Antioxidant Properties and Vasorelaxant Mechanism of Aqueous Extract of Ricinodendron heudelotii (Euphorbiaceae)

Abstract

Ricinodendron heudelotii is a plant of the Euphorbiaceae family, used in traditional medicine to treat numerous diseases, including high blood pressure. The aim of this study is to evaluate the antioxidant and vasorelaxant effects of the aqueous extract of the stem bark of R. heudelotii. The pharmacological studies were carried out using the aqueous extract obtained by infusion. The antioxidant capacity of R. heudelotii was assessed by in vitro tests with DPPH (2,2-diphenyl-1-picryl-hydrazyl), ABTS (2,2'-azino-bis (3-ethylbenz-thiazoline-6-sulfonic acid), iron-reducing capacity (FRAP), and inhibition of nitric oxide (NO) release. In vitro studies, the aortic rings obtained from adult Wistar albino rats of both sexes were used to determine the vasorelaxant effects of the extract of R. heudelotii on the NO and prostacyclin (PGI2) pathways as well as its involvement on various potassium channels were determined on intact or naked fragments of rat aorta precontracted with phenylephrine (10^-6 M) or KCl (60 mM). The aqueous extract of R. heudelotii exhibited a remarkable DPPH (EC₅₀: 1.68 μg/mL) and ABTS (EC₅₀: 106.30 μg/mL) and nitric oxide (53.71% inhibition at 1000 μg/mL) radical scavenging activities as well as reducing power (absorbance of 1.56 at 1000 μg/mL). The nitric oxide inhibitor, N_G-nitro-L-arginine methyl ester (L-NAME), and prostacyclin inhibitor, indomethacin, significantly attenuated the vasodilatory effect of R. heudelotii. Tetraethylammonium could not inhibit the vasodilatory effect of the extract, unlike glibenclamide and barium chloride. Ricinodendron heudelotii extract possesses antioxidant properties and vasorelaxing effect linked to endothelium-related factors, and this relaxation was partially mediated mainly through the inhibition of K_ir and K_ATP channels.

Keywords: endothelium; radical scavenging activities; vasodilatory effects.

Figure 1

(a) DPPH radical scavenging activity, (b) ABTS radical cation scavenging activity, (c) NO radical scavenging activity, and (d) ferric reducing power activity of the aqueous stem bark extract of Ricinodendron heudelotii.

Figure 2

Concentration-dependent relaxant effects of Ricinodendron heudelotii on phenylephrine (PE, 10⁻⁶ M) or KCl (60 mM) precontracted rat aortic rings. The relaxant effects of Ricinodendron heudelotii were calculated as a percentage of contraction in response to PE or KCl. Values are mean ± S.E.M (n = 6).

Figure 3

The effects of (a) L-NAME or (b) indomethacin on cumulative concentration responses of Ricinodendron heudelotii in intact aortic rings precontracted with phenylephrine (PE). The responses are expressed as % values (complete relaxation of PE-induced contraction = 100%). Values are mean ± SEM (n = 6). ^∗∗p < 0.01 and ^∗∗∗p < 0.001, significantly different in comparison with control.

Figure 4

Relaxant responses induced by Ricinodendron heudelotii in rat aortic rings precontracted with phenylephrine (PE) in the absence or presence of (a) TEA, (b) glibenclamide, or (c) barium chloride. The responses are expressed as % values (complete relaxation of PE-induced contraction = 100%). Values are mean ± SEM (n = 6). ^∗∗p < 0.01 and ^∗∗∗p < 0.001, significantly different in comparison with control.