An adenosine A2A agonist, ATL-146e, reduces paralysis and apoptosis during rabbit spinal cord reperfusion

Background. We hypothesized that systemic ATL-146e, an adenosine A(2A) agonist, would decrease spinal cord reperfusion inflammatory stress and inhibit apoptosis and that these effects would correlate with improved neurologic functional outcome. Methods. Thirty rabbits underwent cross-clamping of the infrarenal aorta for 45 minutes. One group of animals (n=14) received 0.06 mug/kg per minute of ATL-146e infused intravenously for 3 hours, beginning 15 minutes before reperfusion. A second group of animals (n=16) underwent spinal cord ischemia with saline vehicle alone and served as ischemic controls. Animals (n=9, 11) from each group survived for 48 hours and assessed for neurologic impairment with the Tarlov (0-5) scoring system. Four animals from each group were humanely killed at the end of the 3-hour treatment period, and the remainder killed after 48 hours' survival. In all animals, lumbar spinal cord tissue specimens were frozen for subsequent Western blot analysis of heat shock protein 70 (HSP 70), and for the p85 fragment of poly (ADP-ribose) polymerase (PARP). Neuronal viability indices were determined at 48 hours with hematoxylin and eosin staining. Results. There was improvement in neurologic function in rabbits receiving ATL-146e (P<.001) compared with ischemic controls. At the end of the 3-hour treatment period there was a 46% (P<.05) decrease in HSP 70 expression in the ATL-146e group compared with the control group, but no difference in PAR-P expression. At 48 hours, there was no difference between control and ATL-146e groups in HSP 70 expression, but there was a 65% (P<.05) reduction in PARP in the spinal cords of animals that had received ATL-146e. There was a significant improvement in neuronal viability indices in animals receiving ATL-146e compared with ischemic controls (P<.05). Conclusions. Systemic ATL-146e infusion during reperfusion after spinal cord ischemia results in preservation of hindlimb motor function. There is evidence of decreased spinal cord inflammatory stress immediately after treatment with ATL-146e as indicated by reduced HSP 70 induction. Treatment with ATL-146e is associated with a reduction in neuronal apoptosis as suggested by a substantial decrease in the fragmentation of PARP at 48 hours. These results suggest that inflammation during reperfusion and subsequent apoptosis contribute to paralysis after restoration of blood flow to the ischemic spinal cord.