Evaluation and management of obesity-related nonalcoholic fatty liver disease

The clinicopathologic spectrum of nonalcoholic fatty liver disease (NAFLD) ranges from simple steatosis to nonalcoholic steatohepatitis (NASH). Simple steatosis has a relatively benign clinical course, but NASH can progress to cirrhosis and hepatocellular carcinoma. NAFLD occurs in the absence of significant alcohol use and is considered to be the hepatic manifestation of metabolic syndrome. NAFLD affects approximately 30% of the US population and the incidence seems to be rising as the obesity epidemic continues. At present, the most accurate modality for the diagnosis of NASH is liver biopsy; however, many patients do not have a liver biopsy, and in the absence of more-accurate imaging technologies and serum markers, the diagnosis is frequently one of exclusion. As yet there is no convincingly effective treatment for NAFLD--a multimodal treatment plan that targets obesity, insulin resistance, hyperlipidemia and hypertension might be the best option for these patients.     

Pathogenesis of nonalcoholic steatohepatitis (NASH)

Nonalcoholic fatty liver disease (NAFLD) represents a spectrum of liver diseases that range from hepatic steatosis at the most clinically benign end of the spectrum, through an intermediate lesion, nonalcoholic steatohepatitis (NASH), to cirrhosis at the opposite extreme. Epidemiology studies have estimated that about 20-30% of adults in the United States and other Western countries have NAFLD, and of these about 10% (2-3% of adults) meet the diagnostic criteria of NASH. Studies of animals and humans with obesity-related fatty liver disease have revealed much about the mechanisms that mediate this common pathology. The pathogenesis of NASH is multifactorial and includes insulin resistance, excessive intracellular fatty acids, oxidant stress, mitochondrial dysfunction and the role of innate immunity. This review will briefly discuss the epidemiology of NAFLD and focus on current understanding of the pathogenesis of NASH.     

Treatment of fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is considered to be a hepatic manifestation of metabolic syndrome. The clinicopathologic spectrum ranges from simple steatosis to nonalcoholic steatohepatitis (NASH). Simple steatosis has a relatively benign clinical course, but NASH can progress to cirrhosis and hepatocellular carcinoma. As yet there is no convincingly effective treatment for NAFLD and the best option for these patients might be a multimodal treatment plan targeting obesity, insulin resistance, diabetes mellitus, hyperlipidemia and hypertension.     

From the metabolic syndrome to NAFLD or vice versa?

The metabolic syndrome encompasses metabolic and cardiovascular risk factors which predict diabetes and cardiovascular disease (CVD) better than any of its individual components. Nonalcoholic fatty liver disease (NAFLD) comprises a disease spectrum which includes variable degrees of simple steatosis (nonalcoholic fatty liver, NAFL), nonalcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is the hepatic manifestation of the metabolic syndrome, with insulin resistance as the main pathogenetic mechanism. Recent data indicate that hyperinsulinemia is probably the consequence rather than cause of NAFLD and NAFLD can be considered an independent predictor of cardiovascular disease. Serum free fatty acids derived from lipolysis of visceral adipose tissue are the main source of hepatic triglycerides in NAFLD, although hepatic de novo lipogenesis and dietary fat supply contribute to the pathogenesis of NAFLD. Approximately 10–25% NAFLD patients develop NASH, the evolutive form of hepatic steatosis. Presumably in a genetically predisposed environment, this increased lipid overload overwhelms the oxidative capacity and reactive oxygen species are generated, leading to lipid peroxidation, cytokine induction, chemoattraction of inflammatory cells, hepatic stellate cell activation and finally fibrogenesis with extracellular matrix deposition. No currently available therapies for NAFLD and NASH exist. Recently nuclear receptors have emerged as key regulators of lipid and carbohydrate metabolism for which specific pharmacological ligands are available, making them attractive therapeutic targets for NAFLD and NASH.     

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...     

Drugs and steatohepatitis

In addition to the usual associations with insulin resistance, type 2 diabetes, central obesity, and hypertriglyceridemia, nonalcoholic steatohepatitis (NASH) has been associated with several drugs and toxins. However, drug-induced liver disease is a relatively uncommon cause of steatohepatitis. The term drug-induced steatohepatitis is preferred when the association appears to result from a direct toxic effect of the drug on the liver. For some agents implicated as causing cirrhosis or fatty liver disorders, the association may be coincidental because NASH is a common component of the insulin resistance (or metabolic) syndrome. In other instances, corticosteroids, tamoxifen, and estrogens may precipitate NASH in predisposed persons by exacerbating insulin resistance, central obesity, diabetes, and hypertriglyceridemia, and methotrexate may worsen hepatic fibrosis in NASH. Drug-induced steatohepatitis is associated with prolonged therapy (more than 6 months) and possibly drug accumulation, which in the case of perhexiline maleate is favored by a genetic polymorphism of CYP2D6 that leads to slow perhexiline oxidation. The toxic mechanism appears to involve mitochondrial injury, which causes steatosis because of impaired beta-oxidation of fatty acids, and leads to generation of reactive oxygen species and ATP depletion. Thus, drug-induced steatohepatitis may provide clues to injurious events in the more common metabolic forms of NASH. A clinical feature of some types of drug-induced steatohepatitis is progression after discontinuation of the causative agent. It follows that early recognition of hepatotoxicity is crucial to prevent the development of severer forms of liver disease and improve the clinical outcome.     

Noninvasive investigations for non alcoholic fatty liver disease and liver fibrosis

Non-alcoholic fatty liver disease (NAFLD) includes a spectrum of diseases that have insulin resistance in common and are associated with metabolic conditions such as obesity, type 2 diabetes mellitus, and dyslipidemia. NAFLD ranges from simple liver steatosis, which follows a benign course, to nonalcoholic steatohepatitis (NASH), a more severe entity, with necroinflmmation and f ibrosis, which can progress to cryptogenic cirrhosis and end-stage liver disease. Liver biopsy remains the gold standard for evalu...     

Nonalcoholic steatohepatitis in children

Nonalcoholic steatohepatitis (NASH) is one entity in a spectrum of chronic liver disease related to obesity, hyperinsulinemia, insulin resistance, and liver cell injury from free fatty acid toxicity or other oxidant stress. The more inclusive term ‘nonalcoholic fatty liver disease’ (NAFLD) is increasingly being used to encompass the entire spectrum, which includes simple hepatic steatosis without inflammation (which may not lead to progressive liver injury), NASH itself, and the resulting cirrhosis (which may be devoid of steatosis). Children get NAFLD, and the incidence of this pediatric liver disease is rising as childhood obesity becomes increasingly prevalent. Although much remains to be learned about pediatric NAFLD, it is already evident that children with NASH risk progressive liver damage, including cirrhosis. Liver biopsy is required for definitive diagnosis, and other causes of fatty liver in childhood must be excluded. Gradual weight loss through increased regular exercise and a low-fat, low-refined carbohydrate diet appears to be effective. Drug treatments are being developed. Pediatric NASH is a serious complication of childhood obesity.     

Acetaminophen‐induced liver injury in obesity and nonalcoholic fatty liver disease

Although acetaminophen (APAP) is usually considered as a safe drug, this painkiller can lead to acute liver failure after overdoses. Moreover, there is evidence that the maximum recommended dosage can induce hepatic cytolysis in some individuals. Several predisposing factors appear to enhance the risk and severity of APAP‐induced liver injury including chronic alcoholic liver disease and nonalcoholic fatty liver disease (NAFLD), which refers to a large spectrum of hepatic lesions linked to obesity. In contrast, obesity by itself does not seem to be associated with a higher risk of APAP‐induced liver injury. Since 1987, seven studies dealt with APAP‐induced hepatotoxicity in rodent models of NAFLD and five of them found that this liver disease was associated with higher APAP toxicity. Unfortunately, these studies did not unequivocally established the mechanism(s) whereby NAFLD could favour APAP hepatotoxicity, although some investigations suggested that pre‐existent induction of hepatic cytochrome P450 2E1 (CYP2E1) could play a significant role by increasing the generation of N‐acetyl‐p‐benzoquinone imine (NAPQI), the toxic metabolite of APAP. Moreover, pre‐existent mitochondrial dysfunction associated with NAFLD could also be involved. In contrast, some investigations suggested that factors that could reduce the risk and severity of APAP hepatotoxicity in obesity and NAFLD include higher hepatic APAP glucuronidation, reduced CYP3A4 activity and increased volume of body distribution. Thus, the occurrence and the outcome of APAP‐induced liver injury in an obese individual with NAFLD might depend on a delicate balance between metabolic factors that can be protective and others that favour large hepatic levels of NAPQI.     

CYP2E1与非酒精性脂肪肝

非酒精性脂肪性肝病(nonalcoholie fatty liver disease,NAFLD)是一种最常见的肝脏疾病,它的高发病率越来越受到广泛重视。细胞色素氧化酶P450-2E1亚型(CYP2E1)是参与氧化应激和脂质过氧化过程中的关键酶。"二次打击"学说为医学界普遍接受的非酒精性脂肪肝的发病机制。在非酒精性脂肪肝的"二次打击学说"中,CYP2E1介导的脂质过氧化亦发挥重要的作用。通过对CYP2E1介导的脂质过氧化在脂肪性肝病发病机制中作用的进一步深入研究,有可能探索出有效治疗脂肪性肝病的新途径。     

Current and emerging therapies in nonalcoholic fatty liver disease

The prevalence of obesity and the metabolic syndrome (MS) is on the rise, and subsequently the hepatic manifestation of MS, nonalcoholic fatty liver disease (NAFLD), has become a common entity in clinical practice. Most patients with NAFLD face medical complications related to their underlying MS in other organ systems; however, a small but significant group of patients with the more aggressive form of fatty liver, nonalcoholic steatohepatitis (NASH), are at risk of developing cirrhosis and hepatocellular carcinoma. As patients are generally asymptomatic, often their disease goes unrecognized. This is particularly true for NASH, where liver biopsy is currently required to make the diagnosis. Once diagnosed, no one treatment has been shown to be universally efficacious and those that are of benefit are not without side effects. Effective treatment regimens directed at both decreasing insulin resistance as well as the processes leading to necroinflammation and hepatic fibrosis have been investigated and include lifestyle modification, surgical therapies, and pharmacotherapy. This review focuses on current and potential future therapies for NASH.     

Liver transplantation and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is an important health problem worldwide. NAFLD encompasses a histological spectrum ranging from bland liver steatosis to severe steatohepatitis (nonalcoholic steatohepatitis, NASH) with the potential of progressing to cirrhosis and its associated morbidity and mortality. NAFLD is thought to be the hepatic manifestation of insulin resistance (or the metabolic syndrome); its prevalence is increasing worldwide in parallel with the obesity epidemic. In many developed countries, NAFLD is the most common cause of liver disease and NASH related cirrhosis is currently the third most common indication for liver transplantation. NASH related cirrhosis is anticipated to become the leading indication for liver transplantation within the next one or two decades. In this review, we discuss how liver transplantation is affected by NAFLD, specifically the following: (1) the increasing need for liver transplantation due to NASH; (2) the impact of the increasing prevalence of NAFLD in the general population on the quality of deceased and live donor livers available for transplantation; (3) the long term graft and patient outcomes after liver transplantation for NASH, and finally; and (4) the de novo occurrence of NAFLD/NASH after liver transplantation and its impact on graft and patient outcomes.     

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.     

Animal models of nonalcoholic fatty liver disease

In 1980, Ludwig and colleagues described a series of patients with liver histology characterized by the accumulation of fat and the presence of hepatic necroinflammation in the absence of a history of excessive alcohol consumption. They coined the term nonalcoholic steatohepatitis (NASH), which today is regarded as one of the most common causes of liver disease in affluent countries. NASH is a subset of a larger spectrum of diseases termed fatty liver disease (including alcoholic and nonalcoholic fatty liver disease; AFLD and NAFLD, respectively). NAFLD and NASH are linked to visceral adiposity, insulin resistance, dyslipidemia and type 2 diabetes, and are increasing due to the prevalence of the metabolic syndrome. In this context, research has been undertaken using animals to model human steatosis and NAFLD to NASH disease progression. This Review discusses the prevalent dietary and inflammation-based genetic animal models described in recent years.     

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.     

Sex difference in the liver of hepatocyte-specific Pten-deficient mice: A model of nonalcoholic steatohepatitis

Aim:  Nonalcoholic fatty liver disease (NAFLD) is considered to be a public health problem worldwide. NAFLD is more prevalent in men than in women. Tamoxifen, a potent estrogen receptor antagonist, causes nonalcoholic steatohepatitis (NASH), a severe form of NAFLD. Thus, there may be a sex difference that is dependent on estrogens in NAFLD and NASH. Hepatocyte-specific Pten-deficient mice exhibit hepatic lesions analogous to NASH and are considered to be a clinical model of NASH. We aimed to shed light on any sex differences in the hepatic lesions of Pten-deficient mice and the underlying mechanisms.
Methods:  At 40 weeks, livers from male and female Pten-deficient mice were processed for measuring lipid content, genes expression analysis, and histological examination. Level of serum reactive oxygen species (ROS) was also determined. Seventy-six-week-old mice were used in tumor burden experiments.
Results:  Hepatic steatosis, inflammation, and even carcinogenesis in Pten-deficient mice were attenuated in females compared to males. Attenuated fatty liver in females was ascribed to inactivation of sterol regulatory element binding protein-1c. Hepatic inflammation in females was suppressed via decreased ROS with increased antioxidant gene expression and decreased proinflammatory cytokine production. Anti-cancer effect in female mice was, at least in part, due to the significantly lower ratio of oleic to stearic acid in the liver.
Conclusions:  Hepatic lesions in Pten-deficient mice were attenuated in females compared to males, as were human NAFLD and NASH. Some of the underlying mechanisms in sex difference appeared to be due to the change of gene expression, dependent on estrogens.     

Dietary approach in the treatment of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease(NAFLD) has been identified as one of the most prevalent chronic liver disease in adults and children populations. NAFLD is usually associated with the metabolic syndrome(MS), which is chiefly related to insulin resistance and its consequences. Insulin resistance has a crucial role in the pathogenesis of hepatic steatosis and potentially nonalcoholic steatohepatitis(NASH). Because of the contemporary epidemics of MS and obesity, the burden of NAFLD is also expected to rise. Unhealthy diets, such as the so-called western diet, are enriched in fructose, trans-fatty acids and saturated fat and seem to be associated with the development of NAFLD. In human studies, certain dietary sugars, particularly fructose, are used as a substrate for lipogenesis leading to hepatic fatty infiltration, inflammation, and possibly fibrosis. Other investigations have shown that fat consumption especially cholesterol and trans/saturated fatty acids are also steatogenic and seem to increase visceral adiposity. The identification of specific dietary components that favor the development of NASH could be important for the management of this disorder. This review focuses on the effects of different dietary approaches to prevent and treat NAFLD emphasizing the macronutrients and energy composition.     

Is there a role for adaptive immunity in nonalcoholic steatohepatitis?

The growing diffusion of nonalcoholic fatty liver disease (NAFLD) is a consequence of the worldwide increase in the prevalence of obesity. Oxidative stress is widely recognized to play a pivotal role in NAFLD evolution to nonalcoholic steatohepatitis (NASH). Here we review recent evidence suggesting that oxidative stress-derived antigens originating within fatty livers stimulate both humoral and cellular adaptive immune responses and the possible mechanisms involved in sustaining hepatic inflammation in NASH.     

Genetically modified mouse models for the study of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is associated with obesity, insulin resistance, and type 2 diabetes. NAFLD represents a large spectrum of diseases ranging from (1) fatty liver (hepatic steatosis); (2) steatosis with inflammation and necrosis; to (3) cirrhosis. The animal models to study NAFLD/nonalcoholic steatohepatitis (NASH) are extremely useful, as there are still many events to be elucidated in the pathology of NASH. The study of the established animal models has provided many clues in the pathogenesis of steatosis and steatohepatitis, but these remain incompletely understood. The different mouse models can be classified in two large groups. The first one includes genetically modified (transgenic or knockout) mice that spontaneously develop liver disease, and the second one includes mice that acquire the disease after dietary or pharmacological manipulation. Although the molecular mechanism leading to the development of hepatic steatosis in the pathogenesis of NAFLD is complex, genetically modified animal models may be a key for the treatment of NAFLD. Ideal animal models for NASH should closely resemble the pathological characteristics observed in humans. To date, no single animal model has encompassed the full spectrum of human disease progression, but they can imitate particular characteristics of human disease. Therefore, it is important that the researchers choose the appropriate animal model. This review discusses various genetically modified animal models developed and used in research on NAFLD.