A peptide of the phylloseptin family from the skin of the frog Hylomantis lemur (Phyllomedusinae) with potent in vitro and in vivo insulin-releasing activity.

A peptide with the ability to release insulin from the rat BRIN-BD11 clonal beta cell line was isolated from norepinephrine-stimulated skin secretions of the Lemur leaf frog Hylomantis lemur Boulenger,1882. Determination of the primary structure (FLSLIPHVISALSSL.NH(2)) demonstrated that the peptide belongs to the phylloseptin family whose members have previously been identified in other Phyllomedusinae species. A synthetic replicate of the peptide, termed phylloseptin-L2, produced a significant stimulation of insulin release (134% of basal rate, P<0.01) from BRIN-BD11 cells at a concentration of 30 nM, with a maximum response (301% of basal rate, P<0.001) at a concentration of 3 microM. Phylloseptin-L2 did not stimulate release of the cytosolic enzyme, lactate dehydrogenase at concentrations up to 3 microM, indicating that the integrity of the plasma membrane had been preserved. The stimulatory action was maintained in the absence of extracellular Ca(2+) and in the presence of verapamil (50 microM) and diazoxide (300 microM) suggesting that mechanism of action of the peptide did not primarily involve influx of Ca(2+) or closure of ATP-sensitive K(+) channels. Administration of phylloseptin-L2 (50 nmol/kgbody weight) into mice significantly (P<0.05) increased total release of insulin and improved glucose tolerance during the 60 min period following an intraperitoneal injection of glucose (18 mmol/kgbody weight). It is concluded that the peptide shows potential for development into a therapeutically valuable agent for the treatment of Type 2 diabetes.