Antioxidant, Glucose Uptake Stimulatory, α-Glucosidase and α-Amylase Inhibitory Effects of Myrianthus arboreus Stem Bark

Myrianthus arboreus is used traditionally in the management of diabetes in Ghana. The study seeks to evaluatethe antioxidant, glucose uptake, α-glucosidase and α-amylase inhibitory activities of the stem bark to support its folkloric use. The ethanol stem bark extract of M. arboreus was partitioned successively with petroleum ether, chloroform, ethyl acetate and n-butanol. The extract and fractions were evaluated for their glucose uptake effects in C2C12 myotubes and 3T3-L1 adipocytes. Their inhibitory action on α-glucosidase and α-amylase were also investigated whereas their antioxidant activities were evaluated using the DPPH and nitric oxide scavenging assays. The crude extract was further evaluated for its phenolic content, antioxidant capacity and reducing power. The stem bark extract significantly (P<0.05) stimulated glucose uptake in C2C12 myotubes and 3T3-L1 adipocytes when compared to control and also showed potent inhibitory activities against α-glucosidase and α-amylase with 11-fold and 5-fold better activity than acarbose respectively. The DPPH and nitric oxide radical scavenging effect of the extract were comparable with the ascorbic acid and α-tocopherol respectively. The extract had high phenol content with tannic acid equivalent of (114.70 ± 10.48) mg/g with an ascorbic acid equivalent of (98.34 ± 14.50) mg/g. The fractions demonstrated varying glucose uptake and enzyme inhibitory activities with the ethyl acetate fraction being the most potent. The ethyl acetate fraction demonstrated the highest scavenging effect on the DPPH and nitric oxide radicals. M. arboreus stem bark extract showed significant antioxidant, glucose uptake and enzyme inhibitory activities justifying its use in traditional medicine.