Screening of the antioxidant and hypotensive activities of some medicinal plants in relation to their polyphenolic contents

Abstract

The present study aimed to analyze chemically and evaluate the hypotensive, diuretic and the antioxidant activities of Crataegus azarolus (CA), Myrtus communis (MC) and Origanum glandulosum (OG) which are widely used as natural remedy for hypertension in the Algerian folk medicine. In vitro antioxidant potential of methanolic extract (ME) and its three fractions: Chloroform (CHE), ethyl acetate (EAE) and water (AqE) extracts has been investigated using several assays. Chemical analysis of EAE of selected plants revealed the isolation of five compounds; two flavonoids((+) - catechin and hyperoside) were isolated from CA, one flavonol glycoside (myricetin -3-O-rhamnoside) was isolated from MC, one flavanone (katuranin), and one monoterpene (5-isopropyl-3-methylphenol) were isolated from OG. The quantification of polyphenols and flavonoids showed that EAE from the three studied plants contained the highest amount of polyphenols. However, CHE-MC, CHE-OG and EAE-CA contained the highest amount of flavonoids. EAE from CA, MC and OG exhibited the highest activity in scavenging DPPH, ABTS and hydroxyl radicals and reducing power test; whereas, ME and AqE exhibited higher chelating activity than CHE and EAE. Inhibition of lipid peroxidation was performed using the β-carotene bleaching assay, ferric thiocyanate method and thiobarburic acid method. CHE-MC, CHE-OG and EAE-CA were found to be the strongest inhibitors of lipid peroxidation in the three methods. Intravenous administration of ME and EAE decreased the mean arterial blood pressure in anesthetized rats dose-dependently, at the dose range of 0.4 to 12 mg/kg, and the strongest hypotensive effect was noticed for CA. The diuretic activity of ME (100, 300 and 600 mg/kg) was assessed orally in rats using furosemide as a standard drug. The results showed that only CA and OG produced an increase in urine output and the urinary excretion of Na+ and Cl-. The present study also assessed the effect of administration of ME (100 and 200 mg/kg) in rats for 14 days on plasma antioxidant capacity (PAC) and oxidative stress markers in liver and kidney. It was found that ME-CA (100 and 200 mg/Kg ) and ME-OG (200 mg/kg) caused significant elevation of PAC using DPPH radical whereas only ME CA at a dose of 200 mg/kg increased significantly the plasma reducing power. The administration of the same doses of ME of the three studied plants increased proteins level in liver. The results showed that ME-CA was more effective in enhancing antioxidant status in liver and kidney than other plant extracts by reducing MDA level and increasing catalase activity and GSH level. These results clearly indicate that these plants can be used as a hypotensive agent and as a protective shield against numerous free-radical mediated diseases.