**3. Biological and clinical effects of uremic toxins**

The fermentation of non-digestible carbohydrates takes places mainly in the cecum and right colon. For bacteria, this is an important source of energy for proliferation and energy recovery from the diet that favors the absorption of ions (Ca, Ng, and Fe) in the cecum. The enteric flora also helps in the production of vitamins (K, B12, biotin, folic, and pantothenic acid) and the synthesis of amino acids from ammonia or urea [22]. Anaerobic metabolism of peptides and proteins that occur in distal segments of the colon generates ammonia, amines, phenols, thiols, and indoles [23].

There are some factors that favor bacterial translocation: bacterial proliferation in small intestine, increased permeability of the mucosal barrier, and deficiencies in immune response. CKD patients share those factors that can contribute to accumulation of uremic toxins [24].

Uremic toxins have different effects at tissue and cellular levels. At the endothelial level, there is an alteration in the balance of nitric oxide production, and there is an increase in the production of free oxygen radicals, inflammation, proliferation, and expression of tissue factor and ICAM-1 and MCP-1 [25]. In the smooth vascular fiber, there is production of free radicals and proliferation and an increase in the expression of osteoblastic proteins. Increased calcification, aortic stiffness, atherosclerosis, and increased leukocyte adhesion to the wall have been seen in the blood vessels [26].

In cardiac myocytes, the presence of these toxins causes alterations in cellular structure and function and has been associated with cardiac hypertrophy and fibrosis [27]. In bone, there are alterations in the differentiation and function of osteoclasts, and in osteoblasts, there is a decrease in the expression of the PTH receptor, with a decrease in cell viability and proliferation [28]; in adipocytes, deposits of uremic toxins have been associated with insulin resistance [29].

*Uremic Toxins: The Role of the Gut and the Kidneys DOI: http://dx.doi.org/10.5772/intechopen.109845*

Uremic toxins have been associated with progression of end-stage kidney disease, cardiovascular complications, and alterations of mineral-bone metabolism, anemia, and insulin resistance. The deposits in the glomeruli, tubules, and interstitium produce monocyte infiltration, glomerulosclerosis, and tubulointerstitial fibrosis [30, 31]. There is interference in the production of erythropoietin, added to a decrease in the life of erythrocytes, which has been related to renal patient anemia [32, 33].
