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| 226P London, UK Pharmacology 2017 |
Effects of Costus pictus extract on GLP-1 secreting L-cell function
Introduction: Glucagon-like peptide-1 (GLP-1) is a glucose-dependent insulinotropic hormone secreted by intestinal L-cells in response to nutrient ingestion. GLP-1 release is impaired in Type 2 Diabetes Mellitus (T2DM), thus, any compounds that might enhance endogenous GLP-1 release may have anti-diabetic therapeutic potential. Costus pictus D. Don (C. Pictus), known as the Insulin plant in southern India, is well known for its glucose lowering and insulin secretory effects (1). It is used as a traditional Indian anti-diabetic medicine, although its mechanism of action is not fully understood (2). As the potential actions of C. Pictus on gut L-cells have not been investigated, this study aimed to elucidate its effects using the murine GLP-1 secreting GLUTag L-cell model.
Methods: GLUTag cells were maintained in DMEM (1g/L D-Glucose) supplemented with 10% FBS, 50U/ml penicillin/streptomycin and 2mM L-Glutamine. C. Pictus dried leaf powder was extracted with ethanol using Soxhlet apparatus at 70°C and residue was concentrated using rotary drum evaporator and reconstituted in ethanol to desired concentration. GLUTag cell viability was determined by MTT following treatment (24-48 h) of cells with different concentrations of C. pictus extract (CPE). Effects of culture (24-48 h) with CPE on L-cell specific gene expression were quantified by qPCR. CPE actions on intracellular calcium were determined in Fura-2AM loaded GLUTag cells. Acute effects of CPE on GLP-1 release were quantified using total GLP-1 ELISA (Millipore).
Results: Low concentrations (3.125 & 6.25 μg/ml) of CPE significantly (p<0.01) enhanced cell viability 1.25-1.29 fold following 24-48h culture, whereas higher concentrations (above 25 μg/ml) reduced cell viability (p<0.001). Following 24 & 48h culture with CPE (6.25μg/ml), glucagon gene expression was significantly downregulated (78% - 55%, p<0.05-0.01). Acutely, CPE raised intracellular calcium in GLUTag cells. Furthermore, CPE stimulated acute GLP-1 secretion up to 6.4 -16.3 fold (n=4) from GLUTag cells at both low (1.1 mM) and high (16.7 mM) glucose (P<0.01) concentrations.
Conclusion: Acute exposure of L-cells to CPE appears to enhance intracellular calcium and promote GLP-1 release, which may be beneficial in T2DM. Long term exposure of the cells to low concentrations also appears to enhance cell number, although down-regulation of glucagon gene expression occurs. Further studies are required to establish the mechanisms underlying CPE effects on L-cell function and GLP-1 secretion.
References:
1. Gireesh G et al. (2009) Journal of Ethnopharmacology, Volume 123, Issue 3, Pages 470-474
2. Hegde PK et al. (2014) Pharmacognosy review, Volume8, Issue 15, Pages 67-72