Biotransformation of the naturally occurring isothiocyanate sulforaphane in the rat: Identification of phase I metabolites and glutathione conjugates
Biotransformation of the naturally occurring isothiocyanate sulforaphane in the rat: Identification of phase I metabolites and glutathione conjugates
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DOI：
10.1021/tx970080t
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发表时间：
1997-11-01
影响因子：
4.1
通讯作者：
Baillie, T
中科院分区：
文献类型：
--
作者：
Kassahun, K;Davis, M;Baillie, T
萝卜硫素是一种天然存在于十字花科蔬菜(如西兰花)中的异硫氰酸酯，已被证实是实验动物谷胱甘肽S转移酶活性的有效诱导剂。本研究旨在阐明SFN在大鼠体内的代谢去向。特别强调的是谷胱甘肽(GSH)依赖的途径，因为与GSH的结合是哺乳动物体内许多异硫氰酸酯被消除的主要途径。雄性SD大鼠一次性给予SFN(50 mg·kg~(-1)ip)，通过抗坏血酸收集胆汁和尿液。采用中性离子扫描(129Da)和前驱体离子(m/z 164)扫描模式，分别检测GSH和N-乙酰半胱氨酸(NAG)结合物，用离子喷雾LC-MS/MS分析生物体液。在胆汁中检测到5种硫醇结合物(命名为M1-M5)。通过与合成标准品的LC-MS/MS性质比较，确定代谢产物M2和M4分别为SFN和Erucin的GSH偶联物。M1是SFN的非饱和代谢物的GSH结合物(暂定为Delta(1)-SFN的结构)，表明母体化合物也经历了氧化代谢。代谢产物M3和M5分别被鉴定为SFN和ERN的NAC结合物，与Delta(1)-SFN的NAC结合物一起在尿中也被检测到。尿中前两种硫代产物的定量测定表明，作为SFN和ERN的NAC结合物，单剂SFN在24 h内的排泄率分别为60%和12%。给予ERN的大鼠相应的数字分别为67%和29%。当SFN的GSH结合物与磷酸盐缓冲液(pH 7.4，37℃)孵育时，1%的结合物解离，释放出游离的SFN。另一方面，当在过量的半胱氨酸存在下孵育时，该偶联物经历了简单的硫醇交换反应(>；70%的转化率)，从而作为有效的氨基甲酰化试剂。结论：三七总皂苷在大鼠体内通过S氧化还原脱氢代谢，谷胱甘肽偶联反应是母体化合物及其I相代谢产物消除的主要途径。
Sulforaphane (SFN) is a naturally occurring isothiocyanate present in cruciferous vegetables, such as broccoli, that has been identified as a potent inducer of glutathione S-transferase activities in laboratory animals. The present studies were carried out to elucidate the metabolic fate of SFN in the rat. Particular emphasis was placed on glutathione (GSH)-dependent pathways because conjugation with GSH is a major route by which many isothiocyanates are eliminated in mammals. Male Sprague-Dawley rats were administered a single dose of SFN (50 mg kg(-1) ip), and bile and urine were collected over ascorbic acid. Analysis of biological fluids was carried out by ionspray LC-MS/MS using the neutral loss (129 Da) and precursor ion (m/z 164) scan modes to detect GSH and N-acetylcysteine (NAG) conjugates, respectively. In bile, five thiol conjugates (designated M1-M5) were detected. Metabolites M2 and M4 were identified as the GSH conjugates of SFN and erucin (ERN, the sulfide analog of SFN), respectively, by comparing their LC-MS/MS properties with those of standards obtained by synthesis. M1 was characterized as the GSH conjugate of a desaturated metabolite of SFN (tentatively assigned the structure of Delta(1)-SFN), suggesting that the parent compound also undergoes oxidative metabolism. Metabolites M3 and M5 were identified as the NAC conjugates of SFN and ERN, respectively, and together with the NAC conjugate of Delta(1)-SFN, these species also were detected in urine. Quantitative determination of the former two mercapturates in urine indicated that similar to 60% and similar to 12% of a single dose of SFN is eliminated in 24 h as the NAC conjugates of SFN and ERN, respectively. The corresponding figures in rats dosed with ERN were similar to 67% and similar to 29%. When the GSH conjugate of SFN was incubated with phosphate buffer (pH 7.4, 37 degrees C), < 1% of the conjugate dissociated to liberate free SFN. On the other hand, the conjugate underwent a facile thiol exchange reaction (> 70% conversion) when incubated in the presence of excess cysteine, thereby acting as an effective carbamoylating agent. It is concluded that SFN undergoes metabolism by S-oxide reduction and dehydrogenation and that GSH conjugation is the major pathway by which the parent compound and its phase I metabolites are eliminated in the rat.