiliation(s)
- G J Schroepfer
- Departments of Biochemistry, Rice University, Houston, Texas, USA.
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30
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Nguyen LB, Xu G, Shefer S, Tint GS, Batta A, Salen G. Comparative regulation of hepatic sterol 27-hydroxylase and cholesterol 7alpha-hydroxylase activities in the rat, guinea pig, and rabbit: effects of cholesterol and bile acids. Metabolism 1999; 48:1542-8. [PMID: 10599986 DOI: 10.1016/s0026-0495(99)90243-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The regulation of the classic and alternative bile acid synthetic pathways by key hepatic enzyme activities (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase, respectively) was examined in bile acid depletion and replacement and cholesterol-feeding experiments with rats, guinea pigs, and rabbits. The bile acid pool was depleted by creating a bile fistula (BF) and collecting bile for 2 to 5 days, and it was replaced by intraduodenal infusion of the major biliary bile acids (taurocholic acid [TCA], glycochenodeoxycholic acid [GCDCA], and glycocholic acid [GCA] in the rat, guinea pig, and rabbit, respectively) at rates equivalent to the measured hepatic flux of the bile acids. To study the effects of cholesterol, the animals were fed for 7 days on a basal diet with and without 2% cholesterol. Cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities, measured by isotope incorporation assays, were related to bile acid output and composition and hepatic cholesterol concentrations. Intraduodenal infusion of bile acids increased the output of the tested bile acids, but did not significantly change hepatic cholesterol concentrations and had no effect on sterol 27-hydroxylase activity. Neither bile acid depletion nor replacement affected sterol 27-hydroxylase activity when three different substrates (cholesterol, 5beta-cholestane-3alpha,7alpha-diol, and 5beta-cholestane-3alpha,7alpha,12alpha-triol) were tested. In contrast, feeding 2% cholesterol increased hepatic cholesterol concentrations in rats, guinea pigs, and rabbits threefold, twofold, and eightfold, respectively, and increased hepatic mitochondrial sterol 27-hydroxylase activity (conversion of cholesterol to 27-hydroxycholesterol) in all three animal models. The stimulation and feedback inhibition of cholesterol 7alpha-hydroxylase activity by bile acid depletion and replacement were observed in all three animal models, whereas the effect of cholesterol feeding was species-dependent (cholesterol 7alpha-hydroxylase activity increased in the rat, did not change in the guinea pig, and was inhibited in the rabbit). Thus, in contrast to sterol 27-hydroxylase, which was upregulated by cholesterol but not affected by bile acid depletion and replacement in all three animal models, cholesterol 7alpha-hydroxylase activity was controlled consistently and inversely by the hepatic flux of bile acids, but was species-dependent in its response to a 1-week feeding with 2% cholesterol.
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Affiliation(s)
- L B Nguyen
- Department of Medicine/Division of Gastroenterology and the Liver Center, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark 07103, USA
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31
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Cheema SK, Agellon LB. Metabolism of cholesterol is altered in the liver of C3H mice fed fats enriched with different C-18 fatty acids. J Nutr 1999; 129:1718-24. [PMID: 10460210 DOI: 10.1093/jn/129.9.1718] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
We examined whether the degree of saturation of C-18 fatty acids influenced hepatic cholesterol metabolism in C3H mice. The mice were fed diets containing 20 g/100 g fat, enriched in stearic (18:0), oleic (18:1) or linoleic acid (18:2) with or without 1 g/100 g cholesterol. Plasma total cholesterol concentration was lower in mice fed the 18:0 diet relative to those fed the 18:1- or 18:2-enriched diets (P < 0.05) regardless of dietary cholesterol supplementation. Dietary cholesterol significantly raised hepatic total cholesterol concentration (P < 0.05) in those fed the 18:1- and 18:2-enriched diets, but not in mice fed the 18:0-enriched diet. Dietary cholesterol raised biliary cholesterol concentration (P < 0. 05) in mice fed the 18:1- and 18:2-enriched diets, but not in mice fed the 18:0-enriched diet. The cholesterol saturation index was variably affected by the fat diets. Feeding diets containing cholesterol suppressed the hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity and induced acyl coenzyme A:cholesterol acyl transferase (ACAT) activity compared with feeding diets without cholesterol (P < 0.05), indicating that the liver was exposed to dietary cholesterol. Hepatic ACAT activity was lower in mice fed the 18:0-enriched diet compared with those fed the 18:1- or 18:2-enriched diets (P < 0.05). Addition of cholesterol to the 18:1 diet induced the largest increase of hepatic ACAT activity, and this was associated with the enrichment of VLDL with cholesterol. Varying the degree of saturation of C-18 fatty acids influences the metabolism and disposition of hepatic cholesterol.
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Affiliation(s)
- S K Cheema
- Lipid and Lipoprotein Research Group and Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2S2, Canada
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32
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Davis RA. Cell and molecular biology of the assembly and secretion of apolipoprotein B-containing lipoproteins by the liver. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1440:1-31. [PMID: 10477822 DOI: 10.1016/s1388-1981(99)00083-9] [Citation(s) in RCA: 145] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Triglycerides are one of the most efficient storage forms of free energy. Because of their insolubility in biological fluids, their transport between cells and tissues requires that they be assembled into lipoprotein particles. Genetic disruption of the lipoprotein assembly/secretion pathway leads to several human disorders associated with malnutrition and developmental abnormalities. In contrast, patients displaying inappropriately high rates of lipoprotein production display increased risk for the development of atherosclerotic cardiovascular disease. Insights provided by diverse experimental approaches describe an elegant biological adaptation of basic chemical interactions required to overcome the thermodynamic dilemma of producing a stable emulsion vehicle for the transport and tissue targeting of triglycerides. The mammalian lipoprotein assembly/secretion pathway shows an absolute requirement for: (1) the unique amphipathic protein: apolipoprotein B, in a form that is sufficiently large to assemble a lipoprotein particle containing a neutral lipid core; and, (2) a lipid transfer protein (microsomal triglyceride transfer protein-MTP). In the endoplasmic reticulum apolipoprotein B has two distinct metabolic fates: (1) entrance into the lipoprotein assembly pathway within the lumen of the endoplasmic reticulum; or, (2) degradation in the cytoplasm by the ubiquitin-dependent proteasome. The destiny of apolipoprotein B is determined by the relative availability of individual lipids and level of expression of MTP. The dynamically varied expression of cholesterol-7alpha-hydroxylase indirectly influences the rate of lipid biosynthesis and the assembly and secretion lipoprotein particles by the liver.
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Affiliation(s)
- R A Davis
- Mammalian Cell and Molecular Biology Laboratory, Department of Biology, The Molecular Biology Institute, San Diego State University, San Diego, CA 92182-0057, USA.
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33
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Post SM, Zoeteweij JP, Bos MH, de Wit EC, Havinga R, Kuipers F, Princen HM. Acyl-coenzyme A:cholesterol acyltransferase inhibitor, avasimibe, stimulates bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and in vivo in the rat. Hepatology 1999; 30:491-500. [PMID: 10421659 DOI: 10.1002/hep.510300230] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Acyl-coenzyme A:cholesterol acyltransferase (ACAT) inhibitors are currently in clinical development as potential lipid-lowering and antiatherosclerotic agents. We investigated the effect of avasimibe (Cl- 1011), a novel ACAT inhibitor, on bile acid synthesis and cholesterol 7alpha-hydroxylase in cultured rat hepatocytes and rats fed different diets. Avasimibe dose-dependently decreased ACAT activity in rat hepatocytes in the presence and absence of beta-migrating very low-density lipoproteins (betaVLDL) (by 93% and 75% at 10 micromol/L) and reduced intracellular storage of cholesteryl esters. Avasimibe (3 micromol/L) increased bile acid synthesis (2.9-fold) after preincubation with betaVLDL and cholesterol 7alpha-hydroxylase activity (1.7- and 2.6-fold, with or without betaVLDL), the latter paralleled by a similar induction of its messenger RNA (mRNA). Hepatocytes treated with avasimibe showed a shift from storage and secretion of cholesteryl esters to conversion of cholesterol into bile acids. In rats fed diets containing different amounts of cholesterol and cholate, avasimibe reduced plasma cholesterol (by 52% to 71%) and triglyceride levels (by 28% to 62%). Avasimibe did not further increase cholesterol 7alpha-hydroxylase activity and mRNA in cholesterol-fed rats, but prevented down-regulation by cholate. Avasimibe did not affect sterol 27-hydroxylase and oxysterol 7alpha-hydroxylase, 2 enzymes in the alternative pathway in bile acid synthesis. No increase in the ratio of biliary excreted cholesterol to bile acids was found, indicating that ACAT inhibition does not result in a more lithogenic bile. Avasimibe increases bile acid synthesis in cultured hepatocytes by enhancing the supply of free cholesterol both as substrate and inducer of cholesterol 7alpha-hydroxylase. These effects may partially explain the potent cholesterol-lowering effects of avasimibe in the rat.
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Affiliation(s)
- S M Post
- Gaubius Laboratory, TNO-PG, Leiden, The Netherlands
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34
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Charest MC, Rhainds D, Falstrault L, Matzouranis T, Brissette L. Selective uptake of cholesteryl ester from low density lipoprotein is involved in HepG2 cell cholesterol homeostasis. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 263:402-9. [PMID: 10406948 DOI: 10.1046/j.1432-1327.1999.00527.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Low density lipoprotein (LDL) can follow either a holoparticle uptake pathway, initiated by the LDL receptor (LDLr), and be completely degraded, or it can deliver its cholesteryl esters (CE) selectively to HepG2 cells. Although high density lipoprotein-CE selective uptake has been shown to be linked to cell cholesterol homeostasis in nonhepatic cells, there is no available information on the effect of LDL-CE selective uptake on hepatic cell cholesterol homeostasis. In order to define the role of the LDL-CE selective uptake pathway in hepatic cell cholesterol homeostasis, we used a cellular model that expresses constitutively a LDLr antisense mRNA and that shows LDLr activity at 31% the normal level (HepG2-all cells). The addition of a specific antibody anti-LDLr (IgG-C7) reduces LDL protein degradation (LDLr activity) to 7%. This cellular model therefore reflects, above all, LDL-CE selective uptake activity when incubated with LDL. The inactivation of LDLr reduces LDL-protein association by 78% and LDL-CE association by only 43%. The LDL-CE selective uptake was not reduced by the inactivation of LDLr. The activities of the various enzymes involved in cell cholesterol homeostasis were measured in normal and LDLr-deficient cells during incubation in the absence or presence of LDL as a cholesterol source. Essentially, 3-hydroxy-3-methylglutaryl coenzyme A reductase and acyl coenzyme A:cholesterol acyltransferase (ACAT) activities responded to LDL in LDLr-deficient cells as well as in normal HepG2 cells. Inhibition of lysosomal hydrolysis with chloroquine abolished the effect measured on ACAT activity in the presence of LDL, suggesting that CE of LDL, but not free cholesterol, maintains cell cholesterol homeostasis. Thus, in HepG2 cells, when LDLr function is virtually abolished, LDL-CE selective uptake is coupled to cell cholesterol homeostasis.
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Affiliation(s)
- M C Charest
- Département des Sciences Biologiques, Université du Québec à Montréal, Canada
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35
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Scheibner J, Fuchs M, Hörmann E, Stange EF. Complex feedback regulation of bile acid synthesis in the hamster: the role of newly synthesized cholesterol. Hepatology 1999; 30:230-7. [PMID: 10385661 DOI: 10.1002/hep.510300135] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Hepatic bile acid synthesis is regulated by recirculating bile acids, possibly by modulating the availability of newly synthesized and preformed cholesterol. Because data in the hamster on this mechanism are lacking, we fitted these animals with an extracorporeal bile duct and administered tritiated water intraperitoneally to label newly formed cholesterol. After interruption of the enterohepatic circulation, physiological and double-physiological doses of conjugated cholate (25 or 50 micromol/100 g. h) or of unconjugated deoxycholate (6 or 12 micromol) were infused intraduodenally for 54 hours and compared with controls. De novo and preformed cholesterol directly secreted into bile or used for cholate and chenodeoxycholate synthesis were quantitated by high-pressure liquid chromatography (HPLC)-liquid scintillation. Directly after depletion of the bile acid pool (6-9 hours) at nearly physiological conditions, chenodeoxycholate synthesis was significantly reduced by cholate and deoxycholate by up to 45% to 51%, whereas cholate formation decreased by approximately 22% during deoxycholate. This short-term effect was mainly mediated by reduced synthesis from preformed cholesterol. After long-term bile depletion (30-54 hours), bile acid synthesis returned to control levels during 25 micromol of cholate and of both deoxycholate doses. In contrast, only 50 micromol of cholate prevented derepression of bile acid synthesis. This long-term effect was mainly attributed to a diminished formation from de novo cholesterol exceeding the reduced synthesis from preformed cholesterol. In summary, short- and long-term regulation of bile acid synthesis in hamsters differs with respect to availabilities of preformed and de novo cholesterol.
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Affiliation(s)
- J Scheibner
- Department of Internal Medicine I, Division of Gastroenterology, Medical University of Luebeck, Luebeck, Germany
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36
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Verd JC, Peris C, Alegret M, Díaz C, Hernández G, Vázquez M, Adzet T, Laguna JC, Sánchez RM. Different effect of simvastatin and atorvastatin on key enzymes involved in VLDL synthesis and catabolism in high fat/cholesterol fed rabbits. Br J Pharmacol 1999; 127:1479-85. [PMID: 10455299 PMCID: PMC1760655 DOI: 10.1038/sj.bjp.0702668] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/1998] [Revised: 03/26/1999] [Accepted: 04/20/1999] [Indexed: 12/14/2022] Open
Abstract
The effects of atorvastatin (3 mg kg(-1)) and simvastatin (3 mg kg(-1)) on hepatic enzyme activities involved in very low density lipoprotein metabolism were studied in coconut oil/cholesterol fed rabbits. Plasma cholesterol and triglyceride levels increased 19 and 4 fold, respectively, after 7 weeks of feeding. Treatment with statins during the last 4 weeks of feeding abolished the progression of hypercholesterolaemia and reduced plasma triglyceride levels. 3-Hydroxy-3-methyl-glutaryl Coenzyme A reductase, acylcoenzyme A:cholesterol acyltransferase, phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities were not affected by drug treatment. Accordingly, hepatic free cholesterol, cholesteryl ester and triglyceride content were not modified. Simvastatin treatment caused an increase (72%) in lipoprotein lipase activity without affecting hepatic lipase activity. Atorvastatin caused a reduction in hepatic phospholipid content and a compensatory increase in CTP:phosphocholine cytidylyl transferase activity. The results presented in this study suggest that, besides the inhibitory effect on 3-hydroxy-3-methyl-glutaryl Coenzyme A reductase, simvastatin and atorvastatin may have additional effects that contribute to their triglyceride-lowering ability.
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Affiliation(s)
- J C Verd
- Unidad de Farmacología y Farmacognosia, Dept. Farmacología y Química Terapéutica, Facultad de Farmacia, Núcleo Universitario de Pedralbes, Barcelona, Spain
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37
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Brunet S, Thibault L, Delvin E, Yotov W, Bendayan M, Levy E. Dietary iron overload and induced lipid peroxidation are associated with impaired plasma lipid transport and hepatic sterol metabolism in rats. Hepatology 1999; 29:1809-17. [PMID: 10347124 DOI: 10.1002/hep.510290612] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Although hemochromatosis is characterized by dramatic morphological and functional alterations in the liver, little is known about the effects of an excess of iron on lipid metabolism. Therefore, we determined the effect of chronic iron overload on plasma lipid profile and lipoprotein composition, as well as on hepatic cholesterol metabolism and biliary sterol output. Rats administered a diet enriched with 3% iron carbonyl for 12 weeks displayed a 30-fold increase in iron (P <.0001) and a 5-fold rise in malondialdehyde (P <.001) in the liver. When compared with pair-fed controls, iron-overload rats showed a significant increase in triglycerides (P <.005), free cholesterol (P <.006), cholesteryl ester (P <.007), and high-density lipoprotein (HDL)-cholesterol (P <. 003). Triglyceride and cholesteryl ester enrichment, protein depletion, size increase, and apolipoprotein composition alterations characterized the very low density lipoprotein (VLDL) and HDL particles of iron-overload rats. Assessment of the activity of intracellular key enzymes for cholesterol homeostasis in these rats disclosed a reduction in 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase (66%, P <.005) and cholesterol 7alpha-hydroxylase (58%, P <.0004) with an increment of acyl-CoA: cholesterol acyltransferase (62%, P <.002). The lack of optimal enzymatic activity may be a result of marked membrane lipid peroxidation that brings about fluidity drop (P <.029) in microsomes of iron-overload rats (5.00 +/- 0.013) versus controls (8.20 +/- 0. 03), reflected by polarization. A decline of the pool size of cholesterol and bile acids was noted in iron-overload rats during a 6-hour bile drainage. Our results show that experimental iron overload causes marked perturbations in plasma lipid transport and hepatobiliary sterol metabolism. Given the positive correlation of malondialdehyde with most of the altered parameters, iron-catalyzed lipid peroxidation may well be one of the involved mechanisms.
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Affiliation(s)
- S Brunet
- Department of Nutrition, Hôpital Sainte-Justine, Université de Montréal, Montréal, Québec, Canada
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38
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Abstract
This article provides a review of the pathways through which cholesterol is degraded to bile acids. Regulation of key enzymes in the bile acid biosynthestic pathways is discussed. The important role of these pathways in the maintenance of cholesterol homeostasis and the possible therapeutic implications for the treatment of hypercholesterolemia are emphasized.
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Affiliation(s)
- Z R Vlahcevic
- Division of Gastroenterology, Medical College of Virginia, Virginia Commonwealth University, Richmond, USA
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Xu G, Salen G, Shefer S, Tint GS, Nguyen LB, Chen TS, Greenblatt D. Increasing dietary cholesterol induces different regulation of classic and alternative bile acid synthesis. J Clin Invest 1999; 103:89-95. [PMID: 9884338 PMCID: PMC407860 DOI: 10.1172/jci4414] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We investigated the effect of increasing dietary cholesterol on bile acid pool sizes and the regulation of the two bile acid synthetic pathways (classic, via cholesterol 7alpha-hydroxylase, and alternative, via sterol 27-hydroxylase) in New Zealand white rabbits fed 3 g cholesterol/per day for up to 15 days. Feeding cholesterol for one day increased hepatic cholesterol 75% and cholesterol 7alpha-hydroxylase activity 1.6 times without significant change of bile acid pool size or sterol 27-hydroxylase activity. After three days of cholesterol feeding, the bile acid pool size increased 83% (P < 0.01), and further feeding produced 10%-20% increments, whereas cholesterol 7alpha-hydroxylase activity declined progressively to 60% below baseline. In contrast, sterol 27-hydroxylase activity rose 58% after three days of cholesterol feeding and remained elevated with continued intake. Bile drainage depleted the bile acid pool and stimulated downregulated cholesterol 7alpha-hydroxylase activity but did not affect sterol 27-hydroxylase activity. Thus, increasing hepatic cholesterol does not directly inhibit cholesterol 7alpha-hydroxylase and initially favors enzyme induction, whereas increased bile acid pool is the most powerful inhibitor of cholesterol 7alpha-hydroxylase. Sterol 27-hydroxylase is insensitive to the bile acid flux but is upregulated by increasing hepatic cholesterol.
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Affiliation(s)
- G Xu
- Medical Service, Veterans Affairs Medical Center, East Orange, New Jersey 07018-1095, USA
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40
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Turley SD, Schwarz M, Spady DK, Dietschy JM. Gender-related differences in bile acid and sterol metabolism in outbred CD-1 mice fed low- and high-cholesterol diets. Hepatology 1998; 28:1088-94. [PMID: 9755247 DOI: 10.1002/hep.510280425] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
These studies were undertaken to determine whether in young adult outbred CD-1 mice there were any gender-related differences in basal bile acid metabolism that might be important in determining how males and females in this species responded to a dietary cholesterol challenge. When fed a plain cereal-based rodent diet without added cholesterol, 3-month-old females, compared with age-matched males, manifested a significantly larger bile acid pool (89.1 vs. 54.1 micromol/100 g body weight), a higher rate of fecal bile acid excretion (13.6 vs. 8.5 micromol/d/100 g body weight), a more efficient level of intestinal cholesterol absorption (41.1% vs. 25. 3%), and a lower rate of hepatic sterol synthesis (338 vs. 847 nmol/h/g). Similar results were found in C57BL/6 and 129Sv inbred mice. In matching groups of CD-1 mice fed a diet containing 1% cholesterol for 21 days, hepatic cholesterol levels increased much more in the females (from 2.4 to 9.1 mg/g) than in the males (from 2. 1 to 5.2 mg/g). This occurred even though the level of stimulation of cholesterol 7-hydroxylase activity in the females (79%) exceeded that in the males (55%), as did the magnitude of the increase in fecal bile acid excretion (females: 262% vs. males: 218%). However, in both sexes, bile acid pool size expanded only modestly and by a comparable degree (females: 19% vs. males: 26%) so that in the cholesterol-fed groups, the pool remained substantially larger in the females than in the males (102.3 vs. 67.6 micromol/100 g body weight). Together, these data demonstrate that while male and female CD-1 mice do not differ qualitatively in the way cholesterol feeding changes their bile acid metabolism, the inherently larger bile acid pool in the female likely facilitates the delivery of significantly more dietary cholesterol to the liver than is the case in males, thereby resulting in higher steady-state hepatic cholesterol levels.
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Affiliation(s)
- S D Turley
- Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75235-8887, USA
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41
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Regulation of classic and alternative bile acid synthesis in hypercholesterolemic rabbits: effects of cholesterol feeding and bile acid depletion. J Lipid Res 1998. [DOI: 10.1016/s0022-2275(20)32190-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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42
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Xu G, Servatius RJ, Shefer S, Tint GS, O'Brien WT, Batta AK, Salen G. Relationship between abnormal cholesterol synthesis and retarded learning in rats. Metabolism 1998; 47:878-82. [PMID: 9667239 DOI: 10.1016/s0026-0495(98)90130-5] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We examined the relationship between brain sterol composition and associative learning (classical conditioning of the eyeblink response) in newly weaned rats fed BM 15.766 (BM) for 4 months. This compound inhibits 7-dehydrocholesterol-delta7-reductase, which catalyzes the conversion of 7-dehydrocholesterol to cholesterol, the last step in the synthetic pathway. As countertreatment, half of the BM-treated rats were fed 2% cholesterol during the last 2 months. With BM, cholesterol concentrations declined 91% in plasma, but with cholesterol feeding, the levels increased 50% compared with baseline values. 7-Dehydrocholesterol, which was not detected at baseline, increased to 55% of plasma sterols with BM but decreased to 5% of total plasma sterols when cholesterol was added. With BM, brain cholesterol levels decreased 60% and did not increase after cholesterol was added. However, 7-dehydrocholesterol, which comprised 39% of brain sterols with BM, decreased to 31% (P < .05) when cholesterol was fed. Hydroxymethyl glutaryl coenzyme A (HMG-CoA) reductase activity in the liver increased 2.2-fold with BM and declined 95% after adding cholesterol, but did not change in the brain. BM treatment for 4 months prevented learning of the conditioned eyeblink response as compared with controls. In contrast, BM-treated rats supplemented with cholesterol acquired the conditioned eyeblink response. Chronic inhibition of 7-dehydrocholesterol-delta7-reductase reduced cholesterol and increased 7-dehydrocholesterol levels in plasma and brain, and was associated with impaired learning. Cholesterol feeding corrected plasma and hepatic sterol levels and reduced brain 7-dehydrocholesterol concentrations to reestablish normal learning.
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Affiliation(s)
- G Xu
- Department of Veterans Affairs Medical Center, East Orange, NJ 07018-1095, USA
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Abstract
The addition of a 7-hydroxyl group is an early and often rate-limiting step in the synthesis of bile acids. This reaction is catalysed by two cytochrome P450 enzymes known as cholesterol 7 alpha-hydroxylase and oxysterol 7 alpha-hydroxylase. cDNAs encoding these proteins have been isolated and used to define two evolutionarily conserved pathways that produce 7 alpha-hydroxylated bile acids.
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Affiliation(s)
- M Schwarz
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75235-9046, USA
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Nagao K, Sakono M, Sakurai H, Sato M, Imaizumi K. Exogenously Hypercholesterolemic Rats, Compared with Their Progenitor Sprague-Dawley Rats, Have Altered mRNAs for Cholesterol 7α-Hydroxylase and Low-Density-Lipoprotein Receptor and Activities of Cholesterol 7α-Hydroxylase and Acyl-CoA:Cholesterol Acyltransferase in the Liver in Response to Dietary Cholesterol. Comp Biochem Physiol B Biochem Mol Biol 1997. [DOI: 10.1016/s0305-0491(97)00283-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Agellon LB, Cheema SK. The 3'-untranslated region of the mouse cholesterol 7alpha-hydroxylase mRNA contains elements responsive to post-transcriptional regulation by bile acids. Biochem J 1997; 328 ( Pt 2):393-9. [PMID: 9371693 PMCID: PMC1218933 DOI: 10.1042/bj3280393] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To investigate the importance of the 3'-untranslated region (UTR) of the mouse cholesterol 7alpha-hydroxylase (cyp7) mRNA in post-transcriptional regulation of expression of the cyp7 gene, chimaeric genes encoding mRNA containing the structural sequence of chloramphenicol acetyltransferase (CAT) linked to either the 3'-UTR of the mouse cyp7 mRNA or the SV40 early gene mRNA were constructed. The human cytomegalovirus (CMV) promoter was used to drive the expression of all the chimaeric genes. Thus the transgenes had identical sequences in the promoter, the regions encoding the 5'-UTR and translated sequence but differed in the region encoding the 3'-UTR of their respective mRNA species. The transgene containing the entire cyp7 3'-UTR (designated CMV.CAT.CYP7) gave rise to CAT activity in transfected hepatoma cells that was one-quarter of that obtained in cells transfected with the transgene containing the SV40 3'-UTR (designated CMV.CAT.SV40). The 3'-UTR of the cyp7 mRNA contains sequences resembling AU-rich elements (AREs). Deleting eight of nine putative AREs from the CYP7 3'-UTR sequence increased the CAT activity to a level greater than that observed for CMV.CAT. SV40, whereas deletion of the intron region had no effect. These results show that the AREs of the 3'-UTR of the cyp7 mRNA decrease transgene expression. Bile acids are known to repress the expression of the cyp7 gene. To test whether the 3'-UTR of the cyp7 mRNA has a role in this process, the expression of the chimaeric genes was evaluated in hepatoma cells competent for bile acid uptake. Conjugated bile acids, but not unconjugated bile acids, further decreased the expression of the CMV.CAT.CYP7 transgene. The same bile acids had no effect on the expression of the CMV.CAT.SV40 transgene. Deletion of the intron from the cyp7 sequence did not alter the CAT activity compared with the parental plasmid, and also did not alter the sensitivity of the transgene to the conjugated bile acids. Deletion of the AREs from the cyp7 3'-UTR, which increased the expression of the transgene, did not abolish the sensitivity of the transgene to repression by conjugated bile acids. Thus the 3'-UTR of the mouse cyp7 mRNA also contains elements that facilitate the further repression of transgene expression in the presence of conjugated bile acids. The results indicate that the 3'-UTR of the mouse cyp7 mRNA contains information specifying regulation at the post-transcriptional level.
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Affiliation(s)
- L B Agellon
- Department of Biochemistry, and the Lipid and Lipoprotein Research Group, University of Alberta, 328 Heritage Medical Research Centre, Edmonton, Alberta T6G 2S2, Canada
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Rodrigueza WV, Mazany KD, Essenburg AD, Pape ME, Rea TJ, Bisgaier CL, Williams KJ. Large versus small unilamellar vesicles mediate reverse cholesterol transport in vivo into two distinct hepatic metabolic pools. Implications for the treatment of atherosclerosis. Arterioscler Thromb Vasc Biol 1997; 17:2132-9. [PMID: 9351382 DOI: 10.1161/01.atv.17.10.2132] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Phospholipid liposomes are synthetic mediators of "reverse" cholesterol transport from peripheral tissue to liver in vivo and can shrink atherosclerotic lesions in animals. Hepatic disposal of this cholesterol, however, has not been examined. We compared hepatic effects of large (approximately equal to 120-nm) and small (approximately equal to 35-nm) unilamellar vesicles (LUVs and SUVs), both of which mediate reverse cholesterol transport in vivo but were previously shown to be targeted to different cell types within the liver. On days 1, 3, and 5, rabbits were intravenously injected with 300 mg phosphatidylcholine (LUVs or SUVs) per kilogram body weight or with the equivalent volume of saline. After each injection, LUV- and SUV-injected animals showed large increases in plasma concentrations of unesterified cholesterol, indicating mobilization of tissue stores. After hepatic uptake of this cholesterol, however, SUV-treated animals developed persistently elevated plasma LDL concentrations, which by day 6 had increased to more than four times the values in saline-treated controls. In contrast, LUV-treated animals showed normal LDL levels. By RNase protection assay, SUVs suppressed hepatic LDL receptor mRNA at day 6 (to 61 +/- 4% of control, mean +/- SEM), whereas LUVs caused a statistically insignificant stimulation. Hepatic HMG-CoA reductase message was also significantly suppressed with SUV, but not LUV treatment, and hepatic 7 alpha-hydroxylase message showed a similar trend. These data on hepatic mRNA levels indicate that SUVs, but not LUVs, substantially perturbed liver cholesterol homeostasis. We conclude that LUVs and SUVs mobilize peripheral tissue cholesterol and deliver it to the liver, but to distinct metabolic pools that exert different regulatory effects. The effects of one of these artificial particles, SUVs, suggest that reverse cholesterol transport may not always be benign. In contrast, LUVs may be a suitable therapeutic agent, because they mobilize peripheral cholesterol to the liver without suppressing hepatic LDL receptor mRNA and without provoking a subsequent rise in plasma LDL levels.
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Affiliation(s)
- W V Rodrigueza
- Department of Biochemistry, Medical College of Pennsylvania, Philadelphia, USA
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47
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Dietary fats modulate the regulatory potential of dietary cholesterol on cholesterol 7 alpha-hydroxylase gene expression. J Lipid Res 1997. [DOI: 10.1016/s0022-2275(20)37444-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Björkhem I, Lund E, Rudling M. Coordinate regulation of cholesterol 7 alpha-hydroxylase and HMG-CoA reductase in the liver. Subcell Biochem 1997; 28:23-55. [PMID: 9090290 DOI: 10.1007/978-1-4615-5901-6_2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- I Björkhem
- Department of Clinical Chemistry, Huddinge University Hospital, Karolinska Institute, Sweden
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49
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The Regulation of Cholesterol Conversion to Bile Acids. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1569-2558(08)60347-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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50
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Xu G, Salen G, Shefer S, Ness GC, Chen TS, Zhao Z, Salen L, Tint GS. Treatment of the cholesterol biosynthetic defect in Smith-Lemli-Opitz syndrome reproduced in rats by BM 15.766. Gastroenterology 1995; 109:1301-7. [PMID: 7557099 DOI: 10.1016/0016-5085(95)90592-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
BACKGROUND & AIMS The Smith-Lemli-Opitz syndrome is a recessive inherited disorder characterized by neurological developmental defects and dysmorphic features with a defect in cholesterol synthesis at the conversion of 7-dehydrocholesterol to cholesterol. BM 15.766 inhibits 7-dehydrocholesterol-delta 7-reductase and reproduces the biochemical defect. The aim of this study was to investigate the effects of cholesterol, cholic acid, and lovastatin feeding on rats fed BM 15.766. METHODS Plasma cholesterol and 7-dehydrocholesterol concentrations were related to the hepatic 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase. RESULTS With the inhibitor treatment, plasma cholesterol concentrations decreased 67%; 7-dehydrocholesterol concentrations increased from trace to 17 mg/dL; and hepatic HMG-CoA reductase activity and messenger RNA levels were stimulated 74% and two times, respectively. In inhibitor-treated rats, feeding cholesterol increased plasma cholesterol concentrations 3.7 times, decreased 7-dehydrocholesterol concentrations 88%, and reduced elevated HMG-CoA reductase activity and messenger RNA levels 74% and 49%. Feeding cholic acid increased plasma cholesterol without reducing 7-dehydrocholesterol concentrations. The combination of cholic acid and cholesterol enhanced plasma cholesterol 9.5 times without decreasing 7-dehydrocholesterol levels. Feeding lovastatin depressed plasma cholesterol further without reducing 7-dehydrocholesterol levels. CONCLUSIONS Cholesterol is essential to correct abnormal cholesterol synthesis induced by BM 15.766 in rats by expanding the pool and inhibiting HMG-CoA reductase. Neither cholic acid nor lovastatin are effective separately, but cholic acid plus cholesterol may offer some additional benefit.
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Affiliation(s)
- G Xu
- Department of Veterans Affairs Medical Center, East Orange, New Jersey, USA
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