Abstract 4171: Olive Oil Phenolic Antioxidants Reduce Metalloproteinase (MMP)-9 Expression and Release in Human Monocytoid Cells: Possible Contribution to Plaque Stability

Abstract

Background: Mediterranean diets, of which olive oil is an important component, are associated with low prevalence of cardiovascular diseases, but active dietary components and their mechanisms of action are incompletely understood. The local production of active matrix metalloproteinases (MMPs) by macrophages likely contributes to plaque matrix degradation and plaque instability leading to acute coronary events. Aim: To examine the effect of the olive oil phenolic antioxidants, hydroxytyrosol (HT)and oleuropein (OE), on MMP-9 expression and activity in monocytoid cells and to explore mechanisms of action. Methods: U937 human monocytoid cells were pre-treated with HT or OE (0–100 μmol/L) for 30 min before stimulation with 50 nmol/L phorbol myristate acetate (PMA) in a serum-free medium for 24 h. Cell supernatants were then tested for the release of MMP-9 and tissue inhibitor of metallopro-teinases (TIMP)-1 antigens (ELISA) and for gelatinase activity by zymography. MMP-9 mRNA expression was investigated by RT-PCR and the activation of transcription factors Nuclear Factor(NF)-κB and Activator Protein(AP)-1 by EMSA. Results: MMP-9 antigen and activity in U937 cells increased by about 50 fold after stimulation with PMA for 24 h (from 0.5 ± 0.3 to 24 ± 1.5, p<0.01). HT and OE (1–100 μmol/L) reduced PMA-induced MMP-9 activity, at zymography analysis, in a concentration dependent manner with inhibitory concentration producing 50% of the effect (IC50) at 10 μmol/L (p<0.01) and 25 μmol/L (p<0.01) respectively. In addition HT and OE reduced MMP-9 protein release and MMP-9 mRNA levels by about 65% and 45% respectively at 25 mmol/L (p<0.01), without significantly TIMP-1 release. HT and OE at micromolar concentrations also significantly (p<0.05) inhibited PMA-induced activation of NF-κB and AP-1, suggesting a plausible mechanism for the downregulation of MMP-9 expression. Conclusions: The olive oil phenolic antioxidants inhibit MMP-9 expression and release in monocytoid cells, associated with reduced activation of NF-κB and AP-1. This may contribute to plaque stabilization explaining at least in part the cardiovascular protection by specific components of Mediterranean diets.