Cigarette smoke as a source of exogenous and endogenous antioxidants in smokers: novel findings
Cellular oxidative stress, derived from imbalance between the production of reactive oxygen species and the efficacy of the antioxidant defence, can be a direct and/or indirect consequence of cigarette smoking. Pro-oxidant properties of cigarette smoke are accounted for by the abundance of smoke oxidants, whose origin may be of free-radical as well as of molecular (peroxides, electrophilic carbonyls, etc.) nature. Oxidants may be additionally generated in a smoker through biochemical transformations of relatively persistent smoke chemicals (e.g. benzo[a]pyrene, aromatic amines). The antioxidant potential of the smoke is scantily addressed in the literature. However, one should take into account that any reactant in oxidation processes may exhibit both oxidant and antioxidant propensities depending on the reaction conditions. Such a bimodal behaviour is unique to a number of smoke chemicals. Thus, hydroquinone, catechol and numerous phenolic and polyphenolic reactants may act as both antioxidants (through scavenging free radicals) and pro-oxidants (through generation of oxygen-contained free radicals) responsible for oxidative damage of biomolecules. As we have recently shown, smoke constituents indeed exhibit at the same time both pro-oxidant and antioxidant activities (Palmina et al., 2014. Aust. J. Chem., 67, 858-866) because of a dual role of the smoke reactants in oxidation processes. Apart from this mechanism, we have studied the possibility of the antioxidants generation directly in smokers. For that purpose, we have developed a model system consisting of a cigarette-smoke extract, peroxidase and amino acids. Using such a system, we have demonstrated that under physiological conditions the oxidation of the smoke tar and its individual components (e.g. catechol) in the presence of H2O2, peroxidase and glycine affords the products whose antioxidant potential is much higher than that of initial, unoxidised, chemicals.