COMPARATIVE IN VITRO ANTIDIABETIC AND ANTIOXIDANT ACTIVITIES OF CURCUMIN, RESVERATROL, QUERCETIN, AND BERBERINE: ENZYME INHIBITION KINETICS AND PANCREATIC BETA-CELL CYTOPROTECTION STUDIES

Abstract

Background: Type 2 diabetes mellitus (T2DM) is a multifactorial metabolic disease characterized by chronic hyperglycemia, insulin resistance, progressive pancreatic beta-cell dysfunction, and heightened oxidative stress. The limitations of existing pharmacotherapy including adverse effects, treatment fatigue, and inadequate durability have renewed interest in phytochemical nutraceuticals with multi-target antidiabetic profiles.

Objectives: This study comparatively evaluated the in vitro antidiabetic potential of four widely studied nutraceuticals curcumin, resveratrol, quercetin, and berberine through alpha-glucosidase inhibition, alpha-amylase inhibition, DPPH and ABTS radical scavenging assays, and high-glucose-induced cytotoxicity protection in rat insulinoma (RIN-m5F) pancreatic beta-cells.

Materials and Methods: All four compounds were obtained at analytical grade and screened across a concentration range of 12.5–400 μg/mL. Enzyme inhibitory activity against yeast alpha-glucosidase (EC 3.2.1.20) and porcine pancreatic alpha-amylase (EC 3.2.1.1) was assessed using chromogenic substrate assays, with acarbose as positive control. Antioxidant capacity was determined by DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging assays. Cytoprotective activity against high-glucose-induced injury in RIN-m5F cells was assessed by MTT assay at 25 μM, with metformin (500 μM) as reference. IC50 values were calculated by nonlinear regression; data are expressed as mean ± SD (n = 3); statistical significance determined by one-way ANOVA with Tukey's post-hoc test (p < 0.05).

Results: Berberine exhibited the strongest alpha-glucosidase inhibitory activity (IC50 = 22.6 ± 1.5 μg/mL), followed by quercetin (31.2 ± 1.8 μg/mL), curcumin (48.3 ± 2.1 μg/mL), and resveratrol (62.7 ± 3.4 μg/mL), compared to acarbose (IC50 = 18.4 ± 0.9 μg/mL). A similar rank order was observed for alpha-amylase inhibition. In antioxidant assays, quercetin demonstrated superior radical scavenging (DPPH IC50 = 19.4 ± 1.2 μg/mL; ABTS IC50 = 15.7 ± 1.1 μg/mL), surpassing resveratrol and curcumin, while berberine was the weakest antioxidant. In MTT cytoprotection assays, berberine most effectively restored beta-cell viability under high-glucose conditions (85.6 ± 2.5%; 62.5% protection), followed by quercetin (82.3 ± 2.7%), metformin reference (83.2 ± 2.8%), and curcumin (78.4 ± 2.9%); all were significantly superior to the high-glucose control (p < 0.001).

Conclusion: All four nutraceuticals demonstrated significant concentration-dependent in vitro antidiabetic and antioxidant activities through complementary mechanisms. Berberine's near-equiactive alpha-glucosidase inhibition relative to acarbose and its superior beta-cell cytoprotection support its potential as an adjunctive antidiabetic agent. Quercetin emerged as the most potent antioxidant, with meaningful implications for oxidative stress-driven beta-cell damage in T2DM. These findings provide a mechanistic basis for further in vivo validation and clinical translation of these nutraceuticals, preferably through bioavailability-optimized nanoformulations.