Effect of ulinastatin on neuron apoptosis and CCAAT/enhancer-binding protein expression of spinal cord after peripheral nerve injury

Objective To evaluate the effect of ulinastatin on neuron apoptosis and CCAAT/enhancer-binding protein (CHOP) expression of spinal cord after peripheral nerve injury. Methods A total of 225 healthy male SPF C57BL/6J mice were divided into three groups by using a random number table: sham-operated group, peripheral nerve injury group and ulinastatin group (n=75). The models of unilateral sciatic nerve transection were established in the latter two groups. After the models being established, intraperitoneal injection of ulinastatin 0.2 mL (10 000 U/kg) was performed once daily for 3 consecutive d in ulinastatin group, and the equal volume of normal saline was given once daily for 3 consecutive d in sham-operated group and peripheral nerve injury group. One, 3, 7, 14 and 28 d after surgery, L4-6 spinal cord segments were removed for pathological examination by HE staining, and for detection of neuron apoptosis and apoptotic index (AI) by TUNEL method; the expressions of CHOP, Bcl-2, Bax and cleaved caspase-3 proteins were determined by Western blotting and the ratio of Bcl-2/Bax was calculated, and the CHOP mRNA expression was detected by RT-PCR. Results HE staining showed that the injury of spinal cord in peripheral nerve injury group was more aggravated as compared with that in the sham-operated group, and the injury of spinal cord in ulinastatin group was more alleviated as compared with that in the peripheral nerve injury group. One, 3, 7, 14 and 28 d after surgery, AI was significantly higher, Bcl-2 protein expression was down-regulated, cleaved caspase-3 and Bax protein expressions were up-regulated, Bcl-2/Bax ratio was lower, and CHOP protein or mRNA expressions were up-regulated in the peripheral nerve injury group and ulinastatin group as compared with those in the sham-operated group, with statistically significant differences (P<0.05). As compared with those in the peripheral nerve injury group, AI was significantly lower, Bcl-2 protein expression was up-regulated, cleaved caspase-3 and Bax protein expressions were down-regulated, Bcl-2/Bax ratio was higher, and CHOP protein or mRNA expressions were down-regulated in ulinastatin group, with statistically significant differences (P<0.05). Conclusion The mechanism by which ulinastatin protects spinal cord injury after peripheral nerve injury is related to down-regulation of CHOP expression and suppression of neuron apoptosis of spinal cord. Key words: Ulinastatin; CCAAT/enhancer-binding protein; Apoptosis; Peripheral nerve; Spinal cord