Polymorphonuclear leukocyte (PMN) accumulation/activation has been implicated as a primary mechanism underlying MI/R injury. Recent studies have demonstrated that PMNs express
inducible nitric oxide synthase (iNOS) and produce toxic
reactive nitrogen species (RNS). However, the role of iNOS-derived
reactive nitrogen species and resultant nitrative stress in PMN-induced cardiomyocyte apoptosis after MI/R remains unclear. Male adult rats were subjected to 30 min of
myocardial ischemia followed by 5 h of reperfusion. Animals were randomized to receive one of the following treatments: MI/R+vehicle; MI/R+L-
arginine; PMN depletion followed by MI/R+vehicle; PMN depletion followed by MI/R+L-
arginine; MI/R+1400 W; MI/R+1400 W+L-
arginine and MI/R+ FeTMPyP.
Ischemia/reperfusion-induced and
L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis were determined. PMN depletion virtually abolished
ischemia/reperfusion- induced PMN accumulation, attenuated ischemic/reperfusion-induced and
L-arginine-enhanced nitrative stress, and reduced ischemic/reperfusion-induced and
L-arginine-enhanced cardiomyocyte apoptosis (P values all <0.01). Pre-treatment with
1400 W, a highly selective iNOS inhibitor, had no effect on PMN accumulation in the ischemic/reperfused tissue. However, this treatment reduced
ischemia/reperfusion-induced and
L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis to an extent that is comparable as that seen in PMN depletion group. Treatment with FeTMPyP, a
peroxynitrite decomposition catalyst, had no effect on either PMN accumulation or total NO production. However, treatment with this ONOO(-) decomposition catalyst also reduced
ischemia/reperfusion-induced and
L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis (P values all <0.01). These results demonstrated that ischemic/reperfusion stimulated PMN accumulation may result in cardiomyocyte injury by an iNOS-derived
nitric oxide initiated and
peroxynitrite-mediated mechanism. Therapeutic interventions that block PMN accumulation, inhibit iNOS activity or scavenge
peroxynitrite may reduce nitrative stress and attenuate tissue injury.