Immunomodulation of macrophage functions by opioids

Immunomodulatory effects of Bacillus subtilis (natto) B4 spores on murine macrophages

To investigate the immunomodulatory effects of Bacillus subtilis (B. subtilis) (natto) B4 spores on murine macrophage, RAW 264.7 cells were cultured alone or with B subtilis (natto) B4 spores at 37°C for 12 hrs, then both cells and culture supernatants were collected for analyses. Exposure of RAW 264.7 cells to B. subtilis (natto) B4 spores had no significant effects on macrophage viability and amounts of extracellular lactate dehydrogenase (LDH). However, it remarkably increased the activities of acid phosphatase (ACP), lactate dehydrogenase (LDH) and inducible nitric oxide synthase (iNOS) in cells and the amounts of nitric oxide (NO) and cytokines (tumor necrosis factor-alpha, interferon-gamma, interleukin [IL]-1 beta, IL-6, IL-12, IL-10 and macrophage inflammatory protein-2) in culture supernatants. These results demonstrate that B. subtilis (natto) B4 spores are harmless to murine macrophages and can stimulate their activation through up-regulation of ACP and LDH activities and enhance their immune function by increasing iNOS activity and stimulating NO and cytokine production. The above findings suggest that B. subtilis (natto) B4 spores have immunomodulatory effects on macrophages.

Lipoteichoic acid from Lactobacillus plantarum induces nitric oxide production in the presence of interferon-γ in murine macrophages

Lipoteichoic acid (LTA) is a major immuno-stimulating component of Gram-positive bacteria. LTA from the beneficial bacterium Lactobacillus plantarum induces weak nitric oxide (NO) production in murine macrophages. Currently, it is not clear if LTA from L. plantarum is able to stimulate the innate immune response, even in the presence of inflammation. In the present study, we prepared highly pure and structurally intact LTA from L. plantarum and investigated its ability to induce NO in the presence of interferon (IFN)-γ in the RAW 264.7 murine macrophage cell line and bone marrow-derived macrophages (BMMs) from mice. L. plantarum LTA alone was unable to induce NO production, even at 30μg/ml. However, LTA in the presence of IFN-γ significantly induced NO production in RAW 264.7 cells. The observed NO production was inhibited by a NO synthase (NOS) inhibitor l-NAME and an inducible NOS (iNOS) inhibitor l-NIL, suggesting that iNOS is specifically required for this action. Western blot analysis and reverse transcription and polymerase chain reaction further confirmed that L. plantarum LTA increased protein and mRNA levels of iNOS, respectively. However, such induction was substantially inhibited in BMMs from Toll-like receptor 2 (TLR2)-deficient mice and the macrophages treated with an inhibitor blocking platelet-activating factor receptor. In addition, L. plantarum LTA plus IFN-γ induced IFN-β expression and STAT1 phosphorylation, which are key pathways for inducing iNOS expression. Electrophoretic mobility shift assay demonstrated that L. plantarum LTA in the presence of IFN-γ remarkably increased the DNA-binding activity of NF-κB transcription factor, which is known to be involved in the iNOS gene expression. Collectively, these results suggest that LTA from L. plantarum alone has no inflammatory potential but does induce NO production under conditions of inflammation, such as the presence of IFN-γ.

Methylnaltrexone: the evidence for its use in the management of opioid-induced constipation

Introduction:

Constipation is a distressing side effect of opioid treatment, being so irksome in some cases that patients would rather suffer the pain than the side effect of opioid analgesics. Stool softeners or stimulating laxatives are often ineffective or even aggravate the situation. A new efficacious and safe drug is needed to limit the frequently observed side effects induced by effective opioid-based analgesic therapy and to improve the quality of life for patients, most of whom are impaired by a severe disease.

Aims:

The purpose of this article is to assess current evidence supporting the use of the peripherally acting μ-opioid receptor antagonist, methylnaltrexone, to restrict passage across the blood–brain barrier in patients with opioid-induced bowel dysfunction.

Evidence review:

There are now convincing data from phase II and multicenter phase III randomized, double-blind, placebo-controlled trials that methylnaltrexone induces laxation in patients with long-term opioid use without affecting central analgesia or precipitation of opioid withdrawal. Onset of the effect is rapid and improvement is maintained for at least 3 months during the drug treatment. The action of methylnaltrexone is dose dependent. Weight-related dosing appeared to be effective. There were no severe side effects or signs of opioid withdrawal. Adverse events, most frequently abdominal cramping or nausea, were usually mild to moderate. Methylnaltrexone is contraindicated in patients with known or suspected mechanical intestinal stenosis. Patients receiving methylnaltrexone must be monitored.

Place in therapy:

Methylnaltrexone applied subcutaneously every other day may be given to patients suffering from chronic constipation due to opioid therapy for whom laxatives do not provide adequate relief of their symptoms.

Novel opioid antagonists for opioid-induced bowel dysfunction and postoperative ileus

Peripherally acting mu-opioid receptor antagonists methylnaltrexone and alvimopan are a new class of drugs designed to reverse opioid-induced side-effects on the gastrointestinal system without compromising pain relief. This article gives an overview of the pharmacology, the efficacy, and adverse effects of these drugs. Both compounds seem to be generally well tolerated and effective for the treatment of opioid-related bowel dysfunction and postoperative ileus. Methylnaltrexone recently received approval by the US Food and Drug Administration (FDA) and the European Medicines Agency for treatment of opioid-related bowel dysfunction in patients with advanced illness. Alvimopan was recently approved by the FDA for treatment of postoperative ileus, but the use of the drug is restricted to inpatients because it has been associated with an increased rate of myocardial infarction. Further research should assess the effectiveness and safety of these drugs in clinical practice.

Macrophage activation and nitric oxide production by water soluble components of Hericium erinaceum

Hericium erinaceum is a medicinal and edible mushroom with anti-microbial and anti-cancer activities. To evaluate the immunoregulatory functions of H. erinaceum, we prepared water extract from H. erinaceum (WEHE) and investigated its ability to activate macrophages and to induce nitric oxide (NO) production in macrophages. Rat peritoneal macrophages stimulated with 1 to 100 mug/ml of WEHE for 24, 48, or 72 h produced NO in a time- and dose-dependent manner. Reverse transcription-polymerase chain reaction demonstrated that WEHE augmented the steady-state level of inducible NO synthase (iNOS) mRNA in both the peritoneal macrophages and a murine macrophage cell-line, RAW 264.7. Electrophoretic mobility shift assay showed that WEHE increased DNA binding activity of the transcription factor NF-kappaB, which is responsible for iNOS gene expression. Furthermore, its trans-acting activity was confirmative as determined by in vitro transfection assay using a reporter gene construct, p(NF-kappaB)(3)-CAT, whose expression is solely regulated by the activity of NF-kappaB. Concomitantly with the activation of NF-kappaB, WEHE markedly decreased intracellular IkappaBalpha level as demonstrated by Western blot assay. These results suggested that WEHE induces iNOS gene expression followed by NO production in macrophages via enhancing the activation of transcription factor, NF-kappaB.

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), a food-born carcinogenic heterocyclic amine, promotes nitric oxide production in murine macrophages

A heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is one of the potent food-born dietary carcinogens derived mainly from burnt meat products. In the present study, we investigated the inductive effect of Trp-P-1 on nitric oxide (NO) production in murine macrophages since NO and its oxidized derivatives are directly involved in triggering mutagenesis and carcinogenesis. Our results show that Trp-P-1 induced mRNA expression of inducible NO synthase (iNOS) and NO production without co-stimulation in murine peritoneal macrophages and RAW 264.7 cells. Trp-P-1 further enhanced both iNOS mRNA expression and NO production, which were primarily induced by lipopolysaccharide (LPS). Electrophoretic mobility shift assay demonstrated that Trp-P-1, alone or in the presence of LPS, facilitated the DNA binding activity of the transcription factor NF-kappaB, and the trans-acting activity of the NF-kappaB was confirmative as determined by in vitro transfection and a luciferase reporter gene assay. Moreover, Trp-P-1 induced increasing intracellular reactive oxygen species (ROS), which play an important role in NF-kappaB activation. These results suggest that Trp-P-1 induces NO production mediated by an increased intracellular ROS, NF-kappaB activation, and subsequent iNOS gene expression.

Alvimopan, a selective peripherally acting mu-opioid antagonist

Alvimopan is a novel, peripherally acting mu-opioid antagonist that is being developed for the management of acute postoperative ileus and for the reversal of the delayed gastrointestinal and colonic transit that result in symptoms such as constipation, nausea and motility disorders in patients treated with opiate analgesics. There is a clinical need for effective medications for the treatment of postoperative ileus and opiate-induced constipation and other motility disorders. This review addresses the basic and applied pharmacology and current evidence for the use of the medication, alvimopan, in clinical gastroenterology.

Mechanisms of postoperative ileus

Postoperative ileus is an iatrogenic condition that follows abdominal surgery. Three main mechanisms are involved in its causation, namely neurogenic, inflammatory and pharmacological mechanisms. In the acute postoperative phase, mainly spinal and supraspinal adrenergic and non-adrenergic pathways are activated. Recent studies, however, show that the prolonged phase of postoperative ileus is caused by an enteric molecular inflammatory response and the subsequent recruitment of leucocytes into the muscularis of the intestinal segments manipulated during surgery. This inflammation impairs local neuromuscular function and activates neurogenic inhibitory pathways, inhibiting motility of the entire gastrointestinal tract. The mechanisms underlying the recruitment of the inflammatory cells, and their interaction with the intestinal afferent innervation, are discussed. Finally, opioids administered for postoperative pain control also contribute to a large extent to the reduction in propulsive gastrointestinal motility observed after abdominal surgery.

Mu and delta receptors mediate morphine effects on phagocytosis by murine peritoneal macrophages

Studies with selective opioid agonists show that mu- and delta(2)-opioid receptors, but not kappa, are involved in opioid inhibition of phagocytosis in elicited murine macrophages. All mu and delta(2) agonists tested had similar maximal effects on phagocytosis, and all dose-response curves suggest positive cooperativity. In addition, mu and delta antagonists antagonized the effect of both mu and delta agonists. Furthermore, in mu-opioid receptor knockout mice (MORKO), we observed a decrease in potency and maximal effect for a delta agonist. These data suggest that mu and delta receptors are not only involved in the modulation of phagocytosis in macrophages, but they also affect each other's activity by an unknown cooperative mechanism.

Immunomodulation by biphalin, dimeric synthetic opioid peptide, and its analog

The opioid pentapeptides called enkephalins were originally described as the endogenous ligands for the opioid receptors. Although their precise physiological significance still remains elusive, the enkephalins have been reported to exhibit analgesic, antidepressant, antianxiety and anticonvulsant activities. In addition, enkephalins have also been shown to act as immunomodulator. The first generation of dimeric peptides was derived from enkephalins. Biphalin [(Tyr-D-Ala-Gly-Phe-NH)2] is a bivalent opioid analog containing two tyrosine residues. We have evaluated the immunomodulatory properties of biphalin and its analogs in various in vitro tests. We report that biphalin and one of its analogs [Tyr-D-Ala-Gly-Phe-NH.NH-Phe(p-Cl)-H] stimulate human T cell proliferation, natural killer (NK) cell cytotoxicity in vitro and interleukin-2 (IL-2) production. Biphalin and its analog also released chemokine like factor in the culture supernatant that was responsible for increased chemotaxis of monocytes. Furthermore, these peptides inhibited tumor necrosis factor (TNF-alpha) production in lipopolysaccharide (LPS) stimulated peripheral blood mononuclear cells (PBMC) and nitric oxide (NO) production in mouse macrophage cells, RAW 264.7. Our observations suggest immunomodulatory property of biphalin and its analog.

Inhibition of interleukin-2 production and downregulation of IL-2 and transferrin receptors on rat splenic lymphocytes following PAG morphine administration: a role in natural killer and T cell suppression

We investigated the effects of acute injection of morphine into the rat mesencephalon periaqueductal gray (PAG), on splenic natural killer (NK) cell and lymphocyte functions, interleukin-2 (IL-2) production, expression of T cell (CD3), T helper cell (CD4), T suppressor cell (CD8), and NK cell (NKR-P1) surface markers, and expression of IL-2 (CD25) and transferrin (CD71) receptors. Bilateral microinjection of 10 nmol of morphine in the PAG significantly (p < 0.001) inhibited IL-2 (31%) production by activated splenic lymphocytes compared with that of PAG saline-injected control rats. In addition, morphine significantly (p < 0.01) suppressed splenic NK cell activity (14-33%) and T lymphocyte proliferative responses (25-48%) to various mitogens compared with controls. Furthermore, morphine did not alter the expression of CD3, CD4, CD8, and NKR-P1 surface markers, but significantly (p < 0.001) downregulated the expression of CD25 and CD71 receptors following in vitro activation. These results suggested that injection of morphine in the PAG suppresses NK and T cell functions by reducing the ability of T cells to produce IL-2 and downregulating the expression of CD25 and CD71 surface activation markers.

Opioid mediated effects on the immune system: sympathetic nervous system involvement

Opioids have been hypothesized to suppress parameters of immune function by acting within the central nervous system to increase the activity of the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Production of catecholamines and adrenocorticoids have been demonstrated to be responsible for many of the observed immunomodulatory effects which occur following opioid administration. In general, the sympathetic nervous system has been shown to play a role in regulating lymphocyte proliferation and natural killer cell activity as well as several other parameters of immune function. Here, we will focus primarily on the role of the sympathetic nervous system in modulating opioid induced immunosuppression. The role of the hypothalamic-pituitary adrenal axis is reviewed elsewhere in this issue.