In vitro and in vivo effects of beta-endorphin and met-enkephalin on leukocyte locomotion

Neuroimmune Interaction in the Regulation of Peripheral Opioid-Mediated Analgesia in Inflammation

Peripheral immune cell-mediated analgesia in inflammation is an important endogenous mechanism of pain control. Opioid receptors localized on peripheral sensory nerve terminals are activated by endogenous opioid peptides released from immune cells to produce significant analgesia. Following transendothelial migration of opioid-containing leukocytes into peripheral sites of inflammation, opioid peptides are released into a harsh milieu associated with an increase in temperature, low pH, and high proteolytic activity. Together, this microenvironment has been suggested to increase the activity of opioid peptide metabolism. Therefore, the proximity of immune cells and nerve fibers may be essential to produce adequate analgesic effects. Close associations between opioid-containing immune cells and peripheral nerve terminals have been observed. However, it is not yet determined whether these immune cells actually form synaptic-like contacts with peripheral sensory terminals and/or whether they secrete opioids in a paracrine manner. This review will provide novel insight into the peripheral mechanisms of immune-derived analgesia in inflammation, in particular, the importance of direct interactions between immune cells and the peripheral nervous system.

Beta-endorphin modulates calcium channel activity in human neutrophils

10(-6) M n-formyl-methionyl-leucyl-phenylalanine (FMLP) stimulated Ca2+ flux in human neutrophils is characterized by a profile composed of two peaks of different amplitude and breadth. beta-Endorphin inhibited the magnitude and modulated the kinetics of the second peak in a manner which was dose-dependent and could reflect either negative cooperativity or heterogeneity of binding sites. The second peak arises from calcium channel activity since in the presence of nifedipine or EGTA it was not evident while the first peak was reduced about 24%. Similarly, at 15 degrees C, where we were unable to detect any channel activity, the first peak was diminished by 35% and beta-endorphin had no detectable effect on this peak. These results led us to conclude that the first peak is chiefly composed of Ca2+ recruited from cytosolic stores which are relatively insensitive to the above treatments and a smaller fraction of calcium originating in calcium channel activity. Hence, we reason that beta-endorphin modulates only the calcium ion flux arising from calcium channel function.

Beta-casomorphin (BCM) and human colonic lamina propria lymphocyte proliferation

BCM is a milk-derived peptide with opiate-like properties which is absorbed through the gastrointestinal mucosa. It has been shown to affect gastrointestinal motility, absorption and secretion. Recently, modulation of the immune system by BCM was also reported. In this study we investigated the in vitro effect of BCM on the human mucosal immune response as represented by lamina propria lymphocyte (LPL) proliferation. Results show that BCM significantly inhibited concanavalin A (ConA) stimulated LPL DNA synthesis. BCM also inhibited ornithine decarboxylase activity (ODC) in ConA-stimulated LPL. Although BCM also inhibited 12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulated LPL DNA synthesis, the degree of inhibition was much lower than in ConA-stimulated LPL. The anti-proliferative effect of BCM was reversed by the opiate receptor antagonist, neloxone. Our results suggest that BCM may affect the human mucosal immune system, possibly via the opiate receptor.

Immunoregulatory effects of alpha-endorphin, beta-endorphin, methionine-enkephalin, and adrenocorticotropic hormone on anti-tetanus toxoid antibody synthesis by human lymphocytes

This study assesses the effects of adrenocorticotropic hormone (ACTH), alpha-endorphin (alpha-endo), beta-endorphin (beta-endo), and methionine-enkephalin (met-enk) on tetanus toxoid-stimulated in vitro specific antibody (anti-TT) synthesis. ACTH and TT-costimulated cultures enhanced antibody (Ab) synthesis over control TT-stimulated cultures at 10(-9) and 10(-11) M and suppressed Ab synthesis at 10(-13) and 10(-17) M. The alpha-endo and TT-costimulated cultures enhanced Ab synthesis over control cultures at all concentrations tested (10(-7) to 10(-15) M). Cultures costimulated with beta-endo and TT enhanced Ab synthesis over control cultures at 10(-11) M and suppressed Ab synthesis at doses above and below 10(-11) M. The met-enk and TT-costimulated cultures produced more Ab than controls at 10(-9) M; and the met-enk and TT-costimulated cultures produced less Ab than controls at other concentrations as low as 10(-17) M and as high as 10(-7) M. The results of this study provide one reason as to why the interactions between the neuroendocrine and immune systems remain unclear.

Alcohol exposure in utero results in diminished T-cell function and alterations in brain corticotropin-releasing factor and ACTH content

The long-term teratogenic effects of prenatal ethanol exposure during the last week of gestation on immune responsiveness and levels of pituitary ACTH and hypothalamic corticotropin-releasing factor (CRF) were examined in Sprague-Dawley rats. Immune responsiveness was measured by T-lymphocyte proliferation in response to mitogenic stimulation with Con A (3 micrograms/ml) in spleen and thymus cells of 21-old-day male rats who were exposed to alcohol in utero. The proliferative response was 8-fold lower in spleen and twofold lower in thymus cells from alcohol-exposed animals compared to responses measured in control rats. Thymus weight was significantly smaller at birth in alcohol exposed males, but significantly larger at 21 days of age compared to controls. Alterations in the content of ACTH and CRF, hormones, known to be direct or indirect modulators of immune responsiveness, were also observed in alcohol exposed males. Hypothalamic content of CRF and pituitary content of ACTH were significantly lower in alcohol exposed males on postnatal Day 1, but hypothalamic ACTH content was significantly higher compared to controls. These results indicate that alcohol exposure during the last week of gestation can produce alterations of the hypothalamic-pituitary-adrenal function in addition to teratogenic effects on the immune system which have been previously observed only with a much longer alcohol exposure regimen.

A stereoselective blockade by naloxone of opioid and non-opioid-induced granulocyte activation

Naloxone was found to prevent both opioid and non-opioid-induced migration of human granulocytes in a stereoselective way. Indeed, besides being able to inhibit morphine-induced migration, (-) but not (+), naloxone isomer proved to abolish either casein, serum of fMLP-induced chemotaxis. It is concluded that opioid-induced modulation of granulocyte migration is likely to be mediated through specific receptors, possibly of the mu type. Moreover, the antichemotactic effect of naloxone suggests an involvement of opioid receptors and/or endogenously released opioids in the mechanism of granulocyte activation by different chemoattractants.

Antitumor activity of enkephalin analogues in inhibiting PYB6 tumor growth in mice and immunological effects of methionine enkephalinamide

Recent evidence has implicated enkephalins as immunomodulators. Several studies have reported the regulation of tumor growth by methionine enkephalin (ME). However, there has been little effort to relate the immunological significance of enkephalins to the development of anticancer drugs. The present study had three aims: first, to compare the antitumor activity of the synthetic peptide, D-[Ala2]methionine enkephalinamide (MEA), with endogenous enkephalins on PYB6 fibrosarcoma tumor growth; second, to determine whether tumor growth inhibition was mediated by an opiate receptor; and third, to investigate the effects of MEA on selected immune responses. Female B6C3F1 mice were injected i.p. daily for 7 days with 50-4000 micrograms/kg of ME, MEA, leucine enkephalin (LE) or D-[Ala2]leucine enkephalinamide (LEA), beginning 1 day after PYB6 inoculation. ME and MEA, but not LE or LEA, decreased the PYB6 growth rate. The dose of 50 micrograms/kg MEA exerted the maximum inhibition of tumor growth (nearly 72% on day 15 post tumor transplantation). MEA was not directly toxic to PYB6 tumor cells, as evaluated by the measurement of DNA synthesis and cellular ATP levels of PYB6 cells exposed to MEA in vitro. No [3H]-etorphine specific bindings were detected on the cell membrane or sonicates of splenic lymphocytes or PYB6 cells. Therefore, the antitumor activity by MEA is likely mediated by an indirect mechanism. Immunological studies indicated that MEA selectively enhanced the lymphoproliferative response to the T-cell mitogen, concanavalin A, but not to the B-cell mitogen, lipopolysaccharide.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute infusion of chemotactic or enkephalin-analog peptides into rat cerebral ventricles: scanning and transmission electron microscopy of leukocyte immigration in vivo

Acute infusions of the formylated chemotactic peptide formyl-methionyl-leucyl-phenylalanine-lysine (FMLPL) or enkephalin analogue (Sandoz peptide) were made to the lateral cerebral ventricle of adult male rats to examine potential cellular responses within the central nervous system (CNS). Ependymal regions lining the third ventricle atop the hypothalamus were examined using scanning and transmission electron microscopy. The formylated peptide induced a significant, primarily neutrophilic cellular response in animals sacrificed 1 h after infusion. Cells were observed within and external to neuropil blood capillaries, suggestive of emigration from vasculature in response to the peptide. In contrast, the enkephalin analogue did not induce any leukocyte cellular response within the same time frame. Earlier studies have shown a monocyte/macrophage response in the same setting to the opioid peptides beta-endorphin, and to a lesser extent, methionine enkephalin. The present findings suggest that a formylated peptide is a potent stimulus for neutrophil migration within a CNS site, while opioid peptides may be variable with respect to effectiveness on cells of the immune system within the CNS, depending upon chemical configuration.

Opioid-induced modification of granulocyte function

Inhibition of human granulocyte chemotaxis towards casein was observed in the presence of both the mu and kappa opioid receptor agonists, which, per se, exhibited chemokinetic activity. Naloxone was found to prevent both the opioid-related and opioid-unrelated increase in granulocyte migration. Moreover, morphine inhibited the aggregation response of granulocytes in a naloxone-sensitive way, while the opioid peptides were ineffective. Although opioid agonists with different receptor specificity were capable of strongly modifying human granulocyte migration, no conclusion can be drawn on the role of opioid receptors in regulating migrating activity. On the other hand, opioid receptor activation by morphine is likely to be responsible for aggregation inhibition.

Endorphinergic modulation of immune function: potent action of the dipeptide glycyl-L-glutamine

Glycyl-L-glutamine (GLG), the carboxy terminal dipeptide of B-endorphin, inhibits brainstem neuronal activity. It also occurs along with B-endorphin in pituitary secretory vesicles suggesting a neurosecretory role for this dipeptide. We have evaluated potential immunoregulatory actions of this compound using the Phytohemaglutinin (PHA) blastogenesis and the concanavalin A (ConA) suppressor cell induction assays. GLG in low doses (10(-12) M) enhanced the response of human lymphocytes to PHA induced blastogenesis, however; with higher doses of the dipeptide (10(-7) M) immunosuppression was consistently observed. In the suppressor cell induction assay, when GLG was used together with ConA, we observed a dose-dependent inhibition of suppressor activity. These results clearly indicate that GLG produces a dose dependent bidirectional modulation of at least two indicies of immune function, and confirm the presence of a second pituitary peptide with the potential for potent immunomodulatory action.

In vivo effects of beta-endorphin on lymphocyte proliferation and interleukin 2 production

Experiments were undertaken in rats to investigate the effects of in vivo infusion of beta-endorphin (BEP) on subsequent Con A-induced proliferation and interleukin 2 (IL-2) production by spleen cells in vitro. BEP administration induced a dose-dependent enhancement of the proliferative response to Con A. Infusion of the opiate antagonist naloxone (NAL) inhibited the Con A response and infusion of NAL prior to BEP resulted in even further inhibition. None of these treatments resulted in detectable alterations in IL-2 production after 48 h in culture. To demonstrate a direct interaction between BEP and lymphocytes, spleen cells were incubated in vitro with varying concentrations of BEP and/or NAL. Enhanced Con A-induced proliferation was observed following incubation with BEP in the range 10(-12) to 10(-9) M (levels comparable to the effective in vivo doses) and this effect was abrogated by NAL pretreatment (10(-6) M). These data indicate a role for BEP in enhancing lymphocyte reactivity which is to some extent dependent on opiate receptors on the cell surface. This report extends the evidence obtained from in vitro experiments implicating endogenous opioids in modulation of host immunity by demonstrating that these effects can be obtained in vivo.

Opioid peptides modulate production of interferon gamma by human mononuclear cells

The opioid neuropeptides have previously been shown to bind to and affect leukocyte function including lymphocyte proliferation, NK-cell activity, mononuclear cell chemotaxis, immunoglobulin synthesis, and lymphokine production. The effect of the opioid peptides beta-endorphin and Met-enkephalin on interferon gamma (IFN) production by concanavalin A-stimulated human mononuclear cells was examined. Both beta-endorphin and Met-enkephalin enhanced IFN production by the majority of donor mononuclear cells tested and did so at concentrations between 10(-14) and 10(-10) M. When 10(-12) M beta-endorphin or Met-enkephalin were included in concanavalin A-stimulated mononuclear cell cultures, IFN concentrations were significantly enhanced to 205 +/- 45 and 252 +/- 67% of control, respectively. Although the majority of cell preparations tested exhibited an enhanced production of IFN in response to these opioid peptides, some did not. When beta-endorphin or Met-enkephalin were utilized at 10(-11) M, 10 of 15 and 7 of 11 responded with IFN production greater than 20% above the control (untreated) level. There was not an absolute correlation between an enhanced response to beta-endorphin and Met-enkephalin, suggesting the presence of multiple receptor types on these cells for opioids. The opioid receptor antagonist, naloxone, did not significantly prevent the opiate effect. When 10(-8) M naloxone was included in cultures containing 10(-12) M beta-endorphin or Met-enkephalin no significant inhibition of the effect of either opioid on IFN production was observed.

Gastrointestinal regulatory peptides modulate in vitro immune reactions of mouse lymphoid cells

The effects of six gastrointestinal regulatory peptides (beta-endorphin, substance P, metenkephalin, vasoactive intestinal peptide, bombesin, and somatostatin) on mouse lymphocytes stimulated with concanavalin A, lipopolysaccharide, phytohemagglutinin, or alloantigens were evaluated. Lymphocytes were stimulated in vitro and the influences of exogenously adding varying concentrations of neuropeptides (10(-6)-10(-11) M) on the incorporation of [methyl-3H-]thymidine were determined. The roles of cell density and antigen concentration on neuropeptide induced immunomodulation were also assessed. We observed that vasoactive intestinal peptide (VIP) would significantly inhibit the response of B10 lymphocytes to concanavalin A (54%) and phytohemagglutinin (56%) but not to lipopolysaccharide (16%). The VIP-induced inhibition was progressively diminished as the neuropeptide concentration was reduced to 10(-11) M. By 24 hr after stimulation the lymph node cells were refractory to the inhibitory effects of VIP. In addition, VIP would not inhibit B10 lymph node cells from responding to B10. K spleen cells in mixed, one-way lymphocyte cultures. The other five peptides did not influence the in vitro responses. The potential role of neuropeptides in the pathophysiology of immunologic-based disorders is discussed.

Gastrointestinal regulatory peptides modulate mouse lymphocyte functions under serum-free conditions in vitro

Conditions are described for performing mitogen (Concanavalin A, Con A; lipopolysaccharide, LPS) and mixed lymphocyte reaction (MLR) cultures using serum-free medium. The effects of exogenously adding several gastrointestinal regulatory peptides (beta-endorphin, substance P, met-enkephalin, vasoactive intestinal peptide, bombesin and somatostatin) on the incorporation of 3H-methyl-thymidine was determined. It was observed that mitogen stimulation of lymph node cells with Con A was inhibited (70% of control) by vasoactive intestinal peptide (VIP) but spleen cells stimulated by LPS were insensitive to immunomodulation (98% of control). The ability of VIP to inhibit Con A induced thymidine incorporation was concentration dependent (10(-6) to 10(-18) M) and was not attributable to kinetic shifts or cell toxicity. None of the other tested neuropeptides affected Con A or LPS induced blastogenesis. MLR cultures were inhibited by VIP, beta-endorphin and somatostatin in a biphasic manner with maximal inhibition observed at 10(-8) to 10(-12) M. Both substance P and bombesin exhibited slight immunoenhancing properties at 10(-14) to 10(-18) M. Met-enkephalin was ineffective as an immunomodulator of MLR cultures. The utility of using serum-free medium in identifying neuropeptides with immunomodulatory properties are discussed.

Inhibition of in vivo neutrophil accumulation by stress. Possible role of neutrophil adherence

Psychological stress results in neural and endocrine changes which can alter various aspects of the immune system. However, the effects of stress on inflammation has not received much attention despite the fact that stress hormones, such as the corticosteroids, are known to reduce inflammation. The present study extends a previous finding that stress itself can reduce inflammation. In the first experiment, zymosan was injected into an air pouch on the dorsum of F344 rats. Half of these rats then received three hours of inescapable, intermittent, electric foot shock as a stressor. The other half of the injected rats served as nonstressed controls. A third group were given air pouches but no zymosan. Fewer neutrophils accumulated at the inflammatory site of stressed rats as compared to nonstressed control rats. However, phagocytosis of zymosan by air pouch neutrophils was higher in stressed rats. Peripheral perfusion was not altered significantly by shock, but vascular permeability was reduced in stressed rats. The effects of stress on peripheral blood leukocytes of rats not injected with zymosan was investigated. It was found that while peripheral blood monocytes and lymphocyte numbers were decreased by stress, neutrophils were not decreased. Increased neutrophil adherence was found in stressed rats. Additionally, in the presence of endotoxin, neutrophils from stressed rats did not increase their adherence as much as those of control rats. The increased adhesiveness of neutrophils in stressed animals may account for the diminished inflammatory response in the shocked rats.

Morphine inhibits the carrageenan-induced oedema and the chemoluminescence of leucocytes stimulated by zymosan

Morphine inhibited the oedema formation induced by carrageenan. The anti-inflammatory activity developed 120 min after carrageenan injection, suggesting that inhibition of the kinin phase might be partly responsible. This assumption is supported by the findings that morphine inhibited bradykinin oedema but did not influence oedema formation induced by histamine, 5-HT or PGE2. The anti-inflammatory activity of morphine was partially inhibited by naloxone (0.5-1 mg kg-1) in the carrageenan oedema test. Zymosan-stimulated chemoluminescence of neutrophils of the rat was inhibited both by morphine (0.1-10 microM) and naloxone (1-100 microM). When morphine and naloxone were administered simultaneously (10 microM) their inhibitory effects were additive. Naloxone also failed to antagonize the inhibitory action of morphine in lower dose (0.1 microM). These results suggest that the effect of morphine in inflammation might be mediated either by one of the opiate receptor subtypes insensitive to naloxone or a non-opiate mechanism might be involved.

Opiates, endorphins, and the developing organism: a comprehensive bibliography, 1982-1983

A comprehensive bibliography of the literature concerned with opiates, endorphins, and the developing organism for 1982 and 1983 is presented. Utilized with a companion paper (Neurosci Biobehav Rev 6: 439-479, 1982) these articles cover clinical and laboratory references beginning in 1875. For the years 1982 and 1983, a total of 385 citations was recorded. A series of indexes accompanies the citations in order to make the literature more accessible. These indexes are divided into clinical and laboratory topics. The clinical section is subdivided into: age of subject examined, maternal aspects, the fetus, and the offspring. The laboratory section is subdivided into: type of opiate/endorphin studied, species utilized, and major subject areas explored.

Chronic infusion of opiate peptides to rat cerebrospinal fluid with osmotic minipumps

Beta-endorphin-related opiate peptides or the opiate antagonist naloxone were chronically infused for periods of 24 to 48 hours to the lateral cerebral ventricle of adult male rats using Alza osmotic minipumps. Previous studies have suggested a "chemotactic"-like effect of opiate peptides for supraependymal macrophages in the region of the third ventricle of the brain. The present study demonstrates a stimulatory effect of beta-endorphin infusion on the appearance of lymphocyte and neutrophil-like cells, in addition to macrophages, in the region of the third ventricle, suggestive of an intracerebral inflammatory response. None of the other molecules, including alpha-endorphin, methionine-enkephalin, naloxone, or sterile saline produced similar cellular responses after infusion, although some of the latter substances may have induced the appearance of supraependymal neuron-like cells in the area. Observations suggest that the chronic presence of beta-endorphin, a biologically active opiate peptide, will interact with cells of the immune system, which have the ability to gain access to the cerebrospinal fluid.

Human neutrophil migration is enhanced by beta-endorphin

Using a serum-free chemotaxis-under-agarose assay, we measured the effect of beta-endorphin on directed migration of human neutrophils toward 10(-7) M N-formyl-methionyl-leucyl-phenylalanine (FMLP). Neutrophils were pre-incubated with a range of beta-endorphin concentrations. beta-endorphin enhanced migration of neutrophils toward FMLP. This effect was maximal at 10(-9) M beta-endorphin. Naloxone inhibited the beta-endorphin effect, suggesting that enhanced migration is mediated via an opiate receptor.