Cyclooxygenase-2,Prostaglandin Synthases,and Prostaglandin H 2 Metabolism in Traumatic Brain Injury in the Rat

Abstract

Inflammatory mediators are important in traumatic brain injury (TBI). The objective of the present study was to investigate the expression of cyclooxygenase-2 (COX-2), prostaglandin E (PGE) and PGD synthases, and PGH₂ metabolism in two rat models of TBI. Fluid percussion injury (FPI) resulted in bilateral induction of COX-2 mRNA in the dentate gyri and the cortex, whereas controlled cortical contusion injury (CCC) induced COX-2 mRNA in the ipsilateral dentate gyrus and intensely in the cortex as judged by in situ hybridization. The induction subsided within 24 h. COX-2 immunoreactivity was detectable in these areas and persisted in the ipsilateral cortex for at least 72 h after CCC. Regions with COX-2 induction co-localized with TUNEL staining, suggesting a link between COX-2 expression and cell damage. COX-2 forms PGH₂, which can be isomerized to PGD₂, PGE₂, and PGF_2α by enzymatic and non-enzymatic mechanisms. In situ hybridization showed that mRNA of PGD synthase and microsomal PGE synthase were present in the choroid plexus. The microsomal PGE synthase was induced bilaterally after FPI and unilaterally after CCC. Liquid chromatography-mass spectrometry showed that low speed supernatant of normal and traumatized cortex and hippocampus transformed PGH₂ to PGD₂ as main product. PGD₂ was dehydrated in brain homogenates to biological active compounds, for example, 15-deoxy-Δ^12,14-PGJ₂. Thus COX-2 increases in certain neurons following TBI without neuronal induction of PGD and microsomal PGE synthases, suggesting that PGH₂ may decompose to PGD₂ and its dehydration products by nonenzymatic mechanisms or to PGD₂ by low constitutive levels of PGD synthase.