Urinary 8-hydroxyguanine may be a better marker of oxidative stress than 8-hydroxydeoxyguanosine in relation to the life spans of various species.

Oxidative DNA damage is believed to be involved in the aging process. Species with shorter potential life spans generally have a higher specific metabolic rate (SMR), and would be expected to have increased levels of oxidative stress and DNA damage, as compared to long-lived species. An automatized HPLC method based on electrochemical detection was used to measure the levels of the oxidative DNA damage markers 8-hydroxydeoxyguanosine (8-OH-dG) and 8-hydroxyguanine (8-OH-Gua) in urinary samples from mammals with various potential life spans (mice, rats, guinea pigs, cats, chimpanzees, and humans). There was no significant linear correlation (r = -0.71, p = 0.11) between the species' potential life spans (log transformed) and the urinary levels of 8-OH-dG as normalized to creatinine (8-OH-dG/creatinine), although the species with longer life spans, such as chimpanzee and human, had among the lowest levels detected. In contrast, the negative linear correlation between the species' potential life span (log transformed) and the urinary levels of 8-OH-Gua as normalized to creatinine (8-OH-Gua/creatinine), was significant (r = -0.97, p = 0.002). In addition, there was a positive linear and significant correlation between SMR and 8-OH-dG/creatinine (r = 0.91, p = 0.01) or 8- OH-Gua/creatinine (r = 0.90, p = 0.01). These results suggest that 8-OH-Gua, rather than 8-OH-dG, may be a more general marker for oxidative damage.

Identification of 4-oxo-2-hexenal and other direct mutagens formed in model lipid peroxidation reactions as dGuo adducts.

We searched for mutagens that react with 2'-deoxyguanosine (dGuo) in model systems of lipid peroxidation. To autoxidation systems of methyl linoleate (model of omega-6 fat), methyl alpha-linolenate (MLN) (model of omega-3 fat), and commercial salad oil, dGuo was added. The reaction mixtures were analyzed by HPLC. Six adducts were detected, and their structures were determined by 1H and 13C NMR, UV, and mass spectra and by comparison with synthetic authentic samples. The mutagens that reacted with dGuo to form these adducts were proposed as glyoxal, glyoxylic acid, ethylglyoxal, and 4-oxo-2-hexenal (4-OHE). The formation of 8-hydroxy-dGuo, an oxidized product of dGuo, was also detected in the model reaction mixtures. Among them, glyoxal and glyoxylic acid are known mutagens, while ethylglyoxal and 4-OHE, produced from MLN, have not been reported as mutagens thus far. We confirmed the mutagenic activity of 4-OHE with Salmonella strains, TA100 and TA104, without S9 mix. These compounds may be involved in lipid peroxide-related cancers.

4-oxo-2-hexenal, a mutagen formed by omega-3 fat peroxidation, causes DNA adduct formation in mouse organs.

To identify mutagens formed in a model reaction of lipid peroxidation, linolenic acid methyl ester and hemin were reacted with dG. As a result, a 4-oxo-2-hexenal-dG adduct (dG*) was identified in the model reaction mixture. The 4-oxo-2-hexenal (4-OHE) showed mutagenic activity in the Salmonella typhimurium strains TA100 and TA104. After 4-OHE was orally administered to mice, dG, 4-OHE-dC- and 4-OHE-5-methyl-dC adducts were detected in esophageal, stomach and intestinal DNA. In the vapor phase released from the methyl linolenate-hemin model system, and in the smoke released during the broiling of fish, 4-OHE was detected by GCMS. The 4-OHE seems to be produced by the auto-oxidation of omega-3 polyunsaturated fatty acids. These results provide a warning to workers dealing with omega-3 fats, who may be exposed to this volatile mutagen.