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

Mental Health Disorders Due to Gut Microbiome Alteration and NLRP3 Inflammasome Activation After Spinal Cord Injury: Molecular Mechanisms, Promising Treatments, and Aids from Artificial Intelligence

Aside from its immediate traumatic effects, spinal cord injury (SCI) presents multiple secondary complications that can be harmful to those who have been affected by SCI. Among these secondary effects, gut dysbiosis (GD) and the activation of the NOD (nucleotide-binding oligomerization domain) like receptor-family pyrin-domain-containing three (NLRP3) inflammasome are of special interest for their roles in impacting mental health. Studies have found that the state of the gut microbiome is thrown into disarray after SCI, providing a chance for GD to occur. Metabolites such as short-chain fatty acids (SCFAs) and a variety of neurotransmitters produced by the gut microbiome are hampered by GD. This disrupts healthy cognitive processes and opens the door for SCI patients to be impacted by mental health disorders. Additionally, some studies have found an increased presence and activation of the NLRP3 inflammasome and its respective parts in SCI patients. Preclinical and clinical studies have shown that NLRP3 inflammasome plays a key role in the maturation of pro-inflammatory cytokines that can initiate and eventually aggravate mental health disorders after SCI. In addition to the mechanisms of GD and the NLRP3 inflammasome in intensifying mental health disorders after SCI, this review article further focuses on three promising treatments: fecal microbiome transplants, phytochemicals, and melatonin. Studies have found these treatments to be effective in combating the pathogenic mechanisms of GD and NLRP3 inflammasome, as well as alleviating the symptoms these complications may have on mental health. Another area of focus of this review article is exploring how artificial intelligence (AI) can be used to support treatments. AI models have already been developed to track changes in the gut microbiome, simulate drug-gut interactions, and design novel anti-NLRP3 inflammasome peptides. While these are promising, further research into the applications of AI for the treatment of mental health disorders in SCI is needed.

Potential role of gut microbiota in major depressive disorder: A review

Interactions between the gut microbiota and host immunity are sophisticated, dynamic, and host-dependent. Scientists have recently conducted research showing that disturbances in the gut bacterial community can lead to a decrease in some metabolites and, consequently, to behaviors such as depression. Exposure to stressors dropped the relative abundance of bacteria in the genus Bacteroides while soaring the relative abundance of bacteria in the genus Clostridium, Coprococcus, Dialister, and Oscillibacter, which were also reduced in people with depression. Microbiota and innate immunity are in a bilateral relationship. The gut microbiota has been shown to induce the synthesis of antimicrobial proteins such as catalysidins, type C lectins, and defensins. Probiotic bacteria can modulate depressive behavior through GABA signaling. The gut microbiome produces essential metabolites such as neurotransmitters, tryptophan metabolites, and short-chain fatty acids (SCFAs) that can act on the CNS. In the case of dysbiosis, due to mucin changes, the ratio of intestinal-derived molecules may change and contribute to depression. Psychotropics, including Bifidobacterium longum NCC3001, Clostridium butyricum CBM588, and Lactobacillus acidophilus, have mental health benefits, and can have a positive effect on the host-brain relationship, and have antidepressant effects. This article reviews current studies on the association between gut microbiota dysbiosis and depression. Comprehensively, these findings could potentially lead to novel approaches to improving depressive symptoms via gut microbiota alterations, including probiotics, prebiotics, and fecal microbiota transplantation.

The Effect of Probiotics on the Prognostication of the Neutrophil-to-Lymphocyte Ratio in Severe Multi-Trauma Patients

BACKGROUND

The ratio of neutrophils to lymphocytes [NLR] is one of the most accepted prognostic indices and demonstrates a positive correlation with the severity of a disease. Given that probiotics exerted immunomodulatory properties and thus positively affected lymphocytopenia induction in severely ill patients, we performed a post hoc analysis in the ProVAP protocol to investigate whether probiotics affected the prognostication of NLR in respect to ventilator-associated pneumonia in multi-trauma patients. This cohort mandatorily involved severe traumatic brain injury patients.

METHODS

The white blood cell data of all patients, after being retrieved for the days 0 and 7, were statistically assessed in respect to neutrophils, lymphocytes and NLR among the 4 sub-groups of the study: placebo/no-VAP, placebo/VAP, probiotics/no-VAP, and probiotics/VAP.

RESULTS

Lymphopenia was dominant in placebo sub-groups, while an increased level of lymphocytes was prominent in probiotics sub-groups. This resulted in an increase [p = 0.018] in the NLR value in the probiotics/VAP group in relation to the probiotics/no-VAP cohort; this was an increase of half the value of the placebo/VAP [p < 0.001], while the NLR value in placebo/no-VAP group increased almost four-fold in relation to probiotics/no-VAP [p < 0.001]. Additionally, the ROC curve for probiotic-treated patients revealed a NLR7 cut-off value of 7.20 as a prognostic factor of VAP (AUC: 78.6%, p = 0.015, 95% CI: 62.6-94.5%), having a high specificity of 90.2% and a sensitivity of 42.9%.

CONCLUSIONS

NLR may considered a credible prognostic biomarker in multi-trauma patients since it can evaluate the immunomodulatory benefits of probiotic treatment. However, the results of the present post hoc analysis should be interpreted meticulously until further evaluation, since they may be basically species- or strain-specific.

Role of NLRP3 Inflammasome in Post-Spinal-Cord-Injury Anxiety and Depression: Molecular Mechanisms and Therapeutic Implications

The majority of research on the long-term effects of spinal cord injury (SCI) has primarily focused on neuropathic pain (NP), psychological issues, and sensorimotor impairments. Among SCI patients, mood disorders, such as anxiety and depression, have been extensively studied. It has been found that chronic stress and NP have negative consequences and reduce the quality of life for individuals living with SCI. Our review examined both human and experimental evidence to explore the connection between mood changes following SCI and inflammatory pathways, with a specific focus on NLRP3 inflammasome signaling. We observed increased proinflammatory factors in the blood, as well as in the brain and spinal cord tissues of SCI models. The NLRP3 inflammasome plays a crucial role in various diseases by controlling the release of proinflammatory molecules like interleukin 1β (IL-1β) and IL-18. Dysregulation of the NLRP3 inflammasome in key brain regions associated with pain processing, such as the prefrontal cortex and hippocampus, contributes to the development of mood disorders following SCI. In this review, we summarized recent research on the expression and regulation of components related to NLRP3 inflammasome signaling in mood disorders following SCI. Finally, we discussed potential therapeutic approaches that target the NLRP3 inflammasome and regulate proinflammatory cytokines as a way to treat mood disorders following SCI.

Targeting the gut-microbiota-brain axis in irritable bowel disease to improve cognitive function - recent knowledge and emerging therapeutic opportunities

The brain-gut axis forms a bidirectional communication system between the gastrointestinal (GI) tract and cognitive brain areas. Disturbances to this system in disease states such as inflammatory bowel disease have consequences for neuronal activity and subsequent cognitive function. The gut-microbiota-brain axis refers to the communication between gut-resident bacteria and the brain. This circuits exists to detect gut microorganisms and relay information to specific areas of the central nervous system (CNS) that in turn, regulate gut physiology. Changes in both the stability and diversity of the gut microbiota have been implicated in several neuronal disorders, including depression, autism spectrum disorder Parkinson's disease, Alzheimer's disease and multiple sclerosis. Correcting this imbalance with medicinal herbs, the metabolic products of dysregulated bacteria and probiotics have shown hope for the treatment of these neuronal disorders. In this review, we focus on recent advances in our understanding of the intricate connections between the gut-microbiota and the brain. We discuss the contribution of gut microbiota to neuronal disorders and the tangible links between diseases of the GI tract with cognitive function and behaviour. In this regard, we focus on irritable bowel syndrome (IBS) given its strong links to brain function and anxiety disorders. This adds to the growing body of evidence supporting targeted therapeutic strategies to modulate the gut microbiota for the treatment of brain/mental-health-related disease.

Gut microbiota changes in animal models of spinal cord injury: a preclinical systematic review and meta-analysis

BACKGROUND

An increasing number of studies show that the intestinal flora is closely related to spinal cord injury. Many researchers are exploring the changes in the richness, diversity, and evenness of intestinal flora in spinal cord injury animal models to identify the characteristic bacteria.

METHODS

A comprehensive literature search was conducted using three databases: PubMed, Embase, and Web of Science. A meta-analysis was performed using R 4.3.1 to evaluate the comparison of microbiota diversity, richness, and evenness and the relative abundance of intestinal microbiota in animals with spinal cord injury and blank controls.

RESULTS

Fifteen studies were included in the meta-analysis, of which 12 involved gut microbiota distribution indicators and 11 included intestinal microflora relative abundance indicators. Meta-analysis of high-dimensional indicators describing the distribution of the gut microbiota identified a substantial decline in the evenness and richness of the intestinal flora. In addition, the Actinobacteria phylum and Erysipelotrichales and Clostridiales orders were significantly different between the spinal cord injury and sham groups; therefore, they may be the characteristic bacteria in spinal cord injury models.

CONCLUSION

Our meta-analysis suggested that the gut microbiota in the spinal cord injury animal model group was altered compared with that in the control group, with varying degrees of changes in richness and evenness and potentially pathogenic characteristic flora. More rigorous methodological studies are needed because of the high heterogeneity and limited sample size. Further research is needed to clinically apply intestinal microbiota and potentially guide fecal microbiota transplantation therapy.

Effects of Recombinant IL-13 Treatment on Gut Microbiota Composition and Functional Recovery after Hemisection Spinal Cord Injury in Mice

In recent years, the gut-central nervous system axis has emerged as a key factor in the pathophysiology of spinal cord injury (SCI). Interleukin-13 (IL-13) has been shown to have anti-inflammatory and neuroprotective effects in SCI. The aim of this study was to investigate the changes in microbiota composition after hemisection injury and to determine whether systemic recombinant (r)IL-13 treatment could alter the gut microbiome, indirectly promoting functional recovery. The gut microbiota composition was determined by 16S rRNA gene sequencing, and correlations between gut microbiota alterations and functional recovery were assessed. Our results showed that there were no changes in alpha diversity between the groups before and after SCI, while PERMANOVA analysis for beta diversity showed significant differences in fecal microbial communities. Phylogenetic classification of bacterial families revealed a lower abundance of the Bacteroidales S24-7 group and a higher abundance of Lachnospiraceae and Lactobacillaceae in the post-SCI group. Systemic rIL-13 treatment improved functional recovery 28 days post-injury and microbiota analysis revealed increased relative abundance of Clostridiales vadin BB60 and Acetitomaculum and decreased Anaeroplasma, Ruminiclostridium_6, and Ruminococcus compared to controls. Functional assessment with PICRUSt showed that genes related to glyoxylate cycle and palmitoleate biosynthesis-I were the predominant signatures in the rIL-13-treated group, whereas sulfolactate degradation super pathway and formaldehyde assimilation-I were enriched in controls. In conclusion, our results indicate that rIL-13 treatment promotes changes in gut microbial communities and may thereby contribute indirectly to the improvement of functional recovery in mice, possibly having important implications for the development of novel treatment options for SCI.

Melatonin, a natural antioxidant therapy in spinal cord injury

Spinal cord injury (SCI) is a sudden onset of disruption to the spinal neural tissue, leading to loss of motor control and sensory function of the body. Oxidative stress is considered a hallmark in SCI followed by a series of events, including inflammation and cellular apoptosis. Melatonin was originally discovered as a hormone produced by the pineal gland. The subcellular localization of melatonin has been identified in mitochondria, exhibiting specific onsite protection to excess mitochondrial reactive oxygen species and working as an antioxidant in diseases. The recent discovery regarding the molecular basis of ligand selectivity for melatonin receptors and the constant efforts on finding synthetic melatonin alternatives have drawn researchers' attention back to melatonin. This review outlines the application of melatonin in SCI, including 1) the relationship between the melatonin rhythm and SCI in clinic; 2) the neuroprotective role of melatonin in experimental traumatic and ischemia/reperfusion SCI, i.e., exhibiting anti-oxidative, anti-inflammatory, and anti-apoptosis effects, facilitating the integrity of the blood-spinal cord barrier, ameliorating edema, preventing neural death, reducing scar formation, and promoting axon regeneration and neuroplasticity; 3) protecting gut microbiota and peripheral organs; 4) synergizing with drugs, rehabilitation training, stem cell therapy, and biomedical material engineering; and 5) the potential side effects. This comprehensive review provides new insights on melatonin as a natural antioxidant therapy in facilitating rehabilitation in SCI.

Gut microbiome and neurosurgery: Implications for treatment

Introduction

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

Background

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

Methods

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

Results

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

Conclusion

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