Down-Regulation of Toll-Like Receptor 4 Gene Expression by Short Interfering RNA Attenuates Bone Cancer Pain in a Rat Model

Abstract

BackgroundThis study demonstrates a critical role in CNS innate immunity of the microglial Toll-like receptor 4 (TLR4) in the induction and maintenance of behavioral hypersensitivity in a rat model of bone cancer pain with the technique of RNA interference (RNAi). We hypothesized that after intramedullary injection of Walker 256 cells (a breast cancer cell line) into the tibia, CNS neuroimmune activation and subsequent cytokine expression are triggered by the stimulation of microglial membrane-bound TLR4.ResultsWe assessed tactile allodynia and spontaneous pain in female Sprague-Dawley (SD) rats after intramedullary injection of Walker 256 cells into the tibia. In a complementary study, TLR4 small interfering RNA(siRNA) was administered intrathecally to bone cancer pain rats to reduce the expression of spinal TLR4. The bone cancer pain rats treated with TLR4 siRNA displayed significantly attenuated behavioral hypersensitivity and decreased expression of spinal microglial markers and proinflammatory cytokines compared with controls. Only intrathecal injection of TRL4 siRNA at post-inoculation day 4 could prevent initial development of bone cancer pain; intrathecal injection of TRL4 siRNA at post-inoculation day 9 could attenuate, but not completely block, well-established bone cancer pain.ConclusionsTLR4 might be the main mediator in the induction of bone cancer pain. Further study of this early, specific, and innate CNS/microglial response, and how it leads to sustained glial/neuronal hypersensitivity, might lead to new therapies for the prevention and treatment of bone cancer pain syndromes.

P2Y1 purinoceptor inhibition reduces extracellular signal-regulated protein kinase 1/2 phosphorylation in spinal cord and dorsal root ganglia: implications for cancer-induced bone pain

“…A distinct feature of bone cancer pain is that the chronic pain state may be driven simultaneously by inflammation, tumorreleased products, and tumor-induced injury to primary afferent neurons [19]. In this study, we also confirmed that the female rat model of bone pain from metastatic bone cancer can closely mimic the human disease [18,20]. Our previous studies [18] on pain behavior have shown that the time window comprising days 6-18 post-inoculation is a reasonable period in which one can investigate the mechanisms of bone cancer pain and the effects of analgesic drugs on that pain.…”

Exploring the Neuroimmunopharmacology of Opioids: An Integrative Review of Mechanisms of Central Immune Signaling and Their Implications for Opioid Analgesia

“…1 for summary). Furthermore, TLR4 blockade not only prevents the initial development of neuropathic pain (Tanga et al, 2005) but also reverses established neuropathic pain (Bettoni et al, 2008;Hutchinson et al, 2008c;Cao et al, 2009;Lan et al, 2010;Liu et al, 2010a;Saito et al, 2010;Wu et al, 2010). The nociceptive consequences of TLR4-induced central immune signaling are due, at least in part, to p38-dependent activation of reactive glial phenotypes (Liu et al, 2010a) and up-regulation of prosta-NEUROIMMUNOPHARMACOLOGIC IMPLICATIONS FOR OPIOID ANALGESIA glandin E2 and TNF-␣ (Saito et al, 2010).…”

Mechanisms of Pain in Sickle Cell Disease

“…TLR4 has been shown to be associated with several modalities of pain including inlammatory pain [46,77], neuropathic pain [46, 78 80], post-operative cognitive dysfunction [81], cancer pain [82], etc. Recent studies in the SCD ield suggest that TLR4 activation may be a signiicant contributor to the multifactorial efects in SCD ranging from vaso-occlusion and inlammation to pain [83].…”