Reductive metabolism of niridazole by adult Schistosoma mansoni. Correlation with covalent drug binding to parasite macromolecules.
Reductive metabolism of niridazole by adult Schistosoma mansoni. Correlation with covalent drug binding to parasite macromolecules.
复制标题
成年曼氏血吸虫对尼达唑的还原代谢。
作者：
J. W. Tracy;B. Catto;L. T. Webster
硝唑是一种抗血吸虫硝基噻唑类化合物，通过[14C]硝唑与寄生虫大分子的广泛共价结合，被曼氏血吸虫成虫代谢成一种或多种活性中间体。当成虫对在含有70微米[14C]硝咪唑的培养液中孵育16小时时，与寄生虫相关的总放射性的26-34%不可逆地结合到三氯乙酸可沉淀的物质上。药物结合既与时间有关，又与[14C]硝硝唑浓度有关。结合药物组分中，85-90%与寄生虫蛋白有关，3-5%与RNA有关，4-7%与DNA有关。当从感染的小鼠身上恢复血吸虫时，用周期性剂量的[14C]硝咪唑治疗，总寄生虫相关放射性的40%以上与大分子结合。硝咪唑使与药物孵育的完整血吸虫的总非蛋白硫醇浓度在8小时内下降了40%。在严格的厌氧条件下，无细胞血吸虫制剂催化硝唑的基本硝基还原为依赖于吡啶核苷酸的还原，在400 nm处吸收消失。在好氧条件下没有发生净硝化还原，尽管该药物确实刺激了吡啶核苷酸辅因子的氧化。在该无细胞体系中也发生了[14C]硝硝唑的共价结合，其要求与酶促硝化还原所需的条件相同。2 mM L-半胱氨酸、N-乙酰基-L-半胱氨酸或谷胱甘肽对共价药物结合有抑制作用，但对硝基还原无抑制作用；不含游离基的S-羧甲基-L-半胱氨酸对药物的共价结合无抑制作用。[14C]4‘-甲基硝唑是硝硝唑的一种非杀灭血吸虫类似物，在体外被完整的血吸虫摄取，但不被代谢，不与寄生虫大分子共价结合。此外，4‘-甲基硝咪唑不影响完整寄生虫体内非蛋白硫醇的浓度，也不作为血吸虫硝酸还原酶的体外底物。这些结果表明硝唑在这些兼性厌氧菌体内的近端代谢活性与其抗寄生虫活性呈正相关。
Niridazole, an antischistosomal nitrothiazole derivative, is metabolized by adult Schistosoma mansoni to one or more reactive intermediates, as evidenced by extensive covalent binding of [14C]niridazole to parasite macromolecules. When worm pairs were incubated for 16 hr in culture medium containing 70 microM [14C]niridazole, 26-34% of the total parasite-associated radioactivity was irreversibly bound to trichloroacetic acid-precipitable material. Drug binding was both time- and [14C]niridazole concentration-dependent. Of the bound drug fraction, 85-90% was associated with parasite proteins, 3-5% with RNA and 4-7% with DNA. When schistosomes were recovered from infected mice, treated with periodic doses of [14C]niridazole, over 40% of the total parasite-associated radioactivity was bound to macromolecules. Niridazole caused up to a 40% decrease in the concentration of total nonprotein thiols in intact schistosomes incubated with the drug over an 8-hr period. Under strictly anaerobic conditions, cell-free schistosome preparations catalyzed a reduced pyridine nucleotide-dependent reduction of niridazole's essential nitro group, as evidenced by disappearance of absorption at 400 nm. Net nitroreduction did not occur under aerobic conditions, although the drug did stimulate oxidation of the pyridine nucleotide cofactor. Covalent binding of [14C]niridazole also took place in this cell-free system, with requirements identical with those needed for enzymatic nitroreduction. Covalent drug binding, but not nitroreduction, was inhibited up to 80-85% by 2 mM L-cysteine, N-acetyl-L-cysteine, or glutathione; S-carboxymethyl-L-cysteine, which has no free sulfhydryl group, was not inhibitory. [14C]4'-Methylniridazole, a nonschistosomicidal analogue of niridazole, was taken up by intact schistosomes in vitro, but was not metabolized and did not bind covalently to parasite macromolecules. Furthermore, 4'-methylniridazole did not affect the concentration of nonprotein thiols in intact parasites and did not serve as a substrate for schistosomal nitroreductase in vitro. These results indicate a positive correlation between proximal metabolic activation of niridazole within these facultative anaerobic organisms and its antiparasitic activity.