Investigation of α-Glucosidase Inhibitory Metabolites from Tetracera scandens Leaves by GC-MS Metabolite Profiling and Docking Studies

Abstract

Stone leaf (Tetracera scandens) is a Southeast Asian medicinal plant that has been traditionally used for the management of diabetes mellitus. The underlying mechanisms of the antidiabetic activity have not been fully explored yet. Hence, this study aimed to evaluate the α-glucosidase inhibitory potential of the hydromethanolic extracts of T. scandens leaves and to characterize the metabolites responsible for such activity through gas chromatography-mass spectrometry (GC-MS) metabolomics. Crude hydromethanolic extracts of different strengths were prepared and in vitro assayed for α-glucosidase inhibition. GC-MS analysis was further carried out and the mass spectral data were correlated to the corresponding α-glucosidase inhibitory IC₅₀ values via an orthogonal partial least squares (OPLS) model. The 100%, 80%, 60% and 40% methanol extracts displayed potent α-glucosidase inhibitory potentials. Moreover, the established model identified 16 metabolites to be responsible for the α-glucosidase inhibitory activity of T. scandens. The putative α-glucosidase inhibitory metabolites showed moderate to high affinities (binding energies of -5.9 to -9.8 kcal/mol) upon docking into the active site of Saccharomyces cerevisiae isomaltase. To sum up, an OPLS model was developed as a rapid method to characterize the α-glucosidase inhibitory metabolites existing in the hydromethanolic extracts of T. scandens leaves based on GC-MS metabolite profiling.

Keywords: GC–MS metabolomics; Tetracera scandens; metabolite profiling; molecular docking; orthogonal partial least squares; α-glucosidase inhibition.

Figure 1

Typical procedure of the gas chromatography–mass spectrometry (GC–MS) metabolomics studies aiming to characterize the active plant metabolites.

Figure 2

Extraction yield (%) (A) and α-glucosidase inhibitory activity (IC₅₀; µg/mL) (B) of T. scandens leaves hydromethanolic extracts. Values expressed as the mean ± standard deviation of six replicates. IC₅₀ value of the positive control (Quercetin) was 3.29 ± 0.48 µg/mL.

Figure 3

Representative chromatogram of the methanol extract (A) and water extract (B) of T. scandens leaves. Peak assignments: 1—palmitic acid, 2—phytol, 3—linoleic acid, 4—α-linolenic acid, 5—1-monopalmitin, 6—5-methoxy-8,8-dimethyl-10-(3-methyl-2-butenyl)-2H,8H-pyrano[3,2-g] chromen-2-one, 7—stearic acid, 8—questin, 9—emodin, 10—catechin, 11—α-tocopherol, 12—stigmasterol, 13—β-sitosterol, 14—1-triacontanol, 15—cycloartenol, 16—24-methylenecycloartenol acetate.

Figure 4

(A) Scores scatter plot of the established orthogonal partial least squares (OPLS) model for T. scandens leaves extracts, showing the highly active extracts on the negative side of the predictive component t[1], while the less active extracts on its positive side. (B) Loading column plot of the developed OPLS model. Assignments in B: 1—palmitic acid, 2—phytol, 3—linoleic acid, 4—α-linolenic acid, 5—1-monopalmitin, 6—5-methoxy-8,8-dimethyl-10-(3-methyl-2-butenyl)-2H,8H-pyrano[3,2-g] chromen-2-one, 7—stearic acid, 8—questin, 9—emodin, 10—catechin, 11—α-tocopherol, 12—stigmasterol, 13—β-sitosterol, 14—1-triacontanol, 15—cycloartenol, 16—24-methylenecycloartenol acetate.

Figure 5

Putative α-glucosidase inhibitory metabolites.

Figure 6

The 2D diagram of the control docking (A) and the positive control (quercetin) docking (B), with the red lashes representing the residues involved in hydrophobic interactions, while the green dotted lines represent the hydrogen bonds.

Figure 7

The superimposed 3D diagram showing all the putative active metabolites as well as quercetin, docked into the active site of Saccharomyces cerevisiae isomaltase. The 2 metabolites away from the remaining overlapped metabolites are 5-methoxy-8,8-dimethyl-10-(3-methyl-2-butenyl)-2H,8H-pyrano[3,2-g] chromen-2-one and catechin.