Abstract
• Euryops arabicus alleviated MetS associated exaggerated vasoconstriction. • The chloroform fraction yielded eight furanoeremophilane derivatives. • All isolated compounds showed significant vasodilation activity. • Vasodilation activity may involve calcium channel blocking mechanism. Abstract Exaggerated vasoconstriction plays a critical role in the development of hypertension in metabolic syndrome (MetS). A crude methanolic extract of Euryops arabicus (EA) was found to alleviate MetS-associated exaggerated vasoconstriction. The methanolic extract of EA had a direct vasodilatory effect which might account for the alleviation of vasoconstriction. Bio-guided fractionation revealed that the chloroform fraction is responsible for this effect. The observed vasodilation was not affected by Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME), a nitric oxide (NO) synthase inhibitor or methylene blue (MB), a guanylate cyclase inhibitor, while it was increased by tetraethylammonium (TEA), a potassium channel blocker. In addition, the chloroform extract showed concentration-dependent inhibition of calcium-induced contraction. Chemical investigations of the chloroform fraction of EA revealed three new furanoeremophilanes, namely, 6-β-(2`-methyl-2`,3`-epoxy-propionyloxy)-10-α-H-9-oxofuranoeremophilane ( 4 ), 6- α -(2`-methyl, 2`,3`-epoxy-butyryloxy)-10-α-H-9-oxofuranoeremophilane ( 7 ), and 6-β-(2`-methyl, 2`,3`-epoxy-butyryloxy)-euryopsin ( 8 ), in addition to five other known metabolites, namely, 6-isovaleryloxy-euryopsin ( 1) , 6-isopropionyl-euryopsin (adenostylone) ( 2 ), 6-senecioyl-euryopsin-9-one ( 3 ) 6-β -(2`-methyl-2`,3`-epoxy-butyryloxy)-10-α-H-9-oxofuranoeremophilane ( 5 ), and euryopsonol-senecioate ( 6 ). All the isolated compounds showed significant vasodilatory effects that might involve calcium channel blocking, and compounds 7 and 8 were found to be the most bioactive ones.
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