Judul: Metabolomic Application in Identification α-Glucosidase Inhibitor from Vegetables and Spices
Abstrak: Diabetes mellitus is a degenerative disease with a high prevalence worldwide. Plant-based foods such as vegetables and spices were often reported to be able to reduce the risk of and even cure diabetes mellitus, especially type 2 (T2DM). Indonesia has many natural resources such as vegetables and spices that can be sources of antidiabetic foods. However, the antidiabetic activity of many vegetables and spices have not been evaluated. Besides, studies to observe the bioactive compounds responsible for the antidiabetic activity of vegetables and spices are still limited. One of the antidiabetic activities commonly studied from plant species is the α-glucosidase inhibition. Therefore, the objective of this study was to evaluate the potency of α-glucosidase inhibition of 11 vegetables and 4 spices commonly consumed in Indonesia and to identify their bioactive compound using a metabolomic approach. This study consisted of 3 stages: 1) Screening α-glucosidase inhibition activity of Indonesian vegetables and spices, (2) characterization of antioxidant compound from selected plant (obtained from the first stage) using UHPLC-HRMS and identification of its α-glucosidase inhibitor using NMR- and HPLC combined with UHPLC-HRMS metabolomics, and (3) verification of α-glucosidase inhibition activity of putative compounds (obtained from the second stage) through in silico analysis. The results of the first study showed that the highest antioxidant and α-glucosidase inhibition activity was found in leaves extract of Syzygium polyanthum followed by Pluchea indica with the values of the IC50 antioxidant activity being 2.46 and 4.34 μg/ml, respectively. The values of their IC50 of α-glucosidase inhibition were 11.76 and 12.17 μg/ml, respectively. Interestingly, the total phenolic content of these two samples was also higher than others with 25.37 and 37.99 μg GAE/mg extract, respectively. The 1H-NMR fingerprinting analysis showed that each sample had different spectral profile, especially at the aromatic region (chemical shift (δ) > 5.7). Further metabolite profiling on the 1H-NMR of S. polyanthum revealed the presence of gallic acid, syringic acid, and myricetin, whereas 5-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid methyl ester, and esculetin were found in the 1H-NMR of P. indica. Previous studies reported that all identified compounds had antidiabetic activity especially through α-glucosidase inhibition. Thus, those compounds might be associated with the α-glucosidase inhibition activity of S. polyanthum and P. Indica, which was investigated further in the next step. Based on the results of the first study, S. polyanthum leaves were chosen for the second stage. Dried leaves of S. polyanthum were fractionated using solvents with different polarity sequentially i.e. hexane, combination of hexane-acetone, acetone, combination of acetone-water and water to obtain 14 fractions. Analysis of antioxidant activity through the ability to reduce radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) indicated that at a tested concentration of 500 μg/ml, Fraction 9/F9 (obtained from acetone:water = 4:1) gave the highest antioxidant activity followed by Fraction 1/F1 (obtained from hexane 100%), Fraction 10/F10 (obtained from acetone:water = 3:2) and Fraction 3 (obtained from hexane:acetone = 4:1) with the values of 95.21, 94.82, 93.37 and 93.19%, respectively. The characterization of the UHPLC-HRMS chromatogram of F9 identified the presence of gallic acid, trans-aconitic acid, and myricetin, while only gallic acid and trans-aconitic acid were identified in
Keyword: α-glucosidase, antioxidant, docking, HPLC-UHPLC-HRMS, metabolomics, NMR, Syzygium polyanthum