Total flavonoids of Flos Chrysanthemi protect arterial endothelial cells against oxidative stress

Total flavonoids of Flos Chrysanthemi (TFFC) are known to modulate vascular functions, but their effect on endothelial cells injured by oxidative stress is unknown. Our objective was to investigate the vasoprotective effect and mechanism of action of TFFC on rat mesenteric artery exposed to superoxide anions produced by pyrogallol.

The vasoprotective effect and mechanism of action of TFFC on primary cultured rat mesenteric arterial endothelial cells and small mesenteric arteries was investigated using small-vessel myography, fluorescent Ca(2+) measurement, fluorescent membrane potential measurement and oxidative fluorescent studies.

Experiments using small-vessel myography of third-order rat mesenteric arterial rings showed that pretreatment with pyrogallol (10-1000μM), an auto-oxidizing source of superoxide anions, dose-dependently decreased ACh-induced endothelium-dependent relaxation. TFFC (2.5-320mg/L) evoked a concentration-dependent dilation (pD(2): 29.6±0.276mg/L), which was weakened by ChTX plus apamin. TFFC markedly attenuated the inhibition of vasorelaxation induced by pyrogallol (E(max) elevated from 50.4±7.36% to 86.2±3.61%, and pD(2) increased from 6.74±0.06 to 7.28±0.12). Furthermore, in primary cultured endothelial cells, fluorescent Ca(2+) measurement, fluorescent membrane potential measurement and oxidative fluorescent studies demonstrated that ACh-induced endothelial Ca(2+) influx and hyperpolarization were significantly weakened by the increased basal superoxide level induced by pyrogallol. When the endothelial cells were concurrently exposed to TFFC, the impairment effect of oxidative stress on ACh-induced Ca(2+) influx, hyperpolarization and vasorelaxation were attenuated due to its superoxide-lowering activity.

This study shows that oxidative stress has a pronounced deleterious effect on EDHF-mediated vasorelaxation to ACh in rat mesenteric artery. TFFC has vasodilating effect and protects EDHF-mediated vasodilator reactivity from oxidative stress. Thus, our experiments suggest that TFFC is potentially useful for the development of therapeutic treatments for cardiovascular diseases associated with oxidative stress.