Mechanisms of non-alcoholic steatohepatitis.

In 1980, the term non-alcoholic steatohepatitis was coined to describe a new syndrome occurring in patients who usually were obese (often diabetic) females who had a liver biopsy picture consistent with alcoholic hepatitis, but who denied alcohol use. The causes of this syndrome were unknown, and there was no defined therapy. More than two decades later, this clinical syndrome is only somewhat better understood, and still there is no Food and Drug Administration-approved or even generally accepted drug therapy. Patients with primary non-alcoholic steatohepatitis typically have the insulin resistance syndrome (synonymous with the metabolic syndrome, syndrome X, and so forth), which is characterized by obesity, diabetes, hyperlipidemia, hypertension, and, in some instances, other metabolic abnormalities such as polycystic ovary disease. Secondary non-alcoholic steatohepatitis may be caused by drugs such as tamoxifen, certain industrial toxins, rapid weight loss, and so forth. The cause of non-alcoholic steatohepatitis remains elusive, but most investigators agree that a baseline of steatosis requires a second hit capable of inducing inflammation, fibrosis, or necrosis for non-alcoholic steatohepatitis to develop. Our research group has focused its efforts on the interactions of nutritional abnormalities, cytokines, oxidative stress with lipid peroxidation, and mitochondrial dysfunction in the induction of steatohepatitis, both alcoholic and non-alcoholic in origin. Research findings from other laboratories also support the role of increased cytokine activity, oxidative stress, and mitochondrial dysfunction in the pathogenesis of non-alcoholic steatohepatitis. The objectives of this article are to review the (1) definition and clinical features of non-alcoholic steatohepatitis, (2) potential mechanisms of non-alcoholic steatohepatitis, and (3) potential therapeutic interventions in non-alcoholic steatohepatitis.     

Role of lipid peroxidation in non-alcoholic steatohepatitis

The liver steatosis is a frequent human disease. The most frequent cause of the process is the alcohol consumption. But it also may arise without significant alcohol abuse. This pathogenetic process is called non-alcoholic steatohepatitis (NASH), that is characterized by the same conditions like the alcoholic steatohepatitis. In the pathogenesis of the NASH various factors participate i.e. obesity, diabetes mellitus type II, hyperlipidaemia, pregnancy, variable chemotoxins, parenteral nutrition, jejunoileal bypass, chronic inflammatory diseases, protein deficient nutrition and inborn metabolic diseases. Pathobiochemically the process consists of oxidative stress and lipid peroxidation. This condition comes from the progressive accumulation of the free fatty acids in mitochondria and from the induction of cytochrome P450, CYP 2E1 isoform in hepatocytes and Kupffer cells. The free fatty acids and ketons can cause the induction of CYP 2E1 system, that is why diabetes mellitus and obesity are the two most important factors in the NASH pathogenesis. This article is concerned mainly in the explanation of NASH pathomechanism.     

雄激素在多囊卵巢综合征合并非酒精性脂肪性肝病中的研究进展

多囊卵巢综合征(polycystic ovary syndrome,PCOS)是育龄期妇女常见的生殖内分泌紊乱性疾病,且常伴肥胖、胰岛素抵抗(insulin resistance,IR)和脂代谢紊乱等代谢异常.非酒精性脂肪性肝病(non-alcoholic fatty liver disease,NAFLD)是常见的慢...     

Medium-chain fatty acid reduces lipid accumulation by regulating expression of lipid-sensing genes in human liver cells with steatosis

Accumulation of lipids in the liver can lead to cell dysfunction and steatosis, an important factor in pathogenesis causing non-alcoholic fatty liver disease. The mechanisms related to lipid deposition in the liver, however, remain poorly understood. This study was aimed to investigate the effects of medium-chain fatty acid (MCFA) on the lipolysis and expression of lipid-sensing genes in human liver cells with steatosis. A cellular steatosis model, which is suitable to experimentally investigate the impact of fat accumulation in the liver, was established in human normal liver cells (LO2 cells) with a mixture of free fatty acids (oleate/palmitate, 2:1) at 200?μm for 24?h incubation. MCFA was found to down-regulate expression of liver X receptor-α, sterol regulatory element binding protein-1, acetyl-CoA carboxylase, fatty acid synthase, CD 36 and lipoprotein lipase in this cellular model, and have positive effects on adipose triglyceride lipase and hormone-sensitive lipase. These results suggest that MCFA may reduce lipid accumulation by regulating key lipid-sensing genes in human liver cells with steatosis.     

Nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disorders that encompasses simple hepatic steatosis and the more serious nonalcoholic steatohepatitis (NASH) that can progress to cirrhosis. Although the prevalence of NAFLD in childhood is not clear, it is apparently more common than originally thought. The major association with NAFLD is obesity, and as the prevalence of obesity in childhood and adolescence increases, fatty liver is recognized with greater frequency. Although the factors associated with progression of liver disease have not been determined fully, the pathogenesis of NASH is a "two hit" process that includes disturbed lipid homeostasis, resistance to the effects of insulin and subsequent hyperinsulinemia, and local toxic effects of triglyceride on hepatocytes. Treatment options are currently limited.     

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.     

Nonalcoholic steatohepatitis: diagnosis, pathogenesis, treatment and prognosis

Nonalcoholic steatohepatitis and chronic viral hepatitis C are the two dominant liver diseases in the Netherlands. Hepatic steatosis is usually innocuous but in twenty percent of patients it develops into steatohepatitis. One-fifth of these patients develop liver cirrhosis and hepatocellular carcinoma can also be a consequence of the disease. Nonalcoholic steatohepatitis is characterized by macrovesicular steatosis, necroinflammation, loss ofhepatocytes and fibrosis. Nonalcoholic steatohepatitis often is associated with type 2 diabetes mellitus, hypertension, dyslipoproteinemia and obesity. Insulin resistance plays a major role in the pathogenesis of this disease. Drugs against insulin resistance can ameliorate nonalcoholic steatohepatitis. Gradual weight loss, a diet including polyunsaturated fatty acids and exercise are other important treatment components of this condition.     

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.     

The Role of Intestinal Bacteria Overgrowth in Obesity-Related Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. It is a progressive disorder involving a spectrum of conditions that include pure steatosis without inflammation, nonalcoholic steatohepatitis (NASH), fibrosis and cirrhosis. The key factor in the pathophysiology of NAFLD is insulin resistance that determines lipid accumulation in the hepatocytes, which may be followed by lipid peroxidation, production of reactive oxygen species and consequent inflammation. Recent studies suggest that the characteristics of the gut microbiota are altered in NAFLD, and also, that small intestinal bacterial overgrowth (SIBO) contributes to the pathogenesis of this condition. This review presents the chief findings from all the controlled studies that evaluated SIBO, gut permeability and endotoxemia in human NAFLD. We also discuss the possible mechanisms involving SIBO, lipid accumulation and development of NASH. The understanding of these mechanisms may allow the development of new targets for NASH treatment in the future.     

Rôle des acides gras alimentaires dans la physiopathologie des hépatopathies alcooliques

Many experimental studies in animals suggest that dietary fat plays an important role in the pathogenesis of alcoholic liver disease. Polyunsaturated fatty acids potentiate alcohol-induced liver injury at least in part by inducing cytochrome P450 2E1, cyclooxygenase-2 and lipid peroxydation. On the other hand, dietary saturated fatty acids reduce steatosis, necrosis, inflammation and fibrosis in conjunction with decreased expression of TNF-α and cyclooxygenase-2, and reduce lipid peroxidation. Dilinoleoyl-phosphatidylcholine prevents alcohol-induced fibrosis and cirrhosis in baboons and stimulates collagenase activity in cultured lipocytes. There are few human studies which confirm these experimental results. Epidemiological studies suggest a relationship between daily fat intake, particularly dietary polyunsaturated fatty acids, and the risk of liver cirrhosis in alcoholics. The studies having demonstrated that being overweight is a risk factor of alcoholic cirrhosis and that the apolipoprotein E polymorphism influences the severity of liver injury in alcoholic cirrhotics strongly favor the role of fatty acids in the pathogenesis of human alcoholic liver disease.     

Total parenteral nutrition induces liver steatosis and apoptosis in neonatal piglets

Total parenteral nutrition (TPN) induces a high rate of liver disease in infants, yet the pathogenesis remains elusive. We used neonatal piglets as an animal model to assess early events leading to TPN-mediated liver injury. Newborn piglets (n = 7) were nourished for 7 d on TPN or enteral nutrition (EN) and the liver tissue and isolated hepatocytes were subjected to morphologic and molecular analysis. Histological analysis revealed prominent steatosis (grade > 2) in 6 of 7 TPN pigs, whereas minimal steatosis (grade < or = 1) was observed in only 2 EN pigs. Abundant cytosolic cytochrome C and DNA fragmentation were observed in hepatocytes from TPN compared with EN piglets. Markers of mitochondrial and Fas-mediated apoptosis were altered in TPN liver tissue, as indicated by a lower ATP concentration (P < 0.05), accumulation of ubiquitin, 9.9-fold activation of caspase-3 activity (P < 0.01), and increased cleavage of poly-(ADP-ribose) polymerase, caspase-8, -9, and -7 when compared with EN livers. Bcl-2 and proliferating cell nuclear antigen expression was downregulated, whereas Fas and Bax were upregulated in TPN livers. However, levels of caspase-12 and Bip/GRP78, both markers of endoplasmic reticulum-mediated apoptosis, did not differ between the groups. Short-term TPN induces steatosis and oxidative stress, which results in apoptosis mediated by the mitochondrial and Fas pathways. Thus, TPN-induced steatosis in newborn piglets may serve as a novel animal model to assess the pathogenesis of fatty liver and apoptosis-mediated liver injury in infants.     

Total parenteral nutrition-induced steatosis: reversal by parenteral lipid infusion

Prolonged use of total parenteral nutrition (TPN) may be associated with hepatic complications, primarily steatosis and cholestasis. A case is reported of an 18-year-old woman with chronic idiopathic intestinal pseudo-obstruction syndrome who was on prolonged home parenteral nutrition without lipid supplementation and developed steatosis. This finding was reversed by addition of lipid emulsion, at a dose of 0.5 g/kg/day, to the parenteral nutrition solution. The lack of lipid supplementation as a possible cause of steatosis, as well as other mechanisms of liver steatosis associated with TPN, are discussed.     

Role of mitochondrial dysfunction in non-alcoholic steatohepatitis

The non alcoholic steatohepatitis is a more and more frequent disease. Great progress in the physiopathologic mechanisms has been recently observed. The mitochondrial dysfunction seems to be the main mechanism implied in the necroticoinflammatory genesis of the non alcoholic steatohepatitis lesions. When this one is of metabolic origin, this dysfunction occurs on a vulnerable to aggressions steatosis liver. Several implied factors leads to the increased liberation of free radicals that will activate the lipidic peroxydation. This one is considered as the main generator of necroticoinflammatory lesions and fibrosis. The future therapeutic alternatives depends on a better comprehension of mitochondrial dysfunction.     

Serum vitamin B12 and folate levels in patients with non-alcoholic fatty liver disease

The aim of the study was the evaluation of serum vitamin B12 and folate levels in patients with biopsy-proven non-alcoholic fatty liver disease (NAFLD) and their association with the disease severity. Thirty patients with biopsy-proven NAFLD and 24 healthy controls matched for gender, age, body mass index and waist circumference were recruited. Blood samples for vitamin B12, folate, insulin and standard biochemical tests were obtained after overnight fasting. Homeostatic model of assessment-insulin resistance was calculated. There was no difference in serum vitamin B12 and folate levels between groups. Neither vitamin B12 nor folate levels were significantly different within any histological category, including steatosis grade, fibrosis stage, lobular inflammation, portal inflammation and ballooning. In conclusion, similar vitamin B12 and folate levels were observed in non-alcoholic steatohepatitis and non-alcoholic fatty liver patients, and controls. Furthermore, vitamin B12 and folate levels were not associated with either insulin resistance or the severity of liver disease.     

Managing liver dysfunction in parenteral nutrition

Parenteral nutrition is life saving in patients with intestinal failure but liver dysfunction is commonly encountered, especially in neonates. Although abnormal liver function tests associated with short-term parenteral nutrition are usually benign and transient, liver dysfunction in both children and adults receiving long-term parenteral nutrition can progress to end-stage liver disease and liver failure. The aetiology of parenteral nutrition-associated liver disease is complex and multifactorial, with a range of patient, disease and nutrition-related factors implicated. Sepsis is of particular importance, as is the lack of enteral nutrition and overfeeding with intravenous glucose and/or lipid. Deficiencies of a number of amino acids including choline and taurine have also been implicated. Management of hepatic dysfunction in parenteral nutrition should initially focus on preventing its occurrence. Sepsis should be managed appropriately, enteral nutrition should be encouraged and maximised where possible and parenteral overfeeding should be avoided. Provision of parenteral lipid should be optimised to prevent the adverse effects of both deficiency and excess, and cyclical rather than continuous parenteral feeding should be administered. There is some evidence of benefit in neonates from oral antibiotics to prevent intestinal bacterial overgrowth and from oral ursodeoxycholic acid, but less to support their use in adults. Similarly, data to support widespread use of parenteral choline or taurine supplementation are lacking at present. Ultimately, severe parenteral nutrition-associated liver disease may necessitate referral for small intestine and/or liver transplantation.     

Serum vitamin B12 and folate levels in patients with non-alcoholic fatty liver disease

The aim of the study was the evaluation of serum vitamin B12 and folate levels in patients with biopsy-proven non-alcoholic fatty liver disease (NAFLD) and their association with the disease severity. Thirty patients with biopsy-proven NAFLD and 24 healthy controls matched for gender, age, body mass index and waist circumference were recruited. Blood samples for vitamin B12, folate, insulin and standard biochemical tests were obtained after overnight fasting. Homeostatic model of assessment-insulin resistance was calculated. There was no difference in serum vitamin B12 and folate levels between groups. Neither vitamin B12 nor folate levels were significantly different within any histological category, including steatosis grade, fibrosis stage, lobular inflammation, portal inflammation and ballooning. In conclusion, similar vitamin B12 and folate levels were observed in non-alcoholic steatohepatitis and non-alcoholic fatty liver patients, and controls. Furthermore, vitamin B12 and folate levels were not associated with either insulin resistance or the severity of liver disease.     

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.     

Treatment of Parenteral Nutrition-Associated Liver Disease: The Role of Lipid Emulsions

Parenteral nutrition is a life-saving therapy for infants with intestinal failure. However, long-term parenteral nutrition carries the risk of progressive liver disease. Substantial data has implicated components of parenteral soybean oil in the pathogenesis of parenteral nutrition-associated liver disease (PNALD). Elevated serum concentrations of phytosterols, an abundance of omega-6 polyunsaturated fatty acids, and a relative paucity of α-tocopherol have been associated with the risk of cholestasis and hepatic injury observed in PNALD. Currently available treatment strategies include the reduction of the dose of administered parenteral soybean oil and/or the replacement of parenteral soybean oil with alternative parenteral lipid emulsions. The purpose of this review is to provide an overview of the pathogenetic mechanisms associated with the development of PNALD and the data evaluating currently available treatment strategies.