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Ooi EMM, Watts GF, Ji J, Rye KA, Johnson AG, Chan DC, Barrett PHR. Plasma phospholipid transfer protein activity, a determinant of HDL kinetics in vivo. Clin Endocrinol (Oxf) 2006; 65:752-9. [PMID: 17121526 DOI: 10.1111/j.1365-2265.2006.02662.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Phospholipid transfer protein (PLTP) is an important regulator in the transport of surface components of triglyceride-rich lipoprotein (TRL) to high density lipoprotein (HDL) during lipolysis and may therefore play an important role in regulating HDL transport. In this study we investigated the relationship of plasma PLTP activity with HDL metabolism in men. DESIGN AND METHODS The kinetics of HDL LpA-I and LpA-I:A-II were measured using intravenous administration of [D3]-leucine, gas chromatography-mass spectrometry (GCMS) and a new multicompartmental model for HDL subpopulation kinetics (SAAM II) in 31 men with wide-ranging body mass index (BMI 18-46 kg/m2). Plasma PLTP activity was determined as the transfer of radiolabelled phosphatidylcholine from small unilamellar phosphatidylcholine vesicles to ultracentrifugally isolated HDL. RESULTS PLTP activity was inversely associated with LpA-I concentration and production rate (PR) after adjusting for insulin resistance (P < 0.05). No significant associations were observed between plasma PLTP activity and LpA-I fractional catabolic rate (FCR). In multivariate analysis, including homeostasis model assessment score (HOMA), triglyceride, cholesteryl ester transfer protein (CETP) activity and PLTP activity, PLTP activity was the only significant determinant of LpA-I concentration and PR (P = 0.020 and P = 0.016, respectively). CONCLUSIONS Plasma PLTP activity may be a significant, independent determinant of LpA-I kinetics in men, and may contribute to the maintenance of the plasma concentration of these lipoprotein particles in setting of hypercatabolism of HDL.
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Affiliation(s)
- Esther M M Ooi
- Metabolic Research Centre, School of Medicine and Pharmacology, Royal Perth Hospital, University of Western Australia, WA, Australia
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52
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Kontush A, Chapman MJ. Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis. Pharmacol Rev 2006; 58:342-74. [PMID: 16968945 DOI: 10.1124/pr.58.3.1] [Citation(s) in RCA: 533] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.
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Affiliation(s)
- Anatol Kontush
- Dyslipoproteinemia and Atherosclerosis Research Unit, National Institute for Health and Medical Research, Hôpital de la Pitié, 83 boulevard de l'Hôpital, 75651 Paris Cedex 13, France.
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Carter CJ. Convergence of genes implicated in Alzheimer's disease on the cerebral cholesterol shuttle: APP, cholesterol, lipoproteins, and atherosclerosis. Neurochem Int 2006; 50:12-38. [PMID: 16973241 DOI: 10.1016/j.neuint.2006.07.007] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2006] [Revised: 06/30/2006] [Accepted: 07/11/2006] [Indexed: 11/24/2022]
Abstract
Polymorphic genes associated with Alzheimer's disease (see ) delineate a clearly defined pathway related to cerebral and peripheral cholesterol and lipoprotein homoeostasis. They include all of the key components of a glia/neurone cholesterol shuttle including cholesterol binding lipoproteins APOA1, APOA4, APOC1, APOC2, APOC3, APOD, APOE and LPA, cholesterol transporters ABCA1, ABCA2, lipoprotein receptors LDLR, LRP1, LRP8 and VLDLR, and the cholesterol metabolising enzymes CYP46A1 and CH25H, whose oxysterol products activate the liver X receptor NR1H2 and are metabolised to esters by SOAT1. LIPA metabolises cholesterol esters, which are transported by the cholesteryl ester transport protein CETP. The transcription factor SREBF1 controls the expression of most enzymes of cholesterol synthesis. APP is involved in this shuttle as it metabolises cholesterol to 7-betahydroxycholesterol, a substrate of SOAT1 and HSD11B1, binds to APOE and is tethered to LRP1 via APPB1, APBB2 and APBB3 at the cytoplasmic domain and via LRPAP1 at the extracellular domain. APP cleavage products are also able to prevent cholesterol binding to APOE. BACE cleaves both APP and LRP1. Gamma-secretase (PSEN1, PSEN2, NCSTN) cleaves LRP1 and LRP8 as well as APP and their degradation products control transcription factor TFCP2, which regulates thymidylate synthase (TS) and GSK3B expression. GSK3B is known to phosphorylate the microtubule protein tau (MAPT). Dysfunction of this cascade, carved out by genes implicated in Alzheimer's disease, may play a major role in its pathology. Many other genes associated with Alzheimer's disease affect cholesterol or lipoprotein function and/or have also been implicated in atherosclerosis, a feature of Alzheimer's disease, and this duality may well explain the close links between vascular and cerebral pathology in Alzheimer's disease. The definition of many of these genes as risk factors is highly contested. However, when polymorphic susceptibility genes belong to the same signaling pathway, the risk associated with multigenic disease is better related to the integrated effects of multiple polymorphisms of genes within the same pathway than to variants in any single gene [Wu, X., Gu, J., Grossman, H.B., Amos, C.I., Etzel, C., Huang, M., Zhang, Q., Millikan, R.E., Lerner, S., Dinney, C.P., Spitz, M.R., 2006. Bladder cancer predisposition: a multigenic approach to DNA-repair and cell-cycle-control genes. Am. J. Hum. Genet. 78, 464-479.]. Thus, the fact that Alzheimer's disease susceptibility genes converge on a clearly defined signaling network has important implications for genetic association studies.
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Lie J, Moerland M, van Gent T, van Haperen R, Scheek L, Sadeghi-Niaraki F, de Crom R, van Tol A. Sex differences in atherosclerosis in mice with elevated phospholipid transfer protein activity are related to decreased plasma high density lipoproteins and not to increased production of triglycerides. Biochim Biophys Acta Mol Cell Biol Lipids 2006; 1761:1070-7. [PMID: 16935026 DOI: 10.1016/j.bbalip.2006.06.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2006] [Revised: 06/14/2006] [Accepted: 06/27/2006] [Indexed: 10/24/2022]
Abstract
Plasma phospholipid transfer protein (PLTP) has atherogenic properties in genetically modified mice. PLTP stimulates hepatic triglyceride secretion and reduces plasma levels of high density lipoproteins (HDL). The present study was performed to relate the increased atherosclerosis in PLTP transgenic mice to one of these atherogenic effects. A humanized mouse model was used which had decreased LDL receptor expression and was transgenic for human cholesterylester transfer protein (CETP) in order to obtain a better resemblance to the plasma lipoprotein profile present in humans. It is well known that female mice are more susceptible to atherosclerosis than male mice. Therefore, we compared male and female mice expressing human PLTP. The animals were fed an atherogenic diet and the effects on plasma lipids and lipoproteins, triglyceride secretion and the development of atherosclerosis were measured. The development of atherosclerosis was sex-dependent. This effect was stronger in PLTP transgenic mice, while PLTP activity levels were virtually identical. Also, the rates of hepatic secretion of triglycerides were similar. In contrast, plasma levels of HDL were about 2-fold lower in female mice than in male mice after feeding an atherogenic diet. We conclude that increased atherosclerosis caused by overexpression of PLTP is related to a decrease in HDL, rather than to elevated hepatic secretion of triglycerides.
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Affiliation(s)
- Jessica Lie
- Department of Biochemistry, Erasmus University Medical Center, Rotterdam, The Netherlands.
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55
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Norata GD, Pirillo A, Catapano AL. Modified HDL: biological and physiopathological consequences. Nutr Metab Cardiovasc Dis 2006; 16:371-386. [PMID: 16829346 DOI: 10.1016/j.numecd.2006.01.012] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Accepted: 01/03/2006] [Indexed: 01/26/2023]
Abstract
Epidemiological and clinical studies have demonstrated the inverse association between HDL cholesterol levels (HDL-C) and the risk of coronary heart disease (CHD). This correlation is believed to relate to the ability of HDL to promote reverse cholesterol transport. Remodeling of HDL due to chemical/physical modifications can dramatically affect its functions, leading to dysfunctional HDL that could promote atherogenesis. HDL modification can be achieved by different means: (i) non-enzymatic modifications, owing to the presence of free metal ions in the atherosclerotic plaques; (ii) cell-associated enzymes, which can degrade the apoproteins without significant changes in the lipid moiety, or can alternatively induce apoprotein cross-linking and lipid oxidation; (iii) association with acute phase proteins, whose circulating levels are significantly increased during inflammation which may modify HDL structure and functions; and (iv) metabolic modifications, such as glycation that occurs under hyperglycaemic conditions. Available data suggest that HDL can easily be modified losing their anti-atherogenic activities. These observation results mainly from in vitro studies, while few in vivo data, are available. Furthermore the in vivo mechanisms involved in HDL modification are ill understood. A better knowledge of these pathways may provide possible therapeutic target aimed at reducing HDL modification.
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Dallinga-Thie GM, van Tol A, Hattori H, Rensen PCN, Sijbrands EJG. Plasma phospholipid transfer protein activity is decreased in type 2 diabetes during treatment with atorvastatin: a role for apolipoprotein E? Diabetes 2006; 55:1491-6. [PMID: 16644710 DOI: 10.2337/db05-1685] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Plasma phospholipid transfer protein (PLTP) plays an important role in lipoprotein metabolism. PLTP activity is elevated in patients with diabetes, a condition with strongly elevated risk for coronary heart disease. The aim of this study was to test the hypothesis that statins reduce PLTP activity and to examine the potential role of apolipoprotein E (apoE). PLTP activity and apoE were measured in patients with type 2 diabetes from the DALI (Diabetes Atorvastatin Lipid Intervention) Study, a 30-week randomized double-blind placebo-controlled trial with atorvastatin (10 and 80 mg daily). At baseline, PLTP activity was positively correlated with waist circumference, HbA(1c), glucose, and apoE (all P < 0.05). Atorvastatin treatment resulted in decreased PLTP activity (10 mg atorvastatin: -8.3%, P < 0.05; 80 mg atorvastatin: -12.1%, P < 0.002). Plasma apoE decreased by 28 and 36%, respectively (P < 0.001). The decrease in apoE was strongly related to the decrease in PLTP activity (r = 0.565, P < 0.001). The change in apoE remained the sole determinant of the change in PLTP activity in a multivariate model. The activity of PLTP in type 2 diabetes is decreased by atorvastatin. The association between the decrease in PLTP activity and apoE during statin treatment supports the hypothesis that apoE may prevent PLTP inactivation.
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Affiliation(s)
- Geesje M Dallinga-Thie
- Department of Internal Medicine, Vascular and Metabolic Diseases, Bd 277, Erasmus Medical Center, Dr Molewaterplein 40, 3000 CA Rotterdam, Netherlands.
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de Vries R, Dallinga-Thie GM, Smit AJ, Wolffenbuttel BHR, van Tol A, Dullaart RPF. Elevated plasma phospholipid transfer protein activity is a determinant of carotid intima-media thickness in type 2 diabetes mellitus. Diabetologia 2006; 49:398-404. [PMID: 16374627 DOI: 10.1007/s00125-005-0088-0] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2005] [Accepted: 09/12/2005] [Indexed: 11/27/2022]
Abstract
AIM/HYPOTHESIS The plasma activity of phospholipid transfer protein (PLTP), which has putative pro- and anti-atherogenic roles in lipoprotein metabolism, is increased in type 2 diabetes mellitus. We analysed the relationship between carotid artery intima-media thickness (IMT), an established marker of atherosclerosis, and PLTP activity in diabetic patients and control subjects. METHODS The IMT (mean of three segments in both carotid arteries by ultrasonography), clinical variables, plasma PLTP activity (phospholipid vesicle-HDL system), lipoproteins, C-reactive protein and insulin were measured in 87 non-smoking men and women, who had type 2 diabetes mellitus, no cardiovascular disease, and were not on insulin or lipid-lowering medication, and in 83 age-matched control subjects. RESULTS In diabetic patients, carotid IMT (p=0.02), pulse pressure (p=0.003), plasma PLTP activity (p<0.001), triglycerides (p=0.01), C-reactive protein (p<0.01) and insulin (p<0.001) were higher, whereas HDL cholesterol was lower (p<0.001) than in control subjects. Multiple stepwise linear regression analysis demonstrated that in type 2 diabetic patients IMT was independently associated with age (p<0.001), sex (p=0.001), pulse pressure (p=0.003), plasma PLTP activity (p=0.03) and HDL cholesterol (p=0.03), but not with very low density lipoprotein+LDL cholesterol, triglycerides, C-reactive protein and insulin (all p>0.20). The relationship between plasma PLTP activity and IMT was not significant in control subjects. CONCLUSIONS/INTERPRETATION Plasma PLTP activity is a positive determinant of IMT in type 2 diabetes mellitus, suggesting that high PLTP activity is involved in accelerated atherosclerosis in this disease.
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Affiliation(s)
- R de Vries
- Department of Endocrinology, University Medical Center Groningen, University of Groningen, P.O. Box 30.001, RB 9700 Groningen, The Netherlands.
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Hannuksela ML, Rämet ME, Nissinen AET, Liisanantti MK, Savolainen MJ. Effects of ethanol on lipids and atherosclerosis. ACTA ACUST UNITED AC 2005; 10:93-103. [PMID: 15006415 DOI: 10.1016/j.pathophys.2003.10.009] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2003] [Accepted: 10/03/2003] [Indexed: 10/26/2022]
Abstract
Moderate alcohol consumption is associated with an increase in plasma high density lipoprotein (HDL) cholesterol concentration and a decrease in low density lipoprotein (LDL) cholesterol concentration. Changes in the concentration and composition of lipoproteins are estimated to account for more than half of alcohol's protective effect for coronary heart disease. Alcohol intake also affects plasma proteins involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, and phospholipases. In addition, alcohol intake may result in acetaldehyde modification of apolipoproteins. Furthermore, "abnormal" lipids, phosphatidylethanol and fatty acid ethyl esters are formed in the presence of ethanol and are associated with lipoproteins in plasma. Ethanol and ethanol-induced modifications of lipids may modulate the effects of lipoproteins on the cells in the arterial wall. The molecular mechanisms involved in these processes are complex, requiring further study to better understand the specific effects of ethanol in the pathogenesis of atherosclerosis. This review discusses the effects of ethanol on lipoproteins and lipoprotein metabolism, as well as the novel effects of lipoproteins on vascular wall cells.
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Affiliation(s)
- Minna L Hannuksela
- Department of Internal Medicine and Biocenter Oulu, University of Oulu, P.O. Box 5000, FIN-90014 Oulu, Finland
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59
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Ishihara M, Kujiraoka T, Iwasaki T, Nagano M, Takano M, Ishii J, Tsuji M, Ide H, Miller IP, Miller NE, Hattori H. A sandwich enzyme-linked immunosorbent assay for human plasma apolipoprotein A-V concentration. J Lipid Res 2005; 46:2015-22. [PMID: 15961791 DOI: 10.1194/jlr.d500018-jlr200] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Apolipoprotein A-V (apoA-V) is a recently discovered apolipoprotein that appears to have a role in plasma triglyceride (TG) transport. We have developed an ELISA for apoA-V using monoclonal antibodies that has a lower limit of detection of 0.3 ng/ml and linearity up to 20 ng/ml. The ELISA was then used to quantify plasma apoA-V in 196 healthy subjects and 106 patients with insulin-resistant diabetes mellitus. In the healthy subjects, total apoA-V concentration was 179.2 +/- 74.8 ng/ml, and it was greater in females than in males (P < 0.005). It was correlated positively with the plasma HDL cholesterol (r = 0.32, P < 0.0001), apoA-I (r = 0.27, P = 0.0001), and apoE (r = 0.18, P = 0.011) concentrations and negatively with plasma TG concentration (r = -0.22, P = 0.021). In relation to single nucleotide polymorphism 3 (-1131C/T) of the apoA-V gene, apoA-V concentration was higher in the T/T type than in the C/C type (P < 0.01). Plasma TG concentration was lower in the T/T type than in the C/C or C/T type (P < 0.05). ApoA-V concentration was lower in the diabetic patients (69.4 +/- 44.3 ng/ml; P < 0.01) than in the healthy controls.
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Affiliation(s)
- Mitsuaki Ishihara
- Department of Advanced Medical Technology and Development, BML, Inc., Saitama, Japan
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Bossé Y, Bouchard L, Després JP, Bouchard C, Pérusse L, Vohl MC. Haplotypes in the phospholipid transfer protein gene are associated with obesity-related phenotypes: the Québec Family Study. Int J Obes (Lond) 2005; 29:1338-45. [PMID: 15953936 DOI: 10.1038/sj.ijo.0803010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND The phospholipid transfer protein (PLTP) may play a role in body fat regulation. OBJECTIVE To investigate the association between PLTP genetic variants and obesity-related phenotypes. METHODS Two intronic variants, one in intron 1 (c.-87G>A) and the other in intron 12 (c.1175+68T>G), were genotyped in 811 participants of the Québec Family Study. Nine obesity-related phenotypes were investigated, including body mass index (BMI), obesity (BMI> or =30 kg/m(2)), and waist circumference, percentage of fat, fat mass and fat-free mass measured by hydrostatic weighing as well as total, visceral and subcutaneous abdominal adipose tissue areas assessed by computed tomography. Single markers and haplotypes were tested for associations in family-based designs using the FBAT program. RESULTS The SNP located in intron 1 showed significant associations with obesity, BMI, waist circumference and fat-free mass (P<0.05). The low-frequency allele (A allele) was associated with higher trait values, suggesting that the transmission of this allele is associated with an increased risk of being obese. Significant associations were observed between haplotypes and obesity, waist circumference, percentage of fat and fat-free mass (P<0.05). The transmission of the AT haplotype (frequency=0.180) was positively associated with obesity-related phenotypes. After sequencing the promoter and the coding regions of the PLTP gene, we were unable to identify a mutation that could replicate these results. CONCLUSION Intronic variants of the PLTP gene are significantly associated with obesity-related phenotypes. Considering the number and the relevance of candidate genes surrounding the PLTP locus and the absence of missense polymorphisms in the coding region, the associations could be mediated by a second gene allele in linkage disequilibrium with the marker locus.
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Affiliation(s)
- Y Bossé
- Lipid Research Center, CHUL Research Center, Laval University, Québec, Canada
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61
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Oomen PHN, van Tol A, Hattori H, Smit AJ, Scheek LM, Dullaart RPF. Human plasma phospholipid transfer protein activity is decreased by acute hyperglycaemia: studies without and with hyperinsulinaemia in Type 1 diabetes mellitus. Diabet Med 2005; 22:768-74. [PMID: 15910630 DOI: 10.1111/j.1464-5491.2005.01521.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIMS Little is known about the regulation of phospholipid transfer protein (PLTP), that plays a key role in lipoprotein metabolism. PLTP secretion may be up-regulated by glucose in vitro, whereas plasma PLTP activity is decreased by exogenous hyperinsulinaemia and glucose-induced hyperinsulinaemia in vivo. In the present study, we evaluated the separate effects of hyperglycaemia and hyperinsulinaemia in C-peptide-negative Type 1 diabetic patients. METHODS The protocol was carried out in 16 patients (eight females). In each individual, plasma PLTP mass and activity (measured by enzyme-linked immuno-sorbent assay and liposome-high density lipoprotein system, respectively) as well as plasma cholesteryl ester transfer protein (CETP) activity, lipids and apolipoprotein levels were determined at the end of four different glucose clamps, each lasting 210 min: standard insulin (30 mU/kg/h) and standard glucose (glucose 5.0 mmol/l) (SI-SG), standard insulin and high glucose (glucose 12 mmol/l) (SI-HG), high insulin (150 mU/kg/h) and standard glucose (HI-SG), and high insulin and high glucose (HI-HG). RESULTS Plasma lipids and (apo)lipoproteins, measured at the end of the SI-HG, HI-SG and HI-HG clamps, were not significantly different compared with the levels obtained at the end of the SI-SG clamp. Median plasma PLTP mass and activity at the end of the SI-SG clamp were 12.8 mg/l and 13.2 micromol/ml/h, respectively. Median plasma PLTP mass decreased by 9.1% at the end of the HI-HG clamp (P < 0.01), whereas the changes at the end of the SI-HG and HI-SG clamps were not significant. Median plasma PLTP activity decreased by 5.7, 4.6 and 8.6% at the end of the SI-HG, HI-SG and HI-HG clamps, respectively (all P < 0.05). Median plasma CETP activity was 177 nmol/ml/h at the end of the SI-SG clamp, and decreased by 4.9% (P < 0.05) and by 8.3% (P < 0.05) at the end of the HI-SG and the HI-HG clamps, respectively. Plasma CETP activity did not change significantly at the end of the SI-HG clamp. CONCLUSIONS The present study demonstrates that plasma PLTP activity is independently decreased by acute hyperglycaemia and hyperinsulinaemia in humans in vivo. These data do not support a direct role of short-term hyperglycaemia in up-regulating plasma PLTP levels.
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Affiliation(s)
- P H N Oomen
- Department of Endocrinology, University Hospital Groningen, Groningen, The Netherlands.
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62
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Schnabl M, Daum G, Pichler H. Multiple lipid transport pathways to the plasma membrane in yeast. Biochim Biophys Acta Mol Cell Biol Lipids 2005; 1687:130-40. [PMID: 15708361 DOI: 10.1016/j.bbalip.2004.11.016] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Revised: 11/18/2004] [Accepted: 11/19/2004] [Indexed: 11/24/2022]
Abstract
The plasma membrane of the yeast Saccharomyces cerevisiae is devoid of lipid-synthesizing enzymes, but contains all classes of bilayer-forming lipids. As the lipid composition of the plasma membrane does not match any of the intracellular membranes, specific trafficking of lipids from internal membranes, especially the endoplasmic reticulum and the Golgi, to the cell periphery is required. Although the secretory pathway is an obvious route to translocate glycerophospholipids, sphingolipids and sterols to the plasma membrane, experimental evidence for the role of this pathway in lipid transport is rare. Addressing this issue in a systematic way, we labeled temperature-sensitive secretory yeast mutants (sec mutants) with appropriate lipid precursors, isolated the plasma membranes at high purity and quantified labeled lipids of this compartment. Shifting sec mutants to the restrictive temperature reduced transport of both proteins and lipids to the plasma membrane, indicating that the latter compounds are also trafficked to the cell periphery through the protein secretory pathway. However, efficient sec blocks did not abrogate protein and lipid transport, suggesting that parallel pathway(s) for the translocation of membrane components to the plasma membrane of yeast must exist.
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Affiliation(s)
- Martina Schnabl
- Institute of Biochemistry, Graz University of Technology, Graz, Austria
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63
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Dullaart RPF, De Vries R, Scheek L, Borggreve SE, Van Gent T, Dallinga-Thie GM, Ito M, Nagano M, Sluiter WJ, Hattori H, Van Tol A. Type 2 diabetes mellitus is associated with differential effects on plasma cholesteryl ester transfer protein and phospholipid transfer protein activities and concentrations. Scandinavian Journal of Clinical and Laboratory Investigation 2005; 64:205-15. [PMID: 15222630 DOI: 10.1080/00365510410005721] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
BACKGROUND Human plasma contains two lipid transfer proteins, cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), which are crucial in reverse cholesterol transport. METHODS Plasma CETP and PLTP activity levels and concentrations in 16 type 2 diabetic patients and 16 matched healthy subjects were determined, and these data were correlated to clinical variables, including insulin sensitivity and lipid levels. RESULTS Plasma triglycerides were higher (p<0.02) and high-density lipoprotein (HDL) cholesterol (p<0.02) was lower in diabetic patients. Plasma CETP activity and concentrations were not significantly different between diabetic and healthy subjects, but CETP specific activity was lower in diabetic patients (p<0.001). Multiple regression analysis showed that plasma CETP activity was positively related to CETP concentration (p=0.0001) and negatively to the diabetic state (p<0.002) or to HbA1c (p<0.02). PLTP activity (p<0.05) and specific activity were higher (p<0.05), whereas there was no difference in PLTP concentration between the two groups. There was no significant bivariate correlation between PLTP concentration and activity, in either healthy or diabetic subjects. Multiple regression analysis did disclose positive relationships of PLTP activity with PLTP concentration (p=0.0001), plasma triglycerides (p=0.0001) and waist/hip ratio (p=0.0001), but not with the diabetic state or HbA1c. CONCLUSIONS Neither CETP nor PLTP activity was independently associated with insulin sensitivity. Specific CETP activity is decreased in type 2 diabetes mellitus. In contrast, specific PLTP activity is higher in diabetes, as a result of the association of plasma PLTP activity with plasma triglycerides and obesity. Measurement of both plasma lipid transfer protein activity and mass levels may thus provide extra information in diabetes mellitus.
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Affiliation(s)
- R P F Dullaart
- Department of Endocrinology, State University Hospital, Groningen, The Netherlands.
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Dorfman SE, Wang S, Vega-López S, Jauhiainen M, Lichtenstein AH. Dietary fatty acids and cholesterol differentially modulate HDL cholesterol metabolism in Golden-Syrian hamsters. J Nutr 2005; 135:492-8. [PMID: 15735083 DOI: 10.1093/jn/135.3.492] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Dietary fatty acids alter HDL cholesterol concentrations, presumably through mechanisms related to reverse cholesterol transport. The effect of dietary fats (coconut oil, butter, traditional stick margarine, soybean oil, canola oil) differing in fatty acid profile on this antiatherogenic process was assessed with respect to plasma lipids; exogenous and endogenous lecithin-cholesterol acyltransferase (LCAT), cholesterol ester transfer protein (CETP), phospholipid transfer protein (PLTP) activities; and LCAT, apolipoprotein (apo) A-I and scavenger receptor B class-1 (SR-B1) mRNA abundance. Golden-Syrian hamsters were fed a nonpurified (6.25 g/100 g fat) diet containing an additional 10 g/100 g experimental fat and 0.1 g/100 g cholesterol for 6 wk. Canola and soybean oils significantly lowered serum HDL cholesterol concentrations relative to butter. Canola oil, relative to butter, resulted in higher exogenous LCAT activity, and both soybean and canola oils significantly increased hepatic apo A-I and SR-B1 mRNA abundance. Butter, relative to margarine, coconut and soybean oils, significantly increased serum non-HDL cholesterol concentrations. Endogenous and exogenous LCAT, CETP, and PLTP activities did not differ in hamsters fed margarine or saturated fat diets, despite lower hepatic LCAT, apo A-I, and SR-B1 mRNA abundance, suggesting that changes in available substrate and/or modification to the LCAT protein may have been involved in lipoprotein changes. These results suggest that lower HDL cholesterol concentrations, as a result of canola and soybean oil feeding, may not be detrimental due to increases in components involved in the reverse cholesterol transport process in these hamsters and may retard the progression of atherosclerosis.
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Affiliation(s)
- Suzanne E Dorfman
- Cardiovascular Nutrition Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111-1524, USA
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65
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Abstract
PURPOSE OF REVIEW Large-scale clinical trials have failed to demonstrate a benefit for vitamin E supplementation in cardiovascular prevention. This contrasts with previous epidemiological studies indicating that individuals with high vitamin E status benefit from protection against chronic illnesses, including cardiovascular diseases. These conflicting results suggest that the metabolism of supplemental versus naturally delivered vitamin E and their potential roles, other than a potent antioxidant action, are not fully understood. The purpose of this review is to provide an update on current knowledge on the intestinal absorption of vitamin E, its plasma transport and its supply to cells. The review will also discuss the intravascular metabolism of intravenously delivered vitamin E. RECENT FINDINGS Although the luminal digestion of vitamin E is fairly well understood, several pathways regulating net vitamin E absorption remain to be elucidated. In several cell types, cholesterol and vitamin E share common mechanisms for cellular uptake (scavenger receptor B type I and LDL receptors) and efflux (ABCA1 transporters). The role of specific binding proteins in alpha-tocopherol intracellular trafficking is increasingly being understood, leading to new insights into the non-antioxidant functions of vitamin E. SUMMARY Substantial progress has been made in characterizing the plasma transport of vitamin E and its delivery to cells. Mechanisms regulating the balance between the cellular uptake and efflux of vitamin E are under investigation. Vitamin E is not only an antioxidant but may also modulate pathways of cell signalling and gene expression. The translation of this new knowledge into clinical studies will help define future indications for vitamin E supplementation.
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Affiliation(s)
- Mirjam Hacquebard
- L. Deloyers Laboratory for Experimental Surgery, Université Libre de Bruxelles, Brussels, Belgium
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66
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Abstract
Amyloid-beta (Abeta) has for a long time been thought to play a central role in the pathogenesis of Alzheimer disease (AD). Analysis of available data indicates that Abeta possesses properties of a metal-binding apolipoprotein influencing lipid transport and metabolism. Protection of lipoproteins from oxidation by transition metals, synaptic activity and role in the acute phase response represent plausible physiological functions of Abeta. However, these important biochemical qualities which may critically influence the development of AD, have been largely ignored by mainstream AD researchers, making Abeta appear to be a "black sheep" in a "good apolipoprotein" family. New studies are needed to shed further light on the physiological role of Abeta in lipid metabolism in the brain.
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Affiliation(s)
- Anatol Kontush
- INSERM Unité 551, Hôpital de la Pitié, Pavilion Benjamin Delessert, 83, Bd de l'Hôpital, 75651 Paris Cedex 13, France.
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67
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Stein O, Stein Y. Lipid transfer proteins (LTP) and atherosclerosis. Atherosclerosis 2005; 178:217-30. [PMID: 15694928 DOI: 10.1016/j.atherosclerosis.2004.10.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2004] [Revised: 09/07/2004] [Accepted: 10/05/2004] [Indexed: 10/26/2022]
Abstract
This review deals with four lipid transfer proteins (LTP): three are involved in cholesteryl ester (CE) synthesis or transport, the fourth deals with plasma phospholipid (PL) transfer. Experimental models of atherosclerosis, clinical and epidemiological studies provided information as to the relationship of these LTP(s) to atherosclerosis, which is the main focus of this review. Thus, inhibition of acyl-CoA:cholesterol acyltransferase (ACAT) 1 and 2 decreases cholesterol absorption, plasma cholesterol and aortic cholesterol esterification in the aorta. The discovery that tamoxifen is a potent ACAT inhibitor explained the plasma cholesterol lowering of the drug. The use of ACAT inhibition in humans is under current investigation. As low cholesteryl ester transfer protein (CETP) activity is connected with high HDL-C, several CETP inhibitors were tried in rabbits, with variable results. A new CETP inhibitor, Torcetrapib, was tested in humans and there was a 50-100% increase in HDL-C. Lecithin cholesterol acyl-transferase (LCAT) influences oxidative stress, which can be lowered by transient LCAT gene transfer in LCAT-/- mice. Phospholipid transfer protein (PLTP) deficiency reduced apo B production in apo E-/- mice, as well as oxidative stress in four models of mouse atherosclerosis. In conclusion, the ability to increase HDL-C so markedly by inhibitors of CETP introduces us into a new era in prevention and treatment of coronary heart disease (CHD).
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Affiliation(s)
- O Stein
- Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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68
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Tan KCB, Shiu SWM, Wong Y, Tam S. Plasma phospholipid transfer protein activity and subclinical inflammation in type 2 diabetes mellitus. Atherosclerosis 2005; 178:365-70. [PMID: 15754464 DOI: 10.1016/j.atherosclerosis.2004.09.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phospholipid transfer protein (PLTP) transfers phospholipids between lipoproteins, and plays an essential role in HDL metabolism. The regulation of PLTP is poorly understood and recent evidence suggests that PLTP activity increases during acute-phase response. Since type 2 diabetes is associated with chronic subclinical inflammation, the objective is to determine whether inflammation modulates PLTP in diabetes. Plasma PLTP activity was assayed by measuring the transfer of radiolabeled phosphatidylcholine from liposomes to HDL and high-sensitivity C-reactive protein (CRP) by immunoturbidimetric assay in 280 type 2 diabetic patients and 105 controls. Plasma PLTP activity (2364+/-651 nmol/ml/h versus 1880+/-586 nmol/ml/h in control, mean +/- S.D., P <0.01) and CRP (1.64(0.89-3.23)mg/l versus 0.99(0.53-2.23 mg/l, median (interquartile range), P<0.01) were increased in diabetic subjects. PLTP activity correlated significantly with age, BMI, HbA1c, log(CRP) and apolipoprotein AI and B in diabetic subjects. General linear model analysis showed that only apolipoprotein AI, age, BMI, and log(CRP) were independent determinants of PLTP activity. In conclusion, PLTP activity is increased in diabetes and apolipoprotein AI is a major determinant of PLTP activity. There is also an independent association between CRP and PLTP activity, suggesting that subclinical inflammation may influence PLTP activity in diabetes.
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Affiliation(s)
- K C B Tan
- Department of Medicine, Queen Mary Hospital, University of Hong Kong, Pokufulam Road, Hong Kong, Hong Kong.
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69
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Abstract
BACKGROUND Phosphatidylethanol (PEth) is an abnormal phospholipid formed only in the presence of ethanol. It has been recently shown that lipoprotein-associated PEth may mediate the effects of ethanol on endothelial cells, and this may explain, at least in part, the beneficial effect of ethanol on atherosclerosis. This study was performed to investigate the transfer of PEth between lipoproteins and the effects of PEth on cholesteryl ester transfer protein (CETP) activity in plasma. METHODS Lipoproteins were isolated from the plasma of healthy male volunteers (n = 16) and male alcoholics (n = 13). The transfer of cholesteryl esters and PEth was determined between labeled low-density lipoprotein (LDL) and unlabeled high-density lipoprotein particles in vitro. The electrophoretic mobility of PEth-modified LDL particles was determined by agarose gel electrophoresis. RESULTS PEth was transferred from PEth-modified LDL to high-density lipoprotein at an initial rate of 25.9 nmol/ml/hr. Monoclonal antibody (TP2) against the putative lipid-binding domain of CETP inhibited the transfer rate of PEth by approximately 64%, whereas the cholesteryl ester transfer was inhibited by 86%. This indicates that most of PEth was transferred by transfer proteins other than CETP. CONCLUSIONS The transfer of PEth between lipoproteins enables the redistribution of PEth from lipoprotein fractions with a slow turnover to those with a rapid clearance. Moreover, the PEth-induced change in the electrical charge of lipoproteins may affect the binding of lipoproteins to their receptors and binding proteins. This in turn may alter the metabolism of lipoproteins and lipid-mediated signaling pathways in the cells delineating the vascular wall.
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Affiliation(s)
- Marja K Liisanantti
- Department of Internal Medicine, University of Oulu, P.O. Box 5000, FIN-90014 Oulu, Finland.
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70
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Kuivenhoven JA, Hovingh GK, van Tol A, Jauhiainen M, Ehnholm C, Fruchart JC, Brinton EA, Otvos JD, Smelt AHM, Brownlee A, Zwinderman AH, Hayden MR, Kastelein JJP. Heterozygosity for ABCA1 gene mutations: effects on enzymes, apolipoproteins and lipoprotein particle size. Atherosclerosis 2004; 171:311-9. [PMID: 14644402 DOI: 10.1016/j.atherosclerosis.2003.08.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A cohort of 13 female and 14 male heterozygotes for ATP binding cassette A1 (ABCA1) gene defects was directly compared with 13 and 14 unaffected female and male family members of almost exact same age. The activities of three proteins that play key roles in HDL metabolism were measured in addition to extensive lipid and (apo) lipoprotein subfraction analysis. Compared to controls, LCAT activity was reduced by 15% in affected subjects (P < 0.001) while PLTP activity was unaffected. Interestingly, CETP activity was elevated by 50% in the heterozygote siblings of one kindred but was unaffected in heterozygotes of the three other families. With respect to lipids, the heterozygotes had normal total cholesterol (TC), and LDL-cholesterol concentrations but presented with a trend towards increased triglyceride levels (13%; P = 0.08). HDL metabolism, by contrast, was severely affected as illustrated by 40% reductions in HDL-cholesterol (P < 0.001) with concomitant reductions in apoAI (25%; P < 0.001) levels and in lipoprotein subfraction LpAI (28%; P < 0.001), LpAI:AII (24%; P=0.014), and LpCIII:nonB (34%; P < 0.001) concentrations. We furthermore observed reduced average HDL particle size (5%; P = 0.004; 16% in female and 3.6% in male) and reduced plasma apoCIII concentration (15%; P = 0.006) while apoAII, apoAIV, apoE and apoB levels were unchanged. In conclusion, heterozygosity for ABCA1 defects was associated with reduced LCAT activity in absence of effects on PLTP activity. Of special interest was our finding that the effects of compromised ABCA1 function on HDL were more pronounced in women than in men.
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Affiliation(s)
- J A Kuivenhoven
- Department of Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
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71
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Yatsuya H, Tamakoshi K, Hattori H, Otsuka R, Wada K, Zhang H, Mabuchi T, Ishikawa M, Murata C, Yoshida T, Kondo T, Toyoshima H. Serum phospholipid transfer protein mass as a possible protective factor for coronary heart diseases. Circ J 2004; 68:11-6. [PMID: 14695459 DOI: 10.1253/circj.68.11] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Phospholipid transfer protein (PLTP) can generate pre-beta high-density lipoprotein (HDL), an efficient acceptor of peripheral cholesterol, by mediating a process called HDL conversion. The transfer of phospholipids to immature HDL is also essential in maintaining reverse cholesterol transport. The phospholipid transfer activity of PLTP has been associated with various patho-physiological conditions; however, little information is available concerning the relationship between PLTP mass and disease. METHODS AND RESULTS Using a sandwich enzyme-linked immunosorbent assay, PLTP concentration was measured and related to the risk of developing cardiovascular disease in a worksite-based cohort of Japanese men (n=2,567). Multiple linear regression analysis showed significant associations between PLTP and HDL cholesterol, triglycerides, low-density lipoprotein cholesterol, and body mass index (standardized beta=0.395, -0.191, -0.064, and -0.064, respectively; R(2)=0.31). During the follow-up period, there were 10 cases of coronary heart disease (CHD) and 7 of stroke. The multivariate adjusted relative risk of CHD was 0.46 (95% confidence interval, 0.20-1.07) for an increase of 1 standard deviation in the PLTP value (p=0.071). PLTP concentration was not related to the risk of stroke. CONCLUSIONS The results of this prospective study indicate that the serum PLTP concentration would serve as a predictor of CHD, independent of HDL cholesterol, triglycerides and other established risk factors.
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Affiliation(s)
- Hiroshi Yatsuya
- Department of Public Health/Health Information Dynamics, Nagoya University Graduate School of Medicine, Japan
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72
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Lie J, de Crom R, van Gent T, van Haperen R, Scheek L, Sadeghi-Niaraki F, van Tol A. Elevation of plasma phospholipid transfer protein increases the risk of atherosclerosis despite lower apolipoprotein B-containing lipoproteins. J Lipid Res 2004; 45:805-11. [PMID: 14993244 DOI: 10.1194/jlr.m300487-jlr200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Plasma phospholipid transfer protein (PLTP) transfers phospholipids between lipoproteins and mediates HDL conversion. PLTP-overexpressing mice have increased atherosclerosis. However, mice do not express cholesteryl ester transfer protein (CETP), which is involved in the same metabolic pathways as PLTP. Therefore, we studied atherosclerosis in heterozygous LDL receptor-deficient (LDLR(+/-)) mice expressing both human CETP and human PLTP. We used two transgenic lines with moderately and highly elevated plasma PLTP activity. In LDLR(+/-)/huCETPtg mice, cholesterol is present in both LDL and HDL. Both are decreased in LDLR(+/-)/huCETPtg/huPLTPtg mice (>50%). An atherogenic diet resulted in high levels of VLDL+LDL cholesterol. PLTP expression caused a strong PLTP dose-dependent decrease in VLDL and LDL cholesterol (-26% and -69%) and a decrease in HDL cholesterol (-70%). Surprisingly, atherosclerosis was increased in the two transgenic lines with moderately and highly elevated plasma PLTP activity (1.9-fold and 4.4-fold, respectively), indicating that the adverse effect of the reduction in plasma HDL outweighs the beneficial effect of the reduction in apolipoprotein B (apoB)-containing lipoproteins. The activities of the antiatherogenic enzymes paraoxonase and platelet-activating factor acetyl hydrolase were both PLTP dose-dependently reduced ( approximately -33% and -65%, respectively). We conclude that expression of PLTP in this animal model results in increased atherosclerosis in spite of reduced apoB-containing lipoproteins, by reduction of HDL and of HDL-associated antioxidant enzyme activities.
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Affiliation(s)
- Jessica Lie
- Departments of Biochemistry, Erasmus University Medical Center, P O Box 1738, 3000 DR Rotterdam, The Netherlands
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73
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Rye KA, Barter PJ. Formation and Metabolism of Prebeta-Migrating, Lipid-Poor Apolipoprotein A-I. Arterioscler Thromb Vasc Biol 2004; 24:421-8. [PMID: 14592845 DOI: 10.1161/01.atv.0000104029.74961.f5] [Citation(s) in RCA: 236] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The preferred extracellular acceptor of cell phospholipids and unesterified cholesterol in the process mediated by the ATP-binding cassette A1 (ABCA1) transporter is a monomolecular, prebeta-migrating, lipid-poor or lipid-free form of apolipoprotein (apo) A-I. This monomolecular form of apoA-I is quite distinct from the prebeta-migrating, discoidal high-density lipoprotein (HDL) that contains two or three molecules of apoA-I per particle and which are present as minor components of the HDL fraction in human plasma. The mechanism of the ABCA1-mediated efflux of phospholipid and cholesterol from cells has been studied extensively. In contrast, much less attention has been given to the origin and subsequent metabolism of the acceptor lipid-free/lipid-poor apoA-I. There is a substantial body of evidence from studies conducted in vitro that a monomolecular, lipid-free/lipid-poor form of apoA-I dissociates from HDL during the remodeling of HDLs by plasma factors such as cholesteryl ester transfer protein, hepatic lipase, and phospholipid transfer protein. The rate at which apoA-I dissociates from HDL is influenced by the phospholipid composition of the particles and by the presence of apoA-II. This review describes current knowledge regarding the formation, metabolism, and regulation of monomolecular, lipid-free/lipid-poor apoA-I in plasma.
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Affiliation(s)
- Kerry-Anne Rye
- Heart Research Institute, Camperdown, Sydney, NSW, Australia
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74
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Bishop-Bailey D, Walsh DT, Warner TD. Expression and activation of the farnesoid X receptor in the vasculature. Proc Natl Acad Sci U S A 2004; 101:3668-73. [PMID: 14990788 PMCID: PMC373520 DOI: 10.1073/pnas.0400046101] [Citation(s) in RCA: 175] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The farnesoid X receptor/bile acid receptor (FXR) is a recently discovered member of the nuclear hormone superfamily. FXR ligands have been proposed as targets in cardiovascular disease, regulating cholesterol metabolism and bile acid transport and metabolism in the liver and gastrointestinal tract. When we used a human cardiovascular tissue array, we found that FXR is expressed in a variety of normal and pathological human tissue. Particularly high levels of FXR were found in the vasculature and in a number of different metastatic cancers, as well as the previously identified target tissues of the liver, small intestine, and kidney. In vitro, FXR is present in rat and human vascular smooth muscle cells. When treated with a range of FXR ligands, vascular smooth muscle cells undergo apoptosis in a manner that correlates with the ligands' ability to activate FXR. Furthermore, FXR activators induce mRNA for the FXR target genes, phospholipid transfer protein, and the small heterodimer partner. FXR therefore is a functional protein in the vasculature that may provide a direct target for the treatment of proliferative and dyslipidaemic diseases.
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MESH Headings
- Animals
- Apoptosis/drug effects
- Base Sequence
- Cardiovascular System/drug effects
- Cardiovascular System/metabolism
- Cells, Cultured
- DNA, Complementary/genetics
- DNA-Binding Proteins/agonists
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Gene Expression/drug effects
- Humans
- Immunohistochemistry
- In Vitro Techniques
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Transcription Factors/agonists
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- David Bishop-Bailey
- Cardiac, Vascular, and Inflammation Research, William Harvey Research Institute, Barts and the London, Queen Mary University of London, Charterhouse Square, London EC1M 6BQ, United Kingdom.
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75
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Abstract
Macrophages play diverse roles in host defense and in maintenance of homeostasis. Based on their ability to promote inflammatory responses, inappropriate macrophage function also contributes to numerous pathological processes, including atherosclerosis, rheumatoid arthritis and inflammatory bowel disease. Members of the nuclear receptor superfamily of ligand-dependent transcriptions factors have emerged as key regulators of inflammation and lipid homeostasis in macrophages. These include the glucocorticoid receptor (GR), which inhibits inflammatory programs of gene expression in response to natural corticosteroids and synthetic anti-inflammatory ligands such as dexamethasone. Also, in response to endogenous eicosanoids and oxysterols, respectively, peroxisome proliferator-activated receptors (PPARs) and liver X receptors (LXRs) regulate transcriptional programs involved in inflammatory responses and lipid homeostasis. Identification of their mechanisms of action should help guide the development of new therapeutic agents useful in the treatment of diseases in which macrophages play critical pathogenic roles.
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Affiliation(s)
- Annabel F Valledor
- Department of Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0651, USA
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76
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Ricote M, Valledor AF, Glass CK. Decoding Transcriptional Programs Regulated by PPARs and LXRs in the Macrophage. Arterioscler Thromb Vasc Biol 2004; 24:230-9. [PMID: 14592855 DOI: 10.1161/01.atv.0000103951.67680.b1] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Macrophages play essential roles in immunity and homeostasis. As professional scavengers, macrophages phagocytose microbes and apoptotic and necrotic cells and take up modified lipoprotein particles. These functions require tightly regulated mechanisms for the processing and disposal of cellular lipids. Under pathological conditions, arterial wall macrophages become foam cells by accumulating large amounts of cholesterol, contributing to the development of atherosclerosis. Peroxisome proliferator–activated receptors (PPARs) and liver X receptors (LXRs) are members of the nuclear receptor superfamily of transcription factors that have emerged as key regulators of macrophage homeostasis. PPARs and LXRs control transcriptional programs involved in processes of lipid uptake and efflux, lipogenesis, and lipoprotein metabolism. In addition, PPARs and LXRs negatively regulate transcriptional programs involved in the development of inflammatory responses. This review summarizes recent efforts to decode the differential and overlapping roles of PPARs and LXRs in the context of macrophage lipid homeostasis and the control of inflammation.
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Affiliation(s)
- Mercedes Ricote
- Department of Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, Calif 92093-0651, USA
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77
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Oram JF, Wolfbauer G, Vaughan AM, Tang C, Albers JJ. Phospholipid transfer protein interacts with and stabilizes ATP-binding cassette transporter A1 and enhances cholesterol efflux from cells. J Biol Chem 2003; 278:52379-85. [PMID: 14559902 DOI: 10.1074/jbc.m310695200] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholipid lipid transfer protein (PLTP) is ubiquitously expressed in animal tissues and plays multiple roles in lipoprotein metabolism, but the function of peripheral PLTP is still poorly understood. Here we show that one of its possible functions is to transport cholesterol and phospholipids from cells to lipoprotein particles by a process involving PLTP interactions with cellular ATP-binding cassette transporter A1 (ABCA1). When ABCA1 was induced in murine macrophages or ABCA1-transfected baby hamster kidney cells, PLTP gained the ability to promote cholesterol and phospholipid efflux from cells. Although PLTP alone had lipid efflux activity, its maximum activity was observed in the presence of high density lipoprotein particles. Pulsechase studies showed that the interaction of PLTP with ABCA1-expressing cells played a role in promoting lipid efflux. Overexpression of ABCA1 dramatically increased binding of both PLTP and apoA-I to common sites on the cell surface. Both PLTP and apoA-I were covalently cross-linked to ABCA1, each protein blocked cross-linking of the other, and both PLTP and apoA-I stabilized ABCA1 protein. These results are consistent with PLTP and apoA-I binding to ABCA1 at the same or closely related sites. Thus, PLTP mimics apolipoproteins in removing cellular lipids by the ABCA1 pathway, except that PLTP acts more as an intermediary in the transfer of cellular lipids to lipoprotein particles.
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Affiliation(s)
- John F Oram
- Department of Medicine, University of Washington, Seattle, Washington 98195-6426, USA.
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78
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Murdoch SJ, Kahn SE, Albers JJ, Brunzell JD, Purnell JQ. PLTP activity decreases with weight loss: changes in PLTP are associated with changes in subcutaneous fat and FFA but not IAF or insulin sensitivity. J Lipid Res 2003; 44:1705-12. [PMID: 12837855 DOI: 10.1194/jlr.m300073-jlr200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Phospholipid transfer protein (PLTP) activity is elevated in obese and diabetic subjects. No prospective studies have examined the effect of weight loss on PLTP activity and assessed whether the resultant changes in activity are related to changes in body weight, insulin resistance, or both. PLTP activity was measured at baseline in 46 subjects (body mass index = 19-64 kg/m2) and after diet-induced weight loss in 19 of the obese subjects. Total body fat mass (FM) by dual-energy X-ray absorptiometry, intraabdominal fat (IAF), and abdominal subcutaneous fat (SQF) by CT scan, insulin sensitivity (SI) by frequently sampled intravenous glucose tolerance test, leptin, and lipids were determined. At baseline, PLTP activity correlated with FM (r = 0.36, P = 0.02) and SQF (r = 0.31, P = 0.045), but not with IAF (r = 0.16, P = 0.32) or SI (r = 0.10, P = 0.52). With diet-induced weight loss (16 +/- 7.3 kg), PLTP activity significantly decreased 9.1% (P = 0.002). The change in PLTP activity correlated with the change in SQF (r = 0.55, P = 0.014) (33.6% decrease), but not with IAF (r = 0.09, P = 0.73) or SI (r = 0.18, P = 0.44), and was highly correlated with the change in nonesterified fatty acid (NEFA) (r = 0.71, P < 0.001). In conclusion, elevated PLTP activity in obese subjects is likely a result of increased body fat, reflected by SQF, and is influenced by NEFAs but is not directly related to insulin resistance.
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Affiliation(s)
- Susan J Murdoch
- Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, University of Washington, Seattle, WA 98195, USA.
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79
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Jonkers IJAM, Smelt AHM, Hattori H, Scheek LM, van Gent T, de Man FHAF, van der Laarse A, van Tol A. Decreased PLTP mass but elevated PLTP activity linked to insulin resistance in HTG: effects of bezafibrate therapy. J Lipid Res 2003; 44:1462-9. [PMID: 12754275 DOI: 10.1194/jlr.m300008-jlr200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hypertriglyceridemia (HTG) is associated with insulin resistance, increased cholesteryl ester transfer (CET), and low HDL cholesterol. Phospholipid transfer protein (PLTP) may be involved in these relationships. Associations between CET, lipids, insulin resistance, CETP and PLTP activities, and PLTP mass were investigated in 18 HTG patients and 20 controls. Effects of 6 weeks of bezafibrate treatment were studied in HTG patients. HTG patients had higher serum triglycerides, insulin resistance, free fatty acid (FFA), and CET, lower levels of HDL cholesterol (-44%) and PLTP mass (-54%), and higher CETP (+20%) and PLTP activity (+48%) than controls. Bezafibrate reduced triglycerides, CET (-37%), insulin resistance (-53%), FFA (-48%), CETP activity (-12%), PLTP activity (-8%), and increased HDL cholesterol (+27%), whereas PLTP mass remained unchanged. Regression analysis showed a positive contribution of PLTP mass (P = 0.001) but not of PLTP activity to HDL cholesterol, whereas insulin resistance positively contributed to PLTP activity (P < 0.01). Bezafibrate-induced change in CET and HDL cholesterol correlated with changes in CETP activity and FFAs, but not with change in PLTP activity. Bezafibrate-induced change in PLTP activity correlated with change in FFAs (r = 0.455, P = 0.058). We propose that elevated PLTP activity in HTG is related to insulin resistance and not to increased PLTP mass. Bezafibrate-induced diminished insulin resistance is associated with a reduction of CET and PLTP activity.
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Affiliation(s)
- Iris J A M Jonkers
- Department of General Internal Medicine, Leiden University Medical Center, Leiden, The Netherlands
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81
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Soro A, Jauhiainen M, Ehnholm C, Taskinen MR. Determinants of low HDL levels in familial combined hyperlipidemia. J Lipid Res 2003; 44:1536-44. [PMID: 12777471 DOI: 10.1194/jlr.m300069-jlr200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In familial combined hyperlipidemia (FCHL), affected family members frequently have reduced levels of HDL cholesterol, in addition to elevated levels of total cholesterol and/or triglycerides (TGs). In the present study, we focused on those determinants that are important regulators of HDL cholesterol levels in FCHL, and measured postheparin plasma activities of hepatic lipase (HL), lipoprotein lipase, cholesterol ester transfer protein, and phospholipid transfer protein (PLTP) in 228 subjects from 49 FCHL families. In affected family members (n = 88), the levels of HDL cholesterol, HDL2 cholesterol, HDL3 cholesterol, and apolipoprotein A-I were lower than in unaffected family members (n = 88) or spouses (n = 52). The main change was the reduction of HDL2 cholesterol by 25.4% in affected family members (P < 0.001 vs. unaffected family members; P = 0.003 vs. spouses). Affected family members had higher HL activity than unaffected family members (P = 0.001) or spouses (P = 0.013). PLTP activity was higher in affected than unaffected family members (P = 0.025). In univariate correlation analysis, a strong negative correlation was observed between HL activity and HDL2 cholesterol (r = -0.339, P < 0.001). Multivariate regression analysis demonstrated that gender, HL activity, TG, and body mass index have independent contributions to HDL2 cholesterol levels. We suggest that in FCHL, TG enrichment of HDL particles and enhanced HL activity lead to the reduction of HDL cholesterol and HDL2 cholesterol.
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Affiliation(s)
- Aino Soro
- Department of Medicine, University of Helsinki, Finland
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82
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Abstract
The term metabolic syndrome refers to a virulent and lethal group of atherosclerotic risk factors, including dyslipidemia, insulin resistance, obesity, and hypertension. This syndrome affects some 47 million people in the United States, placing them at increased risk for coronary artery disease (CAD). Particularly prominent as a risk factor for development of heart disease is central obesity. Immediate treatment of the metabolic syndrome is essential because these patients quickly develop diabetes, CAD, and stroke. Treatment is a multifactorial process and includes diet, exercise, and pharmacologic therapy. The latter consists of statins, fibrates, angiotensin-converting enzyme inhibitors, and thiazolidinediones, all of which can decrease the risk and incidence of CAD.
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Affiliation(s)
- Cranford L Scott
- University of Southern California School of Medicine, Los Angeles, California, USA.
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83
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Tontonoz P, Mangelsdorf DJ. Liver X receptor signaling pathways in cardiovascular disease. Mol Endocrinol 2003; 17:985-93. [PMID: 12690094 DOI: 10.1210/me.2003-0061] [Citation(s) in RCA: 515] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The liver X receptors alpha and beta (LXRalpha and LXRbeta) are members of the nuclear receptor family of proteins that are critical for the control of lipid homeostasis in vertebrates. The endogenous activators of these receptors are oxysterols and intermediates in the cholesterol biosynthetic pathway. LXRs serve as cholesterol sensors that regulate the expression of multiple genes involved in the efflux, transport, and excretion of cholesterol. Recent studies have outlined the importance of LXR signaling pathways in the development of metabolic disorders such as hyperlipidemia and atherosclerosis. Synthetic LXR agonists inhibit the development of atherosclerosis in murine models, an effect that is likely to result from the modulation of both metabolic and inflammatory gene expression. These observations identify the LXR pathway as a potential target for therapeutic intervention in human cardiovascular disease.
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Affiliation(s)
- Peter Tontonoz
- Howard Hughes Medical Institute, University of California, Los Angeles School of Medicine, Box 951662, Los Angeles, California 90095-1662, USA.
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84
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Post SM, de Crom R, van Haperen R, van Tol A, Princen HMG. Increased fecal bile acid excretion in transgenic mice with elevated expression of human phospholipid transfer protein. Arterioscler Thromb Vasc Biol 2003; 23:892-7. [PMID: 12649089 DOI: 10.1161/01.atv.0000067702.22390.20] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
OBJECTIVE HDL plays a key role in protection against development of atherosclerosis by promoting reverse cholesterol transport from peripheral tissues to the liver for secretion into bile. Phospholipid transfer protein (PLTP) promotes the transfer of phospholipids between lipoproteins and modulates HDL size and composition, thereby having a crucial role in HDL metabolism. We investigated the effect of increased PLTP activity on removal of cholesterol from the body. METHODS AND RESULTS On a chow diet, transgenic mice overexpressing human PLTP have a 15-fold increased plasma PLTP activity compared with wild-type mice (572.4+/-59.2 versus 38.6+/-3.6 micromol/mL per h). Plasma cholesterol, mainly present in HDL, is strongly decreased (-92%), caused by a rapid clearance from the circulation by the liver and leading to a 1.8-fold increase in hepatic cholesteryl esters. This results in a 2-fold increase in biliary bile acid secretion without changing the bile saturation index. Consequently, the transgenic mice show a 1.4-fold increase in the amount of excreted fecal bile acids compared with wild-type mice, whereas fecal neutral sterol excretion is unchanged. CONCLUSIONS Our data show that elevation of PLTP activity results in rapid disposal of cholesterol from the body via increased conversion into bile acids and subsequent excretion.
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Affiliation(s)
- Sabine M Post
- Gaubius Laboratory, TNO Prevention and Health, PO Box 2215, 2301 CE, Leiden, The Netherlands
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85
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Laffitte BA, Joseph SB, Chen M, Castrillo A, Repa J, Wilpitz D, Mangelsdorf D, Tontonoz P. The phospholipid transfer protein gene is a liver X receptor target expressed by macrophages in atherosclerotic lesions. Mol Cell Biol 2003; 23:2182-91. [PMID: 12612088 PMCID: PMC149472 DOI: 10.1128/mcb.23.6.2182-2191.2003] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The liver X receptors (LXRs) are members of the nuclear receptor superfamily that are activated by oxysterols. In response to ligand binding, LXRs regulate a variety of genes involved in the catabolism, transport, and uptake of cholesterol and its metabolites. Here we demonstrate that LXRs also regulate plasma lipoprotein metabolism through control of the phospholipid transfer protein (PLTP) gene. LXR ligands induce the expression of PLTP in cultured HepG2 cells and mouse liver in vivo in a coordinate manner with known LXR target genes. Moreover, plasma phospholipid transfer activity is increased in mice treated with the synthetic LXR ligand GW3965. Unexpectedly, PLTP expression was also highly inducible by LXR in macrophages, a cell type not previously recognized to express this enzyme. The ability of synthetic and oxysterol ligands to regulate PLTP mRNA in macrophages and liver is lost in animals lacking both LXRalpha and LXRbeta, confirming the critical role of these receptors. We further demonstrate that the PLTP promoter contains a high-affinity LXR response element that is bound by LXR/RXR heterodimers in vitro and is activated by LXR/RXR in transient-transfection studies. Finally, immunohistochemistry studies reveal that PLTP is highly expressed by macrophages within human atherosclerotic lesions, suggesting a potential role for this enzyme in lipid-loaded macrophages. These studies outline a novel pathway whereby LXR and its ligands may modulate lipoprotein metabolism.
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MESH Headings
- Animals
- Anticholesteremic Agents/pharmacology
- Apolipoproteins E/deficiency
- Apolipoproteins E/genetics
- Arteriosclerosis/metabolism
- Benzoates/pharmacology
- Benzylamines/pharmacology
- Carrier Proteins/analysis
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Cells, Cultured/metabolism
- Coronary Artery Disease/metabolism
- Coronary Artery Disease/pathology
- DNA-Binding Proteins
- Dimerization
- Gene Expression Profiling
- Gene Expression Regulation
- Humans
- Ligands
- Lipoproteins, HDL/metabolism
- Liver/metabolism
- Liver X Receptors
- Macrophages/metabolism
- Macrophages, Peritoneal/metabolism
- Male
- Membrane Proteins/analysis
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Oligonucleotide Array Sequence Analysis
- Organic Chemicals
- Orphan Nuclear Receptors
- Phospholipid Transfer Proteins
- Promoter Regions, Genetic
- Receptors, Cytoplasmic and Nuclear/chemistry
- Receptors, Cytoplasmic and Nuclear/drug effects
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Retinoic Acid/chemistry
- Receptors, Retinoic Acid/metabolism
- Recombinant Fusion Proteins/physiology
- Retinoid X Receptors
- Transcription Factors/chemistry
- Transcription Factors/metabolism
- Transfection
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Affiliation(s)
- Bryan A Laffitte
- Howard Hughes Medical Institute, School of Medicine, University of California-Los Angeles, Los Angeles, CA 90095-1662, USA
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86
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van Haperen R, van Tol A, van Gent T, Scheek L, Visser P, van der Kamp A, Grosveld F, de Crom R. Increased risk of atherosclerosis by elevated plasma levels of phospholipid transfer protein. J Biol Chem 2002; 277:48938-43. [PMID: 12372822 DOI: 10.1074/jbc.m209128200] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Plasma phospholipid transfer protein (PLTP) is thought to be involved in the remodeling of high density lipoproteins (HDL), which are atheroprotective. It is also involved in the metabolism of very low density lipoproteins (VLDL). Hence, PLTP is thought to be an important factor in lipoprotein metabolism and the development of atherosclerosis. We have overexpressed PLTP in mice heterozygous for the low density lipoprotein (LDL) receptor, a model for atherosclerosis. We show that increased PLTP activity results in a dose-dependent decrease in HDL, and a moderate stimulation of VLDL secretion (</=1.5-fold). The mice were given a high fat, high cholesterol diet, which resulted in hypercholesterolemia in all animals. HDL concentrations were dramatically reduced in PLTP-overexpressing animals when compared with LDL receptor controls, whereas VLDL + LDL cholesterol levels were identical. Susceptibility to atherosclerosis was increased in a PLTP dose-responsive manner. We conclude that PLTP increases susceptibility to atherosclerosis by lowering HDL concentrations, and therefore we suggest that an increase in PLTP is a novel, long term risk factor for atherosclerosis in humans.
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Affiliation(s)
- Rien van Haperen
- Department of Cell Biology & Genetics, Erasmus Medical Center, 3000 DR Rotterdam, The Netherlands
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87
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Mak PA, Kast-Woelbern HR, Anisfeld AM, Edwards PA. Identification of PLTP as an LXR target gene and apoE as an FXR target gene reveals overlapping targets for the two nuclear receptors. J Lipid Res 2002; 43:2037-41. [PMID: 12454263 DOI: 10.1194/jlr.c200014-jlr200] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Affymetrix microarray data and Northern blot assays demonstrated that phospholipid transfer protein (PLTP) was induced 6-fold when either murine or human macrophages were incubated in the presence of ligands for the liver X receptor (LXR) and the retinoid X receptor. Two functional LXR response elements (LXREs) were identified and characterized in the proximal promoter of the human PLTP gene. One LXRE corresponds to a traditional direct repeat separated by 4 bp. However, the second LXRE is novel in that it corresponds to an inverted repeat separated by 1 bp, and is identical to the farnesoid X receptor response element. These studies demonstrate that PLTP is a direct target for activated LXR and farnesoid X receptor (FXR). In addition, apolipoprotein E (apoE), a known LXR target gene in macrophages, was shown to be activated in liver cells by FXR ligands. Taken together, the current data suggest that a small number of genes that currently include PLTP, apoE, and apoC-II, are induced in macrophages by activated LXR and in liver by activated FXR.
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Affiliation(s)
- Puiying A Mak
- Departments of Biological Chemistry and Medicine, University of California, Los Angeles, CA 90095, USA
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88
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Repa JJ, Mangelsdorf DJ. The liver X receptor gene team: potential new players in atherosclerosis. Nat Med 2002; 8:1243-8. [PMID: 12411951 DOI: 10.1038/nm1102-1243] [Citation(s) in RCA: 309] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Joyce J Repa
- Department of Physiology, Touchstone Center for Diabetes Research, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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89
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Abstract
Hepatic lipase (HL) plays a role in the metabolism of pro- and anti-atherogenic lipoproteins affecting their plasma level and composition. However, there is controversy regarding whether HL accelerates or retards atherosclerosis. Its effects on different lipoprotein classes show that, potentially, HL may promote as well as decrease atherogenesis. Studies in animals with genetically modulated HL expression show that it depends on the model used whether HL acts pro- or anti-atherogenic. In humans, HL activity seems to correlate inversely with atherosclerosis in (familial) hypercholesterolemia, and positively in hypertriglyceridemia. In normolipidemia, HL activity is weakly associated with coronary artery disease (CAD). Genetically low or absent HL activity is usually associated with increased CAD risk, especially if plasma lipid transport is impaired due to other factors. Since HL promotes the uptake of lipoproteins and lipoprotein-associated lipids, HL may affect intracellular lipid content. We hypothesize that the prime role of HL is to maintain, in concert with other factors (e.g., lipoprotein receptors), intracellular lipid homeostasis. This, and the uncertainties about its impact on human atherosclerosis, makes it difficult to predict whether HL is a suitable target for intervention to lower CAD risk. First, the physiological meaning of changes in HL activity under different conditions should be clarified.
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Affiliation(s)
- Hans Jansen
- Department of Biochemistry, Erasmus MC, Erasmus University Rotterdam, Rotterdam, The Netherlands.
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