The bidirectional gut-brain-microbiota axis as a potential nexus between traumatic brain injury, inflammation, and disease

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.

Unilateral Cervical Vagotomy Modulates Immune Cell Profiles and the Response to a Traumatic Brain Injury

TBI induces splenic B and T cell expansion that contributes to neuroinflammation and neurodegeneration. The vagus nerve, the longest of the cranial nerves, is the predominant parasympathetic pathway allowing the central nervous system (CNS) control over peripheral organs, including regulation of inflammatory responses. One way this is accomplished is by vagus innervation of the celiac ganglion, from which the splenic nerve innervates the spleen. This splenic innervation enables modulation of the splenic immune response, including splenocyte selection, activation, and downstream signaling. Considering that the left and right vagus nerves have distinct courses, it is possible that they differentially influence the splenic immune response following a CNS injury. To test this possibility, immune cell subsets were profiled and quantified following either a left or a right unilateral vagotomy. Both unilateral vagotomies caused similar effects with respect to the percentage of B cells and in the decreased percentage of macrophages and T cells following vagotomy. We next tested the hypothesis that a left unilateral vagotomy would modulate the splenic immune response to a traumatic brain injury (TBI). Mice received a left cervical vagotomy or a sham vagotomy 3 days prior to a fluid percussion injury (FPI), a well-characterized mouse model of TBI that consistently elicits an immune and neuroimmune response. Flow cytometric analysis showed that vagotomy prior to FPI resulted in fewer CLIP+ B cells, and CD4+, CD25+, and CD8+ T cells. Vagotomy followed by FPI also resulted in an altered distribution of CD11bhigh and CD11blow macrophages. Thus, transduction of immune signals from the CNS to the periphery via the vagus nerve can be targeted to modulate the immune response following TBI.

Gut Microbiota Dysbiosis after Traumatic Brain Injury Contributes to Persistent Microglial Activation Associated with Upregulated Lyz2 and Shifted Tryptophan Metabolic Phenotype

Traumatic brain injury (TBI) is a common cause of disability and mortality, affecting millions of people every year. The neuroinflammation and immune response post-TBI initially have neuroprotective and reparative effects, but prolonged neuroinflammation leads to secondary injury and increases the risk of chronic neurodegenerative diseases. Persistent microglial activation plays a critical role in chronic neuroinflammation post-TBI. Given the bidirectional communication along the brain-gut axis, it is plausible to suppose that gut microbiota dysbiosis post-TBI influences microglial activation. In the present study, hippocampal microglial activation was observed at 7 days and 28 days post-TBI. However, in TBI mice with a depletion of gut microbiota, microglia were activated at 7 days post-TBI, but not at 28 days post-TBI, indicating that gut microbiota contributes to the long-term activation of microglia post-TBI. In addition, in conventional mice colonized by the gut microbiota of TBI mice using fecal microbiota transplant (FMT), microglial activation was observed at 28 days post-TBI, but not at 7 days post-TBI, supporting the role of gut microbiota dysbiosis in persistent microglial activation post-TBI. The RNA sequencing of the hippocampus identified a microglial activation gene, Lyz2, which kept upregulation post-TBI. This persistent upregulation was inhibited by oral antibiotics and partly induced by FMT. 16s rRNA gene sequencing showed that the composition and function of gut microbiota shifted over time post-TBI with progressive dysbiosis, and untargeted metabolomics profiling revealed that the tryptophan metabolic phenotype was differently reshaped at 7 days and 28 days post-TBI, which may play a role in the persistent upregulation of Lyz2 and the activation of microglia. This study implicates that gut microbiota and Lyz2 are potential targets for the development of novel strategies to address persistent microglial activation and chronic neuroinflammation post-TBI, and further investigations are warranted to elucidate the specific mechanism.

STING mediates neuroinflammatory response by activating NLRP3-related pyroptosis in severe traumatic brain injury

Long-term neurological deficits after severe traumatic brain injury (TBI), including cognitive dysfunction and emotional impairments, can significantly impair rehabilitation. Glial activation induced by inflammatory response is involved in the neurological deficits post-TBI. This study aimed to investigate the role of the stimulator of interferon genes (STING)-nucleotide-binding oligomerization domain-like receptor pyrin domain-containing-3 (NLRP3) signaling in a rodent model of severe TBI. Severe TBI models were established using weight-drop plus blood loss-reinfusion. Selective STING agonist ADU-S100 or antagonist C-176 was given as a single dose after modeling. Further, NLRP3 inhibitor MCC950 or activator nigericin, or caspase-1 inhibitor VX765, was given as an intracerebroventricular injection 30 min before modeling. After that, a novel object recognition test, open field test, force swimming test, western blot, and immunofluorescence assays were used to assess behavioral and pathological changes in severe TBI. Administration of C-176 alleviated TBI-induced cognitive dysfunction and emotional impairments, neuronal loss, and inflammatory activation of glia cells. However, the administration of STING agonist ADU-S100 exacerbated TBI-induced behavioral and pathological changes. In addition, STING activation exacerbated pyroptosis-associated neuroinflammation via promoting glial activation, as evidenced by increased cleaved caspase-1 and GSDMD N-terminal expression. In contrast, the administration of C-176 showed anti-pyroptotic effects. The neuroprotective effects of C-176 were partially reversed by the NLRP3 activator, nigericin. Collectively, glial STING is responsible for neuroinflammation post-TBI. However, pharmacologic inhibition of STING led to a remarkable improvement of neuroinflammation partly through suppressing NLRP3 signaling. The STING-NLRP3 signaling is a potential therapeutic target in TBI-induced neurological dysfunction.

Poria cocos water-soluble polysaccharide modulates anxiety-like behavior induced by sleep deprivation by regulating the gut dysbiosis, metabolic disorders and TNF-α/NF-κB signaling pathway

Poria cocos (P. cocos) has been traditionally used as folk medicine and functional food in China for more than 2000 years. The water-soluble polysaccharide is the main component of P. cocos decoction. The effects and mechanisms of the water-soluble polysaccharide from P. cocos (PCWP) were investigated in chronic sleep deprivation (CSD)-induced anxiety in rats. CSD induced anxiety, gut dysbiosis, and inflammatory responses, and reduced neurotransmitter levels, whereas PCWP intervention ameliorated anxiety-like behaviors, increased the levels of 5-hydroxytryptamine, dopamine, norepinephrine, and γ-aminobutyric acid in the hypothalamus, regulated gastrointestinal peptide levels, reduced inflammatory factors, and inhibited the tumor necrosis factor (TNF)-α/nuclear factor (NF)-κB signaling pathway in rats with CSD. The changes in the intestinal flora composition were determined using 16S rDNA sequencing, and indicated that PCWP significantly improved species richness and diversity in the intestinal flora of rats with anxiety, and adjusted the abundance of the following dysregulated bacteria closer to that of the normal group: Rikenellaceae_RC9_gut_group, Ruminococcus, Prevotellaceae_UCG-001, Prevotellaceae_NK3B31_group, Fusicatenibacter. Metabolomics was used to analyze fecal samples to identify significantly altered metabolites in the PCWP-treated groups. Thirty-eight PCWP-related metabolites and four metabolic pathways such as sphingolipid metabolism, taurine and hypotaurine metabolism, vitamin B6 metabolism, and glycerophospholipid metabolism were explored. The results of serum metabolomics showed that 26 biomarkers were significantly changed after PCWP intervention compared with the model group. The regulatory effects of metabolic pathway enrichment on sphingolipid, phenylalanine, and taurine and hypotaurine metabolism, and validation results showed that PCWP intervention regulated the activity of enzymes involved in the above metabolic pathways. A strong correlation between intestinal bacteria and potential biomarkers was found. Our findings present new evidence supporting the potential effect of PCWP in preventing the progression of anxiety by inhibiting the TNF-α/NF-κB signaling pathway, alleviating metabolic disorders, and ameliorating the gut microflora imbalance.

Electroacupuncture in Treatment of Acute Gastrointestinal Injury in Patients with Severe Traumatic Brain Injury: A Multicenter Randomized Controlled Trial

OBJECTIVE

To evaluate whether electroacupuncture (EA) would improve gastrointestinal function and clinical prognosis in patients with severe traumatic brain injury (TBI) complicocted by acute gastrointestinal injury (AGI).

METHODS

This multicenter, single-blind trial included patients with TBI and AGI admitted to 5 Chinese hospitals from September 2018 to December 2019. A total of 500 patients were randomized to the control or acupuncture groups using a random number table, 250 cases in each group. Patients in the control group received conventional treatment, including mannitol, nutritional support, epilepsy and infection prevention, and maintenance of water, electrolytes, and acid-base balance. While patients in the acupuncture group received EA intervention at bilateral Zusanli (ST 36), Shangjuxu (ST 37), Xiajuxu (ST 39), Tianshu (ST 25), and Zhongwan (RN 12) acupoints in addition to the conventional treatment, 30 min per time, twice daily, for 7 d. The primary endpoint was 28-d mortality. The secondary endpoints were serum levels of D-lactic acid (D-lac), diamine oxidase (DAO), lipopolysaccharide (LPS), motilin (MTL) and gastrin (GAS), intra-abdominal pressure (IAP), bowel sounds, abdominal circumference, AGI grade, scores of gastrointestinal failure (GIF), Glasgow Coma Scale (GCS), Acute Physiology and Chronic Health Evaluation (APACHE II), Sequential Organ Failure Assessment (SOFA), and Multiple Organ Dysfunction Syndrome (MODS), mechanical ventilation time, intense care unit (ICU) stay, and the incidence of hospital-acquired pneumonia.

RESULTS

The 28-d mortality in the acupuncture group was lower than that in the control group (22.80% vs. 33.20%, P<0.05). Compared with the control group, the acupuncture group at 7 d showed lower GIF, APACHE II, SOFA, MODS scores, D-lac, DAO, LPS, IAP, and abdominal circumference and higher GCS score, MTL, GAS, and bowel sound frequency (all P<0.05). In addition, the above indices showed simillar changes at 7 d compared with days 1 and 3 (all P<0.05) in the EA group.

CONCLUSION

Early EA can improve gastrointestinal function and clinical prognosis in patients with severe TBI complicated by AGI. (Registration No. ChiCTR2000032276).

Interplay of gut microbiota and oxidative stress: Perspective on neurodegeneration and neuroprotection

Background

Recent research on the implications of gut microbiota on brain functions has helped to gather important information on the relationship between them. Pathogenesis of neurological disorders is found to be associated with dysregulation of gut-brain axis. Some gut bacteria metabolites are found to be directly associated with the increase in reactive oxygen species levels, one of the most important risk factors of neurodegeneration. Besides their morbid association, gut bacteria metabolites are also found to play a significant role in reducing the onset of these life-threatening brain disorders.

Aim of Review

Studies done in the recent past raises two most important link between gut microbiota and the brain: "gut microbiota-oxidative stress-neurodegeneration" and gut microbiota-antioxidant-neuroprotection. This review aims to gives a deep insight to our readers, of the collective studies done, focusing on the gut microbiota mediated oxidative stress involved in neurodegeneration along with a focus on those studies showing the involvement of gut microbiota and their metabolites in neuroprotection.

Key Scientific Concepts of Review

This review is focused on three main key concepts. Firstly, the mounting evidences from clinical and preclinical arenas shows the influence of gut microbiota mediated oxidative stress resulting in dysfunctional neurological processes. Therefore, we describe the potential role of gut microbiota influencing the vulnerability of brain to oxidative stress, and a budding causative in Alzheimer's and Parkinson's disease. Secondly, contributing roles of gut microbiota has been observed in attenuating oxidative stress and inflammation via its own metabolites or by producing secondary metabolites and, also modulation in gut microbiota population with antioxidative and anti-inflammatory probiotics have shown promising neuro resilience. Thirdly, high throughput in silico tools and databases also gives a correlation of gut microbiome, their metabolites and brain health, thus providing fascinating perspective and promising new avenues for therapeutic options.

Gut Microbiota–Brain Axis as a Potential Modulator of Psychological Stress after Spinal Cord Injury

A growing body of evidence from preclinical and clinical studies has associated alterations of the gut microbiota–brain axis with the progression and development of a number of pathological conditions that also affect cognitive functions. Spinal cord injuries (SCIs) can be produced from traumatic and non-traumatic causes. It has been reported that SCIs are commonly associated with anxiety and depression-like symptoms, showing an incidence range between 11 and 30% after the injury. These psychological stress-related symptoms are associated with worse prognoses in SCIs and have been attributed to psychosocial stressors and losses of independence. Nevertheless, emotional and mental modifications after SCI could be related to changes in the volume of specific brain areas associated with information processing and emotions. Additionally, physiological modifications have been recognized as a predisposing factor for mental health depletion, including the development of gut dysbiosis. This condition of imbalance in microbiota composition has been shown to be associated with depression in clinical and pre-clinical models. Therefore, the understanding of the mechanisms underlying the relationship between SCIs, gut dysbiosis and psychological stress could contribute to the development of novel therapeutic strategies to improve SCI patients’ quality of life.

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.

Marked Response of Rat Ileal and Colonic Microbiota After the Establishment of Alzheimer’s Disease Model With Bilateral Intraventricular Injection of Aβ (1-42)

Alzheimer’s disease (AD) is a common neurodegenerative disease. More evidence has shown that gut microbiota is closely associated with AD. Also, studies have shown that the distribution of gut microbiota vary in different sections of the intestine. In this study, a rat model of AD was established using a bilateral intraventricular injection of β-amyloid (1-42) [Aβ (1-42)], and the behavior of rats, hippocampal Aβ (1-42) deposition, and the ileal and colonic microbiota in each group were analyzed. We observed that the model rats had obvious memory and cognitive impairment, increased Aβ (1-42) deposition, indicating that the AD model was successfully established. Through 16S rRNA-sequencing analysis, we found that α diversity, β diversity, and dominant microbiota in the ileum and colon of normal rats were significantly different, showing spatial heterogeneity. Additionally, the surgery and injection of Aβ (1-42) caused various degrees of disturbances in the ileal and colonic microbiota of rats. These findings provide new insights for the study of the gut microbiota of AD rats and help advance the development of therapeutic strategies for intervening AD through the gut microbiota.

[Polydatin improves intestinal barrier injury after traumatic brain injury in rats by reducing oxidative stress and inflammatory response via activating SIRT1-mediated deacetylation of SOD2 and HMGB1]

OBJECTIVE

To investigate the protective effect against intestinal mucosal injury in rats following traumatic brain injury (TBI) and explore the underlying mechanism.

METHODS

SD rat models of TBI were established by fluid percussion injury (FPI), and the specimens were collected at 12, 24, 48, and 72 h after TBI. Another 15 rats were randomly divided into shamoperated group (n=5), TBI with saline treatment (TBI+NS) group (n=5), and TBI with PD treatment (TBI+PD) group (treated with 30 mg/kg PD after TBI; n=5). Body weight gain and fecal water content of the rats were recorded, and after the treatments, the histopathology of the jejunum was observed, and the levels of D-lactic acid (D-LAC), diamine oxidase (DAO), ZO-1, claudin-5, and reactive oxygen species (ROS) were detected. Lipid peroxide (LPO) and superoxide dismutase (SOD) 2 content, jejunal pro-inflammatory factors (IL-6, IL-1β, and TNF- α), Sirt1 activity, SOD2 and HMGB1 acetylation level were also determined after the treatments.

RESULTS

The rats showed significantly decreased body weight and fecal water content and progressively increased serum levels of D-LAC and DAO after TBI (P < 0.05) with obvious jejunal injury, significantly decreased expression levels of ZO-1 and claudin-5, lowered SOD2 and Sirt1 activity (P < 0.05), increased expression levels of LPO, ROS, and pro-inflammatory cytokines, and enhanced SOD2 and HMGB1 acetylation levels (P < 0.05). Compared with TBI+NS group, the rats in TBI+PD group showed obvious body weight regain, increased fecal water content, reduced jejunal pathologies, decreased D-LAC and DAO levels (P < 0.05), increased ZO-1, claudin-5, SOD2 expression levels and Sirt1 activity, and significantly decreased ROS, LPO, pro-inflammatory cytokines, and acetylation levels of SOD2 and HMGB1 (P < 0.05).

CONCLUSION

PD alleviates oxidative stress and inflammatory response by activating Sirt1-mediated deacetylation of SOD2 and HMGB1 to improve intestinal mucosal injury in TBI rats.

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.

Gut microbiota modulation by prednisolone in a rat kindling model of pentylenetetrazol (PTZ)-induced seizure

The gut microbiota is a complex community composed by several microorganisms that interact in the maintenance of homeostasis and contribute to physiological processes, including brain function. The relationship of the taxonomic composition of the gut microbiota with neurological diseases such as autism, Parkinson's, Alzheimer's, anxiety, and depression is widely recognized. The immune system is an important intermediary between the gut microbiota and the central nervous system, being one of the communication routes of the gut-brain axis. Although the complexity of the relationship between inflammation and epilepsy has not yet been elucidated, inflammatory processes are similar in many ways to the consequences of dysbiosis and contribute to disease progression. This study aimed to analyze the taxonomic composition of the gut microbiota of rats treated with prednisolone in a kindling model of epilepsy. Male Wistar rats (90 days, n = 24) divided into four experimental groups: sodium chloride solution 0.9 g%, diazepam 2 mg/kg, prednisolone 1 mg/kg, and prednisolone 5 mg/kg administered intraperitoneally (i.p.) for 14 days. The kindling model was induced by pentylenetetrazole (PTZ) 25 mg/kg i.p. on alternate days. The taxonomic profile was established by applying metagenomic DNA sequencing. There was no change in alpha diversity, and the composition of the gut microbiota between prednisolone and diazepam was similar. The significant increase in Verrucomicrobia, Saccharibacteria, and Actinobacteria may be related to the protective activity against seizures and inflammatory processes that cause some cases of epilepsy. Further studies are needed to investigate the functional influence that these species have on epilepsy and the inflammatory processes that trigger it.

Freeze-Thaw Pretreatment Can Improve Efficiency of Bacterial DNA Extraction From Meconium

Although the presence of live microbes in utero remains under debate, newborn gastrointestinal bacteria are undoubtedly important to infant health. Measuring bacteria in meconium is an ideal strategy to understand this issue; however, the low efficiency of bacterial DNA extraction from meconium has limited its utilization. This study aims to improve the efficiency of bacterial DNA extraction from meconium, which generally has low levels of microflora but high levels of PCR inhibitors in the viscous matrix. The research was approved by the ethical committee of the Xiamen Maternity and Child Health Care Hospital, Xiamen, China. All the mothers delivered naturally, and their newborns were healthy. Meconium samples passed by the newborns within 24 h were collected. Each sample was scraped off of a sterile diaper, transferred to a 5-ml sterile tube, and stored at −80°C. For the assay, a freeze-thawing sample preparation protocol was designed, in which a meconium-InhibitEX buffer mixture was intentionally frozen 1–3 times at −20°C, −80°C, and (or) in liquid nitrogen. Then, DNA was extracted using a commercial kit and sequenced by 16S rDNA to verify the enhanced bacterial DNA extraction efficiency. Ultimately, we observed the following: (1) About 30 mg lyophilized meconium was the optimal amount for DNA extraction. (2) Freezing treatment for 6 h improved DNA extraction at −20°C. (3) DNA extraction efficiency was significantly higher with the immediate thaw strategy than with gradient thawing at −20°C, −80°C, and in liquid nitrogen. (4) Among the conditions of −20°C, −80°C, and liquid nitrogen, −20°C was the best freezing condition for both improving DNA extraction efficiency and preserving microbial species diversity in meconium, while liquid nitrogen was the worst condition. (5) Three freeze-thaw cycles could markedly enhance DNA extraction efficiency and preserve the species diversity of meconium microflora. We developed a feasible freeze-thaw pretreatment protocol to improve the extraction of microbial DNA from meconium, which may be beneficial for newborn bacterial colonization studies.

Potential Role of Akkermansia muciniphila in Parkinson's Disease and Other Neurological/Autoimmune Diseases

The composition of the gut microbiota, including Akkermansia muciniphila (A. muciniphila), is altered in many neurological diseases and may be involved in the pathophysiological processes of Parkinson's disease (PD). A. muciniphila, a mucin-degrading bacterium, is a potential next-generation microbe that has anti-inflammatory properties and is responsible for keeping the body healthy. As the role of A. muciniphila in PD has become increasingly apparent, we discuss the potential link between A. muciniphila and various neurological diseases (including PD) in the current review.

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.

The gut microbiota modulates brain network connectivity under physiological conditions and after acute brain ischemia

The gut microbiome has been implicated as a key regulator of brain function in health and disease. But the impact of gut microbiota on functional brain connectivity is unknown. We used resting-state functional magnetic resonance imaging in germ-free and normally colonized mice under naive conditions and after ischemic stroke. We observed a strong, brain-wide increase of functional connectivity in germ-free animals. Graph theoretical analysis revealed significant higher values in germ-free animals, indicating a stronger and denser global network but with less structural organization. Breakdown of network function after stroke equally affected germ-free and colonized mice. Results from histological analyses showed changes in dendritic spine densities, as well as an immature microglial phenotype, indicating impaired microglia-neuron interaction in germ-free mice as potential cause of this phenomenon. These results demonstrate the substantial impact of bacterial colonization on brain-wide function and extend our so far mainly (sub) cellular understanding of the gut-brain axis.

A Retrospective Clinical Analysis of the Serum Bile Acid Alteration Caused by Traumatic Brain Injury

Traumatic brain injury (TBI) can cause damage to peripheral organ systems, such as digestive organ system, and alterations of gut microbiota in addition to brain injury. Our previous study found that TBI induced gastrointestinal dysfunction accompanied by alterations of bile acid metabolism. Bile acid and its receptors have been reported to play important roles in various neurological diseases. To further examine the changes of bile acid metabolism in TBI patients, we performed a retrospective clinical analysis. In this study, 177 patients were included, and the results showed that TBI patients had more frequent antibiotic use compared with a control group. Regression analysis identified TBI as an independent factor for reduction of serum bile acid level (B = -1.762, p = 0.006), even with antibiotic use taken into a regression model. Sub-group regression analysis of TBI patients showed that antibiotic use was negatively associated with bile acid level, while creatinine and triglyceride were positively associated with bile acid level. In conclusion, these data indicated that TBI could greatly reduce serum bile acid. This study provided preliminary but novel clinical evidence of TBI interfering with bile acid metabolism, and further studies with large sample sizes are needed to validate these findings in the future.

The neuromicrobiology of Parkinson's disease: A unifying theory

Recent evidence confirms that PD is indeed a multifactorial disease with different aetiologies and prodromal symptomatology that likely depend on the initial trigger. New players with important roles as triggers, facilitators and aggravators of the PD neurodegenerative process have re-emerged in the last few years, the microbes. Having evolved in association with humans for ages, microbes and their products are now seen as fundamental regulators of human physiology with disturbances in their balance being increasingly accepted to have a relevant impact on the progression of disease in general and on PD in particular. In this review, we comprehensively address early studies that have directly or indirectly linked bacteria or other infectious agents to the onset and progression of PD, from the earliest suspects to the most recent culprits, the gut microbiota. The quest for effective treatments to arrest PD progression must inevitably address the different interactions between microbiota and human cells, and naturally consider the gut-brain axis. The comprehensive characterization of such mechanisms will help design innovative bacteriotherapeutic approaches to selectively shape the gut microbiota profile ultimately to halt PD progression. The present review describes our current understanding of the role of microorganisms and their endosymbiotic relatives, the mitochondria, in inducing, facilitating, or aggravating PD pathogenesis.

Lipocalin 2 as a Putative Modulator of Local Inflammatory Processes in the Spinal Cord and Component of Organ Cross talk After Spinal Cord Injury

Lipocalin 2 (LCN2), an immunomodulator, regulates various cellular processes such as iron transport and defense against bacterial infection. Under pathological conditions, LCN2 promotes neuroinflammation via the recruitment and activation of immune cells and glia, particularly microglia and astrocytes. Although it seems to have a negative influence on the functional outcome in spinal cord injury (SCI), the extent of its involvement in SCI and the underlying mechanisms are not yet fully known. In this study, using a SCI contusion mouse model, we first investigated the expression pattern of Lcn2 in different parts of the CNS (spinal cord and brain) and in the liver and its concentration in blood serum. Interestingly, we could note a significant increase in LCN2 throughout the whole spinal cord, in the brain, liver, and blood serum. This demonstrates the diversity of its possible sites of action in SCI. Furthermore, genetic deficiency of Lcn2 (Lcn2^-/-) significantly reduced certain aspects of gliosis in the SCI-mice. Taken together, our studies provide first valuable hints, suggesting that LCN2 is involved in the local and systemic effects post SCI, and might modulate the impairment of different peripheral organs after injury.

The immunological influence of physical exercise on TBI-induced pathophysiology: Crosstalk between the spleen, gut, and brain

Traumatic brain injury (TBI) is a non-degenerative and non-congenital insult to the brain and is recognized as a global public health problem, with a high incidence of neurological disorders. Despite the causal relationship not being entirely known, it has been suggested that multiorgan inflammatory response involving the autonomic nervous system and the spleen-gut brain axis dysfunction exacerbate the TBI pathogenesis in the brain. Thus, applying new therapeutic tools, such as physical exercise, have been described in the literature to act on the immune modulation induced by brain injuries. However, there are caveats to consider when interpreting the effects of physical exercise on this neurological injury. Given the above, this review will highlight the main findings of the literature involving peripheral immune responses in TBI-induced neurological damage and how changes in the cellular metabolism of the spleen-gut brain axis elicited by different protocols of physical exercise alter the pathophysiology induced by this neurological injury.

Biomimetic Nanoparticles as a Theranostic Tool for Traumatic Brain Injury

Traumatic brain injury (TBI) triggers both central and peripheral inflammatory responses. Existing pharmacological drugs are unable to effectively and quickly target the brain inflamed regions, setting up a major roadblock towards effective brain trauma treatments. Nanoparticles (NPs) have been used in multiple diseases as drug delivery tools with remarkable success due to their rapid diffusion and specificity in the target organ. Here, leukocyte-based biomimetic NPs are fabricated as a theranostic tool to directly access inflamed regions in a TBI mouse model. This NP systemic delivery is visualized using advanced in vivo imaging techniques, including intravital microscopy and in vivo imaging system. The results demonstrate selective targeting of NPs to the injured brain and increased NPs accumulation among the peripheral organs 24 h after TBI. Interestingly, increased microglial proliferation, decreased macrophage infiltration, and reduced brain lesion following the NPs treatments compared to sham vehicle-treated mice are also found. In summary, the results suggest that NPs represent a promising future theranostic tool for TBI treatment.

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.

A Population-Based Study of Pre-Existing Health Conditions in Traumatic Brain Injury

Health factors impacting both the occurrence of, and recovery from traumatic brain injury (TBI) vary in complexity, and present genuine challenges to researchers and healthcare professionals seeking to characterize injury consequences and determine prognosis. However, attempts to clarify causal links between injury characteristics and clinical outcomes (including mortality) often compel researchers to exclude pre-existing health conditions (PECs) in their samples, including psychiatric history, medication usage, and other comorbid conditions. In this pre-registered population-based study (total starting n = 939,123 patients), we examined trends in PEC incidence over 22 years in the state of Pennsylvania (1997-2019) in individuals sustaining TBI (n = 169,452) and individuals with orthopedic injury (n = 87,637). The goal was to determine how PECs interact with age and injury severity to influence short-term outcomes. A further goal was to determine whether number of PECs, or specific PEC clusters contributed to worse outcomes within the TBI cohort, compared with orthopedic injury alone. Primary findings indicate that PECs significantly influenced mortality within the TBI cohort; patients having four or more PECs were associated with approximately a two times greater likelihood of dying in acute care (odds ratio [OR] 1.9). Additionally, cluster analyses revealed four distinct PEC clusters that are age and TBI severity dependent. Overall, the likelihood of zero PECs hovers at ∼25%, which is critical to consider in TBI outcomes work and could potentially contribute to the challenges facing intervention science with regard to reproducibility of findings.

Stress and the Gut-Brain Axis: Implications for Cancer, Inflammation and Sepsis

BACKGROUND

The gut-brain axis has been discussed, directly or indirectly, for centuries, with the ideas of the gut affecting anything from moods to overall physiology being discussed across the centuries. With a recent explosion in research that looks to the microbiota as a mechanistic link between the gut and the brain, one sees that the gut-brain axis has various means of communication, such as through the vagus nerve and the enteric nervous system and can use the metabolites in the gut to communicate to the brain.

METHODS

The purpose of this review is to view the gut-brain axis through the lens of stress and how stress, from the prenatal period all the way through adulthood can impact the physiology of a human being. Studies have shown multiple mechanisms of measurable change with disruption in the microbiota that lead to behavioral changes. There are also effects of gut inflammation on the brain and the corresponding systemic response observed.

CONCLUSION

The overall literature is encouraging that the more understanding of the gut-brain axis, the greater ability to wield that understanding for therapeutic benefits.

Oral Administration of Brain Protein Combined With Probiotics Induces Immune Tolerance Through the Tryptophan Pathway

Excessive inflammation leads to secondary immune damage after traumatic brain injury (TBI). The intestinal mucosa is a key component of immune tolerance due to gut-brain axis regulation, but the curative effect is not optimal. Intestinal dysfunction impairs the establishment of immune tolerance in patients with TBI. Therefore, we orally administered brain protein (BP) combined with probiotics to induce immune tolerance and explored the mechanism by which the homeostasis of the microbiota contributes to the enhancement of curative effects by BPs. Herein, we demonstrated that patients with TBI and surgical brain injury (SBI) models of rats had obvious dysbiosis. Notably, the intestinal barrier, proinflammatory cytokines, and activation of microglia demonstrated that excessive inflammatory damage was better controlled in the combined group (oral administration of BP combined with probiotics) than in the BP group (oral administration of BP). Fundamentally, tandem mass tag (TMT)-based quantitative proteomics analysis revealed that BP and probiotics preferentially affect Try-related pathways. A series of experiments further confirmed that Indoleamine 2,3 dioxygenase (IDO)/Kynurenine (Kyn)/Aryl hydrocarbon receptor (AhR) expression was high in the BP group, while Tryptophan hydroxylase 1(TpH1)/5-hydroxytryptamine (5-HT) only changed in the combined group. This study suggests that probiotics can enhance the efficacy of oral BP-induced immune tolerance through the Try pathway.

Gut Microbiota-Related Effects of Tanhuo Decoction in Acute Ischemic Stroke

Acute ischemic stroke (AIS) is a major cause of acquired adult disability and death. Our previous studies proved the efficacy and effectiveness of Tanhuo decoction (THD) on AIS. However, the therapeutic mechanism remains unclear. We recruited 49 AIS patients and 30 healthy people to explore the effects of THD+basic treatment on the poststroke gut microbiota of AIS patients using 16S rRNA sequencing, in which 23 patients received basic treatment (control group) and 26 patients received THD+basic treatment (THD group). By comparing the data before and after treatments, we found the THD group acquired better outcome than the control group on both clinical outcome indices and the characteristics of gut microbiota. In addition to the mediation on short-chain fatty acid- (SCFA-) producing bacteria in two groups, treatment in the THD group significantly decreased the lipopolysaccharide- (LPS-) producing bacteria to reduce LPS biosynthesis. Besides, the complexity of the cooccurrence of gut microbiota and the competition among LPS-producing bacteria and opportunistic pathogenetic bacteria were enhanced in the THD group. Treatment in the THD group also exhibited the potential in decreasing genes on the biosynthesis of trimethylamine (TMA), the precursor of Trimethylamine N-oxide (TMAO), and increasing genes on the degradation of TMA, especially increasing trimethylamine-corrinoid protein Co-methyltransferase (mttB) which catabolizes TMA to methane. These results hinted that THD+basic treatment might exert its efficacy by mediating the gut microbiota and microbial metabolites, including LPS and TMAO that aggravate the sterile inflammation and platelet aggregation. Moreover, the well-fitting regression model results in predicting the clinical outcome with the alteration of gut microbiota proved gut microbiota as a potential indicator of AIS and provided evidence of the communication between the gut and brain of AIS patients.

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.

Disruption of intestinal barrier and endotoxemia after traumatic brain injury: Implications for post-traumatic epilepsy

OBJECTIVE

Traumatic brain injury (TBI) may lead to the disruption of the intestinal barrier (IB), and to the escape of products of commensal gut bacteria, including lipopolysaccharide (LPS), into the bloodstream. We examined whether lateral fluid percussion injury (LFPI) and post-traumatic epilepsy (PTE) are associated with the increased intestinal permeability and endotoxemia, and whether these events in turn are associated with PTE.

METHODS

LFPI was delivered to adult male Sprague-Dawley rats. Before, 1 week, and 7 months after LFPI, the IB permeability was examined by measuring plasma concentration of fluorescein isothiocyanate-labeled dextran (FD4) upon its enteral administration. Plasma LPS concentration was measured in the same animals, using enzyme-linked immunosorbent assay. PTE was examined 7 months after LFPI, with use of video-EEG (electroencephalography) monitoring.

RESULTS

One week after LFPI, the IB disruption was detected in 14 of 17 and endotoxemia - in 10 of 17 rats, with a strong positive correlation between FD4 and LPS levels, and between plasma levels of each of the analytes and the severity of neuromotor deficit. Seven months after LFPI, IB disruption was detected in 13 of 15 and endotoxemia in 8 of 15 rats, with a strong positive correlation between plasma levels of the two analytes. Five of 15 LFPI rats developed PTE. Plasma levels of both FD4 and LPS were significantly higher in animals with PTE than among the animals without PTE. The analysis of seven rats, which were examined repeatedly at 1 week and at 7 months, confirmed that late IB disruption and endotoxemia were not due to lingering of impairments occurring shortly after LFPI.

SIGNIFICANCE

LFPI leads to early and remote disruption of IB and a secondary endotoxemia. Early and late perturbations may occur in different subjects. Early changes reflect the severity of acute post-traumatic motor dysfunction, whereas late changes are associated with PTE.

Dietary Influences on the Microbiota-Gut-Brain Axis

Over unimaginable expanses of evolutionary time, our gut microbiota have co-evolved with us, creating a symbiotic relationship in which each is utterly dependent upon the other. Far from confined to the recesses of the alimentary tract, our gut microbiota engage in complex and bi-directional communication with their host, which have far-reaching implications for overall health, wellbeing and normal physiological functioning. Amongst such communication streams, the microbiota–gut–brain axis predominates. Numerous complex mechanisms involve direct effects of the microbiota, or indirect effects through the release and absorption of the metabolic by-products of the gut microbiota. Proposed mechanisms implicate mitochondrial function, the hypothalamus–pituitary–adrenal axis, and autonomic, neuro-humeral, entero-endocrine and immunomodulatory pathways. Furthermore, dietary composition influences the relative abundance of gut microbiota species. Recent human-based data reveal that dietary effects on the gut microbiota can occur rapidly, and that our gut microbiota reflect our diet at any given time, although much inter-individual variation pertains. Although most studies on the effects of dietary macronutrients on the gut microbiota report on associations with relative changes in the abundance of particular species of bacteria, in broad terms, our modern-day animal-based Westernized diets are relatively high in fats and proteins and impoverished in fibres. This creates a perfect storm within the gut in which dysbiosis promotes localized inflammation, enhanced gut wall permeability, increased production of lipopolysaccharides, chronic endotoxemia and a resultant low-grade systemic inflammatory milieu, a harbinger of metabolic dysfunction and many modern-day chronic illnesses. Research should further focus on the colony effects of the gut microbiota on health and wellbeing, and dysbiotic effects on pathogenic pathways. Finally, we should revise our view of the gut microbiota from that of a seething mass of microbes to one of organ-status, on which our health and wellbeing utterly depends. Future guidelines on lifestyle strategies for wellbeing should integrate advice on the optimal establishment and maintenance of a healthy gut microbiota through dietary and other means. Although we are what we eat, perhaps more importantly, we are what our gut microbiota thrive on and they thrive on what we eat.

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.

Retinitis pigmentosa is associated with shifts in the gut microbiome

The gut microbiome is known to influence the pathogenesis and progression of neurodegenerative diseases. However, there has been relatively little focus upon the implications of the gut microbiome in retinal diseases such as retinitis pigmentosa (RP). Here, we investigated changes in gut microbiome composition linked to RP, by assessing both retinal degeneration and gut microbiome in the rd10 mouse model of RP as compared to control C57BL/6J mice. In rd10 mice, retinal responsiveness to flashlight stimuli and visual acuity were deteriorated with respect to observed in age-matched control mice. This functional decline in dystrophic animals was accompanied by photoreceptor loss, morphologic anomalies in photoreceptor cells and retinal reactive gliosis. Furthermore, 16S rRNA gene amplicon sequencing data showed a microbial gut dysbiosis with differences in alpha and beta diversity at the genera, species and amplicon sequence variants (ASV) levels between dystrophic and control mice. Remarkably, four fairly common ASV in healthy gut microbiome belonging to Rikenella spp., Muribaculaceace spp., Prevotellaceae UCG-001 spp., and Bacilli spp. were absent in the gut microbiome of retinal disease mice, while Bacteroides caecimuris was significantly enriched in mice with RP. The results indicate that retinal degenerative changes in RP are linked to relevant gut microbiome changes. The findings suggest that microbiome shifting could be considered as potential biomarker and therapeutic target for retinal degenerative diseases.

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.

Nutritional factors in sport-related concussion

BACKGROUND

Sports concussion is a major problem that affects thousands of people every year. Concussion-related neurometabolic changes are thought to underlie neurophysiological alterations and post-concussion symptoms, such as headaches and sensitivity to light and noise, disabilities of concentration and tiredness. The injury triggers a complex neurometabolic cascade involving multiple mechanisms. There are pharmaceutical treatments that target one mechanism, but specific nutrients have been found to impact several pathways, thus offering a broader approach. This has prompted intensive research into the use of nutrient supplements as a concussion prevention and treatment strategy.

METHOD

We realised a bibliographic state of art providing a contemporary clinical and preclinical studies dealing with nutritional factors in sport-related concussion.

RESULTS

Numerous supplements, including n-3 polyunsaturated fatty acids, sulfur amino acids, antioxidants and minerals, have shown promising results as aids to concussion recovery or prevention in animal studies, most of which use a fluid percussion technique to cause brain injury, and in a few human studies of severe or moderate traumatic brain injury. Current ongoing human trials can hopefully provide us with more information, in particular, on new options, i.e. probiotics, lactate or amino acids, for the use of nutritional supplements for concussed athletes.

CONCLUSION

Nutritional supplementation has emerged as a potential strategy to prevent and/or reduce the deleterious effects of sports-related concussion and subconcussive impacts.

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.

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.

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.

Gut-brain axis: A matter of concern in neuropsychiatric disorders…!

The gut microbiota is composed of a large number of microbes, usually regarded as commensal bacteria. It has become gradually clear that gastrointestinal microbiota affects gut pathophysiology and the central nervous system (CNS) function by modulating the signaling pathways of the microbiota-gut-brain (MGB) axis. This bidirectional MGB axis communication primarily acts through neuroendocrine, neuroimmune, and autonomic nervous systems (ANS) mechanisms. Accumulating evidence reveals that gut microbiota interacts with the host brain, and its modulation may play a critical role in the pathology of neuropsychiatric disorders. Recently, neuroscience research has established the significance of gut microbiota in the development of brain systems that are essential to stress-related behaviors, including depression and anxiety. Application of modulators of the MGB, such as psychobiotics (e.g., probiotics), prebiotics, and specific diets, may be a promising therapeutic approach for neuropsychiatric disorders. The present review article primarily focuses on the relevant features of the disturbances of the MGB axis in the pathophysiology of neuropsychiatric disorders and its potential 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.

Hypoxia Augments Cerebral Inflammation in a Dextran Sulfate Sodium-Induced Colitis Mouse Model

The importance of hypoxia in the pathophysiology of inflammatory bowel disease (IBD) is increasingly being realized; also, hypoxia seems to be an important accelerator of brain inflammation, as has been reported by our group and others. IBD is a chronic intestinal disorder that leads to the development of inflammation, which is related to brain dysfunction. However, no studies have reported whether hypoxia is associated with IBD-induced neuroinflammation. Therefore, the objective of the present study was to determine whether hypoxia augments cerebral inflammation in a DSS-induced colitis mouse model. The mouse model was developed using 3% DSS for five days combined with exposure to hypoxic conditions (6,000 m) for two days. Mice were randomly divided into four groups: control group, DSS group, hypoxia group, and DSS plus hypoxia group. The results demonstrated that DSS combined with hypoxia resulted in up-regulation of colonic and plasmatic proinflammatory cytokines. Meanwhile, DSS plus hypoxia increased expression of Iba1, which is a marker of activated microglia, accompanied by increased expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) in the brain. Moreover, the expression of tight junction proteins, such as zonula occludens-1 (ZO-1), occludin, and claudin-5, was markedly downregulated. The current study provides new insight into how hypoxia exposure induces excessive inflammatory responses andpathophysiological consequences in the brain in a DSS-induced colitis model.

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 Kinetics of Intestinal Permeability in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality among trauma patients. Increased intestinal permeability plays an important role in the inflammatory process that accompanies TBI, and therapies that prevent this permeability change may improve outcomes in TBI patients. Different animal models have been developed to test permeability changes, but there has been no agreement on when permeability should be tested after TBI. Here, we describe a method for creating the TBI mouse model and for measuring intestinal permeability. We also detail our permeability measurements at different time points after TBI to help guide future experimental design. The TBI is made using a controlled cortical impact model with the cortical impactor set to speed 6 m/s, depth 3 mm, dwell time 0.2 s, and tip size 3 mm to produce a severe TBI. Permeability is measured at 2, 4, 6, and 24 hr after TBI by removing a piece of terminal ileum, tying the ends, filling the lumen with FITC-labeled dextran, and then measuring how much of the dextran moves into the surrounding solution bath over time using a fluorescent plate reader. Our results show that peak permeability occurs between 4 and 6 hr after TBI. We recommend that future experiments incorporate permeability measurements 4 to 6 hr after TBI in order to take advantage of this peak permeability. © 2020 Wiley Periodicals LLC. Basic Protocol: Mouse CCI traumatic brain injury model and intestinal permeability measurement.

Paths to Successful Translation of New Therapies for Severe Traumatic Brain Injury in the Golden Age of Traumatic Brain Injury Research: A Pittsburgh Vision

New neuroprotective therapies for severe traumatic brain injury (TBI) have not translated from pre-clinical to clinical success. Numerous explanations have been suggested in both the pre-clinical and clinical arenas. Coverage of TBI in the lay press has reinvigorated interest, creating a golden age of TBI research with innovative strategies to circumvent roadblocks. We discuss the need for more robust therapies. We present concepts for traditional and novel approaches to defining therapeutic targets. We review lessons learned from the ongoing work of the pre-clinical drug and biomarker screening consortium Operation Brain Trauma Therapy and suggest ways to further enhance pre-clinical consortia. Biomarkers have emerged that empower choice and assessment of target engagement by candidate therapies. Drug combinations may be needed, and it may require moving beyond conventional drug therapies. Precision medicine may also link the right therapy to the right patient, including new approaches to TBI classification beyond the Glasgow Coma Scale or anatomical phenotyping-incorporating new genetic and physiologic approaches. Therapeutic breakthroughs may also come from alternative approaches in clinical investigation (comparative effectiveness, adaptive trial design, use of the electronic medical record, and big data). The full continuum of care must also be represented in translational studies, given the important clinical role of pre-hospital events, extracerebral insults in the intensive care unit, and rehabilitation. TBI research from concussion to coma can cross-pollinate and further advancement of new therapies. Misconceptions can stifle/misdirect TBI research and deserve special attention. Finally, we synthesize an approach to deliver therapeutic breakthroughs in this golden age of TBI research.

Complement C6 deficiency exacerbates pathophysiology after spinal cord injury

Historically, the membrane attack complex, composed of complement components C5b-9, has been connected to lytic cell death and implicated in secondary injury after a CNS insult. However, studies to date have utilized either non-littermate control rat models, or mouse models that lack significant C5b-9 activity. To investigate what role C5b-9 plays in spinal cord injury and recovery, we generated littermate PVG C6 wildtype and deficient rats and tested functional and histological recovery after moderate contusion injury using the Infinite Horizon Impactor. We compare the effect of C6 deficiency on recovery of locomotor function and histological injury parameters in PVG rats under two conditions: (1) animals maintained as separate C6 WT and C6-D homozygous colonies; and (2) establishment of a heterozygous colony to generate C6 WT and C6-D littermate controls. The results suggest that maintenance of separate homozygous colonies is inadequate for testing the effect of C6 deficiency on locomotor and histological recovery after SCI, and highlight the importance of using littermate controls in studies involving genetic manipulation of the complement cascade.

The microbiota-microglia axis in central nervous system disorders

The innate immune system in the central nervous system (CNS) is mainly represented by specialized tissue-resident macrophages, called microglia. In the past years, various species-, host- and tissue-specific as well as environmental factors were recognized that essentially affect microglial properties and functions in the healthy and diseased brain. Host microbiota are mostly residing in the gut and contribute to microglial activation states, for example, via short-chain fatty acids (SCFAs) or aryl hydrocarbon receptor (AhR) ligands. Thereby, the gut microorganisms are deemed to influence numerous CNS diseases mediated by microglia. In this review, we summarize recent findings of the interaction between the host microbiota and the CNS in health and disease, where we specifically highlight the resident gut microbiota as a crucial environmental factor for microglial function as what we coin "the microbiota-microglia axis."

Functional Medicine: A View from Physical Medicine and Rehabilitation

Using the functional medicine rubric in physical medicine and rehabilitation (PM&R), a physiatrist can capitalize on addressing the root causes and downstream effects in patients with chronic diseases. Similar to the International Classification of Function model in rehabilitation, the functional medicine model uses biopsychosocial understanding with a systems biology approach to find fulcrum points to create the biggest impact on health care. Given the position of rehabilitation medicine with the type and location of patients, both functional medicine and PM&R would benefit from a mutual partnership.

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.