Effects of epigallocatechin gallate, vitamin C and vitamin E on the formation of 1,N2-propanodeoxyguanosine derived from lipid peroxidation

3134 α, β-Unsaturated aldehydes (enals) released from oxidation of polyunsaturated fatty acids (PUFAs) can modify deoxyguanosine (dG) forming 1,N2-propanodeoxyguanosine adducts. The 1,N2-propanodeoxyguanosine adducts of acrolein (Acr), crotonaldehyde and 4-hydroxynonenal have been detected in tissues of rodents and humans as background DNA lesions. In this study, we examined the effects of antioxidants known to inhibit the fatty acid oxidation and/or scavenge electrophilic aldehydes on the formation of Acr-derived 1,N2-propanodeoxyguanosine (Acr-dG) from docosahexaenoic acid (DHA) under oxidative conditions as a major source of Acr. To compare with Acr-dG, we also measured 8-oxodeoxyguanosine (8-oxodG) as a marker of oxidative damage induced by reactive oxygen species. The antioxidants included in this study are epigallocatechin gallate (EGCG), vitamin E and vitamin C. Acr-dG and 8-oxodG were generated by incubating DHA (5 mM) with 25 µM FeSO4 inthe presence of 15 mM dG (37oC, 16h). The levels of the modified dG were quantified by reverse phase HPLC with UV detection. Addition of EGCG (12.5-250 µM) to the incubation mixture resulted in a concentration-dependent decrease of Acr-dG and 8-oxodG. Interestingly, vitamin C at low concentrations (10 to 100 µM) did not affect the formation of Acr-dG, but at higher concentrations (250 to 800 µM) it caused a significant increase of Acr-dG. However, vitamin C had no significant effect on the 8-oxodG formation. Vitamin E at 12.5 and 25 µM decreased Acr-dG yields by 49 and 42%, while at 400 µM and 800 µM it increased Acr-dG formation by 52 and 136%, respectively. Incubation with 12.5 µM vitamin E led to a 34% decrease in 8-oxodG. However, higher concentrations of vitamin E (25-800 µM) did not further decrease 8-oxodG. To determine whether the inhibitory effect of EGCG on Acr-dG derived from DHA is solely due to its antioxidant property or its scavenging effect is also involved, we incubated 0.5 mM Acr and 0.5 mM dG with various concentrations of EGCG (10-500 µM). The results showed that EGCG effectively decreased the Acr-dG formation in a concentration-dependent manner. This suggests that the inhibitory effect of EGCG toward Acr-dG formation in the presence of DHA is likely in part due to its effect as scavenger of Acr. In a similar study, vitamin C also showed a concentration-dependent inhibition of Acr-dG formation by its scavenging effect. The differential effects of vitamin C (scavenging vs. antioxidant) is intriguing; it may indicate that species other than Acr from DHA or a different mechanism may be involved in the formation of Acr-dG. This study shows that EGCG is both a potent antioxidant and an effective enal-scavenger and that vitamins C and E can exhibit both antioxidant and prooxidant effects depending on the concentrations used. (Supported by NIH grant CA 043159).