Antioxidant and Antidiabetic Activities, and UHPLC-ESI-QTOF-MS-Based Metabolite Profiling of an Endophytic Fungus Nigrospora sphaerica BRN 01 Isolated from Bauhinia purpurea L.

Abstract

Diabetes-associated postprandial hyperglycemia is a major risk factor in cardiovascular disease. Since enzyme α-glucosidase is primarily responsible for glucose release during digestion, inhibiting it mitigates post-meal spike in blood glucose level. Metabolites from endophytic fungi could be potential natural inhibitors of this enzyme. Endophytic fungi isolated from Bauhinia purpurea L. were screened for their potential antioxidant and antidiabetic activities. Ethyl acetate extract of Nigrospora sphaerica BRN 01 (NEE) displayed high antioxidant activity with an IC50 value of 9.72 ± 0.91µg/ml for DPPH assay and ferric reducing antioxidant power (FRAP) of 1595 ± 0.23µmol AAE g-1 DW. NEE also showed high degree of inhibition of α-glucosidase activity with an IC50 value of 0.020 ± 0.001mg/ml, significantly greater than the standard drug acarbose (0.494 ± 0.009mg/ml). Metabolite profiling of NEE was carried using ultra-high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS) and 21 metabolites identified based on the MS/MS fragmentation patterns. Docking analysis of all 21 identified metabolites was carried out. Of these, 6 showed binding energies higher than acarbose (- 6.6kcal/mol). Based on the analysis of interactions of feruloyl glucose with active site residues of the enzyme, it could be a potential α-glucosidase inhibitor. Metabolites of Nigrospora sphaerica BRN 01, therefore, could be potential lead molecules for design and development of antidiabetic drugs.