Resumen de Can bird carotenoids play an antioxidant role oxiziding other substances?
Ana María Martínez Vázquez, Miguel Angel Rodríguez Gironés, Andrés Barbosa
Carotenoids have moderate ionization energies and very high and positive electron affinities. In other words: carotenoids are more likely to induce oxidation than to prevent it. This result is in stark contrast with the common assumption that carotenoids are good antioxidants, an assumption going back to 1932 that has been subject to scant critical scrutiny. Numerous studies, from medicine to behavioural ecology, show that birds benefit from a diet rich in carotenoids. One of their hypothesized beneficial properties is that carotenoids contribute to fight oxidative stress. Among behavioural ecologists, this hypothesis has led to the proposal that carotenoids are the handicap that stabilizes the evolutionary trajectories of many sexual displays: if carotenoids are required to fight oxidative stress, only high-quality individuals will be able to divert them from metabolic pathways to colourful ornaments. But this explanation is currently under siege: a number of recent studies in birds have found little correlation between carotenoid concentrations in tissues and their total antioxidant ability. Our results suggest that the current paradigm needs a thorough revision. It is unlikely that carotenoids prevent the oxidation of molecular machinery, but they can nevertheless act as scavengers of free radicals. In particular, they will readily neutralize free electrons that escape from the mitochondrial electron-transport chains. Testing this possibility will require new experimental approaches: carotenoid concentration should correlate with the ability of tissues to absorb free electrons (i.e. to prevent reduction), but not with its antioxidant potential.
