Age matters: Microbiome depletion prior to repeat mild traumatic brain injury differentially alters microbial composition and function in adolescent and adult rats

Breaking down silos: The Gastroenterology Immunology Neuroscience (GIN) Discovery Program - a new model for research

The Gastroenterology Immunology Neuroscience (GIN) Discovery Program represents a new model for research that overcomes the limitations imposed by traditional "research silos" in science. By uniting these three fields, the GIN Program aims to enhance the understanding and treatment of chronic conditions through a system-wide perspective focusing on the gut-immune-brain axis. Key initiatives include monthly interdisciplinary seminars, an annual symposium, and GINnovate, a commercialization and entrepreneurship event. Additionally, the program offers a seed grant competition for early and mid-career researchers, promoting advancements in gut-immune-brain axis research through the power of collaboration. The GIN Program in a short period of time has facilitated the formation of a vibrant community, captivating attention from both national and international institutions. This effort to break down barriers in research aims to inspire similar models that prioritize open communication, mutual respect and a commitment to impactful science.

Antibiotic treatment induces microbiome dysbiosis and reduction of neuroinflammation following traumatic brain injury in mice

Background

The gut microbiome is linked to brain pathology in cases of traumatic brain injury (TBI), yet the specific bacteria that are implicated are not well characterized. To address this gap, in this study, we induced traumatic brain injury (TBI) in male C57BL/6J mice using the controlled cortical impact (CCI) injury model. After 35 days, we administered a broad-spectrum antibiotics (ABX) cocktail (ampicillin, gentamicin, metronidazole, vancomycin) through oral gavage for 2 days to diminish existing microbiota. Subsequently, we inflicted a second TBI on the mice and analyzed the neuropathological outcomes five days later.

Results

Longitudinal analysis of the microbiome showed significant shifts in the diversity and abundance of bacterial genera during both acute and chronic inflammation. These changes were particularly dramatic following treatment with ABX and after the second TBI. ABX treatment did not affect the production of short-chain fatty acids (SCFA) but did alter intestinal morphology, characterized by reduced villus width and a lower count of goblet cells, suggesting potential negative impacts on intestinal integrity. Nevertheless, diminishing the intestinal microbiome reduced cortical damage, apoptotic cell density, and microglial/macrophage activation in the cortical and thalamic regions of the brain.

Conclusions

Our findings suggest that eliminating colonized gut bacteria via broad-spectrum ABX reduces neuroinflammation and enhances neurological outcomes in TBI despite implications to gut health.

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.

Trauma-toxicology: concepts, causes, complications

Trauma and toxic substances are connected in several aspects. On the one hand, toxic substances can be the reason for traumatic injuries in the context of accidental or violent and criminal circumstances. Examples for the first scenario is the release of toxic gases, chemicals, and particles during house fires, and for the second scenario, the use of chemical or biological weapons in the context of terroristic activities. Toxic substances can cause or enhance severe, life-threatening trauma, as described in this review for various chemical warfare, by inducing a tissue trauma accompanied by break down of important barriers in the body, such as the blood-air or the blood-gut barriers. This in turn initiates a "vicious circle" as the contribution of inflammatory responses to the traumatic damage enhances the macro- and micro-barrier breakdown and often results in fatal outcome. The development of sophisticated methods for detection and identification of toxic substances as well as the special treatment of the intoxicated trauma patient is summarized in this review. Moreover, some highly toxic substances, such as the protein toxins from the pathogenic bacterium Clostridioides (C.) difficile, cause severe post-traumatic complications which significantly worsens the outcome of hospitalized patients, in particular in multiply injured trauma patients. Therefore, novel pharmacological options for the treatment of such patients are necessarily needed and one promising strategy might be the neutralization of the toxins that cause the disease. This review summarizes recent findings on the molecular and cellular mechanisms of toxic chemicals and bacterial toxins that contribute to barrier breakdown in the human body as wells pharmacological options for treatment, in particular in the context of intoxicated trauma patients. "trauma-toxicology" comprises concepts regrading basic research, development of novel pharmacological/therapeutic options and clinical aspects in the complex interplay and "vicious circle" of severe tissue trauma, barrier breakdown, pathogen and toxin exposure, tissue damage, and subsequent clinical complications.

Microbiome depletion prior to repeat mild TBI differentially alters social deficits and prefrontal cortex plasticity in adolescent and adult rats

Although aging, repeat mild traumatic brain injury (RmTBI), and microbiome modifications independently change social behavior, there has been no investigation into their cumulative effects on social behavior and neuroplasticity within the prefrontal cortex. Therefore, we examined how microbiome depletion prior to RmTBI affected social behavior and neuroplasticity in adolescent and adult rats. Play, temperament analysis, elevated plus maze, and the hot/cold plate assessed socio-emotional function. Analyses of perineuronal nets (PNNs) and parvalbumin (PV) interneurons was completed. Social-emotional deficits were more pronounced in adults, with microbiome depletion attenuating social behavior deficits associated with RmTBI in both age groups. Microbiome depletion increased branch length and PNN arborization within the PFC but decreased the overall number of PNNs. Adults and males were more vulnerable to RmTBI. Interestingly, microbiome depletion may have attenuated the changes to neuroplasticity and subsequent social deficits, suggesting that the microbiome is a viable, but age-specific, target for RmTBI therapeutics.

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.

The adolescent and young adult microbiome and its association with substance use: a scoping review

AIMS

The microbiome is a critical factor in health throughout human development. The aims of this scoping review are to (i) elucidate the differences between the youth (post-natal day 21-65 for rodents, 2-7 years for non-human primates, and 10-25 years for humans) microbiome with other life stages and (ii) identify youth-specific microbial changes associated with substance use.

METHODS

Peer-reviewed studies published up to May 2023 were identified in PubMed and SCOPUS and included gut and oral microbiome studies from rodents, non-human primates, and humans (N = 1733). Twenty-six articles were determined eligible based on inclusion criteria (aim 1: n = 19, aim 2: n = 7).

RESULTS

The adolescent and young adult oral and gut microbiomes are distinct compared to other life stages, within both non-human and human models. While there is limited research in this area, the microbiome appears to be vulnerable to substance use exposure earlier in life, including substances commonly initiated and escalated during adolescence and young adulthood (i.e. alcohol, cannabis, and tobacco).

CONCLUSIONS

Studies across the lifespan indicate that adolescence and young adulthood are distinct periods of development, where the microbiome is sensitive to exposures, including substance use. There is a need for more studies focused on the adolescent and young adult microbiome and substance use, as well as focused on the oral microbiome during this developmental period. Understanding the gut and oral microbiome during adolescence and young adulthood may provide insight into the pathophysiology of substance use disorders.

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.

Integrating Microbiome Analysis, Metabolomics, Bioinformatics, and Histopathology to Elucidate the Protective Effects of Pomegranate Juice against Benzo-alpha-pyrene-Induced Colon Pathologies

Polycyclic aromatic hydrocarbons, e.g., benzo[a]pyrene (BaP), are common dietary pollutants with potential carcinogenic activity, while polyphenols are potential chemopreventive antioxidants. Although several health benefits are attributed to polyphenol-rich pomegranate, little is known about its interaction with BaP. This study integrates histochemical, microbiomic, and metabolomic approaches to investigate the protective effects of pomegranate juice from BaP-induced pathologies. To this end, 48 Sprague-Dawley rats received, for four weeks, either pomegranate, BaP, both, or neither (n = 12 rats per group). Whereas histochemical examination of the colon indicated tissue damage marked by mucin depletion in BaP-fed animals, which was partially restored by administration of pomegranate juice, the fecal microbiome and metabolome retained their resilience, except for key changes related to pomegranate and BaP biotransformation. Meanwhile, dramatic microbiome restructuring and metabolome shift were observed as a consequence of the elapsed time (age factor). Additionally, the analysis allowed a thorough examination of fecal microbiome-metabolome associations, which delineated six microbiome clusters (marked by a differential abundance of Lactobacillaceae and Prevotellaceae, Rumincococcaceae, and Erysipelotrichaceae) and two major metabolome clusters (a sugar- and amino-acids-dominated metabotype vs. a cluster of fatty acids and hydrocarbons), with sugar alcohols maintaining a unique signature. In conclusion, using paired comparisons to minimize inter-individual animal variations allowed the dissection of temporal vs. treatment-derived variations. Microbiome-metabolome association clusters may be further exploited for metabotype prediction and gut-health biomarker discovery.

Repetitive mild traumatic brain injury alters central and peripheral clock gene expression in the adolescent rat

Mild traumatic brain injury (mTBI) or concussion is a common injury worldwide leading to substantial medical costs and a high burden on society. In adolescents, falls and sports related trauma are often the causes of mTBI. Importantly, critical brain growth and development occurs during this sensitive period making the prospect of a brain injury a worrying phenomenon. Upwards of 70% of patients report circadian disruption following these injuries and this has been shown to impede recovery. Therefore, we sought to determine if core circadian clock gene expression was disrupted in rat model of repetitive mTBI (RmTBI). Male and female adolescent rats (n = 129) received sham or RmTBI. The animals were then euthanized at different times throughout the day and night. Tissue from the hypothalamus, cerebellum, hippocampus, liver, and small intestine were evaluated for the expression of per1, per2, cry1, clock, bmal1 and rev-erb-α. We found most clock genes varied across the day/night indicating circadian expression patterns. In the hypothalamus we found RmTBI altered the expression of cry1 and bmal1 in addition to sex differences in per2, cry1, clock, bmal1 and rev-erb- α. In the cerebellum, per1, per2, cry1, clock, bmal1 and rev-erb-α rhythms were all knocked out by RmTBI in addition to sex differences in cry1, clock and bmal1 expression. We also detected a significant decrease in overall expression of all clock genes in males in the middle of the night. In the hippocampus we found that RmTBI changed the rhythm of rev-erb-α expression in addition to sex differences in bmal1 expression. In the liver we detected strong rhythms in all genes examined, however only per2 expression was knocked out by RmTBI, in addition we also detected sex differences in per2 and cry1. We also detected an overall decrease in female clock gene expression in the early night. In the small intestine, RmTBI altered cry1 expression and there were sex differences in rev-erb-α. These results indicate that RmTBI alters core circadian clock gene expression in the central and peripheral nervous system in a time, tissue and sex dependent manner. This may be disrupting important phase relationships between the brain and peripheral nervous system and contributing to post-injury symptomology and also highlights the importance for time and sex dependent assessment of injury outcomes.