Screening of Endophytic Fungal Secondary Metabolites from Garcinia kola and Cola nitida for Antioxidant Properties

Objectives: Plant endophytic fungi are novel reservoir of bioactive compounds. The aim of this study was to explore endophytic fungi from Garcinia kola and Cola nitida for antioxidant secondary metabolites. Methods: Six fungal endophytes, Gn1-3 and Cn1-3 were isolated from the medicinal plants G. kola and C. nitida respectively. The pure endophytes were fermented, their crude secondary metabolites extracted and screened for antioxidant properties using 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) scavenging activities and reducing power (RP) assay. The bioactive principles were identified by dereplication using High Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD) analysis Results: Extracts of Cn3 (identified as Trichophyton sp.) and Gc3 (identified as Collectotrichum sp.) demonstrated the most potent antioxidant activity. In the DPPH scavenging assay, extracts of Cn3 and Gc3 showed an IC50 of 50.7 and 69.1µg/ml respectively compared to ascorbic acid (12.2µg/ml). Extracts of Cn3, Gc3and positive control (ascorbic acid, 250μg/ml) showed reduction values of 1.112 ± 0.011, 1.075 ± 0.014 and 1.203 ± 0.004, respectively. There was positive correlation between TPC and results obtained in both assay (DPPH, R2 = 0.7039; RP, R2 = 0.9778), thus suggesting phenolics-related antioxidant activity. HPLC-DAD analysis revealed extract of Cn3 contain protocatechuic acid and phydroxybenzoic acid, while Gn3contain 4-hydroxyphenyl acetic acid and indole-3-acetic acid. These compounds have been previously reported to exhibit potent antioxidant activity. In conclusion, this study reveals that endophytic fungi from both plants possess potential antioxidant properties. The secondary metabolites present in these endophytic fungi have potential for pharmaceutical and agrochemical applications.