Effects of Astragalus membranaceus and its main components on the acute phase endothelial dysfunction induced by homocysteine

Objective: This study was designed to investigate the effects of Astragalus membranaceus (AM) and its main components, astragalus saponin (ASP), astragalus polysaccharide (APS) and aminobutyric acid (GABA), on homocysteme (Hey) induced acute impairment of vascular tone and to explore whether the antioxidant mechanism was involved in AM protective effect. Methods: Inhibitory effects of Hcy and protective effects of AM and its main components on endothelium-dependent relaxation of aortic rings were determined by isometric tension recordings and nitric oxide signaling was assayed with I-125-cGMP RIA Kit. Furthermore, generation of reactive oxygen species (ROS) in endothelial cells was detected using 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H2DCF-DA). Results: Hey significantly inhibited endothelium-dependent relaxation to acetylcholine (ACh) in a dose-dependent manner, and decreased cGMP levels increased by ACh in aorta. Furthermore, superoxide dismutase (SOD), AM, and ASP markedly attenuated inhibition of vasorelaxation and downregulation of cGMP level by Hey, and ATS exerted a tendency to reverse both of the depressive responses, while GABA had no similar effects. Additionally, partially impaired relaxation by Hey was completely blocked due to the presence of N(omega)-nitro-L-arginine-methyl ester (L-NAME), which could not be further altered by treatment with AM, ASP, APS or GABA. Finally, Hey significantly increased intracellular ROS levels in endothelial cells as measured by CM-H2DCF-DA fluorescence. SOD, AM, ASP, and APS, but not GABA, inhibited Hey-stimulated ROS generation. Conclusion: This study demonstrated that AM and ASP, potently protected endothelium-dependent relaxation against the acute injury from Hey through nitric oxide regulatory pathways, in which antioxidation played a key role. (c) 2006 Elsevier Inc. All rights reserved.