Prolonged inhibition of cholesterol synthesis by atorvastatin inhibits apo B-100 and triglyceride secretion from HepG2 cells

High-fat diet induced alterations in plasma membrane cholesterol content impairs insulin receptor binding and signalling in mouse liver but is ameliorated by atorvastatin

A high-fat diet (HFD) impairs insulin binding and signalling and may contribute to the development of insulin resistance. In addition, in vitro studies have shown that alterations in plasma membrane cholesterol influence ligand binding and downstream signalling for several receptor-tyrosine kinases (RTKs), including the insulin receptor. Using an ex vivo approach, we explored the effects of a HFD on insulin binding and signalling in mouse liver and relate these to observed changes in plasma membrane cholesterol. Mice fed a HFD demonstrated decreased insulin signalling compared to mice fed a normal chow diet (ND), indicated by a 3-fold decrease in insulin binding (P < 0.001) and a similar decrease in insulin receptor phosphorylation (~2.5-fold; P < 0.0001). Interestingly, we also observed a marked decrease in the cholesterol content of liver plasma membranes in the HFD fed mice (P < 0.0001). These effects of the HFD were found to be ameliorated by atorvastatin treatment (P < 0.0001). However, in ND mice, atorvastatin had no influence on membrane cholesterol content or insulin binding and signalling. The influence of membrane cholesterol on insulin binding and signalling was also corroborated in HepG2 cells. To the best of our knowledge, this is the first demonstration of the effects of a HFD and atorvastatin treatment on changes in plasma membrane cholesterol content and the consequent effects on insulin binding and signalling. Collectively, these findings suggest that changes in membrane cholesterol content could be an important underlying reason for the long-known effects of a HFD on the development of insulin resistance.

The Question of a Role for Statins in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible central vision loss in patients over the age of 65 years in industrialized countries. Epidemiologic studies suggest that high dietary fat intake is a risk factor for the development and progression of both vascular and retinal disease. These, and other associations, suggest a hypothesis linking elevated cholesterol and AMD progression. It follows, therefore, that cholesterol-lowering medications, such as statins, may influence the onset and progression of AMD. However, the findings have been inconclusive as to whether statins play a role in AMD. Due to the significant public health implications of a potential inhibitory effect of statins on the onset and progression of AMD, it is important to continually evaluate emerging findings germane to this question.

Soft Drusen in Age-Related Macular Degeneration: Biology and Targeting Via the Oil Spill Strategies

AMD is a major cause of legal blindness in older adults approachable through multidisciplinary research involving human tissues and patients. AMD is a vascular-metabolic-inflammatory disease, in which two sets of extracellular deposits, soft drusen/basal linear deposit (BLinD) and subretinal drusenoid deposit (SDD), confer risk for end-stages of atrophy and neovascularization. Understanding how deposits form can lead to insights for new preventions and therapy. The topographic correspondence of BLinD and SDD with cones and rods, respectively, suggest newly realized exchange pathways among outer retinal cells and across Bruch's membrane and the subretinal space, in service of highly evolved, eye-specific physiology. This review focuses on soft drusen/BLinD, summarizing evidence that a major ultrastructural component is large apolipoprotein B,E-containing, cholesterol-rich lipoproteins secreted by the retinal pigment epithelium (RPE) that offload unneeded lipids of dietary and outer segment origin to create an atherosclerosis-like progression in the subRPE-basal lamina space. Clinical observations and an RPE cell culture system combine to suggest that soft drusen/BLinD form when secretions of functional RPE back up in the subRPE-basal lamina space by impaired egress across aged Bruch's membrane-choriocapillary endothelium. The soft drusen lifecycle includes growth, anterior migration of RPE atop drusen, then collapse, and atrophy. Proof-of-concept studies in humans and animal models suggest that targeting the “Oil Spill in Bruch's membrane” offers promise of treating a process in early AMD that underlies progression to both end-stages. A companion article addresses the antecedents of soft drusen within the biology of the macula.

The molecular mechanism of the cholesterol-lowering effect of dill and kale: The influence of the food matrix components

Foods are complex matrices containing many different compounds, all of which contribute to the overall effect of the food itself, although they have different mechanisms of action. While evaluating the effect of bioactive compounds, it is important to consider that the use of a single compound can hide the effects of the other molecules that can act synergistically or antagonistically in the same food. The aim of the present study was to evaluate the influence of food matrix components by comparing two edible plants (dill and kale) with cholesterol-lowering potential and similar contents of their most representative bioactive, quercetin. The molecular effects of the extracts were evaluated in HepG2 cells by measuring the expression of sterol-regulatory element-binding proteins (SREBPs), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and low density lipoprotein receptor (LDLR) at the mRNA and protein level. The results reported here show that both extracts reduced the cellular cholesterol level with a similar trend and magnitude. It is conceivable that the slightly different results are due to the diverse composition of minor bioactive compounds, indicating that only by considering food as a whole is it possible to understand the complex relationship between food, nutrition, and health in a foodomics vision.

Statins increase hepatic cholesterol synthesis and stimulate fecal cholesterol elimination in mice

Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis. Statins reduce plasma cholesterol levels, but whether this is actually caused by inhibition of de novo cholesterol synthesis has not been clearly established. Using three different statins, we investigated the effects on cholesterol metabolism in mice in detail. Surprisingly, direct measurement of whole body cholesterol synthesis revealed that cholesterol synthesis was robustly increased in statin-treated mice. Measurement of organ-specific cholesterol synthesis demonstrated that the liver is predominantly responsible for the increase in cholesterol synthesis. Excess synthesized cholesterol did not accumulate in the plasma, as plasma cholesterol decreased. However, statin treatment led to an increase in cholesterol removal via the feces. Interestingly, enhanced cholesterol excretion in response to rosuvastatin and lovastatin treatment was mainly mediated via biliary cholesterol secretion, whereas atorvastatin mainly stimulated cholesterol removal via the transintestinal cholesterol excretion pathway. Moreover, we show that plasma cholesterol precursor levels do not reflect cholesterol synthesis rates during statin treatment in mice. In conclusion, cholesterol synthesis is paradoxically increased upon statin treatment in mice. However, statins potently stimulate the excretion of cholesterol from the body, which sheds new light on possible mechanisms underlying the cholesterol-lowering effects of statins.

Atorvastatin increases miR-124a expression: a mechanism of Gamt modulation in liver cells

Atorvastatin is used to control cholesterol and lipid levels in hyperlipidaemic and hypercholesterolaemic patients. Myopathy and hepatotoxicity, however, have been reported as side effects in a small percentage of statin users. This study aimed to investigate the cytotoxicity and the effect of atorvastatin on microRNA expression in HepG2 cells. The methylthiazol tetrazolium assay was used to assess hepatocyte viability and at 20 μM atorvastatin (24 h) treatment were 82 ± 1.5% viable (P = 0.0002). Levels of intracellular ATP in cells treated with 20 μM atorvastatin were reduced by 1.25-fold, P = 0.002. Cytotoxicity, measured by the release of intracellular lactate dehydrogenase, was increased from 0.95 ± 0.29 units in control cells to 1.12 ± 0.02 units (P = 0.002) in atorvastatin treated cells. A panel of 84-miRNA species was used to evaluate the effect of atorvastatin on miRNA expression. MiR-124a was significantly up-regulated by atorvastatin (12.94-fold). A significant decrease in GAMT expression (3.54-fold) was observed in atorvastatin treated cells following quantitative PCR analysis. In addition, western blotting data showed GAMT protein levels were significantly lower than the controls (3.02-fold) and analysis of creatine levels in treated cells showed a significant decrease in the atorvastatin treated culture supernatant compared to control culture supernatant (32.33 ± 3.51 μM/l vs. 59.67 ± 1.52μM/l, P = 0.0056). This is the first study to show that atorvastatin up-regulates miR-124a levels and consequently modulates GAMT expression in hepatocytes.

MicroRNAs regulating apolipoprotein B-containing lipoprotein production

MicroRNAs (miRs) are small, non-coding RNAs that regulate gene expression and have been implicated in many pathological conditions. Significant progress has been made to unveil their role in lipid metabolism. This review aims at summarizing the role of different miRs that regulate hepatic assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins. Overproduction and/or impaired clearance of these lipoproteins from circulation increase plasma concentrations of lipids enhancing risk for cardiovascular disease. So far, three miRs, miR-122, miR-34a, and miR-30c have been shown to modulate hepatic production of apoB-containing low density lipoproteins. In this review, we will first provide a brief overview of lipid metabolism and apoB-containing lipoprotein assembly to orient readers to different steps that have been shown to be regulated by miRs. Then, we will discuss the role of each miR on plasma lipids and atherosclerotic burden. Furthermore, we will summarize mechanistic studies explaining how these miRs regulate hepatic lipid synthesis, fatty acid oxidation, and lipoprotein secretion. Finally, we will briefly highlight the potential use of each miR as a therapeutic drug for treating cardiovascular diseases. This article is part of a Special Issue entitled: MicroRNAs and lipid/energy metabolism and related diseases edited by Carlos Fernández-Hernando and Yajaira Suárez.

Extraction of a soluble polysaccharide from Auricularia polytricha and evaluation of its anti-hypercholesterolemic effect in rats

Mushroom extracts are a new source of supplements for health and pharmaceutical due to their bioactivities. This study was to optimize the extraction parameters of a soluble polysaccharide from Auricularia polytricha (SPAP) by response surface methodology. The practical optimum parameters were an extraction time of 4h, an extraction temperature of 95 °C and a ratio of water to fruiting bodies of 28 mL/g, and the highest extraction rate was 19.77%. In vivo, male Sprague-Dawley (SD) rats were diet-induced hypercholesterolemic models and oral administration of SPAP to evaluate anti-hypercholesterolemic effects. The results showed that SPAP decreased the serum concentrations of blood lipid, made them close to the normal level. The total cholesterol in the SPAP consumption groups was significantly decreased 34.6 ± 7.6% and 33.3 ± 7.9% with dose of 4.5 and 9.0mg/kg BW in the 29th day. This study suggested that SPAP was a suitable natural agent and may be applied in therapy.

A review on the traditional Chinese medicinal herbs and formulae with hypolipidemic effect

Hyperlipidemia, characterized by the abnormal blood lipid profiles, is one of the dominant factors of many chronic diseases such as diabetes, obesity, and cardiovascular diseases (CVD). For the low cost, effectiveness, and fewer side effects, the popularity of using traditional Chinese medicine (TCM) to handle hyperlipidemia is increasing and its role in health care has been recognized by the public at large. Despite the importance of TCM herbs and formulations, there is no comprehensive review summarizing their scientific findings on handling hyperlipidemia. This review summarizes the recent experimental and clinical results of nine representative single Chinese herbs and seven classic TCM formulae that could improve lipid profiles so as to help understand and compare their underlying mechanisms. Most of single herbs and formulae demonstrated the improvement of hyperlipidemic conditions with multiple and diverse mechanisms of actions similar to conventional Western drugs in spite of their mild side effects. Due to increasing popularity of TCM, more extensive, well-designed preclinical and clinical trials on the potential synergistic and adverse side effects of herb-drug interactions as well as their mechanisms are warranted. Hyperlipidemic patients should be warned about the potential risks of herb-drug interactions, particularly those taking anticoagulants and antiplatelet drugs.

Cholesterol in the retina: the best is yet to come

Historically understudied, cholesterol in the retina is receiving more attention now because of genetic studies showing that several cholesterol-related genes are risk factors for age-related macular degeneration (AMD) and because of eye pathology studies showing high cholesterol content of drusen, aging Bruch's membrane, and newly found subretinal lesions. The challenge before us is determining how the cholesterol-AMD link is realized. Meeting this challenge will require an excellent understanding these genes' roles in retinal physiology and how chorioretinal cholesterol is maintained. In the first half of this review, we will succinctly summarize physico-chemical properties of cholesterol, its distribution in the human body, general principles of maintenance and metabolism, and differences in cholesterol handling in human and mouse that impact on experimental approaches. This information will provide a backdrop to the second part of the review focusing on unique aspects of chorioretinal cholesterol homeostasis, aging in Bruch's membrane, cholesterol in AMD lesions, a model for lesion biogenesis, a model for macular vulnerability based on vascular biology, and alignment of AMD-related genes and pathobiology using cholesterol and an atherosclerosis-like progression as unifying features. We conclude with recommendations for the most important research steps we can take towards delineating the cholesterol-AMD link.

The oil spill in ageing Bruch membrane

Ageing is the largest risk factor for age-related macular degeneration (AMD), and soft drusen and basal linear deposits are lipid-rich extracellular lesions specific to AMD. Oil red O binding neutral lipid represents a major age-related deposition in the Bruch membrane (BrM) and the first identified druse component. Decades after these seminal observations, a natural history of neutral lipid deposition has been articulated and a biochemical model proposed. Results obtained with multiple biochemical, histochemical, and ultrastructural methods, and supported indirectly by epidemiology, suggest that the RPE secretes apolipoprotein B (apoB)-lipoprotein particles of unusual composition into BrM, where they accumulate with age eventually forming a lipid wall, a precursor of basal linear deposit. The authors propose that constituents of these lesions interact with reactive oxygen species to form pro-inflammatory peroxidised lipids that elicit neovascularisation. Here, the authors summarise key evidence supporting both accumulation of BrM lipoproteins leading to lesion formation and lipoprotein production by the RPE. The authors update their model with genetic associations between AMD and genes historically associated with plasma HDL metabolism, and suggest future directions for research and therapeutic strategies based on an oil-spill analogy.

Probucol suppresses enterocytic accumulation of amyloid-β induced by saturated fat and cholesterol feeding

Amyloid-β (Aβ) is secreted from lipogenic organs such as intestine and liver as an apolipoprotein of nascent triacylglycerol rich lipoproteins. Chronically elevated plasma Aβ may compromise cerebrovascular integrity and exacerbate amyloidosis--a hallmark feature of Alzheimer's disease (AD). Probucol is a hypocholesterolemic agent that reduces amyloid burden in transgenic amyloid mice, but the mechanisms for this effect are presently unclear. In this study, the effect of Probucol on intestinal lipoprotein-Aβ homeostasis was explored. Wild-type mice were fed a control low-fat diet and enterocytic Aβ was stimulated by high-fat (HF) diet enriched in 10% (w/w) saturated fat and 1% (w/w) cholesterol for the duration of 1 month. Mice treated with Probucol had the drug incorporated into the chow at 1% (w/w). Quantitative immunofluorescence was utilised to determine intestinal apolipoprotein B (apo B) and Aβ abundance. We found apo B in both the perinuclear region of the enterocytes and the lacteals in all groups. However, HF feeding and Probucol treatment increased secretion of apo B into the lacteals without any change in net villi abundance. On the other hand, HF-induced enterocytic perinuclear Aβ was significantly attenuated by Probucol. No significant changes in Aβ were observed within the lacteals. The findings of this study support the notion that Probucol suppresses dietary fat induced stimulation of Aβ biosynthesis and attenuate availability of apo B lipoprotein-Aβ for secretion.

Human caspase 7 is positively controlled by SREBP-1 and SREBP-2

Statins are lipid-lowering drugs that may help limit cancer occurrence in humans. They drive blockage of the mevalonate pathway, trigger cancer cell apoptosis in vitro and reduce tumour incidence in animals. We have shown in the present study that statins induced apoptosis in HGT-1 human gastric cancer cells, and this was prevented by intermediates of the cholesterol synthetic pathway. In addition, similarly to what we have reported previously for caspase 2 [Logette, Le Jossic-Corcos, Masson, Solier, Sequeira-Legrand, Dugail, Lemaire-Ewing, Desoche, Solary and Corcos (2005) Mol. Cell. Biol. 25, 9621-9631], caspase 7 may also be induced by statins and is under the positive control of SREBP (sterol-regulatory-element-binding protein)-1 and -2, major activators of cholesterol and fatty acid synthesis genes, in HGT-1 cells. Knocking down these proteins strongly reduced caspase 7 mRNA and protein expression, and chromatin immunoprecipitation analyses showed that the proximal promoter region of the CASP7 gene could bind either SREBP-1 or -2. Strikingly, cells selected to grow in the continuous presence of statins showed increased expression of caspase 7 mRNA and protein, which was maintained in the absence of statins for several weeks, suggesting that high expression of this caspase might participate in adaptation to blunting of the mevalonate pathway in this model. Taken together, our results show that caspase 7, as an SREBP-1/2 target, can be induced under mevalonate-restricting conditions, which might help overcome its shortage.

Increased activity of hepatic microsomal triglyceride transfer protein and bile acid synthesis in gallstone disease

A strong interrelationship exists between the regulation of bile acid (BA) metabolism and hepatic very low density lipoprotein (VLDL) production. We have recently shown that BA synthesis is increased in gallstone disease. We investigated the activity of hepatic microsomal triglyceride transfer protein (MTTP) as a surrogate of VLDL production, BA synthesis, and mRNA expression levels of proteins that regulate fatty acid (FA) metabolism in the liver of gallstone (GS) patients compared with GS-free patients. Twenty-seven volunteers subjected to elective surgery; 9 were GS-free and 18 with GS agreed to have a liver biopsy. We quantified by a fluorescence assay the activity of MTTP and by quantitative reverse-transcription PCR (RT-PCR) the mRNA content of hepatic MTTP and genes that regulate hepatic sterol and FA metabolism. Plasma was assayed for lathosterol and 7alpha-hydroxy-4-cholesten-3-one. Liver histology was normal in GS and GS-free patients. Serum VLDL triglycerides and apoB were significantly increased in GS. Hepatic triglycerides tripled in GS (P<0.001) compared with GS-free. MTTP activity increased 70% (P<0.001). Serum lathosterol and hepatic cholesterol concentrations, and mRNA expressions of MTTP, CD36, and FABP1 were similar in GS-free and GS patients. Hepatic mRNA expression of hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) and 3-hydroxyl-3-methyl-glutaryl-CoA synthase (HMGS) were significantly decreased--40% and 27%, respectively--in GS. Serum 7alpha-hydroxy-4-cholesten-3-one was 75% higher, and mRNA expression of CYP7A1 was increased sevenfold (P<0.001) in GS.

CONCLUSION

Hepatic MTTP activity and BA synthesis are increased in GS. Results suggest that hepatic VLDL production and trafficking of BA are increased in gallstone patients.

The effect of high-dose simvastatin on free fatty acid metabolism in patients with type 2 diabetes mellitus

Statins improve all major lipid fractions, reduce coronary heart disease risk, and may have a minor effect on glucose tolerance. A reduction in free fatty acid flux and concentrations could be partly responsible for these effects. We measured nocturnal and postprandial plasma palmitate concentrations and rate of appearance (R(a)) on 2 occasions in 12 obese dyslipidemic subjects with type 2 diabetes mellitus, using a single-blind, crossover format (placebo followed by simvastatin, 80 mg/d), and also on 1 occasion in 6 untreated control subjects. The diabetic subjects had increased average nocturnal (127+/-13 vs 80+/-10 micromol/L, P<.05) and 2-hour postprandial (49+/-6 vs 17+/-2 micromol/L, P<.001) palmitate concentrations, as well as increased nocturnal (31.6+/-3.7 vs 19.5+/-3.7 mmol/m(2) over 9 hours, P<.05) and postprandial (11.5+/-3.7 vs 5.5+/-3.7 mmol/m(2) every 4 hours, P<.005) integrated palmitate R(a) compared to normal controls. High-dose simvastatin reduced serum triglycerides by 35% but had no effect on plasma palmitate concentrations or R(a). These results suggest that the triglyceride-lowering effect of statins is not mediated through an effect on FFA metabolism.

A pilot study of atorvastatin treatment in dyslipemid, non-alcoholic fatty liver patients

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) encompasses a wide spectrum of liver injury. Currently, there are no proven effective therapies available. Atorvastatin is a new 3-hydroxy-3-metylglutaryl coenzyme A reductase inhibitor that reduces lipid serum levels.

AIM

To evaluate the effectiveness and safety of atorvastatin in dyslipemid, non-alcoholic fatty liver patients.

PATIENTS AND METHODS

We prospectively enrolled 25 patients with NAFLD; 22 of them completed the study. Body mass index, serum lipids, liver function tests and liver density assessed by echography were measured at baseline and after 1, 3, 6, 9 and 12 months of treatment. Normalization of transaminases and/or improvement in liver density were treatment end points. Patients received atorvastatin (10-80 mg/daily) according to basal serum choleresterol levels; additionally, they were given standard weight-loss counselling and encouraged to follow a low fat diet.

RESULTS

All 22 patients (14 men, mean age 47 +/- 10 years) had high cholesterol levels at baseline and 11 (44%) also presented high trygliceride levels. After 6 months of treatment, eight patients (36.3%) presented normal transaminase levels. The remaining patients continued treatment for 12 months when 20% of patients presented with normal transaminase levels, while the other patients showed a 10% reduction in basal levels. Mean cholesterol levels were 268.5 +/- 44.2 and 186.8 +/- 14.4 mg/dL before and after treatment, respectively (P < 0.05). The mean body mass index was 27.4 +/- 3.1 at baseline and 26.3 +/- 2.8 kg/cm2 at the end of treatment (P > 0.05). No side effects were reported.

CONCLUSIONS

Serum aminotransferase and lipid levels were reduced significantly in all patients with atorvastatin treatment. Therapy with atorvastatin in NAFLD patients with hyperlipidemia was found to be both effective and safe.

Pharmacological characterization in vitro of EP2306 and EP2302, potent inhibitors of squalene synthase and lipid biosynthesis

We investigated the effects of EP2306 and EP2302, two novel 2-biphenylmorpholine derivatives, on squalene synthase activity in rabbit and human liver microsomes, lipid biosynthesis, low-density lipoprotein (LDL) receptor expression and LDL protein uptake as well as apoB secretion in HepG2 cells. Both EP2306 and EP2302 inhibited squalene synthase activity dose-dependently. In rabbit liver microsomes, the IC50 values were 33 microM for EP2306 and 0.6 microM for EP2302 whereas in human liver microsomes, they were 63 microM for EP2306 and 1 microM for EP2302. Both EP2300 compounds inhibited cholesterol production by HepG2 cells dose dependently with IC50 values of 13.3 microM for EP2306 and 3 microM for EP2302. Furthermore, both EP2300 compounds and simvastatin significantly reduced triglyceride synthesis and apoB secretion and increased LDL receptor expression and LDL uptake in HepG2 cells. In summary, we have shown that EP2300 compounds are potent inhibitors of squalene synthase activity in rabbit and human liver microsomes and also they are effective inhibitors of cholesterol and triglyceride biosynthesis in HepG2 cells. These results suggest that EP2306 and EP2302 might prove to be useful for lipid-lowering and treatment of atherosclerosis in vivo.

The effect of high-dose simvastatin on triglyceride-rich lipoprotein metabolism in patients with type 2 diabetes mellitus

Statins decrease triglycerides (TGs) in addition to decreasing low density lipoprotein-cholesterol. Although the mechanism for the latter effect is well understood, it is still unclear how TG decrease is achieved with statin therapy. Because hypertriglyceridemia is common in obese patients with type 2 diabetes mellitus, we studied triglyceride-rich lipoprotein triglyceride (TRL-TG) turnover in 12 such subjects using stable isotopically labeled glycerol. The diabetic subjects were studied after 12 weeks of placebo and after a similar course of therapy with simvastatin (80 mg daily) in a single-blind design. The results were compared with those from six nonobese nondiabetic control subjects. Simvastatin therapy reduced serum TGs by 35% in the diabetic subjects. Compared with the control subjects, TRL-TG secretion was almost 2-fold higher in the diabetic subjects (45.4 +/- 4.9 vs. 24.4 +/- 1.9 micromol/min; P < 0.002) and was unaffected by simvastatin therapy. However, TRL-TG clearance was significantly increased in the diabetic subjects during simvastatin treatment compared with placebo (0.25 +/- 0.03 vs. 0.16 +/- 0.02 pools/h; P < 0.002). This change was accompanied by a 49% increase in preheparin plasma lipase activity (P < 0.03) and a 21% increase in postheparin LPL activity (P < 0.01). Together, these findings provide strong evidence that the effect of statins on serum TGs is related to an increase in LPL activity, resulting in accelerated delipidation of TRL particles. The effect of high-dose simvastatin on triglyceride-rich lipoprotein metabolism in patients with type 2 diabetes mellitus.

Epigallocatechin gallate increases the formation of cytosolic lipid droplets and decreases the secretion of apoB-100 VLDL

Epigallocatechin gallate (EGCG) increases the formation of cytosolic lipid droplets by a mechanism that is independent of the rate of triglyceride biosynthesis and involves an enhanced fusion between lipid droplets, a process that is crucial for their growth in size. EGCG treatment reduced the secretion of both triglycerides and apolipoprotein B-100 (apoB-100) VLDLs but not of transferrin, albumin, or total proteins, indicating that EGCG diverts triglycerides from VLDL assembly to storage in the cytosol. This is further supported by the observed increase in both intracellular degradation of apoB-100 and ubiquitination of the protein (indicative of increased proteasomal degradation) in EGCG-treated cells. EGCG did not interfere with the microsomal triglyceride transfer protein, and the effect of EGCG on the secretion of VLDLs was found to be independent of the LDL receptor. Thus, our results indicate that EGCG promotes the accumulation of triglycerides in cytosolic lipid droplets, thereby diverting lipids from the assembly of VLDL to storage in the cytosol. Our results also indicate that the accumulation of lipids in the cytosol is not always associated with increased secretion of VLDL.

Influence of microsomal triglyceride transfer protein promoter polymorphism −493 GT on fasting plasma triglyceride values and interaction with treatment response to atorvastatin in subjects with heterozygous familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is an autosomal dominant disease characterized by elevated levels of low-density lipoprotein-cholesterol (LDL-C). Phenotypic expression is highly variable, being influenced by diet, age, gender, body mass index, apolipoprotein E genotype and type of LDL-receptor gene mutation. Microsomal triglyceride (TG) transfer protein (MTP) is a protein involved in lipid metabolism. Polymorphism MTP -493 GT has been shown to modulate lipid levels in several populations. To analyse the effect of this polymorphism in the lipid phenotype expression of FH and treatment response, we studied a sample of 222 Spanish FH patients, of whom 147 were studied before and after treatment with 20 mg of atorvastatin daily during 6 weeks. The variant was analysed by polymerase chain reaction amplification and single-strand confirmation polymorphism. Treatment reduced LDL-C, total cholesterol and TGs. Baseline fasting TGs and very-low-density lipoprotein cholesterol levels were lower in female T allele carriers (TG: 111+/-51 mg/dl GG, 89+/-35 mg/dl GT, 83+/-26 mg/dl TT, P=0.022; very-low-density lipoprotein cholesterol: 24+/-13 mg/dl GG, 16+/-5 mg/dl GT, 17+/-5 mg/dl TT, P=0.018). Triglyceride response to atorvastatin was modulated by this polymorphism in men (P=0.009), but not in women, although differences between genotypes were maintained after treatment. In conclusion, the MTP -493 GT polymorphism modulates pre- and post-treatment plasma TG values of FH in Spanish subjects in a gender-specific way. Other environmental and genetic factors likely also modulate this response.

Endotoxin promotes preferential periportal upregulation of VLDL secretion in the rat liver

Zonation affects liver parenchymal cell function and metabolism as well as nonparenchymal cell activation, but whether VLDL production is zonated has yet to be elucidated. Infection induces enhanced VLDL secretion by the liver. Ex vivo studies were undertaken to examine the liver heterogeneity for VLDL formation and secretion and their in vivo response to endotoxin. Highly pure periportal (PP) and perivenous (PV) hepatocytes were isolated from fasted lipopolysaccharide-treated, fasted, and fed rats. They were used to assess their capacity to release VLDL-apolipoprotein B (apoB) and lipid classes in relation to de novo lipid synthesis and the expression of genes crucial to VLDL production. Despite the common superior ability of PP hepatocytes for lipid release and zonal differences in lipid synthesis, zonated secretion of VLDL particles was observed in septic but not in normal fed or fasted livers. The endotoxin-induced apoB secretion was more accentuated in PP hepatocytes; this was accompanied by a preferential PP increase in apoB and microsomal triglyceride transfer protein mRNA levels, whereas lipogenesis indicators were, if anything, similarly modified in hepatocytes of either acinar origin. We conclude that PP and PV hepatocytes exhibited similar capabilities for VLDL formation/secretion in normal conditions; however, the endotoxic pressure did zonate periportally.

Post-transcriptional regulation of apoC-I synthesis and secretion in human HepG2 cells

ApoC-I plays an important role in controlling plasma lipid metabolism, however little is known about factors regulating the hepatic synthesis and secretion of this apolipoprotein. In the present study, we have carried out experiments with human hepatoma (HepG2) cells, in order to determine the effect of different tissue culture conditions on cellular lipid levels and on the production of apoC-I (and apoE) at the protein and mRNA level. Cells incubated for 48 h with 10% human serum had significantly higher cellular triglyceride (22%, P<0.05) and cholesterol levels (19%, P<0.01), higher medium apoC-I and apoE levels (2.6- and 2.9-fold, respectively), but similar levels of apoC-I and apoE mRNA, compared to cells incubated with 10% human lipoprotein-deficient serum (LPDS). Serum containing only HDL, or containing HDL with LDL, also increased cellular lipids and increased secreted apoC-I and apoE levels without altering apoC-I and apoE mRNA levels. Incubation of cells with Intralipid triglyceride (625 microM), increased cellular triglyceride (2.8-fold, P<0.001), decreased cellular cholesterol (32%, P<0.01), decreased cellular and medium apoC-I (24 and 26%, P<0.01) and had no effect on apoC-I mRNA levels. Additional experiments in which cells were loaded with cholesterol (incubation with 10 microg/ml cholesterol plus 1 microg/ml 25-hydroxycholesterol) or depleted of cholesterol (statin treatment) confirmed that secretion of apoC-I by HepG2 cells was dependent on cellular cholesterol levels and independent of changes in apoC-I mRNA levels. These results demonstrate that cellular cholesterol rather than triglyceride levels play a role in controlling apoC-I production by HepG2 cells and that this regulation occurs at a post-transcriptional level.

Statin induction of liver fatty acid-binding protein (L-FABP) gene expression is peroxisome proliferator-activated receptor-alpha-dependent

Statins are drugs widely used in humans to treat hypercholesterolemia. Statins act by inhibiting cholesterol synthesis resulting in the activation of the transcription factor sterol-responsive element-binding protein-2 that controls the expression of genes involved in cholesterol homeostasis. Statin therapy also decreases plasma triglyceride and non-esterified fatty acid levels, but the mechanism behind this effect remains more elusive. Liver fatty acid-binding protein (L-FABP) plays a role in the influx of long-chain fatty acids into hepatocytes. Here we show that L-FABP is a target for statins. In rat hepatocytes, simvastatin treatment induced L-FABP mRNA levels in a dose-dependent manner. Moreover, L-FABP promoter activity was induced by statin treatment. Progressive 5'-deletion analysis revealed that the peroxisome proliferator-activated receptor (PPAR)-responsive element located at position -67/-55 was responsible for the statin-mediated transactivation of the rat L-FABP promoter. Moreover, treatment with simvastatin and the PPARalpha agonist Wy14,649 resulted in a synergistic induction of L-FABP expression (mRNA and protein) in rat Fao hepatoma cells. This effect was also observed in vivo in wild-type mice but not in PPARalpha-null animals demonstrating the direct implication of PPARalpha in L-FABP regulation by statin treatment. Statin treatment resulted in a rise in PPARalpha mRNA levels both in vitro and in vivo and activated the mouse PPARalpha promoter in a reporter assay. Altogether, these data demonstrate that L-FABP expression is up-regulated by statins through a mechanism involving PPARalpha. Moreover, PPARalpha might be a statin target gene. These effects might contribute to the triglyceride/non-esterified fatty acid-lowering properties of statins.

Apolipoprotein B100 metabolism in autosomal-dominant hypercholesterolemia related to mutations in PCSK9

OBJECTIVE

We have reported further heterogeneity in familial autosomal-dominant hypercholesterolemia (FH) related to mutation in proprotein convertase subtilisin/kexin type 9 (PCSK9) gene previously named neural apoptosis regulated convertase 1 (Narc-1). Our aim was to define the metabolic bases of this new form of hypercholesterolemia.

METHODS AND RESULTS

In vivo kinetics of apolipoprotein B100-containing lipoproteins using a 14-hour primed constant infusion of [2H3] leucine was conducted in 2 subjects carrying the mutation S127R in PCSK9, controls subjects, and FH subjects with known mutations on the low-density lipoprotein (LDL) receptor gene (LDL-R). Apo B100 production, catabolism, and transfer rates were estimated from very LDL (VLDL), intermediate-density lipoprotein (IDL), and LDL tracer enrichments by compartmental analysis. PCSK9 mutation dramatically increased the production rate of apolipoprotein B100 (3-fold) compared with controls or LDL-R mutated subjects, related to direct overproduction of VLDL (3-fold), IDL (3-fold), and LDL (5-fold). The 2 subjects also showed a decrease in VLDL and IDL conversion (10% to 30% of the controls). LDL fractional catabolic rate was slightly decreased (by 30%) compared with controls but still higher than LDL-R-mutated subjects.

CONCLUSIONS

These results showed that the effect of the S127R mutation of PCSK9 on plasma cholesterol homeostasis is mainly related to an overproduction of apolipoprotein B100.

Experimental model of postprandial hypertriglyceridemia in sucrose-fed rats and the effectiveness of atorvastatin in the model

Although postprandial hypertriglyceridemia has drawn attention as an independent risk factor of cardiovascular disease, there is no established animal model that shows a physiological transitory change in lipoprotein metabolism after ingestion of a fatty meal. We developed an animal model of postprandial hypertriglyceridemia using sucrose-fed rats, and used this model to evaluate the effect of atorvastatin on this condition. Compared with normal rats, sucrose-fed rats orally loaded with olive oil showed a high and prolonged increase in plasma triglyceride (TG) concentration accompanied by both an increase in TG secretion and decrease in TG clearance. Atorvastatin (30 mg/kg orally) for 2 weeks reduced not only fasting plasma TG concentration, but also the postprandial TG concentration. Atorvastatin also suppressed rates of TG secretion in both chylomicron (CM)-rich (d < 0.96 g/mL) and very-low-density lipoprotein (VLDL) (d = 0.96 to 1.006 g/mL) fractions after oral fat loading. Further, atorvastatin improved the elimination time of exogenous TG emulsion only in the nonfasted, namely, high plasma TG condition. These results indicate that this animal model satisfactorily replicates the postprandial hypertriglyceridemia observed in humans and may therefore be useful in evaluation of lipid-lowering agents. Furthermore, atorvastatin not only improves fasting but also postprandial lipoprotein metabolism, presumably by reducing TG secretion from the liver or intestine or both, and by secondarily increasing TG-rich lipoprotein clearance by eliminating saturation.

Familial hypercholesterolemia--improving treatment and meeting guidelines

Familial hypercholesterolemia (FH) is a common, inherited disorder that affects around one in 500 individuals in the heterozygous form. By the year 2001, more people in the US had FH than were infected by the human immunodeficiency virus. The disease is caused by mutations within the low-density lipoprotein (LDL) receptor gene. FH is associated with elevated plasma LDL-cholesterol (LDL-C) levels, xanthomatosis, early onset of atherosclerosis and premature cardiac death. Patients with heterozygous FH commonly have plasma LDL-C levels that are two-fold higher than normal, while homozygotes have four- to five-fold elevations in plasma LDL-C. Although FH patients have a high risk of developing premature coronary heart disease (CHD), they remain underdiagnosed and undertreated. Early detection of FH is critical to prolonging the life of these patients. Once identified, patients with heterozygous FH can be placed on a diet and drug management program. As the most efficacious and well-tolerated agents, hydroxy methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are usually the drugs of first choice; bile acid sequestrants, niacin, and occasionally fibrates may be used as supplemental agents. Statins may also provide a realistic option for the treatment of some FH homozygotes with genes that produce partially functional LDL receptors. However, a number of patients are still failing to reach treatment guidelines even with the most effective of the currently available statins. The development of new more efficacious statins or the use of new combination therapies such as statins with the cholesterol absorption inhibitor, ezetimibe may help to reduce the current problem of undertreatment in FH patients.

Dual action of neutral sphingomyelinase on rat hepatocytes: activation of cholesteryl ester metabolism and biliary cholesterol secretion and inhibition of VLDL secretion

To address the role of cell membrane neutral sphingomyelinase (EC 3.1.4.12; SMase) in the regulation of cholesterol metabolism in the liver parenchymal cell, we examined the effect of exogenous neutral SMase on the metabolism of cholesteryl esters and the secretion of VLDL and biliary lipids in isolated rat hepatocytes. We show that treatment of hepatocytes with SMase (20 mU/mL) resulted in the intracellular buildup of cholesteryl esters, increased ACAT (EC 2.3.1.26) activity without affecting the ACAT2 mRNA level, and increased cytosolic and microsomal cholesteryl ester hydrolase (EC 3.1.1.13) activity. This was accompanied by increases in the secretion of biliary bile acid, phospholipid, and cholesterol and in increased cholesterol 7alpha-hydroxylase (EC 1.14.13.17) activity and levels of mRNA, as well as decreased levels of apoB mRNA and a decreased secretion of VLDL apoB (apoB-48, approximately 45%; apoB-100, approximately 32%) and lipids (approximately 55%). Moreover, the VLDL particles secreted had an abnormal size and lipid composition; they were larger than controls, were relatively enriched in cholesteryl ester, and depleted in TG and cholesterol. Cell-permeable ceramides did not replicate any of the reported effects. These findings demonstrate that the increased cholesteryl ester turnover, oversecretion of biliary cholesterol and bile acids, and undersecretion of VLDL cholesterol and particles are concerted responses of the primary hepatocytes to exogenous neutral SMase brought about by regulation at several levels. We suggest that plasma membrane neutral SMase may have a specific, ceramide-independent effect in the regulation of cholesterol output pathways in hepatocytes.

Squalene synthase inhibitors suppress triglyceride biosynthesis through the farnesol pathway in rat hepatocytes

We recently demonstrated that squalene synthase (SQS) inhibitors reduce plasma triglyceride through an LDL receptor-independent mechanism in Watanabe heritable hyperlipidemic rabbits (Hiyoshi et al. 2001. Eur. J. Pharmacol. 431: 345-352). The present study deals with the mechanism of the inhibition of triglyceride biosynthesis by the SQS inhibitors ER-27856 and RPR-107393 in rat primary cultured hepatocytes. Atorvastatin, an HMG-CoA reductase inhibitor, had no effect on triglyceride biosynthesis, but reversed the inhibitory effect of the SQS inhibitors. A squalene epoxidase inhibitor, NB-598, affected neither triglyceride biosynthesis nor its inhibition by ER-27856 and RPR-107393. The reduction of triglyceride biosynthesis by ER-27856 and RPR-107393 was potentiated by mevalonolactone supplementation. Treatment of hepatocytes with farnesol and its derivatives reduced triglyceride biosynthesis. In addition, we found that ER-27856 and RPR-107393 significantly reduced the incorporation of [1-(14)C]acetic acid into oleic acid, but not the incorporation of [1-(14)C]oleic acid into triglyceride. Though ER-27856 and RPR-107393 increased mitochondrial fatty acid beta-oxidation, the inhibition of beta-oxidation by RS-etomoxir had little effect on their inhibition of triglyceride biosynthesis. These results suggest that SQS inhibitors reduce triglyceride biosynthesis by suppressing fatty acid biosynthesis via an increase in intracellular farnesol and its derivatives.

Atorvastatin increases hepatic fatty acid beta-oxidation in sucrose-fed rats: comparison with an MTP inhibitor

We investigated the effects of atorvastatin, a widely used 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, and BMS-201038, a microsomal triglyceride transfer protein (MTP) inhibitor, in sucrose-fed hypertriglyceridemic rats to determine whether the activation of beta-oxidation by these compounds plays a role in their hypotriglyceridemic effect. The decrease in plasma triglyceride concentration and post-Triton very low-density lipoprotein (VLDL) triglyceride concentration, a measure of hepatic triglyceride secretion, by atorvastatin (30 mg/kg p.o.) for 2 weeks was to approximately the same degree as those by BMS-201038 (0.3 mg/kg). Atorvastatin (30 mg/kg) increased hepatic beta-oxidation activity by 54% (P < 0.01), while BMS-201038 (0.3 mg/kg) had no significant effect. Atorvastatin decreased hepatic triglyceride, fatty acid and cholesteryl ester concentrations by 21% to 39%, whereas BMS-201038 increased these variables by 28% to 307%. In the atorvastatin-treated groups, a significant relationship was seen not only between hepatic beta-oxidation activity and hepatic triglyceride concentration (R(2) = 0.535, P < 0.01), but also between hepatic and plasma triglyceride concentrations (R(2) = 0.586, P < 0.01). No effect of atorvastatin on hepatic fatty acid synthesis was observed. These results indicate that the activation of hepatic beta-oxidation by atorvastatin may contribute to the decrease in hepatic triglyceride concentration, leading to its hypotriglyceridemic effect.

Familial combined hyperlipidemia plasma stimulates protein secretion by HepG2 cells: identification of fibronectin in the differential secretion proteome

The aim of this study was to evaluate whether soluble factors in plasma of familial combined hyperlipidemia (FCHL) patients affect hepatic protein secretion. Cultured human hepatocytes, i.e., HepG2 cells, were incubated with fasting plasma (20%, v/v, in DMEM) from untreated FCHL patients or normolipidemic controls. Overall protein secretion was 10-15% higher after incubation with FCHL plasma. This was specifically caused by an increase in four secreted proteins, with estimated sizes of 240, 180, 120, and <40 kD (P < 0.001, P < 0.006, P < 0.002, P < 0.02, respectively). The 240 kD protein in the secretion proteome was identified as fibronectin by mass spectrometry. Plasma fibronectin concentrations were elevated in FCHL patients, confirming biological relevance of these data. Overall protein secretion by HepG2 cells correlated with concentrations of triglycerides (r = 0.61, P < 0.001) in the applied plasma samples. VLDL+IDL isolated from FCHL patients, induced a higher protein secretion than lipoproteins isolated from controls (P < 0.001). Remarkably, secretion of apoB, the structural protein of VLDL, was stimulated to a similar extent by FCHL and control plasma. FCHL plasma did not induce excess secretion of apoB by HepG2 cells compared with control plasma. FCHL plasma did stimulate secretion of several distinct hepatic proteins, among which fibronectin was identified.

Cholestin inhibits cholesterol synthesis and secretion in hepatic cells (HepG2)

Hyperlipidemia is a well-known risk factor for atherosclerosis and statins are widely used to treat patients with elevated levels of lipids in their plasma. Notwithstanding the proven benefits of statin drugs on both primary and secondary prevention of heart disease, the high cost of statin treatment, in addition to possible side effects such as liver function abnormalities, may limit their widespread use. We conducted a study on a natural product as an alternative to statin treatment. Cholestin, a dietary supplement, is prepared from rice fermented with red yeast (Monascus purpureus), which has been shown to significantly decrease total cholesterol levels in hyperlipidemic subjects. Our objective was to determine the cellular effect of Cholestin on cholesterol synthesis in human hepatic cells (HepG2) and the mechanism by which it caused a change in lipid metabolism. Cholestin had a direct inhibitory effect on HMG-CoA reductase activity (78-69% of control). Cholesterol levels in HepG2 cells treated with Cholestin (25-100 microg/mL) were significantly reduced in a dose-dependent manner (81-45% of control, respectively). This reduction was associated with decreased synthesis and secretion of both unesterified cholesterol (54-31 and 33-14% of control, respectively) and cholesteryl ester (18-6 and 37-19% of control, respectively). These results indicate that one of the anti-hyperlipidemic actions of Cholestin is a consequence of an inhibitory effect on cholesterol biosynthesis in hepatic cells and provide the first documentation of a biomolecular action of red yeast rice.