Bay11-7082 attenuates neuropathic pain via inhibition of nuclear factor-kappa B and nucleotide-binding domain-like receptor protein 3 inflammasome activation in dorsal root ganglions in a rat model of lumbar disc herniation

Journal of Pain Research Dovepress open access to scientific and medical research ORIGINAL RESEARCH Journal of Pain Research downloaded from https://www.dovepress.com/ by 37.59.46.207 on 12-Jul-2018 For personal use only. Open Access Full Text Article Bay11-7082 attenuates neuropathic pain via inhibition of nuclear factor-kappa B and nucleotide-binding domain-like receptor protein 3 inflammasome activation in dorsal root ganglions in a rat model of lumbar disc herniation This article was published in the following Dove Press journal: Journal of Pain Research 13 February 2017 Number of times this article has been viewed Ailiang Zhang Kun Wang Lianghua Ding Xinnan Bao Xuan Wang Xubin Qiu Jinbo Liu Spine Surgery, Third Affiliated Hospital of Soochow University, Changzhou, People’s Republic of China Abstract: Lumbar disc herniation (LDH) is an important cause of radiculopathy, but the underlying mechanisms are incompletely understood. Many studies suggested that local inflammation, rather than mechanical compression, results in radiculopathy induced by LDH. On the molecular and cellular level, nuclear factor-kappa B (NF-κB) and nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome have been implicated in the regulation of neuroinflammation formation and progression. In this study, the autologous nucleus pulposus (NP) was implanted in the left L5 dorsal root ganglion (DRG) to mimic LDH in rats. We investigated the expression of NF-κB and the components of NLRP3 inflammasome in the DRG neurons in rats. Western blotting and immunofluorescence for the related molecules, including NLRP3, apoptosis-associated speck-like protein containing caspase-1 activator domain (ASC), caspase-1, interleukin (IL)-1β, IL-18, IκBα, p-IκBα, p65, p-p65, and calcitonin gene-related peptide (CGRP) were examined. In the NP-treated group, the activations of NLRP3, ASC, caspase-1, IL-1β, IL-18, p-IκBα, and p-p65 in DRG neurons in rats were elevated at 1 day after surgery, and the peak occurred at 7 days. Treatment with Bay11-7082, an inhibitor of the actions of IKK-β, was able to inhibit expression and activation of the molecules (NLRP3, ASC, caspase-1, IL-1β, IL-18, p-IκBα, and p-p65) and relieve the pain in rats. Our study shows that NF-κB and NLRP3 inflammasome are involved in the maintenance of NP-induced pain, and that Bay11-7082 could alleviate mechanical allodynia and thermal hyperalgesia by inhibiting NF-κB and NLRP3 inflammasome activation. Keywords: pain, NLRP3, NF-κB, dorsal root ganglion, nucleus pulposus Introduction Correspondence: Jinbo Liu Spine Surgery, Third Affiliated Hospital of Soochow University, 185 Juqian Road, Changzhou 213003, Jiangsu, People’s Republic of China Email 375 submit your manuscript | www.dovepress.com Journal of Pain Research 2017:10 375–382 Dovepress © 2017 Zhang et al. This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms. php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License (http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms (https://www.dovepress.com/terms.php). http://dx.doi.org/10.2147/JPR.S119820 Powered by TCPDF (www.tcpdf.org) Clinically, lumbar disc herniation (LDH) is a common disorder that can cause low back pain and severe radiculopathy, characterized by hyperalgesia, allodynia.1 Long-term chronic pain seriously compromises the quality of life of these patients. Radicular pain, one of the most common types of neuropathic pain, is mostly triggered by the mechanical compression and the local inflammation.2 Although the symptoms and physical sign are clear in clinic, the pathophysiology of neuropathic pain associated with LDH is incompletely clarified. The current therapeutic strategies are incapable of completely relieving the neuropathic pain. Nuclear factor-kappa B (NF-κB) is a transcription factor that has a pivotal role in the onset of inflammation. In the quiescent state, NF-κB proteins exist in an inactive state as Dovepress Journal of Pain Research downloaded from https://www.dovepress.com/ by 37.59.46.207 on 12-Jul-2018 For personal use only. Zhang et al homo- or heterodimers bound to its inhibitor of NF-κB (IκB) molecules in the cytoplasm. The p65/p50 heterodimer appears to be the most abundant form of NF-κB in mammals. IκB is phosphorylated by the IκB kinase (IKK) complex, which is mainly composed of the subunits IKKα and IKKβ. Subsequently, NF-κB is activated and translocated to the nucleus, and then initiates the transcription of downstream target genes involving inflammation.3 Ma and Bisby reported that the expression of genes induced by NF-κB in the dorsal root ganglion (DRG) neurons may finally lead to events responsible for the pain behaviors after partial sciatic nerve injury.4 The nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome is a cytoplasmic multiprotein complex. It consists of the regulatory subunit NLRP3, the adaptor apoptosis-associated speck-like protein containing caspase-1 activator domain (ASC) and the effector subunit caspase-1. NLRP3 inflammasome can be activated by various pathogens such as bacteria, virus and fungi, and has the ability to sense the sterile tissue damage or metabolic stress. Under the hits of the aforementioned stimuli, caspase-1 is cleaved and subsequently switches pro-interleukin (IL)-1β and pro-IL-18 into their active forms.5 In addition, previous studies have showed that proinflammatory cytokine IL-1β and L-18 play an important role in the progression of pain hypersensitivity and the positive feedback between neurons and glial cells.6,7 Bay11-7082 is a selective inhibitor of IKK-β and it irreversibly inhibits IκBα phosphorylation with resulting in the downregulation of NF-κB activation. Previous study reported that Bay11-7082 was a potent inhibitor of the inflammasome independent of their inhibitory effect on the NF-κB pathway.8 In this study, we examined whether Bay11-7082 attenuates neuropathic pain via inhibiting the activations of NLRP3 inflammasome and NF-κB in the LDH-mimicry rat model. Experimental procedures Animals Ninety adult Sprague Dawley rats (female, 200–250 g) were used in this study. The animals were maintained on a 12-h light/dark cycle with food and water provided ad libitum. Housing was kept at a constant room temperature and humidity level. All surgical procedures and experiments were approved by the Ethical Committee of Soochow University and were in accordance with the Guidelines for the Care and Treatment of Laboratory Animals of the US National Institutes of Health. Animal treatments and proc (...truncated)