Chemical Composition, Antioxidative and Antimicrobial Activities of Different Extracts of the Leaves of Parquetina nigrescens (Asclepiadaceae)

Abstract

Oxidative stress has been implicated in the pathogenesis of many diseases, while multiple drug resistance constitutes a major problem in management of infectious diseases. The aforementioned problems necessitate continuous investigations for development of novel antioxidant and antimicrobial agents. Here, phytochemical constituents, antioxidant, and antimicrobial activities of n-hexane, ethyl-acetate, 70%-ethanol and methanol extracts of Parquetina nigrescens leaves were investigated. Antioxidant activities were evaluated by total phenolic content, total flavonoid content, total antioxidant capacity, reducing power, DPPH, nitric oxide, and lipid peroxidation assays. Antibacterial (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli) and antifungal (Aspergillus niger, Aspergillus flavus, Candida albican and Penicillium spp.) activities of the extracts were examined using agar well diffusion method. Phytochemical investigations revealed presence of various phytochemicals, including alkaloids, tannins, flavonoids, cardiac glycosides, and terpenoids. Total phenolic contents were in the range 0.321±0.030–0.432±0.030 mg gallic acid/g extract, while total flavonoid contents were in the range 0.020±0.003–0.064±0.006 mg quercetin/g extract. The extracts displayed moderate total antioxidant capacity (TAC) and ferric reducing power; having TAC values in the range 0.820±0.060–0.876±0.030 mg ascorbic acid/g extract and reducing powers in the range 0.01–0.68. The extracts showed moderate to high activities against DPPH radical, nitric oxide and lipid peroxidation; having IC50 values in the range 59.3±10.8–87. 1±14.2 µg/mL, 52.7±10.6–56.9±10.1 µg/mL, and 58.9±18.6–101.3±10.2 µg/mL, respectively. Furthermore, ethyl-acetate extract showed broad spectrum antibacterial activities, while n-hexane extract demonstrated narrow spectrum antifungal activity. These findings suggest that P. nigrescens leaves have potentials as source of antioxidant and antimicrobial agents.