Systemic TAK-242 prevents intrathecal LPS evoked hyperalgesia in male, but not female mice and prevents delayed allodynia following intraplantar formalin in both male and female mice: The role of TLR4 in the evolution of a persistent pain state

Abstract

Objective Pain resulting from local tissue injury or inflammation typically resolves with time. Frequently, however, this pain may unexpectedly persist, becoming a pathological chronic state. Increasingly, the innate and adaptive immune systems are being implicated in the initiation and maintenance of these persistent conditions. In particular, Toll-like receptor 4 (TLR4) signaling has been shown to mediate the transition to a persistent pain state in a sex-dependent manner. In the present work, we explored this contribution using the TLR4 antagonist, TAK-242. Methods Male and female C57Bl/6 mice were given intravenous (IV), intrathecal (IT), or intraperitoneal (IP) TAK-242 prior to IT delivery of lipopolysaccharide (LPS), and tactile reactivity was assessed at regular intervals over 72-hours. Additional groups of mice were treated with IP TAK-242 prior to intraplantar formalin, and flinching was monitored for 1-hour. Tactile reactivity was assessed at 7-days after formalin delivery. Results LPS evoked TNF release from male and female macrophages and RAW267.4 cells, which was blocked in a concentration dependent fashion by TAK-242. In vivo, IT LPS evoked tactile allodynia to a greater degree in male than female mice. TAK-242, given by all routes, prevented development of IT LPS-induced tactile allodynia in male animals, but did not reverse their established allodynia. TLR4 deficiency and TAK-242 treatment attenuated IT LPS-induced allodynia in male, but not female mice. In the formalin model, pre-treatment with TAK-242 did not affect Phase 1 or Phase 2 flinching, but prevented the delayed tactile allodynia in both male and unexpectedly in female mice (Phase 3). Conclusions Together, these results suggest that TAK-242 is a TLR4 antagonist that has efficacy after systemic and intrathecal delivery and confirms the role of endogenous TLR4 signaling in triggering the development of a delayed allodynia in both male and female mice.

Inhibition of Neuroinflammation by AIBP: Spinal Effects upon Facilitated Pain States

“…As previously reported, the female i.t. LPS response is significantly reduced compared to males (Woller et al, 2016). However, the initial i.t.…”

“…After a 7 day delay, a persistent tactile allodynia progressively develops along with associated activation of spinal microglia (phase 3) (Wu et al, 2004). TLR4 knockout has no effect upon phase 1 or phase 2, but reduces the phase 3 (Woller et al, 2016). In this model, we initially performed i.t.…”

“…LPS displayed a robust and long lasting tactile allodynia (Stokes et al, 2013b; Woller et al, 2016). While i.t.…”

“…TLR4 deficiency in mice prevents the tactile allodynia otherwise evolving over time after afferent activation, as observed with intraplantar formalin (Woller et al, 2016) or as seen with the chemotherapeutic agent cisplatin (Park et al, 2014; Woller et al, 2015). Tellingly, intrathecal (i.t.)…”

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“…The centrally acting drugs (opiate analgesics) such as narcotics inhibited both phases equally, while antiinflammatory drugs (non-opiate analgesics) specially inhibited the second phase 20,21 . As we mentioned before it is also well known that the formalin model may involve sensorial C-fibers 22 in early phase and a combined process generated by peripheral inflammatory tissue and functional changes in the dorsal horn in late phase 23,24 .…”