Shi M, Gozal E, Choy H A, Forman H J
Cell Biology Group, Childrens Hospital Los Angeles, CA.
Free Radic Biol Med. 1993 Jul;15(1):57-67. doi: 10.1016/0891-5849(93)90125-e.
Quinones are intracellular H2O2 generators that have been used extensively in models of oxidant injury; however, their toxicity is mediated partially through direct conjugation with glutathione (GSH). To focus upon the action of extracellular GSH in preventing H2O2-mediated toxicity, we used 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), which cannot conjugate with GSH but does continuously generate H2O2 through redox cycling. A eukaryotic cell line (3T3-GGT) stably overexpressing gamma-glutamyl transpeptidase (GGT) activity was used to study the role of GGT in utilizing extracellular GSH against DMNQ-induced oxidative stress. DMNQ (0 to 150 microM) caused a dose-dependent decrease of intracellular GSH and adenosine 5'-triphosphate (ATP) in both control and 3T3-GGT cells. The rate of H2O2 escape into the medium during DMNQ exposure was also the same in both cell lines. Administration of GSH helped to maintain intracellular GSH and supported resistance to ATP depletion caused by DMNQ in 3T3-GGT cells but not in control cells. The protective effect of extracellular GSH was completely prevented by acivicin, an inhibitor of GGT. Our results suggest that GGT-dependent breakdown of extracellular GSH for subsequent intracellular resynthesis helped to maintain cellular GSH levels and increased cellular resistance against DMNQ-induced oxidative injury.
醌类是细胞内过氧化氢的生成剂，已在氧化损伤模型中广泛应用；然而，它们的毒性部分是通过与谷胱甘肽（GSH）直接结合来介导的。为了聚焦于细胞外GSH在预防过氧化氢介导的毒性中的作用，我们使用了2,3 - 二甲氧基 - 1,4 - 萘醌（DMNQ），它不能与GSH结合，但能通过氧化还原循环持续产生过氧化氢。一种稳定过表达γ - 谷氨酰转肽酶（GGT）活性的真核细胞系（3T3 - GGT）被用于研究GGT在利用细胞外GSH抵抗DMNQ诱导的氧化应激中的作用。DMNQ（0至150微摩尔）在对照细胞和3T3 - GGT细胞中均导致细胞内GSH和三磷酸腺苷（ATP）呈剂量依赖性下降。在DMNQ暴露期间，过氧化氢逸出到培养基中的速率在两种细胞系中也是相同的。给予GSH有助于维持3T3 - GGT细胞中的细胞内GSH，并支持其抵抗由DMNQ引起的ATP耗竭，但对照细胞则不然。GGT的抑制剂阿西维辛完全阻断了细胞外GSH的保护作用。我们的结果表明，GGT依赖的细胞外GSH分解以便随后进行细胞内再合成，有助于维持细胞内GSH水平，并增加细胞对DMNQ诱导的氧化损伤的抵抗力。
