The in vivo effects of opioid peptides on the murine immune response

Bioimmunotherapy of rodent malaria: co-treatment with recombinant mouse granulocyte-macrophage colony-stimulating factor and an enkephalin fragment peptide Tyr-Gly-Gly

We have earlier shown that recombinant mouse granulocyte-macrophage colony-stimulating factor (rmGM-CSF) and methionine-enkephalin co-treatment can protect mice from malaria. We now report the bioimmunotherapeutic effect of rmGM-CSF and a synthetic enkephalin fragment peptide Tyr-Gly-Gly (TGG) co-treatment on blood-induced Plasmodium berghei infection in Swiss mice. Mice were completely aparasitimic following co-treatment with rmGM-CSF (10.0 microg/kg) and TGG (2.0 mg/kg x 3 per day, intraperitoneally (i.p.)) starting from day -1 to day +4; however, in monotherapy, neither of these agents showed any detectable bioimmunotherapeutic effect. Curiously, similar co-treatment with rmGM-CSF (10.0 microg/kg) and higher doses of TGG (10.0 mg/kg) did not protect the mice. The combined bioimmunotherapeutic effect of these agents was abrogated by the separate administration each of rabbit neutralizing anti-rmGM-CSF antibody, non-selective opioid receptor antagonist naltrexone (10.0 mg/kg x 6 per day, i.p.), and silica (3.0 mg per mouse, intravenously (i.v.)). The peritoneal and splenic macrophages from the protected mice showed a significant (P<0.05) increase in their pool-size and the phagocytic activity, ex vivo. Furthermore, the protected mice, as compared to the unprotected ones, showed a significant (P<0.05) maximum increase in their serum nitrate and nitrite, interferon-gamma (IFN-gamma), and tumor necrosis factor-alpha (TNF-alpha) levels in their splenic homogenates, on the day before the beginning of the resolution of parasitaemia. Selective inhibitors of both inducible (aminoguanidine) and all forms (L-N(G)-monomethyl arginine) of nitric oxide (NO) synthase, significantly (P<0.05) augmented the mortality of co-treated mice, suggesting the role of NO in protection. These data show that, in P. berghei-infected mice, co-treatment with rmGM-CSF and conditional doses of TGG can impart protection, apparently through partly NO-dependent and macrophage-mediated mechanism(s).

Effect of naloxone on immune responses after hemorrhagic shock

OBJECTIVE

To determine whether naloxone administration after hemorrhagic shock has any beneficial or deleterious effect on immune responses.

BACKGROUND DATA

Hemorrhagic shock is known to produce immunodepression in both humans and experimental animals. Although studies suggest that endogenous opioids play a role in immune regulation in adverse circulatory conditions, it remains controversial whether these opioids exert beneficial or detrimental effects on immunity after shock. Moreover, little information is available concerning the effects of opioid receptor blockade using naloxone on cell-mediated immunity and endocrine responses after shock.

METHODS

Male C3H/HeN mice (25 g) were bled to and maintained at a mean arterial blood pressure of 35+/-5 mm Hg for 1 hr. The shed blood was then returned along with lactated Ringer's solution (two times the shed blood volume) to provide fluid resuscitation. The animals were randomized to receive either naloxone (1 mg/kg i.v.) or an equal volume of vehicle (saline) after the shed blood was returned, i.e., immediately before crystalloid resuscitation, and were killed at 2 hrs after resuscitation to obtain splenocytes, macrophages (peritoneal and splenic), and blood.

MEASUREMENTS AND MAIN RESULTS

Bioassays revealed significantly decreased release of all studied interleukins (interleukins-1, -2, -3, and -6) by peritoneal and splenic macrophages as well as significantly decreased splenocyte proliferative capacity after shock in vehicle-treated mice. Naloxone administration after hemorrhage resulted in either similar or even more decreased levels of interleukin release compared with vehicle-treated hemorrhaged mice. Significantly increased plasma corticosterone concentrations were observed in vehicle-treated animals compared with control animals. Naloxone administration did not have any significant effects on corticosterone plasma concentrations after hemorrhage.

CONCLUSIONS

These findings indicate the importance of the endogenous opioid system for the maintenance of immunity in adverse circulatory conditions, i.e., hemorrhage. Although additional studies involving different doses and/or times of naloxone administration may provide different results, the present findings raise the concern that naloxone administration in the traumatized host may have deleterious effects because it decreases peritoneal macrophage and splenic immune functions.

Leucine enkephalin degradation in allergopathic versus normal human plasma

The enzyme hydrolysis of labelled leu-enkephalin in the presence of plasma enzymes was studied by kinetic and chromatographic techniques in a group of allergopathic patients in the acute and quiescent stage; data obtained have been compared with those obtained with normal controls. Results shown indicate that in the quiescent stage substrate degradation is reduced, and that the pattern of the hydrolysis by-products is modified with respect to the controls. In the acute as compared to the quiescent stage, enkephalin hydrolysis is further reduced, and the pattern of hydrolysis by-products is further modified. ANOVA analysis of these data indicates that the dependency of hydrolysis reduction upon the grouping of subjects (i.e., controls, quiescent and acute stage) is statistically very significant. Reduced substrate hydrolysis, and modified hydrolysis pattern, appears to be associated with decreased activity of the enzymes involved and more significantly with increased activity of the low molecular weight plasma inhibitors. The combination of these two factors appears to define a hydrolysis pattern characteristic of the allergopathic subjects, similar in the quiescent and acute phase, and different from that observed in the controls.

A comparative study of immunomodulation produced by in vitro exposure to delta opioid receptor agonist peptides

The present study assessed the direct immunomodulatory effect of a panel of synthetic peptides exhibiting delta-opioid receptor agonist activity. Murine splenic lymphocytes and peritoneal macrophages were cultured in vitro with peptides at concentrations of 0.00001-10 microM. Assessment was made of B-cell function by quantitating cellular proliferation, T-cell function by measuring cytokine production, natural immunity by quantitating basal and cytokine-augmented natural killer (NK) cell activity, and macrophage function by production of IL-6. These peptides had minimal effects on B-cell proliferation at any concentration examined. In comparison, enhancement of cytokine production by T-helper cells occurred following exposure to several of the compounds, to a significant extent with DPDPE, DPDPE-trifluoroacetate, or deltorphin-1 and most pronounced at concentrations between 0.00001 and 0.1 microM. Likewise, IL-6 production by macrophages was significantly augmented by exposure to these three peptides. NK cell function was significantly enhanced by in vitro exposure to several of the peptides, with enhancement generally noted at concentrations between 0.00001 and 0.01 microM. However, some of the peptides (most notably DADLE) greatly suppressed NK cell activity. These data suggest that delta opioid agonists are broadly immunomostimulatory.

Positive and negative immunomodulation by opioid peptides

The data that follow review part of the existing evidence concerning the neuroimmune functions mediated by opioid peptides, with particular regard to dual immunomodulatory effects. Limited references to substances other than opioid peptides are included, mainly to emphasize the possible similarities in the mediation of neuroimmune interactions by different informational substances, while the interactions directed from the immune to the nervous system have deliberately been omitted.

Endogenous opiates: 1994

This article is the 17th installment of our annual review of research concerning the opiate system. It includes papers published during 1994 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics covered this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.