Myrothamnus flabellifolius Welw. (Myrothamnaceae) essential oil scavenges free radicals and inhibits carbohydrate-metabolizing enzymes in vitro

Myrothamnus flabellifolius is an important medicinal plant traditionally used in southern Africa to treat an array of diseases, including diabetes mellitus. This study investigates the chemical compositions, antioxidant activity, and the inhibition of carbohydrate-metabolizing enzymes by essential oil from Myrothamnus flabellifolius leaves (MFEO). The oil extracted by hydrodistillation was analyzed by gas chromatography – flame thermionic detector (GC – FTD) and GC – mass spectrometry (GC – MS). The antioxidant and antidiabetic activities of the oil were carried out using standard in vitro methods. MFEO displayed potent antioxidant effects more than standards for superoxide anion, nitric oxide, metal chelation, and hydroxyl radical scavenging assays with half-maximal inhibitory concentration (IC50) values 0.23, 0.71, 0.58, and 0.43 mg/mL respectively. The oil also displayed significantly higher (p < 0.05) inhibition of α-glucosidase and α-amylase enzymes than acarbose, with IC50 values of 0.52 and 0.59 mg/mL, respectively. The chemical analysis of MFEO revealed the presence of twenty (20) compounds dominated mainly by monoterpenes and non-terpenoid derivatives. The major oil constituents were β- myrcene (37.1%), mentha-1,5,8-triene (24.9%), and α-pinene (10.80%). Some of these identified components have been reported to be antioxidative and antidiabetic, buttressing the displayed effects of MFEO.