Cyclooxygenase-2 does not contribute to postischemic production of reactive oxygen species

We sought to determine whether reactive oxygen species ( ROS) derived from cyclooxygenase- 2 ( COX- 2) are involved in ischemic brain injury. Focal cerebral ischemia was induced by transient middle cerebral artery occlusion in C57BL/ 6 mice. The time course of neocortical ROS production was assessed in vivo using hydroethidine as a marker. The same brain sections were used for infarct volume measurements. Transient middle cerebral artery occlusion led to a biphasic increase in ROS production with peaks 2 and 72 h after reperfusion. The COX- 2 inhibitor NS398 ( 10 mg/ kg) attenuated the production of COX- 2- derived prostaglandin E-2 and reduced brain injury, but did not affect ROS production at 2 and 72 h. Similarly, ROS production was not reduced in COX- 2- null mice. In contrast, ROS production and brain injury were reduced in mice lacking the nox2 subunit of the superoxide- producing enzyme nicotinamide adenine dinucleotide phosphate ( reduced form) oxidase. The data suggest that COX- 2 is not a major source of oxygen radicals after cerebral ischemia and raise the possibility that other COX- 2 reaction products, including prostanoids or nonoxygen- based radicals, mediate the COX- 2- dependent component of the injury.