Effect of aging, sex and diet on biotransformation of methylmercury

1.参与甲基汞生物转化的细胞内活性氧的鉴定。用注射甲基汞的大鼠肝片研究了甲基汞的生物转化。在4小时的孵育过程中，无机汞在薄片中的形成以时间依赖的方式进行。在百草枯的存在下，去甲基化急剧加速，表明来自试剂的活性氧的参与。另一方面，生成OH的催化剂Fe^<2+>对去甲基化反应没有影响。此外，去铁胺、Fe^<2+>螯合剂、甘露醇和OH清除剂DMSO对去甲基化也没有影响。这些结果表明，肝脏薄片中甲基汞的去甲基化可能是在OH旁边的超氧化物或超氧化物衍生的活性氧的作用下发生的。鱼藤酮（一种抑制剂复合物I）的存在增强了去甲基化和脂质过氧化，而抗菌素A和NaCN（抑制复合物III的更多itor）的存在抑制了它们。这些抑制剂对脂质过氧化的抑制作用与先前使用线粒体内膜的实验中发现的效果非常相似。对注射MeHg的大鼠肝脏匀浆进行细胞分离实验，发现线粒体部位无机汞含量最高。此外，细胞膜组分的无机汞比高于整个线粒体。这些结果表明，甲基汞生物转化的重要部分是在线粒体内膜中进行的，而线粒体内膜产生了大量的活性氧。老化对甲基汞生物转化的影响。与幼龄小鼠（9周龄）相比，老龄小鼠（40周龄）肝脏中无机汞的生成受到抑制。饲粮蛋白质含量对甲基汞生物转化的影响。研究了正常蛋白质（14%）日粮、低蛋白质（7%）日粮、高蛋白（50%）日粮和正常蛋白质日粮+蛋氨酸（1.6%）对小鼠甲汞生物转化的影响。4组间差异无统计学意义。少

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 … More 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. Less