Hepatic steatosis and insulin resistance: does etiology make a difference?

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.

Fructose consumption: potential mechanisms for its effects to increase visceral adiposity and induce dyslipidemia and insulin resistance

PURPOSE OF REVIEW

Based on interim results from an ongoing study, we have reported that consumption of a high-fructose diet, but not a high-glucose diet, promotes the development of three of the pathological characteristics associated with metabolic syndrome: visceral adiposity, dyslipidemia, and insulin resistance. From these results and a review of the current literature, we present two potential sequences of events by which fructose consumption may contribute to metabolic syndrome.

RECENT FINDINGS

The earliest metabolic perturbation resulting from fructose consumption is postprandial hypertriglyceridemia, which may increase visceral adipose deposition. Visceral adiposity contributes to hepatic triglyceride accumulation, novel protein kinase C activation, and hepatic insulin resistance by increasing the portal delivery of free fatty acids to the liver. With insulin resistance, VLDL production is upregulated and this, along with systemic free fatty acids, increase lipid delivery to muscle. It is also possible that fructose initiates hepatic insulin resistance independently of visceral adiposity and free fatty acid delivery. By providing substrate for hepatic lipogenesis, fructose may result in a direct lipid overload that leads to triglyceride accumulation, novel protein kinase C activation, and hepatic insulin resistance.

SUMMARY

Our investigation and future studies of the effects of fructose consumption may help to clarify the sequence of events leading to development of metabolic syndrome.

Glucose abnormalities are an independent risk factor for nonresponse to antiviral treatment in chronic hepatitis C

OBJECTIVES

The influence of glucose abnormalities on the efficacy of antiviral treatment is unknown. This study investigated whether glucose abnormalities (impaired fasting glucose and type 2 diabetes) influence the response to antiviral therapy with interferon plus ribavirin in patients with chronic hepatitis C.

METHODS

A total of 178 treatment-naïve patients with chronic hepatitis C treated with combination therapy were retrospectively studied. SVR was assessed after completing treatment. Fasting plasmatic glucose was measured prior to therapy.

RESULTS

Compared with nonresponders (N = 111), patients with SVR (N = 67) had lower plasma glucose (94.1 +/- 12.7 vs 104.4 +/- 25.8 mg/dL, P= 0.001) and a lower prevalence of glucose abnormalities (24.24%vs 44.14%, P= 0.012). The SVR rate was 45.13% in patients with normoglycemia (N = 113), 28.26% in patients with impaired fasting glucose (N = 46), and 15.78% in type 2 diabetic patients (N = 19) (P < 0.001). Multivariate logistic regression identified genotype 1 (OR 1.55, 95% CI 1.01-2.41, P= 0.05), gamma-glutamyltranspeptidase level (OR 6.41, 95% CI 1.86-22.07, P= 0.003), and presence of glucose abnormalities (OR 2.33, 95% CI 1.04-5.20, P= 0.039) as being independently associated with the absence of an SVR. In addition, patients with glucose abnormalities (N = 65) showed a lower virological response rate when compared with a subgroup of normoglycemic patients (N = 65) matched for sex, age, and liver fibrosis (24.6%vs 44.6%, P= 0.001).

CONCLUSIONS

Glucose abnormalities are an independent predictor of poor virological response to combined therapy in hepatitis C virus infected patients.

Gamma-glutamyltransferase activity and development of the metabolic syndrome (International Diabetes Federation Definition) in middle-aged men and women: Data from the Epidemiological Study on the Insulin Resistance Syndrome (DESIR) cohort

OBJECTIVE

Among hepatic enzymes, gamma-glutamyltransferase (GGT) is the main predictor of type 2 diabetes incidence, although it has not been shown that GGT predicts pre-diabetes states. Our aim was to study the association of GGT with the development of the metabolic syndrome (MetS).

RESEARCH DESIGN AND METHODS

We analyzed the 3-year data from the Data from Epidemiological Study on the Insulin Resistance Syndrome prospective cohort of 1,656 men and 1,889 women without MetS at baseline, according to the International Diabetes Federation definition.

RESULTS

Over 3 years, 309 participants developed the MetS. After adjustment for age, alcohol intake, physical activity, smoking habits, and alanine aminotransferase (ALT), the odds ratios for incident MetS increased across baseline GGT quartiles (1, 1.96, 2.25, and 3.81 in men, P < 0.03; and 1, 1.23, 1.80, and 1.58 in women, P < 0.05). After additional adjustment for insulin resistance markers (fasting insulin or homeostasis model assessment of insulin resistance index), the association was attenuated and the linear relation no longer significant in both sexes (P = 0.08, P = 0.16). However, men in the highest in comparison to the lowest quartile of GGT retained a significant risk for incident MetS. In women, there was no longer a significant risk. GGT was significantly associated with the 3-year incidence of individual components of the MetS. The incidence of the MetS also increased with ALT, but after adjustment on GGT this association remained significant only in women.

CONCLUSIONS

GGT, a predictor of type 2 diabetes, was associated with a risk of incident MetS. This association was mainly related with insulin resistance but was independent of other confounding factors.

Nitrosative stress predicts the presence and severity of nonalcoholic fatty liver at different stages of the development of insulin resistance and metabolic syndrome: possible role of vitamin A intake

BACKGROUND

Although nonalcoholic fatty liver disease (NAFLD) is associated with the metabolic syndrome, the mechanisms responsible for the development of NAFLD at different stages of the development of insulin resistance are unknown. Diet, adipokines, and nitrosative stress have been linked to both NAFLD and insulin resistance.

OBJECTIVE

We aimed to identify the factors that are specifically associated with NAFLD at different stages in the development of insulin resistance and the metabolic syndrome.

DESIGN

Circulating concentrations of adipokines (ie, tumor necrosis factor-alpha, adiponectin, resistin, leptin, and interleukin-6), markers of nitrosative stress (nitrotyrosine), dietary habits, and MTP -493G/T polymorphism were cross-sectionally related to the presence and severity of insulin resistance (homeostasis model assessment index for insulin resistance: >or=2), the metabolic syndrome, and fatty liver in 64 nonobese nondiabetic patients with NAFLD (33 insulin-sensitive and 31 insulin-resistant subjects) and 74 control subjects without liver disease who were matched for sex, BMI, homeostasis model assessment index for insulin resistance status, and the various features of the metabolic syndrome.

RESULTS

Persons with NAFLD had greater systemic nitrosative stress and a lower intake of vitamins A and E than did control subjects, but the 2 groups did not differ significantly in any other features. Nitrotyrosine and adiponectin concentrations and vitamin A intakes independently predicted alanine aminotransferase concentrations in NAFLD patients and liver histology in a subgroup of 29 subjects with biopsy-proven nonalcoholic steatohepatitis.

CONCLUSIONS

Oxidative stress is operating in NAFLD and nonalcoholic steatohepatitis, even in the absence of insulin resistance, the metabolic syndrome, and hypoadiponectinemia, which aggravate liver histology at more severe stages of metabolic disease. The possible pathogenetic role of reduced vitamin A intake in NAFLD warrants further investigation.

Microarray analyses and molecular profiling of steatosis induction in immortalized human hepatocytes

Hepatic steatosis is an important risk factor for the development of inflammation, fibrosis and impaired liver regeneration. The factors regulating lipid accumulation and driving hepatic steatosis toward inflammation, fibrosis and impaired regeneration are largely unknown. The aim of this study was to identify major alterations in gene expression occurring in steatotic hepatocytes, and to analyze how these changes impact cellular processes associated with steatosis. Microarray gene chips and RT-PCR were performed to analyze changes in gene expression induced in fatty human immortalized hepatocytes after treatment with 50 muM oleic acid for 7 days. Lipid metabolism and triglyceride accumulation in these cells was examined by Oil-Red-O staining, thin-layer chromatography (TLC) and immunofluorescence. Caspase 3 activity, BrdU incorporation and trypan blue exclusion were used to study apoptosis, proliferation and cell viability. Finally, quantitative analysis of signalling induced by insulin was performed by Western blot. Characterization of steatosis in three hepatocyte-derived cell lines indicated that the immortalized human hepatocytes (IHH) line was the most appropriate cell line for this study. Gene expression analysis showed significant alterations in the transcription of two major classes of genes involved either in cholesterol and fatty acid biosynthesis, as well as lipid export, or in apoptosis and cell proliferation. Such changes were functionally relevant, since TLC indicated that synthesis and accumulation of triglycerides were increased in steatotic cells, while synthesis of cholesterol and fatty acids were decreased. Lipid accumulation in IHH was associated with an increased apoptosis and an inhibition of cell proliferation and viability. No detectable changes in genes associated with insulin resistance were observed in steatotic cells, but signalling induced by insulin was more efficient in steatotic IHH as compared to control cells. We conclude that IHH represent a new valuable model of steatosis, not associated with insulin resistance, to study at both the genetic and functional level factors involved in the process of lipid accumulation and steatosis-associated liver injury.

HCV and diabetes. A two-question-based reappraisal

We used available studies to answer two clinically relevant questions, i.e. whether those with type 2 diabetes should undergo hepatitis C virus screening and whether hepatitis C virus positive individuals should be screened for diabetes. Four reasons argue against the hypothesis of screening diabetics for hepatitis C virus. First, although it induces insulin resistance, hepatitis C virus is not directly diabetogenic. Second, the clinical phenotype of hepatitis C virus-associated type 2 diabetes might be a clue to target the specific diabetic population to be screened. Third, diabetic patients are expected to be poor responders to antivirals and evidence that this might result in recovery from type 2 diabetes is insufficient. Fourth, no econometric data are available in the specific subset of those with type 2 diabetes. Case finding of type 2 diabetes in those with hepatitis C virus infection, in contrast, might be considered in those patients with type 2 diabetes who have cirrhosis, in whom--due to increased prevalence and severity of hepatic encephalopathy--diabetes is associated with increased mortality. Preliminary evidence suggests that the prognosis of cirrhosis might benefit from improved glycemic control and thus from earlier diagnosis of type 2 diabetes. Finally, studies are needed to ascertain the most cost-effective strategy of case-finding type 2 diabetes among those who are hepatitis C virus-infected. In conclusion, available data enabled us to answer the two questions. Hepatitis C virus screening should best be restricted to those (lean) diabetic patients with (advanced) liver disease. Glucose tolerance testing should best be performed in those with hepatitis C virus-related cirrhosis. However, additional studies are needed to support the cost-effectiveness of our conclusions.

Has natural selection in human populations produced two types of metabolic syndrome (with and without fatty liver)?

Fatty liver is closely related to the development of the insulin resistance syndrome that largely results from abnormal insulin signaling in three major organs: (i) skeletal muscle in which insulin sensitivity depends on fat content and metabolic activity (exercise); (ii) adipose tissue, which serves as a reservoir of energy in the form of triglycerides; and (iii) the liver, which variably serves as a source or storage site of carbohydrates and lipids. In many respects, the fatty liver resembles a mixture of brown adipose tissue (microvesicular steatosis) and white adipose tissue (macrovesicular steatosis) including the stages of fatty droplet accumulation, and the expression of uncoupling proteins and perilipin-like substances. Furthermore, the development of an inflammatory infiltrate and the increased production of cytokines as occurs in adipose tissue, suggest that the liver in some individuals serves as an extension of adipose tissue. Moreover, current evidence indicates that these morphological changes represent altered gene expression similar to that of adipocytes. However, fatty liver does not appear to be a uniform feature of the metabolic syndrome and there is substantial variation in humans in the development of fatty liver independent of insulin resistance. In this regard, the variable development of fatty liver in Palmipedes (migratory fowl) and its close relationship to skeletal muscle utilization of fatty acids, lipoprotein metabolism and thermoregulation are instructive. The predilection to non-alcoholic fatty liver disease among some varieties of Palmipedes suggests that the development of fatty liver represents an adaptive process, closely integrated with skeletal muscle fat utilization and adipose tissue distribution, and facilitates survival in a very cold, resource-scarce environment. Variation in human populations with metabolic syndrome likewise suggests that the trait evolved in populations exposed in ancient times to different environmental challenges and, because the liver plays a central role in lipid metabolism, the presence or absence of fatty liver is likely to be integrated with insulin sensitivity in other target organs and with lipoprotein metabolism.

Metabolic syndrome and NASH

Clinical and epidemiologic studies have associated non-alcoholic fatty liver with the metabolic syndrome, with insulin resistance as the pivotal pathogenic factor. Obesity, type 2 diabetes mellitus, dyslipidemia, and hypertension contribute to risk for liver disease and to disease progression. The presence of multiple metabolic abnormalities is associated with the severity of liver disease. Patients have a high risk for cardiovascular morbidity and mortality, mediated by early atherosclerosis. This evidence has precise therapeutic implications: only a behavioral approach to lifestyle correction will address all alterations characterizing the metabolic syndrome, including metabolic liver disease.

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.

gamma-Glutamyltransferase as a predictor of chronic kidney disease in nonhypertensive and nondiabetic Korean men

BACKGROUND

Little research has been done to examine whether gamma-glutamyltransferase (GGT) is prospectively associated with the development of chronic kidney disease (CKD). We performed a prospective study to examine the association between GGT and the risk for the development of CKD.

METHODS

The study cohort included a total of 10 337 healthy males with normal baseline kidney functions and no proteinuria. Participants were workers in a semiconductor manufacturing company and its 13 affiliates. CKD was defined as either the presence of proteinuria or a glomerular filtration rate (GFR) of < 60 mL x min(-1) x (1.73(2))(-1). Cox proportional hazards models were used to calculate the adjusted hazard ratios in separate models for CKD.

RESULTS

During a follow-up period of 25,774.4 person-years, 366 men developed CKD. After adjustments were made for age, baseline GFR, triglyceride, and HDL-C, the risk for CKD increased with an increasing quartile of serum GGT (p for trend <0.001). The top one fourth of serum GGT vs the bottom one fourth of relative risks for CKD was 1.90 (95% confidence interval, 1.37-2.63). These associations were also apparent in participants who consumed < or = 20 g/day of alcohol and those with normal weight, with values of alanine aminotransferase within reference intervals, or with C-reactive protein < 3.0 mg/L, and participants without metabolic syndrome.

CONCLUSIONS

Our findings, which were obtained from a large work-site cohort and excluded individuals with diabetes and hypertension, indicated that serum GGT may be an early predictor for the development of CKD, independent of baseline confounding factors.

The changing epidemiology and natural history of hepatitis C virus infection

Injection drug use remains the predominant mode of transmission of hepatitis C virus (HCV) infection. Growing numbers of persons who have been chronically infected with HCV for 20 or more years are coming to medical attention and are at risk for serious complications of chronic infection, including cirrhosis and hepatocellular carcinoma. Factors linked with the development of advanced fibrosis and cirrhosis include age at infection, duration of infection, heavy alcohol use, coinfections with HIV or hepatitis B virus, and male sex. Emerging risk factors for disease progression include steatosis, insulin resistance (and factors associated with the metabolic syndrome), and host genetics.

Non-alcoholic steatohepatitis and metabolic syndrome

PURPOSE OF REVIEW

Non-alcoholic steatohepatitis is part of a disease spectrum, non-alcoholic fatty liver disease, ranging from simple steatosis to cirrhosis, which is the most frequent cause of abnormal liver tests. There is clinical and epidemiological evidence that non-alcoholic fatty liver disease is the hepatic manifestation of the metabolic syndrome, having in common insulin resistance.

RECENT FINDINGS

The interest in the metabolic syndrome concept has been questioned. Insulin resistance, oxidative stress, mitochondrial dysfunction, immune deregulation and adipokines seem to be crucial in the pathogenesis of non-alcoholic fatty liver disease. The main treatment continues to rely on lifestyle changes, including weight loss strategies. Bariatric surgery in morbidly obese patients and insulin-sensitizing agents seem to be beneficial.

SUMMARY

There is strong evidence of the association of non-alcoholic steatohepatitis with the features of the metabolic syndrome, with its increased cardiovascular risk. Population interventions in order to change lifestyles and diet patterns that constitute risk factors for both situations are urgently needed. There is, however, evidence that in the presence of other risk factors, insulin resistance may be less important. These secondary forms of non-alcoholic steatohepatitis must be recognized, as they are potentially treatable by withdrawing the steatogenic factor.