Rebbeor J F, Wang W, Clifton D, Ballatori N
Department of Environmental Medicine, University of Rochester School of Medicine, New York 14642, USA.
J Toxicol Environ Health A. 1998 Apr 24;53(8):651-63. doi: 10.1080/009841098159097.
Mercapturic acid biosynthesis is mediated by a series of at least four enzymatic steps and three cell membrane transport events, and is believed to require the interorgan shuttling of the various metabolic intermediates. To identify a single cell type that can carry out all of these metabolic and transport steps, the present study examined whether HepG2 cells, a human hepatoma-derived cell line, can convert an electrophilic chemical (1-chloro-2,4-dinitrobenzene, CDNB) to its corresponding mercapturic acid (S-dinitrophenyl-N-acetylcysteine, DNP-NAC). The results demonstrate that HepG2 cells are able to convert CDNB to DNP-NAC in a dose- and time-dependent fashion. Intracellular conjugation with glutathione occurred rapidly, and the resulting glutathione S-conjugate was promptly transported into the culture medium, where it was sequentially degraded to the cysteinylglycine and cysteine S-conjugates. The cysteine conjugate was then presumably reabsorbed, and N-acetylated intracellularly to form the mercapturic acid. The mercapturic acid was found to accumulate slowly in the culture medium, such that after 4 h of incubation, 4-10% of the CDNB dose was recovered as the mercapturic acid. These data provide the first demonstration that a single cell type can carry out all of the transport and enzymatic steps required for mercapturic acid biosynthesis. HepG2 cells may provide a useful model system for studying this important detoxification pathway.
硫醚氨酸生物合成由一系列至少四个酶促步骤和三个细胞膜转运事件介导，并且据信需要各种代谢中间体在器官间穿梭。为了鉴定能够执行所有这些代谢和转运步骤的单一细胞类型，本研究检测了人肝癌衍生细胞系HepG2细胞是否能够将亲电子化学物质（1-氯-2,4-二硝基苯，CDNB）转化为其相应的硫醚氨酸（S-二硝基苯基-N-乙酰半胱氨酸，DNP-NAC）。结果表明，HepG2细胞能够以剂量和时间依赖性方式将CDNB转化为DNP-NAC。与谷胱甘肽的细胞内结合迅速发生，并且产生的谷胱甘肽S-共轭物被迅速转运到培养基中，在那里它依次降解为半胱氨酰甘氨酸和半胱氨酸S-共轭物。然后推测半胱氨酸共轭物被重新吸收，并在细胞内进行N-乙酰化以形成硫醚氨酸。发现硫醚氨酸在培养基中缓慢积累，使得在孵育4小时后，4-10%的CDNB剂量以硫醚氨酸形式回收。这些数据首次证明单一细胞类型能够执行硫醚氨酸生物合成所需的所有转运和酶促步骤。HepG2细胞可能为研究这一重要的解毒途径提供一个有用的模型系统。
