| Summary: | 碩士 === 國立成功大學 === 生物學系 === 90 === Recently, a moderately elevated plasma homocystein (Hcy) level has been identified as an independent risk factor for cardiovascular disease (CVD). Normal range of Hcy levels is 5-15 mM in human plasma. Plasma concentration of Hcy > 15 mM is hyperhomocysteinemia (HHcy). In this laboratory, we found that patients with CVD had significantly higher plasma Hcy concentration than normal person (12.2 ± 0.3 vs. 8.5± 0.4 mM). However, the mechanism by which HHcy leads to CVD is not known. HHcy-induced oxidative stress due to the production of reactive oxygen species (ROS) resulted in oxidation of low density lipoprotein (LDL) and endothelial membrane may contribute to the possible mechanism. In addition, peroxidation in cell membrane could activate platelet and promote adhesion leading to thrombosis. Therefore, the purpose of this study was to investigate the antioxidative effects of Dioscores in methionine (Met)-induced HHcy animals. HHcy was induced by oral feeding Met (1 g/Kg body wt./day) for 10 weeks in Sprague-Dawley rats at the age of 6 weeks. HHcy rats were randomly divided into five groups: Met group without Dioscorea feeding, Met＋vitamin C group supplemented with vitamin C 200 mg/Kg body wt./day, and 3 Dioscores groups (D1, D2 and D3) supplemented with freeze-dried Dioscorea powder 1, 2.5 and 5 g/Kg body wt./day, respectively. Animals were sacrificed after 8 or 12 weeks of Dioscorea feeding. Plasma levels of Hcy were assayed based on HPLC of the fluorescent 7-Fluorobenzo-2-oxa-1,3-diazole-4-sulfonic acid (SBD-F) derivative. Platelet aggregation induced by thrombin (3.2 U/ml) was analyzed with an aggregometer. Plasma lipid peroxidation was measured as thiobarbituric acid reactive substances (TBARS) expressed in malondialdehyde (MDA) equivalents. ROS generation was monitored with luminometer using luminal as the probe. Activities of antioxidative enzymes were measured by kinetics of enzymes using UV spectrophotometer. Hepatic concentrations of glutathione and glutathion disulfide were quantified by fluorescence spectrophotometer after derivatized with O-Phthalaldehyde.
The results of this study showed that plasma Hcy levels were significantly increased from 6.7±1.0 to 21.7±4.5 mM after 10 weeks of Met feeding. Eight and 12 weeks after Dioscorea feeding, plasma Hcy of D1, D2, and D3 were significantly lower than that of Met, and similar to the basal level prior to Met feeding. Twelve weeks after Dioscorea feeding, thrombin-induced platelet aggregation of D2 and D3 were significantly lower than that of Met group. Plasma MDA levels and hepatic ROS of D1, D2, and D3 were similar to that of Ctl group and significantly lower than that of Met group after 12 weeks of Dioscorea feeding. The activities of hepatic catalase in D2 and D3 groups were significantly elevated compared to Met group at 12 weeks. However, feeding Dioscorea 8 or 12 weeks did not significantly change hepatic levels of GSH and GSSG.
Results of our study indicated that HHcy induced by Met could be reversed by Dioscorea feeding. In addition, Dioscorea feeding could alleviate platelet aggregation, lipid peroxidation, and oxidative stress in HHcy. The protective effects of Dioscores feeding in oxidative stress induced by high protein (Met) intake. Suggested Dioscores as a valuable functional food.
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