Effect of aging, sex and diet on biotransformation of methylmercury

• Project/Area Number: 07680587
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 環境影響評価(含放射線生物学)
• Research Institution: Kumamoto University, College of Medical Science
• Principal Investigator: HIRAYAMA Kimiko Kumamoto University, College of Medical Science, Professor, 医療技術短期大学部, 教授 (70040235)
• Co-Investigator(Kenkyū-buntansha): YASUTAKE Akira National Institute for Minamata disease, Biochemistry, Chief, 生化学室, 室長
• Project Period (FY): 1995 – 1996
• Project Status: Completed (Fiscal Year 1996)
• Budget Amount: ¥1,900,000 (Direct Cost: ¥1,900,000); Fiscal Year 1996: ¥700,000 (Direct Cost: ¥700,000); Fiscal Year 1995: ¥1,200,000 (Direct Cost: ¥1,200,000)
• Keywords: methylmercury / biotransformation / reactive oxygens / mitochondria / rat / diet / mouse / aging / 無機化反応 / 肝切片 / 食物成分 / 電子伝達系 / 無機水銀

Research Abstract

1.Identification of reactive oxygen species involving in, and of intracellular site of biotransformation of methylmercury.
Biotransformation of methylmercury (MeHg) was examined using liver slices prepared from a MeHg-injected rats. Fortmation of inorganic Hg in the slices proceeded in a time-dependent manner during 4 h incubation. The demethylation was drastically accelerated in the presence of paraquat, suggesting participation of reactive oxygen species derived from the reagent. On the other hand, Fe^<2+>, catalyst of OH production, did not affect on the demetylation. Furthermore, deferoxamine, Fe^<2+> chelator, mannitol nor DMSO,OH scavenger, also showed no effect on the demethylation. These results imply that the demethylation of MeHg in the liver slices would occur by the action of a superoxide or superoxide-derived reactive oxygen species beside OH.
Presence of rotenone (an inhibitor complex I) enhanced the demethylation and lipid peroxidation, whereas antimycine A and NaCN (inhib itor of complex III) depressed them. The depressive effects on the lipid peroxidation of these inhibitors were very similar to the effects found in the previous experiments using mitochondria inner membrane.
Cell fractionation experiment of the liver homogenate prepared from MeHg injected rats revealed that the highest ratio of inorganic Hg was found in the mitochondria fraction. Moreover, the inner membrane fraction showed higher inorganic Hg ratio than the whole mitochondria.
These results suggest that the significant part of MeHg biotransformation proceeds in the mitochondria inner membrane where quite an amount of reactive oxygen are produced.
2.Effect of aging on biotransformation of MeHg.
Inorganic Hg production in the liver was depressed in the aged mice (40 weeks of age) as compared with young mice (9 weeks of age).
3.Effect of protein contents of diet on biotransformation of MeHg.
Effect of normal protein (14%) diet, low protein (7%) diet, high protein (50%) diet and normal protein diet + methionine (1.6%) on biotransformation of MeHg were examined in mice. There were no difference among 4 groups.