Inhibition of Spinal 15-LOX-1 Attenuates TLR4-Dependent, NSAID-Unresponsive Hyperalgesia in Male Rats.

Therapeutic Approaches

Abstract

While nonsteroidal inflammatory drugs (NSAIDs) are the first line of therapeutics for the treatment of mild to moderate somatic pain, they are not generally considered to be effective for neuropathic pain. In the current study, direct activation of spinal Toll-like 4 receptors (TLR4) by the intrathecal (IT) administration of KDO2 lipid A (KLA), the active component of lipopolysaccharide (LPS), elicits a robust tactile allodynia that is unresponsive to cyclooxygenase (COX) inhibition, despite elevated expression of COX metabolites in the spinal cord. IT KLA increases 12-Lipoxygenase-mediated hepoxilin production in the lumbar spinal cord, concurrent with expression of the tactile allodynia. The TLR4-induced hepoxilin production also was observed in primary spinal microglia, but not in astrocytes, and was accompanied by increased microglial expression of the 12/15-lipoxygenase enzyme 15-LOX-1. IT KLA-induced tactile allodynia was completely prevented by spinal pretreatment with the 12/15-Lipoxygenase inhibitor CDC or a selective antibody targeting rat 15-LOX-1. Similarly, pretreatment with the selective inhibitors ML127 or ML351 both reduced activity of the rat homolog of 15-LOX-1 heterologously expressed in HEK-293T cells and completely abrogated NSAID-unresponsive allodynia in vivo following IT KLA. Finally, spinal 12/15-Lipoxygenase inhibition by NDGA both prevents Phase II Formalin flinching and reverses Formalin-induced persistent tactile allodynia. Taken together, these findings suggest that spinal TLR4-mediated hyperpathic states are mediated at least in part through activation of microglial 15-LOX-1.

Authors

Gregus, Ann M; Buczynski, Matthew W; Dumlao, Darren S; Norris, Paul C; Rai Bantukallu, Ganesha; Simeonov, Anton; Maloney, David J; Jadhav, Ajit; Xu, Qinghao; Wei, Spencer C; Fitzsimmons, Bethany L; Dennis, Edward A; Yaksh, Tony L;

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