Rosner J L, Storz G
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892.
Antimicrob Agents Chemother. 1994 Aug;38(8):1829-33. doi: 10.1128/AAC.38.8.1829.
Escherichia coli strains were previously found to be susceptible to the antituberculosis drug isonicotinic acid hydrazide (isoniazid [INH]) when they carried certain mutations that also sensitize them to peroxides: a deletion in oxyR, a redox-sensitive regulator of hydrogen peroxide-inducible genes, or mutations in both katG and ahpCF, OxyR-regulated genes encoding hydroperoxidase I, and an alkyl hydroperoxide reductase. To test whether INH, like peroxides, activates OxyR, the effect of INH on OxyR regulation was examined. Primer extension assays showed that transcription of the OxyR-regulated oxyS gene was not significantly induced by INH in wild-type cells, indicating that INH does not activate OxyR. However, the INH-susceptible katG ahpCF mutant strain was found to have constitutively high levels of oxyS transcription. This suggested that the lack of peroxidase expression in these strains allows endogenous oxidants to accumulate, and this leads not only to constitutive OxyR activation but also to INH susceptibility. Consistent with this concept, hydrogen peroxide or cumene hydroperoxide potentiated the INH susceptibilities of wild-type cells, while the antioxidant ascorbic acid protected the susceptible katG ahpCF mutant strain from INH. Superoxide radicals, generated by paraquat, did not enhance the INH susceptibilities of wild-type cells. Hydrogen peroxide also potentiated the INH susceptibilities of susceptible and resistant (katG mutant) Mycobacterium smegmatis strains. Our results suggest that INH is converted to a more active drug by reaction with peroxides and that the INH susceptibilities of enterobacteria and mycobacteria are mechanistically related.
先前发现，当大肠杆菌菌株携带某些使其对过氧化物敏感的突变时，它们对抗结核药物异烟肼（INH）敏感：oxyR缺失，oxyR是一种对氧化还原敏感的过氧化氢诱导基因的调节因子；或者katG和ahpCF发生突变，katG和ahpCF是由OxyR调节的基因，分别编码过氧化氢酶I和烷基过氧化氢还原酶。为了测试INH是否像过氧化物一样激活OxyR，研究了INH对OxyR调节的影响。引物延伸试验表明，在野生型细胞中，INH不会显著诱导OxyR调节的oxyS基因转录，这表明INH不会激活OxyR。然而，发现对INH敏感的katG ahpCF突变株具有组成性高水平的oxyS转录。这表明这些菌株中过氧化物酶表达的缺乏使得内源性氧化剂积累，这不仅导致OxyR的组成性激活，还导致对INH敏感。与这一概念一致，过氧化氢或异丙苯过氧化氢增强了野生型细胞对INH的敏感性，而抗氧化剂抗坏血酸则保护敏感的katG ahpCF突变株免受INH的影响。百草枯产生的超氧自由基不会增强野生型细胞对INH的敏感性。过氧化氢也增强了敏感和耐药（katG突变）耻垢分枝杆菌菌株对INH的敏感性。我们的结果表明，INH通过与过氧化物反应转化为更具活性的药物，并且肠杆菌和分枝杆菌对INH的敏感性在机制上是相关的。
