Abstract 1607: Mechanisms of Myocardial Protection by Atorvastatin: 5′-Nucleotidase is Upstream to eNOS Activation
Background: Previous studies have shown that statins protect against ischemia-reperfusion injury by activating phosphatidylinositol 3-Kinase (PI3K), leading to phosphorylation of Akt that activates endothelial nitric oxide synthase (eNOS) by phosphorylation. PI3K also activates ecto-5′-nucleotidase (E5N). Blocking E5N abrogates the infarct size (IS)-limiting effects of statins in the dog. It was suggested that E5N and eNOS are activated in parallel. We have shown in the rat that inducible NOS (iNOS) and cycloxygenase-2 (COX2) activation are mandatory steps for mediating the IS-limiting effect of atorvastatin (ATV) and are downstream to eNOS.
Purpose: To assess whether E5N activation is downstream or upstream to eNOS.
Methods: Wild-type (WT), eNOS−/− and iNOS−/− mice were pretreated with oral ATV (ATV+; 10 mg/kg/d) or water alone (ATV-) for 3 days. Mice were subjected to 30 min coronary artery occlusion and 4h reperfusion (IS protocol), or hearts were harvested, without being subjected to ischemia, for measurement of myocardial E5N (ng/mg protein/min), calcium-dependent (cNOS) and independent (ciNOS) NOS activity (X1000 cpm); and adenosine (μg/g) and 6-keto-PGF1α (the stable metabolite of PGI2; pg/ml) levels.
Results: Body weight, LV size and area at risk size (AR) were comparable among groups. ATV decreased IS only in the WT mice. cNOS activity was increased in the ATV+ WT and iNOS−/− mice. ATV increased ciNOS activity and myocardial 6-keto-PGF1α levels only in the WT mice. ATV increased E5N activity and tissue adenosine levels in all groups. E5N activity was significantly higher in the eNOS−/− than in the WT mice (p=0.017) or iNOS−/− group (p=0.025).
Conclusions: ATV activates E5N in the mouse. E5N upregulation by ATV does not limit IS in eNOS−/− and iNOS−/− mice, suggesting that E5N activation is upstream to eNOS, iNOS and PGI2 production.