AMP579 is revealed to be a potent A_2b-adenosine receptor agonist in human 293 cells and rabbit hearts

The mixed A₁/A_2a-adenosine agonist AMP579 given at reperfusion is protective in animal models of myocardial infarction. Receptor-blocking studies have indicated that the protection came from an adenosine receptor (AR), but neither A₁- nor A_2a-selective agonists could duplicate its protection. We recently found that A_2b-selective agonists given at reperfusion are protective, and, therefore, tested whether AMP579 might also be an A_2b agonist. We used human embryonic kidney cells overexpressing human A_2b receptors as an assay system. In these cells, A_2b receptor occupancy causes phosphorylation of ERK. AMP579 induced ERK phosphorylation with an EC₅₀ of 250 nM and this phosphorylation could be blocked by MRS1754 or PSB1115, two highly selective blockers of human A_2b receptors. We attempted to confirm our A_2b hypothesis in a rabbit heart model of ischemia–reperfusion. AMP579 (500 nM) for 1 h starting at reperfusion reduced infarct size in isolated rabbit hearts exposed to 30 min of regional ischemia and 2 h of reperfusion (12.9 ± 2.2% infarction of risk zone vs. 32.0 ± 1.9% in untreated hearts). PSB1115 (500 nM) given for the first 15 min of reperfusion blocked AMP579’s protection (32.2 ± 3.1% infarction) which is consistent with an A_2b mechanism. We conclude that AMP579 is a non-selective, but potent A_2b-AR agonist, and that its protection against infarction is through that receptor.