Evgeny Shutov,Oleg Mishin
Evaluation of the Effect of the PMMA Dialysis Membrane on the Level of Inflammation in Patients on Hemodialysis
Inflammation,Hemodialysis,PMMA membranes
Introduction The inflammation syndrome is typical for chronic kidney disease (CKD) and increases with the progression of CKD. It is extremely important to monitor the markers of inflammation in patients with CKD, as there is a clear relationship between the level of inflammation and mortality in these patients. Currently, there is no single approach to the treatment of chronic inflammation in patients with CKD. Methods This was a prospective open cohort study. We studied 31 patients on hemodialysis from March 1, 2020, to August 1, 2021, in 2 Moscow clinics (No. 7 and S.P. Botkin). Inclusion criteria for patients in the study were an adequate dialysis according to the KT/V index ≥1.4, absence of an active inflammatory process or infections, age over 18 years, standard hemodialysis regimen of 3 times per week, at least 4 h, levels of interleukin-6 (IL-6), IL-8, and C-reactive protein (CRP) above the reference values. Patients were transferred from hemodialysis performed using a standard polysulfone (PS) membrane to a polymethylmethacrylate (PMMA) membrane (Filtryzer BK-2.1F). For dialysis treatment in patients, blood flow rates of 250–350 mL/min were used, and the flow rate of the dialysis solution was set at 500 mL/min. The control group consisted of 19 patients, with similar inclusion parameters, who continued their treatment with hemodialysis using a PS membrane. The aim of the research was to study the effect of the dialysis membrane (Filtryzer BK-2.1F) on the level of inflammation in routine practice compared to a PS membrane. Adverse events were monitored. Results By the end of the study, after 12 months, the levels of cytokines significantly decreased only in patients who had treatment with PMMA membrane, starting from the 3rd month of treatment, and became close to normal levels: IL-6 from 16.9 ± 8.0 to 8.5 ± 4.8 pg/mL (p ≤ 0.0001); IL-8 from 78.5 ± 11.4 to 43.6 ± 11.6 pg/mL (p ≤ 0.0001); and CRP from 10.33 ± 2.83 to 6.15 ± 1.57 mg/L (p ≤ 0.0001). Values of inflammation markers did not change in control group. Conclusion In our study, we demonstrated for the first time a significant reduction in the level of inflammation in patients on standard hemodialysis in routine practice due to the use of PMMA membranes.
Evaluation of the Effect of the PMMA Dialysis Membrane on the Level of Inflammation in Patients on Hemodialysis

The inflammation syndrome is typical for chronic kidney disease (CKD) and increases with the progression of CKD. It is extremely important to monitor the markers of inflammation in patients with CKD, as there is a clear relationship between the level of inflammation and mortality in these patients. Currently, there is no single approach to the treatment of chronic inflammation in patients with CKD.

This was a prospective open cohort study. We studied 31 patients on hemodialysis from March 1, 2020, to August 1, 2021, in 2 Moscow clinics (No. 7 and S.P. Botkin). Inclusion criteria for patients in the study were an adequate dialysis according to the KT/V index ≥1.4, absence of an active inflammatory process or infections, age over 18 years, standard hemodialysis regimen of 3 times per week, at least 4 h, levels of interleukin-6 (IL-6), IL-8, and C-reactive protein (CRP) above the reference values. Patients were transferred from hemodialysis performed using a standard polysulfone (PS) membrane to a polymethylmethacrylate (PMMA) membrane (Filtryzer BK-2.1F). For dialysis treatment in patients, blood flow rates of 250–350 mL/min were used, and the flow rate of the dialysis solution was set at 500 mL/min. The control group consisted of 19 patients, with similar inclusion parameters, who continued their treatment with hemodialysis using a PS membrane. The aim of the research was to study the effect of the dialysis membrane (Filtryzer BK-2.1F) on the level of inflammation in routine practice compared to a PS membrane. Adverse events were monitored.

By the end of the study, after 12 months, the levels of cytokines significantly decreased only in patients who had treatment with PMMA membrane, starting from the 3rd month of treatment, and became close to normal levels: IL-6 from 16.9 ± 8.0 to 8.5 ± 4.8 pg/mL (p ≤ 0.0001); IL-8 from 78.5 ± 11.4 to 43.6 ± 11.6 pg/mL (p ≤ 0.0001); and CRP from 10.33 ± 2.83 to 6.15 ± 1.57 mg/L (p ≤ 0.0001). Values of inflammation markers did not change in control group.

In our study, we demonstrated for the first time a significant reduction in the level of inflammation in patients on standard hemodialysis in routine practice due to the use of PMMA membranes.

Chronic kidney disease (CKD) is one of the most common diseases in the world, which affects 10–12% of the population [1]. Patients with CKD are characterized by high overall mortality, mainly due to cardiovascular disease (CVD). These patients are often hospitalized, and their treatment is very expensive, especially at the terminal stage of the disease, when they are treated with dialysis. Almost 30 years ago, we were the first to present the concept of chronic inflammation as a phenotype of uremia, but at that time, however, it did not find understanding among nephrologists and was not even accepted for presentation at the ERA-EDTA Congress, but it was immediately recognized by specialists in inflammation [2]. In 1999, Stenvinkel et al. [3] associated the presence of inflammation in patients with CKD with protein-energy deficiency and CVD. In the same year, Zimmermann et al. [4] found a clear and strong relationship between the level of inflammation and mortality in patients receiving hemodialysis. The level of inflammation increases with the progression of CKD, and this is mainly due to the presence of cytokines, acidosis, and oxidative stress [5, 6]. The level of chronic inflammation in patients is determined most often by markers such as interleukin-6 (IL-6) and C-reactive protein (CRP) [7]. More than half of patients with CKD stage 3-5 have elevated levels of CRP, and in patients on dialysis, the frequency of detection of elevated levels of CRP is even higher [8, 9]. The pathogenesis of chronic inflammation in adults with CKD is multifactorial and has not yet been fully elucidated. Today, there are known factors that cause chronic inflammation syndrome associated with increased formation of proinflammatory cytokines, oxidative stress, chronic and recurrent infections, fluid overload, sodium overload, intestinal dysbiosis, dialysis procedures [5, 10, 11]. It is extremely important to monitor the markers of inflammation in patients with CKD, as there is a clear relationship between the level of inflammation and mortality in these patients [12]. Currently, there is not an only approach to the treatment of chronic inflammation in patients with CKD, and it is known that a healthy lifestyle and a balanced diet can reduce the level of inflammation. However, this is not enough. And now special attention is being paid to the role of medium molecules as the main pathological factors contributing to inflammation, and the use of special dialysis membranes can help cope with this problem. The use of polymethylmethacrylate (PMMA) membranes in comparison with standard dialysis membranes provides a good removal of inflammatory cytokines and uremic toxins in treatment of septic conditions [13]; however, the study of the anti-inflammatory effect of these dialysis membranes in patients with CKD on hemodialysis with chronic inflammation syndrome has not yet been conducted. The aim of the research was to study the effect of this membrane (Filtryzer BK-2.1F) on the level of inflammation in routine practice compared to a standard polysulfone (PS) membrane.

For this prospective open cohort study, we studied 31 patients on hemodialysis from March 1, 2020, to August 1, 2021, in 2 Moscow clinics, No. 7 (n = 17) and S.P. Botkin (n = 14). Inclusion's criteria of patients in the study were as follows: an adequate dialysis according to the KT/V index ≥1.4, absence of an active inflammatory process, infections, age over 18 years, none of the patients had a previous kidney transplant, did not receive steroids and immunosuppressants, had standard hemodialysis regimen of three times per week, at least for 4 h, levels of IL-6, IL-8, and CRP above the reference values. The patients were transferred from hemodialysis performed with a standard PS membrane to a PMMA membrane (Filtryzer BK-2.1F, Toray, Japan). For dialysis treatment in patients, blood flow rates of 250–350 mL/min were used, and the flow rate of the dialysis solution was set at 500 mL/min. The control group consisted of 19 patients, with similar inclusion parameters, who continued treatment with hemodialysis with a PS membrane. Patients with a history of allergic reactions to dialysis membranes were excluded from the study. We collected demographic and clinical data, standard biochemical analyses from all patients. Laboratory levels of inflammatory markers in CRP, levels of IL-6, IL-8, were checked for a year, 1 month after the start, then every 2 months.

Blood samples collected in polypropylene tubes were centrifuged at 3,200 rpm for 10 min. The plasma was separated by centrifugation and stored at −20°C until analysis. Levels of human CRP, IL-6, IL-8 were determined in plasma with automatic immunochemical analyzer IMMULITE 2000 XPI, Siemens (laboratory kits produced by Siemens Healthcare Diagnostics). The tests were carried out in accordance with the manufacturer's protocol, and the results were expressed for cytokines in pg/mL, CRP in mg/mL. All samples were run in duplicate. Reference values for IL-6 ≤7 pg/mL, for IL-8 ≤62 pg/mL, for CRP ≤7 mg/L. The samples were collected before dialysis.

The data are presented as mean ± standard deviation or median (quartile 3–quartile 1) depending on the distribution. The significance assessment was carried out the pairwise T test (repeated measures ANOVA with Bonferroni correction) or the Mann-Whitney test. Data analysis was performed using the IBM SPSS statistical package (version 20). The value of p < 0.05 was considered statistically significant.

We had 31 hemodialysis patients who were transferred to the PMMA membrane from the PS membrane (mean age 61.9 ± 5.6 years, 17 men) with a dialysis experience of 46 ± 26 months. Twenty-one patients (67.7%) suffered from hypertension, 7 (22.5%) were diabetics, and 20 patients (64.5%) had a history of CVDs. Patients (19) of the control group continued hemodialysis with the PS membrane. This group included 8 men and 11 women, the mean age was 60.7 ± 7.8 years, and dialysis vintage was 56 ± 32 months. Ten patients (52.6%) suffered from hypertension, 5 (26.3%) were diabetics, and 12 patients (63.1%) had a history of CVDs. Patients included in our study received hemodialysis on average for more than 3–4 years, residual kidney function was not significant, and residual diuresis did not exceed 100 mL. The main clinical and laboratory characteristics of the examined patients are presented in Table 1.

The patients included in the study were transferred from hemodialysis performed with a standard PS membrane (Fresenius, FX100, Germany; B. Braun, Diacap HIPS 18, Germany) to hemodialysis treatment with a PMMA Filtryzer BK-2.1F membrane for 12 months, and the results are shown in Table 2. The study of inflammatory markers in patients included in the study showed a statistically significant decrease in their level after 3 months of treatment. For the patients continuously dialyzed with PS membrane, the inflammatory marker levels did not significantly change during the study period (Table 3).

In this study, we were the first who evaluated the effect of the use of a PMMA Filtryzer BK-2.1F dialysis membrane for 12 months on the level of inflammatory markers in patients with CKD 5. The data obtained showed that the decrease in the levels of the studied cytokines and CRP occurred in dynamics, and they almost approached normal values. This result is extremely important in terms of reducing the pathological potential of inflammation associated with CKD, CVD, premature aging, and mortality [14]. Persistent inflammation contributes to the occurrence of many complications, including atherosclerosis, osteoporosis, weakness, diabetes, cancer, depression, etc. With a decrease in kidney function, a large amount of uremic toxins accumulates in patients with CKD, contributing to chronic inflammation, the development of CVD, high morbidity, and mortality [15]. Uremic toxins with a small molecular weight are usually well removed by hemodialysis with standard membranes. A big problem is the toxins, denoted by medium molecules, which are easily removed with urine by healthy kidneys. According to the latest classification, average molecules including cytokines and other proinflammatory mediators account for 23% of the number of identified uremic toxins [16]. An increase in the level of cytokines and CRP is associated with both increased production of these molecules and poor renal clearance of these molecules, and is not compensated for by removal through conventional dialysis methods with standard membranes. Patients with CKD are characterized by an imbalance between pro- and anti-inflammatory cytokines [17], which leads to an unfavorable outcome in CKD [18]. Currently, considered that IL-6 is independent predictors of mortality in patients with ESRD and among cytokines, IL-6 has the highest predictive value for patient death [19, 20]; therefore, this cytokine is most often studied in patients receiving hemodialysis. On the other hand, IL-8 is one of uremic toxins with serum concentration in uremia >10-fold higher than normal values [21]. IL-8 was the first chemoattractant cytokine (chemokine) discovered, in 1978. It is released by macrophages, endothelial and epithelial cells, and recruit's neutrophils to sites of infection or tissue injury. Several studies have identified IL-8 in sites of vascular injury and demonstrated that IL-8 potentially plays a role in various stages of atherosclerosis [22]. Among the inflammatory chemokines, IL-8 plays an important role in atherosclerotic plaque destabilization. IL-8 recruit's monocytes into the subendothelial space [23] have mitogenic and chemotactic effects on vascular smooth muscle cells [24] and contribute to plaque vulnerability by promoting an imbalance between metalloproteinases and metallopeptidases [25]. IL-8 concentration was upregulated in patients with heart failure compared to healthy controls [26]. Increased IL-8 concentrations have been related to a worse clinical prognosis in patients with heart failure [27]. In hemodialysis patients, higher IL-8 levels correlated with increased all-cause and cardiovascular mortality [28]. Due to the fact that we have practically no way to reduce the production of inflammatory molecules in CKD, the strategy of removing these substances with new dialysis membranes by increasing clearance or adsorption, as is the case with PMMA membranes, is coming to the fore. Recent studies have suggested that either adsorption or filtration techniques may help reduce the proinflammatory charge of the uremic plasma. In a few vitro studies [29, 30, 31] was shown that the adsorption of different cytokines to a PMMA hollow fiber membrane was more effective than adsorption to the PS membrane. A correlation was observed between molecular weight and adsorption to the PMMA membrane. Cytokines with low molecular weight were adsorbed with higher rate. The precise adsorption mechanism of cytokine adsorption to the PMMA membrane is unclear. One hypothesis is that since PMMA is a polymer with hydrophobic properties and does not have a strong electrical charge, it is the hydrophobic interactions that drive adsorption. In addition, the PMMA membrane has nanopores on the surface and inside the membrane, and cytokines are likely to be adsorbed by fitting into these nanopores. The high adsorption rate of cytokines with a molecular weight in the range of 8,000–30,000 may be related to the size of these pores, which corresponds to these molecular sizes. Cytokines are also removed by filtration, but the contribution of this mechanism is less for PMMA membrane [29]. Unlike patients dialyzed with PMMA Filtryzer BK-2.1F dialysis membrane, in patients continuously dialyzed with PS membrane, longitudinal changes of inflammatory markers did not significantly decrease for 12 months. We think that these results suggest that PMMA Filtryzer BK-2.1F dialysis membrane would be applicable in patients on hemodialysis with chronic inflammation.

In our study, we demonstrated for the first time a significant reduction in the level of inflammation in patients on standard hemodialysis in routine practice due to the use of PMMA membranes.

This study did not require ethical approval in accordance with local and national regulations as hemodialysis performed with PS membrane and PMMA membrane is our routine clinical practice for many years and cytokine testing is also performed routinely. The study was conducted in accordance with the Helsinki Declaration. All participants provided a written informed consent prior to be included in the study.

The authors have no conflicts of interest to declare.

We did not have additional sources of funding. The study was carried out as part of routine practice.

Evgeny Shutov: substantial contributions to the conception and design of the work; selection of participants and data collection, analysis, and interpretation of data for the work; final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Oleg Mishin: selection of participants and data collection.

All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.