Cyclooxygenase-2 mRNA expression is associated with c-fos mRNA expression and transient water ADC reduction detected with diffusion MRI during acute focal ischemia in rats

Parecoxib is neuroprotective in spontaneously hypertensive rats after transient middle cerebral artery occlusion: a divided treatment response?

Background

Anti-inflammatory treatment affects ischemic damage and neurogenesis in rodent models of cerebral ischemia. We investigated the potential benefit of COX-2 inhibition with parecoxib in spontaneously hypertensive rats (SHRs) subjected to transient middle cerebral artery occlusion (tMCAo).

Methods

Sixty-four male SHRs were randomized to 90 min of intraluminal tMCAo or sham surgery. Parecoxib (10 mg/kg) or isotonic saline was administered intraperitoneally (IP) during the procedure, and twice daily thereafter. Nineteen animals were euthanized after 24 hours, and each hemisphere was examined for mRNA expression of pro-inflammatory cytokines and COX enzymes by quantitative RT-PCR. Twenty-three tMCAo animals were studied with diffusion and T₂ weighted MRI within the first 24 hours, and ten of the SHRs underwent follow-up MRI six days later. Thirty-three SHRs were given 5-bromo-2'-deoxy-uridine (BrdU) twice daily on Day 4 to 7 after tMCAo. Animals were euthanized on Day 8 and the brains were studied with free-floating immunohistochemistry for activated microglia (ED-1), hippocampal granule cell BrdU incorporation, and neuronal nuclei (NeuN). Infarct volume estimation was done using the 2D nucleator and Cavalieri principle on NeuN-stained coronal brain sections. The total number of BrdU⁺ cells in the dentate gyrus (DG) of the hippocampus was estimated using the optical fractionator.

Results

We found a significant reduction in infarct volume in parecoxib treated animals one week after tMCAo (p < 0.03). Cortical ADC values in the parecoxib group were markedly less increased on Day 8 (p < 0.01). Interestingly, the parecoxib treated rats were segregated into two subgroups, suggesting a responder vs. non-responder phenomenon. We found indications of mRNA up-regulation of IL-1β, IL-6, TNF-α and COX-2, whereas COX-1 remained unaffected. Hippocampal granule cell BrdU incorporation was not affected by parecoxib treatment. Presence of ED-1⁺ activated microglia in the hippocampus was related to an increase in BrdU uptake in the DG.

Conclusion

IP parecoxib administration during tMCAo was neuroprotective, as evidenced by a large reduction in mean infarct volume and a lower cortical ADC increment. Increased pro-inflammatory cytokine mRNA levels and hippocampal granule cell BrdU incorporation remained unaffected.

Neuronal prostaglandin endoperoxide synthase 2 responses to oxygen and glucose deprivation are mediated by mitogen-activated protein kinase ERK1/2

Prostanoids in the central nervous system define an important linkage between blood pressure and hormonal responses to hypotension/ischemia. Prostaglandin endoperoxide synthase (PGHS)-2, the inducible isoform of this enzyme, is induced by cerebral hypoperfusion/ischemia. To investigate the mechanism of the PGHS-2 gene expression in response to cerebral hypoperfusion/ischemia in neurons, we used a cell culture model (human SK-N-AS cells) to mimic the oxygen and glucose deprivation (OGD) that usually results from ischemia. Whereas OGD stimulated robust increases in PGHS-2 mRNA abundance, neither oxygen nor glucose deprivation alone was effective. Our data demonstrated that induction of both PGHS-2 mRNA and protein reached peak levels ( approximately 10 fold) after 6 h OGD. This was partially blocked by the inhibition of mitogen-activated protein kinase (MAPK) p38, and was almost completely blocked by the inhibition of extracellular signal-related kinases 1/2 (ERK1/2 or p44/42), another MAPK. These results indicate that PGHS-2 gene expression is induced by oxygen and glucose deprivation synergistically in neurons, and this induction is mediated by one or more members of the MAPK family.

Post-seizures amygdaloallocortical microvascular lesion leading to atrophy and memory impairment

Although the incidence of seizures after a cerebrovascular event including intracerebral hemorrhage has been widely recognized, the present studies have demonstrated that generalized convulsive seizures can cause multifocal amygdaloallocortical hemorrhage and tissue necrosis, the origin of which remains to be established. The seizure-elicited amygdaloallocortical injured area, which we refer to as a focal injury-prone area (FIPA), was caused by cholinergic stimulation of the ventroposterolateral and thalamic reticular nuclei. The amygdaloallocortical injury was preceded by focal absence of neuronal COX-2 and presence of microvascular immunoreactivity to the pro-inflammatory cytokines, IL-1beta and TNF-alpha. The microvascular inflammation was followed by edema and multifocal amygdaloallocortical microhemorrhages, leading to atrophy and cognitive impairment. On the basis of the present results, we conclude that generalized convulsive seizures may be at the origin of amygdaloallocortical microvascular injury suggesting that, in addition to anticonvulsant treatment, an appropriate clinical evaluation and therapy for seizures-associated cerebrovascular accidents should be considered.

Molecular Identification of the Ischemic Penumbra

Review of results of experimental and clinical studies indicates that the penumbra of physiologically impaired but potentially salvageable tissue surrounding the central core of focal cerebral ischemia that develops shortly after onset of major conducting vessel occlusion is complex and dynamic with severity and duration thresholds for hypoxic stress and injury that are specific to tissue site, cell type, molecular pathway or gene expression investigated and efficiency of collateral or residual flow and reperfusion. Imaging methods that have been utilized in vivo to identify penumbra and predict response to reperfusion and other protective therapies include magnetic resonance spectroscopy, diffusion- and perfusion-MRI as well as positron emission tomography. However, resolution of focal lesions characterized by lactic acidosis or cellular edema does not predict tissue survival, and imaging thresholds for resuscitation after reperfusion have not been determined experimentally. HSP-70 stress protein induction represents an endogenous protective mechanism that occurs in penumbra but not core neurones. A robust protective effect has been demonstrated during focal ischemia in transgenic mice overexpressing HSP-70 perhaps by suppressing early cytochrome c release. Delayed manganese mediated striatal neurodegeneration can be detected with T1 MRI after brief episodes of transient focal ischemia. Future studies may define endogenous cytotoxic and cytoprotective molecular penumbras that can be exploited to improve outcome after temporary focal ischemia.