Values of osteoprotegerin in aortic valve tissue differ significantly between calcified aortic valve stenosis and normal aortic valve and are influenced by the presence of coronary atherosclerosis

Abstract

Background: The load of calcium in aortic valve is the most significant predictor of clinical progression of calcified aortic stenosis (CAS). We previously showed that calcium deposition in aortic valve differs significantly in relation to the presence of concomitant coronary atherosclerosis in patients with CAS. Osteoprotegerin (OPG) was identified as a key regulator in vascular calcification. Aim: The study aimed to determine concentrations of OPG in aortic valve tissue in patients with symptomatic CAS without (Group A, angiographically normal coronary arteries) and with concomitant coronary atherosclerosis (Group B, angiographically >50% coronary artery stenosis), and in normal aortic valves (Group C). Methods: Tissue samples were collected at surgery from patients undergoing AVR (N 44, 69.0±10.7 years, 57% male) and from patients undergoing AVR + CABG (N 61, 73.4±8.3 years, 64% male). Normal aortic valve tissues were obtained from explanted hearts (with angiographically normal coronary arteries) during transplantation (N 21, 49.6±13.7 years, 81% male). Tissue samples were immediately frozen at -80°C. The frozen tissue was cut into small pieces and powdered by grinding in a pre-chilled abrasive material with occasionally adding liquid N2 to prevent thawing. Once the tissue was ground to a fine powder, the extraction solution was added and further incubated at room temperature for 1 hour. Mixture was centrifuged at 10000xg and 4°C for 10 minutes and supernatant was immediatelly analyzed by ELISA method. Results: The highest tissue concentration of OPG \[pmol/l\] (median, 25th to 75Th percentile) was found in Group A (6.95 (3.96-18.37)). The lowest was the concentration in normal aortic valves (2.25 (1.01-5.08)). After adjustment for age and sex the difference in tissue OPG between group A and C was highly significant (p=0.001). Levels of OPG in Group B (4.15 (2.47-9.16)) were significantly lower in comparison to group A (p after adjustment = 0.025). The difference between group B and C did not reach significance (p=0.078). Our recently presented study (AHA 2012) found that patients with symptomatic CAS and normal coronary arteries (Group A) have significantly higher load of calcium in aortic valve and were symptomatic in significantly younger age in comparison to patients with CAS and significant coronary atheroscleorsis (Group B). Conclusion: The significant difference in tissue concentrations of OPG was found between patients with symptomatic CAS and normal human aortic valves. The highest tissue OPG was found in patients with CAS and without concomitant coronary atherosclerosis.