Interaction between inducible nitric oxide synthase and cyclooxygenase-2 after cerebral ischemia

Abstract

Focal cerebral ischemia is associated with expression of both inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), enzymes whose reaction products contribute to the evolution of ischemic brain injury. We tested the hypothesis that, after cerebral ischemia, nitric oxide (NO) produced by iNOS enhances COX-2 activity, thereby increasing the toxic potential of this enzyme. Cerebral ischemia was produced by middle cerebral artery occlusion in rats or mice. Twenty-four hours after ischemia in rats, iNOS-immunoreactive neutrophils were observed in close proximity (<20 m) to COX-2-positive cells at the periphery of the infarct. In the olfactory bulb, only COX-2 positive cells were observed. Cerebral ischemia increased the concentration of the COX-2 reaction product prostaglandin E 2 (PGE 2 ) in the ischemic area and in the ipsilateral olfactory bulb. The iNOS inhibitor aminoguanidine reduced PGE 2 concentration in the infarct, where both iNOS and COX-2 were expressed, but not in the olfactory bulb, where only COX-2 was expressed. Postischemic PGE 2 accumulation was reduced significantly in iNOS null mice compared with wild-type controls (C57BL͞6 or SV129). The data provide evidence that NO produced by iNOS inf luences COX-2 activity after focal cerebral ischemia. Proinf lammatory prostanoids and reactive oxygen species produced by COX-2 may be a previously unrecognized factor by which NO contributes to ischemic brain injury. The pathogenic effect of the interaction between NO, or a derived specie, and COX-2 is likely to play a role also in other brain diseases associated with inf lammation.Focal cerebral ischemia is associated with a local inflammatory response that participates in the progression of ischemic brain injury (e.g., refs. 1, 2, 3, and 4; for a review, see ref. 5). Recent evidence indicates that nitric oxide (NO), produced by the ''immunologic'' isoform of NO synthase (iNOS), is one of the mechanisms by which postischemic inflammation contributes to cerebral ischemic damage (see ref. 6 for a review). Occlusion of the rat middle cerebral artery (MCA) leads to iNOS induction in the ischemic brain (7). iNOS expression peaks 24-48 hr after ischemia and occurs in neutrophils infiltrating the ischemic brain and in cerebral vascular cells (7). Delayed administration of the relatively selective iNOS inhibitor aminoguanidine (AG) reduces the size of the infarct produced by MCA occlusion (8). Furthermore, iNOS null mice have smaller infarcts and a better neurological outcome after focal ischemia (9). These observations suggest that large amounts of NO produced by iNOS are toxic to the injured brain and contribute to the late stages of cerebral ischemia.Cerebral ischemia also enhances the expression of the prostaglandin-synthesizing enzyme cyclooxygenase-2 (COX-2) (10,11,12,13). Although the time course of the up-regulation is similar to that of iNOS, COX-2 is expressed predominantly in neurons located at the border between normal and ischemic brain (10). The COX-2 inhibitor NS-398 reduces the s...

Induction of Cyclooxygenase-2 Accounts for Restraint Stress-Induced Oxidative Status in Rat Brain

“…In our model of restraint stress, we have shown that activation of COX-2 precedes NOS-2 probably because, although protein synthesis is required in both cases, COX-2 remains constitutively expressed in the brain (Yamagata et al, 1993). The relations between these two sources of oxidative status are consistent with the fact that, as observed also in brain ischemia, COX-2 is expressed before NOS-2 (6 and 12 h, respectively, after transient occlusion of the MCA) (Nogawa et al, 1998) and 30 min to 2 h after reperfusion (Domoki et al, 1999). On the other hand, these data strongly suggest that both enzymes work in the same direction to produce oxidative status in acute stress.…”

“…COX-2, although an inducible protein, is constitutively expressed in only a few tissues including the brain, particularly in neuronal soma, not in astrocytes, of different regions including cortex, amygdala, hippocampal formation, and the dorsal horn of the spinal cord (Yamagata et al, 1993;Breder et al, 1995). It becomes upregulated brieflyFafter 1-8 hFafter seizure, trauma, intracerebral hemorrhage, ischemia, or other neurodegenerative diseases (Yamagata et al, 1993;Beiche et al, 1996;Nogawa et al, 1998;Knott et al, 2000;Kim et al, 2001;Gong et al, 2001). Other types of brain cells, including microglia, astrocytes, and vascular cells, do not express significant levels of COX-2 normally, but its expression is also increased after cerebral insults (Laflamme et al, 1999).…”

“…COX-2 is constitutively expressed in only a few tissues, for example, the brain, but is upregulated in a wide variety of cells by cytokines, mitogens, growth factors, and bacterial lipopolysaccharides. In the brain, COX-2 is induced in pathological conditions such as seizure, ischemia, or other neurodegenerative diseases (Yamagata et al, 1993;Nogawa et al, 1998), and has been involved in the damage associated in these conditions (reviewed in Pasinetti, 2001). According to its condition of inducible enzyme, and similarly to NOS-2, the promotor of the immediate-early gene COX-2 depends on the activation of several transcription factors including NF-kB (Appleby et al, 1994).…”

Diabetes-induced changes in endothelial mechanisms implicated in rabbit carotid arterial response to 5-hydroxytryptamine

“…iNOS has been suggested to participate in the pathophysiology of certain vascular disor-Ž ders Sayama et al, 1998;Nogawa et al, 1998;Forster et . al., 1999 .…”

Therapeutic Potential of Natural Product-Based Oral Nanomedicines for Stroke Prevention

“…Studies have suggested that large amounts of NO produced by inducible nitric oxide synthase (iNOs) are toxic to the injured brain and contribute to the late stage of cerebral ischemia. 8 Oxidative injury is further worsened when blood flow is restored during reperfusion. 9 Taken together, the research indicates that it is necessary to employ exogenous antioxidant drugs and free radical scavengers to counter cerebral ischemia and reperfusioninduced oxidative stress.…”