Neuropeptides: conductors of the immune orchestra

Neuropeptides in gut-brain axis and their influence on host immunity and stress

In recent decades, neuropeptides have been found to play a major role in communication along the gut-brain axis. Various neuropeptides are expressed in the central and peripheral nervous systems, where they facilitate the crosstalk between the nervous systems and other major body systems. In addition to being critical to communication from the brain in the nervous systems, neuropeptides actively regulate immune functions in the gut in both direct and indirect ways, allowing for communication between the immune and nervous systems. In this mini review, we discuss the role of several neuropeptides, including calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), corticotropin-releasing hormone (CRH) and phoenixin (PNX), in the gut-brain axis and summarize their functions in immunity and stress. We choose these neuropeptides to highlight the diversity of peptide communication in the gut-brain axis.

Naloxone pretreatment prevents kidney injury after liver ischemia reperfusion injury

PURPOSE

The aim of this study was to assess the effects of naloxone, an opioid receptor antagonist, on the renal injury as a remote organ after hepatic ischemia reperfusion (IR) in rats.

MATERIALS AND METHODS

Forty male Wistar rats were randomly allocated into four groups as follows: sham, sham + naloxone, IR and IR + naloxone. In anesthetized rats, hepatic ischemia was applied for 30 min in IR and IR + naloxone groups. Sham + naloxone and IR + naloxone groups were given naloxone (3.0 mg/kg, iv) 30 min before ischemia. After 24 h, blood and tissue samples were obtained for histopathological, tissue malondialdehyde (MDA) and biochemical analyses.

RESULTS

Histopathological study of liver in IR group showed enlarged sinusoids, sinusoidal congestion, cellular degenerative changes and necrosis. The kidney of the rats with hepatic IR showed pathological changes in tubular cell swelling, tubular dilatation, moderate to severe necrosis, glomerular fibrosis and hemorrhage. Histological examination confirmed the extent of hepatic and renal changes in IR group was higher (P < 0.05) than in other groups. Rats that underwent hepatic IR exhibited significant increase in serum concentrations of urea and creatinine levels (P < 0.05). The serum alanine aminotransferase and aminotransferase values were significantly higher in IR group compared to the other groups (P < 0.05). Liver IR produced a significant increase in hepatic and renal tissue MDA levels, while pretreatment with naloxone was associated with a significantly lower MDA levels (P < 0.05).

CONCLUSION

The results of this study showed that naloxone pretreatment protected the renal injury from hepatic IR.

Are stress-induced immunological changes mediated by mood? A closer look at how both desirable and undesirable daily events influence sIgA antibody

This investigation tested a three-path model of mood as a mediator of the relation between stress and immunity. Seventy-two married men completed end-of-day diaries in which they rated their mood for that day and the desirability of the day's events for I2 weeks. Events were coded as either desirable (nonstressful) or undesirable (stressful) in nature. Immunological functioning was assessed by secretory immunoglobulin-A NgA) antibody response lo an oral antigen. Regression analyses indicated that negative mood partially mediated the immunological response to both undesirable and desirable events. Undesirable events lowered antibody levels primarily by increasing negative mood: desirable events increased antibody levels by decreasing negative mood. Evidence for mediation by positive mood beyond that found for negative mood was weak.

Upregulation of proinflammatory cytokines and nerve growth factor by intraplantar injection of capsaicin in rats

Capsaicin-sensitive primary afferents (CSPA) are known to be involved in nociception and neurogenic inflammation. Extensive research has been devoted to the sensory role of these fibres but less attention has been paid to their local effector function. This study aimed at gaining more insight into the molecular mechanisms underlying the neurogenic inflammation induced by this special group of afferent fibres. Different groups of rats (n = 5 in each group), either naive or subjected to selective ablation of their CSPA, received individual intraplantar injections of saline, capsaicin, its vehicle or capsaicin preceded by its antagonist, capsazepine. Acute tests for nociception were used to assess the variations of the nociceptive thresholds. Variations of the levels of proinflammatory cytokines and nerve growth factor (NGF) were measured by enzyme-linked immunosorbent assay (ELISA). Intraplantar injection of capsaicin (10 microg in 50 microl) produced a sustained thermal and mechanical hyperalgesia that peaked at 3-6 h and disappeared 24 h following the injection. Similar capsaicin injection in further groups of rats produced an early upregulation of the proinflammatory cytokines and NGF, which peaked at 30-60 min and returned to control levels within 2-5 h. Similar effects were observed following the application of either capsaicin or intense electrical stimulation on the cut end of the distal portion of the sciatic nerve. The effects of capsaicin were abolished in rats subjected to selective ablation of their CSPA. These results demonstrate that CSPA can simultaneously challenge the immune system through the release of proinflammatory mediators and the central nervous system through nociceptive signalling and can therefore serve as a common afferent pathway to both immune and nervous systems.

Post-traumatic myofascial pain of the head and neck

Post-traumatic myofascial pain describes the majority of chronic head and neck pain seen in clinical practice. If conditions such as vascular headaches, neuropathic pain, degenerative cervical joint disease, and dental pain are excluded, myofascial tissues are directly or indirectly involved in all other forms of head and neck pain. The most common of these include temporomandibular disorders, neck pain such as whiplash-associated disorder, cervicogenic headaches, and tension-type headaches. The pathophysiology of these conditions is not widely understood; however, peripheral and central mechanisms appear to play a role.

Inhibition of antigen specific lymphocyte proliferation and cytokine stimulation by peptidomimetic opioid compound

In sequel to our preliminary observations with peptidomimetic opioid compounds, we have further investigated immunomodulatory activity of one peptidomimetic compound (Tyr-NH-CH2-CH2-O-Phe-NH2) with peripheral blood mononuclear cells (PBMCs) of healthy volunteers/tuberculosis patients. This peptidomimetic compound was evaluated for its effect on purified protein derivative (PPD) stimulated lymphocyte proliferation in vitro, production of Th1 and Th2 cytokines by ELISA and ribonuclease protection assay. Our study shows the immunosuppressive potential of above synthetic peptidomimetic compound. This compound inhibited PPD stimulated human lymphocyte proliferation and this inhibition was reversed by opioid receptor antagonist, naloxone. Its immunosuppressive effect was further demonstrated by inhibition of interleukin-9 (IL-9), IL-10 but failed to influence IL-2, IL-15 and interferon-y (IFN-gamma) in PPD stimulated human PBMCs.

Up-regulation of splenic prohormone convertases PC1 and PC2 in diabetic rats

Organisms respond to infection in a complex manner involving bidirectional interactions between the neuroendocrine and immune systems. Many of the bioactive endocrine/immune factors are synthesized in a precursor form and are expected to be activated by prohormone convertases (PCs). Since patients with both type 1 and type 2 diabetes have an increased incidence and severity of infections, we hypothesized that in a condition of hyperglycemia, these processing enzymes would be activated in an immune tissue, the spleen. To test this hypothesis, we treated rats with intraperitoneal streptozotocin (STZ) (50 mg/kg/day) daily for 5 days and measured splenic PC1 and PC2 mRNA by ribonuclease protection assay. We found that PC1 mRNA was increased 6.0+/-0.02-fold (P<0.05) and PC2 mRNA was increased 1.80+/-0.01-fold (P<0.005) in the spleen of rats that received STZ compared to rats that received vehicle. Western blot indicated that the 75-kDa form of PC1 was the only form of PC1 present in the spleen and that this form increased with STZ treatment. Immunohistochemistry revealed that PC1 was found in both the white pulp (T-lymphocytes) and red pulp (monocytes and macrophages) and that its increase in immunoreactivity occurred primarily in the white pulp. PC2 and pro-opiomelanocortin (POMC, a possible splenic substrate for PC1/PC2) immunoreactivity was found predominantly in the red pulp. STZ induced an increase in splenic PC1 and POMC, but not PC2 protein levels. We conclude that in the STZ model of diabetes, splenic PCs are induced, which could lead to an increased activation of many immune-derived hormones. We speculate that this up-regulation of prohormone converting enzymes may be related to the increased infections seen in patients with both type 1 and type 2 diabetes.

Identification of delta- and mu-type opioid receptors on human and murine dendritic cells

The purpose of this study was to evaluate mu- and delta-opioid receptors (OR) on human and murine dendritic cells (DC). Expression of mu- and delta-OR mRNA on DC was demonstrated by RT-PCR. The immunocytochemical and Western blot analyses revealed the expression of OR protein in DC. Radioreceptor assay demonstrated the specific saturated temperature-dependent binding of [3H]-labeled opioid ligand on DC and B(max)=2.8+/-0.3 fmol/10(6) cells and K(D)=4.8+/-1.0 nM were calculated by a Scatchard analysis. Finally, OR ligands DADLE and DAGO dose-dependently modulated the capacity of DC to induce T cell proliferation in an MLR assay. Importantly, expression of functional OR on DC was significantly increased upon TNF-alpha-induced DC maturation. Thus, these data suggest a new mechanism of opioid-dependent neuroendocrine immunomodulation.

Special feature for the Olympics: effects of exercise on the immune system: neuropeptides and their interaction with exercise and immune function

It is known today that the immune system is influenced by various types of psychological and physiological stressors, including physical activity. It is well known that physical activity can influence neuropeptide levels both in the central nervous system as well as in peripheral blood. The reported changes of immune function in response to exercise have been suggested to be partly regulated by the activation of different neuropeptides and the identification of receptors for neuropeptides and steroid hormones on cells of the immune system has created a new dimension in this endocrine-immune interaction. It has also been shown that immune cells are capable of producing neuropeptides, creating a bidirectional link between the nervous and immune systems. The most common neuropeptides mentioned in this context are the endogenous opioids. The activation of endogenous opioid peptides in response to physical exercise is well known in the literature, as well as the immunomodulation mediated by opioid peptides. The role of endogenous opioids in the exercise-induced modulation of immune function is less clear. The present paper will also discuss the role of other neuroendocrine factors, such as substance P, neuropeptide Y and vasoactive intestinal peptide, and pituitary hormones, including growth hormone, prolactin and adrenocorticotrophin, in exercise and their possible effects on immune function.

Special feature for the Olympics: effects of exercise on the immune system: neuropeptides and their interaction with exercise and immune function

It is known today that the immune system is influenced by various types of psychological and physiological stressors, including physical activity. It is well known that physical activity can influence neuropeptide levels both in the central nervous system as well as in peripheral blood. The reported changes of immune function in response to exercise have been suggested to be partly regulated by the activation of different neuropeptides and the identification of receptors for neuropeptides and steroid hormones on cells of the immune system has created a new dimension in this endocrine-immune interaction. It has also been shown that immune cells are capable of producing neuropeptides, creating a bidirectional link between the nervous and immune systems. The most common neuropeptides mentioned in this context are the endogenous opioids. The activation of endogenous opioid peptides in response to physical exercise is well known in the literature, as well as the immunomodulation mediated by opioid peptides. The role of endogenous opioids in the exercise-induced modulation of immune function is less clear. The present paper will also discuss the role of other neuroendocrine factors, such as substance P, neuropeptide Y and vasoactive intestinal peptide, and pituitary hormones, including growth hormone, prolactin and adrenocorticotrophin, in exercise and their possible effects on immune function.

Effects of nefazodone on the immune system of mice

Mice exposed to a chronic auditory stressor and treated with nefazodone (10 mg/kg/day s.c.), showed a reduction in stress-induced suppression of thymus and spleen cellularity, and in peripheral T-Iymphocyte population. The in vitro blastogenic response of spleen lymphoid cells to mitogen concanavalin A, the in vitro and in vivo activity of phagocytosis, both measured using the zymosan and carbon clearance tests, respectively, were also assessed and nefazodone was found to partially reverse the inhibitory effect of stress on those parameters. Nefazodone did not significantly affect those parameters in unstressed mice. In conclusion, this report provides evidence on the immunoprotective effects of this novel antidepressant drug against the adverse effects of stress in mice.

Psychosocial stressors and mammary tumor growth: an animal model

Stressful life events and the ability to cope with stress may play a role in the progression of breast cancer; however, the complex relationship between stressors and tumor growth is difficult to investigate in humans. Our studies have utilized the androgen-responsive Shionogi mouse mammary carcinoma (AR SC115) in male mice to investigate the effects of social housing condition on tumor growth rates and responses to chemotherapy. We demonstrate that, depending on social housing condition, mammary tumor growth and response to chemotherapy can both increase and decrease. We have examined the possible role(s) of 1) psychosocial variables, 2) testosterone and corticosterone, hormones altered by stress and known to stimulate SC115 cells in vivo and in vitro, 3) NK cells, one of the body's first lines of defense against tumor cells, 4) stress proteins, in mediating the differential tumor growth rates observed in our model. This review discusses the investigations we have undertaken to elucidate the mechanisms through which a psychosocial stressor, social housing condition, can alter tumor growth rate.

A new theory on the common evolutionary origin of natural immunity, inflammation and stress response: the invertebrate phagocytic immunocyte as an eye-witness

Data in favor of the hypothesis of the common evolutionary origin of natural immunity inflammation and stress response are presented. These phenomena seem to be mediated by a common pool of molecules (POMC-derived peptides, cytokines, biogenic amines, glucocorticoids, and nitric oxide). Macrophages are able to release all the above mentioned molecules. They play a primary role in defence mechanisms. Thus, we argue that this cell can be considered the eye-witness of the common evolutionary origin of the immune and neuroendocrine systems.

Differential response to a stress stimulus of proenkephalin peptide content in immune cells of naive and chronically stressed rats

Proenkephalin peptides produced by endocrine and nervous tissues are involved in stress-induced immunosuppression. However, the role of peptides produced by immune cells remains unknown. The present study examines the effect of acute and chronic foot-shock stress on proenkephalin peptide content in bone marrow (BMMC), thymus (TMC), and spleen (SMC) rat mononuclear cells. Proenkephalin was not processed to met-enkephalin in BMMC, while in TMC and SMC met-enkephalin represented 10% and 26% of total met-enkephalin-containing peptides, respectively. Naive rats receiving a stress stimulus showed a significant decrease of proenkephalin derived peptides in BMMC, TMC and SMC. However, in chronically stressed rats that already showed basal low peptide levels, a new stress stimulus produced a differential response in each immune tissue. That is, in BMMC peptide levels reached control rats values; in TMC remained unmodified; and in SMC, although precursors content increased, met-enkephalin levels were even lower than those observed in acutely stressed rats. Free synenkephalin content paralleled met-enkephalin changes in SMC of acutely and chronically stressed rats. The in vitro release of met-enkephalin and free synenkephalin increased in SMC of stressed rats. Met-enkephalin produced in SMC and partially processed proenkephalin peptides detected in BMMC, were only found in macrophages. However, met-enkephalin only appeared in bone marrow macrophages after at least 4 h of cell culture. Altogether, these results suggest that a stress stimulus induced proenkephalin peptide release from immune tissue macrophages. The differential response observed in chronically stressed rats suggest an alternative activation of heterogeneous proenkephalin-storing macrophage subpopulations.

Effects of fluoxetine on the development of lung metastases induced by operative stress in rats

Experiments were performed in order to evaluate the effects of fluoxetine, a selective inhibitor of neural serotonin transporter antidepressant, on the development lung metastases in rats subjected to laparotomy and injected (i.v.) with 10(4) Walker 256 (W-256) carcinosarcoma cells. The number of metastatic nodules on the surface of the lungs, as well as the percentage-area of metastases in the frontal section through pulmonary hilus were increased in rats subjected to sham-surgery or laparotomy. Treatment with fluoxetine (5 mg/kg) partially reversed those adverse effects of surgery, but the difference was clearer when it was administered before surgery was performed. Survival periods were also assessed and fluoxetine was found to decrease the lethality of rats exposed to surgery.

Antibacterial peptides are present in chromaffin cell secretory granules

1. Antibacterial activity has recently been associated with the soluble matrix of bovine chromaffin granules. Furthermore, this activity was detected in the contents secreted from cultured chromaffin cells following stimulation. 2. The agents responsible for the inhibition of Gram+ and Gram- bacteria growth are granular peptides acting in the micromolar range or below. In secretory granules, these peptides are generated from cleavage of chromogranins and proenkephalin A and are released together with catecholamines into the circulation. 3. Secretolytin and enkelytin are the best characterized; these two peptides share sequence homology and similar antibacterial activity with insect cecropins and intestinal diazepam-binding inhibitor. For some of the peptides derived from chromogranin A, posttranslational modifications were essential since antibacterial activity was expressed only when peptides were phosphorylated and/or glycosylated. 4. The significance of this activity is not yet understood. It may be reminiscent of some primitive defense mechanism or may serve as a first barrier to bacteria infection during stress, as these peptides are secreted along with catecholamines.

The C-terminal tetrapeptide of beta-endorphin (MPF) enhances lymphocyte proliferative responses

Human MPF (Lys-Lys-Gly-Glu) stimulates the proliferative response of human lymphocytes to the T-cell mitogen concanavalin A by 121-751% in the concentration range 10(-11)-10(-4) M; the peak effect is at 10(-8) M, lower or higher concentrations eliciting reduced responses, i.e. the dose-response curve is bell-shaped. Species specificity is high. Human MPF similarly stimulates rat lymphocytes, but the peak effect is seen at a 100-fold higher dose (10(-6) M). Rat MPF (Lys-Lys-Gly-Gln) has a peak effect at 10(-6) M with human lymphocytes, but the peak effect with rat lymphocytes is at a 1000-fold lower dose (10(-9) M). Truncated forms of the MPFs (Gly-Glu, Gly-Gln, Gly, Glu, Gln) and opioid peptides (beta-endorphin, [Leu] and [Met]enkephalin) show insignificant or only weak stimulatory or inhibitory effects. These results suggest that MPF acts via specific non-opioid receptors located on lymphocytes and that endogenously released MPF may have an important role in the functioning of the immune system.

Morphine alters the levels of growth hormone receptor mRNA and [125I]growth hormone binding in human IM-9 lymphoblasts via a naloxone-reversible mechanism

The immune system and the neuroendocrine system are functionally interactive. Lymphocytes possess opioid receptors as well as growth hormone receptors (GHR) by which opioids and growth hormone (GH) may modulate immune functions. In this study, we have investigated the effects of morphine on [125I]hGH binding and GHR gene expression in human lymphoblastoid IM-9 cells. Northern blot analysis revealed significantly altered GHR mRNA levels after treatment of the cells with different concentrations of morphine for 12 h. Morphine at 10 microM increased the mRNA levels in a time-dependent biphasic manner, with maximum levels at 6 and 48 h. The receptor protein, measured by [125I]GH binding, showed a time-delayed increase compared with the GHR mRNA changes. Pretreatment with naloxone inhibited the action of morphine, suggesting involvement of classical opioid receptors. The present study demonstrates, for the first time, effects of morphine on GHR mRNA levels and [125I]GH binding in human cultured lymphocytes.

Biosynthesis, uptake, and degradation of anandamide and palmitoylethanolamide in leukocytes

Anandamide (arachidonoylethanolamide, AnNH) and palmitoylethanolamide (PEA) have been proposed as the physiological ligands, respectively, of central and peripheral cannabinoid receptors. Both of these receptors are expressed in immune cells, including macrophages and mast cells/basophils, where immunomodulatory and/or anti-inflammatory actions of AnNH and PEA have been recently reported. We now provide biochemical grounds to these actions by showing that the biosynthesis, uptake, and degradation of AnNH and PEA occur in leukocytes. On stimulation with ionomycin, J774 macrophages and RBL-2H3 basophils produced AnNH and PEA, probably through the hydrolysis of the corresponding N-acylphosphatidylethanolamines, also found among endogenous phospholipids. Immunological challenge of RBL-2H3 cells also caused AnNH and PEA release. The chemical structure and the amounts of AnNH and PEA produced upon ionomycin stimulation were determined by means of double radiolabeling experiments and isotope dilution gas chromatography/electron impact mass spectrometry. Both cell lines rapidly sequestered the two amides from the culture medium through temperature-dependent, saturable and chemically inactivable mechanisms. Once uptaken by basophils, AnNH and PEA compete for the same inactivating enzyme which catalyzes their hydrolysis to ethanolamine. This enzyme was found in both microsomal and 10,000 x g fractions of RBL cell homogenates, and exhibited similar inhibition and temperature/pH dependence profiles but a significantly higher affinity for PEA with respect to neuronal "anandamide amidohydrolase." The finding of biosynthetic and inactivating mechanisms for AnNH and PEA in macrophages and basophils supports the previously proposed role as local modulators of immune/inflammatory reactions for these two long chain acylethanolamides.

Effects of fluoxetine on the immunosuppressive response to stress in mice

Mice exposed to a chronic auditory stressor and treated with fluoxetine (5 mg/kg) showed a reduction in stress-induced suppression of thymus and spleen cellularity, and in peripheral T lymphocyte population. The blastogenic response of spleen lymphoid cells and the delayed type hypersensitivity response (DTH) to sheep red blood cells (SRBC) were also assessed and fluoxetine was found to partially reverse the inhibitory effect of stress on both parameters.

Proopiomelanocortin gene product regulation in keratinocytes

Proopiomelanocortin (POMC) is the precursor for adrenocorticotropic hormone, melanocyte-stimulating hormones, beta-lipotropic hormone (beta LPH), and beta endorphin. These peptides can function as neurotransmitters, modulate immune responses, and affect melanogenesis. We investigated POMC expression and protein processing in normal human keratinocytes. On Northern blot analysis, the baseline expression of the 1.2-kb POMC transcript was upregulated by ultraviolet radiation (UVR) or by stimulation with interleukin-1 alpha (IL-1 alpha) or phorbol 12-tetradecanoate 13-acetate (TPA). On Western blot analysis, POMC, beta LPH, and beta-endorphin were detected in cell extracts under baseline conditions. beta LPH level increased substantially after UVR, IL-1 alpha, or TPA. Within 36 h after TPA stimulation, beta-endorphin became undetectable in cell extracts, coinciding with an increase of beta-endorphin-immunoreactive protein in the culture medium. Our data establish that keratinocytes synthesize POMC protein as well as its derivatives beta LPH and beta-endorphin, and that this process is modulated by TPA, IL-1A, and UVR. beta LPH and beta-endorphin of keratinocyte origin may thus be involved in melanogenesis and/or immunomodulation in the skin after sun exposure, and their release into the circulation may also have systemic effects.

Substance P modulates human immunodeficiency virus replication in human peripheral blood monocyte-derived macrophages

Substance P (SP), a member of the tachykinin family of neuropeptides, is an important immunomodulator of lymphocyte and monocyte/macrophage function. We have examined the effects of SP on human immunodeficiency virus type 1 (HIV-1) infection of peripheral blood monocyte-derived macrophages (MDMs) in vitro. Human monocytes isolated by Ficoll gradient followed by adherence were maintained in vitro for 10 days and infected with HIV-1. The addition of SP resulted in a 2- to 8-fold-enhanced HIV-1 expression in the MDMs isolated from 7 of 13 healthy donors as determined by reverse transcriptase (RT) activity and p24 protein expression assays, as compared to control cultures incubated with HIV-1 alone. There was no correlation observed, however, between SP-stimulated TNF production and HIV-1 expression in MDMs obtained from a subset of these donors. These effects of SP on HIV-1 expression in MDMs in vitro may have in vivo implications relevant to modulation of monocyte/macrophage functions, to HIV-1 infection of monocytes/macrophages, and to the immunopathogenesis of HIV-1 infection.

The C-terminal bisphosphorylated proenkephalin-A-(209-237)-peptide from adrenal medullary chromaffin granules possesses antibacterial activity

The chromaffin granules have been shown to be an excellent model to study the processing of proenkephalin-A and chromogranins. Recently, we reported a study dealing with the processing of chromogranin B/secretogranin I and the occurrence of the C-terminal chromogranin B-derived peptide 614-626 which was shown to have antibacterial activity [Strub, J.M., Garcia-Sablone, P., Looning, K., Taupenot, L., Hubert, P., Van Dorsselaer, A., Aunis, D. & Metz-Boutigue, M.H. (1995) Eur. J. Biochem. 229, 356-368]. We also observed that this new antibacterial activity present in chromaffin granules was associated with other endogenous protein-derived fragments yet to be characterized. The present study reports the isolation and characterization of a peptide which possesses antibacterial activity and which corresponds to the C-terminal 209-237 sequence of proenkephalin-A. A detailed study using microsequencing and matrix-assisted-laser-desorption time-of-flight mass spectrometry (MALD-TOF MS) allowed us to correlate the antibacterial activity of this peptide named enkelytin (FAEPLPSEEEGESYSKEVPEMEKRYGGFM) with post-translational modifications. Endogenous bisphosphorylated proenkephalin-A-(209-237) was active on Micrococcus luteus and Bacillus megaterium killing bacteria in the 0.2 - 0.4 microM range but was inactive in similar conditions towards Escherichia coli. Enkelytin shares sequence and structural similarities with the antibacterial C-terminal domain of diazepam-binding inhibitor. According to this similarity, a prediction of secondary structure is proposed for enkelytin and discussed in relationship to its biological activity.

Proopiomelanocortin, its derived peptides, and the skin

Proopiomelanocortin (POMC) is a protein synthesized predominately in the pituitary gland but also in a variety of other tissues, including the skin. Through enzyme-mediated cleavage that varies among cell types, POMC can give rise to at least eight distinct peptides whose biologic roles are incompletely delineated. Although blood-borne pituitary-derived bioactivity for the skin was first recognized 80 years ago and the responsible neuropeptides isolated 20-40 years ago, our understanding of POMC-derived peptides in skin is still rapidly evolving. In particular, recent work in cultured human and murine skin-derived cells has demonstrated POMC gene expression as well as modulation of POMC and many of its derived peptides in response to physiologic signals including ultraviolet irradiation and cytokines. Immunoreactivity for these peptides has also been detected in normal skin and hair follicles, strongly suggesting cutaneous synthesis in vivo. Candidate autocrine or paracrine functions include enhanced melanogenesis, immunomodulation, and effects on cell cycle regulation and differentiated function in both the epidermis and its appendages. This article reviews recent data concerning POMC gene expression and regulation, protein processing, signal transduction, and biologic functions relevant to cutaneous biology.

Modulatory effects of [Met5]-enkephalin on interleukin-1 beta secretion from microglia in mixed brain cell cultures

In the present study, functional interactions between [Met5]-enkephalin (ME), naloxone and lipopolysaccharide (LPS) on interleukin-1 beta (IL-1 beta) immunostaining and secretion have been assessed in mixed brain cell cultures from embryonic day 17 mice. Adding ME alone or together with LPS to the culture increased the release of IL-1 beta after 48 h in a concentration-dependent fashion. In situ hybridization studies showed that LPS, but not ME, increased the abundance of IL-1 beta mRNA. The enhanced release of IL-1 beta caused by ME or LPS was partially blocked by naloxone. LPS induced concentration-dependent morphological changes in microglia in mixed brain cell cultures, identified by a monoclonal antibody F4/80 which is specific for macrophages/microglia. Despite increasing IL-1 beta release into the media, ME (10(-8) M) did not induce morphological changes in microglia. Naloxone alone also had no effect on glial morphology; however, the LPS-induced morphological changes were blocked by naloxone. Our data indicate that both exogenous and endogenous opioids regulate IL-1 beta production by microglial cells in the mixed brain cell cultures.

Effects of buspirone on the immune response to stress in mice

Several experiments were conducted to evaluate the effects of buspirone, a selective 5-hydroxytryptamine-1A (5-HT1A) anxiolytic, on the immune system of mice exposed to a chronic auditory stressor. Daily injection with 0.5 and 1 mg/kg (intraperitoneally) of buspirone resulted in a dose-dependent reduction in the stress-induced suppression of the natural killer (NK) cell activity and the in vitro and in vivo activity of phagocytosis. Higher doses of buspirone (2.0 mg/kg) showed less robust immunoenhancing effects in stressed mice, and caused a significant suppression of these immune parameters in unstressed mice.

Age-related changes in mitogen-induced beta-endorphin release from human peripheral blood mononuclear cells

beta-Endorphin is an opioid peptide synthesized in the pituitary, hypothalamus, and immunocytes, known to affect immune responses both when added in vitro and when its synthesis is increased in vivo (e.g., during stress). We show here that, similar to its concentrations in peripheral blood mononuclear cells, the release of the opioid peptide from these cells after stimulation with polyclonal mitogens such as PHA or Con-A is also age dependent. Moreover, the effect of both mitogens on Ca2+ homeostasis changes with age. Finally, the ionophore ionomycin and the Ca2+ ATPase blocker thapsigargin induce the same age related effect on beta-endorphin release. For these reasons, we suggest that calcium homeostasis might be important for the differences observed in the release of the opioid from cells obtained from younger (< or = 30 years) or older (> or = 45 years) volunteers.

Immunoendocrine reshaping with age

The interaction of the endocrine, immune, and nervous systems in modulating each other's activity opens the track for a new way of looking to the effects ongoing on each of the three systems. This new approach finds it bases in old times, since evolution shows how we missed for many years a relation between the three systems that was clearly manifested in lower species. In this chapter, the effects of aging on the immune, endocrine and nervous systems are proposed as the consequence of the influences of each system on the others.

Methionine enkephalin combined with AZT therapy reduce murine retrovirus-induced disease

AZT (7.5 or 15 mg/kg/dose) and the neuropeptide methionine enkephalin (Met-ENK, 1 or 3 mg/kg/dose) were used in a combined protocol for therapy of established murine retroviral infection. In both models used, Friend virus leukemia (FV) and BM5 complex (lymphadenopathy and immune deficiency), the drug combination was able to reduce mortality and splenomegaly. While increasing mean survival time of those animals that did not survive infection by FV, when compared to infected control mice or mice treated with AZT alone, Met-ENK used alone at 1 and 3 mg/kg/mouse had no effect in reducing morbidity or mortality due to either virus. This suggested that Met-ENK had no direct antiviral effect at the concentrations used. In fact, mice treated with either single drug therapy or the combination still yielded virus in their spleen, even when splenomegaly was absent. The data suggest that Met-ENK, which has been reported to be immunostimulatory, acts in combination to improve the efficacy of AZT in reducing progression of disease in murine retrovirus models for human AIDS.

Expression of naloxone-resistant beta-endorphin binding sites on A20 cells: effects of concanavalin A and dexamethasone

beta-Endorphin affects mononuclear cell proliferation, cytokine production and calcium uptake in a naloxone-resistant manner. The presence of naloxone-insensitive binding sites for beta-endorphin have been demonstrated on murine EL4-thymoma cells, transformed human mononuclear cells and normal murine splenocytes. Since murine splenic B cells have been shown to express naloxone-resistant receptors for beta-endorphin in response to the mitogen, concanavalin A (Con A), the A20 B-cell lymphoma line was used to further study regulation of this site by Con A and dexamethasone. Analyses showed two sites: a high-affinity site, Kd1 = (8.7 +/- 2.3) x 10(-11) M and binding capacity (Bmax1) of (2.6 +/- 2.0) x 10(3) receptors/cell; and a low-affinity site, Kd2 = (2.2 +/- 0.8) x 10(-8) M with Bmax2 of (1.5 +/- 0.8) x 10(5) receptors/cell. Competition studies showed that N-acetyl-beta-endorphin was approx. 5-fold and beta-endorphin6-31 10-fold less potent than beta-endorphin1-31. Neither beta-endorphin1-27 nor naloxone, morphine or other opioid receptor agonists displaced [125I]beta-endorphin. Con A (20 micrograms/ml) significantly increased the Bmax (3.5-fold; expressed per cell) and resulted in a loss of the higher-affinity site. However, the increased Bmax occurred in proportion to the Con-A-induced increase in protein/cell. Dexamethasone (Dex) also increased Bmax, primarily by increasing (2-3-fold) the number of lower affinity sites. In contrast to Con A, two binding sites persisted after treatment with Dex, which exerted a minimal effect on protein/cell. Therefore, binding/cell and binding/protein/cell were both significantly enhanced by Dex. The combined effects of Dex and Con A on binding failed to show additivity or synergy. When binding was analyzed per protein/cell, the effect of Con A appeared to dominate; the Dex-enhanced binding/protein/cell was no longer evident in the presence of Dex plus Con A. Thus, Dex and Con A may enhance binding by independent mechanisms.

Molecular cloning of NPY-Y1 receptor cDNA from rat splenic lymphocytes: evidence of low levels of mRNA expression and [125I]NPY binding sites

The present study addressed the question of whether the effects of neuropeptide Y (NPY) on parameters of cellular immune activity are mediated by the direct action of this neuropeptide on lymphocyte NPY receptors. A partial cDNA corresponding to bp 3-585 of the NPY-Y1 receptor coding sequence was cloned from rat splenic lymphocytes and found to have 100% nucleotide sequence homology with that segment of the NPY-Y1 receptor in brain. Basal levels of NPY-Y1 mRNA expression and [125I]NPY binding sites of rat splenic lymphocytes were markedly lower than in frontal cortex. These data provide the first direct evidence that cells of the immune system possess NPY receptors, and suggest that further study will be necessary to determine their physiological significance.

Pyrogenic activity of human native and human recombinant interleukins-1 beta: stabilization with albumin enhances the pyrogenic action of recombinant IL-1 beta delivered into the rabbit brain

The pyrogenic potential of natural and recombinant human IL-1 beta in rabbits was found to be very similar when the substances were given intravenously. Under these conditions, stabilization of rIL-1 beta with human serum albumin (HSA) failed to affect the pyrogenic activity of recombinant IL-1 beta. When the two preparations were administered directly into the PO/AH area of the brain, recombinant IL-1 beta was less pyrogenic than its natural counterpart. This lower pyrogenicity of recombinant IL-1 beta was corrected if the injected material contained HSA, which is known to stabilize in vitro the biological activities of IL-1 beta against slow degradation. The possibility is now considered that the central and peripheral systems for IL-1 inactivation are different. The existence of an intrabrain IL-1 pool is suggested and its significance for neuroimmunomodulation is stressed.

Corticotropin-releasing factor reduces lipopolysaccharide-induced pulmonary vascular leak

Previous studies have suggested that corticotropin-releasing factor (CRF) has immunoregulatory effects in addition to its neuroendocrine role. We examined the ability of CRF to inhibit lipopolysaccharide (LPS)-induced pulmonary vascular leak in vivo. Female BALB/C mice were treated with either normal saline (NS) or CRF prior to injection with LPS. Pulmonary vascular leak was inhibited by CRF as assessed by measurement of lung wet-to-dry ratios. The stress-induced increase in serum corticosterone levels in mice injected with LPS alone was not further increased by treatment with CRF. This indicates that the effect of CRF was not mediated centrally by stimulation of endogenous steroid release. Histologic examination of the lungs revealed that leukocyte infiltration was significantly depressed in CRF-treated mice thus confirming the protective effect of CRF. In addition, a modest prolongation of survival was demonstrated in CRF-treated mice following challenge with LPS (p = .08). These data indicate the potential utility of CRF as a modulator of pulmonary vascular leak.

In vitro and in vivo effects of tachykinins on immune cell function in guinea pig airways

The effects of sensory neuropeptides substance P (SP) and neurokinin A (NKA) on immune cell recruitment and macrophage activation were determined. Guinea pigs exposed to capsaicin aerosol exhibited eosinophil and neutrophil influx into their bronchoalveolar lavage (BAL) fluid 24 h after treatment; SP aerosol elicited eosinophil influx, whereas NKA aerosol exposure caused neutrophil recruitment. Inhalation of capsaicin, NKA or SP aerosols also enhanced superoxide production induced by zymosan in cultured alveolar macrophages. Incubation of alveolar macrophages with SP or NKA in culture for the same time (24 h) did not potentiate the response to zymosan. Hence, tachykinin-mediated airway effects may not be the result of direct actions on target cells but rather involve alternate mechanisms and mediators which do not necessarily reflect in vitro data.

Characteristics of receptors for VIP in rat peritoneal macrophage membranes

Vasoactive intestinal peptide (VIP) receptors were investigated in rat peritoneal macrophage membranes (RPMM) using [125I]VIP as ligand. The receptor binding was rapid, reversible, saturable, specific, and dependent on time, temperature, and membrane concentration. The Scatchard analysis of binding data was consistent with the existence of two classes of VIP binding sites with Kd values of 0.60 +/- 0.08 and 275 +/- 39 nM and binding capacities of 580 +/- 71 and 72,500 +/- 810 fmol VIP/mg protein, respectively. The interaction showed a high degree of specificity, as suggested by competitive displacement experiments with several peptides structurally or not structurally related to VIP. These pharmacological studies showed the following order of potency: VIP (IC50 = 1 nM) > rGRF (IC50 = 13 nM) > PHI (IC50 = 421 nM) >> secretin. Glucagon, somatostatin, insulin octapeptide of cholecystokinin [CCK(26-33)], and pancreastatin were ineffective at concentrations up to 1 microM. Binding of [125I]VIP to membranes is markedly reduced by increasing the ionic strength of incubation medium. Treatment of membranes with dithiothreitol, trypsin, and phospholipases A2 and C resulted in a loss of the ability of these membranes to bind VIP. However, treatment with phospholipase D did not affect binding of VIP by membranes. The molecular characterization of VIP receptors in RPMM was performed after [125I]VIP cross-linking to membranes using the cross-linker dithiobis (succinimidyl propionate). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membrane proteins revealed specific [125I]VIP-protein complexes of M(r) 55,000 +/- 1700, 35,000 +/- 900, and 22,000 +/- 500.

Effects of alprazolam on cellular immune response to surgical stress in mice

Mice exposed to surgical stress induced by laparotomy and treated with chronic alprazolam (0.5-2 mg/kg) showed a dose-dependent reduction in stress-induced suppression of the natural killer (NK) cell activity. These immunoenhancing effects of alprazolam were more intense when it administered before the surgery was performed.

Effects of alprazolam on influenza virus infection in stressed mice

The review of the literature shows that stress can adversely affect influenza A virus infection. In this report, we study the effects of chronic alprazolam (1 mg/kg/day), a central benzodiazepine agonist anxiolytic, on the influenza A (PR-8/34) virus specific immune injury in mice exposed to a chronic auditory stressor. Treatment with alprazolam resulted in a significant reduction of stress-induced increase of virus titters and pulmonary vascular permeability. A correlation with the lethality of mice was also observed.

Effects of interferons and hydrogen peroxide on CA3 pyramidal cells in rat hippocampal slice cultures

In viral diseases of the CNS, both interferon-alpha/beta and interferon-gamma are produced intrathecally. At least some of the neurological symptoms associated with these diseases may be due to the effects of these cytokines. We have studied the actions of interferons on CA3 pyramidal cells in hippocampal slice cultures. Bath application of interferon-alpha/beta and interferon-gamma produced an excitatory effect on CA3 pyramidal cells and a decrease in evoked inhibitory postsynaptic potential amplitude, eventually leading to epileptiform bursting. These effects were slow in onset (several minutes), suggesting an indirect mechanism of action. Several lines of evidence suggest that the actions of interferons on pyramidal cells may at least in part be mediated by reactive oxygen intermediates, known to be released from non-neuronal cells: the effects of interferon on CA3 pyramidal cells were blocked by the free radical scavengers catalase and superoxide dismutase. Hydrogen peroxide reduced evoked inhibitory synaptic transmission, eventually leading to epileptiform bursting, thus mimicking several of the effects of interferons on pyramidal cells.