Opioid receptors on white blood cells: effect of HIV infection and methadone treatment

Buprenorphine Increases HIV-1 Infection In Vitro but Does Not Reactivate HIV-1 from Latency

BACKGROUND

medication-assisted treatment (MAT) with buprenorphine is now widely prescribed to treat addiction to heroin and other illicit opioids. There is some evidence that illicit opioids enhance HIV-1 replication and accelerate AIDS pathogenesis, but the effect of buprenorphine is unknown.

METHODS

we obtained peripheral blood mononuclear cells (PBMCs) from healthy volunteers and cultured them in the presence of morphine, buprenorphine, or methadone. We infected the cells with a replication-competent CCR5-tropic HIV-1 reporter virus encoding a secreted nanoluciferase gene, and measured infection by luciferase activity in the supernatants over time. We also surveyed opioid receptor expression in PBMC, genital epithelial cells and other leukocytes by qPCR and western blotting. Reactivation from latency was assessed in J-Lat 11.1 and U1 cell lines.

RESULTS

we did not detect expression of classical opioid receptors in leukocytes, but did find nociception/orphanin FQ receptor (NOP) expression in blood and vaginal lymphocytes as well as genital epithelial cells. In PBMCs, we found that at physiological doses, morphine, and methadone had a variable or no effect on HIV infection, but buprenorphine treatment significantly increased HIV-1 infectivity (median: 8.797-fold increase with 20 nM buprenorphine, eight experiments, range: 3.570-691.9, p = 0.0078). Using latently infected cell lines, we did not detect reactivation of latent HIV following treatment with any of the opioid drugs.

CONCLUSIONS

our results suggest that buprenorphine, in contrast to morphine or methadone, increases the in vitro susceptibility of leukocytes to HIV-1 infection but has no effect on in vitro HIV reactivation. These findings contribute to our understanding how opioids, including those used for MAT, affect HIV infection and reactivation, and can help to inform the choice of MAT for people living with HIV or who are at risk of HIV infection.

Expression of Opioid Receptors in Cells of the Immune System

The observation of the immunomodulatory effects of opioid drugs opened the discussion about possible mechanisms of action and led researchers to consider the presence of opioid receptors (OR) in cells of the immune system. To date, numerous studies analyzing the expression of OR subtypes in animal and human immune cells have been performed. Some of them confirmed the expression of OR at both the mRNA and protein level, while others did not detect the receptor mRNA either. Although this topic remains controversial, further studies are constantly being published. The most recent articles suggested that the expression level of OR in human peripheral blood lymphocytes could help to evaluate the success of methadone maintenance therapy in former opioid addicts, or could serve as a biomarker for chronic pain diagnosis. However, the applicability of these findings to clinical practice needs to be verified by further investigations.

Single cell transcriptomics reveals opioid usage evokes widespread suppression of antiviral gene program

Chronic opioid usage not only causes addiction behavior through the central nervous system, but also modulates the peripheral immune system. However, how opioid impacts the immune system is still barely characterized systematically. In order to understand the immune modulatory effect of opioids in an unbiased way, here we perform single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells from opioid-dependent individuals and controls to show that chronic opioid usage evokes widespread suppression of antiviral gene program in naive monocytes, as well as in multiple immune cell types upon stimulation with the pathogen component lipopolysaccharide. Furthermore, scRNA-seq reveals the same phenomenon after a short in vitro morphine treatment. These findings indicate that both acute and chronic opioid exposure may be harmful to our immune system by suppressing the antiviral gene program. Our results suggest that further characterization of the immune modulatory effects of opioid is critical to ensure the safety of clinical opioids.

Over 100 million of opioid prescriptions are issued yearly in the USA alone, but the impact of opioid use on the immune system is barely characterized. Here the authors report antiviral immune response is blunted in several types of blood cells from opioid-dependent individuals, and when healthy donor cells are exposed to morphine in a dish.

Opioids, gliosis and central immunomodulation

Neuropathic pain is a common health problem that affects millions of people worldwide. Despite being studied extensively, the cellular and molecular events underlying the central immunomodulation and the pathophysiology of neuropathic pain is still controversial. The idea that 'glial cells are merely housekeepers' is incorrect and with respect to initiation and maintenance of neuropathic pain, microglia and astrocytes have important roles to play. Glial cells differentially express opioid receptors and are thought to be functionally modulated by the activation of these receptors. In this review, we discuss evidence for glia-opioid modulation of pain by focusing on the pattern of astrocyte and microglial activation throughout the progress of nerve injury/neuropathic pain. Activation of astrocytes and microglia is a key step in central immunomodulation in terms of releasing pro-inflammatory markers and propagation of a 'central immune response'. Inhibition of astrocytes before and after induction of neuropathic pain has been found to prevent and reverse neuropathic pain, respectively. Moreover, microglial inhibitors have been found to prevent (but not to reverse) neuropathic pain. As they are expressed by glia, opioid receptors are expected to have a role to play in neuropathic pain.

Delta opioid agonists: a concise update on potential therapeutic applications

WHAT IS KNOWN AND OBJECTIVE

The endogenous opioid system co-evolved with chemical defences, or at times symbiotic relationships, between plants and other autotrophs and heterotrophic predators - thus, it is not surprising that endogenous opioid ligands and exogenous mimetic ligands produce diverse physiological effects. Among the endogenous opioid peptides (endomorphins, enkephalins, dynorphins and nociception/orphanin FQ) derived from the precursors encoded by four genes (PNOC, PENK, PDYN and POMC) are the pentapeptides Met-enkephalin (Tyr-Gly-Gly-Phe-Met) and Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu). The physiological effects of the enkephalins are mediated via 7-transmembrane G protein-coupled receptors, including delta opioid receptor (DOR). We present a concise update on the status of progress and opportunities of this approach.

METHODS

A literature search of the PUBMED database and a combination of keywords including delta opioid receptor, analgesia, mood and individual compounds identified therein, from industry and other source, and from www.clinicaltrials.com.

RESULTS AND DISCUSSION

DOR agonist and antagonist ligands have been developed with ever increasing affinity and selectivity for DOR over other opioid receptor subtypes and studied for therapeutic utility, primarily for pain relief, but also for other clinical endpoints.

WHAT IS NEW AND CONCLUSION

Selective DOR agonists have been designed with a large increase in therapeutic window for a variety of potential CNS applications including pain, depression, and learning and memory among others.

Opioids and immune modulation: more questions than answers

Opioid addicts are more likely to present with infections suggesting opioids are immune modulators. The potential sites/mechanism(s) for this modulation are controversial and on close inspection not well supported by the current literature. It has long been assumed that opioid-induced immune modulation occurs via a combination of direct actions on the immune cell itself, via the hypothalamic-pituitary-adrenal (HPA) axis, or both. Opioid receptors are classified as MOP (μ, mu), DOP (δ, delta), and KOP (κ, kappa)--classical naloxone sensitive receptors--or NOP (the receptor for nociceptin/orphanin FQ), which is naloxone insensitive. Opioids currently used in clinical practice predominantly target the MOP receptor. There do not appear to be classical opioid receptors present on immune cells. The evidence for HPA activation is also poor and shows some species dependence. Most opioids used clinically or as drugs of abuse do not target the NOP receptor. Other possible target sites for immune modulation include the sympathetic nervous system and central sites. We are currently unable to accurately define the cellular target for immune modulation and suggest further investigation is required. Based on the differences observed when comparing studies in laboratory animals and those performed in humans we suggest that further studies in the clinical setting are needed.

Endogenous morphine levels are increased in sepsis: a partial implication of neutrophils

Background

Mammalian cells synthesize morphine and the respective biosynthetic pathway has been elucidated. Human neutrophils release this alkaloid into the media after exposure to morphine precursors. However, the exact role of endogenous morphine in inflammatory processes remains unclear. We postulate that morphine is released during infection and can be determined in the serum of patients with severe infection such as sepsis.

Methodology

The presence and subcellular immunolocalization of endogenous morphine was investigated by ELISA, mass spectrometry analysis and laser confocal microscopy. Neutrophils were activated with Interleukin-8 (IL-8) or lipopolysaccharide (LPS). Morphine secretion was determined by a morphine-specific ELISA. μ opioid receptor expression was assessed with flow cytometry. Serum morphine concentrations of septic patients were determined with a morphine-specific ELISA and morphine identity was confirmed in human neutrophils and serum of septic patients by mass spectrometry analysis. The effects of the concentration of morphine found in serum of septic patients on LPS-induced release of IL-8 by human neutrophils were tested.

Principal Findings

We confirmed the presence of morphine in human neutrophil extracts and showed its colocalisation with lactoferrin within the secondary granules of neutrophils. Morphine secretion was quantified in the supernatant of activated human polymorphonuclear neutrophils in the presence and absence of Ca²⁺. LPS and IL-8 were able to induce a significant release of morphine only in presence of Ca²⁺. LPS treatment increased μ opioid receptor expression on neutrophils. Low concentration of morphine (8 nM) significantly inhibited the release of IL-8 from neutrophils when coincubated with LPS. This effect was reversed by naloxone. Patients with sepsis, severe sepsis and septic shock had significant higher circulating morphine levels compared to patients with systemic inflammatory response syndrome and healthy controls. Mass spectrometry analysis showed that endogenous morphine from serum of patient with sepsis was identical to poppy-derived morphine.

Conclusions

Our results indicate that morphine concentrations are increased significantly in the serum of patients with systemic infection and that morphine is, at least in part, secreted from neutrophils during sepsis. Morphine concentrations equivalent to those found in the serum of septic patients significantly inhibited LPS-induced IL-8 secretion in neutrophils.

Morphine inhibits AP-1 activity and CD14 expression in leukocytes by a nitric oxide and opioid receptor-dependent mechanism

BACKGROUND

Activator protein 1 is a transcription factor involved in the regulation of proinflammatory mediators. Activation of phagocytes by lipopolysaccharide depends on the expression of CD14 on the cell surface. In this study, we investigated the effects of morphine and nitric oxide on CD14 expression and activator protein 1 activation in human blood monocytes and neutrophils as well as the leukocyte cell line HL-60.

METHODS

Whole blood was incubated with morphine, the nitric oxide donor S-nitroso-N-acetyl-penicillamine, naloxone or nitric oxide synthase inhibitors Nomega-nitro-l-arginine and Nomega-nitro-l-arginine-methylester and stimulated with lipopolysaccharide. Activator protein 1 nuclear content was determined by flow cytometry in human blood neutrophils and monocytes. CD14 expression on neutrophils was measured after incubation with fluorescein isothiocyanate-labelled antibodies. Electric mobility shift assay served for evaluation of activator protein 1 nuclear binding in HL-60 cells.

RESULTS

Incubation of whole blood with morphine and subsequent stimulation with lipopolysaccharide decreased activator protein 1 nuclear content. Exposure to naloxone before morphine treatment abolished morphine-induced inhibition of activator protein 1 activity in human blood monocytes and neutrophils. Nitric oxide synthase inhibitors also reversed morphine's effects. CD14 expression on neutrophils was reduced after morphine treatment. These effects were antagonized by nitric oxide synthase inhibitors and naloxone.

CONCLUSION

Morphine inhibits activator protein 1 activation by a mu opioid receptor pathway coupled to nitric oxide as second messenger. The decrease in CD14 expression caused by morphine may play a role in inhibition of activator protein 1 activation following lipopolysaccharide treatment of phagocytes.

Human peripheral blood mononuclear cells express nociceptin/orphanin FQ, but not mu, delta, or kappa opioid receptors

BACKGROUND

Expression of opioid receptors on peripheral blood mononuclear cells (PBMC) is controversial. These receptors are currently classified as classical (MOP/mu/mu, DOP/delta/delta and KOP/kappa/kappa) and nonclassical NOP (nociceptin/orphanin FQ; N/OFQ).

METHODS

In this volunteer study we probed for the expression of both classical and nonclassical opioid receptors using 1) radioligand binding, 2) specific antibody binding, and 3) polymerase chain reaction-based experimental paradigms.

RESULTS

Membranes prepared from PBMC from healthy volunteers did not bind either [3H]diprenorphine (a nonselective radioligand for classical opioid receptors) or [3H]N/OFQ. There was significant concentration-dependent binding of each radioligand to control tissues expressing recombinant MOP and NOP. In addition, using fluorescence-activated cell sorting paradigms, there was no binding of fluorescent naloxone or either of two MOP antibodies to whole PBMC, though fluorescent naloxone did bind to recombinant MOP (as a positive control). Using primers specific for classical and nonclassical opioid receptors, and RNA extracted from the PBMC of 10 healthy volunteers, we were also unable to detect MOP, DOP, and KOP transcripts. In contrast, NOP was detected in all samples.

CONCLUSIONS

Despite using several complementary experimental strategies, we failed to demonstrate protein for classical or nonclassical opioid receptors on PBMC from healthy volunteers. We detected NOP mRNA, suggesting low-density NOP expression on these immunocytes. It is possible that N/OFQ, produced by the PBMC itself, may be involved in the control of immune function.

Expression of the mu opioid receptor in the human immunodeficiency virus type 1 transgenic rat model

Opioids, via the mu opioid receptor (MOR), can exacerbate bacterial infections and the immunopathogenesis of human immunodeficiency virus type 1 (HIV-1) infection. Recently, an HIV-1 transgenic (HIV-1Tg) rat model containing circulating HIV-1 gp120 was created. Using real-time reverse transcription-PCR, we found that MOR mRNA levels were significantly higher in the peritoneal macrophages of the HIV-1Tg rat than those in control animals. Lipopolysaccharide, a bacterial endotoxin, induced secretion of the inflammatory cytokines tumor necrosis factor alpha (TNF-alpha), interleukin-beta (IL-beta), and IL-10 in the HIV-1Tg rat and further increased MOR expression. Ex vivo studies showed that MOR expression was up-regulated in the peritoneal macrophages of F344 control rats by exposure to serum from HIV-1Tg rats and that MOR up-regulation was abolished by addition of gp120 antibody to the serum. In human TPA-differentiated HL-60 cells, which are macrophage-like cells, LPS-induced MOR mRNA up-regulation was greater in gp120-pretreated cells than in vehicle-pretreated cells. Our data suggest that in individuals infected with HIV-1, the MOR is up-regulated, possibly by circulating HIV-1 proteins such as gp120, and HIV-1 proteins may play a significant role in modulating the response to bacterial infection in opioid-using HIV-infected individuals. Furthermore, our results demonstrate that the new HIV-1Tg rat model can be a valuable tool with which to study MOR gene expression and its effects in the continuous presence of HIV viral proteins.

[Expression und function of the ORL-1 receptor on human leukocytes]

BACKGROUND

The ORL-1 receptor is expressed by human leukocytes. Limited knowledge exists about the function and interaction between the nervous and immune systems. The aim of our study was to investigate the expression of the nociceptin-ORL-1 receptor system on different leukocyte subsets and the influence of the ORL-1 receptor on the intracellular production of cytokines.

METHODS

Blood from healthy volunteers of different age and sex was analysed for the expression of the ORL-1 receptor by PCR and flow cytometry and the influence of nociceptin on the LPS-induced production of intracellular cytokines by flow cytometry.

RESULTS

The ORL-1 receptor mRNA is expressed by granulocytes, lymphocytes and monocytes. We could also show the expression of the ORL-1 receptor protein on the cell surface of all types of white blood cells. Nociceptin has no influence on LPS-induced cytokine production in human monocytes. There was neither a difference between young and old nor between male or female volunteers.

CONCLUSION

The ORL-1 receptor is expressed by all subtypes of leukocytes. The function of this receptor is not the modulation of cytokine production and requires further studies.

Endogenous opiates and behavior: 2002

This paper is the twenty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2002 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Anticipating and treating opioid-associated adverse effects

Opioids are frequently avoided as viable tools in the management of pain due to perceived dangerous or untoward adverse drug events. Whilst they are relatively safe options for the treatment of pain, side effects and toxicities do exist and should be anticipated by the provider. The central nervous, gastrointestinal, genito-urinary, integumentary, metabolic/endocrine, cardiovascular, pulmonary, hepatic/renal, ocular and immune systems all manifest changes associated with opioid therapy. These adverse events, ranging from nuisance to therapy-limiting, are manageable when addressed quickly and appropriately. Opioids are safe and efficacious analgesics when these effects are considered.