Castro Frederico Augusto Vieira, Mariani Diana, Panek Anita Dolly, Eleutherio Elis Cristina Araújo, Pereira Marcos Dias
Departamento de Bioquímica, Laboratório de Investigação de Fatores de Estresse, Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil.
PLoS One. 2008;3(12):e3999. doi: 10.1371/journal.pone.0003999. Epub 2008 Dec 22.
Quinones are compounds extensively used in studies of oxidative stress due to their role in plants as chemicals for defense. These compounds are of great interest for pharmacologists and scientists, in general, because several cancer chemotherapeutic agents contain the quinone nucleus. However, due to differences in structures and diverse pharmacological effects, the exact toxicity mechanisms exerted by quinones are far from elucidatation.
METHODOLOGY/PRINCIPAL FINDINGS: Using Saccharomyces cerevisiae, we evaluated the main mechanisms of toxicity of two naphthoquinones, menadione and plumbagin, by determining tolerance and oxidative stress biomarkers such as GSH and GSSG, lipid peroxidation levels, as well as aconitase activity. The importance of glutathione transferases (GST) in quinone detoxification was also addressed. The GSSG/GSH ratio showed that menadione seemed to exert its toxicity mainly through the generation of ROS while plumbagin acted as an electrophile reacting with GSH. However, the results showed that, even by different pathways, both drugs were capable of generating oxidative stress through their toxic effects. Our results showed that the control strain, BY4741, and the glutathione transferase deficient strains (gtt1Delta and gtt2Delta) were sensitive to both compounds. With respect to the role of GST isoforms in cellular protection against quinone toxicity, we observed that the Gtt2 deficient strain was unable to overcome lipid peroxidation, even after a plumbagin pre-treatment, indicating that this treatment did not improve tolerance when compared with the wild type strain. Cross-tolerance experiments confirmed distinct cytotoxicity mechanisms for these naphthoquinones since only a pre-treatment with menadione was able to induce acquisition of tolerance against stress with plumbagin.
CONCLUSIONS/SIGNIFICANCE: These results suggest different responses to menadione and plumbagin which could be due to the fact that these compounds use different mechanisms to exert their toxicity. In addition, the Gtt2 isoform seemed to act as a general protective factor involved in quinone detoxification.
醌类化合物因其在植物中作为防御化学物质的作用而广泛应用于氧化应激研究。总体而言，这些化合物引起了药理学家和科学家的极大兴趣，因为几种癌症化疗药物都含有醌核。然而，由于结构差异和多种药理作用，醌类化合物的确切毒性机制仍远未阐明。
方法/主要发现：我们使用酿酒酵母，通过测定耐受性和氧化应激生物标志物，如谷胱甘肽（GSH）和氧化型谷胱甘肽（GSSG）、脂质过氧化水平以及乌头酸酶活性，评估了两种萘醌（甲萘醌和白花丹素）的主要毒性机制。还探讨了谷胱甘肽转移酶（GST）在醌解毒中的重要性。GSSG/GSH 比值表明，甲萘醌似乎主要通过活性氧（ROS）的产生发挥其毒性，而白花丹素作为亲电试剂与 GSH 反应。然而，结果表明，即使通过不同途径，两种药物都能够通过其毒性作用产生氧化应激。我们的结果表明，对照菌株 BY4741 和谷胱甘肽转移酶缺陷菌株（gtt1Δ 和 gtt2Δ）对这两种化合物均敏感。关于 GST 同工型在细胞保护免受醌毒性方面的作用，我们观察到，即使经过白花丹素预处理，gtt2 缺陷菌株仍无法克服脂质过氧化，这表明与野生型菌株相比，这种处理并未提高耐受性。交叉耐受性实验证实了这些萘醌具有不同的细胞毒性机制，因为只有用甲萘醌预处理才能诱导获得对白花丹素应激的耐受性。
结论/意义：这些结果表明对甲萘醌和白花丹素存在不同反应，这可能是由于这些化合物使用不同机制发挥其毒性。此外，Gtt2 同工型似乎作为参与醌解毒的一般保护因子发挥作用。
