Allicin stimulates phosphorylation of eNOS Ser1177 via a PI3K-dependent mechanism in type-I diabetic donor coronary artery endothelial cells

Introduction: The incidence of diabetes mellitus (DM) in the United States continues to increase. Projections are that 7.21% of Americans will have DM by 2050, which is 165% over the incidence in 2000. Cardiovascular disease (CVD) constitutes the number one cause of death globally and is the major source of morbidity and mortality associated with DM. CVD manifests early in DM as vascular dysfunction due to decreased bioavailability of nitric oxide (NO). Recent evidence suggests that garlic consumption may increase NO levels. However, few studies have examined potential beneficial effects of garlic on diabetes-induced CVD.

Objectives: The primary objective of this study was to investigate the mechanism of action for allicin, a naturally-occurring compound in garlic, to increase NO production in human coronary artery endothelial cells obtained from type-I diabetic donors (DHCAEC-I).

Methods: Fluorogenic probes were employed to detect allicin-stimulated production of H2S (SF7-AM) or NO (DAF-FM DA) in control coronary artery endothelial cells (HCAEC) or DHCAEC-I via fluorescence microscopy. Immunoblot analysis was performed to identify potential targets of allicin involved with NO production in endothelial cells (p-eNOSSer1177, eNOS, p-AktSer473, and Akt).

Results: Allicin (5 mM) increased H2S production by 2.20-fold and 2.80-fold (p < 0.05) in HCAEC and DHCAEC-I, respectively. In addition, allicin stimulated NO production by 66% (p < 0.05) in DHCAEC-I, the effect of which was diminished by the use of wortmannin (5 μM, p < 0.05), an inhibitor of PI3 kinase. Allicin did not, however, increase NO production in HCAEC

Conclusion: These data strongly support the hypothesis that allicin can restore DM-induced reductions in NO bioavailability in human coronary artery endothelial cells. Our findings suggest that allicin acts via PI3 kinase-mediated phosphorylation of eNOS at Ser1177. We hypothesize that this effect of allicin involves production of H2S, but further experiments are needed to determine downstream signaling targets of H2S and PI3 kinase.