Associations of cocaine use and HIV infection with the intestinal microbiota, microbial translocation, and inflammation

The interplay between gut microbiome, epigenetics, and substance use disorders: from molecular to clinical perspectives

Substance use disorders (SUDs) involve a complex series of central and peripheral pathologies, leading to impairments in cognitive, behavioral, and physiological processes. Emerging evidence indicates a more significant role for the microbiome-gut-brain axis (MGBA) in SUDs than previously recognized. The MGBA is interconnected with various body systems by producing numerous metabolites, most importantly short-chain fatty acids (SCFAs), cytokines, and neurotransmitters. These mediators influence the human body's epigenome and transcriptome. While numerous epigenetic alterations in different brain regions have been reported in SUD models, the intricate relationship between SUDs and the MGBA suggests that the gut microbiome may partially contribute to the underlying mechanisms of SUDs. Promising results have been observed with gut microbiome-directed interventions in patients with SUDs, including prebiotics, probiotics, antibiotics, and fecal microbiota transplantation. Nonetheless, the long-term epigenetic effects of these interventions remain unexplored. Moreover, various confounding factors and study limitations have hindered the identification of molecular mechanisms and clinical applications of gut microbiome interventions in SUDs. In the present review, we will (i) provide a comprehensive discussion on how the gut microbiome influences SUDs, with an emphasis on epigenetic alterations; (ii) discuss the current evidence on the bidirectional relationship of gut microbiome and SUDs, highlighting potential targets for intervention; and (iii) review recent advances in gut microbiome-directed therapies, along with their limitations and future directions.

Gut microbiome depletion modulates cocaine-induced behavioral and transcriptional responses in female mice

Cocaine use disorder is a chronic relapsing condition with no FDA-approved biological treatments. The gut microbiome has emerged as a key modulator of neurobehavioral responses to drugs of abuse, yet its role in female animals has been under studied. Here, we investigated the effects of gut microbiome depletion on cocaine-induced behavioral and transcriptional responses in female mice. Adult female C57BL/6 J mice were treated with a non-absorbable oral antibiotic (Abx) cocktail for two weeks to deplete the gut microbiome, followed by behavioral assays assessing locomotor sensitization and conditioned place preference (CPP) to cocaine. Abx-treated females displayed reduced locomotor sensitization and a shifted CPP dose-response curve, characterized by attenuated preference at higher cocaine doses. Transcriptional analysis of the nucleus accumbens (NAc) revealed that microbiome depletion suppressed cocaine-induced expression of immediate early genes (c-Fos, FosB, Nr4a1, Egr4) and altered dopamine-related (Drd1) and microglial (Cx3cr1) markers. These findings contrast with prior studies in males, where microbiome depletion enhanced cocaine-induced behavioral plasticity. The observed effects suggest distinct gut-brain signaling as an important contributor to cocaine reinforcement and neuroadaptations in females. This study provides novel insights into microbiome regulation of addiction-relevant behaviors and highlights the necessity of sex-specific investigations in neuropsychiatric disorders. Further research is needed to elucidate the molecular pathways linking gut dysbiosis to substance use vulnerability in females.

Intestinal barrier damage caused by addictive substance use disorder

Addictive substance use disorder has a wide range of effects on the intestinal barrier, including damage to the biological, chemical, mechanical, and immune barriers. Damage to the intestinal barrier caused by addictive substance use disorder allows harmful substances and bacteria to cross the intestinal barrier into the circulatory system, leading to systemic inflammatory responses and immune imbalances. In addition, the interaction between the gut flora and the central nervous system is recognized as an important component of the gut-brain axis. Gut barrier damage leads to dysbiosis, which in turn affects brain function by activating immune cells and releasing inflammatory factors. This may lead to altered mood and cognitive function, increased addictive substance cravings, and dependence. Recent research has indicated that reshaping the gut-brain axis and adjusting the composition and abundance of gut microbiota holds promise in alleviating withdrawal symptoms with addictive substance dependence. This article reviews the effects of addictive substance use disorder on the intestinal barrier and explores the possibility of improving addictive substance dependence by treating gut barrier damage.

Pharmacogenomic and Pharmacomicrobiomic Aspects of Drugs of Abuse

BACKGROUND/OBJECTIVES

This review examines the role of pharmacogenomics in individual responses to the pharmacotherapy of various drugs of abuse, including alcohol, cocaine, and opioids, to identify genetic variants that contribute to variability in substance use disorder treatment outcomes. In addition, it explores the pharmacomicrobiomic aspects of substance use, highlighting the impact of the gut microbiome on bioavailability, drug metabolism, pharmacodynamics, and pharmacokinetics.

RESULTS

Research on pharmacogenetics has identified several promising genetic variants that may contribute to the individual variability in responses to existing pharmacotherapies for substance addiction. However, the interpretation of these findings remains limited. It is estimated that genetic factors may account for 20-95% of the variability in individual drug responses. Therefore, genetic factors alone cannot fully explain the differences in drug responses, and factors such as gut microbiome diversity may also play a significant role. Drug microbial biotransformation is produced by microbial exoenzymes that convert low molecular weight organic compounds into analogous compounds by oxidation, reduction, hydrolysis, condensation, isomerization, unsaturation, or by the introduction of heteroatoms. Despite significant advances in pharmacomicrobiomics, challenges persist including the lack of standardized methodologies, inter-individual variability, limited understanding of drug biotransformation mechanisms, and the need for large-scale validation studies to develop microbiota-based biomarkers for clinical use.

CONCLUSIONS

Progress in the pharmacogenomics of substance use disorders has provided biological insights into the pharmacological needs associated with common genetic variants in drug-metabolizing enzymes. The gut microbiome and its metabolites play a pivotal role in various stages of drug addiction including seeking, reward, and biotransformation. Therefore, integrating pharmacogenomics with pharmacomicrobiomics will form a crucial foundation for significant advances in precision and personalized medicine.

Neuroglia in substance use disorders

Substance use disorders (SUD) remain a major public health concern in which individuals are unable to control their use of substances despite significant harm and negative consequences. Drugs of abuse dysregulate major brain and behavioral functions. Glial cells, primarily microglia and astrocytes, play a crucial role in these drug-induced molecular and behavioral changes. This review explores preclinical and clinical studies of how neuroglia and their associated neuroinflammatory responses contribute to SUD and reward-related properties. We evaluate preclinical and clinical evidence for targeting neuroglia as therapeutic interventions. In addition, we evaluate the literature on the gut microbiome and its role in SUD. Clinical treatments are most effective for reducing drug cravings, and some have yielded promising results in other measures of drug use. N-Acetylcysteine, through modulation of cysteine-glutamate antiporter of glial cells, shows encouraging results across a variety of drug classes. Neuroglia and gut microbiome interactions are important factors to consider with regard to SUD and could lead to novel therapeutic avenues. Age- and sex-dependent properties of neuroglia, gut microbiome, and drug use behaviors are important areas in need of further investigation.

A Mixed Effect Similarity Matrix Regression Model (SMRmix) for Integrating Multiple Microbiome Datasets at Community Level

BACKGROUND

Recent studies have highlighted the importance of human microbiota in our health and diseases. However, in many areas of research, individual microbiome studies often offer inconsistent results due to the limited sample sizes and the heterogeneity in study populations and experimental procedures. This inconsistency underscores the necessity for integrative analysis of multiple microbiome datasets. Despite the critical need, statistical methods that incorporate multiple microbiome datasets and account for the study heterogeneity are not available in the literature.

METHODS

In this paper, we develop a mixed effect similarity matrix regression (SMRmix) approach for identifying community level microbiome shifts between outcomes. SMRmix has a close connection with the microbiome kernel association test, one of the most popular approaches for such a task but is only applicable when we have a single study. SMRmix enables researchers to consolidate findings from diverse microbiome studies.

RESULTS

Via extensive simulations, we show that SMRmix has well-controlled type I error and higher power than some potential competitors. We applied the SMRmix to two real-world datasets. The first, from the HIV-reanalysis consortium, integrated data from 17 studies on gut dysbiosis in HIV. Our analysis confirmed consistent associations between the gut microbiome and HIV infection as well as MSM (men who have sex with men) status, demonstrating greater power than competing methods. The second dataset involved 11 studies on the gut microbiome in colorectal cancer; analysis with SMRmix confirmed significant dysbiosis in affected individuals compared to healthy controls.

CONCLUSION

The development of SMRmix enables the integration of multiple studies and effectively managing study heterogeneity, and provides a powerful tool for uncovering consistent associations between diseases and community-level microbiome data.

Colony-stimulating factor 2 (CSF2) as a gut microbiome dependent immune factor that alters molecular and behavioral responses to cocaine in male mice

Cocaine use disorder is a condition that leads to tremendous morbidity and mortality for which there are currently no FDA-approved pharmacotherapies. Previous research has demonstrated an important role for the resident population of bacteria of the large intestine, collectively dubbed the gut microbiome, in modulating brain and behavior in models of cocaine and other substance use disorders. Importantly, previous work has repeatedly shown that depletion of the gut microbiome leads to increased cocaine taking and seeking behaviors in multiple models. While the precise mechanism of these gut-brain signaling pathways in models of cocaine use is not fully clear, and intriguing possibility is through gut microbiome influences on innate immune system function. In this manuscript we identify the cytokine colony stimulating factor 2 (CSF2) as an immune factor that is increased by cocaine in a gut microbiome dependent manner. Peripherally injected CSF2 crosses the blood-brain barrier into the nucleus accumbens, a brain region central to behavioral responses to cocaine. Treatment with peripheral CSF2 reduces acute and sensitized locomotor responses to cocaine as well as reducing cocaine place preference at high doses. On a molecular level, we find that peripheral injections of CSF2 alter the transcriptional response to both acute and repeated cocaine in the nucleus accumbens. Finally, treatment of microbiome depleted mice with CSF2 reverses the behavioral effects of microbiome depletion on the conditioned place preference assay. Taken together, this work identifies an innate immune factor that represents a novel gut-brain signaling cascade in models of cocaine use and lays the foundations for further translational work targeting this pathway.

Chronic Cocaine Use and Parkinson's Disease: An Interpretative Model

Over the years, the growing "epidemic" spread of cocaine use represents a crucial public health and social problem worldwide. According to the 2023 World Drug Report, 0.4% of the world's population aged 15 to 64 report using cocaine; this number corresponds to approximately 24.6 million cocaine users worldwide and approximately 1 million subjects with cocaine use disorder (CUD). While we specifically know the short-term side effects induced by cocaine, unfortunately, we currently do not have exhaustive information about the medium/long-term side effects of the substance on the body. The scientific literature progressively highlights that the chronic use of cocaine is related to an increase in cardio- and cerebrovascular risk and probably to a greater incidence of psychomotor symptoms and neurodegenerative processes. Several studies have highlighted an increased risk of antipsychotic-induced extrapyramidal symptoms (EPSs) in patients with psychotic spectrum disorders comorbid with psychostimulant abuse. EPSs include movement dysfunction such as dystonia, akathisia, tardive dyskinesia, and characteristic symptoms of Parkinsonism such as rigidity, bradykinesia, and tremor. In the present paper, we propose a model of interpretation of the neurobiological mechanisms underlying the hypothesized increased vulnerability in chronic cocaine abusers to neurodegenerative disorders with psychomotor symptoms. Specifically, we supposed that the chronic administration of cocaine produces significant neurobiological changes, causing a complex dysregulation of various neurotransmitter systems, mainly affecting subcortical structures and the dopaminergic pathways. We believe that a better understanding of these cellular and molecular mechanisms involved in cocaine-induced neuropsychotoxicity may have helpful clinical implications and provide targets for therapeutic intervention.

A gut (microbiome) feeling about addiction: Interactions with stress and social systems

In recent years, an increasing attention has given to the intricate and diverse connection of microorganisms residing in our gut and their impact on brain health and central nervous system disease. There has been a shift in mindset to understand that drug addiction is not merely a condition that affects the brain, it is now being recognized as a disorder that also involves external factors such as the intestinal microbiota, which could influence vulnerability and the development of addictive behaviors. Furthermore, stress and social interactions, which are closely linked to the intestinal microbiota, are powerful modulators of addiction. This review delves into the mechanisms through which the microbiota-stress-immune axis may shape drug addiction and social behaviors. This work integrates preclinical and clinical evidence that demonstrate the bidirectional communication between stress, social behaviors, substance use disorders and the gut microbiota, suggesting that gut microbes might modulate social stress having a significance in drug addiction.

Lycium barbarum polysaccharide mitigated methamphetamine addiction and altered methamphetamine-induced gut microbiota dysbiosis

Methamphetamine (MA) is a highly addictive mental stimulant, and MA abuse remains a significant public health problem worldwide, while effective treatment options are limited. Lycium barbarum polysaccharide (LBP), a major effective component extracted from Lycium barbarum, has potential health-promoting effects on the nervous system; however, its role in MA dependence remains unclear. In this study, the conditioned place preference (CPP) of MA addiction in adult male mice was established to detect changes in gut microbiota profiles after LBP treatment through 16S rRNA gene sequencing. Our results found that LBP administration could alleviate MA-induced CPP and hyperactivity. Interestingly, LBP improved MA-induced gut microbiota dysbiosis by increasing some beneficial autochthonous genus abundances, such as Allobaculum, Gordonibacter, and Ileibacterium. MA exposure induced the co-occurrence network of intestinal microbiota to become weaker and more unstable when compared with the control group, while LBP changed the above effects when compared with the MA group. Bacterial gene function prediction showed that amphetamine addiction, cocaine addiction, and short-chain fatty acid metabolism were enriched. These findings reveal that LBP might regulate MA-induced gut microbiota and behavior changes, which showed potential therapeutic applicability in treating MA addiction by regulating the gut microbiota.

Clinical and Preclinical Evidence for Gut Microbiome Mechanisms in Substance Use Disorders

Substance use disorders are a set of recalcitrant neuropsychiatric conditions that cause tremendous morbidity and mortality and are among the leading causes of loss of disability-adjusted life years worldwide. While each specific substance use disorder is driven by problematic use of a different substance, they all share a similar pattern of escalating and out-of-control substance use, continued use despite negative consequences, and a remitting/relapsing pattern over time. Despite significant advances in our understanding of the neurobiology of these conditions, current treatment options remain few and are ineffective for too many individuals. In recent years, there has been a rapidly growing body of literature demonstrating that the resident population of microbes in the gastrointestinal tract, collectively called the gut microbiome, plays an important role in modulating brain and behavior in preclinical and clinical studies of psychiatric disease. While these findings have not yet been translated into clinical practice, this remains an important and exciting avenue for translational research. In this review, we highlight the current state of microbiome-brain research within the substance use field with a focus on both clinical and preclinical studies. We also discuss potential neurobiological mechanisms underlying microbiome effects on models of substance use disorder and propose future directions to bring these findings from bench to bedside.

Pharmacological and Behavioral Interventions to Mitigate Premature Aging in Patients with HIV

PURPOSE OF REVIEW

We sought to review pharmacological and behavioral interventions that have been publicly presented, published, or are currently ongoing to prevent or mitigate the effect of premature HIV-associated comorbidities.

RECENT FINDINGS

Multiple studies have been conducted in hopes of finding an effective intervention. While the choice of antiretroviral regimen influences recovery of immune function, several drugs used as adjunct treatments have proven effective to mitigate premature aging. Additionally, few behavioral interventions have exhibited some efficacy. Statins, angiotensin-receptor blockers, and anti-hyperglycemic agents as well as optimal adherence, exercise, and intermittent fasting among others have had beneficial impact on markers of immune activation and levels of inflammatory biomarkers. However, several investigations had inconclusive outcomes so further studies with larger sample sizes are warranted.

Cocaine hydrochloride, cocaine methiodide and methylenedioxypyrovalerone (MDPV) cause distinct alterations in the structure and composition of the gut microbiota

Cocaine is a highly addictive psychostimulant drug of abuse that constitutes an ongoing public health threat. Emerging research is revealing that numerous peripheral effects of this drug may serve as conditioned stimuli for its central reinforcing properties. The gut microbiota is emerging as one of these peripheral sources of input to cocaine reward. The primary objective of the present study was to determine how cocaine HCl and methylenedioxypyrovalerone, both of which powerfully activate central reward pathways, alter the gut microbiota. Cocaine methiodide, a quaternary derivative of cocaine that does not enter the brain, was included to assess peripheral influences on the gut microbiota. Both cocaine congeners caused significant and similar alterations of the gut microbiota after a 10-day course of treatment. Contrary to expectations, the effects of cocaine HCl and MDPV on the gut microbiota were most dissimilar. Functional predictions of metabolic alterations caused by the treatment drugs reaffirmed that the cocaine congeners were similar whereas MDPV was most dissimilar from the other two drugs and controls. It appears that the monoamine transporters in the gut mediate the effects of the treatment drugs. The effects of the cocaine congeners and MDPV on the gut microbiome may form the basis of interoceptive cues that can influence their abuse properties.

Gegen-Qinlian decoction alleviates anxiety-like behaviors in methamphetamine-withdrawn mice by regulating Akkermansia and metabolism in the colon

BACKGROUND

Anxiety is a prominent withdrawal symptom of methamphetamine (Meth) addiction. Recently, the gut microbiota has been regarded as a promising target for modulating anxiety. Gegen-Qinlian decoction (GQD) is a classical Traditional Chinese Medicine applied in interventions of various gut disorders by balancing the gut microbiome. We aim to investigate whether GQD could alleviate Meth withdrawal anxiety through balancing gut microbiota and gut microenvironment.

METHODS

Meth withdrawal anxiety models were established in mice. GQD were intragastric administrated into Meth-withdrawn mice and controls. Gut permeability and inflammatory status were examined in mice. Germ-free (GF) and antibiotics-treated (Abx) mice were used to evaluate the role of gut bacteria in withdrawal anxiety. Gut microbiota was profiled with 16s rRNA sequencing in feces. Metabolomics in colon tissue and in Akkermansia culture medium were performed.

RESULTS

Meth withdrawal enhanced anxiety-like behaviors in wild-type mice, and altered gut permeability, and inflammatory status, while GQD treatment during the withdrawal period efficiently alleviated anxiety-like behaviors and improved gut microenvironment. Next, we found Germ-free (GF) and antibiotics-treated (Abx) mice did not develop anxiety-like behaviors by Meth withdrawal, indicating the essential role of gut bacteria in Meth withdrawal induced anxiety. Then, it was observed that gut microbiota was greatly affected in Meth-withdrawn mice, especially the reduction in Akkermansia. GQD can rescue the gut microbiota and reverse Akkermansia abundance in Meth-withdrawn mice. Meanwhile, GQD can also restore the Meth-impaired Akkermansia growth in vitro. Further, GQD restored several common metabolite levels both in colon in vivo and in Akkermansia in vitro.

CONCLUSIONS

We revealed a novel effect of GQD on Meth withdrawal anxiety and identified its pharmacological target axis as "Akkermansia-Akkermansia metabolites-gut metabolites-gut microenvironment". Our findings indicated that targeting gut bacteria with TCM, such as GQD, might be a promising therapeutic strategy for addiction and related withdrawal symptoms.

Small fish, big discoveries: zebrafish shed light on microbial biomarkers for neuro-immune-cardiovascular health

Zebrafish (Danio rerio) have emerged as a powerful model to study the gut microbiome in the context of human conditions, including hypertension, cardiovascular disease, neurological disorders, and immune dysfunction. Here, we highlight zebrafish as a tool to bridge the gap in knowledge in linking the gut microbiome and physiological homeostasis of cardiovascular, neural, and immune systems, both independently and as an integrated axis. Drawing on zebrafish studies to date, we discuss challenges in microbiota transplant techniques and gnotobiotic husbandry practices. We present advantages and current limitations in zebrafish microbiome research and discuss the use of zebrafish in identification of microbial enterotypes in health and disease. We also highlight the versatility of zebrafish studies to further explore the function of human conditions relevant to gut dysbiosis and reveal novel therapeutic targets.

Oral and fecal microbiota perturbance in cocaine users: Can rTMS-induced cocaine abstinence support eubiosis restoration?

The effects of cocaine on microbiota have been scarcely explored. Here, we investigated the gut (GM) and oral (OM) microbiota composition of cocaine use disorder (CUD) patients and the effects of repetitive transcranial magnetic stimulation (rTMS). 16S rRNA sequencing was used to characterize GM and OM, whereas PICRUST2 assessed functional changes in microbial communities, and gas-chromatography was used to evaluate fecal short and medium chain fatty acids. CUD patients reported a significant decrease in alpha diversity and modification of the abundances of several taxa in both GM and OM. Furthermore, many predicted metabolic pathways were differentially expressed in CUD patients' stool and saliva samples, as well as reduced levels of butyric acid that appear restored to normal amounts after rTMS treatment. In conclusion, CUD patients showed a profound dysbiotic fecal and oral microbiota composition and function and rTMS-induced cocaine abstinence determined the restoration of eubiotic microbiota.

The link between chronic cocaine use, B cell perturbations, and blunted immune recovery in HIV-infected individuals on suppressive ART

Background

We recently reveal that anti-CD4 autoantibodies contribute to blunted CD4+ T cell reconstitution in HIV+ individuals on antiretroviral therapy (ART). Cocaine use is common among HIV+ individuals and is associated with accelerated disease progression. However, the mechanisms underlying cocaine-induced immune perturbations remain obscure.

Methods

We evaluated plasma levels of anti-CD4 IgG and markers of microbial translocation, as well as B-cell gene expression profiles and activation in HIV+ chronic cocaine users and non-users on suppressive ART, as well as uninfected controls. Plasma purified anti-CD4 IgGs were assessed for antibody-dependent cytotoxicity (ADCC).

Results

HIV+ cocaine users had increased plasma levels of anti-CD4 IgGs, lipopolysaccharide (LPS), and soluble CD14 (sCD14) versus non-users. An inverse correlation was observed in cocaine users, but not non-drug users. Anti-CD4 IgGs from HIV+ cocaine users mediated CD4+ T cell death through ADCC in vitro. B cells from HIV+ cocaine users exhibited activation signaling pathways and activation (cycling and TLR4 expression) related to microbial translocation versus non-users.

Conclusions

This study improves our understanding of cocaine associated B cell perturbations and immune failure and the new appreciation for autoreactive B cells as novel therapeutic targets.

HIV Tat Expression and Cocaine Exposure Lead to Sex- and Age-Specific Changes of the Microbiota Composition in the Gut

The balance of microbial communities in the gut is extremely important for normal physiological function. Disruption of the balance is often associated with various disorders and diseases. Both HIV infection and cocaine use are known to change the gut microbiota and the epithelial barrier integrity, which contribute to inflammation and immune activation. Our recent study shows that Tat expression and cocaine exposure result in changes of genome-wide DNA methylation and gene expression and lead to worsen the learning and memory impairments. In the current study, we extended the study to determine effects of Tat and cocaine on the gut microbiota composition. We found that both Tat expression and cocaine exposure increased Alteromonadaceae in 6-month-old female/male mice. In addition, we found that Tat, cocaine, or both increased Alteromonadaceae, Bacteroidaceae, Cyanobiaceae, Erysipelotrichaceae, and Muribaculaceae but decreased Clostridiales_vadinBB60_group, Desulfovibrionaceae, Helicobacteraceae, Lachnospiraceae, and Ruminococcaceae in 12-month-old female mice. Lastly, we analyzed changes of metabolic pathways and found that Tat decreased energy metabolism and nucleotide metabolism, and increased lipid metabolism and metabolism of other amino acids while cocaine increased lipid metabolism in 12-month-old female mice. These results demonstrated that Tat expression and cocaine exposure resulted in significant changes of the gut microbiota in an age- and sex-dependent manner and provide additional evidence to support the bidirectional gut-brain axis hypothesis.

Microbial glutamate metabolism predicts intravenous cocaine self-administration in diversity outbred mice

The gut microbiome is thought to play a critical role in the onset and development of psychiatric disorders, including depression and substance use disorder (SUD). To test the hypothesis that the microbiome affects addiction predisposing behaviors and cocaine intravenous self-administration (IVSA) and to identify specific microbes involved in the relationship, we performed 16S rRNA gene sequencing on feces from 228 diversity outbred mice. Twelve open field measures, two light-dark assay measures, one hole board and novelty place preference measure significantly differed between mice that acquired cocaine IVSA (ACQ) and those that failed to acquire IVSA (FACQ). We found that ACQ mice are more active and exploratory and display decreased fear than FACQ mice. The microbial abundances that differentiated ACQ from FACQ mice were an increased abundance of Barnesiella, Ruminococcus, and Robinsoniella and decreased Clostridium IV in ACQ mice. There was a sex-specific correlation between ACQ and microbial abundance, a reduced Lactobacillus abundance in ACQ male mice, and a decreased Blautia abundance in female ACQ mice. The abundance of Robinsoniella was correlated, and Clostridium IV inversely correlated with the number of doses of cocaine self-administered during acquisition. Functional analysis of the microbiome composition of a subset of mice suggested that gut-brain modules encoding glutamate metabolism genes are associated with the propensity to self-administer cocaine. These findings establish associations between the microbiome composition and glutamate metabolic potential and the ability to acquire cocaine IVSA thus indicating the potential translational impact of targeting the gut microbiome or microbial metabolites for treatment of SUD. This article is part of the Special Issue on "Microbiome & the Brain: Mechanisms & Maladies".

Differences in clinical features and gut microbiota between individuals with methamphetamine casual use and methamphetamine use disorder

Background

The transition from methamphetamine (MA) casual use (MCU) to compulsive use is enigmatic as some MA users can remain in casual use, but some cannot. There is a knowledge gap if gut microbiota (GM) play a role in differing MCU from MA use disorder (MUD). We aimed to investigate the clinical features and GM differences between individuals with MCU and MUD.

Method

We recruited two groups of MA users -MCU and MUD - and matched them according to age and body mass index (n=21 in each group). Participants were accessed using the Semi-Structured Assessment for Drug Dependence and Alcoholism, and their fecal samples were undergone 16S ribosomal DNA sequencing. We compared the hosts' clinical features and GM diversity, composition, and structure (represented by enterotypes) between the two groups. We have identified differential microbes between the two groups and performed network analyses connecting GM and the clinical traits.

Result

Compared with the casual users, individuals with MUD had higher incidences of MA-induced neuropsychiatric symptoms (e.g., paranoia, depression) and withdrawal symptoms (e.g., fatigue, drowsiness, and increased appetite), as well as stronger cravings for and intentions to use MA, and increased MA tolerance. The GM diversity showed no significant differences between the two groups, but four genera (Halomonas, Clostridium, Devosia, and Dorea) were enriched in the individuals with MUD (p<0.05). Three distinct enterotypes were identified in all MA users, and Ruminococcus-driven enterotype 2 was dominant in individuals with MUD compared to the MCU (61.90% vs. 28.60%, p=0.03). Network analysis shows that Devosia is the hub genus (hub index = 0.75), which is not only related to the counts of the MUD diagnostic criteria (ρ=0.40; p=0.01) but also to the clinical features of MA users such as reduced social activities (ρ=0.54; p<0.01). Devosia is also associated with the increased intention to use MA (ρ=0.48; p<0.01), increased MA tolerance (ρ=0.38; p=0.01), craving for MA (ρ=0.37; p=0.01), and MA-induced withdrawal symptoms (p<0.05).

Conclusion

Our findings suggest that Ruminococcus-driven enterotype 2 and the genera Devosia might be two influential factors that differentiate MA casual use from MUD, but further studies are warranted.

Diet Quality and Liver Health in People Living with HIV in the MASH Cohort: A Multi-Omic Analysis of the Fecal Microbiome and Metabolome

The gut-liver axis has been recognized as a potential pathway in which dietary factors may contribute to liver disease in people living with HIV (PLWH). The objective of this study was to explore associations between dietary quality, the fecal microbiome, the metabolome, and liver health in PLWH from the Miami Adult Studies on HIV (MASH) cohort. We performed a cross-sectional analysis of 50 PLWH from the MASH cohort and utilized the USDA Healthy Eating Index (HEI)-2015 to measure diet quality. A Fibrosis-4 Index (FIB-4) score < 1.45 was used as a strong indication that advanced liver fibrosis was not present. Stool samples and fasting blood plasma samples were collected. Bacterial composition was characterized using 16S rRNA sequencing. Metabolomics in plasma were determined using gas and liquid chromatography/mass spectrometry. Statistical analyses included biomarker identification using linear discriminant analysis effect size. Compared to participants with FIB-4 ≥ 1.45, participants with FIB-4 < 1.45 had higher intake of dairy (p = 0.006). Fibrosis-4 Index score was inversely correlated with seafood and plant protein HEI component score (r = -0.320, p = 0.022). The relative abundances of butyrate-producing taxa Ruminococcaceae, Roseburia, and Lachnospiraceae were higher in participants with FIB-4 < 1.45. Participants with FIB-4 < 1.45 also had higher levels of caffeine (p = 0.045) and related metabolites such as trigonelline (p = 0.008) and 1-methylurate (p = 0.023). Dietary components appear to be associated with the fecal microbiome and metabolome, and liver health in PLWH. Future studies should investigate whether targeting specific dietary components may reduce liver-related morbidity and mortality in PLWH.

Disrupted diurnal oscillations of the gut microbiota in patients with alcohol dependence

Background

Patients with alcohol dependence (AD) can exhibit gut dysbacteria. Dysbacteria may co-occur with disruptions of circadian rhythmicity of the gut flora, which can aggravate AD. Herein, this study aimed to investigate diurnal oscillations of the gut microbiota in AD patients.

Methods

Thirty-two patients with AD, based on the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, and 20 healthy subjects were enrolled in this study. Demographic and clinical data were collected by self-report questionnaires. Fecal samples at 7:00 AM, 11:00 AM, 3:00 PM, and 7:00 PM were collected from each subject. 16S rDNA sequencing was conducted. Wilcoxon and Kruskal-Wallis tests were performed to characterize alterations and oscillations of the gut microbiota.

Results

We found that β-diversity of the gut microbiota in AD patients oscillated diurnally compared with healthy subjects (p = 0.01). Additionally, 0.66% of operational taxonomic units oscillated diurnally in AD patients versus 1.68% in healthy subjects. At different taxonomic levels, bacterial abundance oscillated diurnally in both groups, such as Pseudomonas and Prevotella pallens (all p < 0.05). β-diversity of the gut microbiota in AD patients with high daily alcohol consumption, high-level cravings, short AD durations, and mild withdrawal symptoms oscillated diurnally compared with other AD patients (all p < 0.05).

Conclusion

The gut microbiota in AD patients exhibits disruptions of diurnal oscillation, which may provide novel insights into mechanisms of AD and the development of therapeutic strategies.

Role of Autophagy in HIV-1 and Drug Abuse-Mediated Neuroinflammaging

Chronic low-grade inflammation remains an essential feature of HIV-1 infection under combined antiretroviral therapy (cART) and contributes to the accelerated cognitive defects and aging in HIV-1 infected populations, indicating cART limitations in suppressing viremia. Interestingly, ~50% of the HIV-1 infected population on cART that develops cognitive defects is complicated by drug abuse, involving the activation of cells in the central nervous system (CNS) and neurotoxin release, altogether leading to neuroinflammation. Neuroinflammation is the hallmark feature of many neurodegenerative disorders, including HIV-1-associated neurocognitive disorders (HAND). Impaired autophagy has been identified as one of the underlying mechanisms of HAND in treated HIV-1-infected people that also abuse drugs. Several lines of evidence suggest that autophagy regulates CNS cells' responses and maintains cellular hemostasis. The impairment of autophagy is associated with low-grade chronic inflammation and immune senescence, a known characteristic of pathological aging. Therefore, autophagy impairment due to CNS cells, such as neurons, microglia, astrocytes, and pericytes exposure to HIV-1/HIV-1 proteins, cART, and drug abuse could have combined toxicity, resulting in increased neuroinflammation, which ultimately leads to accelerated aging, referred to as neuroinflammaging. In this review, we focus on the potential role of autophagy in the mechanism of neuroinflammaging in the context of HIV-1 and drug abuse.

Multiomic analysis reveals microbiome-related relationships between cocaine use and metabolites

OBJECTIVE

Over 19 million individuals globally have a cocaine use disorder, a significant public health crisis. Cocaine has also been associated with a pro-inflammatory state and recently with imbalances in the intestinal microbiota as compared to nonuse. The objective of this pilot study was to characterize the gut microbiota and plasma metabolites in people with HIV (PWH) who use cocaine compared with those who do not.

DESIGN

Cross-sectional study.

METHODS

A pilot study in PWH was conducted on 25 cocaine users and 25 cocaine nonusers from the Miami Adult Studies on HIV cohort. Stool samples and blood plasma were collected. Bacterial composition was characterized using 16S rRNA sequencing. Metabolomics in plasma were determined using gas and liquid chromatography/mass spectrometry.

RESULTS

The relative abundances of the Lachnopspira genus, Oscillospira genus, Bifidobacterium adolescentis species, and Euryarchaeota phylum were significantly higher in the cocaine- using PWH compared to cocaine-nonusing PWH. Cocaine-use was associated with higher levels of several metabolites: products of dopamine catabolism (3-methoxytyrosine and 3-methoxytyramine sulfate), phenylacetate, benzoate, butyrate, and butyrylglycine.

CONCLUSIONS

Cocaine use was associated with higher abundances of taxa and metabolites known to be associated with pathogenic states that include gastrointestinal conditions. Understanding key intestinal bacterial functional pathways that are altered due to cocaine use in PWH will provide a better understanding of the relationships between the host intestinal microbiome and potentially provide novel treatments to improve health.

Potential Role of Host Microbiome in Areca Nut-Associated Carcinogenesis and Addiction

Areca nut (AN) is widely consumed all over the world, bringing great harm to human health and economy. Individuals with AN chewing are at high risk of cardiovascular disease and impaired immune system and metabolic system. Despite a growing number of studies having reported on the adverse effects brought by AN chewing, the exact mechanism of it is limited and the need for additional exploration remains. In recent years, the interaction between microorganisms, especially intestinal microorganism and host, has been extensively studied. AN chewing might disrupt the oral and intestinal microbiota communities through direct connect with the microbes it contains, altering PH, oxygen of oral and intestinal microenvironment, and disturbing the immune homeostasis. These mechanisms provide insights into the interplay between areca nut and host microbiota. Emerging studies have proposed that bidirectional interaction between polyphenols and intestinal microbes might play a potential role in the divergence of polyphenol, extracted from AN, among individuals with or without AN-induced cancer development and progression. Although some AN chewers have been aware of the harmful effects brought by AN, they cannot abolish this habit because of the addiction of AN. Increasing studies have tried to revealed that gut microbiota might influence the onset/development of addictive behaviors. Altogether, this review summarizes the possible reasons for the disturbance of host microbiota caused by areca nut chewing and clarifies the complex interaction between human microbiome and major constituents and the addiction and carcinogenicity of AN, tempting to provide novel insights into the development and utilization of it, and to control the adverse consequences caused by AN chewing.

Gut colonization by Proteobacteria alters host metabolism and modulates cocaine neurobehavioral responses

Gut-microbiota membership is associated with diverse neuropsychological outcomes, including substance use disorders (SUDs). Here, we use mice colonized with Citrobacter rodentium or the human γ-Proteobacteria commensal Escherichia coli HS as a model to examine the mechanistic interactions between gut microbes and host responses to cocaine. We find that cocaine exposure increases intestinal norepinephrine levels that are sensed through the bacterial adrenergic receptor QseC to promote intestinal colonization of γ-Proteobacteria. Colonized mice show enhanced host cocaine-induced behaviors. The neuroactive metabolite glycine, a bacterial nitrogen source, is depleted in the gut and cerebrospinal fluid of colonized mice. Systemic glycine repletion reversed, and γ-Proteobacteria mutated for glycine uptake did not alter the host response to cocaine. γ-Proteobacteria modulated glycine levels are linked to cocaine-induced transcriptional plasticity in the nucleus accumbens through glutamatergic transmission. The mechanism outline here could potentially be exploited to modulate reward-related brain circuits that contribute to SUDs.

Cocaine use associated gut permeability and microbial translocation in people living with HIV in the Miami Adult Study on HIV (MASH) cohort

OBJECTIVE

Determine if cocaine use impacts gut permeability, promotes microbial translocation and immune activation in people living with HIV (PLWH) using effective antiretroviral therapy (ART).

METHODS

Cross-sectional analysis of 100 PLWH (ART ≥6 months, HIV-RNA <200 copies/mL) from the Miami Adult Studies on HIV (MASH) cohort. Cocaine use was assessed by self-report, urine screen, and blood benzoylecgonine (BE). Blood samples were collected to assess gut permeability (intestinal fatty acid-binding protein, I-FABP), microbial translocation (lipopolysaccharide, LPS), immune activation (sCD14, sCD27, and sCD163) and markers of inflammation (hs-CRP, TNF-α and IL-6). Multiple linear regression models were used to analyze the relationships of cocaine use.

RESULTS

A total of 37 cocaine users and 63 cocaine non-users were evaluated. Cocaine users had higher levels of I-FABP (7.92±0.35 vs. 7.69±0.56 pg/mL, P = 0.029) and LPS (0.76±0.24 vs. 0.54±0.27 EU/mL, P<0.001) than cocaine non-users. Cocaine use was also associated with the levels of LPS (P<0.001), I-FABP (P = 0.033), and sCD163 (P = 0.010) after adjusting for covariates. Cocaine users had 5.15 times higher odds to exhibit higher LPS levels than non-users (OR: 5.15 95% CI: 1.89-13.9; P<0.001). Blood levels of BE were directly correlated with LPS (rho = 0.276, P = 0.028), sCD14 (rho = 0.274, P = 0.031), and sCD163 (rho = 0.250, P = 0.049).

CONCLUSIONS

Cocaine use was associated with markers of gut permeability, microbial translocation, and immune activation in virally suppressed PLWH. Mitigation of cocaine use may prevent further gastrointestinal damage and immune activation in PLWH.

Cocaine administration protects gut mucosa barrier and reduces plasma level of TNF-α

Background

Cocaine affects not only the central nervous system, but also systemic immunity. The role of cocaine in gut mucosal integrity is not fully understood.

Methods

Here we evaluated the effect of cocaine use on gut endothelial permeability and system inflammation in rats that self-administered cocaine or saline and in humans using immunohistochemistry, qPCR, ELISA, and Transepithelial/transendothelial electrical resistance (TEER).

Results

Cocaine administration maintained intact and undisturbed intestinal mucosal structures, increased tight junction claudin 1 and 2 mRNA expression, and decreased plasma TNF-α levels, compared to the control group, at the end of study in rats. Further, cocaine treatment decreased gut endothelial permeability in a dose-dependent manner in human epithelial Caco-2 cells in vitro. Consistently, chronic cocaine users exhibited decreased plasma levels of TNF-α compared with non-drug users in vivo. However, plasma IL-6 levels were similar between cocaine use and control groups both in humans and rats in vivo.

Conclusions

Our results from both human and rat studies in vivo and in vitro suggest that cocaine use may exert a protective effect on the integrity of gut mucosa and suppresses plasma TNF-α levels. This study may provide information on some beneficial effects of cocaine use on gut endothelial cells integrity and systemic inflammation.

Substance use, microbiome and psychiatric disorders

Accumulating evidence from several studies has shown association between substance use, dysregulation of the microbiome and psychiatric disorders such as depression, anxiety, and psychosis. Many of the abused substances such as cocaine and alcohol have been shown to alter immune signaling pathways and cause inflammation in both the periphery and the central nervous system (CNS). In addition, these substances of abuse also alter the composition and function of the gut microbiome which is known to play important roles such as the synthesis of neurotransmitters and metabolites, that affect the CNS homeostasis and consequent behavioral outcomes. The emerging interactions between substance use, microbiome and CNS neurochemical alterations could contribute to the development of psychiatric disorders. This review provides an overview of the associative effects of substance use such as alcohol, cocaine, methamphetamine, nicotine and opioids on the gut microbiome and psychiatric disorders involving anxiety, depression and psychosis. Understanding the relationship between substance use, microbiome and psychiatric disorders will provide insights for potential therapeutic targets, aimed at mitigating these adverse outcomes.

Drugs and Bugs: The Gut-Brain Axis and Substance Use Disorders

Substance use disorders (SUDs) represent a significant public health crisis. Worldwide, 5.4% of the global disease burden is attributed to SUDs and alcohol use, and many more use psychoactive substances recreationally. Often associated with comorbidities, SUDs result in changes to both brain function and physiological responses. Mounting evidence calls for a precision approach for the treatment and diagnosis of SUDs, and the gut microbiome is emerging as a contributor to such disorders. Over the last few centuries, modern lifestyles, diets, and medical care have altered the health of the microbes that live in and on our bodies; as we develop, our diets and lifestyle dictate which microbes flourish and which microbes vanish. An increase in antibiotic treatments, with many antibiotic interventions occurring early in life during the microbiome's normal development, transforms developing microbial communities. Links have been made between the microbiome and SUDs, and the microbiome and conditions that are often comorbid with SUDs such as anxiety, depression, pain, and stress. A better understanding of the mechanisms influencing behavioral changes and drug use is critical in developing novel treatments for SUDSs. Targeting the microbiome as a therapeutic and diagnostic tool is a promising avenue of exploration. This review will provide an overview of the role of the gut-brain axis in a wide range of SUDs, discuss host and microbe pathways that mediate changes in the brain's response to drugs, and the microbes and related metabolites that impact behavior and health within the gut-brain axis.

Protective Role of Lactobacillus rhamnosus Probiotic in Reversing Cocaine-Induced Oxidative Stress, Glial Activation and Locomotion in Mice

Cocaine abuse is known to cause inflammation, oxidative injury and alterations in the gut microbiota. Although emerging studies have demonstrated the role of gut microbiota in modulating neurological complications and behavior, the mechanism(s) underlying these processes remain unclear. In the present study, we investigated the protective effect of Lactobacillus rhamnosus probiotic on cocaine-induced oxidative stress, glial activation, and locomotion in mice. In this study, groups of male C56BL6 mice were administered gut-resident commensal bacteria L. rhamnosus probiotic (oral gavage) concurrently with cocaine (20 mg/kg, i.p.) or saline for 28 days and assessed for oxidative stress and cellular activation in both the gut and brain as well as alterations in locomotion behavior. Cocaine-induced gut dysregulation was associated with increased formation of 4-hydroxynonenal (4-HNE) adducts, increased expression of pERK-1/2, pNF-kB-p65 and antioxidant mediators (SOD1, GPx1). In cocaine administered mice, there was increased activation of both microglia and astrocytes in the striatum and cortex of the brain as shown by enhanced expression of CD11b and GFAP, respectively. Cocaine administration also resulted in increased locomotor activity in the open field test in these mice. Administration of L. rhamnosus attenuated cocaine-induced gut oxidative stress and inflammation as well as glial activation and locomotion. These results suggest the potential of microbial-based interventions to attenuate cocaine-mediated behavioral responses and neuroinflammation, in addition to systemic inflammation and oxidative damage.

Sex-Specific Effects of Synbiotic Exposure in Mice on Addictive-Like Behavioral Alterations Induced by Chronic Alcohol Intake Are Associated With Changes in Specific Gut Bacterial Taxa and Brain Tryptophan Metabolism

Chronic alcohol intake has been shown to disrupt gut microbiota homeostasis, but whether microbiota modulation could prevent behavioral alterations associated with chronic alcohol intake remains unknown. We investigated the effects of synbiotic dietary supplementation on the development of alcohol-related addictive behavior in female and male mice and evaluated whether these effects were associated with changes in bacterial species abundance, short-chain fatty acids, tryptophan metabolism, and neurotransmitter levels in the prefrontal cortex and hippocampus. Chronic intermittent exposure to alcohol during 20 days induced escalation of intake in both female and male mice. Following alcohol deprivation, relapse-like behavior was observed in both sexes, but anxiogenic and cognitive deficits were present only in females. Synbiotic treatment reduced escalation and relapse to alcohol intake in females and males. In addition, the anxiogenic-like state and cognitive deficits observed in females following alcohol deprivation were abolished in mice exposed to synbiotic. Alcohol-induced differential alterations in microbial diversity and abundance in both sexes. In females, synbiotic exposure abrogated the alterations provoked by alcohol in Prevotellaceae UCG-001 and Ruminococcaceae UCG-014 abundance. In males, synbiotic exposure restored the changes induced by alcohol in Akkermansia and Muribaculum uncultured bacterium abundance. Following alcohol withdrawal, tryptophan metabolites, noradrenaline, dopamine, and γ-aminobutyric acid concentrations in the prefrontal cortex and the hippocampus were correlated with bacterial abundance and behavioral alterations in a sex-dependent manner. These results suggested that a dietary intervention with a synbiotic to reduce gut dysbiosis during chronic alcohol intake may impact differently the gut-brain-axis in females and males.

The Association of Altered Gut Microbiota and Intestinal Mucosal Barrier Integrity in Mice With Heroin Dependence

The gut microbiota is believed to play a significant role in psychological and gastrointestinal symptoms in heroin addicts. However, the underlying mechanism remains largely unknown. We show here that heroin addicts had a decrease in body mass index (BMI) and abnormal serum D-lactic acid (DLA), endotoxin (ET) and diamine oxidase (DAO) levels during their withdrawal stage, suggesting a potential intestinal injury. The gut microbial profiles in the mouse model with heroin dependence showed slightly decreased alpha diversity, as well as higher levels of Bifidobacterium and Sutterella and a decrease in Akkermansia at genus level compared to the control group. Fecal microbiota transplantation (FMT) further confirmed that the microbiota altered by heroin dependence was sufficient to impair body weight and intestinal mucosal barrier integrity in recipient mice. Moreover, short-chain fatty acids (SCFAs) profiling revealed that microbiota-derived propionic acid significantly decreased in heroin dependent mice compared to controls. Overall, our study shows that heroin dependence significantly altered gut microbiota and impaired intestinal mucosal barrier integrity in mice, highlighting the role of the gut microbiota in substance use disorders and the pathophysiology of withdrawal symptoms.

The Role of Gut Dysbiosis in Acute-on-Chronic Liver Failure

Acute-on-chronic liver failure (ACLF) is an important syndrome of liver failure that has a high risk of short-term mortality in patients with chronic liver disease. The development of ACLF is associated with proinflammatory precipitating events, such as infection, alcoholic hepatitis, and intense systemic inflammation. Recently, the role of the gut microbiome has increasingly emerged in human health and disease. Additionally, the gut microbiome might have a major role in the development of liver disease. In this review, we examine evidence to support the role of gut dysbiosis in cirrhosis and ACLF. Additionally, we explore the mechanism by which the gut microbiome contributes to the development of ACLF, with a focus on alcohol-induced liver disease.

The Microbiome-Gut-Brain Axis, a Potential Therapeutic Target for Substance-Related Disorders

Substance addiction is a complex worldwide public health problem. It endangers both personal life and social stability, causing great loss on economy. Substance-related disorder is considered to be a complicated chronic brain disorder. It resulted from interactions among pharmacological properties of addictive substances, individual susceptibility, and social–environmental factors. Unfortunately, there is still no ideal treatment for this disorder. Recent lines of evidence suggest that gut microbiome may play an important role in the pathogenesis of neuropsychiatric disorders, including substance-related disorders. This review summarizes the research on the relationship between gut microbiome and substance-related disorders, including different types of substance, different individual susceptibility, and the occurrence and development of substance-induced mental disorders. We also discuss the potentiation of gut microbiome in the treatment of substance-related disorders, especially in the treatment of substance-induced mental disorders and manipulation on individuals’ responsiveness to addictive substances.

Bacteroides uniformis CECT 7771 Modulates the Brain Reward Response to Reduce Binge Eating and Anxiety-Like Behavior in Rat

Food addiction (FA) is characterized by behavioral and neurochemical changes linked to loss of food intake control. Gut microbiota may influence appetite and food intake via endocrine and neural routes. The gut microbiota is known to impact homeostatic energy mechanisms, but its role in regulating the reward system is less certain. We show that the administration of Bacteroides uniformis CECT 7771 (B. uniformis) in a rat FA model impacts on the brain reward response, ameliorating binge eating and decreasing anxiety-like behavior. These effects are mediated, at least in part, by changes in the levels of dopamine, serotonin, and noradrenaline in the nucleus accumbens and in the expression of dopamine D1 and D2 receptors in the prefrontal cortex and intestine. B. uniformis reverses the fasting-induced microbiota changes and increases the abundance of species linked to healthy metabolotypes. Our data indicate that microbiota-based interventions might help to control compulsive overeating by modulating the reward response.

Drugs and bugs: Negative affect, psychostimulant use and withdrawal, and the microbiome

BACKGROUND AND OBJECTIVES

A growing body of literature demonstrates that the human microbiota plays a crucial role in health and disease states, as well as in the body's response to stress. In addition, the microbiome plays a role in psychological well-being and regulating negative affect. Regulation of negative affect is a factor in psychostimulant abuse disorders. We propose a risk chain in which stress leads to negative affect that places an individual at risk to develop or relapse to psychostimulant abuse disorder. Stress, negative affect, and psychostimulant use all alter the gut microbiome.

METHODS

This review brings together the literature on affective disorders, stress, and psychostimulant abuse disorders to assess possible modulatory actions of the gut-brain axis to regulate these conditions.

RESULTS

Studies reviewed across the various disciplines suggest that the dysbiosis resulting from drug use, drug withdrawal, or stress may cause an individual to be more susceptible to addiction and relapse. Probiotics and prebiotics reduce stress and negative affect.

SCIENTIFIC SIGNIFICANCE

Treatment during the withdrawal phase of psychostimulant abuse disorder, when the microbiome is altered, may ameliorate the symptoms of stress and negative affect leading to a reduced risk of relapse to psychostimulant use.

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.

Healthy Behaviors Associated with Changes in Mental and Physical Strength in Urban African American and White Adults

Over time, adherence to healthy behaviors may improve physical and mental strength which is essential for successful aging. A plausible mechanism is the reduction of inflammation. Research on the association of risky health behaviors on change in strength with age is limited. This study examined changes in the inflammatory potential of the diet, smoking, illicit drug use with changes in strength in a racially and socioeconomically diverse adult sample from the Healthy Aging in Neighborhoods of Diversity Across the Life Span study. The dietary inflammatory index (DII) was calculated from 35 food components derived from multiple 24-h dietary recalls. Strength was evaluated by handgrip strength (HGS), SF-12 PCS and SF-12 MCS (physical and mental component scores). Repeated measures analyses were used to examine associations. At baseline, mean age was 48.4 ± 0.25 years, 56% of the sample were women, and 58% African American. Significant 4-way interactions were found between age, race, socioeconomic status, and DII for women, on change in HGS (p < 0.05) and in SF-12 PCS (p < 0.05) and for men, in change in SF-12 PCS (p < 0.05). Improvements in SF-12 MCS were associated with all three health behaviors as main effects. This study provided evidence that changes towards improving healthy behaviors, diet with anti-inflammatory potential, not smoking cigarettes and not using illicit drugs, were associated with improved strength. Health professionals, especially registered dietitians and health coaches, should create lifestyle interventions to reduce inflammation targeting change in more than one risky health behavior.

Evidence for Modulation of Substance Use Disorders by the Gut Microbiome: Hidden in Plain Sight

The gut microbiome modulates neurochemical function and behavior and has been implicated in numerous central nervous system (CNS) diseases, including developmental, neurodegenerative, and psychiatric disorders. Substance use disorders (SUDs) remain a serious threat to the public well-being, yet gut microbiome involvement in drug abuse has received very little attention. Studies of the mechanisms underlying SUDs have naturally focused on CNS reward circuits. However, a significant body of research has accumulated over the past decade that has unwittingly provided strong support for gut microbiome participation in drug reward. β-Lactam antibiotics have been employed to increase glutamate transporter expression to reverse relapse-induced release of glutamate. Sodium butyrate has been used as a histone deacetylase inhibitor to prevent drug-induced epigenetic alterations. High-fat diets have been used to alter drug reward because of the extensive overlap of the circuitry mediating them. This review article casts these approaches in a different light and makes a compelling case for gut microbiome modulation of SUDs. Few factors alter the structure and composition of the gut microbiome more than antibiotics and a high-fat diet, and butyrate is an endogenous product of bacterial fermentation. Drugs such as cocaine, alcohol, opiates, and psychostimulants also modify the gut microbiome. Therefore, their effects must be viewed on a complex background of cotreatment-induced dysbiosis. Consideration of the gut microbiome in SUDs should have the beneficial effects of expanding the understanding of SUDs and aiding in the design of new therapies based on opposing the effects of abused drugs on the host's commensal bacterial community. SIGNIFICANCE STATEMENT: Proposed mechanisms underlying substance use disorders fail to acknowledge the impact of drugs of abuse on the gut microbiome. β-Lactam antibiotics, sodium butyrate, and high-fat diets are used to modify drug seeking and reward, overlooking the notable capacity of these treatments to alter the gut microbiome. This review aims to stimulate research on substance abuse-gut microbiome interactions by illustrating how drugs of abuse share with antibiotics, sodium butyrate, and fat-laden diets the ability to modify the host microbial community.

Microbiome and substances of abuse

There is a growing amount of evidence showing a reciprocal relation between the gut microbiota and the brain. Substance use disorders (SUD), which are a major cause of preventable morbidity and mortality worldwide, have an influence on the gut microbiota and on the gut-brain axis. The communication between the microbiota and the brain exists through different pathways: (1) the immune response elicited by bacterial products, coupled with alterations of the intestinal barrier allowing these products to enter the bloodstream, (2) the direct and indirect effects of bacterial metabolites such as short chain fatty acids (SCFAs) or tryptophan on the brain, (3) and the hypothalamic-pituitary-adrenal (HPA) axis, whose peripheral afferents can be influenced by the microbiota, and can in turn activate microglia. Among substances of abuse, alcohol has been the subject of the greatest number of studies in this field. In some but not all patients suffering from alcohol-use-disorder (AUD), alcohol alters the composition of the gut microbiota and the permeability of the intestinal barrier, directly and through dysbiosis. It has also been well demonstrated that alcohol induces a peripheral inflammation; it is still unclear whether it induces a central inflammation, as there are contradictory results in human studies. In animal studies, it has been shown that neuroinflammation increases during alcohol withdrawal. Literature on opioids and stimulants is less numerous. Chronic morphine intake induces dysbiosis, increased intestinal permeability and a probable neuroinflammation, which could explain symptoms such as tolerance, hyperalgesia and deficit in reward behavior. Cocaine induces a dysbiosis and conversely the microbiome can modulate the behavioral response to stimulant drugs. Tobacco cessation is associated with an increase in microbiota diversity. Taken together, the findings of our narrative literature review suggest a bidirectional influence in the pathogenesis of substance use disorders.

Narrative review on potential role of gut microbiota in certain substance addiction

As a neuropsychiatric disorder, substance addiction represents a major public health issue with high prevalence and mortality in many countries. Recently, gut microbiota has been certified to play a part in substance addiction through various mechanisms. Hence, we mainly focused on three substance including alcohol, cocaine and methamphetamine in this review, and summarized their relationships with gut microbiota, respectively. Besides, we also concluded the possible treatments for substance addiction from the perspective of applying gut microbiota. This review aims to build a bridge between substance addiction and gut microbiota according to existing evidences, so as to excavate the possible bi-directional function of microbiota-gut-brain axis in substance addiction for developing therapeutic strategies in the future.

The concomitant use of cannabis and cocaine coexists with increased LPS levels and systemic inflammation in male drug users

Illicit drug use can cause a variety of effects including alterations in the immune system. The aim of this study was to investigate the effects of illicit drugs on circulating lipopolysaccharide (LPS), systemic inflammation and oxidative stress markers in drug users. We evaluated the levels of soluble CD14 (sCD14), LPS, inflammatory (TNF-α and IL-6) and regulatory (IL-10) cytokines, as well as C-reactive protein (CRP), lipid peroxidation (TBARS) and total thiols in the peripheral blood of 81 men included in groups of cannabis (n = 21), cocaine (n = 12), cannabis-plus-cocaine users (n = 27), and non-drug users (n = 21). The use of cannabis plus cocaine leads to higher systemic levels of LPS, CRP, IL-6 and higher IL-6/IL-10 ratio, characterizing a proinflammatory profile. In contrast, a regulatory profile as viewed by lower systemic TNF-α and IL-6 levels and lower TNF-α/IL-10 ratio were observed in cannabis users compared to the control group. Moreover, cocaine users presented a lower content of non-enzymatic antioxidant thiol compared to control group, cannabis group and cannabis plus cocaine group. In conclusion, our results indicate that the use of cannabis contributes to an anti-inflammatory/or regulatory profile while the concomitant cannabis plus cocaine consumption coexists with increased circulating amounts of LPS and proinflammatory status.

Microbiota-gut-brain axis as a regulator of reward processes

Our gut harbours trillions of microorganisms essential for the maintenance of homeostasis and host physiology in health and disease. In the last decade, there has been a growing interest in understanding the bidirectional pathway of communication between our microbiota and the central nervous system. With regard to reward processes there is accumulating evidence from both animal and human studies that this axis may be a key factor in gating reward valence. Focusing on the mesocorticolimbic pathway, we will discuss how the intestinal microbiota is involved in regulating brain reward functions, both in natural (i.e. eating, social or sexual behaviours) and non-natural reinforcers (drug addiction behaviours including those relevant to alcohol, psychostimulants, opioids and cannabinoids). We will integrate preclinical and clinical evidence suggesting that the microbiota-gut-brain axis could be implicated in the development of disorders associated with alterations in the reward system and how it may be targeted as a promising therapeutic strategy. Cover Image for this issue: https://doi.org/10.1111/jnc.15065.

Food Addiction and Tobacco Use Disorder: Common Liability and Shared Mechanisms

As food addiction is being more commonly recognized within the scientific community, parallels can be drawn between it and other addictive substance use disorders, including tobacco use disorder. Given that both unhealthy diets and smoking are leading risk factors for disability and death, a greater understanding of how food addiction and tobacco use disorder overlap with one another is necessary. This narrative review aimed to highlight literature that investigated prevalence, biology, psychology, and treatment options of food addiction and tobacco use disorder. Published studies up to August 2020 and written in English were included. Using a biopsychosocial lens, each disorder was assessed together and separately, as there is emerging evidence that the two disorders can develop concurrently or sequentially within individuals. Commonalities include but are not limited to the dopaminergic neurocircuitry, gut microbiota, childhood adversity, and attachment insecurity. In addition, the authors conducted a feasibility study with the purpose of examining the association between food addiction symptoms and tobacco use disorder among individuals seeking tobacco use disorder treatment. To inform future treatment approaches, more research is necessary to identify and understand the overlap between the two disorders.

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.

Effect of Opioid Use on Immune Activation and HIV Persistence on ART

While there is an emerging consensus that engagement of the Mu opioid receptor by opioids may modulate various stages the HIV life cycle (e.g.: increasing cell susceptibility to infection, promoting viral transcription, and depressing immune responses to virally-infected cells), the overall effect on latency and viral reservoirs remains unclear. Importantly, the hypothesis that the increase in immune activation observed in chronic opioid users by direct or indirect mechanisms (i.e., microbial translocation) would lead to a larger HIV reservoir after ART-suppression has not been supported to date. The potential for a subsequent decrease in reservoirs after ART-suppression has been postulated and is supported by early reports of opioid users having lower latent HIV burden. Here, we review experimental data supporting the link between opioid use and HIV modulation, as well as the scientific premise for expecting differential changes in immune activation and HIV reservoir between different medications for opioid use disorder. A better understanding of potential changes in HIV reservoirs relative to the engagement of the Mu opioid receptor and ART-mediated immune reconstitution will help guide future cure-directed studies in persons living with HIV and opioid use disorder. Graphical Abstract Review. HIV replication, immune activation and dysbiosis: opioids may affect immune reconstitution outcomes despite viral suppression.

Methamphetamine and Cannabis: A Tale of Two Drugs and their Effects on HIV, Brain, and Behavior

HIV infection and drug use intersect epidemiologically, and their combination can result in complex effects on brain and behavior. The extent to which drugs affect the health of persons with HIV (PWH) depends on many factors including drug characteristics, use patterns, stage of HIV disease and its treatment, comorbid factors, and age. To consider the range of drug effects, we have selected two that are in common use by PWH: methamphetamine and cannabis. We compare the effects of methamphetamine with those of cannabis, to illustrate how substances may potentiate, worsen, or even buffer the effects of HIV on the CNS. Data from human, animal, and ex vivo studies provide insights into how these drugs have differing effects on the persistent inflammatory state that characterizes HIV infection, including effects on viral replication, immune activation, mitochondrial function, gut permeability, blood brain barrier integrity, glia and neuronal signaling. Moving forward, we consider how these mechanistic insights may inform interventions to improve brain outcomes in PWH. This review summarizes literature from clinical and preclinical studies demonstrating the adverse effects of METH, as well as the potentially beneficial effects of cannabis, on the interacting systemic (e.g., gut barrier leakage/microbial translocation, immune activation, inflammation) and CNS-specific (e.g., glial activation/neuroinflammation, neural injury, mitochondrial toxicity/oxidative stress) mechanisms underlying HIV-associated neurocognitive disorders.