Study On The Role Of Peroxisome Proliferator Activated Receptor Alpha In The Pathogensis Of Nonalcoholic Steatohepatitis

Objective:Nonalcoholic steatohepatitis(NASH)is a chronic liver disease with histologic features of alcohol-induced fatty liver disease in individuals who consume little or no alcohol, and is an acquired metabolic disease. It is an underdiagnosed liver disease characterized by diffuse adipose infiltration and inflammation. NASH is becoming increasingly more prevalent in both children and adolescents and the incidence of it is increasing. NASH is usually regarded as a benign disease, but more and more studies show it can lead to liver fibrosis in about 30% NASH patients and become one important causes of cryptogenic cirrhosis. However, there is no widely accepted approach to treating NASH at present. Peroxisome proliferator activated receptor alpha(PPARα) is a ligand-activated transcription factor that belongs to the superfamily of nuclear hormone receptors. PPARαis expressed in metabolically active tissues including the liver, heart, kidney, skeletal muscle, and brown fat of human. It is also present in the artery wall in monocyte/macrophages, vascular smooth muscle cells, and endothelial cells. PPARαcontrols expression of genes implicated in lipid metabolism and inflammatory reaction whose functional defect can cause steatosis, necrosis and inflammation of hepatocyte and form NASH finally. But the mechanism of it is poorly understood. In this study, NASH rat model was established by high fat diet to measure the expression of PPARαin the liver of rat by means of RT-PCR and explore the role of PPARαin the pathogensis of NASH, and provide potential way for prevent and treat patients with NASH. Methods:Forty healthy male Wistar rats were divided into two groups of twenty rats each randomly. Normal group fed with standard diet and fat-riched diet group fed with standard diet added by 10% lard and 2% cholesterol. All rats were sacrificed at the end of the 20th week from the feeding day. Serum from rats was isolated and stored in refrigerator. Serum TC, TG, FFA and TNF-αwere measured using an auto-biochemical analyzer(Olympus AU 2700, Japan), colorimetric method and radio-immune assay respectively. Some of livers were fixded in 10% buffered formalin and stained with hematoxylin-eosin for routine examination, with Sudan Ⅳfor steatosis and with Masson for fibrosis. The percentage of steatosis and collagen was calculated by multifunctional pathological image analyzer(Beijing Aerospace University). The expression of PPARαmRNA and NF-κB binding activity in the liver was detected by means of RT-PCR and electrophoretic mobility shift assay (EMSA, Promega) respectively. Results: 1 The common behavior of rats: Normal rats wereactive, their hair were bright and weight increased gradually. Body weight of rats in model group increased remarkably at first, but the increase went down slightly after the 12th week. At the end of the 20th week, the body weight and liver index of model group were high remarkably compared to that of control group (283±7.23, 5.65±0.41)(p<0.05). 2 The examination of biochemical markers of serum and liver tissue: The levels of serum FFA, TC, TG and TNFαof rats in model groups were significantly increased compared to that in control groups(802±175, 4.25±0.38, 3.31±0.42, 3.02±0.37) (p<0.01). 3 Routine pathologic examination: The normal rat livers were henna and bright. The model rat livers were buff and obviously large, which can be seen focal degeneration of yellow and white. The sections were greasy and dim. The normal hepatocyte arranged in radiation from the central veins under light microscope. There was very little collagen in central veins and portal area with Masson staining. At the end of the 20th week, all hepatocytes of the rats in fat-rich diet group presented modest to severe steatosis with the inflammation of the interlobular and portal areas. Fibrosis around the hepatic sinusoids and venofibrosis also could be seen in some rats. The quantitative evaluation of steatosis in rats of normal group and fat-rich diet group were(1.34±0.33, 35.82±8.52); scores of inflammation were(0.71±0.41,3.05±0.72); scores of fibrosis were (2.03±0.87, 7.90±2.79) (p<0.01).