Experimental study of oxidative DNA damage

Animal experiments allow the study of oxidative DNA damage in target organs and the elucidation of dose-response relationships of carcinogenic and oth er harmful chemicals and conditions as well as the study of interactions of several factors. So far the effects of more than 50 different chemical com pounds have been studied in animal experiments mainly in rats and mice, and generally with measurement of 8-oxodG with HPLC-EC. A large number of well -known carcinogens induce 8-oxodG formation in liver and/or kidneys. Moreov er several animal studies have shown a close relationship between induction of dative DNA damage and tumour formation. In principle the level of oxidative DNA damage in an organ or cell may be s tudied by measurement of modified bases in extracted DNA by immunohistochem ical visualisation, and from assays of strand breakage before and after tre atment with repair enzymes. However, this level is a balance between the ra tes of damage and repair. Until the repair rates and capacity can be adequa tely assessed the rate of damage can only be estimated from the urinary exc retion of repair products albeit only as an average of the entire body. A number of model compounds have been used to induce oxidative DNA damage i n experimental animals. The hepatocarcinogen 2-nitropropane induces up to 1 0-fold increases in 8-oxodG levels in rat liver DNA. The level of 8-oxodG i s also increased in kidneys and bone marrow but not in the testis. By means of 2-nitropropane we have shown correspondence between the increases in 8- oxodG in target organs and the urinary excretion of 8-oxodG and between 8-o xodG formation and the comet assay in bone marrow as well potent preventive effects of extracts of Brussels sprouts. Others have shown similar effects of green tea extracts and its components. Drawbacks of the use of 2-nitrop ropane as a model for oxidative DNA damage relate particularly to formation of 8-aminoguanine derivatives that may interfere with HPLC-EC assays and h ave unknown consequences. Other model compounds for induction of oxidative DNA damage, such as ferric nitriloacetate, iron dextran, potassium bromate and paraquat, are less potent and/or more organ specific. Inflammation and activation of an inflammatory response by phorbol esters o r E. coli lipopolysaccharide (LPS) induce oxidative DNA damage in many targ et cells and enhance benzene-induced DNA damage in mouse bone marrow. Experimental studies provide powerful tools to investigate agents inducing and preventing oxidative damage to DNA and its role in carcinogenesis. So f ar, most animal experiments have concerned 8-oxodG and determination of add itional damaged bases should be employed. An ideal animal model for prevent ion of oxidative DNA damage has yet to he developed.