Phytopharmacological Evaluation of ACE Inhibitors from Medicinal Plants of Ayurveda

Abstract

Hypertension is a becoming a major threat to the world. In the search of lead molecules from plant origin as a substitute for toxic synthetic drugs, 26 Indian medicinal plants and foods were screened for their ACE (Angiotensin Converting Enzyme) inhibitory activity. IC50 (50% inhibition of ACE) values of hydroalcoholic crude extracts and fraction were determined by a colorimetric method. Active fractions were further screened to determine the enzyme kinetics, mode, specificity and mechanism of inhibition. Standardization was done by determining total phenolics and flavonoids as gallic acid and quercetin equivalents/mg of extract respectively. Among 26 crude extracts, Cynara scolymus extract showed the best activity, IC50 value 356.62μg/mL. ACE inhibition resulting from protein precipitation was highest in Coscinium fenestratum. Lineweaver-Burk plots revealed a competitive mode of inhibition for Punica granatum ethyl acetate fraction. Fractions of Cassia occidentalis, Cynara scolymus and Embelia ribes were found to be non-specific inhibitors of ACE. Embelia ribes, Cassia occidentalis and Coscinium fenestratum fractions inhibited the ACE by Zn2+ ion chelation. Further, in the search for safe and effective lead molecules from natural sources, (MP) Mucuna pruriens L. (Fabaceae) seeds were utilized for exploring the antihypertensive potential. Traditionally it is used as diuretic and Hypotensive. Bioassay-guided fractions were utilized for the isolation of active compounds by column chromatography. IC50 value, enzyme kinetics and inhibition mechanism were determined. In vivo time and dose-dependent hypotensive study followed by changes in the MAP (Mean arterial pressure) induced by angiotensin I (3 nmol/kg), angiotensin II (3 nmol/kg), and to bradykinin (10 nmol/kg) in anesthetized rats was done. Plasma & tissue ACE activities were also determined. Phytochemical analysis by spectroscopic techniques revealed the presence of known compounds like genistein, ursolic acid and L-DOPA from the ethyl acetate and water fraction respectively. In vitro study revealed MP ethyl acetate fraction (MPEA) & genistein as the most active fraction (IC50 156.45μg/mL) & compound (IC50 253.81μM) respectively. Lineweaver-Burk plots revealed a non-competitive mode of inhibition. ACE protein precipitation was the suggested mechanism for inhibition. The extract showed a time and dose-dependent decrease in the MAP. Genistein was able to dose-dependently reduce the MAP, up to 53 ± 1.5 mm Hg (40 mg/kg, i.v.). As compared to control it showed a dosedependent decrease in plasma ACE activity of 40.61 % and 54.76 % at 10mg/kg & 20mg/kg vi respectively. It also decreased the ACE activity in the aorta (107.67nM/ml min at 10mg, P<0.001; 95.33nM/ml min at 20mg P<0.001. Captopril was used as a standard for various in vitro and in vivo assays. Research revealed the potential of tested plants fractions as ACE inhibitors along with their inhibition kinetics and mechanism of inhibition, these fractions might find importance in the development of potential antihypertensive agents after further investigations using preclinical & clinical trials. The study also revealed the antihypertensive potential of MP seed compounds via ACE inhibition.