Implications of central immune signaling caused by drugs of abuse: mechanisms, mediators and new therapeutic approaches for prediction and treatment of drug dependence

Abstinent patients with alcohol use disorders show an altered plasma cytokine profile: Identification of both interleukin 6 and interleukin 17A as potential biomarkers of consumption and comorbid liver and pancreatic diseases

BACKGROUND

Recent studies have demonstrated that alcohol consumption can modulate the immune system by directly activating natural immunity and triggering inflammatory processes in the central nervous system and in peripheral organs, such as the liver and pancreas. Patients with alcohol use disorders have an elevated frequency of comorbid mental disorders and gut diseases (i.e. fatty liver and pancreatitis) that complicate diagnosis, treatment and prognosis.

AIMS

The present study aims to explore possible associations in circulating plasma cytokine concentrations in abstinent patients diagnosed with alcohol use disorders.

METHODS

To this end, 85 abstinent subjects with alcohol use disorders from an outpatient setting and 55 healthy subjects were evaluated for both substance and mental disorders. The plasma levels of cytokines interleukin 1 beta, interleukin 4, interleukin 6, interleukin 17A, interferon gamma and tumour necrosis alpha were determined and their association with (a) history of alcohol consumption, (b) psychiatric comorbidity and (c) liver/pancreas comorbidities was explored.

RESULTS

We found that plasma concentrations of interleukin 1 beta, interleukin 6 and tumour necrosis alpha were increased, whereas plasma concentrations of interleukin 4, interleukin 17A and interferon gamma were decreased in abstinent alcohol use disorder patients as compared with control subjects. Moreover, we found that changes in interleukin 6 and interleukin 17A plasma concentrations in alcohol use disorder patients were associated with the presence of liver and pancreatic diseases.

CONCLUSION

The present results suggest alcohol use disorder is associated with alterations of plasma cytokines, being interleukin 6 and interleukin 17A potential biomarkers of the presence of comorbidities of digestive organs. The clinical relevance of these findings is discussed in the context of alcohol-induced inflammatory processes.

The role of gut-immune-brain signaling in substance use disorders

Substance use disorders (SUDs) are debilitating neuropsychiatric conditions that exact enormous costs in terms of loss of life and individual suffering. While much progress has been made defining the neurocircuitry and intracellular signaling cascades that contribute to SUDs, these studies have yielded limited effective treatment options. This has prompted greater exploration of non-traditional targets in addiction. Emerging data suggest inputs from peripheral systems, such as the immune system and the gut microbiome, impact multiple neuropsychiatric diseases, including SUDs. Until recently the gut microbiome, peripheral immune system, and the CNS have been studied independently; however, current work shows the gut microbiome and immune system critically interact to modulate brain function. Additionally, the gut microbiome and immune system intimately regulate one another via extensive bidirectional communication. Accumulating evidence suggests an important role for gut-immune-brain communication in the pathogenesis of substance use disorders. Thus, a better understanding of gut-immune-brain signaling could yield important insight to addiction pathology and potential treatment options.

Region-dependent regulation of acute ethanol on γ oscillation in the rat hippocampal slices

BACKGROUND

Ethanol use disorders are a serious medical and public health problem in the world today. Acute ethanol intoxication can lead to cognitive dysfunction such as learning and memory impairment. Gamma oscillations (γ, 30-80 Hz) are synchronized rhythmic activity generated by population of neurons within local network, and closely related to learning and memory function. The hippocampus is a critical anatomic structure that supports learning and memory. On the grounds of structure and function, hippocampus can be divided into the intermediate (IH), the dorsal (DH), and ventral hippocampus (VH). The current study is the first to investigate the effects of acute ethanol on γ oscillations in these sub-regions of rat hippocampal slices.

METHODS

The sustained γ oscillations were induced by 200 nM kainate (KA) in the CA3c of IH, DH, and VH. When KA-induced γ oscillation reached the steady state, ethanol (50 mM or 100 mM) was applied and the effects of ethanol on γ oscillation power was measured in the slices sequentially sectioned from ventral to dorsal hippocampus of adult rats.

RESULTS

In the intermediate hippocampal slices, compared with control (KA only), ethanol (50 mM) caused 36.1 ± 3.9% decrease in γ power (p < 0.05, n = 10), while ethanol (100 mM) caused 55.3 ± 5.5% decrease in γ power (p < 0.001, n = 14). In the dorsal hippocampus, only ethanol (100 mM) caused 18.1 ± 8.6% decrease in γ power (p < 0.05, n = 12). However, in the ventral hippocampus, neither 50 mM nor 100 mM ethanol affected γ oscillation.

CONCLUSIONS

Our results demonstrate that ethanol may produce the differential suppression of γ oscillations in a dose-dependent manner in different sub-regions of hippocampus, suggesting that the modulation of ethanol on hippocampal γ oscillation is region-dependent.

The "Culture" of Pain Control: A Review of Opioid-Induced Dysbiosis (OID) in Antinociceptive Tolerance

It is increasingly recognized that chronic opioid use leads to maladaptive changes in the composition and localization of gut bacteria. Recently, this "opioid-induced dysbiosis" (OID) has been linked to antinociceptive tolerance development in preclinical models and may therefore identify promising targets for new opioid-sparing strategies. Such developments are critical to curb dose escalations in the clinical setting and combat the ongoing opioid epidemic. In this article, we review the existing literature that pertains to OID, including the current evidence regarding its qualitative nature, influence on antinociceptive tolerance, and future prospects. PERSPECTIVE: This article reviews the current literature on OID of gut bacteria, including its qualitative nature, influence on antinociceptive tolerance, and future prospects. This work may help identify targets for new opioid-sparing strategies.

Fentanyl self-administration impacts brain immune responses in male Sprague-Dawley rats

Opioid use disorder (OUD) affects over two million in the United States and is an increasing public health crisis. The abuse of fentanyl and the emergence of potent fentanyl derivatives increases the risk for the user to succumb to overdose, but also to develop OUD. While intense attention is currently focused on understanding the complexity of behaviors and neural functions that contribute to OUD, much remains to be discovered concerning the interactions of opioid intake with the immune response in the central nervous system (CNS). In the present studies, we tested the hypothesis that short-term abstinence from fentanyl self-administration associates with altered expression of innate immune markers. Male Sprague-Dawley rats were trained to self-administer fentanyl (0.0032 mg/kg/infusion) to stability followed by 24 h of abstinence. Several innate immune markers, as well as opioid receptors (ORs) and intracellular pattern recognition receptors (PRRs), were interrogated within nodes of the neurocircuitry involved in OUD processes, including the prefrontal cortex (PFC), nucleus accumbens (NAc), caudate putamen (CPu), hippocampus (HIP) and midbrain (MB). In the present study, few immune targets were impacted in the PFC and MB during short-term abstinence from fentanyl (relative to saline) self-administration. However, increased expression of cytokines [e.g., interleukin (IL)1β, IL5], chemokines [e.g., C-C motif chemokine 20 (MIP3α)], tumor necrosis factor α (TNFα) and interferon (IFN) proteins (e.g., IFNβ and IFNγ)] was seen in the NAc, while decreased expression of cytokines (e.g., several ILs), chemokines [e.g., granulocyte-macrophage colony-stimulating factor (GMCSF), monocyte chemoattractant protein (MCP) MCP1, MIP3α], the chemokine ligand 5 (RANTES) and interferons (e.g., IFNβ and IFNγ) in the HIP. Positive correlations were observed between cumulative fentanyl intake and expression of IL1β and IL6 in the NAc, and significant negative correlations with fentanyl intake and IFN β, IL2, IL5, IL12p70 and IL17 in the HIP. Few changes in OR expression was observed during early abstinence from fentanyl self-administration. Excitingly, the expression of the PRR, stimulator of interferon genes (STING) negatively correlated with cumulative fentanyl intake and significantly correlated to specific cytokines, chemokines and interferon proteins in the HIP. Although the CPu appears relatively invulnerable to changes in innate immune markers, the highest correlations between cumulative fentanyl intake with MAVS and/or STING was measured in the CPu. Our findings provide the first evidence of CNS innate immune responses and implicate STING as novel mechanistic targets of immunomodulation during short-term abstinence from fentanyl self-administration.

Activation of Melanocortin-4 Receptor by a Synthetic Agonist Inhibits Ethanolinduced Neuroinflammation in Rats

BACKGROUND

High ethanol intake induces a neuroinflammatory response resulting in the subsequent maintenance of chronic alcohol consumption. The melanocortin system plays a pivotal role in the modulation of alcohol consumption. Interestingly, it has been shown that the activation of melanocortin-4 receptor (MC4R) in the brain decreases the neuroinflammatory response in models of brain damage other than alcohol consumption, such as LPS-induced neuroinflammation, cerebral ischemia, glutamate excitotoxicity, and spinal cord injury.

OBJECTIVES

In this work, we aimed to study whether MC4R activation by a synthetic MC4R-agonist peptide prevents ethanol-induced neuroinflammation, and if alcohol consumption produces changes in MC4R expression in the hippocampus and hypothalamus.

METHODS

Ethanol-preferring Sprague Dawley rats were selected offering access to 20% ethanol on alternate days for 4 weeks (intermittent access protocol). After this time, animals were i.p. administered an MC4R agonist peptide in the last 2 days of the protocol. Then, the expression of the proinflammatory cytokines interleukin 6 (IL-6), interleukin 1-beta (IL-1β), and tumor necrosis factor-alpha (TNF-α) were measured in the hippocampus, hypothalamus and prefrontal cortex. It was also evaluated if ethanol intake produces alterations in the expression of MC4R in the hippocampus and the hypothalamus.

RESULTS

Alcohol consumption increased the expression of MC4R in the hippocampus and the hypothalamus. The administration of the MC4R agonist reduced IL-6, IL-1β and TNF-α levels in hippocampus, hypothalamus and prefrontal cortex, to those observed in control rats that did not drink alcohol.

CONCLUSION

High ethanol consumption produces an increase in the expression of MC4R in the hippocampus and hypothalamus. The administration of a synthetic MC4R-agonist peptide prevents neuroinflammation induced by alcohol consumption in the hippocampus, hypothalamus, and prefrontal cortex. These results could explain the effect of α-MSH and other synthetic MC4R agonists in decreasing alcohol intake through the reduction of the ethanol-induced inflammatory response in the brain.

Curcumin treatment attenuates alcohol-induced alterations in a mouse model of foetal alcohol spectrum disorders

Alcohol exposure during development produces physical and mental abnormalities in the foetus that result in long-term molecular adjustments in the brain, which could underlie the neurobehavioural deficits observed in individuals suffering from foetal alcohol spectrum disorders. In this study, we assessed the effects of curcumin on cognitive impairments caused by prenatal and lactational alcohol exposure (PLAE). Furthermore, we examined whether curcumin could counteract the molecular alterations that may underlie these behavioural impairments. We focused on inflammatory and epigenetic mechanisms by analysing the expression of pro-inflammatory mediators, such as IL-6, TNF-α, and NF-κB, in the hippocampus and prefrontal cortex, as well as microglia and astrocyte activation in the dentate gyrus. We also assessed the activity of histone acetyltransferase in these brain areas. To model binge alcohol drinking, we exposed pregnant C57BL/6 mice to a 20% v/v alcohol solution during gestation and lactation, with limited access periods. We treated male offspring with curcumin during postnatal days (PD28-35) and then evaluated their behaviour in adulthood (PD60). Our results showed that curcumin treatment during the peri-adolescence period improved the anxiety and memory deficits observed in PLAE mice. At the molecular level, we found enhanced histone acetyltransferase activity in mice subjected to PLAE that curcumin treatment could not reverse to baseline levels. These mice also showed increased expression of pro-inflammatory mediators, which could be rescued by curcumin treatment. They also displayed astrogliosis and microglia activation. Our study provides further evidence to support the use of curcumin as a therapeutic agent for counteracting behavioural and molecular alterations induced by PLAE.

Where Is Dopamine and how do Immune Cells See it?: Dopamine-Mediated Immune Cell Function in Health and Disease

Dopamine is well recognized as a neurotransmitter in the brain, and regulates critical functions in a variety of peripheral systems. Growing research has also shown that dopamine acts as an important regulator of immune function. Many immune cells express dopamine receptors and other dopamine related proteins, enabling them to actively respond to dopamine and suggesting that dopaminergic immunoregulation is an important part of proper immune function. A detailed understanding of the physiological concentrations of dopamine in specific regions of the human body, particularly in peripheral systems, is critical to the development of hypotheses and experiments examining the effects of physiologically relevant dopamine concentrations on immune cells. Unfortunately, the dopamine concentrations to which these immune cells would be exposed in different anatomical regions are not clear. To address this issue, this comprehensive review details the current information regarding concentrations of dopamine found in both the central nervous system and in many regions of the periphery. In addition, we discuss the immune cells present in each region, and how these could interact with dopamine in each compartment described. Finally, the review briefly addresses how changes in these dopamine concentrations could influence immune cell dysfunction in several disease states including Parkinson's disease, multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, as well as the collection of pathologies, cognitive and motor symptoms associated with HIV infection in the central nervous system, known as NeuroHIV. These data will improve our understanding of the interactions between the dopaminergic and immune systems during both homeostatic function and in disease, clarify the effects of existing dopaminergic drugs and promote the creation of new therapeutic strategies based on manipulating immune function through dopaminergic signaling. Graphical Abstract.

Cannabidiol modulates the expression of neuroinflammatory factors in stress- and drug-induced reinstatement of methamphetamine in extinguished rats

Methamphetamine (METH) is a highly potent and addictive psychostimulant that is frequently abused worldwide. Although the biggest challenge to the efficient treatment of drug dependence is relapse, its mechanism is completely unclear. Plenty of evidence suggests that inflammation contributes to drug-induced reward especially in brain regions that are involved in the reward system, but there is no document about relapse. Cannabidiol (CBD) is a nonpsychoactive cannabinoid that has powerful anti-inflammatory and immunosuppressive properties. A previous research in our laboratory has demonstrated that CBD prevents reinstatement of METH even in 24-hour rapid eye movement (REM) sleep-deprived (RSD) rats. The aim of this study was to assess whether CBD prevents reinstatement of METH through change of gene expression of cytokines such as interleukin-1β, interleukin-6, interleukin-10, and tumor necrosis factor α (TNF-α) in extinguished rats. Real-time polymerase chain reaction (PCR) was used in this research to assay gene expression of cytokines. We found that stress- and drug-induced reinstatement of METH enhanced mRNA expression of cytokines in the prefrontal cortex (PFC) and hippocampus. Furthermore, CBD treatment significantly reduced the mRNA expression of cytokines in the PFC and hippocampus, but CBD treatment in RSD rats increased expression of cytokines in the hippocampus. It seems that enhancement of cytokines leads to change in neurotransmission and so triggers reinstatement of METH.

Prenatal opioid exposure: The next neonatal neuroinflammatory disease

The rates of opioid use disorder during pregnancy have more than quadrupled in the last decade, resulting in numerous infants suffering exposure to opioids during the perinatal period, a critical period of central nervous system (CNS) development. Despite increasing use, the characterization and definition of the molecular and cellular mechanisms of the long-term neurodevelopmental impacts of opioid exposure commencing in utero remains incomplete. Thus, in consideration of the looming public health crisis stemming from the multitude of infants with prenatal opioid exposure entering school age, we undertook an investigation of the effects of perinatal methadone exposure in a novel preclinical model. Specifically, we examined the effects of opioids on the developing brain to elucidate mechanisms of putative neural cell injury, to identify diagnostic biomarkers and to guide clinical studies of outcome and follow-up. We hypothesized that methadone would induce a pronounced inflammatory profile in both dams and their pups, and be associated with immune system dysfunction, sustained CNS injury, and altered cognition and executive function into adulthood. This investigation was conducted using a combination of cellular, molecular, biochemical, and clinically translatable biomarker, imaging and cognitive assessment platforms. Data reveal that perinatal methadone exposure increases inflammatory cytokines in the neonatal peripheral circulation, and reprograms and primes the immune system through sustained peripheral immune hyperreactivity. In the brain, perinatal methadone exposure not only increases chemokines and cytokines throughout a crucial developmental period, but also alters microglia morphology consistent with activation, and upregulates TLR4 and MyD88 mRNA. This increase in neuroinflammation coincides with reduced myelin basic protein and altered neurofilament expression, as well as reduced structural coherence and significantly decreased fractional anisotropy on diffusion tensor imaging. In addition to this microstructural brain injury, adult rats exposed to methadone in the perinatal period have significant impairment in associative learning and executive control as assessed using touchscreen technology. Collectively, these data reveal a distinct systemic and neuroinflammatory signature associated with prenatal methadone exposure, suggestive of an altered CNS microenvironment, dysregulated developmental homeostasis, complex concurrent neural injury, and imaging and cognitive findings consistent with clinical literature. Further investigation is required to define appropriate therapies targeted at the neural injury and improve the long-term outcomes for this exceedingly vulnerable patient population.

Activation of Melanocortin-4 Receptor Inhibits Both Neuroinflammation Induced by Early Exposure to Ethanol and Subsequent Voluntary Alcohol Intake in Adulthood in Animal Models: Is BDNF the Key Mediator?

The concept that neuroinflammation induced by excessive alcohol intake in adolescence triggers brain mechanisms that perpetuate consumption has strengthened in recent years. The melanocortin system, composed of the melanocortin 4 receptor (MC4R) and its ligand α-melanocyte-stimulating hormone (α-MSH), has been implicated both in modulation of alcohol consumption and in ethanol-induced neuroinflammation decrease. Chronic alcohol consumption in adolescent rats causes a decrease in an α-MSH release by the hypothalamus, while the administration of synthetic agonists of MC4R causes a decrease in neuroinflammation and a decrease in voluntary alcohol consumption. However, the mechanism that connects the activation of MC4R with the decrease of both neuroinflammation and voluntary alcohol consumption has not been elucidated. Brain-derived neurotrophic factor (BDNF) has been implicated in alcohol drinking motivation, dependence and withdrawal, and its levels are reduced in alcoholics. Deficiencies in BDNF levels increased ethanol self-administration in rats. Further, BDNF triggers important anti-inflammatory effects in the brain, and this could be one of the mechanisms by which BDNF reduces chronic alcohol intake. Interestingly, MC4R signaling induces BDNF expression through the activation of the cAMP-responsive element-binding protein (CREB). We hypothesize that ethanol exposure during adolescence decreases the expression of α-MSH and hence MC4R signaling in the hippocampus, leading to a lower BDNF activity that causes dramatic changes in the brain (e.g., neuroinflammation and decreased neurogenesis) that predispose to maintain alcohol abuse until adulthood. The activation of MC4R either by α-MSH or by synthetic agonist peptides can induce the expression of BDNF, which would trigger several processes that lead to lower alcohol consumption.

Microglial activation increases cocaine self-administration following adolescent nicotine exposure

With the rise of e-cigarette use, teen nicotine exposure is becoming more widespread. Findings from clinical and preclinical studies show that the adolescent brain is particularly sensitive to nicotine. Animal studies have demonstrated that adolescent nicotine exposure increases reinforcement for cocaine and other drugs. However, the mechanisms that underlie these behaviors are poorly understood. Here, we report reactive microglia are critical regulators of nicotine-induced increases in adolescent cocaine self-administration. Nicotine has dichotomous, age-dependent effects on microglial morphology and immune transcript profiles. A multistep signaling mechanism involving D2 receptors and CX3CL1 mediates nicotine-induced increases in cocaine self-administration and microglial activation. Moreover, nicotine depletes presynaptic markers in a manner that is microglia-, D2- and CX3CL1-dependent. Taken together, we demonstrate that adolescent microglia are uniquely susceptible to perturbations by nicotine, necessary for nicotine-induced increases in cocaine-seeking, and that D2 receptors and CX3CL1 play a mechanistic role in these phenomena.

Adolescents are particularly sensitive to nicotine. Here the authors show that in mice, microglial activation contributes to the enhanced sensitivity to cocaine caused by nicotine exposure in young mice.

Cocaine-induced changes in CX3CL1 and inflammatory signaling pathways in the hippocampus: Association with IL1β

Cocaine induces neuroinflammatory response and interleukin-1 beta (IL1β) is suggested a final effector for many cocaine-induced inflammatory signals. Recently, the chemokine fractalkine (CX₃CL1) has been reported to regulate hippocampus-dependent neuroinflammation and synaptic plasticity via CX₃C-receptor 1 (CX₃CR1), but little is known about the impact of cocaine. This study is mainly focused on the characterization of CX₃CL1, IL1β and relevant inflammatory signal transduction pathways in the hippocampus in acute and repeated cocaine-treated male mice. Complementarily, the rewarding properties of cocaine were also assessed in Cx3cr1-knockout (KO) mice using a conditioned place preference (CPP). We observed significant increases in CX₃CL1 and IL1β concentrations after cocaine, although repeated cocaine produced an enhancement of CX₃CL1 concentrations. CX₃CL1 and IL1β concentrations were positively correlated in acute (r = +0.61) and repeated (r = +0.82) cocaine-treated mice. Inflammatory signal transduction pathways were assessed. Whereas acute cocaine-treated mice showed transient increases in p-ERK1/2/ERK1/2 and p-p65/p65 NFκB ratios after cocaine injection, repeated cocaine-treated mice showed transient increases in p-ERK1/2/ERK1/2, p-p38/p38 MAPK, p-NFκB p65/NF-κB p65 and p-CREB/CREB ratios. Baseline p-p38/p38 MAPK and p-CREB/CREB ratios were downregulated in repeated cocaine-treated mice. Regarding the cocaine-induced CPP, Cx3cr1-KO mice showed a notably impaired extinction but no differences during acquisition and reinstatement. These results indicate that cocaine induces alterations in CX₃CL1 concentrations, which are associated with IL1β concentrations, and activates convergent inflammatory pathways in the hippocampus. Furthermore, the CX₃CL1/CX₃CR1 signaling could mediate the processes involved in the extinction of cocaine-induced CPP.

Correlation between interleukin-6 levels and methadone maintenance therapy outcomes

BACKGROUND

The outcome of methadone maintenance therapy (MMT) varies in each patient with opioid use disorder (OUD). Opioid abuse activates proinflammatory processes by increasing cytokine production and impairing neurotrophic factor expression, and possibly leads to a vicious cycle that hinders recovery. Therefore, we investigated whether markers of inflammation and neurotrophic expression correlate with the MMT outcomes in OUD patients.

METHOD

We investigated OUD patients undergoing MMT and followed them up for 12 weeks. We measured plasma tumor necrosis factor (TNF)-α, C-reactive protein (CRP), interleukin (IL)-6, IL-1β, transforming growth factor (TGF)-β1, brain-derived neurotrophic factor (BDNF), urinary morphine tests, and plasma morphine levels at baseline and on weeks 1, 4, 8, and 12 during MMT. Multiple linear regressions and generalized estimating equations (GEEs) were used to examine the correlation between the cytokine and BDNF levels and MMT outcomes.

RESULTS

We initially enrolled 104 patients, but only 78 patients completed end-of-study assessments. Plasma levels of CRP, TGF-β1, and BDNF fell during MMT. Plasma IL-6 levels were significantly associated with plasma morphine levels (P = 0.005) and urinary morphine-positive (⁺) results (P = 0.04), and significantly associated with poor compliance (P = 0.009) and early dropout from MMT (P = 0.001). However, other cytokine and BDNF levels were not consistently associated with MMT outcomes.

CONCLUSION

Higher IL-6 levels were associated with poor MMT outcomes. Additional studies on regulating IL-6 expression to improve treatment outcomes in OUD patients might be warranted.

Cocaine Use Disorder Is Associated With Changes in Th1/Th2/Th17 Cytokines and Lymphocytes Subsets

Background: Cocaine is a psychostimulant drug with high addictive proprieties. Evidence suggests that cocaine use leads to critical changes in the immune system, with significant effects on T, B, and natural killer (NK) cells and influencing peripheral levels of cytokines. The presence of abstinence-related symptoms during detoxification treatment is known to influence the prognosis. Here, our aim was to investigate immune profiles in women with cocaine use disorder (CUD) according to withdrawal symptoms severity.

Methods: Blood samples and clinical data were collected at onset of detoxification treatment of 50 women with CUD. The patients were stratified according to Cocaine Selective Severity Assessment (CSSA) scores in low withdrawal (L-W) and high withdrawal (H-W) categories. In addition, we also included a control group with 19 healthy women as reference to immune parameters. Peripheral blood was collected and lymphocyte subsets were phenotyped by multi-color flow cytometry (B cells, CD4⁺ T, CD8⁺ T, NK cells, and different stages of T-cell differentiation). PBMCs from patients and healthy controls were stimulated in vitro with phytohemagglutinin (1%) for 72 h to assess the production of Th1/Th2/Th17 cytokines.

Results: Following stimulation, lymphocytes from women with CUD produced increased levels of Th1/Th2/Th17 cytokines. However, higher levels of IL-2 and IL-17 were observed only in the L-W group, while higher levels of IL-6 were detected in the H-W group compared to controls. H-W group showed lower percentage of early-differentiated Th cells (CD4⁺CD27⁺CD28⁺), elevated percentage of Th cells (CD3⁺CD4⁺), intermediate-differentiated Th cells (CD4⁺CD27⁻CD28⁺), and B cells (CD3⁻CD19⁺). Both CUD groups showed decreased percentages of naïve T cells (CD3⁺CD4⁺CD45RA⁺ and CD3⁺CD8⁺CD45RA⁺).

Conclusion: Our data demonstrated that CUD can lead to increased production of Th1/Th2/Th17 cytokines and lymphocyte changes.

Calcineurin signaling as a target for the treatment of alcohol abuse and neuroinflammatory disorders

Converging lines of evidence point to a significant role of neuroinflammation in a host of psychiatric conditions, including alcohol use disorder, TBI, and PTSD. A complex interaction of both peripheral and central signaling underlies processes involved in neuroinflammation. Calcineurin is a molecule that sits at the nexus of these processes and has been clearly linked to a number of psychiatric disorders including alcohol use disorder (AUD). Like its role in regulating peripheral immune cells, calcineurin (CN) plays an integral role in processes regulating neuroimmune function and neuroinflammatory processes. Targeting CN or elements of its signaling pathways at critical points may aid in the functional recovery from neuroinflammatory related disorders. In this review we will highlight the role of neuroinflammation and calcineurin signaling in AUD, TBI and stress-induced disorders and discuss recent findings demonstrating a therapeutic effect of immunosuppressant-induced calcineurin inhibition in a pre-clinical model of binge alcohol drinking.

Targeting neuroinflammation with minocycline in heavy drinkers

RATIONALE

Alcohol has both acute and chronic effects on neuroimmune signaling, including triggering pro-inflammatory cytokine release by microglia. Minocycline, a second-generation tetracycline antibiotic, inhibits microglial activation and reduces neuroinflammation in preclinical studies. In mice, minocycline also reduces ethanol intake, attenuates ethanol-induced conditioned place preference, and inhibits ethanol-induced microglial activation and pro-inflammatory cytokine release.

OBJECTIVE

Here, for the first time, we tested the effects of minocycline on subjective response to ethanol and acute ethanol-induced inflammation in humans.

METHODS

Forty-eight heavy drinkers participated in a double-blind, placebo-controlled trial in which they were randomized to receive placebo, 100 mg, or 200 mg of minocycline for 10 days. Each subject then underwent two experimental sessions in which they were given a fixed dose of intravenous ethanol using a "clamp" procedure (100 mg%) or placebo (normal saline) on days 8 and 10 of treatment.

RESULTS

Minocycline was well tolerated, but there was no effect of either dose of minocycline on subjective response to ethanol or ethanol-induced craving; minocycline effects on cognitive function seem to interact with age. Minocycline treatment did not alter serum cytokine levels at baseline or during ethanol-exposure, although certain baseline cytokine levels predict sedative response to ethanol.

CONCLUSION

These findings indicate that a short-term treatment with minocycline may not alter ethanol-related inflammation or subjective response to ethanol in humans. Further research is needed to identify pharmacological agents with robust effects on ethanol-induced inflammation to determine whether neuroimmune modulation represents a viable treatment strategy for alcohol use disorder.

A potential role for microglia in stress- and drug-induced plasticity in the nucleus accumbens: A mechanism for stress-induced vulnerability to substance use disorder

Stress is an important risk factor for the development of substance use disorder (SUD). Exposure to both stress and drugs abuse lead to changes in synaptic plasticity and stress-induced alterations in synaptic plasticity may contribute to later vulnerability to SUD. Recent developmental neuroscience studies have identified microglia as regulators of synaptic plasticity. As both stress and drugs of abuse lead to microglial activation, we propose this as a potential mechanism underlying their ability to change synaptic plasticity. This review focuses on three components of synaptic plasticity: spine density, brain-derived neurotrophic factor (BDNF) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor expression. Their roles in addiction, stress, and development will be reviewed, as well as possible mechanisms by which microglia could regulate their function. Potential links between stress, vulnerability to addiction, and microglial activity will be explored.

Stereochemistry and innate immune recognition: (+)-norbinaltorphimine targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling

Deregulation of innate immune TLR4 signaling contributes to various diseases including neuropathic pain and drug addiction. Naltrexone is one of the rare TLR4 antagonists with good blood-brain barrier permeability and showing no stereoselectivity for TLR4. By linking 2 naltrexone units through a rigid pyrrole spacer, the bivalent ligand norbinaltorphimine was formed. Interestingly, (+)-norbinaltorphimine [(+)-1] showed ∼25 times better TLR4 antagonist activity than naltrexone in microglial BV-2 cell line, whereas (-)-norbinaltorphimine [(-)-1] lost TLR4 activity. The enantioselectivity of norbinaltorphimine was further confirmed in primary microglia, astrocytes, and macrophages. The activities of meso isomer of norbinaltorphimine and the molecular dynamic simulation results demonstrate that the stereochemistry of (+)-1 is derived from the (+)-naltrexone pharmacophore. Moreover, (+)-1 significantly increased and prolonged morphine analgesia in vivo. The efficacy of (+)-1 is long lasting. This is the first report showing enantioselective modulation of the innate immune TLR signaling.-Zhang, X., Peng, Y., Grace, P. M., Metcalf, M. D., Kwilasz, A. J., Wang, Y., Zhang, T., Wu, S., Selfridge, B. R., Portoghese, P. S., Rice, K. C., Watkins, L. R., Hutchinson, M. R., Wang, X. Stereochemistry and innate immune recognition: (+)-norbinaltorphimine targets myeloid differentiation protein 2 and inhibits toll-like receptor 4 signaling.

Single-Cell Glia and Neuron Gene Expression in the Central Amygdala in Opioid Withdrawal Suggests Inflammation With Correlated Gut Dysbiosis

Drug-seeking in opioid dependence is due in part to the severe negative emotion associated with the withdrawal syndrome. It is well-established that negative emotional states emerge from activity in the amygdala. More recently, gut microflora have been shown to contribute substantially to such emotions. We measured gene expression in single glia and neurons gathered from the amygdala using laser capture microdissection and simultaneously measured gut microflora in morphine-dependent and withdrawn rats to investigate drivers of negative emotion in opioid withdrawal. We found that neuroinflammatory genes, notably Tnf, were upregulated in the withdrawal condition and that astrocytes, in particular, were highly active. We also observe a decreased Firmicutes to Bacteroides ratio in opioid withdrawal indicating gut dysbiosis. We speculate that these inflammatory and gut microflora changes contribute to the negative emotion experienced in opioid withdrawal that motivates dependence.

Members of the same pharmacological family are not alike: Different opioids, different consequences, hope for the opioid crisis?

Pain management is the specialized medical practice of modulating pain perception and thus easing the suffering and improving the life quality of individuals suffering from painful conditions. Since this requires the modulation of the activity of endogenous systems involved in pain perception, and given the large role that the opioidergic system plays in pain perception, opioids are currently the most effective pain treatment available and are likely to remain relevant for the foreseeable future. This contributes to the rise in opioid use, misuse, and overdose death, which is currently characterized by public health officials in the United States as an epidemic. Historically, the majority of preclinical rodent studies were focused on morphine. This has resulted in our understanding of opioids in general being highly biased by our knowledge of morphine specifically. However, recent in vitro studies suggest that direct extrapolation of research findings from morphine to other opioids is likely to be flawed. Notably, these studies suggest that different opioid analgesics (opioid agonists) engage different downstream signaling effects within the cell, despite binding to and activating the same receptors. This recognition implies that, in contrast to the historical status quo, different opioids cannot be made equivalent by merely dose adjustment. Notably, even at equianalgesic doses, different opioids could result in different beneficial and risk outcomes. In order to foster further translational research regarding drug-specific differences among opioids, here we review basic research elucidating differences among opioids in pharmacokinetics, pharmacodynamics, their capacity for second messenger pathway activation, and their interactions with the immune system and the dopamine D2 receptors.

Imaging Biomarkers of the Neuroimmune System among Substance Use Disorders: A Systematic Review

There is tremendous interest in the role of the neuroimmune system and inflammatory processes in substance use disorders (SUDs). Imaging biomarkers of the neuroimmune system in vivo provide a vital translational bridge between preclinical and clinical research. Herein, we examine two imaging techniques that measure putative indices of the neuroimmune system and review their application among SUDs. Positron emission tomography (PET) imaging of 18 kDa translocator protein availability is a marker associated with microglia. Proton magnetic resonance spectroscopy quantification of myo-inositol levels is a putative glial marker found in astrocytes. Neuroinflammatory responses are initiated and maintained by microglia and astrocytes, and thus represent important imaging markers. The goal of this review is to summarize neuroimaging findings from the substance use literature that report data using these markers and discuss possible mechanisms of action. The extant literature indicates abused substances exert diverse and complex neuroimmune effects. Moreover, drug effects may change across addiction stages, i.e. the neuroimmune effects of acute drug administration may differ from chronic use. This burgeoning field has considerable potential to improve our understanding and treatment of SUDs. Future research is needed to determine how targeting the neuroimmune system may improve treatment outcomes.

A comparison of hippocampal microglial responses in aged and young rodents following dependent and non-dependent binge drinking

Alcoholism is a highly visible and prevalent issue in the United States. Although binge-drinking is assumed to be a college-age problem, older adults (ages 65+) consume binge amounts of alcohol and have alcohol use disorders (AUDs). Moreover, individuals with alcohol dependence in their youth often continue to drink as they age. As such, this study tested the hypothesis that the effects of alcohol on hippocampal microglia are exacerbated in aged versus younger rodents in two AUD models. Briefly, adult (2-3 months) and aged (15+ months) Sprague-Dawley rats were administered alcohol or control diet using the Majchrowicz model to study alcohol-induced neurodegeneration. To study the effects of non-dependent binge consumption on microglia, adolescent (6-8 weeks) and aged (18+ months) C57/BL6N were subjected to the Drinking in the Dark paradigm. Microglia number and densitometry were assessed using immunohistochemistry. Hippocampal subregional and model/species-specific effects of alcohol were observed, but overall, aging did not appear to increase the alcohol-induced microglia reactivity as measured by Iba-1 densitometry. However, analysis of microglial counts revealed a significant decrease in the number microglia cells in both the alcohol-induced neurodegeneration and DID model across age groups. In the dentate gyrus, the loss of microglia was exacerbated by aging, particularly in mice after DID, non-dependent model. Using qRT-PCR, the persistence of alcohol and aging effects was assessed following the DID model. Allograft Inflammatory Factor 1 mRNA was increased in both young and aged mice by alcohol exposure; however, only in the aged mice did the alcohol effect persist. Overall, these data imply that the microglial response to alcohol is complex with evidence of depressed numbers of microglia but also increased reactivity with advanced age.

Indomethacin blocks the increased conditioned rewarding effects of cocaine induced by repeated social defeat

It is well established that repeated social defeat stress can induce negative long-term consequences such as increased anxiety-like behavior and enhances the reinforcing effect of psychostimulants in rodents. In the current study, we evaluated how the immune system may play a role in these long-term effects of stress. A total of 148 OF1 mice were divided into different experimental groups according to stress condition (exploration or social defeat) and pre-treatment (saline, 5 or 10 mg/kg of the anti-inflammatory indomethacin) before each social defeat or exploration episode. Three weeks after the last social defeat, anxiety was evaluated using an elevated plus maze paradigm. After this test, conditioned place preference (CPP) was induced by a subthreshold dose of cocaine (1 mg/kg). Biological samples were taken four hours after the first and the fourth social defeat, 3 weeks after the last defeat episode, and after the CPP procedure. Plasma and brain tissue (prefrontal cortex, striatum and hippocampus) were used to determine the levels of the pro-inflammatory cytokine interleukin 6 (IL-6). Results showed an increase of peripheral and brain IL-6 levels after the first and fourth social defeat that was reverted three weeks later. Intraperitoneal administration of the anti-inflammatory drug indomethacin before each episode of stress prevented this enhancement of IL-6 levels and also reversed the increase in the rewarding effects of cocaine in defeated mice. Conversely, this protective effect was not observed with respect to the anxiogenic consequences of social stress. Our results confirm the hypothesis of a modulatory proinflammatory contribution to stress-induced vulnerability to drug abuse disorders and highlight anti-inflammatory interventions as a potential therapeutic tool to treat stress-related addiction disorders.

The Toll-Like Receptor 3 Agonist Poly(I:C) Induces Rapid and Lasting Changes in Gene Expression Related to Glutamatergic Function and Increases Ethanol Self-Administration in Rats

BACKGROUND

Growing evidence suggests that neuroimmune signaling via Toll-like receptors (TLRs) alters brain circuitry related to alcohol use disorders. Both ethanol (EtOH) exposure and the TLR3 agonist, poly(I:C), increase brain TLR3 expression in neurons and glia. Furthermore, previous studies have shown that cortical TLR3 expression is correlated with lifetime EtOH intake in humans.

METHODS

The current experiments investigated the consequences of poly(I:C) treatment on gene expression in 2 brain regions contributing to alcohol reinforcement, the insular cortex (IC) and nucleus accumbens (Acb) and on operant EtOH self-administration, in Long Evans rats.

RESULTS

TLR3 activation increased mRNA levels of neuroimmune genes (TLR3, COX2), glutamatergic genes (mGluR2, mGluR3, GLT1), and the trophic factor BDNF in Acb and IC. Furthermore, increases in each of these genes were correlated with increases in TLR3 mRNA, suggesting that TLR3 induction of these genes may impact excitatory transmission in IC and Acb. TLR3 activation also increased EtOH self-administration 18 days postinjection and enhanced the effects of the mGluR2/3 agonist LY379268 to reduce EtOH self-administration following poly(I:C).

CONCLUSIONS

Together, these findings suggest lasting consequences of TLR3 activation on gene expression including increases in Group II mGluRs in the Acb. Furthermore, we show an important role for TLR3 signaling in EtOH intake, and a functional involvement of Group II mGluRs.

Anhedonia in cocaine use disorder is associated with inflammatory gene expression

Treatments for Cocaine Use Disorder (CUD) are variably effective, and there are no FDA-approved medications. One approach to developing new treatments for CUD may be to investigate and target poor prognostic signs. One such sign is anhedonia (i.e. a loss of pleasure or interest in non-drug rewards), which predicts worse outcomes in existing CUD treatments. Inflammation is thought to underlie anhedonia in many other disorders, but the relationship between anhedonia and inflammation has not been investigated in CUD. Therefore, we assessed peripheral genome-wide gene expression in n = 48 individuals with CUD with high (n = 24) vs. low (n = 24) levels of anhedonia, defined by a median split of self-reported anhedonia. Our hypothesis was that individuals with high anhedonia would show differential gene expression in inflammatory pathways. No individual genes were significantly different between the low and high anhedonia groups when using t-tests with a stringent false discovery rate correction (FDR-corrected p < 0.05). However, an exploratory analysis identified 166 loci where t-tests suggested group differences at a nominal p < 0.05. We used DAVID, a bioinformatics tool that provides functional interpretations of complex lists of genes, to examine representation of this gene list in known pathways. It confirmed that mechanisms related to immunity were the top significant associations with anhedonia in the sample. Further, the two top differentially expressed genes in our sample, IRF1 and GBP5, both have primary inflammation and immune functions, and were significantly negatively correlated with total scores on our self-report of anhedonia across all 48 subjects. These results suggest that prioritizing development of anti-inflammatory medications for CUD may pay dividends, particularly in combination with treatment-matching strategies using either phenotypic measures of anhedonia or biomarkers of inflammatory gene expression to individualize treatment.

Differential effect of the DRD3 genotype on inflammatory cytokine responses during abstinence in amphetamine-dependent women

Amphetamine exposure impacts on innate and adaptive immunity and DRD3 may modulate the effect of amphetamine on the immune response. We assessed the immune-cytokine markers in 72 female patients with amphetamine dependence (AD) at baseline and after 4-week drug abstinence and in 51 healthy women. Multiplex magnetic bead assay was used to measure the plasma cytokine expression level simultaneously in all participants and DRD3 rs6280 polymorphism was genotyped in patients. We demonstrated an increase of the T helper 1 (Th1) cytokines (IL-2), Th2 cytokines (IL-4, IL-5, IL-6 and IL-10) and other cytokines (IL-1β) in the entire AD cohort. A similar cytokine pattern, along with a significantly decreased IL-8 and IL-10 levels was observed after 4-week abstinence. Among AD patients with DRD3 rs6280 TT genotype, the cytokine expression profile was consistent with total AD cohort at baseline and revealed a significant down-regulated plasma level of the Th1, Th2, and other cytokines except for IL-6 after 4-week abstinence. In AD group with DRD3 rs6280 C allele carrier, we found IL-2 level was significantly higher than healthy controls at baseline and remained higher, accompanied with a borderline increase in IL-4, IL-6 and IL-1β levels after 4-week abstinence. Our results suggest that chronic use of amphetamine increased both pro- and anti-inflammatory cytokines in AD patients, indicating the immune imbalance that may persist for 4 weeks or more. Besides, DRD3 rs6280 TT genotype may be associated with favorable recovery in general inflammatory cytokines during period of abstinence.

Glial mechanisms underlying substance use disorders

Addiction is a devastating disorder that produces persistent maladaptive changes to the central nervous system, including glial cells. Although there is an extensive body of literature examining the neuronal mechanisms of substance use disorders, effective therapies remain elusive. Glia, particularly microglia and astrocytes, have an emerging and meaningful role in a variety of processes beyond inflammation and immune surveillance, and may represent a promising therapeutic target. Indeed, glia actively modulate neurotransmission, synaptic connectivity and neural circuit function, and are critically poised to contribute to addictive-like brain states and behaviors. In this review, we argue that glia influence the cellular, molecular, and synaptic changes that occur in neurons following drug exposure, and that this cellular relationship is critically modified following drug exposure. We discuss direct actions of abused drugs on glial function through immune receptors, such as Toll-like receptor 4, as well as other mechanisms. We highlight how drugs of abuse affect glia-neural communication, and the profound effects that glial-derived factors have on neuronal excitability, structure, and function. Recent research demonstrates that glia have brain region-specific functions, and glia in different brain regions have distinct contributions to drug-associated behaviors. We will also evaluate the evidence demonstrating that glial activation is essential for drug reward and drug-induced dopamine release, and highlight clinical evidence showing that glial mechanisms contribute to drug abuse liability. In this review, we synthesize the extensive evidence that glia have a unique, pivotal, and underappreciated role in the development and maintenance of addiction.

Can neuroimmune mechanisms explain the link between ultraviolet light (UV) exposure and addictive behavior?

High ultraviolet (UV) light exposure on the skin acts as a reinforcing stimulus, increasing sun-seeking behavior and even addiction-like sun seeking behavior. However, the physiological mechanisms that underlie this process remain to be defined. Here, we propose a novel hypothesis that neuroimmune signaling, arising from inflammatory responses in UV-damaged skin cells, causes potentiated signaling within the cortico-mesolimbic pathway, leading to increased sun-seeking behaviors. This hypothesized UV-induced, skin-to-brain signaling depends upon cell stress signals, termed alarmins, reaching the circulation, thereby triggering the activation of innate immune receptors, such as toll-like receptors (TLRs). This innate immune response is hypothesized to occur both peripherally and centrally, with the downstream signaling from TLR activation affecting both the endogenous opioid system and the mesolimbic dopamine pathway. As both neurotransmitter systems play a key role in the development of addiction behaviors through their actions at key brain regions, such as the nucleus accumbens (NAc), we hypothesize a novel connection between UV-induced inflammation and the activation of pathways that contribute to the development of addiction. This paper is a review of the existing literature to examine the evidence which suggests that chronic sun tanning resembles a behavioral addiction and proposes a novel pathway by which persistent sun-seeking behavior could affect brain neurochemistry in a manner similar to that of repeated drug use.

Correlation of cytokines, BDNF levels, and memory function in patients with opioid use disorder undergoing methadone maintenance treatment

BACKGROUND

Patients with opioid use disorder (OUD) show memory deficiencies and impaired treatment outcomes. Emerging evidence suggests that opioid abuse activates proinflammatory processes by increasing cytokine production and impairing neuroprotection, which damages the memory function in OUD patients. Therefore, we investigated whether plasma-based inflammatory and neurotrophic markers correlate with memory function in OUD patients.

METHOD

OUD patients undergoing methadone maintenance therapy (MMT) were investigated and followed up for 12 weeks. Plasma tumor necrosis factor (TNF)-α, C-reactive protein (CRP), interleukin (IL)-6, transforming growth factor (TGF)-β1, brain-derived neurotrophic factor (BDNF) levels, and Wechsler Memory Scale-Revised (WMS-R) scores were assessed at baseline and after 12 weeks of MMT. Multiple linear regressions and generalized estimating equations (GEEs) were used to examine the correlation between cytokines and memory performance.

RESULTS

We enrolled 89 patients at baseline; 47 patients completed the end-of-study assessments. Although Pearson correlations showed that CRP and TGF-β1 levels were significantly, negatively associated with some memory indices, the results were not significant after correction. The GEE results, controlled for several confounding factors and multiple testing, showed that changes in TNF-α levels were negatively correlated with changes in the visual memory index (P = 0.01), and that changes in IL-6 levels were negatively correlated with changes in the verbal memory index (P = 0.009).

CONCLUSION

Memory performance, TNF-α, and IL-6 levels in OUD patients were negative correlated. Additional studies on regulating TNF-α and IL-6 expression to improve memory function in OUD patients might be warranted.

A Pharmacological Rationale to Reduce the Incidence of Opioid Induced Tolerance and Hyperalgesia: A Review

Chronic pain is an important health and social problem. Misuse and abuse of opioids in chronic non-cancer pain management seem to be a huge problem, in some countries. This could probably affect the normal use of such analgesics in patients in need of them. Basic and clinical researches should find the solution to mitigate the potential damage. Dysregulation of mast cell and microglia activation plays an important role in the pathogenesis and management of chronic pain. Persistent mast cell activation sensitizes nociceptors and initiates central nervous system inflammatory processes, involving microglial cell activation and sensitization of spinal somatosensory neurons. Exposure of mast cells and microglia to opioids is well known to provoke activation of these non-neuronal immune cell populations, thereby contributing to an exacerbation of pro-inflammatory and pro-nociceptive processes and promoting, over the long-term, opioid-induced hyperalgesia and tolerance. This review is intended to provide the reader with an overview of the role for these non-neuronal cells in opioid-induced chronic pain and tolerance as a consequence of prolonged exposure to these drugs. In addition, we will examine a potential strategy with the aim to modulate opioid-induced over-activation of glia and mast cells, based on endogenous defense mechanisms and fatty acid amide signaling molecules.

Toll-like receptor 3 modulates the behavioral effects of cocaine in mice

BACKGROUND

The nucleus accumbens in the midbrain dopamine limbic system plays a key role in cocaine addiction. Toll-like receptors (TLRs) are important pattern-recognition receptors (PPRs) in the innate immune system that are also involved in drug dependence; however, the detailed mechanism is largely unknown.

METHODS

The present study was designed to investigate the potential role of TLR3 in cocaine addiction. Cocaine-induced conditioned place preference (CPP), locomotor activity, and self-administration were used to determine the effects of TLR3 in the rewarding properties of cocaine. Lentivirus-mediated re-expression of Tlr3 (LV-TLR3) was applied to determine if restoration of TLR3 expression in the NAc is sufficient to restore the cocaine effect in TLR3^-/- mice. The protein levels of phospho-NF-κB p65, IKKβ, and p-IκBα both in the cytoplasm and nucleus of cocaine-induced CPP mice were detected by Western blot.

RESULTS

We showed that both TLR3 deficiency and intra-NAc injection of TLR3 inhibitors significantly attenuated cocaine-induced CPP, locomotor activity, and self-administration in mice. Importantly, the TLR3^-/- mice that received intra-NAc injection of LV-TLR3 displayed significant increases in cocaine-induced CPP and locomotor activity. Finally, we found that TLR3 inhibitor reverted cocaine-induced upregulation of phospho-NF-κB p65, IKKβ, and p-IκBα.

CONCLUSIONS

Taken together, our results describe that TLR3 modulates cocaine-induced behaviors and provide further evidence supporting a role for central pro-inflammatory immune signaling in drug reward. We propose that TLR3 blockade could be a novel approach to treat cocaine addiction.

Intravenous administration of anti-inflammatory mesenchymal stem cell spheroids reduces chronic alcohol intake and abolishes binge-drinking

Chronic alcohol intake leads to neuroinflammation and astrocyte dysfunction, proposed to perpetuate alcohol consumption and to promote conditioned relapse-like binge drinking. In the present study, human mesenchymal stem cells (MSCs) were cultured in 3D-conditions to generate MSC-spheroids, which greatly increased MSCs anti-inflammatory ability and reduced cell volume by 90% versus conventionally 2D-cultured MSCs, enabling their intravenous administration and access to the brain. It is shown, in an animal model of chronic ethanol intake and relapse-drinking, that both the intravenous and intra-cerebroventricular administration of a single dose of MSC-spheroids inhibited chronic ethanol intake and relapse-like drinking by 80–90%, displaying significant effects over 3–5 weeks. The MSC-spheroid administration fully normalized alcohol-induced neuroinflammation, as shown by a reduced astrocyte activation, and markedly increased the levels of the astrocyte Na-glutamate (GLT-1) transporter. This research suggests that the intravenous administration of MSC-spheroids may constitute an effective new approach for the treatment of alcohol-use disorders.

MHC class I in dopaminergic neurons suppresses relapse to reward seeking

Major histocompatibility complex class I (MHCI) is an important immune protein that is expressed in various brain regions, with its deficiency leading to extensive synaptic transmission that results in learning and memory deficits. Although MHCI is highly expressed in dopaminergic neurons, its role in these neurons has not been examined. We show that MHCI expressed in dopaminergic neurons plays a key role in suppressing reward-seeking behavior. In wild-type mice, cocaine self-administration caused persistent reduction of MHCI specifically in dopaminergic neurons, which was accompanied by enhanced glutamatergic synaptic transmission and relapse to cocaine seeking. Functional MHCI knockout promoted this addictive phenotype for cocaine and a natural reward, namely, sucrose. In contrast, wild-type mice overexpressing a major MHCI gene (H2D) in dopaminergic neurons showed suppressed cocaine seeking. These results show that persistent cocaine-induced reduction of MHCI in dopaminergic neurons is necessary for relapse to cocaine seeking.

Central Administration of Cyclosporine A Decreases Ethanol Drinking

Aims

Abstinence among alcohol dependent liver graft recipients is remarkably high. The routine use of anti-immune agents in these patients led to rodent studies showing that immunosuppressants acting through inhibition of calcineurin (CLN) are highly effective in decreasing alcohol consumption. It remained unclear, however, whether the decreased alcohol consumption in rodent models is mediated through peripheral suppression of immune response or centrally through direct inhibition of cyclophilin-CLN in the brain. We tested the hypothesis that direct brain inhibition of CLN with intracerebroventricular (ICV) injections of the immunosuppressant cyclosporine A (CsA) is sufficient to decrease ethanol consumption in a rodent model of binge-like drinking.

Methods

Male C57BL/6NHsd mice were put through a modified 'drinking in the dark' (DID) paradigm. Effects of both peripheral (IP) and central (ICV) injections of CsA on ethanol consumption were assessed.

Results

Here, as in earlier work, IP CsA administration significantly decreased alcohol consumption. Supporting our hypothesis, central administration of CsA was sufficient to decrease alcohol consumption in a dose-dependent manner. There was no significant effect of CsA on water or sucrose consumption.

Conclusions

These results clearly implicate a CLN-mediated mechanism in brain in the inhibitory effects of CsA on ethanol consumption and provide novel targets for investigation of treatment for Alcohol Use Disorders (AUD). These results also add to the growing body of literature implicating neuroimmune mechanisms in the etiology, pathophysiology and behaviors driving AUD.

Short Summary

The unusually high abstinence rate and routine use of immunosuppressants in AUD liver graft recipients led us to rodent studies showing that immunosuppressants acting through inhibition of calcineurin (CLN) are highly effective in decreasing drinking. Here we demonstrate that this effect is mediated by brain rather than peripheral immune mechanisms.

Circulating cytokine levels are associated with symptoms of depression and anxiety among people with alcohol and drug use disorders

BACKGROUND

Psychological distress is common among people with a substance abuse disorder in treatment. Identifying correlates of psychological distress may serve as points of intervention to improve substance abuse treatment outcomes. Immune function measured as cytokine levels have been associated with psychological distress, but this association remains unexplored among people with a substance abuse disorder in treatment. This study aimed to examine whether cytokine levels in patients treated for a substance use disorder were related to depression, anxiety, and overall psychological distress, and to observe these associations separately among people with a past year alcohol use disorder and those with a past year drug use disorder.

METHODS

We collected cross-sectional data from 80 inpatients at five alcohol and substance abuse treatment centers in Norway. We determined alcohol and drug diagnoses, and assessed symptoms of depression, anxiety, and overall psychological distress. We tested blood samples for IL-1, IL-6, TNF-α, INF-γ, and IL-10. We used multivariate linear regressions to examine the associations between cytokine levels and psychological distress measures.

RESULTS

All cytokines were significantly and positively associated with depression score. INF-γ was significantly and negatively associated with anxiety, and IL-6 was significantly and positively associated psychological distress. Among people with only an alcohol use disorder, IL-6 was positively associated with depression and psychological distress scores, and IL-10 was negatively associated with anxiety score. Among people with only a drug use disorder, TNF-α was positively associated with depression score.

CONCLUSION

The relationship between immune function and psychological distress is robust in the context of substance abuse, and further research is warranted.

Investigating the Relationships Between Alcohol Consumption, Cannabis Use, and Circulating Cytokines: A Preliminary Analysis

BACKGROUND

In recent years, human and animal studies have converged to support altered inflammatory signaling as a molecular mechanism underlying the pathophysiology of alcohol use disorders (AUDs). Alcohol binds to receptors on immune cells, triggering signaling pathways that produce pro-inflammatory cytokines. Chronic inflammation is associated with tissue damage, which may contribute to negative effects of AUD. Conversely, cannabis is associated with decreased inflammatory signaling, and animal studies suggest that cannabinoids may impact alcohol-induced inflammation. Thus, the impact of cannabis on inflammation in AUDs in humans warrants examination.

METHODS

We explored the relationship between self-reported alcohol and cannabis use and circulating levels of the pro-inflammatory cytokines interleukin 6 (IL-6), IL-8, and IL-1β in the blood. Among 66 regular drinkers (mean age = 30.08), we examined circulating cytokines and administered questionnaires assessing alcohol consumption and days of cannabis use over the past 90 days. We examined whether alcohol consumption, cannabis use, and gender were associated with changes in circulating cytokines, and whether there was a significant interaction between alcohol and cannabis use predicting blood levels of circulating cytokines.

RESULTS

A positive association between alcohol and IL-6 emerged. We also observed a negative association between cannabis and IL-1β. Follow-up moderation analyses indicated a cannabis by alcohol interaction predicting circulating IL-6, such that cannabis nonusers showed a stronger relationship between alcohol and IL-6 compared to cannabis users.

CONCLUSIONS

These preliminary findings suggest that cannabinoid compounds may serve to mitigate inflammation associated with alcohol use. In addition, the present results provide data to inform future investigations, with the goal of ultimately leveraging knowledge of the role of inflammation in AUDs to develop more effective treatments focused on novel immune targets.

Withdrawal-associated injury site pain (WISP): a descriptive case series of an opioid cessation phenomenon

Supplemental Digital Content is Available in the Text.

This descriptive case series among adults documents that pain can return temporarily at healed, previously pain-free injury sites during acute opioid withdrawal.

Withdrawal pain can be a barrier to opioid cessation. Yet, little is known about old injury site pain in this context. We conducted an exploratory mixed-methods descriptive case series using a web-based survey and in-person interviews with adults recruited from pain and addiction treatment and research settings. We included individuals who self-reported a past significant injury that was healed and pain-free before the initiation of opioids, which then became temporarily painful upon opioid cessation—a phenomenon we have named withdrawal-associated injury site pain (WISP). Screening identified WISP in 47 people, of whom 34 (72%) completed the descriptive survey, including 21 who completed qualitative interviews. Recalled pain severity scores for WISP were typically high (median: 8/10; interquartile range [IQR]: 2), emotionally and physically aversive, and took approximately 2 weeks to resolve (median: 14; IQR: 24 days). Withdrawal-associated injury site pain intensity was typically slightly less than participants' original injury pain (median: 10/10; IQR: 3), and more painful than other generalized withdrawal symptoms which also lasted approximately 2 weeks (median: 13; IQR: 25 days). Fifteen surveyed participants (44%) reported returning to opioid use because of WISP in the past. Participants developed theories about the etiology of WISP, including that the pain is the brain's way of communicating a desire for opioids. This research represents the first known documentation that previously healed, and pain-free injury sites can temporarily become painful again during opioid withdrawal, an experience which may be a barrier to opioid cessation, and a contributor to opioid reinitiation.

More inflammation but less brain-derived neurotrophic factor in antisocial personality disorder

Antisocial personality disorder (ASPD) is highly comorbid with substance use disorders (SUDs). We hypothesize that chronic neuroinflammation and the loss of neurotrophic factors prompts the pathogenesis of both disorders. We used ELISA to measure plasma levels of proinflammatory (tumor necrosis factor-α [TNF-α], C-reactive protein [CRP]) and anti-inflammatory factors (transforming growth factor-β1 [TGF-β1] and interleukin-10 [IL-10]), and brain-derived neurotrophic factor (BDNF) in male patients with ASPD (n=74), SUDs (n=168), ASPD comorbid with SUDs (ASPD+SUDs) (n=438), and Healthy Controls (HCs) (n=81). A multivariate analysis of covariance (MANCOVA) controlled for possible confounders was used to compare cytokines and BDNF levels between groups. The results of MANCOVA adjusted for age showed a significant (p<0.001) main effect of diagnosis on inflammatory factors and BDNF expression in these groups. ASPD, SUDs, and ASPD+SUDs patients had significantly (p<0.001) higher TNF-α levels but lower TGF-β1 and BDNF levels. SUDs and ASPD+SUDs patients had higher IL-10 levels than did ASPD patients and HCs. There was no difference in IL-10 levels between HCs and ASPD. Moreover, subgrouping SUDs and ASPD±SUDs into opioid use disorder (OUD) and other SUDs groups showed that the IL-10 levels were specifically higher in OUD and ASPD±OUD groups than other SUDs (P≤0.001). We conclude that uncontrolled inflammation and losing neurotrophic factors, with or without comorbid SUDs, underlies ASPD. IL-10 expression might be more specifically associated with OUD.

Evaluation of plasma cytokines in patients with cocaine use disorders in abstinence identifies transforming growth factor alpha (TGFα) as a potential biomarker of consumption and dual diagnosis

BACKGROUND

Cocaine use disorder (CUD) is a complex health condition, especially when it is accompanied by comorbid psychiatric disorders (dual diagnosis). Dual diagnosis is associated with difficulties in the stratification and treatment of patients. One of the major challenges in clinical practice of addiction psychiatry is the lack of objective biological markers that indicate the degree of consumption, severity of addiction, level of toxicity and response to treatment in patients with CUD. These potential biomarkers would be fundamental players in the diagnosis, stratification, prognosis and therapeutic orientation in addiction. Due to growing evidence of the involvement of the immune system in addiction and psychiatric disorders, we tested the hypothesis that patients with CUD in abstinence might have altered circulating levels of signaling proteins related to systemic inflammation.

METHODS

The study was designed as a cross-sectional study of CUD treatment-seeking patients. These patients were recruited from outpatient programs in the province of Malaga (Spain). The study was performed with a total of 160 white Caucasian subjects, who were divided into the following groups: patients diagnosed with CUD in abstinence (N = 79, cocaine group) and matched control subjects (N = 81, control group). Participants were clinically evaluated with the diagnostic interview PRISM according to the DSM-IV-TR, and blood samples were collected for the determination of chemokine C-C motif ligand 11 (CCL11, eotaxin-1), interferon gamma (IFNγ), interleukin-4 (IL-4), interleukin-8 (IL-8), interleukin-17α (IL-17α), macrophage inflammatory protein 1α (MIP-1α) and transforming growth factor α (TGFα) levels in the plasma. Clinical and biochemical data were analyzed in order to find relationships between variables.

RESULTS

While 57% of patients with CUD were diagnosed with dual diagnosis, approximately 73% of patients had other substance use disorders. Cocaine patients displayed greater cocaine symptom severity when they were diagnosed with psychiatric comorbidity. Regarding inflammatory factors, we observed significantly lower plasma levels of IL-17α (p < 0.001), MIP-1α (p < 0.001) and TGFα (p < 0.05) in the cocaine group compared with the levels in the control group. Finally, there was a significant primary effect of dual diagnosis on the plasma concentrations of TGFα (p < 0.05) in the cocaine group, and these levels were lower in patients with dual diagnoses.

DISCUSSION

IL-17α, MIP-1α and TGFα levels are different between the cocaine and control groups, and TGFα levels facilitate the identification of patients with dual diagnosis. Because TGFα reduction is associated with enhanced responses to cocaine in preclinical models, we propose TGFα as a potential biomarker of complex CUD in humans.

Hyper-oligodendrogenesis at the vascular niche and reduced blood-brain barrier integrity in the prefrontal cortex during protracted abstinence

Alcoholism is a relapsing disorder with limited treatment options, in part due to our limited understanding of the disease etiology. We have recently shown that increased ethanol-seeking in a behavioral model of relapse in a rat model of alcoholism was associated with increased oligodendrogenesis which was positively correlated with platelet/endothelial cell adhesion molecule (PECAM-1) expression in the medial prefrontal cortex (mPFC). The current study investigated whether newly born oligodendrocytes form close physical associations with endothelial cells expressing PECAM-1 and whether these changes were accompanied by altered blood-brain barrier (BBB) integrity. Colableling and confocal analysis demonstrate that newly born oligodendroglia were always located in close physical proximity to PECAM-1 in the mPFC of rats that were ethanol dependent and demonstrated high propensity for relapse. Notably, the endothelial proximity of new oligodendrocytes was associated with reduced expression of endothelial barrier antigen (SMI-71), a marker for BBB integrity. Furthermore, voluntary wheel running during abstinence enhanced SMI-71 expression in endothelial cells, indicating protection against abstinence-induced reduction in BBB integrity. Taken together, these results suggest that ethanol experience and abstinence disrupts homeostasis in the oligo-vascular niche in the mPFC. Reversing these mechanisms may hold the key to reducing propensity for relapse in individuals with moderate to severe alcohol use disorder.

Medications development for the treatment of alcohol use disorder: insights into the predictive value of animal and human laboratory models

Development of effective treatments for alcohol use disorder (AUD) represents an important public health goal. This review provides a summary of completed preclinical and clinical studies testing pharmacotherapies for the treatment of AUD. We discuss opportunities for improving the translation from preclinical findings to clinical trial outcomes, focusing on the validity and predictive value of animal and human laboratory models of AUD. Specifically, while preclinical studies of medications development have offered important insights into the neurobiology of the disorder and alcohol's molecular targets, limitations include the lack of standardized methods and streamlined processes whereby animal studies can readily inform human studies. Behavioral pharmacology studies provide a less expensive and valuable opportunity to assess the feasibility of a pharmacotherapy prior to initiating larger scale clinical trials by providing insights into the mechanism of the drug, which can then inform recruitment, analyses, and assessments. Summary tables are provided to illustrate the wide range of preclinical, human laboratory, and clinical studies of medications development for alcoholism. Taken together, this review highlights the challenges associated with animal paradigms, human laboratory studies, and clinical trials with the overarching goal of advancing treatment development and highlighting opportunities to bridge the gap between preclinical and clinical research.

Ethanol, TLR3, and TLR4 Agonists Have Unique Innate Immune Responses in Neuron-Like SH-SY5Y and Microglia-Like BV2

BACKGROUND

Ethanol (EtOH) consumption leads to an increase of proinflammatory signaling via activation of Toll-like receptors (TLRs) such as TLR3 and TLR4 that leads to kinase activation (ERK1/2, p38, TBK1), transcription factor activation (NFκB, IRF3), and increased transcription of proinflammatory cytokines such as TNF-α, IL-1β, and IL-6. This immune signaling cascade is thought to play a role in neurodegeneration and alcohol use disorders. While microglia are considered to be the primary macrophage in brain, it is unclear what if any role neurons play in EtOH-induced proinflammatory signaling.

METHODS

Microglia-like BV2 and retinoic acid-differentiated neuron-like SH-SY5Y were treated with TLR3 agonist Poly(I:C), TLR4 agonist lipopolysaccharide (LPS), or EtOH for 10 or 30 minutes to examine proinflammatory immune signaling kinase and transcription factor activation using Western blot, and for 24 hours to examine induction of proinflammatory gene mRNA using RT-PCR.

RESULTS

In BV2, both LPS and Poly(I:C) increased p-ERK1/2, p-p38, and p-NFκB by 30 minutes, whereas EtOH decreased p-ERK1/2 and increased p-IRF3. LPS, Poly(I:C), and EtOH all increased TNF-α and IL-1β mRNA, and EtOH further increased TLR2, 7, 8, and MD-2 mRNA in BV2. In SH-SY5Y, LPS had no effect on kinase or proinflammatory gene expression. However, Poly(I:C) increased p-p38 and p-IRF3, and increased expression of TNF-α, IL-1β, and IL-6, while EtOH increased p-p38, p-IRF3, p-TBK1, and p-NFκB while decreasing p-ERK1/2 and increasing expression of TLR3, 7, 8, and RAGE mRNA. HMGB1, a TLR agonist, was induced by LPS in BV2 and by EtOH in both cell types. EtOH was more potent at inducing proinflammatory gene mRNA in SH-SY5Y compared with BV2.

CONCLUSIONS

These results support a novel and unique mechanism of EtOH, TLR3, and TLR4 signaling in neuron-like SH-SY5Y and microglia-like BV2 that likely contributes to the complexity of brain neuroimmune signaling.

Effects of acute buspirone administration on inhibitory control and sexual discounting in cocaine users

OBJECTIVE

Cocaine users display deficits in inhibitory control and make impulsive choices that may increase risky behavior. Buspirone is an anxiolytic that activates dopaminergic and serotonergic systems and improves impulsive choice (i.e., reduces sexual risk-taking intent) in cocaine users when administered chronically. We evaluated the effects of acutely administered buspirone on inhibitory control and impulsive choice.

METHODS

Eleven subjects with a recent history of cocaine use completed this within-subject, placebo-controlled study. Subjects performed two cued go/no-go and a sexual risk delay-discounting task following oral administration of buspirone (10 and 30 mg), triazolam (0.375 mg; positive control), and placebo (negative control). Physiological and psychomotor performance and subject-rated data were also collected.

RESULTS

Buspirone failed to change inhibitory control or impulsive choice; however, slower reaction times were observed at the highest dose tested. Buspirone did not produce subject-rated drug effects but dose-dependently decreased diastolic blood pressure. Triazolam impaired psychomotor performance and increased ratings of positive subject-rated effects (e.g., Like Drug).

CONCLUSIONS

These findings indicate that acutely administered buspirone has little impact on behavioral measures of inhibitory control and impulsive sexual decision-making. Considering previous findings with chronic dosing, these findings highlight that the behavioral effects of buspirone differ as a function of dosing conditions.

Evaluation of TSPO PET imaging, a marker of glial activation, to study the neuroimmune footprints of morphine exposure and withdrawal

INTRODUCTION

A growing area of research suggests that neuroimmunity may impact the pharmacology of opioids. Microglia is a key component of the brain immunity. Preclinical and clinical studies have demonstrated that microglial modulators may improve morphine-induced analgesia and prevent the development of tolerance and dependence. Positron emission tomography (PET) using translocator protein 18kDa (TSPO) radioligand is a clinically validated strategy for the non-invasive detection of microglial activation. We hypothesized that TSPO PET imaging may be used to study the neuroimmune component of opioid tolerance and withdrawal.

METHODS

Healthy rats (n=6 in each group) received either saline or escalating doses of morphine (10-40mg/kg) on five days to achieve tolerance and a withdrawal syndrome after morphine discontinuation. MicroPET imaging with [¹⁸F]DPA-714 was performed 60h after morphine withdrawal. Kinetic modeling was performed to estimate [¹⁸F]DPA-714 volume of distribution (V_T) in several brain regions using dynamic PET images and corresponding metabolite-corrected input functions. Immunohistochemistry (IHC) experiments on striatal brain slices were performed to assess the expression of glial markers (Iba1, GFAP and CD68) during 14days after morphine discontinuation.

RESULTS

The baseline binding of [¹⁸F]DPA-714 to the brain (V_T=0.086±0.009mLcm^-3) was not increased by morphine exposure and withdrawal (V_T=0.079±0.010mLcm^-3) indicating the absence of TSPO overexpression, even at the regional level. Accordingly, expression of glial markers did not increase after morphine discontinuation.

CONCLUSIONS

Morphine tolerance and withdrawal did not detectably activate microglia and had no impact on [¹⁸F]DPA-714 brain kinetics in vivo.