Clues from the carotids: an appraisal of cardiovascular disease risk in non-alcoholic fatty liver disease

NAFLD in Asia--as common and important as in the West

NAFLD--regarded as a consequence of the modern sedentary, food-abundant lifestyle prevalent in the West--was recorded in Japan nearly 50 years ago and its changing epidemiology during the past three decades is well-documented. NAFLD, and its pathologically more severe form NASH, occur in genetically susceptible people who are over-nourished. Asian people are particularly susceptible, partly owing to body composition differences in fat and muscle. Community prevalence ranges between 20% (China), 27% (Hong Kong), and 15-45% (South Asia, South-East Asia, Korea, Japan and Taiwan). This Review presents emerging data on genetic polymorphisms that predispose Asian people to NAFLD, NASH and cirrhosis, and discusses the clinical and pathological outcomes of these disorders. NAFLD is unlikely to be less severe in Asians than in other populations, but the associated obesity and diabetes pandemics have occurred more recently in Asia than in Europe and the USA, and occur with reduced degrees of adiposity. Cases of cryptogenic cirrhosis and hepatocellular carcinoma have also been attributed to NAFLD. Public health efforts to curb over-nutrition and insulin resistance are needed to prevent and/or reverse NAFLD, as well as its adverse health outcomes of type 2 diabetes, cardiovascular events, cirrhosis and liver cancer.

NASH is an Inflammatory Disorder: Pathogenic, Prognostic and Therapeutic Implications

While non-alcoholic fatty liver disease (NAFLD) is highly prevalent (15% to 45%) in modern societies, only 10% to 25% of cases develop hepatic fibrosis leading to cirrhosis, end-stage liver disease or hepatocellular carcinoma. Apart from pre-existing fibrosis, the strongest predictor of fibrotic progression in NAFLD is steatohepatitis or non-alcoholic steatohepatitis (NASH). The critical features other than steatosis are hepatocellular degeneration (ballooning, Mallory hyaline) and mixed inflammatory cell infiltration. While much is understood about the relationship of steatosis to metabolic factors (over-nutrition, insulin resistance, hyperglycemia, metabolic syndrome, hypoadiponectinemia), less is known about inflammatory recruitment, despite its importance for the perpetuation of liver injury and fibrogenesis. In this review, we present evidence that liver inflammation has prognostic significance in NAFLD. We then consider the origins and components of liver inflammation in NASH. Hepatocytes injured by toxic lipid molecules (lipotoxicity) play a central role in the recruitment of innate immunity involving Toll-like receptors (TLRs), Kupffer cells (KCs), lymphocytes and neutrophils and possibly inflammasome. The key pro-inflammatory signaling pathways in NASH are nuclear factor-kappa B (NF-κB) and c-Jun N-terminal kinase (JNK). The downstream effectors include adhesion molecules, chemokines, cytokines and the activation of cell death pathways leading to apoptosis. The upstream activators of NF-κB and JNK are more contentious and may depend on the experimental model used. TLRs are strong contenders. It remains possible that inflammation in NASH originates outside the liver and in the gut microbiota that prime KC/TLR responses, inflamed adipose tissue and circulating inflammatory cells. We briefly review these mechanistic considerations and project their implications for the effective treatment of NASH.