## 4 Discussion  
In the present study, we investigated the relationship between CIMT, plasma ADMA as a marker of ED, and MDA as a marker for oxidative stress, as well as the expressions of Nrf2, HO-1, and NF-kB in PBMCs in MetS. Data in Figure 1 indicate a gradual increase in CIMT with age. However, a statistically significant higher average IMT was established in the age \(<\) 55 MetS subgroup only, compared with the control group (0.96 \(\pm\) 0.29 vs. 0.74 \(\pm\) 0.21, \(p\)\(<\) 0.05). It has been reported that CIMT is elevated in diabetes mellitus, hypertension, and obesity, all of them components of MetS [27; 28; 29]. An increase in CIMT, measured by ultrasonography, is directly associated with an increased risk of myocardial infarction and stroke, even in older people without a history of CVD [23]. It has been reported that the presence and severity of MetS is associated with an increase in vascular thickness in different populations, a phenomenon conceptualized as early vascular aging [30]. The consequences of oxidative stress and low-grade inflammation, causing ED and impairment, are exacerbated with the increase in age [31]. There is strong evidence suggesting that Nrf2 protects against the induction of cellular senescence. Vascular oxidative stress in aging is associated with Nrf-2 dysfunction [31]. Nrf2, a redox-sensitive transcription factor, transcribes HO-1 and many antioxidant genes [31]. They play an important role in endothelial protection in oxidative stress in MetS [11; 12]. Reactive oxygen species and products of lipid peroxidation, as well as low-grade inflammation, are crucial factors for the activation of Nrf2 and NF-kB [32; 33]. We can speculate that protective mechanisms involving Nrf2 and HO-1 decline with age. This could be a reason for the worsening of endothelial function and the accelerated endothelial damage in vessels, registered by an increase in CIMT and risk of cardiovascular complications and incidents. For this reason, we analysed how the average IMT in the MetS group depended on age on the one hand and how NF-kB, Nrf2, and HO-1 expression in PBMC depended on IMT on the other. Data are shown in Figures 2 and 3. We studied how expression levels of NF-kB, Nrf2, and HO-1 in PBMCs of MetS individuals varied according to age and CIMT. The control group was designed to contain  
Figure 5: Plasma levels of MDA, ADMA, and HO-1 in study subjects based on CIMT. Control group: CIMT \(<\) 0.90 mm. The MetS group was divided into two subgroups: MetS with CIMT \(<\) 0.90 mm and MetS with CIMT \(\geq\) 0.90 mm. * \(p\)\(<\) 0.05, ** \(p\)\(<\) 0.01, *** \(p\)\(<\) 0.001.  
healthy individuals aged \(<\) 55 years. The MetS group included individuals both under and over 55 years of age. As shown in Figure 2, a significantly increased expression of the three studied genes in the age \(<\) 55 MetS subgroup was detected. The increase in the mRNA levels in the age \(<\) 50 MetS subgroup was as follows: 83% for NF-kB (\(p<\) 0.05), 251% for Nrf2 (\(p<\) 0.05), and 337% for HO-1 (\(p<\) 0.05). It is obvious that the expression level of these genes in PBMC changes with age and that HO-1 appears to be the most affected among the studied genes. In contrast, in the MetS subgroup with individuals aged over 55 years, it is visible that these genes are under-regulated, achieving the levels of the control group. Thus, the difference between the age \(<\) 55 MetS and age \(\geq\) 55 MetS subgroups was determined to be statistically significant (Figure 2). As shown in Figure 3, a significantly increased expression of the three studied genes in the MetS group with IMT \(<\) 0.9 mm was detected. The increase in the mRNA levels in the MetS with CIMT \(<\) 0.90 mm subgroup was as follows: 80% for NF-kB (\(p<\) 0.01), 260% for Nrf2 (\(p<\) 0.05), and 303% for HO-1 (\(p<\) 0.05). Again, a trend was detected with NF-kB, NRf2, and HO-1 expression levels in PBMC changing with age and HO-1 being the most affected among the studied genes.