Extracts of endophytic fungi from leaves of selected Nigerian ethnomedicinal plants exhibited antioxidant activity

Background: Plants with an ethnobotanical history are known to harbor diverse group of endophytic fungi, which constitute major natural sources of bioactive compounds. In the present study, we evaluated the antioxidant activity of endophytic fungi from eight Nigerian ethnomedicinal plants. Endophytic fungi were isolated from the leaves of Acalypha ornata, Albizia zygia, Alchornea cordifolia, Chrysophyllum albidum, Ficus exasperata, Gomphrena celosioides, Millettia thonningii, and Newbouldia laevis.

Methods: Endophytic fungi were isolated from the leaves of selected plants via surface sterilization. Isolated fungi were identified by internal transcribed spacer (ITS-rDNA) sequence analysis. Pure fungal strains were subjected to fermentation process on solid rice medium and metabolites extracted using ethyl-acetate. Fungal crude extracts were screened for antioxidant activity using 2, 2- diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and reduction of ferric ion assays. Gas chromatography/mass spectrometry (GC/MS) analysis was used to identify the major chemical constituents in active fungal extracts.

Results: A total of eighteen fungal endophytes with fungal codes CU (061 and 062); ZA (161, 162, 163, and 164); LO (261); CA (041, 042, and 043); FE (081, 082, and 084); GE (091); MO (211 and 212); and NA (021 and 022) were isolated from the eight ethnomedicinal plants A. ornata, A. zygia, A. cordifolia, C. albidum, F. exasperata, G. celosioides, M. thonningii, and N. laevis respectively. ZA 163 and MO 211 fungal extracts showed significant (p < 0.05) radical scavenging activity with IC₅₀ values of 50.53 ± 0.01 and 86.69 ± 0.02 μg/ml respectively. Fungal extract CA 041 demonstrated significantly (p < 0.01) higher iron chelating activity than standard gallic acid with absorbance values of 0.803 and 1.107 at 250 and 500 μg/ml concentrations respectively. Pyrogallol, phenol, 2,6-dimethoxy-, phytol, dl-alpha-tocopherol, alpha-tocospiro, oleamide, methyl stearate, oleic acid, palmitic acid, campesterol, stigmasterol, β-sitosterol, urs-12-en-24-oic acid, 3-oxo-, methyl ester, lup-20(29)-en-3-one, and lupeol were detected in the selected active extracts.

Conclusion: These results showed that leaves of the selected Nigerian plants harbor diverse group of endophytic fungi, which can be potential antioxidant resource.