Finding intestinal fortitude: Integrating the microbiome into a holistic view of depression mechanisms, treatment, and resilience

Exploring the Pathogenesis and Treatment of PSD from the Perspective of Gut Microbiota

Post-stroke depression (PSD) is a psychological disease that can occur following a stroke and is associated with serious consequences. Research on the pathogenesis and treatment of PSD is still in the infancy stage. Patients with PSD often exhibit gastrointestinal symptoms; therefore the role of gut microbiota in the pathophysiology and potential treatment effects of PSD has become a hot topic of research. In this review, describe the research on the pathogenesis and therapy of PSD. We also describe how the gut microbiota influences neurotransmitters, the endocrine system, energy metabolism, and the immune system. It was proposed that the gut microbiota is involved in the pathogenesis and treatment of PSD through the regulation of neurotransmitter levels, vagal signaling, hypothalamic-pituitary-adrenal axis activation and inhibition, hormone secretion and release, in addition to immunity and inflammation.

Postbiotics as Metabolites and Their Biotherapeutic Potential

This review highlights the role of postbiotics, which may provide an underappreciated avenue doe promising therapeutic alternatives. The discovery of natural compounds obtained from microorganisms needs to be investigated in the future in terms of their effects on various metabolic disorders and molecular pathways, as well as modulation of the immune system and intestinal microbiota in children and adults. However, further studies and efforts are needed to evaluate and describe new postbiotics. This review provides available knowledge that may assist future research in identifying new postbiotics and uncovering additional mechanisms to combat metabolic diseases.

Biosignals in the Gut-Brain Axis Transmission: Function and Detection

The gut-brain axis (GBA) is an important information pathway connecting the brain, the central nervous system (CNS), and the gastrointestinal (GI) tract. On the one hand, gut microbiota can influence the function brain through GBA; on the other hand, the brain can also change the structural composition of gut microbiota via GBA. It contains a myriad of biosignals, such as monoamines, inflammatory cytokines, and macro-biomolecules, as the information carriers. Highly selective, sensitive, and reliable sensing techniques are essential to resolve the specific function of individual biosignals. This review summarizes the widely reported biosignals related to GBA and their functions, and organizes the latest sensing tools to provide feasible characterization ideas for GBA-related work. In addition, these low-cost, fast-responding sensors can also be used for early identification and diagnosis of GBA-related diseases (e.g., depression). Finally, the problems and deficiencies in this field are pointed out to provide a reference for the orientation of researchers in the sensing field.

A Randomized Controlled Trial Comparing Efficacy and Safety of Antidepressant Monotherapy

BACKGROUND AND OBJECTIVES

The majority of mainstream antidepressants lack the promise of complete amelioration of symptoms. Other pitfalls include the latency period and side effects. These issues prompted investigations concerning the various roles of serotonin (5-HT) neurotransmissions in the etiology of depression. In this study, each study participant received vilazodone, vortioxetine, and escitalopram monotherapy for major depressive disorder (MDD) for 16 weeks. After that, the subject's scores on the Hamilton Depression Rating Scale (HDRS)-17 item version and the Montgomery Åsberg Depression Rating Scale (MADRS) were evaluated. In the study population, we kept track of the incidence of adverse events.

METHODS

Ninety-six patients with MDD participated in this open-label, randomized, three-arm study. Participants were allotted into three groups according to a 1:1:1 ratio and given vilazodone (20-40 mg/day), vortioxetine (5-20 mg/day), or escitalopram (10-20 mg/day) for 16 weeks. Vortioxetine and vilazodone are test medications, with escitalopram serving as the control. After the baseline visit, follow-up appointments were scheduled every four weeks. Per-protocol (PP) and intent-to-treat (ITT) populations served as means for efficacy and safety evaluations, respectively. We prospectively registered this research in the Clinical Trial Registry, India (CTRI) (2022/07/043808).

RESULTS

Out of the 134 patients we screened, 109 (81.34%) were eligible. Ninety-six (88.07%) of them completed the 16-week trial. In the PP population (n = 96), we analyzed efficacy. They had a mean age of 46.3 ± 6.2 years. At baseline, each group's median HDRS score was 30.0 (p = 0.964). Following 16 weeks of antidepressant therapy, these scores dropped to 15.0, 14.0, and 13.0 (p = 0.002). Baseline MADRS scores for all groups were 36.0 (p = 0.741). They had corresponding values of 20.0, 18.0, and 17.0 at 16 weeks (p < 0.001). Regarding both efficacy endpoints, the post-hoc analysis with the Bonferroni correction demonstrated statistically significant differences (p < 0.001). We performed the safety assessments within our ITT population (n = 109). Ninety-six adverse events were recorded. Nonetheless, none of them seemed serious. Still, five participants opted out because of their side effects. Vomiting and nausea were the most frequent side effects.

CONCLUSION

Compared to escitalopram and vilazodone, vortioxetine demonstrated a statistically significant reduction in HDRS and MADRS scores. It also had fewer and milder side effects. We recommend conducting studies involving a broader population to investigate the antidepressant effects of these medications further.

The Changes of Blood and CSF Ion Levels in Depressed Patients: a Systematic Review and Meta-analysis

Micronutrient deficiencies and excesses are closely related to developing and treating depression. Traditional and effective antidepressants include tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), and lithium. There is no consensus on the fluctuation of zinc (Zn2+), magnesium (Mg2+), calcium (Ca2+), copper (Cu2+), iron (Fe2+), and manganese (Mn2+) ion levels in depressed individuals before and after therapy. In order to determine whether there were changes in blood and cerebrospinal fluid (CSF) levels of these ions in depressed patients compared with healthy controls and depressed patients treated with TCAs, SSRIs, or lithium, we applied a systematic review and meta-analysis. Using the Stata 17.0 software, we performed a systematic review and meta-analysis of the changes in ion levels in human samples from healthy controls, depressive patients, and patients treated with TCAs, SSRIs, and lithium, respectively. By searching the PubMed, EMBASE, Google Scholar, Web of Science, China National Knowledge Infrastructure (CNKI), and WAN FANG databases, 75 published analyzable papers were chosen. In the blood, the levels of Zn2+ and Mg2+ in depressed patients had decreased while the Ca2+ and Cu2+ levels had increased compared to healthy controls, Fe2+ and Mn2+ levels have not significantly changed. After treatment with SSRIs, the levels of Zn2+ and Ca2+ in depressed patients increased while Cu2+ levels decreased. Mg2+ and Ca2+ levels were increased in depressed patients after Lithium treatment. The findings of the meta-analysis revealed that micronutrient levels were closely associated with the onset of depression and prompted more research into the underlying mechanisms as well as the pathophysiological and therapeutic implications.

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.

Chronic Stress as a Risk Factor for Type 2 Diabetes: Endocrine, Metabolic, and Immune Implications

BACKGROUND

Chronic stress is a condition of pressure on the brain and whole body, which in the long term may lead to a frank disease status, even including type 2 diabetes (T2D). Stress activates the hypothalamus-pituitary-adrenal axis with release of glucocorticoids (GCs) and catecholamines, as well as activation of the inflammatory pathway of the immune system, which alters glucose and lipid metabolism, ultimately leading to beta-cell destruction, insulin resistance and T2D onset. Alteration of the glucose and lipid metabolism accounts for insulin resistance and T2D outcome. Furthermore, stress-related subversion of the intestinal microbiota leads to an imbalance of the gut-brain-immune axis, as evidenced by the stress-related depression often associated with T2D. A condition of generalized inflammation and subversion of the intestinal microbiota represents another facet of stress-induced disease. In fact, chronic stress acts on the gut-brain axis with multiorgan consequences, as evidenced by the association between depression and T2D. Oxidative stress with the production of reactive oxygen species and cytokine-mediated inflammation represents the main hallmarks of chronic stress. ROS production and pro-inflammatory cytokines represent the main hallmarks of stress-related disorders, and therefore, the use of natural antioxidant and anti-inflammatory substances (nutraceuticals) may offer an alternative therapeutic approach to combat stress-related T2D. Single or combined administration of nutraceuticals would be very beneficial in targeting the neuro-endocrine-immune axis, thus, regulating major pathways involved in T2D onset. However, more clinical trials are needed to establish the effectiveness of nutraceutical treatment, dosage, time of administration and the most favorable combinations of compounds. Therefore, in view of their antioxidant and anti-inflammatory properties, the use of natural products or nutraceuticals for the treatment of stress-related diseases, even including T2D, will be discussed. Several evidences suggest that chronic stress represents one of the main factors responsible for the outcome of T2D.

The Gut-Brain Axis and the Microbiome in Anxiety Disorders, Post-Traumatic Stress Disorder and Obsessive-Compulsive Disorder

A large body of research supports the role of stress in several psychiatric disorders in which anxiety is a prominent symptom. Other research has indicated that the gut microbiome-immune system- brain axis is involved in a large number of disorders and that this axis is affected by various stressors. The focus of the current review is on the following stress-related disorders: generalized anxiety disorder, panic disorder, social anxiety disorder, post-traumatic stress disorder and obsessivecompulsive disorder. Descriptions of systems interacting in the gut-brain axis, microbiome-derived molecules and of pro- and prebiotics are given. Preclinical and clinical studies on the relationship of the gut microbiome to the psychiatric disorders mentioned above are reviewed. Many studies support the role of the gut microbiome in the production of symptoms in these disorders and suggest the potential for pro- and prebiotics for their treatment, but there are also contradictory findings and concerns about the limitations of some of the research that has been done. Matters to be considered in future research include longer-term studies with factors such as sex of the subjects, drug use, comorbidity, ethnicity/ race, environmental effects, diet, and exercise taken into account; appropriate compositions of pro- and prebiotics; the translatability of studies on animal models to clinical situations; and the effects on the gut microbiome of drugs currently used to treat these disorders. Despite these challenges, this is a very active area of research that holds promise for more effective, precision treatment of these stressrelated disorders in the future.

Modulating microbiome-immune axis in the deployment-related chronic diseases of Veterans: report of an expert meeting

The present report summarizes the United States Department of Veterans Affairs (VA) field-based meeting titled "Modulating microbiome-immune axis in the deployment-related chronic diseases of Veterans." Our Veteran patient population experiences a high incidence of service-related chronic physical and mental health problems, such as infection, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), various forms of hematological and non-hematological malignancies, neurologic conditions, end-stage organ failure, requiring transplantation, and posttraumatic stress disorder (PTSD). We report the views of a group of scientists who focus on the current state of scientific knowledge elucidating the mechanisms underlying the aforementioned disorders, novel therapeutic targets, and development of new approaches for clinical intervention. In conclusion, we dovetailed on four research areas of interest: 1) microbiome interaction with immune cells after hematopoietic cell and/or solid organ transplantation, graft-versus-host disease (GVHD) and graft rejection, 2) intestinal inflammation and its modification in IBD and cancer, 3) microbiome-neuron-immunity interplay in mental and physical health, and 4) microbiome-micronutrient-immune interactions during homeostasis and infectious diseases. At this VA field-based meeting, we proposed to explore a multi-disciplinary, multi-institutional, collaborative strategy to initiate a roadmap, specifically focusing on host microbiome-immune interactions among those with service-related chronic diseases to potentially identify novel and translatable therapeutic targets.

Analysis of the Efficacy of Diet and Short-Term Probiotic Intervention on Depressive Symptoms in Patients after Bariatric Surgery: A Randomized Double-Blind Placebo Controlled Pilot Study

(1) Background: studies have shown that some patients experience mental deterioration after bariatric surgery. (2) Methods: We examined whether the use of probiotics and improved eating habits can improve the mental health of people who suffered from mood disorders after bariatric surgery. We also analyzed patients' mental states, eating habits and microbiota. (3) Results: Depressive symptoms were observed in 45% of 200 bariatric patients. After 5 weeks, we noted an improvement in patients' mental functioning (reduction in BDI and HRSD), but it was not related to the probiotic used. The consumption of vegetables and whole grain cereals increased (DQI-I adequacy), the consumption of simple sugars and SFA decreased (moderation DQI-I), and the consumption of monounsaturated fatty acids increased it. In the feces of patients after RYGB, there was a significantly higher abundance of two members of the Muribaculaceae family, namely Veillonella and Roseburia, while those after SG had more Christensenellaceae R-7 group, Subdoligranulum, Oscillibacter, and UCG-005. (4) Conclusions: the noted differences in the composition of the gut microbiota (RYGB vs. SG) may be one of the determinants of the proper functioning of the gut-brain microbiota axis, although there is currently a need for further research into this topic using a larger group of patients and different probiotic doses.

The Association between the Gut Microbiome and Development and Progression of Cancer Treatment Adverse Effects

Adverse effects are a common consequence of cytotoxic cancer treatments. Over the last two decades there have been significant advances in exploring the relationship between the gut microbiome and these adverse effects. Changes in the gut microbiome were shown in multiple clinical studies to be associated with the development of acute gastrointestinal adverse effects, including diarrhoea and mucositis. However, more recent studies showed that changes in the gut microbiome may also be associated with the long-term development of psychoneurological changes, cancer cachexia, and fatigue. Therefore, the aim of this review was to examine the literature to identify potential contributions and associations of the gut microbiome with the wide range of adverse effects from cytotoxic cancer treatments.

Direct and indirect effects of pathogenic bacteria on the integrity of intestinal barrier

Bacterial translocation is a pathological process involving migration of pathogenic bacteria across the intestinal barrier to enter the systemic circulation and gain access to distant organs. This phenomenon has been linked to a diverse range of diseases including inflammatory bowel disease, pancreatitis, and cancer. The intestinal barrier is an innate structure that maintains intestinal homeostasis. Pathogenic infections and dysbiosis can disrupt the integrity of the intestinal barrier, increasing its permeability, and thereby facilitating pathogen translocation. As translocation represents an essential step in pathogenesis, a clear understanding of how barrier integrity is disrupted and how this disruption facilitates bacterial translocation could identify new routes to effective prophylaxis and therapy. In this comprehensive review, we provide an in-depth analysis of bacterial translocation and intestinal barrier function. We discuss currently understood mechanisms of bacterial-enterocyte interactions, with a focus on tight junctions and endocytosis. We also discuss the emerging concept of bidirectional communication between the intestinal microbiota and other body systems. The intestinal tract has established 'axes' with various organs. Among our regulatory systems, the nervous, immune, and endocrine systems have been shown to play pivotal roles in barrier regulation. A mechanistic understanding of intestinal barrier regulation is crucial for the development of personalized management strategies for patients with bacterial translocation-related disorders. Advancing our knowledge of barrier regulation will pave the way for future research in this field and novel clinical intervention strategies.

Emerging epigenetic dynamics in gut-microglia brain axis: experimental and clinical implications for accelerated brain aging in schizophrenia

Brain aging, which involves a progressive loss of neuronal functions, has been reported to be premature in probands affected by schizophrenia (SCZ). Evidence shows that SCZ and accelerated aging are linked to changes in epigenetic clocks. Recent cross-sectional magnetic resonance imaging analyses have uncovered reduced brain reserves and connectivity in patients with SCZ compared to typically aging individuals. These data may indicate early abnormalities of neuronal function following cyto-architectural alterations in SCZ. The current mechanistic knowledge on brain aging, epigenetic changes, and their neuropsychiatric disease association remains incomplete. With this review, we explore and summarize evidence that the dynamics of gut-resident bacteria can modulate molecular brain function and contribute to age-related neurodegenerative disorders. It is known that environmental factors such as mode of birth, dietary habits, stress, pollution, and infections can modulate the microbiota system to regulate intrinsic neuronal activity and brain reserves through the vagus nerve and enteric nervous system. Microbiota-derived molecules can trigger continuous activation of the microglial sensome, groups of receptors and proteins that permit microglia to remodel the brain neurochemistry based on complex environmental activities. This remodeling causes aberrant brain plasticity as early as fetal developmental stages, and after the onset of first-episode psychosis. In the central nervous system, microglia, the resident immune surveillance cells, are involved in neurogenesis, phagocytosis of synapses and neurological dysfunction. Here, we review recent emerging experimental and clinical evidence regarding the gut-brain microglia axis involvement in SCZ pathology and etiology, the hypothesis of brain reserve and accelerated aging induced by dietary habits, stress, pollution, infections, and other factors. We also include in our review the possibilities and consequences of gut dysbiosis activities on microglial function and dysfunction, together with the effects of antipsychotics on the gut microbiome: therapeutic and adverse effects, role of fecal microbiota transplant and psychobiotics on microglial sensomes, brain reserves and SCZ-derived accelerated aging. We end the review with suggestions that may be applicable to the clinical setting. For example, we propose that psychobiotics might contribute to antipsychotic-induced therapeutic benefits or adverse effects, as well as reduce the aging process through the gut-brain microglia axis. Overall, we hope that this review will help increase the understanding of SCZ pathogenesis as related to chronobiology and the gut microbiome, as well as reveal new concepts that will serve as novel treatment targets for SCZ.

Evaluation of nutritional status and clinical depression classification using an explainable machine learning method

Introduction

Depression is a prevalent disorder worldwide, with potentially severe implications. It contributes significantly to an increased risk of diseases associated with multiple risk factors. Early accurate diagnosis of depressive symptoms is a critical first step toward management, intervention, and prevention. Various nutritional and dietary compounds have been suggested to be involved in the onset, maintenance, and severity of depressive disorders. Despite the challenges to better understanding the association between nutritional risk factors and the occurrence of depression, assessing the interplay of these markers through supervised machine learning remains to be fully explored.

Methods

This study aimed to determine the ability of machine learning-based decision support methods to identify the presence of depression using publicly available health data from the Korean National Health and Nutrition Examination Survey. Two exploration techniques, namely, uniform manifold approximation and projection and Pearson correlation, were performed for explanatory analysis among datasets. A grid search optimization with cross-validation was performed to fine-tune the models for classifying depression with the highest accuracy. Several performance measures, including accuracy, precision, recall, F1 score, confusion matrix, areas under the precision-recall and receiver operating characteristic curves, and calibration plot, were used to compare classifier performances. We further investigated the importance of the features provided: visualized interpretation using ELI5, partial dependence plots, and local interpretable using model-agnostic explanations and Shapley additive explanation for the prediction at both the population and individual levels.

Results

The best model achieved an accuracy of 86.18% for XGBoost and an area under the curve of 84.96% for the random forest model in original dataset and the XGBoost algorithm with an accuracy of 86.02% and an area under the curve of 85.34% in the quantile-based dataset. The explainable results revealed a complementary observation of the relative changes in feature values, and, thus, the importance of emergent depression risks could be identified.

Discussion

The strength of our approach is the large sample size used for training with a fine-tuned model. The machine learning-based analysis showed that the hyper-tuned model has empirically higher accuracy in classifying patients with depressive disorder, as evidenced by the set of interpretable experiments, and can be an effective solution for disease control.

Aged brain and neuroimmune responses to COVID-19: post-acute sequelae and modulatory effects of behavioral and nutritional interventions

Advanced age is one of the significant risk determinants for coronavirus disease 2019 (COVID-19)-related mortality and for long COVID complications. The contributing factors may include the age-related dynamical remodeling of the immune system, known as immunosenescence and chronic low-grade systemic inflammation. Both of these factors may induce an inflammatory milieu in the aged brain and drive the changes in the microenvironment of neurons and microglia, which are characterized by a general condition of chronic inflammation, so-called neuroinflammation. Emerging evidence reveals that the immune privilege in the aging brain may be compromised. Resident brain cells, such as astrocytes, neurons, oligodendrocytes and microglia, but also infiltrating immune cells, such as monocytes, T cells and macrophages participate in the complex intercellular networks and multiple reciprocal interactions. Especially changes in microglia playing a regulatory role in inflammation, contribute to disturbing of the brain homeostasis and to impairments of the neuroimmune responses. Neuroinflammation may trigger structural damage, diminish regeneration, induce neuronal cell death, modulate synaptic remodeling and in this manner negatively interfere with the brain functions.In this review article, we give insights into neuroimmune interactions in the aged brain and highlight the impact of COVID-19 on the functional systems already modulated by immunosenescence and neuroinflammation. We discuss the potential ways of these interactions with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and review proposed neuroimmune mechanisms and biological factors that may contribute to the development of persisting long COVID conditions. We summarize the potential mechanisms responsible for long COVID, including inflammation, autoimmunity, direct virus-mediated cytotoxicity, hypercoagulation, mitochondrial failure, dysbiosis, and the reactivation of other persisting viruses, such as the Cytomegalovirus (CMV). Finally, we discuss the effects of various interventional options that can decrease the propagation of biological, physiological, and psychosocial stressors that are responsible for neuroimmune activation and which may inhibit the triggering of unbalanced inflammatory responses. We highlight the modulatory effects of bioactive nutritional compounds along with the multimodal benefits of behavioral interventions and moderate exercise, which can be applied as postinfectious interventions in order to improve brain health.

Influence of mental health medication on microbiota in the elderly population in the Valencian region

Spain has an aging population; 19.93% of the Spanish population is over 65. Aging is accompanied by several health issues, including mental health disorders and changes in the gut microbiota. The gut-brain axis is a bidirectional network linking the central nervous system with gastrointestinal tract functions, and therefore, the gut microbiota can influence an individual’s mental health. Furthermore, aging-related physiological changes affect the gut microbiota, with differences in taxa and their associated metabolic functions between younger and older people. Here, we took a case–control approach to study the interplay between gut microbiota and mental health of elderly people. Fecal and saliva samples from 101 healthy volunteers over 65 were collected, of which 28 (EE|MH group) reported using antidepressants or medication for anxiety or insomnia at the time of sampling. The rest of the volunteers (EE|NOMH group) were the control group. 16S rRNA gene sequencing and metagenomic sequencing were applied to determine the differences between intestinal and oral microbiota. Significant differences in genera were found, specifically eight in the gut microbiota, and five in the oral microbiota. Functional analysis of fecal samples showed differences in five orthologous genes related to tryptophan metabolism, the precursor of serotonin and melatonin, and in six categories related to serine metabolism, a precursor of tryptophan. Moreover, we found 29 metabolic pathways with significant inter-group differences, including pathways regulating longevity, the dopaminergic synapse, the serotoninergic synapse, and two amino acids.

Evolutionary Aspects of Diverse Microbial Exposures and Mental Health: Focus on "Old Friends" and Stress Resilience

The prevalence of inflammatory disease conditions, including allergies, asthma, and autoimmune disorders, increased during the latter half of the twentieth century, as societies transitioned from rural to urban lifestyles. A number of hypotheses have been put forward to explain the increasing prevalence of inflammatory disease in modern urban societies, including the hygiene hypothesis and the "Old Friends" hypothesis. In 2008, Rook and Lowry proposed, based on the evidence that increased inflammation was a risk factor for stress-related psychiatric disorders, that the hygiene hypothesis or "Old Friends" hypothesis may be relevant to psychiatric disorders. Since then, it has become more clear that chronic low-grade inflammation is a risk factor for stress-related psychiatric disorders, including anxiety disorders, mood disorders, and trauma- and stressor-related disorders, such as posttraumatic stress disorder (PTSD). Evidence now indicates that persons raised in modern urban environments without daily contact with pets, relative to persons raised in rural environments in proximity to farm animals, respond with greater systemic inflammation to psychosocial stress. Here we consider the possibility that increased inflammation in persons living in modern urban environments is due to a failure of immunoregulation, i.e., a balanced expression of regulatory and effector T cells, which is known to be dependent on microbial signals. We highlight evidence that microbial signals that can drive immunoregulation arise from phylogenetically diverse taxa but are strain specific. Finally, we highlight Mycobacterium vaccae NCTC 11659, a soil-derived bacterium with anti-inflammatory and immunoregulatory properties, as a case study of how single strains of bacteria might be used in a psychoneuroimmunologic approach for prevention and treatment of stress-related psychiatric disorders.

Understanding treatment-resistant depression using "omics" techniques: A systematic review

BACKGROUND

Treatment-resistant depression (TRD) results in huge healthcare costs and poor patient clinical outcomes. Most studies have adopted a "candidate mechanism" approach to investigate TRD pathogenesis, however this is made more challenging due to the complex and heterogeneous nature of this condition. High-throughput "omics" technologies can provide a more holistic view and further insight into the underlying mechanisms involved in TRD development, expanding knowledge beyond already-identified mechanisms. This systematic review assessed the information from studies that examined TRD using hypothesis-free omics techniques.

METHODS

PubMed, MEDLINE, Embase, APA PsycInfo, Scopus and Web of Science databases were searched on July 2022. 37 human studies met the eligibility criteria, totalling 17,518 TRD patients, 571,402 healthy controls and 62,279 non-TRD depressed patients (including antidepressant responders and untreated MDD patients).

RESULTS

Significant findings were reported that implicate the role in TRD of various molecules, including polymorphisms, genes, mRNAs and microRNAs. The pathways most commonly reported by the identified studies were involved in immune system and inflammation, neuroplasticity, calcium signalling and neurotransmitters.

LIMITATIONS

Small sample sizes, variability in defining TRD, and heterogeneity in study design and methodology.

CONCLUSIONS

These findings provide insight into TRD pathophysiology, proposing future research directions for novel drug targets and potential biomarkers for clinical staging and response to antidepressants (citalopram/escitalopram in particular) and electroconvulsive therapy (ECT). Further validation is warranted in large prospective studies using standardised TRD criteria. A multi-omics and systems biology strategy with a collaborative effort will likely deliver robust findings for translation into the clinic.

Impacts of breast cancer and chemotherapy on gut microbiome, cognitive functioning, and mood relative to healthy controls

Women diagnosed with breast cancer undergoing chemotherapy experience cognitive impairment, symptoms of anxiety and depression, and physical side effects including disruption in the diversity and community composition of the gut microbiome. To date, there is limited research exploring the associations among these specific challenges. The present cross-sectional study explored the associations of self-reported cognitive functioning, depression, and anxiety symptoms, and gut microbiome diversity and community composition in women who were diagnosed with and undergoing chemotherapy treatment for breast cancer (BC) compared to cancer-free healthy controls (HC). The BC group displayed higher rates of cognitive dysfunction (p < 0.001) and depressive symptoms (p < 0.05) relative to HC. There was a significant difference in microbiome community composition between BC and HC, particularly characterized by a decreased relative abundance of the mucin-degrading genus Akkermansia in BC compared to HC (p < 0.05). Association models identified significant associations among group, cognitive, depression, and microbiome variables (p < 0.001). Overall, the study identified that BC participants experienced significant differences in self-reported cognitive functioning, self-reported depression symptoms, microbiome community composition, and mucin-degrading bacteria of the gut-mucosal barrier, relative to HC. The present study is consistent with the hypothesis that gut microbiome community composition impacts a woman's experience with breast cancer and treatment suggesting that microbiome-based interventions have potential for improving quality of life outcomes in individuals with breast cancer.

The clinical evidence for postbiotics as microbial therapeutics

An optimally operating microbiome supports protective, metabolic, and immune functions, but disruptions produce metabolites and toxins which can be involved in many conditions. Probiotics have the potential to manage these. However, their use in vulnerable people is linked to possible safety concerns and maintaining their viability is difficult. Interest in postbiotics is therefore increasing. Postbiotics contain inactivated microbial cells or cell components, thus are more stable and exert similar health benefits to probiotics. To review the evidence for the clinical benefits of postbiotics in highly prevalent conditions and consider future potential areas of benefit. There is growing evidence revealing the diverse clinical benefits of postbiotics in many prevalent conditions. Postbiotics could offer a novel therapeutic approach and may be a safer alternative to probiotics. Establishing interaction mechanisms between postbiotics and commensal microorganisms will improve the understanding of potential clinical benefits and may lead to targeted postbiotic therapy.

Key features of the genetic architecture and evolution of host-microbe interactions revealed by high-resolution genetic mapping of the mucosa-associated gut microbiome in hybrid mice

Determining the forces that shape diversity in host-associated bacterial communities is critical to understanding the evolution and maintenance of metaorganisms. To gain deeper understanding of the role of host genetics in shaping gut microbial traits, we employed a powerful genetic mapping approach using inbred lines derived from the hybrid zone of two incipient house mouse species. Furthermore, we uniquely performed our analysis on microbial traits measured at the gut mucosal interface, which is in more direct contact with host cells and the immune system. Several mucosa-associated bacterial taxa have high heritability estimates, and interestingly, 16S rRNA transcript-based heritability estimates are positively correlated with cospeciation rate estimates. Genome-wide association mapping identifies 428 loci influencing 120 taxa, with narrow genomic intervals pinpointing promising candidate genes and pathways. Importantly, we identified an enrichment of candidate genes associated with several human diseases, including inflammatory bowel disease, and functional categories including innate immunity and G-protein-coupled receptors. These results highlight key features of the genetic architecture of mammalian host-microbe interactions and how they diverge as new species form.

The digestive system, particularly the large intestine, hosts many types of bacteria which together form the gut microbiome. The exact makeup of different bacterial species is specific to an individual, but microbiomes are often more similar between related individuals, and more generally, across related species. Whether this is because individuals share similar environments or similar genetic backgrounds remains unclear. These two factors can be disentangled by breeding different animal lineages – which have different genetic backgrounds while belonging to the same species – and then raising the progeny in the same environment.

To investigate this question, Doms et al. studied the genes and microbiomes of mice resulting from breeding strains from multiple locations in a natural hybrid zone between different subspecies. The experiments showed that 428 genetic regions affected the makeup of the microbiome, many of which were known to be associated with human diseases. Further analysis revealed 79 genes that were particularly interesting, as they were involved in recognition and communication with bacteria. These results show how the influence of the host genome on microbiome composition becomes more specialized as animals evolve.

Overall, the work by Doms et al. helps to pinpoint the genes that impact the microbiome; this knowledge could be helpful to examine how these interactions contribute to the emergence of conditions such as diabetes or inflammatory bowel disease, which are linked to perturbations in gut bacteria.

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

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

A Reciprocal Link Between Gut Microbiota, Inflammation and Depression: A Place for Probiotics?

Depression is a severe mental disorder that places a significant economic burden on public health. The reciprocal link between the trillions of bacteria in the gut, the microbiota, and depression is a controversial topic in neuroscience research and has drawn the attention of public interest and press coverage in recent years. Mounting pieces of evidence shed light on the role of the gut microbiota in depression, which is suggested to involve immune, endocrine, and neural pathways that are the main components of the microbiota-gut-brain axis. The gut microbiota play major roles in brain development and physiology and ultimately behavior. The bidirectional communication between the gut microbiota and brain function has been extensively explored in animal models of depression and clinical research in humans. Certain gut microbiota strains have been associated with the pathophysiology of depression. Therefore, oral intake of probiotics, the beneficial living bacteria and yeast, may represent a therapeutic approach for depression treatment. In this review, we summarize the findings describing the possible links between the gut microbiota and depression, focusing mainly on the inflammatory markers and sex hormones. By discussing preclinical and clinical studies on probiotics as a supplementary therapy for depression, we suggest that probiotics may be beneficial in alleviating depressive symptoms, possibly through immune modulation. Still, further comprehensive studies are required to draw a more solid conclusion regarding the efficacy of probiotics and their mechanisms of action.

Effects of the Lipid Metabolites and the Gut Microbiota in ApoE−/− Mice on Atherosclerosis Co-Depression From the Microbiota-Gut-Brain Axis

Background: The diagnosis, treatment, and prevention of atherosclerosis co-depression are poor, so it is urgent to explore new targets. Based on the “microbiota-gut-brain axis,” this study aimed to investigate the changes of lipid metabolites in the prefrontal cortex and hippocampus regions and the characteristics of the gut microbiota in ApoE−/− mice with atherosclerosis co-depression.

Methods: ApoE−/− mice (hyperlipid feeding combined with binding, HFB group, n = 14, male) fed a high-fat diet for 16 weeks with binding stimulation were used as an animal model for atherosclerosis co-depression. The depression degree of mice was evaluated by body weight, sucrose preference test, open field test, and tail suspension test. Oil-red O staining, HE staining, and biochemical parameters were used to evaluate the damage degree of atherosclerosis in mice. LC-MS/MS technique for non-targeted lipidomics analysis was used to analyze the differential lipid metabolites in the prefrontal cortex and hippocampus regions of mice. 16S rDNA amplification sequencing was used to screen the differential gut microbial, and association analysis was performed with the differential lipid metabolites.

Results: Compared with the normal control group (NC group), the HFB group showed depression-like behaviors and atherosclerosis-related pathological indicators. The differential lipid metabolites in the prefrontal cortex and hippocampus regions were mainly LPC, LPE, LPS, PC, PE, PS, PI, and GD1a, and were mainly enriched in the glycerophospholipid metabolism pathway and the retrograde endocannabinoid signaling pathway. At the same time, there were significant differences in the structure of the gut microbial community between the two groups. The abundance of Deferribacteres and Proteobacteria in the HFB group increased, while the abundance of Verrucomicrobia and Actinobacteria decreased at the phylum level; the abundance of Desulfovibrio, Clostridium_IV, Helicobacter and Pseudoflavonifractor increased, while the abundance of Akkermansia decreased at the genus level.

Conclusion: Atherosclerosis co-depression of ApoE−/− mice of the prefrontal cortex and hippocampus lipid metabolism pathways of disorder and the changes of to the gut microbiota, which leads to abnormal white matter and synaptic dysfunction, increased gut inflammation, and decreased gut permeability, leading to the release of inflammatory cytokines, there is a strong correlation between both, it further confirmed the existence of the “microbiota-gut-brain axis.”

Effects of 4G-beta-D-Galactosylsucrose in patients with depression: A randomized, double-blinded, placebo-controlled, parallel-group comparative study

Advances in genetic research on microbiome have led to several trials on the effectiveness of synbiotics or probiotics in patients with depression; however, none have evaluated the efficacy of prebiotics. 4G-beta-D-Galactosylsucrose (Lactosucrose, LS) is selectively assimilated by Bifidobacterium as a prebiotic and improves microbiome diversity. However, as it is not clear if LS consumption can improve symptoms of depression, we investigated whether LS intake can improve depressive symptoms, quality of life (QOL), and self-efficacy by conducting a single cite, double-blinded, randomized controlled trial in 20 outpatients with depressive episodes (F32, ICD-10) for 24 weeks. Participants (age range, 36-72 years) were randomized to the LS (n = 9) or placebo groups (n = 11). Primary outcome was improvement in total Montgomery Asberg Depression Rating Scale (MADRS) score, and the secondary outcomes were MADRS subscores, global self-efficacy scale (GSES) score, World Health Organization QOL (WHO/QOL-26) score, and 16S rRNA analysis of the fecal microbiome. LS consumption did not significantly improve total MADRS scores (-2 (-16 to 16) vs 0 (-6 to 10), p = 0.552), but GSES tended to improve in the LS group (2.00 ± 4.24 vs -1.36 ± 4.15, p = 0.091) with a large effect size (Cohen's d = 0.802). Sequencing of 16S rRNA revealed individual-level differences in microbiome diversity changes due to the intervention. Thus, we show that LS intake can improve self-efficacy, but not depressive symptoms, even in a small sample. Additional studies that also regulate diet and ensure adherence may help determine a correlation between depression and the gut microbiome.

The Future Potential of Biosensors to Investigate the Gut-Brain Axis

The multifaceted and heterogeneous nature of depression presents challenges in pinpointing treatments. Among these contributions are the interconnections between the gut microbiome and neurological function termed the gut-brain axis. A diverse range of microbiome-produced metabolites interact with host signaling and metabolic pathways through this gut-brain axis relationship. Therefore, biosensor detection of gut metabolites offers the potential to quantify the microbiome's contributions to depression. Herein we review synthetic biology strategies to detect signals that indicate gut-brain axis dysregulation that may contribute to depression. We also highlight future challenges in developing living diagnostics of microbiome conditions influencing depression.

Gut Microbiota Metabolites in Major Depressive Disorder-Deep Insights into Their Pathophysiological Role and Potential Translational Applications

The gut microbiota is a complex and dynamic ecosystem essential for the proper functioning of the organism, affecting the health and disease status of the individuals. There is continuous and bidirectional communication between gut microbiota and the host, conforming to a unique entity known as "holobiont". Among these crosstalk mechanisms, the gut microbiota synthesizes a broad spectrum of bioactive compounds or metabolites which exert pleiotropic effects on the human organism. Many of these microbial metabolites can cross the blood-brain barrier (BBB) or have significant effects on the brain, playing a key role in the so-called microbiota-gut-brain axis. An altered microbiota-gut-brain (MGB) axis is a major characteristic of many neuropsychiatric disorders, including major depressive disorder (MDD). Significative differences between gut eubiosis and dysbiosis in mental disorders like MDD with their different metabolite composition and concentrations are being discussed. In the present review, the main microbial metabolites (short-chain fatty acids -SCFAs-, bile acids, amino acids, tryptophan -trp- derivatives, and more), their signaling pathways and functions will be summarized to explain part of MDD pathophysiology. Conclusions from promising translational approaches related to microbial metabolome will be addressed in more depth to discuss their possible clinical value in the management of MDD patients.

The ketogenic diet: its impact on human gut microbiota and potential consequent health outcomes: a systematic literature review

Aim

This systematic review examined the diet's impact on the human gut microbiota to identify potential consequent health outcomes.

Background

The extreme macronutrient profile of the ketogenic diet (KD) instigates compositional shifts in the gut's microbial community.

Methods

In this systematic literature review, an evidence-based and methodical approach was undertaken, which involved systematic searches of the Medical Literature Analysis and Retrieval System Online (MEDLINE), PubMed and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases, generating a total of 263 relevant research papers. Following the application of inclusion and exclusion criteria, eight papers were deemed suitable for inclusion. These papers were critically appraised using a checklist tool adapted from the National Institute of Care and Excellence (NICE). The findings were analysed using a simplified thematic analysis.

Results

The results provide strong evidence for a persistent reduction in Bifidobacterium abundance following KD adherence. A reduced abundance of key Firmicutes butyrate-producing bacteria was found to be a likely impact, although two studies with extended intervention periods indicate this may be time-limited. Studies investigating short-chain fatty acids (SCFA's) indicate KD reduces total faecal SCFA's, acetate, and butyrate.

Conclusion

Changes to microbial communities resulting from KD adherence are potentially detrimental to colonic health. The persistent reduction in Bifidobacterium abundance was concerning, with obesity, type-2 diabetes, and depression highlighted as potential consequent risks. For nutrition and healthcare professionals, the findings emphasize the importance of considering KDs microbial effects and resulting health implications at an individual level.

Baseline Depression-Like Behaviors in Wild-Type Adolescent Mice Are Strain and Age but Not Sex Dependent

Depression is a major neuropsychiatric disorder, decreasing the ability of hundreds of millions of individuals worldwide to function in social, academic, and employment settings. Beyond the alarming public health problem, depression leads to morbidity across the entire age including adolescence and adulthood. Modeling depression in rodents has been used to understand the pathophysiological mechanisms behind this disorder and create new therapeutics. Although women are two times more likely to be diagnosed with depression compared to men, behavioral experiments on rodent models of depression are mainly performed in males based on the assumption that the estrous cycles in females may affect the behavioral outcome and cause an increase in the intrinsic variability compared to males. Still, the inclusion of female rodents in the behavioral analysis is mandatory to establish the origin of sex bias in depression. Here, we investigated the baseline depression-like behaviors in male and female mice of three adolescent wild-type inbred strains, C57BL/6N, DBA/2, and FVB/N, that are typically used as background strains for mouse models of neuropsychiatric disorders. Our experiments, performed at two different developmental stages during adolescence (P22-P26 and P32-P36), revealed strain but no sex differences in a set of depression-related tests, including tail suspension, sucrose preference and forced swim tests. Additionally, the 10-day interval during this sensitive period uncovered a strong impact on the behavioral outcome of C57BL/6N and FVB/N mice, highlighting a significant effect of maturation on behavioral patterns. Since anxiety-related behavioral tests are often performed together with depression tests in mouse models of neuropsychiatric disorders, we extended our study and included hyponeophagia as an anxiety test. Consistent with a previous study revealing sex differences in other anxiety tests in adolescent mice, male and females mice behaved differently in the hyponeophagia test at P27. Our study gives insight into the behavioral experiments assessing depression and stresses the importance of considering strain, age and sex when evaluating neuropsychiatric-like traits in rodent models.

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.

The Relationship Between the Gut Microbiome-Immune System-Brain Axis and Major Depressive Disorder

Major depressive disorder (MDD) is a prominent cause of disability worldwide. Current antidepressant drugs produce full remission in only about one-third of MDD patients and there are no biomarkers to guide physicians in selecting the best treatment for individuals. There is an urgency to learn more about the etiology of MDD and to identify new targets that will lead to improved therapy and hopefully aid in predicting and preventing MDD. There has been extensive interest in the roles of the immune system and the gut microbiome in MDD and in how these systems interact. Gut microbes can contribute to the nature of immune responses, and a chronic inflammatory state may lead to increased responsiveness to stress and to development of MDD. The gut microbiome-immune system-brain axis is bidirectional, is sensitive to stress and is important in development of stress-related disorders such as MDD. Communication between the gut and brain involves the enteric nervous system (ENS), the autonomic nervous system (ANS), neuroendocrine signaling systems and the immune system, and all of these can interact with the gut microbiota. Preclinical studies and preliminary clinical investigations have reported improved mood with administration of probiotics and prebiotics, but large, carefully controlled clinical trials are now necessary to evaluate their effectiveness in treating MDD. The roles that several gut microbe-derived molecules such as neurotransmitters, short chain fatty acids and tryptophan play in MDD are reviewed briefly. Challenges and potential future directions associated with studying this important axis as it relates to MDD are discussed.

Effect of Psychobiotics on Psychometric Tests and Inflammatory Markers in Major Depressive Disorder: Meta-Analysis of Randomized Controlled Trials with Meta-Regression

Probiotics were shown to act positively on gut–brain axis signaling. We aimed to assess the effect of the administration of a new class of probiotics—psychobiotics—using data from individual psychometric scales, markers of the immune system and neuroactive metabolites. Medical databases were searched from database inception until 22 April 2021 for randomized clinical trials in clinically proven Major Depressive Disorder (MDD) patients treated with either probiotics or placebo reporting any psychometric score (PROSPERO registration number: CRD42021253024). Ten studies with 705 randomized participants and 603 analyzed were included. The mean age of individuals was 38.43 ± 12.1 years, predominantly women (n = 461, 76.45). The mean study duration was 48.8 ± 12.3 (range = 28–62) days. The dosage ranged between 1 × 10⁹ to 2 × 10¹⁰ colony forming units (CFU)/day. We found that probiotics might alleviate symptoms of MDD; endpoint data (pooled scores): SMD = −0.292, 95%CI = −0.577 to −0.007, p < 0.044; change scores (BDI): SMD = −0.482, 95%CI = −0.854 to –0.109, p < 0.011; DM = −4.848, 95%CI = −8.559 to −1.137, p < 0.01. The therapy tended to be more effective with time of psychobiotic supplementation (coefficient = −0.12, SE = 0.06, Z = −1.84, p = 0.06) and in men (% of females: coefficient = 0.1, SE = 0.06, Z = 1.78, p = 0.07). Psychobiotics have great potential in the treatment of MDD. However, no specific strain/strains, dosage or duration of treatment can currently be recommended.

The effects of psychobiotics on the microbiota-gut-brain axis in early-life stress and neuropsychiatric disorders

Psychobiotics are considered among potential avenues for modulating the bidirectional communication between the gastrointestinal tract and central nervous system, defined as the microbiota-gut-brain axis (MGBA). Even though causality has not yet been established, intestinal dysbiosis has emerged as a hallmark of several diseases, including neuropsychiatric disorders (NPDs). The fact that the microbiota and central nervous system are co-developing during the first years of life has provided a paradigm suggesting a potential role of psychobiotics for earlier interventions. Studies in animal models of early-life stress (ELS) have shown that they can counteract the pervasive effects of stress during this crucial developmental period, and rescue behavioral symptoms related to anxiety and depression later in life. In humans, evidence from clinical studies on the efficacy of psychobiotics at improving mental outcomes in most NPDs remain limited, except for major depressive disorder for which more studies are available. Consequently, the beneficial effect of psychobiotics on depression-related outcomes in adults are becoming clearer. While the specific mechanisms at play remain elusive, the effect of psychobiotics are generally considered to involve the hypothalamic-pituitary-adrenal axis, intestinal permeability, and inflammation. It is anticipated that future clinical studies will explore the potential role of psychobiotics at mitigating the risk developing NPDs in vulnerable individuals or in the context of childhood adversity. However, such studies remain challenging at present in terms of design and target populations; the profound impact of stress on the proper development of the MGBA during the first year of life is becoming increasingly recognized, but the trajectories post-ELS in humans and the mechanisms by which stress affects the susceptibility to various NPDs are still ill-defined. As psychobiotics are likely to exert both shared and specific mechanisms, a better definition of target subpopulations would allow to tailor psychobiotics selection by aligning mechanistic properties with known pathophysiological mechanisms or risk factors. Here we review the available evidence from clinical and preclinical studies supporting a role for psychobiotics at ameliorating depression-related outcomes, highlighting the knowledge gaps and challenges associated with conducting longitudinal studies to address outstanding key questions in the field.

Effects of Immunization With the Soil-Derived Bacterium Mycobacterium vaccae on Stress Coping Behaviors and Cognitive Performance in a "Two Hit" Stressor Model

Previous studies demonstrate that Mycobacterium vaccae NCTC 11659 (M. vaccae), a soil-derived bacterium with anti-inflammatory and immunoregulatory properties, is a potentially useful countermeasure against negative outcomes to stressors. Here we used male C57BL/6NCrl mice to determine if repeated immunization with M. vaccae is an effective countermeasure in a "two hit" stress exposure model of chronic disruption of rhythms (CDR) followed by acute social defeat (SD). On day -28, mice received implants of biotelemetric recording devices to monitor 24-h rhythms of locomotor activity. Mice were subsequently treated with a heat-killed preparation of M. vaccae (0.1 mg, administered subcutaneously on days -21, -14, -7, and 27) or borate-buffered saline vehicle. Mice were then exposed to 8 consecutive weeks of either stable normal 12:12 h light:dark (LD) conditions or CDR, consisting of 12-h reversals of the LD cycle every 7 days (days 0-56). Finally, mice were exposed to either a 10-min SD or a home cage control condition on day 54. All mice were exposed to object location memory testing 24 h following SD. The gut microbiome and metabolome were assessed in fecal samples collected on days -1, 48, and 62 using 16S rRNA gene sequence and LC-MS/MS spectral data, respectively; the plasma metabolome was additionally measured on day 64. Among mice exposed to normal LD conditions, immunization with M. vaccae induced a shift toward a more proactive behavioral coping response to SD as measured by increases in scouting and avoiding an approaching male CD-1 aggressor, and decreases in submissive upright defensive postures. In the object location memory test, exposure to SD increased cognitive function in CDR mice previously immunized with M. vaccae. Immunization with M. vaccae stabilized the gut microbiome, attenuating CDR-induced reductions in alpha diversity and decreasing within-group measures of beta diversity. Immunization with M. vaccae also increased the relative abundance of 1-heptadecanoyl-sn-glycero-3-phosphocholine, a lysophospholipid, in plasma. Together, these data support the hypothesis that immunization with M. vaccae stabilizes the gut microbiome, induces a shift toward a more proactive response to stress exposure, and promotes stress resilience.

Gut Microbiota and Depressive Symptoms at the End of CRT for Rectal Cancer: A Cross-Sectional Pilot Study

BACKGROUND

The role of alterations in gut microbiota composition (termed dysbiosis) has been implicated in the pathobiology of depressive symptoms; however, evidence remains limited. This cross-sectional pilot study is aimed at exploring whether depressive symptom scores changed during neoadjuvant chemotherapy and radiation therapy to treat rectal cancer, and if gut microbial taxa abundances and predicted functional pathways correlate with depressive symptoms at the end of chemotherapy and radiation therapy.

METHODS

40 newly diagnosed rectal cancer patients (ages 28-81; 23 males) were assessed for depressive symptoms using the Hamilton Rating Scale for Depression (HAM-D) and provided stool samples for 16S rRNA sequencing. Gut microbiome data were analyzed using QIIME2, and correlations and regression analyses were performed in R.

RESULTS

Participants had significantly higher depressive symptoms at the end as compared to before CRT. The relative abundances of Gemella, Bacillales Family XI, Actinomyces, Streptococcus, Lactococcus, Weissella, and Leuconostocaceae were positively correlated (Spearman's rho = 0.42 to 0.32), while Coprobacter, Intestinibacter, Intestimonas, Lachnospiraceae, Phascolarctobacterium, Ruminiclostridium, Ruminococcaceae (UCG-005 and uncultured), Tyzzerella, and Parasutterella (Spearman's rho = -0.43 to - 0.31) were negatively correlated with HAM-D scores. Of the 14 predicted MetaCyc pathways that correlated with depressive symptom scores at the end of CRT, 11 (79%) were associated with biosynthetic pathways.

CONCLUSIONS

Significant bacterial taxa and predicted functional pathways correlated with depressive symptoms at the end of chemotherapy and radiation therapy for rectal cancer which warrants further examination and replication of our findings.

The Complex Molecular Picture of Gut and Oral Microbiota-Brain-Depression System: What We Know and What We Need to Know

Major depressive disorder (MDD) is a complex mental disorder where the neurochemical, neuroendocrine, immune, and metabolic systems are impaired. The microbiota-gut-brain axis is a bidirectional network where the central and enteric nervous systems are linked through the same endocrine, immune, neural, and metabolic routes dysregulated in MDD. Thus, gut-brain axis abnormalities in MDD patients may, at least in part, account for the symptomatic features associated with MDD. Recent investigations have suggested that the oral microbiome also plays a key role in this complex molecular picture of relationships. As on one hand there is a lot of what we know and on the other hand little of what we still need to know, we structured this review focusing, in the first place, on putting all pieces of this complex puzzle together, underlying the endocrine, immune, oxidative stress, neural, microbial neurotransmitters, and metabolites molecular interactions and systems lying at the base of gut microbiota (GM)-brain-depression interphase. Then, we focused on promising but still under-explored areas of research strictly linked to the GM and potentially involved in MDD development: (i) the interconnection of GM with oral microbiome that can influence the neuroinflammation-related processes and (ii) gut phageome (bacteria-infecting viruses). As conclusions and future directions, we discussed potentiality but also pitfalls, roadblocks, and the gaps to be bridged in this exciting field of research. By the development of a broader knowledge of the biology associated with MDD, with the inclusion of the gut/oral microbiome, we can accelerate the growth toward a better global health based on precision medicine.

The Role of the Oral Microbiota Related to Periodontal Diseases in Anxiety, Mood and Trauma- and Stress-Related Disorders

The prevalence of anxiety, mood and trauma- and stress-related disorders are on the rise; however, efforts to develop new and effective treatment strategies have had limited success. To identify novel therapeutic targets, a comprehensive understanding of the disease etiology is needed, especially in the context of the holobiont, i.e., the superorganism consisting of a human and its microbiotas. Much emphasis has been placed on the role of the gut microbiota in the development, exacerbation, and persistence of psychiatric disorders; however, data for the oral microbiota are limited. The oral cavity houses the second most diverse microbial community in the body, with over 700 bacterial species that colonize the soft and hard tissues. Periodontal diseases encompass a group of infectious and inflammatory diseases that affect the periodontium. Among them, periodontitis is defined as a chronic, multi-bacterial infection that elicits low-grade systemic inflammation via the release of pro-inflammatory cytokines, as well as local invasion and long-distance translocation of periodontal pathogens. Periodontitis can also induce or exacerbate other chronic systemic inflammatory diseases such as atherosclerosis and diabetes and can lead to adverse pregnancy outcomes. Recently, periodontal pathogens have been implicated in the etiology and pathophysiology of neuropsychiatric disorders (such as depression and schizophrenia), especially as dysregulation of the immune system also plays an integral role in the etiology and pathophysiology of these disorders. This review will discuss the role of the oral microbiota associated with periodontal diseases in anxiety, mood and trauma- and stress-related disorders. Epidemiological data of periodontal diseases in individuals with these disorders will be presented, followed by a discussion of the microbiological and immunological links between the oral microbiota and the central nervous system. Pre-clinical and clinical findings on the oral microbiota related to periodontal diseases in anxiety, mood and trauma- and stress-related phenotypes will be reviewed, followed by a discussion on the bi-directionality of the oral-brain axis. Lastly, we will focus on the oral microbiota associated with periodontal diseases as a target for future therapeutic interventions to alleviate symptoms of these debilitating psychiatric disorders.

Biological and Psychological Factors Determining Neuropsychiatric Outcomes in COVID-19

PURPOSE OF REVIEW

We present biological and psychological factors implicated in psychiatric manifestations of SARS-CoV-2, as well as its neuroinvasive capability and immune pathophysiology.

RECENT FINDINGS

Preexisting mental illness leads to worse clinical outcomes in COVID-19. The presence of the virus was reported in the cerebrospinal fluid (CSF) and brain tissue post-mortem. Most common psychiatric manifestations include delirium, mood disorders, anxiety disorders, and posttraumatic stress disorder. "Long-COVID" non-syndromal presentations include "brain-fogginess," autonomic instability, fatigue, and insomnia. SARS-CoV-2 infection can trigger prior vulnerabilities based on the priming of microglia and other cells, induced or perpetuated by aging and mental and physical illnesses. COVID-19 could further induce priming of neuroimmunological substrates leading to exacerbated immune response and autoimmunity targeting structures in the central nervous system (CNS), in response to minor immune activating environmental exposures, including stress, minor infections, allergens, pollutants, and traumatic brain injury.

Analysis of the Gut Microbiota and Inflammatory Factors in mGluR5-Knockout Mice

INTRODUCTION

Accumulating evidence indicates that the glutamatergic system plays an important role in the development of depression. Notably, the antidepressant effect of metabotropic glutamate receptor 5 (mGluR5) modulation is inconsistent across studies. Here, we attempted to identify the involvement of the gut microbiota and inflammation in mGluR5^-/- mice.

METHODS

mGluR5^-/- mice and their wild-type littermates were used in our study. We used the open field (OF) and elevated plus maze (EPM) tests to assess anxiety-like behaviors, and we used the two-day forced swim test (FST) and tail suspension test (TST) to test despair-like behaviors. 16S rDNA was used to analyze the gut microbiota. Enzyme-linked immunosorbent assays (ELISAs) were used to measure the levels of inflammatory factors. Western blotting was used to detect the levels of various proteins.

RESULTS

mGluR5^-/- mice had no significant increase or decrease of despair-like behavior in the absence of stress exposure. However, mGluR5^-/- mice exhibited despair-like behaviors following stress exposure. No significant changes in other glutamate receptors or representative synaptic proteins were detected in the prefrontal cortex (PFC) or hippocampus of mGluR5^-/- mice. Very similar bacterial groups were observed in mGluR5^-/- mice and wild-type controls. In addition, there was no significant difference in the α-diversity of the microbiota between mGluR5^-/- mice and wild-type controls. The levels of all measured cytokines (IL-1β, IL-2, IL-4, IL-6, IL-10, and TNF-α) did not change significantly in the PFCs or colons of mGluR5^-/- mice.

CONCLUSION

In conclusion, we deduced that mGluR5^-/- mice are susceptible to despair-like behavior. The systemic knockout of mGluR5 did not affect the gut microbiota or inflammatory factors in mice.