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Microglia Cyclooxygenase-2 Activity in Experimental Gliomas

Possible Role in Cerebral Edema Formation¹

Departments of Neurological Surgery [B. Bad., J. M. S., A. R. H., S. P., B. Bar., S. L., D. K. R., J. V.] and Radiology [T. R. P.], University of Wisconsin School of Medicine, Madison, Wisconsin 53792

Purpose: Cerebral edema is responsible for significant morbidity and mortality in patients harboring malignant gliomas. To examine the role of inflammatory cells in brain edema formation, we studied the expression cyclooxygenase (COX)-2, a key enzyme in arachidonic acid metabolism, by microglia in the C6 rodent glioma model.

Experimental Design: The expression of COX-2 in primary microglia cultures obtained from intracranial rat C6 gliomas was examined using reverse transcription-PCR, Western analysis, and prostaglandin E₂ (PGE₂) enzyme immunoassay. Blood–tumor barrier permeability was studied in the same tumor model using magnetic resonance imaging.

Results: In contrast to C6 glioma cells, microglia isolated from intracranial C6 tumors produced high levels of PGE₂ through a COX-2-dependent pathway. To test whether the observed microglia COX-2 activity played a role in brain edema formation in gliomas, tumor-bearing rats were treated with rofecoxib, a selective COX-2 inhibitor. Rofecoxib was as effective as dexamethasone in decreasing the diffusion of contrast material into the brain parenchyma (P = 0.01, rofecoxib versus control animals), suggesting a reduction in blood–tumor barrier permeability.

Conclusions: These findings suggest that glioma-infiltrating microglia are a major source of PGE₂ production through the COX-2 pathway and support the use of COX-2 inhibitors as possible alternatives to glucocorticoids in the treatment of peritumoral edema in patients with malignant brain tumors.

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