Received for publication February 28, 2008.
Revised June 22, 2008.
Accepted for publication June 23, 2008.

Isoflavone attenuates vascular contraction through inhibition of RhoA/Rho-kinase signaling pathway

Abstract

Isoflavones decrease blood pressure, improve lipid profiles, and restore vascular function. We hypothesized that isoflavone attenuates vascular contraction by inhibiting RhoA/Rho-kinase signaling pathway. Rat aortic rings were denuded of endothelium, mounted in organ baths, and contracted with U46619, a thromboxane A2 analogue or KCl 30 min after the pretreatment with genistein, daidzein or vehicle. We determined the phosphorylation level of the myosin light chain (MLC₂₀), myosin phosphatase targeting subunit 1 (MYPT1) and protein kinase C (PKC) -potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa (CPI17) by means of the Western blot. We also measured the amount of GTP RhoA as a marker regarding RhoA activation. The cumulative additions of U46619 or KCl increased vascular tension in a concentration-dependent manner, which were inhibited by pretreatment with genistein or daidzein. Both U46619 (30 nM) and KCl (50 mM) increased MLC₂₀ phosphorylation levels which were inhibited by genistein as well as daidzein. Furthermore, both genistein and daidzein decreased the amount of GTP RhoA activated by either U46619 or KCl. U46619 (30 nM) increased phosphorylation of the MYPT1_Thr855 and CPI17_Thr38, which were also inhibited by genistein or daidzein. However, neither genistein nor daidzein inhibited PDBu-induced vascular contraction and CPI17 phosphorylation. In conclusion, isoflavone attenuates vascular contraction, at least in part, through inhibition of the RhoA/Rho-kinase signaling pathway.

Key words: Isoflavones, Rho-kinase, contraction, daidzein, genistein, myosin light chain phosphatase