Antagonising TLR4-TRIF signalling before or after a low-dose alcohol binge during adolescence prevents alcohol drinking but not seeking behaviour in adulthood

Opioid Enantiomers: Exploring the Complex Interplay of Stereochemistry, Pharmacodynamics, and Therapeutic Potential

Opioids have been essential in pain management, particularly when other analgesics prove insufficient, but their use is complicated by risks of addiction, tolerance, and a range of adverse effects. These challenges are further exacerbated by the presence of opioid enantiomers that interact in a variety of ways with biological systems. This Perspective provides a comprehensive exploration of opioid enantiomers, focusing on their synthesis, pharmacodynamics, and potential therapeutic applications beyond traditional pain management. It highlights the complexity of synthesizing morphine enantiomers and additional challenges in producing the less-studied (+)-morphine. The Perspective also examines structure-activity relationship studies on (+)-opioid compounds, revealing their potential in modulating neuroinflammatory responses through non-opioid pathways and suggesting new therapeutic avenues for conditions like neuropathic pain and drug addiction. Furthermore, it discusses the differential safety profiles of opioid enantiomers, emphasizing the need for future research to advance precision medicine in opioid therapy, ultimately aiming to develop safer and more effective pain management strategies.

Neuroimmune modulators as novel pharmacotherapies for substance use disorders

One promising avenue of research is the use of neuroimmune modulators to treat substance use disorders (SUDs). Neuroimmune modulators target the interactions between the nervous system and immune system, which have been found to play a crucial role in the development and maintenance of SUDs. Multiple classes of substances produce alterations to neuroimmune signaling and peripheral immune function, including alcohol, opioids, and psychostimulants Preclinical studies have shown that neuroimmune modulators can reduce drug-seeking behavior and prevent relapse in animal models of SUDs. Additionally, early-phase clinical trials have demonstrated the safety and feasibility of using neuroimmune modulators as a treatment for SUDs in humans. These therapeutics can be used as stand-alone treatments or as adjunctive. This review summarizes the current state of the field and provides future directions with a specific focus on personalized medicine.

Acute and Chronic Ethanol Effects during Adolescence on Neuroimmune Responses: Consequences and Potential Pharmacologic Interventions

Heavy ethanol consumption during adolescence has been linked to neuroimmune response dysregulation and cognitive deficits in the developing adolescent brain. During adolescence, the brain is particularly susceptible to the pharmacological effects of ethanol that are induced by acute and chronic bouts of exposure. Numerous preclinical rodent model studies have used different ethanol administration techniques, such as intragastric gavage, self-administration, vapor, intraperitoneal, and free access, and while most models indicated proinflammatory neuroimmune responses in the adolescent brain, there are various factors that appear to influence this observation. This review synthesizes the most recent findings of the effects of adolescent alcohol use on toll-like receptors, cytokines, and chemokines, as well as the activation of astrocytes and microglia with an emphasis on differences associated with the duration of ethanol exposure (acute vs. chronic), the amount of exposure (e.g., dose or blood ethanol concentrations), sex differences, and the timing of the neuroimmune observation (immediate vs. persistent). Finally, this review discusses new therapeutics and interventions that may ameliorate the dysregulation of neuroimmune maladaptations after ethanol exposure.

Impact of adolescent intermittent ethanol exposure in male and female rats on social drinking and neuropeptide gene expression

BACKGROUND

Alcohol use during adolescence can alter maturational changes that occur in brain regions associated with social and emotional responding. Our previous studies have shown that adult male, but not female rats demonstrate social anxiety-like alterations and enhanced sensitivity to ethanol-induced social facilitation following adolescent intermittent ethanol exposure (AIE). These consequences of AIE may influence adult social drinking in a sex-specific manner.

METHODS

To test the effects of AIE on social drinking, male and female Sprague-Dawley rats exposed to water or ethanol (0 or 4 g/kg, intragastrically, every other day, between postnatal day [P] 25 and 45) were tested as adults (P72-83) in a social drinking paradigm (30-minute access to a 10% ethanol solution in supersac or supersac alone in groups of three same-sex littermates across two 4-day cycles separated by 4 days off). Social behavior was assessed during the last drinking session, along with assessment of oxytocin (OXT), oxytocin receptor (OXTR), vasopressin (AVP), and vasopressin receptors 1a and 1b (AVPR1a, AVPR1b) in the hypothalamus and lateral septum.

RESULTS

Males exposed to AIE consumed more ethanol than water-exposed controls during the second drinking cycle, whereas AIE did not affect supersac intake in males. AIE-exposed females consumed less ethanol and more supersac than water-exposed controls. Water-exposed females drinking ethanol showed more social investigation and significantly higher hypothalamic OXTR, AVP, and AVPR1b gene expression than their counterparts ingesting supersac and AIE females drinking ethanol. In males, hypothalamic AVPR1b gene expression was affected by drinking solution, with significantly higher expression evident in males drinking ethanol than those consuming supersac.

CONCLUSIONS

Collectively, these findings provide new evidence regarding sex-specific effects of AIE on social drinking and suggest that the hypothalamic OXT and AVP systems are implicated in the effects of ingested ethanol on social behavior in a sex- and adolescent-exposure-dependent manner.

Novel Agents for the Pharmacological Treatment of Alcohol Use Disorder

Alcohol use disorder (AUD) is a highly prevalent but severely under-treated disorder, with only three widely-approved pharmacotherapies. Given that AUD is a very heterogeneous disorder, it is unlikely that one single medication will be effective for all individuals with an AUD. As such, there is a need to develop new, more effective, and diverse pharmacological treatment options for AUD with the hopes of increasing utilization and improving care. In this qualitative literature review, we discuss the efficacy, mechanism of action, and tolerability of approved, repurposed, and novel pharmacotherapies for the treatment of AUD with a clinical perspective. Pharmacotherapies discussed include: disulfiram, acamprosate, naltrexone, nalmefene, topiramate, gabapentin, varenicline, baclofen, sodium oxybate, aripiprazole, ondansetron, mifepristone, ibudilast, suvorexant, prazosin, doxazosin, N-acetylcysteine, GET73, ASP8062, ABT-436, PF-5190457, and cannabidiol. Overall, many repurposed and novel agents discussed in this review demonstrate clinical effectiveness and promise for the future of AUD treatment. Importantly, these medications also offer potential improvements towards the advancement of precision medicine and personalized treatment for the heterogeneous AUD population. However, there remains a great need to improve access to treatment, increase the menu of approved pharmacological treatments, and de-stigmatize and increase treatment-seeking for AUD.

Toll-Like Receptor 4: A Novel Target to Tackle Drug Addiction?

Drug addiction is a chronic brain disease characterized by compulsive drug-seeking and drug-taking behaviors despite the major negative consequences. Current well-established neuronal underpinnings of drug addiction have promoted the substantial progress in understanding this disorder. However, non-neuronal mechanisms of drug addiction have long been underestimated. Fortunately, increased evidence indicates that neuroimmune system, especially Toll-like receptor 4 (TLR4) signaling, plays an important role in the different stages of drug addiction. Drugs like opioids, psychostimulants, and alcohol activate TLR4 signaling and enhance the proinflammatory response, which is associated with drug reward-related behaviors. While extensive studies have shown that inhibition of TLR4 attenuated drug-related responses, there are conflicting findings implicating that TLR4 signaling may not be essential to drug addiction. In this chapter, preclinical and clinical studies will be discussed to further evaluate whether TLR4-based neuroimmune pharmacotherapy can be used to treat drug addiction. Furthermore, the possible mechanisms underlying the effects of TLR4 inhibition in modulating drug-related behaviors will also be discussed.

Primed for addiction: A critical review of the role of microglia in the neurodevelopmental consequences of adolescent alcohol drinking

Alcohol is one of the most widely used recreational substances worldwide, with drinking frequently initiated during adolescence. The developmental state of the adolescent brain makes it vulnerable to initiating alcohol use, often in high doses, and particularly susceptible to alcohol-induced brain changes. Microglia, the brain parenchymal macrophages, have been implicated in mediating some of these effects, though the role that these cells play in the progression from alcohol drinking to dependence remains unclear. Microglia are uniquely positioned to sense and respond to central nervous system insult, and are now understood to exhibit innate immune memory, or "priming," altering their future functional responses based on prior exposures. In alcohol use disorders (AUDs), the role of microglia is debated. Whereas microglial activation can be pathogenic, contributing to neuroinflammation, tissue damage, and behavioral changes, or protective, it can also engage protective functions, providing support and mediating the resolution of damage. Understanding the role of microglia in adolescent AUDs is complicated by the fact that microglia are thought to be involved in developmental processes such as synaptic refinement and myelination, which underlie the functional maturation of multiple brain systems in adolescence. Thus, the role microglia play in the impact of alcohol use in adolescence is likely multifaceted. Long-term sequelae may be due to a failure to recover from EtOH-induced tissue damage, altered neurodevelopmental trajectories, and/or persistent changes to microglial responsivity and function. Here, we review critically the literature surrounding the effects of alcohol on microglia in models of adolescent alcohol misuse. We attempt to disentangle what is known about microglia from other neuroimmune effectors, to which we apply recent discoveries on the role of microglia in development and plasticity. Considered altogether, these studies challenge assumptions that proinflammatory microglia drive addiction. Alcohol priming microglia and thereby perturbing their homeostatic roles in neurodevelopment, especially during critical periods of plasticity such as adolescence, may have more serious implications for the neuropathogenesis of AUDs in adolescents.

Immune treatments for alcohol use disorder: A translational framework

While the immune system is essential for survival, an excessive or prolonged inflammatory response, such as that resulting from sustained heavy alcohol use, can damage the host and contribute to psychiatric disorders. A growing body of literature indicates that the immune system plays a critical role in the development and maintenance of alcohol use disorder (AUD). As such, there is enthusiasm for treatments that can restore healthy levels of inflammation as a mechanism to reduce drinking and promote recovery. In this qualitative literature review, we provide a conceptual rationale for immune therapies and discuss progress in medications development for AUD focused on the immune system as a treatment target. This review is organized into sections based on primary signaling pathways targeted by the candidate therapies, namely: (a) toll-like receptors, (b) phosphodiesterase inhibitors, (c) peroxisome proliferator-activated receptors, (d) microglia and astrocytes, (e) other immune pharmacotherapies, and (f) behavioral therapies. As relevant within each section, we examine the basic biological mechanisms of each class of therapy and evaluate preclinical research testing the role of the therapy on mitigating alcohol-related behaviors in animal models. To the extent available, translational findings are reviewed with discussion of completed and ongoing randomized clinical trials and their findings to date. An applied and clinically focused approach is taken to identify the potential clinical applications of the various treatments reviewed. We conclude by delineating the most promising candidate treatments and discussing future directions by considering opportunities for immune treatment development and personalized medicine for AUD.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

Ethanol Stimulation of Microglia Release Increases ERK1/2-Dependent Neuronal cPLA2 Activity in Immature Cultured Cortical Preparations

Ethanol consumption typically begins during adolescence and is associated with age-dependent responses and maladaptive neuronal consequences. Our previous work established the role of a putative signaling cascade involving cytoplasmic phospholipase A₂ (cPLA₂), arachidonic acid (AA) and novel protein kinase C isoforms in adolescent hypnotic sensitivity. The current study aimed to further delineate this pathway by ascertaining the cellular specificity as well as the upstream activators of cPLA₂ using an immature cultured cortical preparation. A threefold increase in cPLA₂ was detected within 2 min of 100 mM ethanol exposure as measured by phosphorylation of serine 505 (Ser505). Increases in cPLA₂ activity were further observed to be primarily confined to neuronal cells. Increases in the number of neurons co-expressing cPLA2 Ser505 phosphorylation were prevented by preincubation with an ERK1/2 inhibitor, but not P38 MAPK inhibition. Finally, conditioned media studies were used to determine whether glial cells were involved in the ethanol-induced neuronal cPLA₂ activity. Rapid increases in neuronal cPLA2 activity appears to be initiated through ethanol stimulated microglial, but not astrocytic releasable factors. Taken together, these data extend the proposed signaling cascade involved in developmental ethanol responding.

Adolescent Ethanol Exposure: Anxiety-Like Behavioral Alterations, Ethanol Intake, and Sensitivity

Adolescence is a developmental period associated with rapid age-specific physiological, neural, and hormonal changes. Behaviorally, human adolescents are characterized by age-typical increases in novelty-seeking and risk-taking, including the frequent initiation of alcohol and drug use. Alcohol use typically begins during early adolescence, and older adolescents often report high levels of alcohol consumption, commonly referred to as high-intensity drinking. Early-onset and heavy drinking during adolescence are associated with an increased risk of developing alcohol use disorders later in life. Yet, long-term behavioral consequences of adolescent alcohol use that might contribute to excessive drinking in adulthood are still not well understood. Recent animal research, however, using different exposure regimens and routes of ethanol administration, has made substantial progress in identifying the consequences of adolescent ethanol exposure that last into adulthood. Alterations associated with adolescent ethanol exposure include increases in anxiety-like behavior, impulsivity, risk-taking, and ethanol intake, although the observed alterations differ as a function of exposure regimens and routes of ethanol administration. Rodent studies have also shown that adolescent ethanol exposure produces alterations in sensitivity to ethanol, with these alterations reminiscent of adolescent-typical ethanol responsiveness. The goal of this mini-review article is to summarize the current state of animal research, focusing on the long-term consequences related to adolescent ethanol exposure, with a special emphasis on the behavioral alterations and changes to ethanol sensitivity that can foster high levels of drinking in adulthood.

Neuroimmune signaling in alcohol use disorder

Alcohol use disorder (AUD) is a widespread disease with limited treatment options. Targeting the neuroimmune system is a new avenue for developing or repurposing effective pharmacotherapies. Alcohol modulates innate immune signaling in different cell types in the brain by altering gene expression and the molecular pathways that regulate neuroinflammation. Chronic alcohol abuse may cause an imbalance in neuroimmune function, resulting in prolonged perturbations in brain function. Likewise, manipulating the neuroimmune system may change alcohol-related behaviors. Psychiatric disorders that are comorbid with AUD, such as post-traumatic stress disorder, major depressive disorder, and other substance use disorders, may also have underlying neuroimmune mechanisms; current evidence suggests that convergent immune pathways may be involved in AUD and in these comorbid disorders. In this review, we provide an overview of major neuroimmune cell-types and pathways involved in mediating alcohol behaviors, discuss potential mechanisms of alcohol-induced neuroimmune activation, and present recent clinical evidence for candidate immune-related drugs to treat AUD.