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

癌症化学预防在预防医学中占有重要地位。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，这些抗氧化剂被认为是有前途的化学预防剂。然而，最近的一项流行病学研究显示，男性吸烟者服用β-胡萝卜素会增加肺癌的发病率。在本研究中，为了建立抗氧化剂安全性评价方法，我们使用人类培养细胞和从人类c-Ha-ras原癌基因和p16和p53肿瘤抑制基因中获得的^<32> p标记DNA片段检测抗氧化剂诱导的DNA损伤。我们发现β-胡萝卜素代谢物视黄醇和视网膜在Cu（II）存在下通过产生活性氧诱导DNA损伤。在人类培养的细胞中，这些代谢物导致DNA分裂，并在低浓度下显著增加8-氧-7,8-二氢-2'-脱氧鸟苷（8-oxodG）的形成。8-氧-7,8-二氢-2'-脱氧鸟苷是鸟嘌呤的氧化产物。维生素E （α-生育酚）和n -乙酰半胱氨酸也能引起DNA氧化损伤。在所测试的黄酮类化合物中，槲皮素引起培养细胞的DNA氧化损伤，而木犀草素则没有。异硫氰酸酯还通过形成硫醇化合物引起DNA氧化损伤。异硫氰酸烯丙酯对DNA的损伤强于异硫氰酸苄酯和异硫氰酸苯乙酯。这些发现表明，抗氧化剂可以作为氧化剂，能够通过氧化DNA损伤引起致癌。本研究为开发一种基于dna损伤能力来评估化学预防剂安全性的敏感方法提供了见解。

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.