The Role of Opioid Receptors in Immune System Function

Research progress on the impact of opioids on the tumor immune microenvironment (Review)

Opioids have been extensively used in cancer pain management because they can significantly improve the quality of life of patients with advanced cancer. However, recent evidence suggests that opioids can also modulate the tumor immune microenvironment by interacting with opioid receptors on immune cells, potentially regulating tumor progression and efficacy of cancer treatments. Notably, morphine can exhibit a dose-dependent effect on tumor immunity in pancreatic cancer and renal cell models, with lower doses potentially promoting tumor migration and invasion of pancreatic cancer cells, whereas higher doses shows the effect of inhibiting migration and invasion through distinct molecular pathways. The present review therefore comprehensively explored the mechanisms by which opioids can regulate the tumor immune microenvironment, focusing on their effects on immune cells, oxidative stress and angiogenesis. It also examined the interactions between opioids and other analgesics, along with their potential impact on immune modulation. All relevant articles and materials were retrieved from PubMed using the key words 'opioids', 'immune system', 'T cells', 'monocytes', 'macrophages', 'lymphocytes', 'natural killer cell', 'immunotherapy', 'immune cell function' and 'dose dependent effect'. The immunosuppressive effects of opioids, particularly through the µ-opioid receptor, can suppress the activity of natural killer cells, impair antigen presentation and promote the function of regulatory T cells (Tregs). These effects may contribute to tumor progression and metastasis. The severity of these immunosuppressive effects appears to be dose-dependent and can vary among different tumor types. There is evidence to suggest that tumors with higher immune responsiveness will experience more pronounced suppression, including the reduction of tumor angiogenesis, resulting in a decrease in tumor volume and decrease in tumor metastases. Furthermore, the combination of opioids with other analgesics, such as non-steroidal anti-inflammatory drugs, has the potential to exacerbate immunosuppression, which can in turn increase the risk of infections. Therefore, although opioids are essential for pain management in patients with cancer, their potential to modulate the immune microenvironment and promote tumor progression requires careful consideration. Clinicians should evaluate the advantages and disadvantages of opioids, especially regarding emerging immunotherapies, to minimize their potential negative effects on the outcomes of cancer treatments. Future studies are recommended to prioritize the development of strategies that optimize pain management whilst preserving immune function, such as receptor-specific opioid formulations or adjunctive therapies targeting immunosuppressive pathways.

Xenon gas as a potential treatment for opioid use disorder, alcohol use disorder, and related disorders

Xenon gas is considered to be a safe anesthetic and imaging agent. Research on its other potentially beneficial effects suggests that xenon may have broad efficacy for treating health disorders. A number of reviews on xenon applications have been published, but none have focused on substance use disorders. Accordingly, we review xenon effects and targets relevant to the treatment of substance use disorders, with a focus on opioid use disorder and alcohol use disorder. We report that xenon inhaled at subsedative concentrations inhibits conditioned memory reconsolidation and opioid withdrawal symptoms. We review work by others reporting on the antidepressant, anxiolytic, and analgesic properties of xenon, which could diminish negative affective states and pain. We discuss research supporting the possibility that xenon could prevent analgesic- or stress-induced opioid tolerance and, by so doing could reduce the risk of developing opioid use disorder. The rapid kinetics, favorable safety and side effect profiles, and multitargeting capability of xenon suggest that it could be used as an ambulatory on-demand treatment to rapidly attenuate maladaptive memory, physical and affective withdrawal symptoms, and pain drivers of substance use disorders when they occur. Xenon may also have human immunodeficiency virus and oncology applications because its effects relevant to substance use disorders could be exploited to target human immunodeficiency virus reservoirs, human immunodeficiency virus protein-induced abnormalities, and cancers. Although xenon is expensive, low concentrations exert beneficial effects, and gas separation, recovery, and recycling advancements will lower xenon costs, increasing the economic feasibility of its therapeutic use. More research is needed to better understand the remarkable repertoire of effects of xenon and its potential therapeutic applications.

Peripheral Blood Cytokines as Markers of Longitudinal Change in White Matter Microstructure Following Inpatient Treatment for Opioid Use Disorders

Background

Opioid use disorder (OUD) causes major public health morbidity and mortality. Although standard-of-care treatment with medications for OUD (MOUDs) is available, there are few biological markers of the clinical process of recovery. Neurobiological aspects of recovery can include normalization of brain white matter (WM) microstructure, which is sensitive to cytokine signaling. Here, we determined whether blood-based cytokines can be markers of change in WM microstructure following MOUD.

Methods

Inpatient individuals with heroin use disorder (iHUDs) (n = 21) with methadone or buprenorphine MOUD underwent magnetic resonance imaging (MRI) scans with diffusion tensor imaging (DTI) and provided ratings of drug cue-induced craving, arousal, and valence earlier in treatment (MRI1) and ≈14 weeks thereafter (MRI2). Healthy control participants (HCs) (n = 24) also underwent 2 MRI scans during a similar time interval. At MRI2, participants provided a peripheral blood sample for multiplex quantification of serum cytokines. We analyzed the correlation of a multitarget biomarker score (from a principal component analysis of 19 cytokines that differed significantly between iHUDs and HCs) with treatment-related change in DTI metrics (ΔDTI; MRI2 - MRI1).

Results

The cytokine biomarker score was negatively correlated with ΔDTI metrics in frontal, frontoparietal, and corticolimbic WM tracts in iHUDs but not in HCs. Also, serum levels of specific cytokines in the cytokine biomarker score, including the interleukin-related oncostatin M (OSM), similarly correlated with ΔDTI metrics in iHUDs but not in HCs. Serum levels of other specific cytokines were negatively correlated with changes in cue-induced craving and arousal in the iHUDs.

Conclusions

Specific serum cytokines, studied alone or as a group, may serve as accessible biomarkers of WM microstructure changes and potential recovery in iHUDs undergoing treatment with MOUD.

Effects of intravenous morphine and lidocaine on bacterial growth

BACKGROUND

Infection prevention and control remain critical challenges in the ICU. Morphine, a frequently used opioid for postoperative pain management, may indirectly promote infections, whereas lidocaine might have protective effects. However, data regarding the direct influence of morphine and lidocaine, at concentrations within the range of plasma concentrations, on common ICU bacterial strains are lacking. This is the first study to investigate the direct effects of morphine and lidocaine at plasma concentrations corresponding to possible clinical settings, as seen in multimodal analgesia regimens, on bacterial growth using microbiological assays and transmission electron microscopy.

METHODS

Morphine (1000 ng/ml, 2000 ng/ml) and lidocaine (4 µg/ml, 10 µg/ml) were placed in contact with standard strains of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus and tested using diffusion method, broth dilution method, and time-kill assay. Additionally, E. coli, P. aeruginosa and S. aureus were exposed to lidocaine 10 µg/ml and examined via transmission electron microscopy.

RESULTS

Morphine and lidocaine exhibited neither stimulatory nor inhibitory effects on bacterial growth, regardless of concentration, volume, or exposure time in microbiological testing. In contrast, transmission electron microscopy revealed that lidocaine exposure altered bacterial ultrastructure, causing significant cell wall disorganization and rupture, alterations in cytoplasmic and nucleolar structure, and the appearance of "ghost cells", indicative of cell lysis.

CONCLUSIONS

At plasma concentrations, morphine and lidocaine do not directly affect bacterial growth in vitro microbiological laboratory testing. Lidocaine on the other hand, in higher plasma concentrations, disrupts bacterial ultrastructure. Further studies are needed to investigate the significance and clinical impact of these findings.

Intestinal immunoglobulins under microbial dysbiosis: implications in opioid-induced microbial dysbiosis

Intestinal immunoglobulins (Igs) maintain homeostasis between the microbiome and host. IgA facilitates microbial balance through a variety of increasingly well-described mechanisms. However, IgM and IgG have less defined intestinal functions but have the potential to activate clearance mechanisms such as the complement system and receptor-mediated bacterial killing. Very little is known regarding the role of Igs under microbial dysbiosis. In this review, we explore how Igs sculpt the intestinal microbiome and respond to microbial dysbiosis. We discuss how IgM, IgA, IgG, and complement individually maintain harmony with the microbiome and consider how these mechanisms could work in synergy. Finally, we explore using an opioid-induced microbial dysbiosis as a model to elucidate immediate changes in Ig-bacterial interactions.

Exploring the impact of opioid use on outcomes in allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Hematological malignancies and allogeneic hematopoietic cell transplantation (alloHCT) often necessitate the use of opioids due to significant pain. This study aimed to investigate the impact of opioid use on the clinical outcomes of patients undergoing alloHCT.

METHODS

A retrospective cohort study was conducted by merging data from our local transplant database with anonymized pharmacy records obtained from the Institute for Clinical Evaluative Sciences (ICES). We analyzed 681 patients who underwent alloHCT at Princess Margaret Cancer Centre between January 2010 and December 2019. Patients who initiated opioid use within one-year post-alloHCT and had opioid prescriptions for more than 30 days were categorized as intense opioid users (IOU). Additionally, patients who started opioids before or within one-year post-alloHCT and had opioid prescriptions for less than 30 days but died while on opioids were also classified as IOU. The analytical code used for the analysis is available in the Supporting Information file.

RESULTS

Among the 681 patients, 51 were identified as IOU. The two-year overall survival (OS) was significantly lower in the IOU group, with 29.4% survival compared to 53% in non-IOU (HR 1.77, 95% CI 1.26-2.48, p = 0.0008). Multivariate analysis indicated that IOU status was associated with a 2.32 times higher instantaneous rate of death compared to non-IOU (HR 2.32, 95% CI 1.5-3.5, p = 0.002). The median time for relapse was 147 days in the IOU group (range 52-393) and 209 day for non-IOU (range 96-1793), p = 0.0082. Furthermore, the relapse rate at two years was notably higher in the IOU group (31.4% vs. 16.4%, p = 0.0049). The analysis of factors independently associated with relapse-free survival (LFS) showed that IOU status, age, donor type, and cytogenetic risk were significant predictors. At two years, relapse-free survival was 29.4% in the IOU group compared to 52.5% in the non-IOU group (p < 0.001).

CONCLUSIONS

In our study, we found a correlation between intense opioid use in alloHCT patients and worse overall survival, particularly concerning higher relapse rates. These findings highlight the need for further research into pain management strategies to improve outcomes and reduce potential toxicity.

Antibody immunotherapies for personalized opioid addiction treatment

Approved therapies for managing opioid addiction involve intensive treatment regimens which remain both costly and ineffective. As pharmaceutical interventions have achieved variable success treating substance use disorders (SUD), alternative therapeutics must be considered. Antidrug antibodies induced by vaccination or introduced as monoclonal antibody formulations can neutralize or destroy opioids in circulation before they reach their central nervous system targets or act as enzymes to deactivate opioid receptors, preventing the physiologic and psychoactive effects of the substance. A lack of "reward" for those suffering from SUD has been shown to result in cessation of use and promote long-term abstinence. Decreased antibody production costs and the advent of novel gene therapies that stimulate in vivo production of monoclonal antibodies have renewed interest in this strategy. Furthermore, advances in understanding of SUD immunopathogenesis have revealed distinct mechanisms of neuroimmune dysregulation underlying the disorder. Beyond assisting with cessation of drug use, antibody therapies could treat or reverse pathophysiologic hallmarks that contribute to addiction and which could be the cause of chronic cognitive defects resulting from drug use. In this review, we synthesize key current literature regarding the efficacy of immunotherapies in managing opioid addiction and SUD. We will explore the neuropharmacology underlying these treatments by relating evidence from studies on the use of antibody therapeutics to counteract various drug behaviors and by drawing parallels to the similar immunopathology observed in neurodegenerative disorders. Finally, we will discuss the implications of novel immunization technologies and the application of computational methods in developing personalized addiction treatments. SIGNIFICANCE STATEMENT: Significant new evidence contributing to our understanding of substance use disorders has recently emerged leading to a paradigm shift concerning the role of immunology in the neuropathogenesis of opioid use disorder. Concurrently, immunotherapeutic technologies such as antibody therapeutics have advanced the capabilities regarding applications that take advantage of these key principles. This article reviews key antibody-based treatments being studied and highlights directions for further research that may contribute to the management of opioid use disorder.

Morphine's role in macrophage polarization: Exploring M1 and M2 dynamics and disease susceptibility

Morphine is a globally prevalent substance of misuse, renowned for its immunosuppressive effects mediated through opioid receptors expressed on immune cells. Macrophages are crucial antigen-presenting cells that fulfill diverse roles, such as antigen presentation, phagocytosis, wound healing, and disease protection. They are typically classified based on their activation states: M1 (proinflammatory), M2 (anti-inflammatory), and M0 (resting). Morphine significantly modulates immune responses and neuroinflammation, further complicating the landscape of opioid dependency and disease susceptibility. The association of macrophages under the influence of morphine needs to be understood under various diseased conditions. Several studies have been focused on investigating the impact of morphine on macrophage function and its implications in infectious diseases and brain-associated diseases. To light this subject, we have discussed recent advancements in understanding the influences between morphine, macrophage function, polarization, infection, brain tumors, and drug dependency. This article explores the complex relationship between morphine, macrophages, and related pathologies. Consequently, discussing deeper insights into these dynamics could guide effective treatments for substance abuse disorders.

Methadone and Buprenorphine as Medication for Addiction Treatment Diversely Affect Inflammation and Craving Depending on Their Doses

Buprenorphine and methadone are widely used as medication for addiction treatment (MAT) in patients with opioid use disorders. However, there is no compelling evidence of their impact on the immune-endocrine response. Therefore, the aim of this study was to examine the effects of the aforementioned medications on craving and on biomarkers of inflammation and cortisol, approaching the dose issue concurrently. Sixty-six patients (thirty-four under methadone and thirty-two under buprenorphine) who had just entered a MAT program and were stabilized with the suitable administered doses after a two-week process were divided into four groups based on medication dose (i.e., methadone high dose, buprenorphine high dose, methadone medium dose, and buprenorphine medium dose). The heroin craving questionnaire for craving assessment was completed, and the blood biomarkers were measured on Days 1 and 180. According to the results, high doses of both medications were accompanied by low levels of craving, cortisol, and inflammation on Day 1, and no alterations were observed on Day 180. On the contrary, medium doses reduced the tested psychosocial and biochemical parameters in terms of time, indicating a positive action for the patients. Concludingly, modifications in MAT doses are needed soon after the stabilization process to prevent inflammation and avoid relapse, thus helping opioid-addicted patients toward rehabilitation.

Sex differences in the antinociceptive effect of codeine and its peripheral but not central metabolism in adult mice

Codeine is a natural opiate extracted from opium poppy (Papaver somniferum) and used to alleviate mild to moderate pain. The analgesic effect of this molecule results from its metabolism into morphine which is an agonist of the mu opioid receptor. Morphine's major metabolite morphine-3-glucuronide induces both thermal and mechanical hypersensitivies while codeine-6-glucuronide has been proposed to be antinociceptive. However, sex differences in codeine antinociceptive effect and pharmacokinetics were barely studied. To this purpose, we injected male and female mice with codeine (2.5, 5, 10, 20 and 40 mg/kg) and thermal hypersensitivity was assessed 30 min after injection using the Tail Immersion Test. Moreover, both peripheral and central metabolism of codeine were evaluated respectively in the blood or pain-related brain structures in the central nervous system. The amounts of codeine and its metabolites were quantified using the isotopic dilution method by liquid chromatography coupled to a mass spectrometer. Our results show that codeine induces a greater antinociceptive effect in males than females mice independently of the estrous cycle. Moreover, major sex differences were found in the peripheral metabolism of this molecule, with higher amounts of pronociceptive morphine-3-glucuronide and less antinociceptive codeine-6-glucuronide in females than in males. Concerning the central metabolism of codeine, we did not find significant sex differences in pain-related brain structures. Collectively, these findings support a greater codeine antinociceptive effect in males than females in mice. These sex differences could be influenced by a higher peripheral metabolism of this molecule in female mice rather than central metabolism.

Naltrexone Alters Neurochemical and Behavioral Parameters in a Zebrafish Model of Repeated Alcohol Exposure

Between the neurotransmission systems modulated by alcohol, the opioid system has been receiving attention in studies that seek to understand its relationship to the effects of addictive substances and different neuropsychiatric disorders. The use of naltrexone stands out in determining the mechanisms of the opioid system, as it acts as an opioid antagonist and consequently generates neurochemical responses. This study aimed to evaluate the pharmacological modulation of opioids on behavioral and neurobiological aspects in adult zebrafish submitted to the protocol of repeated exposure to ethanol and treated with naltrexone. Opioid modulation using naltrexone has been shown to modulate anxiety-like behavior, presenting anxiolytic properties in isolation, in addition to reversing the anxiogenic effect of ethanol through the Novel tank and Light/dark test. Naltrexone increased serotonin and dopamine levels, while ethanol antagonized these effects. In contrast, the interaction between ethanol and naltrexone raised noradrenaline levels. Naltrexone altered glutamate levels, however, ethanol reversed it. Ethanol acted on glutamate transporters increasing their activities, while naltrexone treatment reduced activities. No significant results were found in the pro-oxidant parameters, however, ethanol reduced SOD activity while naltrexone reversed. The same occurred in CAT activity. Also, naltrexone up-regulated the expression of genes related to the dopaminergic, glutamatergic, and opioid systems. The genes used as markers of the inflammatory process and glial activity were modulated by ethanol and together with naltrexone, respectively. Taken together, our findings reinforce the importance of opioid signaling on biochemical and molecular bases related to neuropsychiatric behaviors and diseases, such as anxiety and substance dependence.

μ-Opioid receptor transcriptional variants in the murine forebrain and spinal cord

Oprm1, the gene encoding the μ-opioid receptor, has multiple reported transcripts, with a variable 3' region and many alternative sequences encoding the C-terminus of the protein. The functional implications of this variability remain mostly unexplored, though a recurring notion is that it could be exploited by developing selective ligands with improved clinical profiles. Here, we comprehensively examined Oprm1 transcriptional variants in the murine central nervous system, using long-read RNAseq as well as spatial and single-cell transcriptomics. The results were validated with RNAscope in situ hybridization. We found a mismatch between transcripts annotated in the mouse genome (GRCm38/mm10) and the RNA-seq results. Sequencing data indicated that the primary Oprm1 transcript has a 3' terminus located on chr10:6,860,027, which is ∼ 9.5 kilobases downstream of the longest annotated exon 4 end. Long-read sequencing confirmed that the final Oprm1 exon included a 10.2 kilobase long 3' untranslated region, and the presence of the long variant was unambiguously confirmed using RNAscope in situ hybridization in the thalamus, striatum, cortex and spinal cord. Conversely, expression of the Oprm1 reference transcript or alternative transcripts of the Oprm1 gene was absent or close to the detection limit. Thus, the primary transcript of the Oprm1 mouse gene is a variant with a long 3' untranslated region, which is homologous to the human OPRM1 primary transcript and encodes the same conserved C-terminal amino acid sequence.

Immunocyte profiling changes in patients received epidural versus intravenous analgesia after pancreatectomy: A randomized controlled trial

BACKGROUND

Perioperative immunosuppressants, such as surgical stress and opioid use may downregulate anti-cancer immunocytes for patients undergoing pancreatectomy. Thoracic epidural analgesia (TEA) may attenuate these negative effects and provide better anti-cancer immunocyte profile change than intravenous analgesia using opioid.

METHODS

We randomly assigned 108 adult patients undergoing pancreatectomy to receive one of two 72-h postoperative analgesia protocols: one was TEA, and the other was intravenous patient-controlled analgesia (IV-PCA). The perioperative proportional changes of immunocytes relevant to anticancer immunity-namely natural killer (NK) cells, cytotoxic T cells, helper T cells, mature dendritic cells, and regulatory T (Treg) cells were determined at 1 day before surgery, at the end of surgery and on postoperative day 1,4 and 7 using flow cytometry. In addition, the progression-free survival and overall survival between the two groups were compared.

RESULTS

After surgery, the proportions of NK cells and cytotoxic T cells were significantly decreased; the proportion of B cells and mature dendritic cells and Treg cells were significantly increased. However, the proportions of helper T cells exhibited no significant change. These results were comparable between the two groups. Furthermore, there were no significant differences in progression-free survival (52.75 [39.96] and 57.48 [43.66] months for patients in the TEA and IV-PCA groups, respectively; p = 0.5600) and overall survival (62.71 [35.48] and 75.11 [33.10] months for patients in the TEA and IV-PCA groups, respectively; p = 0.0644).

CONCLUSION

TEA was neither associated with favorable anticancer immunity nor favorable oncological outcomes for patients undergoing pancreatectomy.

The Effect of Clostridium butyricum-Derived Lipoteichoic Acid on Lipopolysaccharide-Stimulated Porcine Intestinal Epithelial Cells

BACKGROUND

Clostridium butyricum is a probiotic widely used in animal husbandry, and there is evidence to suggest that it can alleviate intestinal inflammation in pigs and may be related to its lipoteichoic acid (LTA), but the mechanism is still unclear.

OBJECTIVE

This study aimed to determine the regulatory effect and potential mechanism of C. butyricum LTA on LPS-stimulated inflammation in intestinal porcine epithelial line-J2 (IPEC-J2).

METHODS

IPEC-J2 cells were treated with LPS and different concentrations of LTA (0.05, 0.1 and 0.15 mM). After treatment of 0.5, 1.5 and 4.5 h, the cell culture media were collected for the measurement of TNF-α and IL-10 by using ELISA kits, and the cells were collected for RT-qPCR and Western blotting detections. Further elucidating the pathway of LTA regulating IL-10 and TNF-α gene expression by inhibiting key proteins in the toll-like receptor pathway with antagonists C34, PDTC, SB230580 and U0126.

RESULTS

High-dose LTA significantly promoted the secretion of the anti-inflammatory factor IL-10 in IPEC-J2 cells, and inhibited the expression and secretion of pro-inflammatory TNF-α in the short term. LTA inhibited the gene expression of TLR4 in LPS-stimulated cells and reduced the protein phosphorylation levels of p38, ERK1/2 and p65. The inhibition of TLR4, p38, ERK1/2 and p65 reduced the TNF-α gene expression caused by LPS; LTA increased TLR2 gene expression, inhibition of p38, ERK and p65 rather than TLR4 reduced the IL-10 gene expression.

CONCLUSION

Our study found that C. butyricum LTA was an important component of C. butyricum regulating the inflammatory response of IPEC-J2 cells. LTA mainly reduced the expression of TNF-α by inhibiting TLR4, while stimulating TLR2 increased the expression of IL-10. Downstream p65, p38 and ERK1/2 were involved in regulating both TNF-α and IL-10. However, TLR4 was only related to the increase in TNF-α caused by LPS and not to the increase in IL-10 caused by LTA. Our work supplemented the probiotic mechanism of C. butyricum and provided a theoretical basis for the application of C. butyricum LTA.

TLR4 promotes smooth muscle cell-derived foam cells formation by inducing receptor-independent macropinocytosis

Foam cells are primarily formed through scavenger receptors that mediate the uptake of various modified low-density lipoproteins (LDL) into cells. In addition to the receptor-dependent pathway, macropinocytosis is an essential nonreceptor endocytic pathway for vascular smooth muscle cells (VSMCs) to take up lipids. However, the molecular mechanisms underlying this process remain unclear. Primary cultured VSMCs were stimulated with 200 ng/mL lipopolysaccharide (LPS) and 200 µg/mL native LDL (nLDL). We observed a significant increase in Toll-like receptor 4 (TLR4) protein expression and a significant activation of macropinocytosis, which correlated with the highest uptake of nLDL and intracellular lipid deposition in WT VSMCs. However, macropinocytosis was inhibited and lipid accumulation decreased after treatment with macropinocytosis inhibitors and Syk inhibitors in WT VSMCs. Consistently, TLR4 knockout significantly suppressed macropinocytosis and lipid droplets accumulation in VSMCs. Taken together, our findings suggest a critical role of TLR4/Syk signaling in promoting receptor-independent macropinocytosis leading to VSMC-derived foam cells formation.

Anesthetic Approaches and Their Impact on Cancer Recurrence and Metastasis: A Comprehensive Review

Cancer recurrence and metastasis remain critical challenges following surgical resection, influenced by complex perioperative mechanisms. This review explores how surgical stress triggers systemic changes, such as neuroendocrine responses, immune suppression, and inflammation, which promote the dissemination of residual cancer cells and circulating tumor cells. Key mechanisms, such as epithelial-mesenchymal transition and angiogenesis, further enhance metastasis, while hypoxia-inducible factors and inflammatory responses create a microenvironment conducive to tumor progression. Anesthetic agents and techniques modulate these mechanisms in distinct ways. Inhaled anesthetics, such as sevoflurane, may suppress immune function by increasing catecholamines and cytokines, thereby promoting cancer progression. In contrast, propofol-based total intravenous anesthesia mitigates stress responses and preserves natural killer cell activity, supporting immune function. Opioids suppress immune surveillance and promote angiogenesis through the activation of the mu-opioid receptor. Opioid-sparing strategies using NSAIDs show potential in preserving immune function and reducing recurrence risk. Regional anesthesia offers benefits by reducing systemic stress and immune suppression, though the clinical outcomes remain inconsistent. Additionally, dexmedetomidine and ketamine exhibit dual effects, both enhancing and inhibiting tumor progression depending on the dosage and context. This review emphasizes the importance of individualized anesthetic strategies to optimize long-term cancer outcomes. While retrospective studies suggest potential benefits of propofol-based total intravenous anesthesia and regional anesthesia, further large-scale trials are essential to establish the definitive role of anesthetic management in cancer recurrence and survival.

Neuroinflammatory history results in overlapping transcriptional signatures with heroin exposure in the nucleus accumbens and alters responsiveness to heroin in male rats

Recent progress in psychiatric research has highlighted neuroinflammation in the pathophysiology of opioid use disorder (OUD), suggesting that heightened immune responses in the brain may exacerbate opioid-related mechanisms. However, the molecular mechanisms resulting from neuroinflammation that impact opioid-induced behaviors and transcriptional pathways remain poorly understood. In this study, we have begun to address this critical knowledge gap by exploring the intersection between neuroinflammation and exposure to the opioid heroin, utilizing lipopolysaccharide (LPS)-induced neuroinflammation, to investigate transcriptional changes in the nucleus accumbens (NAc), an essential region in the mesolimbic dopamine system that mediates opioid reward. By integrating RNA sequencing with bioinformatic and statistical analyses, we observed significant transcriptional overlaps between neuroinflammation and experimenter-administered heroin exposure in the NAc. Furthermore, we identified a subset of NAc genes synergistically regulated by LPS and heroin, suggesting that LPS history may exacerbate some heroin-induced molecular neuroadaptations. We extended our findings to examine the impact of neuroinflammatory history on responsiveness to heroin in a locomotor sensitization assay and observed LPS-induced exacerbation of heroin sensitization, indicating that neuroinflammation may increase sensitivity to opioids' behavioral effects. Lastly, we performed comparative analysis of the NAc transcriptional profiles of LPS-heroin rats with those obtained from voluntary heroin intake in a rat model of heroin self-administration (SA) and published human OUD datasets. We observed significant convergence of the three datasets and identified transcriptional patterns in the preclinical models that recapitulated human OUD neuropathology, highlighting the utility of preclinical models to further investigate molecular mechanisms of OUD pathology. Overall, our study elucidates transcriptional interconnections between neuroinflammation and heroin exposure, and also provides evidence of the behavioral ramifications of such interactions. By bridging the gap between neuroinflammation and heroin exposure at the transcriptional level, our work provides valuable insights for future research aimed at mitigating the influence of inflammatory pathways in OUD.

Morphine-Driven m6A Epitranscriptomic Neuroadaptations in Primary Cortical Cultures

Opioid overdose is the leading cause of accidental death in the United States and remains a major public health concern, despite significant resources aimed at combating opioid misuse. Neurobiological research to elucidate molecular and cellular consequences of opioid exposure is required to define avenues to explore for reversal of opioid-induced neuroadaptations. Opioids impart well-documented regulation of the transcriptome and epigenetic modifications in the brain, but opioid-induced epitranscriptomic posttranscriptional regulation of RNA is vastly understudied. N6-methyladenosine (m6A) RNA methylation is significantly enriched in the brain and involved in learning, memory, and reward. m6A modifications have not been studied in opioid use disorder, despite being the most common RNA modification. We detected significant regulation of m6A-modifying enzymes in rat primary cortical cultures following morphine treatment, including AlkB Homolog 5 (Alkbh5). The m6a demethylase ALKBH5 functions as an m6A eraser, removing m6A modifications from mRNA. We hypothesized that chronic opioid treatment regulates m6A modifications through modulation of Alkbh5 and profiled m6A modifications in primary cortical cultures following chronic morphine treatment and Alkbh5 knock-down. We observed differential regulation of m6A modifications for a common set of transcripts following morphine or Alkbh5 knock-down, and the two treatments elicited concordant m6A epitranscriptomic profiles, suggesting that a subset of morphine-driven m6A modifications may be mediated through downregulation of Alkbh5 in cortical cultures. Gene Ontology terms of commonly regulated transcripts included serotonin secretion, synapse disassembly, neuron remodeling, and immune response. Thus, we conclude that morphine can drive epitranscriptomic changes, a subset of which may occur in an Alkbh5-dependent manner.

Effects of anesthesia with sevoflurane on outcome parameters in murine experimental studies

PURPOSE

Multiple murine studies modelling the immuno-pathophysiological consequences of trauma, shock, burn or sepsis were performed during the last decades. Almost every animal model requires anesthesia for practical and ethical reasons. Furthermore, often, corresponding control groups involve untreated animals without or with a limited exposure to anesthetics. However, the influences of anesthetic drugs on immuno-pathophysiological reactions remain insufficiently investigated. Therefore, we aimed to closer characterize the anesthetic impact exemplified by sevoflurane on the organ performance in mice and thereby investigate the influence of anesthesia itself on major outcome parameters in animal studies.

METHODS

C57/BL6 mice were subjected either to 270 min of sevoflurane narcosis or directly euthanized. Plasma, BAL-fluids, lungs, kidneys, liver and intestine were collected and examined for immunological, functional and morphological changes.

RESULTS

Systemic levels of the cytokine keratinocyte chemoattractant (KC) were raised in the narcosis group, while concentrations of high mobility group box protein 1 (HMGB-1) as a major inflammatory marker were reduced. In the lungs, levels of HMGB-1 and interleukin 6 (IL-6) were reduced. In contrast, systemic concentrations of intestinal fatty acid binding-protein (i-FABP) as an intestinal damage marker were elevated. Furthermore, liver-type fatty acid binding-protein (L-FABP) levels were lower in the narcosis animals, and inflammatory markers were reduced in liver tissues. Anesthesia also ameliorated the inflammatory reaction in renal tissues, while plasma levels of urea and creatinine were elevated, reflecting either dehydration and/or impaired renal function.

CONCLUSION

As anesthesia with sevoflurane exhibited distinct effects in different organs, it is difficult to predict its specific impact on targets of interest in in vivo studies. Therefore, further studies are required to clarify the effects of different anesthetic drugs. Overall, the inclusion of a control group subjected to the same anesthesia protocol as the experimental groups of interest seems helpful to precisely define the inherent impact of the anesthetic when investigating immuno-pathophysiologic conditions in vivo.

Morphine treatment restricts response to immunotherapy in oral squamous cell carcinoma

BACKGROUND

Immune checkpoint inhibitors (ICIs) are becoming the standard of care for recurrent and metastatic cancer. Opioids, the primary treatment for cancer-related pain, are immunosuppressive raising concerns about their potential to interfere with the efficacy of ICIs. We hypothesize that exogenous opioids given for analgesia suppress antitumor immunity via T cell-mediated mu opioid receptor 1 (OPRM1) signaling.

METHODS

In silico bioinformatics were used to assess OPRM1 receptor expression on tumor-infiltrating immune cells in patients with head and neck squamous cell carcinoma (HNSCC) and across different cancer types. A syngeneic orthotopic mouse model of oral squamous cell carcinoma was used to study the impact of morphine and OPRM1 antagonism on tumor-infiltrating immune cells, tumor growth and antitumor efficacy of anti-Programmed cell death protein 1 (PD-1) monoclonal antibody treatment.

RESULTS

In patients with HNSCC, OPRM1 expression was most abundant in CD8+ T cells, particularly in patients who had not been prescribed opioids prior to resection and exhibited increased expression of exhaustion markers. Exogenous morphine treatment in tumor-bearing mice reduced CD4+ and CD8+ T-cell infiltration and subsequently anti-PD1 ICI efficacy. Peripherally acting mu opioid receptor antagonism, when administered in the adjunctive setting, was able to block morphine-induced immunosuppression and recover the antitumor efficacy of anti-PD1.

CONCLUSIONS

These findings suggest that morphine acts via a peripheral OPRM1-mediated mechanism to suppress CD8+ T cells, thereby fostering a pro-tumor-impaired immune response. Importantly, peripherally-restricted OPRM1 antagonism can effectively block this morphine-induced immunosuppression while still allowing for centrally-mediated analgesia, indicating a potential therapeutic strategy for mitigating the adverse effects of opioid pain relief in cancer treatment.

The Role of Anesthetic Management in Lung Cancer Recurrence and Metastasis: A Comprehensive Review

Lung cancer remains a leading cause of cancer-related mortality worldwide. Although surgical treatment is a primary approach, residual cancer cells and surgery-induced pathophysiological changes may promote cancer recurrence and metastasis. Anesthetic agents and techniques have recently been shown to potentially impact these processes by modulating surgical stress responses, immune function, inflammatory pathways, and the tumor microenvironment. Anesthetics can influence immune-modulating cytokines, induce pro-inflammatory factors such as HIF-1α, and alter natural-killer cell activity, affecting cancer cell survival and spread. Preclinical studies suggest volatile anesthetics may promote tumor progression by triggering pro-inflammatory signaling, while propofol shows potential antitumor properties through immune-preserving effects and reductions in IL-6 and other inflammatory markers. Additionally, opioids are known to suppress immune responses and stimulate pathways that may support cancer cell proliferation, whereas regional anesthesia may reduce these risks by decreasing the need for systemic opioids and volatile agents. Despite these findings, clinical data remain inconclusive, with studies showing mixed outcomes across patient populations. Current clinical trials, including comparisons of volatile agents with propofol-based total intravenous anesthesia, aim to provide clarity but highlight the need for further investigation. Large-scale, well-designed studies are essential to validate the true impact of anesthetic choice on cancer recurrence and to optimize perioperative strategies that support long-term oncologic outcomes for lung cancer patients.

Activated microglia secretome and proinflammatory cytokines increase neuronal mu-opioid receptor signalling and expression

Due to its potential role in processes which rely on mu-opioid receptor function, investigating the relationship between Mu-Opioid receptors (MORs), neuroinflammation, and glial cells has gained momentum. Traditionally, MOR activation has been associated with immunosuppression, but recent findings suggest a more nuanced, bidirectional relationship with the immune system. To further investigate this relationship, herein, we investigated the role of the activated microglia secretome and proinflammatory cytokines in neuronal MOR expression and signalling. Our results show that both microglial secretome and specific cytokines increase neuronal MOR expression and enhance the [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO)-induced MOR activation. We also show that DAMGO-induced neuroinflammation increases neuronal MOR expression, activation, and regulation. Our findings suggest a feedback loop between microglial activation, cytokine release, and neuronal MOR dynamics. Future research should delve into the temporal dynamics and functional implications of this relationship, particularly concerning clinically relevant opioids like morphine and fentanyl and pain management.

The Impact of Opioid Prescription on the Occurrence and Outcome of Pneumonia: A Nationwide Cohort Study in South Korea

BACKGROUND

Opioids are known to cause respiratory depression, aspiration, and to suppress the immune system. This study aimed to investigate the relationship between short- and long-term opioid use and the occurrence and clinical outcomes of pneumonia in South Korea.

METHODS

The data for this population-based retrospective cohort analysis were obtained from the South Korean National Health Insurance Service. The opioid user group consisted of those prescribed opioids in 2016, while the non-user group, who did not receive opioid prescriptions that year, was selected using a 1:1 stratified random sampling method. The opioid users were categorized into short-term (1-89 d) and long-term (≥90 d) users. The primary end point was pneumonia incidence from January 1, 2017-December 31, 2021, with secondary end points including pneumonia-related hospitalizations and mortality rates during the study period.

RESULTS

In total, 4,556,606 adults were enrolled (opioid group, 2,070,039). Opioid users had a 3% higher risk of pneumonia and an 11% higher risk of pneumonia requiring hospitalization compared to non-users. Short-term users had a 3% higher risk of pneumonia, and long-term users had a 4% higher risk compared to non-users (P < .001). Additionally, short-term users had an 8% higher risk of hospital-treated pneumonia, and long-term users had a 17% higher risk compared to non-users (P < .001).

CONCLUSIONS

Both short- and long-term opioid prescriptions were associated with higher incidences of pneumonia and hospital-treated pneumonia. In addition, long-term opioid prescriptions were linked to higher mortality rates due to pneumonia.

Risk of infections among persons treated with opioids for chronic pain: a systematic review and meta-analysis protocol

INTRODUCTION

Millions of persons with chronic pain across North America and Europe use opioids. While the immunosuppressive properties of opioids are associated with risks of infections, these outcomes could be mitigated through careful patient selection and monitoring practices when appropriate. It is important to recognise that some patients do benefit from a carefully tailored opioid therapy. Enough primary studies have been published to date regarding the role of opioids in potential immunosuppression presenting as an increased rate of infection acquisition, infectious complications and mortality. There is thus a critical need for a consensus in this area.

METHODS AND ANALYSIS

The methodology is based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, the MOOSE Guidelines for Meta-Analyses and Systematic Reviews of Observational Studies and the Cochrane Handbook for Systematic Reviews of Interventions. We plan to systematically search Ovid MEDLINE, CINAHL, PsycINFO, EMB Review, EMBASE, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials and Google Scholar databases from their inception date to December 2023. Full-text primary studies that report measurable outcomes in adults with chronic pain, all routes of opioid use, all types of infections and all settings will be included. We will identify a scope of reported infections and the evidence on the association of opioid use (including specific opioid, dosage, formulation and duration of use) with the risk of negative infectious outcomes. Opioid use-associated outcomes, comparing opioid use with another opioid or a non-opioid medication, will be reported. The meta-analysis will incorporate individual risk factors. If data are insufficient, the results will be synthesised narratively. Publication bias and confounding evaluation will be performed. The Grading of Recommendations Assessment, Development and Evaluation framework will be used.

ETHICS AND DISSEMINATION

Approval for the use of published data is not required. The results will be published, presented at conferences and discussed in deliberative dialogue groups.

PROSPERO REGISTRATION NUMBER

CRD42023402812.

Serum cytokines and inflammatory proteins in individuals with heroin use disorder: potential mechanistically based biomarkers for diagnosis

Opioid use disorders cause major morbidity and mortality, and there is a pressing need for novel mechanistic targets and biomarkers for diagnosis and prognosis. Exposure to mu-opioid receptor (MOR) agonists causes changes in cytokine and inflammatory protein networks in peripheral blood, and also in brain glia and neurons. Individuals with heroin use disorder (iHUD) show dysregulated levels of several cytokines in the blood. However, there is limited data on a comprehensive panel of such markers in iHUD versus healthy controls (HC), especially considered as a multi-target biomarker. We used a validated proximity extension assay for the relative quantification of 92 cytokines and inflammatory proteins in the serum of iHUD on medication-assisted therapy (MAT; n = 21), compared to HC (n = 24). Twenty-nine targets showed significant group differences (primarily iHUD>HC), surviving multiple comparison corrections (p = 0.05). These targets included 19 members of canonical cytokine families, including specific chemokines, interleukins, growth factors, and tumor necrosis factor (TNF)-related proteins. For dimensionality reduction, data from these 19 cytokines were entered into a principal component (PC) analysis, with PC1 scores showing significant group differences (iHUD > HC; p < 0.0001). A receiver-operating characteristic (ROC) curve analysis yielded an AUROC = 91.7% (p < 0.0001). This PC1 score remained a positive predictor of being in the HUD group in a multivariable logistic regression, that included select demographic/clinical variables. Overall, this study shows a panel of cytokines that differ significantly between iHUD and HC, providing a multi-target "cytokine biomarker score" for potential diagnostic purposes, and future examination of disease severity.

Cryo-EM structure of small-molecule agonist bound delta opioid receptor-Gi complex enables discovery of biased compound

Delta opioid receptor (δOR) plays a pivotal role in modulating human sensation and emotion. It is an attractive target for drug discovery since, unlike Mu opioid receptor, it is associated with low risk of drug dependence. Despite its potential applications, the pharmacological properties of δOR, including the mechanisms of activation by small-molecule agonists and the complex signaling pathways it engages, as well as their relation to the potential side effects, remain poorly understood. In this study, we use cryo-electron microscopy (cryo-EM) to determine the structure of the δOR-Gi complex when bound to a small-molecule agonist (ADL5859). Moreover, we design a series of probes to examine the key receptor-ligand interaction site and identify a region involved in signaling bias. Using ADL06 as a chemical tool, we elucidate the relationship between the β-arrestin pathway of the δOR and its biological functions, such as analgesic tolerance and convulsion activities. Notably, we discover that the β-arrestin recruitment of δOR might be linked to reduced gastrointestinal motility. These insights enhance our understanding of δOR's structure, signaling pathways, and biological functions, paving the way for the structure-based drug discovery.

Impact of opioids and mu-opioid receptors on oncologic metastasis

Opioids are the most effective and widely used treatments for acute and chronic pain in patients with cancer. This review focuses on the impact of opioids and mu-opioid receptors (MORs) on the stages of oncologic metastasis. Studies have shown that opioids can facilitate tumor progression and are related to a poor prognosis in patients with cancer. As the primary receptor for opioids, MORs play a significant role in regulating malignant tumor transformation and are involved in processes, such as proliferation, angiogenesis, epithelial-mesenchymal transition (EMT), circulating tumor cells (CTCs) and the tumor microenvironment (TME). While clinical trials have investigated the relationship between opioids and patient prognosis, further research is needed to clarify the relationship between opioids, MORs and metastasis.

Why do patients with cancer die?

Cancer is a major cause of global mortality, both in affluent countries and increasingly in developing nations. Many patients with cancer experience reduced life expectancy and have metastatic disease at the time of death. However, the more precise causes of mortality and patient deterioration before death remain poorly understood. This scarcity of information, particularly the lack of mechanistic insights, presents a challenge for the development of novel treatment strategies to improve the quality of, and potentially extend, life for patients with late-stage cancer. In addition, earlier deployment of existing strategies to prolong quality of life is highly desirable. In this Roadmap, we review the proximal causes of mortality in patients with cancer and discuss current knowledge about the interconnections between mechanisms that contribute to mortality, before finally proposing new and improved avenues for data collection, research and the development of treatment strategies that may improve quality of life for patients.

A novel strategy to elicit enduring anti-morphine immunity and relief from addiction by targeting Acr1 protein nano vaccine through TLR-2 to dendritic cells

Morphine addiction poses a significant challenge to global healthcare. Current opioid substitution therapies, such as buprenorphine, naloxone and methadone are effective but often lead to dependence. Thus, exploring alternative treatments for opioid addiction is crucial. We have developed a novel vaccine that presents morphine and Pam3Cys (a TLR-2 agonist) on the surface of Acr1 nanoparticles. This vaccine has self-adjuvant properties and targets TLR-2 receptors on antigen-presenting cells, particularly dendritic cells. Our vaccination strategy promotes the proliferation and differentiation of morphine-specific B-cells and Acr1-reactive CD4 T-cells. Additionally, the vaccine elicited the production of high-affinity anti-morphine antibodies, effectively eliminating morphine from the bloodstream and brain in mice. It also reduced the expression of addiction-associated μ-opioid receptor and dopamine genes. The significant increase in memory CD4 T-cells and B-cells indicates the vaccine's ability to induce long-lasting immunity against morphine. This vaccine holds promise as a prophylactic measure against morphine addiction.

Enkephalins and Pain Modulation: Mechanisms of Action and Therapeutic Perspectives

Enkephalins, a subclass of endogenous opioid peptides, play a pivotal role in pain modulation. Enkephalins primarily exert their effects through opioid receptors located widely throughout both the central and peripheral nervous systems. This review will explore the mechanisms by which enkephalins produce analgesia, emotional regulation, neuroprotection, and other physiological effects. Furthermore, this review will analyze the involvement of enkephalins in the modulation of different pathologies characterized by severe pain. Understanding the complex role of enkephalins in pain processing provides valuable insight into potential therapeutic strategies for managing pain disorders.

Immune response and cytokine profiles in post-laminectomy pain syndrome: comparative analysis after treatment with intrathecal opioids, oral opioids, and non-opioid therapies

INTRODUCTION

This study explores the interaction between cytokines, cell-mediated immunity (T cells, B cells, and NK cells), and prolonged morphine administration in chronic neuropathic pain patients without cancer-related issues. Despite evidence of opioid immunomodulation, few studies have compared these interactions.

METHODS

In a cross-sectional and comparative study, 50 patients with chronic low back radicular pain ("Failed Back Surgery Syndrome") were categorized into intrathecal morphine infusion (IT group, n = 18), oral morphine (PO group, n = 17), and non-opioid treatment (NO group, n = 15). Various parameters, including plasma and cerebrospinal fluid (CSF) cytokine concentrations, lymphocyte immunophenotyping, opioid escalation indices, cumulative morphine dose, and treatment duration, were assessed.

RESULTS

CSF IL-8 and IL-1β concentrations exceeded plasma levels in all patients. No differences in T, B, and NK lymphocyte numbers were observed between morphine-treated and non-treated patients. Higher plasma IL-5 and GM-CSF concentrations were noted in IT and PO groups compared to NO. CSF IFNγ concentrations were higher in PO and NO than IT. Positive correlations included CD4 concentrations with opioid escalation indices, and negative correlations involved NK cell concentrations, CSF TNFα concentrations, and opioid escalation indices. Positive correlations were identified between certain cytokines and pain intensity in IT patients, and between NK cells and cumulative morphine dose. Negative correlations were observed between CSF IL-5 concentrations and pain intensity in IT and PO, and between opioid escalation indices and CSF cytokine concentrations in PO and IT.

CONCLUSION

Associations between cytokines, cellular immunity, and prolonged morphine treatment, administered orally and intrathecally were identified.

Comparisons of different general anesthetic techniques on immune function in patients undergoing flap reconstruction for oral cancer

BACKGROUND

Anesthetic-induced immunosuppression is of particular interest in tumor surgery. This study aimed to investigate the influence of the 4 most common general anesthetic techniques on immune function in patients undergoing flap reconstruction for oral cancer.

METHODS

116 patients were randomly divided into 4 groups. Patients in group S were given sevoflurane-based anesthesia. Group P was administered propofol-based anesthesia. The SD group received sevoflurane combined with dexmedetomidine anesthesia. The propofol combined with dexmedetomidine anesthesia (PD) group received PD. Blood samples were obtained at 5 time points: baseline (T0), 1 hour after the start of the operation (T1), end of the operation (T2), 24 hours (T3), and 48 hours (T4) after the operation. Lymphocyte subsets (including CD3+, CD4+, CD8+, and B lymphocytes) and dendritic cells were analyzed by flow cytometry. Blood glucose, norepinephrine, and cortisol levels were measured using ELISA and a blood gas analyzer respectively.

RESULTS

In total, 107 patients were included in the final analysis. Immunological indicators, except CD8+ counts, were all decreased in groups S, P, and SD at T1-4 compared with the baseline value, and the counts of CD3+, CD4+, and dendritic cells, as well as CD4+/CD8+ ratios, were significantly higher in the PD group than in the S, P, and SD at T1-3 (P < .05). There were no significant differences between groups P and SD at any observation time point. Intraoperative stress indices, including norepinephrine and cortisol levels, were significantly lower in the PD group than in the other 3 groups at T1-2 (P < .05).

CONCLUSION

These findings suggest that PD as a probably optimal choice can alleviate immunosuppression in patients undergoing flap reconstruction for oral cancer.

Effect of repeated intraperitoneal injections of different concentrations of oxycodone on immune function in mice

Background

The effect of oxycodone as an opioid receptor agonist on immune function is still controversial. In this study, we investigated the possible effects of oxycodone on immune function in mice and its possible mechanisms of action.

Methods

By repeated intraperitoneal injections of 25 mg/kg morphine and 5 mg/kg, 20 mg/kg, and 60 mg/kg oxycodone, we assessed possible changes in the number of splenic lymphocytes and inflammatory cytokines in the serum of mice. CD4+ T cells and CD8+ T cells were sorted from the spleen to observe whether the expression levels of opioid receptors and downstream signals were altered.

Results

Repeated administration of oxycodone at a dose above 20 mg/kg resulted in significant weight loss. Repeated administration of oxycodone exhibits significant dose-dependent reduction in CD4+ T cells, with little effect on CD8+ T cells and little effect on inflammatory cytokine levels. Low- and intermediate-dose oxycodone increased the mRNA expression level of MOR, KOR, and DOR to varying degrees. Moreover, oxycodone increases the mRNA expression levels of the TLR4 signaling pathway to varying degrees.

Conclusion

Repeated intraperitoneal injection of oxycodone induces immunosuppression in mice.

Injection Drug Use Alters Plasma Regulation of the B Cell Response

The opioid epidemic continues to be a major public health issue that includes millions of people who inject drugs (PWID). PWID have increased incidence of serious infections, including HIV as well as metabolic and inflammatory sequelae. We sought to discern the extent of systemic alterations in humoral immunity associated with injection drug use, including alterations in the plasma proteome and its regulation of B cell responsiveness. Comprehensive plasma proteomics analysis of HIV negative/hepatitis C negative individuals with a history of recent injection heroin use was performed using mass spectrometry and ELISA. The effects of plasma from PWID and healthy controls on the in vitro proliferation and transcriptional profile of B cell responses to stimulation were determined by flow cytometry and RNA-Seq. The plasma proteome of PWID was distinct from healthy control individuals, with numerous immune-related analytes significantly altered in PWID, including complement (C3, C5, C9), immunoglobulin (IgD, IgM, kappa light chain), and other inflammatory mediators (CXCL4, LPS binding protein, C-reactive protein). The plasma of PWID suppressed the in vitro proliferation of B cells. Transcriptome analysis indicated that PWID plasma treatment increased B cell receptor and CD40 signaling and shifted B cell differentiation from plasma cell-like toward germinal center B cell-like transcriptional profiles. These results indicate that the systemic inflammatory milieu is substantially altered in PWID and may impact their B cell responses.

Inflammation, Autoimmunity, and Infection in Fibromyalgia: A Narrative Review

Fibromyalgia (FM) is a chronic disease characterized by widespread musculoskeletal pain of unknown etiology. The condition is commonly associated with other symptoms, including fatigue, sleep disturbances, cognitive impairment, and depression. For this reason, FM is also referred to as FM syndrome. The nature of the pain is defined as nociplastic according to the latest international classification and is characterized by altered nervous sensitization both centrally and peripherally. Psychosocial conditions have traditionally been considered critical in the genesis of FM. However, recent studies in animal models and humans have provided new evidence in favor of an inflammatory and/or autoimmune pathogenesis. In support of this hypothesis are epidemiological data of an increased female prevalence, similar to that of autoimmune diseases, and the frequent association with immune-mediated inflammatory disorders. In addition, the observation of an increased incidence of this condition during long COVID revived the hypothesis of an infectious pathogenesis. This narrative review will, therefore, discuss the evidence supporting the immune-mediated pathogenesis of FM in light of the most current data available in the literature.

Serum cytokine and inflammatory markers in individuals with heroin use disorder: potential biomarkers for diagnosis and disease severity

Opioid use disorders cause major morbidity and mortality, and there is a pressing need for novel mechanistic targets and biomarkers for diagnosis and prognosis. Exposure to mu-opioid receptor (MOR) agonists causes changes in cytokine and inflammatory protein networks in peripheral blood, and also in brain glia and neurons. Individuals with heroin use disorder (iHUD) show dysregulated levels of several cytokines in blood. However, there is limited data on a comprehensive panel of such markers in iHUD versus healthy controls (HC), especially as a multi-target biomarker. We used a validated proximity extension assay for relative quantification of 92 cytokines and inflammatory proteins in serum of iHUD on medication assisted therapy (MAT; n=21), versus HC (n=24). Twenty-nine targets showed significant group differences (primarily iHUD>HC), surviving multiple comparison correction (p=0.05). This included 19 members of canonical cytokine families, including specific chemokines, interleukins, growth factors, and tumor necrosis factor (TNF)-related proteins. For dimensionality reduction, data from these 19 cytokines were entered into a principal component (PC) analysis, and PC1 scores were iHUD>HC (p<0.0001). A receiver-operating characteristic (ROC) curve analysis yielded an AUROC=91.7% (p<0.0001). This PC1 score remained a positive predictor of being in the HUD group in a multivariable logistic regression, which included demographic/clinical variables. Overall, this study shows a panel of cytokines that differ significantly between iHUD and HC, and provides a multi-target "cytokine biomarker score" for potential diagnostic purposes, and examination of disease severity.

Drug use and COVID-19 testing, vaccination, and infection among underserved, minority communities in Miami, Florida

The Coronavirus Disease 2019 (COVID-19) pandemic has disproportionately impacted people who use drugs (PWUD). This study explored relationships between drug use, COVID-19 testing, vaccination, and infection. This cross-sectional study was conducted in Miami, Florida between March 2021 and October 2022 as part of the National Institutes of Health (NIH) Rapid Acceleration of Diagnostics-Underserved Populations (RADx-UP) initiative and the Miami Adult Studies on HIV (MASH) cohort. Users of cannabis, cocaine/crack, heroin/fentanyl, methamphetamines, hallucinogens, and/or prescription drug misuse in the previous 12 months were considered PWUD. Sociodemographic data, COVID-19 testing history, and vaccination-related beliefs were self-reported. Vaccinations were confirmed with medical records and positivity was determined with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) testing. Statistical analyses included chi-square tests and logistic regression. Of 1,780 participants, median age was 57 years, 50.7% were male, 50.2% Non-Hispanic Black, and 66.0% reported an annual income less than $15,000. Nearly 28.0% used drugs. PWUD were less likely than non-users to self-report ever testing positive for SARS-CoV-2 (14.7% vs. 21.0%, p = 0.006). However, 2.6% of participants tested positive for SARS-CoV-2, with no significant differences between PWUD and non-users (3.7% vs. 2.2%, p = 0.076). PWUD were more likely than non-users to experience difficulties accessing testing (10.2% vs. 7.1%, p = 0.033), vaccine hesitancy (58.9% vs. 43.4%, p = 0.002) and had lower odds of receiving any dose of a COVID-19 vaccine compared to non-users (aOR, 0.63; 95% CI, 0.49-0.81; p<0.001). PWUD presented with greater difficulties accessing COVID-19 testing, greater vaccine hesitancy, and lower odds of vaccination. Testing and immunization plans that are tailored to the needs of PWUD and consider access, trust-building campaigns, and education may be needed.

Effect of Intraoperative Opioid Dose on Perioperative Neutrophil-to-Lymphocyte Ratio and Lymphocyte-to-Monocyte Ratio in Glioma

Background

The neutrophil-to-lymphocyte ratio (NLR) and lymphocyte-to-monocyte ratio (LMR) are inflammatory biomarkers. Until now, it is unknown the impact of opioid dosage on perioperative immunity in glioma patients. The aim of this study was to explore the effect of intraoperative opioid dosage on perioperative immune perturbations using NLR and LMR as inflammatory biomarkers and evaluate the correlation between inflammatory biomarkers and pathological grade of glioma.

Methods

The study included 208 patients with primary glioma who underwent glioma resection from February 2012 to November 2019 at Harbin Medical University Cancer Hospital. Complete blood count (CBC) was collected at 3 time points: one week before surgery, and 24 hours and one week after surgery. Patients were divided into high-dose and low-dose groups, based on the median value of intraoperative opioid dose. The relationships between perioperative NLR, LMR and intraoperative opioid dosage were analyzed using repeated measurement analysis of variance (ANOVA). Correlations between preoperative various factors and pathological grade were analyzed by Spearman analysis. Receiver operating characteristic (ROC) curves were performed to assess the predictive performance of the NLR and LMR for pathological grade.

Results

The NLR (P=0.020) and lower LMR (P=0.037) were statistically significant different between high-dose and low-dose groups one week after surgery. The area under the curve (AUC) of the NLR to identify poor diagnosis was 0.685, which was superior to the LMR (AUC: 0.607) and indicated a correlation between the NLR with pathological grade. The preoperative NLR (P=0.000), LMR (P=0.009), age (P=0.000) and tumor size (P=0.001) exhibited a significant correlation with the pathological grade of glioma.

Conclusion

Intraoperative opioids in the high-dose group were associated with higher NLR and lower LMR in postoperative glioma patients. The preoperative NLR and LMR demonstrated predictive value for distinguishing between high-grade and low-grade gliomas.

The opioid peptide leucine enkephalin modulates hypothalamic-hypophysial axis in the cichlid fish Oreochromis mossambicus

In vertebrates, opioid peptides are thought to be involved in the regulation of reproduction; however, the significance of enkephalins in testicular function remains unclear. We examined the influence of δ-opioid receptor agonist leucine enkephalin (L-ENK) on the hypophysial-testicular axis of the cichlid fish Oreochromis mossambicus. Treatment with a low dose of L-ENK (60 µg) caused a significant increase in the numbers of primary and secondary spermatocytes and early and late spermatids, concomitant with intense immunolabelling of testicular androgen receptors, but did not significantly alter serum luteinizing hormone (LH) and 11-ketotestosterone (11-KT) levels compared to those of controls. Nevertheless, treatment with a high dose of L-ENK (200 µg) caused a significant reduction in the numbers of secondary spermatocytes as well as late spermatids associated with marginal immunolabelling of androgen receptors and significantly lower concentrations of serum 11-KT and LH compared to controls. In addition, the serum cortisol level was not affected in low-dose L-ENK-treated fish, but its level was significantly increased in the high-dose L-ENK-treated group. Together, these findings indicate that a low dose of L-ENK stimulates the germ cells at the meiosis stage and promotes further stages of spermatogenesis, whereas a high concentration of L-ENK inhibits spermatogenesis at the advanced stages. This effect appears to be mediated through the suppression of testicular steroidogenesis and the reduction of LH release in the pituitary gland of tilapia. The findings also suggest that elevated L-ENK levels in teleosts may exert their inhibitory influence on the hypophysial-testicular axis via glucocorticoids.

Progress in the study of intestinal microbiota involved in morphine tolerance

Morphine is a widely used opioid for treatment of pain. The attendant problems including morphine tolerance and morphine dependence pose a major public health challenge. In recent years, there has been increasing interest in the gastrointestinal microbiota in many physiological and pathophysiological processes. The connectivity network between the gut microbiota and the brain is involved in multiple biological systems, and bidirectional communication between them is critical in gastrointestinal tract homeostasis, the central nervous system, and the microbial system. Many research have previously shown that morphine has a variety of effects on the gastrointestinal tract, but none have determined the function of intestinal microbiota in morphine tolerance. This study reviewed the mechanisms of morphine tolerance from the perspective of dysregulation of microbiota-gut-brain axis homeostasis, by summarizing the possible mechanisms originating from the gut that may affect morphine tolerance and the improvement of morphine tolerance through the gut microbiota.

The genetic susceptibility analysis of TAAR1 rs8192620 to methamphetamine and heroin abuse and its role in impulsivity

Abnormal genetic polymorphism of trace amine-associated receptor 1 (TAAR1) rs8192620 site has been confirmed to induce methamphetamine (MA) use and drug craving. However, the genetic susceptibility difference between MA addicts and heroin addicts is unknown. This study evaluated genetic heterogeneity of TAAR1 rs8192620 between MA and heroin addicts and elucidated whether rs8192620 genotypes associated with discrepancy in emotional impulsivity, which would help to instruct individualized treatment in addiction via acting on TAAR1 and evaluate risk of varied drug addiction. Participants consisting of gender-matched 63 MA and 71 heroin abusers were enrolled in the study. Due to mixed drug usage in some MA addicts, MA users were further subdivided into 41 only-MA (only MA taking) and 22 mixed-drug (Magu composed of about 20% MA and 70% caffeine) abusers. Via inter-individual single nucleotide polymorphism (SNP) analysis and two-sample t tests, respectively, the genotypic and Barratt Impulsiveness Scale-11 (BIS-11) scores differences between groups were completed. With following genotypic stratification, the differences in BIS-11 scores between groups were analyzed through two-sample t test. Individual SNP analysis showed significant differences in alleles distribution of rs8192620 between MA and heroin subjects (p = 0.019), even after Bonferroni correction. The TT homozygotes of rs8192620 dominated in MA participants, while C-containing genotypes in heroin (p = 0.026). There was no association of genotypes of TAAR1 rs8192620 with addicts' impulsivity. Our research indicates that the TAAR1 gene polymorphism might mediate the susceptibility discrepancy between MA and heroin abuse.

Problems with opioids - beyond misuse

The U.S. is grappling with an opioid epidemic, with millions of adults on long-term opioid therapy (LTOT). Although patients often report pain relief and improved daily function with opioids, research shows no significant differences in short-term outcomes between opioid and non-opioid users, as well as no long-term opioid benefits. This scoping review aims to identify lesser-known side effects of long-term opioid use and increase awareness of them, allowing healthcare providers and patients to better assess the risks and benefits of opioid use. Our data search from PubMed and Google Scholar used keywords related to opioids, chronic pain, hypogonadism, endocrinopathies, cancer progression, cardiovascular events, renovascular events, sleep disturbances, mood disorders and others, narrowing down to English-language full articles published from January 2018 to April 2023. This review emphasizes the probable serious adverse consequences of long-term opioid use on various body systems in patients with chronic pain. Given the lack of long-term benefits and significant adverse effects, our review underscores the critical need for healthcare providers to include these risks in discussions with patients when considering the long-term use of opioid therapy.

The Role of Opioid Receptor Antagonists in Regulation of Blood Pressure and T-Cell Activation in Mice Selected for High Analgesia Induced by Swim Stress

Opioid peptides and their G protein-coupled receptors are important regulators within the cardiovascular system, implicated in the modulation of both heart and vascular functions. It is known that naloxone-an opioid antagonist-may exert a hypertensive effect. Recent experimental and clinical evidence supports the important role of inflammatory mechanisms in hypertension. Since opioids may play a role in the regulation of both blood pressure and immune response, we studied these two processes in our model. We aimed to evaluate the effect of selective and non-selective opioid receptor antagonists on blood pressure and T-cell activation in a mouse model of high swim stress-induced analgesia. Blood pressure was measured before and during the infusion of opioid receptor antagonists using a non-invasive tail-cuff measurement system. To assess the activation of T-cells, flow cytometry was used. We discovered that the non-selective antagonism of the opioid system by naloxone caused a significant elevation of blood pressure. The selective antagonism of μ and κ but not δ opioid receptors significantly increased systolic blood pressure. Subsequently, a brief characterization of T-cell subsets was performed. We found that the blockade of μ and δ receptors is associated with the increased expression of CD69 on CD4 T-cells. Moreover, we observed an increase in the central memory CD4 and central memory CD8 T-cell populations after the δ opioid receptor blockade. The antagonism of the μ opioid receptor increased the CD8 effector and central memory T-cell populations.

Opioids and Immunosuppression: Clinical Evidence, Mechanisms of Action, and Potential Therapies

Background

In addition to the more well-known adverse effects of opioids, such as constipation, mounting evidence supports underlying immunosuppressive effects as well.

Methods

In this study, we provide a narrative review of preclinical and clinical evidence of opioid suppression of the immune system as well as possible considerations for therapies.

Results

In vitro and animal studies have shown clear effects of opioids on inflammatory cytokine expression, immune cell activity, and pathogen susceptibility. Observational data in humans have so far supported preclinical findings, with multiple reports of increased rates of infections in various settings of opioid use. However, the extent to which this risk is due to the impact of opioids on the immune system compared with other risk factors associated with opioid use remains uncertain. Considering the data showing immunosuppression and increased risk of infection with opioid use, measures are needed to mitigate this risk in patients who require ongoing treatment with opioids. In preclinical studies, administration of opioid receptor antagonists blocked the immunomodulatory effects of opioids.

Conclusions

As selective antagonists of peripheral opioid receptors, peripherally acting mu-opioid receptor (MOR) antagonists may be able to protect against immune impairment while still allowing for opioid analgesia. Future research is warranted to further investigate the relationship between opioids and infection risk as well as the potential application of peripherally acting MOR antagonists to counteract these risks.

Impact of anesthesia choice in cutaneous melanoma surgery

Invasive cutaneous melanoma is the most lethal skin cancer, but fortunately, the vast majority can be surgically treated with wide local excision, and sometimes additionally with sentinel or index lymph node biopsy for prognostication. Melanomas are particularly immunogenic malignancies, and preclinical studies have demonstrated that use of volatile anesthetics and opioids, unlike local agents, can suppress the immune system during the perioperative period. Immunosuppression has implications for creating a potentially favorable microenvironment for the survival and propagation of residual melanoma cells or micro-metastases, which could lead to disease relapse, both in the local tumor bed and distally. Results from observational clinical studies are mixed, but the literature would suggest that patients are at risk of decreased melanoma-specific survival after undergoing general anesthesia compared to regional anesthesia and spinal blocks. With the safety of close observation now established rather than automatic completion or total lymph node dissection for patients with either a positive sentinel lymph node biopsy or significant clinical response to neoadjuvant immunotherapy after index node sampling, the indications for definitive surgery with local or regional anesthesia have increased tremendously in recent years. Therefore, cutaneous melanoma patients might benefit from avoidance of general anesthesia and other perioperative drugs that suppress cell-mediated immunity if the option to circumvent systemic anesthesia agents is feasible.

Prenatal Opioid Exposure and Immune-Related Conditions in Children

Importance

Prenatal opioid exposure (POE) may alter with fetal development of the immune system, which may influence long-term health and susceptibility to immune-related conditions.

Objective

To compare the risk of hospitalization and emergency department presentation for immune-related conditions in children with and without POE.

Design, Setting, and Participants

This retrospective, population-based cohort study used linked administrative health records of all children born in Western Australia between January 1, 2003, and December 31, 2018 (N = 401 462).

Exposure

Prenatal exposure to prescription opioids (overall and by trimester), neonatal abstinence syndrome diagnosis, and opioid indication (pain or opioid use disorder [OUD]).

Main Outcomes and Measures

The main outcome was hospital admissions and emergency department presentations during which a child was diagnosed with an immune-related condition, including infections, conditions associated with an overactive immune system (eg, asthma, eczema, and allergy and anaphylaxis), and autoimmune diseases diagnosed before age 5 years or June 30, 2020. Data were analyzed between August 30, 2022, and February 27, 2023.

Results

Neonates with POE (1656 [0.4%]; mean [SD] gestational age, 37.7 [2.1] weeks; 836 females [50.5%]; 820 males [49.5%]) were more likely to be born preterm, have low birth weight for gestational age, and be coexposed to cigarette smoke compared with nonexposed neonates. Perinatal opioid exposure was associated with an increased risk of perinatal infection (adjusted odds ratio [AOR], 1.62; 95% CI, 1.38-1.90) and eczema and dermatitis (AOR, 11.91; 95% CI, 9.84-14.41) compared with nonexposure. Neonatal abstinence syndrome was also associated with both conditions (AOR, 2.91 [95% CI, 2.36-3.57] and 31.11 [95% CI, 24.64-39.28], respectively). Prenatal opioid exposure was also associated with an increased risk of childhood asthma (adjusted hazard ratio [AHR], 1.44; 95% CI, 1.16-1.79), but not allergies and anaphylaxis. It was also associated with an increased risk of childhood eczema and dermatitis, but only in children with POE from opioids used to treat OUD (AHR, 1.47; 95% CI, 1.08-1.99) rather than pain. In contrast, POE from opioids used for pain was associated with an increased risk of infection (AHR, 1.44; 95% CI, 1.32-1.58), but POE to opioids used to treat OUD was not. Autoimmune conditions were rare and were not observed to be associated with POE.

Conclusions and Relevance

In this cohort study, POE was associated with an increased risk of infection, eczema and dermatitis, and asthma, but not allergies and anaphylaxis or autoimmune conditions. These findings highlight the importance of further study of opioid-induced immune changes during pregnancy, the potential impact on long-term health in exposed children, and the mechanisms of opioid-induced immune dysregulation.

Comparative study of oral microbiota in the experimental long-term opioid exposure, after its withdrawal and the use of complex drug correction

OBJECTIVE

Aim: To study changes of dental biofilm microbiota composition during experimental opioid exposure, after its withdrawal and when using of complex drug correction..

PATIENTS AND METHODS

Materials and Methods: Microbiological studies (48 rats) included microscopic and bacteriological methods, as well as determination of antibiotic susceptibility of microbial isolates. Ceftriaxone and pentoxifylline were used to correction the changes.

RESULTS

Results: The action of opioid for 10 weeks caused considerable changes in the microbiocenosis, which was illustrated by a significant increasing of the opportunistic pathogens quantitative indicators and the emergence of pathogenic microbiota. Changes in the microbiocenosis at 6 weeks of opioid exposure and after its withdrawal for 4 weeks were expressed in the appearance of pathogenic microbiota and the absence of significant differences in quantitative indicators of saprophytic and opportunistic microflora compared to similar indicators in animals with 10 weeks opioid exposure. This indicated a slow progression of dysbiotic changes and the inflammatory process in the oral cavity of rats.

CONCLUSION

Conclusions: After 10 weeks of experiment with opioid administration for 6 weeks and the use of ceftriaxone and pentoxifylline on the background of 4-week opioid withdrawal, a significant reduction of quantitative indicators of opportunistic bacteria and elimination of pathogenic species of microorganisms was determined. The use of complex drug correction on the background of 10 weeks of opioid exposure led to a significant reduction in the quantitative indicators of opportunistic pathogens and contributed to the elimination of most pathogenic species of microbiota under the action of ceftriaxone.

Morphine-induced intestinal microbial dysbiosis drives TLR-dependent IgA targeting of gram-positive bacteria and upregulation of CD11b and TLR2 on a sub-population of IgA+ B cells

IgA binding dictates the composition of the intestinal microbiome and reflects dysbiotic states during chronic disease. Both pathogenic and commensal bacteria differentially bind to IgA with varying outcomes. Little is known regarding IgA dynamics immediately following microbial dysbiosis. Recent work shows that morphine treatment rapidly induces microbial dysbiosis within hours of administration. This microbial shift is characterized by the expansion of pathogenic bacteria with a concurrent decrease in commensal bacteria. Because of this rapid microbial shift, a murine model of chronic morphine treatment was used to gain insight on the host IgA response during early microbial disruption. Within 24 h, morphine treatment induces microbial dysbiosis which disrupts IgA-bacterial homeostasis, resulting in an increased concentration of unbound IgA with a corresponding decrease in the frequency of IgA-bound bacteria. Additionally, the increased concentration of unbound IgA is dependent on the microbiome, as microbial depletion abolishes the increase. At 48 h of morphine treatment, the frequency of IgA-bound bacteria increases and IgA-seq reveals increased IgA targeting of gram-positive bacteria. Both a whole-body TLR2 KO and treatment with the TLR inhibitor OxPAPC resulted in abrogation of IgA binding to bacteria, implicating modulation of IgA binding through TLR signaling. Finally, we identify that a sub-population of IgA+ B cells in the intestinal lamina propria has increased CD11b and TLR2 expression at 24 h of morphine treatment which could be a potential source of the observed IgA that targets gram-positive bacteria. Together, we demonstrate for the first time the role of TLR2 in IgA targeting of intestinal bacteria, and this study sheds light on the IgA dynamics during the initial hours of microbial dysbiosis.

The effect of morphine on rat microglial phagocytic activity: An in vitro study of brain region-, plating density-, sex-, morphine concentration-, and receptor-dependency

Opioids have long been used for clinical pain management, but also have addictive properties that have contributed to the ongoing opioid epidemic. While opioid activation of opioid receptors is well known to contribute to reward and reinforcement, data now also suggest that opioid activation of immune signaling via toll-like receptor 4 (TLR4) may also play a role in addiction-like processes. TLR4 expression is enriched in immune cells, and in the nervous system is primarily expressed in microglia. Microglial phagocytosis is important for developmental, homeostatic, and pathological processes. To examine how morphine impacts microglial phagocytosis, we isolated microglia from adult male and female rat cortex and striatum and plated them in vitro at 10,000 (10K) or 50,000 cells/well densities. Microglia were incubated with neutral fluorescent microbeads to stimulate phagocytosis in the presence of one of four morphine concentrations. We found that the brain region from which microglia are isolated and plating density, but not morphine concentration, impacts cell survival in vitro. We found that 10-12 M morphine, but not higher concentrations, increases phagocytosis in striatal microglia in vitro independent of sex and plating density, while 10-12 M morphine increased phagocytosis in cortical microglia in vitro independent of sex, but contingent on a plating density. Finally, we demonstrate that the effect of 10-12 M morphine in striatal microglia plated at 10 K density is mediated via TLR4, and not μORs. Overall, our data suggest that in rats, a morphine-TLR4 signaling pathway increases phagocytic activity in microglia independent of sex. This may is useful information for better understanding the possible neural outcomes associated with morphine exposures.

Buprenorphine and methadone differentially alter early brain development in human cortical organoids

Buprenorphine (BUP) and methadone (MTD) are used for medication-assisted treatment (MAT) in opioid use disorder. Although both medications show improved maternal and neonatal outcomes compared with illicit opioid use during pregnancy, BUP has exhibited more favorable outcomes to newborns than MTD. The underlying cellular and molecular mechanisms for the difference between BUP and MTD are largely unknown. Here, we examined the growth and neuronal activity in human cortical organoids (hCOs) exposed to BUP or MTD. We found that the growth of hCOs was significantly restricted in the MTD-treated but not in the BUP-treated hCOs and BUP attenuated the growth-restriction effect of MTD in hCOs. Furthermore, a κ-receptor agonist restricted while an antagonist alleviated the growth-restriction effect of MTD in hCOs. Since BUP is not only a μ-agonist but a κ-antagonist, the prevention of this growth-restriction by BUP is likely due to its κ-receptor-antagonism. In addition, using multielectrode array (MEA) technique, we discovered that both BUP and MTD inhibited neuronal activity in hCOs but BUP showed suppressive effects only at higher concentrations. Furthermore, κ-receptor antagonist nBNI did not prevent the MTD-induced suppression of neuronal activity in hCOs but the NMDA-antagonism of MTD (that BUP lacks) plays a role in the inhibition of neuronal activity. We conclude that, although both MTD and BUP are μ-opioid agonists, a) the additional κ-receptor antagonism of BUP mitigates the MTD-induced growth restriction during neurodevelopment and b) the lack of NMDA antagonism of BUP (in contrast to MTD) induces much less suppressive effect on neural network communications.