Nitrite reductase activity of myoglobin regulates respiration and cellular viability in myocardial ischemia-reperfusion injury

The nitrite anion is reduced to nitric oxide (NO(center dot)) as oxygen tension decreases. Whereas this pathway modulates hypoxic NO(center dot) signaling and mitochondrial respiration and limits myocardial infarction in mammalian species, the pathways to nitrite bioactivation remain uncertain. Studies suggest that hemoglobin and myoglobin may subserve a fundamental physiological function as hypoxia dependent nitrite reductases. Using myoglobin wild-type ((+/+)) and knockout ((-/-)) mice, we here test the central role of myoglobin as a functional nitrite reductase that regulates hypoxic NO(center dot) generation, controls cellular respiration, and therefore confirms a cytoprotective response to cardiac ischemia-reperfusion (I/R) injury. We find that myoglobin is responsible for nitrite-dependent NO(center dot) generation and cardiomyocyte protein iron-nitrosylation. Nitrite reduction to NO(center dot) by myoglobin dynamically inhibits cellular respiration and limits reactive oxygen species generation and mitochondrial enzyme oxidative inactivation after I/R injury. In isolated myoglobin(+/+) but not in myoglobin(-/-) hearts, nitrite treatment resulted in an improved recovery of post-ischemic left ventricular developed pressure of 29%. In vivo administration of nitrite reduced myocardial infarction by 61% in myoglobin(+/+) mice, whereas in myoglobin(-/-) mice nitrite had no protective effects. These data support an emerging paradigm that myoglobin and the heme globin family subserve a critical function as an intrinsic nitrite reductase that regulates responses to cellular hypoxia and reoxygenation. myoglobin knockout mice.