Impaired coupling of naloxone sensitive opiate receptors to adenylate cyclase in PMNLs of aged male subjects

Functional alteration of granulocytes, NK cells, and natural killer T cells in centenarians

The immune system in centenarians was characterized as elevated levels in the proportion and number of granulocytes, NK cells, and extrathymic T cells (including NKT cells) in the peripheral blood. Conventional T cells, abundant in youth, were decreased in proportion and number. In addition to this numerical change in centenarians, the function was significantly altered in comparison with that in middle-aged subjects. The phagocytic function and cytokine production of granulocytes in centenarians increased whereas the production of superoxides from granulocytes decreased. This tendency was almost the same in both healthy and unhealthy centenarians. IFN gamma production by NK and extrathymic T cells in centenarians seemed to be augmented and resulted in an elevated level of serum IFN gamma. Possibly due to the effect of this endogenous IFN gamma, the proportion of CD64(+) (Fc gamma RI) cells among granulocytes was elevated. The expansion of CD64 antigens on granulocytes is known to be regulated by IFN gamma and to be associated with their induction of phagocytosis. These results suggest that the immune system of centenarians is not merely impaired, but altered in terms of the number and functions of granulocytes, NK cells, NKT cells.

Proopiomelanocortin and the immune-neuroendocrine connection

This presentation will cover the history, recent developments in, and implications of the ability of both the immune and neuroendocrine systems to produce POMC. The discovery of POMC in immune cells was one of the events that heralded a molecular understanding of neuroimmunomodulation. This, together with the presence of opiate and ACTH receptors on lymphocytes and macrophages, provided the first biochemical circuit for which the same signal molecules and receptors could be used for intrasystem regulation, as well as bidirectional communication between the immune and neuroendocrine systems. Today we have a quite good understanding of the regulation and processing of POMC in immune cells, as well as the interaction of its product peptides with other cytokines. For instance, IL-1 causes POMC production by immune cells, and the POMC product, alpha-MSH, in turn, acts functionally as an IL-1 antagonist. In the past year, the expression of full-length POMC mRNA has been reported and this solved one of the paradoxes with respect to POMC production, processing, and secretion. We provide data on these developments together with quite startling findings on the physiologic function of POMC peptides in the immune system. Among these are the local antinociceptive effects of immune cell-derived beta-endorphin, altered hematopoiesis in opiate receptor-deficient animals, and the diagnosis of ACTH insensitivity by a deficiency of ACTH receptors on lymphocytes.

Effect of the opioid methionine enkephalinamide on signal transduction in human T-lymphocytes

T cell receptor (TCR/CD3) induced fluctuations in intracellular free ionizied calcium, [Ca2+]i, was analysed in the human T leukemia cell clone, Jurkat, cultured in the presence of the opioid methionine enkephalinamide (Met-Enk) in titrated concentrations (10[-7] to 10[-15] M) or saline (PBS). In the majority of individual experiments, the activation-induced fluctuations in [Ca2+]i were similar in cells cultured in the presence of Met-Enk and PBS, respectively. However, when all the experimental data from 101 separate TCR/CD3-activation experiments with Met-Enk were compared with the 67 separate control experiments, we found that a fraction (20-40%) of the individual sets of Met-Enk experiments responded significantly different when compared to PBS-controls. In this fraction of experiments the increase in [Ca2+]i after ligation of the TCR/CD3 complex was extremely slow compared to controls. Moreover, the levels of [Ca2+]i in this particular fraction were lower than control levels prior to ligation of the TCR/CD3 complex. The data support the idea that signal transduction in T cells can be influenced by endogenous opioid. The data therefore give credit to the evolving hypothesis of a functional relationship between the neuroendocrine system and the immune system.

Changes in apoptosis of human polymorphonuclear granulocytes with aging

Many alterations with aging occur at the cellular and organic levels in the immune system ultimately leading to a decrease in the immune response. Our aim in the present work was to study apoptosis of polymorphonuclear granulocytes (PMN) with aging under various stimulations since apoptosis might play an important role in several pathologies encountered with aging. The PMN of healthy young (20-25 years) and elderly (65-85 years) subjects were examined after 24 h of sterile culture with and without stimulation. The stimulating agents included: phorbol myristate acetate (PMA), hydrogen peroxide (H2O2), N-formyl-methionyl-leucyl phenylalanine (FMLP), granulocyte-macrophage colony stimulating factor (GM-CSF), reduced glutathione (GSH), lipopolysaccharide (LPS) and interleukin 2 (IL-2). Apoptosis was assessed by traditional staining of the plates, by flow cytometric staining and DNA gel electrophoresis. It was found that without stimulation the susceptibility of PMN to apoptosis was slightly increased with aging. Under various stimulations, such as PMA. H2O2, apoptosis was almost 100%, while the treatment by FMLP, oxLDL and GSH did not change its extent in PMN obtained either from young or elderly subjects. Marked age-related changes were observed in the extent of apoptosis under stimulation with GM-CSF, IL-2 and LPS. These agents were able to significantly prevent apoptosis in PMN of young subjects, while only the GM-CSF was able to slightly modulate it in neutrophils of elderly subjects. From these results, we suggest that changes in apoptosis of PMN with aging could play a role in the increased incidence of certain immune system related pathologies of aging, such as cancer, infections and autoimmune disorders.

Signal transduction changes in granulocytes and lymphocytes with ageing

It is well known that the immune response declines with ageing. However, the exact cause of this decline is still unknown. In recent years signal transduction events leading to the transmission of a signal from the cell surface to the nucleus have been extensively studied in various cell systems. These studies have indicated that an alteration in signal transduction occurs with ageing. It is not possible to identify a single age-sensitive step in this sequence, but rather a series of deficiencies contributing to the decline in competency of aged lymphocytes and granulocytes to undergo normal activation. Thus, signal transduction events such as calcium mobilization, phosphatidylinositol breakdown, accumulation of proto-oncogene transcripts, expression of activation markers, and synthesis of new proteins are deficient in the aged. Other events in signal transduction have been much less studied such as protein tyrosine kinase activity and G-protein functions. alterations in these various intracellular signalling events may fundamentally influence the functional activity of lymphocytes and granulocytes in the aged, as suggested by several investigations performed in recent years and reviewed in the subsequent sections. Future study on the signal transduction pathways using well-defined experimental models and healthy individuals should help to elucidate the molecular basis of immunosenescence and to develop effective approaches for reducing age-associated deficits and thereby reducing the incidence of age-associated diseases.

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.

Age-dependent changes in transmembrane signalling: identification of G proteins in human lymphocytes and polymorphonuclear leukocytes

In human neutrophils (PMNLs) we found that in the elderly IP3 formation was significantly decreased compared to that of young subjects. For FMLP receptor binding affinity and number no measurable differences occurred upon ageing, studying both the low or the high affinity receptors. The amount of ADP-ribosylated G proteins, catalysed by pertussis toxin (PT) or cholera toxin (CT), was significantly increased in PMNLs of the elderly. In lymphocytes, the PT-catalysed ADP ribosylation of G proteins was also increased with ageing, while the CT-catalysed ribosylation was decreased. The autoradiogram of [32P]ADP-ribosylated proteins by CT in lymphocytes of young individuals showed a major polypeptide of 40,000 M(r). In contrast, in lymphocytes of the elderly, the major polypeptide was 45,000 M(r). In PMNLs, CT labelled quite strongly the 45,000 M(r) band, mainly in the elderly. When PT was used, no age-related pattern changes could be demonstrated, while differences could be observed between the two types of cells. The use of antiserum P680 (G alpha common) showed no age-related pattern changes, while the intensity of the labelled proteins varies with age and cell type. The antiserum U46 (Go alpha) could identify in lymphocytes of young subjects two polypeptides 68,000 and 41,000 M(r). The prominent polypeptide in lymphocytes of the elderly was the 70,000 M(r) and no other polypeptides could be recognized. In PMNLs of young subjects the U46 and serum identified a range of species. In PMNLs of the elderly all these bands were weakly labelled. The present data indicate changes in the pattern and the quantity of G proteins in lymphocytes and PMNLs of elderly subjects.

Delta- and kappa-opioid agonists inhibit plasma extravasation induced by bradykinin in the knee joint of the rat

We used an experimental model of neurogenic inflammation, plasma extravasation induced by bradykinin or capsaicin, to study the effect of receptor-selective opioid agonists on plasma extravasation. Plasma extravasation was induced in the knee joint of the rat by continuous perfusion of either bradykinin (160 ng/ml), an inflammatory mediator produced at sites of tissue injury, that produces plasma extravasation significantly dependent on the sympathetic postganglionic neuron, or capsaicin (5 mg/ml), a C-fiber excitotoxin, that induces plasma extravasation that is dependent on both primary afferents and sympathetic post-ganglionic neurons. When selective delta-((d-Pen2,5)-enkephalin) or kappa-(trans-3,4-dichloro-N-methyl-N[2-(- pyrolidinyl)cyclohexyl]benzeneacetamide; U50,488H) opioid agonists were perfused with bradykinin, plasma extravasation was significantly attenuated. Co-perfusion of the non-selective opioid antagonist naloxone (1 microM), reversed this opioid-induced inhibition of bradykinin-induced plasma extravasation. In contrast, co-perfusion of a selective mu-opioid agonist (Tyr-d-Ala-Gly-NMe-Phe-Gly-ol) did not reduce bradykinin-induced plasma extravasation. Tyr-d-Ala-Gly-NMe-Phe-Gly-ol was, however, able to completely inhibit the plasma extravasation produced by capsaicin. These results suggest that delta- and kappa-, but not mu-selective opioids inhibit bradykinin-stimulated plasma extravasation, while a mu-selective opioid inhibits primary afferent-dependent plasma extravasation. Therefore, inhibition of neurogenic plasma extravasation by receptor-selective opioids may depend on the relative contribution to plasma extravasation of unmyelinated afferent and sympathetic postganglionic neuron terminals. Our findings can also explain, in part, the variation in anti-inflammatory effects of receptor-selective opioids reported in different inflammatory conditions.

Physiological basis for neuroimmunomodulation

A large number of clinical and experimental observations indicate that immune responses may be modulated by the central nervous system (CNS). The immune system (IS) and CNS are known to communicate via the endocrine and the autonomic nervous systems. In this overview, we will focus on the immunomodulating role of neurotransmitters and neuropeptides. Immune cells appear to express membrane antigens similar to those of neural cells. Similarities re-enforce analogies between CNS and IS cells. The concept that the CNS modulates immune functions implies that the immune system feeds back information to the CNS. In fact, interleukins have neuroendocrine functions whether they are produced at the periphery by immune cells or at the CNS level by glial cells. Finally, the possible endocrine functions of lymphocytes are described and it is suggested that a complete regulatory loop between immune and neuro-endocrine systems exists. Studies in neuro-immunomodulation are of great importance from a theoretical point of view, the CNS-IS inter-relationships may not be considered only between the CNS and the periphery but also at the level of the immune micro-environment which may be considered as an immune-neuro-endocrine complex.

Altered post-receptorial signal transduction mechanism under various stimulation in polymorphonuclear granulocytes of Alzheimer's disease

The cyclic nucleotide changes were studied under 10(-6) M isoproterenol (IP), 10(-6) M carbachol and 10(-8) M Met-enkephalin (Met-enk) stimulations in polymorphonuclear granulocytes (PMNLs) of middle-aged (aged 35-52 years) and elderly (aged 61-97 years) healthy subjects, as well as of patients with Alzheimer's disease (AD) (aged 58-65 years). From our results we can conclude that in the case of middle-aged healthy subjects only the IP caused a marked cAMP elevation while in elderly and AD all the applied substances stimulated the cAMP at different degrees. Concerning the cGMP levels in PMNLs, we observed a marked increase under carbachol and Met-enk stimulation, in middle-aged subjects, while in the elderly a weak change was obtained by carbachol. In AD practically no change of cGMP levels could be obtained. Thus, the main features of AD are a cAarP response to Met-enk and an abolition of a GarP response to carbachol. We can conclude that in PMNLs of elderly and patients with AD we assist to an altered post-receptorial signal transduction mechanism, which seems to be even more marked in the case of AD comparing to normal aging.

Beta-endorphin and related peptides suppress phorbol myristate acetate-induced respiratory burst in human polymorphonuclear leukocytes

In the present study, the immunomodulatory effect of beta-endorphin (beta-E) and shorter pro-opiomelanocortin (POMC) fragments was evaluated by assessing their influence on respiratory burst in human polymorphonuclear leukocytes (PMN). The effect of the peptides (10(-17)M - 10(-10)M) on phorbol myristate acetate (PMA)-stimulated production of reactive oxygen metabolites was measured in a lucigenin-enhanced chemiluminescence (CL) assay. Both POMC peptides with opiate-like activity (i.e. alpha-endorphin (alpha-E), beta-E and gamma-endorphin (gamma-E] and their non-opioid derivatives (i.e. des-TYR1-beta-endorphin (dT beta E), des-TYR1-gamma-endorphin (dT gamma E), and des-ENK-gamma-endorphin (dE gamma E] were tested. With the exception of alpha-E, PMA-stimulated respiratory burst was suppressed by all POMC fragments tested. A U-shaped dose-response relation was observed. Doses lower than 10(-17)M and higher than 10(-8)M were without effect. beta-E and dT beta E both suppressed PMA-induced oxidative burst in human PMN at physiological concentrations (10(-16)M - 10(-10)M). gamma-E and dT gamma E proved to be less potent inhibitors, reaching maximal effect at higher concentrations (10(-12)M - 10(-10)M). DE gamma E exerted an even less pronounced but still significant suppressive effect at the concentration of 10(-10)M. None of the endorphins tested was shown to affect resting oxidative metabolism in the PMN. The modulatory effects of the opioid peptides could not be blocked by the opioid antagonist naloxone (10(-8)M). These data show that fragments derived from the POMC-precursor molecule modulate the activation of PMN by suppressing PMA-stimulated oxidative metabolism and that this activity does not involve a classical opiate-like receptor.

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)

Opioid peptides modulate immune functions. A review

In the past few years it has become evident that neuropeptides may be direct mediators in the modulation of the immune response and the unspecific defense by the brain. Lymphocytes have been thought to have opioid receptors and to respond to opioids with an increase in blastogenesis, cytotoxicity and factor release. Lymphocytes are said to release various neuropeptides. Furthermore, there are some unexplained effects of morphine on the immune system and of the immune system on morphine withdrawal. The purpose of this paper is to review what has been previously published in this field. The well established modulation of phagocyte functions by opioids will only be scanned.

The production of antibodies which recognize opiate receptors on murine leukocytes

An antibody has been developed which recognizes opiate receptors on cells of the immune system. This antibody blocks specific binding of the radiolabeled opiate receptor ligand, 3H-dihydromorphine, to receptors on murine splenocytes. Additionally, the anti-receptor antibody competes with beta-endorphin, met-enkephalin, and naloxone for the same binding site on the leukocytes. Moreover, the anti-receptor antibody possesses agonist activity similar to beta-endorphin in suppressing cAMP production by lymphocytes. These results suggest the development of an antibody which recognizes classical opiate receptors on cells of the immune system.