Extraction and Evaluation of Secondary Metabolites as green Antiotensin Converting Enzyme (ACE) Inhibitor.

Abstract

Secondary metabolites, substantially available in the medicinal plants, have divulged their pharmacological properties and can be used in its isolated form or as integral component of the plant‟s part, to cure a variety of disorders. High blood pressure is considered as silent killer as it sneaks up in the body and may leads to serious cardiovascular disorders. Many allopathic antihypertensive medicines are presently available but these are taking their toll in the form of serious side effects. Therefore, the present study was designed for extraction and evaluation of plant‟s secondary metabolites as green Angiotensin Converting Enzyme (ACE) inhibitors for management of hypertension. In the first phase of this research, aqueous and ethanol extracts of 22 plants were initially screened as green ACE inhibitors. Among them four plants Coriandrum sativum, Amomum subulatum, Rauvolfia serpentina and Curcuma longa showed highest ACE inhibition potential. Secondary metabolites were extracted from these four medicinal plants and evaluated for ACE inhibition potential. The highest ACE inhibition potential was observed with flavonoid (81.4±0.48%) of Coriandrum sativum, tannin (77.9±0.24%) of Amomum subulatum, flavonoid (79.9±0.42%) and tannin (88.3±0.26%) of Rauvolfia serpentina and alkaloid (44.4±1.32%) of Curcuma longa. Plants are traditionally recognized for their synergic therapeutic effects, therefore, combinations of plants and their secondary metabolites were evaluated for synergistic ACE inhibition potential. The results revealed that the combination No.1 comprising of Rauvolfia serpentina and Curcuma longa (RS+CL) exhibited significant ACE inhibitory activity (65.08±0.33%) with IC50 value of 73.67μg/mL. The combination No. 13 of secondary metabolite comprising of tannins and flavonoids of Rauvolfia serpentina and alkaloids of Curcuma longa (TRS+FRS+ACL) showed highest ACE inhibition potential (69.64±0.80%) with IC50 value of 39.67μg/mL. Secondary metabolites present in combination No. 13 were further fractionated through column chromatography. Different fractions of flavonoids, tannins and alkaloids were collected, but among them only F3 fraction of flavonoids, T3 fraction of tannins of Rauvolfia serpentina and A6 fraction of alkaloids of Curcuma longa showed ACE inhibition potential. In 2nd phase of the study, characterization of five secondary metabolites fractions extracted from four selected medicinal plants and secondary metabolites present in combination No. 13 were performed by LC-ESI-MS/MS technique to find out the actual bioactive compounds responsible for ACE inhibition potential. The ACE inhibitors identified from flavonoids fraction were included pinocembrin, apigenin, pseudobaptigenin, quercetin, myricetin-3-O-glucoside, quercetin- dimethyl ether-O-glucuronide, quercetagetin, Luteolin-7-O-glycoronyl and quercetin-3-O-hexose-pentoside. Tannins fraction contained ellagic acid, megiferin gallate, prodelphinidin B4, tri galloyl glucose and geraniin as ACE inhibitors. Pyrazolo[1,5-a]pyridine,3,3a,4,7-tetrahydro-3,3-dimethyl;(3aS) and 2-(2‟-methyl-1‟-propyl)-4, 6-dimethyl-7-hydroxyquinoline were identified as alkaloidal ACE inhibitors. In the 3rd phase of this study, the combination No. 1 of plant (RS+CL) and combination No. 13 of secondary metabolites (TRS+FRS+ACL) were investigated for in vivo antihypertensive potential through spontaneous induction of hypertension by two kidney one clip (2K1C) renal artery ligation method. In vivo trial revealed that the combination No. 13 of secondary metabolites showed comparatively better antihypertensive potential as compared to the combination No.1 of whole plants. It is pertinent to mention that the antihypertensive potential of the isolated secondary metabolites was better even than the standard drug (Captopril) which was used as reference.