Effects of hypoxia preconditioning on inflammatory responses and apoptosis in the rat model after spinal cord injury

Abstract

Objective To observe the effects of hypoxia preconditioning on inflammatory cytokines and apoptosis after spinal cord injury in the rat model.Methods 154 adult female wistar rats were randomly divided into three groups,including the spinal cord injury group,the spinal cord injury ± hypoxia precondition (HP) group,the sham operation group.Immunohistochemistry was performed to determine the expressions of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)in spinal cord injury area at five time points (2,6,12 h,1,3 d).BBB score was used to evaluate the function recovery of hind limb.The method of immunohistochemistry and terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) were adopted to detect the level of B cell lymphoma/leukemia-2 (bcl-2) protein and the apoptotic cells at five time points (6 h,1,3,7,14 d)after spinal cord injury.Results The integral absorbance (IA) of TNF-α in HP group was decreased at 6 h and 12 h,compared with that in spinal cord injury group (5.187±0.628 vs.7.962±2.185; 3.219±0.724 vs.5.361 ±1.246,P＜0.05).The IA ofIL-1β in HP group was lower than spinal cord injury group at three time points (6,12 h,1 d) (3.845 ± 1.669 vs.6.674 ± 1.537 ; 6.241 ± 1.142 vs.9.961 ± 2.814 ; 2.264 ± 1.476 vs.4.418 ± 0.973,P ＜ 0.05).In HP group,the IA of bcl-2 protein was significantly higher than spinal cord injury group at any time point (4.335 ±0.563 vs.3.256 ± 1.024,P ＜0.05; 6.873 ±2.032 vs.5.029 ± 1.537,P ＜0.01 ; 11.869 ± 2.560 vs.6.893 ± 2.164,P ＜ 0.01 ; 10.340 ± 1.469 vs.8.074 ± 2.175,P ＜ 0.05 ; 8.143 ± 2.376 vs.5.238 ± 1.467,P ＜0.05).The apoptosis index (AI) of HP group was decreased on 1 d,3 d,7 d,14 d (20.63 ±5.86 vs.26.37 ±4.76,P＜0.05; 29.85 ±8.12 vs.37.96 ±3.81,P＜0.05; 31.56 ±4.01 vs.41.74 ±6.69,P ＜0.01 ; 22.66 ±5.24 vs.32.87 ±9.90,P ＜0.05),compared with the spinal cord injury group.The BBB scores of HP group was higher than spinal cord injury group on 7 d and 14 d (5.68 ±1.83 vs.3.06 ±1.21; 10.21 ±2.64 vs.6.45 ±1.97,P＜0.05).Conclusion Hypoxiapreconditioning can inhibit the inflammatory response of local tissue damage and reduce apoptosis through the high expression of bcl-2 protein,thus promote the neural functional recovery after spinal cord injury. Key words: Hypoxia precondition ; Spinal cord injury; Inflammation ; Apoptosis