**1.2 Specific risk factors for the development of cerebrovascular pathology in patients with chronic kidney disease**

Risk factors for cerebrovascular diseases in CKD and dialysis patients can be conditionally divided into "traditional" (arterial hypertension, diabetes mellitus, hypercholesterolemia) and "specific" (associated with renal pathology and dialysis procedures). Specific risk factors remain poorly understood and less well known to medical practitioners. The spectrum of specific factors of cerebrovascular risk in patients with dialysis stage of the CKD includes specific dialysis factors that form during programmed HD, as well as impaired phosphorus-calcium metabolism,

#### *Multidisciplinary Experiences in Renal Replacement Therapy*

increased blood levels of β2-microglobulin, homocysteine, malondialdehyde and superoxide dismutase, a decrease in the level of nitric oxide (II) metabolites, accumulation of uremic toxins and toxins of intestinal bacteria, development of nephrogenic anemia, dietary features of patients with renal pathology, etc.) [16–18]. Some of them are presented in more detail below.


Long-term elevated levels of FGF23 in combination with destruction of the proximal renal tubules in CKD lead to a decrease in calcitriol levels, which means a decrease in calcium absorption in the intestine and suppression of its reabsorption in the kidneys, followed by the formation of hypocalcemia. At the next stage of the vicious circle of disorders of phosphorus-calcium metabolism, the loss of calcium by the body is compensated mainly due to the development of secondary hyperparathyroidism and increased resorption of bone tissue. When calcium is released from the bone, the level of serum phosphorus increases compensatory, thus, the vicious circle of phosphorus-calcium metabolism is closed [19]. Excess serum calcium is subsequently deposited in ectopic soft tissues and in the in the vascular system (in other words, vascular calcification is observed) [20]. It is believed that the process of calcification and increased stiffness of the vascular

*Specific Cerebrovascular Risk Factors, Colon Microbiocenosis and Its Correction in Patients… DOI: http://dx.doi.org/10.5772/intechopen.101300*

wall are associated with an increased risk of cardiovascular events, but there is no separate data on the cerebrovascular risk associated with arterial calcification and calcifying uremic arteriolopathy development [21]. The literature provides data on another possible mechanism by which an excess of phosphates leads to calcification of arteries, namely, a change in the phenotype of vascular smooth muscle cells (SMC) according to the "osteogenic type". Vascular wall SMCs stop producing SM22α-actin and instead synthesize bone formation factors involved in vascular calcification (alkaline phosphatase, osteocalcin) [22]. There is evidence that the mineralization of the vascular wall is also aggravated by the degradation of elastin against the background of the occurrence of osteogenically modified SMCs [23]. The degraded elastin increases the affinity of calcium and promotes the growth of hydroxyapatites along the elastic fibers. The gradual reduction of vascular smooth muscle leads to additional fibrosis of the median membrane of small and medium arteries, a decrease in cerebral blood flow and possible cerebrovascular risks. It is known that in CKD in the pre-dialysis period, there is also a lack of endogenous factors that inhibit the calcification of the arterial wall: FGF-23 klotho coreceptor, MGP protein (matrix glutamate protein), pyrophosphate, etc. reabsorption in the renal tubules [24]. The role of klotho as a protective factor of the vascular wall, which prevents osteogenic differentiation of SMCs, is discussed [25]. It is believed that as CKD progresses, the level of klotho gradually decreases, however, there is insufficient data on the effect of reduced concentrations of klotho on the development of cerebrovascular diseases [26]. Pyrophosphate and MGP protein (vitamin K-dependent glutamate-containing protein) are normally synthesized by healthy SMCs and inhibit vascular mineralization [27].

3.Anemia and dysfunction of blood cells: It is necessary to note another important specific risk factor for the development of cerebral vascular disorders in patients with CKD—the presence of anemia and dysfunction of blood cells, mainly platelets. The development of anemia in patients with CKD is associated with prolonged proteinuria, which is accompanied by losses of erythropoietin, transferrin and ionized iron, leading to a persistent decrease in hemoglobin levels [28]. As renal failure progresses, the anatomical structures that produce erythropoietin are gradually replaced by fibrous tissue, which is accompanied by the loss of hormone-producing properties. Observations by Chang et al. (2013), show that the presence of anemia in CKD increases the prevalence and severity of cerebrovascular disorders in patients with CKD [29]. The results of epidemiological studies indicate that the likelihood of developing an ischemic stroke is significantly higher in patients with anemia associated with CKD, and when the target values of hemoglobin and erythrocytes are reached, the risk of stroke is significantly reduced [30]. Platelet dysfunction in CKD is the result of a combination of intrinsic platelet abnormalities and disorders of platelet–vascular wall interaction [31]. This leads to a deterioration in platelet aggregation and impaired binding between the surface glycoprotein complex GPIIb/IIIa and fibrinogen on the subendothelial surface, thereby contributing to hypoaggregation and possible hemorrhagic events. The anemia that accompanies CKD exacerbates platelet dysfunction. This is due to a deficiency of erythropoietin, which normally improves platelet function by increasing the density of surface GPIIb/IIIa receptors [32]. There are works in the literature on the role of the transmembrane receptor RAGE in the formation of chronic vascular inflammation by inducing proinflammatory cytokines and chemokines. An increase in the concentration of end products of glycation observed in CKD patients due to impaired excretory function leads to an increase in the expression of RAGE in the cells of the vascular wall. This leads

to an increase in the concentration of sRAGE, the serum form of this receptor, which is a marker of inflammation and, in contrast to RAGE itself, can neutralize some of the inflammatory effects through competitive binding to circulating ligands [33]. In patients with CKD, the sRAGE level is 2.4 times higher than in the general population, and the concentration of proinflammatory ligands is 4 times higher than in the control group without CKD [34]. It is assumed that this may affect the formation of microangiopathy in the deep regions of the brain by activating the inflammatory response, impaired permeability of the blood–brain barrier and the occurrence of microbleeds [35], however, there is no convincing data on this yet.


#### *Specific Cerebrovascular Risk Factors, Colon Microbiocenosis and Its Correction in Patients… DOI: http://dx.doi.org/10.5772/intechopen.101300*

below in the form of an original study—intestinal bacterial toxins is distinguished. One of the negative consequences of the use of extracorporeal detoxification methods can be a violation of intestinal microbiocenosis. Recent studies have shown the presence of changes in intestinal microbiocenosis in patients with end-stage CKD. At the same time, in comparison with the predialysis stage patients, the patients receiving programmed HD had more pronounced disorders in the composition of the intestinal microbiota [42, 43]. At present time, the greatest attention is paid to two possible mechanisms for the development of changes in the composition of the intestinal microbiota in the literature: the characteristics of the diet and drugs taken in dialysis patients, as well as the regimen of the selected method of extracorporeal detoxification (HD, PD, or a functioning kidney transplant). Opportunistic gut microorganisms can produce uremic toxins, in particular, indoxyl sulfate and paracresol sulfate, which are associated with an increased risk of inflammation, increased oxidative stress, progression of CKD, and a higher risk of cardiovascular disease (CVD), which appears to predispose to disorders of intestinal microbiocenosis and mediated vascular risks.

Restrictions on the consumption of fruits and vegetables (sources of potassium), cheese, milk and dairy products (sources of phosphorus) contribute to the predominance of bacteria that produce toxic metabolites [44], which negatively affects the integrity of colonocytes and impairs the protective barrier of the colon mucosa [45]. Insufficient protein intake and loss of albumin during dialysis, especially when using high-flux membranes, also lead to a change in the species structure of the intestinal microbiome and increase the risk of bacterial translocation (penetration of microorganisms from the lumen of the gastrointestinal tract through the mucous barrier into the blood and lymph flow) and endotoxemia [42, 46]. On the contrary, if a high-fiber diet is properly followed in patients on PD, circulating concentrations of uremic toxins (in particular, paracresol sulfate) and some other markers of inflammation are reduced [47–49]. The dialysis procedure itself is associated with inevitable dietary restrictions for the dialysis patient, which may partly explain the differences between patients on PH and PD [50]. Thus, patients receiving PD are less prone to hyperkalemia than patients receiving PD [51]. Dietary restrictions in this category of patients are considered milder, and the diet is more varied.

Patients receiving renal replacement therapy are forced to take several medications regularly, which, as well as dietary habits, can negatively affect the composition of the intestinal microbiocenosis. However, the data on this issue are inconsistent. In particular, Khoury et al. (2016), postulate that the frequent use of antibiotics and phosphate binders in patients with end-stage CKD can alter the composition of the intestinal microbiota and, therefore, jeopardize the intestinal barrier [52]. Researchers consider phosphate binders, immunosuppressants, antibiotics, and proton pump inhibitors as drugs that negatively affect the intestinal microbiocenosis of dialysis patients [53].

The aim of our investigation was to study the species composition of colon microbiocenosis in patients with CKD receiving programmed HD treatment and to evaluate the effectiveness of its correction using a new immobilized synbiotic.

## **2. Materials and methods**

The examined patients were on planned outpatient treatment in the department of gravitational surgery of blood and hemodialysis in 2018–2020. Patients were enrolled in this parallel-group randomized controlled clinical trial using a

continuous sample method. The study involved 62 patients, including 36 women (58.1%) and 26 men (41.9%). Inclusion criteria were: age from 18 to 85 years; the presence of the dialysis stage of chronic kidney disease, the experience of program hemodialysis for more than 1 year; the adequacy of the programmed hemodialysis (at least 3 sessions per week, at least 4 hours/session and 720 minutes per week, the calculated dialysis adequacy index (purification coefficient Kt/V for urea) is at least 1.4, calculated based on the proportion of urea reduction weight loss during dialysis, dialysis time and patient weight); no antibiotic intake for 2 months and more, signed informed consent of the patient.

The patients were divided into the main group and the comparison group matched by sex and age. Basic therapy for patients with dialysis stage CKD of both groups included a high-protein diet and, if necessary, the appointment of drug therapy: antihypertensive—β-blockers (bisoprolol), blockers of Ca-channel (amlodipine), blockers of imidazoline receptors (moxonidine) and hypolipidemic—atorvastatin or rosuvastatin; as well as the treatment of anemia: erythropoietin α (or β) or methoxypolyethylene-glycol-epoetin-β; iron preparations (iron (III) hydroxide sucrose complex); correction of mineral-bone disorders: active metabolites of vitamin D (calcitriol, paricalcitol), calcimimetics (cinacalcet), phosphate-binding agents (β-iron (III) oxyhydroxide complex); correction of protein-energy deficiency (keto analogs of amino acids) [43].

The main group consisted of 32 patients with dialysis stage of CKD, including 19 women (59%) and 13 men (41%) aged 38–65 years (mean age 57.1 ± 7.9 years). Dialysis experience—from 12 to 123 months (40.6 ± 29.8 months). They received basic therapy and, as a probiotic, a new immobilized synbiotic "LB-complex L". The comparison group included 30 patients, including 17 women (57%) and 13 men (43%) aged 34–65 years (54.7 ± 8.4 years) with comparable dialysis experience. They received basic therapy and a placebo. All patients underwent an assessment of the nature of complaints, clinical and laboratory data (general blood test with determination of the number of leukocytes, ESR; biochemical blood test with determination of creatinine, blood urea, C-reactive protein); the dialysis adequacy index (purification coefficient Kt/V for urea) was calculated for each patient. The quality of life was assessed using the SF-36 (Short form medical outcomes study) questionnaire [11]. The study of the species composition of the intestinal microbiota and the assessment of the state of the microbiocenosis was carried out using the unified methodology developed by us and OST 91500.11.0004-2003 "Patient Management Protocol. Intestinal dysbiosis" [54, 55]. Microorganisms were identified on an autoflex speed time-of-flight MALDI-TOF mass spectrometer (Bruker Daltonik, Germany) using the Biotyper 4.1.80 RTC program. The author's immobilized multistrain synbiotic LB-complex L (SGR RU.77.99.88.003.E.002522.06.18) [56], recommended as a source of probiotic microorganisms (bifidobacteria and lactobacilli) and zeolites (enterosorbent), which increase the body's nonspecific resistance and have a detoxifying effect. Six strains that make up the synbiotic under study belong to species with a documented history of safe use and are approved for the production of medical immunobiological preparations. They do not have genetically modified analogues, meet the requirements for probiotic strains [36, 57], in particular, they have high antagonistic activity against a wide range of pathogenic and opportunistic microorganisms, antibiotic resistance undetermined by plasmids, and are sufficiently resistant to the action of gastric juice and bile. Zeolites of the Kholinsky deposit, selected as a matrix for the immobilization of probiotic strains, are approved for use in medical practice (SGR KZ.16.01.78.003.E.004706.08.15 from 18.08.2015). A unique property of clinoptilolites is the property of selective ion exchange: they are ultra-elements, if they are not enough, and they remove substances that are in excess from the body. Zeolites

*Specific Cerebrovascular Risk Factors, Colon Microbiocenosis and Its Correction in Patients… DOI: http://dx.doi.org/10.5772/intechopen.101300*

have pronounced sorption properties, since the openwork of the crystal lattice creates a large adsorption volume, they do not break down and do not undergo any changes in the human body [19]. Statistical processing was performed using standard software packages Statistica 6.1 and Microsoft Excel 2007. Data were presented as arithmetic mean (*M*) and standard error of the mean (*m*). If the distribution of data in the samples was not characterized as normal, nonparametric methods of analysis were used. The significance of the differences was assessed using the Mann–Whitney test. Differences between independent groups were considered statistically significant with a probability of error *p* < 0.05.
