The tripeptide FEG ameliorates systemic inflammatory responses to rat intestinal anaphylaxis

Tripeptide feG prevents and ameliorates acute pancreatitis-associated acute lung injury in a rodent model

BACKGROUND

The synthetic tripeptide feG (D-Phe-D-Glu-Gly) is a novel pharmacologic agent that decreases neutrophil recruitment, infiltration, and activation in various animal models of inflammatory disease. We aimed to investigate the effect of feG as both a preventive treatment when administered before acute lung injury and as a therapeutic treatment administered following initiation of acute lung injury.

METHODS

Lung injury was assessed following prophylactic or therapeutic intratracheal feG administration in a “two-hit” rodent model of acute pancreatitis plus intratracheal lipopolysaccharide.

RESULTS

Following both prophylactic and therapeutic feG administration, there were significant improvements in arterial blood oxygenation and respiratory mechanics and decreased lung edema, BAL protein concentration, histologic tissue injury scores, BAL cell infiltration, and lung myeloperoxidase activity. Most indices of lung damage were reduced to baseline control values.

CONCLUSIONS

feG reduced leukocyte infiltration, ameliorated the severity of inflammatory damage, and restored lung function when administered either prophylactically or therapeutically in a two-hit rat model of acute pancreatitis plus intratracheal lipopolysaccharide.

Salivary gland derived peptides as a new class of anti-inflammatory agents: review of preclinical pharmacology of C-terminal peptides of SMR1 protein

The limitations of steroidal and non steroidal anti-inflammatory drugs have prompted investigation into other biologically based therapeutics, and identification of immune selective anti-inflammatory agents of salivary origin. The traditional view of salivary glands as accessory digestive structures is changing as their importance as sources of systemically active immunoregulatory and anti-inflammatory factors is recognized. Salivary gland involvement in maintenance of whole body homeostasis is regulated by the nervous system and thus constitutes a "neuroendocrine axis". The potent anti-inflammatory activities, both in vivo and in vitro, of the tripeptide Phe-Glu-Gly (FEG) are reviewed. FEG is a carboxyl terminal peptide of the prohormone SMR1 identified in the rat submandibular salivary gland, The D-isomeric form (feG) mimics the activity of its L-isomer FEG. Macropharmacologically, feG attenuates the cardiovascular and inflammatory effects of endotoxemia and anaphylaxis, by inhibition of hypotension, leukocyte migration, vascular leak, and disruption of pulmonary function and intestinal motility. Mechanistically, feG affects activated inflammatory cells, especially neutrophils, by regulating integrins and inhibiting intracellular production of reactive oxygen species. Pharmacodynamically, feG is active at low doses (100 μg/kg) and has a long (9-12 hour) biological half life. As a therapeutic agent, feG shows promise in diseases characterized by over exuberant inflammatory responses such as systemic inflammatory response syndrome and other acute inflammatory diseases. Arthritis, sepsis, acute pancreatitis, asthma, acute respiratory inflammation, inflammatory bowel disease, and equine laminitis are potential targets for this promising therapeutic peptide. The term "Immune Selective Anti-Inflammatory Derivatives" (ImSAIDs) is proposed for salivary-derived peptides to distinguish this class of agents from corticosteroids and nonsteroidal anti-inflammatory drugs.

The efficacy of combining feG and galantide in mild caerulein-induced acute pancreatitis in mice

We have previously shown that galantide ameliorates mild acute pancreatitis (AP), and the salivary tripeptide analogue, feG, ameliorates severe AP in mice. In this study, we compared the efficacy of combining galantide and feG with that of the individual agents in treating mild AP induced in mice with 7-hourly caerulein injections. Galantide was co-administered with each caerulein injection commencing with the first injection. feG was co-administered with the first injection of caerulein as a single intraperitoneal injection. Combination of the agents was also administered. Control animals received galantide, feG, or saline alone. Pancreata were harvested for histological examination and estimation of myeloperoxidase (MPO) activity. Plasma enzyme activities were measured. Galantide significantly reduced AP-induced hyperenzymemia by 41-49%. The combination of galantide and feG significantly reduced AP-induced hyperenzymemia by 39-40%, whereas feG alone was without effect. Plasma enzyme activity in the control groups was comparable with pre-treatment activity. Galantide, feG, and their combination significantly reduced MPO activity by 83, 44 and 74% respectively, and % abnormal acinar cells by 32, 29 and 36% respectively. This study demonstrates for the first time the beneficial effect of feG in mild caerulein-induced AP. Moreover the data indicate that the hyperenzymemia in mild caerulein-induced AP at 12h possibly reflect a larger secretory component as compared to enzyme release due to neutrophil-mediated acinar cell damage. The effects of the treatment with both peptides indicate a possible role for galantide in modulating neutrophil chemotaxis/activation and supports the hypothesis that galantide may influence neurogenic inflammation in AP.

Autonomic nervous system regulates secretion of anti-inflammatory prohormone SMR1 from rat salivary glands

The autonomic nervous system regulates the secretion of bioactive proteins and peptides from salivary glands that can be important in systemic physiological responses. The prohormone submandibular rat-1, which is highly expressed in rat submandibular glands, can be cleaved to produce polypeptides with analgesic and anti-inflammatory activities. Human genes related to submandibular rat-1 have conserved biological functions and are potentially important in pain suppression, erectile function, and inflammation. In this study we describe the differential expression and posttranslational modification of submandibular rat-1 protein in salivary glands, the urogenital tract, lung, blood, and saliva in male Sprague-Dawley and Brown Norway rats. Submandibular rat-1 protein is secreted into saliva after the administration of beta-adrenergic or cholinergic agonists. Removal of the sympathetic ganglion that innervates the salivary glands results in increased levels of submandibular rat-1 protein in salivary glands. The secretion of submandibular rat-1 in response to physiological stress may provide a large pool of submandibular rat-1-derived peptide products that can promote analgesia and decrease inflammation locally and systemically. This pathway may be conserved among mammals and may constitute an important anti-inflammatory and analgesic response to stress.

The tripeptide feG inhibits leukocyte adhesion

Background

The tripeptide feG (D-Phe-D-Glu-Gly) is a potent anti-inflammatory peptide that reduces the severity of type I immediate hypersensitivity reactions, and inhibits neutrophil chemotaxis and adhesion to tissues. feG also reduces the expression of β1-integrin on circulating neutrophils, but the counter ligands involved in the anti-adhesive actions of the peptide are not known. In this study the effects of feG on the adhesion of rat peritoneal leukocytes and extravasated neutrophils to several different integrin selective substrates were evaluated.

Results

The adhesion of peritoneal leukocytes and extravasated neutrophils from rats to adhesive proteins coated to 96-well plates was dependent upon magnesium (Mg²⁺) ion, suggestive of integrin-mediated adhesion. feG inhibited leukocyte adhesion, but only if the cells were stimulated with PAF (10^-9M), indicating that feG's actions in vitro require cell activation. In the dose range of 10^-10M to 10^-12M feG inhibited the adhesion of peritoneal leukocytes to fibrinogen and fibronectin, but not IgG, vitronectin or ICAM-1. feG inhibited the binding of extravasated neutrophils to heparin, IgG, fibronectin and CD16 antibody. Antigen-challenge of sensitized rats reduced the adhesion of peritoneal leukocytes to most substrates and abolished the inhibitory effects of feG. However, pretreating the animals with intraperitoneal feG (100 μg/kg) 18 h before collecting the cells from the antigen-challenged animal restored the inhibition of adhesion by in vitro feG of peritoneal leukocytes and extravasated neutrophils to fibronectin.

Conclusion

The modulation of leukocyte adhesion by feG appears to involve actions on αMβ2 integrin, with a possible interaction with the low affinity FcγRIII receptor (CD16). The modulation of cell adhesion by feG is dual in nature. When administered in vivo, feG prevents inflammation-induced reductions in cell adhesion, as well as restoring its inhibitory effect in vitro. The mechanism by which in vivo treatment with feG exerts these effects remains to be elucidated.

The tripeptide feG regulates the production of intracellular reactive oxygen species by neutrophils

BACKGROUND

The D-isomeric form of the tripeptide FEG (feG) is a potent anti-inflammatory agent that suppresses type I hypersensitivity (IgE-mediated allergic) reactions in several animal species. One of feG's primary actions is to inhibit leukocyte activation resulting in loss of their adhesive and migratory properties. Since activation of neutrophils is often associated with an increase in respiratory burst with the generation of reactive oxygen species (ROS), we examined the effect of feG on the respiratory burst in neutrophils of antigen-sensitized rats. A role for protein kinase C (PKC) in the actions of feG was evaluated by using selective isoform inhibitors for PKC.

RESULTS

At 18 h after antigen (ovalbumin) challenge of sensitized Sprague-Dawley rats a pronounced neutrophilia occurred; a response that was reduced in animals treated with feG (100 microg/kg). With antigen-challenged animals the protein kinase C (PKC) activator, PMA, significantly increased intracellular ROS of circulating neutrophils, as determined by flow cytometry using the fluorescent probe dihydrorhodamine-123. This increase was prevented by treatment with feG at the time of antigen challenge. The inhibitor of PKCdelta, rottlerin, which effectively prevented intracellular ROS production by circulating neutrophils of animals receiving a naïve antigen, failed to inhibit PMA-stimulated ROS production if the animals were challenged with antigen. feG treatment, however, re-established the inhibitory effects of the PKCdelta inhibitor on intracellular ROS production. The extracellular release of superoxide anion, evaluated by measuring the oxidative reduction of cytochrome C, was neither modified by antigen challenge nor feG treatment. However, hispidin, an inhibitor of PKCbeta, inhibited the release of superoxide anion from circulating leukocytes in all groups of animals. feG prevented the increased expression of the beta1-integrin CD49d on the circulating neutrophils elicited by antigen challenge.

CONCLUSION

feG reduces the capacity of circulating neutrophils to generate intracellular ROS consequent to an allergic reaction by preventing the deregulation of PKCdelta. This action of feG may be related to the reduction in antigen-induced up-regulation of CD49d expression on circulating neutrophils.

Identification of a binding site for the anti-inflammatory tripeptide feG

The mechanism of action of feG, an anti-inflammatory peptide, was explored using data mining, molecular modeling, and enzymatic techniques. The molecular coordinates of protein kinase A (PKA) were used to create six virtual isoforms of protein kinase C (PKCalpha, betaI, betaII, delta, iota, and zeta). With in silico techniques a binding site for feG was identified on PKCbetaI that correlated significantly with a biological activity, the inhibition of intestinal anaphylaxis. Since feG selectively increased the binding of a PKCbetaI antibody, it is proposed that this peptide inhibits the reassociation of the hydrophobic tail of PKCbetaI with its binding site and prevents the enzyme from assuming an inactive conformation.