Fecal Microbiota Transfer Attenuates Gut Dysbiosis and Functional Deficits After Traumatic Brain Injury

Bidirectional regulation of the brain-gut-microbiota axis following traumatic brain injury

JOURNAL/nrgr/04.03/01300535-202508000-00002/figure1/v/2024-09-30T120553Z/r/image-tiff Traumatic brain injury is a prevalent disorder of the central nervous system. In addition to primary brain parenchymal damage, the enduring biological consequences of traumatic brain injury pose long-term risks for patients with traumatic brain injury; however, the underlying pathogenesis remains unclear, and effective intervention methods are lacking. Intestinal dysfunction is a significant consequence of traumatic brain injury. Being the most densely innervated peripheral tissue in the body, the gut possesses multiple pathways for the establishment of a bidirectional "brain-gut axis" with the central nervous system. The gut harbors a vast microbial community, and alterations of the gut niche contribute to the progression of traumatic brain injury and its unfavorable prognosis through neuronal, hormonal, and immune pathways. A comprehensive understanding of microbiota-mediated peripheral neuroimmunomodulation mechanisms is needed to enhance treatment strategies for traumatic brain injury and its associated complications. We comprehensively reviewed alterations in the gut microecological environment following traumatic brain injury, with a specific focus on the complex biological processes of peripheral nerves, immunity, and microbes triggered by traumatic brain injury, encompassing autonomic dysfunction, neuroendocrine disturbances, peripheral immunosuppression, increased intestinal barrier permeability, compromised responses of sensory nerves to microorganisms, and potential effector nuclei in the central nervous system influenced by gut microbiota. Additionally, we reviewed the mechanisms underlying secondary biological injury and the dynamic pathological responses that occur following injury to enhance our current understanding of how peripheral pathways impact the outcome of patients with traumatic brain injury. This review aimed to propose a conceptual model for future risk assessment of central nervous system-related diseases while elucidating novel insights into the bidirectional effects of the "brain-gut-microbiota axis."

Gut-microbiota-brain Axis and post-traumatic epilepsy

There has been growing evidence that perturbations in gut-microbiota-brain axis (GMBA) are involved in mechanisms of chronic sequelae of traumatic brain injury (TBI). This review discusses the connection between GMBA and post-traumatic epilepsy (PTE), the latter being a common outcome of TBI. The focus is on two aspects of post-TBI GMBA dysfunction that are relevant to epilepsy. First are impairments in intestinal permeability with subsequent translocation of gut bacteria into the bloodstream. Specifically, endotoxemia following TBI may have a serendipitous protective effect against PTE through lipopolysaccharide conditioning, which may be leveraged for the development of therapeutic interventions. Second are changes in microbial composition (i.e., dysbiosis). Here, the GMBA-PTE connection is explored from predictive biomarker perspective, whereby the risk of PTE can be stratified based on specific microbial profiles. Finally, microbiota transplantation is discussed both as a tool to examine the role of gut microbiota in PTE and as a prelude to novel approaches for PTE therapy and prevention.

Short-chain fatty acids are a key mediator of gut microbial regulation of T cell trafficking and differentiation after traumatic brain injury

The gut microbiota has emerged as a pivotal regulator of host inflammatory processes after traumatic brain injury (TBI). However, the mechanisms by which the gut microbiota communicates to the brain in TBI are still under investigation. We previously reported that gut microbiota depletion (GMD) using antibiotics after TBI resulted in increased microglial activation, reduced neurogenesis, and reduced T cell infiltration. In the present study, we have demonstrated that intestinal T cells contribute to the pool of cells infiltrating the brain after TBI. Depletion or genetic deletion of T cells before injury reversed GMD induced reductions in post-TBI neurogenesis. Short-chain fatty acid supplementation increased T regulatory and T helper1 cell infiltration to the brain along with restoring neurogenesis and microglia activation after TBI with GMD. These data suggest that T cell subsets are essential cellular mediators by which the gut microbiota modulates TBI pathogenesis, a finding with important therapeutic implications.

Lactobacillus Helveticus Improves Controlled Cortical Impact Injury-Generated Neurological Aberrations by Remodeling of Gut-Brain Axis Mediators

Considerable studies augured the potential of gut microbiota-based interventions in brain injury-associated complications. Based on our earlier study results, we envisaged the sex-specific neuroprotective effect of Lactobacillus helveticus by remodeling of gut-brain axis. In this study, we investigated the effect of L. helveticus on neurological complications in a mouse model of controlled cortical impact (CCI). Adult, male and female, C57BL/6 mice underwent CCI surgery and received L. helveticus treatment for six weeks. Sensorimotor function was evaluated via neurological severity score and rotarod test. Long-term effects on anxiety-like behavior and cognition were assessed using the elevated-zero maze (EZM) and novel object recognition test (NORT). Brain perilesional area, blood, colon, and fecal samples were collected post-CCI for molecular biology analysis. CCI-operated mice displayed significant neurological impairments at 1-, 3-, 5-, and 7-days post-injury (dpi) and exhibited altered behavior in EZM and NORT compared to sham-operated mice. However, these behavioral changes were ameliorated in mice receiving L. helveticus. GFAP, Iba-1, TNF-α, and IL-1β expressions and corticotrophin-releasing hormone (CRH) levels were elevated in the perilesional cortex of CCI-operated male/female mice. These elevated biomarkers and decreased BDNF levels in both male/female mice were modified by L. helveticus treatment. Additionally, L. helveticus treatment restored altered short-chain fatty acids (SCFAs) levels in fecal samples and improved intestinal integrity but did not affect decreased plasma levels of progesterone and testosterone in CCI mice. These results indicate that L. helveticus exerts beneficial effects in the CCI mouse model by mitigating inflammation and remodeling of gut microbiota-brain mediators.

Gut microbiota metabolites: potential therapeutic targets for Alzheimer's disease?

Background

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive decline in cognitive function, which significantly increases pain and social burden. However, few therapeutic interventions are effective in preventing or mitigating the progression of AD. An increasing number of recent studies support the hypothesis that the gut microbiome and its metabolites may be associated with upstream regulators of AD pathology.

Methods

In this review, we comprehensively explore the potential mechanisms and currently available interventions targeting the microbiome for the improvement of AD. Our discussion is structured around modern research advancements in AD, the bidirectional communication between the gut and brain, the multi-target regulatory effects of microbial metabolites on AD, and therapeutic strategies aimed at modulating gut microbiota to manage AD.

Results

The gut microbiota plays a crucial role in the pathogenesis of AD through continuous bidirectional communication via the microbiota-gut-brain axis. Among these, microbial metabolites such as lipids, amino acids, bile acids and neurotransmitters, especially sphingolipids and phospholipids, may serve as central components of the gut-brain axis, regulating AD-related pathogenic mechanisms including β-amyloid metabolism, Tau protein phosphorylation, and neuroinflammation. Additionally, interventions such as probiotic administration, fecal microbiota transplantation, and antibiotic use have also provided evidence supporting the association between gut microbiota and AD. At the same time, we propose an innovative strategy for treating AD: a healthy lifestyle combined with targeted probiotics and other potential therapeutic interventions, aiming to restore intestinal ecology and microbiota balance.

Conclusion

Despite previous efforts, the molecular mechanisms by which gut microbes act on AD have yet to be fully described. However, intestinal microorganisms may become an essential target for connecting the gut-brain axis and improving the symptoms of AD. At the same time, it requires joint exploration by multiple centers and multiple disciplines.

Dysregulated brain-gut axis in the setting of traumatic brain injury: review of mechanisms and anti-inflammatory pharmacotherapies

Traumatic brain injury (TBI) is a chronic and debilitating disease, associated with a high risk of psychiatric and neurodegenerative diseases. Despite significant advancements in improving outcomes, the lack of effective treatments underscore the urgent need for innovative therapeutic strategies. The brain-gut axis has emerged as a crucial bidirectional pathway connecting the brain and the gastrointestinal (GI) system through an intricate network of neuronal, hormonal, and immunological pathways. Four main pathways are primarily implicated in this crosstalk, including the systemic immune system, autonomic and enteric nervous systems, neuroendocrine system, and microbiome. TBI induces profound changes in the gut, initiating an unrestrained vicious cycle that exacerbates brain injury through the brain-gut axis. Alterations in the gut include mucosal damage associated with the malabsorption of nutrients/electrolytes, disintegration of the intestinal barrier, increased infiltration of systemic immune cells, dysmotility, dysbiosis, enteroendocrine cell (EEC) dysfunction and disruption in the enteric nervous system (ENS) and autonomic nervous system (ANS). Collectively, these changes further contribute to brain neuroinflammation and neurodegeneration via the gut-brain axis. In this review article, we elucidate the roles of various anti-inflammatory pharmacotherapies capable of attenuating the dysregulated inflammatory response along the brain-gut axis in TBI. These agents include hormones such as serotonin, ghrelin, and progesterone, ANS regulators such as beta-blockers, lipid-lowering drugs like statins, and intestinal flora modulators such as probiotics and antibiotics. They attenuate neuroinflammation by targeting distinct inflammatory pathways in both the brain and the gut post-TBI. These therapeutic agents exhibit promising potential in mitigating inflammation along the brain-gut axis and enhancing neurocognitive outcomes for TBI patients.

Fecal microbiota transplantation unveils sex-specific differences in a controlled cortical impact injury mouse model

Introduction

Contusion type of traumatic brain injury (TBI) is a major cause of locomotor disability and mortality worldwide. While post-TBI deleterious consequences are influenced by gender and gut dysbiosis, the sex-specific importance of commensal gut microbiota is underexplored after TBI. In this study, we investigated the impact of controlled cortical impact (CCI) injury on gut microbiota signature in a sex-specific manner in mice.

Methods

We depleted the gut microflora of male and female C57BL/6 mice using antibiotic treatment. Thereafter, male mice were colonized by the gut microbiota of female mice and vice versa, employing the fecal microbiota transplantation (FMT) method. CCI surgery was executed using a stereotaxic impactor (Impact One™). For the 16S rRNA gene amplicon study, fecal boli of mice were collected at 3 days post-CCI (dpi).

Results and discussion

CCI-operated male and female mice exhibited a significant alteration in the genera of Akkermansia, Alistipes, Bacteroides, Clostridium, Lactobacillus, Prevotella, and Ruminococcus. At the species level, less abundance of Lactobacillus helveticus and Lactobacillus hamsteri was observed in female mice, implicating the importance of sex-specific bacteriotherapy in CCI-induced neurological deficits. FMT from female donor mice to male mice displayed an increase in genera of Alistipes, Lactobacillus, and Ruminococcus and species of Bacteroides acidifaciens and Ruminococcus gnavus. Female FMT-recipient mice from male donors showed an upsurge in the genus Lactobacillus and species of Lactobacillus helveticus, Lactobacillus hamsteri, and Prevotella copri. These results suggest that the post-CCI neurological complications may be influenced by the differential gut microbiota perturbation in male and female mice.

Fecal Microbiota Transplantation-Mediated Ghrelin Restoration Improves Neurological Functions After Traumatic Brain Injury: Evidence from 16S rRNA Sequencing and In Vivo Studies

This study aimed to investigate how gut microbiota dysbiosis impacts the repair of the blood-brain barrier and neurological deficits following traumatic brain injury (TBI). Through 16S rRNA sequencing analysis, we compared the gut microbiota of TBI rats and normal controls, discovering significant differences in abundance, species composition, and ecological function, potentially linked to Ghrelin-mediated brain-gut axis functionality. Further, in vivo experiments showed that fecal microbiota transplantation or Ghrelin injection could block the intracerebral TNF signaling pathway, enhance GLP-1 expression, significantly reduce brain edema post-TBI, promote the repair of the blood-brain barrier, and improve neurological deficits. However, the TNF signaling pathway activation could reverse these beneficial effects. In summary, our research suggests that by restoring the balance of gut microbiota, the levels of Ghrelin can be elevated, leading to the blockade of intracerebral TNF signaling pathway and enhanced GLP-1 expression, thereby mitigating post-TBI blood-brain barrier disruption and neurological injuries.

Emerging trends and focus of research on the relationship between traumatic brain injury and gut microbiota: a visualized study

Background

Traumatic brain injury (TBI) is one of the most serious types of trauma and imposes a heavy social and economic burden on healthcare systems worldwide. The development of emerging biotechnologies is uncovering the relationship between TBI and gut flora, and gut flora as a potential intervention target is of increasing interest to researchers. Nevertheless, there is a paucity of research employing bibliometric methodologies to scrutinize the interrelation between these two. Therefore, this study visualized the relationship between TBI and gut flora based on bibliometric methods to reveal research trends and hotspots in the field. The ultimate objective is to catalyze progress in the preclinical and clinical evolution of strategies for treating and managing TBI.

Methods

Terms related to TBI and gut microbiota were combined to search the Scopus database for relevant documents from inception to February 2023. Visual analysis was performed using CiteSpace and VOSviewer.

Results

From September 1972 to February 2023, 2,957 documents published from 98 countries or regions were analyzed. The number of published studies on the relationship between TBI and gut flora has risen exponentially, with the United States, China, and the United Kingdom being representative of countries publishing in related fields. Research has formed strong collaborations around highly productive authors, but there is a relative lack of international cooperation. Research in this area is mainly published in high-impact journals in the field of neurology. The "intestinal microbiota and its metabolites," "interventions," "mechanism of action" and "other diseases associated with traumatic brain injury" are the most promising and valuable research sites. Targeting the gut flora to elucidate the mechanisms for the development of the course of TBI and to develop precisely targeted interventions and clinical management of TBI comorbidities are of great significant research direction and of interest to researchers.

Conclusion

The findings suggest that close attention should be paid to the relationship between gut microbiota and TBI, especially the interaction, potential mechanisms, development of emerging interventions, and treatment of TBI comorbidities. Further investigation is needed to understand the causal relationship between gut flora and TBI and its specific mechanisms, especially the "brain-gut microbial axis."

Fecal microbial transplantation limits neural injury severity and functional deficits in a pediatric piglet traumatic brain injury model

Pediatric traumatic brain injury (TBI) is a leading cause of death and disability in children. Due to bidirectional communication between the brain and gut microbial population, introduction of key gut bacteria may mitigate critical TBI-induced secondary injury cascades, thus lessening neural damage and improving functional outcomes. The objective of this study was to determine the efficacy of a daily fecal microbial transplant (FMT) to alleviate neural injury severity, prevent gut dysbiosis, and improve functional recovery post TBI in a translational pediatric piglet model. Male piglets at 4-weeks of age were randomly assigned to Sham + saline, TBI + saline, or TBI + FMT treatment groups. A moderate/severe TBI was induced by controlled cortical impact and Sham pigs underwent craniectomy surgery only. FMT or saline were administered by oral gavage daily for 7 days. MRI was performed 1 day (1D) and 7 days (7D) post TBI. Fecal and cecal samples were collected for 16S rRNA gene sequencing. Ipsilateral brain and ileum tissue samples were collected for histological assessment. Gait and behavior testing were conducted at multiple timepoints. MRI showed that FMT treated animals demonstrated decreased lesion volume and hemorrhage volume at 7D post TBI as compared to 1D post TBI. Histological analysis revealed improved neuron and oligodendrocyte survival and restored ileum tissue morphology at 7D post TBI in FMT treated animals. Microbiome analysis indicated decreased dysbiosis in FMT treated animals with an increase in multiple probiotic Lactobacilli species, associated with anti-inflammatory therapeutic effects, in the cecum of the FMT treated animals, while non-treated TBI animals showed an increase in pathogenic bacteria, associated with inflammation and disease such in feces. FMT mediated enhanced cellular and tissue recovery resulted in improved motor function including stride and step length and voluntary motor activity in FMT treated animals. Here we report for the first time in a highly translatable pediatric piglet TBI model, the potential of FMT treatment to significantly limit cellular and tissue damage leading to improved functional outcomes following a TBI.

The Intestinal Microbiome after Traumatic Injury

The intestinal microbiome plays a critical role in host immune function and homeostasis. Patients suffering from-as well as models representing-multiple traumatic injuries, isolated organ system trauma, and various severities of traumatic injury have been studied as an area of interest in the dysregulation of immune function and systemic inflammation which occur after trauma. These studies also demonstrate changes in gut microbiome diversity and even microbial composition, with a transition to a pathobiome state. In addition, sex has been identified as a biological variable influencing alterations in the microbiome after trauma. Therapeutics such as fecal transplantation have been utilized to ameliorate not only these microbiome changes but may also play a role in recovery postinjury. This review summarizes the alterations in the gut microbiome that occur postinjury, either in isolated injury or multiple injuries, along with proposed mechanisms for these changes and future directions for the field.

Association of sub-acute changes in plasma amino acid levels with long-term brain pathologies in a rat model of moderate-severe traumatic brain injury

Introduction

Traumatic brain injury (TBI) induces a cascade of cellular alterations that are responsible for evolving secondary brain injuries. Changes in brain structure and function after TBI may occur in concert with dysbiosis and altered amino acid fermentation in the gut. Therefore, we hypothesized that subacute plasma amino acid levels could predict long-term microstructural outcomes as quantified using neurite orientation dispersion and density imaging (NODDI).

Methods

Fourteen 8-10-week-old male rats were randomly assigned either to sham (n = 6) or a single moderate-severe TBI (n = 8) procedure targeting the primary somatosensory cortex. Venous blood samples were collected at days one, three, seven, and 60 post-procedure and NODDI imaging were carried out at day 60. Principal Component Regression analysis was used to identify time dependent plasma amino acid concentrations after in the subacute phase post-injury that predicted NODDI metric outcomes at day 60.

Results

The TBI group had significantly increased plasma levels of glutamine, arginine, alanine, proline, tyrosine, valine, isoleucine, leucine, and phenylalanine at days three-seven post-injury. Higher levels of several neuroprotective amino acids, especially the branched-chain amino acids (valine, isoleucine, leucine) and phenylalanine, as well as serine, arginine, and asparagine at days three-seven post-injury were also associated with lower isotropic diffusion volume fraction measures in the ventricles and thus lesser ventricular dilation at day 60.

Discussion

In the first such study, we examined the relationship between the long-term post-TBI microstructural outcomes across whole brain and the subacute changes in plasma amino acid concentrations. At days three to seven post-injury, we observed that increased plasma levels of several amino acids, particularly the branched-chain amino acids and phenylalanine, were associated with lesser degrees of ventriculomegaly and hydrocephalus TBI neuropathology at day 60 post-injury. The results imply that altered amino acid fermentation in the gut may mediate neuroprotection in the aftermath of TBI.

Multicompartmental traumatic injury and the microbiome: Shift to a pathobiome

BACKGROUND

Previous animal models have demonstrated altered gut microbiome after mild traumatic injury; however, the impact of injury severity and critical illness is unknown. We hypothesized that a rodent model of severe multicompartmental injuries and chronic stress would demonstrate microbiome alterations toward a "pathobiome" characterized by an overabundance of pathogenic organisms, which would persist 1 week after injury.

METHODS

Male Sprague-Dawley rats (n = 8 per group) were subjected to either multiple injuries (PT) (lung contusion, hemorrhagic shock, cecectomy, and bifemoral pseudofractures), PT plus daily chronic restraint stress for 2 hours (PT/CS), or naive controls. Fecal microbiome was measured on days 0, 3, and 7 using high-throughput 16S rRNA sequencing and Quantitative Insights Into Microbial Ecology 2 bioinformatics analysis. Microbial α diversity was assessed using Chao1 and Shannon indices, and β diversity with principle coordinate analysis. Intestinal permeability was evaluated by plasma occludin; ileum and descending colon tissues were reviewed for injury. Analyses were performed in GraphPad (GraphPad Software, La Jolla, CA) and R (R Foundation for Statistical Computing, Vienna, Austria), with significance defined as p < 0.05.

RESULTS

There were significant alterations in β diversity at day 3 and between all groups. By day 3, both PT and PT/CS demonstrated significantly depleted bacterial diversity (Chao1) ( p = 0.01 and p = 0.001, respectively) versus naive, which persisted up to day 7 in PT/CS only ( p = 0.001). Anaerostipes and Rothia dominated PT and Lactobacillus bloomed in PT/CS cohorts by day 7. Plasma occludin was significantly elevated in PT/CS compared with naive ( p = 0.04), and descending colon of both PT and PT/CS showed significantly higher injury compared with naive ( p = 0.005, p = 0.006).

CONCLUSIONS

Multiple injuries with and without chronic stress induces significant alterations in microbiome diversity and composition within 3 days; these changes are more prominent and persist for 1 week postinjury with stress. This rapid and persistent transition to a "pathobiome" phenotype represents a critical phenomenon that may influence outcomes after severe trauma and critical illness.

Gut microbiome and neurosurgery: Implications for treatment

Introduction

The aim of this review is to summarize the current understanding of the gut-brain axis (GBA), its impact on neurosurgery, and its implications for future treatment.

Background

An abundance of research has established the existence of a collection of pathways between the gut microbiome and the central nervous system (CNS), commonly known as the GBA. Complicating this relationship, the gut microbiome bacterial diversity appears to change with age, antibiotic exposure and a number of external and internal factors.

Methods

In this paper, we present the current understanding of the key protective and deleterious roles the gut microbiome plays in the pathogenesis of several common neurosurgical concerns.

Results

Specifically, we examine how spinal cord injury, traumatic brain injury and stroke may cause gut microbial dysbiosis. Furthermore, this link appears to be bidirectional as gut dysbiosis contributes to secondary CNS injury in each of these ailment settings. This toxic cycle may be broken, and the future secondary damage rescued by timely, therapeutic, gut microbiome modification. In addition, a robust gut microbiome appears to improve outcomes in brain tumour treatment. There are several primary routes by which microbiome dysbiosis may be ameliorated, including faecal microbiota transplant, oral probiotics, bacteriophages, genetic modification of gut microbiota and vagus nerve stimulation.

Conclusion

The GBA represents an important component of patient care in the field of neurosurgery. Future research may illuminate ideal methods of therapeutic microbiome modulation in distinct pathogenic settings.

POSTINJURY FECAL MICROBIOME TRANSPLANT DECREASES LESION SIZE AND NEUROINFLAMMATION IN TRAUMATIC BRAIN INJURY

ABSTRACT

Background: Traumatic brain injury (TBI) is an underrecognized public health threat. The constitutive activation of microglia after TBI has been linked to long-term neurocognitive deficits and the progression of neurodegenerative disease. Evolving evidence indicates a critical role for the gut-brain axis in this process. Specifically, TBI has been shown to induce the depletion of commensal gut bacteria. The resulting gut dysbiosis is associated with neuroinflammation and disease. Hypothesis: We hypothesized that fecal microbiota transplantation would attenuate microglial activation and improve neuropathology after TBI. Methods: C57Bl/6 mice were subjected to severe TBI (n = 10) or sham injury (n = 10) via an open-head controlled cortical impact. The mice underwent fecal microbiota transplantation (FMT) or vehicle alone via oral gavage once weekly for 4 weeks after injury. At 59 days after TBI, mice underwent three-dimensional, contrast-enhanced magnetic resonance imaging. Following imaging, mice were killed, brains harvested at 60 DPI, and CD45+ cells isolated via florescence-activated cell sorting. cDNA libraries were prepared using the 10x Genomics Chromium Single Cell 3' Reagent kit followed by sequencing on a HiSeq4000 instrument, and computational analysis was performed. Results: Fecal microbiota transplantation resulted in a >marked reduction of ventriculomegaly (P < 0.002) and preservation of white matter connectivity at 59 days after TBI (P < 0.0001). In addition, microglia from FMT-treated mice significantly reduced inflammatory gene expression and enriched pathways involving the heat-shock response compared with mice treated with vehicle alone. Conclusions: We hypothesized that restoring gut microbial community structure via FMT would attenuate microglial activation and reduce neuropathology after TBI. Our data demonstrated significant preservation of cortical volume and white matter connectivity after an injury compared with mice treated with vehicle alone. This preservation of neuroanatomy after TBI was associated with a marked reduction in inflammatory gene expression within the microglia of FMT-treated mice. Microglia from FMT-treated mice enriched pathways in the heat-shock response, which is known to play a neuroprotective role in TBI and other neurodegenerative disease processes.