David van der Poorten

Visceral fat: A key mediator of steatohepatitis in metabolic liver disease†

Visceral obesity is intimately associated with metabolic disease and adverse health outcomes. However, a direct association between increasing amounts of visceral fat and end‐organ inflammation and scarring has not been demonstrated. We examined the association between visceral fat and liver inflammation in patients with nonalcoholic fatty liver disease (NAFLD) to delineate the importance of visceral fat to progressive steatohepatitis and hence the inflammatory pathogenesis of the metabolic syndrome. We undertook a cross‐sectional, proof of concept study in 38 consecutive adults with NAFLD at a tertiary liver clinic. All subjects had a complete physical examination, anthropometric assessment, and fasting blood tests on the day of liver biopsy. Abdominal fat volumes were assessed by magnetic resonance imaging within 2 weeks of liver biopsy. The extent of hepatic inflammation and fibrosis augmented incrementally with increases in visceral fat (P < 0.01). For each 1% increase in visceral fat, the odds ratio for increasing liver inflammation and fibrosis was 2.4 (confidence interval [CI]: 1.3‐4.2) and 3.5 (CI: 1.7‐7.1), respectively. Visceral fat remained an independent predictor of advanced steatohepatitis (odds ratio [OR] 2.1, CI: 1.1‐4.2, P = 0.05) and fibrosis (OR 2.9, CI: 1.4‐6.3, P = 0.006) even when controlled for insulin resistance and hepatic steatosis. Interleukin‐6 (IL‐6) levels, which correlated with visceral fat, also independently predicted increasing liver inflammation. Visceral fat was associated with all components of the metabolic syndrome. Conclusion: Visceral fat is directly associated with liver inflammation and fibrosis independent of insulin resistance and hepatic steatosis. Visceral fat should therefore be a central target for future interventions in nonalcoholic steatohepatitis and indeed all metabolic disease. (HEPATOLOGY 2008.)

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)

Adipocyte fatty acid binding protein levels relate to inflammation and fibrosis in nonalcoholic fatty liver disease

Several circulating cytokines are increased with obesity and may combine with the influence of visceral fat to generate insulin resistance, inflammation, and fibrosis in nonalcoholic fatty liver disease (NAFLD). Little information exists in NAFLD about three recently recognized tissue‐derived cytokines that are all lipid‐binding and involved in inflammation, namely adipocyte fatty acid–binding protein (AFABP), lipocalin‐2, and retinol‐binding protein 4 (RBP4). We examined the association of these three peptides with hepatic steatosis, inflammation, and fibrosis plus indices of adiposity, insulin resistance, and dyslipidaemia in 100 subjects with NAFLD and 129 matched controls. Levels of AFABP and lipocalin‐2, but not RBP4, were significantly elevated in NAFLD versus control (AFABP, 33.5 ± 14.4 versus 23.1 ± 12.1 ng/mL [P < 0.001]; lipocalin‐2, 63.2 ± 26 versus 48.6 ± 20 ng/mL [P < 0.001]) and correlated with indices of adiposity. AFABP correlated with indices of subcutaneous rather than visceral fat. AFABP alone distinguished steatohepatitis from simple steatosis (P= 0.02). Elevated AFABP independently predicted increasing inflammation and fibrosis, even when insulin resistance and visceral fat were considered; this applied to lobular inflammation and ballooning (odds ratio 1.4, confidence interval 1.0‐1.8) and fibrosis stage (odds ratio 1.3, confidence interval 1.0‐1.7) (P ≤ 0.05 for all). None of the cytokines correlated with steatosis grade. AFABP levels correlated with insulin resistance (homeostasis model assessment of insulin resistance) in controls and NAFLD, whereas lipocalin‐2 and RBP4 only correlated positively with insulin resistance in controls. Conclusion: Circulating AFABP, produced by adipocytes and macrophages, and lipocalin‐2, produced by multiple tissues, are elevated and may contribute to the metabolic syndrome in NAFLD. AFABP levels, which correlate with subcutaneous, but not visceral fat, independently predict inflammation and fibrosis in NAFLD and may have a direct pathogenic link to disease progression. (HEPATOLOGY 2009;49:1926–1934.)

Chronic Hepatitis C Is Associated With Peripheral Rather Than Hepatic Insulin Resistance

BACKGROUND & AIMS Chronic hepatitis C (CHC) is associated with insulin resistance (IR), liver steatosis (genotype 3), and increased diabetes risk. The site and mechanisms of IR are unclear. METHODS We compared cross-sectionally 29 nonobese, normoglycemic males with CHC (genotypes 1 and 3) to 15 adiposity and age-matched controls using a 2-step hyperinsulinemic-euglycemic clamp with [6,6-(2)H(2)] glucose to assess insulin sensitivity in liver and peripheral tissues and (1)H-magnetic resonance spectroscopy to evaluate liver and intramyocellular lipid. Insulin secretion was assessed after intravenous glucose. RESULTS Insulin secretion was not impaired in CHC. Peripheral insulin sensitivity was 35% higher in controls vs CHC (P < .001) during high-dose (264.3 +/- 25 [standard error] mU/L) insulin (P < .001); this was negatively associated with viral load (R(2) = .12; P = .05) and subcutaneous fat (R(2) = .41; P < .001). IR was similar in both genotypes despite 3-fold increased hepatic fat in genotype 3 (P < .001). Hepatic glucose production (P = .25) and nonesterified free fatty acid (P = .84) suppression with insulin were not different between CHC and controls inferring no adipocyte IR, and suggesting IR is mainly in muscle. In CHC, intramyocellular lipid was nonsignificantly increased but levels of glucagon (73.8 +/- 3.6 vs 52.8 +/- 3.1 ng/mL; P < .001), soluble tumor necrosis factor receptor 2 (3.1 +/- 0.1 vs 2.3 +/- 0.1 ng/mL; P < .001), and Lipocalin-2 (36.4 +/- 2.9 vs 19.6 +/- 1.6 ng/mL; P < .001) were elevated. CONCLUSIONS CHC represents a unique infective/inflammatory model of IR, which is predominantly in muscle, correlates with subcutaneous, not visceral, adiposity, and is independent of liver fat.

Complex non-invasive fibrosis models are more accurate than simple models in non-alcoholic fatty liver disease

Background and Aim:  Significant hepatic fibrosis is prognostic of liver morbidity and mortality in non‐alcoholic fatty liver disease (NAFLD); however, it remains unclear whether non‐invasive fibrosis models can determine this end‐point. We therefore compared the accuracy of simple bedside versus complex fibrosis models across a range of fibrosis in a multi‐centre NAFLD cohort.

Hepatic fat loss in advanced nonalcoholic steatohepatitis: Are alterations in serum adiponectin the cause?

Advanced liver fibrosis in nonalcoholic steatohepatitis (NASH) is often accompanied by a reduction in hepatic fat to the point of complete fat loss (burnt‐out NASH), but the mechanisms behind this phenomenon have not been elucidated. Adiponectin is raised in cirrhosis of any cause and has potent antisteatotic activity. In this study we examined 65 patients with advanced biopsy‐proven NASH (fibrosis stage 3‐4) and 54 with mild disease (fibrosis stage 0‐1) to determine if disappearance of steatosis correlated with changes in serum adiponectin. All patents had fasting blood tests and anthropometric measures at the time of liver biopsy. Liver fat was accurately quantitated by morphometry. Serum adiponectin was measured by immunoassay. When compared to those with early disease, patients with advanced NASH were more insulin‐resistant, viscerally obese, and older, but there was no difference in liver fat content or adiponectin levels. Adiponectin had a significant negative correlation with liver fat percentage in the whole cohort (r = −0.28, P < 0.01), driven by patients with advanced NASH (r = −0.40, P < 0.01). In advanced NASH, for each 4 μg/L increase in adiponectin there was an odds ratio OR of 2.0 (95% confidence interval [CI]: 1.3‐3.0, P < 0.01) for a 5% reduction in hepatic fat. Adiponectin was highly and significantly associated with almost complete hepatic fat loss or burnt‐out NASH (12.1 versus 7.4 μg/L, P = 0.001) on multivariate analysis. A relationship between adiponectin, bile acids, and adipocyte fexaramine activation was demonstrated in vivo and in vitro, suggestive of hepatocyte‐adipocyte crosstalk. Conclusion: Serum adiponectin levels in advanced NASH are independently associated with hepatic fat loss. Adiponectin may in part be responsible for the paradox of burnt‐out NASH. (HEPATOLOGY 2012)

Visceral adiposity in gastrointestinal and hepatic carcinogenesis

There is emerging evidence that the association between obesity and cancer is mediated by visceral rather than generalised body fat. Visceral fat has been directly implicated in the risk and progression of several gastrointestinal cancers including colorectal, oesophageal, pancreatic and hepatocellular carcinomas. Excess visceral adipose tissue induces a state of chronic systemic inflammation and altered metabolic activity that promotes a pro-oncogenic environment. This review examines the evidence linking visceral fat in gastrointestinal and hepatic carcinogenesis and explores our current understanding of the mechanisms underlying this relationship.

Hepatitis C virus induces the cannabinoid receptor 1.

Background Activation of hepatic CB1 receptors (CB1) is associated with steatosis and fibrosis in experimental forms of liver disease. However, CB1 expression has not been assessed in patients with chronic hepatitis C (CHC), a disease associated with insulin resistance, steatosis and metabolic disturbance. We aimed to determine the importance and explore the associations of CB1 expression in CHC. Methods CB1 receptor mRNA was measured by real time quantitative PCR on extracted liver tissue from 88 patients with CHC (genotypes 1 and 3), 12 controls and 10 patients with chronic hepatitis B (CHB). The Huh7/JFH1 Hepatitis C virus (HCV) cell culture model was used to validate results. Principal Findings CB1 was expressed in all patients with CHC and levels were 6-fold higher than in controls (P<0.001). CB1 expression increased with fibrosis stage, with cirrhotics having up to a 2 fold up-regulation compared to those with low fibrosis stage (p<0.05). Even in mild CHC with no steatosis (F0-1), CB1 levels remained substantially greater than in controls (p<0.001) and in those with mild CHB (F0-1; p<0.001). Huh7 cells infected with JFH-1 HCV showed an 8-fold upregulation of CB1, and CB1 expression directly correlated with the percentage of cells infected over time, suggesting that CB1 is an HCV inducible gene. While HCV structural proteins appear essential for CB1 induction, there was no core genotype specific difference in CB1 expression. CB1 significantly increased with steatosis grade, primarily driven by patients with genotype 3 CHC. In genotype 3 patients, CB1 correlated with SREBP-1c and its downstream target FASN (SREBP-1c; R = 0.37, FASN; R = 0.39, p<0.05 for both). Conclusions/Significance CB1 is up-regulated in CHC and is associated with increased steatosis in genotype 3. It is induced by the hepatitis C virus.

Visceral adiposity index is not a predictor of liver histology in patients with non-alcoholic fatty liver disease

BACKGROUND & AIMS Visceral adiposity is associated with hepatic steatosis, inflammation, and fibrosis in non-alcoholic fatty liver disease (NAFLD). The visceral adiposity index (VAI), a novel marker of visceral fat distribution and dysfunction, has been correlated with histology in hepatitis C. We assessed the ability of VAI to predict disease severity in NAFLD and hence its role as a non-invasive marker of liver damage. METHODS We examined 190 adults with biopsy-proven NAFLD and 129 controls. All had anthropometric and metabolic profiling. VAI was calculated using waist circumference (WC), body mass index, triglycerides, and HDL-cholesterol. Abdominal fat was quantified by magnetic resonance imaging (MRI) in 38 patients. RESULTS On multivariate analysis, NAFLD diagnosis and fasting glucose were independently associated with VAI (p <0.05). VAI increased across control, steatosis, and NASH groups (1.5, 2.3, and 3.2, respectively; p=0.000), however, this association was no stronger than the increase in WC across groups (r=0.452 vs. 0.540 respectively, p <0.001). VAI was not associated with steatosis, lobular inflammation or fibrosis, but WC was associated with fibrosis (p=0.01). VAI and WC correlated with an increasing number of metabolic syndrome components (r=0.623 vs. 0.614, p <0.001) and with metabolic syndrome diagnosis (r=0.559 vs. 0.509, p <0.001). VAI only modestly correlated with visceral fat on MRI (r=0.39, p <0.05) compared to WC (r=0.52, p <0.01). CONCLUSIONS In NAFLD, VAI is not associated with steatosis, inflammation or fibrosis. VAI is no more powerful than WC in discriminating steatosis from steatohepatitis, reflecting limitations of the formula with what is known about the pathogenesis of NAFLD.

Liver disease in adolescents: A cohort study of high-risk individuals†‡

Little is known about the health and behavior of adolescent offenders as they relate to abnormalities of liver biochemistry and hepatitis C virus (HCV) infection. A large study of male juvenile offenders was undertaken that allowed a re‐evaluation of the normal limits of alanine aminotransferase (ALT), associations with elevated ALT, and HCV antibody positivity. Young offenders (age 12–19 years) serving community orders participated in a wide‐ranging health survey and laboratory assessment between October 2003 and December 2005. Normal ranges for liver biochemistry were calculated from the 95th percentile of males at the lowest risk for liver disease. The final sample comprised 682 males, of whom 439 (64%) gave blood. The calculated upper limit of normal for ALT was 28 IU/L. Seventeen percent of adolescents had an elevated ALT. Strong associations with elevated ALT included HCV antibody positivity [odds ratio (OR) 14.6], overweight and obesity (OR 6.9), and elevated total cholesterol (OR 3.6). More than 90% of adolescents with elevated ALT levels had 1 or more features of the metabolic syndrome. HCV antibody was positive in approximately 3% of the cohort, with the most significant risk factor being injecting drug use (OR 7.8; P < 0.01). The new infection rate was 3.7% per year. Conclusion: New upper limits for ALT provide greater sensitivity for the early diagnosis of liver disease in adolescents. High rates of HCV infection and obesity‐related liver disease exist in this group, and targeted interventions are needed to reduce future health‐related morbidity. (HEPATOLOGY 2007.)