Hydroxytyrosol Induces Vascular Smooth Muscle Cells Apoptosis through NO Production and PP2A Activation with Subsequent Inactivation of Akt

Olive oil has been shown to exhibit beneficial effects in the prevention of cardiovascular diseases although its molecular mechanism still remains unclear. In the present study, we investigated the effect of hydroxytyrosol (HT), a major phenolic component in olive oil and leaves from Olea europaea L. (Oleaceae family), on vascular smooth muscle cells (VSMCs) survival, migration, and apoptosis. HT treatment resulted in a dose-dependent decrease of cell survival and migration in the presence or absence of platelet-derived growth factor (PDGF) by inducing apoptosis of VSMCs. HT enhanced nitric oxide (NO) production in a dose-dependent manner, and the NO synthase inhibitor L-NMMA blocked HT-mediated effects on VSMCs survival. HT as well as the NO donor SNAP reduced the phosphorylation levels of Akt, suggesting that HT inactivates Akt via NO production with subsequent apoptosis of VSMCs. Moreover, HT-dependent apoptosis and reduction in the phosphorylation level of Akt were suppressed by okadaic acid, an inhibitor of protein phosphatase 2A (PP2A) that dephosphorylates Akt. In contrast, the phosphorylation of phosphoinositide-dependent protein kinase 1 (PDK1), an upstream activator of Akt, was not affected by HT. Together, these findings indicate that HT could induce VSMCs apoptosis through NO production and PP2A activation followed by inactivation of Akt signaling pathway.