Enkephalinase-inhibitors modulate immune responses

Transcriptome analysis of hemocytes from the white shrimp Litopenaeus vannamei with the injection of dopamine

As a crucial neuroendocrine-immune factor, dopamine (DA) could regulate the immune system of Litopenaeus vannamei. To understand the immune mechanisms and regulatory pathways of DA in L. vannamei, the transcriptome analysis of hemocytes of L. vannamei with injection of DA (10^-6 mol/shrimp) at 3 and 12 h were performed in this study. Moreover, quantitative real-time PCR (qPCR) method was applied to validate the accuracy of transcriptome sequencing and analyze the expression pattern of candidate differentially expressed genes (DEGs) at different time points (0, 3, 6, 12, and 24 h) after DA injection. The results showed that a total of 51382 unigenes with a N50 length of 2341 bp were generated. And 1397 and 457 DEGs were obtained by comparative transcriptome at 3 and 12h respectively. Moreover, the results of functional annotation and enriched pathway showed that the DEGs were involved in phagosome (ko04145), lysosome (ko04142), Endocytosis (ko04144), and NOD-like receptor signaling pathway (ko04621). Besides, the Pearson's correlation coefficient (R) between transcriptome sequencing and qPCR was 0.845, which confirmed the reliability of the transcriptome sequencing results and the accuracy of assembly. Furthermore, the expression pattern of 15 candidate DEGs, containing 9 up-regulated and 6 down-regulated DEGs at 3 h, indicated the regulation of DA in physiological functions especially in the immune system. Therefore, these results revealed that DA induced the expressions of membrane receptors or proteins, activated intracellular signaling pathways, regulated cellular and humoral immune systems, controlled antioxidation and apoptosis, and was involved in the regulation of neuroendocrine system. These findings are helpful to promote the understanding on the effects of biogenic amines on physiological functions and regulatory networks of crustacean, and offer a substantial material and foundation for researching the immune response of crustacean.

Opioid therapy and immunosuppression: a review

The idea that opioids modulate the immune system is not new. By the late 19th century, Cantacuzene, used morphine to suppress cellular immunity and lower the resistance of guinea pigs to bacterial infection. While exogenous opioids mediate immunosuppression, endogenous opiates exert opposite actions. Acute and chronic opioid administration is known to have inhibitory effects on humoral and cellular immune responses including antibody production, natural killer cell activity, cytokine expression, and phagocytic activity. Opiates behave like cytokines, modulating the immune response by interaction with their receptors in the central nervous system and in the periphery. Potential mechanisms by which central opiates modulate peripheral immune functions may involve both the hypothalamic-pituitary-adrenal axis and the autonomic nervous system. The presence of opioid receptors outside the central nervous system is increasingly recognized. Those receptors have been identified not only in peripheral nerves but also in immune inflammatory cells. The immunosuppression mediated by opiates may explain the increased incidence of infection in heroin addicts. Opiates may also promote immunodeficiency virus infection by decreasing the secretion of alpha and beta chemokines (important inhibitory cytokines for the expression of HIV) and at the same time increasing the expression of chemoreceptors CCR5 and CCR3, coreceptors for the virus. The fact that peripheral immunosupression is mediated at least in part by opioid receptors located in the central nervous system and that intrathecally administered opioids do not exert the same immunosuppressive effects may have important clinical implications for those patients receiving long-term opioid therapy for malignant and nonmalignant pain.

Intracerebroventricular met-enkephalin administration modulates adjuvant arthritis

The purpose of this study was to investigate the anti-inflammatory properties of intracerebroventricular met-enkephalin (met-enk) administration in an animal model of arthritis. Adjuvant arthritis was induced in rats by intradermal inoculation of mycobacterium butyricum and the effects of intraventricular met-enk+thiorphan (enkephalinase inhibitor) were studied. Treatment was initiated either simultaneously with the bacterial inoculation (preventive group) or on post-inoculation day 17 after the appearance of inflammation (treatment group). The degree of inflammation was evaluated by measuring the diameter and the circumference of the ankle joint immediately before the sacrifice (day 31) and by histologic examination of ankle joint sections. The results of this study revealed that combined intraventricular injections of met-enk+thiorphan reduced the arthritic-like inflammation in the preventive group as well as in the treatment group. These findings suggest that centrally applied met-enk+thiorphan may suppress the development adjuvant arthritis as well as the symptoms of manifest arthritis. Thus central met-enk may be involved in both hypothalamic pituitary adrenal axis and immune forms of stress-induced modulation.

Evidence for central opioid receptors in the immunomodulatory effects of morphine: review of potential mechanism(s) of action

This review will discuss studies demonstrating that activation of opioid receptors within the central nervous system alters various immune system parameters. Specifically, natural killer cell cytolytic activity and lymphocyte proliferative responses to mitogen appear to be modulated predominantly, if not exclusively, through central opioid receptors. The potential mechanisms by which central opioid receptors appear to modulate these peripheral immune functions will be examined by evaluating the role of both the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system. The studies discussed below indicate that acute administration of morphine or related compounds appears to primarily alter peripheral immune function through the sympathetic nervous system, while more prolonged exposure to opioids alter the immune system predominantly by activation of the HPA axis. Finally, the potential clinical relevance of these observations are discussed in relationship to both the therapeutic use, as well as the abuse of opioid compounds.

The fetal expression of proenkephalin mRNAs and Met-enkephalin immunoreactivity in the hypothalamoseptal tract and adjacent hypothalamic areas of the guinea pig brain

The development of the enkephalinergic hypothalamoseptal tract in the guinea pig brain was studied from embryonic day 30 until birth. Proenkephalin (PE) mRNAs were detected in the hypothalamic magnocellular dorsal nucleus (MDN) by in situ hybridization with a synthetic 35S-labeled oligonucleotide. The Met-enkephalin-like immunoreactivity (Met-enk-LI) in the MDN and the lateral septum (LS) was detected with antibodies against Met-enkephalin, on adjacent cryostat sections. At the same time, an immunohistochemical study of the arrangement of enkephalinergic axon terminals in the LS at birth was performed at the electron microscopic level. PE mRNAs were first found to be expressed in the MDN at embryonic day 32 (E32) and increased to reach a maximal level at E48. Met-enk-LI was consistently detectable from E38 in numerous perikarya of the MDN as well as in nerve terminals of the LS. The number of Met-enk-LI cells of the MDN decreased after this stage until birth, whereas positive nerve endings in the LS increased. At the electron microscopic level, numerous cell bodies of the LS at birth were consistently surrounded by Met-enk immunoreactive nerve terminals. Cells expressing the PE gene and Met-enk-LI were also observed from E38 to E44 in the periventricular area. Some of these cells were found double-labeled with Met-enkephalin and Somatostatin antisera. The enkephalinergic system of the hypothalamoseptal tract appears at early embryonic stages and may be essential in regulating septal neuronal functions early in gestation. Differing ontogenic onsets of the enkephalinergic hypothalamoseptal and periventricular-median eminence tracts suggest possible developmental and functional differences.

Quaternary naltrexone: its immunomodulatory activity and interaction with brain delta and kappa opioid receptors

To investigate the role of brain opioid receptors in immune reactions, quaternary naltrexone (QNtx), a nonselective opioid antagonist which does not cross the brain-blood barrier, was tested for its immunomodulatory activity and ability to antagonize immunological changes produced by centrally applied delta-receptor agonist methionine-enkephalin (Met-Enk) and kappa-opioid receptor agonist MR 2034. Plaque-forming cell (PFC) response served as an immunological model. For this purpose, different groups of Wistar rats were centrally (intracerebroventricularly, i.c.v.) and peripherally (intraperitoneally, i.p., or subcutaneously, s.c.) treated with different doses of Met-Enk. MR 2034 and QNtx. Centrally injected Met-Enk and MR 2034 induced a dose-dependent potentiation and suppression of PFC response, respectively. Small amounts of i.c.v. given QNtx produced a dose-dependent increase in the number of PFC, whereas peripherally administered antagonist potentiated immune response in a dose-independent manner. A dose of 10 micrograms/kg of QNtx given i.c.v. completely abolished the immunopotentiation by Met-Enk. However, a large dose of 5 mg/kg of QNtx given s.c., did not affect the Met-Enk-induced immunoenhancement. Immunosuppression produced by i.c.v. injected MR 2034 was totally abrogated by prior i.c.v. application of QNtx, but partially blocked by s.c. administration of the antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of brain-immune interactions in immunotoxicology

Certain xenobiotics (or the metabolites) can damage immunocompetence by directly interacting with one or more of the cells of the immune system and adversely affecting its function. It has also been proposed that xenobiotics may indirectly affect immune function by affecting other organ systems that will in turn affect immunocompetence. This review surveys evidence that supports the existence of a functional link between the brain and the immune system. In addition, we review data that support the concept that a xenobiotic-induced dysfunction in the neuroendocrine system may be associated with an immune dysfunction as well. Such chemicals do not necessarily interact directly with immunocompetent cells but would instead act to disrupt regulatory brain-immune interactions. This class of indirectly acting immunotoxic xenobiotics would not be detected in the typical in vitro screening assays.

Brain self-stimulation and immunity: effect on humoral and cell-mediated immune responses

This study was designed to evaluate the effect of intracranial self-stimulation (ICSS) on specific immunological reactivity in the rat. Male Wistar rats were implanted with stimulating electrodes in the lateral hypothalamus (LH) and ventral tegmental area (VTA). After recovery from surgery and screening procedure, animals were allowed to self-stimulate 30 minutes daily during different periods of time before or after immunization with sheep red blood cells (SRBC) and bovine serum albumin (BSA). We report here on the in vivo immunoregulating effects of ICSS on plaque-forming cell (PFC) response, hemagglutinin production to SRBC, and antibody titer and hypersensitivity skin reactions to BSA. The effects produced were dependent on the brain area which was stimulated, time relationship of ICSS and immunization, type of immune reaction, and antigen used for immunization. Therefore, ICSS appears to be a significant tool in the regulation of the immune system function, and thus provides further evidence of the interconnections between the immune system and behavior.

Endogenous opiates: 1991

This paper is the fourteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1991 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal 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.

Enkephalins, brain and immunity: modulation of immune responses by methionine-enkephalin injected into the cerebral cavity

There is a large number of interactions at molecular and cellular levels between the nervous system and the immune system. It has been demonstrated that the opioid neuropentapeptide methionine-enkephalin (Met-Enk) is involved in humoral and cell-mediated immune reactions. Met-Enk injected peripherally produces a dual and dose-dependent immunomodulatory effect: high doses suppress, whereas low doses potentiate the immune reactivity. The present mini-review concerns the immunological activity of Met-Enk after its administration into the lateral ventricles of the rat brain, and describes the extraordinary capacity of centrally applied Met-Enk to regulate/modulate the immune function. This survey is composed of sections dealing with (a) the role of opioid peptides in the central nervous system (CNS); (b) the activity of opioid peptides in the immune system; (c) the application of Met-Enk into the cerebral cavity; (d) the influence of centrally administered Met-Enk on nonspecific local inflammatory reaction; (e) the effect of Met-Enk injected intracerebroventricularly (i.c.v.) on specific delayed hypersensitivity skin reaction, experimental allergic encephalomyelitis, anaphylactic shock, plaque-forming cell response, and hemagglutinin production; (f) the central antagonizing action of quaternary naltrexone, an opioid antagonist that does not cross the brain-blood barrier, on Met-Enk-induced immunomodulation; (g) the alteration of immune responsiveness by i.c.v. injection of enkephalinase-degrading enzymes; (h) the participation of the brain-blood/blood-brain barrier in the CNS-immune system interaction; and (i) the role of opioid receptors in immunological activity of Met-Enk. A hypothesis has been advanced for the reaction of Met-Enk and opioid receptor sitting on the cell membrane. This concept suggests that the constellation of chemical residues of enkephalin and receptor in the microenvironment determines the binding between the opioid partners. The plurality of conformational structures of enkephalins and receptors makes possible their involvement in a variety of processes which occur in different physiological systems, including the nervous system and the immune system, and intercommunications between the two systems.

Species variability in the expression of met- and leu-enkephalin-like immunoreactivity in mammalian Merkel cell dense-core granules. A light- and electron-microscopic immunohistochemical study

Immunogold staining failed to show met-enkephalin immunoreactivity in the Merkel cell dense-core granules of rats when examined by electron microscopy, but showed gold particle staining in the Merkel cell dense-core granules of mice and nude mice. Merkel cells of hamster, guinea pig, rabbit, cat and dog were also examined using a similar method, and different antisera dilutions. Immunogold particles were consistently found in the dense-core granules of mice and nude mice at all antisera dilutions, but not in the other species, except in the dog, where a very low labelling response was encountered. Merkel cells from skin touch domes or sinus hair follicles, did not exhibit any difference in peptide expression as far as met-enkephalin immunoreactivity was concerned. In addition, all species studied, including mice and nude mice, did not show leu-enkephalin immunoreactivity in their Merkel cell dense-core granules. It is concluded that species variability in peptide expression occurs in the Merkel cell dense-core granules, and may be closely related to the different methodologies used.

The central effect of methionine-enkephalin on NK cell activity

The central effect of opioid peptide on natural killer (NK) cell activity in BALB/c mice was investigated. Injection of methionine-enkephalin (Met-Enk), 0.02 microgram/mouse or 1 microgram/kg, directly into the cisterna magna (CM) of the brain, resulted in a significant enhancement of NK cell activity. This enhancement was blocked by opiate antagonists, naltrexone and quaternary naltrexone. The same dose of Met-Enk had no effect on NK cell activity when given to the mouse intraperitoneally or intravenously. Moreover, des-tyrosine-methionine-enkephalin injected into the CM at 1 microgram/kg, had no effect on NK cell activity. The results indicate that activation of an opioid-mediated pathway in the central nervous system is capable of activating the pathways that stimulate the NK cell response in the periphery.