Anti-Hyperglycemic Effects of Thai Herbal Medicines

Abstract

This study aims to investigate selected medicinal plants' anti-oxidative and antihyperglycemic activities to develop an effective remedy for lowering blood glucose levels and/or reducing diabetes complications. Thai medicinal plants, reported to have blood sugar-lowering effects, were selected for the study: Coccinia grandis, Gymnema inodorum, Gynostemma pentaphyllum, Hibiscus sabdariffa, Momordica charantia, Morus alba, and Zingiber officinale. Each species was extracted by Soxhlet's extraction using ethanol as solvent. The ethanolic crude extract of each species was then evaluated for its phytochemicals, anti-oxidant, and antihyperglycemic activities. The results showed that the extract of Z. officinale gave the highest values of total phenolic and total flavonoid content (167.95 mg gallic acid equivalents (GAE)/g and 81.70 mg CE/g, respectively). Anti-oxidant activity was determined using DPPH and ABTS radical scavenging activity. Among the ethanolic extracts, Z. officinale exhibited the highest anti-oxidant activity with IC₅₀ values of 19.16 and 8.53 µg/mL, respectively. The antihyperglycemic activity was assessed using α-glucosidase inhibitory and glucose consumption activities. M. alba and G. pentaphyllum demonstrated the highest α-glucosidase inhibitory activity among the ethanolic extracts, with IC₅₀ values of 134.40 and 329.97 µg/mL, respectively. Z. officinale and H. sabdariffa showed the highest percentage of glucose consumption activity in induced insulin-resistant HepG2 cells at a concentration of 50 µg/mL with 145.16 and 107.03%, respectively. The results from α-glucosidase inhibitory and glucose consumption activities were developed as an effective antihyperglycemic remedy. Among the remedies tested, the R1 remedy exhibited the highest potential for reducing blood glucose levels, with an IC₅₀ value of 122.10 µg/mL. Therefore, the R1 remedy should be further studied for its effects on animals.

Keywords: Thai herbal medicine; anti-oxidant; antihyperglycemic; remedy; type 2 diabetes.

Figure 1

Effect of medicinal plants on cell viability in insulin-resistant HepG2 cells by SRB assay. The results were represented as mean ± SD (n = 3) and significantly different from the control group (untreated group) (* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).

Figure 2

Glucose consumption percentage of ethanolic extracts; (a) C. grandis extract; (b) G. inodorum extract; (c) G. pentaphyllum extract; (d) H. sabdariffa extract; (e) M. charantia extract; (f) M. alba extract and (g) Z. officinale extract. The results were represented as mean ± SD (n = 3), and significantly differed from the control group (insulin-resistant group) (* p < 0.05).

Figure 3

Glucose consumption percentage of remedies: (a) R2 remedy and (b) R3 remedy. The results were represented as mean ± SD (n = 3) and significantly differed from the control group (insulin-resistant group) (* p < 0.05).

Figure 4

TLC chromatograms of ethanolic extract of remedy: (a) visible light; (b) UV at 254 nm; (c) UV at 366 nm; (d) 20% sulfuric acid spraying reagent; (1) rutin; (2) quercetin; (3) chlorogenic acid; (4) ginsenoside Rb1; (5) G. pentaphyllum extract; (6) M. alba extract and (7) the R1 remedy.

Figure 5

Compound structures of standard references: (a) rutin, (b) quercetin, (c) chlorogenic acid and (d) ginsenoside Rb1.

Figure 6

Densitograms of the remedy: (a) UV 254 nm, (b) UV at 366 nm, (1) rutin, (2) quercetin, (3) chlorogenic acid, (4) ginsenoside Rb1, (5) G. pentaphyllum extract, (6) M. alba extract and (7) the R1 remedy.