Biologically active phenolic acids produced by Aspergillus sp., an endophyte of Moringa oleifera

摘要

This study investigates the secondary metabolites of an endophytic Aspergillus sp. isolated from leaves of M. oleifera growing in Anambra State, South-Eastern Nigeria. Antimicrobial and antioxidant screening of the fungal extract and isolated compounds, as well as cytotoxicity assay of the extract against cisplatin-sensitive A2780 (sens) and cisplatin-resistant A2780 (cisR) ovarian cancer cell lines were carried out using standard methods. Chemical investigations of the fungal extract involving a combination of different chromato-graphic methods and spectroscopic techniques were carried out to isolate and characterize the constituents of the extract. At a concentration range of 1-4 mg/ml, the crude extract of Aspergillus sp. showed mild antimicrobial activity against Bacillus subtilis, Klebsiella pneumoniae, and Candida albicans. The fungal extract showed good antioxidant activity at 500 μg/ml, with an inhibition of 72.1%. Also, at 100 μg/ml, the extract showed excellent cytotoxic activity against A2780 (sens) and A2780 (cisR), with growth inhibitions of 105.1% and 105.5% respectively. Two known pharmacologically active phenolic compounds (p-hydroxyphenyl acetic acid and ferulic acid) were isolated from the fermentation extract of the endophytic fungus. At 250 μg/ml, ferulic acid exhibited an excellent antioxidant activity with an inhibition of 90.4%, while an inhibition of 35.4% was recorded for p-hydroxyphenyl acetic acid. Ferulic acid also showed a mild antifungal activity at 500 μg/ml against A. niger with an IZD of 2 mm. p-Hydroxyphenyl acetic acid showed no antimicrobial activity. These results further confirm the potentials of endophytic fungi associated with Nigerian plants as source of bioactive compounds with pharmaceutical or industrial applications.