Distinct Commensal Bacterial Signature in the Gut Is Associated With Acute and Long-Term Protection From Ischemic Stroke

Alterations in the gut microbiome with hemorrhagic transformation in experimental stroke

OBJECTIVE

Hemorrhagic transformation (HT) is a life-threatening complication of stroke. Whether changes in gut microbial composition underlie the development of HT remains unknown. This study aimed to investigate whether the gut microbiota is altered in HT rats and examine the association between these changes and inflammatory responses.

METHODS

HT was successfully established in rats injected with 50% glucose (6 ml/Kg, i.p.) 15 min before middle cerebral artery occlusion (MCAO, 90 min occlusion) with reperfusion. After 5 days, rats were euthanized, and their brains used to estimate infarct volume. The inflammatory factors, the analysis of gut microbiota, and short-chain fatty acids (SCFA) were assessed.

RESULTS

In contrast with non-HT rats, gut microbiota sequencing showed an elevation in the relative abundance of Proteobacteria and Actinobacteria in HT rats. Total SCFAs, especially butyrate and valeric acid, were significantly lower in the cecal contents of HT rats than in those of non-HT rats. Hyperglycemia-induced HT exacerbation was not observed when rats were treated with antibiotics, suggesting that altered microbiota play a critical role in hyperglycemic HT pathogenesis. Furthermore, rats whose gut was colonized with HT rat microbiota showed increased susceptibility to HT.

CONCLUSION

This study provides important information about the gut microbiota profiles and SCFA levels of MCAO rats with HT or non-HT. The susceptibility to HT in MCAO rats is associated with inflammation and gut microbiota modulation.

Influence of the gut microbiome on inflammatory and immune response after stroke

Researches on the bidirectional communications between the gut microbiota and brain, termed the gut-brain axis, often bring about discoveries and drive the development of medicine and biology for stroke. Following stroke, the gut-brain axis is perturbed significantly on dysbiotic gut microbiome, intestinal dysfunction, enteric nervous system, increased gut permeability, and activated immune cells in the gut, which in turn results in infiltration of pro-inflammatory cells or bacterial toxins into brain tissue through impaired blood-brain barrier (BBB), finally exacerbated brain infarction. Herein, we illuminate the changes in the immune system and highlight the possible mechanisms of the gut microbiota to regulate inflammatory and immune processes in the context of stroke. We conducted a systematic literatures search in PubMed, Web of Science, Embase, and guideline-specific databases until May 2021 using the following key terms: gut microbiota, stroke, immune, and inflammation.

Gut-Brain Connection: Microbiome, Gut Barrier, and Environmental Sensors

The gut is an important organ with digestive and immune regulatory function which consistently harbors microbiome ecosystem. The gut microbiome cooperates with the host to regulate the development and function of the immune, metabolic, and nervous systems. It can influence disease processes in the gut as well as extra-intestinal organs, including the brain. The gut closely connects with the central nervous system through dynamic bidirectional communication along the gut-brain axis. The connection between gut environment and brain may affect host mood and behaviors. Disruptions in microbial communities have been implicated in several neurological disorders. A link between the gut microbiota and the brain has long been described, but recent studies have started to reveal the underlying mechanism of the impact of the gut microbiota and gut barrier integrity on the brain and behavior. Here, we summarized the gut barrier environment and the 4 main gut-brain axis pathways. We focused on the important function of gut barrier on neurological diseases such as stress responses and ischemic stroke. Finally, we described the impact of representative environmental sensors generated by gut bacteria on acute neurological disease via the gut-brain axis.

Calorie restriction conferred improvement effect on long-term rehabilitation of ischemic stroke via gut microbiota

Calorie restriction can modulate the gut microbiota and protect against many diseases including ischemic stroke. However, the role of calorie-restriction-induced microbiota alteration remained unknown in ischemic stroke rehabilitation. Here we conducted 30% reduction of caloric intake on mice for four weeks, to evaluate its role on ischemic stroke rehabilitation. Significantly, this calorie restriction led to better long-term rehabilitation in comparison of normal control. Notably, the transplantation of gut microbiome from calorie-restriction-treated mice to post-stroke mice was eligible to obtain better long-term rehabilitation of stroke mice. Bifidobacterium identified by 16 S ribosomal RNA sequencing were enriched in those of calorie-restriction mice. Then we administrated Bifidobacterium to stroke mice and found Bifidobacterium treatment could successfully improve the long-term rehabilitation of cerebral ischemia mice. Furthermore, the metabolomics analysis revealed a panel of upshifting metabolites, suggesting that calorie restriction greatly altered the gut microbiota composition and its metabolism. Hence, we discovered the novel effect of CR on long-term rehabilitation of ischemic stroke and the underlying role of gut microbiota, which might provide novel thoughts for the clinical post-stroke rehabilitation.

Rapid gut dysbiosis induced by stroke exacerbates brain infarction in turn

OBJECTIVE

Stroke is a leading cause of death and disability worldwide. Neuroprotective approaches have failed in clinical trials, thus warranting therapeutic innovations with alternative targets. The gut microbiota is an important contributor to many risk factors for stroke. However, the bidirectional interactions between stroke and gut microbiota remain largely unknown.

DESIGN

We performed two clinical cohort studies to capture the gut dysbiosis dynamics after stroke and their relationship with stroke prognosis. Then, we used a middle cerebral artery occlusion model to explore gut dysbiosis post-stroke in mice and address the causative relationship between acute ischaemic stroke and gut dysbiosis. Finally, we tested whether aminoguanidine, superoxide dismutase and tungstate can alleviate post-stroke brain infarction by restoring gut dysbiosis.

RESULTS

Brain ischaemia rapidly induced intestinal ischaemia and produced excessive nitrate through free radical reactions, resulting in gut dysbiosis with Enterobacteriaceae expansion. Enterobacteriaceae enrichment exacerbated brain infarction by enhancing systemic inflammation and is an independent risk factor for the primary poor outcome of patients with stroke. Administering aminoguanidine or superoxide dismutase to diminish nitrate generation or administering tungstate to inhibit nitrate respiration all resulted in suppressed Enterobacteriaceae overgrowth, reduced systemic inflammation and alleviated brain infarction. These effects were gut microbiome dependent and indicated the translational value of the brain-gut axis in stroke treatment.

CONCLUSIONS

This study reveals a reciprocal relationship between stroke and gut dysbiosis. Ischaemic stroke rapidly triggers gut microbiome dysbiosis with Enterobacteriaceae overgrowth that in turn exacerbates brain infarction.

The Role of Gut Microbiota in an Ischemic Stroke

The intestinal microbiome, the largest reservoir of microorganisms in the human body, plays an important role in neurological development and aging as well as in brain disorders such as an ischemic stroke. Increasing knowledge about mediators and triggered pathways has contributed to a better understanding of the interaction between the gut-brain axis and the brain-gut axis. Intestinal bacteria produce neuroactive compounds and can modulate neuronal function, which affects behavior after an ischemic stroke. In addition, intestinal microorganisms affect host metabolism and immune status, which in turn affects the neuronal network in the ischemic brain. Here we discuss the latest results of animal and human research on two-way communication along the gut-brain axis in an ischemic stroke. Moreover, several reports have revealed the impact of an ischemic stroke on gut dysfunction and intestinal dysbiosis, highlighting the delicate play between the brain, intestines and microbiome after this acute brain injury. Despite our growing knowledge of intestinal microflora in shaping brain health, host metabolism, the immune system and disease progression, its therapeutic options in an ischemic stroke have not yet been fully utilized. This review shows the role of the gut microflora-brain axis in an ischemic stroke and assesses the potential role of intestinal microflora in the onset, progression and recovery post-stroke.

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

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

Gut dysbiosis and age-related neurological diseases; an innovative approach for therapeutic interventions

The gut microbiota is a complex ecosystem of bacteria, fungi, and viruses that acts as a critical regulator in microbial, metabolic, and immune responses in the host organism. Imbalances in the gut microbiota, termed "dysbiosis," often induce aberrant immune responses, which in turn disrupt the local and systemic homeostasis of the host. Emerging evidence has highlighted the importance of gut microbiota in intestinal diseases, and more recently, in age-related central nervous systems diseases, for example, stroke and Alzheimer's disease. It is now generally recognized that gut microbiota significantly influences host behaviors and modulates the interaction between microbiota, gut, and brain, via the "microbiota-gut-brain axis." Several approaches have been utilized to reduce age-related dysbiosis in experimental models and in clinical studies. These include strategies to manipulate the microbiome via fecal microbiota transplantation, administration of prebiotics and probiotics, and dietary interventions. In this review, we explore both clinical and preclinical therapies for treating age-related dysbiosis.

The Gut Ecosystem: A Critical Player in Stroke

The intestinal microbiome is emerging as a critical factor in health and disease. The microbes, although spatially restricted to the gut, are communicating and modulating the function of distant organs such as the brain. Stroke and other neurological disorders are associated with a disrupted microbiota. In turn, stroke-induced dysbiosis has a major impact on the disease outcome by modulating the immune response. In this review, we present current knowledge on the role of the gut microbiome in stroke, one of the most devastating brain disorders worldwide with very limited therapeutic options, and we discuss novel insights into the gut-immune-brain axis after an ischemic insult. Understanding the nature of the gut bacteria-brain crosstalk may lead to microbiome-based therapeutic approaches that can improve patient recovery.