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Conflict of interest
Acknowledgement
Introduction Diabetes mellitus (DM) is a serious global health program which is characterized by high blood glucose levels, which lead to complications such as retinopathy, hypertension, neuropathy and diabetic foot ulcers [1]. Type 2 DM caused by defects in insulin secretion or insulin resistance [2] is the most frequently encountered form of DM, accounting for more than 80% of all cases [3]. The α-glucosidase enzyme in the intestine is essential for carbohydrate degradation so that the resulted monosaccharides can be absorbed. The inhibition of α-glucosidase enzyme leads to a delay in the digestion of ingested androgen receptor inhibitor [4]. Thus α-glucosidase inhibitors exhibit high promise as therapeutic agents for the treatment of type 2 of DM [5]. Most of DM treatments are based on the use of synthetic drugs, which are associated with several side effects [6]. Therefore, the development of natural compounds as alternatives pharmaceuticals for the treatment of DM without any side effects is urgently needed. Another advantage is that natural compounds may be safely consumed in the daily diet, thereby reducing the risk of DM [7]. Endophytic fungi are the microorganisms that spend all or part of their life cycles within plant tissue without causing harmful effects on the plant [8]. Endophytic fungi usually get nutrition and protection from their host plant and promote the growth of the plant by producing certain bioactive substances [9]. Endophytic fungi in plants are promising sources of bioactive metabolites. Recent studies show that endophytic fungi have an ability to produce many novel chemicals that could be directly use as drugs or source of bioactive natural products [10]. Several research indicate endophytic fungi have bioactive compounds that could potentially be applied in various applications such as antioxidant [11], antifungal [12], antiviral [13], antibacterial [14] and cyotoxic [15]. In our previous study, we found that several bioactive compounds such as catechin, epicatechin, tiliroside, β-sitosterol glucoside and condensed tannins were isolated from Quercus gilva Blume and Quercus phillyraeoides A. Gray [16,17]. Catechin and epicatechin isolated from Q. gilva Blume were having good antioxidant properties while tiliroside had strong ability as α-glucosidase inhibitor activity; therefore, in this study we conducted isolation of endophytic fungi from Quercus gilva Blume (Q. gilva). Endophytic fungus QGS 01 from Q. gilva was found to have a strong α-glucosidase inhibitory activity. This QGS 01 fungus was identified as a Xylariaceae sp. This present work highlighted the α-glucosidase inhibitory activity of constituents isolated from the mycelium extract of Xylariaceae sp. QGS 01. Extract of Xylariaceae sp. QGS 01 mycelium were obtained using ethyl acetate and the isolation of active constituent was conducted using bioassay-guided fractionation technique. An in vitro assay of α-glucosidase inhibitory activity was conducted using α-glucosidase enzyme obtained from Saccharomyces cerevisiae (S. cerevisiae) yeast. This assay may be used for preliminary observations in the evaluation of pharmalogical activities and also to verify the medicinal effects of these active constituents isolated from endophytic fungus.
Materials and methods
Results and discussion
Conclusion Endophytic fungi Xylariaceae sp. QGS 01 was isolated from the stem of Quercus gilva Blume and showed high activity of α-glucosidase inhibitory activity. One active constituent: 8-hydroxy-6,7-dimethoxy-3-methylisocoumarine (1) was isolated from endophytic fungi Xylariaceae sp. QGS 01. Compound 1 had inhibitory concentration (IC50) values against α-glucosidase from Saccharomyces cerevisiae of 41.75μg/mL.
Acknowledgement