Role of NFkappaB in an animal model of complex regional pain syndrome-type I (CRPS-I)

Abstract

NFkappaB is involved in several pathogenic mechanisms that are believed to underlie the complex regional pain syndrome (CRPS), including ischemia, inflammation and sensitization. Chronic postischemia pain (CPIP) has been developed as an animal model that mimics the symptoms of CRPS-I. The possible involvement of NFkappaB in CRPS-I was studied using CPIP rats. Under sodium pentobarbital anesthesia, a tourniquet was placed around the rat left ankle joint, producing 3 hours of ischemia, followed by rapid reperfusion (IR injury). NFkappaB was measured in nuclear extracts of muscle and spinal cord tissue using ELISA. Moreover, the anti-allodynic (mechanical and cold) effect was tested for systemic, intrathecal, or intraplantar treatment with the NFkappaB inhibitor pyrrolidine dithiocarbamate (PDTC). At 2 and 48 hours after IR injury, NFkappaB was elevated in muscle and spinal cord of CPIP rats compared to shams. At 7 days, NFkappaB levels were normalized in muscle, but still elevated in spinal cord tissue. Systemic PDTC treatment relieved mechanical and cold allodynia in a dose-dependent manner, lasting for at least 3 hours. Intrathecal-but not intraplantar-administration also relieved mechanical allodynia. The results suggest that muscle and spinal NFkappaB plays a role in the pathogenesis of CPIP and potentially of human CRPS.

Perspective: Using the CPIP model, we demonstrate that NFkappaB is involved in the development of allodynia after a physical injury (ischemia and reperfusion) without direct nerve trauma. Since CPIP animals exhibit many features of human CRPS-I, this observation indicates a potential role for NFkappaB in human CRPS.

Fig. 1

A) NFκB levels in muscle from the ipsilateral (ipsi) and contralateral (contra) hind paw of CPIP rats compared to shams at 2 hrs, 48 hrs and 7 days post-reperfusion, measured by ELISA. CPIP ipsilateral at 2 and 48 hrs: N = 15, at 7 days: N = 6. CPIP contralateral at 2 and 48 hrs: N = 15, at 7 days: N = 6. Sham at 2 and 48 hrs: N = 18, at 7 days N = 14. *p < 0.05, **p < 0.005. B) NFκB levels in spinal cord from the ipsilateral (ipsi) and contralateral (contra) side of CPIP rats compared to shams at 2 hrs, 48 hrs and 7 days post reperfusion, measured by ELISA. CPIP ipsilateral at 2 and 48 hrs: N = 15, at 7 days: N = 6. CPIP contralateral at 2 and 48 hrs: N =15, at 7 days: N = 6. Sham at 2 and 48 hrs: N = 18, at 7 days N=14. *p < 0.05, **p < 0.005.

Fig. 2

A) Mechanical paw-withdrawal threshold in CPIP rats after systemic saline or PDTC treatment 48 hrs post-reperfusion. CPIP saline: N = 7; CPIP PDTC 10 mg/kg: N = 9; CPIP PDTC 30 mg/kg: N = 9; CPIP PDTC 100 mg/kg: N = 7; Sham saline: N = 10; Sham CPIP: N = 10. * p < 0.05 **p < 0.005. B) Relative changes in cold water responses in the ipsilateral hind paw of CPIP rats after systemic saline or PDTC treatment 48 hrs post-reperfusion, compared to cold water responses before treatment. CPIP saline: N = 9; CPIP PDTC 10 mg/kg: N = 6; CPIP PDTC 30 mg/kg: N = 4; CPIP PDTC 100 mg/kg: N = 7. *p < 0.05.

Fig. 3

A) Mechanical paw-withdrawal thresholds in CPIP rats after intrathecal treatment with PDTC 48 hrs post-reperfusion. Saline ipsilateral (ipsi): N = 8; PDTC ipsilateral: N = 8; Saline contralateral (contra): N = 8; PDTC contralateral N=8; t p < 0.05) in mean paw-withdrawal threshold compared to before treatment. B) Mechanical paw-withdrawal thresholds in CPIP rats after intraplantar treatment with PDTC 48 hrs post-reperfusion. Saline ipsilateral (ipsi): N = 5; PDTC ipsilateral: N = 5; Saline contralateral (contra): N = 5; PDTC contralateral: N = 5.