Abstract 1484: Inhaled NO in Myocardial Ischemia/Reperfusion Injury: Pharmacokinetics and Pharmacodynamics of Protective NO Metabolites
Background: Reperfusion injury limits the beneficial effects of revascularization in the treatment of myocardial infarction (MI). Breathing nitric oxide (NO) for more than 4 hours has been reported to reduce myocardial ischemia-reperfusion (I/R) injury without causing systemic hypotension. The objective of this study was to characterize the circulating NO metabolites and their tissue levels during NO inhalation, which could contribute to the protective effects of inhaled NO in cardiac I/R injury.
Methods: The quantity of NO absorbed during NO inhalation (80 parts per million, ppm) was measured in awake mice in a chamber at ambient pressure. NO metabolites (i.e. RSNO, RNNO, NO-heme, nitrite, and nitrate) were measured in whole-body and tissue extracts and in blood, before and after breathing 80 ppm NO for 0.5, 5, 15, and 60 min. The ability of 0.5, 5, and 60 min of NO inhalation during ischemia to protect against cardiac I/R injury was evaluated in mice subjected to coronary ligation for 1 h and reperfusion for 24 h, at which time MI size and area at risk (MI/AAR) were measured.
Results: Mice breathing NO for 60 min absorbed 0.18±0.03 μmol/g, and 0.10±0.02 μmol/g was recovered as NO metabolites in whole body extracts, of which nitrate represented 97%. During NO inhalation, NO metabolites accumulated rapidly in blood and tissues reaching a plateau within 15 min except for nitrate, which continued to accumulate. Breathing NO led to greater than 3000-fold increases in RSNO, RNNO, and NO heme levels in erythrocytes and a 5-fold increase of plasma nitrite within 15 min (P<0.005 for all 4). In the heart, RSNO and NO-heme concentrations increased within 5 min and attained maximal levels after 15 min (7- and 9-fold, respectively, P<0.001 for both). Cardiac RNNO and nitrite levels did not change. In mice subjected to 60 min of myocardial ischemia and 24 h reperfusion, breathing NO for 60 min and 5 min just before reperfusion decreased MI/AAR vs. control (36 and 31%, respectively, P<0.05 for both), but breathing NO for 0.5 min did not reduce MI/AAR.
Conclusions: Brief periods of 80 ppm NO inhalation decrease myocardial I/R injury in mice. During NO breathing, the NO metabolites levels rapidly accumulate in blood and tissues, all of which may contribute to protection against cardiac I/R injury.