Pharmacological assessment of standardized Curcuma longa L. and Centella asiatica (L.) Urban extracts for diabetes management

Abstract

Context: Diabetes mellitus is a chronic metabolic disorder characterized by hyperglycemia and insulin resistance, often linked to oxidative stress. Curcuma longa (turmeric) and Centella asiatica (gotu kola) are traditionally recognized for antidiabetic and antioxidant properties. Aims: To identify major active compounds and evaluate the antioxidant and antidiabetic activities of these extracts individually and in combination. Methods: Extracts were standardized using TLC densitometry according to the Indonesian Herbal Pharmacopoeia. Antioxidant activity was assessed via DPPH scavenging and malondialdehyde (MDA) inhibition, while antidiabetic effects were evaluated through α-glucosidase inhibition and in vivo testing in alloxan-induced diabetic rats. Insulin resistance was measured by the highest tolerated level of insulin (HTLI). Results: Both extracts met pharmacopeial quality standards. The 1:1 combination exhibited markedly stronger α-glucosidase inhibition (IC50 = 45.45 μg/mL) than C. longa (135.03 μg/mL), C. asiatica (88.07 μg/mL), and acarbose (113.92 μg/mL). Antioxidant activity was also greater in the combination (IC50 = 40.68 μg/mL). In vivo, combination treatment reduced blood glucose comparably to glibenclamide and improved insulin sensitivity, with HTLI reaching 1.634 mg/dL versus 1.308 mg/dL for metformin. MDA levels were significantly reduced, indicating lower lipid peroxidation. A moderate correlation between antioxidant and enzyme inhibition (r = 0.685) suggests a mechanistic link between oxidative stress and carbohydrate metabolism. Conclusions: The combination of C. longa and C. asiatica demonstrated synergistic antioxidant and antidiabetic effects, meeting quality standards, which supports its potential as an adjunctive therapy for diabetes management.