Nakagawa Y, Moldéus P
Department of Toxicology, Tokyo Metropolitan Research Laboratory of Public Health, Japan.
Biochem Pharmacol. 1998 Jun 1;55(11):1907-14. doi: 10.1016/s0006-2952(98)00097-5.
The relationship between the metabolism and the cytotoxic effects of the alkyl esters of p-hydroxybenzoic acid (parabens) has been studied in freshly isolated rat hepatocytes. Incubation of hepatocytes with propyl-paraben (0.5 to 2.0 mM) elicited a concentration- and time-dependent cell death that was enhanced when enzymatic hydrolysis of propyl-paraben to p-hydroxybenzoic acid was inhibited by a carboxylesterase inhibitor, diazinon. The cytotoxicity was accompanied by losses of cellular ATP, total adenine nucleotide pools, and reduced glutathione, independently of lipid peroxidation and protein thiol oxidation. In the comparative toxic effects based on cell viability, ATP level, and rhodamine 123 retention, butyl- and isobutyl-parabens were more toxic than propyl- and isopropyl-parabens, and ethyl- and methyl-parabens and p-hydroxybenzoic acid were less toxic than propyl-paraben. The addition of propyl-paraben to isolated hepatic mitochondria reduced state 3 respiration with NAD+-linked substrates (pyruvate plus malate) and/or with an FAD-linked substrate (succinate plus rotenone), whereas state 3 respiration with ascorbate plus tetramethyl-p-phenylenediamine (cytochrome oxidase-linked respiration) was not affected significantly by propyl-paraben. Further, the addition of these parabens caused a concentration-dependent increase in the rate of state 4 oxygen consumption, indicating an uncoupling effect. The rate of state 3 oxygen consumption was inhibited by propyl-paraben, butyl-paraben, and their chain isomers. These results indicate that a) propyl-paraben-induced cytotoxicity is mediated by the parent compound rather than by its metabolite p-hydroxybenzoic acid; b) the toxicity is associated with ATP depletion via impairment of mitochondrial function related to membrane potential and/or oxidative phosphorylation; and c) the toxic potency of parabens to hepatocytes or mitochondria depends on the relative elongation of alkyl side-chains esterified to the carboxyl group of p-hydroxybenzoic acid.
对羟基苯甲酸烷基酯（对羟基苯甲酸酯）的代谢与细胞毒性作用之间的关系已在新鲜分离的大鼠肝细胞中进行了研究。用对羟基苯甲酸丙酯（0.5至2.0 mM）孵育肝细胞会引发浓度和时间依赖性的细胞死亡，当对羟基苯甲酸丙酯通过羧酸酯酶抑制剂二嗪农抑制其酶促水解为对羟基苯甲酸时，这种细胞死亡会增强。细胞毒性伴随着细胞ATP、总腺嘌呤核苷酸池和还原型谷胱甘肽的损失，与脂质过氧化和蛋白质硫醇氧化无关。在基于细胞活力、ATP水平和罗丹明123保留的比较毒性作用中，对羟基苯甲酸丁酯和异丁酯比丙酯和异丙酯毒性更大，而对羟基苯甲酸乙酯、甲酯和对羟基苯甲酸的毒性比丙酯小。向分离的肝线粒体中添加对羟基苯甲酸丙酯会降低与NAD+相关底物（丙酮酸加苹果酸）和/或与FAD相关底物（琥珀酸加鱼藤酮）的状态3呼吸，而对羟基苯甲酸丙酯对对羟基苯甲酸丙酯加四甲基对苯二胺（细胞色素氧化酶相关呼吸）的状态3呼吸没有显著影响。此外，添加这些对羟基苯甲酸酯会导致状态4耗氧率呈浓度依赖性增加，表明存在解偶联效应。对羟基苯甲酸丙酯、丁酯及其链异构体抑制状态3耗氧率。这些结果表明：a）对羟基苯甲酸丙酯诱导的细胞毒性是由母体化合物介导的，而不是由其代谢产物对羟基苯甲酸介导的；b）毒性与通过与膜电位和/或氧化磷酸化相关的线粒体功能受损导致的ATP耗竭有关；c）对羟基苯甲酸酯对肝细胞或线粒体的毒性效力取决于酯化到对羟基苯甲酸羧基上的烷基侧链的相对长度。
