The Involvement Of MCP-1/ERK Signaling Pathway In A Rat Model Of Bone Cancer Pain

Part one: Intrathecal MCP-1neutralizing antibody injectionreduces mechanical allodynia in a rat model of bone cancer painObjective To observe the effection of intrathecal MCP-1neutralizing antibodyinjection on pain behavior and the level of P-ERK1/2expression in spinal cord in a ratmodel of bone cancer pain, then explore its possible mechanisms.Methods50female SD rats weighting180～220g were randomly divided into5groups(n=8): group Ⅰ,control group; group Ⅱ, model group; group Ⅲ, control+Anti-MCP-1intrathecal (i. t.); group Ⅳ, model+IgG i. t.; group Ⅴ, model+Anti-MCP-1i. t. Rats ingroupⅠand group Ⅲ were injected with10μl Hank’s solution into the leftproximal tibial medullary cavity;Rats in group Ⅱ, group Ⅳ and group Ⅴ were injectedwith10μl Walker256breast cancer cells (1×10~7/ml) into the left proximal tibial medullarycavity.ResultsCompared with rats in group Ⅰ and group Ⅲ,Von-Frey thresholdssignificantly decreased in rats of group Ⅱ,ⅣandⅤat the6th day post-inoculation; Atthe same time, Von-Frey thresholds profoundlyelevated in rats of group Ⅴcompared withthose in group Ⅱ and Ⅳ.Compared with rats in group Ⅰ, the expression of P-ERKinspinal dorsal horn from group Ⅱ and Ⅳ apparently increased (P<0.01)and doubleimmunolabeling showed that P-ERK1/2-IR was restricted to OX-42-IR-labeled microgliacells.Spinal dorsal hornP-ERK1/2protein levels of rats in group Ⅴwere lower relative togroup Ⅱ and group Ⅳ. There was no remarkable difference between group Ⅲ andgroupⅠin the expression of spinal dorsal horn P-ERK(P>0.05).Conclusion Intrathecal MCP-1neutralizing antibody injection can partialyrelease mechanical allodynia induced by bone cancer pain, and this effect may be related toblockade of P-ERK1/2in the spinal dorsal horn. These results indicate that spinalMCP-1/ERK signal pathway may be involved in the development of rats bone cancer painvia activation of ERK in thespinal dorsal horn.Part two: Anti-nociceptive effect of intrathecal U0126incancer-induced pain ratsObjective To research the effect of intrathecal U0126on mechanical allodynia and inthe regulation for the expression of CX3CR1in the dorsal horn of spinal cord in bonecancer pain rats.Methods Fifty female rats weighing150~180g were randomly divided into5groups(n=10each): sham-operated group(group Ⅰ),BCP group(group Ⅱ),sham-operated+U0126group(group Ⅲ), BCP+5%DMSO group(group Ⅳ), BCP+U0126group(group Ⅴ). Bone cancer pain was induced by inoculating Walker256mammarygland carcinoma cells into the tibia medullary cavity. Rats in group Ⅲ、group Ⅳ andgroupⅤgroup received an intrathecal injection U012610μg/10μl or5%DMSO10μlindividually at24h intervals from10to12d after inoculation. Mechanical withdrawalthreshold(MWT) was measured at1d before (baseline) and3、6、9、10、11and12d afterinoculation.MWT was measured before administration and0.5、1、3、6、9、12、24h afteradministration on10d after inoculation.12d after inoculation, the L4~6spinal cord wereremoved fordetermination of CX3CR1expression (byWestern blot andimmunohistochemistry).Results Compared with group Ⅰand group Ⅲ,MWT of rats in group Ⅱ andgroup Ⅳ was decreased at6~12dafter inoculation (P<0.01), the number of CX3CR1positive cells and the expression of CX3CR1in spinal cord was increased (P<0.01);Compared with group Ⅱand group Ⅳ, intrathecal injection of U0126can reversemechanical hyperalgesia caused by bone cancer pain, and its peak attained at6h afterinjection(P<0.01), continued to12h(P>0.05) in group Ⅴ; the number of CX3CR1positive cells cells and the expression of CX3CR1in spinal dorsal horn wasdecreased(P<0.01). Conclusion Intrathecal injection U0126can alleviate bone cancer pain and suppressthe expression of CX3CR1. The ERK signal pathway may be involved in the mechanismof the development and maintenance of bone cancer pain.