Nonalcoholic fatty liver disease: pathogenesis and the role of antioxidants

Nonalcoholic fatty liver disease (NAFLD) includes a wide spectrum of liver injury ranging from simple steatosis to steatohepatitis, fibrosis, and cirrhosis. Whereas simple steatosis has a benign clinical course, steatohepatitis is a recognized cause of progressive liver fibrosis and can develop into cirrhosis. NAFLD and nonalcoholic steatohepatitis (NASH) are the two most common chronic liver diseases in United States general population with a prevalence of 20% and 3%, respectively. Hepatic steatosis is frequently associated with obesity, type 2 diabetes, and hyperlipidemia with insulin resistance as a key pathogenic factor. A two-hit theory best describes the progression from simple steatosis to NASH, fibrosis, or cirrhosis. These two hits consist of the accumulation of excessive hepatic fat primarily owing to insulin resistance, and oxidative stress owing to reactive oxygen species (ROS). Mitochondria are the major cellular source of ROS in cases of NASH. Currently, treatment is focused on modifying risk factors such as obesity, diabetes mellitus, and hyperlipidemia. Antioxidants such as vitamin E, N-acetylcysteine, betaine, and others may be beneficial in the treatment of NASH.     

A Cross-Sectional Study Assessing Dietary Intake and Physical Activity in Canadian Patients with Nonalcoholic Fatty Liver Disease vs Healthy Controls

BackgroundPoor diet and a sedentary lifestyle can contribute to nonalcoholic fatty liver disease (NAFLD).ObjectiveOur aim was to compare diet and physical activity of patients with NAFLD and healthy controls with current recommendations.DesignThis was a cross-sectional study.Participants/settingsSeventy-four patients with biopsy-proven NAFLD (33 simple steatosis and 41 steatohepatitis [NASH]) and 27 healthy controls participated between 2003 and 2011.Main outcome measuresFood records and activity logs were completed for 7 days. Results were compared with Dietary Reference Intakes and Canadian Physical Activity Guidelines. Plasma vitamin C was measured to assess food record accuracy.Statistical analyses performedIntake/activity for each participant was compared with the recommendations and proportion of subjects not meeting the requirements was calculated. Groups were compared by Kruskal-Wallis and Mann-Whitney U test or z-test with Bonferroni adjustment.ResultsMore patients with NASH (58.5%) were obese compared with patients with simple steatosis (24.2%) and healthy controls (7.4%; P<0.01). Patients with NAFLD showed more insulin resistance than healthy controls. The reported energy intake was below estimated requirements in all groups (P≤0.001). The proportion of subjects from each group exceeding acceptable energy intake from fat was as follows: simple steatosis: 27.3%; NASH: 46.3%; healthy controls: 63.0% (simple steatosis vs health controls; P<0.05) and from saturated fat: simple steatosis: 42.4%; NASH: 70.7%; healthy controls: 63.0% (simple steatosis vs. NASH; P<0.05). In each group, >80% of subjects did not consume enough linoleic or linolenic acid, vitamin D, and vitamin E, and >60% exceeded the upper intake level for sodium. Only 53.1% of patients with simple steatosis and 53.8% of patients with NASH, but 84.6% of healthy controls, met recommendations for physical activity (P=0.020). Plasma vitamin C was normal, similar among groups, and correlated with vitamin C intakes.ConclusionsAll participants followed a similar Western diet with high fat and sodium intakes and suboptimal micronutrient intakes. However, physical activity was lower in NAFLD compared with healthy controls and was associated with higher body mass index and insulin resistance.     

Nutritional Modulation of Non-Alcoholic Fatty Liver Disease and Insulin Resistance

Non-alcoholic fatty liver disease (NAFLD) covers a spectrum of disorders ranging from simple steatosis (non-alcoholic fatty liver, NAFL) to non-alcoholic steatohepatitis (NASH) and cirrhosis. NAFL increases the risk of liver fibrosis. If the liver is fatty due to causes of insulin resistance such as obesity and physical inactivity, it overproduces glucose and triglycerides leading to hyperinsulinemia and a low high-density lipoprotein (HDL) cholesterol concentration. The latter features predispose to type 2 diabetes and cardiovascular disease (CVD). Understanding the impact of nutritional modulation of liver fat content and insulin resistance is therefore of interest for prevention and treatment of NAFLD. Hypocaloric, especially low carbohydrate ketogenic diets rapidly decrease liver fat content and associated metabolic abnormalities. However, any type of caloric restriction seems effective long-term. Isocaloric diets containing 16%–23% fat and 57%–65% carbohydrate lower liver fat compared to diets with 43%–55% fat and 27%–38% carbohydrate. Diets rich in saturated (SFA) as compared to monounsaturated (MUFA) or polyunsaturated (PUFA) fatty acids appear particularly harmful as they increase both liver fat and insulin resistance. Overfeeding either saturated fat or carbohydrate increases liver fat content. Vitamin E supplementation decreases liver fat content as well as fibrosis but has no effect on features of insulin resistance.     

Fatty liver and global cardiometabolic risk

Non-alcoholic fatty liver disease (NAFLD) can be found in approximately 30% of adults in industrialized societies. Non-alcoholic steatohepatitis (NASH) is its most severe histological form and progresses to cirrhosis in 20% of these patients. Once developed, 30% to 40% of patients with cirrhosis will suffer liver-related death. NAFLD is considered the hepatic manifestation of the metabolic syndrome. Recent findings linking the components of metabolic syndrome with NAFLD and the progression to nonalcoholic steatohepatitis will be reviewed; in particular, the role of visceral adipose tissue, insulin resistance, adipocytokines, oxidative stress and diminished antioxidants within the liver in the exacerbation of these conditions. It is now widely accepted that non-hepatic mechanisms are largely responsible for the development of insulin resistance, which causes hepatic steatosis. Insulin resistance, a key feature of metabolic syndrome, is crucial for NASH development. We have a classical chicken-egg problem: insulin resistance causes hepatic steatosis or vice-versa? A possible sequence of the pathogenetic events is the following: increased free fatty acid supply - increased de novo lipogenesis - triglyceride and VLDL overproduction - atherogenic dyslipidemia- oxidative stress (lipid oxidation and peroxidation) - exhaustion of antioxidant defense system- "Tsunami" of inflammatory cytokines- fibrosis- carcinogenesis. Given the strong association of NAFLD with metabolic syndrome, early recognition, assessment and management are essential. The management emphasizes weight reduction and attention to global cardiometabolic risk factors, similar to recommendations for management of the elements of metabolic syndrome.     

Dietary habits and nutrient intake in non-alcoholic steatohepatitis

OBJECTIVE: Non-alcoholic steatohepatitis (NASH) is one of the most important emerging health issues. Insulin resistance and metabolic syndrome play a central role in the pathogenesis of NASH. Intake of nutrients strongly affects insulin resistance, carbohydrate and lipid metabolism, and hepatic steatosis. However, there are few reports about the intake of various nutrients in non-alcoholic fatty liver disease. In this work, we identified the characteristics of dietary habits and nutrient intake in patients with NASH. METHODS: Twenty-eight patients with NASH and 18 with simple steatosis (FL) were diagnosed from histologic findings, and their dietary habits and intake of nutrients were analyzed by detailed questioning by physicians and dieticians. RESULTS: There was an excess intake of carbohydrates/energy in patients with NASH 20-59 y of age compared with patients with FL. Among carbohydrates, intake of simple carbohydrates was higher in those with NASH. There also was a low intake of protein/energy in patients with NASH 40-59 y of age and a low intake of zinc in those 20-59 y of age compared with patients with FL. Ratio of intake of polyunsaturated fatty acid to saturated fatty acid was lower in patients with NASH and those with FL compared with the general Japanese subjects. CONCLUSION: These results suggest that imbalanced diets play important roles in development and progression of NASH and correction of these diets may be necessary in patients with NASH.     

The role of hepatic fat accumulation in pathogenesis of non-alcoholic fatty liver disease (NAFLD)

Nonalcoholic fatty liver disease is increasingly regarded as a hepatic manifestation of metabolic syndrome, and the severity of nonalcoholic fatty liver disease seems to increase in parallel with other features of metabolic syndrome. Excess lipid accumulation in the liver cells is not only a mediator of Metabolic Syndrome and indicator of a lipid overload but also accompanied by a range of histological alterations varying from 'simple' steatosis to nonalcoholic steatohepatitis, with time progressing to manifest cirrhosis. Hepatocellular carcinoma may also occur in nonalcoholic steatohepatitis -related cirrhosis with a mortality rate similar to or worse than for cirrhosis associated with hepatitis C. This review summarizes the knowledge about the causal relationship between hepatic fat accumulation, insulin resistance, liver damage and the etiological role of hepatic fat accumulation in pathogenesis of extra- and intra-hepatic manifestations. Special emphasis is given suggestions of new targets treatment and prevention of nonalcoholic fatty liver disease.     

Model of nonalcoholic steatohepatitis

BACKGROUND: Obesity and diabetes are frequently associated with nonalcoholic steatohepatitis (NASH), but studies have been hampered by the absence of a suitable experimental model. OBJECTIVE: Our objective was to create a rat model of NASH. DESIGN: Sprague-Dawley rats were fed a high-fat, liquid diet (71% of energy from fat, 11% from carbohydrates, 18% from protein) or the standard Lieber-DeCarli diet (35% of energy from fat, 47% from carbohydrates, 18% from protein). The diets were given ad libitum or as two-thirds of the amount consumed ad libitum. RESULTS: Rats fed the high-fat diet ad libitum for 3 wk developed panlobular steatosis, whereas those fed the standard diet had few fat droplets. Accordingly, total lipid concentrations with the high-fat and standard diets were 129.9 +/- 9.1 ( +/- SEM) and 66.7 +/- 4.6 mg/g liver, respectively (P < 0.001). The high-fat diet caused abnormal mitochondria and mononuclear inflammation, which were accompanied by increased hepatic tumor necrosis factor alpha (TNF-alpha; P < 0.001), TNF-alpha messenger RNA (mRNA) (P < 0.001), collagen type 1, and alpha1(I) procollagen mRNA (P < 0.001). In addition, these rats had increased cytochrome P4502E1 (CYP2E1) mRNA (P < 0.001), which was accompanied by CYP2E1 induction (P < 0.001) and oxidative stress with increased 4-hydroxynonenal (P < 0.001). Plasma insulin was elevated, which reflected insulin resistance, a NASH pathogenic factor. Rats fed a restricted high-fat diet developed only mild steatosis with attenuated biochemical changes, whereas those given a restricted standard diet had normal livers. CONCLUSION: This rat model reproduces the key features of human NASH and provides a realistic experimental model for elucidating its treatment.     

Epigenetic Mechanisms Underlying the Link between Non-Alcoholic Fatty Liver Diseases and Nutrition

Non-alcoholic fatty liver disease (NAFLD) is defined as a pathologic accumulation of fat in the form of triglycerides (TG) in the liver (steatosis) that is not caused by alcohol. A subgroup of NAFLD patients shows liver cell injury and inflammation coupled with the excessive fat accumulation (steatohepatitis), which is referred to as non-alcoholic steatohepatitis (NASH). Patients with NASH may develop cirrhosis and hepatocellular carcinoma (HCC). NAFLD shares the key features of metabolic syndrome including obesity, hyperlipidemia, hypertension, and insulin resistance. The pathogenesis of NAFLD is multi-factorial, however the oxidative stress seems to plays a major role in the development and progression of the disease. The emerging field of epigenetics provides a new perspective on the pathogenesis of NAFLD. Epigenetics is an inheritable but reversible phenomenon that affects gene expression without altering the DNA sequence and refers to DNA methylation, histone modifications and microRNAs. Epigenetic manipulation through metabolic pathways such as one-carbon metabolism has been proposed as a promising approach to retard the progression of NAFLD. Investigating the epigenetic modifiers in NAFLD may also lead to the development of preventive or therapeutic strategies for NASH-associated complications.     

大黄素对非酒精性脂肪肝大鼠胰岛素抵抗及瘦素作用的影响

目的 观察大黄素对非酒精性脂肪肝大鼠胰岛素抵抗、瘦素的作用,探讨其防治脂肪肝的可能机制.方法 将42只SD大鼠按体重大小编号后采用随机数字表法分为2组：正常组（A组、8只）,给予普通饲料喂养;高脂饲料喂养组（M组、34只）,给予高脂饲料喂养.于4周末验证有脂肪肝后,M组32只大鼠按体重大小编号后用随机数字表法分为M1、M2、M3、M4四个亚组,每组8只,各大鼠饲养饲料不变,其中,M2、M3、M4组分别予低剂量大黄素、高剂量大黄素、二甲双胍干预,大黄素、二甲双胍以0.5％羧甲基纤维素钠溶解,A组、M1组予0.5％羧甲基纤维素钠灌胃.8周末测定血清瘦素、稳态模式评估法胰岛素抵抗指数（HOMA-IR）、胰岛素敏感指数（ISI）,评价肝脂肪变和炎症程度.结果 与M1组比较,低、高剂量大黄素均能改善由HOMA-IR和ISI所评价的胰岛素抵抗（P ＜0.05,P＜0.01）.M1组血清瘦素较A组升高（P＜0.01）,M2、M3组血清瘦素较M1组降低（P ＜0.05,P＜0.01）;M1组血清瘦素水平与HOMA-IR呈正相关（r=0.746,P＜0.05）,与ISI呈负相关（r=-0.731,P＜0.05）.与M1组比较,低、高剂量大黄素对大鼠肝脏脂肪变有不同改善（P ＜0.05,P＜0,01）,而对肝脏炎症均有改善（P＜0.01）.结论 大黄素降低血清瘦素水平,改善胰岛素抵抗,可能是其防治大鼠非酒精性脂肪肝的重要机制之一.