Tigerinin-1R: a potent, non-toxic insulin-releasing peptide isolated from the skin of the Asian frog, Hoplobatrachus rugulosus.

AIM: Characterization of peptides in the skin of the Vietnamese common lowland frog Hoplobatrachus rugulosus with the ability to stimulate insulin release in vitro and improve glucose tolerance in vivo. METHODS: Peptides in an extract of skin were purified by reversed-phase HPLC, and their abilities to stimulate the release of insulin and the cytosolic enzyme lactate dehydrogenase were determined using BRIN-BD11 clonal ß cells. Insulin-releasing potencies of synthetic peptides and their effects on membrane potential and intracellular Ca²âº concentration were also measured using BRIN-BD11 cells. Effects on glucose tolerance and insulin release in vivo were determined in mice fed a high-fat diet to induce obesity and insulin resistance. RESULTS: A cyclic dodecapeptide (RVCSAIPLPICH.NH2), termed tigerinin-1R, was isolated from the skin extract that lacked short-term cytotoxic and haemolytic activity but significantly (p < 0.01) stimulated the rate of release of insulin from BRIN-BD11 cells at concentrations ≥ 0.1 nM. The maximum response was 405% of the basal rate at 5.6 mM ambient glucose concentration and 290% of basal rate at 16.7 mM glucose. C-terminal α-amidation was necessary for high potency and a possible mechanism of action of the peptide-involved membrane depolarization and an increase in intracellular Ca²âº concentration. Administration of tigerinin-1R (75 nmol/kg body weight) to high fat-fed mice significantly (p < 0.05) enhanced insulin release and improved glucose tolerance during the 60-min period following an intraperitoneal glucose load. CONCLUSION: Tigerinin-1R is a potent, non-toxic insulin-releasing peptide that shows potential for development into an agent for the treatment of type 2 diabetes.

The organophosphate paraoxon has no demonstrable effect on the murine immune system following subchronic low dose exposure.

Paraoxon is the bioactive metabolite of the organophosphate pesticide parathion. Desulphuration of parathion by liver enzymes or sunlight results in the formation of paraoxon which inhibits acetylcholine esterase (AChE) activity. In the present study, we analyzed the effect of a 6-week, subchronic treatment with two different daily intraperitoneal doses (30 or 40 nmol) of paraoxon on the immune system of BALB/c mice. At a dose of 30 nmol/day, body weight of treated animals was unchanged compared to the controls. In contrast, the higher dose (40 nmol/day) induced a reduction in body growth, particularly in the first 3 weeks of treatment, peaking at week 2 when the saline group showed a 14.2-fold increase in body weight gain compared to paraoxon-treated animals. Moreover, mice treated with either dose of paraoxon had a >50% reduction in AChE activity during the first 3 weeks of treatment, but by the end of the treatment (week 6), AChE activity returned to normal. With regard to immunological parameters, there was no significant difference in either total spleen weight or in the ratios of various spleen cell populations between control and paraoxon-treated animals. Furthermore, no changes were observed in mitogen-induced cytokine secretion from splenocytes of paraoxon-treated mice. Finally, subchronic exposure to paraoxon did not alter mortality of mice exposed to a bacterial infection with Salmonella typhimurium. These data suggest that although subchronic exposure to paraoxon induced a transient inhibition in AChE activity, it had no demonstrable effect on the host immune system.