Inflammatory process and virgin olive oil phenols: modulation of platelet aggregation and metalloprotease-9 expression in monocytes

Abstract

Olive oil polyphenols have been shown to counteract the effects of pro-inflammatory stimuli on target molecules, in different cell types, including cells of the arterial wall [1,2]. To investigate the effects and the mechanisms by which olive oil phenols modulate specific aspects of the inflammatory response, i.e. platelet aggregation and monocyte infiltration, the effects of olive oil phenol extracts on aggregation, platelet-derived cAMP-phosphodiesterase (PDE) activity and metalloprotease-9 (MMP-9) expression in monocytes were investigated. Total phenol content was measured by Folin-Ciocalteu; individual compounds were quantified by GC and LC-MS/MS analysis. cAMP-PDE assay was performed as previously reported [3], whereas MMP-9 expression was evaluated by zimography and real time PCR. Statistical analysis was performed using GraphPad Prism 4. Quantitative analysis revealed that oleuropein aglycon (OleA) was the most abundant phenol (20–40% of total phenols). Phenol extracts reduced thrombin-induced platelet aggregation (IC50s 1–11µg/ml of total phenols) while OleA was the most active phenol (75% inhibition at 10µM). Phenol extracts reduced cAMP-PDE activity (IC50s 15–30µg/ml), thus demonstrating that cAMP-PDE inhibition could be one mechanism by which olive oil phenols inhibit aggregation. Olive oil phenol extracts (1–7.5µg/ml) and pure phenols dampened the TNF-α-induced MMP-9 secretion and gene expression in monocytes. Both MMP-9 proximal promoter activity and the NF-kB system were down-regulated by the phenol extracts (2.5–10µg/ml) and pure compounds in transfection assays. In summary, we provide further evidences on the mechanisms by which olive oil may contribute to the prevention of inflammatory-based diseases.