Role of cathepsin S in spinal microglia in maintenance of bone cancer pain in rats

Abstract

Objective To investigate the role of cathepsin S (CatS) in spinal microglia in the maintenance of bone cancer pain (BCP) in rats.Methods Fifty unmated female Sprague-Dawley rats,aged 4-6 months,weighing 150-180 g,were randomly divided into 5 groups with 10 rats in each group:sham operation group (group S) ; group BCP; sham operation + CatS inhibitor morpholinurea-leucine-homophenylalanine-vinyl phenyl sulfone (LHVS) group (group S + L); BCP + dimethyl sulfoxide (DMSO) group (group BCP + D); BCP + LHVS group (group BCP + L).BCP was induced by inoculating 2 × 107/ml Walker256 mammary gland carcinoma cells 5 μl into the medullary cavity of the left tibia,while in S and S + L groups,Hank' s solution 5μl was injected into left tibia instead of Walker256 cells.At 10,11 and 12 days after inoculation,the rats in S + L and BCP + L groups received an intrathecal injection of LHVS 50 nmol/10μl,and the rats in group BCP + D received an intrathecal injection of 5 ％ DMSO 10 μl.Mechanical paw withdrawal threshold (MWT) was measured at 1 day before inoculation (baseline) and 3,6,9,10,11 and 12 days after inoculation (T0-6).MWT was measured before intrathecal administration and at 0.5,1.0,3.0,6.0,9.0,12.0 and 24.0 h after intrathecal administration.The rats were sacrificed and the L4-6 segments of the spinal cord were removed for determination of the expression of OX-42 in the spinal dorsal horn by immunohistochemistry.Results Compared with group S,MWT was significantly decreased at T2-6 and the expression of OX-42 in spinal dorsal horn was up-regulated in BCP,BCP + D and BCP + L groups (P ＜ 0.01),and no significant changes in MWT and expression of OX-42 in spinal dorsal horn were found in S + L group (P ＞ 0.05).Compared with group BCP,MWT was significantly increased at T4-6 and the expression of OX-42 in spinal dorsal horn was down-regulated in group BCP+ L (P ＜ 0.01),and no significant change in MWT and the expression of OX-42 in spinal dorsal horn was found in group BCP + D (P ＞ 0.05).MWT was significantly decreased at 3.0,6.0 and 9.0 h after intrathecal administration in S + L and BCP + D groups as compared with BCP + D group (P ＜ 0.01).Conclusion Activation of CatS in spinal microglia is involved in the maintenance of BCP in rats. Key words: Cysteine endopeptidases; Microglia ; Spinal cord ; Pain ; Bone neoplasms