Elisabetta Bugianesi

Insulin resistance: a metabolic pathway to chronic liver disease.

Insulin resistance (IR) is the pathophysiological hallmark of nonalcoholic fatty liver disease (NAFLD), one of the most common causes of chronic liver disease in Western countries. We review the definition of IR, the methods for the quantitative assessment of insulin action, the pathophysiology of IR, and the role of IR in the pathogenesis of chronic liver disease. Increased free fatty acid flux from adipose tissue to nonadipose organs, a result of abnormal fat metabolism, leads to hepatic triglyceride accumulation and contributes to impaired glucose metabolism and insulin sensitivity in muscle and in the liver. Several factors secreted or expressed in the adipocyte contribute to the onset of a proinflammatory state, which may be limited to the liver or more extensively expressed throughout the body. IR is the common characteristic of the metabolic syndrome and its related features. It is a systemic disease affecting the nervous system, muscles, pancreas, kidney, heart, and immune system, in addition to the liver. A complex interaction between genes and the environment favors or enhances IR and the phenotypic expression of NAFLD in individual patients. Advanced fibrotic liver disease is associated with multiple features of the metabolic syndrome, and the risk of progressive liver disease should not be underestimated in individuals with metabolic disorders. Finally, the ability of insulin‐sensitizing, pharmacological agents to treat NAFLD by reducing IR in the liver (metformin) and in the periphery (thiazolidinediones) are discussed. (HEPATOLOGY 2005;42:987–1000.)

A randomized controlled trial of metformin versus vitamin E or prescriptive diet in nonalcoholic fatty liver disease.

OBJECTIVES:Metformin proved useful in the treatment of nonalcoholic fatty liver disease (NAFLD), but its superiority over nutritional treatment and antioxidants has never been demonstrated. We aimed to compare the usefulness of metformin versus prescriptive diet or vitamin E.METHODS:In an open label, randomized trial, nondiabetic NAFLD patients were given metformin (2 g/day; n = 55) for 12 months. The control cases were given either vitamin E (800 IU/day; n = 28) or were treated by a prescriptive, weight-reducing diet (n = 27). Outcome measures were liver enzymes, insulin resistance (homeostasis model assessment), parameters of the metabolic syndrome, and histology.RESULTS:Aminotransferase levels improved in all groups, in association with weight loss. The effects in the metformin arm were larger (p < 0.0001), and alanine aminotransferase normalized in 56% of cases (odds ratio (OR) versus. controls, 3.11; 95% confidence interval (CI), 1.56–6.20; p = 0.0013). In multivariate analysis, metformin treatment was associated with higher rates of aminotransferase normalization, after correction for age, gender, basal aminotransferases, and change in body mass index (OR, 5.98; 95% CI, 2.05–17.45). Differences were maintained when the two control groups were separately analyzed. The distribution of positive criteria for the metabolic syndrome was reduced only in the metformin arm (p = 0.001, signed rank test). A control biopsy in 17 metformin-treated cases (14 nonresponders) showed a significant decrease in liver fat (p = 0.0004), necroinflammation, and fibrosis (p = 0.012 for both). No side effects were observed during metformin treatment.CONCLUSIONS:Metformin treatment is better than a prescriptive diet or vitamin E in the therapy of NAFLD patients receiving nutritional counseling. Limited histological data support an association between improved aminotransferases and biopsy findings, which require confirmation in a double-blind trial with appropriate statistical power based on liver histology.

Endothelial dysfunction and cardiovascular risk profile in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is consistently associated with features of the metabolic syndrome, a condition carrying a high risk of cardiovascular events. We measured the vasodilatory response of the brachial artery in response to ischemia (a test of endothelial function) (FMV) as well as cardiovascular risk profile in 52 NAFLD cases and 28 age‐ and sex‐matched controls. The 10‐year risk of coronary events was calculated according to the Framingham equation and the scores derived from the PROCAM study and NCEP‐ATPIII proposals. FMV was 6.33% ± 5.93% in NAFLD versus 12.22% ± 5.05% in controls (P < .0001), and higher in pure fatty liver (9.93%) compared with nonalcoholic steatohepatitis (4.94%) (P = .010). No differences were observed in flow‐independent vasodilation (response to sublingual nitroglycerin). Percent FMV was negatively associated with insulin resistance (homeostasis model assessment) in the whole population (r = −0.243; P = .030). In logistic regression analysis, NAFLD was associated with a percent FMV in the lower tertile (OR, 6.7; 95% CI, 1.26–36.1), after adjustment for age, sex, body mass index, and insulin resistance. Among NAFLD patients, low FMV was associated with nonalcoholic steatohepatitis (adjusted OR, 6.8; 95% CI, 1.2–40.2). The 10‐year probability of cardiovascular events was moderately increased in NAFLD, and particularly in nonalcoholic steatohepatitis. In conclusion, our study provides evidence of endothelial dysfunction and increased risk of cardiovascular events in NAFLD. The risk of advanced liver disease is well recognized in NAFLD patients, but the large majority of cases might experience cardiovascular disease in the long term, indirectly limiting the burden of liver failure. (HEPATOLOGY 2005.)

Homozygosity for the patatin-like phospholipase-3/adiponutrin i148m polymorphism influences liver fibrosis in patients with nonalcoholic fatty liver disease

Inherited factors play a major role in the predisposition to nonalcoholic fatty liver disease (NAFLD), and the rs738409 C→G polymorphism of PNPLA3/adiponutrin, encoding for the isoleucine‐to‐methionine substitution at residue 148 (I148M) protein variant, has recently been recognized as a major determinant of liver fat content. However, the effect of the rs738409 polymorphism on the severity of liver fibrosis in patients with NAFLD is still unknown. In this study, we considered 253 Italian patients, 179 healthy controls, and 71 family trios with an affected child with NAFLD. Analyses were replicated in 321 patients from the United Kingdom. The rs738409 polymorphism was determined by TaqMan assays. Liver histology was scored according to Kleiner et al. Hepatic expression of genes regulating liver damage was assessed by real‐time polymerase chain reaction in 52 patients. The rs738409 GG genotype was more prevalent in patients than in controls (14% versus 3%, adjusted odds ratio [OR] = 3.29, 95% confidence interval [CI] = 1.8‐6.9), and in the family study, the G allele was overtransmitted to affected children (P = 0.001). In Italian and United Kingdom patients, adiponutrin genotype influenced alanine aminotransferase levels and the severity of steatosis. Adiponutrin genotype was associated with the expression of genes involved in the steatosis‐related liver damage, including the proapoptotic molecule Fas ligand. In the whole series combined, adiponutrin genotype was associated with steatosis grade >1 (OR = 1.35, 95% CI = 1.04‐1.76), nonalcoholic steatohepatitis (OR = 1.5, 95% CI = 1.12‐2.04), and fibrosis stage >1 (OR = 1.5, 95% CI = 1.09‐2.12), independent of age, body mass index, and diabetes. Adiponutrin genotype demonstrated a dose effect with heterozygote risk intermediate between CC and GG homozygotes. Conclusion: In patients with NAFLD, adiponutrin rs738409 C→G genotype, encoding for I148M, is associated with the severity of steatosis and fibrosis and the presence of nonalcoholic steatohepatitis. (Hepatology 2010;51:1209–1217)

Risk of severe liver disease in nonalcoholic fatty liver disease with normal aminotransferase levels: A role for insulin resistance and diabetes

It is uncertain whether patients with nonalcoholic fatty liver disease (NAFLD) and normal alanine aminotransferase (ALT) have a milder disease and should undergo liver biopsy. We reviewed the histological data of 458 Italian patients with NAFLD in whom liver biopsy was indicated by altered liver enzymes (395 cases, 86%), or persistently elevated ferritin or long‐lasting severe steatosis (63 cases). Factors associated with nonalcoholic steatohepatitis (NASH) and fibrosis ≥ 2 were identified by multivariate analysis. Patients with normal ALT were significantly older, had lower body mass index, fasting triglycerides, insulin resistance according to homeostasis model assessment (HOMA‐IR), ALT, and gamma‐glutamyltransferase, but a higher prevalence of hypertension. NASH was diagnosed in 59% and 74% of the patients with normal and increased ALT, respectively (P = 0.01). In the overall series of patients, NASH was independently predicted by ALT (odds ratio [OR], 1.11; 95% confidence interval [CI], 1.04–1.19 per 10‐IU/mL increase) and diabetes (OR, 1.5; 95% CI, 1.1–2.0). The same variables were selected in patients with increased ALT, whereas in those with normal ALT, HOMA‐IR and ALT were independent predictors. Severe fibrosis was independently predicted by serum ferritin (OR, 1.04; 95% CI, 1.001–1.08 per 50‐ng/mL increase), ALT (OR, 1.07; 95% CI, 1.02–1.14), and diabetes (OR, 1.8; 95% CI, 1.4–2.3) in the overall series, serum ferritin and diabetes in those with increased ALT, and only HOMA‐IR (OR, 1.97; 95% CI, 1.2–3.7) in patients with normal ALT. Conclusion: Normal ALT is not a valuable criterion to exclude patients from liver biopsy. Alterations in glucose metabolism and insulin resistance in subjects with normal ALT should also be considered in the selection of NAFLD cases for histological assessment of disease severity and progression. (HEPATOLOGY 2008.)

Relative contribution of iron burden, HFE mutations, and insulin resistance to fibrosis in nonalcoholic fatty liver

The mechanism(s) determining the progression from fatty liver to steatohepatitis is currently unknown. Our goal was to define the relative impact of iron overload, genetic mutations of HFE, and insulin resistance on the severity of liver fibrosis in a population of subjects with nonalcoholic fatty liver disease (NAFLD) who had low prevalence of obesity and no overt symptoms of diabetes. In a cohort of 263 prospectively enrolled patients with NAFLD, 7.4% of patients had signs of peripheral iron overload and 9% had signs of hepatic iron overload, but 21.1% had hyperferritinemia. The prevalence of C282Y and H63D HFE mutations was similar to the general population and mutations were not associated with iron overload. Although subjects were on average only moderately overweight, insulin sensitivity, measured both in the fasting state and in response to oral glucose, was lower. Univariate analysis demonstrated that the presence of severe fibrosis was independently associated with older age, female sex, overweight, aspartate/alanine aminotransferase ratio, serum ferritin level, fasting glucose and insulin levels, decreased insulin sensitivity, and with histologic features (degree of necroinflammation and steatosis). After adjustment for body mass index (BMI), age, sex, and degree of steatosis, ferritin levels (odds ratio [OR] = 1.77; 95% CI = 1.21‐ 2.58; P = .0032) and the oral glucose insulin sensitivity (OR = 0.53; CI = 0.33‐0.87; P = .0113) were independent predictors of severe fibrosis. In conclusion, the current study indicates that insulin resistance is a major, independent risk factor for advanced fibrosis in patients with NAFLD. Increased ferritin levels are markers of severe histologic damage, but not of iron overload. Iron burden and HFE mutations do not contribute significantly to hepatic fibrosis in the majority of patients with NAFLD. (HEPATOLOGY 2004;39:179–187.)

From the metabolic syndrome to NAFLD or vice versa

The metabolic syndrome encompasses metabolic and cardiovascular risk factors which predict diabetes and cardiovascular disease (CVD) better than any of its individual components. Nonalcoholic fatty liver disease (NAFLD) comprises a disease spectrum which includes variable degrees of simple steatosis (nonalcoholic fatty liver, NAFL), nonalcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is the hepatic manifestation of the metabolic syndrome, with insulin resistance as the main pathogenetic mechanism. Recent data indicate that hyperinsulinemia is probably the consequence rather than cause of NAFLD and NAFLD can be considered an independent predictor of cardiovascular disease. Serum free fatty acids derived from lipolysis of visceral adipose tissue are the main source of hepatic triglycerides in NAFLD, although hepatic de novo lipogenesis and dietary fat supply contribute to the pathogenesis of NAFLD. Approximately 10-25% NAFLD patients develop NASH, the evolutive form of hepatic steatosis. Presumably in a genetically predisposed environment, this increased lipid overload overwhelms the oxidative capacity and reactive oxygen species are generated, leading to lipid peroxidation, cytokine induction, chemoattraction of inflammatory cells, hepatic stellate cell activation and finally fibrogenesis with extracellular matrix deposition. No currently available therapies for NAFLD and NASH exist. Recently nuclear receptors have emerged as key regulators of lipid and carbohydrate metabolism for which specific pharmacological ligands are available, making them attractive therapeutic targets for NAFLD and NASH.

Nonalcoholic fatty liver disease and the metabolic syndrome.

Purpose of review Clinical, epidemiological and biochemical data strongly support the concept that nonalcoholic fatty liver disease is the hepatic manifestation of the metabolic syndrome. Insulin resistance is the common factor connecting obesity, diabetes, hypertension and dyslipidemia with fatty liver and the progression of hepatic disease to steatohepatitis, fibrosis, cirrhosis and hepatocellular carcinoma. Recent findings The association of nonalcoholic fatty liver disease with the features of the metabolic syndrome has been confirmed in several epidemiological studies. The diagnostic and clinical significance of raised liver enzymes has been questioned; advanced hepatic disease may also be present in individuals with ultrasonographically detected steatosis and normal aminotransferase levels. The role of adipokines (leptin, adiponectin) and cytokines (tumor necrosis factor-α, interleukin-6, transforming growth factor-β) in disease progression is probably pivotal, mediated by oxidative stress. The importance of iron accumulation in this process has not been confirmed. Treatments aimed at weight loss remain a primary option; among pharmacological interventions, insulin sensitizers (glitazones and metformin) have confirmed beneficial effects on both biochemical and histological data, but new treatments are on the horizon. Summary Nonalcoholic fatty liver disease prevalence in Western countries is high and there is a trend towards a further increase, with millions of people at risk of advanced liver disease. The epidemiological evidence, the lifestyle origin of the disease and the cost of pharmacotherapy make prevention a primary goal, and will contribute to making behavior therapy the background treatment. We need specific programs and carefully controlled, randomized studies to tackle simultaneously all the components of the metabolic syndrome.

Non-Alcoholic Fatty Liver Disease (NAFLD) and Its Connection with Insulin Resistance, Dyslipidemia, Atherosclerosis and Coronary Heart Disease

Non-alcoholic fatty liver disease is marked by hepatic fat accumulation not due to alcohol abuse. Several studies have demonstrated that NAFLD is associated with insulin resistance leading to a resistance in the antilipolytic effect of insulin in the adipose tissue with an increase of free fatty acids (FFAs). The increase of FFAs induces mitochondrial dysfunction and development of lipotoxicity. Moreover, in subjects with NAFLD, ectopic fat also accumulates as cardiac and pancreatic fat. In this review we analyzed the mechanisms that relate NAFLD with metabolic syndrome and dyslipidemia and its association with the development and progression of cardiovascular disease.

The natural history of nonalcoholic fatty liver disease with advanced fibrosis or cirrhosis: An international collaborative study†‡§

Information on the long‐term prognosis of nonalcoholic fatty liver disease (NAFLD) is limited. We sought to describe the long‐term morbidity and mortality of patients with NAFLD with advanced fibrosis or cirrhosis by prospectively studying 247 such patients from four international centers (in Australia, USA, UK and Italy). Their natural history was then compared with 264 patients with HCV infection who were either naïve or non‐responders to treatment. Both cohorts were Child‐Pugh class A and had advanced fibrosis (stage 3) or cirrhosis (stage 4) confirmed by liver biopsy at enrollment. In the NAFLD cohort, followed up for a mean of 85.6 months (range, 6‐297), there were 48 (19.4%) liver‐related complications and 33 (13.4%) deaths or liver transplants. In the HCV cohort, followed up for 74.9 months (mean; range, 6‐238), there were 47 (16.7%) liver‐related complications and 25 (9.4%) deaths or liver transplants. When adjusting for baseline differences in age and gender, the cumulative incidence of liver‐related complications was lower in the NAFLD than the HCV cohort (P = 0.03), including incident hepatocellular cancer (6 versus 18; P = 0.03), but that of cardiovascular events (P = 0.17) and overall mortality (P = 0.6) were similar in both groups. In the NAFLD cohort, platelet count, stage 4 fibrosis, lowered platelet count, and lowered serum cholesterol and alanine aminotrasferase (ALT) levels were associated with liver‐related complications; an aspartate aminotransferase/ALT ratio >1 and older age were associated with overall mortality, and higher serum bilirubin levels and stage 4 fibrosis were associated with liver‐related mortality. Conclusions: Patients with NAFLD with advanced fibrosis or cirrhosis have lower rates of liver‐related complications and hepatocellular cancer than corresponding patients with HCV infection, but similar overall mortality. Some clinical and laboratory features predict liver‐related complications and other outcomes in patients with NAFLD. (HEPATOLOGY 2011;54:1208–1216)