Morphological and functional characteristics of retrosternal adipose tissue and their relation to arterial stiffness parameters in patients after coronary artery bypass grafting

Background. The attention of many researchers is focused on studying the role of adipokines secreted by subcutaneous, visceral, epicardial, and perivascular adipose tissues in the pathogenesis of diseases of the cardiovascular system. At the same time, adipose tissue of retrosternal localization remains out of research focus. This pool of fat cells is formed at the site of the thymic involution and has a significant volume. However, their functional activity and participation in the development of cardiovascular pathology remain unexplored.

Aim. To study the morphological characteristics of adipocytes of the retrosternal adipose tissue (RSAT) and their production of adipokines in comparison with epicardial (EAT) and subcutaneous adipose tissue (SCAT) and to investigate their relationships with arterial stiffness parameters in patients who underwent coronary artery bypass grafting.

Materials and methods. The study included 17 patients (12 men/5 women aged 40–70 years) with the diagnosed coronary artery disease (CAD) who underwent coronary artery bypass grafting (CABG). Each patient underwent measurement of carotid-femoral pulse wave velocity (PWV) and aortic augmentation index (AIx) with the oscillometric device. Isolated adipocytes were obtained enzymatically from explants of SCAT, EAT and RSAT during coronary artery bypass grafting. The adipocytes were analyzed under the microscope at 200x magnification. The release of adiponectin, leptin and insulin was studied in the adipocyte supernatant after 1 hour incubation using ELISA.

Results. It was found that adipocytes of the RSAT are smaller than adipocytes of SCAT: 83.96 ± 2.21 vs 98.62 ± 2.67 μm (p = 0.00002), respectively, and comparable in size to adipocytes of EAT: 86.65 ± 1.33 μm. The release of adiponectin by adipocytes of the RSAT turned out to be comparable to the production of this adipokine in SCAT and EAT, however, adipocytes of the RSAT produce less leptin than SCAT and EAT: 0.26 (0.19; 0.27) ng/l vs 0.37 (0.28; 0.55) (р = 0.01) and vs 0.32 (0.28; 0.44) (р = 0.006) ng/ml, respectively. Furthermore, RSAT produce less insulin than SCAT and EAT: 1.56 (1.03; 2.08) vs 1.70 (0.99; 2.18) ng/ml, (р = 0.0022) and 1.76 (1.16; 2.40) ng/ml (р = 0.006), respectively.
A positive correlation was found between the secretion of leptin by adipocytes of the RSAT and the AIx  (rs = 0.52, p = 0.046). An inverse relationship was found between insulin secretion by retrosternal adipocytes and PWV rs = –0.55, p = 0.035). There was no relationship between the size of the  retrosternal adipocyte or hypertrophy of the thymic adipocytes (more than 100 μm) and the production of leptin and insulin and arterial stiffness parameters. 

Conclusions. The data of our pilot study show that adipocyte hypertrophy of the retrosternal AT is not a significant marker of adipokine production disturbance. The observed relationships suggest that an increase in leptin production and reduced insulin secretion by retrosternal AT may contribute to the formation of adipokine-related arterial stiffness. Based on the data obtained, it can be assumed that adipokines produced by the retrosternal AT can participate in the formation of arterial stiffness in patients with coronary artery disease.  

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