Antibiotic-induced microbiome depletion is associated with resilience in mice after chronic social defeat stress

Melatonin Ameliorates Depressive-Like Behaviors in Ovariectomized Mice by Improving Tryptophan Metabolism via Inhibition of Gut Microbe Alistipes Inops

Melatonin (N-acetyl-5-methoxytryptamine) is reported to improve mood disorders in perimenopausal women and gut microbiome composition is altered during menopausal period. The possible role of microbiome in the treatment effect of melatonin on menopausal depression remains unknown. Here, it is shown that melatonin treatment reverses the gut microbiota dysbiosis and depressive-like behaviors in ovariectomy (OVX) operated mice. This effect of melatonin is prevented by antibiotic cocktails (ABX) treatment. Transferring microbiota harvested from adolescent female mice to OVX-operated mice is sufficient to ameliorate depressive-like behaviors. Conversely, microbiota transplantation from OVX-operated mice or melatonin-treated OVX-operated mice to naïve recipient mice exhibits similar phenotypes to donors. The colonization of Alistipes Inops, which is abundant in OVX-operated mice, confers the recipient with depressive-like behaviors. Further investigation indicates that the expansion of Alistipes Inops induced by OVX leads to the degradation of intestinal tryptophan, which destroys systemic tryptophan availability. Melatonin supplementation restores systemic tryptophan metabolic disorders by suppressing the growth of Alistipes Inops, which ameliorates depressive-like behaviors. These results highlight the previously unrecognized role of Alistipes Inops in the modulation of OVX-induced behavioral disorders and suggest that the application of melatonin to inhibit Alistipes Inops may serve as a potential strategy for preventing menopausal depressive symptoms.

Antibiotic-induced intestinal microbiota depletion can attenuate the acute kidney injury to chronic kidney disease transition via NADPH oxidase 2 and trimethylamine-N-oxide inhibition

Intestinal microbiota and their metabolites affect systemic inflammation and kidney disease outcomes. Here, we investigated the key metabolites associated with the acute kidney injury (AKI)-to chronic kidney disease (CKD) transition and the effect of antibiotic-induced microbiota depletion (AIMD) on this transition. In 61 patients with AKI, 59 plasma metabolites were assessed to determine the risk of AKI-to-CKD transition. An AKI-to-CKD transition murine model was established four weeks after unilateral ischemia-reperfusion injury (IRI) to determine the effects of AIMD on the gut microbiome, metabolites, and pathological responses related to CKD transition. Human proximal tubular epithelial cells were challenged with CKD transition-related metabolites, and inhibitory effects of NADPH oxidase 2 (NOX2) signals were tested. Based on clinical metabolomics, plasma trimethylamine N-oxide (TMAO) was associated with a significantly increased risk for AKI-to-CKD transition [adjusted odds ratio 4.389 (95% confidence interval 1.106-17.416)]. In vivo, AIMD inhibited a unilateral IRI-induced increase in TMAO, along with a decrease in apoptosis, inflammation, and fibrosis. The expression of NOX2 and oxidative stress decreased after AIMD. In vitro, TMAO induced fibrosis with NOX2 activation and oxidative stress. NOX2 inhibition successfully attenuated apoptosis, inflammation, and fibrosis with suppression of G2/M arrest. NOX2 inhibition (in vivo) showed improvement in pathological changes with a decrease in oxidative stress without changes in TMAO levels. Thus, TMAO is a key metabolite associated with the AKI-to-CKD transition, and NOX2 activation was identified as a key regulator of TMAO-related AKI-to-CKD transition both in vivo and in vitro.

A new evaluation system for drug-microbiota interactions

The drug response phenotype is determined by a combination of genetic and environmental factors. The high clinical conversion failure rate of gene-targeted drugs might be attributed to the lack of emphasis on environmental factors and the inherent individual variability in drug response (IVDR). Current evidence suggests that environmental variables, rather than the disease itself, are the primary determinants of both gut microbiota composition and drug metabolism. Additionally, individual differences in gut microbiota create a unique metabolic environment that influences the in vivo processes underlying drug absorption, distribution, metabolism, and excretion (ADME). Here, we discuss how gut microbiota, shaped by both genetic and environmental factors, affects the host's ADME microenvironment within a new evaluation system for drug-microbiota interactions. Furthermore, we propose a new top-down research approach to investigate the intricate nature of drug-microbiota interactions in vivo. This approach utilizes germ-free animal models, providing foundation for the development of a new evaluation system for drug-microbiota interactions.

Antibiotic-induced microbiome depletion promotes intestinal colonization by Campylobacter jejuni in mice

BACKGROUND

To establish a method to induce Campylobacter jejuni colonization in the intestines of C57BL/6 mice through antibiotic-induced microbiome depletion.

RESULTS

Fifty-four female C57BL/6 mice were divided into the normal, control, and experimental groups. The experimental group was administered intragastric cefoperazone sodium and sulbactam sodium (50 mg/mL) for 2 days; then, the experimental and control mice were intragastrically administered 200 µL C. jejuni, which was repeated once more after 2 days. Animal feces were collected, and the HipO gene of C. jejuni was detected using TaqMan qPCR from day 1 to day 14 after modeling completion. Immunofluorescence was used to detect intestinal C. jejuni colonization on day 14, and pathological changes were observed using hematoxylin and eosin staining. Additionally, 16S rDNA analyses of the intestinal contents were conducted on day 14. In the experimental group, C. jejuni was detected in the feces from days 1 to 14 on TaqMan qPCR, and immunofluorescence-labeled C. jejuni were visibly discernable in the intestinal lumen. The intestinal mucosa was generally intact and showed no significant inflammatory-cell infiltration. Diversity analysis of the colonic microbiota showed significant inter-group differences. In the experimental group, the composition of the colonic microbiota differed from that in the other 2 groups at the phylum level, and was characterized by a higher proportion of Bacteroidetes and a lower proportion of Firmicutes.

CONCLUSIONS

Microbiome depletion induced by cefoperazone sodium and sulbactam sodium could promote long-term colonization of C. jejuni in the intestines of mice.

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.

Microbiome depletion prior to repeat mild TBI differentially alters social deficits and prefrontal cortex plasticity in adolescent and adult rats

Although aging, repeat mild traumatic brain injury (RmTBI), and microbiome modifications independently change social behavior, there has been no investigation into their cumulative effects on social behavior and neuroplasticity within the prefrontal cortex. Therefore, we examined how microbiome depletion prior to RmTBI affected social behavior and neuroplasticity in adolescent and adult rats. Play, temperament analysis, elevated plus maze, and the hot/cold plate assessed socio-emotional function. Analyses of perineuronal nets (PNNs) and parvalbumin (PV) interneurons was completed. Social-emotional deficits were more pronounced in adults, with microbiome depletion attenuating social behavior deficits associated with RmTBI in both age groups. Microbiome depletion increased branch length and PNN arborization within the PFC but decreased the overall number of PNNs. Adults and males were more vulnerable to RmTBI. Interestingly, microbiome depletion may have attenuated the changes to neuroplasticity and subsequent social deficits, suggesting that the microbiome is a viable, but age-specific, target for RmTBI therapeutics.

Gut microbiota regulate stress resistance by influencing microglia-neuron interactions in the hippocampus

Communication among the brain, gut and microbiota in the gut is known to affect the susceptibility to stress, but the mechanisms involved are unclear. Here we demonstrated that stress resistance in mice was associated with more abundant Lactobacillus and Akkermansia in the gut, but less abundant Bacteroides, Alloprevotella, Helicobacter, Lachnoclostridium, Blautia, Roseburia, Colidextibacter and Lachnospiraceae NK4A136. Stress-sensitive animals showed higher permeability and stronger immune responses in their colon, as well as higher levels of pro-inflammatory cytokines in serum. Their hippocampus also showed more extensive microglial activation, abnormal interactions between microglia and neurons, and lower synaptic plasticity. Transplanting fecal microbiota from stress-sensitive mice into naïve ones perturbed microglia-neuron interactions and impaired synaptic plasticity in the hippocampus, translating to more depression-like behavior after stress exposure. Conversely, transplanting fecal microbiota from stress-resistant mice into naïve ones protected microglia from activation and preserved synaptic plasticity in the hippocampus, leading to less depression-like behavior after stress exposure. These results suggested that gut microbiota may influence resilience to chronic psychological stress by regulating microglia-neuron interactions in the hippocampus.

Stressed to the Core: Inflammation and Intestinal Permeability Link Stress-Related Gut Microbiota Shifts to Mental Health Outcomes

Stress levels are surging, alongside the incidence of stress-related psychiatric disorders. Perhaps a related phenomenon, especially in urban areas, the human gut contains fewer bacterial species than ever before. Although the functional implications of this absence are unclear, one consequence may be reduced stress resilience. Preclinical and clinical evidence has shown how stress exposure can alter the gut microbiota and their metabolites, affecting host physiology. Also, stress-related shifts in the gut microbiota jeopardize tight junctions of the gut barrier. In this context, bacteria and bacterial products can translocate from the gut to the bloodstream, lymph nodes, and other organs, thereby modifying systemic inflammatory responses. Heightened circulating inflammation can be an etiological factor in stress-related psychiatric disorders, including some cases of depression. In this review, we detail preclinical and clinical evidence that traces these brain-to-gut-to-brain pathways that underlie stress-related psychiatric disorders and potentially affect their responsivity to conventional psychiatric medications. We also review evidence for interventions that modulate the gut microbiota (e.g., antibiotics, probiotics, prebiotics) to reduce stress responses and psychiatric symptoms. Lastly, we discuss challenges to translation and opportunities for innovations that could impact future psychiatric clinical practice.

Decoding the role of the gut microbiome in gut-brain axis, stress-resilience, or stress-susceptibility: A review

Increased exposure to stress is associated with stress-related disorders, including depression, anxiety, and neurodegenerative conditions. However, susceptibility to stress is not seen in every individual exposed to stress, and many of them exhibit resilience. Thus, developing resilience to stress could be a big breakthrough in stress-related disorders, with the potential to replace or act as an alternative to the available therapies. In this article, we have focused on the recent advancements in gut microbiome research and the potential role of the gut-brain axis (GBA) in developing resilience or susceptibility to stress. There might be a complex interaction between the autonomic nervous system (ANS), immune system, endocrine system, microbial metabolites, and bioactive lipids like short-chain fatty acids (SCFAs), neurotransmitters, and their metabolites that regulates the communication between the gut microbiota and the brain. High fiber intake, prebiotics, probiotics, plant supplements, and fecal microbiome transplant (FMT) could be beneficial against gut dysbiosis-associated brain disorders. These could promote the growth of SCFA-producing bacteria, thereby enhancing the gut barrier and reducing the gut inflammatory response, increase the expression of the claudin-2 protein associated with the gut barrier, and maintain the blood-brain barrier integrity by promoting the expression of tight junction proteins such as claudin-5. Their neuroprotective effects might also be related to enhancing the expression of brain-derived neurotrophic factor (BDNF) and glucagon-like peptide (GLP-1). Further investigations are needed in the field of the gut microbiome for the elucidation of the mechanisms by which gut dysbiosis contributes to the pathophysiology of neuropsychiatric disorders.

Role of the gut-brain axis via the subdiaphragmatic vagus nerve in stress resilience of 3,4-methylenedioxymethamphetamine in mice exposed to chronic restrain stress

3,4-Methylenedioxymethamphetamine (MDMA) is the most widely used illicit substance worldwide. Nevertheless, recent observational studies demonstrated that lifetime MDMA use among U.S. adults was associated with a lower risk of depression and suicide thoughts. We recently reported that the gut-brain axis may contribute to MDMA-induced stress resilience in mice. To further explore this, we investigated the effects of subdiaphragmatic vagotomy (SDV) in modulating the stress resilience effects of MDMA in mice subjected to chronic restrain stress (CRS). Pretreatment with MDMA (10 mg/kg/day for 14 days) blocked anhedonia-like behavior and reduced expression of synaptic proteins and brain-derived neurotrophic factor in the prefrontal cortex (PFC) of CRS-exposed mice. Interestingly, SDV blocked the beneficial effects of MDMA on these alterations in CRS-exposed mice. Analysis of gut microbiome revealed alterations in four measures of α-diversity between the sham + MDMA + CRS group and the SDV + MDMA + CRS group. Moreover, specific microbes differed between the vehicle + CRS group and the MDMA + CRS group, and further differences in microbial composition were observed among all four groups. Untargeted metabolomics analysis showed that SDV prevented the increase in plasma levels of three compounds [lactic acid, 1-(2-hydroxyethyl)-2,2,6-tetramethyl-4-piperidinol, 8-acetyl-7-hydroxyvumaline] observed in the sham + MDMA + CRS group. Interestingly, positive correlations were found between the plasma levels of two of these compounds and the abundance of several microbes across all groups. In conclusion, our data suggest that the gut-brain axis via the subdiaphragmatic vagus nerve might contribute to the stress resilience of MDMA.

Cefaclor causes vagus nerve-mediated depression-like symptoms with gut dysbiosis in mice

Antibiotics are increasingly recognized as causing neuropsychiatric side effects including depression and anxiety. Alterations in central serotonin and 5-HT receptor expression are implicated in the pathogenesis of anxiety and depression, which are highly comorbid with gastrointestinal disorders. Nevertheless, it is still unclear how antibiotics can cause anxiety and depression. In this study, oral administration of cefaclor, a second-generation cephalosporin antibiotic, induced anxiety- and depression-like behaviors and colitis with gut microbiota alteration in mice. Cefaclor reduced serotonin levels and fluctuated 5-HT receptor mRNA expressions such as Htr1a, Htr1b, and Htr6 in the hippocampus. Vagotomy attenuated the cefaclor-induced anxiety- and depression-like symptoms, while the cefaclor-induced changes in gut bacteria alteration and colitis were not affected. Fluoxetine attenuated cefaclor-induced anxiety- and depression-like behaviors. Furthermore, fluoxetine decreased cefaclor-resistant Enterobacteriaceae and Enterococcaceae. Taken together, our findings suggest that the use of antibiotics, particularly, cefaclor may cause gut dysbiosis-dependent anxiety and depression through the microbiota-gut-blood-brain and microbiota-gut-vagus nerve-brain pathway. Targeting antibiotics-resistant pathogenic bacteria may be a promising therapeutic strategy for the treatment of anxiety and depression.

Antibiotic-induced gut dysbiosis and cognitive, emotional, and behavioral changes in rodents: a systematic review and meta-analysis

There are previous epidemiological studies reporting associations between antibiotic use and psychiatric symptoms. Antibiotic-induced gut dysbiosis and alteration of microbiota-gut-brain axis communication has been proposed to play a role in this association. In this systematic review and meta-analysis, we reviewed published articles that have presented results on changes in cognition, emotion, and behavior in rodents (rats and mice) after antibiotic-induced gut dysbiosis. We searched three databases-PubMed, Web of Science, and SCOPUS to identify such articles using dedicated search strings and extracted data from 48 articles. Increase in anxiety and depression-like behavior was reported in 32.7 and 40.7 percent of the study-populations, respectively. Decrease in sociability, social novelty preference, recognition memory and spatial cognition was found in 18.1, 35.3, 26.1, and 62.5 percent of the study-populations, respectively. Only one bacterial taxon (increase in gut Proteobacteria) showed statistically significant association with behavioral changes (increase in anxiety). There were no consistent findings with statistical significance for the potential biomarkers [Brain-derived neurotrophic factor (BDNF) expression in the hippocampus, serum corticosterone and circulating IL-6 and IL-1β levels]. Results of the meta-analysis revealed a significant association between symptoms of negative valence system (including anxiety and depression) and cognitive system (decreased spatial cognition) with antibiotic intake (p < 0.05). However, between-study heterogeneity and publication bias were statistically significant (p < 0.05). Risk of bias was evaluated to be high in the majority of the studies. We identified and discussed several reasons that could contribute to the heterogeneity between the results of the studies examined. The results of the meta-analysis provide promising evidence that there is indeed an association between antibiotic-induced gut dysbiosis and psychopathologies. However, inconsistencies in the implemented methodologies make generalizing these results difficult. Gut microbiota depletion using antibiotics may be a useful strategy to evaluate if and how gut microbes influence cognition, emotion, and behavior, but the heterogeneity in methodologies used precludes any definitive interpretations for a translational impact on clinical practice.

Isoalantolactone relieves depression-like behaviors in mice after chronic social defeat stress via the gut-brain axis

RATIONALE

The management of depression continues to be challenging despite the variety of available antidepressants. Herbal medicines are used in many cultures but lack stringent testing to understand their efficacy and mechanism of action. Isoalantolactone (LAT) from Elecampane (Inula helenium) improved the chronic social defeat stress (CSDS)-induced anhedonia-like phenotype in mice comparable to fluoxetine, a selective serotonin reuptake inhibitor (SSRI).

OBJECTIVES

Compare the effects of LAT and fluoxetine on depression-like behaviors in mice exposed to CSDS.

RESULT

The CSDS-induced decrease in protein expression of postsynaptic density (PSD95), brain derived neurotrophic factor (BDNF), and glutamate receptor subunit-1 (GluA1) in the prefrontal cortex was restored by LAT. LAT showed robust anti-inflammatory activity and can lessen the increase in IL-6 and TNF-α caused by CSDS. CSDS altered the gut microbiota at the taxonomic level, resulting in significant changes in α- and β-diversity. LAT treatment reestablished the bacterial abundance and diversity and increased the production of butyric acid in the gut that was inhibited by CSDS. The levels of butyric acid were negatively correlated with the abundance of Bacteroidetes, and positively correlated with those of Proteobacteria and Firmicutes across all treatment groups.

CONCLUSIONS

The current data suggest that, similar to fluoxetine, LAT show antidepressant-like effects in mice exposed to CSDS through the modulation of the gut-brain axis.

Gut Microbiota in Anxiety and Depression: Unveiling the Relationships and Management Options

The gut microbiota is critical for maintaining human health and the immunological system. Several neuroscientific studies have shown the significance of microbiota in developing brain systems. The gut microbiota and the brain are interconnected in a bidirectional relationship, as research on the microbiome-gut-brain axis shows. Significant evidence links anxiety and depression disorders to the community of microbes that live in the gastrointestinal system. Modified diet, fish and omega-3 fatty acid intake, macro- and micro-nutrient intake, prebiotics, probiotics, synbiotics, postbiotics, fecal microbiota transplantation, and 5-HTP regulation may all be utilized to alter the gut microbiota as a treatment approach. There are few preclinical and clinical research studies on the effectiveness and reliability of various therapeutic approaches for depression and anxiety. This article highlights relevant research on the association of gut microbiota with depression and anxiety and the different therapeutic possibilities of gut microbiota modification.

Komagataella pastoris KM71H Mitigates Depressive-Like Phenotype, Preserving Intestinal Barrier Integrity and Modulating the Gut Microbiota in Mice

The role of intestinal microbiota in the genesis of mental health has received considerable attention in recent years, given that probiotics are considered promising therapeutic agents against major depressive disorder. Komagataella pastoris KM71H is a yeast with probiotic properties and antidepressant-like effects in animal models of depression. Hence, we evaluated the antidepressant-like effects of K. pastoris KM71H in a model of antibiotic-induced intestinal dysbiosis in male Swiss mice. The mice received clindamycin (200 μg, intraperitoneal) and, after 24 h, were treated with K. pastoris KM71H at a dose of 8 log CFU/animal by intragastric administration (ig) or PBS (vehicle, ig) for 14 consecutive days. Afterward, the animals were subjected to behavioral tests and biochemical analyses. Our results showed that K. pastoris KM71H administration decreased the immobility time in the tail suspension test and increased grooming activity duration in the splash test in antibiotic-treated mice, thereby characterizing its antidepressant-like effect. We observed that these effects of K. pastoris KM71H were accompanied by the modulation of the intestinal microbiota, preservation of intestinal barrier integrity, and restoration of the mRNA levels of occludin, zonula occludens-1, zonula occludens-2, and toll-like receptor-4 in the small intestine, and interleukin-1β in the hippocampi of mice. Our findings provide solid evidence to support the development of K. pastoris KM71H as a new probiotic with antidepressant-like effects.

Analysis of the spinal and vagal afferent innervation of the mouse colon using neuronal retrograde tracers

The gut-brain axis has received increasing attention recently due to evidence that colonic microbes can affect brain function and behavior. However, little is known about the innervation of the colon by a major component of the gut-brain axis, vagal afferent neurons. Furthermore, it is currently unknown whether individual NG neurons or DRG neurons innervate both the proximal and distal colon. We aimed to quantify the number of vagal and spinal afferent neurons that innervate the colon; and determine whether these individual neurons simultaneously innervate the mouse proximal and distal colon. C57Bl/6 mice received injections of a combination of retrograde tracers that were either injected into the muscularis externa of the proximal or the distal colon: fast blue, DiI and DiO. Five to seven percent of lumbosacral and thoracolumbar spinal afferent neurons, and 25% of vagal afferent neurons were labelled by injections of DiI and DiO into the colon. We also found that approximately 8% of NG neurons innervate the distal colon. Ten percent of labeled thoracolumbar and 15% of labeled lumbosacral DRG neurons innervate both the distal and proximal colon. Eighteen percent of labeled NG neurons innervated both the distal and proximal colon. In conclusion, vagal afferent innervation of the distal colon is less extensive than the proximal colon, whereas a similar gradient was not observed for the spinal afferent innervation. Furthermore, overlap appears to exist between the receptive fields of vagal and spinal afferent neurons that innervate the proximal and distal colon.

Abnormal compositions of gut microbiota and metabolites are associated with susceptibility versus resilience in rats to inescapable electric stress

BACKGROUND

Increasing evidence suggests the role of gut microbiota in resilience versus vulnerability after stress. However, the role of gut microbiota and microbiome-derived metabolites in resilience versus susceptibility in rodents exposed to stress remains unclear.

METHODS

Adult male rats were exposed to inescapable electric stress under the learned helplessness (LH) paradigm. The composition of gut microbiota and metabolites in the brain and blood from control (no stress) rats, LH resilient rats, and LH susceptible rats were examined.

RESULTS

At the genus level, the relative abundances of Asaccharobacter, Eisenbergiella, and Klebsiella in LH susceptible rats were significantly higher than that of LH resilient rats. At the species level, the relative abundances of several microbiome were significantly altered between LH susceptible rats and LH resilient rats. Furthermore, there were several metabolites in the brain and blood altered between LH susceptible rats and LH resilient rats. A network analysis showed correlations between the abundance of several microbiome and metabolites in the brain (or blood).

LIMITATIONS

Detailed roles of microbiome and metabolites are unclear.

CONCLUSIONS

These findings suggest that abnormal compositions of the gut microbiota and metabolites might contribute to susceptibility versus resilience in rats subjected to inescapable electric foot shock.

Mesenchymal stem-cell-derived microvesicles ameliorate MPTP-induced neurotoxicity in mice: a role of the gut-microbiota-brain axis

RATIONALE

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder. Increasing evidence suggests the role of the gut-microbiota-brain axis in the pathogenesis of PD. Mesenchymal stem-cell-derived microvesicles (MSC-MVs) have emerged as a therapeutic potential for neurological disorders over the last years.

OBJECTIVE

The objective of this study was to investigate whether MSC-MVs could improve PD-like neurotoxicity in mice after administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine).

RESULTS

MPTP-induced reductions in the dopamine transporter and tyrosine hydroxylase expressions in the striatum and substantia nigra (SNr) were attenuated after a subsequent single administration of MSC-MVs. Increases in the phosphorylated α-synuclein (p-α-Syn)/α-Syn ratio in the striatum, SNr, and colon after MPTP injection were also attenuated after MSC-MVs injection. Furthermore, MSC-MVs restored MPTP-induced abnormalities of the gut microbiota composition. Interestingly, positive correlations between the genus Dubosiella and the p-α-Syn/α-Syn ratio were observed in the brain and colon, suggesting their roles in the gut-microbiota-brain communication. Moreover, MSC-MVs attenuated MPTP-induced reduction of the metabolite, 3,6-dihydroxy-2-[3-methoxy-4-(sulfooxy)phenyl]-7-(sulfinooxy)-3,4-dihydro-2H-1-benzopyran-5-olate, in the blood. Interestingly, a negative correlation between this compound and the p-α-Syn/α-Syn ratio was observed in the brain and colon.

CONCLUSIONS

These data suggest that MSC-MVs could ameliorate MPTP-induced neurotoxicity in the brain and colon via the gut-microbiota-brain axis. Therefore, MSC-MVs would have a new therapeutic potential for neurological disorders such as PD.

Emotional-Single Prolonged Stress: A promising model to illustrate the gut-brain interaction

Excessive stress can precipitate depression and anxiety diseases, and damage gastrointestinal functionality and microbiota changes, favoring the development of functional gastrointestinal disorders (FGIDs) - defined by dysregulation in the brain-gut interaction. Therefore, the present study investigated if Emotional-Single Prolonged Stress (E-SPS) induces depressive/anxiety-like phenotype and gut dysfunction in adult Swiss male mice. For this, mice of the E-SPS group were subjected to three stressors sequential exposure: immobilization, swimming, and odor of the predator for 7 days (incubation period). Next, animals performed behavior tests and 24 h later, samples of feces, blood, and colon tissue were collected. E-SPS increased the plasma corticosterone levels, immobility time in the tail suspension and forced swim test, decreased the grooming time in the splash test, OAT%, and OAE% in the elevated plus-maze test, as well as increased anxiety index. Mice of E-SPS had increased % of intestinal transit rate, % of fecal moisture content, and fecal pellets number, and decreased Claudin1 content in the colon. E-SPS decreased the relative abundance of Bacteroidetes phylum, Bacteroidia class, Bacteroidales order, Muribaculaceae and Porphyromonadaceae family, Muribaculum, and Duncaniella genus. However, E-SPS increased Firmicutes and Actinobacteria phylum, Coriobacteriales order, and the ratio of Firmicutes/Bacteroidetes, and demonstrated Mucispirillum genus presence. The present study showed that E-SPS induced depressive/anxiety-like phenotype, predominant diarrhea gut dysfunction, and modulated the gut bacterial microbiota profile in male adult Swiss mice. E-SPS might be a promising model for future studies on the brain-gut interaction and the development of FGIDs with psychological comorbidities.

Repeated use of 3,4-methylenedioxymethamphetamine is associated with the resilience in mice after chronic social defeat stress: A role of gut-microbiota-brain axis

3,4-Methylenedioxymethamphetamine (MDMA), the most widely used illicit compound worldwide, is the most attractive therapeutic drug for post-traumatic stress disorder (PTSD). Recent observational studies of US adults demonstrated that lifetime MDMA use was associated with lower risk of depression. Here, we examined whether repeated administration of MDMA can affect resilience versus susceptibility in mice exposed to chronic social defeat stress (CSDS). CSDS produced splenomegaly, anhedonia-like phenotype, and higher plasma levels of interleukin-6 (IL-6) in the saline-treated mice. In contrast, CSDS did not cause these changes in the MDMA-treated mice. Analysis of gut microbiome found several microbes altered between saline + CSDS group and MDMA + CSDS group. Untargeted metabolomics analysis showed that plasma levels of N-epsilon-methyl-L-lysine in the saline + CSDS group were significantly higher than those in the control and MDMA + CSDS groups. Interestingly, there were positive correlations between plasma IL-6 levels and the abundance of several microbes (or plasma N-epsilon-methyl-L-lysine) in the three groups. Furthermore, there were also positive correlations between the abundance of several microbes and N-epsilon-methyl-L-lysine in the three groups. In conclusion, these data suggest that repeated administration of MDMA might contribute to stress resilience in mice subjected to CSDS through gut-microbiota-brain axis.

A role of gut-microbiota-brain axis via subdiaphragmatic vagus nerve in depression-like phenotypes in Chrna7 knock-out mice

The α7 subtype of the nicotinic acetylcholine receptor (α7 nAChR: coded by Chrna7) is known to regulate the cholinergic ascending anti-inflammatory pathway. We previously reported that Chrna7 knock-out (KO) mice show depression-like behaviors through abnormal composition of gut microbiota and systemic inflammation. Given the role of subdiaphragmatic vagus nerve in gut-microbiota-brain axis, we investigated whether subdiaphragmatic vagotomy (SDV) could affect depression-like behaviors, abnormal composition of gut microbiota, and microbes-derived metabolites in Chrna7 KO mice. SDV blocked depression-like behaviors and reduced expression of synaptic proteins in the medial prefrontal cortex (mPFC) of Chrna7 KO mice. LEfSe (linear discriminant analysis effect size) analysis revealed that the species Lactobacillus sp. BL302, the species Lactobacillus hominis, and the species Lactobacillus reuteri, were identified as potential microbial markers in the KO + SDV group. There were several genus and species altered among the three groups [wild-type (WT) + sham group, KO + sham group, KO + SDV group]. Furthermore, there were several plasma metabolites altered among the three groups. Moreover, there were correlations between relative abundance of several microbiome and behavioral data (or synaptic proteins). Network analysis showed correlations between relative abundance of several microbiome and plasma metabolites (or behavioral data). These data suggest that Chrna7 KO mice produce depression-like behaviors and reduced expression of synaptic proteins in the mPFC through gut-microbiota-brain axis via subdiaphragmatic vagus nerve.

Impact of broad-spectrum antibiotics on the gut-microbiota-spleen-brain axis

The spleen is a key immune-related organ that plays a role in communication between the brain and the immune system through the brain-spleen axis and brain-gut-microbiota axis. However, how the gut microbiota affects spleen and brain function remains unclear. Here, we investigated whether microbiome depletion induced by administration of an antibiotic cocktail (ABX) affects spleen and brain function. Treatment with ABX for 14 days resulted in a significant decrease in spleen weight and significant alterations in splenic functions, including the percentage of neutrophils, NK cells, macrophages, and CD8⁺ T cells. Furthermore, ABX treatment resulted in the depletion of a large portion of the gut microbiota. Untargeted metabolomics analysis showed that ABX treatment caused alterations in the levels of certain compounds in the plasma, spleen, and brain. Moreover, ABX treatment decreased the expression of microglia marker Iba1 in the cerebral cortex. Interestingly, correlations were found between the abundance of different microbiome components and metabolites in various tissues, as well as splenic cell populations and spleen weight. These findings suggest that ABX-induced microbiome depletion and altered metabolite levels may affect spleen and brain function through the gut-microbiota-spleen-brain axis.

Age matters: Microbiome depletion prior to repeat mild traumatic brain injury differentially alters microbial composition and function in adolescent and adult rats

Dysregulation of the gut microbiome has been shown to perpetuate neuroinflammation, alter intestinal permeability, and modify repetitive mild traumatic brain injury (RmTBI)-induced deficits. However, there have been no investigations regarding the comparative effects that the microbiome may have on RmTBI in adolescents and adults. Therefore, we examined the influence of microbiome depletion prior to RmTBI on microbial composition and metabolome, in adolescent and adult Sprague Dawley rats. Rats were randomly assigned to standard or antibiotic drinking water for 14 days, and to subsequent sham or RmTBIs. The gut microbiome composition and metabolome were analysed at baseline, 1 day after the first mTBI, and at euthanasia (11 days following the third mTBI). At euthanasia, intestinal samples were also collected to quantify tight junction protein (TJP1 and occludin) expression. Adolescents were significantly more susceptible to microbiome depletion via antibiotic administration which increased pro-inflammatory composition and metabolites. Furthermore, RmTBI induced a transient increase in 'beneficial bacteria' (Lachnospiraceae and Faecalibaculum) in only adolescents that may indicate compensatory action in response to the injury. Finally, microbiome depletion prior to RmTBI generated a microbiome composition and metabolome that exemplified a potentially chronic pathogenic and inflammatory state as demonstrated by increased Clostridium innocuum and Erysipelatoclostridium and reductions in Bacteroides and Clostridium Sensu Stricto. Results highlight that adolescents are more vulnerable to RmTBI compared to adults and dysbiosis prior to injury may exacerbate secondary inflammatory cascades.

Neoagaro-Oligosaccharides Ameliorate Chronic Restraint Stress-Induced Depression by Increasing 5-HT and BDNF in the Brain and Remodeling the Gut Microbiota of Mice

Neoagaro-oligosaccharides (NAOs) belong to the algae oligosaccharides. NAOs have been found to have diverse biological activities. However, the effects of NAOs on depression and their underlying mechanism have not been thoroughly studied. A chronic restraint stress (CRS)-induced C57BL/6J mouse model was used to assess the antidepressant effects of NAOs. Anxiety and depression behaviors were assessed by open field tests (OFT) and forced swimming tests (FST), while interleukin 18 (IL-18), 5-hydroxytryptamine (5-HT) and brain-derived neurotrophic factor (BDNF) were the molecular biomarkers of depression. Fecal microbiota transplantation (FMT) was performed. The results showed that NAO treatment significantly improved the body weight of depressed mice and reduced the central area time in the OFT and immobility time in the FST. NAO treatment decreased the levels of IL-18 in the serum and increased the levels of 5-HT in the serum and whole brain and of BDNF in the whole brain. NAO treatment mitigated the gut microbiota dysbiosis in the depressed mice and reversed the decreased levels of short-chain fatty acids (SCFAs) in the cecum of the depressed mice. FMT indicated that the gut microbiota is, indeed, linked to depression, which was reflected in the changes in weight gain and behaviors. In a word, NAOs effectively reversed the CRS-induced mice model of depression, which depended on the changes in the gut microbiota and SCFAs, as well as its modulation of 5-HT and BDNF.

Effects of different amoxicillin treatment durations on microbiome diversity and composition in the gut

Antibiotics seize an effect on bacterial composition and diversity and have been demonstrated to induce disruptions on gut microbiomes. This may have implications for human health and wellbeing, and an increasing number of studies suggest a link between the gut microbiome and several diseases. Hence, reducing antibiotic treatments may be beneficial for human health status. Further, antimicrobial resistance (AMR) is an increasing global problem that can be counteracted by limiting the usage of antibiotics. Longer antibiotic treatments have been demonstrated to increase the development of AMR. Therefore, shortening of antibiotic treatment durations, provided it is safe for patients, may be one measure to reduce AMR. In this study, the objective was to investigate effects of standard and reduced antibiotic treatment lengths on gut microbiomes using a murine model. Changes in the murine gut microbiome was assessed after using three different treatment durations of amoxicillin (3, 7 or 14 days) as well as a control group not receiving amoxicillin. Fecal samples were collected before and during the whole experiment, until three weeks past end of treatment. These were further subject for 16S rRNA Illumina MiSeq sequencing. Our results demonstrated significant changes in bacterial diversity, richness and evenness during amoxicillin treatment, followed by a reversion in terms of alpha-diversity and abundance of major phyla, after end of treatment. However, a longer restitution time was indicated for mice receiving amoxicillin for 14 days, and phylum Patescibacteria did not fully recover. In addition, an effect on the composition of Firmicutes was indicated to last for at least three weeks in mice treated with amoxicillin for 14 days. Despite an apparently reversion to a close to original state in overall bacterial diversity and richness, the results suggested more durable changes in lower taxonomical levels. We detected several families, genera and ASVs with significantly altered abundance three weeks after exposure to amoxicillin, as well as bacterial taxa that appeared significantly affected by amoxicillin treatment length. This may strengthen the argument for shorter antibiotic treatment regimens to both limit the emergence of antibiotic resistance and risk of gut microbiome disturbance.

Depression and antidepressant effects of ketamine and its metabolites: The pivotal role of gut microbiota

The discovery of the robust antidepressant actions of ketamine is regarded as one of the greatest advancements in depression treatment in the past 60 years. Recent findings have provided strong evidence for the presence of bidirectional communication networks between the gastrointestinal tract and the brain in depression. Moreover, increasing evidence supports the antidepressant role of ketamine in regulating the gut microbiome and microbiota-derived molecules; however, the mechanisms underpinning such effects are still ambiguous. This review summarizes the current understanding of the anti-depressant mechanisms of ketamine and its metabolites regarding the bidirectional regulation by microbiota-gut-brain axis. We review the relationship between gut microbiota and the antidepressant mechanisms of ketamine, and discuss the role of stress response, brain-derived neurotrophic factor (BDNF)-mediated neurogenesis, anti-inflammatory effect and neurotransmitters.

Antibiotic-induced microbiome depletion improves LPS-induced acute lung injury via gut-lung axis

AIMS

Acute lung injury (ALI) is an acute inflammatory disorder. However, the precise mechanisms underlying the pathology of ALI remain elusive. An increasing evidence suggests the role of the gut-microbiota axis in the pathology of lung injury. This study aimed to investigate whether antibiotic-induced microbiome depletion could affect ALI in mice after lipopolysaccharide (LPS) administration.

MAIN METHODS

The effects of antibiotic cocktail (ABX) on ALI in the mice after intratracheally administration of LPS (5 mg/kg) were examined. Furthermore, 16s rRNA analysis and measurement of short-chain fatty acids in feces samples and metabolomics analysis of blood samples were performed.

KEY FINDINGS

LPS significantly increased the interleukin-6 (IL-6) levels in the bronchoalveolar lavage fluid (BALF) of water-treated mice. Interestingly, an ABX significantly attenuated the LPS-induced increase in IL-6 in BALF and lung injury scores. Furthermore, ABX and/or LPS treatment markedly altered the α- and β-diversity of the gut microbiota. There were significant differences in the α- and β-diversity of the water + LPS group and ABX + LPS group. LEfSe analysis identified Enterococusfaecalis, Clostriumtertium, and Bacteroidescaecimyris as potential microbial markers for ABX + LPS group. Untargeted metabolomics analysis identified several plasma metabolites responsible for discriminating water + LPS group from ABX + LPS group. There were correlations between the relative abundance of the microbiome and plasma metabolites. Integrative network analysis showed correlations between IL-6 levels in BALF and several gut microbes (or plasma metabolites).

SIGNIFICANCE

These data suggest that ABX-induced microbiome depletion could protect against LPS-induced ALI via the gut-microbiota-lung axis.

Depression-like behaviors in mouse model of Sjögren's syndrome: A role of gut-microbiota-brain axis

Depression is a common psychiatric symptom in patients with Sjögren's syndrome (SS). Prevalence of depression in SS patients is significantly higher than that in the general population. Increasing evidence suggests a crucial role of gut-microbiota-brain axis in depression. In this study, we investigated whether non-obese diabetic (NOD) mice, a widely used animal model of SS, exhibit depression-like phenotypes and abnormal composition of gut microbiota. Eleven-week-old NOD mice spontaneously exhibited SS-related symptoms without pancreatic destruction. NOD mice displayed depression-like behaviors, decreased expression of synaptic proteins in the prefrontal cortex (PFC), and abnormal composition of gut microbiota. Interestingly, SS-related proinflammatory factors in the submandibular gland (SMG) and autoantibodies (anti-SSA and anti-SSB) in the plasma were correlated with the expression of synaptic proteins in the PFC or depression-like behaviors. In addition, there were correlations between the relative abundance of microbiota and SS-related symptoms (or depression-related phenotypes). These data suggest that SS-related symptoms and abnormal composition of gut microbiota may play a role in depression-like phenotypes in NOD mice through gut-microbiota-brain axis.

Antibiotic-Induced Gut Microbiota Depletion Accelerates the Recovery of Radiation-Induced Oral Mucositis in Rats

PURPOSE

Due to its pivotal role in the modulation of immune and inflammatory responses, the gut microbiota has emerged as a key modulator of cancer treatment-induced gastrointestinal mucositis. However, it is not clear yet how it affects radiation therapy-induced oral mucositis (OM). As such, this study aimed to explore the gut microbiota's role in the pathogenesis of radiation-induced OM in rats.

METHODS AND MATERIALS

Male Sprague Dawley rats were treated with 20 Gy x-ray radiation (Rx) delivered to the snout, with or without antibiotic-induced microbiota depletion (AIMD). OM severity was assessed, and tongue tissues were collected on day 9 and 15 postradiation for tissue injury and inflammatory markers assessment.

RESULTS

AIMD+Rx had a significantly shorter duration of severe OM compared with Rx alone group. Macroscopically, the tongue ulcer-like area was smaller in AIMD+Rx compared with the Rx group. Microscopically, a smaller percentage of the mucosal ulcer was observed in the dorsal tongue of AIMD+Rx compared with the Rx group. AIMD+Rx also had significantly lower levels of interleukin 6, interleukin 1 beta, and toll like receptor 4 in the tongue tissues than the Rx group.

CONCLUSIONS

The gut microbiota plays a role in OM pathogenesis, mainly in the recovery phase, through the modulation of proinflammatory pathways. Future microbiota-targeted interventions may improve OM in clinical settings.

Fecal microbiota transplantation from patients with rheumatoid arthritis causes depression-like behaviors in mice through abnormal T cells activation

Depression is common in patients with rheumatoid arthritis (RA); however, the precise mechanisms underlying a link between depression and RA remain unclear. Accumulating evidence suggests the role of gut-microbiota-brain axis in depression. In this study, we investigated whether collagen-induced arthritis (CIA) mice produce depression-like behaviors and abnormal composition of gut microbiota. Furthermore, we investigated whether fecal microbiota transplantation (FMT) from RA patients causes depression-like phenotypes in antibiotic cocktail (ABX)-treated mice. CIA mice displayed depression-like behaviors, increased blood levels of pro-inflammatory cytokine interleukin-6 (IL-6), decreased expression of synaptic proteins in the prefrontal cortex (PFC), and abnormal composition of gut microbiota. Furthermore, FMT from RA patients caused depression-like phenotypes, alterations of gut microbiota composition, increased levels of IL-6 and tumor necrosis factor-α (TNF-α), and downregulation of synaptic proteins in the PFC compared to FMT from healthy controls. There were correlations between relative abundance of microbiota and plasma cytokines, expression of synaptic proteins in the PFC or depression-like behaviors. Interestingly, FMT from RA patients induced T cells differentiation in Peyer's patches and spleen. Reduced percentage of Treg cells with an increase of Th1/Th2 index was observed in the mice after FMT from RA patients. These findings suggest that CIA mice exhibit depression-like behaviors, systemic inflammation, and abnormal composition of gut microbiota, and that FMT from RA patients produces depression-like behaviors in ABX-treated mice via T cells differentiation. Therefore, abnormalities in gut microbiota in RA patients may contribute to depression via gut-microbiota-brain axis.

Resilience and the Gut Microbiome: Insights from Chronically Socially Stressed Wild-Type Mice

The microbiome is an important player within physiological homeostasis of the body but also in pathophysiological derailments. Chronic social stress is a challenge to the organism, which results in psychological illnesses such as depression in some individuals and can be counterbalanced by others, namely resilient individuals. In this study, we wanted to elucidate the potential contribution of the microbiome to promote resilience. Male mice were subjected to the classical chronic social defeat paradigm. Defeated or undefeated mice were either controls (receiving normal drinking water) or pre-treated with antibiotics or probiotics. Following social defeat, resilient behavior was assessed by means of the social interaction test. Neither depletion nor probiotic-shifted alteration of the microbiome influenced stress-associated behavioral outcomes. Nevertheless, clear changes in microbiota composition due to the defeat stress were observed such as elevated Bacteroides spp. This stress-induced increase in Bacteroides in male mice could be confirmed in a related social stress paradigm (instable social hierarchy) in females. This indicates that while manipulation of the microbiome via the antibiotics- and probiotics-treatment regime used here has no direct impact on modulating individual stress susceptibility in rodents, it clearly affects the microbiome in the second line and in a sex-independent manner regarding Bacteroides.

Microglial depletion and abnormalities in gut microbiota composition and short-chain fatty acids in mice after repeated administration of colony stimulating factor 1 receptor inhibitor PLX5622

PLX5622, a brain-penetrant highly specific inhibitor of the colony-stimulating factor 1 receptor (CSF1R), is used to eliminate microglia in the brain. Considering the role of microglia and gut microbiota in the brain homeostasis, this study was undertaken to investigate whether repeated intragastric administration of PLX5622 (65 mg/kg/day for consecutive 7 days) could affect the composition of gut microbiota and the concentration of short-chain fatty acids (SCFAs) in fresh feces of adult mice. Repeated administration of PLX5622 caused significant reductions of the expression of genes and proteins for microglial markers in the prefrontal cortex (PFC) and hippocampus compared to control mice although the elimination of brain's microglia was partial. There was a significant alteration in the β-diversity of intestine microbiota in the PLX5622-treated group. Linear discriminant analysis effect size identified eight significant enriched bacteria as microbial markers for PLX5622-treated group. Repeated administration of PLX5622 affected the relative abundance of several bacteria at the genus and species levels. Furthermore, repeated administration of PLX5622 caused a significant change in lactic acid compared to control group. Interestingly, we found significant correlations between microglial markers in the brain and the relative abundance of several bacteria, suggesting microbiome-microglia crosstalk through the brain-gut axis. These data demonstrate that repeated administration of PLX5622 leads to an abnormal composition of the gut microbiota and lactic acid in adult mice. Therefore, abnormalities in the composition of gut microbiota after repeated treatment of PLX5622 should be considered for behavioral and biological functions in animals treated with CSF1R inhibitors.

Gut microbiota is involved in the antidepressant effects of adipose-derived mesenchymal stem cells in chronic social defeat stress mouse model

RATIONALE

Growing evidence supports the role of microbiota in regulating gut-brain interactions and, thus, contributing to the pathogenesis of depression and the antidepressant actions. Adipose-derived mesenchymal stem cells (ADSCs), as important members of the stem cell family, were demonstrated to alleviate depression behaviors. However, the role of gut microbiota in ADSCs alleviating depression in chronic social defeat stress (CSDS) model is unknown.

OBJECTIVES

To examine the effects of ADSCs on depression symptoms and detect the changes in the composition of gut microbiota.

RESULTS

We found that ADSCs administration significantly ameliorated CSDS-induced depression behaviors, which was accompanied by alteration in the gut microbiota. The principal co-ordinates analysis (PCoA) results showed that there was a significant difference between the gut microbiota among the groups. Remarkably, receiver operating characteristic (ROC) curves revealed that order Micrococcales, order Rhizobiales and species Bacteroides acidifaciens are potentially important biomarkers for the antidepressant effects of ADSCs in CSDS model.

CONCLUSIONS

ADSCs are effective in treating depression behaviors in CSDS model, which might be partly due to the regulation of abnormal composition of gut microbiota. Thus, ADSCs offer a promising therapeutic strategy for treating depression in patients.

Novel Pharmacological Approaches to the Treatment of Depression

Major depressive disorder is one of the most prevalent mental health disorders. Monoamine-based antidepressants were the first drugs developed to treat major depressive disorder. More recently, ketamine and other analogues were introduced as fast-acting antidepressants. Unfortunately, currently available therapeutics are inadequate; lack of efficacy, adverse effects, and risks leave patients with limited treatment options. Efforts are now focused on understanding the etiology of depression and identifying novel targets for pharmacological treatment. In this review, we discuss promising novel pharmacological targets for the treatment of major depressive disorder. Targeting receptors including N-methyl-D-aspartate receptors, peroxisome proliferator-activated receptors, G-protein-coupled receptor 39, metabotropic glutamate receptors, galanin and opioid receptors has potential antidepressant effects. Compounds targeting biological processes: inflammation, the hypothalamic-pituitary-adrenal axis, the cholesterol biosynthesis pathway, and gut microbiota have also shown therapeutic potential. Additionally, natural products including plants, herbs, and fatty acids improved depressive symptoms and behaviors. In this review, a brief history of clinically available antidepressants will be provided, with a primary focus on novel pharmaceutical approaches with promising antidepressant effects in preclinical and clinical studies.

One Giant Leap from Mouse to Man: The Microbiota-Gut-Brain Axis in Mood Disorders and Translational Challenges Moving towards Human Clinical Trials

The microbiota–gut–brain axis is a bidirectional communication pathway that enables the gut microbiota to communicate with the brain through direct and indirect signaling pathways to influence brain physiology, function, and even behavior. Research has shown that probiotics can improve several aspects of health by changing the environment within the gut, and several lines of evidence now indicate a beneficial effect of probiotics on mental and brain health. Such evidence has prompted the arrival of a new term to the world of biotics research: psychobiotics, defined as any exogenous influence whose effect on mental health is bacterially mediated. Several taxonomic changes in the gut microbiota have been reported in neurodevelopmental disorders, mood disorders such as anxiety and depression, and neurodegenerative disorders such as Alzheimer’s disease. While clinical evidence supporting the role of the gut microbiota in mental and brain health, and indeed demonstrating the beneficial effects of probiotics is rapidly accumulating, most of the evidence to date has emerged from preclinical studies employing different animal models. The purpose of this review is to focus on the role of probiotics and the microbiota–gut–brain axis in relation to mood disorders and to review the current translational challenges from preclinical to clinical research.

Reduced calorie diet combined with NNMT inhibition establishes a distinct microbiome in DIO mice

Treatment with a nicotinamide N-methyltransferase inhibitor (NNMTi; 5-amino-1-methylquinolinium) combined with low-fat diet (LD) promoted dramatic whole-body adiposity and weight loss in diet-induced obese (DIO) mice, rapidly normalizing these measures to age-matched lean animals, while LD switch alone was unable to restore these measures to age-matched controls in the same time frame. Since mouse microbiome profiles often highly correlate with body weight and fat composition, this study was designed to test whether the cecal microbiomes of DIO mice treated with NNMTi and LD were comparable to the microbiomes of age-matched lean counterparts and distinct from microbiomes of DIO mice maintained on a high-fat Western diet (WD) or subjected to LD switch alone. There were minimal microbiome differences between lean and obese controls, suggesting that diet composition and adiposity had limited effects. However, DIO mice switched from an obesity-promoting WD to an LD (regardless of treatment status) displayed several genera and phyla differences compared to obese and lean controls. While alpha diversity measures did not significantly differ between groups, beta diversity principal coordinates analyses suggested that mice from the same treatment group were the most similar. K-means clustering analysis of amplicon sequence variants by animal demonstrated that NNMTi-treated DIO mice switched to LD had a distinct microbiome pattern that was highlighted by decreased Erysipelatoclostridium and increased Lactobacillus relative abundances compared to vehicle counterparts; these genera are tied to body weight and metabolic regulation. Additionally, Parasutterella relative abundance, which was increased in both the vehicle- and NNMTi-treated LD-switched groups relative to the controls, significantly correlated with several adipose tissue metabolites' abundances. Collectively, these results provide a novel foundation for future investigations.

Molecular mechanisms underlying the antidepressant actions of arketamine: beyond the NMDA receptor

The discovery of robust antidepressant actions exerted by the N-methyl-D-aspartate receptor (NMDAR) antagonist (R,S)-ketamine has been a crucial breakthrough in mood disorder research. (R,S)-ketamine is a racemic mixture of equal amounts of (R)-ketamine (arketamine) and (S)-ketamine (esketamine). In 2019, an esketamine nasal spray from Johnson & Johnson was approved in the United States of America and Europe for treatment-resistant depression. However, an increasing number of preclinical studies show that arketamine has greater potency and longer-lasting antidepressant-like effects than esketamine in rodents, despite the lower binding affinity of arketamine for the NMDAR. In clinical trials, non-ketamine NMDAR-related compounds did not exhibit ketamine-like robust antidepressant actions in patients with depression, despite these compounds showing antidepressant-like effects in rodents. Thus, the rodent data do not necessarily translate to humans due to the complexity of human psychiatric disorders. Collectively, the available studies indicate that it is unlikely that NMDAR plays a major role in the antidepressant action of (R,S)-ketamine and its enantiomers, although the precise molecular mechanisms underlying antidepressant actions of (R,S)-ketamine and its enantiomers remain unclear. In this paper, we review recent findings on the molecular mechanisms underlying the antidepressant actions of (R,S)-ketamine and its potent enantiomer arketamine. Furthermore, we discuss the possible role of the brain-gut-microbiota axis and brain-spleen axis in stress-related psychiatric disorders and in the antidepressant-like action of arketamine. Finally, we discuss the potential of arketamine as a treatment for cognitive impairment in psychiatric disorders, Parkinson's disease, osteoporosis, inflammatory bowel diseases, and stroke.

Inflamed brain: Targeting immune changes and inflammation for treatment of depression

Although there are a number of clinically effective treatments for depression, many patients exhibit treatment resistance. Recent clinical and preclinical studies reveal that peripheral and brain immune changes and inflammation are involved in the pathophysiology of depression. This 'Inflamed Brain' research provides critical clues for understanding of disease pathophysiology and many candidate molecules that are potentially useful for identifying novel drug targets for the treatment of depression. In this review, we will present clinical evidence on the role of inflammation in the pathophysiology of depression. We will also summarize current clinical trials which test drugs targeting inflammation for the treatment of patients with depression. Furthermore, we will briefly provide preclinical evidence demonstrating altered immune system function and inflammation in stress-induced animal models and will discuss the future potential of inflammation-related drug targets. Collectively, inflammatory signatures identified in clinical and preclinical studies may allow us to stratify depressive patients based on biotypes, contributing to the development of novel mechanism-based interventions that target specific patient populations.

Abnormalities of the composition of the gut microbiota and short-chain fatty acids in mice after splenectomy

The brain–gut–microbiota axis is a complex multi-organ bidirectional signaling system between the brain and microbiota that participates in the host immune system. The spleen, as the largest immune organ in the body, has a key role in the brain–gut–microbiota axis. Here, we investigated whether splenectomy could affect depression-like phenotypes and the composition of the gut microbiota in adult mice. In behavioral tests, splenectomy did not cause depression-like behaviors in mice. Conversely, splenectomy led to significant alterations in the diversity of gut microbes compared with the findings in control (no surgery) and sham-operated mice. In an unweighted UniFrac distance analysis, the boxplots representing the splenectomy group were distant from those representing the other two groups. We found differences in abundance for several bacteria in the splenectomy group at the taxonomic level compared with the other two groups. Finally, splenectomy induced significant changes in lactic acid and n-butyric acid levels compared with those in the other groups. Interestingly, there were significant correlations between the counts of certain bacteria and lactic acid (or n-butyric acid) levels in all groups. These data suggest that splenectomy leads to an abnormal composition of the gut microbiota. It is likely that the spleen–gut–microbiota axis plays a crucial role in the composition of the gut microbiota by regulating immune homeostasis.

Regulation of neurotoxicity in the striatum and colon of MPTP-induced Parkinson's disease mice by gut microbiome

Increasing evidence suggests the role of gut-microbiota-brain axis in the pathogenesis of Parkinson's disease (PD). The objective of this study was to examine whether repeated administration of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) can influence the neurotoxicity in the striatum and colon, and the composition of gut microbiota and short-chain fatty acids (SCFAs) in feces of adult mice. MPTP caused the reduction of dopamine transporter (DAT) and tyrosine hydroxylase (TH) in the striatum, and increases in phosphorylated α-synuclein (p-α-Syn) in the striatum and colon. There was a negative correlation between the expression of TH in the striatum and the expression of p-α-Syn in the colon, suggesting a role of gut-brain communication. MPTP caused abnormalities in the α- and β-diversity of gut microbiota in the mice. Furthermore, the relative abundance of the genus Faecalicatena in the MPTP-treated group was significantly lower than that of control group. Interestingly, there was a positive correlation between the genus Faecalicatena and the expression of TH in the striatum. Moreover, MPTP did not alter the levels of SCFAs in feces samples. However, there was a positive correlation between the relative abundance of the genus Faecalicatena and propionic acid. The data suggest that MPTP-induced increases in colonic p-α-Syn expression might be associated with dopaminergic neurotoxicity in the striatum via gut-microbiota-brain axis.

Ingestion of Faecalibaculum rodentium causes depression-like phenotypes in resilient Ephx2 knock-out mice: A role of brain-gut-microbiota axis via the subdiaphragmatic vagus nerve

BACKGROUND

The brain-gut-microbiota axis plays a crucial role in the bidirectional interactions between the brain and the gut. Soluble epoxide hydrolase (coded by the Ephx2 gene) plays an important role in inflammation, which has been implicated in stress-related depression. Ephx2 knock-out (KO) mice exposed to chronic social defeat stress (CSDS) did not show depression-like behaviors, indicating stress resilience. Here we examined whether the brain-gut-microbiota axis influences the resilience in Ephx2 KO mice.

METHODS

Effects of fecal microbiota transplantation (FMT) from CSDS-susceptible (or control) mice in wild-type (WT) mice and Ephx2 KO mice treated with an antibiotic cocktail (ABX) were investigated. Behavioral, biochemical tests and 16S ribosome RNA analysis were performed.

RESULTS

FMT from CSDS-susceptible mice produced anhedonia-like behavior in ABX-treated WT and Ephx2 KO mice. The 16S ribosome RNA analysis showed that Faecalibaculum rodentium (F. rodentium) may be responsible for the observed anhedonia-like behavior following FMT from CSDS-susceptible mice. Ingestion of F. rodentium for 14 days produced depression- and anhedonia-like behaviors, higher blood levels of interleukin-6, and reduced expression of synaptic proteins in the prefrontal cortex of ABX-treated Ephx2 KO mice. Furthermore, subdiaphragmatic vagotomy blocked the development of these behavioral abnormalities after ingestion of F. rodentium.

LIMITATIONS

Detailed mechanisms are unclear.

CONCLUSIONS

These findings suggest that F. rodentium might contribute to the conversion of resilient Ephx2 KO mice into KO mice with depression-like phenotypes. The brain-gut-microbiota axis via the subdiaphragmatic vagus nerve plays a crucial role in susceptibility and resilience to stress.

Stress-Related Dysfunction of Adult Hippocampal Neurogenesis-An Attempt for Understanding Resilience?

Newborn neurons in the adult hippocampus are regulated by many intrinsic and extrinsic cues. It is well accepted that elevated glucocorticoid levels lead to downregulation of adult neurogenesis, which this review discusses as one reason why psychiatric diseases, such as major depression, develop after long-term stress exposure. In reverse, adult neurogenesis has been suggested to protect against stress-induced major depression, and hence, could serve as a resilience mechanism. In this review, we will summarize current knowledge about the functional relation of adult neurogenesis and stress in health and disease. A special focus will lie on the mechanisms underlying the cascades of events from prolonged high glucocorticoid concentrations to reduced numbers of newborn neurons. In addition to neurotransmitter and neurotrophic factor dysregulation, these mechanisms include immunomodulatory pathways, as well as microbiota changes influencing the gut-brain axis. Finally, we discuss recent findings delineating the role of adult neurogenesis in stress resilience.

Puerarin ameliorates depression-like behaviors of with chronic unpredictable mild stress mice by remodeling their gut microbiota

BACKGROUND

Puerarin is an isoflavone derivative isolated from the traditional Chinese medicine Pueraria Lobelia, which has proven to relieve depression-like behavior. However, its underlying antidepressant mechanisms have been poorly characterized. Herein, we explored whether Puerarin's antidepressant effect is associated with changes in the gut microbiota (GM).

METHODS

The model of depression in mice featuring chronic unpredictable mild stress (CUMS) was eastablished, and its antidepressant effect was estimated by sugar water preference and forced swimming test. Genomic DNA extracted from fecal samples was employed to sequence the 16S rRNA gene for gut microbiota identification.

RESULTS

Puerarin (100 mg/kg) treatment was found to alleviate the CUMS-induced depression-like behaviors. Furthermore, chronic stress led to pathological microbial flora, which was principally marked by the increased abundance of pathogenic bacteria (Proteobacteria, Flexispira, Desulfovibrio) and the decreased abundance of beneficial bacteria (Firmicutes, Bacillales, Lactobacillus). Intriguingly, puerarin treatment reversed these changes.

LIMITATIONS

The specific role and anti-depression mechanism of characteristic gut microflora were not confirmed.

CONCLUSION

Puerarin can remedy stress-induced disruptions of normal gut microflora. It is suggested that the antidepressant mechanism of puerarin may closely interact with restoring beneficial microflora.

Gut microbiota is involved in the antidepressant-like effect of (S)-norketamine in an inflammation model of depression

The non-competitive glutamatergic N-methyl-d-aspartate receptor (NMDAR) antagonist, (R, S)-ketamine (ketamine), is known to exert rapid and long-lasting antidepressant-like effects. However, the widely use of ketamine is restricted owing to severe psychotomimetic side-effects and abuse liability. Very recently, we demonstrated that a major metabolite of ketamine, norketamine, in particular the (S)-enantiomer, had a potent antidepressant-like effect. We here examined the effects of a low-dose of norketamine enantiomers on depression symptoms and detected the changes in the composition of gut microbiota. In the behavioral tests, (S)-norketamine, but not (R)-norketamine, showed antidepressant-like effects in the lipopolysaccharide (LPS)-induced mice. At the genus level, (S)-norketamine, but not (R)-norketamine, significantly attenuated the increase in the levels of Escherichia-Shigella and Adlercreutzia, as well as the reduction in the levels of Harryflintia. At the species level, both (S)-norketamine and (R)-norketamine significantly attenuated the increase in the levels of bacterium ic1379 and Bacteroides sp. Marseille-P3166. Notably, (S)-norketamine was more potent than (R)-norketamine at reducing the levels of bacterium ic1379 and Bacteroides sp. Marseille-P3166. Furthermore, (S)-norketamine, but not (R)-norketamine, significantly attenuated the increased levels of Bacteroides caecigallinarum. In conclusion, this study suggests that the antidepressant-like effects of (S)-norketamine might be associated with the changes in the composition of gut microbiota. Therapeutic strategies improving the gut microbiota might facilitate the benefits for depression treatment.

Washed Microbiota Transplantation Accelerates the Recovery of Abnormal Changes by Light-Induced Stress in Tree Shrews

The gut and brain interact constantly in a complex fashion. Its intricacy and intrigue is progressively being revealed in the study of the "gut-brain axis". Among many factors, abnormal light exposure is a potential powerful stressor, which is becoming ever more pervasive in our modern society. However, little is known about how stress, induced by staying up late by light, affects the gut-brain axis. We addressed this question by extending the normal circadian light for four hours at night in fifteen male tree shrews to simulate the pattern of staying up late in humans. The behavior, biochemical tests, microbiota dynamics, and brain structure of tree shrews were evaluated. The simple prolongation of light in the environment resulted in substantial changes of body weight loss, behavioral differences, total sleep time reduction, and an increased level of urine cortisol. These alterations were rescued by the treatment of either ketamine or washed microbiota transplantation (WMT). Importantly, the sustainability of WMT effect was better than that of ketamine. Magnetic Resonance Imaging analysis indicated that ketamine acted on the hippocampus and thalamus, and WMT mainly affected the piriform cortex and lateral geniculate nucleus. In conclusion, long-term light stimulation could change the behaviors, composition of gut microbiota and brain structure in tree shrews. Targeting microbiota thus certainly holds promise as a treatment for neuropsychiatric disorders, including but not limited to stress-related diseases.

Antibiotic exposure and potential risk of depression in the Chinese elderly: a biomonitoring-based population study

OBJECTIVE

To examine the associations between urinary antibiotics from various sources and depression in the elderly using the biomonitoring method.

METHODS

In the current study, we investigated 990 elderly individuals (≥ 60 years old) from a community-based elderly cohort in West Anhui, China. The participants were interviewed by the Geriatric Depression Scale and self-developed questionnaires. A total of 45 antibiotics belonging to nine categories were screened in urine samples by the developed liquid chromatography electrospray tandem mass spectrometry method. Creatinine-corrected concentrations of antibiotics in urines were used to assess their exposure. Logistic regression analysis was employed to test the relationships between exposure to antibiotics and depression.

RESULTS

Compared to the control group, the multinomial logistic regression analyses showed the elderly exposed to higher concentrations of azithromycin (OR = 1.81, 95% CI: 1.09-3.00) and sulfaclozine (OR = 1.54, 95% CI: 1.05-2.28) had increased risks of depression, respectively. After categorizing the detected antibiotics, tetracyclines (OR = 1.48, 95% CI: 1.02-2.16) and veterinary antibiotics (VAs) (OR = 1.53, 95% CI: 1.06-2.20) were positively correlated with increased risks of depression. After stratified by sex, the VAs (OR = 2.04, 95% CI: 1.13-3.71) at higher concentrations were associated with elevated risks of depression in males, while the associations between depression and antibiotic exposures were observed in tetracyclines (OR = 1.74, 95% CI: 1.04-2.85) and all antibiotics (OR = 2.24, 95% CI: 1.01-2.94) at higher levels in females, respectively. Notably, after the stratification by age, the significant associations were mainly present in the subjects under the age of 70.

CONCLUSIONS

Our findings reveal that azithromycin, sulfaclozine, tetracyclines, and the VAs were significantly associated with elevated risks of depression in the elderly. Importantly, sex- and age-specific differences were observed in the associations between antibiotic exposures and depression.

Abnormal composition of microbiota in the gut and skin of imiquimod-treated mice

Psoriasis is a chronic, inflammatory skin disease. Although the precise etiology of psoriasis remains unclear, gut-microbiota axis might play a role in the pathogenesis of the disease. Here we investigated whether the composition of microbiota in the intestine and skin is altered in the imiquimod (IMQ)-treated mouse model of psoriasis. Topical application of IMQ to back skin caused significant changes in the composition of microbiota in the intestine and skin of IMQ-treated mice compared to control mice. The LEfSe algorithm identified the species Staphylococcus lentus as potential skin microbial marker for IMQ group. Furthermore, there were correlations for several microbes between the intestine and skin, suggesting a role of skin-gut-microbiota in IMQ-treated mice. Levels of succinic acid and lactic acid in feces from IMQ-treated mice were significantly higher than control mice. Moreover, the predictive functional analysis of the microbiota in the intestine and skin showed that IMQ caused alterations in several KEGG pathways. In conclusion, the current data indicated that topical application with IMQ to skin alters the composition of the microbiota in the gut and skin of host. It is likely that skin-gut microbiota axis plays a role in pathogenesis of psoriasis.