| [Objective]To investigate the hepatotoxicity of topiramate (TPM) in low dosage or high dosage or in combination with valproate sodium (VPA) in growing rats ,which may provide the experimental basis for rational administration.[Methods]Seventy-two 3-week-old male Wistar rats were weight matched and randomly divided into six groups. The rats in the experimental groups (group A,B,C and D) were administered intragastrically with TPM 40 mg/(kg.d),TPM 80 mg/(kg.d),VPA 300 mg/(kg.d) and TPM 40 mg/(kg.d)+VPA 300 mg/(kg.d) respectively, while the rats in the negative control group (group E) with distilled water partes aequales. And the ones in the positive control group (group F) were treated by injection of 10% carbon tetrachloride dissolved in olive oil subcutaneously at a dose of 5ml/kg twice a week..After 3-month administration,changes of body weight and liver pathomorphology were observed, biochemical markers in serum and indexes of oxidative stress in liver homogenate associated with hepatotoxicity were examined. The liver microsomes were prepared with a procedure using polyethylene glycol and the total content of P450 was measured.[Results]1.Effect on body weightTPM had influence on body weight gain of rats at this experimental condition.Body weight gain of rats in group A,B,D were lower than that of rats in group E (P﹤0.01,P﹤0.001, P﹤0.01),and rats in group B were affected more significantly than ones in group A (P﹤0.01), while there′s no significant difference in group A and D (P﹥0.05).Body weight gain of rats in group C were higher than that of rats in group E (P﹤0.05).2.Effect on biochemical markers in serumCompared with group E,levels of aspartate aminotransferase (AST) were significantly increased (P﹤0.001,P﹤0.001,P﹤0.01,P﹤0.001) in group A,B,C and D.And group B had been influenced more than group A (P﹤0.001).Compared with group C,levels of AST had significantly increased in group D (P﹤0.001).While the levels of serum alanine aminotransferase (ALT),alkaline phosphatase (ALP) and gamma-glutamyltranspeptidase(GGT)didn′t change significantly in group A,B,C,D compared with those in group E (P﹥0.05).3.Effect on indexs of oxidative stress in liverCompared with group E,the contents of malondialdehyde (MDA) and the activities of superoxide dismutase (SOD) in liver tissue didn′t change significantly in the experimental groups (P﹥0.05),so were the contents of glutathion (GSH) in group A (P﹥0.05),while the contents of GSH in group B,C and D were significantly decreased (P﹤0.05).The contents of GSH in group B and D were lower than those of group A (P all﹤0.05).4.Effect on microsome cytochrome P450 contents of liver tissueCompared with group E,the P450 contents of hepatic microsome in group A didn't change significantly (P﹥0.05) ,but were obviously increased in group B,C and D (P﹤0.05,P﹤0.001,P﹤0.05).And the P450 contents in group B and group D were significantly higher than those of group A (P all﹤0.05).Compared with group C,the P450 contents in group D were significantly decreased (P﹤0.05).5. Effect on liver pathomorphology5.1 Light microscope: There were granular degeneration of some hepatocytes near the central veins of hepatic lobules in group A , punctate necrosis of some hepatocytes in group B and fatty degeneration of partial liver cells in group C. While in group D, histological findings showed granular degeneration ,fatty degeneration and punctate necrosis of partial liver cells. There were polygon-shaped hepatocytes in lobules without degeneration or necrosis in group E.5.2 Electron microscopy: As for the group A, ultrastructural liver changes included slight mitochondrial swelling and derangement and breakage of mitochondria crista in some hepatocytes. Hepatocytes in group B, C and D revealed marked ultrastructural changes, indicated by karyopyknosis, significant mitochondrial swelling, breakage and disappearance of mitochondria crista, vacuolar degeneration and disruption of the outer membrane of hepatic cell mitochondria. Lipid droplet in cytoplasm was also evident in group C and group D. In group E ultrastructural showed the sharply demarcated hepatocyte boundary, clear nuclear membrane, clear inner and outer membrane and crista of mitochondria in hepatocytes.6. The results of positive control group6.1 Body weight gain of rats were decelerated.6.2 The levels of ALT,AST,ALP and GGT were higher than those in group E.6.3 Compared with group E, the content of MDA increased, the activity of SOD decreased and the content of GSH decreased. And all have significant difference.6.4 The content of cytochrome P450 was reduced.6.5 Extensive steatosis and diffuse punctate necrosis of hepatocytes distributed in the portal area could be found by light microscope. Obvious ultrastructural liver changes were enlargement of mitochondria with disruption of limiting membranes, deletion and breakage of mitochondria crista, extensive fatty degeneration.[Conclusion]TPM can slow down body weight gain of growing rats in low dosage or high dosage or in combination with VPA.The elevation of partial liver enzymes, increased cytochrome P450 content and oxidant/antioxidant disequilibrium of liver were induced by TPM.The higher dosage administered, the more serious signs of hepatotoxicity will become manifest.TPM can damage structure and function of hepatic mitochondria, and then lead to hepatic degeneration, punctate necrosis and apoptosis.The pathological changes in liver caused by high dosage or in combination with VPA was more serious than that caused by low dosage of TPM.
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