CC BY
7MEDICAL SCIENCES
PROTEIN DEGRADATION IN PATIENTS WITH CHRONIC KIDNEY DISEASE RECEIVING
HEMODIALYSIS
Adamokova I.,
Clinical Resident, FSBEIFPE " Russian Medical Academy of Continuous Professional Education ", Moscow, Russia ORCID: 0000-0001-8623-0162 Plyashkevich M., Clinical Resident,
FSBI "National Medical Research Center of Endocrinology",
Moscow, Russia ORCID: 0000-0001-5135-937X Avetisyan D., Clinical Resident, SBIH MR " Moscow regional Research Institute of Obstetrics and Gynecology", Moscow, Russia ORCID: 0000-0001-0794-3442 Lipartiani T., Clinical Resident,
FSAEI HE Pirogov Russian National Research Medical University
Moscow, Russia ORCID: 0000-0001-8781-1006 Tishchenko Yu. Student
FSBEI HE "Rostov State Medical University" Rostov-on-Don, Russia ORCID: 0000-0002-2680-2007
Abstract
Hemodialysis and peritoneal dialysis are currently the main methods of renal replacement therapy. According to statistics, about 80% of all patients with chronic kidney disease V dialysis stage in the world receive this type of treatment . An important aspect in the management of this category of patients is not only the proper dialysis program, timely detection and correction of developing complications, but also the survival of patients. It often depends on the severity of protein-energy deficiency and sarcopenia associated with CKD and dialysis . However, sarcopenia is one of the causes of increased cardiovascular mortality and occurs in 37% of patients with CKD 5D . In this regard, identifying the causes of loss of muscle mass and strength in this category of patients is prognos-tically important.
Keywords: chronic kidney disease, sarcopenia, ubiquitin-proteasome system
Introduction. Chronic kidney disease (CKD) is an important medical and social problem due to its prevalence, high cardiovascular risk, impact on life expectancy and quality of life, etc. The most common way of the renal replacement therapy is hemodialysis (HD), the use of which in patients with 5 stages of CKD is associated with the development of various complications, in particular, oxidative stress, systemic inflammatory process, protein metabolism disorders, and body composition [1]. These changes in the early stages of the disease can proceed unnoticed, but later lead to the development of a dangerous clinical condition - sar-copenia, as a result of an imbalance of catabolic and anabolic processes [2]. Its development is associated with high cardiovascular mortality in the discussed group of patients, the search for ways to reduce which is of scientific interest [3]. Risk factors for sarcopenia are old age, the presence of diabetes mellitus, increased
levels of creatinine and serum phosphate in the blood, the duration of dialysis treatment [4, 5].
The following intracellular systems are involved in the process of catabolism of muscle proteins: lysoso-mal (autophagic), caspase, calpain and ubiquitin-pro-teasome. The latter has a special role in patients with CKD, as the leading one in the development of muscle tissue deficiency. Pro-inflammatory mediators often act as its activating factors. (C-reactive protein, IL-6 etc.), oxidative stress, vitamin D deficiency, etc. [6, 7].
It is known that protein degradation in the pro-teasome is preceded by its ubiquitination - ATP-dependent attachment of low-molecular-weight protein residues ubiquitin involving three types of enzymes: ubiquitin-activating, ubiquitin-conjugating and ubiqui-tin ligases. Thus, labeled proteins of the cytoplasm and nucleoplasm undergo cleavage in the 26S proteasome. However, in recent years it has become more and more
obvious that in this way the cell gets rid of only a part of unwanted proteins. Many proteins can be cleaved by the 20S proteasome in an ATP-independent manner and without prior ubiquitination [8, 9]. At the same time, only about 30% of proteasomes in mammalian cells are represented by 26S proteasomes, while most of them are 20S complexes [8, 9]. Within the framework of the ubiquitin-proteasome model, special attention was paid to the activity of ubiquitin ligases [10, 11], whose work is mediated through the 26S proteasome. There are data on the determination of the activity of ubiquitin-independent degradation mediated through the 20S-proteasome, with modeling in mice [11], however, its role in patients with CKD is not completely clear. Thus, the true value of 20S complexes in the processes of ubiquitin-independent protein degradation (for example, under conditions of oxidative stress, chronic inflammation) remains insufficiently studied and is of scientific interest.
The aim of the study was to assess the effect of ubiquitin-independent protein degradation on the development of protein metabolism disorders in patients with CKD receiving hemodialysis treatment.
Patients and methods. We examined 80 patients with stage 5 chronic kidney disease (CKD), who were treated with programmed hemodialysis. The study group included 47 men and 33 women, whose average age was 51.7 ± 11.6 years, the duration of dialysis was 33.5 (0.5; 236) months.
The study did not include patients under the age of 18 and over 80 years old, suffering from CKD stages 1-
4 and 5, not receiving renal replacement therapy, with a muscle tissue pathology, a history of alcoholism or drug addiction, or confirmed mental disorders. In addition to collecting complaints, anamnestic information, physical examination and assessment of the objective status, the patients underwent three measurements of muscle strength on the fistula arm using a wrist dynamometer (the best result was used for calculations) and bioimpedance measurements. Determination of the level of the 20S proteasome was carried out by the method of quantitative enzyme immunoassay once for all patients of the study group using a 20S-Proteasome (20S-PSM) ELISA Kit (USA).
Statistical analysis of the data was carried out using the Statistica 10.0 software package (StatSoft, USA). The statistical significance of the differences between the two means was determined using the MannWhitney test. The assessment of the strength of the interaction between quantitative signs in a normal distribution was carried out using the Pearson coefficient, in case of an abnormal one - the Spearman coefficient. To analyze the relationships between different indicators, the x2-square test was used for categorical features. The null statistical hypothesis of the absence of differences and relationships was refuted at p <0.05.
Research results. The patients were divided by gender into 2 groups, each of which was divided into 2 subgroups, depending on the presence or absence of a decrease in muscle strength (Table 1).
Table 1.
Characteristic of the group
Men, n=47 Women, n=33
Indicator Preserved muscle strength, n=41 Decreased muscle strength, n=6 Preserved muscle strength, n=24 Decreased muscle strength, n=9
Systolic blood pressure, mmHg. 142±15,13 137,83±20,094 144,8±13,8 139,22±16,56
Diastolic blood pressure, mmHg. 79,41±10,28 74,17±22,534 73,3±9 71,1±15,4
BMI, kg/m2 26,32±4,41 26,40±4,479 28,4±4,61* 27,37±4,24*
Dry weight, kg 78,62±15,89 79,88±19,905 72,7±13,1 65,57±9,78
Fat mass, % 18,07±9,81 21,17±8,010 29,4±7,64 29,1±5,64
Laboratory indicators
Hemoglobin, g/l 110,44±12,27* 121,17±10,61* 106,8±12,8 112,33±9,15
Leukocytes,109 /l 6,72±2,06 6,05±2,17 6,4±1,98 5,96±1,87
Lymphocytes, 109 /l 1,61±0,50 1,52±0,48 1,47±0,46 1,58±0,64
Albumin, g/l 43,59±2,90 41±3,16 43,8±1,88 42,22±2,33
Total protein, g/l 69,51±5,17 68±6,48 67,38±3,6 66,89±3,76
CRP, mg/l 9,83±8,10 16,68±6,43 4,48±5,37 6,17±3,83
B2- microglobulin, mg/l 26,84±5,84 26,8±6,14 24,97±5,38 26,33±4,62
20S-PSM, ng/ml 54,18±15,12 48,5±9,47 59,64±5,37 58,52±12,3
Concomitant pathology
Diabetes 3/41 - 3/24 1/9
Arterial hypertension 36/41 5/6 23/24 8/9
Congestive heart failure 10/41 1/6 5/24 3/9
Heart rhythm disturbance 6/41 1/6 - 1/9
Postinfarction cardiosclerosis 7/41 1/6 2/24 -
Acute cerebrovascular accident 1/41 - 4/24 -
*- p<0,05, BMI - Body mass index; CRP - C-reactive protein; 20S-PSM - 20S-Proteasome.
In a subgroup of women, a significant association was found between decreased muscle strength, duration of dialysis, and albumin levels (x2=8,38; p=0,015, figure 1). In men, age correlated with the level of the 20S proteasome (%2=7,4, p=0,024, figure 2). There were no other statistically significant relationships in the sub-
groups, as well as in the general study group. Nevertheless, for the general group, the effect of impaired protein metabolism on the functional state of skeletal muscles is confirmed. Thus, it was found that with an increase in the level of the 20S proteasome and a decrease in the level of serum albumin, dysfunction of muscle
tissue significantly increases (figure 3).
Figure 1. Probability of reducing muscle strength depending on the serum albumin level and durance of dialysis
treatment among women (x2=8,38, p=0,015).
Figure 2. Probability of reducing muscle strength depending on age, 20S-PSM level among men
(X2=7,4, p=0,024).
Figure 3. Probability of reducing muscle strength depending on serum albumin, 20S-PSM (%2=7,12, p=0,028).
There were no significant differences in the mean values of the 20S proteasome levels in patients in groups with normal and reduced muscle strength, as well as in the corresponding groups by gender (p = 0.88; p = 0.83 in the subgroup of men; p = 0.77 in the subgroup of women).
There was no statistically significant correlation between the level of the 20S proteasome and serum albumin, total protein (p = 0.78; p = 0.80). However, in
CRP - C-reactive protein; 20S-PSM - 20S-Proteasome.
Despite the available literature data in favor of an increase in the volume of adipose tissue with a loss of muscle mass, in patients with reduced muscle strength compared to the group with intact values according to bioimpedance data, in our work, deviations in the percentage of fat mass were not convincing (25.9 ± 7.57; 22.26 ± 10.56, p = 0.12). Most likely, these results are
multiple regression models, an additional dependence of the 20S proteasome on the level of C-reactive protein was determined, which indicates the contribution of inflammation not only to the activation of catabolism, but also to the inhibition of anabolic processes (Tables 2, 3).
Table 2.
associated with the insufficient sensitivity of the bioim-pedance method in comparison with other imaging methods (computed tomography, magnetic resonance imaging, dual-energy X-ray absorptiometry).
DISCUSSION. In patients with CKD undergoing hemodialysis treatment, there is a complex effect of the
Model of dependence level of serum albumin from 20S-PSM, CRP
Beta Std.Err. B Std.Err. t(77) p-level
44,289 1,254 35,296 0,001
CRP, mg/l -0,301 0,109 -0,069 0,025 -2,746 0,007
20S-PSM, ng/ml -0,035 0,109 -0,007 0,021 -0,323 0,747
Table 3.
Model of dependence level of total protein from 20S-PSM, CRP__
Beta Std.Err. B Std.Err. t(77) p-level
69,738 2,341 29,781 0,001
CRP, mg/l 0,069 0,114 0,028 0,047 0,605 0,546
20S-PSM, ng/ml -0,075 0,114 -0,026 0,040 -0,655 0,514
CRP - C-reactive protein; 20S-PSM - 20S-Proteasome.
ubiquitin-proteasome system, developing protein-energy malnutrition, a reduced level of serum albumin, etc. on metabolic processes in the skeletal muscles. The found relationship between the age of patients, the duration of dialysis and the level of the 20S proteasome, as well as the decreased muscle strength, may serve as an indirect confirmation of the involvement of the 20s proteasome in the loss of muscle mass and strength in patients receiving RRT and the development of sarco-penia in them.
The absence of reliable correlations between muscle strength, total protein, and serum albumin with the level of the 20S proteasome may be explained by its insufficient concentration in the blood serum compared to the cellular level, which requires further study. The revealed contribution of C-reactive protein in the construction of multiple regression models makes it relevant among other markers of the inflammatory process, and therefore it seems promising to evaluate it in patients of the study group. The association of the high-sensitivity test (high-sensitivity CRP) with the volume of muscle mass and total protein content in the body was also confirmed [11, 12].
Along with the insufficient sensitivity of biompen-sometry in assessing the body composition in comparison with imaging techniques, the multifactorial nature of the increase in adipose tissue should be taken into account, in particular, the contribution of nutritional status, dialysis parameters, concomitant comorbid background, as well as the possibility of myosteatosis development. These processes lead to increased oxida-tive stress, progression of insulin resistance, and a decrease in the strength of muscle contraction [13, 14].
Conclusion. The study demonstrated the relationship between the level of the 20S proteasome and the characteristics of dialysis treatment and the level of chronic inflammation. Despite the absence of an independent correlation between this indicator and muscle strength, serum protein levels, using multiple regression models, the effect of ubiquitin-independent protein degradation on the functional state of muscle tissue, the level of total protein and serum albumin was assessed. No statistically significant change in the body composition in the form of a compensatory increase in the absolute content of adipose tissue against the background of sarcopenia was revealed according to the results of bioimpedance measurement, which requires further study. Expanding the possibilities of using bioimped-ansometry to assess muscle mass in patients with stage CKD5D is of research interest in view of the availability of the method, compared with others.
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