An endogenous peptide isolated from the gut, NK-lysin, stimulates insulin secretion without changes in cytosolic free Ca2+ concentration

The cytotoxic effects of the anti-bacterial peptides on leukocytes

Antimicrobial peptides are small molecular weight proteins with a large antibacterial spectrum. They can reach high local concentrations in tissues with active inflammation, being largely produced by immunocompetent cells. However, their effect on eukaryotic cells is still unclear. We have, therefore, studied three structurally different antimicrobial peptides (cecropin P1, PR-39 and NK-lysin) for their cytotoxic effects on blood mononuclear cells. None of the antimicrobial peptides tested exhibited significant cytotoxic effect on resting lymphocytes isolated either from peripheral blood or from the spleen with the exception of high concentrations (ten times higher than IC100 for Escherichia coli) of NK-lysin. Activated lymphocytes were, however, more sensitive to the cytotoxic effect of the antimicrobial peptides. Both activated T-cells and B-cells were dose dependent sensitive to NK-lysin while only activated B-cells but not activated T-cells were sensitive to PR-39. Cecropin did not exhibit any cytotoxic effect on activated lymphocytes either. By using several cell lines (3B6, K562, U932 and EL-4) we were able to show that NK-lysin has a broad necrotic effect while PR-39 has a cell specific apoptotic effect dependent on the specifically cellular uptake. In conclusion we show here that antimicrobial peptides are not cytotoxic for the resting eukaryotic cells but can be cytotoxic on activated immune cells through distinct mechanisms of cell death.

Porcine host defense peptides: expanding repertoire and functions

Host defense peptides (HDPs) are a large group of innate immune effectors that are also termed antimicrobial peptides. Because of the rapid progress that has been made in completing several animal genomes, many HDPs have been systemically defined using bioinformatic analysis and partially characterized using reverse genomic approaches. In pigs, about 30 HDPs have been identified and partially characterized relative to structure and function. Antimicrobial activity of porcine HDPs has been extensively evaluated against a broad spectrum of microorganisms in vitro and evaluated for their protective role in vivo. Increasing evidence indicates that HDPs are functionally differentiated during posttranslational and postsecretory processing, and that the structural units for antimicrobial and immunoregulatory functions are separate. These findings suggest promising new avenues for therapeutic drug design based on HDPs, including porcine HDPs. This review summarizes and discusses advances in porcine HDPs research during the last decade with an emphasis on the rapidly expanding profiles and biological functions.

Effects of galnon, a non-peptide galanin-receptor agonist, on insulin release from rat pancreatic islets

Galanin is a neurotransmitter peptide that suppresses insulin secretion. The present study aimed at investigating how a non-peptide galanin receptor agonist, galnon, affects insulin secretion from isolated pancreatic islets of healthy Wistar and diabetic Goto-Kakizaki (GK) rats. Galnon stimulated insulin release potently in isolated Wistar rat islets; 100 microM of the compound increased the release 8.5 times (p<0.001) at 3.3 mM and 3.7 times (p<0.001) at 16.7 mM glucose. Also in islet perifusions, galnon augmented several-fold both acute and late phases of insulin response to glucose. Furthermore, galnon stimulated insulin release in GK rat islets. These effects were not inhibited by the presence of galanin or the galanin receptor antagonist M35. The stimulatory effects of galnon were partly inhibited by the PKA and PKC inhibitors, H-89 and calphostin C, respectively, at 16.7 but not 3.3 mM glucose. In both Wistar and GK rat islets, insulin release was stimulated by depolarization of 30 mM KCl, and 100 microM galnon further enhanced insulin release 1.5-2 times (p<0.05). Cytosolic calcium levels, determined by fura-2, were increased in parallel with insulin release, and the L-type Ca2+-channel blocker nimodipine suppressed insulin response to glucose and galnon. In conclusion, galnon stimulates insulin release in islets of healthy rats and diabetic GK rats. The mechanism of this stimulatory effect does not involve galanin receptors. Galnon-induced insulin release is not glucose-dependent and appears to involve opening of L-type Ca2+-channels, but the main effect of galnon seems to be exerted at a step distal to these channels, i.e., at B-cell exocytosis.

Properties of cytotoxic peptide-formed ion channels

Cytotoxic peptides are relatively small cationic molecules such as those found 1) in venoms, e.g., melittin in bee, scorpion toxins in scorpion, pilosulin 1 in jumper ant, and lycotoxin I and II in wolf spider; 2) in skin secretions (e.g., magainin I and II from Xenopus laevis, dermaseptin from frog, antimicrobials from carp) and cells of the immune system (e.g., insect, scorpion, and mammalian defensins and cryptdins); 3) as autocytotoxicity peptides, e.g., amylin cytotoxic to pancreatic beta-cells, prion peptide fragment 106-126 [PrP-(106-126)], and amyloid beta-protein (AbetaP) cytotoxic to neurons; and 4) as designed synthetic peptides based on the sequences and properties of naturally occurring cytotoxic peptides. The small cytotoxic peptides are composed of beta-sheets, e.g., mammalian defensins, AbetaP, amylin, and PrP-(106-126), whereas the larger cytotoxic peptides have several domains composed of both alpha-helices and beta-sheets stabilized by cysteine bonds, e.g., scorpion toxins, scorpion, and insect defensins. Electrophysiological and molecular biology techniques indicate that these structures modify cell membranes via 1) interaction with intrinsic ion transport proteins and/or 2) formation of ion channels. These two nonexclusive mechanisms of action lead to changes in second messenger systems that further augment the abnormal electrical activity and distortion of the signal transduction causing cell death.