HMG-CoA reductase, cholesterol 7alpha-hydroxylase, LDL receptor, SR-B1, and ACAT in diet-induced syndrome X

The anti-hyperlipidemic effects of Poria cocos (Schw.) Wolf extract: Modulating cholesterol homeostasis in hepatocytes via PPARα pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Poria cocos (Schw.) Wolf (Polyporaceae, P.cocos), which is born on the pine root, has a history of more than two thousand years of medicine in China. P.cocos was first recorded in the Shennong's Herbal Classic, studies have proved its lipid-lowering effect.

AIM OF STUDY

The aim of study was to investigate the underlying mechanism of P.cocos extract on hyperlipidemia.

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats aged 9-12 weeks were intraperitoneally (IP) injected with Triton-WR 1339 to establish an acute hyperlipidemia model. At 0 h and 20 h after the model was established, low and high doses of P.cocos extract or simvastatin were given twice. After 48 h, the rats were sacrificed, and liver and serum samples were collected for analysis. The cell model was constructed by treating L02 cells with 1% fat emulsion-10% FBS-RPMI 1640 medium for 48 h. At the same time, low and high doses of P.cocos extract and simvastatin were administered. Oil red O staining was used to evaluate the lipid accumulation in the cells, and H&E staining was used to evaluate the liver lesions of rats. Real-time quantitative PCR and western blotting were used to detect the expressions of lipid metabolism-related genes.

RESULTS

P.cocos extract relieved lipid accumulation in vitro and alleviated hyperlipidemia in vivo. Both gene and protein expressions of peroxisome proliferator-activated receptor α (PPARα) were shown to be up-regulated by P.cocos extract. Additionally, P.cocos extract down-regulated the expressions of fatty acid synthesis-related genes sterol regulatory element-binding protein-1 (SREBP-1), Acetyl-CoA Carboxylase 1 (ACC1) and fatty acid synthase (FAS), while up-regulated the expressions of cholesterol metabolism-related genes liver X receptor-α (LXRα), ATP-binding cassette transporter A1 (ABCA1), cholesterol 7alpha-hydroxylase (CYP7A1) and low density lipoprotein receptor (LDLR), which were reversed by the treatment with the PPARα inhibitor GW6471.

CONCLUSION

P.cocos extract ameliorates hyperlipidemia and lipid accumulation by regulating cholesterol homeostasis in hepatocytes through PPARα pathway. This study provides evidence that supplementation with P.cocos extract could be a potential strategy for the treatment of hyperlipidemia.

An innovative viewpoint on the existing and prospectiveness of SR-B1

Scavenger Receptor Class B Type 1 (SR-B1), a receptor protein expressed on the cell membrane, plays a crucial role in the metabolism and transport of cholesterol and other lipids, contributing significantly to the homeostasis of lipid levels within the body. Bibliometric analysis involves the application of mathematical and statistical methods to quantitatively analyze different types of documents. It involves the analysis of structural and temporal trends in scholarly articles, coupled with the identification of subject emphasis and variations. Through a bibliometric analysis, this study examines the historical background, current research trends, and future directions in the exploration of SR-B1. By offering insights into the research status and development of SR-B1, this paper aims to assist researchers in identifying novel pathways and areas of investigation in this field of study. Following the screening process, it can be concluded that research on SR-B1 has consistently remained a topic of significant interest over the past 17 years. Interestingly, SR-B1 has recently garnered attention in areas beyond its traditional research focus, including the field of cancer. The primary objective of this review is to provide a concise and accessible overview of the development process of SR-B1 that can help readers who are not well-versed in SR-B1 research quickly grasp its key aspects. Furthermore, this review aims to offer insights and suggestions to researchers regarding potential future research directions and areas of emphasis relating to SR-B1.

Metabolomics of peripheral artery disease

The science of metabolomics has emerged as a novel tool for studying changes in metabolism that accompany different disease states. Several studies have applied this evolving field to the study of various cardiovascular disease states, which has led to improved understanding of metabolic changes that underlie heart failure and ischemic heart disease. A significant amount of progress has also been made in the identification of novel biomarkers of cardiovascular disease. Another common atherosclerotic disease, peripheral artery disease (PAD) affects arteries of the lower extremities. Although certain aspects of the disease pathophysiology overlap with other cardiovascular diseases in general, PAD patients suffer unique manifestations that lead to significant morbidity and mortality as well as severe functional limitations. Furthermore, because over half of PAD patients are asymptomatic, there is a need for improved diagnostic and screening methods. Identification of metabolites associated with the disease may thus be a promising approach for PAD. However, PAD remains highly understudied. In this chapter, we discuss the application of metabolomics to the study of PAD.

Effects of Danhong injection on dyslipidemia and cholesterol metabolism in high-fat diets fed rats

ETHNOPHARMACOLOGICAL RELEVANCE

Danhong injection (DHI) is a Chinese medical injection applied to the clinical treatment of cardiovascular diseases that has anti-inflammatory, antiplatelet aggregation and antithrombotic effects. This study aimed to explore the effects of DHI on dyslipidemia and cholesterol metabolism in high-fat diet-fed rats.

METHODS

Sprague Dawley (SD) rats were randomly divided into six groups: normal group (Normal); hyperlipidemia model group (Model); DHI-treated groups at doses of 1.0 mL/kg, 2.0 mL/kg, 4.0 mL/kg; and simvastatin positive control group (2.0 mg/kg). The hypolipidemic effects of DHI were evaluated by measuring serum lipid levels, hepatic function and oxidative stress, respectively. And pathological changes in liver tissues were determined using hematoxylin-eosin (H&E) and oil red O staining. Moreover, the mRNA and protein expression levels of cholesterol metabolism related genes were detected by real-time PCR (RT-PCR) and Western blot.

RESULTS

Compared with the Model group, DHI treatment markedly decreased the liver index and improved the pathological morphology of liver tissues. DHI treatment dose-dependently decreased the levels of total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), malondialdehyde (MDA), and free fatty acids (FFA) in serum or liver tissues (P < 0.01 or P < 0.05), and increased the high-density lipoprotein cholesterol (HDL-C) and tripeptide glutathione (GSH) (P < 0.01 or P < 0.05). The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) were increased in the DHI-treated groups (P < 0.01 or P < 0.05), while the alanine transaminase (ALT) and aspartate transaminase (AST) were decreased (P < 0.01 or P < 0.05). Furthermore, the expression levels of LDL receptor (LDLR), cholesterol 7-α-hydroxylase (CYP7A1), liver X receptor α (LXRα), and peroxisome proliferator-activated receptor α (PPARα) were dose-dependently upregulated in the DHI-treated groups, whereas the expression of sterol regulatory element-binding protein-2 (SREBP-2) was downregulated.

CONCLUSIONS

Our study demonstrated that DHI markedly ameliorated hyperlipidemia rats by regulating serum lipid levels, inhibiting hepatic lipid accumulation and steatosis, improving hepatic dysfunction, and reducing oxidative stress. The potential mechanism was also tentatively investigated and may be related to the promotion of bile acid synthesis via activation of the PPARα-LXRα-CYP7A1 pathway. Therefore, DHI could be regarded as a potential hypolipidemic drug for the treatment of hyperlipidemia.

HDL (High-Density Lipoprotein) Remodeling and Magnetic Resonance Imaging-Assessed Atherosclerotic Plaque Burden: Study in a Preclinical Experimental Model

OBJECTIVE

HDL (high-density lipoprotein) role in atherosclerosis is controversial. Clinical trials with CETP (cholesterylester transfer protein)-inhibitors have not provided benefit. We have shown that HDL remodeling in hypercholesterolemia reduces HDL cardioprotective potential. We aimed to assess whether hypercholesterolemia affects HDL-induced atherosclerotic plaque regression. Approach and Results: Atherosclerosis was induced in New Zealand White rabbits for 3-months by combining a high-fat-diet and double-balloon aortic denudation. Then, animals underwent magnetic resonance imaging (basal plaque) and randomized to receive 4 IV infusions (1 infusion/wk) of HDL isolated from normocholesterolemic (NC-HDL; 75 mg/kg; n=10), hypercholesterolemic (HC-HDL; 75 mg/Kg; n=10), or vehicle (n=10) rabbits. Then, animals underwent a second magnetic resonance imaging (end plaque). Blood, aorta, and liver samples were obtained for analyses. Follow-up magnetic resonance imaging revealed that NC-HDL administration regressed atherosclerotic lesions by 4.3%, whereas, conversely, the administration of HC-HDLs induced a further 6.5% progression (P<0.05 versus basal). Plaque characterization showed that HC-HDL administered animals had a 2-fold higher lipid and cholesterol content versus those infused NC-HDL and vehicle (P<0.05). No differences were observed among groups in CD31 levels, nor in infiltrated macrophages or smooth muscle cells. Plaques from HC-HDL administered animals exhibited higher Casp3 (caspase 3) content (P<0.05 versus vehicle and NC-HDL) whereas plaques from NC-HDL infused animals showed lower expression of Casp3, Cox1 (cyclooxygenase 1), inducible nitric oxide synthase, and MMP (metalloproteinase) activity (P<0.05 versus HC-HDL and vehicle). HDLs isolated from animals administered HC-HDL displayed lower antioxidant potential and cholesterol efflux capacity as compared with HDLs isolated from NC-HDL-infused animal and vehicle or donor HDL (P<0.05). There were no differences in HDL-ApoA1 content, ABCA1 (ATP-binding cassette transporter A1) vascular expression, and SRB1 (scavenger receptor B1) and ABCA1 liver expression.

CONCLUSIONS

HDL particles isolated from a hypercholesterolemic milieu lose their ability to regress and stabilize atherosclerotic lesions. Our data suggest that HDL remodeling in patients with co-morbidities may lead to the loss of HDL atheroprotective functions.

Altered Metabolomic Profile in Patients with Peripheral Artery Disease

Peripheral artery disease (PAD) is a common atherosclerotic disease characterized by narrowed or blocked arteries in the lower extremities. Circulating serum biomarkers can provide significant insight regarding the disease progression. Here, we explore the metabolomics signatures associated with different stages of PAD and investigate potential mechanisms of the disease. We compared the serum metabolites of a cohort of 26 PAD patients presenting with claudication and 26 PAD patients presenting with critical limb ischemia (CLI) to those of 26 non-PAD controls. A difference between the metabolite profiles of PAD patients from non-PAD controls was observed for several amino acids, acylcarnitines, ceramides, and cholesteryl esters. Furthermore, our data demonstrate that patients with CLI possess an altered metabolomic signature different from that of both claudicants and non-PAD controls. These findings provide new insight into the pathophysiology of PAD and may help develop future diagnostic procedures and therapies for PAD patients.

Rats Selectively Bred for High Voluntary Physical Activity Behavior are Not Protected from the Deleterious Metabolic Effects of a Western Diet When Sedentary

BACKGROUND

Physical activity and diet are well-established modifiable factors that influence chronic disease risk. We developed a selectively bred, polygenic model for high and low voluntary running (HVR and LVR, respectively) distances. After 8 generations, large differences in running distance were noted. Despite these inherent behavioral differences in physical activity levels, it is unknown whether HVR rats would be inherently protected from diet-induced metabolic dysfunction.

OBJECTIVES

The aim of this study was to determine whether HVR rats without voluntary running wheels would be inherently protected from diet-induced metabolic dysfunction.

METHODS

Young HVR, LVR, and a wild-type (WT) control group were housed with no running wheel access and fed either a normal diet (ND) or a high-sugar/fat Western diet (WD) for 8 wk. Body weight, percentage body fat (by dual-energy X-ray absorptiometry scan), blood lipids [total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglycerides (TGs), nonesterified fatty acids], and hepatic TG content were measured, and indices of insulin sensitivity were determined via an intravenous glucose tolerance test. Additionally, weekly energy intake and feed efficiency were calculated.

RESULTS

After 8 wk, significant differences in body weight and body fat percentage were noted in all WD animals compared with ND animals, with the LVR-WD exhibiting the greatest increase due, in part, to their enhanced feed efficiency. Lipid dysregulation was present in all WD rat lines compared with ND counterparts. Furthermore, LVR-WD rats had higher total cholesterol, HDL cholesterol, and TG concentrations, and higher areas under the curve (AUC) for insulin than HVR-WD and WT-WD, although HVR-WD animals had higher AUCglucose than both LVR-WD and WT-WD and higher LDL than WT-WD.

CONCLUSIONS

In the absence of high voluntary running behavior, the genetic predisposition for high running in HVR did not largely protect them from the deleterious effects of a WD compared with LVR, suggesting genetic factors influencing physical activity levels may, in part, be independent from genes influencing metabolism.

Effect of lemongrass water extract supplementation on atherogenic index and antioxidant status in rats

Cymbopogon citratus (DC) Stapf., commonly known as lemongrass, possesses strong antioxidant and cardiotonic properties. Lemongrass water extract contains several polyphenolic compounds including gallic acid, isoquercetin, quercetin, rutin, catechin and tannic acid. Rutin, isoquercetin catechin and quercetin are the flavonoids most abundantly found in the extract. The extract significantly decreased total cholesterol, low-density lipoprotein and atherogenic index in rats after treatment (p < 0.05). Expression of genes and protein of sterol regulatory element binding protein-1c (SREBP1c) and HMG-CoA reductase (HMGR) was also lowered significantly in treated groups (p < 0.05). Moreover, serum antioxidant capacity increased in treated rats in comparison with untreated ones (p < 0.05) and was associated with decreased serum lipid peroxidation.

Regulation of hepatic hydroxy methyl glutarate - CoA reductase for controlling hypercholesterolemia in rats

Hypercholesterolemia is a major risk factor upon developing cardiovascular diseases. This study is aiming to investigate the inhibition role of quercetin on hydroxy methyl glutarate - CoA reductase activity and its gene for attenuating hypercholesterolemia. The kinetic characteristics of HMG-CoA reductase activity were evaluated on extracellular rat liver microsomes. For studying the effect of quercetin by inducing hypercholesterolemia rats by Tyloxapol (i.v.). In addition, rats were treated with different doses of quercetin according to the inhibition constant of this inhibitor. Our results showed that in quercetin rats groups plasma cholesterol, triglycerides, LDL -cholesterol and total lipids levels and hepatic (TBARS) level were significantly decreased as compared with negative control. However, plasma HDL level, hepatic total thiol level, catalase activity and total protein level significantly increased groups as compared with negative control. In addition, HMG-CoA reductase activity was decreased in quercetin groups and this confirmed in gene expression that these groups caused downregulation for HMG-CoA reductase. However, LDL receptor (LDLr) gene expression was upregulated by quercetin. Moreover, histopathological examination of rat liver showed the ameliorative effect of quercetin on hypercholesterolemic effect of triton. In conclusion, quercetin may consider as a new saving candidate for the future development of hypocholesterolemia agents.

Comparison of potential preventive effects of pomegranate flower, peel and seed oil on insulin resistance and inflammation in high-fat and high-sucrose diet-induced obesity mice model

OBJECTIVE

The potentially beneficial effects of pomegranate peel (PPE), flower (PFE) and seed oil (PSO) extracts, in comparison with rosiglitazone, on adiposity, lipid profile, glucose homoeostasis, as well as on the underlying inflammatory mechanisms, were examined in high-fat and high-sucrose (HF/HS) diet-induced obese (DIO) mice.

MEASUREMENTS

Body weight, body fat, energy expenditure, food and liquid intake, blood glucose, and plasma levels of insulin, lipids and cytokines were measured.

RESULTS

After two weeks, PSO (2 ml/kg/day) and rosiglitazone (3 mg/kg/day) had not improved glucose intolerance. After 4 weeks, both treatments significantly reduced fasting blood glucose and an insulin tolerance test showed that they also improved insulin sensitivity. Treatment with PPE, PFE and PSO, reduced the plasma levels of the pro-inflammatory cytokines such as interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α), and PFE increased the level of the anti-inflammatory cytokine interleukin-10 (IL-10).

CONCLUSION

PPE, PFE and PSO have anti-inflammatory properties. PSO also improved insulin sensitivity.

Tributyltin promoted hepatic steatosis in zebrafish (Danio rerio) and the molecular pathogenesis involved

Endocrine disruptor effects of tributyltin (TBT) are well established in fish. However, the adverse effects on lipid metabolism are less well understood. Since the liver is the predominant site of de novo synthesis of lipids, the present study uses zebrafish (Danio rerio) to examine lipid accumulation in the livers and hepatic gene expression associated with lipid metabolism pathways. After exposure for 90 days, we found that the livers in fish exposed to TBT were yellowish in appearance and with accumulation of lipid droplet, which is consistent with the specific pathological features of steatosis. Molecular analysis revealed that TBT induced hepatic steatosis by increasing the gene expression associated with lipid transport, lipid storage, lipiogenic enzymes and lipiogenic factors in the livers. Moreover, TBT enhanced hepatic caspase-3 activity and up-regulated genes related to apoptosis and cell-death, which indicated steatotic livers of fish exposed to TBT and the subsequent liver damage were likely due to accelerated hepatocyte apoptosis or cell stress. In short, TBT can produce multiple and complex alterations in transcriptional activity of lipid metabolism and cell damage, which provides potential molecular evidence of TBT on hepatic steatosis.

Plasma proprotein convertase subtilisin/kexin type 9 is associated with Lp(a) in type 2 diabetic patients

AIM

Recent in vitro researches have shown that plasma Lp(a) can be reduced using a proprotein convertase subtilisin/kexin type 9 (PCSK9)-inhibitory monoclonal antibody. In our clinical study we tried to investigate the association between plasma Lp(a) and PCSK9 in Type 2 diabetic patients with elevated plasma Lp(a), and to check whether such an association would be related to LDL-receptor (LDL-R) levels.

METHODS

Plasma PCSK9 and LDL-R concentrations were measured by sandwich ELISA methods using recombinant human PCSK9 protein and LDL-R protein as standards in a cohort with type 2 diabetic patients (n=50) compared to an age- and sex-matched control group (n=50). Both clinical and biochemical parameters were determined in all patients.

RESULTS

Plasma PCSK9 level was significantly elevated in T2DM patients compared to controls (44.61±14.44 and 33.22±11.79ng/mL, respectively, P<0.0001). However LDL-R levels did not differ between the two groups. Remarkably, plasma PCSK9 levels were positively correlated with Lp(a) levels in whole population (r=+0.227, P=0.03) as well as in T2DM group (r=+0.398, P=0.0061) but not in control group. Multiple linear regression analysis showed that plasma Lp(a) levels were independently associated to those of PCSK9.

CONCLUSION

Lp(a) has been proposed as a contributing factor to the accelerated development of macrovascular complications in T2DM. Its synergic effect with PCSK9 may explain the enhanced atherogenicity in T2DM patients.

Lipidomic analysis of serum from high fat diet induced obese mice

Lipid metabolites regulate fatty acid and glucose homeostasis. The intention of the current study is to identify circulating lipid species, which are altered in rodent obesity and strongly correlate with the classically measured metabolites glucose, triglycerides, and cholesterol. Mice fed a high fat diet (HFD) for 14 weeks have increased body weight and fasting glucose. Serum triglycerides are not altered, while cholesterol tends to be increased. Accordingly, major cholesteryl ester (CE) species and free cholesterol are not significantly raised in obesity while minor metabolites, including CE 20:3 and CE 18:3, are increased or reduced, respectively. Distinct sphingomyelin (SM) species are elevated while ceramides are not raised. Phosphatidylinositol (PI) species, including PI 34:1, are raised while others are decreased. PI 34:1 strongly correlates with fasting glucose and proinsulin levels. Phosphatidylcholine (PC) 26:0, 40:2, and 40:5, which are induced in obesity, correlate with cholesterol. PC 38:4 and PC 40:6 are also raised in fat fed mice and positively correlate with fasting glucose. Lysophosphatidylcholine (LPC) species are also changed in obesity and the already shown reduction of LPC 16:1 has been confirmed. LPC 22:4, which is increased, correlates with serum cholesterol. The data indicate that circulating levels of various lipid species are changed in the obesity model studied and some of them are strongly associated with classically measured metabolites.

The Influence of an Obesogenic Diet on Oxysterol Metabolism in C57BL/6J Mice

Our current understanding of oxysterol metabolism during different disease states such as obesity and dyslipidemia is limited. Therefore, the aim of this study was to determine the effect of diet-induced obesity on the tissue distribution of various oxysterols and the mRNA expression of key enzymes involved in oxysterol metabolism. To induce obesity, male C57BL/6J mice were fed a high fat-cholesterol diet for 24 weeks. Following diet-induced obesity, plasma levels of 4β-hydroxycholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, and 27-hydroxycholesterol were significantly (P < 0.05) increased. In the liver and adipose tissue of the obese mice, 4β-hydroxycholesterol was significantly (P < 0.05) increased, whereas 27-hydroxycholesterol was increased only in the adipose tissue. No significant changes in either hepatic or adipose tissue mRNA expression were observed for oxysterol synthesizing enzymes 4β-hydroxylase, 27-hydroxylase, or 7α-hydroxylase. Hepatic mRNA expression of SULT2B1b, a key enzyme involved in oxysterol detoxification, was significantly (P < 0.05) elevated in the obese mice. Interestingly, the appearance of the large HDL₁ lipoprotein was observed with increased oxysterol synthesis during obesity. In diet-induced obese mice, dietary intake and endogenous enzymatic synthesis of oxysterols could not account for the increased oxysterol levels, suggesting that nonenzymatic cholesterol oxidation pathways may be responsible for the changes in oxysterol metabolism.

Effect of combined mulberry leaf and fruit extract on liver and skin cholesterol transporters in high fat diet-induced obese mice

Obesity is an epidemic disease characterized by an increased inflammatory state and chronic oxidative stress with high levels of pro-inflammatory cytokines and lipid peroxidation. Moreover, obesity alters cholesterol metabolism with increases in low-density lipoprotein (LDL) cholesterols and triglycerides and decreases in high-density lipoprotein (HDL) cholesterols. It has been shown that mulberry leaf and fruit ameliorated hyperglycemic and hyperlipidemic conditions in obese and diabetic subjects. We hypothesized that supplementation with mulberry leaf combined with mulberry fruit (MLFE) ameliorate cholesterol transfer proteins accompanied by reduction of oxidative stress in the high fat diet induced obesity. Mice were fed control diet (CON) or high fat diet (HF) for 9 weeks. After obesity was induced, the mice were administered either the HF or the HF with combination of equal amount of mulberry leaf and fruit extract (MLFE) at 500mg/kg/day by gavage for 12 weeks. MLFE treatment ameliorated HF induced oxidative stress demonstrated by 4-hydroxynonenal (4-HNE) and modulated the expression of 2 key proteins involved in cholesterol transfer such as scavenger receptor class B type 1 (SR-B1) and ATP-binding cassette transporter A1 (ABCA1) in the HF treated animals. This effect was mainly noted in liver tissue rather than in cutaneous tissue. Collectively, this study demonstrated that MLFE treatment has beneficial effects on the modulation of high fat diet-induced oxidative stress and on the regulation of cholesterol transporters. These results suggest that MLFE might be a beneficial substance for conventional therapies to treat obesity and its complications.

Multiple sclerosis is not a disease of the immune system

Multiple sclerosis is a complex neurodegenerative disease, thought to arise through autoimmunity against antigens of the central nervous system. The autoimmunity hypothesis fails to explain why genetic and environmental risk factors linked to the disease in one population tend to be unimportant in other populations. Despite great advances in documenting the cell and molecular mechanisms underlying MS pathophysiology, the autoimmunity framework has also been unable to develop a comprehensive explanation of the etiology of the disease. I propose a new framework for understanding MS as a dysfunction of the metabolism of lipids. Specifically, the homeostasis of lipid metabolism collapses during acute-phase inflammatory response triggered by a pathogen, trauma, or stress, starting a feedback loop of increased oxidative stress, inflammatory response, and proliferation of cytoxic foam cells that cross the blood brain barrier and both catabolize myelin and prevent remyelination. Understanding MS as a chronic metabolic disorder illuminates four aspects of disease onset and progression: 1) its pathophysiology; 2) genetic susceptibility; 3) environmental and pathogen triggers; and 4) the skewed sex ratio of patients. It also suggests new avenues for treatment.

Apolipoprotein B secretion is regulated by hepatic triglyceride, and not insulin, in a model of increased hepatic insulin signaling

OBJECTIVE

States of insulin resistance, hyperinsulinemia, and hepatic steatosis are associated with increased secretion of triglycerides (TG) and apolipoprotein B (apoB), even though insulin targets apoB for degradation. We used hepatic-specific "phosphatase and tensin homologue deleted on chromosome 10" (Pten) knockout (hPten-ko) mice, with increased hepatic insulin signaling, to determine the relative roles of insulin signaling and hepatic TG in regulating apoB secretion.

METHODS AND RESULTS

TG and apoB secretion was elevated in hPten-ko mice. When hepatic TG was reduced by inhibition of diacylglycerol acyltransferase 1/diacylglycerol acyltransferase 2 or sterol regulatory element-binding protein-1c, both TG secretion and apoB secretion fell without changes in hepatic insulin signaling. Acute reconstitution of hPten reduced hepatic TG content, and both TG and apoB secretion fell within 4 days despite decreased hepatic insulin signaling. Acute depletion of hepatic Pten by adenoviral introduction of Cre into Pten floxed mice caused steatosis within 4 days, and secretion of both TG and apoB increased despite increased hepatic insulin signaling. Even when steatosis after acute Pten depletion was prevented by pretreatment with SREBP-1c antisense oligonucleotides, apoB secretion was not reduced after 4 days. Ex vivo results were in primary hepatocytes were similar.

CONCLUSIONS

Either hepatic TG is the dominant regulator of apoB secretion or any inhibitory effects of hepatic insulin signaling on apoB secretion is very short-lived.

TNF-related apoptosis-inducing ligand (TRAIL) protects against diabetes and atherosclerosis in Apoe ⁻/⁻ mice

AIMS/HYPOTHESIS

TNF-related apoptosis-inducing ligand (TRAIL) is implicated in the regulation of diabetes and is reduced in patients with cardiovascular disease. Although TRAIL receptors are widespread, and TRAIL can promote cell proliferation and apoptosis, it is not known how TRAIL might protect against diabetes and atherosclerosis.

METHODS

We examined the development of atherosclerosis and diabetes in Apoe (-/-), Trail (also known as Tnfsf10)( -/- ) Apoe ( -/- ) and Trail ( -/- ) mice that were fed a high-fat diet. Plasma cholesterol, triacylglycerol, glucose and insulin, as well as changes in various metabolic enzymes and regulators were assessed. Glucose and insulin tolerance tests were performed. Pancreatic islets were examined for insulin and beta cell dysfunction (apoptosis and macrophage infiltration).

RESULTS

Compared with Apoe ( -/- ) mice, Trail ( -/- ) Apoe ( -/- ) and Trail ( -/- ) mice exhibited several features of diabetes, including increased weight, hyperglycaemia, reduced plasma insulin, impaired glucose tolerance, beta cell dysfunction, reduced islet insulin, macrophage infiltration and increased apoptosis. Trail ( -/- ) Apoe ( -/- ) mice had increased plasma cholesterol, triacylglycerol, and VLDL- and LDL-cholesterol, and increased expression of genes involved in cholesterol synthesis and lipogenesis. Trail ( -/- ) Apoe ( -/- ) mice also had increased atherosclerosis, with several features of plaque instability.

CONCLUSIONS/INTERPRETATION

We show for the first time that TRAIL deficiency promotes numerous features of diabetes that are typical of human disease, and are associated with reduced insulin and pancreatic inflammation/apoptosis. TRAIL also regulates cholesterol and triacylglycerol homeostasis in Apoe ( -/- ) mice by increasing the expression of genes involved in (1) cholesterol synthesis and absorption, and (2) triacylglycerol production.

Hepatoprotective activity of scutellariae radix extract in mice fed a high fat diet with chronic alcohol exposure

Scutellariae radix (SR) is an herbal medicine used for the treatment of inflammatory diseases. To investigate whether the SR water extract has a hepatoprotective effect in mice fed a high fat diet with chronic alcohol consumption, ICR mice were fed one of the following diets: a control diet (CD, 16% fat), a high fat diet (HFD, 40% fat), a high fat diet with either ethanol (HFDE, 25% v/v, ad libitum) alone or ethanol with SR extract (HFDESR, 100 mg/kg, p.o.) for 28 days, respectively. The combination of high fat diet with ethanol exposure induced hepatic damage that was manifested by a significant increase in the activities of functional enzymes, alanine transaminase (ALT), aspartate transaminase (AST) and lactate dehydrogenase (LDH) in serum. Also, the liver and visceral fat weights were increased and the lipid profiles in serum and liver homogenate including triglyceride, total cholesterol, LDL-cholesterol were significantly deteriorated. The SR supplements significantly reversed these altered parameters to near the values of the CD mice. Specifically, the expression of 3-hydroxy-3-methylglutaryl-coenzymeA (HMG-CoA) reductase in liver homogenate was significantly lowered in the HFDESR group compared with that of either the HFD or HFDE groups, which revealed that the SR extract could afford protection in the alleviation of high fat and alcoholic liver damage.

Intestinal and hepatic cholesterol carriers in diabetic Psammomys obesus

Insulin resistance and type 2 diabetes (T2D) are characterized by hyperlipidemia. The aim of the present study was to elucidate whether T2D contributes to abnormal cholesterol (CHOL) homeostasis. Experiments were carried out in the small intestine and liver of Psammomys obesus, a model of nutritionally induced T2D. Our results show that diabetic animals exhibited a lower intestinal CHOL uptake, which was associated with a decrease in 1) the gene and protein expression of Niemann-Pick C1 like 1 that plays a pivotal role in CHOL incorporation in the enterocytes; and 2) mRNA of ATP-binding cassette transporters (ABC)A1 that mediates CHOL efflux from intestinal cells to apolipoprotein A-I and high-density lipoprotein. No changes were observed in the other intestinal transporters scavenger receptor-class B type I (SR-BI) and annexin 2. On the other hand, in diabetic animals, a significant mRNA decrease was noticed in intestinal ABCG5 and ABCG8 responsible for the secretion of absorbed CHOL back into the lumen. Furthermore, jejunal PCSK9 protein was diminished and low-density lipoprotein receptor was raised, along with a significant down-regulation in jejunal 3-hydroxy-3-methylglutaryl-coenzyme A reductase in P. obesus with T2D. Finally, among the transcription factors tested, only an increase in liver X receptors alpha and a decrease in peroxisome proliferator-activated receptors delta/beta mRNAs were detected in the intestine. In the liver, there was 1) an augmentation in the protein mass of Niemann-Pick C1 like 1, SR-BI, and annexin 2; 2) an up-regulation of SR-BI mRNA; 3) a fall in ABCG8 protein content as well as in ABCG5 and ABCA1 mRNA; and 4) an augmentation in liver X receptors alpha and peroxisome proliferator-activated receptors beta/delta mRNA, together with a drop in sterol regulatory element binding protein-2 protein. Our findings show that the development in P. obesus with T2D modifies the whole intraenterocyte and hepatocyte machinery responsible for CHOL homeostasis.

Beneficial effects of curcumin on hyperlipidemia and insulin resistance in high-fat-fed hamsters

This study investigated the effect of curcumin (0.05-g/100-g diet) supplementation on a high-fat diet (10% coconut oil, 0.2% cholesterol, wt/wt) fed to hamsters, one of the rodent species that are most closely related to humans in lipid metabolism. Curcumin significantly lowered the levels of free fatty acid, total cholesterol, triglyceride, and leptin and the homeostasis model assessment of insulin resistance index, whereas it elevated the levels of high-density lipoprotein cholesterol and apolipoprotein (apo) A-I and paraoxonase activity in plasma, compared with the control group. The levels of hepatic cholesterol and triglyceride were also lower in the curcumin group than in the control group. In the liver, fatty acid beta-oxidation activity was significantly higher in the curcumin group than in the control group, whereas fatty acid synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, and acyl coenzyme A:cholesterol acyltransferase activities were significantly lower. Curcumin significantly lowered the lipid peroxide levels in the erythrocyte and liver compared with the control group. These results indicate that curcumin exhibits an obvious hypolipidemic effect by increasing plasma paraoxonase activity, ratios of high-density lipoprotein cholesterol to total cholesterol and of apo A-I to apo B, and hepatic fatty acid oxidation activity with simultaneous inhibition of hepatic fatty acid and cholesterol biosynthesis in high-fat-fed hamsters.

Hepatic insulin resistance is sufficient to produce dyslipidemia and susceptibility to atherosclerosis

Insulin resistance plays a central role in the development of the metabolic syndrome, but how it relates to cardiovascular disease remains controversial. Liver insulin receptor knockout (LIRKO) mice have pure hepatic insulin resistance. On a standard chow diet, LIRKO mice have a proatherogenic lipoprotein profile with reduced high-density lipoprotein (HDL) cholesterol and very low-density lipoprotein (VLDL) particles that are markedly enriched in cholesterol. This is due to increased secretion and decreased clearance of apolipoprotein B-containing lipoproteins, coupled with decreased triglyceride secretion secondary to increased expression of Pgc-1 beta (Ppargc-1b), which promotes VLDL secretion, but decreased expression of Srebp-1c (Srebf1), Srebp-2 (Srebf2), and their targets, the lipogenic enzymes and the LDL receptor. Within 12 weeks on an atherogenic diet, LIRKO mice show marked hypercholesterolemia, and 100% of LIRKO mice, but 0% of controls, develop severe atherosclerosis. Thus, insulin resistance at the level of the liver is sufficient to produce the dyslipidemia and increased risk of atherosclerosis associated with the metabolic syndrome.

Nutrigenomics: concepts and applications to pharmacogenomics and clinical medicine

The maintenance of health and the prevention and treatment of chronic diseases are influenced by naturally occurring chemicals in foods. In addition to supplying the substrates for producing energy, a large number of dietary chemicals are bioactive--that is, they alter the regulation of biological processes and, either directly or indirectly, the expression of genetic information. Nutrients and bioactives may produce different physiological phenotypes among individuals because of genetic variability and not only alter health, but also disease initiation, progression and severity. The study and application of gene-nutrient interactions is called nutritional genomics or nutrigenomics. Nutrigenomic concepts, research strategies and clinical implementation are similar to and overlap those of pharmacogenomics, and both are fundamental to the treatment of disease and maintenance of optimal health.

Roles of nuclear receptors in the up-regulation of hepatic cholesterol 7alpha-hydroxylase by cholestyramine in rats

Nuclear receptors are involved in regulating the expression of cholesterol 7alpha-hydroxylase (CYP7A1), however, their roles in the up-regulation of CYP7A1 by cholestyramine (CSR) are still unclear. In the present study, male Wistar rats were divided into four groups and fed [high sucrose + 10% lard diet] (H), [H + 3% CSR diet] (H + CSR), [H + 0.5% cholesterol + 0.25% sodium cholate diet] (C), or [C + 3% CSR diet] (C + CSR) for 2 weeks. Cholestyramine decreased serum and liver cholesterol levels significantly in rats fed C-based diets, but had no effect on these parameters in rats fed H-based diets. Cholestyramine raised hepatic levels of CYP7A1 mRNA and activity in both groups. The gene expression of hepatic ATP-binding cassettes A1 and G5, regulated by liver X receptor (LXR), were unchanged and down-regulated by cholestyramine, respectively. The mRNA levels of the hepatic ATP-binding cassette B11 and short heterodimer partner (SHP), regulated by farnesoid X receptor (FXR), were not changed by cholestyramine. C-based diets, which contained cholesterol and cholic acid, increased SHP mRNA levels compared to H-based diets. Consequently, in rats fed the C+CSR diet, hepatic FXR was activated by dietary bile acids, but the hepatic CYP7A1 mRNA level was increased 16-fold compared to that in rats fed an H diet. These results suggest that cholestyramine up-regulates the expression of CYP7A1 independently via LXR- or FXR-mediated pathways in rats.

Oxidative stress and dysregulation of NAD(P)H oxidase and antioxidant enzymes in diet-induced metabolic syndrome

Previously, we have demonstrated that chronic consumption of a high-fat, high-refined sugar (HFS) diet results in metabolic syndrome which is marked by obesity, insulin resistance, hyperlipidemia, and hypertension in Fischer rats. Metabolic syndrome in this model is associated with oxidative stress, avid nitric oxide (NO) inactivation by reactive oxygen species (ROS), diminished NO bioavailability, and dysregulation of NO synthase isotypes. Although occurrence of oxidative stress and its impact on NO metabolism are well established, the molecular source(s) of ROS in this model is unknown. In an attempt to explore this issue, we measured protein expressions of the key ROS-producing enzyme, NAD(P)H oxidase, and the main antioxidant enzymes, superoxide dismutase (CuZn SOD and Mn SOD), catalase, glutathione peroxidase (GPX), and heme oxygenase-2 (HO-2), in the kidney and aorta of Fischer rats fed an HFS or low-fat, complex-carbohydrate diet for 7 months. In addition, plasma lipid peroxidation product (malondialdehyde) as well as endothelium-dependent and -independent vasorelaxation (aorta rings) was determined. The results showed a significant upregulation of gp91(phox) subunit of NAD(P)H oxidase and downregulations of SOD isoforms, GPX, and HO-2 in the kidney and aorta of the HFS-fed animals. This was associated with increased plasma malondialdehyde concentration and impaired vasodilatory response to acetylcholine, but not the NO donor, Na nitroprusside. The latter findings confirm the presence of oxidative stress and endothelial dysfunction in the HFS-fed rats. Oxidative stress and endothelial dysfunction in the diet-induced metabolic syndrome are accompanied by upregulation of NAD(P)H oxidase, pointing to increased ROS production capacity, and downregulation of SOD isoforms, GPX, and HO-2, the key enzymes in the antioxidant defense system.

Low molecular weight chitosan inhibits obesity induced by feeding a high-fat diet long-term in mice

Three low molecular weight chitosans (molecular weight: 21, 46 and 130 kDa) obtained by enzymatic hydrolysis of a high molecular weight chitosan (average molecular weight: 650 kDa) had low viscosity and were water-soluble. The effects of these water-soluble chitosans on pancreatic lipase (in-vitro) and the elevation of plasma triacylglycerol concentration after the oral lipid tolerance test were examined in mice. The water-soluble 46-kDa chitosan was the most effective at inhibiting pancreatic lipase activity (in-vitro) and plasma triacylglycerol elevation after the oral lipid tolerance test. Based on this result, the effects of the 46-kDa chitosan on increases in bodyweight, various white adipose tissue weights, and plasma and liver lipids were examined in mice fed a high-fat diet for 20 weeks. Water-soluble 46-kDa chitosan (300 mg kg(-1), twice daily) prevented increases in bodyweight, various white adipose tissue weights and liver lipids (cholesterol and triacylglycerol) in mice fed a high-fat diet, and further increased the faecal bile acid and fat. The results suggest that the lipid-lowering effects of the 46-kDa chitosan may be mediated by increases in faecal fat and/or bile acid excretion resulting from the binding of bile acids, and by a decrease in the absorption of dietary lipids (triacylglycerol and cholesterol) from the small intestine as a result of the inhibition of pancreatic lipase activity. Water-soluble 46-kDa chitosan (100 and 300 mg kg(-1), twice daily) did not cause liver damage with the elevation of glutamic oxaloacetic transaminase and glutamic pyruvic transaminase, or kidney damage with the elevation of blood nitrogen urea. It was concluded that water-soluble 46-kDa chitosan is a safe functional food.

Potential role of acyl-coenzyme A:cholesterol transferase (ACAT) Inhibitors as hypolipidemic and antiatherosclerosis drugs

Acyl-coenzyme A:cholesterol transferase (ACAT) is an integral membrane protein localized in the endoplasmic reticulum. ACAT catalyzes the formation of cholesteryl esters from cholesterol and fatty acyl coenzyme A. The cholesteryl esters are stored as cytoplasmic lipid droplets inside the cell. This process is very important to the organism as high cholesterol levels have been associated with cardiovascular disease. In mammals, two ACAT genes have been identified, ACAT1 and ACAT2. ACAT1 is ubiquitous and is responsible for cholesteryl ester formation in brain, adrenal glands, macrophages, and kidneys. ACAT2 is expressed in the liver and intestine. The inhibition of ACAT activity has been associated with decreased plasma cholesterol levels by suppressing cholesterol absorption and by diminishing the assembly and secretion of apolipoprotein B-containing lipoproteins such as very low density lipoprotein (VLDL). ACAT inhibition also prevents the conversion of macrophages into foam cells in the arterial walls, a critical event in the development of atherosclerosis. This review paper will focus on the role of ACAT in cholesterol metabolism, in particular as a target to develop novel therapeutic agents to control hypercholesterolemia, atherosclerosis, and Alzheimer's disease.