Nonalcoholic steatohepatitis and insulin resistance: interface between gastroenterologists and endocrinologists

Nonalcoholic steatohepatitis (NASH), along with other forms of nonalcoholic fatty liver disease, is an increasingly common clinico-pathological syndrome. It is frequently associated with obesity, especially visceral fat, and type 2 diabetes, and is intimately related to markers of the insulin resistance syndrome. Both the prevalence and the severity of liver steatosis are related to body mass index, waist circumference, hyperinsulinaemia, hypertriglyceridemia and impaired glucose tolerance. The pathophysiology of NASH involves two steps: 1) insulin resistance, which causes steatosis; 2) and oxidative stress, which produces lipid peroxidation and activates inflammatory cytokines. The identification of subjects who may progress from fatty liver to NASH, and from NASH to fibrosis/cirrhosis is an important clinical challenge as well as the finding of appropriate therapy that could prevent such deleterious process. Substantial weight loss is accompanied by a marked attenuation of insulin resistance and related metabolic syndrome and, concomitantly, by an important regression of liver steatosis in most patients, although mild inflammation may be detected in some subjects. Thus, NASH may be considered as another disease of affluence, as is the insulin resistance syndrome and perhaps being part of it.     

Nonalcoholic fatty liver disease in severely obese subjects

BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) has been consistently associated with obesity and insulin resistance. Nonalcoholic steatohepatitis (NASH) is a histological entity within NAFLD that can progress to cirrhosis. The exact prevalence of NASH in severe obesity is unknown. It is unclear whether differences in insulin sensitivity exist among subjects with NASH and simple fatty liver. OBJECTIVE: To evaluate the prevalence and correlates of NASH and liver fibrosis in a racially diverse cohort of severely obese subjects. DESIGN: Ninety-seven subjects were enrolled. Liver biopsies, indirect markers of insulin resistance, metabolic parameters, and liver function tests were obtained. RESULTS: Thirty-six percent of subjects had NASH and 25% had fibrosis. No cirrhosis was diagnosed on histology. Markers of hyperglycemia, insulin resistance, and the metabolic syndrome but not body mass index were associated with the presence of NASH and fibrosis. Elevated transaminase levels correlated strongly with NASH and fibrosis but 46% subjects with NASH had normal transaminases. Subjects with NASH had more severe insulin resistance when compared to those with simple fatty liver. A signal detection model incorporating AST and the presence of diabetes predicted the presence of NASH while another incorporating ALT and HbA1C predicted the presence of fibrosis. CONCLUSIONS: NAFLD is associated with the metabolic syndrome rather than excess adipose tissue in severe obesity. Insulin resistance is higher in subjects with NASH versus those with simple fatty liver. Statistical models incorporating markers of liver injury and hyperglycemia may be useful in predicting the presence of liver pathology in this population.     

Role of fatty acids in the pathogenesis of obesity and fatty liver: impact of bariatric surgery

Nonalcoholic fatty liver disease (NAFLD) spans a spectrum from simple steatosis to nonalcoholic steatohepatitis (NASH) to cirrhosis. Simple steatosis is the substrate upon which the more serious entities in the spectrum develop; it is the first "hit" in the multistep pathogenesis of NASH, which is considered the hepatic manifestation of the metabolic syndrome. Demonstration of the existence of regulatable fatty acid transport mechanisms has contributed to clarifying the role of fatty acid disposition in obesity, the various components of NAFLD, and the metabolic syndrome. Hepatic steatosis is closely linked to obesity. This linkage is based on the fact that obesity results in marked enlargement of the intraabdominal visceral fat depots. The eventual development of insulin resistance leads to continuous lipolysis within these depots, releasing fatty acids into the portal circulation, where they are rapidly translocated to the liver and reassembled into triglycerides. Reactive oxygen species, generated in the liver from oxidation of fatty acids, are precipitating factors in the cascade of events leading from simple steatosis to NASH. Dysregulation of fatty acid disposition, with ectopic lipid accumulation in other tissues, is a major contributing factor to other components of the metabolic syndrome. Bariatric surgery is an effective treatment for severe obesity, but its role in the management of the various forms of fatty liver disease is unclear. Our review of the literature that includes both initial and follow-up liver biopsies suggests that most obese patients with simple steatosis and NASH who undergo bariatric surgery will achieve improvement in hepatic histology, but that occasional patients, especially those who lose weight very rapidly, may show worsening of either fibrosis or steatohepatitis.     

Interaction of iron,insulin resistance,and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) has emerged as a ubiquitous liver disorder with occasional serious overtones. Although diabetes and obesity were initially held culpable, insulin resistance (IR) is now considered the fundamental operative mechanism. IR is probably the "first step" in nonalcoholic steatohepatitis (NASH). Oxidative stress may be the elusive "second" of possibly multiple steps in the progression of steatosis to fibrosing steatohepatitis. Because hepatic iron promotes oxidative stress, it was mooted as a contributory cofactor in NASH. This proposal was strengthened by an association with hepatic fibrosis. Subsequent studies have shown neither a significant increase in hepatic iron nor an association between hepatic iron and any of the histologic determinants in NASH. Likewise, the increased prevalence of hemochromatosis gene (HFE) mutations in some studies appears to be largely irrelevant to the development of hepatic fibrosis. Excess hepatic iron may occur in insulin resistance-associated iron overload (IRHIO), characterized by hyperferritinemia with normal to mild increases in transferrin saturation. Although patients with IRHIO have a high prevalence of IR-related metabolic disorders, the relationship of IRHIO to NASH is unclear. A recent study showed improvement in insulin sensitivity with the use of venesection in patients with NAFLD, but this approach cannot be implemented without extensive review.     

Noninvasive predictors for liver fibrosis in patients with nonalcoholic steatohepatitis

AIM: To evaluate certain anthropometric, clinical and laboratory features indicating liver fibrosis in nonalcoholic steatohepatitis and to establish the noninvasive markers for liver fibrosis.METHODS: Eighty-one patients (40 male, 41 female) who were diagnosed with fatty liver by ultrasonographic examination and fulfilled the inclusion criteria participated in the study. Anamnesis, anthropometric, clinical and laboratory features of all cases were recorded and then liver biopsy was performed after obtaining patient consent. Steatosis, necroinflammation and liver fibrosis were examined according to age ≥ 45, gender, body mass index, central obesity, aspartate aminotransferase (AST)/alanine aminotransferase (ALT) > 1, γ-glutamyltransferase (GGT)/ALT > 1, platelet count, insulin, c-peptide levels and the presence of hypertension, diabetes, hypertriglyceridemia and insulin resistance.RESULTS: Eighty-one patients with non-alcoholic steatohepatitis (NASH) enrolled in the study. 69 of 81 patients were diagnosed with NASH, 11 were diagnosed with simple fatty liver and 1 was diagnosed with cirrhosis. AST/ALT > 1, GGT/ALT > 11, high serum ferritin and fasting insulin levels, the presence of diabetes, hypertension, hypertriglyceridemia and insulin resistance seemed to enhance the severity of steatosis, necroinflammation and fibrosis but these results were not statistically significant.CONCLUSION: Liver steatosis and fibrosis can occur in individuals with normal weight. There was no significant concordance between severity of liver histology and the presence of predictors for liver fibrosis including metabolic risk factors.     

Nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) encompasses a broad clinicopathologic spectrum ranging from simple steatosis to nonalcoholic steatohepatitis (NASH), which may advance to cirrhosis and end-stage liver disease. Steatosis alone does not appear to be progressive. The prevalence of NAFLD averages 20% and that of NASH, 2% to 3%, making these conditions the most common liver diseases in the United States. NAFLD is associated with insulin resistance, which may be evident clinically with obesity, type 2 diabetes mellitus, and hypertriglyceridemia. The pathogenesis of NAFLD consists of hepatic fat accumulation and oxidative stress with formation of free radicals. The clinical diagnosis is based on the presence of the insulin resistance syndrome and exclusion of alcohol abuse as well as viral, autoimmune, genetic, and drug-induced liver diseases. Liver biopsy is essential for diagnosis but may not be necessary for clinical management. Treatment is aimed at correcting the risk factors for NAFLD and using potentially hepatoprotective agents. Ursodeoxycholic acid and betaine appear particularly promising in early trials.     

Obesity and liver disease

Non-alcoholic steatohepatitis (NASH) is a disease of emerging identity and importance. It is frequently associated with obesity, especially visceral fat, and is intimately related to fatty liver and markers of the insulin resistance syndrome. Both the prevalence and the severity of liver steatosis are related to body mass index, waist circumference, hyperinsulinaemia, hypertriglyceridaemia and impaired glucose tolerance or type 2 diabetes. The identification of obese patients who may progress from steatosis to NASH and from NASH to fibrosis/cirrhosis is an important clinical challenge. Substantial weight loss is accompanied by a marked attenuation of insulin resistance and related metabolic syndrome and, concomitantly, by a remarkable regression of liver steatosis in most patients, although increased inflammation may be detected in some subjects. Thus, NASH may be considered as another disease of affluence, as is the insulin resistance syndrome, and perhaps being part of it, especially in obese patients.     

胰高血糖素样肽1受体激动剂对代谢相关脂肪性肝病作用机制的研究进展

非酒精性脂肪性肝病(NAFLD)(现已更名为代谢相关脂肪性肝病)是一种以肝实质内脂质过度沉积为特征,常与中心性肥胖、2型糖尿病、胰岛素抵抗、代谢综合征等疾病合并存在,被认为是代谢综合征的肝脏表现.非酒精性脂肪性肝炎(NASH)是一种可能导致肝硬化、肝细胞癌的进行性肝病.目前尚无批准用于治疗NAFLD/NASH的药物.近...     

Drug-induced steatohepatitis

Drugs rarely cause steatohepatitis, but amiodarone, perhexiline, and DH, have unequivocally been found to independently induce the histologic picture of alcoholic liver disease or NASH. All three agents have similar pathogenetic mechanisms of hepatotoxicity, targeting mitochondrial ATP production and fatty acid catabolism. Other drugs that occasionally cause steatohepatitis, most importantly steroid hormones, likely exacerbate the pathogenetic mechanisms leading to NASH. Similar to NASH, lipid peroxidation resulting from mitochondrial injury may account for all of the histologic findings in drug-induced steatohepatitis. Further research should determine the mechanisms by which drug-induced steatosis, a benign lesion, evolves to steatohepatitis and progressive fibrosis.     

Epidemiology of the metabolic syndrome in the USA

The metabolic syndrome is a common complex entity that has emerged as a worldwide epidemic and major public health care concern with a prevalence of approximately 25% in the United States. There have been a number of different definitions of the metabolic syndrome but all center around the metabolic abnormalities of central obesity, hypertension, decreased high-density lipoproteins and elevated triglycerides with insulin resistance as the uniting physiologic factor. The importance of the metabolic syndrome is not just related to its high prevalence rate but also because it predicts the development of diabetes and cardiovascular disease. Nonalcoholic fatty liver disease is now recognized to be the hepatic component of the metabolic syndrome, which along with its individual components - particularly diabetes and elevated triglycerides, are the major risk factors for the development of nonalcoholic steatohepatitis (NASH); the most severe form of nonalcoholic fatty liver disease. NASH may progress to cirrhosis, hepatocellular carcinoma, and liver failure. It is currently the third most common cause for liver transplantation and is projected to be the leading cause for liver transplantation in 2020. Weight loss (via diet or bariatric surgery) and vitamin E have recently been demonstrated to be effective treatments of NASH. Although these and other agents may prove to be effective treatments for NASH, the most effective therapeutic strategy would be early screening and intervention to prevent the development of insulin resistance and oxidative stress at a societal level.     

Non-alcoholic steatohepatitis: association with obesity and insulin resistance, and influence of weight loss

Non-alcoholic steatohepatitis (NASH) is a disease of emerging identity and importance, and is now considered as one of the commonest liver diseases in western countries. It is frequently associated with severe obesity, especially abdominal adiposity, and is intimately related to various clinical and biological markers of the insulin resistance syndrome. Especially, both the prevalence and the severity of liver steatosis are related to male sex, body mass index, waist circumference, hyperinsulinaemia, hypertriglyceridaemia and impaired glucose tolerance or type 2 diabetes. A substantial weight loss following gastroplasty is accompanied by a marked reduction in the prevalence and the severity of the various biological abnormalities of the metabolic syndrome and, concomitantly, by an important regression of liver steatosis in most obese patients. However, in some patients, this rapid and drastic weight loss may result in a mild increase in inflammatory lesions (hepatitis), despite the regression of steatosis, which might result from the rapid mobilization of fatty acids or cytokines from adipose tissue, especially visceral fat. The intimate relationship between NASH and obesity leads to the concept that NASH may be considered as another disease of affluence, as is the insulin resistance syndrome and perhaps being part of it.     

Steatosis and steatohepatitis in diabetic patient

Nonalcoholic fatty liver disease (NAFLD) is an increasingly recognized condition of excess fat deposition within the liver. NAFLD includes a spectrum of liver pathology ranging from bland hepatic steatosis to steatohepatitis and cirrhosis. Nonalcoholic steatohepatitis (NASH) is an inflammatory and fibrosing condition of the liver thought to be an intermediate stage of NAFLD that may progress to endstage liver disease, liver-related death and hepatocellular carcinoma. Nonalcoholic steatohepatitis (NASH) is a common liver disease that is characterized histologically by hepatic steatosis, lobular inflammation, and hepatocellular ballooning, it can progress to cirrhosis in up to 15% of patients. There is currently no therapy that is of proven benefit for nonalcoholic steatohepatitis. The disease is closely associated with insulin resistance and features of the metabolic syndrome such as obesity (increased waist circumference), hypertriglyceridemia, and type 2 diabetes. The pathologic criteria are now well established and the diagnosis can only be made once the absence or limited use of alcohol is confirmed. In addition to insulin resistance, oxidative stress has been implicated as a key factor contributing to hepatic injury in patients with nonalcoholic steatohepatitis. Thus, both insulin resistance and oxidative stress are attractive targets for therapy in patients with this disease. Several pilot studies have provided evidence that insulin sensitizers such as thiazolidinediones and antioxidants such as vitamin E improve clinical and histologic features of nonalcoholic steatohepatitis. The medical evidence of a benefit, however, is limited, because these studies had small samples and were performed at single centers. Moreover, a recent multicenter trial showed a reduction in hepatic steatosis but no improvement in markers of cell injury after a year of rosiglitazone therapy. The value of these remains uncertain. Until now the best trial was done by Sanyal, who studied 240 patients divided into 3 groups (pioglitazone versus vitamin E versus placebo)--multicenter, randomized, double-blind clinical trial in non-diabetics.     

Nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is being increasingly recognized as a common liver disorder that represents the hepatic manifestation of the metabolic syndrome, a variably defined aggregate of disorders related to obesity, insulin resistance, type II diabetes, hypertension and hyperlipidemia. Nonalcoholic steatohepatitis (NASH) is the progressive form of liver injury that carries a risk for progressive fibrosis, cirrhosis, and end-stage liver disease. Hepatocellular carcinoma (HCC) is a documented complication in an as yet unknown percentage of cases of NASH cirrhosis. The diagnosis of nonalcoholic steatohepatitis requires histopathologic evaluation because the lesions of parenchymal injury and fibrosis cannot be detected by imaging studies or laboratory tests. This article will briefly discuss prevalence studies and the pathophysiology of NAFLD and focus on current discussions related to the specific lesions in the pathology of NASH, including the challenges of pediatric NASH and NASH-related cirrhosis.     

Diabetes mellitus, obesity, and hepatic steatosis

Nonalcoholic fatty liver disease is emerging as the most common liver disease in North America. The histological spectrum of nonalcoholic fatty liver disease ranges from fatty liver alone to steatohepatitis and to the most serious form--nonalcoholic steatohepatitis (NASH). An increasing body of evidence suggests that NASH is associated with the development of progressive fibrosis and eventually cirrhosis in approximately 20% of cases. These data emphasize the need to develop effective therapy for the treatment of NASH. Cases occur most commonly in obese middle age women with diabetes. However, NASH may also occur in children and normal weight men with normal glucose and lipid metabolism. The pathophysiology involves 2 steps. The first is insulin resistance, which causes steatosis. The second is oxidative stress, which produces lipid peroxidation and activates inflammatory cytokines resulting in NASH. Liver biopsy provides prognostic information and identifies NASH patients who may benefit from therapy. Treatment consists of managing the comorbidities: obesity, diabetes, and hyperlipidemia. Nascent clinical trials suggest that a number of therapies may be beneficial. These include anti-oxidants such as vitamin E and betaine, bile acid therapy with ursodeoxycholic acid, and improved insulin sensitivity with metformin. Another potential therapeutic strategy is the reduction of inflammatory cytokines.     

Nonalcoholic steatohepatitis and the metabolic syndrome

Nonalcoholic fatty liver disease (NAFLD) is a major form of chronic liver disease in adults and children. It is one of the consequences of the current obesity epidemic, and can progress to nonalcoholic steatohepatitis (NASH), characterized by steatosis, inflammation, and progressive fibrosis, ultimately leading to cirrhosis and end-stage liver disease. The factors implicated in this progression are poorly understood. NASH is closely associated with obesity and the metabolic syndrome. Recent studies emphasize the role of insulin resistance, oxidative stress, lipid peroxidation, and cytokine release in the development of NASH. This review summarizes the current knowledge on the etiology and pathomechanism of NASH and the role of the metabolic syndrome in NASH development.     

1. Fatty liver and non-alcoholic steatohepatitis

Although steatohepatitis can be induced by an excessive intake of alcohol, it can also arise through various other causes, in which case it is known as non-alcoholic fatty liver disease (NAFLD). NAFLD is classified into two categories:simple fatty liver with a favorable clinical outcome, and non-alcoholic steatohepatitis (NASH), which is intractable and progressive. Recently in Japan, there has been an increase in the number of individuals at risk of lifestyle-related diseases, due to increased insulin resistance and visceral fat obesity. The metabolic syndrome (MS) is associated with several risk factors for atherosclerosis, including diabetes mellitus (DM), hypertension, and hyperlipidemia. Visceral fat obesity is the prime cause of NASH in the liver, and is therefore considered to be one of the phenotypic features of MS. Furthermore, most chronic liver diseases are associated with hepatitis C virus (HCV) infection. Fatty degeneration of hepatocytes is often observed in the liver of HCV-infected individuals, and results from viral suppression of mitochondrial beta-oxidation of fatty acid. The natural outcome of HCV infection is worse in patients with lifestyle-related high insulin resistance and visceral fat obesity. In this review, we describe the recent advances in research on progressive liver diseases that are the result of fat accumulation in the liver, with special reference to MS.     

The role of the gut microbiota in nonalcoholic fatty liver disease

Important metabolic functions have been identified for the gut microbiota in health and disease. Several lines of evidence suggest a role for the gut microbiota in both the etiology of nonalcoholic fatty liver disease (NAFLD) and progression to its more advanced state, nonalcoholic steatohepatitis (NASH). Both NAFLD and NASH are strongly linked to obesity, type 2 diabetes mellitus and the metabolic syndrome and, accordingly, have become common worldwide problems. Small intestinal bacterial overgrowth of Gram-negative organisms could promote insulin resistance, increase endogenous ethanol production and induce choline deficiency, all factors implicated in NAFLD. Among the potential mediators of this association, lipopolysaccharide (a component of Gram-negative bacterial cell walls) exerts relevant metabolic and proinflammatory effects. Although the best evidence to support a role for the gut microbiota in NAFLD and NASH comes largely from animal models, data from studies in humans (albeit at times contradictory) is accumulating and could lead to new therapeutic avenues for these highly prevalent conditions.     

NASH and insulin resistance: Insulin hypersecretion and specific association with the insulin resistance syndrome

Nonalcoholic steatohepatitis (NASH) is often linked with disorders that are clearly associated with insulin resistance (IR): obesity, type 2 diabetes mellitus, and hypertriglyceridemia. We tested the hypotheses that (1) IR is an essential requirement for the development of NASH and (2) a high association between IR and liver disease is relatively specific for NASH. We measured body mass index (BMI), waist/hip ratio, and fasting serum lipid, insulin, C-peptide, and glucose levels in 66 patients with NASH (21 with advanced fibrosis and 45 with mild fibrosis). IR was determined by the homeostasis model assessment (HOMA). We also determined the strength of the association of NASH with insulin resistance syndrome (IRS) as defined by World Health Organization criteria. To assess whether the finding of IR was relatively specific to NASH rather than simply to obesity or liver disease, we compared the results of a subset of 36 patients with less-severe NASH with 36 age- and sex-matched patients with chronic hepatitis C virus (HCV) of comparable fibrotic severity. IR was confirmed in 65 patients (98%) with NASH, and 55 (87%) fulfilled minimum criteria for IRS. IR was found in lean as well as in overweight and obese patients. The IR values and the prevalence of IRS (75% vs. 8.3%) were significantly higher in those with NASH than in comparable cases of HCV. Hyperinsulinemia was attributable to increased insulin secretion rather than decreased hepatic extraction. In conclusion, most patients with NASH have IRS, and there is a near-universal association between NASH and IR irrespective of obesity. IR is present in mild as well as advanced cases of NASH but is unusual in chronic HCV of similar fibrotic severity.     

The metabolic triad of non-alcoholic fatty liver disease,visceral adiposity and type 2 diabetes: Implications for treatment

Non-alcoholic fatty liver disease (NAFLD) is associated with visceral obesity, insulin resistance, type 2 diabetes (T2D) and has been often considered as the hepatic expression of the metabolic syndrome (MetS). Epidemiological studies highlight a bidirectional relationship of NAFLD with T2D in which NAFLD increases the risk of incident T2D and T2D increases the risk of severe non-alcoholic steatohepatitis (NASH) and liver fibrosis. Regarding the molecular determinants of NAFLD, we specifically focused in this review on adipocyte dysfunction as a key molecular link between visceral adipose tissue, MetS and NAFLD. Notably, the subcutaneous white adipose tissue expandability appears a critical adaptive buffering mechanism to prevent lipotoxicity and its related metabolic complications, such as NAFLD and T2D. There is a clinical challenge to consider therapeutic strategies targeting the metabolic dysfunction common to NASH and T2D pathogenesis. Strategies that promote significant and sustained weight loss (~10% of total body weight) such as metabolic and bariatric surgery or incretin-based therapies (GLP-1 receptor agonists or dual GLP-1/GIP or GLP-1/glucagon receptor co-agonists) are among the most efficient ones. In addition, insulin sensitizers such as PPARγ (pioglitazone) and pan-PPARs agonists (lanifibranor) have shown some beneficial effects on both NASH and liver fibrosis. Since NASH is a complex and multifactorial disease, it is conceivable that targeting different pathways, not only insulin resistance but also inflammation and fibrotic processes, is required to achieve NASH resolution.