Mohammad Yaseen Khan∗ and Vimal Kumar

Abstract

Hypertension is a becoming a major threat to the world. Angiotensin converting enzyme (ACE) is a key part in the renin angiotensin aldosterone system (RAAS) which control blood pressure. Over expression of RAAS is related with vascular hypertension, ACE inhibition has turned into a noteworthy target for controlling hypertension. In the search of lead molecules from plant origin as a substitute for toxic synthetic drugs, 25 Indian medicinal plants and foods were screened for their ACE 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 25 crude extracts, Cynara scolymus extract showed the best activity, IC50 value 356.62 μg/mL. ACE inhibition resulting from protein precipitation was highest in Coscinium fenestratum. Lineweaver-Burk plots revealed a competitive mode of inhibition forPunica 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. Research revealed the potential of tested plants fractions as ACE inhibitors along with their inhibition kinetics and mechanism of inhibition. These active plant fractions might find importance in the development of potential antihypertensive agents after further investigations using preclinical and clinical trials.

Keywords: Angiotensin converting enzyme, Lineweaver-burk plots, Enzyme kinetics, Mode of inhibition

Abbreviations: ACE, Angiotensin I Converting Enzyme; BAPNA, a-N-benzoyl-dl-arginine-Pnitroanilide HCl; BP, blood pressure; BSA, bovine serum albumin; BSC, benzene sulphonyl chloride; CH2Cl2, dichloromethane; DMSO, dimethyl sulphoxide; EtOAc, Ethyl acetate; EtOH, ethanol; GAEs, gallic acid equivalents; HA, hippuric acid; HCl, Hydrochloric acid; HHL, hippury-l-histidyl-l-leucine; IC50, half maximal inhibitory concentration; Km, Michaelis-Menten constant; M, Molar; MeOH, methanol; mg, milligram; mL, milli litre; Mm, Milli mole; Mu, Milli units; n-BuOH, n-butanol; ng, nano gram; QEs, quercetin equivalents; RAS, renin-angiotensin system; TCA, Trichloroacetic acid; TFA, trifluoroacetic acid; UV, ultra violet; Vmax, Maximum velocity; Zn2+, Zinc ion; ZnCl2, Zinc chloride