Although the inducible
isoform of
NO synthase (iNOS) mediates late preconditioning (PC), it is unknown whether iNOS gene transfer can replicate the cardioprotective effects of late PC, and the role of this
protein in
myocardial ischemia is controversial. Thus, the
cDNA for human iNOS was cloned behind the Rous sarcoma virus (RSV) promoter to create adenovirus (
Ad) 5/iNOS lacking E1, E2a, and E3 regions. Intramyocardial injection of Ad5/iNOS in mice increased local iNOS
protein expression and activity and markedly reduced
infarct size. The
infarct-sparing effects of Ad5/iNOS were at least as powerful as those of ischemic PC. The increased iNOS expression was associated with increased
cyclooxygenase-2 (COX-2)
protein expression and
prostanoid levels. Pretreatment with the COX-2-selective inhibitor
NS-398 completely abrogated the
infarct-sparing actions of Ad5/iNOS, demonstrating that COX-2 is an obligatory downstream effector of iNOS-dependent cardioprotection. We conclude that gene transfer of iNOS (an
enzyme commonly thought to be detrimental) affords powerful cardioprotection the magnitude of which is equivalent to that of late PC. This is the first report that upregulation of iNOS, in itself, is sufficient to reduce
infarct size. The results provide proof-of-principle for gene therapy against
ischemia/reperfusion injury, which increases local myocardial
NO synthase levels without the need for continuous
intravenous infusion of NO donors and without altering systemic hemodynamics. The data also reveal the existence of a close coupling between iNOS and COX-2, whereby induction of the former
enzyme leads to secondary induction of the latter, which in turn mediates the cytoprotective effects of iNOS. We propose that iNOS and COX-2 form a stress-responsive functional module that mitigates
ischemia/reperfusion injury.