Investigating causality with fecal microbiota transplantation in rodents: applications, recommendations and pitfalls

Natural sweetener glycyrrhizin protects against precocious puberty by modulating the gut microbiome

AIMS

Precocious puberty (PP) may lead to many adverse outcomes. Recent evidence suggests that PP is a gut-brain disease. On the other hand, the use of glycyrrhizin, a natural sweetener, has become popular in the past decade. Glycyrrhizin possesses various health benefits, but its impact on PP has yet to be investigated. We aimed to explore the protective effects of glycyrrhizin against PP in both humans (observational) and animals (interventional).

MATERIALS AND METHODS

In the human cohort, we investigated the association between glycyrrhizin consumption and risk of PP. In the animal experiment, we observed puberty onset after feeding danazol-induced PP rats with glycyrrizin. Blood, fecal, and hypothalamic samples were harvested to evaluate potential mechanistic pathways. We also performed a fecal microbiota transplantation to confirm to causal relationship between glycyrrhizin and PP risk.

KEY FINDINGS

Glycyrrhizin exhibited a protective effect against PP in children (OR 0.60, 95%CI: 0.39-0.89, p = 0.013), primarily driven by its significance in girls, while no significant effect was observed in boys. This effect was consistent with findings in rodents. These benefits were achieved through the modulation of the gut microbiome, which functionally suppressed the hypothalamic-pituitary-gonadal axis and prevented PP progression. A fecal microbiota transplantation indicated that the causal correlation between glycyrrhizin intake and PP is mediated by the gut microbiome alterations.

SIGNIFICANCE

Our findings suggest that glycyrrhizin can protect against PP by altering the gut microbiome. Long term use of glycyrrhizin is safe and tolerable. Therefore, glycyrrhizin can serve as a safe and affordable complementary therapy for PP.

Fecal microbiota transplantation of patients with anorexia nervosa did not alter flexible behavior in rats

OBJECTIVE

Patients with anorexia nervosa (AN) are often anxious, display inflexible behavior and disrupted reward processing. Emerging evidence suggests that gut dysbiosis in patients contributes to the disease phenotype and progression.

METHODS

In a preclinical study, we explored whether AN-derived microbiota impacts cognitive flexibility, anxiety, and dopamine signaling using fecal microbiota transplantation (FMT) in tyrosine hydroxylase-cre rats. We performed probabilistic reversal learning task (PRLT) at the baseline, after antibiotic treatment, and following FMT from patients with AN and controls. We assessed flexible behavior, task engagement, and ventral tegmental area (VTA) dopamine signaling during and in the absence of reward. Furthermore, anxiety-like behavior was evaluated with open field (OF) and elevated plus maze (EPM) tests.

RESULTS

Neither antibiotic-induced dysbiosis nor AN FMT led to significant alterations in the number of reversals or lever press strategies after reinforced or nonreinforced lever presses (win and lose-stay) in the PRLT. However, the number of initiated trials decreased after antibiotic treatment while remaining unchanged after FMT. No significant differences were observed in VTA dopamine activity, anxiety measures in the OF and EPM tests. Microbiome analysis revealed limited overlap between the microbiota of the donors and recipients.

DISCUSSION

No evidence was found that the microbiota of patients compared to controls, nor a depleted microbiome impacts cognitive flexibility. Nonetheless, antibiotic-induced dysbiosis resulted in reduced task engagement during the PRLT. The relatively low efficiency of the FMT is a limitation of our study and highlights the need for improved protocols to draw robust conclusions in future studies.

PUBLIC SIGNIFICANCE

While our study did not reveal direct impacts of AN-associated gut microbiota on cognitive flexibility or anxiety behaviors in our preclinical model, we observed a decrease in task engagement after antibiotic-induced dysbiosis, underscoring that the presence of a gut microbiome matters. Our findings underscore the need for further refinement in FMT protocols to better elucidate the complex interplay between gut microbiota and behaviors characteristic of anorexia nervosa.

Gut microbiota and serum metabolomic alterations in modulating the impact of fecal microbiota transplantation on ciprofloxacin-induced seizure susceptibility

Introduction

The gut microbiota and the microbiota-gut-brain axis have gained considerable attention in recent years, emerging as key players in the mechanisms that mediate the occurrence and progression of many central nervous system-related diseases, including epilepsy. In clinical practice, one of the side effects of quinolone antibiotics is a lower seizure threshold or aggravation. However, the underlying mechanism remains unclear.

Methods

We aimed to unravel the intrinsic mechanisms through 16S rRNA sequencing and serum untargeted metabolomic analysis to shed light on the effects of gut microbiota in ciprofloxacin-induced seizure susceptibility and lithium pilocarpine-induced epilepsy rat models.

Results

We observed that ciprofloxacin treatment increased seizure susceptibility and caused gut dysbiosis. We also found similar changes in the gut microbiota of rats with lithium pilocarpine-induced epilepsy. Notably, the levels of Akkermansia and Bacteroides significantly increased in both the ciprofloxacin-induced seizure susceptibility and lithium pilocarpine-induced epilepsy rat models. However, Marvinbryantia, Oscillibacter, and Ruminococcaceae_NK4A214_group showed a coincidental reduction. Additionally, the serum untargeted metabolomic analysis revealed decreased levels of indole-3-propionic acid, a product of tryptophan-indole metabolism, after ciprofloxacin treatment, similar to those in the plasma of lithium pilocarpine-induced epilepsy in rats. Importantly, alterations in the gut microbiota, seizure susceptibility, and indole-3-propionic acid levels can be restored by fecal microbiota transplantation.

Conclusion

In summary, our findings provide evidence that ciprofloxacin-induced seizure susceptibility is partially mediated by the gut microbiota and tryptophan-indole metabolism. These associations may play a role in epileptogenesis, and impacting the development progression and treatment outcomes of epilepsy.

Unravelling the Link between the Gut Microbiome and Autoimmune Kidney Diseases: A Potential New Therapeutic Approach

The gut microbiota and short chain fatty acids (SCFA) have been associated with immune regulation and autoimmune diseases. Autoimmune kidney diseases arise from a loss of tolerance to antigens, often with unclear triggers. In this review, we explore the role of the gut microbiome and how disease, diet, and therapy can alter the gut microbiota consortium. Perturbations in the gut microbiota may systemically induce the translocation of microbiota-derived inflammatory molecules such as liposaccharide (LPS) and other toxins by penetrating the gut epithelial barrier. Once in the blood stream, these pro-inflammatory mediators activate immune cells, which release pro-inflammatory molecules, many of which are antigens in autoimmune diseases. The ratio of gut bacteria Bacteroidetes/Firmicutes is associated with worse outcomes in multiple autoimmune kidney diseases including lupus nephritis, MPO-ANCA vasculitis, and Goodpasture's syndrome. Therapies that enhance SCFA-producing bacteria in the gut have powerful therapeutic potential. Dietary fiber is fermented by gut bacteria which in turn release SCFAs that protect the gut barrier, as well as modulating immune responses towards a tolerogenic anti-inflammatory state. Herein, we describe where the current field of research is and the strategies to harness the gut microbiome as potential therapy.

Faecal microbial transfer and complex carbohydrates mediate protection against COPD

OBJECTIVE

Chronic obstructive pulmonary disease (COPD) is a major cause of global illness and death, most commonly caused by cigarette smoke. The mechanisms of pathogenesis remain poorly understood, limiting the development of effective therapies. The gastrointestinal microbiome has been implicated in chronic lung diseases via the gut-lung axis, but its role is unclear.

DESIGN

Using an in vivo mouse model of cigarette smoke (CS)-induced COPD and faecal microbial transfer (FMT), we characterised the faecal microbiota using metagenomics, proteomics and metabolomics. Findings were correlated with airway and systemic inflammation, lung and gut histopathology and lung function. Complex carbohydrates were assessed in mice using a high resistant starch diet, and in 16 patients with COPD using a randomised, double-blind, placebo-controlled pilot study of inulin supplementation.

RESULTS

FMT alleviated hallmark features of COPD (inflammation, alveolar destruction, impaired lung function), gastrointestinal pathology and systemic immune changes. Protective effects were additive to smoking cessation, and transfer of CS-associated microbiota after antibiotic-induced microbiome depletion was sufficient to increase lung inflammation while suppressing colonic immunity in the absence of CS exposure. Disease features correlated with the relative abundance of Muribaculaceae, Desulfovibrionaceae and Lachnospiraceae family members. Proteomics and metabolomics identified downregulation of glucose and starch metabolism in CS-associated microbiota, and supplementation of mice or human patients with complex carbohydrates improved disease outcomes.

CONCLUSION

The gut microbiome contributes to COPD pathogenesis and can be targeted therapeutically.

The Power of Psychobiotics in Depression: A Modern Approach through the Microbiota-Gut-Brain Axis: A Literature Review

The microbiota-gut-brain (MGB) axis is a complex communication network linking the gut, microbiota, and brain, influencing various aspects of health and disease. Dysbiosis, a disturbance in the gut microbiome equilibrium, can significantly impact the MGB axis, leading to alterations in microbial composition and function. Emerging evidence highlights the connection between microbiota alterations and neurological and psychiatric disorders, including depression. This review explores the potential of psychobiotics in managing depressive disorders, emphasizing their role in restoring microbial balance and influencing the MGB axis. Psychobiotics exhibit positive effects on the intestinal barrier, immune response, cortisol levels, and the hypothalamic-pituitary-adrenal (HPA) axis. Studies suggest that probiotics may serve as an adjunct therapy for depression, especially in treatment-resistant cases. This review discusses key findings from studies on psychobiotics interventions, emphasizing their impact on the gut-brain axis and mental health. The increasing acceptance of the expanded concept of the MGB axis underscores the importance of microorganisms in mental well-being. As our understanding of the microbiome's role in health and disease grows, probiotics emerge as promising agents for addressing mental health issues, providing new avenues for therapeutic interventions in depressive disorders.

Gut Microbiome Integration in Drug Discovery and Development of Small Molecules

Human microbiomes, particularly in the gut, could have a major impact on the efficacy and toxicity of drugs. However, gut microbial metabolism is often neglected in the drug discovery and development process. Medicen, a Paris-based human health innovation cluster, has gathered more than 30 international leading experts from pharma, academia, biotech, clinical research organizations, and regulatory science to develop proposals to facilitate the integration of microbiome science into drug discovery and development. Seven subteams were formed to cover the complementary expertise areas of 1) pharma experience and case studies, 2) in silico microbiome-drug interaction, 3) in vitro microbial stability screening, 4) gut fermentation models, 5) animal models, 6) microbiome integration in clinical and regulatory aspects, and 7) microbiome ecosystems and models. Each expert team produced a state-of-the-art report of their respective field highlighting existing microbiome-related tools at every stage of drug discovery and development. The most critical limitations are the growing, but still limited, drug-microbiome interaction data to produce predictive models and the lack of agreed-upon standards despite recent progress. In this paper we will report on and share proposals covering 1) how microbiome tools can support moving a compound from drug discovery to clinical proof-of-concept studies and alert early on potential undesired properties stemming from microbiome-induced drug metabolism and 2) how microbiome data can be generated and integrated in pharmacokinetic models that are predictive of the human situation. Examples of drugs metabolized by the microbiome will be discussed in detail to support recommendations from the working group. SIGNIFICANCE STATEMENT: Gut microbial metabolism is often neglected in the drug discovery and development process despite growing evidence of drugs' efficacy and safety impacted by their interaction with the microbiome. This paper will detail existing microbiome-related tools covering every stage of drug discovery and development, current progress, and limitations, as well as recommendations to integrate them into the drug discovery and development process.

Probiotic, prebiotic, synbiotic and fermented food supplementation in psychiatric disorders: A systematic review of clinical trials

The use of probiotics, prebiotics, synbiotics or fermented foods can modulate the gut-brain axis and constitute a potentially therapeutic intervention in psychiatric disorders. This systematic review aims to identify current evidence regarding these interventions in the treatment of patients with DSM/ICD psychiatric diagnoses. Forty-seven articles from 42 studies met the inclusion criteria. Risk of bias was assessed in all included studies. Major depression was the most studied disorder (n = 19 studies). Studies frequently focused on schizophrenia (n = 11) and bipolar disorder (n = 5) and there were limited studies in anorexia nervosa (n = 4), ADHD (n = 3), Tourette (n = 1), insomnia (n = 1), PTSD (n = 1) and generalized anxiety disorder (n = 1). Except in MDD, current evidence does not clarify the role of probiotics and prebiotics in the treatment of mental illness. Several studies point to an improvement in the immune and inflammatory profile (e.g. CRP, IL6), which may be a relevant mechanism of action of the therapeutic response identified in these studies. Future research should consider lifestyle and dietary habits of patients as possible confounders that may influence inter-individual treatment response.

Social anxiety disorder-associated gut microbiota increases social fear

Social anxiety disorder (SAD) is a crippling psychiatric disorder characterized by intense fear or anxiety in social situations and their avoidance. However, the underlying biology of SAD is unclear and better treatments are needed. Recently, the gut microbiota has emerged as a key regulator of both brain and behaviour, especially those related to social function. Moreover, increasing data supports a role for immune function and oxytocin signalling in social responses. To investigate whether the gut microbiota plays a causal role in modulating behaviours relevant to SAD, we transplanted the microbiota from SAD patients, which was identified by 16S rRNA sequencing to be of a differential composition compared to healthy controls, to mice. Although the mice that received the SAD microbiota had normal behaviours across a battery of tests designed to assess depression and general anxiety-like behaviours, they had a specific heightened sensitivity to social fear, a model of SAD. This distinct heightened social fear response was coupled with changes in central and peripheral immune function and oxytocin expression in the bed nucleus of the stria terminalis. This work demonstrates an interkingdom basis for social fear responses and posits the microbiome as a potential therapeutic target for SAD.

From hype to hope: Considerations in conducting robust microbiome science

Microbiome science has been one of the most exciting and rapidly evolving research fields in the past two decades. Breakthroughs in technologies including DNA sequencing have meant that the trillions of microbes (particularly bacteria) inhabiting human biological niches (particularly the gut) can be profiled and analysed in exquisite detail. This microbiome profiling has profound impacts across many fields of research, especially biomedical science, with implications for how we understand and ultimately treat a wide range of human disorders. However, like many great scientific frontiers in human history, the pioneering nature of microbiome research comes with a multitude of challenges and potential pitfalls. These include the reproducibility and robustness of microbiome science, especially in its applications to human health outcomes. In this article, we address the enormous promise of microbiome science and its many challenges, proposing constructive solutions to enhance the reproducibility and robustness of research in this nascent field. The optimisation of microbiome science spans research design, implementation and analysis, and we discuss specific aspects such as the importance of ecological principals and functionality, challenges with microbiome-modulating therapies and the consideration of confounding, alternative options for microbiome sequencing, and the potential of machine learning and computational science to advance the field. The power of microbiome science promises to revolutionise our understanding of many diseases and provide new approaches to prevention, early diagnosis, and treatment.

Opioid trail: Tracking contributions to opioid use disorder from host genetics to the gut microbiome

Opioid use disorder (OUD) is a worldwide public health crisis with few effective treatment options. Traditional genetics and neuroscience approaches have provided knowledge about biological mechanisms that contribute to OUD-related phenotypes, but the complexity and magnitude of effects in the brain and body remain poorly understood. The gut-brain axis has emerged as a promising target for future therapeutics for several psychiatric conditions, so characterizing the relationship between host genetics and the gut microbiome in the context of OUD will be essential for development of novel treatments. In this review, we describe evidence that interactions between host genetics, the gut microbiome, and immune signaling likely play a key role in mediating opioid-related phenotypes. Studies in humans and model organisms consistently demonstrated that genetic background is a major determinant of gut microbiome composition. Furthermore, the gut microbiome is susceptible to environmental influences such as opioid exposure. Additional work focused on gene by microbiome interactions will be necessary to gain improved understanding of their effects on OUD-related behaviors.

Co-Housing and Fecal Microbiota Transplantation: Technical Support for TCM Herbal Treatment of Extra-Intestinal Diseases Based on Gut Microbial Ecosystem Remodeling

Dysregulation of the gut microbial ecosystem (GME) (eg, alterations in the gut microbiota, gut-derived metabolites, and gut barrier) may contribute to the onset and progression of extra-intestinal diseases. Previous studies have found that Traditional Chinese Medicine herbs (TCMs) play an important role in manipulating the GME, but a prominent obstacle in current TCM research is the causal relationship between GME and disease amelioration. Encouragingly, co-housing and fecal microbiota transplantation (FMT) provide evidence-based support for TCMs to treat extra-intestinal diseases by targeting GME. In this review, we documented the principles, operational procedures, applications and limitations of the key technologies (ie, co-housing and FMT); furthermore, we provided evidence that TCM works through the GME, especially the gut microbiota (eg, SCFA- and BSH-producing bacteria), the gut-derived metabolites (eg, IS, pCS, and SCFAs), and intestinal barrier to alleviate extra-intestinal diseases. This will be beneficial in constructing microecological pathways for TCM treatment of extra-intestinal diseases in the future.

Microbiota from Alzheimer's patients induce deficits in cognition and hippocampal neurogenesis

Alzheimer's disease is a complex neurodegenerative disorder leading to a decline in cognitive function and mental health. Recent research has positioned the gut microbiota as an important susceptibility factor in Alzheimer's disease by showing specific alterations in the gut microbiome composition of Alzheimer's patients and in rodent models. However, it is unknown whether gut microbiota alterations are causal in the manifestation of Alzheimer's symptoms. To understand the involvement of Alzheimer's patient gut microbiota in host physiology and behaviour, we transplanted faecal microbiota from Alzheimer's patients and age-matched healthy controls into microbiota-depleted young adult rats. We found impairments in behaviours reliant on adult hippocampal neurogenesis, an essential process for certain memory functions and mood, resulting from Alzheimer's patient transplants. Notably, the severity of impairments correlated with clinical cognitive scores in donor patients. Discrete changes in the rat caecal and hippocampal metabolome were also evident. As hippocampal neurogenesis cannot be measured in living humans but is modulated by the circulatory systemic environment, we assessed the impact of the Alzheimer's systemic environment on proxy neurogenesis readouts. Serum from Alzheimer's patients decreased neurogenesis in human cells in vitro and were associated with cognitive scores and key microbial genera. Our findings reveal for the first time, that Alzheimer's symptoms can be transferred to a healthy young organism via the gut microbiota, confirming a causal role of gut microbiota in Alzheimer's disease, and highlight hippocampal neurogenesis as a converging central cellular process regulating systemic circulatory and gut-mediated factors in Alzheimer's.

Fuzi decoction treats chronic heart failure by regulating the gut microbiota, increasing the short-chain fatty acid levels and improving metabolic disorders

Fuzi decoction (FZD) is clinically used to treat chronic heart failure (CHF) in China, but the mechanism underlying FZD treatment in CHF remains unclear. Here, we investigated the potential mechanism underlying FZD treatment of CHF in rats. First, the compounds in FZD-containing serum of rats were identified, and 16 S rRNA sequencing and GC-MS-based untargeted metabolomics analysis were then performed. The levels of fecal short-chain fatty acids (SCFAs) were determined and compared, and fecal microbiota transplantation (FMT) was used to verify the role of the gut microbiota. Our results identified 27 in FD-containing serum. FZD increased the Firmicutes-to-Bacteroidetes ratio and the Lactobacillus abundance and affected the β diversity of the gut microbiota in rats with CHF. Differential species analysis showed that Lactobacillus and Prevotella were biomarkers of FZD treatment of CHF. Untargeted metabolomics analysis revealed that FZD affected valine, leucine and isoleucine biosynthesis; galactose metabolism; and aminoacyl-tRNA biosynthesis in rats with CHF. Furthermore, FZD significantly increased the acetic acid, propionic acid, butyric acid and isopentanoic acid levels in the feces of rats with CHF. Correlation analysis showed that the butyric acid and Lactobacillus levels had the strongest correlation in the control, sham and high-dose FZD (HFZD) groups, and many microbiota components were closely related to differentially abundant metabolites. FMT revealed that the fecal microbiota obtained from the HFZD group changed the heart rate; the brain natriuretic peptide (BNP), acetic acid, propionic acid, butyric acid, and metabolite levels; and the gut microbiota in rats with CHF. In summary, our study revealed that the mechanism of action of FZD in CHF treatment may be related to improvements in the gut microbiota, elevations in the SCFA content and the regulation of valine, leucine, and isoleucine biosynthesis; galactose metabolism; and other metabolic pathways.

Horizontal transmission of gut microbiota attenuates mortality in lung fibrosis

Pulmonary fibrosis is a chronic and often fatal disease. The pathogenesis is characterized by aberrant repair of lung parenchyma, resulting in loss of physiological homeostasis, respiratory failure, and death. The immune response in pulmonary fibrosis is dysregulated. The gut microbiome is a key regulator of immunity. The role of the gut microbiome in regulating the pulmonary immunity in lung fibrosis is poorly understood. Here, we determine the impact of gut microbiota on pulmonary fibrosis in substrains of C57BL/6 mice derived from different vendors (C57BL/6J and C57BL/6NCrl). We used germ-free models, fecal microbiota transplantation, and cohousing to transmit gut microbiota. Metagenomic studies of feces established keystone species between substrains. Pulmonary fibrosis was microbiota dependent in C57BL/6 mice. Gut microbiota were distinct by β diversity and α diversity. Mortality and lung fibrosis were attenuated in C57BL/6NCrl mice. Elevated CD4+IL-10+ T cells and lower IL-6 occurred in C57BL/6NCrl mice. Horizontal transmission of microbiota by cohousing attenuated mortality in C57BL/6J mice and promoted a transcriptionally altered pulmonary immunity. Temporal changes in lung and gut microbiota demonstrated that gut microbiota contributed largely to immunological phenotype. Key regulatory gut microbiota contributed to lung fibrosis, generating rationale for human studies.

Microbiota-Gut-Brain Axis and Antidepressant Treatment

In the treatment of depressive disorders, conventional antidepressant therapy has been the mainstay of clinical management, along with well-established nonpharmacological interventions such as various kinds of psychotherapy. Over the last 2 decades, there has been considerable interest in the role of the gastrointestinal system and its microbiota on brain function, behavior, and mental health. Components of what is referred to as the microbiota-gut-brain axis have been uncovered, and further research has elicited functional capabilities such as "gut-brain modules." Some studies have found associations with compositional alterations of gut microbiota in patients with depressive disorders and individuals experiencing symptoms of depression. Regarding the pathogenesis and neurobiology of depression itself, there appears to be a multifactorial contribution, in addition to the theories involving deficits in catecholaminergic and monoamine neurotransmission. Interestingly, there is evidence to suggest that antidepressants may play a role in modulating the gut microbiota, thereby possibly having an impact on the microbiota-gut-brain axis in this manner. The development of prebiotics, probiotics, and synbiotics has led to studies investigating not only their impact on the microbiota but also their therapeutic value in mental health. These psychobiotics have the potential to be used as therapeutic adjuncts in the treatment of depression. Regarding future directions, and in an attempt to further understand the role of the microbiota-gut-brain axis in depression, more studies such as those involving fecal microbiota transplantation will be required. In addition to recent findings, it is also suggested that more research will have to be undertaken to elicit whether specific strains of gut organisms are linked to depression. In terms of further investigation of the therapeutic potential of prebiotics, probiotics, and synbiotics as adjuncts to antidepressant treatment, we also expect there to be more research targeting specific microorganisms, as well as a strong focus on the effects of specific prebiotic fibers from an individualized (personalized) point of view.

Gut-derived metabolites mediating cognitive development in 5-year-old children: Early-life transplant in mice has lasting effects throughout adulthood

The gut microbiota has been causally linked to cognitive development. We aimed to identify metabolites mediating its effect on cognitive development, and foods or nutrients related to most promising metabolites. Faeces from 5-year-old children (DORIAN-PISAC cohort, including 90 general population families with infants, 42/48 females/males, born in 2011-2014) were transplanted (FMT) into C57BL/6 germ-free mice. Children and recipient mice were stratified by cognitive phenotype, or based on protective metabolites. Food frequency questionnaires were obtained in children. Cognitive measurements in mice included five Y-maze tests until 23 weeks post-FMT, and (at 23 weeks) PET-CT for brain metabolism and radiodensity, and ultrasound-based carotid vascular indices. Children (faeces, urine) and mice (faeces, plasma) metabolome was measured by 1H NMR spectroscopy, and the faecal microbiota was profiled in mice by 16S rRNA amplicon sequencing. Cognitive scores of children and recipient mice were correlated. FMT-dependent modifications of brain metabolism were observed. Mice receiving FMT from high-cognitive or protective metabolite-enriched children developed superior cognitive-behavioural performance. A panel of metabolites, namely xanthine, hypoxanthine, formate, mannose, tyrosine, phenylalanine, glutamine, was found to mediate the gut-cognitive axis in donor children and recipient mice. Vascular indices partially explained the metabolite-to-phenotype relationships. Children's consumption of legumes, whole-milk yogurt and eggs, and intake of iron, zinc and vitamin D appeared to support protective gut metabolites. Overall, metabolites involved in inflammation, purine metabolism and neurotransmitter synthesis mediate the gut-cognitive axis, and holds promise for screening. The related dietary and nutritional findings offer leads to microbiota-targeted interventions for cognitive protection, with long-lasting effects.

The microbiome-gut-brain axis in nutritional neuroscience

Emerging evidence is highlighting the microbiome as a key regulator of the effect of nutrition on gut-brain axis signaling. Nevertheless, it is not yet clear whether the impact of nutrition is moderating the microbiota-gut-brain interaction or if diet has a mediating role on microbiota composition and function to influence central nervous system function, brain phenotypes and behavior. Mechanistic evidence from cell-based in vitro studies, animal models and preclinical intervention studies are linking the gut microbiota to the effects of diet on brain function, but they have had limited translation to human intervention studies. While increasing evidence demonstrates the triangulating relationship between diet, microbiota, and brain function across the lifespan, future mechanistic and translational studies in the field of microbiota and nutritional neuroscience are warranted to inform potential strategies for prevention and management of several neurological, neurodevelopmental, neurodegenerative, and psychiatric disorders. This brief primer provides an overview of the most recent advances in the nutritional neuroscience - microbiome field, highlighting significant opportunities for future research.

Gut bacterial consortium enriched in a biofloc system protects shrimp against Vibrio parahaemolyticus infection

BACKGROUND

Shrimp cultured in a biofloc system (BFS) have a lower disease incidence than those farmed in a water exchange system (WES). Although a number of studies have reported that the gut bacterial community induced by BFS is highly associated with shrimp disease resistance, the causal relationship remains unknown. Here, the promotive roles of gut bacterial community induced by BFS in pathogenic Vibrio infection resistance and its potential micro-ecological and physiological mechanisms were investigated by gut bacterial consortium transplantation and synthetic community (SynCom) construction.

RESULTS

The BFS induced a more stable and resistant gut bacterial community, and significantly enriched some beneficial bacterial taxa, such as Paracoccus, Ruegeria, Microbacterium, Demequina, and Tenacibaculum. Transplantation of a gut bacterial consortium from BFS shrimp (EnrichBFS) greatly enhanced the stability of the bacterial community and resistance against pathogenic V. parahaemolyticus infection in WES shrimp, while transplantation of a gut bacterial consortium from WES shrimp significantly disrupted the bacterial community and increased pathogen susceptibility in both WES and BFS shrimp. The addition of EnrichBFS in shrimp postlarvae also improved the pathogen resistance through increasing the relative abundances of beneficial bacterial taxa and stability of bacterial community. The corresponding strains of five beneficial bacterial taxa enriched in BFS shrimp were isolated to construct a SynComBFS. The addition of SynComBFS could not only suppress disease development, but also improve shrimp growth, boost the digestive and immune activities, and restore health in diseased shrimp. Furthermore, the strains of SynComBFS well colonized shrimp gut to maintain a high stability of bacterial community.

CONCLUSIONS

Our study reveals an important role for native microbiota in protecting shrimp from bacterial pathogens and provides a micro-ecological regulation strategy towards the development of probiotics to ameliorate aquatic animal diseases. Video Abstract.

Systematic review and meta-analysis of the effect of fecal microbiota transplantation on behavior in animals

The bi-directional interaction between gut microbiota and the central nervous system has been coined the gut microbiota-brain axis. Fecal microbiota transplantation (FMT) is the administration of a solution of fecal matter from a donor into the intestinal tract of a recipient. Preclinical FMT experiments are essential to prove causality in the context of the gut microbiota-brain axis. In this systematic review, we assess the body of evidence related to the ability of FMT to modulate an animal's behavior. Accordingly, we provide a detailed summary of the use of FMT in behavior-related animal studies, an extensive risk of bias analysis, and a meta-analysis of the overall effect of FMT on behavioral outcome measures in 64 studies, representing 4889 animals. The resulting meta-analysis revealed FMT was effective at changing animal behavior, thereby substantiating evidence for the gut microbiota-brain axis. However, our study also highlights an urgent need for methodological safeguards within this research field to reduce the risk of bias and improve the internal validity of future studies.

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

The role of the gut-microbiota-brain axis via the subdiaphragmatic vagus nerve in chronic inflammatory pain and comorbid spatial working memory impairment in complete Freund's adjuvant mice

Chronic inflammatory pain (CIP) is a common public medical problem, often accompanied by memory impairment. However, the mechanisms underlying CIP and comorbid memory impairment remain elusive. This study aimed to examine the role of the gut-microbiota-brain axis in CIP and comorbid memory impairment in mice treated with complete Freund's adjuvant (CFA). 16S rRNA analysis showed the altered diversity of gut microbiota from day 1 to day 14 after CFA injection. Interestingly, fecal microbiota transplantation (FMT) from healthy naive mice ameliorated comorbidities, such as mechanical allodynia, thermal hyperalgesia, spatial working memory impairment, neuroinflammation, and abnormal composition of gut microbiota in the CFA mice. Additionally, subdiaphragmatic vagotomy (SDV) blocked the onset of these comorbidities. Interestingly, the relative abundance of the bacterial genus or species was also correlated with these comorbidities after FMT or SDV. Therefore, our results suggest that the gut-microbiota-brain axis via the subdiaphragmatic vagus nerve is crucial for the development of CIP and comorbid spatial working memory impairment in CFA mice.

Roles of the gut microbiome in weight management

Overweight, obesity, undernutrition and their respective sequelae have devastating tolls on personal and public health worldwide. Traditional approaches for treating these conditions with diet, exercise, drugs and/or surgery have shown varying degrees of success, creating an urgent need for new solutions with long-term efficacy. Owing to transformative advances in sequencing, bioinformatics and gnotobiotic experimentation, we now understand that the gut microbiome profoundly impacts energy balance through diverse mechanisms affecting both sides of the energy balance equation. Our growing knowledge of microbial contributions to energy metabolism highlights new opportunities for weight management, including the microbiome-aware improvement of existing tools and novel microbiome-targeted therapies. In this Review, we synthesize current knowledge concerning the bidirectional influences between the gut microbiome and existing weight management strategies, including behaviour-based and clinical approaches, and incorporate a subject-level meta-analysis contrasting the effects of weight management strategies on microbiota composition. We consider how emerging understanding of the gut microbiome alters our prospects for weight management and the challenges that must be overcome for microbiome-focused solutions to achieve success.

Pesticide exposure and the microbiota-gut-brain axis

The gut microbiota exist within a dynamic ecosystem shaped by various factors that includes exposure to xenobiotics such as pesticides. It is widely regarded that the gut microbiota plays an essential role in maintaining host health, including a major influence on the brain and behaviour. Given the widespread use of pesticides in modern agriculture practices, it is important to assess the long-term collateral effects these xenobiotic exposures have on gut microbiota composition and function. Indeed, exposure studies using animal models have shown that pesticides can induce negative impacts on the host gut microbiota, physiology and health. In tandem, there is a growing body of literature showing that the effects of pesticide exposure can be extended to the manifestation of behavioural impairments in the host. With the increasing appreciation of the microbiota-gut-brain axis, in this review we assess whether pesticide-induced changes in gut microbiota composition profiles and functions could be driving these behavioural alterations. Currently, the diversity of pesticide type, exposure dose and variation in experimental designs hinders direct comparisons of studies presented. Although many insights presented, the mechanistic connection between the gut microbiota and behavioural changes remains insufficiently explored. Future experiments should therefore focus on causal mechanisms to examine the gut microbiota as the mediator of the behavioural impairments observed in the host following pesticide exposure.

Antibiotic Conditioning Shapes Pseudosterile Mouse Models by Deleting Colonic Microbes Rather than Small Intestinal Microbes

A simple model of alternative microbiota in the developing intestinal environment has been highly desirable for the study of health and disease in the gut. The pattern of antibiotic depletion of natural gut microbes is necessary for this model. However, the effects and loci of antibiotic deletion of gut microbes remain unclear. In this study, a mixture of three proven broad-spectrum antibiotics was selected to study their effects on microbial deletions in the jejunum, ileum, and colon of mice. The 16S rRNA sequencing results showed that antibiotics significantly reduced colonic microbial diversity, with limited effects on the jejunum and ileum. At the level of microbial genera, only 93.38% of Burkholderia-Caballeronia-Paraburkholderia and 5.89% of Enterorhabdus were present in the colon after antibiotic treatment. However, such changes were not observed in the microbial composition of the jejunum and ileum. Our results suggest that the antibiotics depleted intestinal microorganisms by acting primarily in the colon and not in the small intestine (jejunum and ileum). IMPORTANCE Many studies have applied antibiotics to delete intestinal microbes to shape pseudosterile mouse models and further used for fecal microbial transplantation. However, few studies have explored the spatial location of antibiotic action in the intestine. This study shows that the selected antibiotics effectively deleted microbiota in the colon of mice, with limited effects on microbes in the jejunum and ileum. Our study provides guidance for the application of a mouse model of antibiotic deletion of intestinal microbes.

Yijung-tang improves thermogenesis and reduces inflammation associated with gut microbiota in hypothyroid rats

Currently, considerable attention is focused on exploring the potential relationship between herbal medicine (HM) and the gut microbiome in terms of thermoregulation, which is an important aspect of human health, in modern system biology. However, our knowledge of the mechanisms of HM in thermoregulation is inadequate. Here, we demonstrate that the canonical herbal formula, Yijung-tang (YJT), protects against hypothermia, hyperinflammation, and intestinal microbiota dysbiosis in PTU-induced hypothyroid rats. Notably, these properties were associated with alterations in the gut microbiota and signaling crosstalk between the thermoregulatory and inflammatory mediators in the small intestine and brown adipose tissue (BAT). In contrast to the conventional drug L-thyroxine for curing hypothyroidism, YJT has an efficacy for attenuating systematic inflammatory responses, related with depression in intestinal TLR4 and Nod2/Pglyrp1 signaling pathways. Our findings suggest that YJT could promote BAT thermogenesis and prevent systemic inflammation in PTU-induced hypothyroid rats, which was associated with its prebiotic effect on modulating of the gut microbiota and gene expression with relevance in the enteroendocrine function and innate immune systems. These findings may strengthen the rationale of the microbiota-gut-BAT axis for a paradigm shift to enable holobiont-centric medicine.

Fecal microbiota transplantation holds the secret to youth

Aging shows itself not just at the cellular level, with shortened telomeres and cell cycle arrest, but also at the organ and organismal level, with diminished brainpower, dry eyes, intestinal inflammation, muscular atrophy, wrinkles, etc. When the gut microbiota, often called the "virtual organ of the host," fails to function normally, it can lead to a cascade of health problems including, but not limited to, inflammatory bowel disease, obesity, metabolic liver disease, type II diabetes, cardiovascular disease, cancer, and even neurological disorders. An effective strategy for restoring healthy gut bacteria is fecal microbiota transplantation (FMT). It can reverse the effects of aging on the digestive system, the brain, and the vision by transplanting the functional bacteria found in the excrement of healthy individuals into the gut tracts of patients. This paves the way for future research into using the microbiome as a therapeutic target for disorders associated with aging.

Blocking coprophagy increases the levels of inflammation and depression in healthy mice as well as mice receiving fecal microbiota transplantation from disease model mice donors

Rodents have been extensively used as animal models in microbiome studies. However, all rodents have a habitual nature called coprophagy, a phenomenon that they self-reinoculate feces into their gastrointestinal tract. Recent studies have shown that blocking coprophagy can alter rodents' diversity of gut microbiota, metabolism, neurochemistry, and cognitive behavior. However, whether rodents' coprophagy behavior affects the levels of inflammation and depression is unclear. In order to address this problem, we first blocked coprophagy in healthy mice. It displayed an increase in the levels of depression, verified by depressive-like behaviors and mood-related indicators, and inflammation, verified by the increased levels of the pro-inflammatory cytokine, in coprophagy-blocked mice. Furthermore, we transplanted fecal microbiota from chronic restraint stress (CRS) depression model mice and lipopolysaccharide (LPS) inflammation model mice to healthy recipient mice, respectively. It showed that the disease-like phenotypes in the coprophagy-blocked group were worse than those in the coprophagy-unblocked group, including severer depressive symptoms and higher levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α and IFN-γ) in serum, prefrontal cortex (PFC), and hippocampus (HIP). These findings showed that blocking coprophagy in mice not only increased the levels of inflammation and depression in healthy mice but also aggravated inflammation and depression induced by fecal microbiota from disease donors. The discovery may provide a vital reference for future research involving FMT in rodents.

From Pathogenesis to Intervention: The Importance of the Microbiome in Oral Mucositis

Oral mucositis (OM) is a common and impactful toxicity of standard cancer therapy, affecting up to 80% of patients. Its aetiology centres on the initial destruction of epithelial cells and the increase in inflammatory signals. These changes in the oral mucosa create a hostile environment for resident microbes, with oral infections co-occurring with OM, especially at sites of ulceration. Increasing evidence suggests that oral microbiome changes occur beyond opportunistic infection, with a growing appreciation for the potential role of the microbiome in OM development and severity. This review collects the latest articles indexed in the PubMed electronic database which analyse the bacterial shift through 16S rRNA gene sequencing methodology in cancer patients under treatment with oral mucositis. The aims are to assess whether changes in the oral and gut microbiome causally contribute to oral mucositis or if they are simply a consequence of the mucosal injury. Further, we explore the emerging role of a patient's microbial fingerprint in OM development and prediction. The maintenance of resident bacteria via microbial target therapy is under constant improvement and should be considered in the OM treatment.

Microbiota-derived tryptophan catabolites mediate the chemopreventive effects of statins on colorectal cancer

Epidemiological studies have indicated an association between statin use and reduced incidence of colorectal cancer (CRC), and work in preclinical models has demonstrated a potential chemopreventive effect. Statins are also associated with reduced dysbiosis in the gut microbiome, yet the role of the gut microbiome in the protective effect of statins in CRC is unclear. Here we validated the chemopreventive role of statins by retrospectively analysing a cohort of patients who underwent colonoscopies. This was confirmed in preclinical models and patient cohorts, and we found that reduced tumour burden was partly due to statin modulation of the gut microbiota. Specifically, the gut commensal Lactobacillus reuteri was increased as a result of increased microbial tryptophan availability in the gut after atorvastatin treatment. Our in vivo studies further revealed that L. reuteri administration suppressed colorectal tumorigenesis via the tryptophan catabolite, indole-3-lactic acid (ILA). ILA exerted anti-tumorigenic effects by downregulating the IL-17 signalling pathway. This microbial metabolite inhibited T helper 17 cell differentiation by targeting the nuclear receptor, RAR-related orphan receptor γt (RORγt). Together, our study provides insights into an anti-cancer mechanism driven by statin use and suggests that interventions with L. reuteri or ILA could complement chemoprevention strategies for CRC.

Connecting the Dots: The Interplay Between Stroke and the Gut-Brain Axis

This article discusses the interplay between the gut-brain axis and stroke, a multifaceted neurological disorder that affects millions of people worldwide. The gut-brain axis is a bidirectional communication network linking the central nervous system (CNS) to the gastrointestinal tract (GIT), including the enteric nervous system (ENS), vagus nerve, and gut microbiota. Dysbiosis in the gut microbiota, alterations in the ENS and vagus nerve, and gut motility changes have been linked to increased inflammation and oxidative stress, which are contributing factors in the development and progression of stroke. Research on animals has shown that modifying the gut microbiota can impact the results of a stroke. Germ-free mice displayed improved neurological function and decreased infarct volumes, indicating a positive effect. Furthermore, studies in stroke patients have shown alterations in the gut microbiota composition, indicating that targeting dysbiosis could be a potential therapeutic strategy for stroke. The review suggests that targeting the gut-brain axis may represent a potential therapeutic approach to reduce the morbidity and mortality associated with stroke.

Basal Diet Fed to Recipient Mice Was the Driving Factor for Colitis and Colon Tumorigenesis, despite Fecal Microbiota Transfer from Mice with Severe or Mild Disease

Consumption of the total Western diet (TWD) in mice has been shown to increase gut inflammation, promote colon tumorigenesis, and alter fecal microbiome composition when compared to mice fed a healthy diet, i.e., AIN93G (AIN). However, it is unclear whether the gut microbiome contributes directly to colitis-associated CRC in this model. The objective of this study was to determine whether dynamic fecal microbiota transfer (FMT) from donor mice fed either the AIN basal diet or the TWD would alter colitis symptoms or colitis-associated CRC in recipient mice, which were fed either the AIN diet or the TWD, using a 2 × 2 factorial experiment design. Time-matched FMT from the donor mice fed the TWD did not significantly enhance symptoms of colitis, colon epithelial inflammation, mucosal injury, or colon tumor burden in the recipient mice fed the AIN diet. Conversely, FMT from the AIN-fed donors did not impart a protective effect on the recipient mice fed the TWD. Likewise, the composition of fecal microbiomes of the recipient mice was also affected to a much greater extent by the diet they consumed than by the source of FMT. In summary, FMT from the donor mice fed either basal diet with differing colitis or tumor outcomes did not shift colitis symptoms or colon tumorigenesis in the recipient mice, regardless of the basal diet they consumed. These observations suggest that the gut microbiome may not contribute directly to the development of disease in this animal model.

A systematic review of the effects of gut microbiota depletion on social and anxiety-related behaviours in adult rodents: Implications for translational research

The microbiota-gut-brain axis is associated with several behaviours, including those relevant to anxiety or sociability in rodents, however, no conceptual framework has yet been available. Summary of the effects of antibiotic-mediated gut microbiota depletion on anxiety and sociability is essential to both inform further preclinical investigations and to guide translational research into human studies. The main objective is to examine the role of gut microbiota depletion on anxiety and sociability in rodents, and to consider how the findings can be translated to inform the design of research in humans. We reviewed 13 research articles, indicating significant changes in gut microbiota composition and diversity have been found in animals treated with a mix or a single antibiotic. Nonetheless, there is no consensus regarding the impact of gut microbiota depletion on anxiety-like or social behaviour. Gut microbiota depletion may be a useful strategy to examine the role of gut microbes in anxiety and sociability, but the lack of data from rigorous animal investigations precludes any definitive interpretations for a translational impact on human health.

Inflammation, Lifestyle Factors, and the Microbiome-Gut-Brain Axis: Relevance to Depression and Antidepressant Action

Depression is considered a major public health concern, where existing pharmacological treatments are not equally effective across all patients. The pathogenesis of depression involves the interaction of complex biological components, such as the immune system and the microbiota-gut-brain axis. Adjunctive lifestyle-oriented approaches for depression, including physical exercise and special diets are promising therapeutic options when combined with traditional antidepressants. However, the mechanisms of action of these strategies are incompletely understood. Accumulating evidence suggests that physical exercise and specific dietary regimens can modulate both the immune system and gut microbiota composition. Here, we review the current information about the strategies to alleviate depression and their crosstalk with both inflammatory mechanisms and the gut microbiome. We further discuss the role of the microbiota-gut-brain axis as a possible mediator for the adjunctive therapies for depression through inflammatory mechanisms. Finally, we review existing and future adjunctive strategies to manipulate the gut microbiota with potential use for depression, including physical exercise, dietary interventions, prebiotics/probiotics, and fecal microbiota transplantation.

The role of the gut microbiome and its metabolites in cerebrovascular diseases

The gut microbiome is critically involved in maintaining normal physiological function in the host. Recent studies have revealed that alterations in the gut microbiome contribute to the development and progression of cerebrovascular disease via the microbiota-gut-brain axis (MGBA). As a broad communication network in the human body, MGBA has been demonstrated to have significant interactions with various factors, such as brain structure and function, nervous system diseases, etc. It is also believed that the species and composition of gut microbiota and its metabolites are intrinsically linked to vascular inflammation and immune responses. In fact, in fecal microbiota transplantation (FMT) research, specific gut microbiota and downstream-related metabolites have been proven to not only participate in various physiological processes of human body, but also affect the occurrence and development of cerebrovascular diseases directly or indirectly through systemic inflammatory immune response. Due to the high mortality and disability rate of cerebrovascular diseases, new treatments to improve intestinal dysbacteriosis have gradually attracted widespread attention to better ameliorate the poor prognosis of cerebrovascular diseases in a non-invasive way. This review summarizes the latest advances in the gut microbiome and cerebrovascular disease research and reveals the profound impact of gut microbiota dysbiosis and its metabolites on cerebrovascular diseases. At the same time, we elucidated molecular mechanisms whereby gut microbial metabolites regulate the expression of specific interleukins in inflammatory immune responses. Moreover, we further discuss the feasibility of novel therapeutic strategies targeting the gut microbiota to improve the outcome of patients with cerebrovascular diseases. Finally, we provide new insights for standardized diagnosis and treatment of cerebrovascular diseases.

Utility of Human Relevant Preclinical Animal Models in Navigating NAFLD to MAFLD Paradigm

Fatty liver disease is an emerging contributor to disease burden worldwide. The past decades of work established the heterogeneous nature of non-alcoholic fatty liver disease (NAFLD) etiology and systemic contributions to the pathogenesis of the disease. This called for the proposal of a redefinition in 2020 to that of metabolic dysfunction-associated fatty liver disease (MAFLD) to better reflect the current understanding of the disease. To date, several clinical cohort studies comparing NAFLD and MAFLD hint at the relevancy of the new nomenclature in enriching for patients with more severe hepatic injury and extrahepatic comorbidities. However, the underlying systemic pathogenesis is still not fully understood. Preclinical animal models have been imperative in elucidating key biological mechanisms in various contexts, including intrahepatic disease progression, interorgan crosstalk and systemic dysregulation. Furthermore, they are integral in developing novel therapeutics against MAFLD. However, substantial contextual variabilities exist across different models due to the lack of standardization in several aspects. As such, it is crucial to understand the strengths and weaknesses of existing models to better align them to the human condition. In this review, we consolidate the implications arising from the change in nomenclature and summarize MAFLD pathogenesis. Subsequently, we provide an updated evaluation of existing MAFLD preclinical models in alignment with the new definitions and perspectives to improve their translational relevance.

Fecal microbiota transplantation ameliorates bone loss in mice with ovariectomy-induced osteoporosis via modulating gut microbiota and metabolic function

Background

Osteoporosis (OP) is a systemic metabolic bone disease characterized by decreased bone mass and destruction of bone microstructure, which tends to result in enhanced bone fragility and related fractures. The postmenopausal osteoporosis (PMOP) has a relatively high proportion, and numerous studies reveal that estrogen-deficiency is related to the imbalance of gut microbiota (GM), impaired intestinal mucosal barrier function and enhanced inflammatory reactivity. However, the underlying mechanisms remain unclear and the existing interventions are also scarce.

Methods

In this study, we established a mouse model induced by ovariectomy (OVX) and conducted fecal microbiota transplantation (FMT) by gavage every day for 8 weeks. Subsequently, the bone mass and microarchitecture of mice were evaluated by the micro computed tomography (Micro-CT). The intestinal permeability, pro-osteoclastogenic cytokines expression, osteogenic and osteoclastic activities were detected by the immunohistological analysis, histological examination, enzyme-linked immunosorbent assay (ELISA) and western blot analysis accordingly. Additionally, the composition and abundance of GM were assessed by 16S rRNA sequencing and the fecal short chain fatty acids (SCFAs) level was measured by metabolomics.

Results

Our results demonstrated that FMT inhibited the excessive osteoclastogenesis and prevented the OVX-induced bone loss. Specifically, compared with the OVX group, FMT enhanced the expressions of tight junction proteins (zonula occludens protein 1 (ZO-1) and Occludin) and suppressed the release of pro-osteoclastogenic cytokines (tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)). Furthermore, FMT also optimized the composition and abundance of GM, and increased the fecal SCFAs level (mainly acetic acid and propionic acid).

Conclusions

Collectively, based on GM-bone axis, FMT prevented the OVX-induced bone loss by correcting the imbalance of GM, improving the SCFAs level, optimizing the intestinal permeability and suppressing the release of pro-osteoclastogenic cytokines, which may be an alternative option to serve as a promising candidate for the prevention and treatment of PMOP in the future.

The translational potential of this article

This study indicates the ingenious involvement of GM-bone axis in PMOP and the role of FMT in reshaping the status of GM and ameliorating the bone loss in OVX-induced mice. FMT might serve as a promising candidate for the prevention and treatment of PMOP in the future.

Gnotobiotic mice housing conditions critically influence the phenotype associated with transfer of faecal microbiota in a context of obesity

OBJECTIVE

Faecal microbiota transplantation (FMT) in germ-free (GF) mice is a common approach to study the causal role of the gut microbiota in metabolic diseases. Lack of consideration of housing conditions post-FMT may contribute to study heterogeneity. We compared the impact of two housing strategies on the metabolic outcomes of GF mice colonised by gut microbiota from mice treated with a known gut modulator (cranberry proanthocyanidins (PAC)) or vehicle.

DESIGN

High-fat high-sucrose diet-fed GF mice underwent FMT-PAC colonisation in sterile individual positive flow ventilated cages under rigorous housing conditions and then maintained for 8 weeks either in the gnotobiotic-axenic sector or in the specific pathogen free (SPF) sector of the same animal facility.

RESULTS

Unexpectedly, 8 weeks after colonisation, we observed opposing liver phenotypes dependent on the housing environment of mice. Mice housed in the GF sector receiving the PAC gut microbiota showed a significant decrease in liver weight and hepatic triglyceride accumulation compared with control group. Conversely, exacerbated liver steatosis was observed in the FMT-PAC mice housed in the SPF sector. These phenotypic differences were associated with housing-specific profiles of colonising bacterial in the gut and of faecal metabolites.

CONCLUSION

These results suggest that the housing environment in which gnotobiotic mice are maintained post-FMT strongly influences gut microbiota composition and function and can lead to distinctive phenotypes in recipient mice. Better standardisation of FMT experiments is needed to ensure reproducible and translatable results.

Gut Dysbiosis Promotes Preeclampsia by Regulating Macrophages and Trophoblasts

BACKGROUND

Preeclampsia is one of the leading causes of maternal and perinatal morbidity and is characterized by hypertension, inflammation, and placental dysfunction. Gut microbiota plays key roles in inflammation and hypertension. However, its roles and mechanisms in preeclampsia have not been fully elucidated.

METHODS

16S rRNA gene sequencing and targeted metabolomics were conducted on stool samples from 92 preeclamptic patients and 86 normal late-pregnant women. Then, fecal microbiota transplantation and in vitro and in vivo functional experiments were performed to explore the roles and mechanisms of gut microbiota in preeclampsia development.

RESULTS

We revealed the gut microbiota dysbiosis in preeclamptic patients, including significant reductions in short-chain fatty acid-producing bacteria and short-chain fatty acids. The gut microbiota of preeclamptic patients significantly exacerbated pathologies and symptoms of preeclamptic rats, whereas the gut microbiota of healthy pregnant women had significant protective effects. Akkermansia muciniphila, propionate, or butyrate significantly alleviated the symptoms of preeclamptic rats. Mechanistically, they significantly promoted autophagy and M2 polarization of macrophages in placental bed, thereby suppressing inflammation. Propionate also significantly promoted trophoblast invasion, thereby improved spiral arterial remodeling. Additionally, we identified a marker set consisting of Akkermansia, Oscillibacter, and short-chain fatty acids that could accurately diagnose preeclampsia.

CONCLUSIONS

Our study revealed that gut microbiota dysbiosis is an important etiology of preeclampsia. Gut microbiota and their active metabolites have great potential for the treatment and diagnosis of preeclampsia. Our findings enrich the gut-placenta axis theory and contribute to the development of microecological products for preeclampsia.

Potential of Establishing the Corresponding Human Microbial Community in Pseudo Germ-Free Mice through Fecal Microbe Transfer from Three Urolithin Metabotypes

Three urolithin metabotypes (UMs) have been defined in the population according to final urolithins converted by gut microbiota. Currently, it is difficult to establish the cause-and-effect relationship between urolithins and microbiota in human studies. Studies on the health effects of ellagic acid (EA) in animal models rarely consider the differences in the urolithin production. Therefore, the objective of this study is to establish human microbiota-associated (HMA) mice, imitating the microbiota composition of the three UMs. Antibiotic-induced pseudo germ-free mice were gavaged with fecal bacteria of the three UM donors for four weeks. The results showed that the ability to produce corresponding urolithins was successfully transferred from the donor of the three UMs to HMA mice. The three UM HMA mice adopted a humanized microbiota profile similar to their corresponding donor. The family Eggerthellaceae and genera Eggerthella and Gordonibacter were successfully transferred and colonized from UM-A/B donors to HMA mice. Overall, the three UM HMA mouse models were successfully established, which provide a basis for exploring the health effects of EA.

Targeted gut microbiota manipulation attenuates seizures in a model of infantile spasms syndrome

Infantile spasms syndrome (IS) is a devastating early-onset epileptic encephalopathy associated with poor neurodevelopmental outcomes. When first-line treatment options, including adrenocorticotropic hormone and vigabatrin, are ineffective, the ketogenic diet (KD) is often employed to control seizures. Since the therapeutic impact of the KD is influenced by the gut microbiota, we examined whether targeted microbiota manipulation, mimicking changes induced by the KD, would be valuable in mitigating seizures. Employing a rodent model of symptomatic IS, we show that both the KD and antibiotic administration reduce spasm frequency and are associated with improved developmental outcomes. Spasm reductions were accompanied by specific gut microbial alterations, including increases in Streptococcus thermophilus and Lactococcus lactis. Mimicking the fecal microbial alterations in a targeted probiotic, we administered these species in a 5:1 ratio. Targeted probiotic administration reduced seizures and improved locomotor activities in control diet–fed animals, similar to KD-fed animals, while a negative control (Ligilactobacillus salivarius) had no impact. Probiotic administration also increased antioxidant status and decreased proinflammatory cytokines. Results suggest that a targeted probiotic reduces seizure frequency, improves locomotor activity in a rodent model of IS, and provides insights into microbiota manipulation as a potential therapeutic avenue for pediatric epileptic encephalopathies.

Debugging the gut-brain axis in depression

In this issue of Cell Host & Microbe, Li et al. take a step toward a better understanding of the microbiome-gut-brain axis in mental health. They report gastrointestinal testosterone degradation by a specific bacterial strain as a potential mechanism impacting symptom expression in males with depression.

Evaluating live microbiota biobanking using an ex vivo microbiome assay and metaproteomics

Biobanking of live microbiota is becoming indispensable for mechanistic and clinical investigations of drug-microbiome interactions and fecal microbiota transplantation. However, there is a lack of methods to rapidly and systematically evaluate whether the biobanked microbiota maintains their cultivability and functional activity. In this study, we use a rapid ex vivo microbiome assay and metaproteomics to evaluate the cultivability and the functional responses of biobanked microbiota to treatment with a prebiotic (fructo-oligosaccharide, FOS). Our results indicate that the microbiota cultivability and their functional responses to FOS treatment were well maintained by freezing in a deoxygenated glycerol buffer at -80°C for 12 months. We also demonstrate that the fecal microbiota is functionally stable for 48 hours on ice in a deoxygenated glycerol buffer, allowing off-site fecal sample collection and shipping to laboratory for live microbiota biobanking. This study provides a method for rapid evaluation of the cultivability of biobanked live microbiota. Our results show minimal detrimental influences of long-term freezing in deoxygenated glycerol buffer on the cultivability of fecal microbiota.

Guidelines for reporting on animal fecal transplantation (GRAFT) studies: recommendations from a systematic review of murine transplantation protocols

Fecal microbiota transplant (FMT) is a powerful tool used to connect changes in gut microbial composition with a variety of disease states and pathologies. While FMT enables potential causal relationships to be identified, the experimental details reported in preclinical FMT protocols are highly inconsistent and/or incomplete. This limitation reflects a current lack of authoritative guidance on reporting standards that would facilitate replication efforts and ultimately reproducible science. We therefore systematically reviewed all FMT protocols used in mouse models with the goal of formulating recommendations on the reporting of preclinical FMT protocols. Search strategies were applied across three databases (PubMed, EMBASE, and Ovid Medline) until June 30, 2020. Data related to donor attributes, stool collection, processing/storage, recipient preparation, administration, and quality control were extracted. A total of 1753 papers were identified, with 241 identified for data extraction and analysis. Of the papers included, 92.5% reported a positive outcome with FMT intervention. However, the vast majority of studies failed to address core methodological aspects including the use of anaerobic conditions (91.7% of papers lacked information), storage (49.4%), homogenization (33.6%), concentration (31.5%), volume (19.9%) and administration route (5.3%). To address these reporting limitations, we developed theGuidelines for Reporting Animal Fecal Transplant (GRAFT) that guide reporting standards for preclinical FMT. The GRAFT recommendations will enable robust reporting of preclinical FMT design, and facilitate high-quality peer review, improving the rigor and translation of knowledge gained through preclinical FMT studies.

The Developing Microbiome From Birth to 3 Years: The Gut-Brain Axis and Neurodevelopmental Outcomes

The volume and breadth of research on the role of the microbiome in neurodevelopmental and neuropsychiatric disorders has expanded greatly over the last decade, opening doors to new models of mechanisms of the gut-brain axis and therapeutic interventions to reduce the burden of these outcomes. Studies have highlighted the window of birth to 3 years as an especially sensitive window when interventions may be the most effective. Harnessing the powerful gut-brain axis during this critical developmental window clarifies important investigations into the microbe-human connection and the developing brain, affording opportunities to prevent rather than treat neurodevelopmental disorders and neuropsychiatric illness. In this review, we present an overview of the developing intestinal microbiome in the critical window of birth to age 3; and its prospective relationship with neurodevelopment, with particular emphasis on immunological mechanisms. Next, the role of the microbiome in neurobehavioral outcomes (such as autism, anxiety, and attention-deficit hyperactivity disorder) as well as cognitive development are described. In these sections, we highlight the importance of pairing mechanistic studies in murine models with large scale epidemiological studies that aim to clarify the typical health promoting microbiome in early life across varied populations in comparison to dysbiosis. The microbiome is an important focus in human studies because it is so readily alterable with simple interventions, and we briefly outline what is known about microbiome targeted interventions in neurodevelopmental outcomes. More novel examinations of known environmental chemicals that adversely impact neurodevelopmental outcomes and the potential role of the microbiome as a mediator or modifier are discussed. Finally, we look to the future and emphasize the need for additional research to identify populations that are sensitive to alterations in their gut microbiome and clarify how interventions might correct and optimize neurodevelopmental outcomes.