Anti–hyperglycemic Effect of Gymnema inodorum (Lour.) Decne Leaf Extract in Streptozotocin-Induced Diabetic Rats

Abstract

Introduction and Objectives: Diabetes mellitus is a chronic metabolic disorder with high prevalence worldwide, representing a significant public health problem. The treatments currently rely on pharmacotherapy, which sometimes cause adverse effects and have limitations. This has led to a growing interest in the use of herbal medicine as an alternative therapy. Gymnema inodorum (Lour.) Decne (‘phak chiang da’ in Thai) is a plant that has received considerable attention from both the public and researchers due to its purported hypoglycemic properties and its widespread commercialization into various products. This study aims to investigate the effect of the aqueous extract of Gymnema inodorum leaves on blood glucose levels in streptozotocin (STZ)–induced diabetic rats.

Methods: The collected medicinal plant was identified by a botanist (voucher specimen: DMSC 5260). The aqueous extract was prepared and its chemical quality was controlled by analyzing the content of gymnemic acid, total flavonoids, moisture, total ash, and acid-insoluble ash. For the anti-hyperglycemic test, 6 normal rats were placed in Group 1 (Normal control) receiving reverse osmosis (RO) water, while 30 streptozotocin-induced diabetic rats were divided into five groups (Groups 2-6, n=6 each), i.e., Group 2 (Negative control) received RO water, Group 3 (Positive control) received metformin (300 mg/kg/day). Groups 4–6 (Experimental groups) received the extract at doses of 125, 250, and 500 mg/kg/day, respectively, for 14 days. On days 3, 7, 10, and 14 after treatment began, animals were fasted for 8 hours prior to venipuncture to measure fasting blood glucose (FBG) levels. Differences of FBG levels between groups and percentage change of FBS levels were analyzed using two-way repeated measures ANOVA followed by Bonferroni post-hoc test for multiple comparisons. A p-value of less than 0.05 was considered statistically significant.

Results: The aqueous extract was a dark brown coarse powder with % yield of 46.01. Chemical analysis showed total flavonoids of 64.33 mg quercetin equivalent per gram extract, 7.67% moisture, 12.80% total ash, 0.22% acid-insoluble ash, and 1.79% gymnemic acid. In the animal model, the metformin group showed a continuous and significant reduction in FBS levels compared to the negative control group (p < 0.05) from day 3 to day 14. Similarly, diabetic rats treated with 250 and 500 mg/kg of the extract showed significantly lower FBS levels compared to the negative control group (p < 0.05). However, the group receiving 125 mg/kg extract did not show a statistically significant difference (p > 0.05). Regarding the percentage change in fasting blood glucose from Day 0 (% change in FBS), the groups treated with 500 mg/kg of the extract and metformin showed a continuous decline from day 3 to 14. These reductions of % change in FBS were statistically significant compared to the diabetic control group (p < 0.05). Furthermore, the glucose-lowering efficacy of the extract at this dosage was not different from that of metformin.

Discussion: The aqueous extract containing 1.79% gymnemic acid at doses of 250 and 500 mg/kg effectively reduced blood glucose levels in diabetic rats. These findings are consistent with previous experimental studies in other countries.

          Conclusion and Recommendations: This study demonstrates that G. inodorum is a promising plant for managing blood glucose or developing health products for diabetic and pre-diabetic individuals. However, caution is advised when using it alongside anti-diabetic drugs to avoid potential hypoglycemia (low blood sugar). Consumers with underlying diseases or those taking other medications should consult a physician, as drug-herb interactions have not yet been fully studied. Future research should focus on chronic toxicity and the specific mechanisms of action to ensure safety and enhance the quality of G. inodorum products.

Key words: Gymnema inodorum, gymnemic acid, anti–hyperglycemic, animal model, streptozotocin