Anti-glycemic activity of ethanolic extract and essential oils obtained by solvent-free microwave extraction and hydro-distillation of rhizomes and leaves of Alpinia calcarata Roscoe

Abstract

Alpinia calcarata Roscoe is a rhizomatous herb used in Ayurveda and traditional Sri Lankan indigenous medicine for treatment of metabolic disorders, including diabetes. Although its anti-diabetic properties have been preliminarily investigated, comprehensive studies evaluating the glycemic regulatory properties of both rhizomes and leaves have not been reported. This study evaluated the anti-glycemic activity of rhizomes and leaves of A. calcarata ethanolic extracts (EE) and essential oils (EOs) obtained by hydro-distillation (HD), and Solvent-Free Microwave Extraction (SFME). HD was performed with a Clevenger apparatus, while SFME used a NEOS GR microwave extractor to obtain EOs. EEs of rhizomes and leaves were obtained following standard protocols. Anti-glycemic activity of EOs and EEs were assessed through α-glucosidase and α-amylase inhibition, and an advanced glycation end product (AGE) formation assay with acarbose as the positive control. The leaf EE exhibited the highest α-glucosidase inhibitory activity (IC₅₀ = 7.05 ± 0.37 μg/mL), followed by the rhizome EE (IC₅₀ = 23.79 ± 0.56 μg/mL) and both were more active than the standard drug acarbose (IC₅₀ = 430.55 ± 0.14 μg/mL). α-amylase inhibitory activity of the rhizome EE was notably higher IC₅₀ = 5.70 ± 0.09 μg/mL) compared to acarbose (IC₅₀ = 76.28 ± 0.25 μg/mL). In contrast, the EOs extracted by HD and SFME showed weak inhibition in both enzyme assays, with inhibition values below 10% at 500 μg/mL. However, in the anti-AGE formation assay, EOs from leaf HD (13.08 mg RE/g) and leaf SFME (10.17 mg RE/g) showed higher inhibition compared to leaf EE (4.5 mg RE/g) and rhizome EE (3.42 mg RE/g). The EEs of A. calcarata rhizomes and leaves are rich in bioactive compounds and indicate strong anti-hyperglycemic effects. Additionally, the moderate anti-AGE activity observed in the EOs may further enhance therapeutic potential of this plant. Overall, these results highlight A. calcarata as a promising candidate for studies to identify phytochemicals, isolation and characterization of bioactive constituents and in vivo studies for development of natural anti-diabetic formulations.