Obesity affects the liver - the link between adipocytes and hepatocytes

The incidence of obesity has dramatically increased in recent years. Consequently, obesity and associated disorders such as nonalcoholic fatty liver disease (NAFLD) constitute a serious threat. Therefore, the contribution of visceral adipose tissue to metabolic homeostasis has become a focus of interest. Visceral adipose tissue secretes free fatty acids (FFAs) and hormones, known as adipokines, and thus seems to play a major role in the development of NAFLD. Apoptotic cell death is a prominent feature in nonalcoholic steatohepatitis (NASH). Indeed, toxic FFAs can activate the intrinsic apoptosis pathway in hepatocytes via c-Jun N-terminal kinase (JNK). JNK activates the proapoptotic protein Bim, resulting in Bax activation and enhanced apoptosis, termed 'lipoapoptosis'. Reduced adiponectin levels may establish a proinflammatory milieu, thus increasing vulnerability to lipotoxicity, which promotes progression from simple steatosis to NASH and even advanced hepatic fibrosis. Moreover, obesity seems to be a risk factor for hepatocellular carcinoma, the most frequent liver cancer subtype. Even in acute liver failure, a high body mass index is associated with poor outcome, and recent data suggest a major role of obesity in the progression of chronic hepatitis C and B. This review summarizes current knowledge - highlighting the inflammatory and cytokine view - of the intimate relationship between adipose and liver tissue.