The Potential Role Of Calpain In The Zymosan-Induced Paw Inflammatory Pain Rats

Part One: Spinal calpain is activated after zymosan-induced paw inflammation in rats and promotes to the generation of inflammatory painObjective: To investigate the potential role of calpain in the spinal cord in the zymosan-induced paw inflammatory pain model.Methods: Sprague-Dawley rats were divided into three groups: 1) control rats (n=8), 2) sham surgery rats (n=16), 3) zymosan-induced paw inflammation rats (n=24). The group 3) is divided into three sub-groups according to killing time points. Mechanical withdrawal threshold was tested with von Frey filament and maximum thickness of paw was measured with calibrated micrometer at 0.5h,1h,2h,4h,8h,24h and 48h after zymosan injection, respectively. All rats were killed at different occasions following surgery to examine calpain activity, IκBαand nuclear NFκB express in the spinal dorsal horn with the means of western blot analysis.Results: Mechanical withdrawal threshold and maximum thickness of paw in the zymosan-induced paw imflammation rats significantly increased comopared with control and sham rats (P<0.05, P<0.01). Calpain in the ipsilateral spinal dorsal horn was dramatically activated after zymosan injection, together with significant decreased express of IκBαand increased express of nuclear NFκB. Conclusion: Calpain activation in the spinal dorsal horn maybe paly a major role in the development of zymosan-induced inflammatory pain through degrading IκBαand activating NFκB.Part Two: Analgesic effect of calpain inhibitor ALLN on the zymosan-induced paw inflammatory pain and the COX-2 express in the spinal dorsal hornObjective: Calpain activation plays a positive role in the development of peripheral inflammatory pain. This study examined the analgesic effect of calpain inhibitor ALLN on the zymosan-induced paw inflammatory pain and the COX-2 express in the spinal dorsal horn.Methods: Sprague-Dawley rats were divided into three groups: 1) sham surgery rats (n=16), 2) zymosan-induced paw inflammation rats with intraperitoneal DMSO treatment 30min before zymosan injection (n=24), and 3) zymosan-induced paw inflammation rats with intraperitoneal calpain inhibitor ALLN treatment 30min before zymosan injection (n=24). The group 2) and group 3) were divided into three sub-groups according to killing time points, respectively. Mechanical withdrawal threshold was tested with von Frey filament and maximum thickness of paw was measured with calibrated micrometer at 0.5h,1h,2h,4h,8h,24h and 48h after zymosan injection, respectively. All rats were killed at different occasions following surgery to examine the COX-2 express in the spinal dorsal horn with western blot analysis.Results: Intraperitoneal ALLN injection 30min before zymosan injection significantly reduced zymosan-induced mechanical withdrawal threshold and paw edema at 4h, 8h, 24h and 48h after zymosan injection compared with DMSO treatment. Meanwhile, calpain inhibitor ALLN treatment significantly decreased the COX-2 express in the spinal dorsal horn compared with DMSO treatment.Conclusion: Administration of ALLN, a calpain inhibitor, was effective to attenuate zymosan-induced paw inflammatory pain. Calpain activation maybe one aspect of the signaling cascade that increase the COX-2 express in the spinal cord and contributes to mechanical hyperalgesia after peripheral inflammatory injury.