Freyberger A, Degen G H
Bayer AG, PH PDT Research Toxicology, Wuppertal, Germany.
Arch Toxicol. 1998 Oct;72(10):637-44. doi: 10.1007/s002040050554.
Chronic administration of o-phenylphenol (OPP) is known to induce urinary bladder tumours in the Fischer rat. The underlying toxic mechanism is poorly understood. Recently, arachidonic acid (ARA)-dependent, prostaglandin-H-synthase (PHS)-catalysed metabolic activation of the OPP metabolite phenylhydroquinone (PHQ) to a genotoxic species was suggested to be involved in OPP toxicity. To investigate this hypothesis in more detail, we have studied the effects of OPP and its metabolites on PHS. When microsomal PHS from ovine seminal vesicles (OSV) was used as enzyme source, both OPP, PHQ, and 2-phenyl-1,4-benzoquinone (PBQ) inhibited PHS-cyclooxygenase. The inhibitory potency was inversely related to the ARA concentration in the assay; at 7 microM ARA IC50-values were: 13 microM (OPP), 17 microM (PHQ), and 190 microM (PBQ). In cells cultured from OSV, which express high PHS activity, 40 microM OPP almost completely suppressed prostaglandin formation. Studies with microsomal PHS demonstrated that PHQ was an excellent substrate for PHS-peroxidase; both ARA and hydrogen peroxide supported oxidation to PBQ. OPP was only a poor substrate for PHS, but inhibited the ARA-mediated and to a lesser extent also the hydrogen peroxide-mediated in vitro oxidation of PHQ. Moreover, PHQ at up to moderately cytotoxic concentrations (50 microM) did not induce micronuclei in OSV cell cultures. Taken together, our findings do not provide evidence for an ARA-dependent, PHS-catalysed formation of genotoxic species from PHQ. Moreover, it seems to be questionable whether such activation can effectively occur in vivo, since OPP and PHQ turned out to be efficient cyclooxygenase inhibitors, and high levels of OPP and PHQ were found at least in the urine of OPP-treated rats. On the other hand, inhibition of the formation of cytoprotective prostaglandins in the urogenital tract may play a crucial role in OPP-induced bladder carcinogenesis.
已知长期给予邻苯基苯酚（OPP）可在Fischer大鼠中诱发膀胱肿瘤。其潜在的毒性机制尚不清楚。最近，有人提出花生四烯酸（ARA）依赖性、前列腺素-H-合酶（PHS）催化的OPP代谢物苯基氢醌（PHQ）代谢活化生成基因毒性物质与OPP毒性有关。为了更详细地研究这一假设，我们研究了OPP及其代谢物对PHS的影响。当使用来自绵羊精囊（OSV）的微粒体PHS作为酶源时，OPP、PHQ和2-苯基-1,4-苯醌（PBQ）均抑制PHS-环氧化酶。抑制效力与测定中的ARA浓度呈负相关；在7 microM ARA时，IC50值分别为：13 microM（OPP）、17 microM（PHQ）和190 microM（PBQ）。在从OSV培养的细胞中，这些细胞表达高PHS活性，40 microM OPP几乎完全抑制前列腺素的形成。对微粒体PHS的研究表明，PHQ是PHS-过氧化物酶的优良底物；ARA和过氧化氢均支持其氧化为PBQ。OPP只是PHS的不良底物，但抑制了ARA介导的以及在较小程度上过氧化氢介导的PHQ体外氧化。此外，高达中度细胞毒性浓度（50 microM）的PHQ在OSV细胞培养物中未诱导微核形成。综上所述，我们的研究结果并未提供证据支持由ARA依赖性、PHS催化的从PHQ生成基因毒性物质。此外，这种活化是否能在体内有效发生似乎也值得怀疑，因为OPP和PHQ被证明是有效的环氧化酶抑制剂，并且至少在OPP处理的大鼠尿液中发现了高水平的OPP和PHQ。另一方面，抑制泌尿生殖道中细胞保护性前列腺素的形成可能在OPP诱导的膀胱癌发生中起关键作用。
