The state of the intestinal microbial-tissue complex in patients with chronic kidney disease

Abstract

The gut microbiota plays a fundamental role in maintaining normal organism homeostasis, regulating a wide range of metabolic, biosynthetic, and immune functions. This complex ecosystem, together with cellular, and stromal components of the intestinal wall, forms the intestinal microbial-tissue complex, which pathology is considered a universal mechanism for the development of many diseases, including chronic kidney disease. Accumulation of nitrogen metabolism products in the intestine, specific diet, polypharmacy, sedentary lifestyle, limited fluid intake, and violation of gastrointestinal motility in patients with chronic kidney disease lead to a decrease in the number of bacteria synthesizing short-chain fatty acids with crucial physiological effects, along with an increase in the content of anaerobic proteolytic bacteria expressing uricase, urease, and p-cresol-, and indole-forming enzymes. The features of gut dysbiosis depend on the etiology of chronic kidney disease and severity of renal insufficiency and differ significantly in individuals receiving various renal replacement therapies (hemodialysis, peritoneal dialysis, kidney transplant recipients). Abnormal microbial metabolism enhances the production and accumulation of microbial-derived uremic toxins: p-cresyl sulfate, indoxyl sulfate, and trimethylamine-N-oxide. Renal insufficiency, through mechanisms mainly associated with the hydrolysis of accumulated in the lumen of the intestine urea, leads to inflammation, and swelling of the intestinal wall, which is accompanied by disorders of the immune tolerance of the mucous layer and disorganization of intercellular junctional complexes, which are critical modulators of intestinal intercellular transepithelial transport. Uremia-induced impairment of the gut epithelial barrier integrity induces the systemic translocation of numerous immunogenic substances generated by the aberrant microbiota, followed by the development of oxidative stress and chronic subclinical inflammation that causes the progression of chronic kidney disease and related complications. The most pronounced changes were observed in people with end-stage chronic kidney disease. Further study of the bidirectional relationship between the kidneys and intestinal microbial-tissue complex will contribute to the development of new directions of pathogenetic therapy and prevention of adverse outcomes in patients with chronic kidney disease.