Phenolic composition, antioxidant and enzyme inhibitory activities of Parkia biglobosa (Jacq.) Benth., Tithonia diversifolia (Hemsl) A. Gray, and Crossopteryx febrifuga (Afzel.) Benth

Abstract

Medicinal plants from Chad grow under special climatic conditions in between the equatorial forest of Central Africa and the desert of North Africa and are understudied. Three medicinal plants from Chad (T. diversifolia, P. Biglobosa and C. Febrifuga) were evaluated for their phenolic composition, antioxidant and enzyme inhibition activities. The total phenolic composition varied from 203.19 ± 0.58 mg GAE/g DW in the ethyl acetate extract of P. biglobosa, to 56.41 ± 0.89 mg GAE/g DW in the methanol extract of C. febrifuga while the total flavonoid content varied from 51.85 ± 0.91 mg QE/g DW in the methanol extract of P. biglobosa to 08.56 ± 0.25 mg QE/g DW in the methanol extract of C. febrifuga. HPLC-DAD revealed that rutin, gallic acid and protocatechuic acid were the most abundant phenolics in T. diversifolia, P. Biglobosa and C. Febrifuga respectively. The antioxidant activity assayed by five different methods revealed very good activity especially in the DPPH•, ABTS•+ and CUPRAC assays where the extracts were more active than the standard compounds used. Good inhibition was exhibited against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with methanol (IC50: 15.63 ± 0.72 µg/mL), ethyl acetate (IC50: 16.20 ± 0.67 µg/mL) extracts of P. biglobosa, and methanol (IC50: 21.53 ± 0.65 µg/mL) and ethyl acetate (IC50: 30.81 ± 0.48 µg/mL) extracts of T. diversifolia showing higher inhibition than galantamine (IC50: 42.20 ± 0.44 µg/mL) against BChE. Equally, good inhibition was shown on α-amylase and α-glucosidase. On the α-glucosidase, the ethyl acetate (IC50 = 12.47 ± 0.61 µg/mL) and methanol extracts (IC50 = 16.51 ± 0.18 µg/mL) of P. biglobosa showed higher activity compared to the standard acarbose (IC50 = 17.35 ± 0.71 µg/mL) and on α-amylase, the ethyl acetate (IC50 = 13.50 ± 0.90 µg/mL) and methanol (IC50 = 18.12 ± 0.33 µg/mL) extracts of P. biglobosa showed higher activity compared to acarbose (IC50 = 23.84 ± 0.25 µg/mL). The results indicate that these plants are good sources of antioxidant phenolics and can be used to manage oxidative stress linked illnesses such as Alzheimer’s disease and diabetes.