Chang M, Shi M, Forman H J
Cell Biology Group, Childrens Hospital, Los Angeles, California 90027.
Am J Physiol. 1992 May;262(5 Pt 1):L637-43. doi: 10.1152/ajplung.1992.262.5.L637.
Administration of menadione (vitamin K3; 2-methyl-1,4-naphthoquinone) to cultured bovine pulmonary artery endothelial cells caused a dose- and time-dependent depletion of cellular ATP and depletion of intracellular glutathione (GSH). The toxicity of menadione was correlated with an increase of menadione-glutathione conjugate in the medium and with an increase in H2O2 generation. Recent studies have suggested that GSH may be useful as a pharmacological agent to prevent oxidant injury. In the present study, treatment with exogenous GSH prevented the loss of cellular GSH and ATP caused by menadione. Protection by extracellular GSH involved two mechanisms. In one mechanism, extracellular GSH was degraded by gamma-glutamyl transpeptidase, producing substrates for subsequent intracellular de novo GSH synthesis. We found that the protective effect of extracellular GSH was decreased by inhibiting gamma-glutamyl transpeptidase. In the other mechanism, GSH reacted in the medium with menadione to form a conjugate. Although formation of the menadione-glutathione conjugate within cells may contribute to menadione toxicity, addition of menadione-glutathione conjugate to the medium was found to be nontoxic to endothelial cells. Thus exogenous GSH protected endothelial cells by two mechanisms: maintenance of intracellular GSH and prevention of menadione entrance into cells.
向培养的牛肺动脉内皮细胞施用甲萘醌（维生素K3；2-甲基-1,4-萘醌）会导致细胞ATP呈剂量和时间依赖性消耗以及细胞内谷胱甘肽（GSH）耗竭。甲萘醌的毒性与培养基中甲萘醌-谷胱甘肽共轭物的增加以及过氧化氢生成的增加相关。最近的研究表明，谷胱甘肽可能作为一种预防氧化损伤的药物。在本研究中，用外源性谷胱甘肽处理可防止甲萘醌引起的细胞内谷胱甘肽和ATP的损失。细胞外谷胱甘肽的保护作用涉及两种机制。在一种机制中，细胞外谷胱甘肽被γ-谷氨酰转肽酶降解，产生随后细胞内从头合成谷胱甘肽的底物。我们发现，抑制γ-谷氨酰转肽酶会降低细胞外谷胱甘肽的保护作用。在另一种机制中，谷胱甘肽在培养基中与甲萘醌反应形成共轭物。虽然细胞内甲萘醌-谷胱甘肽共轭物的形成可能导致甲萘醌毒性，但发现向培养基中添加甲萘醌-谷胱甘肽共轭物对内皮细胞无毒。因此，外源性谷胱甘肽通过两种机制保护内皮细胞：维持细胞内谷胱甘肽和防止甲萘醌进入细胞。
