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

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 ± 0.91 µg/ml for DPPH assay and ferric reducing antioxidant power (FRAP) of 1595 ± 0.23 µmol AAE g-1 DW. NEE also showed high degree of inhibition of α-glucosidase activity with an IC50 value of 0.020 ± 0.001 mg/ml, significantly greater than the standard drug acarbose (0.494 ± 0.009 mg/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 (- 6.6 kcal/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.

Metabolic fingerprinting of Ganoderma spp. using UHPLC-ESI-QTOF-MS and its chemometric analysis

A UHPLC-QTOF-MS method was developed to separate and identify 70 triterpenes present in each of the 18 strains of Ganoderma spp. Collected from various parts of India. A PCDL MS library was used to retrieve and identify these 70 triterpenes by meticulous analysis of MS/MS fragments. The MS data from these 18 strains were further statistically analysed to arrive at meaningful conclusions. Heatmap analysis suggested that Ganoderma spp. G44, G25 and G36 were the top three strains of Ganoderma mushrooms based on their metabolic concentration in Indian biota. From the PCA loading plot, it was observed that the triterpenes Ganoderic acid A, Ganoderic acid D, Ganoderic acid F, Ganoderic acid J, Ganoderic acid M, Ganoderic acid N, Ganoderenic acid B, Ganoderiol H, 3β,7β-Dihydroxy-11,15,23-trioxo-lanost-8,16-dien-26-oic acid, 3β,7β,15β-trihydroxy-11,23-dioxo-lanost-8,16-dien-26-oic acid and 20 - hydroxy ganoderic acid AM1 were identified as the principal contributors for the discrimination of a particular strain of the mushroom. We have also identified the samples obtained from different regions of India with the highest concentration of metabolites with potent biological activity. The results presented here could be very helpful for both scientific and industrial applications such as quality control of various medicines and food additives containing triterpenes.