The Olive oil antioxidant hydroxytyrosol (HT) reduces the matrix metalloproteinase-9 activity and expression in human mocytoid cells through a prostaglandin (PG) E2-dependent mechanisms

Abstract

Objectives: Olive oil HT is believed to be among the most active cardio-protective components of Mediterranean diets. Since the PGE2-dependent secretion of metalloproteinase(MMP)-9 by macrophages plays a key role in matrix degradation underlying plaque instability, we studied the effects of HT on the release and activity of MMP-9 in cultured human monocytoid cells as a possible explanation to the olive oil vascular protective effect. Methods: Human monocytoid cells were treated with 1-50 &#956;mol/L HT or, alternatively, with selective inhibitors of PKC isoenzymes and cyclooxygenase(COX)-2 for 60 min before stimulation with phorbol myristate acetate (PMA) or PGE2 for 24 h. Cell supernatants were then tested for the release of MMP-9, PGE2 and tissue inhibitor of metalloproteinases (TIMP)-1 and -2, while cell extracts were analysed by Western blot for COX-2 expression and PKCs membrane translocation (as an index of PKCs activation). Results: PMA and, to a lesser extent, PGE2, induced the cell release of MMP-9. Cell exposure to HT (as well as to NS-398 and G?6976, inhibitors of COX-2 and PKC&#945; and &#946; respectively) before PMA stimulation reduced MMP-9 release (IC50 for HT of 10 &#956;mol/L p<0.01) without affecting the release of TIMP-1 and -2. Correspondingly, HT inhibited PMA-induced PGE2 production (by 54?7%) and the expression of COX-2 (by 43?5%) without affecting COX-1. Furthermore, HT also reduced the membrane transloction of PKC&#945;, which is critically involved in the expression of COX-2. Conclusions: Our findings support the involvement of COX-2 derived PGE2 in the expression of MMP-9 by monocyte-like cells and demonstrate that HT inhibits the expression and the release of MMP-9. This effect appears to be mediated by the interference by HT with the stimulated expression of COX-2 and, upstream of this, with the activation of PKC&#945;. Overall, such results contribute to explaining the vascular protective effects exerted by olive oil in Mediterranean diets