Contributions of neuroimmune and gut-brain signaling to vulnerability of developing substance use disorders.

Epidemiology and clinical research indicate that only a subset of people who are exposed to drugs of abuse will go on to develop a substance use disorder. Numerous factors impact individual susceptibility to developing a substance use disorder, including intrinsic biological factors, environmental factors, and interpersonal/social factors. Given the extensive morbidity and mortality that is wrought as a consequence of substance use disorders, a substantial body of research has focused on understanding the risk factors that mediate the shift from initial drug use to pathological drug use. Understanding these risk factors provides a clear path for the development of risk mitigation strategies to help reduce the burden of substance use disorders in the population. Here we will review the rapidly growing body of literature that examines the importance of interactions between the peripheral immune system, the gut microbiome, and the central nervous system (CNS) in mediating the transition to pathological drug use. While these systems had long been viewed as distinct, there is growing evidence that there is bidirectional communication between both the immune system and the gut microbiome that drive changes in neural and behavioral plasticity relevant to substance use disorders. Further, both of these systems are highly sensitive to environmental perturbations and are implicated in numerous neuropsychiatric conditions. While the field of study examining these interactions in substance use disorders is in its relative infancy, clarifying the relationship between gut-immune-brain signaling and substance use disorders has potential to improve our understanding of individual propensity to developing addiction and yield important insight into potential treatment options.

Interactions of neuroimmune signaling and glutamate plasticity in addiction.

Chronic use of drugs of abuse affects neuroimmune signaling; however, there are still many open questions regarding the interactions between neuroimmune mechanisms and substance use disorders (SUDs). Further, chronic use of drugs of abuse can induce glutamatergic changes in the brain, but the relationship between the glutamate system and neuroimmune signaling in addiction is not well understood. Therefore, the purpose of this review is to bring into focus the role of neuroimmune signaling and its interactions with the glutamate system following chronic drug use, and how this may guide pharmacotherapeutic treatment strategies for SUDs. In this review, we first describe neuroimmune mechanisms that may be linked to aberrant glutamate signaling in addiction. We focus specifically on the nuclear factor-kappa B (NF-κB) pathway, a potentially important neuroimmune mechanism that may be a key player in driving drug-seeking behavior. We highlight the importance of astroglial-microglial crosstalk, and how this interacts with known glutamatergic dysregulations in addiction. Then, we describe the importance of studying non-neuronal cells with unprecedented precision because understanding structure-function relationships in these cells is critical in understanding their role in addiction neurobiology. Here we propose a working model of neuroimmune-glutamate interactions that underlie drug use motivation, which we argue may aid strategies for small molecule drug development to treat substance use disorders. Together, the synthesis of this review shows that interactions between glutamate and neuroimmune signaling may play an important and understudied role in addiction processes and may be critical in developing more efficacious pharmacotherapies to treat SUDs.

Current status of immunotherapies for addiction.

The treatment of substance use disorders has always been challenging because multiple neurotransmitters mediate addiction. However, with smoking being the leading cause of preventable death and the recent opioid epidemic in the United States, the search for novel solutions becomes more imperative. In this review, we discuss the use of antibodies to treat addictions and highlight areas of success and areas that require improvement, using examples from cocaine, nicotine, and opioid vaccines. Through each example, we examine creative problem-solving strategies for developing future vaccines, such as using an adenovirus vector as a carrier, designing bivalent vaccines, stimulating Toll-like receptors for adjuvant effects, and altering the route of administration. Our review also covers passive immunization alone to override or prevent drug toxicity as well as in combination with vaccines for more rapid and potentially greater efficacy.

Reward and immune responses in adolescent females following experimental traumatic brain injury.

The pathology of traumatic brain injury (TBI) adversely affects many brain regions, often resulting in the development of comorbid psychiatric disorders including substance use disorders (SUD). Although traditionally thought to be an epidemic that predominantly affects males, recent clinical studies report females have higher rates of concussions and longer recovery times than males. Yet, how neurotrauma, particularly deep within the brain, between the sexes is differentially manifested remains largely unknown. The risk of TBI peaks during adolescence when neuronal networks that regulate reward behaviors are not fully developed. Previously, using the conditioned place preference (CPP) assay, we found that adolescent TBI increased susceptibility to the rewarding effects of cocaine in male mice. Further, we observed augmented inflammatory profiles, increased microglial phagocytosis of neuronal proteins, and decreased neuronal spine density in the NAc. Notably, the extent of sex differences in SUD susceptibility following TBI has not be investigated. Thus, here we ask the central question of whether the adolescent TBI-induced neuroinflammatory profile at reward centers is divergent in a sex-dependent manner. Using the CPP assay, we found that female mice with high levels of female sex hormones at the time of adolescent TBI demonstrated neuroprotection against increased sensitivity to the rewarding effects of cocaine. These studies also provide evidence of significantly reduced microglial activation and phagocytosis of neuronal proteins within the NAc of females. Overall, our results offer crucial insight into how adolescent TBI impacts the reward pathway in a sex depending manner that could explain a vulnerability to addiction-like behavior.

Role of olfactory reactions, nociception, and immunoendocrine shifts in addictive disorders.

BACKGROUND AND OBJECTIVES: Addictive pathology is associated with nervous, immune, and endocrine shifts. Meanwhile, the nature of intersystemic relationship lying beneath addictive disorders remains unclear. The purpose of the study was to identify neuroimmunoendocrine markers of addictive disorders in male subjects defining the nature of their interaction. METHODS: The study enrolled 69 subjects aged 18-43 years: 59 males and 10 females divided into those with addictive disorders (n = 39) and conditionally healthy subjects (n = 30). EEG testing with olfactory stimulation, olfactometric, and pressure algometric examinations was carried out. Multiplex technique was applied to determine mitogen-induced production of cytokines IL-10, IL-1, IL-1RA, IL-2, IFN-gamma, TNF-alpha. ELISA method was applied to measure serum cortisol and testosterone levels. RESULTS: Olfactory responses to isopropanol with open eyes in addicted patients manifested as increase in alpha-rhythm and beta1-rhythm, with closed eyes presentation of this odorant was accompanied by increase of theta-rhythm in opioid-addicted patients. Male subjects with addictive disorders showed reduced alpha-rhythm in terms of olfactory stimulation with modified emotional evaluation of the odorant, deficient mitogen-induced production of IFN-gamma, and reduced pain sensitivity. Male subjects with opioid addiction had reduced beta1-rhythm in terms of olfactory stimulation, mitogen-induced production of IFN-gamma, and elevated testosterone level. CONCLUSIONS: The findings obtained verify potential involvement of nociception, olfaction, and cytokine production in addiction pathogenesis evidencing their various roles depending on the range of psychoactive substances (PAS) and pathology progression. SCIENTIFIC SIGNIFICANCE: The data obtained may provide background for unification of reward circuit and inhibitory control concepts in regulation of addictive behavior. (Am J Addict 2017;26:640-648).

The role of neuroimmune signaling in alcoholism.

Alcohol consumption and stress increase brain levels of known innate immune signaling molecules. Microglia, the innate immune cells of the brain, and neurons respond to alcohol, signaling through Toll-like receptors (TLRs), high-mobility group box 1 (HMGB1), miRNAs, pro-inflammatory cytokines and their associated receptors involved in signaling between microglia, other glia and neurons. Repeated cycles of alcohol and stress cause a progressive, persistent induction of HMGB1, miRNA and TLR receptors in brain that appear to underlie the progressive and persistent loss of behavioral control, increased impulsivity and anxiety, as well as craving, coupled with increasing ventral striatal responses that promote reward seeking behavior and increase risk of developing alcohol use disorders. Studies employing anti-oxidant, anti-inflammatory, anti-depressant, and innate immune antagonists further link innate immune gene expression to addiction-like behaviors. Innate immune molecules are novel targets for addiction and affective disorders therapies. This article is part of the Special Issue entitled "Alcoholism".

Toll-like receptor signaling and stages of addiction.

BACKGROUND: Athina Markou and her colleagues discovered persistent changes in adult behavior following adolescent exposure to ethanol or nicotine consistent with increased risk for developing addiction. Building on Dr. Markou's important work and that of others in the field, researchers at the Bowles Center for Alcohol Studies have found that persistent changes in behavior following adolescent stress or alcohol exposure may be linked to induction of immune signaling in brain. AIM: This study aims to illuminate the critical interrelationship of the innate immune system (e.g., toll-like receptors [TLRs], high-mobility group box 1 [HMGB1]) in the neurobiology of addiction. METHOD: This study reviews the relevant research regarding the relationship between the innate immune system and addiction. CONCLUSION: Emerging evidence indicates that TLRs in brain, particularly those on microglia, respond to endogenous innate immune agonists such as HMGB1 and microRNAs (miRNAs). Multiple TLRs, HMGB1, and miRNAs are induced in the brain by stress, alcohol, and other drugs of abuse and are increased in the postmortem human alcoholic brain. Enhanced TLR-innate immune signaling in brain leads to epigenetic modifications, alterations in synaptic plasticity, and loss of neuronal cell populations, which contribute to cognitive and emotive dysfunctions. Addiction involves progressive stages of drug binges and intoxication, withdrawal-negative affect, and ultimately compulsive drug use and abuse. Toll-like receptor signaling within cortical-limbic circuits is modified by alcohol and stress in a manner consistent with promoting progression through the stages of addiction.

Beyond the association. Toxoplasma gondii in schizophrenia, bipolar disorder, and addiction: systematic review and meta-analysis.

OBJECTIVE: To perform a meta-analysis on studies reporting prevalence of Toxoplasma gondii (T. gondii) infection in any psychiatric disorder compared with healthy controls. Our secondary objective was to analyze factors possibly moderating heterogeneity. METHOD: A systematic search was performed to identify studies into T. gondii infection for all major psychiatric disorders versus healthy controls. Methodological quality, publication bias, and possible moderators were assessed. RESULTS: A total of 2866 citations were retrieved and 50 studies finally included. Significant odds ratios (ORs) with IgG antibodies were found in schizophrenia (OR 1.81, P < 0.00001), bipolar disorder (OR 1.52, P = 0.02), obsessive-compulsive disorder (OR 3.4, P < 0.001), and addiction (OR 1.91, P < 0.00001), but not for major depression (OR 1.21, P = 0.28). Exploration of the association between T. gondii and schizophrenia yielded a significant effect of seropositivity before onset and serointensity, but not IgM antibodies or gender. The amplitude of the OR was influenced by region and general seroprevalence. Moderators together accounted for 56% of the observed variance in study effects. After controlling for publication bias, the adjusted OR (1.43) in schizophrenia remained significant. CONCLUSION: These findings suggest that T. gondii infection is associated with several psychiatric disorders and that in schizophrenia reactivation of latent T. gondii infection may occur.

The anti-(+)-methamphetamine monoclonal antibody mAb7F9 attenuates acute (+)-methamphetamine effects on intracranial self-stimulation in rats.

Passive immunization with monoclonal antibodies (mAbs) against (+)-methamphetamine (METH) is being evaluated for the treatment of METH addiction. A human/mouse chimeric form of the murine anti-METH mAb7F9 has entered clinical trials. This study examined the effects of murine mAb7F9 on certain addiction-related behavioral effects of METH in rats as measured using intracranial self-stimulation (ICSS). Initial studies indicated that acute METH (0.1-0.56 mg/kg, s.c.) lowered the minimal (threshold) stimulation intensity that maintained ICSS. METH (0.3 mg/kg, s.c.) also blocked elevations in ICSS thresholds (anhedonia-like behavior) during spontaneous withdrawal from a chronic METH infusion (10 mg/kg/day x 7 days). In studies examining effects of i.v. pretreatment with mAb7F9 (at 30, 100, or 200 mg/kg), 200 mg/kg blocked the ability of an initial injection of METH (0.3 mg/kg, s.c.) to reduce baseline ICSS thresholds, but was less capable of attenuating the effect of subsequent daily injections of METH. MAb7F9 (200 mg/kg) also produced a small but significant reduction in the ability of METH (0.3 mg/kg, s.c.) to reverse METH withdrawal-induced elevations in ICSS thresholds. These studies demonstrate that mAb7F9 can partially attenuate some addiction-related effects of acute METH in an ICSS model, and provide some support for the therapeutic potential of mAb7F9 for the treatment of METH addiction.

Neuroinflammation as a possible link between cannabinoids and addiction.

OBJECTIVE: Substance dependence disorder is a chronically relapsing condition characterised by neurobiological changes leading to loss of control in restricting a substance intake, compulsion and withdrawal syndrome. In the past few years, (endo)cannabinoids have been raised as a possible target in the aetiology of drug addiction. On the other hand, although the exact mechanisms of the genesis of addiction remain poorly understood, it is possible that neuroinflammation might also play a role in the pathophysiology of this condition. Studies demonstrated that (endo)cannabinoids act as immunomodulators by inhibiting cytokines production and microglial cell activation. Thus, in the present review, we explore the possible role of neuroinflammation on the therapeutic effects of cannabinoids on drug addiction. METHODS: We conducted an evidence-based review of the literature in order to assess the role of cannabinoids on the neuroinflammatory hypothesis of addiction (terms: addiction, cannabinoids and inflammation). We searched PubMed and BioMedCentral databases up to April 2014 with no date restrictions. RESULTS: In all, 165 eligible articles were included in the present review. Existing evidence suggests that disruption in cannabinoid signalling during the drug addiction process leads to microglial activation and neuroinflammation. CONCLUSION: The literature showed that inflammation and changes in endocannabinod signalling occur in drug abuse; however, it remains uncertain whether these changes are causally or coincidentally associated with addiction. Additional studies, therefore, are needed to elucidate the contribution of neuroinflammation on the behavioural and neuroprotective effects of cannabinoids on drug addiction.

Neuroimmune pathways in alcohol consumption: evidence from behavioral and genetic studies in rodents and humans.

Immune or brain proinflammatory signaling has been linked to some of the behavioral effects of alcohol. Immune signaling appears to regulate voluntary ethanol intake in rodent models, and ethanol intake activates the immune system in multiple models. This bidirectional link raises the possibility that consumption increases immune signaling, which in turn further increases consumption in a feed-forward cycle. Data from animal and human studies provide overlapping support for the involvement of immune-related genes and proteins in alcohol action, and combining animal and human data is a promising approach to systematically evaluate and nominate relevant pathways. Based on rodent models, neuroimmune pathways may represent unexplored, nontraditional targets for medication development to reduce alcohol consumption and prevent relapse. Peroxisome proliferator-activated receptor agonists are one class of anti-inflammatory medications that demonstrate antiaddictive properties for alcohol and other drugs of abuse. Expression of immune-related genes is altered in animals and humans following chronic alcohol exposure, and the regulatory influences of specific mRNAs, microRNAs, and activated cell types are areas of intense study. Ultimately, the use of multiple datasets combined with behavioral validation will be needed to link specific neuroimmune pathways to addiction vulnerability.

Immune to addiction: the ethical dimensions of vaccines against substance abuse.

Promising advances have been made in recent years for a unique class of immunotherapies that use vaccination to combat substance-use disorders. Although such vaccines are potentially useful for addictions, they raise a variety of ethical and social questions.

Vaccines against drug abuse.

The currently available medications for the treatment of drug abuse have had only limited success. Anti-addiction vaccines, aimed at eliciting antibodies that block the pharmacological effects of drugs, have great potential for treating drug abuse. We review the status of two vaccines that are undergoing clinical trials (for cocaine and nicotine addiction) and two that are still in preclinical development (for methamphetamine and heroin addiction). We also outline the challenges and ethical concerns associated with the development of anti-addiction vaccines and their use as future therapeutics.

Induction of innate immune genes in brain create the neurobiology of addiction.

Addiction occurs through repeated abuse of drugs that progressively reduce behavioral control and cognitive flexibility while increasing limbic negative emotion. Recent discoveries indicate neuroimmune signaling underlies addiction and co-morbid depression. Low threshold microglia undergo progressive stages of innate immune activation involving astrocytes and neurons with repeated drug abuse, stress, and/or cell damage signals. Increased brain NF-κB transcription of proinflammatory chemokines, cytokines, oxidases, proteases, TLR and other genes create loops amplifying NF-κB transcription and innate immune target gene expression. Human post-mortem alcoholic brain has increased NF-κB and NF-κB target gene message, increased microglial markers and chemokine-MCP1. Polymorphisms of human NF-κB1 and other innate immune genes contribute to genetic risk for alcoholism. Animal transgenic and genetic studies link NF-κB innate immune gene expression to alcohol drinking. Human drug addicts show deficits in behavioral flexibility modeled pre-clinically using reversal learning. Binge alcohol, chronic cocaine, and lesions link addiction neurobiology to frontal cortex, neuroimmune signaling and loss of behavioral flexibility. Addiction also involves increasing limbic negative emotion and depression-like behavior that is reflected in hippocampal neurogenesis. Innate immune activation parallels loss of neurogenesis and increased depression-like behavior. Protection against loss of neurogenesis and negative affect by anti-oxidant, anti-inflammatory, anti-depressant, opiate antagonist and abstinence from ethanol dependence link limbic affect to changes in innate immune signaling. The hypothesis that innate immune gene induction underlies addiction and affective disorders creates new targets for therapy.

CREB-mediated alterations in the amygdala transcriptome: coordinated regulation of immune response genes following cocaine.

The neuronal circuitry underlying stress- and drug-induced reinstatement of cocaine-seeking has been relatively well characterized; however, less is known regarding the long-term molecular changes following cocaine administration that may promote future reinstatement. The transcription factor cAMP response element-binding protein (CREB) is necessary for stress- but not cocaine-induced reinstatement of conditioned reward, suggesting that different molecular mechanisms may underlie these two types of reinstatement. To explore the relationship between this transcription factor and reinstatement, we utilized the place-conditioning paradigm to examine alterations in gene expression in the amygdala, a neural substrate critically involved in stress-induced reinstatement, following the development of cocaine reward and subsequent extinction. Our findings demonstrate that the amygdala transcriptome was altered by CREB deficiency more than by previous cocaine experience, with an over-representation of genes involved in the immune response. However, a subset of genes involved in stress and immune response demonstrated a drug×genotype interaction, indicating that cocaine produces different long-term alterations in gene expression depending on the presence or absence of CREB. This profile of gene expression in the context of addiction enhances our understanding of the long-term molecular changes that occur throughout the addiction cycle and identifies novel genes and pathways that might lead to the creation of better therapeutic agents.

Immunotherapy for drug abuse.

Substance use disorders continue to be major medical and social problems worldwide. Current medications for substance use disorders have many limitations such as cost, availability, medication compliance, dependence, diversion of some to illicit use and relapse to addiction after discontinuing their use. Immunotherapies using either passive monoclonal antibodies or active vaccines have distinctly different mechanisms and therapeutic utility from small molecule approaches to treatment. They have great potential to help the patient achieve and sustain abstinence and have fewer of the above limitations. This review covers the cocaine vaccine development in detail and provides an overview of directions for developing anti-addiction vaccines against the abuse of other substances. The notable success of the first placebo-controlled clinical trial of a cocaine vaccine, TA-CD, has led to an ongoing multi-site, Phase IIb clinical trial in 300 subjects. The results from these trials are encouarging further development of the cocaine vacine as one of the first anti-addiction vaccines to go forward to the U.S. Food and Drug Administration for review and approval for human use.

Borna disease virus (BDV) circulating immunocomplex positivity in addicted patients in the Czech Republic: a prospective cohort analysis.

BACKGROUND: Borna disease virus (BDV) is an RNA virus belonging to the family Bornaviridae. Borna disease virus is a neurotropic virus that causes changes in mood, behaviour and cognition. BDV causes persistent infection of the central nervous system. Immune changes lead to activation of infection. Alcohol and drug dependence are associated with immune impairment. METHODS: We examined the seropositivity of BDV circulating immunocomplexes (CIC) in patients with alcohol and drug dependence and healthy individuals (blood donors). We examined 41 addicted patients for the presence of BDV CIC in the serum by ELISA at the beginning of detoxification, and after eight weeks of abstinence. This is the first such study performed in patients with alcohol and drug dependence. RESULTS: BDV CIC positivity was detected in 36.59% of addicted patients on day 0 and in 42.86% on day 56. The control group was 37.3% positive. However, we did not detect higher BDV CIC positivity in addicted patients in comparison with blood donors (p = 0.179). The significantly higher level of BDV CIC was associated with lower levels of GGT (gamma glutamyl transferase) (p = 0.027) and approached statistical significance with the lower age of addicted patients (p = 0.064). We did not find any association between BDV CIC positivity and other anamnestic and demographic characteristics. CONCLUSIONS: In our study addicted patients did not have significantly higher levels of BDV CIC than the control group. The highest levels of BDV CIC were detected in patients with lower levels of GGT and a lower age. TRIAL REGISTRATION: This study was approved by the ethical committee of the University Hospital Medical Faculty of Charles University in Pilsen, Czech Republic (registration number 303/2001).

CREB binding and activity in brain: regional specificity and induction by electroconvulsive seizure.

BACKGROUND: The transcription factor cyclic adenosine monophosphate response element binding protein (CREB) orchestrates diverse neurobiological processes including cell differentiation, survival, and plasticity. Alterations in CREB-mediated transcription have been implicated in numerous central nervous system (CNS) disorders including depression, anxiety, addiction, and cognitive decline. However, it remains unclear how CREB contributes to normal and aberrant CNS function, as the identity of CREB-regulated genes in brain and the regional and temporal dynamics of CREB function remain largely undetermined. METHODS: We combined microarray and chromatin immunoprecipitation technology to analyze CREB-DNA interactions in brain. We compared the occupancy and activity of CREB at gene promoters in rat frontal cortex, hippocampus, and striatum before and after a rodent model of electroconvulsive therapy. RESULTS: Our analysis identified >860 CREB binding sites in rat brain. We identified multiple genomic loci enriched with CREB binding sites and find that CREB-occupied transcripts interact extensively to promote cell proliferation, plasticity, and resiliency. We discovered regional differences in CREB occupancy and activity that explain, in part, the diverse biological and behavioral outputs of CREB activity in frontal cortex, hippocampus, and striatum. Electroconvulsive seizure rapidly increased CREB occupancy and/or phosphorylation at select promoters, demonstrating that both events contribute to the temporal regulation of the CREB transcriptome. CONCLUSIONS: Our data provide a mechanistic basis for CREB's ability to integrate regional and temporal cues to orchestrate state-specific patterns of transcription in the brain, indicate that CREB is an important mediator of the biological responses to electroconvulsive seizure, and provide global mechanistic insights into CREB's role in psychiatric and cognitive function.