Karczewski J M, Peters J G, Noordhoek J
Department of Toxicology, University of Nijmegen, The Netherlands.
Biochem Pharmacol. 1999 Jan 1;57(1):27-37. doi: 10.1016/s0006-2952(98)00288-3.
The human colon carcinoma cell lines Caco-2 and HT-29 were exposed to three structurally related naphthoquinones. Menadione (MEN), 1,4-naphthoquinone (NQ), and 2,3-dimethoxy-1,4-naphthoquinone (DIM) redoxcycle at similar rates, NQ is a stronger arylator than MEN, and DIM does not arylate thiols. The Caco-2 cell line was particularly vulnerable to NQ and MEN and displayed moderate toxic effects of DIM. The HT-29 cell line was only vulnerable to NQ and MEN after inhibition of DT-diaphorase (DTD) with dicoumarol, whereas dicoumarol did not affect the toxicity of quinones to Caco-2 cells. DTD activity in the HT-29 and Caco-2 cell lines, as estimated by the dicoumarol-sensitive reduction of 2,6-dichlorophenolindophenol, was 393.7 +/- 46.9 and 6.4 +/- 2.2 nmol NADPH x min(-1) x mg protein(-1), respectively. MEN depleted glutathione to a small extent in the HT-29 cell line, but a rapid depletion similar to Caco-2 cells was achieved when dicoumarol was added. The data demonstrated that the DTD-deficient Caco-2 cell line was more vulnerable to arylating or redoxcycling quinones than DTD-expressing cell lines. Exposure of the Caco-2 cell line to quinones produced a rapid rise in protein disulphides and oxidised glutathione. In contrast to NQ and DIM, no intracellular GSSG was observed with MEN. The relatively higher levels of ATP in MEN-exposed cells may account for the efficient extrusion of intracellular GSSG. The reductive potential of the cell as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reduction was only increased by MEN and not with NQ and DIM. We conclude that arylation is a major contributing factor in the toxicity of quinones. For this reason, NQ was the most toxic quinone, followed by MEN, and the pure redoxcycler DIM elicited modest toxicity in Caco-2 cells.
将人结肠癌细胞系Caco - 2和HT - 29暴露于三种结构相关的萘醌。甲萘醌（MEN）、1,4 - 萘醌（NQ）和2,3 - 二甲氧基 - 1,4 - 萘醌（DIM）以相似的速率进行氧化还原循环，NQ是比MEN更强的芳基化剂，而DIM不使硫醇芳基化。Caco - 2细胞系对NQ和MEN特别敏感，对DIM表现出中等毒性作用。HT - 29细胞系在用双香豆素抑制DT - 黄递酶（DTD）后才对NQ和MEN敏感，而双香豆素不影响醌类对Caco - 2细胞的毒性。通过双香豆素敏感的2,6 - 二氯酚靛酚还原法估算，HT - 29和Caco - 2细胞系中的DTD活性分别为393.7±46.9和6.4±2.2 nmol NADPH·min⁻¹·mg蛋白质⁻¹。MEN在HT - 29细胞系中使谷胱甘肽有少量消耗，但加入双香豆素后能实现与Caco - 2细胞类似快速的消耗程度。数据表明，缺乏DTD的Caco - 2细胞系比表达DTD的细胞系对芳基化或氧化还原循环醌类更敏感。将Caco - 2细胞系暴露于醌类会使蛋白质二硫键和氧化型谷胱甘肽迅速增加。与NQ和DIM不同，MEN处理的细胞中未观察到细胞内的氧化型谷胱甘肽（GSSG）。MEN处理的细胞中相对较高的ATP水平可能是细胞内GSSG有效排出的原因。用3 -（4,5 - 二甲基噻唑 - 2 - 基）- 2,5 - 二苯基溴化四氮唑还原法测定的细胞还原电位仅在MEN处理时升高，而NQ和DIM处理时未升高。我们得出结论，芳基化是醌类毒性的主要促成因素。因此，NQ是毒性最强的醌，其次是MEN，而单纯的氧化还原循环剂DIM在Caco - 2细胞中引起适度毒性。
