Gatehouse D, Wedd D J
Carcinogenesis. 1984 Mar;5(3):391-7. doi: 10.1093/carcin/5.3.391.
The anti-tuberculostatic drug, isoniazid (INH) was evaluated for its mutagenic potential using Salmonella plate tests and fluctuation assays with various strains of bacteria, and different metabolic activation systems. In the Salmonella plate test INH proved to be a weak directly-acting base-substitution mutagen which was detoxified by S9-mix. S. typhimurium TA 1530 and TA 1535 were the sensitive strains, and this result confirmed some of the published data. In the present studies mutagenic activity was further diminished in the presence of larger concentrations of rat liver S9-mix. Furthermore, the reduction in mutagenic activity was observed with S9-mix derived from untreated, Aroclor 1254-treated or phenobarbitone/beta-naphthoflavone treated rats. In direct contrast, using the microtitre fluctuation assay, the mutagenic activity of INH was elevated in the presence of rat liver S9-mix, and continued to increase with increasing S9-concentration. This result was obtained irrespective of the S9-source. S. typhimurium strains TA 1530, TA 1535 and his G46, and E. coli strains TA 85, TA 86 and WP2 uvrA were all sensitive to the mutagenicity of INH after metabolic activation. The primary step in the metabolic activation of INH in the fluctuation test was mediated by a cytosolic enzyme, and the activity of dapsone as a competitive substrate implicated the involvement of an N-acetyl transferase. The rapid diffusion of the cytosolic enzyme into the basal agar layer, or the non-specific binding of the enzyme (or the active mutagenic INH metabolite) to components of the agar, may explain the contradictory data obtained in the Salmonella plate test. The modifying effects of agar on the distribution of drug metabolising enzymes within liver S9 fractions should be carefully considered when evaluating data from Salmonella plate tests.
使用沙门氏菌平板试验和波动试验，在不同菌株的细菌以及不同的代谢激活系统中，对抗结核抑菌药物异烟肼（INH）的致突变潜力进行了评估。在沙门氏菌平板试验中，INH被证明是一种弱的直接作用碱基置换诱变剂，可被S9混合物解毒。鼠伤寒沙门氏菌TA 1530和TA 1535是敏感菌株，这一结果证实了一些已发表的数据。在本研究中，当存在更高浓度的大鼠肝脏S9混合物时，诱变活性进一步降低。此外，从未经处理、经多氯联苯混合物1254处理或经苯巴比妥/β-萘黄酮处理的大鼠获得的S9混合物都观察到诱变活性降低。与之形成直接对比的是，使用微量滴定波动试验时，在大鼠肝脏S9混合物存在的情况下，INH的诱变活性升高，并且随着S9浓度的增加持续升高。无论S9来源如何，均获得了这一结果。鼠伤寒沙门氏菌菌株TA 1530、TA 1535和his G46，以及大肠杆菌菌株TA 85、TA 86和WP2 uvrA在代谢激活后均对INH的诱变性敏感。波动试验中INH代谢激活的第一步由一种胞质酶介导，氨苯砜作为竞争性底物的活性表明涉及一种N-乙酰转移酶。胞质酶快速扩散到基础琼脂层中，或者该酶（或活性诱变INH代谢物）与琼脂成分的非特异性结合，可能解释了在沙门氏菌平板试验中获得的矛盾数据。在评估沙门氏菌平板试验数据时，应仔细考虑琼脂对肝脏S9组分中药物代谢酶分布的修饰作用。
