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

Prevotella copri transplantation promotes neurorehabilitation in a mouse model of traumatic brain injury

BACKGROUND

The gut microbiota plays a critical role in regulating brain function through the microbiome-gut-brain axis (MGBA). Dysbiosis of the gut microbiota is associated with neurological impairment in Traumatic brain injury (TBI) patients. Our previous study found that TBI results in a decrease in the abundance of Prevotella copri (P. copri). P. copri has been shown to have antioxidant effects in various diseases. Meanwhile, guanosine (GUO) is a metabolite of intestinal microbiota that can alleviate oxidative stress after TBI by activating the PI3K/Akt pathway. In this study, we investigated the effect of P. copri transplantation on TBI and its relationship with GUO-PI3K/Akt pathway.

METHODS

In this study, a controlled cortical impact (CCI) model was used to induce TBI in adult male C57BL/6J mice. Subsequently, P. copri was transplanted by intragastric gavage for 7 consecutive days. To investigate the effect of the GUO-PI3K/Akt pathway in P. copri transplantation therapy, guanosine (GUO) was administered 2 h after TBI for 7 consecutive days, and PI3K inhibitor (LY294002) was administered 30 min before TBI. Various techniques were used to assess the effects of these interventions, including quantitative PCR, neurological behavior tests, metabolite analysis, ELISA, Western blot analysis, immunofluorescence, Evans blue assays, transmission electron microscopy, FITC-dextran permeability assay, gastrointestinal transit assessment, and 16 S rDNA sequencing.

RESULTS

P. copri abundance was significantly reduced after TBI. P. copri transplantation alleviated motor and cognitive deficits tested by the NSS, Morris's water maze and open field test. P. copri transplantation attenuated oxidative stress and blood-brain barrier damage and reduced neuronal apoptosis after TBI. In addition, P. copri transplantation resulted in the reshaping of the intestinal flora, improved gastrointestinal motility and intestinal permeability. Metabolomics and ELISA analysis revealed a significant increase in GUO levels in feces, serum and injured brain after P. copri transplantation. Furthermore, the expression of p-PI3K and p-Akt was found to be increased after P. copri transplantation and GUO treatment. Notably, PI3K inhibitor LY294002 treatment attenuated the observed improvements.

CONCLUSIONS

We demonstrate for the first time that P. copri transplantation can improve GI functions and alter gut microbiota dysbiosis after TBI. Additionally, P. copri transplantation can ameliorate neurological deficits, possibly via the GUO-PI3K/Akt signaling pathway after TBI.

Association of Blast Exposure in Military Breaching with Intestinal Permeability Blood Biomarkers Associated with Leaky Gut

Injuries and subclinical effects from exposure to blasts are of significant concern in military operational settings, including tactical training, and are associated with self-reported concussion-like symptomology and physiological changes such as increased intestinal permeability (IP), which was investigated in this study. Time-series gene expression and IP biomarker data were generated from "breachers" exposed to controlled, low-level explosive blast during training. Samples from 30 male participants at pre-, post-, and follow-up blast exposure the next day were assayed via RNA-seq and ELISA. A battery of symptom data was also collected at each of these time points that acutely showed elevated symptom reporting related to headache, concentration, dizziness, and taking longer to think, dissipating ~16 h following blast exposure. Evidence for bacterial translocation into circulation following blast exposure was detected by significant stepwise increase in microbial diversity (measured via alpha-diversity p = 0.049). Alterations in levels of IP protein biomarkers (i.e., Zonulin, LBP, Claudin-3, I-FABP) assessed in a subset of these participants (n = 23) further evidenced blast exposure associates with IP. The observed symptom profile was consistent with mild traumatic brain injury and was further associated with changes in bacterial translocation and intestinal permeability, suggesting that IP may be linked to a decrease in cognitive functioning. These preliminary findings show for the first time within real-world military operational settings that exposures to blast can contribute to IP.

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.

Acute gastrointestinal permeability after traumatic brain injury in mice precedes a bloom in Akkermansia muciniphila supported by intestinal hypoxia

Traumatic brain injury (TBI) increases gastrointestinal morbidity and associated mortality. Clinical and preclinical studies implicate gut dysbiosis as a consequence of TBI and an amplifier of brain damage. However, little is known about the association of gut dysbiosis with structural and functional changes of the gastrointestinal tract after an isolated TBI. To assess gastrointestinal dysfunction, mice received a controlled cortical impact or sham brain injury and intestinal permeability was assessed at 4 h, 8 h, 1 d, and 3 d after injury by oral administration of 4 kDa FITC Dextran prior to euthanasia. Quantification of serum fluorescence revealed an acute, short-lived increase in permeability 4 h after TBI. Despite transient intestinal dysfunction, no overt morphological changes were evident in the ileum or colon across timepoints from 4 h to 4 wks post-injury. To elucidate the timeline of microbiome changes after TBI, 16 s gene sequencing was performed on DNA extracted from fecal samples collected prior to and over the first month after TBI. Differential abundance analysis revealed that the phylum Verrucomicrobiota was increased at 1, 2, and 3 d after TBI. The Verrucomicrobiota species was identified by qPCR as Akkermansia muciniphila, an obligate anaerobe that resides in the intestinal mucus bilayer and produces short chain fatty acids (e.g. butyrate) utilized by intestinal epithelial cells. We postulated that TBI promotes intestinal changes favorable for the bloom of A. muciniphila. Consistent with this premise, the relative area of mucus-producing goblet cells in the medial colon was significantly increased at 1 d after injury, while colon hypoxia was significantly increased at 3 d. Our findings reveal acute gastrointestinal functional changes coupled with an increase of beneficial bacteria suggesting a potential compensatory response to systemic stress after TBI.

Gut Microbiota Ecological and Functional Modulation in Post-Stroke Recovery Patients: An Italian Study

Ischemic stroke (IS) can be caused by perturbations of the gut-brain axis. An imbalance in the gut microbiota (GM), or dysbiosis, may be linked to several IS risk factors and can influence the brain through the production of different metabolites, such as short-chain fatty acids (SCFAs), indole and derivatives. This study examines ecological changes in the GM and its metabolic activities after stroke. Fecal samples of 10 IS patients were compared to 21 healthy controls (CTRLs). GM ecological profiles were generated via 16S rRNA taxonomy as functional profiles using metabolomics analysis performed with a gas chromatograph coupled to a mass spectrometer (GC-MS). Additionally fecal zonulin, a marker of gut permeability, was measured using an enzyme-linked immuno assay (ELISA). Data were analyzed using univariate and multivariate statistical analyses and correlated with clinical features and biochemical variables using correlation and nonparametric tests. Metabolomic analyses, carried out on a subject subgroup, revealed a high concentration of fecal metabolites, such as SCFAs, in the GM of IS patients, which was corroborated by the enrichment of SCFA-producing bacterial genera such as Bacteroides, Christensellaceae, Alistipes and Akkermansia. Conversely, indole and 3-methyl indole (skatole) decreased compared to a subset of six CTRLs. This study illustrates how IS might affect the gut microbial milieu and may suggest potential microbial and metabolic biomarkers of IS. Expanded populations of Akkermansia and enrichment of acetic acid could be considered potential disease phenotype signatures.

Making migraine easier to stomach: the role of the gut-brain-immune axis in headache disorders

BACKGROUND AND PURPOSE

Headache disorders place a significant burden on the healthcare system, being the leading cause of disability in those under 50 years. Novel studies have interrogated the relationship between headache disorders and gastrointestinal dysfunction, suggesting a link between the gut-brain-immune (GBI) axis and headache pathogenesis. Although the exact mechanisms driving the complex relationship between the GBI axis and headache disorders remain unclear, there is a growing appreciation that a healthy and diverse microbiome is necessary for optimal brain health.

METHODS

A literature search was performed through multiple reputable databases in search of Q1 journals within the field of headache disorders and gut microbiome research and were critically and appropriately evaluated to investigate and explore the following; the role of the GBI axis in dietary triggers of headache disorders and the evidence indicating that diet can be used to alleviate headache severity and frequency. The relationship between the GBI axis and post-traumatic headache is then synthesized. Finally, the scarcity of literature regarding paediatric headache disorders and the role that the GBI axis plays in mediating the relationship between sex hormones and headache disorders are highlighted.

CONCLUSIONS

There is potential for novel therapeutic targets for headache disorders if understanding of the GBI axis in their aetiology, pathogenesis and recovery is increased.

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.

Gut microbiota and transcriptome dynamics in every-other-day fasting are associated with neuroprotection in rats with spinal cord injury

Introduction

Every-other-day fasting (EODF) is a classical intermittent fasting (IF) mode with neuroprotective effects that promotes motor function recovery after spinal cord injury (SCI) in rats. However, its dynamic effects on the gut microbiota and spinal cord transcriptome remain unknown.

Methods

In this study, 16S rRNA sequencing and RNA-seq analysis were used to investigate the effects of ad libitum (AL) and EODF dietary modes on the structural characteristics of rat gut microbiota in rats and the spinal cord transcriptome at various time points after SCI induction.

Results

Our results showed that both dietary modes affected the bacterial community composition in SCI rats, with EODF treatment inducing and suppressing dynamic changes in the abundances of potentially anti-inflammatory and pro-inflammatory bacteria. Furthermore, the differentially expressed genes (DEGs) enriched after EODF intervention in SCI rats were associated with various biological events, including immune inflammatory response, cell differentiation, protein modification, neural growth, and apoptosis. In particular, significant spatiotemporal differences were apparent in the DEGs associated with neuroprotection between the EODF and AL interventions. These DGEs were mainly focused on days 1, 3, and 7 after SCI. The relative abundance of certain genera was significantly correlated with DEGs associated with neuroprotective effects in the EODF-SCI group.

Discussion

Our results showed that EODF treatment may exert neuroprotective effects by modulating the transcriptome expression profile following SCI in rats. Furthermore, gut microbiota may be partially involved in mediating these effects.

Pre-traumatic antibiotic-induced microbial depletion reduces neuroinflammation in acute murine traumatic brain injury

The connection between dysbiosis of the gut microbiome and diseases and injuries of the brain has attracted considerable interest in recent years. Interestingly, antibiotic-induced microbial dysbiosis has been implicated in the pathogenesis of traumatic brain injury (TBI), while early administration of antibiotics associates with improved survival in TBI patients. In animal models of TBI, short- or long-term administration of antibiotics, both peri- or post-operatively, were shown to induce gut microbiome dysbiosis but also anti-inflammatory and neuroprotective effects. However, the acute consequences of microbial dysbiosis on TBI pathogenesis after discontinuation of antibiotic treatment are elusive. In this study, we tested whether pre-traumatic antibiotic-induced microbial depletion by vancomycin, amoxicillin, and clavulanic acid affects pathogenesis during the acute phase of TBI in adult male C57BL/6 mice. Pre-traumatic microbiome depletion did not affect neurological deficits over 72 h post injury (hpi) and brain histopathology, including numbers of activated astrocytes and microglia, at 72 hpi. However, astrocytes and microglia were smaller after pre-traumatic microbiome depletion compared to vehicle treatment at 72hpi, indicating less inflammatory activation. Accordingly, TBI-induced gene expression of the inflammation markers Interleukin-1β, complement component C3, translocator protein TSPO and the major histocompatibility complex MHC2 was attenuated in microbiome-depleted mice along with reduced Immunoglobulin G extravasation as a proxy of blood-brain barrier (BBB) impairment. These results suggest that the gut microbiome contributes to early neuroinflammatory responses to TBI but does not have a significant impact on brain histopathology and neurological deficits.

TRAUMATIC BRAIN INJURY-INDUCED INFLAMMATION AND GASTROINTESTINAL MOTILITY DYSFUNCTION

ABSTRACT

Background: Traumatic brain injury (TBI) is a significant cause of morbidity and mortality in the United States, with an annual cost of 60 billion dollars. There is evidence suggesting that in the post-TBI period, the gastrointestinal tract plays a central role in driving organ and immune dysfunction and may be the source of increased circulating proinflammatory mediators. In this study, we examined systemic inflammation and bacterial dysbiosis in patients who sustained a TBI with or without polytrauma. Using a mouse model of TBI, we further show how neuroinflammation after TBI is potentially linked to disruptions in gut homeostasis such as intestinal transit and inflammation. Methods: During a study of trauma patients performed from September 1, 2018, to September 1, 2019, at a single, level 1 trauma center, TBI patients aged 21 to 95 years were enrolled. Patients were categorized as TBI based on evidence of acute abnormal findings on head computed tomographic scan, which was a combination of isolated TBI and TBI with polytrauma. Blood and stool samples were collected between 24 h and 3 days after admission. Twelve plasma samples and 10 fecal samples were used for this study. Healthy control samples were obtained from a healthy control biobank. We examined systemic inflammation and bacterial changes in patients who sustained a TBI. In addition, TBI was induced in 9- to 10-week-old male mice; we assessed neuroinflammation, and intestine transit (motility) and bacterial changes 24 h after TBI. Results: When compared with healthy controls, TBI patients had increased systemic inflammation as evidenced by increased levels of IFN-γ and MCP-1 and a trend toward an increase of IL-6 and IL-8 ( P = 0.0551 and P = 0.0549), respectively. The anti-inflammatory cytokine, IL-4, was also decreased in TBI patients. Although there was a trend of an increase in copy number of Enterobacteriaceae and a decrease in copy number of Lactobacillus in both patients and mice after TBI, these trends were not found to be significantly different. However, TBI significantly increased the copy number of another potential pathogenic bacteria Bilophila wadsworthia in TBI patients compared with healthy controls. After a moderate TBI, mice had increased expression of TNF-α, IL-6 and IL-1β, CXCL1, s100a9, and Ly6G and decreased IL-10 in the brain lesion after TBI. This accompanied decreased transit and increased TNF-α in the small intestine of mice after TBI. Conclusions: Our findings suggest that TBI increases systemic inflammation, intestinal dysfunction, and neuroinflammation. More studies are needed to confirm whether changes in intestinal motility play a role in post-TBI neuroinflammation and cognitive deficit.

Characteristics of Gut Microbiome After Traumatic Brain Injury

BACKGROUND

Preclinical studies have reported significant changes in the gut microbiome after traumatic brain injury (TBI). We hypothesized that TBI induces the growth of Proteobacteria in the human gut. Our primary outcome was to study the profile of the human fecal microbiome after TBI and the secondary outcome was to identify colonization with colistin-resistant and multidrug-resistant pathogens.

METHODS

Consecutive patients with moderate-severe TBI admitted to the neurotrauma-intensive care unit within 48 hours of injury were enrolled into this observational study. Samples from rectal swabs obtained on days 0, 3, and 7 after admission were assessed for microbial growth and antibiotic resistance. Demographic data and variables such as hypotension, blood transfusion, surgery, start of nasogastric feeding, use of antibiotics, length of hospital stay and mortality were noted.

RESULTS

One hundred one patients were enrolled into this study; 57 (56.4%) underwent surgery, 80 (79.2%) required blood transfusion, 15 (14.9%) had an episode of hypotension, 37 (36.6%) received enteral feed within the first 3 days, and 79 (78.2%) received antibiotics. Rectal microbiological samples were collected from 101, 95, and 85 patients on days 0, 3, and 7, respectively. All organisms isolated at the 3 time-points belonged to the Proteobacteria phylum, with Enterobacteriaceae forming the largest group. Colistin-resistant organisms were found in 17 (16.8%) of 101 patients and multidrug-resistant organisms in 25 (64.1%) of the 39 patients in whom isolates were tested against the entire panel of antimicrobials.

CONCLUSION

TBI is associated with widespread colonization with Proteobacteria as early as 48 hours after injury. Colonization with colistin and multidrug-resistant organisms highlights the importance of the judicious use of antibiotics.

The Role of G-tube Placement for Neurologic Injury Patients

Neurologic injury often influences various bodily functions associated with digestion. It is imperative for an individual to obtain proper nutrients to maintain a healthy lifestyle and recover from injury. In this review, we explore variables and methods of enteral tube placement in neurologic injury patients influencing recovery, specifically G- and J-tubes. We will first review the patient population by identifying leading causes for enteral tube placement among both pediatric and adult neurologic patients. We will then discuss the general procedures for placement and safety considerations for specified patient populations. We will explore interventions limiting placement of the G- and J-tubes by focusing on two interventions: ventriculoperitoneal shunt (VPS) and intrathecal baclofen (ITB). Then, we will highlight nutritional enhancers that may influence general treatment. Finally, we discuss proper weaning procedures and eJective methods fitting patient needs.

Diet-microbiome-gut-brain nexus in acute and chronic brain injury

In recent years, appreciation for the gut microbiome and its relationship to human health has emerged as a facilitator of maintaining healthy physiology and a contributor to numerous human diseases. The contribution of the microbiome in modulating the gut-brain axis has gained significant attention in recent years, extensively studied in chronic brain injuries such as Epilepsy and Alzheimer’s Disease. Furthermore, there is growing evidence that gut microbiome also contributes to acute brain injuries like stroke(s) and traumatic brain injury. Microbiome-gut-brain communications are bidirectional and involve metabolite production and modulation of immune and neuronal functions. The microbiome plays two distinct roles: it beneficially modulates immune system and neuronal functions; however, abnormalities in the host’s microbiome also exacerbates neuronal damage or delays the recovery from acute injuries. After brain injury, several inflammatory changes, such as the necrosis and apoptosis of neuronal tissue, propagates downward inflammatory signals to disrupt the microbiome homeostasis; however, microbiome dysbiosis impacts the upward signaling to the brain and interferes with recovery in neuronal functions and brain health. Diet is a superlative modulator of microbiome and is known to impact the gut-brain axis, including its influence on acute and neuronal injuries. In this review, we discussed the differential microbiome changes in both acute and chronic brain injuries, as well as the therapeutic importance of modulation by diets and probiotics. We emphasize the mechanistic studies based on animal models and their translational or clinical relationship by reviewing human studies.

Modification of post-traumatic epilepsy by fecal microbiota transfer

It has been well established that traumatic brain injury (TBI) modifies the composition of gut microbiome. Epilepsy, which represents one of the common sequelae of TBI, has been associated with dysbiosis. Earlier study showed that the risk of post-traumatic epilepsy (PTE) after lateral fluid percussion injury (LFPI) in rats can be stratified based on pre-existing (i.e., pre-TBI) gut microbiome profile. In the present study, we examined whether fecal microbiota transfer (FMT) from naïve rats with different prospective histories of PTE would affect the trajectory of PTE in recipients. Fecal samples were collected from naïve adult male Sprague-Dawley rats, followed by LFPI. Seven months later, upon four weeks of vide-EEG monitoring (vEEG), the rats were categorized as those with and without PTE. Recipients were subjected to LFPI, followed by FMT from donors with and without impending PTE. Control groups included auto-FMT and no-FMT subjects. Seven month after LFPI, recipients underwent four-week vEEG to detect spontaneous seizures. After completing vEEG, rats of all groups underwent kindling of basolateral amygdala. Fecal microbiota transfer from donors with impending PTE exerted mild-to-moderate pro-epileptic effects in recipients, evident as marginal increase in multiple spontaneous seizure incidence, and facilitation of kindling. Analysis of fecal samples in selected recipients and their respective donors confirmed that FMT modified microbiota in recipients along the donors' lines, albeit without full microbiome conversion. The findings provide further evidence that gut microbiome may actively modulate the susceptibility to epilepsy.

Changes in Oral Microbial Diversity in a Piglet Model of Traumatic Brain Injury

Dynamic changes in the oral microbiome have gained attention due to their potential diagnostic role in neurological diseases such as Alzheimer's disease and Parkinson's disease. Traumatic brain injury (TBI) is a leading cause of death and disability in the United States, but no studies have examined the changes in oral microbiome during the acute stage of TBI using a clinically translational pig model. Crossbred piglets (4-5 weeks old, male) underwent either a controlled cortical impact (TBI, n = 6) or sham surgery (sham, n = 6). The oral microbiome parameters were quantified from the upper and lower gingiva, both buccal mucosa, and floor of the mouth pre-surgery and 1, 3, and 7 days post-surgery (PS) using the 16S rRNA gene. Faith's phylogenetic diversity was significantly lower in the TBI piglets at 7 days PS compared to those of sham, and beta diversity at 1, 3, and 7 days PS was significantly different between TBI and sham piglets. However, no significant changes in the taxonomic composition of the oral microbiome were observed following TBI compared to sham. Further studies are needed to investigate the potential diagnostic role of the oral microbiome during the chronic stage of TBI with a larger number of subjects.

Pediatric Traumatic Brain Injury: An Update on Preclinical Models, Clinical Biomarkers, and the Implications of Cerebrovascular Dysfunction

Traumatic brain injury (TBI) is a leading cause of pediatric morbidity and mortality. Recent studies suggest that children and adolescents have worse post-TBI outcomes and take longer to recover than adults. However, the pathophysiology and progression of TBI in the pediatric population are studied to a far lesser extent compared to the adult population. Common causes of TBI in children are falls, sports/recreation-related injuries, non-accidental trauma, and motor vehicle-related injuries. A fundamental understanding of TBI pathophysiology is crucial in preventing long-term brain injury sequelae. Animal models of TBI have played an essential role in addressing the knowledge gaps relating to pTBI pathophysiology. Moreover, a better understanding of clinical biomarkers is crucial to diagnose pTBI and accurately predict long-term outcomes. This review examines the current preclinical models of pTBI, the implications of pTBI on the brain’s vasculature, and clinical pTBI biomarkers. Finally, we conclude the review by speculating on the emerging role of the gut-brain axis in pTBI pathophysiology.

Susceptibility to epilepsy after traumatic brain injury is associated with preexistent gut microbiome profile

OBJECTIVE

We examined whether post-traumatic epilepsy (PTE) is associated with measurable perturbations in gut microbiome.

METHODS

Adult Sprague-Dawley rats were subjected to Lateral Fluid Percussion Injury (LFPI). PTE was examined 7 months after LFPI, during a 4-week continuous video-EEG monitoring. 16S ribosomal ribonucleic acid gene sequencing was performed in fecal samples collected before LFPI/sham-LFPI and 1 week, 1 and 7 months thereafter. Longitudinal analyses of alpha diversity, beta diversity, and differential microbial abundance were performed. Short-chain fatty acids (SCFA) were measured in fecal samples collected before LFPI by Liquid Chromatography with Tandem Mass Spectrometry.

RESULTS

Alpha diversity changed over time in both LFPI and sham-LFPI subjects; no association was observed between alpha diversity and LFPI, the severity of post-LFPI neuromotor impairments, and PTE. LFPI produced significant changes in beta diversity and selective changes in microbial abundances associated with the severity of neuromotor impairments. No association between LFPI-dependent microbial perturbations and PTE was detected. PTE was associated with beta diversity irrespective of timepoint vis-à-vis LFPI, including at baseline. Preexistent fecal microbial abundances of four amplicon sequence variants belonging to the Lachnospiraceae family (three enriched and one depleted) predicted the risk of PTE with area under the curve (AUC) of 0.73. Global SCFA content was associated with the increased risk of PTE with AUC of 0.722, and with 2-Methylbutyric (depleted), valeric (depleted), isobutyric (enriched) and isovaleric (enriched) acids being most important factors (AUC of 0.717). When the analyses of baseline microbial and SCFA compositions were combined, AUC to predict PTE increased to 0.78.

SIGNIFICANCE

While LFPI produces no perturbations in the gut microbiome that are associated with PTE, the risk of PTE can be stratified based on preexistent microbial abundances and SCFA content.

Cerebral Intraparenchymal Hemorrhage Changes Patients’ Gut Bacteria Composition and Function

Gut bacteria consists of 150 times more genes than humans that are vital for health. Several studies revealed that gut bacteria are associated with disease status and influence human behavior and mentality. Whether human brain injury alters the gut bacteria is yet unclear, we tested 20 fecal samples from patients with cerebral intraparenchymal hemorrhage and corresponding healthy controls through metagenomic shotgun sequencing. The composition of patients’ gut bacteria changed significantly at the phylum level; Verrucomicrobiota was the specific phylum colonized in the patients’ gut. The functional alteration was observed in the patients’ gut bacteria, including high metabolic activity for nutrients or neuroactive compounds, strong antibiotic resistance, and less virulence factor diversity. The changes in the transcription and metabolism of differential species were more evident than those of the non-differential species between groups, which is the primary factor contributing to the functional alteration of patients with cerebral intraparenchymal hemorrhage.

Alteration of Gut Microbiota: New Strategy for Treating Autism Spectrum Disorder

Autism spectrum disorder (ASD) is defined as a complex heterogeneous disorder and characterized by stereotyped behavior and deficits in communication and social interactions. The emerging microbial knowledge has pointed to a potential link between gut microbiota dysbiosis and ASD. Evidence from animal and human studies showed that shifts in composition and activity of the gut microbiota may causally contribute to the etiopathogenesis of core symptoms in the ASD individuals with gastrointestinal tract disturbances and act on microbiota-gut-brain. In this review, we summarized the characterized gut bacterial composition of ASD and the involvement of gut microbiota and their metabolites in the onset and progression of ASD; the possible underlying mechanisms are also highlighted. Given this correlation, we also provide an overview of the microbial-based therapeutic interventions such as probiotics, antibiotics, fecal microbiota transplantation therapy, and dietary interventions and address their potential benefits on behavioral symptoms of ASD. The precise contribution of altering gut microbiome to treating core symptoms in the ASD needs to be further clarified. It seemed to open up promising avenues to develop microbial-based therapies in ASD.

Traumatic Brain Injury and Gut Brain Axis: The Disruption of an Alliance

BACKGROUND

Traumatic brain injury (TBI) can be considered a "silent epidemic", causing morbidity, disability, and mortality in all age cohorts. Therefore, a greater understanding of the underlying pathophysiological intricate mechanisms and interactions with other organs and systems is necessary to intervene not only in the treatment but also in the prevention of complications. In this complex of reciprocal interactions, the complex brain-gut axis has captured a growing interest.

SCOPE

The purpose of this manuscript is to examine and systematize existing evidence regarding the pathophysiological processes that occur following TBI and the influences exerted on these by the brain-gut axis.

LITERATURE REVIEW

A systematic review of the literature was conducted according to the PRISMA methodology. On the 8th of October 2021, two independent databases were searched: PubMed and Scopus. Following the inclusion and exclusion criteria selected, 24 (12 from PubMed and 12 from Scopus) eligible manuscripts were included in the present review. Moreover, references from the selected articles were also updated following the criteria mentioned above, yielding 91 included manuscripts.

DISCUSSION

Published evidence suggests that the brain and gut are mutually influenced through four main pathways: microbiota, inflammatory, nervous, and endocrine.

CONCLUSION

These pathways are bidirectional and interact with each other. However, the studies conducted so far mainly involve animals. An autopsy methodological approach to corpses affected by traumatic brain injury or intestinal pathology could represent the keystone for future studies to clarify the complex pathophysiological processes underlying the interaction between these two main systems.

Traumatic Brain Injury Induces Gastrointestinal Dysfunction and Dysbiosis of Gut Microbiota Accompanied by Alterations of Bile Acid Profile

Gastrointestinal dysfunction is a common peripheral organ complication after traumatic brain injury (TBI), yet the underlying mechanism remains unknown. TBI has been demonstrated to cause gut microbiota dysbiosis in animal models, although the impacts of gut microbiota dysbiosis on gastrointestinal dysfunction were not examined. Bile acids are key metabolites between gut microbiota and host interactions. Therefore, the aim of this study was to investigate the mechanistic links between them by detecting the alterations of gut microbiota and bile acid profile after TBI. For that, we established TBI in mice using a lateral fluid percussion injury model. Gut microbiota was examined by 16S rRNA sequencing, and bile acids were profiled by ultra-performance liquid chromatography-tandem mass spectrometry. Our results showed that TBI caused intestinal inflammation and gut barrier impairment. Alterations of gut microbiota and bile acid profile were observed. The diversity of gut microbiota experienced a time dependent change from 1 h to 7 days post-injury. Levels of bile acids in feces and plasma were decreased after TBI, and the decrease was more significant in secondary bile acids, which may contribute to intestinal inflammation. Specific bacterial taxa such as Staphylococcus and Lachnospiraceae that may contribute to the bile acid metabolic changes were identifed. In conclusion, our study suggested that TBI-induced gut microbiota dysbiosis may contribute to gastrointestinal dysfunction via altering bile acid profile. Gut microbiota may be a potential treatment target for TBI-induced gastrointestinal dysfunction.

Mice Born to Mothers with Gravida Traumatic Brain Injury Have Distorted Brain Circuitry and Altered Immune Responses

Intimate partner violence (IPV) increases risk of traumatic brain injury (TBI). Physical assaults increase in frequency and intensity during pregnancy. The consequences of TBI during pregnancy (gravida TBI; gTBI) on offspring development is unknown, for which stress and inflammation during pregnancy worsen fetal developmental outcomes. We hypothesized that gTBI would lead to increased anxiety- and depression-related behavior, altered inflammatory responses and gut pathology, and distorted brain circuitry in mixed-sex offspring compared to mice born to control mothers. Pregnant dams received either diffuse TBI or sham injury (control) 12 days post-coitum. We found that male gTBI offspring were principal drivers of the gTBI effects on health, physiology, and behavior. For example, male, but not female, gTBI offspring weighed significantly less at weaning compared to male control offspring. At post-natal day (PND) 28, gTBI offspring had significantly weaker intralaminar connectivity onto layer 5 pre-frontal pyramidal neurons compared to control offspring. Neurological performance on anxiety-like behaviors was decreased, with only marginal differences in depressive-like behaviors, for gTBI offspring compared to control offspring. At PND42 and PND58, circulating neutrophil and monocyte populations were significantly smaller in gTBI male offspring than control male offspring. In response to a subsequent inflammatory challenge at PND75, gTBI offspring had significantly smaller circulating neutrophil populations than control offspring. Anxiety-like behaviors persisted during the immune challenge in gTBI offspring. However, spleen immune response and gut histology showed no significant differences between groups. The results compel further studies to determine the full extent of gTBI on fetal and maternal outcomes.

Ceftriaxone therapy attenuates brain trauma in rats by affecting glutamate transporters and neuroinflammation and not by its antibacterial effects

BACKGROUND

Ceftriaxone is a β-lactam antibiotic used to treat central nervous system infections. Whether the neuroprotective effects of ceftriaxone after TBI are mediated by attenuating neuroinflammation but not its antibacterial actions is not well established.

METHODS

Anesthetized male Sprague-Dawley rats were divided into sham-operated, TBI + vehicle, and TBI + ceftriaxone groups. Ceftriaxone was intraperitoneally injected at 0, 24, and 48 h with 50 or 250 mg/kg/day after TBI. During the first 120 min after TBI, we continuously measured heart rate, arterial pressure, intracranial pressure (ICP), and cerebral perfusion pressure. The infarct volume was measured by TTC staining. Motor function was measured using the inclined plane. Glutamate transporter 1 (GLT-1), neuronal apoptosis and TNF-α expression in the perilesioned cortex were investigated using an immunofluorescence assay. Bacterial evaluation was performed by Brown and Brenn's Gram staining. These parameters above were measured at 72 h after TBI.

RESULTS

Compared with the TBI + vehicle group, the TBI + ceftriaxone 250 mg/kg group showed significantly lower ICP, improved motor dysfunction, reduced body weight loss, decreased infarct volume and neuronal apoptosis, decreased TBI-induced microglial activation and TNF-α expression in microglia, and increased GLT-1 expression in neurons and microglia. However, the grades of histopathological changes of antibacterial effects are zero.

CONCLUSIONS

The intraperitoneal injection of ceftriaxone with 250 mg/kg/day for three days may attenuate TBI by increasing GLT-1 expression and reducing neuroinflammation and neuronal apoptosis, thereby resulting in an improvement in functional outcomes, and this neuroprotective effect is not related to its antibacterial effects.

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.

The effect of doxycycline on neuron-specific enolase in patients with traumatic brain injury: a randomized controlled trial

Objective:

We aimed to examine the effect of doxycycline on serum levels of neuron-specific enolase (NSE), a marker of neuronal damage in traumatic brain injury (TBI) patients.

Methods:

Patients were randomly assigned into two groups (n = 25 each) to receive either placebo or doxycycline (200 mg daily), with their standard management for 7 days.

Results:

NSE serum levels in the doxycycline and control groups on day 3 were 14.66 ± 1.78 versus 18.09 ± 4.38 ng/mL, respectively (p = 0.008), and on day 7 were 12.3 ± 2.0 versus 16.43 ± 3.85 ng/mL, respectively (p = 0.003). Glasgow Coma Scale (GCS) on day 7 was 11.90 ± 2.83 versus 9.65 ± 3.44 in the doxycycline and control groups, respectively (p = 0.031). NSE serum levels and GCS scores were negatively correlated (r = −0.569, p < 0.001).

Conclusion:

Adjunctive early use of doxycycline might be a novel option that halts the ongoing secondary brain injury in patients with moderate to severe TBI. Future larger clinical trials are warranted to confirm these findings.

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.

Inflammation in Traumatic Brain Injury

There is an increasing evidence that inflammation contributes to clinical and functional outcomes in traumatic brain injury (TBI). Many successful target-engaging, lesion-reducing, symptom-alleviating, and function-improving interventions in animal models of TBI have failed to show efficacy in clinical trials. Timing and immunological context are paramount for the direction, quality, and intensity of immune responses to TBI and the resulting neuroanatomical, clinical, and functional course. We present components of the immune system implicated in TBI, potential immune targets, and target-engaging interventions. The main objective of our article is to point toward modifiable molecular and cellular mechanisms that may modify the outcomes in TBI, and contribute to increasing the translational value of interventions that have been identified in animal models of TBI.

Local Necrotic Cells Trigger Systemic Immune Activation via Gut Microbiome Dysbiosis in Drosophila

Necrotic cells elicit an inflammatory response through their endogenous factors with damage-associated molecular patterns. Blocking apoptosis in Drosophila wings leads to the necrosis-driven systemic immune response by unknown mechanisms. Here, we demonstrate that immune activation in response to necrotic cells is mediated by commensal gut microbiota. Removing the microbiome attenuates hyperactivation of the innate immune signaling IMD pathway in necrosis-induced flies. Necrotic cells in wings trigger Gluconobacter expansion in the gut. An isolated Gluconobacter sp. strain is sufficient for pathological IMD activation in necrosis-induced flies, while it is not inflammatory for control animals. In addition, bacterial colonization shifts the host metabolome and shortens the lifespan of necrosis-induced flies. This study shows that local necrosis triggers a pathological systemic inflammatory response through interaction between the host and the dysbiotic gut microbiome.

Urinary metabolites predict mortality or need for renal replacement therapy after combat injury

BACKGROUND

Traditionally, patient risk scoring is done by evaluating vital signs and clinical severity scores with clinical intuition. Urinary biomarkers can add objectivity to these models to make risk prediction more accurate. We used metabolomics to identify prognostic urinary biomarkers of mortality or need for renal replacement therapy (RRT). Additionally, we assessed acute kidney injury (AKI) diagnosis, injury severity score (ISS), and AKI stage.

METHODS

Urine samples (n = 82) from a previous study of combat casualties were evaluated using proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Chenomx software was used to identify and quantify urinary metabolites. Metabolite concentrations were normalized by urine output, autoscaled, and log-transformed. Partial least squares discriminant analysis (PLS-DA) and statistical analysis were performed. Receiver operating characteristic (ROC) curves were used to assess prognostic utility of biomarkers for mortality and RRT.

RESULTS

Eighty-four (84) metabolites were identified and quantified in each urine sample. Of these, 11 were identified as drugs or drug metabolites and excluded. The PLS-DA models for ISS and AKI diagnosis did not have acceptable model statistics. Therefore, only mortality/RRT and AKI stage were analyzed further. Of 73 analyzed metabolites, 9 were significantly associated with mortality/RRT (p < 0.05) and 11 were significantly associated with AKI stage (p < 0.05). 1-Methylnicotinamide was the only metabolite to be significantly associated (p < 0.05) with all outcomes and was significantly higher (p < 0.05) in patients with adverse outcomes. Elevated lactate and 1-methylnicotinamide levels were associated with higher AKI stage and mortality and RRT, whereas elevated glycine levels were associated with patients who survived and did not require RRT, or had less severe AKI. ROC curves for each of these metabolites and the combined panel had good predictive value (lactate AUC = 0.901, 1-methylnicotinamide AUC = 0.864, glycine AUC = 0.735, panel AUC = 0.858).

CONCLUSIONS

We identified urinary metabolites associated with AKI stage and the primary outcome of mortality or need for RRT. Lactate, 1-methylnicotinamide, and glycine may be used as a panel of predictive biomarkers for mortality and RRT. 1-Methylnicotinamide is a novel biomarker associated with adverse outcomes. Additional studies are necessary to determine how these metabolites can be utilized in clinically-relevant risk prediction models.

Tryptophan Metabolism and Gut-Brain Homeostasis

Tryptophan is an essential amino acid critical for protein synthesis in humans that has emerged as a key player in the microbiota-gut-brain axis. It is the only precursor for the neurotransmitter serotonin, which is vital for the processing of emotional regulation, hunger, sleep, and pain, as well as colonic motility and secretory activity in the gut. Tryptophan catabolites from the kynurenine degradation pathway also modulate neural activity and are active in the systemic inflammatory cascade. Additionally, tryptophan and its metabolites support the development of the central and enteric nervous systems. Accordingly, dysregulation of tryptophan metabolites plays a central role in the pathogenesis of many neurologic and psychiatric disorders. Gut microbes influence tryptophan metabolism directly and indirectly, with corresponding changes in behavior and cognition. The gut microbiome has thus garnered much attention as a therapeutic target for both neurologic and psychiatric disorders where tryptophan and its metabolites play a prominent role. In this review, we will touch upon some of these features and their involvement in health and disease.

CORM-3 exerts a neuroprotective effect in a rodent model of traumatic brain injury via the bidirectional gut-brain interactions

OBJECTIVE

Traumatic brain injury (TBI) induced the gastrointestinal inflammation that is associated with TBI-related morbidity and mortality. Carbon monoxide-releasing molecule (CORM)-3 is a water-soluble exogenous carbon monoxide that exerts protective effects against inflammation-induced pyroptosis. We investigated the gastrointestinal inflammation in a rodent model of traumatic brain injury (TBI) with subsequent hemorrhagic shock and resuscitation (HSR), as well as effects of CORM-3 using an intestinal injection on both gut and brain.

METHODS

Following exposure to TBI plus HSR, rats were administrated with CORM-3 (8 mg/kg) through an intestinal injection after resuscitation immediately. The pathological changes and pyroptosis in the gut were measured at 24 h and 30 day post-trauma. We also assessed the intestinal and cortical CO content, as well as IL-1β and IL-18 levels in the serum within 48 h after trauma. We then explored pathological changes in the ventromedial prefrontal cortex (vmPFC) and neurological behavior deficits on 30 day post-trauma.

RESULTS

After TBI + HSR exposure, CORM-3-treated rats presented significantly decreased pyroptosis, more CO content in the jejunum, and lower IL-1β, IL-18 levels in the serum at 24 h after trauma. Moreover, the rats treated with CORM-3 exerted ameliorated jejunal and vmPFC injury, enhanced learning/memory ability and exploratory activity, improved anxiety-like behaviors than the TBI + HSR-treated rats on 30 day post-trauma.

CONCLUSION

These experimental data demonstrated and bidirectional gut-brain interactions after TBI, anti-inflammatory effects of CORM-3, which may improve late outcomes after brain injury.

[Intestine morphology and microbiocenosis changes in critically ill patients in neurosurgery]

In recent years, the effect of critical conditions on intestine and the role of such changes in maintenance and progression of systemic disorders are of particular attention. This issue is relevant in critically ill neurosurgical patients too. Intestine morphology and microbiome changes in these patients represent a wide field for researches in intensive care and prevention of secondary damage to other organs and systems. This review ensures a current approach to the problem of intestine morphology and microbiome changes in critically ill neurosurgical patients. We reviewed the data from clinical studies and experiments reproducing a critical condition in animals. Most publications are indexed in the PubMed, e-library, Google Scholar databases. We also analyzed the data from NEJM, JAMA, Lancet, Critical Care and other issues. The manuscript contains an overview of 44 foreign and 13 domestic references; over 50% of researches were published within the past 5 years. Searching depth was over 50 years.

PART 3 Bypassing TBI: Metabolic Surgery and the Link Between Obesity and Traumatic Brain Injury-a Review

Obesity is a common outcome of traumatic brain injury (TBI) that exacerbates principal TBI symptom domains identified as common areas of post-TBI long-term dysfunction. Obesity is also associated with increased risk of later-life dementia and Alzheimer's disease. Patients with obesity and chronic TBI may be more vulnerable to long-term mental abnormalities. This review explores the question of whether weight loss induced by bariatric surgery could delay or perhaps even reverse the progression of mental deterioration. Bariatric surgery, with its induction of weight loss, remission of type 2 diabetes, and other expressions of the metabolic syndrome, improves metabolic efficiency, leads to reversal of brain lesions seen on imaging studies, and improves function. These observations suggest that metabolic/bariatric surgery may be a most effective therapy for TBI.

Acute colitis during chronic experimental traumatic brain injury in mice induces dysautonomia and persistent extraintestinal, systemic, and CNS inflammation with exacerbated neurological deficits

BACKGROUND

Disruptions of brain-gut axis have been implicated in the progression of a variety of gastrointestinal (GI) disorders and central nervous system (CNS) diseases and injuries, including traumatic brain injury (TBI). TBI is a chronic disease process characterized by persistent secondary injury processes which can be exacerbated by subsequent challenges. Enteric pathogen infection during chronic TBI worsened cortical lesion volume; however, the pathophysiological mechanisms underlying the damaging effects of enteric challenge during chronic TBI remain unknown. This preclinical study examined the effect of intestinal inflammation during chronic TBI on associated neurobehavioral and neuropathological outcomes, systemic inflammation, and dysautonomia.

METHODS

Dextran sodium sulfate (DSS) was administered to adult male C57BL/6NCrl mice 28 days following craniotomy (Sham) or TBI for 7 days to induce intestinal inflammation, followed by a return to normal drinking water for an additional 7 to 28 days for recovery; uninjured animals (Naïve) served as an additional control group. Behavioral testing was carried out prior to, during, and following DSS administration to assess changes in motor and cognitive function, social behavior, and mood. Electrocardiography was performed to examine autonomic balance. Brains were collected for histological and molecular analyses of injury lesion, neurodegeneration, and neuroinflammation. Blood, colons, spleens, mesenteric lymph nodes (mLNs), and thymus were collected for morphometric analyses and/or immune characterization by flow cytometry.

RESULTS

Intestinal inflammation 28 days after craniotomy or TBI persistently induced, or exacerbated, respectively, deficits in fine motor coordination, cognition, social behavior, and anxiety-like behavior. Behavioral changes were associated with an induction, or exacerbation, of hippocampal neuronal cell loss and microglial activation in Sham and TBI mice administered DSS, respectively. Acute DSS administration resulted in a sustained systemic immune response with increases in myeloid cells in blood and spleen, as well as myeloid cells and lymphocytes in mesenteric lymph nodes. Dysautonomia was also induced in Sham and TBI mice administered DSS, with increased sympathetic tone beginning during DSS administration and persisting through the first recovery week.

CONCLUSION

Intestinal inflammation during chronic experimental TBI causes a sustained systemic immune response and altered autonomic balance that are associated with microglial activation, increased neurodegeneration, and persistent neurological deficits.

Differential Fecal Microbiome Dysbiosis after Equivalent Traumatic Brain Injury in Aged Versus Young Adult Mice

Traumatic brain injury (TBI) has a bimodal age distribution with peak incidence at age 24 and age 65 with worse outcomes developing in aged populations. Few studies have specifically addressed age at the time of injury as an independent biologic variable in TBI-associated secondary pathology. Within the framework of our published work, identifying age related effects of TBI on neuropathology, cognition, memory and motor function we analyzed fecal pellets collected from young and aged TBI animals to assess for age-induced effects in TBI induced dysbiosis. In this follow up, work we hypothesized increased dysbiosis after TBI in aged (80-week-old, N=10) versus young (14-week-old, N=10) mice. C57BL/6 males received a sham incision or TBI via open-head controlled cortical impact. Fresh stool pellets were collected 1-day pre-TBI, then 1, 7, and 28-days post-TBI for 16S rRNA gene sequencing and taxonomic analysis. Data revealed an age induced increase in disease associated microbial species which were exacerbated by injury. Consistent with our hypothesis, aged mice demonstrated a high number of disease associated changes to the gut microbiome pre- and post-injury. Our data suggest divergent microbiome phenotypes in injury between young and aged reflecting a previously unknown interaction between age, TBI, and the gut-brain axis implying the need for different treatment strategies.

Gut microbiota-brain interaction: An emerging immunotherapy for traumatic brain injury

Individuals suffering from traumatic brain injury (TBI) often experience the activation of the immune system, resulting in declines in cognitive and neurological function after brain injury. Despite decades of efforts, approaches for clinically effective treatment are sparse. Evidence on the association between current therapeutic strategies and clinical outcomes after TBI is limited to poorly understood mechanisms. For decades, an increasing number of studies suggest that the gut-brain axis (GBA), a bidirectional communication system between the central nervous system (CNS) and the gastrointestinal tract, plays a critical role in systemic immune response following neurological diseases. In this review, we detail current knowledge of the immune pathologies of GBA after TBI. These processes may provide a new therapeutic target and rehabilitation strategy developed and used in clinical treatment of TBI patients.

The brain-gut axis: A prime therapeutic target in traumatic brain injury

Traumatic brain injury (TBI) is a significant cause of morbidity and mortality in trauma patients. The primary focus of treating TBI is to prevent additional injury to the damaged brain tissue, known as secondary brain injury. This treatment can include treating the body's inflammatory response. Despite promise in animal models, anti-inflammatory therapy has failed to improve outcomes in human patients, suggesting a more targeted and precise approach may be needed. There is a bidirectional axis between the intestine and the brain that contributes to this inflammation in acute and chronic injury. The mechanisms for this interaction are not completely understood, but there is evidence that neural, inflammatory, endocrine, and microbiome signals all participate in this process. Therapies that target the intestine as a source of inflammation have potential to lessen secondary brain injury and improve outcomes in TBI patients, but to develop these treatments we need to better understand the mechanisms behind this intestinal inflammatory response.

The gut microbiota may be a novel pathogenic mechanism in loosening of orthopedic implants in rats

Particles released from implants cause inflammatory bone loss, which is a key factor in aseptic loosening, the most common reason for joint replacement failure. With the anticipated increased incidence of total joint replacement in the next decade, implant failure will continue to burden patients. The gut microbiome is increasingly recognized as an important factor in bone physiology, however, its role in implant loosening is currently unknown. We tested the hypothesis that implant loosening is associated with changes in the gut microbiota in a preclinical model. When the particle challenge caused local joint inflammation, decreased peri-implant bone volume, and decreased implant fixation, the gut microbiota was affected. When the particle challenge did not cause this triad of local effects, the gut microbiota was not affected. Our results suggest that cross-talk between these compartments is a previously unrecognized mechanism of failure following total joint replacement.

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.

Gut Microbiota Dysbiosis as a Target for Improved Post-Surgical Outcomes and Improved Patient Care: A Review of Current Literature

ABSTRACT

Critical illness results in significant changes in the human gut microbiota, leading to the breakdown of the intestinal barrier function, which plays a role in the pathogenesis of multiple organ dysfunction. Patients with sepsis/acute respiratory distress syndrome (ARDS) have a profoundly distorted intestinal microbiota rhythm, which plays a considerable role in the development of gut-derived infections and intestinal dysbiosis. Despite recent medical developments, postsurgical complications are associated with a high morbidity and mortality rate. Bacterial translocation, which is the movement of bacteria and bacterial products across the intestinal barrier, was shown to be a mechanism behind sepsis. Current research is focusing on a solution by addressing significant factors that contribute to intestinal dysbiosis, which subsequently leads to multiple organ failure and, thus, mortality. It may, however, be challenging to manipulate the microbiota in critically ill patients for enhanced therapeutic gain. Probiotic manipulation is advantageous for maintaining the gut-barrier defense and for modulating the immune response. Based on available published research, this review aims to address the application of potential strategies in the intensive care unit, supplemented with current therapeutics by the administration of probiotics, prebiotics, and fecal microbiota transplant, to reduce post-surgical complications of sepsis/ARDS in critically ill patients.

Traumatic brain injury causing intestinal dysfunction: A review

Traumatic brain injuries (TBI) and its sequelae are becoming one of the most pressing public health concerns worldwide. It is one of the leading causes of increased morbidity and mortality. The primary insult to the brain can cause ischemic brain injury, paralysis, concussions, death, and other serious complications. Brain injury also involves other systems through a secondary pathway resulting in multiple complications during and after hospitalization. The focus of our article is to assess the literature available on traumatic brain injury and intestinal dysfunctional to highlight the aspects of epidemiology, pathophysiology, and different diagnostic approaches for early diagnosis of gut dysfunction. We review studies done in both humans and animals, to better understand this underrated topic, as it costs billions of dollars to the healthcare industry because of delayed diagnosis.

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.

Bidirectional Brain-gut-microbiota Axis in increased intestinal permeability induced by central nervous system injury

Central nervous system injuries may lead to the disorders of the hypothalamic‐pituitary‐adrenal axis, autonomic nervous system, and enteric nervous system. These effects then cause the changes in the intestinal microenvironment, such as a disordered intestinal immune system as well as alterations of intestinal bacteria. Ultimately, this leads to an increase in intestinal permeability. Inflammatory factors produced by the interactions between intestinal neurons and immune cells as well as the secretions and metabolites of intestinal flora can then migrate through the intestinal barrier, which will aggravate any peripheral inflammation and the central nervous system injury. The brain‐gut‐microbiota axis is a complex system that plays a crucial role in the occurrence and development of central nervous system diseases. It may also increase the consequences of preventative treatment. In this context, here we have summarized the factors that can lead to the increased intestinal permeability and some of the possible outcomes.

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.

Probiotics, prebiotics, and synbiotics regulate the intestinal microbiota differentially and restore the relative abundance of specific gut microorganisms

Fermented milk is an effective carrier for probiotics, the consumption of which improves host health. The beneficial effects of probiotics, prebiotics, and synbiotics on gut dysbiosis have been reported previously. However, the way in which specific probiotics, prebiotics, and synbiotics regulate intestinal microbes remains unclear. Therefore, the probiotics Lactobacillus rhamnosus AS 1.2466 and Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 and the prebiotics xylooligosaccharide and red ginseng extracts were fed to mice to determine their effects on the intestinal microbiota. Then, mice were administered xylooligosaccharide and L. rhamnosus (synthesis) by gavage, and the number of L. rhamnosus was determined in the intestine at different times. The results show that probiotics and prebiotics can quickly reduce the Firmicutes/Bacteroidetes ratio, inhibit harmful bacteria (such as Klebsiella and Escherichia coli), and accelerate the recovery of beneficial intestinal microorganisms (such as Lactobacillus). In a complex intestinal microecology, different probiotics and prebiotics have different effects on specific intestinal microorganisms that cannot be recovered in the short term. In addition, after 20 d of intragastric xylooligosaccharide addition at 0.12 g/kg of body weight, L. rhamnosus colonization in the mouse ileum was 7.48 log cfu/mL, which was higher than in the low-dose group, prolonging colonization time and increasing the number of probiotics in the intestine. Therefore, this study demonstrated that probiotics and prebiotics can promote the balance of intestinal microbiota by regulating specific microbes in the intestine, and the effects of a suitable combination of synbiotics are beneficial, laying the foundation for the development of new dairy products rich in synbiotics.

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.

Traditional Chinese Medicine in Emergency Treatment Mechanism and Application

Traditional Chinese medicine has usually been recognized to be efficacious to treat chronic diseases from the western point-of-view. However, there is a long history in China of applying traditional Chinese medicine in many acute and urgent medical conditions. In this review, selected methods documented in traditional Chinese medicine including blowing air to ear, nose insufflating therapy, acupuncture and moxibustion were presented as the common practices to promote consciousness recovery from coma. We aimed to explore the mechanism of these four methods with current scientific evidence, further discuss the potential of traditional Chinese medicine to be applied in emergency medicine and provide a path forward to more rigorously validate these procedures. The development of the integrated traditional Chinese medicine and western medicines provides a new therapeutic direction for the new first-aid treatment.