β-Carotene and its biological oxidation products: are they good modulators of pro-oxidant reactive species in human blood and neutrophils assay systems?

β-carotene is the most abundant carotenoid found in the diet and human tissues [1]. High ingestion of carotenoids has been associated with low incidence of degenerative diseases and it has been mainly attributed to their ability to scavenge physiologically relevant reactive species. In humans, β-carotene is metabolized by oxidative cleavage into trans-β-apo-8’-carotenal and β-ionone [2]. Therefore, it is crucial to disclose the potential antioxidant effects of β-carotene and its oxidation products. In this sense, the main aim of this work was to elucidate the potential antioxidant effects of β-carotene, trans-β-apo-8’-carotenal and β-ionone, at relevant physiologic concentrations. The two selected biological systems were human blood, a complex matrix that most approximately mimic the in vivo biologic environment; and human neutrophils, the first line of defense cells utterly implicated in the immune and inflammatory responses. Two fluorescent probes were used in both matrices: 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) that unspecifically detects hydrogen peroxide (H 2 O 2 ), hydroxyl radical, nitric oxide and peroxynitrite anion, and amplex red (AR) that specifically detects H 2 O 2 . In both matrices, none of the tested carotenoids showed any ability to stimulate reactive species production. As so, they do not seem to be pro-oxidants. For the study of the antioxidant potential, phorbol 12-myristate 13-acetate was used to stimulate reactive species production by human blood cells. Interestingly, in what concerns the human blood matrix, none of the tested carotenoids (0.3 - 49 µM) showed antioxidant activity. In what respects human neutrophils, also none of the tested compounds (0.3 - 100 µM) was able to inhibit DCFH-DA oxidation; trans-β-apo-8’-carotenal was the only one that showed a slight ability to inhibit AR oxidation, suggesting some modulation of H 2 O 2 production. The obtained results show that β-carotene and its oxidation products, at biological relevant concentrations, did not provide acute pro- or antioxidant activity, in the studied experimental conditions. These results indicate that carotenoids and/or its oxidation products probably require different types of exposure on biological systems to enable a better incorporation in the lipidic system opening a window to new studies with this kind of compounds.