The potential antioxidant effect of caffeine was studied by using adenine as a biological model compound and the hydroxyl radical as the responsible for the establishment of oxidative stress conditions. For this purpose, equimolar binary aqueous solutions of adenine and caffeine were exposed to the hydroxyl radical generated by gamma irradiation of water or by UV-photolysis (in the presence of H2O2). The results show that there is an effective protection of caffeine against oxidative degradation of adenine. However, this protective effect cannot be attributed (at least exclusively) to a scavenging effect, since both caffeine and adenine react with similar rate constants with the hydroxyl radical. Furthermore, it was already demonstrated that caffeine itself is not able to repair oxidized products from adenine by reduction back to the parent compound. For a deeper comprehension of this phenomenon, another set of experiments was set up to study the reaction products of caffeine with the hydroxyl radical and identify them by HPLC. It was observed that some of these products, resulting from hydroxylation and/or demethylation of caffeine, are good antioxidants, capable of regenerating oxidized products of adenine by repair effect. It was concluded that the observed protective effect of caffeine against oxidative degradation of adenine is due to a combination of the scavenging effect of caffeine with the repair effect of some of its products with the hydroxyl radical, constituting the so-called cascade effect.
- Cascade effect
- Hydroxyl radical