Moderate Traumatic Brain Injury Alters the Gastrointestinal Microbiome in a Time-Dependent Manner

Air-Evacuation-Relevant Hypobaria Following Traumatic Brain Injury Plus Hemorrhagic Shock in Rats Increases Mortality and Injury to the Gut, Lungs, and Kidneys

ABSTRACT

Rats exposed to hypobaria equivalent to what occurs during aeromedical evacuation within a few days after isolated traumatic brain injury exhibit greater neurologic injury than those remaining at sea level. Moreover, administration of excessive supplemental O2 during hypobaria further exacerbates brain injury. This study tested the hypothesis that exposure of rats to hypobaria following controlled cortical impact (CCI)-induced brain injury plus mild hemorrhagic shock worsens multiple organ inflammation and associated mortality. In this study, at 24 h after CCI plus hemorrhagic shock, rats were exposed to either normobaria (sea level) or hypobaria (=8,000 ft altitude) for 6 h under normoxic or hyperoxic conditions. Injured rats exhibited mortality ranging from 30% for those maintained under normobaria and normoxia to 60% for those exposed to 6 h under hypobaric and hyperoxia. Lung histopathology and neutrophil infiltration at 2 days postinjury were exacerbated by hypobaria and hyperoxia. Gut and kidney inflammation at 30 days postinjury were also worsened by hypobaric hyperoxia. In conclusion, exposure of rats after brain injury and hemorrhagic shock to hypobaria or hyperoxia results in increased mortality. Based on gut, lung, and kidney histopathology at 2 to 30 days postinjury, increased mortality is consistent with multi-organ inflammation. These findings support epidemiological studies indicating that increasing aircraft cabin pressures to 4,000 ft altitude (compared with standard 8,000 ft) and limiting excessive oxygen administration will decrease critical complications during and following aeromedical transport.

Clinical effects of Lactobacillus acidophilus combined with mosapride in treatment of gastrointestinal dysfunction after craniocerebral injury

BACKGROUND

Most patients with severe craniocerebral injury have gastrointestinal motility deficiency. When the body is exposed to external mechanical trauma, infection, vomiting, and gastric content reflux tend to occur, which causes early gastrointestinal dysfunction, affects nutrient intake, aggravates brain edema, delays wound healing, and is not conducive to the prognosis of patients. Mosapride is a commonly used gastrointestinal motility agent, which can improve gastrointestinal motility and speed up gastric emptying. Lactobacillus acidophilus can regulate the intestinal flora, protect the intestinal mucosal barrier, maintain intestinal balance, and relieve gastric motility. The purpose of this study was to investigate the effects of Lactobacillus acidophilus combined with mosapride treatment on the time to reach enteral nutrition standards, intestinal flora, rehabilitation process, and other aspects of patients with gastrointestinal dysfunction after craniocerebral injury, and to evaluate its clinical effects.

AIM

To observe the clinical effects of Lactobacillus acidophilus combined with mosapride in the treatment of gastrointestinal dysfunction after craniocerebral injury.

METHODS

A total of 92 patients with gastrointestinal dysfunction after craniocerebral injury at our hospital from February 2018 to February 2021 were selected and divided into a study group and a control group at a ratio of 1:1 using a random number table, with 46 cases in each group. On the basis of conventional treatment, the control group was given mosapride, and the study group was given Lactobacillus acidophilus combined with mosapride for 1 wk. The clinical efficacy, time to reach enteral nutrition standards, recovery progress, 28-d mortality rate, gastric motility indexes [intra-abdominal pressure (IAP) and residual gastric volume (GRA)], and intestinal motility before treatment and after 3 d and 1 wk of treatment were compared between the two groups. Intestinal barrier function indexes [D-lactic acid (D-LA) and diamine oxidase (DAO)] and intestinal flora (Bifidobacterium, Lactobacillus, Enterococcus, and Enterobacter) were also compared.

RESULTS

The total effective rate of the study group was higher than that of the control group (93.48% vs 78.26%, P < 0.05). The time to reach enteral nutrition standards, time to mechanical ventilation, and the length of ICU stay in the study group were shorter than those of the control group (P < 0.05). There was no significant difference in the 28-d mortality rate between the two groups (P > 0.05). The APACHE II and SOFA scores of the study group were lower than those of the control group after 3 d and 1 wk of treatment, and the Glasgow Coma scale scores were higher than those of the control group (P < 0.05). The levels of IAP, GRA, D-LA, and DAO in the study group were lower than those of the control group after 3 d and 1 wk of treatment (P < 0.05). The numbers of Bifidobacterium and Lactobacillus in the study group were more than those of the control group after 3 d and 1 wk of treatment, and the numbers of Enterococcus and Enterobacter were less than those of the control group (P < 0.05).

CONCLUSION

Lactobacillus acidophilus and mosapride are effective in treating gastrointestinal dysfunction after craniocerebral injury. They can shorten the time to reach enteral nutrition standards, adjust the intestinal flora, protect the intestinal mucosal barrier, promote the recovery of the gastrointestinal tract and nerve function, and accelerate the recovery process of patients.

Sustained Dysbiosis and Decreased Fecal Short-Chain Fatty Acids after Traumatic Brain Injury and Impact on Neurologic Outcome

Traumatic brain injury (TBI) alters microbial populations present in the gut, which may impact healing and tissue recovery. However, the duration and impact of these changes on outcome from TBI are unknown. Short-chain fatty acids (SCFAs), produced by bacterial fermentation of dietary fiber, are important signaling molecules in the microbiota gut-brain axis. We hypothesized that TBI would lead to a sustained reduction in SCFA producing bacteria, fecal SCFAs concentration, and administration of soluble SCFAs would improve functional outcome after TBI. Adult mice (n = 10) had the controlled cortical impact (CCI) model of TBI performed (6 m/sec, 2-mm depth, 50-msec dwell). Stool samples were collected serially until 28 days after CCI and analyzed for SCFA concentration by high-performance liquid chromatography-mass spectrometry/mass spectrometry and microbiome analyzed by 16S gene sequencing. In a separate experiment, mice (n = 10/group) were randomized 2 weeks before CCI to standard drinking water or water supplemented with the SCFAs acetate (67.5 mM), propionate (25.9 mM), and butyrate (40 mM). Morris water maze performance was assessed on post-injury Days 14-19. Alpha diversity remained stable until 72 h, at which point a decline in diversity was observed without recovery out to 28 days. The taxonomic composition of post-TBI fecal samples demonstrated depletion of bacteria from Lachnospiraceae, Ruminococcaceae, and Bacteroidaceae families, and enrichment of bacteria from the Verrucomicrobiaceae family. Analysis from paired fecal samples revealed a reduction in total SCFAs at 24 h and 28 days after TBI. Acetate, the most abundant SCFA detected in the fecal samples, was reduced at 7 days and 28 days after TBI. SCFA administration improved spatial learning after TBI versus standard drinking water. In conclusion, TBI is associated with reduced richness and diversity of commensal microbiota in the gut and a reduction in SCFAs detected in stool. Supplementation of soluble SCFAs improves spatial learning after TBI.

Multiorgan Dysfunction After Severe Traumatic Brain Injury: Epidemiology, Mechanisms, and Clinical Management

Traumatic brain injury (TBI) is a major global health problem and a major contributor to morbidity and mortality following multisystem trauma. Extracranial organ dysfunction is common after severe TBI and significantly impacts clinical care and outcomes following injury. Despite this, extracranial organ dysfunction remains an understudied topic compared with organ dysfunction in other critical care paradigms. In this review, we will: 1) summarize the epidemiology of extracranial multiorgan dysfunction following severe TBI; 2) examine relevant mechanisms that may be involved in the development of multi-organ dysfunction following severe TBI; and 3) discuss clinical management strategies to care for these complex patients.

Beyond the Brain: Peripheral Interactions after Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of death and disability, and there are currently no pharmacological treatments known to improve patient outcomes. Unquestionably, contributing toward a lack of effective treatments is the highly complex and heterogenous nature of TBI. In this review, we highlight the recent surge of research that has demonstrated various central interactions with the periphery as a potential major contributor toward this heterogeneity and, in particular, the breadth of research from Australia. We describe the growing evidence of how extracranial factors, such as polytrauma and infection, can significantly alter TBI neuropathology. In addition, we highlight how dysregulation of the autonomic nervous system and the systemic inflammatory response induced by TBI can have profound pathophysiological effects on peripheral organs, such as the heart, lung, gastrointestinal tract, liver, kidney, spleen, and bone. Collectively, this review firmly establishes TBI as a systemic condition. Further, the central and peripheral interactions that can occur after TBI must be further explored and accounted for in the ongoing search for effective treatments.

Specific Pathogen-Free Animals for Civilian and Military Trauma: a Cautionary Note in the Translation of New Drug Therapies

Specific-pathogen free (SPF) animals were introduced into biomedical research in the early 1960s to reduce the incidence of disease into experimental design. The goal was to provide animals with selected microbiota compatible with sustained health. Sixty years later, SPF status has become a variable itself in biomedical research. Alterations in the gut microbiome-host relationship can profoundly influence basic physiology, immune/inflammatory function, susceptibility to infection and disease, and behavior. In addition, it can influence the translational success of a drug or technology from animal models to humans. We discuss this aspect of SPF status in animal models used for military or civilian trauma and shock research. Currently, there is a broad spectrum of SPF exclusion and inclusion criteria which vary from one supplier or animal husbandry facility. If translation to humans is the end-game of trauma research, we recommend replicating a gut microbiome similar to the wild-type for optimal success. We further suggest that at the end of each publication a URL access be provided on Animal Microbial/Pathogen Exclusion Status that a study was based upon. This may help address the differences in results within a single laboratory or between laboratories around the world and improve translation success.

Brain-gut axis dysfunction in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) is a chronic and progressive disease, and management requires an understanding of both the primary neurological injury and the secondary sequelae that affect peripheral organs, including the gastrointestinal (GI) tract. The brain-gut axis is composed of bidirectional pathways through which TBI-induced neuroinflammation and neurodegeneration impact gut function. The resulting TBI-induced dysautonomia and systemic inflammation contribute to the secondary GI events, including dysmotility and increased mucosal permeability. These effects shape, and are shaped by, changes in microbiota composition and activation of resident and recruited immune cells. Microbial products and immune cell mediators in turn modulate brain-gut activity. Importantly, secondary enteric inflammatory challenges prolong systemic inflammation and worsen TBI-induced neuropathology and neurobehavioral deficits. The importance of brain-gut communication in maintaining GI homeostasis highlights it as a viable therapeutic target for TBI. Currently, treatments directed toward dysautonomia, dysbiosis, and/or systemic inflammation offer the most promise.

Challenges and opportunities for neuroimaging in young patients with traumatic brain injury: a coordinated effort towards advancing discovery from the ENIGMA pediatric moderate/severe TBI group

Traumatic brain injury (TBI) is a major cause of death and disability in children in both developed and developing nations. Children and adolescents suffer from TBI at a higher rate than the general population, and specific developmental issues require a unique context since findings from adult research do not necessarily directly translate to children. Findings in pediatric cohorts tend to lag behind those in adult samples. This may be due, in part, both to the smaller number of investigators engaged in research with this population and may also be related to changes in safety laws and clinical practice that have altered length of hospital stays, treatment, and access to this population. The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Pediatric Moderate/Severe TBI (msTBI) group aims to advance research in this area through global collaborative meta-analysis of neuroimaging data. In this paper, we discuss important challenges in pediatric TBI research and opportunities that we believe the ENIGMA Pediatric msTBI group can provide to address them. With the paucity of research studies examining neuroimaging biomarkers in pediatric patients with TBI and the challenges of recruiting large numbers of participants, collaborating to improve statistical power and to address technical challenges like lesions will significantly advance the field. We conclude with recommendations for future research in this field of study.

Nutrition in the Neurocritical Care Unit: a New Frontier

PURPOSE OF REVIEW

This review presents the most current recommendations for providing nutrition to the neurocritical care population. This includes updates on initiation of feeding, immunonutrition, and metabolic substrates including ketogenic diet, cerebral microdialysis (CMD) monitoring, and the microbiome.

RECENT FINDINGS

Little evidence exists to support differences in feeding practices among the neurocritical care population. New areas of interest with limited data include use of immunonutrition, pre/probiotics for microbiome manipulation, ketogenic diet, and use of CMD catheters for substrate utilization monitoring.

SUMMARY

Acute neurologic injury incites a cascade of adrenergic and neuroendocrine events resulting in a pro-inflammatory and hypercatabolic state, which is associated with an increase in morbidity and mortality. Nutritional support provides substrates to mitigate the damaging effects of hypermetabolism. Despite this practice, studies on feeding delivery outcomes remain inconsistent. Guidelines suggest use of early enteral nutrition using standard polymeric formulas. Population heterogeneity, variability in interventions, complexities of the metabolic and inflammatory responses, and paucity of nutrition research in patients requiring neurocritical care have led to controversies in the field. It is imperative that more pragmatic and reproducible research be conducted to better understand underlying pathophysiology and develop interventions that may improve outcomes.

Rebuilding Microbiome for Mitigating Traumatic Brain Injury: Importance of Restructuring the Gut-Microbiome-Brain Axis

Traumatic brain injury (TBI) is a damage to the brain from an external force that results in temporary or permanent impairment in brain functions. Unfortunately, not many treatment options are available to TBI patients. Therefore, knowledge of the complex interplay between gut microbiome (GM) and brain health may shed novel insights as it is a rapidly expanding field of research around the world. Recent studies show that GM plays important roles in shaping neurogenerative processes such as blood-brain-barrier (BBB), myelination, neurogenesis, and microglial maturation. In addition, GM is also known to modulate many aspects of neurological behavior and cognition; however, not much is known about the role of GM in brain injuries. Since GM has been shown to improve cellular and molecular functions via mitigating TBI-induced pathologies such as BBB permeability, neuroinflammation, astroglia activation, and mitochondrial dysfunction, herein we discuss how a dysbiotic gut environment, which in fact, contributes to central nervous system (CNS) disorders during brain injury and how to potentially ward off these harmful effects. We further opine that a better understanding of GM-brain (GMB) axis could help assist in designing better treatment and management strategies in future for the patients who are faced with limited options.

The association of traumatic brain injury, gut microbiota and the corresponding metabolites in mice

BACKGROUND

Traumatic Brain Injury (TBI) present a significant burden to global health. Close association and mutual regulation exist between the brain and gut microbiota. In addition, metabolites may play an important role as intermediary mediators of the brain and gut microbiota. Consequently, the study sought to investigate the alterations in gut microbiota and metabolites after TBI and conducted a comprehensive analysis of the correlation between gut microbiota and metabolites after TBI in mice.

METHODS

Changes in intestinal microbiota and metabolites in mice after moderate or severe traumatic brain injury were detected through 16S rDNA sequencing and the non-target LC-MS technology. Additionally, Pearson correlation analysis was used to explore the association between the microbiota and metabolites.

RESULTS

TBI was able to change the composition of intestinal microbiota, resulting to a decrease in microbial diversity in the intestinal tract (sham vs sTBI: 8.35 ± 0.12 vs 7.71 ± 0.5, p < 0.01; sTBI vs mTBI: 7.71 ± 0.5 vs 8.25 ± 0.34, p < 0.05). The results also showed that TBI could change the types and abundance of metabolites (723 in mTBI and sham groups; 1221 in sTBI and sham groups; 324 in mTBI and sTBI groups). Moreover, some of the altered gut metabolites were significantly correlated with part of the altered gut microbes after TBI.

CONCLUSIONS

TBI significantly changed intestinal microbiota as well as metabolites. Some of the altered microbiota and metabolites had a significant association. The results from this study provide information that paves way for future studies utilizing the brain gut axis theory in the diagnosis and treatment of TBI.

Fecal Microbiota Transplantation Is a Promising Method to Restore Gut Microbiota Dysbiosis and Relieve Neurological Deficits after Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) can induce persistent fluctuation in the gut microbiota makeup and abundance. The present study is aimed at determining whether fecal microbiota transplantation (FMT) can rescue microbiota changes and ameliorate neurological deficits after TBI in rats.

METHODS

A controlled cortical impact (CCI) model was used to simulate TBI in male Sprague-Dawley rats, and FMT was performed for 7 consecutive days. 16S ribosomal RNA (rRNA) sequencing of fecal samples was performed to analyze the effects of FMT on gut microbiota. Modified neurological severity score and Morris water maze were used to evaluate neurobehavioral functions. Metabolomics was used to screen differential metabolites from the rat serum and ipsilateral brains. The oxidative stress indices were measured in the brain.

RESULTS

TBI induced significance changes in the gut microbiome, including the alpha- and beta-bacterial diversity, as well as the microbiome composition at 8 days after TBI. On the other hand, FMT could rescue these changes and relieve neurological deficits after TBI. Metabolomics results showed that the level of trimethylamine (TMA) in feces and the level of trimethylamine N-oxide (TMAO) in the ipsilateral brain and serum was increased after TBI, while FMT decreased TMA levels in the feces, and TMAO levels in the ipsilateral brain and serum. Antioxidant enzyme methionine sulfoxide reductase A (MsrA) in the ipsilateral hippocampus was decreased after TBI but increased after FMT. In addition, FMT elevated SOD and CAT activities and GSH/GSSG ratio and diminished ROS, GSSG, and MDA levels in the ipsilateral hippocampus after TBI.

CONCLUSIONS

FMT can restore gut microbiota dysbiosis and relieve neurological deficits possibly through the TMA-TMAO-MsrA signaling pathway after TBI.

Bidirectional Brain-Systemic Interactions and Outcomes After TBI

Traumatic brain injury (TBI) is a debilitating disorder associated with chronic progressive neurodegeneration and long-term neurological decline. Importantly, there is now substantial and increasing evidence that TBI can negatively impact systemic organs, including the pulmonary, gastrointestinal (GI), cardiovascular, renal, and immune system. Less well appreciated, until recently, is that such functional changes can affect both the response to subsequent insults or diseases, as well as contribute to chronic neurodegenerative processes and long-term neurological outcomes. In this review, we summarize evidence showing bidirectional interactions between the brain and systemic organs following TBI and critically assess potential underlying mechanisms.

Altered physiology of gastrointestinal vagal afferents following neurotrauma

The adaptability of the central nervous system has been revealed in several model systems. Of particular interest to central nervous system-injured individuals is the ability for neural components to be modified for regain of function. In both types of neurotrauma, traumatic brain injury and spinal cord injury, the primary parasympathetic control to the gastrointestinal tract, the vagus nerve, remains anatomically intact. However, individuals with traumatic brain injury or spinal cord injury are highly susceptible to gastrointestinal dysfunctions. Such gastrointestinal dysfunctions attribute to higher morbidity and mortality following traumatic brain injury and spinal cord injury. While the vagal efferent output remains capable of eliciting motor responses following injury, evidence suggests impairment of the vagal afferents. Since sensory input drives motor output, this review will discuss the normal and altered anatomy and physiology of the gastrointestinal vagal afferents to better understand the contributions of vagal afferent plasticity following neurotrauma.

Dynamic Changes in the Gut Microbiome at the Acute Stage of Ischemic Stroke in a Pig Model

Stroke is a major cause of death and long-term disability affecting seven million adults in the United States each year. Recently, it has been demonstrated that neurological diseases, associated pathology, and susceptibility changes correlated with changes in the gut microbiota. However, changes in the microbial community in stroke has not been well characterized. The acute stage of stroke is a critical period for assessing injury severity, therapeutic intervention, and clinical prognosis. We investigated the changes in the gut microbiota composition and diversity using a middle cerebral artery (MCA) occlusion ischemic stroke pig model. Ischemic stroke was induced by cauterization of the MCA in pigs. Blood samples were collected prestroke and 4 h, 12 h, 1 day, and 5 days poststroke to evaluate circulating proinflammatory cytokines. Fecal samples were collected prestroke and 1, 3, and 5 days poststroke to assess gut microbiome changes. Results showed elevated systemic inflammation with increased plasma levels of tumor necrosis factor alpha at 4 h and interleukin-6 at 12 h poststroke, relative to prestroke. Microbial diversity and evenness were reduced at 1 day poststroke compared to prestroke. Microbial diversity at 3 days poststroke was negatively correlated with lesion volume. Moreover, beta-diversity analysis revealed trending overall differences over time, with the most significant changes in microbial patterns observed between prestroke and 3 days poststroke. Abundance of the Proteobacteria was significantly increased, while Firmicutes decreased at 3 days poststroke, compared to prestroke populations. Abundance of the lactic acid bacteria Lactobacillus was reduced at 3 days poststroke. By day 5, the microbial pattern returned to similar values as prestroke, suggesting the plasticity of gut microbiome in an acute period of stroke in a pig model. These findings provide a basis for characterizing gut microbial changes during the acute stage of stroke, which can be used to assess stroke pathology and the potential development of therapeutic targets.

Evaluation of an Immunomodulatory Probiotic Intervention for Veterans With Co-occurring Mild Traumatic Brain Injury and Posttraumatic Stress Disorder: A Pilot Study

Background: US military Veterans returned from Operation Enduring Freedom/Operation Iraqi Freedom/Operation New Dawn (OEF/OIF/OND) with symptoms associated with mild traumatic brain injury [mTBI; i.e., persistent post-concussive (PPC) symptoms] and posttraumatic stress disorder (PTSD). Interventions aimed at addressing symptoms associated with both physical and psychological stressors (e.g., PPC and PTSD symptoms) are needed. This study was conducted to assess the feasibility, acceptability, and safety of a probiotic intervention, as well as to begin the process of evaluating potential biological outcomes.

Methods: A pilot randomized controlled trial was implemented among US military Veterans from recent conflicts in Iraq and Afghanistan. Those enrolled had clinically significant PPC and PTSD symptoms. Participants were randomized to intervention (Lactobacillus reuteri DSM 17938) or placebo supplementation (daily for 8 weeks +/- 2 weeks) at a 1:1 ratio, stratified by irritable bowel syndrome status. Thirty-one Veterans were enrolled and randomized (15 to the placebo condition and 16 to the probiotic condition).

Results: Thresholds for feasibility, acceptability, and safety were met. Probiotic supplementation resulted in a decrease in plasma C-reactive protein (CRP) concentrations relative to the placebo group that approached statistical significance (p = 0.056). Although during the Trier Social Stress Test (TSST; administered post-supplementation) no between-group differences were found on a subjective measure of stress responsivity (Visual Analog Scale), there was a significantly larger increase in mean heart beats per minute between baseline and the math task for the placebo group as compared with the probiotic group (estimated mean change, probiotic 5.3 [95% Confidence Interval: −0.55, 11.0], placebo 16.9 [11.0, 22.7], p = 0.006).

Conclusions: Findings from this trial support the feasibility, acceptability, and safety of supplementation with an anti-inflammatory/immunoregulatory probiotic, L. reuteri DSM 17938, among Veterans with PPC and PTSD symptoms. Moreover, results suggest that CRP may be a viable inflammatory marker of interest. A larger randomized controlled trial aimed at measuring both biological and clinical outcomes is indicated.

Clinical Trial Registration:ClinicalTrials.gov, Identifier NCT02723344.

Alterations of the GH/IGF-I Axis and Gut Microbiome after Traumatic Brain Injury: A New Clinical Syndrome?

CONTEXT

Pituitary dysfunction with abnormal growth hormone (GH) secretion and neurocognitive deficits are common consequences of traumatic brain injury (TBI). Recognizing the comorbidity of these symptoms is of clinical importance; however, efficacious treatment is currently lacking.

EVIDENCE ACQUISITION

A review of studies in PubMed published between January 1980 to March 2020 and ongoing clinical trials was conducted using the search terms "growth hormone," "traumatic brain injury," and "gut microbiome."

EVIDENCE SYNTHESIS

Increasing evidence has implicated the effects of TBI in promoting an interplay of ischemia, cytotoxicity, and inflammation that renders a subset of patients to develop postinjury hypopituitarism, severe fatigue, and impaired cognition and behavioral processes. Recent data have suggested an association between abnormal GH secretion and altered gut microbiome in TBI patients, thus prompting the description of a hypothesized new clinical syndrome called "brain injury associated fatigue and altered cognition." Notably, these patients demonstrate distinct characteristics from those with GH deficiency from other non-TBI causes in that their symptom complex improves significantly with recombinant human GH treatment, but does not reverse the underlying mechanistic cause as symptoms typically recur upon treatment cessation.

CONCLUSION

The reviewed data describe the importance of alterations of the GH/insulin-like growth factor I axis and gut microbiome after brain injury and its influence in promoting neurocognitive and behavioral deficits in a bidirectional relationship, and highlight a new clinical syndrome that may exist in a subset of TBI patients in whom recombinant human GH therapy could significantly improve symptomatology. More studies are needed to further characterize this clinical syndrome.

Microbial Diversity and Community Structures Among Those With Moderate to Severe TBI: A United States-Veteran Microbiome Project Study

OBJECTIVE

To evaluate the association between distal moderate/severe traumatic brain injury (TBI) history and the human gut microbiome.

SETTING

Veterans Affairs Medical Center.

PARTICIPANTS

Veterans from the United States-Veteran Microbiome Project (US-VMP). Veterans with moderate/severe TBI (n = 34) were compared with (1) Veterans with a history of no TBI (n = 79) and (2) Veterans with a history of no TBI or mild TBI only (n = 297).

DESIGN

Microbiome analyses from 16S rRNA gene sequencing with gut microbiota function inferred using PICRUSt2.

MAIN MEASURES

α-Diversity and β-diversity of the gut microbiome, as well as taxonomic and functional signatures associated with moderate/severe TBI.

RESULTS

There were no significant differences in gut bacterial α- and β-diversity associated with moderate/severe TBI status. No differentially abundant taxa were identified when comparing samples from moderate/severe TBI to those with no TBI or no TBI/mild TBI.

CONCLUSION

Results suggest that moderate/severe TBI-related changes to the gut microbiome do not persist for years postinjury.

Depletion of gut microbiota is associated with improved neurologic outcome following traumatic brain injury

Signaling between intestinal microbiota and the brain influences neurologic outcome in multiple forms of brain injury. The impact of gut microbiota following traumatic brain injury (TBI) has not been well established. Our objective was to compare TBI outcomes in specific pathogen-free mice with or without depletion of intestinal bacteria. Adult male C57BL6/J SPF mice (n = 6/group) were randomized to standard drinking water or ampicillin (1 g/L), metronidazole (1 g/L), neomycin (1 g/L), and vancomycin (0.5 g/L) (AMNV) containing drinking water 14 days prior to controlled cortical impact (CCI) model of TBI. 16S rRNA gene sequencing of fecal pellets was performed and alpha and beta diversity determined. Hippocampal neuronal density and microglial activation was assessed 72 h post-injury by immunohistochemistry. In addition, mice (n = 8-12/group) were randomized to AMNV or no treatment initiated immediately after CCI and memory acquisition (fear conditioning) and lesion volume assessed. Mice receiving AMNV had significantly reduced alpha diversity (p < 0.05) and altered microbiota community composition compared to untreated mice (PERMANOVA: p < 0.01). Mice receiving AMNV prior to TBI had increased CA1 hippocampal neuronal density (15.2 ± 1.4 vs. 8.8 ± 2.1 cells/0.1 mm; p < 0.05) and a 26.6 ± 6.6% reduction in Iba-1 positive cells (p < 0.05) at 72 h. Mice randomized to AMNV immediately after CCI had attenuated associative learning deficit on fear conditioning test (%freeze Cue: 63.7 ± 2.7% vs. 41.0 ± 5.1%, p < 0.05) and decreased lesion volume (27.2 ± 0.8 vs. 24.6 ± 0.7 mm³, p < 0.05). In conclusion, depletion of intestinal microbiota was consistent with a neuroprotective effect whether initiated before or after injury in a murine model of TBI. Further investigations of the role of gut microbiota in TBI are warranted.

Complex Feed-Forward and Feedback Mechanisms Underlie the Relationship Between Traumatic Brain Injury and the Gut-Microbiota-Brain Axis

Traumatic brain injury (TBI) contributes to nearly 1 in 3 injury-related deaths in the United States and accounts for a substantial public health burden and cost. The current literature reports that physiologic responses in the gastrointestinal system after TBI include, but are not limited to, epithelial barrier dysfunction, microbiota changes, and immunologic transformations. Recent evidence suggests gut alterations after TBI modify the homeostasis of the bidirectional gut-microbiota-brain axis, resulting in altered immune responses in the periphery and the brain. This cascade possibly contributes to impaired central nervous system (CNS) healing. Although attention to the gut-brain-microbiota axis has been increasing in the literature, the precise mechanisms underlying the changes observed after TBI remain unclear. The purpose of this review are to describe our current understanding regarding alterations to the gut-microbiota-brain axis after TBI, highlight the pathophysiologic changes involved, and evaluate how these variations modify healing in the CNS or even contribute to secondary injury. We also discuss current investigations into potential medical therapies directed at the gut-microbiota-brain axis, which might offer improved outcomes after TBI.

Western diet aggravates neuronal insult in post-traumatic brain injury: Proposed pathways for interplay

Traumatic brain injury (TBI) is a global health burden and a major cause of disability and mortality. An early cascade of physical and structural damaging events starts immediately post-TBI. This primary injury event initiates a series of neuropathological molecular and biochemical secondary injury sequelae, that last much longer and involve disruption of cerebral metabolism, mitochondrial dysfunction, oxidative stress, neuroinflammation, and can lead to neuronal damage and death. Coupled to these events, recent studies have shown that lifestyle factors, including diet, constitute additional risk affecting TBI consequences and neuropathophysiological outcomes. There exists molecular cross-talk among the pathways involved in neuronal survival, neuroinflammation, and behavioral outcomes, that are shared among western diet (WD) intake and TBI pathophysiology. As such, poor dietary intake would be expected to exacerbate the secondary damage in TBI. Hence, the aim of this review is to discuss the pathophysiological consequences of WD that can lead to the exacerbation of TBI outcomes. We dissect the role of mitochondrial dysfunction, oxidative stress, neuroinflammation, and neuronal injury in this context. We show that currently available data conclude that intake of a diet saturated in fats, pre- or post-TBI, aggravates TBI, precludes recovery from brain trauma, and reduces the response to treatment.

Evaluation of Probiotics for Warfighter Health and Performance

The probiotic industry continues to grow in both usage and the diversity of products available. Scientific evidence supports clinical use of some probiotic strains for certain gastrointestinal indications. Although much less is known about the impact of probiotics in healthy populations, there is increasing consumer and scientific interest in using probiotics to promote physical and psychological health and performance. Military men and women are a unique healthy population that must maintain physical and psychological health in order to ensure mission success. In this narrative review, we examine the evidence regarding probiotics and candidate probiotics for physical and/or cognitive benefits in healthy adults within the context of potential applications for military personnel. The reviewed evidence suggests potential for certain strains to induce biophysiological changes that may offer physical and/or cognitive health and performance benefits in military populations. However, many knowledge gaps exist, effects on health and performance are generally not widespread among the strains examined, and beneficial findings are generally limited to single studies with small sample sizes. Multiple studies with the same strains and using similar endpoints are needed before definitive recommendations for use can be made. We conclude that, at present, there is not compelling scientific evidence to support the use of any particular probiotic(s) to promote physical or psychological performance in healthy military personnel. However, plausibility for physical and psychological health and performance benefits remains, and additional research is warranted. In particular, research in military cohorts would aid in assessing the value of probiotics for supporting physical and psychological health and performance under the unique demands required of these populations.

Repetitive, mild traumatic brain injury results in a progressive white matter pathology, cognitive deterioration, and a transient gut microbiota dysbiosis

Traumatic brain injury (TBI) is often accompanied by gastrointestinal and metabolic disruptions. These systemic manifestations suggest possible involvement of the gut microbiota in head injury outcomes. Although gut dysbiosis after single, severe TBI has been documented, the majority of head injuries are mild, such as those that occur in athletes and military personnel exposed to repetitive head impacts. Therefore, it is important to determine if repetitive, mild TBI (rmTBI) will also disrupt the gut microbiota. Male mice were exposed to mild head impacts daily for 20 days and assessed for cognitive behavior, neuropathology and disruptions in the gut microbiota at 0, 45 or 90 days after injury. Deficits in recognition memory were evident at the late post-injury points. Brains show an early increase in microglial activation at the 0-day time point that persisted until 90 days post-injury. This was compounded by substantial increases in astrocyte reactivity and phosphorylated tau at the 90-day time point. In contrast, changes in the microbial community were minor and transient, and very few differences were observed in mice exposed to rmTBI compared to controls. While the progressive emergence of white matter damage and cognitive alterations after rmTBI resembles the alterations observed in athletes and military personnel exposed to rmTBI, these changes could not be linked to systematic modifications in the gut microbiota.

A prospective study in severely injured patients reveals an altered gut microbiome is associated with transfusion volume

BACKGROUND

Traumatic injury can lead to a compromised intestinal epithelial barrier and inflammation. While alterations in the gut microbiome of critically injured patients may influence clinical outcomes, the impact of trauma on gut microbial composition is unknown. Our objective was to determine if the gut microbiome is altered in severely injured patients and begin to characterize changes in the gut microbiome due to time and therapeutic intervention.

METHODS

We conducted a prospective, observational study in adult patients (n = 72) sustaining severe injury admitted to a Level I Trauma Center. Healthy volunteers (n = 13) were also examined. Fecal specimens were collected on admission to the emergency department and at 3, 7, 10, and 13 days (±2 days) following injury. Microbial DNA was isolated for 16s rRNA sequencing, and α and β diversities were estimated, according to taxonomic classification against the Greengenes database.

RESULTS

The gut microbiome of trauma patients was altered on admission (i.e., within 30 minutes following injury) compared to healthy volunteers. Patients with an unchanged gut microbiome on admission were transfused more RBCs than those with an altered gut microbiome (p < 0.001). Although the gut microbiome started to return to a β-diversity profile similar to that of healthy volunteers over time, it remained different from healthy controls. Alternatively, α diversity initially increased postinjury, but subsequently decreased during the hospitalization. Injured patients on admission had a decreased abundance of traditionally beneficial microbial phyla (e.g., Firmicutes) with a concomitant decrease in opportunistic phyla (e.g., Proteobacteria) compared to healthy controls (p < 0.05). Large amounts of blood products and RBCs were both associated with higher α diversity (p < 0.001) and a β diversity clustering closer to healthy controls.

CONCLUSION

The human gut microbiome changes early after trauma and may be aided by early massive transfusion. Ultimately, the gut microbiome of trauma patients may provide valuable diagnostic and therapeutic insight for the improvement of outcomes postinjury.

LEVEL OF EVIDENCE

Prognostic and Epidemiological, level III.

Traumatic Spinal Cord Injury and the Gut Microbiota: Current Insights and Future Challenges

Individuals with traumatic spinal cord injury (SCI) suffer from numerous peripheral complications in addition to the long-term paralysis that results from disrupted neural signaling pathways. Those living with SCI have consistently reported gastrointestinal dysfunction as a significant issue for overall quality of life, but most research has focused bowel management rather than how altered or impaired gut function impacts on the overall health and well-being of the affected individual. The gut-brain axis has now been quite extensively investigated in other neurological conditions but the gastrointestinal compartment, and more specifically the gut microbiota, have only recently garnered attention in the context of SCI because of their vast immunomodulatory capacity and putative links to infection susceptibility. Most studies to date investigating the gut microbiota following SCI have employed 16S rRNA genomic sequencing to identify bacterial taxa that may be pertinent to neurological outcome and common sequalae associated with SCI. This review provides a concise overview of the relevant data that has been generated to date, discussing current understanding of how the microbial content of the gut after SCI appears linked to both functional and immunological outcomes, whilst also emphasizing the highly complex nature of microbiome research and the need for careful evaluation of correlative findings. How the gut microbiota may be involved in the increased infection susceptibility that is often observed in this condition is also discussed, as are the challenges ahead to strategically probe the functional significance of changes in the gut microbiota following SCI in order to take advantage of these therapeutically.

The gut microbiome distinguishes mortality in trauma patients upon admission to the emergency department

BACKGROUND

Traumatic injury can lead to a compromised intestinal epithelial barrier, decreased gut perfusion, and inflammation. While recent studies indicate that the gut microbiome (GM) is altered early following traumatic injury, the impact of GM changes on clinical outcomes remains unknown. Our objective of this follow-up study was to determine if the GM is associated with clinical outcomes in critically injured patients.

METHODS

We conducted a prospective, observational study in adult patients (N = 67) sustaining severe injury admitted to a level I trauma center. Fecal specimens were collected on admission to the emergency department, and microbial DNA from all samples was analyzed using the Quantitative Insights Into Microbial Ecology pipeline and compared against the Greengenes database. α-Diversity and β-diversity were estimated using the observed species metrics and analyzed with t tests and permutational analysis of variance for overall significance, with post hoc pairwise analyses.

RESULTS

Our patient population consisted of 63% males with a mean age of 44 years. Seventy-eight percent of the patients suffered blunt trauma with 22% undergoing penetrating injuries. The mean body mass index was 26.9 kg/m. Significant differences in admission β-diversity were noted by hospital length of stay, intensive care unit hospital length of stay, number of days on the ventilator, infections, and acute respiratory distress syndrome (p < 0.05). β-Diversity on admission differed in patients who died compared with patients who lived (mean time to death, 8 days). There were also significantly less operational taxonomic units in samples from patients who died versus those who survived. A number of species were enriched in the GM of injured patients who died, which included some traditionally probiotic species such as Akkermansia muciniphilia, Oxalobacter formigenes, and Eubacterium biforme (p < 0.05).

CONCLUSION

Gut microbiome diversity on admission in severely injured patients is predictive of a variety of clinically important outcomes. While our study does not address causality, the GM of trauma patients may provide valuable diagnostic and therapeutic targets for the care of injured patients.

LEVEL OF EVIDENCE

Prognostic and epidemiological, level III.

Gut microbiota in surgical and critically ill patients

Microbiota-defined as a collection of microbial organisms colonising different parts of the human body-is now recognised as a pivotal element of human health, and explains a large part of the variance in the phenotypic expression of many diseases. A reduction in microbiota diversity, and replacement of normal microbes with non-commensal, pathogenic or more virulent microbes in the gastrointestinal tract-also known as gut dysbiosis-is now considered to play a causal role in the pathogenesis of many acute and chronic diseases. Results from animal and human studies suggest that dysbiosis is linked to cardiovascular and metabolic disease through changes to microbiota-derived metabolites, including trimethylamine-N-oxide and short-chain fatty acids. Dysbiosis can occur within hours of surgery or the onset of critical illness, even without the administration of antibiotics. These pathological changes in microbiota may contribute to important clinical outcomes, including surgical infection, bowel anastomotic leaks, acute kidney injury, respiratory failure and brain injury. As a strategy to reduce dysbiosis, the use of probiotics (live bacterial cultures that confer health benefits) or synbiotics (probiotic in combination with food that encourages the growth of gut commensal bacteria) in surgical and critically ill patients has been increasingly reported to confer important clinical benefits, including a reduction in ventilator-associated pneumonia, bacteraemia and length of hospital stay, in small randomised controlled trials. However, the best strategy to modulate dysbiosis or counteract its potential harms remains uncertain and requires investigation by a well-designed, adequately powered, randomised controlled trial.

Approaches to Monitor Circuit Disruption after Traumatic Brain Injury: Frontiers in Preclinical Research

Mild traumatic brain injury (TBI) often results in pathophysiological damage that can manifest as both acute and chronic neurological deficits. In an attempt to repair and reconnect disrupted circuits to compensate for loss of afferent and efferent connections, maladaptive circuitry is created and contributes to neurological deficits, including post-concussive symptoms. The TBI-induced pathology physically and metabolically changes the structure and function of neurons associated with behaviorally relevant circuit function. Complex neurological processing is governed, in part, by circuitry mediated by primary and modulatory neurotransmitter systems, where signaling is disrupted acutely and chronically after injury, and therefore serves as a primary target for treatment. Monitoring of neurotransmitter signaling in experimental models with technology empowered with improved temporal and spatial resolution is capable of recording in vivo extracellular neurotransmitter signaling in behaviorally relevant circuits. Here, we review preclinical evidence in TBI literature that implicates the role of neurotransmitter changes mediating circuit function that contributes to neurological deficits in the post-acute and chronic phases and methods developed for in vivo neurochemical monitoring. Coupling TBI models demonstrating chronic behavioral deficits with in vivo technologies capable of real-time monitoring of neurotransmitters provides an innovative approach to directly quantify and characterize neurotransmitter signaling as a universal consequence of TBI and the direct influence of pharmacological approaches on both behavior and signaling.

The sex-specific interaction of the microbiome in neurodegenerative diseases

Several neurologic diseases exhibit different prevalence and severity in males and females, highlighting the importance of understanding the influence of biologic sex and gender. Beyond host-intrinsic differences in neurologic development and homeostasis, evidence is now emerging that the microbiota is an important environmental factor that may account for differences between men and women in neurologic disease. The gut microbiota is composed of trillions of bacteria, archaea, viruses, and fungi, that can confer benefits to the host or promote disease. There is bidirectional communication between the intestinal microbiota and the brain that is mediated via immunologic, endocrine, and neural signaling pathways. While there is substantial interindividual variation within the microbiota, differences between males and females can be detected. In animal models, sex-specific microbiota differences can affect susceptibility to chronic diseases. In this review, we discuss the ways in which neurologic diseases may be regulated by the microbiota in a sex-specific manner.

Gut Microbiota as a Therapeutic Target to Ameliorate the Biochemical, Neuroanatomical, and Behavioral Effects of Traumatic Brain Injuries

Current efficacious treatments for traumatic brain injury (TBI) are lacking. Establishment of a protective gut microbiota population offers a compelling therapeutic avenue, as brain injury induces disruptions in the composition of the gut microbiota, i.e., gut dysbiosis, which has been shown to contribute to TBI-related neuropathology and impaired behavioral outcomes. The gut microbiome is involved in the modulation of a multitude of cellular and molecular processes fundamental to the progression of TBI-induced pathologies including neuroinflammation, blood brain barrier permeability, immune system response, microglial activation, and mitochondrial dysfunction, as well as intestinal motility and permeability. Additionally, gut dysbiosis further aggravates behavioral impairments in animal models of TBI and spinal cord injury, as well as negatively affects health outcomes in murine stroke models. Recent studies indicate that microbiota transplants and probiotics ameliorate neuroanatomical damage and functional impairments in animal models of stroke and spinal cord injury. In addition, probiotics have been shown to reduce the rate of infection and time spent in intensive care of hospitalized patients suffering from brain trauma. Perturbations in the composition of the gut microbiota and its metabolite profile may also serve as potential diagnostic and theragnostic biomarkers for injury severity and progression. This review aims to address the etiological role of the gut microbiome in the biochemical, neuroanatomical, and behavioral/cognitive consequences of TBI, as well as explore the potential of gut microbiome manipulation in the form of probiotics as an effective therapeutic to ameliorate TBI-induced pathology and symptoms.

Intestinal barrier dysfunction following traumatic brain injury

Traumatic brain injury (TBI) can cause non-neurological injuries to other organs such as the intestine. Newer studies have shown that paracellular hyperpermeability is the basis of intestinal barrier dysfunction following TBI. Ischemia-reperfusion injury, inflammatory response, abnormal release of neurotransmitters and hormones, and malnutrition contribute to TBI-induced intestinal barrier dysfunction. Several interventions that may protect intestinal barrier function and promote the recovery of TBI have been proposed, but relevant studies are still limited. This review is to clarify the established mechanisms of intestinal barrier dysfunction following TBI and to describe the possible strategies to reduce or prevent intestinal barrier dysfunction.

Traumatic Brain Injury in Mice Induces Acute Bacterial Dysbiosis Within the Fecal Microbiome

The secondary injury cascade that is activated following traumatic brain injury (TBI) induces responses from multiple physiological systems, including the immune system. These responses are not limited to the area of brain injury; they can also alter peripheral organs such as the intestinal tract. Gut microbiota play a role in the regulation of immune cell populations and microglia activation, and microbiome dysbiosis is implicated in immune dysregulation and behavioral abnormalities. However, changes to the gut microbiome induced after acute TBI remains largely unexplored. In this study, we have investigated the impact of TBI on bacterial dysbiosis. To test the hypothesis that TBI results in changes in microbiome composition, we performed controlled cortical impact (CCI) or sham injury in male 9-weeks old C57BL/6J mice. Fresh stool pellets were collected at baseline and at 24 h post-CCI. 16S rRNA based microbiome analysis was performed to identify differential abundance in bacteria at the genus and species level. In all baseline vs. 24 h post-CCI samples, we evaluated species-level differential abundances via clustered and annotated operational taxonomic units (OTU). At a high-level view, we observed significant changes in two genera after TBI, Marvinbryantia, and Clostridiales. At the species-level, we found significant decreases in three species (Lactobacillus gasseri, Ruminococcus flavefaciens, and Eubacterium ventriosum), and significant increases in two additional species (Eubacterium sulci, and Marvinbryantia formatexigens). These results pinpoint critical changes in the genus-level and species-level microbiome composition in injured mice compared to baseline; highlighting a previously unreported acute dysbiosis in the microbiome after TBI.

A Review of Traumatic Brain Injury and the Gut Microbiome: Insights into Novel Mechanisms of Secondary Brain Injury and Promising Targets for Neuroprotection

The gut microbiome and its role in health and disease have recently been major focus areas of research. In this review, we summarize the different ways in which the gut microbiome interacts with the rest of the body, with focus areas on its relationships with immunity, the brain, and injury. The gut–brain axis, a communication network linking together the central and enteric nervous systems, represents a key bidirectional pathway with feed-forward and feedback mechanisms. The gut microbiota has a central role in this pathway and is significantly altered following injury, leading to a pro-inflammatory state within the central nervous system (CNS). Herein, we examine traumatic brain injury (TBI) in relation to this axis and explore potential interventions, which may serve as targets for improving clinical outcomes and preventing secondary brain injury.