The method of safety evaluation of chemopreventive agents based on the ability of damaging human genes

癌症的化学预防在预防医学中非常重要。人们已经尝试使用抗氧化剂进行癌症化学预防，如维生素和类黄酮类，这些被认为是很有前途的化学预防药物。然而，最近的一项流行病学研究显示，男性吸烟者服用β-胡萝卜素会导致肺癌发病率增加。在这项研究中，为了建立抗氧化剂安全性评估的方法，我们使用人类培养细胞和从人c-Ha-ras原癌基因以及p16和p53抑癌基因获得的标记DNA片段来检测抗氧化剂对DNA的损伤。我们发现，β-胡萝卜素的代谢物视黄醇和视网膜，在铜(II)存在的情况下，通过产生活性氧物种而诱导DNA损伤。在人类培养细胞中，这些代谢物在低浓度时引起DNA裂解，并显著增加鸟嘌呤氧化产物8-氧-7，8-二氢-2‘-脱氧鸟苷(8-oxodG)的形成。维生素E(α-生育酚)和N-乙酰半胱氨酸也能引起氧化dna损伤。在所测试的黄酮类化合物中，槲皮素会引起培养细胞的DNA氧化损伤，而木犀草素则不会。异硫氰酸酯还通过形成硫醇化合物造成DNA氧化损伤。异硫氰酸烯丙酯对DNA的损伤作用强于异硫氰酸苄酯和异硫氰酸苯乙酯。这些发现表明，抗氧化剂可以作为替代品，能够通过氧化DNA损伤导致癌症发生。本研究提供了一种根据化学预防药物的DNA损伤能力来评估其安全性的灵敏方法的发展。

Cancer chemoprevention is very important in preventive medicine. Attempts have been made for cancer chemoprevention using antioxidants, such as vitamins and flavonoids, which have been believed to be promising chemopreventive agents. However, a recent epidemiological study revealed that the administration of β-carotene to male smokers caused an increase in the incidence of lung cancer. In this study, to develop the method for safety evaluation of antioxidants, we examined DNA damage induced by antioxidants using human cultured cells and ^<32>P-labeled DNA fragments obtained from the human c-Ha-ras protooncogene and the p16 and p53 tumor suppressor genes. We found that β-carotene metabolites, retinol and retinal, induced DNA damage by generating reactive oxygen species in the presence of Cu(II). In human cultured cells, these metabolites caused DNA cleavage and a significant increase in the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an oxidative product of guanine, at low concentrations. Vitamin E (α-tocopherol) and N-acetylcysteine were also capable of causing oxidative DNA damage. Among the flavonoids tested, quercetin caused oxidative DNA damage in cultured cells, whereas luteolin did not. Isothiocyanates also caused oxidative DNA damage through the formation of thiol compounds. Allyl isothiocyanate caused stronger DNA damage than benzyl isothiocyanate and phenethyl isothiocyanate. These finding indicate that antioxidants can serve as proxidants, capable of causing carcinogenesis via oxidative DNA damage. The present study provided insight into the development of a sensitive method to evaluate the safety of chemopreventive agents on the basis of their DNA-damaging ability.