| Background:Neuropathic pain is a common and difficult-to-treat chronic disease. The International Association for the Study of Pain introduced the term neuropathic pain, defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system. Recent studies revealed that the proliferation and activation of neuroglial cells participated in the modulation of neuropathic pain. Toll-like receptor4(TLR4) is a pattern recognition receptor which associated with immunity and inflammation diseases. The activation of TLR4caused abundant production of proinflammatory cytokines through NF-κB signal pathway. In the central nervous system, TLR4are mainly expressed on microglia cells and play an important role in the activation of microglia cells as well as neuroimmune activation and neuroinflammation processes. High mobility group box-1protein (HMGB1), an important endogenic ligand of TLR4, is significantly upregulated in the spinal cord of neuropathic pain and bone cancer pain rats. These studies indicated that the activation of HMGB1/TLR4/NF-κB signal pathway contributes to the activation of spinal microglia cells and the modulation of neuropathic pain.Objectives:To investigate the roles of HMGB1/TLR4/NF-κB signal pathway in the activation of spinal microglia cells and modulation of neuropathic pain.Methods:Male SD rats successfully received intrathecal catheter implantation and without motor dysfunction were randomly divided into 5groups:Normal group (N group), Sham-operation group (Sham group), Chronic sciatic nerve constriction injury group (CCI group), EGCG treated group (EGCG group), Normal Saline group (NS group). Rats in CCI group, NS group and EGCG group were received with sciatic never ligation. Rats in Sham group were treated with sham operation but without sciatic nerve ligation, no treatment with rats in N group. Rats in EGCG group were intrathecally injected with epigallo catechin gallate (EGCG)10μl (1mg/kg) followed by1010μl normal saline form Day1before sciatic nerve ligation to Day3after surgery, while rats in other groups were received equal volume of normal saline. Paw withdrawal mechanical threshold (PWMT) and paw withdrawal thermal latency (PWTL) were tested on Day1before surgery and Day1,4,7,10,14after surgery. Lumbar spinal cord was sampled and the mRNA and protein expressions of HMGB1, TLR4and NF-κB were detected by RT-PCR, Western blot and immunohistochemistry; OX-42positive cells in the spinal dorsal horn were detected by fluorescent antibody technique and the contents of tumor necrosis factor alpha (TNF-α), interleukin-1beta (IL-1β) and interleukin-10(IL-10) were measured by ELISA.Results:Compared with Sham group, both PWMT (P<0.01) and PWTL (P<0.01) were significantly decreased after sciatic nerve ligation on the ipsilateral side, the expression of HMGB1, TLR4and NF-κB were significantly upregulated, microglia cells in the ipsilateral side spinal dorsal horn showed a remarkable proliferation and activation; the content of IL-10, IL-1βand TNF-α in the spinal cord were also significantly upregulated(P<0.05). No significant difference was found in Sham group (P>0.05) and on the contralateral side (P>0.05). In comparison to vehicle-treated CCI rats, intrathecal injection of EGCG significantly reduced mechanical allodynia and thermal hyperalgesia (P<0.05). Consistently, the expression of HMGB1, TLR4and NF-κB (P<0.05), the number of OX-42positive cells (P<0.05) and the content of IL-1βand TNF-α(P<0.05) in the spinal cord were significantly downregulated, while the expression of IL-10significantly upregulated (P<0.05).Conclusion:HMGB1/TLR4/NF-κB signal pathway plays an important role in the modulation of neuropathic pain. EGCG can inhibit the activation of HMGB1/TLR4/NF-κB signal pathway and decrease the proliferation and activation of spinal microglia cell which may contribute to its therapeutic effects on neuropathic pain introduced by chronic sciatic nerve constriction injury.
|
PDF Full Text Request