Besides damaging the brain, stroke causes systemic changes, including to the gastrointestinal system. A growing body of evidence supports the role of the gut and its microbiota in stroke, stroke prognosis, and recovery. The gut microbiota can increase the risk of a cerebrovascular event, playing a role in the onset of stroke. Conversely, stroke can induce dysbiosis of the gut microbiota and epithelial barrier integrity. This has been proposed as a contributor to systemic infections. In this review, we describe the role of the gut microbiota, microbiome and microbiota-derived metabolites in experimental and clinical stroke, and their potential use as therapeutic targets. Fourteen clinical studies have identified 62 upregulated (eg, Streptococcus , Lactobacillus, Escherichia ) and 29 downregulated microbial taxa (eg, Eubacterium, Roseburia ) between stroke and healthy participants. The majority found that stroke patients have reduced gut microbiome diversity. However, other nonbacterial microorganisms are yet to be studied. In experimental stroke, severity is dependent on gut microbiome composition, whereas the latter can greatly change with antibiotics, age, and diet. Consumption of foods rich in choline and L-carnitine are positively associated with stroke onset via production of trimethylamine N-oxide in experimental and clinical stroke. Conversely, in mice, consumption of dietary fiber improves stroke outcome, likely via gut microbiota–derived metabolites called short-chain fatty acids, such as acetate, propionate, and butyrate. The majority of the evidence, however, comes from experimental studies. Clinical interventions targeted at gut microbiota–derived metabolites as new therapeutic opportunities for stroke prevention and treatment are warranted.

There is increasing evidence of the influence of the gut microbiota on hypertension and its complications, such as chronic kidney disease, stroke, heart failure, and myocardial infarction. This is not surprising considering that the most common risk factors for hypertension, such as age, sex, medication, and diet, can also impact the gut microbiota. For example, sodium and fermentable fiber have been studied in relation to both hypertension and the gut microbiota. By combining second- and, now, third-generation sequencing with metabolomics approaches, metabolites, such as short-chain fatty acids and trimethylamine N-oxide, and their producers, have been identified and are now known to affect host physiology and the cardiovascular system. The receptors that bind these metabolites have also been explored with positive findings—examples include known short-chain fatty acid receptors, such as G-protein coupled receptors GPR41, GPR43, GPR109a, and OLF78 in mice. GPR41 and OLF78 have been shown to have inverse roles in blood pressure regulation, whereas GPR43 and GPR109A have to date been demonstrated to impact cardiac function. New treatment options in the form of prebiotics (eg, dietary fiber), probiotics (eg, Lactobacillus spp.), and postbiotics (eg, the short-chain fatty acids acetate, propionate, and butyrate) have all been demonstrated to be beneficial in lowering blood pressure in animal models, but the underlying mechanisms remain poorly understood and translation to hypertensive patients is still lacking. Here, we review the evidence for the role of the gut microbiota in hypertension, its risk factors, and cardiorenal complications and identify future directions for this exciting and fast-evolving field.

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Dietary fibre regulates blood pressure (BP) through gut microbial production of acidic metabolites known as short-chain fatty acids (SCFAs). The specific mechanisms of how SCFAs regulate BP are still emerging. We hypothesised that acidic metabolites that are abundant in the large intestine may activate proton-sensing G-protein coupled receptors, such as GPR65, thus conferring BP regulating effects. Using mouse models, we found that dietary fibre levels determined the luminal pH in the large intestine, through production of SCFAs by the gut microbiota. We then investigated a new mouse model lacking GPR65, which spontaneously developed higher BP, cardiac and renal hypertrophy and fibrosis. We identified that low pH, acting via GPR65 signalling, increased cAMP production and phosphorylation of CREB, and regulated inflammatory cytokine production involved in hypertension. We showed that the benefits of diets high in fibre, which usually prevent hypertension and its associated phenotypes, were decreased in mice lacking GPR65. Finally, we provided proof-of-concept evidence that the luminal pH profile in the colon of hypertensive participants is higher than that of normotensive participants. Colonic pH was further associated with dietary fibre, particularly in the colonic regions where fibre is fermented by the gut microbiota. Together, we show that pH sensing by GPR65 underlies at least some of the cardiovascular benefits of dietary fibre.