Vasorelaxan Effect and Potent Antioxidant Activity of Natural Flavones Isolated from Lourteigia stoechadifolia and Ageratina stevioides, Two Venezuelan Plants

Aims: This study was undertaken to investigate the vasorelaxant and antioxidant effects of natural flavones, 5,3’-dihydroxy-6,7,4’-trimetoxyflavone (eupatorin) (1), 5-hydroxy-6,7,3’,4’-tetrametoxyflavone (2), and 5,4’-dihydroxy-7-metoxyflavone (genkwanin) (3).

Study Design: Biomedical assays in isolated vascular tissue.

Place and Duration of Study: Department of Pharmacology, Faculty of Medicine, University of Panama, Panama Between March 2015 and September 2016.

Methodology: The relaxation responses to cumulative concentrations of flavones 1, 2 and 3 (10-6 - 10-4 M) were tested on aortic rings, with or without endothelium, precontracted with phenylephrine (10-6 M). In complementary experiments, the tissues were preincubated with Nw-nitro-L-arginine methyl ester (L-NAME), methylene blue or indomethacin. In order to evaluate their antioxidant capacity, the effect of each compound on acetylcholine-response was studied in aortic pre-treated with high dose of lucigenin. Additionally, superoxide anion generation was measured in isolated aortic rings using the lucigenin-enhanced chemiluminescence method.

Results: Flavones 1, 2 and 3 induced a significantly vasorelaxant effect above 80% in aortic with endothelium. Mechanical removal of endothelium significantly decreased vasorelaxation of flavones 1 and 3 (15.6±4.6 and 28.4±2.9%, respectively). The vasorelaxant effect of flavones 1 and 3 were almost abolished when tissue was incubated with L-NAME or methylene blue. In aortic rings pre-treated with high dose of lucigenin reduced the relaxation to acetylcholine (28.4%) and it was prevented by all flavones (1=80.5; 2=81.4; and 3=66.2%). Complementary, all flavones significantly reduced superoxide levels.

Conclusion: Flavones isolated from two tropical plants are able to induce vasorelaxation, improve the impaired response to acetylcholine induced by lucigenin and exhibit radical scavenging activity.