Methylreductic acid and hydroxymethylreductic acid: oxygen radical-forming agents in heated starch

What causes human cancer? Approaches from the chemistry of DNA damage

To prevent human cancers, environmental mutagens must be identified. A common mechanism of carcinogenesis is DNA damage, and thus it is quite possible that environmental mutagens can be trapped as adducts by DNA components. It is also important to identify new types of DNA damaging reactions and clarify their mechanisms. In this paper, I will provide typical examples of our efforts to identify DNA damage by environmental agents, from chemistry-based studies. 1) Oxidative DNA damage: 8-Hydroxydeoxyguanosine (8-OHdG, 8-oxodG) was discovered during a structural study of DNA modifications caused in vitro by heating glucose, which was used as a model of cooked foods. We found that various oxygen radical-forming agents induced the formation of 8-OHdG in DNA, in vitro and in vivo. Analyses of the urinary 8-OHdG levels are useful to assess the extent of oxidative DNA damage in a human population. 2) Lipid peroxide-derived DNA adducts: We searched for mutagens that react with deoxynucleosides, in model systems of lipid peroxidation. The reaction mixtures were analyzed by high performance liquid chromatography (HPLC), and we discovered various lipid peroxide-derived mutagens, including new mutagens. Some of these adducts were detected in human DNA. These mutagens may be involved in lipid peroxide-related cancers. 3) Methylation of cytosine by free radicals: Methylation of the cytosine C-5 position is an important mechanism of carcinogenesis, in addition to gene mutations. However, the actual mechanisms of de novo methylation in relation to environmental agents are not clear. We found that cytosine C-5 methylation occurred by a free radical mechanism. The possible role of this radical-induced DNA methylation in carcinogenesis will be discussed, in relation to the presently accepted concept of cancer epigenetics. In these studies, chemical analyses of the adducts formed in model reactions led to the discoveries of new mutagens and important types of DNA modifications, which seem to be involved in human carcinogenesis.

8-Hydroxyguanine: From its discovery in 1983 to the present status

8-Hydroxyguanine (8-OH-G) was discovered in 1983 in our laboratory at the National Cancer Center Research Institute, Tokyo. Since it could be formed in DNA not only in vitro but also in vivo by oxygen radical forming agents, we immediately hypothesized the importance of this discovery in connection with its biological consequence. Further intensive efforts by us from 1983 to 1990 confirmed that 8-OH-G is a highly significant oxidated DNA lesion involved in mutation and/or carcinogenesis in mammals, including humans. With the subsequent entry of many investigators to this research field the number of publications on 8-OH-G increased exponentially, reaching more than several thousands by the end of 2005. In this article, a summary is given of the important works carried out in the early days, and further notable contributions by many investigators are reviewed, focusing on 8-OH-G in the mammalian system. A special emphasis is given to research on knockout mice that are deficient in genes involved in the repair systems of the 8-OH-G lesion. Lastly, our own recent work is summarized involving a one-year carcinogenesis study of Ogg1 (the gene for 8-OH-G specific glycosylase/AP lyase) knockout mice that have been exposed to oxidative stress.

Analysis of a form of oxidative DNA damage, 8-hydroxy-2'-deoxyguanosine, as a marker of cellular oxidative stress during carcinogenesis

8-hydroxy-2'-deoxyguanosine (8-OH-dG) was first reported in 1984 as a major form of oxidative DNA damage product by heated sugar, Fenton-type reagents and X-irradiation in vitro. 8-OH-dG has been detected in cellular DNA using an HPLC-ECD method in many laboratories. Analyses of 8-OH-dG in animal organ DNA after the administration of oxygen radical-forming chemicals will be useful for assessments of their carcinogenic risk. Its analysis in human leucocyte DNA and in urine is a new approach to the assessment of an individual's cancer risk due to oxidative stress. The increase of the 8-OH-dG level in the cellular DNA, detected by HPLC-ECD method, was supported by its immunochemical detection and its enhanced repair activity. The validity of the general use of 8-OH-dG as a marker of cellular oxidative stress is discussed.