Endocrine Abstracts

Aim: Insulin-releasing effects and potential anti-diabetic actions of peptides isolated from the skin secretion of the African clawed frog, Xenopus amieti has been reported. However, peptides such as magainin-AM1 has not been previously studied for its ability to stimulate insulin secretion or promote glucose uptake. This study investigated insulin releasing effects as well as possible underlying mechanisms.

Methods: Acute and chronic actions of magainin-AM1 were investigated using clonal pancreatic beta cells, BRIN-BD11, in buffers containing increasing glucose concentrations, magainin-AM1 alone (0–3 µM) or magainin-AM1 (1 µM) with modulators of insulin secretion. Insulin concentrations were measured by ELISA. Cytotoxicity and cell viability were examined in peptide-treated cells. Membrane potential and intracellular calcium concentrations were measured using Flexstation scanning fluorimeter. Glucose tolerance and insulin secretion were monitored in peptide-treated diabetic mice.

Results: Magainin-AM1 acutely stimulated insulin release from BRIN-BD11 cells in a concentration-dependent manner (1.4–1.6-fold, 100 nM–3 µM, P < 0.001–0.05). The stimulatory effects of magainin-AM1 reduced in the presence of diazoxide (28%, P < 0.01), verapamil 31%, P < 0.01), calcium-free buffer (31%, P < 0.001) and increased in incubations containing KCl (1.1-fold, P < 0.05). Pre-treatment of cells with magainin-AM1 increased secretory responses to KCl (1.3-fold, P < 0.05) but had no effect on responses to other secretagogues. These actions are not associated with reduced cell viability and cytotoxicity. Membrane potential and intracellular calcium concentration were increased by 1.9-fold (P < 0.01) and 1.5-fold (P < 0.001) in peptide-treated cells. Reduced blood glucose 24%, P < 0.05) and enhanced insulin secretion (1.6-fold, P < 0.05) were observed in peptide-treated mice.

Conclusions: These results suggest that the anti-diabetic properties of magainin-AM1 may involve the K_ATP-dependent pathway.