Free radical scavenging activity, total phenolic and flavonoid constituents of medicinal plants used in Nigerian ethnobotany

Abstract

Introduction: Plant polyphenols have the ability to protect biomolecules and cell membrane from oxidative stress thereby offering protection against the development of wide range of diseases. This study evaluated the antioxidant property of the methanol extract of twelve medicinal plants, identified and selected from a previous ethnos botanical studies conducted in South-western region of Nigeria. Methods: 2, 2-Diphenyl l-picryl hydrazyl (DPPH) free radical scavenging and nitric oxide inhibitory assays were used to evaluate the antioxidant activities. Total phenolic content (expressed as garlic acid equivalent), total flavonoid (expressed in terms of quercetin equivalent) and total antioxidant capacity were also determined by standard methods. Garlic and ascorbic acid were included in the study as reference standards. Results were expressed as the mean ± SEM. Differences between means were tested for statistical significance using student t-test (p≥ 0.05). Results: The extracts exhibited scavenging activities against the DPPH radical. Uvaria chamae (stem bark) and Thonningia Sanguinea (whole plant) had IC50 values of 4.30 and 6.12 respectively, though not comparable to standard drug (ascorbic acid) with IC50 value of 1.4 µg/mL However, T.sanguinea extracts exhibited the highest nitric oxide inhibitory activity with IC50 values of 1.3±0.1 µg/mL significantly comparable to garlic acid with an IC50 of 1.1 ±0.1 µg /mL (p≥ 0.05). Methanol extract of T. sanguinea and K. senegalensis (stem bark) had the highest phenolic contents 343 ± 1.79 and 346 ± 0.02 mg/g respectively. Thonningia sanguinea had the highest total antioxidant capacity (TAC) of 374.46 ± 8.41 AAE (mg/g). Uvaria chamae, had the highest flavonoid content of 84.84 ± 6.26 QE mg/g of quercetin equivalent. Conclusion: This study suggests that the screened plants, especially Thonningia sanguinea can serve as a valuable source of plant antioxidants.