Background: Knockout of 2′,3′-cyclic-nucleotide 3′-phosphodiesterse (an enzyme that converts 2′,3′-cAMP to 2′-AMP) reduces 2′-AMP production and improves renal perfusion in renal ischemia-reperfusion injury (R-IRI). These findings motivated our hypothesis, herein tested, that 2′-AMP causes renal vasoconstriction. Methods: The effect of 2′-AMP on renal vascular resistance (RVR) was investigated in rat kidneys, both in vitro and in vivo. 2′-AMP interactions with P2X1 receptors (P2X1Rs) were investigated in membrane preparations and HEK cells. Urinary 2′-AMP levels were assessed in cardiac surgery/cardiopulmonary bypass (CS-CPB) patients using mass spectrometry. Results: In vitro , intra-renal-artery-infused 2′-AMP was rapidly metabolized to adenosine and did not increase RVR. Co-administration of a tissue non-specific alkaline phosphatase (TNAP) inhibitor (TNAPI) reduced 2′-AMP metabolism, thus enabling 2′-AMP to trigger renal vasoconstriction. In vivo , kidneys rapidly metabolized intra-renal-artery-infused 2′-AMP to adenosine; this was blocked with a TNAPI. In vivo , intra-renal-artery-infused 2′-AMP decreased RVR, as did adenosine. By contrast, when co-administered with a TNAPI, 2′-AMP increased RVR, and this response was inhibited by NF449 (P2X1R antagonist). In membranes, 2′-AMP enhanced 3 H-αβ-methylene-ATP (P2X1R agonist) binding to P2X1Rs, and in HEK cells 2′-AMP doubled αβ-methylene-ATP-induced (and P2X1R-mediated) calcium influx. In TNAPI+2′-AMP-pretreated, but not naïve, rats, βγ-methylene-ATP (P2X1R agonist) caused renal vasoconstriction. In rats, R-IRI reduced renal TNAP activity, and TNAP inhibition worsened R-IRI. In CS-CPB patients, urinary 2′-AMP levels were elevated 169% during CS-CPB and were associated with a 45% increase in peak 24-hour post-procedure serum creatinine. Conclusions: 2′-AMP is a renal vasoconstrictor; however, TNAP, by metabolizing 2′-AMP to adenosine, protects against 2′-AMP-induced renal vasoconstriction. This protection is lost when TNAP activity is reduced. 2′-AMP-induced renal vasoconstriction involves positive allosteric modulation of P2X1Rs that enhances ATP-induced opening of P2X1R channels. R-IRI reduces renal TNAP activity, and TNAP inhibition worsens R-IRI outcomes.
Jackson et al. (Tue,) studied this question.