DEPENDENCE OF THE ACTIVITY OF THE SYSTEM OF OXIDATIVE STRESS – ANTIOXIDANT PROTECTION ON INSULIN RESISTANCE IN PATIENTS WITH ESSENTIAL HYPERTENSION AND OBESITY.

Relevance. The activation of free radical oxidative processes and the development of oxidative stress is one of the most important pathogenetic mechanisms of cardiovascular diseases. Active forms of oxygen can change cellular infiltration of vessels and endothelial function, having an impact on a functional condition of the adhesive molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. Under condition of insulin resistance (IR), the balance in the system of oxidative stress – antioxidant protection is disturbed, the result of which is insufficient resistance to the damaging effect of the LPO products. The aim of the study was to assess the dependence of the activity of the system of oxidative stress – antioxidant protection on insulin resistance (IR) in patients with comorbidity of arterial hypertension and obesity. patients hypertensive patients with obesity and no IR, an increase in HOMA-IR was associated with a decrease in total antioxidant protection, and in patients with IR, an increase in HOMA-IR was associated with an increase in MDA and DC, as well as a decrease in total antioxidant protection.


Introduction
The results of recent studies have shown that the activation of free radical oxidative processes and the development of oxidative stress is one of the most important pathogenetic mechanisms of cardiovascular diseases [1,3,5,14]. Increased production of free radicals contributes to the development of endothelial dysfunction (ED) with a violation of the ratio of the influence of vasoactive substances and factors with a predominance of vasoconstrictor effects [2,8,12,13]. The activity of free radical oxidative processes is estimated by the content of lipid peroxidation products (LPO)diene conjugates (DC), malondialdehyde (MDA) and Schiff bases in blood serum. The effectiveness of antioxidant protection is evaluated by changes in the activity of superoxide dismutase, which binds reactive oxygen species with formation of hydrogen peroxide, glutathione peroxidase, which reduces lipid hydroperoxides, glutathione reductase, which restores glutathione by oxidation of NADPH, catalase, which destructs peroxide into lipid hydroperoxides, as well as by the overall antioxidant activity [1,4,5,9].
In general, LPO is a process in which oxidants, such as free radicals, attack lipids, primarily polyunsaturated fatty acids (PUFA), as a result of which hydrogen is cleaved from carbon, and released oxygen forms peroxide radicals and hydroperoxides. The main substrates for LPO are PUFA. In general, LPO consists of three stages: initiation, propagation and termination resulting in the formation of a wide range of oxidation products. In healthy individuals, the activity of the LPO system is opposed by the system of antioxidant protection, but in insulin-resistant (IR) states, the balance in the system of oxidative stress -antioxidant protection is disturbed, the result of which is insufficient resistance to the damaging effect of the LPO products [3,4,6,9].
It has been established that IR and ED are closely associated conditions, since IR is considered an independent risk factor for dyslipidemia, systemic inflammation, and oxidative stress, and ED is the link between IR and cardiovascular disease [7,8,11,[15][16][17].
At the same time, hypotheses regarding the primacy of the origin and relationships of IR and ED are quite contradictory, which leads to further study of these states.
Thus, the aim of the study was to assess the dependence of the activity of the system of oxidative stressantioxidant protection from the presence of IR in patients with comorbidity AH and obesity.
Clinical characteristics of patients and research methods. 200 patients with essential hypertension (EH) and class І-ІІ obesity, who gave informed written consent to participate in the study and met the inclusion criteria, were examined. Patients were divided into two groups depending on IR presence: the first group included 80 patients without IR, the second -120 patients with IR.
Criteria for exclusion from the study: the presence of comorbidities in patients with EH (acute coronary syndrome, post-infarction cardiosclerosis, severe rhythm and conduction disorders, rheumatic heart disease, systemic connective tissue diseases, oncological diseases, symptomatic arterial hypertension (AH), thyroid diseases, acute inflammatory processes); stage III, grade 3 EH; class III obesity; type 1 and type 2 diabetes; III-IV FC CHF; moderately reduced and reduced LV EF; reduced GFR, the presence of proteinuria; age of patients less than 45 and more than 55 years; refusal of patients to participate in the study.
HOMA-IR value 2.77 and greater was considered as IR presence.
The concentration of insulin in the blood serum was determined using "Insulin ELISA" ("DRG Diagnostics", Germany) sets using solid-phase radioimmunological analysis.
The condition of the prooxidant system was assessed by the levels of molecular products of LPO -DC and MDA, and the condition of the antioxidant protection systemby the overall antioxidant activity (during spectrophotometry).
The results were processed by methods of variation statistics using the "STATISTICA" software. The data are presented as M ± σ, where M is the average value; σ is the standard deviation. During the significance analysis of the differences between the two groups in the severity of the index, expressed by a number, the Student's t-test was used. To estimate the degree of connectivity or synchronicity in the changes of indicators, the Rcoefficient of linear correlation (Pearson productmoment correlation) was calculated.

Results and discussion
The results of the study showed that the activity of the system of oxidative stress in hypertensive patients with obesity in the presence of IR was more pronounced than in patients without IR (Table 1). Thus, patients with IR had significantly (p = 0.000) higher levels of DC ((33.444 ± 3.142) nmol/ml) than patients with EH without IR ((29.591 ± 2.094) nmol/ml). Similar differences were observed in MDA levels: (36.924 ± 2.860) nmol/ml with IR and (33.729 ± 3.447) nmol/ml without IR, which significantly (p = 0.000) distinguished the groups from each other. The established features are a confirmation of the important role of IR in the occurrence and progression of endothelial dysfunction. Thus, in the presence of IR endothelial dysfunction occurs long before the appearance of obvious disorders of carbohydrate metabolism. Considering the results and the presence of conflicting hypotheses of the relationship of IR and ED, IR can be considered, on the one hand, as a factor in the development of endothelial dysfunction, and on the otheras a consequence [1,3,5,10].
As for the indicator of activity of the antioxidant protection system (total antioxidant protection), during the study there was no significant difference in its levels in the presence and absence of IR (p = 0.149). It can be assumed that these features are associated with the fact that the system of oxidative stress is more sensitive to IR than the system of antioxidant protection. The next stage of the study was to assess the degree of coherence and synchronicity in the changes of indicators by conducting a correlation analysis with the calculation of the coefficient of linear correlation (r) (Pearson product-moment correlation).

Table 1 -Indicators of the system of oxidative stressantioxidant protection in patients in the presence and absence of IR
As a result of the correlation analysis in patients with comorbidity EH and obesity, the relationship of indicators of the system of oxidative stressantioxidant protection and HOMA-IR was established (Table 2-4).

Indicators
Рatients with EH and obesity, n = 200 r р MDA 0.457 0.000 DC 0.608 0.000 Total antioxidant protection -0.250 0.000 In particular, it was found that in the General group of patients with EH and concomitant obesity (without division into groups based on the absence of IR) indicators of oxidative stress system (MDA and DC) had direct correlations with HOMA-IR (r = 0.457, p = 0.000 and r = 0.608, p = 0.000, respectively), the indicator of total antioxidant protection had inverse correlations with HOMA-IR (r = -0.250, p = 0.000) ( Table 2). Table 3  The division of patients into groups according to IR showed that the presence of IR affects the association of HOMA-IR with indicators of the system of oxidative stressantioxidant protection.
In patients without IR, HOMA-IR was associated with a decrease in overall antioxidant protection, which was confirmed by the presence of an inverse correlation (r = 0.409, p = 0.000) ( Table 3). It should be noted that in the presence of IR increase of HOMA-IR was also accompanied by a decrease in the activity of the total antioxidant protection, as evidenced by the inverse correlation with HOMA-IR (r = -0.314, p = 0.000) (Table 4). However, in patients with comorbidity EH and obesity in the presence of IR, the increase of HOMA-IR was associated with an increase in oxidative stress system indicators (MDA and DC), which was confirmed by the presence of their direct correlations with HOMA-IR (r = 0.219, p = 0.016 and r = 0.353, p = 0.000, respectively).

Conclusions
The presence of IR affects the activity of the system of oxidative stressantioxidant protection in comorbidity EH and obesity.
In the presence of IR, patients with EH and concomitant obesity have significantly higher levels of the oxidative stress system indicators (MDA and DC) compared to patients without IR.
In patients with comorbidity EH and obesity HOMA-IR directly correlates with oxidative stress system indicators (MDA and DC) and inversely correlates with the indicator of total antioxidant protection.
In hypertensive patients with obesity in the absence of IR, increased HOMA-IR is associated with reduced total antioxidant protection and in patients with IRwith an increase of MDA and DC, as well as a decline in overall antioxidant protection.

Prospects for further research
Prospects for further research are to assess the effect of IR on haemodynamic and metabolic parameters of patients with EH and concomitant obesity.