Recently, an increase in free radicals in the blood from persons undergoing HBO exposure was directly demonstrated by low temperature electron spin resonance. Using the comet assay in conjunction with an enzyme specific for oxidized DNA bases, we can now provide evidence for the induction of oxidative DNA base damage by HBO.The FPG protein removes oxoguanine, the imidazole ringopened purines, diaminohydroxyformamidopyrimidine as well as small amounts of oxoadenine. The resulting abasic sites are converted into DNA singlestrand breaks by the associated endonuclease activity and can be quantified by the comet assay. Furthermore, it has been suggested that oxoguanine is directly involved in the process of carcinogenesis. However, a review of the present literature did not support a cancercausing or growth enhancing effect by HBO. As well as an involvement in cancer, damage induced by oxygenderived species also seems to be important for other kinds of disease such as neurodegenerative disease, chronic inflammatory disease and cardiovascular disease. Therefore, the observed genotoxic effect of HBO treatment should be taken seriously.Although our results indicate rapid repair of the induced DNA damage and an adaptive reaction of the human body, the intial DNA damage of an HBO therapy should be avoided.Our study indicates the first directions for an improved treatment protocol.A simple and effective way to avoid a genotoxic effect is a stepwise increased treatment time which obviously enables the human body to intensify the antioxidant defences.An increase in antioxidant defences after oxidative stress has already been suggested, and the possible mechanisms are under investigation.For example in rats exposed to HBO treatment, an increase in the content of reduced glutathione in lung tissue was observed and interpreted as an adaptive process to protect the lung from oxidative stress. Taken together, our study provides evidence for a genotoxic effect of HBO therapy due to oxidative DNA damage.Biochemistry. Mutagenesis. . Received on June; accepted on August I, DNA damage detection after HBO therapy Dowlnoadedfromhttps: academi. coupco. mm tu age a rti l ce bygueston Sepetmber The antioxidant effects of pretreatment with flavonoids and vitamin C, at standardized concentrations, on oxygen radicalgenerated DNA damage from hydrogen peroxide in human lymphocytes were examined by using the singlecell gel electrophoresis assay. Pretreatment with all flavonoids and vitamin C produced dosedependent reductions in oxidative DNA damage.At a concentration of mmolL, they were ranked in decreasing order of potency as follows: luteolin, quercitrin, rutin. Flavonoids are polyphenolic compounds whose main dietary sources are fruit and vegetables and whose consumption has been linked to protection against heart disease and cancers. Flavonoids were initially considered to be substances without any nutritive value for humans.A study with ultravioletinduced oxidation of LDL showed that rutin, a polyphenolic flavonoid, vitamin C, and vitamin E were able to inhibit the peroxidation of LDL and its subsequent cytotoxicity.Quercetin prevents oxidation of LDL by macrophages in vitro by reducing the formation of free radicals and dietary intake of quercetin estimated from dietary records is inversely related to ischemic heart disease mortality. Several more recent studies using different assays have confirmed that quercetin is a strong antioxidant and that most flavonoids show antioxidant activity is a sensitive and rapid method for the detection of DNA damage at the individual cell level.