Effects of Colored and Noncolored Phenolics of Echium plantagineum L. Bee Pollen in Caco-2 Cells under Oxidative Stress Induced by tert-Butyl Hydroperoxide

Bee pollen is used as a dietary supplement, being promoted as a health food. Echium plantagineum L. bee pollen fractions enriched in flavonols (fraction I) or anthocyanins (fraction II) and the whole extract were characterized by HPLC-DAD. Both in the whole extract and in fraction II seven flavonols and five anthocyanins were identified, while fraction I contained six flavonols (in higher levels than fraction II) and small amounts of petunidin-3-O-rutinoside. Antioxidant capacity was evaluated in Caco-2 cells under oxidative stress induced by tert-butyl hydroperoxide (t-BHP). Fraction I pre-exposure imparted a tendency to protect cells, while fraction II and the whole extract aggravated t-BHP toxicity at some concentrations. The protective effects seem to be correlated with the levels of total glutathione, while no correlation between cellular viability and reactive species was seen. The extracts displayed no significant effect on antioxidant enzymes activity. Overall, anthocyanins seem to abrogate the antioxidant potential of flavonoid-rich extracts.