Inhibition of spinal 15-LOX-1 attenuates TLR4-dependent, nonsteroidal anti-inflammatory drug–unresponsive hyperalgesia in male rats

Abstract

Although nonsteroidal anti-inflammatory drugs 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, elicits a robust tactile allodynia that is unresponsive to cyclooxygenase inhibition, despite elevated expression of cyclooxygenase metabolites in the spinal cord. Intrathecal KLA increases 12-lipoxygenase-mediated hepoxilin production in the lumbar spinal cord, concurrent with expression of the tactile allodynia. The TLR4-induced hepoxilin production was also 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. Intrathecal 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 nonsteroidal anti-inflammatory drug-unresponsive allodynia in vivo after IT KLA. Finally, spinal 12/15-lipoxygenase inhibition by nordihydroguaiaretic acid (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.

Phenelzine-based probes reveal Secernin-3 is involved in thermal nociception

“…Tactile allodynia: Tactile allodynia was evaluated using manual von Frey filaments with buckling forces between 0.02 and 2 g (Touch Test, Stoelting Co.) applied to the mid-plantar surface of each hind paw using the up-down method as previously described (Chaplan et al, 1994;Gregus et al, 2018). Mice were acclimated to the testing room in a 4-sided acrylic chamber with only one transparent wall (3 x 3 x 7.5 in) and placed on a metal mesh grid under controlled lighting conditions (~100 lux) for a minimum of 60 min (baseline measurements) or 15 min (experimental timepoints).…”

Pain Mechanism in Rheumatoid Arthritis: From Cytokines to Central Sensitization

“…Pretreatment with TLR4 antagonist (TAK-242) had no effect on the initial hypersensitivity, but the late paralgesia can be prevented [ 80 ]. It was found that TLR4-induced production of the bioactive lipids by 12/15-lipoxygenase (12/15-LO) partially mediates neural sensitization, although the contribution of 12/15-LO expressed in other cell types cannot be excluded [ 81 ]. In conclusion, these studies indicated that TLR mediates RA pain through direct or indirect mechanism.…”

Soluble Epoxide Hydrolase Regulation of Lipid Mediators Limits Pain

“…LOX enzymes can also metabolize linoleic acid (LA) into 9-or 13hydroxyoctadecadienoic acid which have demonstrated some bioactivity [32]. In addition, inhibiting 15-LOX has demonstrated anti-hyperalgesic effects in an intrathecal LPS pain model and prevented formalin flinching and tactile allodynia [33].…”