Kohl C, Gescher A
Medical Research Council Toxicology Unit, University of Leicester, UK.
Chem Biol Interact. 1996 Jan 5;99(1-3):219-26. doi: 10.1016/0009-2797(95)03671-7.
2-Nitropropane (2-NP) is a genotoxicant and hepatocarcinogen in rodents. Conversion to propane 2-nitronate (P2N), the anion of the tautomeric aci form of 2-NP, seems to be a pivotal part of the mechanism by which 2-NP causes its toxicity. We tested the hypothesis that the tautomeric equilibrium is influenced by enzymes in the liver, the target organ of 2-NP toxicity. Rat or mouse hepatocytes were incubated with 2-NP, P2N or the 2-NP isotopomer 2-deutero 2-nitropropane (2H-2-NP), which equilibrates with P2N much more slowly than 2-NP. Tautomers were analyzed by HPLC. The rates of conversion of 2-NP to P2N expressed as nmol P2N x (10(6) cells/ml)-1 x min-1 were 4.0 and 4.2 in the presence of hepatocytes from rats or mice, respectively, and 2.6 in the absence of cells. Production of 2-NP to P2N expressed as nmol 2-NP x (10(6) cells/ml)-1 x min-1 was increased from 6.1 in the absence of cells to 11.9 or 9.9 in the presence of hepatocytes from rats or mice, respectively. The rate of formation of P2N from 2H-2-NP as compared to 2-NP was characterised by a primary isotope effect of 3.4 and 3.8 in hepatocytes from rats and mice, respectively, contrasting with a value of 9.6 measured in medium omitting cells. When 2-NP was incubated with subfractions of rodent or human liver homogenate, production of P2N by cytosol was between 7.3 (mouse liver) and 28.1 times (human liver) higher than that observed in microsomes. Similarly generation of 2-NP from P2N by cytosol exceeded that in microsomes by a factor of two. Tautomerism in heat-activated cytosol, mitochondria or microsomes was not different from that in buffer only. The results suggest that the nitro-aci tautomerism of secondary nitroalkanes is catalysed by a hepatic enzyme which resides predominantly in the cytosol and may thus contribute to the generation of the toxic species via which 2-NP exerts its toxicity.
2-硝基丙烷（2-NP）是一种在啮齿动物中具有基因毒性和肝致癌性的物质。转化为丙烷2-硝基酸盐（P2N），即2-NP互变异构酸式的阴离子，似乎是2-NP产生毒性机制的关键部分。我们检验了互变异构平衡受2-NP毒性的靶器官肝脏中的酶影响这一假设。将大鼠或小鼠肝细胞与2-NP、P2N或2-NP同位素异构体2-氘代2-硝基丙烷（2H-2-NP）一起孵育，2H-2-NP与P2N达到平衡的速度比2-NP慢得多。通过高效液相色谱法分析互变异构体。以nmol P2N x（10⁶个细胞/ml）⁻¹ x min⁻¹表示的2-NP向P2N的转化速率，在存在大鼠或小鼠肝细胞时分别为4.0和4.2，在无细胞时为2.6。以nmol 2-NP x（10⁶个细胞/ml）⁻¹ x min⁻¹表示的2-NP生成P2N的量，从无细胞时的6.1增加到存在大鼠或小鼠肝细胞时的11.9或9.9。与2-NP相比，2H-2-NP生成P2N的速率在大鼠和小鼠肝细胞中的一级同位素效应分别为3.4和3.8，这与在无细胞培养基中测得的9.6的值形成对比。当2-NP与啮齿动物或人类肝脏匀浆的亚组分一起孵育时，胞质溶胶产生P2N的量比微粒体中观察到的高7.3倍（小鼠肝脏）至28.1倍（人类肝脏）。同样，胞质溶胶从P2N生成2-NP的量比微粒体中的高出两倍。热激活的胞质溶胶、线粒体或微粒体中的互变异构现象与仅在缓冲液中的情况没有差异。结果表明，仲硝基烷的硝基-酸式互变异构由一种主要存在于胞质溶胶中的肝脏酶催化，因此可能有助于生成2-NP发挥其毒性作用的有毒物质。
