2000 George Lyman Duff Memorial Lecture: atherosclerosis is a liver disease of the heart

L-carnitine ameliorated weight loss in fasting therapy: A propensity score-matched study

l-carnitine infusion has been proven to reduce fasting-induced fatigue and hunger in patients with metabolic syndrome in our former study. However, the association between l-carnitine and clinical outcomes of fasting therapy is yet to be investigated. In this study, data from 192 patients who finished fasting therapy from September 2008 to July 2018 were reviewed, among which 142 patients received l-carnitine infusion in fasting regimen. Propensity matching was used to overcome retrospective bias. Patients' anthropometric measurements and metabolic markers were evaluated. After propensity matching, 40 patients were included in each group. Weight (-4.05 ± 1.65 kg vs -3.25 ± 1.68 kg, P = 0.031) and BMI (-1.51±0.61 kg/m² vs -1.20 ± 0.62 kg/m², P = 0.036) decreased in both groups, but significantly more in l-carnitine group, while diastolic blood pressure (-1.67±9.82 mmHg vs -6.21±8.83 mmHg, P = 0.043) and triglycerides (-0.18±0.63 mmol/L vs -1.05±1.70 mmol/L, P = 0.007) decreased significantly more in non-l-carnitine group compared between groups, blood glucose did not differ significantly between groups. l-carnitine can boost the positive effects of fasting therapy on weight loss and maintain the stability of blood pressure.

Correlation between Mitochondrial Reactive Oxygen and Severity of Atherosclerosis

Atherosclerosis has been associated with mitochondria dysfunction and damage. Our group demonstrated previously that hypercholesterolemic mice present increased mitochondrial reactive oxygen (mtROS) generation in several tissues and low NADPH/NADP+ ratio. Here, we investigated whether spontaneous atherosclerosis in these mice could be modulated by treatments that replenish or spare mitochondrial NADPH, named citrate supplementation, cholesterol synthesis inhibition, or both treatments simultaneously. Robust statistical analyses in pooled group data were performed in order to explain the variation of atherosclerosis lesion areas as related to the classic atherosclerosis risk factors such as plasma lipids, obesity, and oxidative stress, including liver mtROS. Using three distinct statistical tools (univariate correlation, adjusted correlation, and multiple regression) with increasing levels of stringency, we identified a novel significant association and a model that reliably predicts the extent of atherosclerosis due to variations in mtROS. Thus, results show that atherosclerosis lesion area is positively and independently correlated with liver mtROS production rates. Based on these findings, we propose that modulation of mitochondrial redox state influences the atherosclerosis extent.

Iron dextran increases hepatic oxidative stress and alters expression of genes related to lipid metabolism contributing to hyperlipidaemia in murine model

The objective of this study was to investigate the effects of iron dextran on lipid metabolism and to determine the involvement of oxidative stress. Fischer rats were divided into two groups: the standard group (S), which was fed the AIN-93M diet, and the standard plus iron group (SI), which was fed the same diet but also received iron dextran injections. Serum cholesterol and triacylglycerol levels were higher in the SI group than in the S group. Iron dextran was associated with decreased mRNA levels of pparα, and its downstream gene cpt1a, which is involved in lipid oxidation. Iron dextran also increased mRNA levels of apoB-100, MTP, and L-FABP indicating alterations in lipid secretion. Carbonyl protein and TBARS were consistently higher in the liver of the iron-treated rats. Moreover, a significant positive correlation was found between oxidative stress products, lfabp expression, and iron stores. In addition, a negative correlation was found between pparα expression, TBARS, carbonyl protein, and iron stores. In conclusion, our results suggest that the increase observed in the transport of lipids in the bloodstream and the decreased fatty acid oxidation in rats, which was promoted by iron dextran, might be attributed to increased oxidative stress.

Nur77 decreases atherosclerosis progression in apoE(-/-) mice fed a high-fat/high-cholesterol diet

Rationale

It is clear that lipid disorder and inflammation are associated with cardiovascular diseases and underlying atherosclerosis. Nur77 has been shown to be involved in inflammatory response and lipid metabolism.

Objective

Here, we explored the role of Nur77 in atherosclerotic plaque progression in apoE^−/− mice fed a high-fat/high cholesterol diet.

Methods and Results

The Nur77 gene, a nuclear hormone receptor, was highly induced by treatment with Cytosporone B (Csn-B, specific Nur77 agonist), recombinant plasmid over-expressing Nur77 (pcDNA-Nur77), while inhibited by treatment with siRNAs against Nur77 (si-Nur77) in THP-1 macrophage-derived foam cells, HepG2 cells and Caco-2 cells, respectively. In addition, the expression of Nur77 was highly induced by Nur77 agonist Csn-B, lentivirus encoding Nur77 (LV-Nur77), while silenced by lentivirus encoding siRNA against Nur77 (si-Nur77) in apoE^−/− mice fed a high-fat/high cholesterol diet, respectively. We found that increased expression of Nur77 reduced macrophage-derived foam cells formation and hepatic lipid deposition, downregulated gene levels of inflammatory molecules, adhesion molecules and intestinal lipid absorption, and decreases atherosclerotic plaque formation.

Conclusion

These observations provide direct evidence that Nur77 is an important nuclear hormone receptor in regulation of atherosclerotic plaque formation and thus represents a promising target for the treatment of atherosclerosis.

Dihydrocapsaicin Attenuates Plaque Formation through a PPARγ/LXRα Pathway in apoE(-/-) Mice Fed a High-Fat/High-Cholesterol Diet

Aims

Atherosclerosis is a chronic inflammatory disease and represents the major cause of cardiovascular morbidity and mortality. There is evidence that dihydrocapsaicin (DHC) can exert multiple pharmacological and physiological effects. Here, we explored the effect of DHC in atherosclerotic plaque progression in apoE^−/− mice fed a high-fat/high-cholesterol diet.

Methods and Results

apoE^−/− mice were randomly divided into two groups and fed a high-fat/high-cholesterol diet with or without DHC for 12 weeks. We demonstrated that cellular cholesterol content was significantly decreased while apoA1-mediated cholesterol efflux was significantly increased following treatment with DHC in THP-1 macrophage-derived foam cells. We also observed that plasma levels of TG, LDL-C, VLDL-C, IL-1β, IL-6, TNF-α and CRP were markedly decreased while plasma levels of apoA1 and HDL-C were significantly increased, and consistent with this, atherosclerotic lesion development was significantly inhibited by DHC treatment of apoE^−/− mice fed a high-fat/high-cholesterol diet. Moreover, treatment with both LXRα siRNA and PPARγ siRNA made the up-regulation of DHC on ABCA1, ABCG1, ABCG5, SR-B1, NPC1, CD36, LDLR, HMGCR, apoA1 and apoE expression notably abolished while made the down-regulation of DHC on SRA1 expression markedly compensated. And treatment with PPARγ siRNA made the DHC-induced up-regulation of LXRα expression notably abolished while treatment with LXRα siRNA had no effect on DHC-induced PPARγ expression.

Conclusion

These observations provide direct evidence that DHC can significantly decrease atherosclerotic plaque formation involving in a PPARγ/LXRα pathway and thus DHC may represent a promising candidate for a therapeutic agent for the treatment or prevention of atherosclerosis.

VASP increases hepatic fatty acid oxidation by activating AMPK in mice

Activation of AMP-activated protein kinase (AMPK) signaling reduces hepatic steatosis and hepatic insulin resistance; however, its regulatory mechanisms are not fully understood. In this study, we sought to determine whether vasodilator-stimulated phosphoprotein (VASP) signaling improves lipid metabolism in the liver and, if so, whether VASP's effects are mediated by AMPK. We show that disruption of VASP results in significant hepatic steatosis as a result of significant impairment of fatty acid oxidation, VLDL-triglyceride (TG) secretion, and AMPK signaling. Overexpression of VASP in hepatocytes increased AMPK phosphorylation and fatty acid oxidation and reduced hepatocyte TG accumulation; however, these responses were suppressed in the presence of an AMPK inhibitor. Restoration of AMPK phosphorylation by administration of 5-aminoimidazole-4-carboxamide riboside in Vasp(-/-) mice reduced hepatic steatosis and normalized fatty acid oxidation and VLDL-TG secretion. Activation of VASP by the phosphodiesterase-5 inhibitor, sildenafil, in db/db mice reduced hepatic steatosis and increased phosphorylated (p-)AMPK and p-acetyl CoA carboxylase. In Vasp(-/-) mice, however, sildendafil treatment did not increase p-AMPK or reduce hepatic TG content. These studies identify a role of VASP to enhance hepatic fatty acid oxidation by activating AMPK and to promote VLDL-TG secretion from the liver.

Modulation of lipoprotein metabolism by antisense technology: preclinical drug discovery methodology

Antisense oligonucleotides (ASOs) are a new class of specific therapeutic agents that alter the intermediary metabolism of mRNA, resulting in the suppression of disease-associated gene products. ASOs exert their pharmacological effects after hybridizing, via Watson-Crick base pairing, to a specific target RNA. If appropriately designed, this event results in the recruitment of RNase H, the degradation of targeted mRNA or pre-mRNA, and subsequent inhibition of the synthesis of a specific protein. A key advantage of the technology is the ability to selectively inhibit targets that cannot be modulated by traditional therapeutics such as structural proteins, transcription factors, and, of topical interest, lipoproteins. In this chapter, we will first provide an overview of antisense technology, then more specifically describe the status of lipoprotein-related genes that have been studied using the antisense platform, and finally, outline the general methodology required to design and evaluate the in vitro and in vivo efficacy of those drugs.

Rescue of Mtp siRNA-induced hepatic steatosis by DGAT2 siRNA silencing

Microsomal triglyceride transfer protein (Mtp) inhibitors represent a novel therapeutic approach to lower circulating LDL cholesterol, although therapeutic development has been hindered by the observed increase in hepatic triglycerides and liver steatosis following treatment. Here, we used small interfering RNAs (siRNA) targeting Mtp to achieve target-specific silencing to study this phenomenon and to determine to what extent liver steatosis is induced by changes in Mtp expression. We observed that Mtp silencing led to a decrease in many genes involved in hepatic triglyceride synthesis. Given the role of diacylglycerol O-acyltransferase 2 (Dgat2) in regulating hepatic triglyceride synthesis, we then evaluated whether target-specific silencing of both Dgat2 and Mtp were sufficient to attenuate Mtp silencing-induced liver steatosis. We showed that the simultaneous inhibition of Dgat2 and Mtp led to a decrease in plasma cholesterol and a reduction in the accumulation of hepatic triglycerides caused by the inhibition of Mtp. Collectively, these findings provide a proof-of-principle for a triglyceride synthesis/Mtp inhibitor combination and represent a potentially novel approach for therapeutic development in which targeting multiple pathways can achieve the desired response.

Genotype rs8099917 near the IL28B gene and amino acid substitution at position 70 in the core region of the hepatitis C virus are determinants of serum apolipoprotein B-100 concentration in chronic hepatitis C

The life cycle of the hepatitis C virus (HCV) is closely related to host lipoprotein metabolism. Serum levels of lipid are associated with the response to pegylated interferon plus ribavirin (PEG-IFN/RBV) therapy, while single nucleotide polymorphisms (SNPs) around the human interleukin 28B (IL28B) gene locus and amino acid substitutions in the core region of the HCV have been reported to affect the efficacy of PEG-IFN/RBV therapy in chronic hepatitis with HCV genotype 1b infection. The aim of this study was to elucidate the relationship between serum lipid and factors that are able to predict the efficacy of PEG-IFN/RB therapy, with specific focus on apolipoprotein B-100 (apoB-100) in 148 subjects with chronic HCV G1b infection. Our results demonstrated that both the aa 70 substitution in the core region of the HCV and the rs8099917 SNP located proximal to the IL28B were independent factors in determining serum apoB-100 and low-density lipoprotein (LDL) cholesterol levels. A significant association was noted between higher levels of apoB-100 (P = 1.1 × 10(-3)) and LDL cholesterol (P = 0.02) and the subjects having Arg70. A significant association was also observed between subjects carrying the rs8099917 TT responder genotype and higher levels of apoB-100 (P = 6.4 × 10(-3)) and LDL cholesterol (P = 4.2 × 10(-3)). Our results suggest that apoB-100 and LDL cholesterol are markers of impaired cellular lipoprotein pathways and/or host endogenous interferon response to HCV in chronic HCV infection. In particular, serum apoB-100 concentration might be an informative marker for judging changes in HCV-associated intracellular lipoprotein metabolism in patients carrying the rs8099917 responder genotype.

HCV and the hepatic lipid pathway as a potential treatment target

Atherosclerosis has been described as a liver disease of the heart [1]. The liver is the central regulatory organ of lipid pathways but since dyslipidaemias are major contributors to cardiovascular disease and type 2 diabetes rather than liver disease, research in this area has not been a major focus for hepatologists. Virus-host interaction is a continuous co-evolutionary process [2] involving the host immune system and viral escape mechanisms [3]. One of the strategies HCV has adopted to escape immune clearance and establish persistent infection is to make use of hepatic lipid pathways. This review aims to: • update the hepatologist on lipid metabolism • review the evidence that HCV exploits hepatic lipid pathways to its advantage • discuss approaches to targeting host lipid pathways as adjunctive therapy.

ApoB siRNA-induced liver steatosis is resistant to clearance by the loss of fatty acid transport protein 5 (Fatp5)

The association between hypercholesterolemia and elevated serum apolipoprotein B (APOB) has generated interest in APOB as a therapeutic target for patients at risk of developing cardiovascular disease. In the clinic, mipomersen, an antisense oligonucleotide (ASO) APOB inhibitor, was associated with a trend toward increased hepatic triglycerides, and liver steatosis remains a concern. We found that siRNA-mediated knockdown of ApoB led to elevated hepatic triglycerides and liver steatosis in mice engineered to exhibit a human-like lipid profile. Many genes required for fatty acid synthesis were reduced, suggesting that the observed elevation in hepatic triglycerides is maintained by the cell through fatty acid uptake as opposed to fatty acid synthesis. Fatty acid transport protein 5 (Fatp5/Slc27a5) is required for long chain fatty acid (LCFA) uptake and bile acid reconjugation by the liver. Fatp5 knockout mice exhibited lower levels of hepatic triglycerides due to decreased fatty acid uptake, and shRNA-mediated knockdown of Fatp5 protected mice from diet-induced liver steatosis. Here, we evaluated if siRNA-mediated knockdown of Fatp5 was sufficient to alleviate ApoB knockdown-induced steatosis. We determined that, although Fatp5 siRNA treatment was sufficient to increase the proportion of unconjugated bile acids 100-fold, consistent with FATP5's role in bile acid reconjugation, Fatp5 knockdown failed to influence the degree, zonal distribution, or composition of the hepatic triglycerides that accumulated following ApoB siRNA treatment.

n-3 fatty acids ameliorate hepatic steatosis and dysfunction after LXR agonist ingestion in mice

Liver X receptor (LXR) agonists slow atherogenesis, but cause hepatic steatosis and dysfunction in part by increasing expression of sterol regulatory element binding protein 1-c (SREBP1-c), a transcription factor that upregulates fatty acid (FA) synthesis. n-3 FAs decrease hepatic FA synthesis by down-regulating SREBP1-c. To test the hypothesis that n-3 FAs decrease hepatic steatosis in mice given LXR agonist, C57BL/6 mice received daily gavage of an LXR agonist T0901317 (LXR(T)) or vehicle for 4weeks with concomitant intakes chow or high-fat diets enriched in saturated fat (SAT) or n-3 fat (n-3). Mice on LXR(T) and SAT developed hepatomegaly with a large increase in size and number of hepatic lipid droplets; an n-3 diet reduced liver weight/body weight with decreased hepatic steatosis and triglyceride levels. Effects of n-3 diet on hepatic lipogenesis were linked to a blunting of LXR(T) upregulation of hepatic SREBP1-c and FA synthase mRNA. n-3 diets also normalized LXR(T)-mediated increases of plasma ALT and AST levels, whereas SAT diet increased these markers.

CONCLUSION

These studies suggest that n-3 FAs when given together with LXR agonists have the potential to improve both hepatic steatosis and hepatotoxicity in humans that might receive LXR agonists to decrease risk of atherosclerosis.

siRNA-induced liver ApoB knockdown lowers serum LDL-cholesterol in a mouse model with human-like serum lipids

Increased serum apolipoprotein (apo)B and associated LDL levels are well-correlated with an increased risk of coronary disease. ApoE⁻/⁻ and low density lipoprotein receptor (LDLr)⁻/⁻ mice have been extensively used for studies of coronary atherosclerosis. These animals show atherosclerotic lesions similar to those in humans, but their serum lipids are low in apoB-containing LDL particles. We describe the development of a new mouse model with a human-like lipid profile. Ldlr CETP⁺/⁻ hemizygous mice carry a single copy of the human CETP transgene and a single copy of a LDL receptor mutation. To evaluate the apoB pathways in this mouse model, we used novel short-interfering RNAs (siRNA) formulated in lipid nanoparticles (LNP). ApoB siRNAs induced up to 95% reduction of liver ApoB mRNA and serum apoB protein, and a significant lowering of serum LDL in Ldlr CETP⁺/⁻ mice. ApoB targeting is specific and dose-dependent, and it shows lipid-lowering effects for over three weeks. Although specific triglycerides (TG) were affected by ApoB mRNA knockdown (KD) and the total plasma lipid levels were decreased by 70%, the overall lipid distribution did not change. Results presented here demonstrate a new mouse model for investigating additional targets within the ApoB pathways using the siRNA modality.

Apolipoprotein B-associated cholesterol is a determinant of treatment outcome in patients with chronic hepatitis C virus infection receiving anti-viral agents interferon-alpha and ribavirin

BACKGROUND

Hepatitis C virus (HCV) co-opts very-low-density lipoprotein (VLDL) pathways for replication, secretion and entry into hepatocytes and associates with apolipoprotein B (apoB) in plasma. Each VLDL contains apoB-100 and variable amounts of apolipoproteins E and C, cholesterol and triglycerides.

AIM

To determine whether baseline lipid levels predicted treatment outcome.

METHODS

Retrospective analysis was performed of 250 chronic hepatitis C (CHC) patients who had received anti-viral agents interferon-alpha and ribavirin; 165 had a sustained virological response (SVR). Pre- and post-treatment nonfasting lipid profiles were measured and non-high-density lipoprotein (non-HDL) cholesterol (i.e. apoB-associated) was calculated. Binary logistic regression analysis assessed factors independently associated with treatment outcome.

RESULTS

There was an independent association between higher apoB-associated cholesterol (non-HDL-C) and increased odds of SVR (odds ratio 2.09, P = 0.042). In multivariate analysis, non-HDL-C was significantly lower in HCV genotype 3 (g3) than genotype 1 (P = 0.007); this was reversible upon eradication of HCVg3 (pre-treatment non-HDL-C = 2.8 mmol/L, SVR = 3.6 mmol/L, P < 0.001).

CONCLUSIONS

Higher apoB-associated cholesterol is positively associated with treatment outcome in CHC patients receiving anti-viral therapy, possibly due to competition between apoB-containing lipoproteins and infectious low-density HCV lipo-viral particles for hepatocyte entry via shared lipoprotein receptors.

Polymorphisms of microsomal triglyceride transfer protein in different hepatitis B virus-infected patients

AIM: To identify the two polymorphisms of microsomal triglyceride transfer protein (MTP) gene in the Chinese population and to explore their correlation with both hepatitis B virus (HBV) self-limited infection and persistent infection.

METHODS: A total of 316 subjects with self-limited HBV infection and 316 patients with persistent HBV infection (195 subjects without familial history), matched with age and sex, from the Chinese Han population were enrolled in this study. Polymorphisms of MTP at the promoter region -493 and at H297Q were determined by the allele specific polymerase chain reaction (PCR).

RESULTS: The ratio of males to females was 2.13:1 for each group and the average age in the self-limited and chronic infection groups was 38.36 and 38.28 years, respectively. None of the allelic distributions deviated significantly from that predicted by the Hardy-Weinberg equilibrium. There was a linkage disequilibrium between H297Q and -493G/T (D’ = 0.77). As the χ² test was used, the genotype distribution of MTP-493G/T demonstrated a significant difference between the self-limited infection group and the entire chronic group or the chronic patients with no family history (χ² = 8.543, P = 0.015 and χ² = 7.199, P = 0.019). The allele distribution at the MTP-493 position also demonstrated a significant difference between the study groups without family history (χ² = 6.212, P = 0.013). The T allele emerged as a possible protective factor which may influence the outcomes of HBV infection (OR: 0.59; 95% CI: 0.389-0.897).

CONCLUSION: The polymorphism of the MTP gene, T allele at -493, may be involved in determining the HBV infection outcomes, of which the mechanism needs to be further investigated.

Structural and dynamic interfacial properties of the lipoprotein initiating domain of apolipoprotein B

To better understand the earliest steps in the assembly of triglyceride (TG)-rich lipoproteins, we compared the biophysical and interfacial properties of two closely related apolipoprotein B (apoB) truncation mutants, one of which contains the complete lipoprotein initiating domain (apoB20.1; residues 1-912), and one of which, by virtue of a 50 amino acid C-terminal truncation, is incapable of forming nascent lipoproteins (apoB19; residues 1-862). Spectroscopic studies detected no major differences in secondary structure, and only minor differences in conformation and thermodynamic stability, between the two truncation mutants. Monolayer studies revealed that both apoB19 and apoB20.1 bound to and penetrated egg phosphatidylcholine (EPC) monolayers; however, the interfacial exclusion pressure of apoB20.1 was higher than apoB19 (25.1 mN/m vs. 22.8 mN/m). Oil drop tensiometry revealed that both proteins bound rapidly to the hydrophobic triolein/water interface, reducing interfacial tension by approximately 20 mN/m. However, when triolein drops were first coated with phospholipids (PL), apoB20.1 bound with faster kinetics than apoB19 and also displayed greater interfacial elasticity (26.9 +/- 0.8 mN/m vs. 22.9 +/- 0.8 mN/m). These data establish that the transition of apoB to assembly competence is accompanied by increases in surface activity and elasticity, but not by significant changes in global structure.

Central nervous system neuropeptide Y signaling modulates VLDL triglyceride secretion

OBJECTIVE

Elevated triglyceride (TG) is the major plasma lipid abnormality in obese and diabetic patients and contributes to cardiovascular morbidity in these disorders. We sought to identify novel mechanisms leading to hypertriglyceridemia. Resistance to negative feedback signals from adipose tissue in key central nervous system (CNS) energy homeostatic circuits contributes to the development of obesity. Because triglycerides both represent the largest energy depot in the body and are elevated in both the plasma and adipose in obesity and diabetes, we hypothesized that the same neural circuits that regulate energy balance also regulate the secretion of TGs into plasma.

RESEARCH DESIGN AND METHODS

In normal fasting rats, the TG secretion rate was estimated by serial blood sampling after intravascular tyloxapol pretreatment. Neuropeptide Y (NPY) signaling in the CNS was modulated by intracerebroventricular injection of NPY, receptor antagonist, and receptor agonist.

RESULTS

A single intracerebroventricular injection of NPY increased TG secretion by 2.5-fold in the absence of food intake, and this was determined to be VLDL by fast performance liquid chromatography (FPLC). This effect was recapitulated by activating NPY signaling in downstream neurons with an NPY-Y5 receptor agonist. An NPY-Y1 receptor antagonist decreased the elevated TGs in the form of VLDL secretion rate by 50% compared with vehicle. Increased TG secretion was due to increased secretion of VLDL particles, rather than secretion of larger particles, because apolipoprotein B100 was elevated in FPLC fractions corresponding to VLDL.

CONCLUSIONS

We find that a key neuropeptide system involved in energy homeostasis in the CNS exerts control over VLDL-TG secretion into the bloodstream.

Secretion of atherogenic risk factor apolipoprotein B-100 is increased by a potential mechanism of JNK/PKC-mediated insulin resistance in liver cells

Apolipoprotein B-100 (ApoB) is the main protein of the atherogenic lipoproteins and plasma ApoB levels reflect the total numbers of atherogenic lipoproteins. Induction of insulin resistance was accompanied by a considerable rise in the production of hepatic very low density lipoprotein (VLDL) containing ApoB and triglyceride. Increased plasma levels of ApoB and triglyceride in VLDL are common characteristics of the dyslipidemia associated with insulin resistance and type 2 diabetes mellitus. Thus, we investigate whether phorbol 12-myristate-13-acetate (PMA)-induced insulin resistance affects the increase of ApoB secretion. PMA increased ApoB secretion and transcriptional level of microsomal triglyceride transfer protein (MTP). PMA treatment also resulted in increase of insulin receptor substrate 1 (IRS1) serine312 (Ser312) and serine1101 (Ser1101) phosphorylation and induction of IRS1 degradation. Additionally, PMA induced activation of c-jun N-terminal kinase (JNK) and protein kinase C (PKC) isoforms (alpha, betaI, delta, zeta, theta), and reduced AKT8 virus oncogene cellular homolog (AKT) activation in a time dependent manner. PMA-induced ApoB secretion, MTP promoter activities, and IRS1 degradation was significantly decreased by treatment of JNK and PKCs inhibitors. Orthovanadate, a potent tyrosine phosphatase inhibitor, increased tyrosine phosphorylation of IRS1 and decreased ApoB secretion of Chang liver cells although PMA was co-treated. From the results, it was concluded that PMA-induced insulin resistance, through induction of serine phosphorylation of IRS1 mediated by activated JNK and PKCs, increases ApoB secretion in Chang liver cells.

SHP-2 and PI3-kinase genes PTPN11 and PIK3R1 may influence serum apoB and LDL cholesterol levels in normal women

Insulin regulates apoB metabolism via activation of PI3K or regulation of MTP via MAPK/ERK signalling. SHP-2 enhances both pathways through increased IRS-1 phosphorylation. We hypothesized that variants in the SHP-2 gene PTPN11 and PI3K p85alpha subunit gene PIK3R1 may influence fasting levels of plasma apoB and/or LDL cholesterol. We tested association of tagging SNPs (tSNPs) in each gene with serum lipids in a large sample of unselected population-based Caucasian female twins (n=2771, mean age 47.4+/-12.5 years) and then tested interaction between tSNPs in determining apoB and LDL levels. PTPN11 tSNP rs11066322 was associated with apoB (P=0.007) and rs11066320 was associated with LDL cholesterol (P=0.016). PIK3R1 tSNP rs251406 was associated with apoB (P=0.0003) and rs706713 was associated with LDL cholesterol (P=0.009). PTPN11 tSNP rs11066322 interacted with PIK3R1 tSNP rs251406 in determining serum apoB levels (P=0.012) and with PIK3R1 tSNP rs40318 in determining LDL cholesterol levels (P=0.009). Association of single tSNPs with both apoB and LDL cholesterol as well as interactions between the two genes suggest that variants influencing SHP-2 activity may modulate the acute pathway by which insulin regulates these lipids.

Primary sclerosing cholangitis--the arteriosclerosis of the bile duct?

Primary sclerosing cholangitis (PSC) is a chronic inflammatory disease of unknown aetiology affecting the large bile ducts and characterized by periductal fibrosis and stricture formation, which ultimately result in biliary cirrhosis and liver failure. Arteriosclerosis involves the accumulation of altered lipids and lipoproteins in large arteries; this drives inflammation and fibrosis and ultimately leads to narrowing of the arteries and hypoperfusion of dependent organs and tissues. Knowledge of the causative factors is crucial to the understanding of disease mechanisms and the development of specific treatment. Based on pathogenetic similarities between PSC and arteriosclerosis, we hypothesize that PSC represents "arteriosclerosis of the bile duct" initiated by toxic biliary lipids. This hypothesis is based on common molecular, cellular, and morphological features providing the conceptual framework for a deeper understanding of their pathogenesis. This hypothesis should stimulate translational research to facilitate the search for novel treatment strategies for both diseases.

Effect of probucol on HDL metabolism and class B type I scavenger receptor (SR-BI) expression in the liver of hypercholesterolemic rabbits

BACKGROUND

Scavenger receptor class B type I (SR-BI) is a major receptor for high-density lipoproteins (HDL) in the liver. Overexpression of SR-BI attenuated experimental atherosclerosis in murine models, concomitant with a reduction in plasma HDL-cholesterol levels. Probucol is known to be a potent hypolipidemic drug to regress xanthoma formation and carotid atherosclerosis in conjunction with a marked reduction in HDL-cholesterol levels. However, the mechanism by which probucol affects atherosclerosis is not completely understood, and the effect of probucol on the expression of SR-BI was controversial. The aim of this study was to know the effect of probucol on HDL metabolism and SR-BI expression in the liver.

METHODS

Sixteen rabbits fed with high cholesterol diet for 8 weeks were randomly divided into two groups: (1) high cholesterol group (n = 8): maintained high cholesterol diet for 6 weeks; (2) probucol group (n = 8): the same cholesterol diet plus 1% probucol for 6 weeks. Control group (n = 8) was fed with normal diet for 14 weeks. The classical in situ two steps perfusion of the liver with collagenase IV was used to isolate the parenchymal hepatocytes. The selective uptake of HDL by hepatocytes was performed using the double radiolabelled HDL. Immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR) were used to evaluate SR-BI expression in the liver.

RESULTS

Compared with control group, rabbits fed with high cholesterol diet showed higher levels of serum total cholesterol (TC), low-density lipoprotein (LDL) cholesterol and HDL-C, all of which were significantly reduced by probucol treatment. The selective uptake of HDL CEs in probucol group (249.68 +/- 60.13 ng/mg cell protein) was about two folds higher as compared with the control group (122.47 +/- 54.06 ng/mg cell protein, P < 0.01) and high cholesterol group (104.92 +/- 47.91 ng/mg cell protein, P < 0.01), but it could not be reproduced in vitro. The expression of SR-BI were significantly decreased in the high cholesterol group (0.48 +/- 0.06) as compared with control group (0.65 +/- 0.06, P < 0.01). Probucol increased SR-BI expression (0.68 +/- 0.06, P < 0.01) as compared with high cholesterol group. The expression of SR-BI was positively associated with the selective CEs uptake (r = 0.47, P = 0.032).

CONCLUSIONS

Probucol up-regulates SR-BI expression and enhance the uptake of HDL CEs by hepatocytes, which may help us to understand the anti-atherogenic properties and the HDL-C-lowering effect of probucol.

Coordinate transcriptional repression of liver fatty acid-binding protein and microsomal triglyceride transfer protein blocks hepatic very low density lipoprotein secretion without hepatosteatosis

Unlike the livers of humans and mice, and most hepatoma cells, which accumulate triglycerides when treated with microsomal triglyceride transfer protein (MTP) inhibitors, L35 rat hepatoma cells do not express MTP and cannot secrete very low density lipoprotein (VLDL), yet they do not accumulate triglyceride. In these studies we show that transcriptional co-repression of the two lipid transfer proteins, liver fatty acid-binding protein (L-FABP) and MTP, which cooperatively shunt fatty acids into de novo synthesized glycerolipids and the transfer of lipids into VLDL, respectively, act together to maintain hepatic lipid homeostasis. FAO rat hepatoma cells express L-FABP and MTP and demonstrate the ability to assemble and secrete VLDL. In contrast, L35 cells, derived as a single cell clone from FAO cells, do not express L-FABP or MTP nor do they assemble and secrete VLDL. We used these hepatoma cells to elucidate how a conserved DR1 promoter element present in the promoters of L-FABP and MTP affects transcription, expression, and VLDL production. In FAO cells, the DR1 elements of both L-FABP and MTP promoters are occupied by peroxisome proliferator-activated receptor alpha-retinoid X receptor alpha (RXRalpha), with which PGC-1beta activates transcription. In contrast, in L35 cells the DR1 elements of both L-FABP and MTP promoters are occupied by chicken ovalbumin upstream promoter transcription factor II, and transcription is diminished. The combined findings indicate that peroxisome proliferator-activated receptor alpha-RXRalpha and PGC-1beta coordinately up-regulate L-FABP and MTP expression, by competing with chicken ovalbumin upstream promoter transcription factor II for the DR1 sites in the proximal promoters of each gene. Additional studies show that ablation of L-FABP prevents hepatic steatosis caused by treating mice with an MTP inhibitor. Our findings show that reducing both L-FABP and MTP is an effective means to reduce VLDL secretion without causing hepatic steatosis.

Differential effects of pharmacological liver X receptor activation on hepatic and peripheral insulin sensitivity in lean and ob/ob mice

Liver X receptor (LXR) agonists have been proposed to act as anti-diabetic drugs. However, pharmacological LXR activation leads to severe hepatic steatosis, a condition usually associated with insulin resistance and type 2 diabetes mellitus. To address this apparent contradiction, lean and ob/ob mice were treated with the LXR agonist GW-3965 for 10 days. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamp studies. Hepatic glucose production (HGP) and metabolic clearance rate (MCR) of glucose were determined with stable isotope techniques. Blood glucose and hepatic and whole body insulin sensitivity remained unaffected upon treatment in lean mice, despite increased hepatic triglyceride contents (61.7 +/- 7.2 vs. 12.1 +/- 2.0 nmol/mg liver, P < 0.05). In ob/ob mice, LXR activation resulted in lower blood glucose levels and significantly improved whole body insulin sensitivity. GW-3965 treatment did not affect HGP under normo- and hyperinsulinemic conditions, despite increased hepatic triglyceride contents (221 +/- 13 vs. 176 +/- 19 nmol/mg liver, P < 0.05). Clamped MCR increased upon GW-3965 treatment (18.2 +/- 1.0 vs. 14.3 +/- 1.4 ml x kg(-1) x min(-1), P = 0.05). LXR activation increased white adipose tissue mRNA levels of Glut4, Acc1 and Fasin ob/ob mice only. In conclusion, LXR-induced blood glucose lowering in ob/ob mice was attributable to increased peripheral glucose uptake and metabolism, physiologically reflected in a slightly improved insulin sensitivity. Remarkably, steatosis associated with LXR activation did not affect hepatic insulin sensitivity.

Effect of L-carnitine on plasma glycemic and lipidemic profile in patients with type II diabetes mellitus

OBJECTIVE

We designed this study to investigate the effects of oral L-carnitine administration on fasting plasma glucose (FPG), glycosylated hemoglobin (HbA1c) and lipid parameters in patients with diabetes mellitus type II.

PATIENTS AND METHODS

The effect of L-carnitine on FPG and lipid parameters was investigated in 22 male and 13 female type II diabetic patients; the mean age +/- s.d. was 51.3 +/- 3.7 y. The patients were randomly allocated to two groups (L-carnitine and placebo group) and 1 g of L-carnitine or of placebo was given orally three times a day for a period of 12 weeks.

RESULTS

FPG in the L-carnitine group decreased significantly from 143 +/- 35 to 130 +/- 33 mg/dl (P = 0.03), and we observed a significant increase of triglycerides (TG) from 196+/-61 to 233+/-12 mg/dl (P = 0.05), of Apo A1 from 94 +/- 20 to 103 +/- 23 mg/dl (P = 0.02), and of Apo B100 from 98 +/- 18 to 108 +/- 22 mg/dl (P = 0.02) after 12 weeks of treatment. There was no significant change in LDL-C, HDL-C, HbA1C, LP(a) or total cholesterol.

CONCLUSION

L-Carnitine significantly lowers FPG but increases fasting triglyceride in type II diabetic patients.

An apolipoprotein B antisense oligonucleotide lowers LDL cholesterol in hyperlipidemic mice without causing hepatic steatosis

High levels of plasma apolipoprotein B-100 (apoB-100), the principal apolipoprotein of LDL, are associated with cardiovascular disease. We hypothesized that suppression of apoB-100 mRNA by an antisense oligonucleotide (ASO) would reduce LDL cholesterol (LDL-C). Because most of the plasma apoB is made in the liver, and antisense drugs distribute to that organ, we tested the effects of a mouse-specific apoB-100 ASO in several mouse models of hyperlipidemia, including C57BL/6 mice fed a high-fat diet, Apoe-deficient mice, and Ldlr-deficient mice. The lead apoB-100 antisense compound, ISIS 147764, reduced apoB-100 mRNA levels in the liver and serum apoB-100 levels in a dose- and time-dependent manner. Consistent with those findings, total cholesterol and LDL-C decreased by 25-55% and 40-88%, respectively. Unlike small-molecule inhibitors of microsomal triglyceride transfer protein, ISIS 147764 did not produce hepatic or intestinal steatosis and did not affect dietary fat absorption or elevate plasma transaminase levels. These findings, as well as those derived from interim phase I data with a human apoB-100 antisense drug, suggest that antisense inhibition of this target may be a safe and effective approach for the treatment of humans with hyperlipidemia.

Inhibition of the synthesis of apolipoprotein B-containing lipoproteins

Increased serum concentrations of low density lipoproteins represent a major cardiovascular risk factor. Low-density lipoproteins are derived from very low density lipoproteins secreted by the liver. Apolipoprotein (apo)B that constitutes the essential structural protein of these lipoproteins exists in two forms, the full length form apoB-100 and the carboxy-terminal truncated apoB-48. The generation of apoB-48 is due to editing of the apoB mRNA which generates a premature stop translation codon. The editing of apoB mRNA is an important regulatory event because apoB-48-containing lipoproteins cannot be converted into the atherogenic low density lipoproteins. The apoB gene is constitutively expressed in liver and intestine, and the rate of apoB secretion is regulated post-transcriptionally. The translocation of apoB into the endoplasmic reticulum is complicated by the hydrophobicity of the nascent polypeptide. The assembly and secretion of apoB-containing lipoproteins within the endoplasmic reticulum is strictly dependent on the microsomal tricylceride transfer protein which shuttles triglycerides onto the nascent lipoprotein particle. The overall synthesis of apoB lipoproteins is regulated by proteosomal and nonproteosomal degradation and is dependent on triglyceride availability. Noninsulin dependent diabetes mellitus, obesity and the metabolic syndrome are characterized by an increased hepatic synthesis of apoB-containing lipoproteins. Interventions aimed to reduce the hepatic secretion of apoB-containing lipoproteins are therefore of great clinical importance. Lead targets in these pathways are discussed.

The hepatitis B virus X protein inhibits secretion of apolipoprotein B by enhancing the expression of N-acetylglucosaminyltransferase III

The X protein of hepatitis B virus (HBx) plays a major role on hepatocellular carcinoma (HCC). Apolipoprotein B (apoB) in the liver is an important glycoprotein for transportation of very low density lipoproteins and low density lipoproteins. Although lipid accumulation in the liver is known as one of the factors for the HCC, the relationship between HBx and apoB during the HCC development is poorly understood. To better understand the biological significance of HBx in HCC, liver Chang cells that specifically express HBx were established and characterized. In this study we demonstrate that overexpression of HBx significantly up-regulates the expression of UDP-N-acetylglucosamine:beta-d-mannoside-1,4-N-acetylglucosaminyltransferase-III (GnT-III), an enzyme that functions as a bisecting-N-acetylglucosamine (GlcNAc) transferase in apoB, and increases GnT-III promoter activity in a chloramphenicol acetyltransferase assay. GnT-III expression levels of HBx-transfected cells appeared to be higher than that of hepatocarcinoma cells as well as GnT-III-transfected cells, indicating that HBx may has a strong GnT-III promotor-enhancing activity. Intracellular levels of apoBs, which contained the increased bisecting GlcNAc, were accumulated in HBx-transfected liver cells. These cells as well as GnT-III-transfected liver cells revealed the inhibition of apoB secretion and the increased accumulation of intracellular triglyceride and cholesterol compared with vector-transfected cells. Moreover, overexpression of GnT-III and HBx in liver cells was shown to down-regulate the transcriptional level of microsomal triglyceride transfer protein, which regulates the assembly and secretion of apoB. Therefore, our study strongly suggested that the HBx increase in intracellular accumulation of aberrantly glycosylated apoB resulted in inhibition of secretion of apoB as well as intracellular lipid accumulation by elevating the expression of GnT-III.

ARP-1/COUP-TF II determines hepatoma phenotype by acting as both a transcriptional repressor of microsomal triglyceride transfer protein and an inducer of CYP7A1

L35 and FAO cells were derived as single cell isolates from H35 cells. Whereas L35 cells do not express microsomal triglyceride transfer protein (MTP), which regulates lipoprotein secretion, they express CYP7A1, which regulates bile acid synthesis from cholesterol. FAO cells display the opposite phenotype (i.e. expression of MTP but not CYP7A1). We examined the molecular basis of the transcriptional inactivation of the MTP gene in L35 cells. Nested deletion and mutagenesis studies show that a conserved DR1 element within the 135-bp proximal MTP promoter is responsible for differential expression by L35 and FAO cells. Yeast one-hybrid screening identified apolipoprotein A1 regulatory protein-1/chicken ovalbumin upstream promoter transcription factor II (ARP-1/COUP-TFII) and retinoid X receptor (RXRalpha) as the protein factors that can bind to the conserved DR1 element. Nuclear extracts from L35 cells contained 2-fold more ARP-1/COUP-TFII and 50% less RXRalpha than those from FAO cells. Immunologic studies show that in L35 cells, ARP-1/COUP-TFII is bound to the DR1 element, whereas in FAO cells, a complex containing RXRalpha is bound to the DR1 element. Co-transfection studies show that ARP-1/COUP-TFII repressed MTP promoter activity by approximately 70% in FAO hepatoma cells, whereas RXRalpha and its ligand 9-cis-retinoic acid increased MTP promoter activity by 6-fold in L35 cells. The combined data suggest that in the context of the MTP promoter, ARP-1/COUP-TFII (repressor) and a complex containing RXRalpha (inducer) compete for the DR1 element. Analysis of the CYP7A1 promoter revealed that it is approximately 5-fold more active in L35 cells than in FAO cells. Co-transfection of an ARP-1/COUP-TFII expression vector showed that it enhances CYP7A1 promoter activity by 6-fold in FAO cells. These combined findings indicate that ARP-1/COUP-TFII acts as both a transcriptional repressor (of MTP) and as a transcription activator (of CYP7A1). This dual function of ARP-1/COUP-TFII may play an important role in determining the metabolic phenotype of individual liver cells.

Evolution of cholesterol management therapies: exploiting potential for further improvement

The development of therapies for the control of atherosclerosis is an important example of the drug discovery process. Findings from population studies initiated 4 decades ago have been gradually translated to today's therapies, the most effective of which are the statins. Driven by an increased understanding of the atherosclerotic process and shortfalls of current treatments, the development of therapies for cholesterol control continues, with new agents in the pipeline promising therapeutic benefits over existing treatments. The advent of new statins such as rosuvastatin and pitavastatin, with improved efficacy for reducing cholesterol and the ability to positively affect other disease risk factors, may exploit the potential for improvement of current treatments.

Regulation of microsomal triglyceride transfer protein gene by insulin in HepG2 cells: roles of MAPKerk and MAPKp38

Microsomal triglyceride transfer protein (MTP) is rate limiting for the assembly and secretion of apolipoprotein B-containing lipoproteins. Elevated hepatic MTP mRNA level, presumably as a result of impaired insulin signaling, has been implicated in the pathophysiology of dyslipidemia associated with insulin resistance/type 2 diabetes. In this study, we showed that insulin decreases MTP mRNA level mainly through transcriptional regulation in HepG2 cells. We further characterized the corresponding signal transduction pathway, using chemical inhibitors and constitutively active and dominant negative forms of regulatory enzymes. We demonstrated that insulin inhibits MTP gene transcription through MAPK(erk) cascade but not through the PI 3-kinase pathway. Activation of ras through farnesylation is not a prerequisite for the inhibition. In addition, cellular MAPK(erk) and MAPK(p38) activities play a counterbalancing role in regulating the MTP gene transcription. These complex regulations may represent a means to fine-tuning MTP gene transcription in response to a diverse set of environmental stimuli and may have important implications for the onset and development of diabetes-associated dyslipidemia.

Familial hypobetalipoproteinemia: a review

We review the genetics and pathophysiology of familial hypobetalipoproteinemia (FHBL), a mildly symptomatic genetically heterogeneous autosomal trait. The minority of human FHBL is caused by truncation-specifying mutations of the APOB gene on chromosome 2. In seven families, linkage to chromosome 2 is absent, linkage is instead to chromosome 3 (3p21). In others, linkage is absent to both APOB and to 3p21. Apolipoprotein B-100 (apoB-100) levels are approximately 25% of normal, instead of the 50% expected based on the presence of one normal allele due to reduced rates of production. The presence of the truncating mutation seems to have a "dominant recessive" effect on apoB-100 secretion. Concentrations of apoB truncations in plasma differ by truncation but average at approximately 10% of normal levels. Lipoproteins bearing truncated forms of apoB are cleared more rapidly than apoB-100 particles. In contrast with apoB-100 particles cleared primarily in liver via the LDL receptor, most apoB truncation particles are cleared in renal proximal tubular cells via megalin. Since apoB defects cause a dysfunctional VLDL-triglyceride transport system, livers accumulate fat. Hepatic synthesis of fatty acids is reduced in compensation. Informational lacunae remain about genes affecting fat accumulation in liver, and the modulation of liver fat in the presence apoB truncation defects.

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.

Rab7 gene is up-regulated by cholesterol-rich diet in the liver and artery

To identify genes responding to the cholesterol-rich diet, differentially expressed hepatic genes have been searched from a diet-induced hypercholesterolemic rabbit by differential display reverse transcription-polymerase chain reaction (DDRT-PCR). Among the many screened genes, Rab7 gene was shown to be distinctively up-regulated in response to the cholesterol-loading into the rabbit. To visualize the location of elevated Rab7 expression in tissues, patterns of the gene expression were monitored within hepatic and aortic tissues by in situ hybridization and immunohistochemistry. The expression of Rab7 was obviously increased in the hepatic tissues, especially in the endothelial cells and hepatocytes around central veins of the high cholesterol-fed rabbit, compared to the tissues from rabbit fed a normal diet. To find out a potential relationship between the Rab7 and the atherogenesis, the same experiments were conducted with the atherosclerotic plaques obtained from rabbit and human. The elevated expression of Rab7 gene was clearly evident in both tissues, suggesting that the Rab7 may be involved in the process of atherogenesis.