Nelson S D, Mitchell J R, Snodgrass W R, Timbrell J A
J Pharmacol Exp Ther. 1978 Sep;206(3):574-85.
Iproniazid (1-isonicotinoyl-2-isopropylhydrazine), an antidepressant drug removed from clinical use because of hepatic injury, and isopropylhydrazine, a metabolite of iproniazid, were found to be potent hepatotoxins in rats. This animal model was used in studies in vivo and in vitro to define better the biochemical and chemical mechanism(s) by which iproniazid and isopropylhydrazine mediate hepatotoxicity. Phenobarbital, an inducer of a class of hepatic microsomal cytochrome P-450 enzymes, greatly potentiated the necrosis, whereas inhibitors of these microsomal enzymes such as cobalt chloride, piperonyl butoxide and alpha-naphthylisothiocyanate, prevented the necrosis. Bis-para-nitrophenyl phosphate, an inhibitor of esterase and amidase enzymes, prevented the necrosis caused by iproniazid but had no effect on the necrosis caused by isopropylhydrazine. Iproniazid and isopropylhydrazine labeled with tritium or carbon-14 in the isopropyl group were found to bind covalently to hepatic tissue macromolecules, and those pretreatments that increased hepatic necrosis significantly increased covalent binding, whereas those pretreatments which prevented necrosis significantly decreased covalent binding. Iproniazid labeled with tritium in the pyridine ring or carbon-14 in the carbonyl group did not bind significantly to hepatic tissue. Rats that were given iproniazid or isopropylhydrazine, labeled specifically with tritium and carbon-14 on the c-2 methine position of the isopropyl group, expired acetone and carbon dioxide labeled with carbon-14. More importantly, propane was expired and contained a ratio of 3H/14C that was identical to that in the administered iproniazid or isopropylhydrazine and also identical to the 3H/14C ratio of the metabolite that was covalently bound to hepatic tissue macromolecules. Experiments carried out with rat liver microsomes and isopropylhydrazine specifically labeled with deuterium, tritium and carbon-14 support the view that isopropylhydrazine is the metabolite of iproniazid that is oxidized by a microsomal P-450 enzyme to a species that alkylates tissue macromolecules. Some of the urinary metabolites excreted by rats that were administered hepatotoxic doses of iproniazid and isopropylhydrazine have been identified by cochromatography and isotope dilution with synthetic standards and by comparative mass spectra. Compounds excreted into the urine of rats dosed with iproniazid include iproniazid, iproniazid-1-oxide, isonicotinic acid, isonicotinoyl glycine, acetylisoniazid, isopropylhydrazine, 1-acetyl-2-isopropylhydrazine and acetone. Isopropylhydrazine, 1-acetyl-2-isopropylhydrazine, and acetone have been found in the urine of animals administered toxic doses of isopropylhydrazine.
异烟肼（1-异烟酰基-2-异丙基肼）是一种因肝损伤而被停止临床使用的抗抑郁药物，而异烟肼的代谢产物异丙基肼被发现是大鼠体内的强效肝毒素。该动物模型被用于体内和体外研究，以更好地确定异烟肼和异丙基肼介导肝毒性的生化和化学机制。苯巴比妥是一类肝微粒体细胞色素P-450酶的诱导剂，它能极大地增强坏死作用，而这些微粒体酶的抑制剂，如氯化钴、胡椒基丁醚和α-萘基异硫氰酸盐，则可防止坏死。磷酸双对硝基苯酯是酯酶和酰胺酶的抑制剂，它能防止异烟肼引起的坏死，但对异丙基肼引起的坏死没有影响。在异丙基上用氚或碳-14标记的异烟肼和异丙基肼被发现能与肝组织大分子共价结合，那些能显著增加肝坏死的预处理能显著增加共价结合，而那些能防止坏死的预处理则能显著降低共价结合。在吡啶环上用氚标记或在羰基上用碳-14标记的异烟肼与肝组织没有明显结合。给大鼠给予在异丙基的c-2次甲基位置上用氚和碳-14特异性标记的异烟肼或异丙基肼后，呼出的丙酮和二氧化碳带有碳-14标记。更重要的是，呼出的丙烷中3H/14C的比例与所给予的异烟肼或异丙基肼中的相同，也与共价结合到肝组织大分子上的代谢产物的3H/14C比例相同。用大鼠肝微粒体和用氘、氚和碳-14特异性标记的异丙基肼进行的实验支持了这样一种观点，即异丙基肼是异烟肼的代谢产物，它被微粒体P-450酶氧化成一种能使组织大分子烷基化的物质。通过与合成标准品共色谱分析、同位素稀释以及比较质谱，已鉴定出给予肝毒性剂量的异烟肼和异丙基肼的大鼠所排泄的一些尿液代谢产物。给予异烟肼的大鼠尿液中排泄的化合物包括异烟肼、异烟肼-1-氧化物、异烟酸、异烟酰甘氨酸、乙酰异烟肼、异丙基肼、1-乙酰-2-异丙基肼和丙酮。在给予毒性剂量异丙基肼的动物尿液中发现了异丙基肼、1-乙酰-2-异丙基肼和丙酮。
