Chemical profile and anti-diabetic activity of Ipomoea aquatica Forssk. extract elucidated by NMR-based metabolomics

Diabetes mellitus (DM) is one of non-communicable disease (NCDs) that is characterized by high glucose content in blood or hyperglycemia, which can lead to long term complications and even death in the case of no proper treatment performed. Therefore, effective control of blood sugar has been known to be one the main issue in dealing with DM and its associated complications. In this study, the influence of various ethanol ratios (0, 20, 50, 80, and 100%) as an extraction solvent and different drying methods including air drying (AD), sun drying (SD) and oven drying (OD) on phytochemical constituents of I. aquatica were investigated using a proton nuclear magnetic resonance (1H NMR) based metabolomics approach. The highest α- glucosidase inhibitory activity was observed for absolute ethanol extract from the OD method with an IC50 value of 204.0 ± 59.0 μg/mL and TPC value of 22.0 ± 0.7 μg GAE/mg extract. Correlation between the α-glucosidase inhibitory activity and the metabolite were analyzed using a partial least square (PLS) analysis. The metabolites that might be responsible for the activity were quercetin derivatives, chlorogenic acid derivatives, sucrose and fructose. Along with our in vitro study, the 1H NMR based metabolomics also been applied to the in vivo model (Sprague-Dawley rats). The in vivo model was first evaluated for understanding the metabolic link between the obesity (OB), lean diabetic (ND+STZ) and obese diabetic (OB+STZ). In this model, the OB+STZ rats mimics the symptom in the type 2 diabetes (T2DM), whereas the lean diabetic rats (ND+STZ) mimics type 1 diabetes (T1DM). The results of multivariate data analysis (MVDA) managed to highlight several similarities and dissimilarities in metabolites level in OB, ND+STZ and OB+STZ. This finding indicates both of the diabetic group (ND+STZ and OB+STZ) and OB rats shared some similar features especially in metabolic traits (2- oxoglutarate, succinate, tryptophan (TRP) and dimethylamine (DMA)), where it manage to highlights the importance of tricarboxylic acid cycle (TCA) and tryptophan (TRP) metabolism in diabetes progression. On the other hand, the differences between ND+STZ and OB+STZ can be seen in the synthesis of ketone bodies and branched chain amino acid (BCAA). Additionally, the effectiveness of the I. aquatica (IA) extracts as a hypoglycemic agent was also tested in vivo using obese Sprague-Dawley streptozotocin (STZ) -induced rats (OB+STZ). The rats were treated for 1 month, and the pathophysiological changes in serum and urine of these treated rats (OB+STZ+IA) and non-treated obese-diabetic rats (OB+STZ) were compared. The serum was assessed for biochemical parameter while the urine was evaluated using 1H NMR. The result from serum showed there was no significant difference (p > 0.05) between the serum glucose of OB+STZ+IA (20.32 ± 8.79 mmol/L) and OB+STZ (24.60 ± 1.67 mmol/L) due to huge variation between the individuals. Interestingly, we found that there was clear discrimination between the urine spectra of OB+STZ+IA and OB+STZ by using 1H-NMR metabolomic approach. The differences between the biochemical results from serum as compared to urine are probably due to the sensitivity of the instruments and the nature of the sample. Analysis of altered metabolites reveals that administration of I. aquatica extracts affects TCA cycle, creatine and creatinine metabolism, amino acids metabolism and nicotine and nicotinamide metabolism. This study highlights the basis for future investigations of I. aquatica as a source of food that has the potential for nutraceutical enhancement and as an ingredient in medicinal preparation.

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