Significance of marrow-derived nicotinamide adenine dinucleotide phosphate oxidase in experimental ischemic stroke.

OBJECTIVE: Reperfusion after stroke leads to infiltration of inflammatory cells into the ischemic brain. Nicotinamide adenine dinucleotide phosphate oxidase (NOX2) is a major enzyme system that generates superoxide in immune cells. We studied the effect of NOX2 derived from the immune cells in the brain and in blood cells in experimental stroke.
METHODS: To establish whether NOX2 plays a role in brain ischemia, strokes were created in mice, then mice were treated with the NOX2 inhibitor apocynin or vehicle and compared to mice deficient in NOX2's gp91 subunit and their wild-type littermates. To determine whether NOX2 in circulating cells versus brain resident cells contribute to ischemic injury, bone marrow chimeras were generated by transplanting bone marrow from wild-type or NOX2-deficient mice into NOX2 or wild-type hosts, respectively.
RESULTS: Apocynin and NOX2 deletion both significantly reduced infarct size, blood-brain barrier disruption, and hemorrhagic transformation of the infarcts, compared to untreated wild-type controls. This was associated with decreased matrix metalloproteinase 9 expression and reduced loss of tight junction proteins. NOX2-deficient mice receiving wild-type marrow had better outcomes compared to the wild-type mice receiving wild-type marrow. Interestingly, wild-type mice receiving NOX2-deficient marrow had even smaller infarct sizes and less hemorrhage than NOX2-deficient mice receiving wild-type marrow.
INTERPRETATION: This indicates that NOX2, whether present in circulating cells or brain resident cells, contributes to ischemic brain injury and hemorrhage. However, NOX2 from the circulating cells contributed more to the exacerbation of stroke than that from brain resident cells. These data suggest the importance of targeting the peripheral immune system for treatment of stroke.