On-pump inhibition of es-ENT1 nucleoside transporter and adenosine deaminase during aortic crossclamping entraps intracellular adenosine and protects against reperfusion injury: role of adenosine A1 receptor.
OBJECTIVE
The inhibition of adenosine deaminase with erythro-9 (2-hydroxy-3-nonyl)-adenine (EHNA) and the es-ENT1 transporter with p-nitro-benzylthioinosine (NBMPR), entraps myocardial intracellular adenosine during on-pump warm aortic crossclamping, leading to a complete recovery of cardiac function and adenosine triphosphate (ATP) during reperfusion. The differential role of entrapped intracellular and circulating adenosine in EHNA/NBMPR-mediated protection is unknown. Selective (8-cyclopentyl-1,3-dipropyl-xanthine) or nonselective [8-(p-sulfophenyl)theophyline] A1 receptor antagonists were used to block adenosine A1-receptor contribution in EHNA/NBMPR-mediated cardiac recovery.


METHODS
Anesthetized dogs (n = 45), instrumented to measure heart performance using sonomicrometry, were subjected to 30 minutes of warm aortic crossclamping and 60 minutes of reperfusion. Three boluses of the vehicle (series A) or 100 μM EHNA and 25 μM NBMPR (series B) were infused into the pump at baseline, before ischemia and before reperfusion. 8-Cyclopentyl-1,3-dipropyl-xanthine (10 μM) or 8-(p-sulfophenyl)theophyline (100 μM) was intra-aortically infused immediately after aortic crossclamping distal to the clamp in series A and series B. The ATP pool and nicotinamide adenine dinucleotide was determined using high-performance liquid chromatography.


RESULTS
Ischemia depleted ATP in all groups by 50%. The adenosine/inosine ratios were more than 10-fold greater in series B than in series A (P < .001). ATP and function recovered in the EHNA/NBMPR-treated group (P < .05 vs control group). 8-Cyclopentyl-1,3-dipropyl-xanthine and 8-(p-sulfophenyl)theophyline partially reduced cardiac function in series A and B to the same degree but did not abolish the EHNA/NBMPR-mediated protection in series B.


CONCLUSIONS
In addition to the cardioprotection mediated by activation of the adenosine receptors by extracellular adenosine, EHNA/NBMPR entrapment of intracellular adenosine provided a significant component of myocardial protection despite adenosine A1 receptor blockade.
Division of Cardiothoracic Surgery, Department of Surgery, Virginia Commonwealth University Medical Center, Richmond, VA 23298-0068, USA. anwar@vcu.edu
Anwar Saad
AS
Abd-Elfattah
Mai
M
Ding
Michael E
ME
Jessen
Andrew S
AS
Wechsler
D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058892:Adenosine Deaminase Inhibitors / Q000494:pharmacology*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003250:Constriction; D004195:Disease Models, Animal; D004285:Dogs; D019194:Ischemic Preconditioning / Q000379:methods*; D017202:Myocardial Ischemia / Q000503:physiopathology*; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology / Q000517:prevention & control*; D017682:Myocardial Stunning / Q000503:physiopathology / Q000517:prevention & control*; D033703:Nucleoside Transport Proteins / Q000494:pharmacology*; D043682:Receptor, Adenosine A1 / Q000378:metabolism*; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D013868:Thioinosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D058892:Adenosine Deaminase Inhibitors; D033703:Nucleoside Transport Proteins; D043682:Receptor, Adenosine A1; D014970:Xanthines; D013868:Thioinosine; C010192:9-(2-hydroxy-3-nonyl)adenine; C031433:8-(4-sulfophenyl)theophylline; C051360:1,3-dipropyl-8-cyclopentylxanthine; D013806:Theophylline; C001789:4-nitrobenzylthioinosine; D000225:Adenine