Phytochemical study, antioxidant and vasodilatation activities of leafy stem extracts of Flemingia faginea Guill. & Perr. (Barker), a medicinal plant used for the traditional treatment of arterial hypertension

Background: Flemingia faginea Guill. & Perr. is a medicinal plant used for the endogenous treatment of hypertension. This study aimed to establish the phytochemical profile, antioxidant power, and vasodilation effects of aqueous decoction (FAD), ethyl acetate (EAF) and aqueous residual fractions (ARF) of the leafy stem of Flemingia faginea (F. faginea). Methods: The phytochemical study was performed using high-performance thin-layer chromatography technique and high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS). Folin-Ciocalteu and aluminum trichloride colorimetric methods were used, respectively, to quantify total polyphenols and flavonoids. The antioxidant properties of the extracts were determined using 2,29-azinobis-3-ethylbenzothiazoline-6-sulfonic (ABTS•), 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and ferric ion reduction (FRAP) methods. The vasodilatory effects of F. faginea extracts were performed using the DMT 620M myograph technique for an ex vivo study. Results: The phytochemical study revealed the presence of flavonoids, tannins, coumarins, sterols, and triterpenes, alkaloids, and saponins in the extracts studied. HPLC MS analysis identified as the main phenolic compounds, gallic acid-glucoside (16.56 ± 0.06 mg/g), myricetin rhamnoside (15.39 ± 0.04 mg/g), myricetin rutinoside (9.32 ± 0.00 mg/g), quercetin rutinoside (9.05 ± 0.00 mg/g), caffeoyl-glucoside (6.07 ± 0.02 mg/g) and 5-Caffeoylquinic acid (4.52 ± 0.00 mg/g). The present data also showed higher contents of phenolic compounds and flavonoids in fractions of ARF (280.49 ± 0.08 mgGAE/g) and EAF (33.31 ± 0.33 mgQE/g) fractions respectively. Furthermore, the ARF fraction had the best iron ion reduction capacity (16.96 ± 0.01µgAAE/100 mg), while, the EAF (ABTS: IC50=67.33 ± 0.04 µg/mL; DPPH: IC50=4.69 ± 0.20 µg/mL) was the best free radical scavenger. In endothelium-intact rings, study extracts showed a vasodilation effect in a concentration-dependent manner with half-maximum effective concentration (EC50) of 0.24 ± 0.03 mg/mL, 0.85 ± 0.07 mg/mL and 0.05±0.01 mg/mL respectively for FAD, ARF and EAF. In endothelium-denuded vessels, these values were 0.26 ± 0.09 mg/mL, 0.57 ± 0.05 mg/mL, and 0.85 ± 0.01 mg/mL for EAF, FAD, and ARF, respectively. The maximum effects were of 99.94 ± 0.15%, 86.89 ± 5.58%, and 62.69 ± 5.14% (endothelium-intact) and of 100 ± 0.06%, 96.55 ± 4.68%, and 74.16 ± 4.06% (endothelium-denuded), respectively, for EAF, FAD, and ARF with a significant difference between them. Conclusion: This study reports that the decoction and fractions of F. faginea are rich in various chemical compounds and possess antioxidant and vasodilatory properties. These preliminary data provide a scientific basis which contributed to justify that plant used in traditional medicine.