Antioxidant activity of extracts from Xanthium strumarium – A medicinal plant from the Kingdom of Lesotho

Xanthium strumarium L. finds therapeutic applications in traditional medicines. The objective of the current study was to evaluate the antioxidant activity and to determine the total phenolic contents (TPCs) and total flavonoid contents (TFCs) of hexane, chloroform, ethyl acetate, acetone, methanol, and water extracts obtained from the leaves and stem bark of X. strumarium. Maceration and hot solvent extraction techniques were used to obtain various solvent extracts. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric-reducing power assays were used to evaluate the antioxidant activity. Folin-Ciocalteu colorimetric and aluminum chloride colorimetric methods were used to determine the TPCs and TFCs, respectively. The extracts from the leaves and stem bark exhibited radical scavenging activity in the ranges of 18.06 ± 0.3-185.67 ± 11.54% and 9.13 ± 0.54-84.18 ± 0.92%, respectively at a concentration range of 200-3000 µg/ml. The positive control, ascorbic acid, exhibited radical scavenging activity in a range of 56.64 ± 1.26-88.98 ± 0.31% at a concentration range of 200-3000 µg/ml. Additionally, the IC50 values of all these extracts were determined. The hexane and chloroform extracts from both leaves and stem bark and methanol leaf extract were found to be the most potent extracts with an IC50 value of < 200 µg/ml for each extract. The IC50 value of positive control, ascorbic acid was determined to be < 200 µg/ml. Furthermore, in the ferric-reducing power assay, ethyl acetate extract from both leaves and stem bark exhibited the highest ferric-reducing power of 0.996 ± 0.101 and 0.947 ± 0.018 at a concentration of 100 µg/ml. Moreover, the methanol extract from the leaves showed the highest TPCs of 133.41 ± 3.23 mg GAE/g of DW of extract followed by the methanol extract from stem bark and the acetone extract from the leaves with TPCs of 121.21 ± 3.14 and 118.01 ± 1.85 mg GAE/g of DW of extract, respectively. Similarly, the methanol extract from the leaves also showed the highest TFCs of 20.61 ± 1.81 mg QE/g of DW of extract followed by the methanol extract from stem bark with TFCs of 14.90 ± 1.18 mg QE/g of DW of extract. From this study, we concluded that various extracts obtained from the leaves and stem bark of X. strumarium exhibited a moderate-to-strong radical scavenging activity and ferric-reducing power and possessed a significant amount of TPCs and TFCs.