Morphine induces changes in the gut microbiome and metabolome in a morphine dependence model

The ketogenic diet mitigates opioid-induced hyperalgesia by restoring short-chain fatty acids-producing bacteria in the gut

ABSTRACT

Opioids are commonly prescribed to patients with chronic pain. Chronic opioid usage comes with a slew of serious side effects, including opioid-induced hyperalgesia (OIH). The patients with long-term opioid treatment experience paradoxical increases in nociceptive hypersensitivity, namely, OIH. Currently, treatment options for OIH are extremely lacking. In this study, we show that the ketogenic diet recovers the abnormal pain behavior caused by chronic morphine treatment in male mice, and we further show that the therapeutic effect of the ketogenic diet is mediated through gut microbiome. Our 16S rRNA sequencing demonstrates that chronic morphine treatment causes changes in mouse gut microbiota, specifically a decrease in short-chain fatty acids-producing bacteria, and the sequencing data also show that the ketogenic diet rescues those bacteria in the mouse gut. More importantly, we show that supplementation with short-chain fatty acids (butyrate, propionate, and acetate) can delay the onset of OIH, indicating that short-chain fatty acids play a direct role in the development of OIH. Our findings suggest that gut microbiome could be targeted to treat OIH, and the ketogenic diet can be used as a complementary approach for pain relief in patients with chronic opioid treatment. We only used male mice in this study, and thus, our findings cannot be generalized to both sexes.

Comparing withdrawal- and anxiety-like behaviors following oral and subcutaneous oxycodone administration in C57BL/6 mice

Excessive prescribing and misuse of prescription opioids, such as oxycodone, significantly contributed to the current opioid crisis. Although oxycodone is typically consumed orally by humans, parenteral routes of administration have primarily been used in preclinical models of oxycodone dependence. To address this issue, more recent studies have used oral self-administration procedures to study oxycodone seeking and withdrawal in rodents. Behavioral differences, however, following oral oxycodone intake versus parenteral oxycodone administration remain unclear. Thus, the goal of the current studies was to compare anxiety- and withdrawal-like behaviors using established opioid dependence models of either home cage oral intake of oxycodone (0.5 mg/ml) or repeated subcutaneous (s.c.) injections of oxycodone (10 mg/kg) in male and female mice. Here, mice received 10 days of oral or s.c. oxycodone administration, and following 72 h of forced abstinence, anxiety- and withdrawal-like behaviors were measured using elevated zero maze, open field, and naloxone-induced precipitated withdrawal procedures. Global withdrawal scores were increased to a similar degree following oral and s.c. oxycodone use, while both routes of oxycodone administration had minimal effects on anxiety-like behaviors. When examining individual withdrawal-like behaviors, mice receiving s.c. oxycodone exhibited more paw tremors and jumps during naloxone-induced precipitated withdrawal compared with oral oxycodone mice. These results indicate that both models of oxycodone administration are sufficient to elevate global withdrawal scores, but, when compared with oral consumption, s.c. oxycodone injections yielded more pronounced effects on some withdrawal-like behaviors.

Opioid Use and Gut Dysbiosis in Cancer Pain Patients

Opioids are commonly used for the management of severe chronic cancer pain. Their well-known pharmacological effects on the gastrointestinal system, particularly opioid-induced constipation (OIC), are the most common limiting factors in the optimization of analgesia, and have led to the wide use of laxatives and/or peripherally acting mu-opioid receptor antagonists (PAMORAs). A growing interest has been recently recorded in the possible effects of opioid treatment on the gut microbiota. Preclinical and clinical data, as presented in this review, showed that alterations of the gut microbiota play a role in modulating opioid-mediated analgesia and tolerability, including constipation. Moreover, due to the bidirectional crosstalk between gut bacteria and the central nervous system, gut dysbiosis may be crucial in modulating opioid reward and addictive behavior. The microbiota may also modulate pain regulation and tolerance, by activating microglial cells and inducing the release of inflammatory cytokines and chemokines, which sustain neuroinflammation. In the subset of cancer patients, the clinical meaning of opioid-induced gut dysbiosis, particularly its possible interference with the efficacy of chemotherapy and immunotherapy, is still unclear. Gut dysbiosis could be a new target for treatment in cancer patients. Restoring the physiological amount of specific gut bacteria may represent a promising therapeutic option for managing gastrointestinal symptoms and optimizing analgesia for cancer patients using opioids.

The Role of the Intestinal Flora and Its Derivatives in Neurocognitive Disorders: A Narrative Review from Surgical Perspective

Perioperative neurocognitive dysfunction is a significant concern for population health, impacting postoperative recovery and increasing the financial burden on patients. With an increasing number of surgical procedures being performed, the prevention and management of perioperative neurocognitive dysfunction have garnered significant attention. While factors such as age, lifestyle, genetics, and education are known to influence the development of cognitive dysfunction, recent research has highlighted the role of the gut microbiota in neurological health. An increased abundance of pro-inflammatory gut microbiota can trigger and worsen neuroinflammation, neuronal cell damage, and impaired cellular autophagy. Moreover, the inflammation-promoting gut microbiota can disrupt immune function, impair neuroautophagy, and affect the production and circulation of extracellular vesicles and neurotransmitters. These factors collectively play a role in the onset and advancement of cognitive impairment. This narrative review delves into the molecular mechanisms through which gut microbiota and their derivatives contribute to cognitive impairment, focusing on the impact of anesthesia surgery, changes in gut microbial populations, and perioperative cognitive impairment associations. The study suggests that alterations in the abundance of various bacterial species and their metabolites pre- and post-surgery may be linked to postoperative cognitive impairment. Furthermore, the potential of probiotics or prebiotics in addressing cognitive impairment is discussed, offering a promising avenue for investigating the treatment of perioperative neurocognitive disorders.

Opioids and the Gastrointestinal Tract: The Role of Peripherally Active µ-Opioid Receptor Antagonists in Modulating Intestinal Permeability

Opioid receptors are found throughout the gastrointestinal tract, including the large intestine. Many patients treated with opioids experience opioid-induced constipation (OIC). Laxatives are not effective in most patients, and in those who do initially respond, the efficacy of laxatives generally diminishes over time. In addition, OIC does not spontaneously resolve for most patients. However, complications of opioids extend far beyond simply slowing gastrointestinal transit. Opioid use can affect intestinal permeability through a variety of mechanisms. Toll-like receptors are a crucial component of innate immunity and are tightly regulated within the gut epithelium. Pathologic µ-opioid receptor (MOR) and toll-like receptor signaling, resulting from chronic opioid exposure, disrupts intestinal permeability leading to potentially harmful bacterial translocation, elevated levels of bacterial toxins, immune activation, and increased cytokine production. Peripherally active MOR antagonists, including methylnaltrexone, are effective at treating OIC. Benefits extend beyond simply blocking the MOR; these agents also act to ameliorate opioid-induced disrupted intestinal permeability. In this review, we briefly describe the physiology of the gastrointestinal epithelial border and discuss the impact of opioids on gastrointestinal function. Finally, we consider the use of peripherally active MOR antagonists to treat disrupted intestinal permeability resulting from opioid use and discuss the potential for improved morbidity and mortality in patients treated with methylnaltrexone for opioid-induced bowel disorders.

The interplay between the microbiota and opioid in the treatment of neuropathic pain

Neuropathic pain (NP) is characterized by its complex and multifactorial nature and limited responses to opioid therapy; NP is associated with risks of drug resistance, addiction, difficulty in treatment cessation, and psychological disorders. Emerging research on gut microbiota and their metabolites has demonstrated their effectiveness in alleviating NP and augmenting opioid-based pain management, concurrently mitigating the adverse effects of opioids. This review addresses the following key points: (1) the current advances in gut microbiota research and the challenges in using opioids to treat NP, (2) the reciprocal effects and benefits of gut microbiota on NP, and (3) the interaction between opioids with gut microbiota, as well as the benefits of gut microbiota in opioid-based treatment of NP. Through various intricate mechanisms, gut microbiota influences the onset and progression of NP, ultimately enhancing the efficacy of opioids in the management of NP. These insights pave the way for further pragmatic clinical research, ultimately enhancing the efficacy of opioid-based pain management.

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.

The role of morphine- and fentanyl-induced impairment of intestinal epithelial antibacterial activity in dysbiosis and its impact on the microbiota-gut-brain axis

Recent evidence suggests that chronic exposure to opioid analgesics such as morphine disrupts the intestinal epithelial layer and causes intestinal dysbiosis. Depleting gut bacteria can preclude the development of tolerance to opioid-induced antinociception, suggesting an important role of the gut-brain axis in mediating opioid effects. The mechanism underlying opioid-induced dysbiosis, however, remains unclear. Host-produced antimicrobial peptides (AMPs) are critical for the integrity of the intestinal epithelial barrier as they prevent the pathogenesis of the enteric microbiota. Here, we report that chronic morphine or fentanyl exposure reduces the antimicrobial activity in the ileum, resulting in changes in the composition of bacteria. Fecal samples from morphine-treated mice had increased levels of Akkermansia muciniphila with a shift in the abundance ratio of Firmicutes and Bacteroidetes. Fecal microbial transplant (FMT) from morphine-naïve mice or oral supplementation with butyrate restored (a) the antimicrobial activity, (b) the expression of the antimicrobial peptide, Reg3γ, (c) prevented the increase in intestinal permeability and (d) prevented the development of antinociceptive tolerance in morphine-dependent mice. Improved epithelial barrier function with FMT or butyrate prevented the enrichment of the mucin-degrading A. muciniphila in morphine-dependent mice. These data implicate impairment of the antimicrobial activity of the intestinal epithelium as a mechanism by which opioids disrupt the microbiota-gut-brain axis.

Gut dysbiosis was inevitable, but tolerance was not: temporal responses of the murine microbiota that maintain its capacity for butyrate production correlate with sustained antinociception to chronic voluntary morphine

The therapeutic benefits of opioids are compromised by the development of analgesic tolerance, which necessitates higher dosing for pain management thereby increasing the liability for dependence and addiction. Rodent models indicate opposing roles of the gut microbiota in tolerance: morphine-induced gut dysbiosis exacerbates tolerance, whereas probiotics ameliorate tolerance. Not all individuals develop tolerance which could be influenced by differences in microbiota, and yet no study has capitalized upon this natural variation to identify specific features linked to tolerance. We leveraged this natural variation in a murine model of voluntary oral morphine self-administration to elucidate the mechanisms by which microbiota influences tolerance. Although all mice shared similar and predictive morphine-driven microbiota changes that largely masked informative associations with variability in tolerance, our high-resolution temporal analyses revealed a divergence in the progression of dysbiosis that best explained differences in the development in tolerance. Mice that did not develop tolerance also maintained a higher abundance of taxa capable of producing the short-chain fatty acid (SCFA) butyrate, known to bolster intestinal barriers, suppress inflammation, and promote neuronal homeostasis. Furthermore, dietary butyrate supplementation significantly reduced the development of tolerance. These findings could inform immediate therapies to extend the analgesic efficacy of opioids.

Opioid exposure as a potential risk factor for vancomycin-resistant enterococci colonization in the absence of antimicrobial exposure

BACKGROUND

Antimicrobial exposure leads to an increased risk of colonization and spread of vancomycin-resistant enterococci. Studies have also implicated exposure to nonantimicrobial medications as a potential risk factor for an increased risk of colonization with these pathogens.

METHODS

A matched case-control study was performed to determine specific nonantimicrobial medications associated with vancomycin-resistant enterococci rectal colonization. Cases and controls were defined as persons who were not exposed to antimicrobials in the preceding 12 months and in whom vancomycin-resistant enterococci rectal colonization was and was not detected at hospital admission, respectively. Matching was performed by the date of admission. Data were extracted from electronic medical records and included patient demographics, clinical data, and exposure to non-antimicrobial medications in the preceding 90 days.

RESULTS

Vancomycin-resistant enterococci colonization was identified among 2,919 (4.8%) patients during their first admission among 59,986 admissions. Among these patients, 27 cases were identified and were matched to 63 controls. Exposure to opioids was the only independent risk factor associated with colonization (adjusted odds ratio 3.8 [95% confidence interval 1.4-10.8], P-value = .01).

CONCLUSIONS

Opioid exposure may increase the risk of vancomycin-resistant enterococci colonization. Preventing the acquisition of these pathogens may require infection-prevention efforts targeting persons exposed to opioids.

Progress in the study of intestinal microbiota involved in morphine tolerance

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

Blocking IL-17A prevents oxycodone-induced depression-like effects and elevation of IL-6 levels in the ventral tegmental area and reduces oxycodone-derived physical dependence in rats

Oxycodone is the most prescribed opioid for pain management and has been available in clinics for almost a century, but effects of chronic oxycodone have been studied less than morphine in preclinical and clinical studies. Newly developed depression has been coupled with chronic oxycodone use in a few clinical studies, but no preclinical studies have investigated the pathogenesis of oxycodone-induced depression. Gut microbiome changes following oxycodone use is an understudied area, and interleukin-17A (IL-17A) is linked to both the development of mood disorders and regulation of gut microbiome. The present study investigated effects of chronic oxycodone exposure on mood-related behaviors (depression and anxiety), pain hypersensitivity, physical dependence, immune markers, and the gut microbiome and tested the hypothesis that blocking IL-17A with a systemically administered monoclonal antibody reduces oxycodone-derived effects. Oxycodone (using an incremental dosing regimen) or saline was injected twice a day for 12 days. IL-17A Ab (200 µg/100 µl) or saline was administered every 3rd day during the 12-day interval. Chronic oxycodone induced a depression-like effect, but not anxiogenic- or anxiolytic-like effects; promoted hyperalgesia; increased IL-17A and IL-6 levels in the ventral tegmental area (VTA); and induced physical dependence. IL-17A Ab co-administration with oxycodone prevented the depression-like effect and hyperalgesia, reduced naloxone-precipitated withdrawal signs, and normalized the increase in cytokine levels. Chronic oxycodone exposure did not affect gut microbiome and integrity. Our results identify a role for IL-17A in oxycodone-related behavioral and neuroimmune effects and show that IL-17A Ab has potential therapeutic value in blocking these effects. Given that humanized IL-17A Ab is approved for treatment of psoriasis and psoriatic arthritis, our findings point toward studying it for use in the treatment of oxycodone use disorder.

Long access heroin self-administration significantly alters gut microbiome composition and structure

Introduction

It is well known that chronic opioid use disorder is associated with alterations in gastrointestinal (GI) function that include constipation, reduced motility, and increased bacterial translocation due to compromised gut barrier function. These signs of disrupted GI function can be associated with alterations in the gut microbiome. However, it is not known if long-access opioid self-administration has effects on the gut microbiome.

Methods

We used 16S rRNA gene sequencing to investigate the gut microbiome in three independent cohorts (N=40 for each) of NIH heterogeneous stock rats before onset of long-access heroin self-administration (i.e., naïve status), at the end of a 15-day period of self-administration, and after post-extinction reinstatement. Measures of microbial α- and β-diversity were evaluated for all phases. High-dimensional class comparisons were carried out with MaAsLin2. PICRUSt2 was used for predicting functional pathways impacted by heroin based on marker gene sequences.

Results

Community α-diversity was not altered by heroin at any of the three phases by comparison to saline-yoked controls. Analyses of β-diversity showed that the heroin and saline-yoked groups clustered significantly apart from each other using the Bray-Curtis (community structure) index. Heroin caused significant alterations at the ASV level at the self-administration and extinction phases. At the phylum level, the relative abundance of Firmicutes was increased at the self-administration phase. Deferribacteres was decreased in heroin whereas Patescibacteria was increased in heroin at the extinction phase. Potential biomarkers for heroin emerged from the MaAsLin2 analysis. Bacterial metabolomic pathways relating to degradation of carboxylic acids, nucleotides, nucleosides, carbohydrates, and glycogen were increased by heroin while pathways relating to biosynthesis of vitamins, propionic acid, fatty acids, and lipids were decreased.

Discussion

These findings support the view that long access heroin self-administration significantly alters the structure of the gut microbiome by comparison to saline-yoked controls. Inferred metabolic pathway alterations suggest the development of a microbial imbalance favoring gut inflammation and energy expenditure. Potential microbial biomarkers and related functional pathways likely invoked by heroin self-administration could be targets for therapeutic intervention.

Safety, feasibility, and impact on the gut microbiome of kefir administration in critically ill adults

BACKGROUND

Dysbiosis of the gut microbiome is frequent in the intensive care unit (ICU), potentially leading to a heightened risk of nosocomial infections. Enhancing the gut microbiome has been proposed as a strategic approach to mitigate potential adverse outcomes. While prior research on select probiotic supplements has not successfully shown to improve gut microbial diversity, fermented foods offer a promising alternative. In this open-label phase I safety and feasibility study, we examined the safety and feasibility of kefir as an initial step towards utilizing fermented foods to mitigate gut dysbiosis in critically ill patients.

METHODS

We administered kefir in escalating doses (60 mL, followed by 120 mL after 12 h, then 240 mL daily) to 54 critically ill patients with an intact gastrointestinal tract. To evaluate kefir's safety, we monitored for gastrointestinal symptoms. Feasibility was determined by whether patients received a minimum of 75% of their assigned kefir doses. To assess changes in the gut microbiome composition following kefir administration, we collected two stool samples from 13 patients: one within 72 h of admission to the ICU and another at least 72 h after the first stool sample.

RESULTS

After administering kefir, none of the 54 critically ill patients exhibited signs of kefir-related bacteremia. No side effects like bloating, vomiting, or aspiration were noted, except for diarrhea in two patients concurrently on laxatives. Out of the 393 kefir doses prescribed for all participants, 359 (91%) were successfully administered. We were able to collect an initial stool sample from 29 (54%) patients and a follow-up sample from 13 (24%) patients. Analysis of the 26 paired samples revealed no increase in gut microbial α-diversity between the two timepoints. However, there was a significant improvement in the Gut Microbiome Wellness Index (GMWI) by the second timepoint (P = 0.034, one-sided Wilcoxon signed-rank test); this finding supports our hypothesis that kefir administration can improve gut health in critically ill patients. Additionally, the known microbial species in kefir were found to exhibit varying levels of engraftment in patients' guts.

CONCLUSIONS

Providing kefir to critically ill individuals is safe and feasible. Our findings warrant a larger evaluation of kefir's safety, tolerability, and impact on gut microbiome dysbiosis in patients admitted to the ICU.

TRIAL REGISTRATION

NCT05416814; trial registered on June 13, 2022.

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.

Genetically supported causality between gut microbiota, immune cells and morphine tolerance: a two-sample Mendelian randomization study

Background

Previous researches have suggested a significant connection between the gut microbiota/immune cells and morphine tolerance (MT), but there is still uncertainty regarding their causal relationship. Hence, our objective is to inverstigate this causal association and reveal the impact of gut microbiota/immune cells on the risk of developing MT using a two-sample Mendelian randomization (MR) study.

Methods

We conducted a comprehensive analysis using genome-wide association study (GWAS) summary statistics for gut microbiota, immune cells, and MT. The main approach employed was the inverse variance-weighted (IVW) method in MR. To assess horizontal pleiotropy and remove outlier single-nucleotide polymorphisms (SNPs), we utilized the Mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO) technique as well as MR-Egger regression. Heterogeneity detection was performed using Cochran's Q-test. Additionally, leave-one-out analysis was carried out to determine if any single SNP drove the causal association signals. Finally, we conducted a reverse MR to evaluate the potential of reverse causation.

Results

We discovered that 6 gut microbial taxa and 16 immune cells were causally related to MT (p < 0.05). Among them, 2 bacterial features and 9 immunophenotypes retained a strong causal relationship with lower risk of MT: genus. Lachnospiraceae NK4A136group (OR: 0.962, 95% CI: 0.940-0.987, p = 0.030), genus. RuminococcaceaeUCG011 (OR: 0.960, 95% CI: 0.946-0.976, p = 0.003), BAFF-R on B cell (OR: 0.972, 95% CI: 0.947-0.998, p = 0.013). Furthermore, 4 bacterial features and 7 immunophenotypes were identified to be significantly associated with MT risk: genus. Flavonifractor (OR: 1.044, 95% CI: 1.017-1.069, p = 0.029), genus. Prevotella9 (OR: 1.054, 95% CI: 1.020-1.090, p = 0.037), B cell % CD3-lymphocyte (OR: 1.976, 95% CI: 1.027-1.129, p = 0.026). The Cochrane's Q test revealed no heterogeneity (p > 0.05). Furthermore, the MR-Egger and MR-PRESSO analyses reveal no instances of horizontal pleiotropy (p > 0.05). Besides, leave-one-out analysis confirmed the robustness of MR results. After adding BMI to the multivariate MR analysis, the gut microbial taxa and immune cells exposure-outcome effect were attenuated.

Conclusion

Our research confirm the potential link between gut microbiota and immune cells with MT, shedding light on the mechanism by which gut microbiota and immune cells may contribute to MT. These findings lay the groundwork for future investigations into targeted prevention strategies.

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

Background

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

Methods

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

Results

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

Conclusions

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

Gastrointestinal complications in pediatric lung transplant recipients: Incidence, risk factors, and effects on patient outcomes

BACKGROUND

Gastrointestinal (GI) complications in lung transplant recipients can occur any time during the post-operative period, leading to prolonged morbidity and mortality. Despite the negative association between GI complications and patient outcomes, little is known about their incidence and risk factors for their development in pediatric lung transplant recipients.

METHODS

We performed a retrospective chart review at one pediatric tertiary center to describe the frequency of GI complications in lung transplant recipients. We identified potential risk factors for the diagnosis of gastroparesis, gastroesophageal reflux disease (GERD) and aspiration in the post-transplant period. Lastly, we investigated the association of these complications with mortality and graft survival.

RESULTS

84.3% of lung transplant recipients experienced at least one GI complication in the post-transplant period. Gastroparesis (52.9%), GERD (41.2%), and oropharyngeal dysphagia/laryngeal penetration (33.3%) were the most common complications diagnosed. Post-operative opioid exposure was a risk factor for gastroparesis, with the odds increasing 3.0% each day a patient was prescribed opioids (p = .021). The risk of death or retransplant in individuals who experienced gastroparesis was 2.7 times higher than those not diagnosed with gastroparesis (p = .027).

CONCLUSION

Exposure to opioids in the post-operative period is a risk factor for gastroparesis and a prolonged hospitalization placed patients at risk for aspiration. Gastroparesis was associated with increased patient mortality and graft failure, while aspiration and GERD had no effect on long term outcomes. Future prospective studies investigating the relationship between opioid use and the development of a gastroparesis are necessary to improve patient outcomes.

The human gut microbiome in critical illness: disruptions, consequences, and therapeutic frontiers

With approximately 39 trillion cells and over 20 million genes, the human gut microbiome plays an integral role in both health and disease. Modern living has brought a widespread use of processed food and beverages, antimicrobial and immunomodulatory drugs, and invasive procedures, all of which profoundly disrupt the delicate homeostasis between the host and its microbiome. Of particular interest is the human gut microbiome, which is progressively being recognized as an important contributing factor in many aspects of critical illness, from predisposition to recovery. Herein, we describe the current understanding of the adverse impacts of standard intensive care interventions on the human gut microbiome and delve into how these microbial alterations can influence patient outcomes. Additionally, we explore the potential association between the gut microbiome and post-intensive care syndrome, shedding light on a previously underappreciated avenue that may enhance patient recuperation following critical illness. There is an impending need for future epidemiological studies to encompass detailed phenotypic analyses of gut microbiome perturbations. Interventions aimed at restoring the gut microbiome represent a promising therapeutic frontier in the quest to prevent and treat critical illnesses.

Microbiome Depletion Increases Fentanyl Self-Administration and Alters the Striatal Proteome Through Short-Chain Fatty Acids

Opioid use disorder (OUD) is a public health crisis currently being exacerbated by increased rates of use and overdose of synthetic opioids, primarily fentanyl. Therefore, the identification of novel biomarkers and treatment strategies to reduce problematic fentanyl use and relapse to fentanyl taking is critical. In recent years, there has been a growing body of work demonstrating that the gut microbiome can serve as a potent modulator of the behavioral and transcriptional responses to both stimulants and opioids. Here, we advance this work to define how manipulations of the microbiome drive fentanyl intake and fentanyl-seeking in a translationally relevant drug self-administration model. Depletion of the microbiome of male rats with broad spectrum antibiotics leads to increased drug administration on increased fixed ratio, progressive ratio, and drug seeking after abstinence. Utilizing 16S  sequencing of microbiome contents from these animals, specific populations of bacteria from the gut microbiome correlate closely with levels of drug taking. Additionally, global proteomic analysis of the nucleus accumbens following microbiome manipulation and fentanyl administration to define how microbiome status alters the functional proteomic landscape in this key limbic substructure. These data demonstrate that an altered microbiome leads to marked changes in the synaptic proteome in response to repeated fentanyl treatment. Finally, behavioral effects of microbiome depletion are reversible by upplementation of the microbiome derived short-chain fatty acid metabolites. Taken together, these findings establish clear relevance for gut-brain signaling in models of OUD and lay foundations for further translational work in this space.

Altered gut microbiome drives heightened pain sensitivity in a murine model of metastatic triple-negative breast cancer

The microbiota residing in the gut environment is essential for host homeostasis. Increasing evidence suggests that microbial perturbation (dysbiosis) regulates cancer initiation and progression at local and distant sites. Here, we have identified microbial dysbiosis with the depletion of commensal bacteria as a host-intrinsic factor associated with metastatic dissemination to the bone. Using a mouse model of triple-negative mammary cancer, we demonstrate that a pre-established disruption of microbial homeostasis using an antibiotic cocktail increases tumor growth, enhanced circulating tumor cells, and subsequent dissemination to the bone. We found that the presence of pathogenic bacteria and loss of commensal bacteria in an antibiotic-induced gut environment is associated with sustained inflammation. Increased secretion of G-CSF and MMP-9 in intestinal tissues, followed by increased neutrophil infiltration and severe systemic inflammation in tumor-bearing mice, indicates the direct consequence of a dysbiotic microbiome. Increased neutrophil infiltration to the bone metastatic niche facilitates extravasation and transendothelial migration of tumor cells. It provides a novel, pre-established, and favorable environment to form an immunosuppressive pre-metastatic niche. The presence of tumor cells in immunosuppressive metastatic tumor niche disrupts the balance between osteoblasts and osteoclasts, promotes osteoclast differentiation, and remodels the bone structure. Excessive bone resorption by osteoclasts causes bone degradation and ultimately causes extreme pain in a bone metastatic mouse model. In clinical settings, bone metastasis is associated with intractable severe pain that severely compromises the quality of life in these patients.

Opioid-induced dysbiosis of maternal gut microbiota during gestation alters offspring gut microbiota and pain sensitivity

There has been a rapid increase in neonates born with a history of prenatal opioid exposure. How prenatal opioid exposure affects pain sensitivity in offspring is of interest, as this may perpetuate the opioid epidemic. While few studies have reported hypersensitivity to thermal pain, potential mechanisms have not been described. This study posits that alterations in the gut microbiome may underly hypersensitivity to pain in prenatally methadone-exposed 3-week-old male offspring, which were generated using a mouse model of prenatal methadone exposure. Fecal samples collected from dams and their offspring were subjected to 16s rRNA sequencing. Thermal and mechanical pain were assessed using the tail flick and Von Frey assays. Transcriptomic changes in whole brain samples of opioid or saline-exposed offspring were investigated using RNA-sequencing, and midbrain sections from these animals were subjected to qPCR profiling of genes related to neuropathic and inflammatory pain pathways. Prenatal methadone exposure increased sensitivity to thermal and mechanical pain and elevated serum levels of IL-17a. Taxonomical analysis revealed that prenatal methadone exposure resulted in significant alterations in fecal gut microbiota composition, including depletion of Lactobacillus, Bifidobacterium, and Lachnospiracea sp and increased relative abundance of Akkermansia, Clostridium sensu stricto 1, and Lachnoclostridium. Supplementation of the probiotic VSL#3 in dams rescued hypersensitivity to thermal and mechanical pain in prenatally methadone-exposed offspring. Similarly, cross-fostering prenatally methadone-exposed offspring to control dams also attenuated hypersensitivity to thermal pain in opioid-exposed offspring. Modulation of the maternal and neonatal gut microbiome with probiotics resulted in transcriptional changes in genes related to neuropathic and immune-related signaling in whole brain and midbrain samples of prenatally methadone-exposed offspring. Together, our work provides compelling evidence of the gut-brain-axis in mediating pain sensitivity in prenatally opioid-exposed offspring.

Microbial short-chain fatty acids regulate drug seeking and transcriptional control in a model of cocaine seeking

Cocaine use disorder represents a public health crisis with no FDA-approved medications for its treatment. A growing body of research has detailed the important connections between the brain and the resident population of bacteria in the gut, the gut microbiome, in psychiatric disease models. Acute depletion of gut bacteria results in enhanced reward in a mouse cocaine place preference model, and repletion of bacterially-derived short-chain fatty acid (SCFA) metabolites reverses this effect. However, the role of the gut microbiome and its metabolites in modulating cocaine-seeking behavior after prolonged abstinence is unknown. Given that relapse prevention is the most clinically challenging issue in treating substance use disorders, studies examining the effects of microbiome manipulations in relapse-relevant models are critical. Here, male Sprague-Dawley rats received either untreated water or antibiotics to deplete the gut microbiome and its metabolites. Rats were trained to self-administer cocaine and subjected to either within-session threshold testing to evaluate motivation for cocaine or 21 days of abstinence followed by a cue-induced cocaine-seeking task to model relapse behavior. Microbiome depletion did not affect cocaine acquisition on an fixed-ratio 1 schedule. However, microbiome-depleted rats exhibited significantly enhanced motivation for low dose cocaine on a within-session threshold task. Similarly, microbiome depletion increased cue-induced cocaine-seeking following prolonged abstinence and altered transcriptional regulation in the nucleus accumbens. In the absence of a normal microbiome, repletion of bacterially-derived SCFA metabolites reversed the behavioral and transcriptional changes associated with microbiome depletion. These findings suggest that gut bacteria, via their metabolites, are key regulators of drug-seeking behaviors, positioning the microbiome as a potential translational research target.

The bidirectional relationship between opioids and the gut microbiome: Implications for opioid tolerance and clinical interventions

Opioids are widely used in treating patients with acute and chronic pain; however, this class of drugs is also commonly abused. Opioid use disorder and associated overdoses are becoming more prevalent as the opioid crisis continues. Chronic opioid use is associated with tolerance, which decreases the efficacy of opioids over time, but also puts individuals at risk of fatal overdoses. Therefore, it is essential to identify strategies to reduce opioid tolerance in those that use these agents. The gut microbiome has been found to play a critical role in opioid tolerance, with opioids causing dysbiosis of the gut, and changes in the gut microbiome impacting opioid tolerance. These changes in turn have a detrimental effect on the gut microbiome, creating a positive feedback cycle. We review the bidirectional relationship between the gut microbiome and opioid tolerance, discuss the role of modulation of the gut microbiome as a potential therapeutic option in opioid-induced gut dysbiosis, and suggest opportunities for further research and clinical interventions.

Multi-omics analysis revealing the interplay between gut microbiome and the host following opioid use

Opioid crisis is an ongoing epidemic since the past several decades in the United States. Opioid use-associated microbial dysbiosis is emerging as a key regulator of intestinal homeostasis and behavioral responses to opioid. However, the mechanistic insight into the role of microbial community in modulating host response is unavailable. To uncover the role of opioid-induced dysbiosis in disrupting intestinal homeostasis we utilized whole genome sequencing, untargeted metabolomics, and mRNA sequencing to identify changes in microbiome, metabolome, and host transcriptome respectively. Morphine treatment resulted in significant expansion of Parasuterella excrementihominis, Burkholderiales bacterium 1_1_47, Enterococcus faecalis, Enterorhabdus caecimuris and depletion of Lactobacillus johnsonii. These changes correlated with alterations in lipid metabolites and flavonoids. Significant alteration in microbial metabolism (metabolism of lipids, amino acids, vitamins and cofactors) and increased expression of virulence factors and biosynthesis of lipopolysaccharides (LPS) and lipoteichoic acid (LTA) were observed in microbiome of morphine-treated animals. In concurrence with changes in microbiome and metabolome extensive changes in innate and adaptive immune response, lipid metabolism, and gut barrier dysfunction were observed in the host transcriptome. Microbiome depleted mice displayed lower levels of inflammation, immune response and tissue destruction compared to mice harboring a dysbiotic microbiome in response to morphine treatment, thus establishing dysbiotic microbiome as mediator of morphine gut pathophysiology. Integrative analysis of multi-omics data highlighted the associations between Parasutterella excrementihominis, Burkholderiales bacterium 1_1_47, Enterococcus faecalis, Enterorhabdus caecimuris and altered levels of riboflavin, flavonoids, and lipid metabolites including phosphocholines, carnitines, bile acids, and ethanolamines with host gene expression changes involved in inflammation and barrier integrity of intestine. Omic analysis also highlighted the role of probiotic bacteria Lactobacillus johnsonii, metabolites flavonoids and riboflavin that were depleted with morphine as important factors for intestinal homeostasis. This study presents for the first time ever an interactive view of morphine-induced changes in microbial metabolism, strain level gut microbiome analysis and comprehensive view of changes in gut transcriptome. We also identified areas of potential therapeutic interventions to limit microbial dysbiosis and present a unique resource to the opioid research community.

Functional hydrogel-based wound dressings: A review on biocompatibility and therapeutic efficacy

Chronic wounds, burns, and surgical incisions represent critical healthcare challenges that significantly impact patient quality of life and strain healthcare resources. In response to these pressing needs, the field of wound healing has witnessed a radical advancement with the emergence of functional hydrogel-based dressings. This review article underscores the severity and importance of this transformative study in the domain of wound healing. The hydrogel matrix offers a moist and supportive environment that facilitates cellular migration, proliferation, and tissue regeneration, vital for efficient wound closure. Their conformable nature ensures patient comfort, reducing pain and uneasiness during dressing changes, particularly in chronic wounds where frequent interventions are required. Beyond their structural merits, functional hydrogel dressings possess the capability of incorporating bioactive molecules such as growth factors and antimicrobial agents. This facilitates targeted and sustained delivery of therapeutics directly to the wound site, addressing the multifactorial nature of chronic wounds and enhancing the healing trajectory. The integration of advanced nanotechnology has propelled the design of hydrogel dressings with enhanced mechanical strength and controlled drug release profiles, amplifying their therapeutic potential. In conclusion, the significance of this study lies in its ability to revolutionize wound healing practices and positively impact the lives of countless individuals suffering from chronic wounds and burns. As this transformative technology gains momentum, it holds the promise of addressing a major healthcare burden worldwide, thus heralding a new era in wound care management.

Probiotics in Postoperative Pain Management

Postoperative pain is the unpleasant sensory and emotional experience after surgery, its origin being both the inflammatory reaction induced by the surgical trauma on the abdominal wall and the splanchnic pain induced by the activation of nociceptors of the viscera, which are highly sensitive to distension, ischemia, and inflammation. Nowadays, it is well recognized that there is a close relationship between the gut microbiome and pain perception, and that microbiome is highly affected by both anesthesia and surgical manipulation. Thus, efforts to restore the disturbed microbiome via supplementation with beneficial bacteria, namely probiotics, seem to be effective. In this article, the knowledge gained mainly from experimental research on this topic is analyzed, the concluding message being that each probiotic strain works in its own way towards pain relief.

Insights into the Current and Possible Future Use of Opioid Antagonists in Relation to Opioid-Induced Constipation and Dysbiosis

Opioid receptor agonists, particularly those that activate µ-opioid receptors (MORs), are essential analgesic agents for acute or chronic mild to severe pain treatment. However, their use has raised concerns including, among others, intestinal dysbiosis. In addition, growing data on constipation-evoked intestinal dysbiosis have been reported. Opioid-induced constipation (OIC) creates an obstacle to continuing treatment with opioid analgesics. When non-opioid therapies fail to overcome the OIC, opioid antagonists with peripheral, fast first-pass metabolism, and gastrointestinal localized effects remain the drug of choice for OIC, which are discussed here. At first glance, their use seems to only be restricted to constipation, however, recent data on OIC-related dysbiosis and its contribution to the appearance of several opioid side effects has garnered a great of attention from researchers. Peripheral MORs have also been considered as a future target for opioid analgesics with limited central side effects. The properties of MOR antagonists counteracting OIC, and with limited influence on central and possibly peripheral MOR-mediated antinociception, will be highlighted. A new concept is also proposed for developing gut-selective MOR antagonists to treat or restore OIC while keeping peripheral antinociception unaffected. The impact of opioid antagonists on OIC in relation to changes in the gut microbiome is included.

Methadone maintenance treatment is more effective than compulsory detoxification in addressing gut microbiota dysbiosis caused by heroin abuse

Introduction

Heroin use disorder (HUD) is commonly accompanied by gut dysbiosis, but the roles of gut microbiota in HUD treatment, such as compulsory detoxification and methadone maintenance treatment (MMT), remain poorly understood.

Methods

In this study, we performed 16 s rDNA and whole metagenome sequencing to analyze the gut microbial profiles of HUD patients undergoing heroin addiction, heroin withdrawal (compulsory detoxification), and MMT.

Results

Our findings revealed that, compared to healthy controls, microbial diversity was significantly decreased in HUD patients who were in a state of heroin addiction and withdrawal, but not in those receiving MMT. We observed significant alterations in 10 bacterial phyla and 20 bacterial families in HUD patients, while MMT partially restored these changes. Whole metagenome sequencing indicated gut microbiota functions were significantly disrupted in HUD patients experiencing heroin addiction and withdrawal, but MMT was found to almost reverse these dysfunctions. In addition, we identified 24 featured bacteria at the genus level that could be used to effectively distinguish between healthy individuals and those with heroin addiction, heroin withdrawal, or receiving MMT. Furthermore, we found the relative abundance of Actinomyces, Turicibacter and Weissella were positively associated with the Hamilton Depression Scale score in different states of HUD patients.

Discussion

This study provides evidence from the gut microbiota perspective that MMT is a more effective approach than compulsory detoxification for HUD treatment.

Short-chain fatty acid, butyrate prevents morphine-and paclitaxel-induced nociceptive hypersensitivity

Nociceptive hypersensitivity is a significant side effect with the chronic administration of opioids as well as chemotherapeutics. Both opioid-induced hypersensitivity (OIH) and chemotherapy-induced hypersensitivity (CIH) are characterized by an increased sensitivity to painful stimuli which can significantly reduce the quality of life for individuals on either drug(s). Here we demonstrate the nociceptive hypersensitivity associated with repeated administration of morphine (opioid) and paclitaxel (chemotherapeutic) treatment can be reversed by oral supplementation with the short-chain fatty acid (SCFA) sodium butyrate (NaBut). In two separate mouse behavioral models for nociceptive hypersensitivity, we found that thermal hyperalgesia (for OIH) and cold allodynia (for CIH) were prevented by treatment with oral butyrate (p.o, b.i.d). Electrophysiological recordings of small diameter dorsal root ganglia (DRG) neurons from morphine and paclitaxel treated mice showed an increase in neuronal hyperexcitability in both drug models which was likewise prevented by oral butyrate treatment. Using colonic conditioned media obtained from excised colon segments we found that gut mediators of morphine treated mice can induce hyperexcitability in naïve DRG neurons, but such enhanced excitability is not present when animals are co-treated with NaBut suggesting gut derived mediators modulate neuronal hyperexcitability. In-vitro NaBut treatment did not prevent morphine-induced excitability, suggesting an indirect role of butyrate in modulating neuronal hypersensitivity. These data taken together suggest that gut derived mediators affect opioid and chemotherapeutic-induced neuronal hypersensitivity that is prevented by the SCFA butyrate.

Perinatal Morphine Exposure Induces Long-Term Changes in the Intestinal Microbiota of Male and Female Rats

The increased use of opioids by women of reproductive age has resulted in a dramatic rise in number of infants exposed to opioids in utero. Although perinatal opioid exposure (POE) has been associated with an elevated risk of infection and hospitalization later in life, the mechanism(s) by which opioids influence immune development and maturation is not fully elucidated. Alterations in the intestinal microbiota composition, which leads to changes in immune training and maturation, could be at play. Chronic opioid use in adults is associated with a proinflammatory and pathogenic microbiota composition; therefore, we hypothesized here that in utero morphine exposure could negatively affect intestinal microbiota composition, leading to alterations in immune system function. We report that a clinically-relevant model of perinatal opioid exposure, in rats, induces profound intestinal microbiota dysbiosis that is maintained into adulthood. Furthermore, microbial maturity was reduced in morphine-exposed offspring. This suggests that increased risk of infection observed in children exposed to opioids during gestation may be a consequence of microbiota alterations with downstream impact on immune system development. Further investigation of how perinatal morphine induces dysbiosis will be critical to the development of early life interventions designed to ameliorate the increased risk of infection observed in these children.

Effect of germ-free status on transcriptional profiles in the nucleus accumbens and transcriptomic response to chronic morphine

Opioid use disorder is a public health crisis that causes tremendous suffering for patients as well as substantial social and economic costs for society. There are currently available treatments for patients with opioid use disorder, but they remain intolerable or ineffective for many. Thus the need to develop new avenues for therapeutics development in this space is great. Substantial work in models of substance use disorders, including opioid use disorder, demonstrates that prolonged exposure to drugs of abuse leads to marked transcriptional and epigenetic dysregulation in limbic substructures. It is widely believed that these changes in gene regulation in response to drugs are a key driving factor in the perpetuation of drug taking and seeking behaviors. Thus, development of interventions that could shape transcriptional regulation in response to drugs of abuse would be of high value. Over the past decade there has been a surge in research demonstrating that the resident bacteria of the gastrointestinal tract, collectively the gut microbiome, can have tremendous influence on neurobiological and behavioral plasticity. Previous work from our group and others has demonstrated that alterations in the gut microbiome can alter behavioral responses to opioids in multiple paradigms. Additionally, we have previously reported that depletion of the gut microbiome with antibiotics markedly shifts the transcriptome of the nucleus accumbens following prolonged morphine exposure. In this manuscript we present a comprehensive analysis of the effects of the gut microbiome on transcriptional regulation of the nucleus accumbens following morphine by utilizing germ-free, antibiotic treated, and control mice. This allows for detailed understanding of the role of the microbiome in regulating baseline transcriptomic control, as well as response to morphine. We find that germ-free status leads to a marked gene dysregulation in a manner distinct to adult mice treated with antibiotics, and that altered gene pathways are highly related to cellular metabolic processes. These data provide additional insight into the role of the gut microbiome in modulating brain function and lay a foundation for further study in this area.

The role of the gut microbiome and microbial metabolism in mediating opioid-induced changes in the epigenome

The current opioid pandemic is a major public health crisis in the United States, affecting millions of people and imposing significant health and socioeconomic burdens. Preclinical and clinical research over the past few decades has delineated certain molecular mechanisms and identified various genetic, epigenetic, and environmental factors responsible for the pathophysiology and comorbidities associated with opioid use. Opioid use-induced epigenetic modifications have been identified as one of the important factors that mediate genetic changes in brain regions that control reward and drug-seeking behavior and are also implicated in the development of tolerance. Recently, it has been shown that opioid use results in microbial dysbiosis, leading to gut barrier disruption, which drives systemic inflammation, impacting the perception of pain, the development of analgesic tolerance, and behavioral outcomes. In this review, we highlight the potential role of microbiota and microbial metabolites in mediating the epigenetic modifications induced by opioid use.

Immune profiling in Puerto Rican injection drug users with and without HIV-1 infection

Antiretroviral therapy has been effective in suppressing HIV viral load and enabling people living with HIV to experience longer, more conventional lives. However, as people living with HIV are living longer, they are developing aging-related diseases prematurely and are more susceptible to comorbidities that have been linked to chronic inflammation. Coincident with HIV infection and aging, drug abuse has also been independently associated with gut dysbiosis, microbial translocation, and inflammation. Here, we hypothesized that injection drug use would exacerbate HIV-induced immune activation and inflammation, thereby intensifying immune dysfunction. We recruited 50 individuals not using injection drugs (36/50 HIV+) and 47 people who inject drugs (PWID, 12/47 HIV+). All but 3 of the HIV+ subjects were on antiretroviral therapy. Plasma immune profiles were characterized by immunoproteomics, and cellular immunophenotypes were assessed using mass cytometry. The immune profiles of HIV+/PWID-, HIV-/PWID+, and HIV+/PWID+ were each significantly different from controls; however, few differences between these groups were detected, and only 3 inflammatory mediators and 2 immune cell populations demonstrated a combinatorial effect of injection drug use and HIV infection. In conclusion, a comprehensive analysis of inflammatory mediators and cell immunophenotypes revealed remarkably similar patterns of immune dysfunction in HIV-infected individuals and in people who inject drugs with and without HIV-1 infection.

Gut-derived bacterial LPS attenuates incubation of methamphetamine craving via modulating microglia

BACKGROUND

The microbiota-gut-brain axis plays a critical role in the pathophysiology of neuropsychiatric disorders, and the compositions of gut microbiota are altered by addictive drugs. However, the role of gut microbiota in the incubation of methamphetamine (METH) craving remains poorly understood.

METHODS

16S rRNA gene sequencing was performed to assess the richness and diversity of gut microbiota in METH self-administration model. Hematoxylin and eosin staining was performed to evaluate the integrity of intestinal barrier. Immunofluorescence and three-dimensional reconstruction were performed to assess the morphologic changes of microglia. Serum levels of lipopolysaccharide (LPS) were determined using the rat enzyme-linked immunosorbent assay kits. Quantitative real-time PCR was performed to assess transcript levels of dopamine receptor, glutamate ionotropic AMPA receptor 3 and brain-derived neurotrophic factor.

RESULTS

METH self-administration induced gut microbiota dysbiosis, intestinal barrier damage and microglia activation in the nucleus accumbens core (NAcc), which was partially recovered after prolonged withdrawal. Microbiota depletion via antibiotic treatment increased LPS levels and induced a marked change in the microglial morphology in the NAcc, as indicated by the decreases in the lengths and numbers of microglial branches. Depleting the gut microbiota also prevented the incubation of METH craving and increased the population of Klebsiella oxytoca. Furthermore, Klebsiella oxytoca treatment or exogenous administration of the gram-negative bacterial cell wall component LPS increased serum and central LPS levels, induced microglial morphological changes and reduced the dopamine receptor transcription in the NAcc. Both treatments and NAcc microinjections of gut-derived bacterial LPS significantly decreased METH craving after prolonged withdrawal.

CONCLUSIONS

These data suggest that LPS from gut gram-negative bacteria may enter circulating blood, activate microglia in the brain and consequently decrease METH craving after withdrawal, which may have important implications for novel strategies to prevent METH addiction and relapse.

Alterations of gut microbiome following gastrointestinal surgical procedures and their potential complications

Intestinal microorganisms play a crucial role in shaping the host immunity and maintaining homeostasis. Nevertheless, alterations in gut bacterial composition may occur and these alterations have been linked with the pathogenesis of several diseases. In surgical practice, studies revealed that the microbiome of patients undergoing surgery changes and several post-operative complications seem to be associated with the gut microbiota composition. In this review, we aim to provide an overview of gut microbiota (GM) in surgical disease. We refer to several studies which describe alterations of GM in patients undergoing different types of surgery, we focus on the impacts of peri-operative interventions on GM and the role of GM in development of post-operative complications, such as anastomotic leak. The review aims to enhance comprehension regarding the correlation between GM and surgical procedures based in the current knowledge. However, preoperative and postoperative synthesis of GM needs to be further examined in future studies, so that GM-targeted measures could be assessed and the different surgery complications could be reduced.

Short-chain fatty acid, Butyrate prevents Morphine and Paclitaxel induced peripheral hypersensitivity

Peripheral hypersensitivity is a significant side effect with the chronic administration of opioids as well as chemotherapeutics. Both opioid-induced hypersensitivity (OIH) and chemotherapy induced hypersensitivity (CIH) are characterized by an increased sensitivity to painful stimuli which can significantly reduce the quality of life for individuals on either drug(s). Here we demonstrate the peripheral hypersensitivity associated with chronic morphine (opioid) and paclitaxel (chemotherapeutic) treatment can be reversed by oral supplementation with the short-chain fatty acid (SCFA) sodium butyrate. In two separate mouse behavioral models for peripheral hypersensitivity, we found that thermal hyperalgesia (for OIH) and cold allodynia (for CIH) were prevented by co-treatment with oral butyrate. Electrophysiological recordings of small diameter dorsal root ganglia (DRG) neurons from morphine and paclitaxel treated mice showed an increase in neuronal hyperexcitability in both drug models which was likewise prevented by oral butyrate treatment. Using colonic conditioned media obtained from excised colon segments we found that gut mediators of morphine treated mice can induce hyperexcitability in naïve DRG neurons, but such enhanced excitability is not present when animals are co-treated with butyrate suggesting gut derived mediators modulate neuronal hyperexcitability. In-vitro butyrate treatment did not prevent morphine induced excitability, suggesting an indirect role of sodium butyrate in modulating neuronal hypersensitivity. These data taken together suggest that gut derived mediators affect opioid and chemotherapeutic induced neuronal hypersensitivity that is prevented by the SCFA butyrate.

Opioid-induced microbial dysbiosis disrupts irinotecan (CPT-11) metabolism and increases gastrointestinal toxicity in a murine model

BACKGROUND AND PURPOSE

Opioids are commonly used for the management of cancer-associated pain and chemotherapy-induced diarrhoea. The chemotherapeutic irinotecan (CPT-11) causes severe gastrointestinal (GI) toxicity due to deconjugation of inactive metabolite SN-38 glucuronide (SN-38G) by bacterial β-glucuronidases to the active 7-ethyl-10-hydroxycamptothecin (SN-38). Opioids are known to cause gut microbial dysbiosis, this study evaluated whether CPT-11 anti-tumour efficacy and GI toxicity are exacerbated by opioid co-administration.

EXPERIMENTAL APPROACH

Eight-week-old C57BL/6 male mice were co-administration with CPT-11 ± opioid. 16S rRNA sequencing was used for gut microbiome analysis. LC-MS analyses of plasma and intestinal extracts were performed to investigate the pharmacokinetic profile of CPT-11. Histological analysis and quantitative real-time polymerase chain reaction were used to determine the severity of intestinal tissue damage. Human liver microsome In vitro assay was performed to confirm the effects of opioids on CPT-11 metabolism.

KEY RESULTS

Gut microbiome analysis showed that morphine treatment induced enrichment of β-glucuronidase-producing bacteria in the intestines of CPT-11-treated mice, resulting in SN-38 accumulation and exacerbation of GI toxicity in the small intestine. Oral administration of both antibiotics and glucuronidase inhibitor protected mice against GI toxicity induced with CPT-11 and morphine co-administration, implicating a microbiome-dependent mechanism. Additionally, morphine and loperamide decreased the plasma concentration of SN-38 and compromised CPT-11 anti-tumour efficacy, this seemed to be microbiome independent.

CONCLUSION AND IMPLICATIONS

Gut microbiota play a significant role in opioid and chemotherapeutic agent drug-drug interactions. Inhibition of gut microbial glucuronidase may also prevent adverse GI effects of CPT-11 in patients on opioids.

HIV, opioid use, and alterations to the gut microbiome: elucidating independent and synergistic effects

Background

The microbiome is essential to immune development, defense against pathogens, and modulation of inflammation. Microbial dysbiosis has been reported in various diseases including human immunodeficiency virus (HIV) and opioid use disorder (OUD). Notably, people living with HIV (PLWH) have been reported to both have higher rates of OUD and use opioids at higher rates than the general public. Thus, studying gut microbial alterations in people living with HIV and with OUD could elucidate mechanisms pertaining to how these conditions both shape and are shaped by the microbiome. However, to date few studies have investigated how HIV and OUD in combination impact the microbiome.

Aim of review

Here, we review previous studies outlining interactions between HIV, opioid use, and microbial dysbiosis and describe attempts to treat this dysbiosis with fecal microbial transplantation, probiotics, and dietary changes.

Key scientific concepts of review

While the limited number of studies prevent overgeneralizations; accumulating data suggest that HIV and opioid use together induce distinct alterations in the gut microbiome. Among the three existing preclinical studies of HIV and opioid use, two studies reported a decrease in Lachnospiraceae and Ruminococcaceae, and one study reported a decrease in Muribaculaceae in the combined HIV and opioid group relative to HIV-alone, opioid-alone, or control groups. These bacteria are known to modulate immune function, decrease colonic inflammation, and maintain gut epithelial barrier integrity in healthy individuals. Accordingly, modulation of the gut microbiome to restore gut homeostasis may be attempted to improve both conditions. While mixed results exist regarding treating dysbiosis with microbial restoration in PLWH or in those with opioid dependency, larger well-defined studies that can improve microbial engraftment in hosts hold much promise and should still be explored.

Microbiome Contributions to Health

The human microbiome is vast and is present in spaces previously thought to be sterile such as the lungs. A healthy microbiome is diverse and functions in an adaptive way to support local as well as organism health and function. Furthermore, a normal microbiome is essential for normal immune system development rendering the array of microbes that live in and on the human body key components of homeostasis. A wide array of clinical conditions and interventions including anesthesia, analgesia, and surgical intervention may derange the human microbiome in a maladaptive fashion with bacterial responses spanning decreased diversity to transformation to a pathogenic phenotype. Herein, we explore the normal microbiome of the skin, gastrointestinal tract, and the lungs as prototype sites to describe the influence of the microbiomes in each of those locations on health, and how care may derange those relations.

Changes in Plasma Metabolic Signature upon Acute and Chronic Morphine Administration in Morphine-Tolerant Mice

Morphine administration causes system-level metabolic changes. Here, we show that morphine-tolerant mice exhibited distinct plasma metabolic signatures upon acute and chronic administration. We utilized a mouse model of morphine tolerance by exposing mice to increasing doses of the drug over 4 days. We collected plasma samples from mice undergoing acute or chronic morphine or saline injections and analyzed them using targeted GC–MS-based metabolomics to profile approximately 80 metabolites involved in the central carbon, amino acid, nucleotide, and lipid metabolism. Our findings reveal distinct alterations in plasma metabolite concentrations in response to acute or chronic morphine intake, and these changes were linked to the development of tolerance to morphine’s analgesic effects. We identified several metabolites that had been differentially affected by acute versus chronic morphine use, suggesting that metabolic changes may be mitigated by prolonged exposure to the drug. Morphine-tolerant mice showed a restoration of amino acid and glycolytic metabolites. Additionally, we conducted reconstructed metabolic network analysis on the first 30 VIP-ranked metabolites from the PLSDA of the saline, acute, and morphine-tolerant mice groups, which uncovered four interaction networks involving the amino acid metabolism, the TCA cycle, the glutamine-phenylalanine-tyrosine pathway, and glycolysis. These pathways were responsible for the metabolic differences observed following distinct morphine administration regimens. Overall, this study provides a valuable resource for future investigations into the role of metabolites in morphine-induced analgesia and associated effects following acute or chronic use in mice.

The Microbiome and Mental Health Across the Lifespan

INTRODUCTION

The combined genetic material of the microorganisms in the human body, known as the microbiome, is being increasingly recognized as a major determinant of human health and disease. Although located predominantly on mucosal surfaces, these microorganisms have profound effects on brain functioning through the gut-brain axis.

METHOD

The content of the chapter is based on a study group session at the annual meeting of the American College of Neuropsychopharmacology (ACNP). The objective was to discuss the emerging relationship between the human microbiome and mental health as relevant to ACNP's interests in developing and evaluating novel neuropsychiatric treatment strategies. The focus is on specific brain disorders, such as schizophrenia, substance use, and Alzheimer's disease, as well as on broader clinical issues such as suicidality, loneliness and wisdom in old age, and longevity.

RESULTS

Studies of schizophrenia indicate that the microbiome of individuals with this disorder differs from that of non-psychiatric comparison groups in terms of diversity and composition. Differences are also found in microbial metabolic pathways. An early study in substance use disorders found that individuals with this disorder have lower levels of beta diversity in their oral microbiome than a comparison group. This measure, along with others, was used to distinguish individuals with substance use disorders from controls. In terms of suicidality, there is preliminary evidence that persons who have made a suicide attempt differ from psychiatric and non-psychiatric comparison groups in measures of beta diversity. Exploratory studies in Alzheimer's disease indicate that gut microbes may contribute to disease pathogenesis by regulating innate immunity and neuroinflammation and thus influencing brain function. In another study looking at the microbiome in older adults, positive associations were found between wisdom and alpha diversity and negative associations with subjective loneliness. In other studies of older adults, here with a focus on longevity, individuals with healthy aging and unusually long lives had an abundance of specific microorganisms which distinguished them from other individuals.

DISCUSSION

Future studies would benefit from standardizing methods of sample collection, processing, and analysis. There is also a need for the standardized collection of relevant demographic and clinical data, including diet, medications, cigarette smoking, and other potentially confounding factors. While still in its infancy, research to date indicates a role for the microbiome in mental health disorders and conditions. Interventions are available which can modulate the microbiome and lead to clinical improvements. These include microbiome-altering medications as well as probiotic microorganisms capable of modulating the inflammation in the brain through the gut-brain axis. This research holds great promise in terms of developing new methods for the prevention and treatment of a range of human brain disorders.

Clinical significance of microbiota changes under the influence of psychotropic drugs. An updated narrative review

Relationship between drugs and microbiota is bilateral. Proper composition thus function of microbiota is a key to some medications used in modern medicine. However, there is also the other side of the coin. Pharmacotherapeutic agents can modify the microbiota significantly, which consequently affects its function. A recently published study showed that nearly 25% of drugs administered to humans have antimicrobial effects. Multiple antidepressants are antimicrobials,. and antibiotics with proven antidepressant effects do exist. On the other hand, antibiotics (e.g., isoniaside, minocycline) confer mental phenotype changes, and adverse effects caused by some antibiotics include neurological and psychological symptoms which further supports the hypothesis that intestinal microbiota may affect the function of the central nervous system. Here we gathered comprehensively data on drugs used in psychiatry regarding their antimicrobial properties. We believe our data has strong implications for the treatment of psychiatric entities. Nevertheless the study of ours highlights the need for more well-designed trials aimed at analysis of gut microbiota function.

Interactions between NSAIDs, opioids and the gut microbiota - Future perspectives in the management of inflammation and pain

The composition of intestinal microbiota is influenced by a number of factors, including medications, which may have a substantial impact on host physiology. Nonsteroidal anti-inflammatory drugs (NSAIDs) and opioid analgesics are among those widely used medications that have been shown to alter microbiota composition in both animals and humans. Although much effort has been devoted to identify microbiota signatures associated with these medications, much less is known about the underlying mechanisms. Mucosal inflammation, changes in intestinal motility, luminal pH and bile acid metabolism, or direct drug-induced inhibitory effect on bacterial growth are all potential contributors to NSAID- and opioid-induced dysbiosis, however, only a few studies have addressed directly these issues. In addition, there is a notable overlap between the microbiota signatures of these drugs and certain diseases in which they are used, such as spondyloarthritis (SpA), rheumatoid arthritis (RA) and neuropathic pain associated with type 2 diabetes (T2D). The aims of the present review are threefold. First, we aim to provide a comprehensive up-to-date summary on the bacterial alterations caused by NSAIDs and opioids. Second, we critically review the available data on the possible underlying mechanisms of dysbiosis. Third, we review the current knowledge on gut dysbiosis associated with SpA, RA and neuropathic pain in T2D, and highlight the similarities between them and those caused by NSAIDs and opioids. We posit that drug-induced dysbiosis may contribute to the persistence of these diseases, and may potentially limit the therapeutic effect of these medications by long-term use. In this context, we will review the available literature data on the effect of probiotic supplementation and fecal microbiota transplantation on the therapeutic efficacy of NSAIDs and opioids in these diseases.

The gut microbiome contributes to somatic morphine withdrawal behavior and implicates a TLR2 mediated mechanism

The ongoing opioid epidemic has left millions of people suffering from opioid use disorder due to the over-prescription of highly addictive substances. Chronic opioid exposure leads to dependence, where the absence of the drug results in negative symptoms of withdrawal, often driving patients to continue drug use; however, few therapeutic strategies are currently available to combat the cycle of addiction and the severity of morphine withdrawal. This study investigates the microbiome as a potential therapeutic target for morphine withdrawal, as gut dysbiosis caused by morphine use has been proven to contribute to other aspects of opioid use disorders, such as tolerance. Results show that although the microbiome during morphine withdrawal trends toward recovery from morphine-induced dysbiosis, there continues to be a disruption in the alpha and beta diversity as well as the abundance of gram-positive bacteria that may still contribute to the severity of morphine withdrawal symptoms. Germ-free mice lacking the microbiome did not develop somatic withdrawal symptoms, indicating that the microbiome is necessary for the development of somatic withdrawal behavior. Notably, only TLR2 but not TLR4 whole-body knockout models display less withdrawal severity, implicating that the microbiome, through a gram-positive, TLR2 mediated mechanism, drives opioid-induced somatic withdrawal behavior.

Antibiotic Knockdown of Gut Bacteria Sex-Dependently Enhances Intravenous Fentanyl Self-Administration in Adult Sprague Dawley Rats

Communication between the brain and gut bacteria impacts drug- and addiction-related behaviors. To investigate the role of gut microbiota on fentanyl reinforcement and reward, we depleted gut bacteria in adult Sprague Dawley male and female rats using an oral, nonabsorbable antibiotic cocktail and allowed rats to intravenously self-administer fentanyl on an escalating schedule of reinforcement. We found that antibiotic treatment enhanced fentanyl self-administration in males, but not females, at the lowest schedule of reinforcement (i.e., fixed ratio 1). Both males and females treated with antibiotics self-administered greater amounts of fentanyl at higher schedules of reinforcement. We then replete microbial metabolites via short-chain fatty acid administration to evaluate a potential mechanism in gut-brain communication and found that restoring metabolites decreases fentanyl self-administration back to controls at higher fixed ratio schedules of reinforcement. Our findings highlight an important relationship between the knockdown and rescue of gut bacterial metabolites and fentanyl self-administration in adult rats, which provides support for a significant relationship between the gut microbiome and opioid use. Further work in this field may lead to effective, targeted treatment interventions in opioid-related disorders.

Linking the gut microbiome to microglial activation in opioid use disorder

Substance use disorder (SUD) is a physical and psychological disorder globally prevalent today that has resulted in over 107,000 drug overdose deaths in 2021 in the United States alone. This manuscript reviews the potential relationship between opioid use disorder (OUD), a prevalent subset of SUD, and the microglia, the resident macrophages of the central nervous system (CNS), as they have been found to become significantly more activated during opioid exposure. The inflammatory response mediated by the microglia could contribute to the pathophysiology of SUDs, in particular OUD. Further understanding of the microglia and how they respond to not only signals in the CNS but also signals from other areas of the body, such as the gut microbiome, could explain how the microglia are involved in drug use. Several studies have shown extensive communication between the gut microbiome and the microglia, which may be an important factor in the initiation and development of OUD. Particularly, strategies seeking to manipulate and restore the gut microbiome have been shown to reduce microglial activation and attenuate inflammation. In this review, we discuss the evidence for a link between the microglia and OUD and how the gut microbiome might influence microglial activation to drive the disorder and its associated behaviors. Understanding this connection between microglia and the gut microbiome in the context of drug use may present additional therapeutic targets to treat the different stages of drug use.

Dysbiosis of Fecal Microbiota in Tg2576 Mice for Alzheimer's Disease during Pathological Constipation

Tg2576 transgenic mice for Alzheimer's disease (AD) exhibited significant phenotypes for neuropathological constipation, but no research has been conducted on the association of the fecal microbiota with dysbiosis. The correlation between fecal microbiota composition and neuropathological constipation in Tg2576 mice was investigated by examining the profile of fecal microbiota and fecal microbiota transplantation (FMT) in 9-10-month-old Tg2576 mice with the AD phenotypes and constipation. Several constipation phenotypes, including stool parameters, colon length, and histopathological structures, were observed prominently in Tg2576 mice compared to the wild-type (WT) mice. The fecal microbiota of Tg2576 mice showed decreases in Bacteroidetes and increases in the Firmicutes and Proteobacteria populations at the phylum level. The FMT study showed that stool parameters, including weight, water content, and morphology, decreased remarkably in the FMT group transplanted with a fecal suspension of Tg2576 mice (TgFMT) compared to the FMT group transplanted with a fecal suspension of WT mice (WFMT). The distribution of myenteric neurons and the interstitial cells of Cajal (ICC), as well as the enteric nervous system (ENS) function, remained lower in the TgFMT group. These results suggest that the neuropathological constipation phenotypes of Tg2576 mice may be tightly linked to the dysbiosis of the fecal microbiota.

Gut microbiota alterations may increase the risk of prescription opioid use, but not vice versa: A two-sample bi-directional Mendelian randomization study

INTRODUCTION

Gut microbiota alterations are strongly associated with prescription opioid use (POU) and multisite chronic pain (MCP). However, whether or not these associations are causal remains unknown. Therefore, we aim to explore the causal relationships between them comprehensively.

METHODS

A two-sample bi-directional Mendelian randomization was conducted to assess the potential associations between gut microbiota and POU/MCP using summary level Genome-wide association studies (GWASs) that were based on predominantly European ancestry.

RESULTS

Potential causal effects were identified between seven host genetic-driven traits of gut microbiota on POU, including Adlercreutzia, Allisonella, Dialister, Anaerofilum, Anaerostipes, ChristensenellaceaeR.7group, and LachnospiraceaeNC2004group at the genus level (p < 0.05) by the Inverse-variance weighted method, with significant causal effects of ChristensenellaceaeR.7group and Allisonella on POU (p < 0.025). A total of five genetically greater abundance of gut microbiota traits were identified to be possibly related to the level of MCP (p < 0.05), including genus ErysipelotrichaceaeUCG003, family Clostridiaceae1, order Gastranaerophilales, order Actinomycetales, and family Actinomycetaceae. In the other direction, no clear evidence was found to support a significant causal relationship between POU and gut microbiota, as well as MCP and gut microbiota. In addition, evidence was also provided for the relationship between triacylglycerols and diacylglycerol elevation, and an increased risk of POU and MCP. No evidence was found across various sensitivity analyses, including reverse causality, pleiotropy, and heterogeneity.

CONCLUSION

The findings from this study provide robust evidence that gut microbiota alterations may be a risk of POU/MCP, but not vice versa.

The role of gut microbial β-glucuronidase in drug disposition and development

Gut microbial β-glucuronidase (gmGUS) is involved in the disposition of many endogenous and exogenous compounds. Preclinical studies have shown that inhibiting gmGUS activity affects drug disposition, resulting in reduced toxicity in the gastrointestinal tract (GIT) and enhanced systemic efficacy. Additionally, manipulating gmGUS activity is expected to be effective in preventing/treating local or systemic diseases. Although results from animal studies are promising, challenges remain in developing drugs by targeting gmGUS. Here, we review the role of gmGUS in host health under physiological and pathological conditions, the impact of gmGUS on the disposition of phenolic compounds, models used to study gmGUS activity, and the perspectives and challenges in developing drugs by targeting gmGUS.