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Non-alcoholic steatohepatitis

Chapter 11. Non-alcoholic steatohepatitis. Wen-Ying, Chen 2006, 10. Definition of nonalcoholic fatty liver disease.

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Non-alcoholic steatohepatitis

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  1. Chapter 11 Non-alcoholic steatohepatitis Wen-Ying, Chen 2006, 10

  2. Definition of nonalcoholic fatty liver disease • Nonalcoholic Fatty Liver Disease (NAFLD) or Non-alcoholic steatohepatitis (NASH) is fatty inflammation of the liver when this is not due to excessive alcohol use. It is a major cause of cryptogenic cirrhosis of the liver. • It differs from the simple accumulation of fat in the liver (fatty liver, or hepatic steatosis) in that the inflammation of NASH causes damage to the liver cells while simple fatty liver probably does not.

  3. Chronic liver diseaseprevalence in the U.S. • Nonalcoholic fatty liver disease 20 % • Nonalcoholic steatohepatitis 3 % • Chronic hepatitis C 2 % • Alcoholic liver disease 0.7 % • Chronic hepatitis B 0.4 % NASH is one of the commonest liver diseases in Western countries.

  4. Introduction • NASH is the most prevalent from of progressive liver disease and it is suggested that it affects between 10-39% of the global population, with an average incidence of 20%. • Diabetes, obesity and hypertriacylglycerolaemia are all well-known risk factors for NASH.

  5. Progression of NAFLD Fibrosis (35 %) Cirrhosis (15 %) 10 % STEATOSIS NASH Liver Failure Hepatocellular Carcinoma (Caldwell SH. Hepatol. 2003; 37: 1202)

  6. Aetiology Conditions associated with non-alcoholic fatty liver disease

  7. Diagnosis • Clinical features • Biochemistry tests • Imaging • Histopathological features

  8. Clinical features • often asymptomatic----delays early diagnosis • Discomfort in the upper right quadrant, fatigue---- • NASH is another feature of the metabolic syndrome • In one study of 66 patients: 98% insulin resistance and 39% diabetic • Obesity and insulin resistance are linked with NASH

  9. Biochemistry tests • Liver dysfunction in NASH serum alkaline phosphatase (ALP) and γ-glutamyltransferase (γ-GT) are increased • Increased serum ferritin----- 50%

  10. Imaging • Ultrasound 87% sensitivity and 77% specificity • Computed tomography scanning • Magnetic resonance imaging quantitative assessment of fatty infiltration is best achieved

  11. Histopathological features • Steatosis • Inflammatory cell infiltration • Hepatocyte ballonning and necrosis • Glycogen nuclei • Mallory’s hyaline • Fibrosis liver biopsy is recommended for : 1. increased liver enzymes 2. metabolic syndrome: type 2 diabetes, hyperlipidaemia and obesity.

  12. Pathogenesis • Insulin resistance • Obesity • Oxidative stress • Nuclear receptor regulation of gene expression

  13. Pathogenesis insulin resistance Insulin resistance enhances TG lipolysis and inhibits esterification of free fatty acids (FFA) within adipose tissue. Hepatic TG synthesis is driven by the increased influx of FFA and favoured by insulin upregulated lipogenic transcription factors, such as PPARγ and SREBP-1c. TG export via VLDL may be inhibited by decreased synthesis of apo B.

  14. Pathogenesis insulin resistance Several molecular targets have now been identified linked to the actions of insulin that contribute to the dyslipidaemia that may inform the pathogenesis of NASH. • Rad (ras associated withDM),which interferes with essential cell functions(growth, differentiation, vesicular transport, and signal transduction). • PC-1 (a membrane glycoprotein that has a role in I.R.),which reduces insulin-stimulated tyrosine kinase activity. • leptin, which induces dephosphorylation of insulin-receptor substrate-1 • fatty acids, which inhibit insulin-stimulated peripheral glucoseuptake. • TNF-  ,which down-regulates insulin-inducedphosphorylation of insulin-receptor substrate-1 and reducesthe expression of the insulin-dependent glucose-transport moleculeGlut4. • Adiponectin, which suppress TNF-  .

  15. Pathogenesis Obesity • 70-100 % of NASH patients are obese. • Steatosis is a common observation in obesity and may be associated with inflammatory signs of non-specific hepatitis. • The TNF-α gene is overexpressed in adipose tissue in the obese and in overweight or obese patients with type 2 diabetes, resulting in higher plasma TNF-α concentations that may contribute NASH.

  16. Pathogenesis Oxidative stress • Mitochondria are the main cellular source of reactive oxygen species, which may trigger the inflammatory component of NASH. • Numberous studies have emphasized the critical importance of oxidative stress as a crucial pathophysiological mechanism of NASH.

  17. Pathogenesis Oxidative stress • Nitric oxide: iNOS may facilitate regeneration by inhibiting cell death in NASH. In iNOS knockout mice: unscavenged superoxide production may cause toxic lipid peroxidation and ultimately microvesicular steatosis and NASH. • Adiponectin: have hepatoprotective effects. 1). Increased lipid clearance through β-oxidation possibly mediated via activation of CPT-1. 2). Direct anti-inflammatory effects through inhibition of TNF-α 3). Reduce hepatomegaly, steatosis and serum ALT Adiponectin may play a role in directly or indirectly regulating factors involved in the development of NASH.

  18. Pathogenesis Oxidative stress • Cytochrome P450 enzymes: CYP2E1 & CYP4A are capable of generating free radicals to increase oxidative stress. CYP2E1: 1). to be up-regulated persistently in type 2 diabetes, insulin resistance, central obesity and NASH; 2). also is up-regulated by a high-fat/low-carbohydrate diet. 3). may play a role in initiating hepatic fibrosis.

  19. Obesity/lipodystrophy Increased lipolysis/decreased Re-esterification PPARγ activity Insulin resistance adiponectin Leptin FFA Rad TNF-α PC-1 NEFAs NO TNF-α ATP Hepatocytes/stellate/ Kupffer cells Inadequate oxidation of FFA & di/triacylglycerols Cyto P450 A P450E1 Glutathione Decreased: PPARα activity PPARδ activity Increased: SREBP 1a/1c SREBP2 activity Kupffer cell Free radicals antioxidants Oxidative stress NF-κB Oxidative stress & inflammation NASH

  20. PathogenesisNuclear receptor regulation of gene expression • Peroxisome proliferator-activated receptors (PPAR) membersa nuclaer receptor superfamily and key regulators of adipogenesis----involved in the pathogenesis of NASH.

  21. Obesity/lipodystrophy Increased lipolysis/decreased Re-esterification PPARγ activity Insulin resistance adiponectin Leptin FFA Rad TNF-α PC-1 NEFAs NO TNF-α ATP Hepatocytes/stellate/ Kupffer cells Inadequate oxidation of FFA & di/triacylglycerols Cyto P450 A P450E1 Glutathione Decreased: PPARα activity PPARδ activity Increased: SREBP 1a/1c SREBP2 activity Kupffer cell Free radicals antioxidants Oxidative stress NF-κB Oxidative stress & inflammation NASH

  22. PathogenesisNuclear receptor regulation of gene expression • Sterol regulatory element-binding proteins (SREBPs): important members of transcription factors that regulate hepatocyte cholesterol homeostasis. In the liver, three SREBP isoforms, SREBP-1a, SREBP-1c and SREBP-2, regulate the production of lipid for export into the plasma as lipoproteins and into the bile as micelles. Expression of SREBP-1c in the liver is regulated by LXR, which increases fatty acid synthesis.

  23. PathogenesisNuclear receptor regulation of gene expression • Sterol regulatory element-binding proteins (SREBPs) 1). SREBP-1c levels are increased in the fatty livers of obese (ob/ob) mice with insulin resistance and hyperinsulinaemia caused by leptin deficiency, and SREBP-1c increases lipogenic gene expression, enhances fatty acid synthesis and accelerates triacyglycerol accumulation. 2). Overexpression of SREBP-1a in rats resulted in a 26-fold increase in fatty acid synthesis and a 5-fold increase in cholesterol synthesis. 3). SREBP-2 overexpression in transgenic mice resulted in a 28-fold increase in cholesterol synthesis and a 4-fold increase in fatty acid synthesis.

  24. Obesity/lipodystrophy Increased lipolysis/decreased Re-esterification PPARγ activity Insulin resistance adiponectin Leptin FFA Rad TNF-α PC-1 NEFAs NO TNF-α ATP Hepatocytes/stellate/ Kupffer cells Inadequate oxidation of FFA & di/triacylglycerols Cyto P450 A P450E1 Glutathione Decreased: PPARα activity PPARδ activity Increased: SREBP 1a/1c SREBP2 activity Kupffer cell Free radicals antioxidants NF-κB Oxidative stress & inflammation NASH

  25. Treatment • Peroxisome proliferator-activated receptor gamma agonists • Biguanides • Peroxisome proliferator-activated receptor alpha agonists • Antioxidants • Weight loss

  26. TreatmentPPARγ agonists • Rosiglitazone (24 weeks) in 30 NASH: improved insulin sensitivity, reduced liver fat content and improved ALT level. (may be due in part to the anti-inflammatory effects of PPARγ ligants. • Troglitazone (400 mg for 6 months) in 10 NASH women: normal ALT level and mild histological improvement. for 48 weeks: improved insulin sensitivity, reduced liver fat content and improved the biochemical and histological features of NASH. The main side-effects reported in these studies were weight gain and in total body fat.

  27. TreatmentBiguanides • Metformin is the only biguanide FDA-approved for use in the United Stated. It regulates AMP-activated protein kinase in hepatocytes, which is a major cellular regulator of lipid and glucose metabolism. • Improvement in liver biochemical test, insulin sensitivity and decreasing hepatic volume and body weight. Thus, metformin may be beneficial in the treatment of NASH but some of the benefit may be a direct benefit of weight loss.

  28. TreatmentPPARα agonists a). Clofibrate (2g/day): no significant benefit in liver tests or hepatic histology b). Gemfibrozil (600 mg/day) in 46 NAFLD patients: a significant improvement in aminotransferase levles More evidence is needed from long-term studies with the newer PPARα agonists.

  29. TreatmentAntioxidants • It is uncertain at present whether antioxidant therapy is beneficial in the treatment of NASH. 1. Ursodeoxycholic acid (UDCA) (a epimer of chenodeoxycholic acid and non-hepatotoxic) a). 4 open-label pilot studies: have evaluated the therapeutic benefit of UDCA in patients with NAFLD. b). 2 years randomized trials concluded that no significant differences in the degree of stestosis, inflammation or fibrosis occurred between the UDCA and placebo groups.

  30. TreatmentAntioxidants 2. Betaine is a normal component of themetabolism of methionine and increases the S-adenosylmethionine (SAM) level, which has been shown to protect against triacyglycerol deposition and liver injury in ethanol-fed rats. a). In a recent study: betaine (20g/day for 12 months)---7 NAFLD patients ------decrease hepatic steatosis

  31. TreatmentAntioxidants 3. N-Acetylcysteine is an antioxidant that increases glutathione levels in hepatocytes. a). 11 NAFLD patients: N-acetylcysteine (1g/day for 3 m)----well tolerated and with a significant improvement in aminotransferase levles. 4. Vit E 5. α-tocopherol Thus, it is still uncertain whether there is benefit from treatment with antioxidants.

  32. TreatmentWeight loss • Obesity is the condition most commonly associated with NASH and therefore weight loss is frequently advocated. • However, the benefit of weight loss is difficult to evaluate because obese patients with NASH rarely achieve or maintain sustained reductions in body weight. • Moreover, the effect of weight loss on NASH is not consistent.

  33. TreatmentWeight loss • For the future, weight loss combined with PPARα or perhaps PPARγ agonists will most likely be the treatments of choice but before this recommendation can be advocated more evidence of efficacy and safety is required.

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