The health benefits of bio-active phenolic compounds have been largely investigated in vitro at concentrations which exceed those reachable in vivo. We investigated and compared the anti-inflammatory effects of resveratrol, hydroxytyrosol and oleuropein at physiologically relevant concentrations by using in vitro models of inflammation.
Human granulocytes and monocytes were stimulated with phorbol myristate acetate (PMA) and the ability of resveratrol, hydroxytyrosol and oleuropein to inhibit the oxidative burst and CD11b expression was measured. Nitric oxide (NO), prostaglandin E2 (PGE2) levels, COX-2, iNOS, TNFα, IL-1β and miR-146a expression and activation of the transcription factor Nrf2 were evaluated in macrophages RAW 264.7 stimulated with LPS (1 μg/ml) for 18 h, exposed to resveratrol, hydroxytyrosol and oleuropein (5 and 10 μM). Synergistic effects were explored as well, together with the levels of PGE2, COX-2 and IL-1β expression in macrophages after 6 h of LPS stimulation. PGE2 and COX-2 expression were also assessed on human monocytes.
All the tested compounds inhibited granulocytes oxidative burst in a concentration dependent manner and CD11b expression was also significantly counteracted by resveratrol and hydroxytyrosol. The measurement of oxidative burst in human monocytes produced similar effects being resveratrol more active. Hydroxytyrosol and resveratrol inhibited the production of NO and PGE2 but did not reduce iNOS, TNFα or IL-1β gene expression in LPS-stimulated RAW 264.7 for 18 h. Resveratrol slightly decreased COX-2 expression after 18 h but not after 6 h, but reduced PGE2 levels after 6 h. Resveratrol and hydroxytyrosol 10 μM induced NRf2 nuclear translocation and reduced miR-146a expression in LPS treated RAW 264.7.
Overall, we reported an anti-inflammatory effect of resveratrol and hydroxytyrosol at low, nutritionally relevant concentrations, involving the inhibition of granulocytes and monocytes activation, the modulation of miR-146a expression and the activation of Nrf2. A regular dietary intake of resveratrol and hydroxytyrosol may be a useful complementary strategy to control inflammatory diseases.