Inhibiting protease-activated receptor 4 limits myocardial ischemia/reperfusion injury in rat hearts by unmasking adenosine signaling.
Harnessing endogenous cardioprotectants is a novel therapeutic strategy to combat ischemia/reperfusion (I/R) injury. Thrombin causes I/R injury, whereas exogenous adenosine prevents I/R injury. We hypothesized that blocking thrombin receptor activation with a protease-activated receptor (PAR) 4 antagonist would unmask the cardioprotective effects of endogenous adenosine. The protective role of two structurally unrelated PAR4 antagonists, trans-cinnamoyl-YPGKF-amide (tc-Y-NH(2)) and palmitoyl-SGRRYGHALR-amide (P4pal10), were evaluated in two rat models of myocardial I/R injury. P4pal10 (10 microg/kg) treatment before ischemia significantly decreased infarct size (IS) by 31, 21, and 19% when given before, during, and after ischemia in the in vivo model. tc-Y-NH(2) (5 microM) treatment before ischemia decreased IS by 51% in the in vitro model and increased recovery of ventricular function by 26%. To assess whether the cardioprotective effects of PAR4 blockade were due to endogenous adenosine, isolated hearts were treated with a nonselective adenosine receptor blocker, 8-sulfaphenyltheophylline (8-SPT), and tc-Y-NH(2) before ischemia. 8-SPT abolished the protective effects of tc-Y-NH(2) but did not affect IS when given alone. Adenosine-mediated survival pathways were then explored. The cardioprotective effects of tc-Y-NH(2) were abolished by inhibition of Akt (wortmannin), extracellular signal-regulated kinase 1/2 [PD98059 (2'-amino-3'-methoxyflavone)], nitric-oxide synthase [N(G)-monomethyl-l-arginine (l-NMA)], and K(ATP) channels (glibenclamide). PD98059, l-NMA, and glibenclamide alone had no effect on cardioprotection in vitro. Furthermore, inhibition of mitochondrial K(ATP) channels [5-hydroxydecanoic acid (5-HD)] and sarcolemmal K(ATP) channels (sodium (5-(2-(5-chloro-2-methoxybenzamido)ethyl)-2-methoxyphenylsulfonyl)(methylcarbamothioyl)amide; HMR 1098) abolished P4pal10-induced cardioprotection in vivo. Thrombin receptor blockade by PAR4 inhibition provides protection against injury from myocardial I/R by unmasking adenosine receptor signaling and supports the hypothesis of a coupling between thrombin receptors and adenosine receptors.
Division of Cardiovascular Medicine, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA. jstrande@mcw.edu
Jennifer L
JL
Strande
Anna
A
Hsu
Jidong
J
Su
Xiangping
X
Fu
Garrett J
GJ
Gross
John E
JE
Baker
D000241:Adenosine / Q000378:metabolism*; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology / Q000627:therapeutic use; D006321:Heart / Q000187:drug effects / Q000502:physiology; D008297:Male; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000517:prevention & control*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018179:Receptors, Thrombin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*
D002316:Cardiotonic Agents; D018179:Receptors, Thrombin; C112908:protease-activated receptor 4; D000241:Adenosine