Enhanced free cholesterol, SREBP-2 and StAR expression in human NASH

Histamine regulation in glucose and lipid metabolism via histamine receptors: model for nonalcoholic steatohepatitis in mice

Histamine has been proposed to be an important regulator of energy intake and expenditure. The aim of this study was to evaluate histamine regulation of glucose and lipid metabolism and development of nonalcoholic steatohepatitis (NASH) with a hyperlipidemic diet. Histamine regulation of glucose and lipid metabolism, adipocytokine production, and development of hyperlipidemia-induced hepatic injury were studied in histamine H1 (H1R(-/-)) and H2 (H2R(-/-)) receptor knockout and wild-type mice. H1R(-/-) mice showed mildly increased insulin resistance. In contrast, H2R(-/-) mice manifested profound insulin resistance and glucose intolerance. High-fat/high-cholesterol feeding enhanced insulin resistance and glucose intolerance. Studies with two-deoxy-2-[(18)F]-fluoro-d-glucose and positron emission tomography showed a brain glucose allocation in H1R(-/-) mice. In addition, severe NASH with hypoadiponectinemia as well as hepatic triglyceride and free cholesterol accumulation and increased blood hepatic enzymes were observed in H2R(-/-) mice. H1R(-/-) mice showed an obese phenotype with visceral adiposity, hyperleptinemia, and less severe hepatic steatosis and inflammation with increased hepatic triglyceride. These data suggest that H1R and H2R signaling may regulate glucose and lipid metabolism and development of hyperlipidemia-induced NASH.

Cholesterol and peroxidized cardiolipin in mitochondrial membrane properties, permeabilization and cell death

Mitochondria are known to actively regulate cell death with the final phenotype of demise being determined by the metabolic and energetic status of the cell. Mitochondrial membrane permeabilization (MMP) is a critical event in cell death, as it regulates the degree of mitochondrial dysfunction and the release of intermembrane proteins that function in the activation and assembly of caspases. In addition to the crucial role of proapoptotic members of the Bcl-2 family, the lipid composition of the mitochondrial membranes is increasingly recognized to modulate MMP and hence cell death. The unphysiological accumulation of cholesterol in mitochondrial membranes regulates their physical properties, facilitating or impairing MMP during Bax and death ligand-induced cell death depending on the level of mitochondrial GSH (mGSH), which in turn regulates the oxidation status of cardiolipin. Cholesterol-mediated mGSH depletion stimulates TNF-induced reactive oxygen species and subsequent cardiolipin peroxidation, which destabilizes the lipid bilayer and potentiates Bax-induced membrane permeabilization. These data suggest that the balance of mitochondrial cholesterol to peroxidized cardiolipin regulates mitochondrial membrane properties and permeabilization, emerging as a rheostat in cell death.

Cholesterol absorption decreases after Roux-en-Y gastric bypass but not after gastric banding

The differences in cholesterol metabolism after the 2 most common forms of obesity surgery, Roux-en-Y gastric bypass (RYGB) and gastric banding (GB), have not been well characterized. In this study, effects of RYGB and GB on cholesterol absorption and synthesis were investigated. To this aim, 1-year follow-up of cholesterol metabolism in 2 nonrandomized cohorts undergoing either RYGB (n = 29; age, 45.2 +/- 7.7 years; body mass index [BMI], 46.0 +/- 6.1 kg/m(2)) or GB (n = 26; age, 45.9 +/- 8.6 years; BMI, 50.1 +/- 7.7 kg/m(2)) was performed in a university hospital center specializing in the treatment of morbid obesity. Serum markers of cholesterol synthesis (cholestenol, desmosterol, and lathosterol) and cholesterol absorption (campesterol, sitosterol, avenasterol, and cholestanol) were measured preoperatively and at follow-up and expressed as ratios to cholesterol. As expected based on observed weight loss (25% after RYGB and 17% after GB, P < .001 between groups), both operations decreased serum levels of cholesterol synthesis markers by 12% to 28% (all Ps < .001). A decrease in cholesterol absorption markers was only observed after RYGB (-26% for sitosterol) and not after GB (+16%, P = 2 x 10(-6) for difference between the groups). The difference in sitosterol ratio between the groups remained significant after adjustment for age, BMI, fasting insulin levels, and nutritional status (P = 2 x 10(-4)), indicating a specific effect related to RYGB. We conclude that decrease in cholesterol absorption is a novel beneficial effect of RYGB. Together with an improved control of blood glucose, this may contribute to a better cardiovascular risk profile after RYGB.

Redox control of liver function in health and disease

Reactive oxygen species (ROS), a heterogeneous population of biologically active intermediates, are generated as by-products of the aerobic metabolism and exhibit a dual role in biology. When produced in controlled conditions and in limited quantities, ROS may function as signaling intermediates, contributing to critical cellular functions such as proliferation, differentiation, and cell survival. However, ROS overgeneration and, particularly, the formation of specific reactive species, inflicts cell death and tissue damage by targeting vital cellular components such as DNA, lipids, and proteins, thus arising as key players in disease pathogenesis. Given the predominant role of hepatocytes in biotransformation and metabolism of xenobiotics, ROS production constitutes an important burden in liver physiology and pathophysiology and hence in the progression of liver diseases. Despite the recognized role of ROS in disease pathogenesis, the efficacy of antioxidants as therapeutics has been limited. A better understanding of the mechanisms, nature, and location of ROS generation, as well as the optimization of cellular defense strategies, may pave the way for a brighter future for antioxidants and ROS scavengers in the therapy of liver diseases.

Recovery from liver disease in a Niemann-Pick type C mouse model

Loss of function of Niemann-Pick C1 (NPC1) leads to lysosomal free cholesterol storage, resulting in the neurodegenerative disease Niemann-Pick disease type C (NPC). Significant numbers of patients with NPC also suffer from liver disease. Currently, no treatments exist that alter patient outcome, and it is unknown if recovery from tissue damage can occur even if a treatment were found. Our laboratory developed a strategy to test whether mice can recover from NPC liver disease. We used antisense oligonucleotides to knock down hepatic expression of NPC1 in BALB/C mice for either 9 or 15 weeks. This recapitulated liver disease with hepatomegaly, cell death, and fibrosis. Then, antisense oligonucleotide treatment was halted for an additional 4, 9, or 15 weeks. We report that significant liver recovery occurred even when NPC1 protein expression only partially returned to normal. Several pathological phenotypes were alleviated, including hepatomegaly, cholesterol storage, and liver cell death. Histological examination revealed that foamy cell accumulation was relieved; however, liver fibrosis increased. Additionally, resolution of cholesterol storage and liver cell death took longer in mice with long-term knockdown. Finally, we found that transcription of cholesterol homeostatic genes was significantly disrupted during the recovery phase after long-term knockdown.

Specific contribution of methionine and choline in nutritional nonalcoholic steatohepatitis: impact on mitochondrial S-adenosyl-L-methionine and glutathione

The pathogenesis and treatment of nonalcoholic steatohepatitis (NASH) are not well established. Feeding a diet deficient in both methionine and choline (MCD) is one of the most common models of NASH, which is characterized by steatosis, mitochondrial dysfunction, hepatocellular injury, oxidative stress, inflammation, and fibrosis. However, the individual contribution of the lack of methionine and choline in liver steatosis, advanced pathology and impact on mitochondrial S-adenosyl-L-methionine (SAM) and glutathione (GSH), known regulators of disease progression, has not been specifically addressed. Here, we examined the regulation of mitochondrial SAM and GSH and signs of disease in mice fed a MCD, methionine-deficient (MD), or choline-deficient (CD) diet. The MD diet reproduced most of the deleterious effects of MCD feeding, including weight loss, hepatocellular injury, oxidative stress, inflammation, and fibrosis, whereas CD feeding was mainly responsible for steatosis, characterized by triglycerides and free fatty acids accumulation. These findings were preceded by MCD- or MD-mediated SAM and GSH depletion in mitochondria due to decreased mitochondrial membrane fluidity associated with a lower phosphatidylcholine/phosphatidylethanolamine ratio. MCD and MD but not CD feeding resulted in increased ceramide levels by acid sphingomyelinase. Moreover, GSH ethyl ester or SAM therapy restored mitochondrial GSH and ameliorated hepatocellular injury in mice fed a MCD or MD diet. Thus, the depletion of SAM and GSH in mitochondria is an early event in the MCD model of NASH, which is determined by the lack of methionine. Moreover, therapy using permeable GSH prodrugs may be of relevance in NASH.

Intrahepatic cholesterol influences progression, inhibition and reversal of non-alcoholic steatohepatitis in hyperlipidemic mice

Hepatic inflammation is the key factor in non-alcoholic steatohepatitis (NASH) and promotes progression to liver damage. We recently identified dietary cholesterol as the cause of hepatic inflammation in hyperlipidemic mice. We now show that hepatic transcriptome responses are strongly dependent on cholesterol metabolism during diet-induced NASH and its inhibition by fenofibrate. Furthermore, we show that, despite doubling hepatic steatosis, pharmacological LXR activation reverses hepatic inflammation, in parallel with reversing hepatic cholesterol levels. Together, the results indicate a prominent role of cholesterol during the development, inhibition and reversal of hepatic inflammation in NASH and reveal potential new therapeutic strategies against NASH.

Chronic alcohol consumption disrupted cholesterol homeostasis in rats: down-regulation of low-density lipoprotein receptor and enhancement of cholesterol biosynthesis pathway in the liver

BACKGROUND

Chronic alcohol consumption causes alcoholic liver disease, which is associated, or initiated, with dysregulated lipid metabolism. Very recent evidence suggested that dysregulated cholesterol metabolism plays an important role in the pathogenesis of alcoholic fatty liver diseases, however, the effects of chronic alcohol exposure on cholesterol homeostasis have not been well studied and underlying mechanisms behind are still elusive.

METHODS

Male Sprague-Dawley rats weighing 250 +/- 5.5 g (mean +/- SEM) divided into 2 groups (8 rats per group) and pair-fed with liquid diets containing (in percent of energy intake) 18% protein, 35% fat, 12% carbohydrate, and 35% either ethanol (ethanol diet) or an isocaloric maltose-dextrin mixture (control diet), according to Lieber and De Carli, for 4 weeks.

RESULTS

Long-term excessive alcohol feeding to rats caused fatty liver and liver injury, which was associated with disrupted cholesterol homeostasis, characterized by increased hepatic cholesterol levels and hypercholesterolemia. Hepatic cholesterol increases were concomitant with constantly activated sterol regulatory element-binding protein-2 (SREBP-2) in the liver and increased expression of 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase, a rate-limiting enzyme for cholesterol de novo synthesis, indicating enhanced cholesterol biosynthesis. Alcohol-induced hypercholesterolemia was accompanied by decreased LDL receptor (LDLr) levels in the liver. Further investigations revealed that chronic alcohol exposure increased hepatic proprotein convertase subtilisin/kexin type 9 (PCSK9) contents to down-regulate LDLr via a post-translational mechanism. Moreover, alcohol feeding suppressed extracellular signal-regulated kinase (ERK) activation in the liver. In vitro studies showed that inhibition of ERK activation was associated with decreased LDLr expression in HepG2 cells.

CONCLUSIONS

Our study provides the first evidence that both increased PCSK9 expression and suppressed ERK activation in the liver contributes to alcohol-induced hypercholesterolemia in rats.

Cholesterol metabolism and expression of its relevant genes in cultured steatotic hepatocytes

OBJECTIVE

To investigate the cholesterol metabolism and mRNA expression of the relevant genes in cholesterol synthesis of the cultured steatotic hepatocytes model.

METHODS

A steatotic model of hepatocytes was constructed by adding palmitic acid to the growing L-02 cells. These cells were collected at day 3 and 6, respectively. Cells with the culture solution without palmitic acid added served as the control. The contents of intracellular triglyceride (TG) and total cholesterol (TC) were detected by the analysis kit. The expression of sterol-regulatory element binding protein-2 (SREBP-2) and its target gene hydroxymethylglutaryl CoA reductase (HMGCR) and low-density lipoprotein receptor (LDLR) were measured by RT-PCR.

RESULTS

Hepatocyte steatosis was observed at day 3 and became more intense at day 6. The contents of intracellular TG and TC were increased and the expression of the SREBP-2, HMGCR and LDLR mRNA were upregulated in a time-dependent manner in the model group. Compared with the control group, the content of intracellular TG was higher at both day 3 and 6 (P < 0.05), while the content of intracellular TC was significantly increased only at day 6; The expression of HMGCR and LDLR mRNA was upregulated in steatotic hepatocytes at both day 3 and 6 (P < 0.05), whereas the SREBP-2 mRNA was increased only at day 6 (P < 0.05).

CONCLUSION

Cholesterol accumulation is probably due to the upregulated expression of the relevant genes in the cholesterol synthesis of the steatotic hepatocytes.

Lipotoxicity in nonalcoholic fatty liver disease: not all lipids are created equal

Nonalcoholic fatty liver disease (NAFLD) is currently the most common form of chronic liver disease affecting both adults and children in the USA and many other parts of the world. NAFLD encompasses a wide spectrum of conditions associated with the overaccumulation of lipids in the liver, ranging from steatosis to nonalcoholic steatohepatitis, to cirrhosis and its feared complications of portal hypertension, liver failure and hepatocellular carcinoma. In this article, we will focus on the growing evidence linking changes in hepatic lipid metabolism and accumulation of specific lipid types in the liver with hepatocellular damage, inflammation and apoptosis, resulting in disease progression to the more serious forms of this condition.