Influence of vitamin C and vitamin E on redox signalling: implications for exercise adaptations

The exogenous antioxidants vitamin C (ascorbate) and vitamin E (α-tocopherol) often blunt favourable cell signalling responses to exercise, suggesting that redox signalling contributes to exercise adaptations. Current theories posit that this antioxidant paradigm interferes with redox signalling by attenuating exercise-induced reactive oxygen species (ROS) and reactive nitrogen species (RNS) generation. The well-documented in vitro antioxidant actions of ascorbate and α-tocopherol and characterisation of the type and source of the ROS/RNS produced during exercise theoretically enables identification of the redox-dependent mechanism responsible for the blunting of favourable cell signalling responses to exercise. This review aimed to apply this reasoning to determine how the aforementioned antioxidants might attenuate exercise-induced ROS/RNS production. The principal outcomes of this analysis are (1) neither antioxidant is likely to attenuate nitric oxide signalling either directly (reaction with nitric oxide) or indirectly (reaction with derivatives, e.g. peroxynitrite) (2) neither antioxidant reacts appreciably with hydrogen peroxide, a key effector of redox signalling (3) ascorbate but not α-tocopherol has the capacity to attenuate exercise-induced superoxide generation and (4) alternate mechanisms, namely pro-oxidant side reactions and/or reduction of bioactive oxidised macromolecule adducts, are unlikely to interfere with exercise-induced redox signalling. Out of all the possibilities considered, ascorbate mediated suppression of superoxide generation with attendant implications for hydrogen peroxide signalling is arguably the most cogent explanation for blunting of favourable cell signalling responses to exercise. However, this mechanism is dependent on ascorbate accumulating at sites rich in NADPH oxidases, principal contributors to contraction mediated superoxide generation, and outcompeting nitric oxide and superoxide dismutase isoforms. The major conclusions of this review are: (1) direct evidence for interference of ascorbate and α-tocopherol with exercise-induced ROS/RNS production is lacking (2) theoretical analysis reveals that both antioxidants are unlikely to have a major impact on exercise-induced redox signalling and (3) it is worth considering alternate redox-independent mechanisms.