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Non-alcoholic fatty liver disease (NAFLD) has a global prevalence of 25% and is a leading cause of cirrhosis and hepatocellular carcinoma. NAFLD encompasses a disease continuum from steatosis with or without mild inflammation (non-alcoholic fatty liver), to non-alcoholic steatohepatitis (NASH), which is characterised by necroinflammation and faster fibrosis progression than non-alcoholic fatty liver. NAFLD has a bidirectional association with components of the metabolic syndrome, and type 2 diabetes increases the risk of cirrhosis and related complications. Although the leading causes of death in people with NAFLD are cardiovascular disease and extrahepatic malignancy, advanced liver fibrosis is a key prognostic marker for liver-related outcomes and overall mortality, and can be assessed with combinations of non-invasive tests. Patients with cirrhosis should be screened for hepatocellular carcinoma and oesophageal varices. There is currently no approved therapy for NAFLD, although several drugs are in advanced stages of development. Because of the complex pathophysiology and substantial heterogeneity of disease phenotypes, combination treatment is likely to be required for many patients with NAFLD. Healthy lifestyle and weight reduction remain crucial to the prevention and treatment of NAFLD.
Nonalcoholic fatty liver disease (NAFLD) and its inflammatory and often progressive subtype nonalcoholic steatohepatitis (NASH) are becoming the leading cause of liver-related morbidity and mortality worldwide, and a primary indication for liver transplantation. The pathophysiology of NASH is multifactorial and not yet completely understood; however, innate immunity is a major contributing factor in which liver-resident macrophages (Kupffer cells) and recruited macrophages play a central part in disease progression. In this Review, we assess the evidence for macrophage involvement in the development of steatosis, inflammation and fibrosis in NASH. In this process, not only the polarization of liver macrophages towards a pro-inflammatory phenotype is important, but adipose tissue macrophages, especially in the visceral compartment, also contribute to disease severity and insulin resistance. Macrophage activation is mediated by factors such as endotoxins and translocated bacteria owing to increased intestinal permeability, factors released from damaged or lipoapoptotic hepatocytes, as well as alterations in gut microbiota and defined nutritional components, including certain free fatty acids, cholesterol and their metabolites. Reflecting the important role of macrophages in NASH, we also review studies investigating drugs that target macrophage recruitment to the liver, macrophage polarization and their inflammatory effects as potential treatment options for patients with NASH.
It is estimated that 30% of the adult population in Japan is affected by nonalcoholic fatty liver disease (NAFLD). Fatty changes of the liver are generally diagnosed using imaging methods such as abdominal ultrasonography (US) and computed tomography (CT), but the sensitivity of these imaging techniques is low in cases of mild steatosis. Alanine aminotransferase levels may be normal in some of these patients, warranting the necessity to establish a set of parameters useful for detecting NAFLD, and the more severe form of the disease, nonalcoholic steatohepatitis (NASH). Although liver biopsy is currently the gold standard for diagnosing progressive NASH, it has many drawbacks, such as sampling error, cost, and risk of complications. Furthermore, it is not realistic to perform liver biopsies on all NAFLD patients. Diagnosis of NASH using various biomarkers, scoring systems and imaging methods, such as elastography, has recently been attempted. The NAFIC score, calculated from the levels of ferritin, fasting insulin, and type IV collagen 7S, is useful for the diagnosis of NASH, while the NAFLD fibrosis score and the FIB-4 index are useful for excluding NASH in cases of advanced fibrosis. This article reviews the limitations and merits of liver biopsy and noninvasive diagnostic tests in the diagnosis of NAFLD/NASH.
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