RESULTS:
Nucleotide and
adenosine degradation rates were adversely modified on the aortic surface of stenotic valve as compared to ventricular side, including decreased
ATP removal (1.25 ± 0.35 vs. 2.24 ± 0.61 nmol/min/cm2) and
adenosine production (1.32 ± 0.12 vs. 2.49 ± 0.28 nmol/min/cm2) as well as increased
adenosine deamination (1.28 ± 0.31 vs. 0.67 ± 0.11 nmol/min/cm2). The rates of
nucleotide to
adenosine conversions were lower, while
adenosine deamination was higher on the aortic sides of stenotic vs. non-stenotic valve. There were no differences in extracellular
nucleotide metabolism between aortic and ventricular sides of non-stenotic valves. Furthermore,
nucleotide degradation rates, measured on aortic side in CAVD (n = 62), negatively correlated with echocardiographic and biochemical parameters of disease severity (aortic jet velocity vs.
ATP hydrolysis: r = - 0.30, p < 0.05; vs.
AMP hydrolysis: r = - 0.44, p < 0.001; valvular
phosphate concentration vs.
ATP hydrolysis: r = - 0.26, p < 0.05; vs.
AMP hydrolysis: r = - 0.25, p = 0.05) while
adenosine deamination showed positive correlation trend with valvular
phosphate deposits (r = 0.23, p = 0.07).
Nucleotide and
adenosine conversion rates also correlated with CAVD risk factors, including
hyperlipidemia (
AMP hydrolysis vs. serum
LDL cholesterol: r = - 0.28, p = 0.05;
adenosine deamination vs. total
cholesterol: r = 0.25, p = 0.05;
LDL cholesterol: r = 0.28, p < 0.05;
triglycerides: r = 0.32, p < 0.05),
hypertension (
adenosine deamination vs. systolic blood pressure: r = 0.28, p < 0.05) and
thrombosis (
ATP hydrolysis vs. prothrombin time: r = - 0.35, p < 0.01). Functional assays as well as histological and immunofluorescence, flow cytometry and RT-PCR studies identified all major ecto-
enzymes engaged in
nucleotide metabolism in aortic valves that included ecto-
nucleotidases,
alkaline phosphatase, and ecto-
adenosine deaminase. We have shown that changes in
nucleotide-converting ecto-
enzymes were derived from their altered activities on valve cells and immune cell infiltrate. We have also demonstrated a presence of A1, A2a and A2b
adenosine receptors with diminished expression of A2a and A2b in stenotic vs. non-stenotic valves. Finally, we revealed that augmenting
adenosine effects by blocking
adenosine deamination with
deoxycoformycin decreased aortic valve thickness and reduced markers of calcification via
adenosine-dependent pathways in a mouse model of CAVD.
CONCLUSIONS: