Natural product extract of Dicksonia sellowiana induces endothelium-dependent relaxations by a redox-sensitive Src- and Akt-dependent activation of eNOS in porcine coronary arteries.

BACKGROUND/AIMS The consumption of polyphenol-rich food is associated with a decreased mortality from coronary diseases. This study examined whether a standardized hydroalcoholic extract of Dicksonia sellowiana (HEDS) triggered endothelium-dependent relaxations in porcine coronary artery rings and characterized the underlying mechanism. METHODS The phosphorylation level of Src, Akt and eNOS was assessed by Western blot analysis, the formation of reactive oxygen species by dihydroethidine staining and the level of eNOS Ser1177 phosphorylation by immunohistochemical staining in sections of coronary arteries. RESULTS HEDS-induced endothelium-dependent relaxations were strongly reduced by Nω-nitro-L-arginine, an eNOS inhibitor, and by its combination with charybdotoxin plus apamin, inhibitors of endothelium-derived hyperpolarizing factor-mediated responses. These relaxations were markedly reduced by MnTMPyP (a membrane-permeant mimetic of superoxide dismutase), polyethylene glycol catalase (PEG-catalase; a membrane-permeant analog of catalase), and by wortmannin (an inhibitor of PI3-kinase). HEDS-induced sustained phosphorylation of Akt and eNOS in endothelial cells was abolished by MnTMPyP, PEG-catalase and wortmannin. Oral administration of HEDS induced a significant decrease of mean arterial pressure in spontaneously hypertensive rats. CONCLUSION These findings indicate that HEDS caused endothelium-dependent relaxations of coronary artery rings through the redox-sensitive activation of the endothelial PI3-kinase/Akt pathway leading to the subsequent activation of eNOS by phosphorylation. HEDS also has antihypertensive properties.