Spinal phospholipase A2 in inflammatory hyperalgesia: role of Group IVA cPLA2

Abstract

1 Current work has shown the importance of spinal cyclooxygenase (COX) products in facilitatory processes leading to tissue injury induced hyperalgesia. This cascade must originate with free arachidonic acid (AA) released by the activity of spinal phospholipase A₂'s (PLA₂). In the present work, we studied the role of PLA₂'s in spinal sensitization. 2 We first demonstrate the presence of constitutive mRNA in the spinal cord for PLA₂ Groups IB, IIA, IIC, IVA, V and VI by reverse transcription–polymerase chain reaction (RT–PCR) and sequencing. Using quantitative‐PCR, we found that Group IVA cPLA₂ and Group VI iPLA₂ are the predominant PLA₂ messages in the spinal cord. Western blotting and activity assays specific for Group IVA cPLA₂ and Group VI iPLA₂ verified the presence of these enzymes. PLA₂ activity in spinal cord homogenates was suppressed by methyl arachidonyl fluorophosphonate (MAFP) and arachidonyl trifluoromethylketone (AACOCF₃), mixed inhibitors of Group IVA cPLA₂ and Group VI iPLA₂ as well as by bromoenol lactone (BEL), a Group VI iPLA₂ inhibitor. The spinal expression of PLA₂ mRNA or protein was not altered in the face of peripheral inflammation. Secondly, we showed that intrathecal (i.t.) administration of MAFP and AACOCF₃, but not BEL, dose‐dependently prevented thermal hyperalgesia induced by intraplantar carrageenan as well as formalin‐induced flinching. Finally, i.t. injection of AACOCF₃, at antihyperalgesic doses, decreased the release of prostaglandin E₂ (PGE₂) into spinal dialysate evoked by i.t. NMDA, while i.t. injection of BEL had no effect. 3 Taken together, this work points to a role for constitutive Group IVA cPLA₂ in spinal nociceptive processing. British Journal of Pharmacology (2005) 144, 940–952. doi:10.1038/sj.bjp.0706116