Necrostatin-1 Attenuates Delayed Paraplegia after Transient Spinal Cord Ischemia in Rabbits by Inhibiting the Upregulation of Receptor-Interacting Protein Kinase 1 and 3

Abstract

Delayed-onset paraplegia is a disastrous complication after thoracoabdominal aortic open surgery and thoracic endovascular aortic repair. Studies have revealed that transient spinal cord ischemia caused by temporary occlusion of the aorta induces delayed motor neuron death owing to apoptosis and necroptosis. Recently, necrostatin-1 (Nec-1), a necroptosis inhibitor, has been reported to reduce cerebral and myocardial infarction in rats or pigs. In this study, we investigated the efficacy of Nec-1 in delayed paraplegia after transient spinal cord ischemia in rabbits and assessed the expression of necroptosis- and apoptosis-related proteins in motor neurons. This study used rabbit transient spinal cord ischemia models using a balloon catheter. They were divided into a vehicle-treated group (n=24), Nec-1-treated group (n=24), and sham-controls (n=6). In the Nec-1-treated group, 1mg/kg of Nec-1 was intravascularly administered immediately before ischemia induction. Neurological function was assessed using the modified Tarlov score, and the spinal cord was removed 8hr and 1, 2, and 7days after reperfusion. Morphological changes were examined using hematoxylin and eosin staining. The expression levels of necroptosis-related proteins (receptor-interacting protein kinase [RIP] 1 and 3) and apoptosis-related proteins (Bax and caspase-8) were assessed using western blotting and histochemical analysis. We also performed double-fluorescence immunohistochemical studies of RIP1, RIP3, Bax, and caspase-8. Neurological function significantly improved in the Nec-1-treated group compared with that in the vehicle-treated group 7days after reperfusion (median 3 and 0, P=0.025). Motor neurons observed 7days after reperfusion were significantly decreased in both groups compared with the sham group (vehicle-treated, P<0.001; Nec-1-treated, P<0.001). However, significantly more motor neurons survived in the Nec-1-treated group than in the vehicle-treated group (P<0.001). Western blot analysis revealed RIP1, RIP3, Bax, and caspase-8 upregulation 8hr after reperfusion in the vehicle-treated group (RIP1, P=0.001; RIP3, P=0.045; Bax, P=0.042; caspase-8, P=0.047). In the Nec-1-treated group, the upregulation of RIP1 and RIP3 was not observed at any time point, whereas that of Bax and caspase-8 was observed 8hr after reperfusion (Bax, P=0.029; caspase-8, P=0.021). Immunohistochemical study revealed the immunoreactivity of these proteins in motor neurons. Double-fluorescence immunohistochemistry revealed the induction of RIP1 and RIP3, and that of Bax and caspase-8, in the same motor neurons. These data suggest that Nec-1 reduces delayed motor neuron death and attenuates delayed paraplegia after transient spinal cord ischemia in rabbits by selectively inhibiting necroptosis of motor neurons with minimal effect on their apoptosis.