Role of glutathione in the accumulation of anticarcinogenic isothiocyanates and their glutathione conjugates by murine hepatoma cells
Role of glutathione in the accumulation of anticarcinogenic isothiocyanates and their glutathione conjugates by murine hepatoma cells
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DOI：
10.1093/carcin/21.6.1175
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发表时间：
2000-06-01
期刊：
影响因子：
4.7
通讯作者：
Zhang, YS
中科院分区：
文献类型：
--
作者：
Zhang, YS
异硫氰酸酯（ITCs）在人类饮食中含量丰富，许多具有抑制多种化学致癌物诱导的啮齿动物肿瘤发生的作用。最近，我们观察到几种ITCs在培养细胞中积累到非常高的浓度，并且它们的积累水平与它们诱导解毒致癌物的II期酶[NAD(P)H：醌还原酶和谷胱甘肽转移酶]的能力密切相关。为了阐明这种积累的分子机制，我们在小鼠肝癌细胞中研究了两种ITCs，萝卜硫素[SF， 1-异硫氰酸-(4R，S)-（甲基亚砜基）丁烷]和苄基- itc的细胞内化学特性。这两种ITCs在细胞内迅速积累到很高的浓度，但值得注意的是，大多数细胞内形式的ITCs是与还原型谷胱甘肽（GSH）结合产生的二硫代氨基甲酸酯。例如，当细胞在37℃下暴露于100 μ M SF中30 min时，细胞内浓度达到6.4 mM，积累产物的95%是GSH偶联物。每种ITC的细胞积累都伴随着细胞GSH水平的显著降低。这些发现，加上我们之前观察到的ITC的积累依赖于细胞GSH水平，强烈表明ITC与GSH的细胞内结合是ITC积累的主要原因。令人惊讶的是，当细胞暴露于GSH-ITC偶联物时，也会迅速积累到高浓度。然而，这些缀合物显然没有被完整地吸收，而是在细胞外水解以释放被细胞吸收的ITCs。过量谷胱甘肽或其他硫醇抑制偶联物的解离可阻止偶联物的积累，这一发现支持了这一结论。
Isothiocyanates (ITCs) are abundant in the human diet, Many potently inhibit tumorigenesis induced by a wide variety of chemical carcinogens in rodents. Recently, we observed that several ITCs accumulated to very high concentrations in cultured cells and that their accumulated levels were closely related to their potencies in inducing phase II enzymes [NAD(P)H:quinone reductase and glutathione transferases] that detoxify carcinogens. To elucidate the molecular mechanism responsible for this accumulation, the intracellular chemical identities of two ITCs, sulforaphane [SF, 1-isothiocyanato-(4R,S)-(methylsulfinyl)butane] and benzyl-ITC, were investigated in murine hepatoma cells. Both ITCs accumulated very rapidly to high intracellular concentrations, but, remarkably, most of the intracellular forms of the ITCs were dithiocarbamates resulting from conjugation with reduced glutathione (GSH). For example, the intracellular concentration reached 6.4 mM when cells were exposed to 100 mu M SF for 30 min at 37 degrees C and 95% of the accumulated product was the GSH conjugate. Cellular accumulation of each ITC was accompanied by a profound reduction in cellular GSH levels. These findings, together with our previous observation that accumulation of ITCs depended on cellular GSH levels, strongly suggest that intracellular conjugation of ITCs with GSH is mainly responsible for ITC accumulation. Surprisingly, rapid accumulation to high concentrations also occurred when cells were exposed to the GSH-ITC conjugates. However, these conjugates were apparently not absorbed intact, but were hydrolyzed extracellularly to free ITCs that were taken up by the cells. This conclusion is supported by the finding that suppression of dissociation of the conjugates by excess GSH or other thiols blocks accumulation of the conjugates.