3′,4′-Dimethoxythioflavone induces endothelium-dependent vasorelaxation through activation of epidermal growth factor receptor

It is of interest to investigate whether synthetic thioflavonoids have vasorelaxant actions as natural flavonoids. We tested the hypothesis that 3′,4′-dimethoxythioflavone induces endothelium-dependent vasorelaxation through activation of epidermal growth factor (EGF) receptor. Rat aortic rings were mounted in organ baths and subjected to relaxation upon contraction. 3′,4′-Dimethoxythioflavone induced endothelium- dependent vasorelaxation, which was attenuated by pretreatment with either l-N^ω-nitroarginine methyl ester, an inhibitor of nitric oxide synthase, or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. 3′,4′-Dimethoxythioflavone-induced vasorelaxation was not affected by pretreatment with a general estrogen receptor antagonist ICI 182,780, a selective estrogen receptor-α antagonist methyl-piperidino-pyrazole dihydrochloride, or a G protein-coupled receptor 30 antagonist G15. However, pretreatment with EGF receptor blockers AG1478 or DAPH, but not with a phosphatidylinositol-3 kinase inhibitor LY294002 or an Akt1/2 kinase inhibitor Akt inhibitor VIII, attenuated 3′,4′- dimethoxythioflavone-induced vasorelaxation. In addition, pretreatment with a Src inhibitor PP2 or an ERK inhibitor U0126 also attenuated vascular relaxation induced by the cumulative addition of 3′,4′-dimethoxythioflavone. However, neither a mitochondrial electron transport inhibitor rotenone, an NADPH oxidase inhibitor apocynin, nor a superoxide dismutase mimetic MnTMPyP affected the vascular relaxation induced by the cumulative addition of 3′,4′-dimethoxythioflavone. In conclusion, 3′,4′- dimethoxythioflavone induces endothelium-dependent vasorelaxation through activation of EGF receptor and Src/ERK pathway in rat aorta.