Liver microsomal triglyceride transfer protein is involved in hepatitis C liver steatosis

Coinfection with HIV-1 and HCV--a one-two punch

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease, cirrhosis, and death; it is estimated that 180 million persons are infected with HCV worldwide. The consequences of HCV are worse in those who are coinfected with human immunodeficiency virus 1 (HIV-1), which is unfortunately a common scenario because of shared risk factors of the viruses. More studies into effects of HCV/HIV-1 coinfection are needed, but efforts have been hampered by limitations in our understanding of the combined pathogenesis of the 2 viruses. Gaining insight into the mechanisms that underlie the immunopathogenesis of these persistent viral infections could lead to new therapeutic strategies for patients with HCV/HIV-1 coinfection.

Hepatitis C virus infection: molecular pathways to steatosis, insulin resistance and oxidative stress

The persistent infection with hepatitis C virus is a major cause of chronic liver disease worldwide. However, the morbidity associated with hepatitis C virus widely varies and depends on several host-related cofactors, such as age, gender, alcohol consumption, body weight, and co-infections. The objective of this review is to discuss three of these cofactors: steatosis, insulin resistance and oxidative stress. Although all may occur independently of HCV, a direct role of HCV infection in their pathogenesis has been reported. This review summarizes the current understanding and potential molecular pathways by which HCV contributes to their development.

Hepatic VLDL assembly is disturbed in a rat model of nonalcoholic fatty liver disease: is there a role for dietary coenzyme Q?

The overproduction of very-low-density lipoprotein (VLDL) is a characteristic feature of nonalcoholic fatty liver disease (NAFLD). The aim of this study was to use a high-fat diet-induced model of NAFLD in rats to investigate 1) the influence of the disease on hepatic VLDL processing in the endoplasmic reticulum and 2) the potential modulatory effects of dietary coenzyme Q (CoQ). Rats were fed a standard low-fat diet (control) or a diet containing 35% fat (57% metabolizable energy). After 10 wk, high-fat diet-fed animals were divided into three groups: the first group was given CoQ9 (30 mg*kg body wt(-1)*day(-1) in 0.3 ml olive oil), the second group was given olive oil (0.3 ml/day) only, and the third group received no supplements. Feeding (3 high-fat diets and the control diet) was then continued for 8 wk. In all high-fat diet-fed groups, the content of triacylglycerol (TG) and cholesterol in plasma VLDL, the liver, and liver microsomes was increased, hepatic levels of apolipoprotein B48 were raised, and the activities of microsomal TG transfer protein and acyl CoA:cholesterol acyltransferase were reduced. These findings provide new evidence indicating that VLDL assembly and the inherent TG transfer to the endoplasmic reticulum are altered in NAFLD and suggest a possible explanation for both the overproduction of VLDL associated with the condition and the disease etiology itself. Dietary CoQ caused significant increases in apolipoprotein B mRNA and microsomal TG levels and altered the phospholipid content of microsomal membranes. These changes, however, may not be beneficial as they may lead to the secretion of larger, more atherogenic VLDL.

Influence of insulin resistance on hepatic fibrosis and steatosis in hepatitis C virus (HCV) mono-infected compared with HIV-HCV co-infected patients

BACKGROUND

Insulin resistance (IR), the major feature of the metabolic syndrome, is also common in patients with chronic HCV infection. Liver fibrosis and steatosis are known potential outcome of chronic hepatitis B or C infection. Studies have shown that HIV positive individuals co-infected with HCV have more rapid live disease progression than those with HIV alone. Few data have reported the influence of IR on steatosis and fibrosis in the context of HIV-HCV coinfection.

AIM

To test the association among insulin resistance (IR), liver fibrosis and liver steatosis in HIV-HCV and HCV-infected patients.

PATIENTS AND METHODS

A total of 170 HIV-HCV-infected patients matched by age, gender and genotype with 170 HCV mono-infected patients were included. Patients were considered to be IR when the homeostasis model assessment of IR >2. Significant fibrosis was considered if METAVIR >or=F2 and significant steatosis if >or=10%.

RESULTS

Insulin resistance was independently associated in HCV patients with fibrosis [odds ratio (OR) = 2.04 (95% CI 1.02-4)], a body mass index (BMI) >25 kg/m(2) [OR = 3.33 (1.47-7.69)] and steatosis [OR = 3.33 (1.67-6.67)]. Fibrosis >or=F2 was associated in HCV patients with high liver activity grade (>or=A2) [OR = 8.33 (3.85-16.67)], male gender [OR = 3.03 (1.33-7.14)] and IR [OR = 2.44 (1.15-5)]. In HIV-HCV patients, >or=A2 [OR = 5.56 (1.64-20)] was associated with fibrosis. Steatosis >or=10% was associated in HCV patients with IR [OR = 3.13 (1.59-6.25) and >or=F2 (OR = 2.22 (1.15-4.17)]. In HIV-HCV, a BMI >25 kg/m(2) [OR = 3.85 (1.64-9.10)], >or=A2 [OR = 2.16 (1.02-4.55); P = 0.044] and nucleoside reverse transcriptase inhibitor [OR = 3.61 (1.19-10.96); P = 0.023] were independently associated with significant liver steatosis.

CONCLUSIONS

Insulin resistance is associated with liver fibrosis and steatosis in HCV mono-infected, but not in HIV-HCV co-infected patients. Significant liver fibrosis is associated with IR independent of liver steatosis only in HCV mono-infected patients.

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 gene and phosphatidylethanolamine N-methyltransferase gene in alcoholic and nonalcoholic fatty liver disease in Koreans

BACKGROUND

The pathogenesis of fatty liver is likely to depend on a complex interaction of environmental and genetic factors. We investigated a large-scale analysis of the association between microsomal triglyceride transfer protein (MTTP) and phosphatidylethanolamine N-methyltransferase (PEMT) polymorphism in alcoholic and nonalcoholic fatty liver disease.

METHODS

Five hundred and eighty-eight patients who visited the health promotion center were enrolled. To elucidate the possible role of genetic variation affecting triglyceride metabolism in fatty liver disease, the MTTP-I128T and PEMT-V175M polymorphisms were studied.

RESULTS

The I/I genotype and I allele frequency of MTTP polymorphism with alcoholic fatty liver was significantly higher than that of the normal control group (P=0.026 vs. 0.005). Genotype and allele frequency of PEMT, however, did not show a significant difference between control and fatty liver. I/I genotype of MTTP gene frequency in the drinkers with fatty livers was 85.4%, which was significantly higher than that in the drinkers without fatty liver, which was 68.4% (P=0.013). With regard to biochemical indicators, the alanine aminotransferase value of the I/I group was significantly higher than that of the I/T and T/T groups (P=0.04). Asparate aminotransferase, gamma-glutamyl transpeptidase, triglyceride, apolipoprotein B, and glucose concentration tended to be lower in the I/T and T/T groups than in the I/I group, but no statistically significant difference was found.

CONCLUSION

In this study, MTTP-I128T polymorphism is associated with central obesity, elevated liver enzymes, and alcoholic fatty liver disease.

Hypobetalipoproteinaemia secondary to chronic hepatitis C virus infection in a patient with familial hypercholesterolaemia

Familial hypercholesterolaemia (FH) is a common genetic disorder characterized by high plasma low-density lipoprotein (LDL)-cholesterol and premature coronary artery disease. Many factors, such as illness, high-dose statin therapy or a strict vegan diet can cause hypobetalipoproteinaemia (HBL). The more common secondary causes of HBL in the hospital setting include cachexia, intestinal malabsorption, malnutrition, severe liver disease and hyperthyroidism. We report a case of HBL in a 43-year-old man with previously demonstrated marked hypercholesterolaemia who attended a lipid disorders clinic for FH cascade screening. Surprisingly, a lipid profile taken at that time showed low plasma LDL-cholesterol and apolipoprotein B concentrations of 1.6 mmol/L and 0.61 g/L, respectively. He was not on lipid-lowering therapy. DNA sequencing showed that he was heterozygous for the LDLR gene mutation (C677R) present in other affected family members. Of interest, his serum transaminases were increased by approximately 3-fold and hepatitis serology and genotyping confirmed a diagnosis of hepatitis C virus (HCV) infection. In summary, we describe a case of HBL secondary to chronic HCV infection in a patient with FH, confirmed by mutational analysis.

Microsomal triglyceride transfer protein polymorphism (-493G/T) is associated with hepatic steatosis in patients with chronic hepatitis C

BACKGROUND

Hepatic steatosis may promote progression of chronic hepatitis C (CHC). Microsomal triglyceride transfer protein (MTP) is required for assembly and secretion of ApoB lipoprotein and is implicated in hepatitis C virus (HCV)-related steatosis. The MTP -493G/T polymorphism may promote liver fat accumulation, but its role in HCV-related steatosis is still unclear.

METHODS

Two hundred ninety-eight CHC patients were studied and genotyped for MTP -493G/T variants. Hepatic MTP mRNA expression and activity were determined in a subgroup.

RESULTS

Patients with grades 2/3 steatosis were older, had a higher body mass index (BMI), more advanced fibrosis and lower MTP mRNA expression and carried more often HCV genotype 3 and the MTP T allele. Age, BMI, HCV-3 and MTP T allele [odds ratio (OR) 2.05; 95% confidence interval (CI) 1.2-3.53; P=0.009] were independent risk factors for steatosis grades 2/3, and in HCV genotype non-3 patients, the MTP T allele was the strongest predictor for steatosis grade 2/3 (OR 2.17; 95% CI 1.22-3.86; P=0.008). Moreover, TT carriers had higher high-density lipoprotein (65.6+/-14.6 vs 56.1+/-16.2 mg/dl; P=0.003) and apolipoprotein AI (1.80+/-0.3 vs 1.60+/-0.3 g/L; P=0.005) levels than G allele carriers.

CONCLUSIONS

Chronic hepatitis C patients with the MTP -493T allele reveal higher grades of steatosis, indicating a relevant contribution to liver fat accumulation, particularly in HCV non-3 patients.

Hepatitis C and diabetes: the inevitable coincidence?

Type 2 diabetes (T2D) and HCV infection are common conditions involving, respectively, at least 170 and 130 million people worldwide. However, the distribution of such cases does not overlap in the same age groups in different geographic areas. Following pioneering reports of increased prevalence of T2D in HCV-positive cirrhosis, interest concerning the relationship between HCV and T2D has escalated. HCV is able to induce insulin resistance (IR) directly and the role of specific viral genotypes responsible for such effect is disputed. IR has consistently been found to be closely linked to fibrosis in HCV infection, although also typically associated with T2D in prefibrotic stages. HCV infection could be associated with a reduced prevalence of metabolic syndrome owing to virus-associated reduction in BMI (reported in population but not clinical studies) and hypobetaliproteinemia. A three- to ten-fold increased risk of HCV infection was reported among diabetic patients in comparison with different control groups and a meta-analysis showed a 1.8-fold excess risk of T2D among HCV-positive compared with HBV-positive patients. Moreover, HCV positivity is associated with an increased risk of T2D in patients receiving liver or kidney transplantations. T2D and IR are independent predictors of a more rapid progression of liver fibrosis and impaired response to antiviral treatment in chronic hepatitis C. Patients with cirrhosis and T2D have an increased susceptibility to hepatic encephalopathy and hepatocellular carcinoma (HCC). However, the beneficial effects of antiviral treatment on IR and T2D are controversial. Theoretically, glycemic control in chronic hepatitis C, and particularly in cirrhotic patients, could improve the prognosis and the response to antivirals, although the evidence for this is limited. Future studies should elucidate the relationship between insulin signaling, HCV and interferon signaling, entity of cardiovascular risk in patients with HCV infection, the potential role of 'metabolic' strategies added to antiviral treatment schedules, the impact of IR on liver failure, portal hypertension and HCC, particularly in patients managed in a transplant setting.

Insulin resistance and metabolic syndrome in chronic liver diseases: old entities with new implications

Insulin resistance (IR) and metabolic syndrome have recently been implicated in the pathogenesis and progression of chronic liver diseases, especially chronic hepatitis C (CHC) and non-alcoholic fatty liver disease (NAFLD). In this review, we provide current information on their deleterious effect on the liver, with particular interest in those two entities. In NAFLD, IR causes both the accumulation of fat in hepatocytes and the progression to non-alcoholic steatohepatitis (NASH). Moreover, the presence of metabolic syndrome seems to be associated with severe fibrosis in NASH patients. In CHC, IR develops early in the course of the disease and precedes steatosis. It is also independently associated with histological severity and negatively affects treatment response, irrespective of genotype. Consequently, therapies targeting IR and metabolic syndrome could indirectly ameliorate the prognosis of both NAFLD and CHC. As specific therapies do not exist, patients with metabolic syndrome and CHC and NAFLD should be counseled to lose weight and ameliorate their glycemic control and lipid profile.

Hepatitis C virus, steatosis and lipid abnormalities: clinical and pathogenic data

Abnormal accumulation of fat in the liver (steatosis) is commonly observed in hepatitis C virus (HCV) infection, and the severity of steatosis has been well correlated with the degree of hepatic fibrosis. In patients with chronic HCV infection, steatosis may occur in conjunction with other metabolic risk factors such as insulin resistance and the metabolic syndrome. This was observed primarily in patients infected with non-genotype 3 virus. Otherwise, in HCV-infected patients, especially those infected with genotype 3a, reductions in total cholesterol as well as high-density lipoprotein and low-density lipoprotein cholesterol are observed compared with matched controls, and the normalization of these parameters appears to be an important correlate of the response to antiviral therapy. In that setting, the pathogenic mechanisms involved in HCV-induced steatosis are mediated in large part by the HCV core protein, whose expression is associated with lipid droplet accumulation, changes in lipogenic gene expression and/or the activity of lipogenic proteins, and effects on mitochondrial oxidative function. The importance of genes such as peroxisome proliferator-activated receptor-alpha and the proteasome activator PA28-gamma in HCV-mediated steatosis has been elucidated from studies in genetically altered mice, and the manipulation of these and other pathways may provide an avenue for therapeutic intervention.

Association of lipid profiles with hepatitis C viral load in chronic hepatitis C patients with genotype 1 or 2 infection

OBJECTIVES

Metabolic profiles correlate with hepatitis C virus (HCV) infection and are known to be predictors of virologic responses in chronic hepatitis C patients on interferon-based treatment. However, little is known about the differential association of lipid profiles with hepatitis C viral load between genotype 1 and 2 infections. The aim of this study was to evaluate the impact of lipid profiles on HCV RNA levels in patients with genotypes 1 and 2.

METHODS

A total of 531 chronic hepatitis C patients infected patients with HCV genotype 1 or 2 were consecutively enrolled. Univariate and multivariate approaches were used to estimate the associations between demographic, metabolic, and viral variables and HCV RNA levels.

RESULTS

Higher serum triglyceride, total cholesterol, and low-density lipoprotein levels correlated with higher HCV RNA levels. In multivariate analysis, genotype 1 infection, severe hepatitis activity, milder hepatic fibrosis, higher homeostasis model assessment of insulin resistance (HOMA-IR) index and triglyceride levels are associated with higher HCV viral loads (P<0.05). Subanalysis on patients with lower body mass index values showed higher HCV viral load was associated with higher HOMA-IR index and total cholesterol level (P<0.05). After stratification by HCV genotype, lipid profiles were significantly associated with HCV viral load in genotype 2 infection (P<0.05), but not genotype 1 infection.

CONCLUSIONS

A proportional relationship is found between serum lipid profiles and hepatitis C viral load in patients with genotype 2 infection; however, whether manipulation of lipid profiles would improve the response to current anti-HCV therapy is to be determined in further studies.

Effect of steatosis and inflammation on liver fibrosis in chronic hepatitis C

BACKGROUND/AIMS

The role of liver biopsy has been questioned in the management of patients with hepatitis C viral (HCV) infection. The aims of this study were to determine the impact of clinical parameters and degree of inflammation and steatosis on liver fibrosis.

PATIENTS/METHODS

Clinical data and liver histology findings in 510 HCV patients were analysed.

RESULTS

Hepatitis C virus genotype 1 (GT-1) was found in 38%, GT-2 in 15% and GT-3 in 45% of patients. In liver biopsy specimens, inflammation activity was present in 68%, increased fibrosis in 19% and marked steatosis in 17% of patients. Independent clinical risk factors for the increased fibrosis were patients' age at biopsy, body mass index (BMI) and duration of HCV. Steatosis and inflammation activity were independent histological risk factors for fibrosis only in GT-1; in GT-3, only inflammation correlated independently with fibrosis.

CONCLUSIONS

Age at liver biopsy, BMI and duration of HCV were independent risk factors for increased fibrosis in HCV patients. Steatosis as a risk factor for fibrosis is evident in GT-1. When scoring liver biopsies of HCV patients, the degree of steatosis should be included in addition to fibrosis and inflammation activity.

Secretion of hepatitis C virus envelope glycoproteins depends on assembly of apolipoprotein B positive lipoproteins

The density of circulating hepatitis C virus (HCV) particles in the blood of chronically infected patients is very heterogeneous. The very low density of some particles has been attributed to an association of the virus with apolipoprotein B (apoB) positive and triglyceride rich lipoproteins (TRL) likely resulting in hybrid lipoproteins known as lipo-viro-particles (LVP) containing the viral envelope glycoproteins E1 and E2, capsid and viral RNA. The specific infectivity of these particles has been shown to be higher than the infectivity of particles of higher density. The nature of the association of HCV particles with lipoproteins remains elusive and the role of apolipoproteins in the synthesis and assembly of the viral particles is unknown. The human intestinal Caco-2 cell line differentiates in vitro into polarized and apoB secreting cells during asymmetric culture on porous filters. By using this cell culture system, cells stably expressing E1 and E2 secreted the glycoproteins into the basal culture medium after one week of differentiation concomitantly with TRL secretion. Secreted glycoproteins were only detected in apoB containing density fractions. The E1-E2 and apoB containing particles were unique complexes bearing the envelope glycoproteins at their surface since apoB could be co-immunoprecipitated with E2-specific antibodies. Envelope protein secretion was reduced by inhibiting the lipidation of apoB with an inhibitor of the microsomal triglyceride transfer protein. HCV glycoproteins were similarly secreted in association with TRL from the human liver cell line HepG2 but not by Huh-7 and Huh-7.5 hepatoma cells that proved deficient for lipoprotein assembly. These data indicate that HCV envelope glycoproteins have the intrinsic capacity to utilize apoB synthesis and lipoprotein assembly machinery even in the absence of the other HCV proteins. A model for LVP assembly is proposed.

Investigation of the role of SREBP-1c in the pathogenesis of HCV-related steatosis

BACKGROUND/AIMS

Increased expression of sterol regulatory element binding protein (SREBP)-1c, a transcription factor regulating lipogenesis, has been reported in HCV core protein-transfected hepatocytes. Our aim was to investigate the role of SREBP-1c in the pathogenesis of HCV-related steatosis.

METHODS

One hundred and twenty-four patients with HCV and 13 subjects with histologically normal liver (NDL) were studied. The mRNA expression of SREBP-1c, fatty acid synthase (FAS), glycerol-3-phosphate acyltransferase (GPAT) and microsomal triglyceride transfer protein (MTP) was measured by qPCR, and SREBP-1 protein quantitated by immunohistochemistry.

RESULTS

There was no significant difference in the hepatic expression of SREBP-1c mRNA between subjects with HCV and NDL. In patients with HCV, a significant negative relationship was seen between hepatic SREBP-1c mRNA expression and grade of steatosis (r(s)=-0.28, p=0.002), stage of fibrosis (r(s)=-0.375, p<0.001) and severity of inflammation (r(s)=-0.313, p<0.001). These relationships were observed for patients infected with either viral genotype 1 or 3. Following multivariate logistic regression analysis, hepatic SREBP-1c expression remained independently associated with fibrosis (p=0.008) and hepatic inflammation (p=0.005). HCV-infected patients with HOMA>2 had significantly higher expression of FAS mRNA than HCV-infected subjects with HOMA2 (p=0.006) and NDL (p=0.016).

CONCLUSIONS

SREBP-1c may not play a prominent role in the pathogenesis of HCV-related steatosis.

New approaches to target microsomal triglyceride transfer protein

PURPOSE OF REVIEW

Microsomal triglyceride transfer protein (MTP), a chaperone for the biosynthesis of apolipoprotein B lipoproteins and CD1d, is a therapeutic candidate to decrease plasma lipids and to diminish inflammation. MTP inhibition increases plasma transaminases and tissue lipids, and therefore new approaches are needed to avoid them.

RECENT FINDINGS

Inositol requiring enzyme1beta has been identified as a novel intestine-specific regulator of MTP. A new function of MTP in cholesterol ester biosynthesis has been reported. The importance of the phospholipid transfer activity of MTP in the lipidation of apolipoprotein B and CD1d has been indicated. Diurnal variations in MTP expression and its induction by food availability have been observed. On the basis of these and other findings, we propose that upregulation of inositol requiring enzyme 1beta, a combined reduction of cellular free cholesterol or triglyceride or both and MTP activity, specific inhibition of phospholipid or triglyceride transfer activities, and targeting of apolipoprotein B-MTP protein-protein interactions might be pursued to avoid some of the side effects associated with the inhibition of triglyceride transfer activity of MTP. We further speculate that short-lived MTP antagonists may be useful in controlling plasma and tissue lipids and in avoiding steatosis.

SUMMARY

We have highlighted the importance of addressing the causal relationship between MTP inhibition and aberrant elevations in plasma liver enzymes. The proposed approaches may show that MTP targeting is a viable approach to lower plasma lipids.

HIV Coinfection and Antiretroviral Therapy Enhances Liver Steatosis in Patients with Hepatitis C, but Only in those Infected by HCV Genotype other than 3

Background

Liver steatosis is a common finding in hepatitis C virus (HCV) infection and is associated with an increased progression of the disease. However, HCV genotype 3 steatosis presents a peculiar and virus-induced pathogenesis. We analysed the effect of HIV coinfection and antiretroviral therapy on hepatic steatosis and the effect of the steatosis on fibrosis in patients with or without HCV genotype 3 infection.

Methods

All consecutive HIV-infected and uninfected patients who had undergone a liver biopsy for evaluation of HCV infection at the Infectious Diseases Clinic (Modena, Italy) were included in this study. Primary outcomes were the presence or absence of steatosis or the presence of moderate or advanced fibrosis.

Results

A total of 284 patients were enrolled: 187 infected by HCV and 97 coinfected with HIV and HCV. In HCV genotype 3 patients, only HCV-related variables, such as plasma HCV RNA levels (odds ratio [OR] per log10 1.68, P<0.001) and estimated duration of HCV infection (OR per year 1.17, P=0.004) were associated with steatosis. In patients infected with other HCV genotypes, steatosis was associated with older age (OR per 5 years 1.47, P<0.001), with exposure to d-drugs in HIV–HCV-coinfected patients (OR 2.60, P=0.04) and specifically exposure to stavudine (OR 2.76 HIV–HCV-coinfected versus not HIV-infected patients, P=0.04). Steatosis was independently associated with bridging fibrosis only in patients infected by HCV genotype other than 3 (OR 4.03, P=0.01).

Conclusions

Hepatic steatosis, in both HCV-monoinfected and in HIV–HCV-coinfected patients, is strongly correlated with HCV genotype 3, probably through interactions between HCV virus and liver cells. HIV-related increase of steatosis in patients with HCV is probably related to anti-retroviral drugs, especially stavudine, in patients infected by HCV genotype other than 3.

Microsomal triglyceride transfer protein (MTP) -493G/T gene polymorphism contributes to fat liver accumulation in HCV genotype 3 infected patients

(A) A reduced activity of microsomal triglyceride transfer protein (MTP), a key enzyme of assembly/secretion of lipoproteins, is related to HCV steatosis. Host genetic background may influence development of steatosis. The aim of the study was to investigate the association between MTP-493 G/T gene polymorphism, fat liver accumulation and fibrosis progression in HCV infected patients. A total of 102 naïve patients with liver biopsy proven chronic hepatitis C were evaluated for MTP-493 G/T gene polymorphism, HCV RNA, HCV genotype, HOMA-IR, serum adiponectin, TNF-alpha and serum lipid levels. HCV genotype 3 infected patients carrying the T allele of the MTP gene polymorphism showed higher degree of steatosis than those carrying GG genotype (3.45 +/- 0.37 vs 1.30 +/- 0.45, respectively; P < 0.001). MTP'T' allele carriers also had higher HCV RNA serum levels (P < 0.01) and hepatic fibrosis (P < 0.001). Irrespective of MTP genotype, patients with HCV genotype 3 had lower levels of cholesterol, ApoB, HDL and LDL. In HCV genotype non-3 infected patients no parameters were associated with MTP gene polymorphism. In conclusion the presence of T allele of MTP-493G/T gene polymorphism predisposes patients infested with HCV genotype 3 to develop higher degree of fatty liver accumulation.

Microsomal triglyceride transfer protein in plasma and cellular lipid metabolism

PURPOSE OF REVIEW

This review summarizes recent advances about the role of microsomal triglyceride transfer protein in plasma and tissue lipid homeostasis.

RECENT FINDINGS

Microsomal triglyceride transfer protein emerged as a phospholipid transfer protein and acquired triacylglycerol transfer activity during evolution from invertebrates to vertebrates. These activities are proposed to participate in 'nucleation' and 'desorption' steps during the biosynthesis of primordial apoB-containing lipoproteins. Microsomal triglyceride transfer protein also transfers phospholipids to the glycolipid antigen presentation molecule CD1d. Under physiologic conditions, plasma apoB-containing lipoproteins and microsomal triglyceride transfer protein expression exhibit diurnal variations synchronized by food and light. Microsomal triglyceride transfer protein is regulated at the transcriptional level. HNF4alpha is critical for its transcription. Other transcription factors along with coactivators and corepressors modulate microsomal triglyceride transfer protein expression. Reductions in microsomal triglyceride transfer protein mRNA and activity are related to steatosis in HCV-3 infected patients. CCl4 induces steatosis by enhancing proteasomal degradation of microsomal triglyceride transfer protein and can be partially avoided by inhibiting this degradation. Chemical antagonists cause hepatosteatosis, but this was not seen in the absence of fatty acid binding protein.

SUMMARY

Microsomal triglyceride transfer protein is a target to lower plasma lipids and to reduce inflammation in certain immune disorders. More knowledge is required, however, regarding its regulation and its role in the biosynthesis of apoB-containing lipoproteins and CD1d.

Dysmetabolic changes associated with HCV: a distinct syndrome?

Although not associated with the metabolic syndrome, HCV is linked with impaired insulin signalling, insulin resistance, hypocholesterolemia and steatosis which represent a distinct HCV-associated dysmetabolic syndrome. Insulin resistance affects the development of diabetes, fibrosis, impaired response to antivirals and perhaps hepatocellular carcinoma risk. HCV infection is associated with hypocholesterolemia and steatosis reversible after sustained virologic response. A "viral", and a "metabolic" steatosis exist as function of viral genotypes. Little is known about the possible role of HCV in further components of the metabolic syndrome such as atherosclerosis, obesity, arterial hypertension, hyperuricemia and thrombotic risk factors.

Binding of liver derived, low density hepatitis C virus to human hepatoma cells

HCV recovered from low density fractions of infected blood is associated with lipid and host apo-lipoproteins in lipo-viro-particles (LVP). It has been proposed that these particles are capable of binding and entering hepatocytes by viral glycoprotein independent mechanisms utilizing uptake pathways of normal host lipoproteins after binding to cell surface glycosaminoglycans (GAG), the low density lipoprotein receptor (LDL-r) or scavenger receptor B1 (SR-B1). In this study binding to human hepatoma cells of HCV low density RNA containing particles, semi-purified from macerates of infected human liver, is compared with that of normal host low density lipoprotein (LDL). Binding of both LDL and HCV low density RNA containing particles paralleled LDL-r but not SR-B1 expression on the recipient cells. Binding of both particle types was sensitive to suramin at 0 degrees C but less so at 37 degrees C suggesting that they both bind initially to GAG but, at 37 degrees C, are internalized or transferred to a suramin resistant receptor. Suramin resistant uptake of both particles was blocked in the presence of excess LDL or oxidized LDL. However, whilst LDL uptake was blocked by anti-apoB-100, HCV low density RNA uptake was enhanced by anti-apoB100 and further enhanced by a cocktail of anti-apo-B100 and anti-apoE. Pre-incubation of HCV low density RNA containing particles with antibodies to the E2 glycoprotein had little or no effect on uptake. These data indicate that whilst liver derived HCV RNA containing particles are taken up by HepG2 cells by a virus glycoprotein independent mechanism, the mechanism differs from that of LDL uptake.

Review article: nonalcoholic fatty liver disease and hepatitis C virus--partners in crime

BACKGROUND

Both nonalcoholic fatty liver disease (NAFLD) and chronic hepatitis C (CHC) are frequent causes of chronic liver disease. In recent years, there have been significant revelations as regards the relationship between NAFLD and CHC.

AIM

To conduct a systematic, evidence-based review of the epidemiology, pathophysiology and potential treatments of coexistent NAFLD and CHC.

METHODS

The terms such as hepatitis C, fatty liver, NAFLD, nonalcoholic steatohepatitis and steatosis were searched on PubMed up to January 2008. References from selected articles and pertinent abstracts were also included.

RESULTS

Hepatic steatosis affects up to 80% of patients with CHC and is dependent on both viral and host factors. While insulin resistance (IR) is associated with hepatic steatosis and hepatitis C virus, genotype-specific pathogenic mechanisms have been identified and are currently the focus of intense investigation in the literature. Clinical implications of concurrent NAFLD, CHC and IR include increased disease progression, elevated risk of hepatocellular carcinoma, and decreased response to antiviral therapy.

CONCLUSIONS

NAFLD and IR are common in patients with CHC virus infection. IR is a driving force in the development of hepatic steatosis. Because of the clinical implications of hepatic steatosis and IR in the setting of CHC, further studies evaluating treatments, which may increase response to antiviral therapy, are needed.

Interplay between oxidative stress and hepatic steatosis in the progression of chronic hepatitis C

BACKGROUND/AIMS

The contribution of oxidative stress to the pathogenesis of chronic hepatitis C (CHC) is still poorly elucidated. This study investigated the relationship between oxidative stress, insulin resistance, steatosis and fibrosis in CHC.

METHODS

IgG against malondialdehyde-albumin adducts and HOMA-IR were measured as markers of oxidative stress and insulin resistance, respectively, in 107 consecutive CHC patients.

RESULTS

Oxidative stress was present in 61% of the patients, irrespective of age, gender, viral load, BMI, aminotransferase level, histology activity index (HAI) and HCV genotype. Insulin resistance and steatosis were evident in 80% and 70% of the patients, respectively. In the patients infected by HCV genotype non-3, but not in those with genotype 3 infection HOMA-IR (p<0.03), steatosis (p=0.02) and fibrosis (p<0.05) were higher in the subjects with oxidative stress than in those without. Multiple regression analysis revealed that, HOMA-IR (p<0.01), fibrosis (p<0.01) and oxidative stress (p<0.05) were independently associated with steatosis, whereas steatosis was independently associated with oxidative stress (p<0.03) and HOMA-IR (p<0.02). Steatosis (p<0.02) and HAI (p=0.007) were also independent predictors of fibrosis.

CONCLUSIONS

In patients infected by HCV genotype non-3, oxidative stress and insulin resistance contribute to steatosis, which in turn exacerbates both insulin resistance and oxidative stress and accelerates the progression of fibrosis.

Insulin resistance in chronic hepatitis C: association with genotypes 1 and 4, serum HCV RNA level, and liver fibrosis

BACKGROUND & AIMS

Our study was designed to test the association between insulin resistance (IR) and hepatitis C virus (HCV) genotypes, serum HCV RNA level and liver fibrosis stage in a large prospective cohort of chronic hepatitis C (CHC) patients.

METHODS

Six hundred consecutive patients (CHC, n = 500; chronic hepatitis B (CHB), n = 100) were evaluated on the day of liver biopsy. IR (Homeostasis Model for Assessment of Insulin Resistance) and all components of the metabolic syndrome were assessed. By logistic regression, independent factors associated with IR and those associated with significant fibrosis were assessed in nondiabetic and noncirrhotic CHC, respectively. Parameters of IR were compared between hepatitis B and 240 CHC matched by epidemiologic, metabolic, and histologic features.

RESULTS

IR was present in 32.4% of the 462 nondiabetic CHC and associated with the metabolic syndrome, genotypes 1 and 4, significant fibrosis, and severe steatosis. IR was diagnosed in 15% of 145 CHC without metabolic syndrome or significant fibrosis, and associated with genotypes 1 and 4, high serum HCV RNA level, and moderate-severe necroinflammation. Significant fibrosis was present in 51.1% of the 454 noncirrhotic CHC patients and associated with male sex, age >40 years, IR, moderate-severe necroinflammation, and severe steatosis. IR was less frequent in CHB than in matched CHC (5% vs 35%, respectively, P < .001).

CONCLUSIONS

IR is a specific feature of CHC, associated with genotypes 1 and 4 and high serum HCV RNA level. Significant fibrosis is associated with IR independent from steatosis.

Insulin resistance and response to therapy in patients infected with chronic hepatitis C virus genotypes 2 and 3

BACKGROUND/AIMS

Obesity is associated with impaired treatment responses in chronic hepatitis C. The aim of this study was to determine the relationship between the insulin resistance frequently seen in obese subjects and sustained virological response to anti-viral therapy (SVR) in patients with genotype 2 or 3 infection.

METHODS

Eighty-two patients were studied; 59 received interferon/ribavirin while 23 received peg-interferon/ribavirin.

RESULTS

The overall SVR was (77%). Patients with a SVR had lower mean serum insulin (10.7+/-0.8 microU/ml vs. 22.2+/-4.9; P = 0.03), fibrosis stage (1.9+/-0.1 vs. 2.7+/-0.3; P = 0.007) and insulin resistance measured by the homeostasis model (HOMA-IR) (2.5+/-0.2 vs. 6.1+/-1.5; P = 0.03). Age, gender, ethnicity, alcohol consumption, treatment regimen, viral load, portal activity and steatosis did not influence the SVR. By linear regression, body mass index (P < 0.001) and fibrosis stage (P < 0.001) were independently associated with HOMA-IR. After adjusting for fibrosis stage, patients with HOMA-IR of < 2 were 6.5 times more likely to achieve SVR than those with HOMA-IR > or = 2.

CONCLUSIONS

Even in treatment-responsive genotypes 2 and 3, high HOMA-IR is associated with a reduced response. Improving insulin sensitivity may be a useful adjunct to anti-viral therapy in these individuals.

Hepatic steatosis in HIV-HCV coinfected patients in France: comparison with HCV monoinfected patients matched for body mass index and HCV genotype

BACKGROUND

Significance of steatosis in HIV-HCV coinfection remains controversial.

AIM

To compare the prevalence and predictors of hepatic steatosis between HIV-HCV and HCV patients matched for steatosis known determinants.

METHODS

A total of 564 HCV-naive patients undergoing liver biopsy were studied: 137 with HIV-HCV coinfection and 427 with HCV monoinfection, among whom 137 were matched for age, gender, body mass index and HCV genotype.

RESULTS

Steatosis of any grade (67.1% vs. 41.6%, P < 0.0001), mixed steatosis (55.4% vs. 21.1%, P < 0.0001), severe histological activity (A2-A3: 78.1% vs. 55.5%, P < 0.0001) and severe fibrosis (F3-F4: 33.1% vs. 15.3%, P < 0.0001) were significantly more common in coinfected than in matched monoinfected patients. In multivariate analysis, steatosis was associated only with severe histological activity [odds ratio (OR): 3.1 (95% CI: 1.3-7.1)] in coinfected patients and with elevated body mass index [OR; 1.3 (1.1-1.5)], HCV genotype 3 [OR: 5.6 (2.3-13.9)], severe histological activity [OR: 3.1 (1.3-7.3)] and severe fibrosis [OR: 4.7 (1.3-17.3)] in monoinfected patients.

CONCLUSIONS

Steatosis is significantly more common and severe in HIV-HCV coinfected than in HCV monoinfected French patients, even after matching for body mass index and HCV genotype. Steatosis is associated only with severe histological activity in coinfected patients and with previously reported factors in monoinfected patients, thus suggesting different underlying mechanisms.

Nonalcoholic steatohepatitis (NASH) in ob/ob mice treated with yo jyo hen shi ko (YHK): effects on peroxisome proliferator-activated receptors (PPARs) and microsomal triglyceride transfer protein (MTP)

YHK has antioxidant properties, has a hypoglycemic effect, and may reduce plasma lipid levels. In this study, we examined the hepatic expression of PPAR-alpha and -gamma and MTP in ob/ob mice receiving or not receiving YHK. Ob/ob mice were assigned to receive oral YHK (20 mg/kg/day) fed solution (methionine/choline-deficient [MCD] diet+YHK group) or vehicle (MCD group) by gavage for 4 weeks. Liver fragments were collected for histologic examination and mRNA isolation. PPAR-alpha and -gamma and MTP gene expression was examined by RT-qPCR. YHK treatment was associated with NASH prevention, weight loss, and reduction of visceral fat and of serum concentrations of aminotransferases in comparison to the MCD group. YHK promoted an increment in PPAR-alpha and MTP and a decrement in PPAR-gamma mRNA contents. These findings suggest that modulation of PPAR-alpha and -gamma and MTP RNA expression may be implicated in the protective effect of YHK in experimental NASH, limiting hepatocyte lipid accumulation.

Very low density lipoprotein and low density lipoprotein isolated from patients with hepatitis C infection induce altered cellular lipid metabolism

Several abnormalities of lipid metabolism, including hypo-beta-lipoproteinemia and liver steatosis are associated with infection by hepatitis C virus (HCV). The aim of this study was to determine whether circulating lipoproteins of patients with HCV infection could directly cause alterations of lipid cellular metabolism. To this end the metabolic response of human monocyte-derived macrophages (HMDM) to very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL), measuring the cholesteryl ester (CE) and triglyceride (TG) production was analyzed. Lipoproteins were isolated from 18 patients infected with hepatitis C virus (HCV-VLDL and HCV-LDL) and from normal healthy donors (ct-VLDL and ct-LDL). In comparison to ct-lipoproteins, HCV-lipoproteins induced significant differences in HMDM CE and TG production. HCV-VLDL decreased CE and TG production; while HCV-LDL induced an increased TG synthesis. The present findings suggest that HCV infection modifies VLDL and LDL molecular composition, affecting cellular lipid metabolism, thus promoting intracellular lipid accumulation and hypo-beta-lipoproteinemia.

Inhibiting proteasomal degradation of microsomal triglyceride transfer protein prevents CCl4-induced steatosis

Carbon tetrachloride (CCl(4)) interferes with triglyceride secretion and causes steatosis, fibrosis, and necrosis. In mice, CCl(4) decreased plasma triglyceride-rich lipoproteins, increased cellular lipids, and reduced microsomal triglyceride transfer protein (MTP) without diminishing mRNA levels. Similarly, CCl(4) decreased apoB-lipoprotein production and MTP activity but had no effect on mRNA levels in primary enterocytes and colon carcinoma and hepatoma cells. CCl(4) did not affect MTP synthesis but induced post-translational degradation involving ubiquitinylation and proteasomes in McA-RH7777 cells. By contrast, MTP inhibitor increased cellular lipids without affecting MTP protein. MTP was covalently modified when cells were incubated with (14)CCl(4). This modification was prevented by the inhibition of P450 oxygenases, indicating that CCl(3)(.) generated by these enzymes targets MTP for degradation. To determine whether inhibition of proteolysis could prevent CCl(4) toxicity, mice were fed with CCl(4) with or without lactacystin. Lactacystin increased ubiquitinylated MTP and prevented lipid accumulation in tissues. Thus, CCl(4) induces post-translational degradation without affecting lipid transfer activity, whereas MTP antagonist inhibits lipid transfer activity without causing its destruction. These studies identify MTP as a major target of CCl(4) and its degradation as a novel mechanism involved in the onset of steatosis, suggesting that inhibition of proteolysis may prevent some forms of steatosis.

Hepatitis C virus induces proteolytic cleavage of sterol regulatory element binding proteins and stimulates their phosphorylation via oxidative stress

Hepatic steatosis is a common histological feature of chronic hepatitis C. Hepatitis C virus (HCV) gene expression has been shown to alter host cell cholesterol/lipid metabolism and thus induce hepatic steatosis. Since sterol regulatory element binding proteins (SREBPs) are major regulators of lipid metabolism, we sought to determine whether genotype 2a-based HCV infection induces the expression and posttranslational activation of SREBPs. HCV infection stimulates the expression of genes related to lipogenesis. HCV induces the proteolytic cleavage of SREBPs. HCV core and NS4b derived from genotype 3a are also individually capable of inducing the proteolytic processing of SREBPs. Further, we demonstrate that HCV stimulates the phosphorylation of SREBPs. Our studies show that HCV-induced oxidative stress and subsequent activation of the phosphatidylinositol 3-kinase (PI3-K)-Akt pathway and inactivation (phosphorylation) of PTEN (phosphatase and tensin homologue) mediate the transactivation of SREBPs. HCV-induced SREBP-1 and -2 activities were sensitive to antioxidant (pyrrolidine dithiocarbamate), Ca(2+) chelator 1,2-bis(aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-tetra(acetoxymethyl) ester (BAPTA-AM), and PI3-K inhibitor (LY294002). Collectively, these studies provide insight into the mechanisms of hepatic steatosis associated with HCV infection.

Hepatobiliary pathology

PURPOSE OF REVIEW

Recent papers on disorders of the liver and biliary tract which clarify their pathogenesis and attendant morphologic changes are highlighted.

RECENT FINDINGS

The concept of 'bystander hepatitis' was cited in studies showing hepatic infiltration of CD8-positive T cells in the setting of extrahepatic infections such as influenza virus and severe acute respiratory syndrome. Diabetic liver lesions include glycogenic hepatopathy (in which poor diabetic control leads to swollen, glycogen-filled hepatocytes without fat, steatohepatitis or fibrosis) and diabetic hepatosclerosis in which there is diffuse perisinusoidal fibrosis (type IV collagen) without zonal predilection. Ground-glass hepatocellular inclusions (positive with periodic acid-Schiff stain for glycogen) were reported in three separate series of patients who were hepatitis B virus-negative, often transplant recipients, immunosuppressed and on multiple medications. A Banff consensus paper expertly compared and contrasted the histologic features which characterize the various causes of late liver allograft dysfunction.

SUMMARY

Informative papers emerged this past year concerning collateral damage to the liver in extrahepatic infections, diabetic lesions and causes of liver dysfunction after transplantation, among other topics.

Modulation of hepatic microsomal triglyceride transfer protein (MTP) induced by S-nitroso-N-acetylcysteine in ob/ob mice

We evaluated the effects of a potent NO donor, S-nitroso-N-acetylcysteine (SNAC), on microsomal triglyceride transfer protein (MTP) expression in ob/ob mice. NAFLD was induced in male ob/ob mice using a methionine-choline deficient diet (MCD) concomitantly with oral SNAC fed solution (n=5) or vehicle (control; n=5) by gavage daily for 4 weeks. Livers were collected for histology and for assessing MTP by RT-qPCR, Western blot, immunohistochemistry and immunogold electron microscopy analyses. Histological analysis showed diffuse macro and microvesicular steatosis, moderate hepatocellular ballooning and moderate inflammatory infiltrate in ob/ob mice fed the MCD diet. With SNAC, mice showed a marked reduction in liver steatosis (p<0.01), in parenchymal inflammation (p=0.02) and in MTP protein immunoexpression in zone III (p=0.05). Moreover, SNAC caused reduction of MTP protein in Western blot analysis (p<0.05). In contrast, MTP mRNA content was significantly higher (p<0.05) in mice receiving SNAC. Immuno-electron microscopy showed MTP localized in the rough endoplasmic reticulum of hepatocytes in both treated and untreated groups. However with SNAC treatment, MTP was also observed surrounding fat globules. Histological improvement mediated by a nitric oxide donor is associated with significantly altered expression and distribution of MTP in this animal model of fatty liver disease. Further studies are in progress to examine possible mechanisms and to develop SNAC as a possible therapy for human fatty liver disease.

Differential regulation of cholesterol homeostasis in transgenic mice expressing human cholesterol ester transfer proteinThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute

We investigated whether expression of cholesterol ester transfer protein (CETP) in mice alters the regulation of cholesterol metabolism. Transgenic mice expressing human CETP (CETP-TG) and nontransgenic littermates (non-TG) were fed either a monounsaturated fatty acid (MUFA) or a saturated fatty acid (SFA)-rich diet in the presence or absence of cholesterol. Mice fed with MUFA diet had higher CETP activity compared with SFA-fed mice. Addition of cholesterol to the MUFA diet decreased CETP activity, whereas addition of cholesterol to the SFA diet had no effect. Cholesterol 7α-hydroxylase (Cyp7a) activity was higher in CETP-TG mice compared with non-TG mice when fed a MUFA diet, whereas SFA fed CETP-TG mice showed lower Cyp7a activity as compared with non-TG. Microsomal triglyceride transfer protein (MTTP) activity was higher in CETP-TG mice compared with non-TG mice when fed a MUFA diet. HMG-CoA reductase activity was lower in CETP-TG mice compared with non-TG mice when fed a MUFA or a SFA diet. These data demonstrate that the regulation of Cyp7a, HMG-CoA reductase, and MTTP is altered in CETP-TG mice as compared with non-TG mice and these alterations are further modulated by the quality of dietary fats. These findings highlight the importance of CETP in regulating cholesterol homeostasis.

Fibrosis in genotype 3 chronic hepatitis C and nonalcoholic fatty liver disease: Role of insulin resistance and hepatic steatosis

Hepatic steatosis has been associated with fibrosis, but it is unknown whether the latter is independent of the etiology of fat infiltration. We analyzed the relationship between clinical characteristics, insulin resistance (HOMA-R) and histological parameters in 132 patients with "viral" steatosis caused by genotype 3 chronic hepatitis C (CHC-3) and 132 patients with "metabolic" steatosis caused by nonalcoholic fatty liver disease (NAFLD), matched by age, BMI, and degree of liver fat accumulation. Tests of liver function were comparable in the two study populations. The prevalence of features of insulin resistance was higher in NAFLD, as was HOMA-R (P = .008). Logistic regression analysis confirmed that steatosis was associated with a high viral load and low serum cholesterol in CHC-3, and with high aminotransferase, glucose, ferritin and hypertriglyceridemia in NAFLD. At univariate analysis, advanced fibrosis was associated with steatosis in NAFLD, but not in CHC-3. Other parameters related to fibrosis severity were HOMA-R and a low platelet count in CHC-3, and high aminotransferases, HOMA-R, ferritin and low HDL-cholesterol in NAFLD. On multivariate analysis, only low platelet count (OR = 0.78; 95% CI, 0.67-0.92) and HOMA-R (OR = 2.98; 1.13-7.89) were independent predictors of advanced fibrosis in CHC-3. In NAFLD, severe fibrosis was predicted by fat grading (OR = 3.03; 1.41-6.53), ferritin (OR = 1.13; 1.03-1.25) and HOMA-R (OR = 1.16; 1.02-1.31). In conclusion, insulin resistance is an independent predictor of advanced fibrosis in both NAFLD and CHC-3, but the extent of steatosis contributes to advanced disease only in NAFLD. Virus-induced hepatic steatosis as seen in CHC-3 does not contribute significantly to liver fibrosis.

Mechanisms and significance of liver steatosis in hepatitis C virus infection

The pathogenesis of liver damage associated with chronic hepatitis C virus (HCV) infection is thought to be largely immunomediated. However, some frequent histopathological features, such as steatosis, suggest a direct cytopathic effect of HCV. The direct responsibility of HCV in the pathogenesis of steatosis is shown by: (1) the association with HCV genotype 3 infection, suggesting that some viral sequences are involved in the intracellular accumulation of lipids; (2) the correlation between severity of steatosis and HCV replication levels; (3) association between response to treatment and disappearance of steatosis. Experimental studies have shown that the nucleocapsid protein of HCV (core protein) is capable and sufficient to induce lipid accumulation in hepatocytes. Moreover, the observation that chronic hepatitis C patients have reduced serum levels of ApoB suggests an interference with the very-low density lipoprotein (VLDL) assembly, although other mechanisms are possible. In patients with sustained virological response induced by antiviral therapy, such levels are normalized. Other observations suggest that the pathogenesis of steatosis in chronic hepatitis C is not solely due to HCV. The origin of the mild steatosis observed in most patients may be metabolic, since its severity correlates with body mass index and insulin resistance. Most studies have shown a correlation between presence and/or severity of steatosis and fibrosis stage, but it is unclear whether this effect is direct or mediated by the associated insulin resistance, increased susceptibility to apoptosis, or by inflammatory cytokines. Finally, steatosis negatively influences the rate of response to antiviral treatment, as confirmed by large clinical trials. Management of steatosis in chronic hepatitis C requires knowledge of its pathogenesis and may involve both life-style changes and pharmacological interventions, although the latter remain largely experimental.