Endocrine Abstracts

We reported the isolation and structural characterization of CPF-AM1 and other peptides from the skin secretion of Xenopus amieti. This study investigated the insulin-releasing activities of synthetic CPF-AM1 using clonal pancreatic cell line, BRIN-BD11 and Swiss TO mice with diet-induced insulin resistance.

Acute insulin-release studies were performed in Krebs Ringer bicarbonate buffer supplemented with 5.6 mM or 16.7 mM glucose, purified synthetic peptide (0–3 mM) and known modulators of insulin secretion. Insulin-release was measured by radioimmunoassay. Membrane potential and intracellular calcium ([Ca2+]i) were measured by flourometric assay using FLEXstationTM. Degradation of CPF-AM1 by plasma enzymes was investigated using reversed-phase HPLC and MALDI-TOF spectrometer.

At 5.6 mM glucose, CPF-AM1 significantly stimulated insulin-release over concentration range of 30 nM (1.4-fold, P<0.05) to 3 μM (3.4-fold, P<0.001) without beta-cell cytotoxicity. Without extracellular calcium, the stimulation was reduced by 25.3%. CPF-AM1(1 μM)-induced stimulatory effects were inhibited by co-incubation with 50 μM verapamil (57.4%, P<0.001) and 300 μM diazoxide (51.8%, P<0.001). Insulin-secretion increased by 3.3-fold with KCl (30 mM, 16.7 mM glucose) and CPF-AM1 (1 μM). At 5.6 mM glucose and 1 μM CPF-AM1, co-incubation with 200 μM IBMX and 200 μM tolbutamide caused 1.2-fold and 1.1-fold increase in insulin-release respectively. The peptide induced membrane depolarization (2.6-fold) and increased [Ca2+]i (2.0-fold) at 5.6 mM glucose. In vivo, intraperitoneal administration of CPF-AM1 (75 nmol/kg bw) with 18 mmol/ kg glucose significantly enhanced insulin-release (1.5-fold) and improved glucose tolerance by 28% (n=6, P<0.05). CPF-AM1 is resistant to degradation by plasma proteolytic enzymes up to 8 hr.

The study showed that CPF-AM1 is a novel peptide with potential for development into a new antidiabetic drug.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.