| Nonalcoholic fatty liver disease (NAFLD) is a clinicopathological term that encompasses a disease spectrum ranging from simple triglyceride accumulation in hepatocytes (hepatic steatosis) to hepatic steatosis with inflammation (nonalcoholic steatohepatitis, NASH) and cirrhosis. NASH is a very important stage. Given appropriate prevention or treatment, NASH can be recovered to steatosis, otherwise, it can evolve to fiborsis, even cirrhosis.At present, most research about treating NASH focus on drugs. Although many drugs have certain effect, their disadvantages are also obvious. Appropriate exercise training probably can prevent or treat NASH effectively for its role of enhancing FFA's oxidation, elevating antioxidant, improving insulin sensitivity and decreasing inflammatory cytokine. No researchs about preventing NASH by exercise training are found. As for treatment of NAFLD by training, most researchs focused on steatosis. A few researchs had studied the treatment of NASH by training combined with other intervention, so it is not known whether training has independent role.The present research aims to study the effect of swimming training on the prevention and treatment of NASH by observing hepatohistological sections and evaluating the severity of steatosis and histological activity index (HAI), and to discuss the probable mechanisms by measuring insulin sensitivity index, serum and liver free fatty acid (FFA), serum tumor necrosis factorα(TNF-α), liver malondealdehyde (MDA) and superoxide dismutase (SOD), liver TNF-αmRNA, peroxisome proliferator-activated receptorα(PPARα) mRNA and cytochrome P450 (CYP450) 2E1 mRNA. At same time, the pathogenesis of NASH is also discussed based on the results.The experiment is consisted of two parts, prevention part and treatment part.Part I Prevention experimentThirty Sprague-Dawley (SD) rats were randomly assigned into four groups: rats in group C were fed by standard diet without exercise training, rats in group H were fed by high-fat diet (standard diet supplemented with 10% lard oil and 2% cholesterol) without exercise training, rats in group HE were exercised by swimming training (90min/d, 5d/w) and fed by high-fat diet, rats in group E were exercised by same training but fed by standard diet. By the end of 12th week, all rats were killed and serum and liver parameters were evaluated.1. Hepatohistological examination Under light microscope, the hepatic sections in group H showed severe macrovesicular steatosis, and the steatosis severity as well as HAI scores were all higher than that of group C (very significant difference, P<0.01). The steatosis in group HE was improved obviously compared with that in group H, and slight hepatic inflammation was showd. The steatosis severity and HAI scores in group HE were all lower than that in group H (very significant difference, P<0.01). The steatosis severity and HAI scores in group HE were all higher than that in group E (very significant difference, P<0.01). Results indicate that concurrent swimming training can prevent NASH.2. Serum parameter The serum triglyceride (TG), FFA, TNF-α, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and total cholesterol (TC ) in group H were all higher than that in group C (significant or very significant difference, P<0.05 or P<0.01). Compared with group H, the serum TG, FFA and TNF-αin group HE were lower (significant or very significant difference, P<0.05 or P<0.01), but the serum ALT, AST and TC had no statistic difference (P>0.05). The insulin sensitivity index in group H were lower that in group C and HE (all very significant diference, P<0.01). Compared with group HE, serum TG, TC and AST in group E were lower, but insulin sensitivity was higher (significant or very significant difference, P<0.05 or P<0.01). Compared with group C, serum FFA in group E was lower, but insulin sensitivity was higher (significant or very significant difference, P<0.05 or P<0.01). Results indicate that concurrent swimming training can decrease the high serum lipid resulted from high-fat diet and improve insulin sensitivity.3. Liver biochemical parameter Compared with group C, liver FFA and MDA in group H were higher, but SOD was lower (all very significant difference, P<0.01). Compared with group H, liver FFA and MDA in group HE were lower (very significant difference, P<0.01), but SOD between the two groups had no statistic difference (P>0.05). Results indicate that concurrent swimming training can alleviate liver lipid peroxidation due to high-fat diet.4. Liver molecular biological parameter Compared with group C, liver TNF-αmRNA and CYP2E1 mRNA in group H were all higher, but PPARαmRNA was lower (all very significant difference, P<0.01). Compared with group H, liver TNF-αmRNA was lower and PPARαmRNA was higher in group HE (all very significant difference, P<0.01). The liver CYP2E1 mRNA between the above two groups had no statistic difference (P>0.05). Compared with group C and HE, liver PPARαmRNA and CYP2E1 mRNA in group E were all higher (all very significant difference, P<0.01). Results indicate that concurrent swimming training can decrease the high expression of liver TNF-αmRNA and CYP2E1 mRNA, and increase the low expression of PPARαmRNA.Part II Treatment experimentFifty Sprague-Dawley rsts were randomly assigned into seven groups: rats in control group C12 and C20 were fed by standard diet for 12 weeks and 20 weeks respectively without exercise training; rats in group H12 and H20 were fed by high-fat diet (the composition was same as part I ) for 12 weeks and 20 weeks respectively without exercise training; the rats in group HD20 were fed by high-fat diet for 12 weeks then fed by standard diet for 8 weeks; the rats in group HE20 were fed by high-fat diet for 12 weeks then exercised by swimming training (60min/d, 5d/w) for 8 weeks; the rats in group HDE20 were fed by high-fat diet for 12 weeks then fed by standard diet and exercised by same training for 8 weeks.1. Comparisons between group C12 and H12 The hepatic sections in group H12 showed severe macrovesicular steatosis and intralobular or portal inflammation. Compared with group C12, the steatosis severity, HAI, body weight, liver weight, liver index, serum TG, ALT and AST in group H12 were all higher, but insulin sensitivity was lower (all significant or very significant difference, P<0.05 or P<0.01). These results indicate that the NASH model is successful.2. Comparisons of hepatohistological parameters among groups of 20 week The hepatic sections in group H20 showed severe macrovesicular steatosis and intralobular or portal inflammation. Compared with group C20, the steatosis severity, HAI in group H20 were all higher (all very significant difference, P<0.01). Compared with group H20, the steatosis severity in group HD20, HE20 and HDE20 are all lower (all very significant difference, P<0.01). Compared with group H20, the HAI in group HD20 and HDE20 were lower (significant or very significant difference, P<0.05 or P<0.01), but there was no statistic difference between group HE20 and H20 (P>0.05). Results indicate that swimming training can improve steatosis not inflammation after NASH is formed.3. Comparisons of serum parameters among groups of 20 week Compared with group C20, serum FFA, TNF-α, ALT, AST and TC in group H20 were all higher, but insulin sensitivity was lower (significant or very significant difference, P<0.05 or P<0.01). Serum TG had no statistic difference between the above two groups (P>0.05). Compared with group H20 , serum FFA, ALT, AST, TG and TC in group HE20 were all lower, but insulin sensitivity was higher (significant or very significant difference, P<0.05 or P< 0.01). Serum TNF-αhad no statistic difference between the above two groups (P>0.05). Compared with group H20, the serum FFA, TNF-α, ALT, AST and TC in group HDE20 were all lower (significant or very significant difference, P<0.05 or P<0.01), but insulin sensitivity and serum TG had no statistic difference between the above two groups (P>0.05). Compared with group H20, serum FFA, TNF-α, ALT, AST and TC in group HD20 were all lower, but insulin sensitivity was higher (significant or very significant difference, P<0.05 or P<0.01). Serum TG had no statistic difference between the above two groups (P>0.05). Results indicate that swimming training can decrease serum lipid and improve insulin sensitivity after NASH is formed.4.Comparisons of liver biochemical parameters among groups of 20 week Compared with group C20, liver FFA and MDA in group H20 were higher but SOD was lower (significant or very significant difference, P<0.05 or P<0.01). Compared with group H20, liver FFA in group HE20 was lower but SOD was higher (all very significant difference, P<0.01). Liver MDA had no statistic difference between the above two groups (P>0.05). Compared with group H20, liver FFA and MDA in group HDE20 were all lower, but SOD was higher (significant or very significant difference, P<0.05 or P<0.01). Compared with group H20, liver FFA and MDA in group HD20 were all lower (all very significant difference, P<0.01). Liver SOD had no statistic difference between the above two groups (P>0.05).Results indicate that swimming training can not alleviate liver lipid peroxidation after NASH is formed.5. Comparisons of liver molecular biological parameters among groups of 20 week Compared with group C20, liver TNF-αmRNA and CYP2E1 mRNA in group H20 were higher, but PPARαmRNA was lower (all very significant difference, P<0.01). Compared with group H20, liver TNF-αmRNA and CYP2E1 mRNA in group HE20 were lower, but PPARαmRNA was higher (significant or very significant difference, P<0.05 or P<0.01). Compared with group H20, liver TNF-αmRNA and CYP2E1 mRNA in group HDE20 were lower, but PPARαmRNA was higher (all very significant difference, P<0.01). Compared with H20, liver TNF-αmRNA in group HD20 was lower, but PPARαmRNA was higher (significant or very significant difference, P<0.05 or P<0.01). Liver CYP2E1 mRNA had no statistic difference between the above two groups (P>0.05).Results indicate that swimming training can decrease expression of liver TNF-αmRNA and CYP2E1 mRNA and increase PPARαmRNA.Conclusions1. Rat NASH model can be copied successfully by 12 week high-fat diet (standard diet supplemented with 10% lard oil and 2% cholesterol) and the probable pathogenesy are as follows:①decreasing insulin sensitivity;②increasing serum FFA, TG, TNF-αand liver FFA;③increasing liver oxidative stress and lipid peroxidation;④increasing the expression of liver TNF-αmRNA and CYP2E1 mRNA and decreasing the expression of liver PPARαmRNA;2. Concurrent swimming training can prevent NASH resulted from 12-wk high-fat diet effectively;3. The steatosis resulted from 12-wk high-fat diet can be improved by 8-wk swimming training, but 8-wk swimming training can not improve hepatic inflammation when the NASH has been formed.4. The mechanisms of preventive effect of swimming training on NASH are probably as follows:①increasing insulin sensitivity;②decreasing serum FFA, TG, TNF-αand liver FFA;③improving liver oxidative stress and lipid peroxidation;④decreasing the expression of liver TNF-αmRNA and CYP2E1 mRNA and increasing the expression of liver PPARαmRNA.
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