Antioxidant activity of the leaves extracts of Boscia coriacea Graells and Uvaria leptocladon Oliv

Background: Synthetic antioxidants used for the management of oxidative stress have been shown to have severe side effects. Some medicinal plants that belong to the genus Uvaria and Boscia contain chemicals with antioxidant properties such as flavonoids and alkaloids.

Objective: This study was aimed to evaluate the antioxidant activities of the leaf extracts of Boscia coriacea Graells and Uvaria leptocladon Oliv.

Method: Fresh leaves of B. coriacea and U. leptocladon were collected in April 2021 from Alie and Konso,  located in Southern Ethiopia. First, the leaves of the medicinal plants were dried in dark conditions. Maceration extraction method was used to extract the powdered leaf of Boscia coriacea and Uvaria leptocladon. The crude extract of B. coriacea was fractionated using chloroform (CHCl₃₎, methanol (CH₃OH), CHCl₃: CH₃OH(1:1 v/v) and petroleum ether. The crude extract of U. leptocladon was fractionated using CHCl₃, ethanol (C₂H₆OH), and ethyl acetate (C₄H₈O₂). Evaluation of the antioxidant activity was done using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), and ferric reducing antioxidant power (FRAP) assays. Data analysis was done using one-way analysis of variance.

Result: The antioxidant evaluation demonstrated that the leaf extracts of B. coriacea and U. leptocladon have 2,2-diphenyl-1-picrylhydrazyl and 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid radical scavenging activity. Based on IC₅₀ value, the CH₃OH: CHCl₃ (1:1) fraction of B. coriacea (IC₅₀=38.2 μg/mL) and the C₂H₆OH fraction of U. leptocladon (IC₅₀=30.5 μg/mL) are highly active in 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity. The total flavonoid content in the CH₃OH:CHCl₃ fraction of B.coricea and in the C₂H₆OH fraction of U.leptocladon were calculated to be 136.8±0.04 mg/g of extract and 172.9±0.41 mg/g of extract, respectively. The total phenol content in the CH₃OH: CHCl₃ fraction of B.coricea and in the C₂H₆OH fraction of U.leptocladon were calculated to be 145 ± 0.025 mg/g and 187.7 ± 0.055 mg/g, respectively. The CH₃OH: CHCl₃ (1:1) fraction of B. coriacea and the C₂H₆OH fraction of U. leptocladon  showed the highest ferric reducing antioxidant power. The antioxidant effects of the leaf extract of B. coriacea are due to β-sitosterol and lucidine-type compound. The antioxidant effects of the leaf extract of U. leptocladon  are attributed to β-sitosterol, β-sitosterol glucoside, and α-humulene.

Conclusion: The leaf extracts of B. coriacea and U. leptocladon have high antioxidant activity. Further study is needed to determine the mechanism of action of compounds isolated from the leaf extracts of B. coriacea and U. leptocladon.