Background and purpose
Recently, it has been reported that Poly (ADP-ribose) polymerase (PARP), a nuclear protein that participates in DNA base excision repair in response to DNA damage, is involved in the mechanism of ischemic neuronal cell death1, 2. Over-activation of PARP-1 induced by extensive DNA damage consumes NAD+ and ATP consequently, leading to necrotic cell death. PARP-1 also induces the activation of nuclear factor kB (NF-kB)-dependent gene expression that initiates cell injury, or induces the release the apoptosis-inducing factor, resulting in PARP-1-dependent apoptotic cell death. Nevertheless, the mechanism of PARP over-activation on the ischemic brain have not been fully understood. The aim of this study is, therefore, to determine whether a newly synthesized PARP inhibitor, KCL-440, which have strong inhibition of PARP-1, would prevent neuronal cell death following transient focal ischemia in rats compared to a free radical scavenger, edaravone, which is the first clinical neuroprotective agent used in Japan for the treatment of acute stroke patients.
Methods
Sprague-Dawley rats were subjected to MCAo using an intraluminal suture technique for 2 hours 3 . The rats were reperfused for 24 hours and decapitated for infarct and edema analysis 4 . Animals were randomly divided into the following four groups. (I) vehicle-treated control group (II) low dose of KCL-440 (3.0 mg/kg)-treated group (III) high dose of KCL-440 (10.0 mg/kg)-treated group (IV) edaravone-treated group. PARP inhibitor-treated animals received a continuous injection of KCL-440 (3.0 or 10.0 mg/kg) intravenously for 6 hours after the onset of ischemia, while vehicle-treated groups received same dose of vehicle. Edaravone-treated animals received twice injection of edaravone (3.0 mg/kg) intravenously after the onset of ischemia and 30 minutes after ischemia. During ischemia, temporal muscle and rectal temperatures were monitored and maintained at 37° in the experimental animals. Neurological symptoms evaluation were performed immediately before infarct and edema analysis.
Results
The cortical infarct volume (120+/−35 mm3) in the edaravone-treated group was significantly less than those in group I (251+/−42 mm3, p<0.05), while there was no significant difference in the striatum. KCL-440 (group II, III) decreased the cortical or striatal infarct volume (105+/−34 mm3, 31+/−10 mm3 in group II, 64+/−21 mm3, 25+/−9 mm3 in group III) significantly compared with those of groups I (251+/−42 mm3, 66+/−7 mm3, p<0.05), dose-dependently. KCL-440 also improved the cortical or striatal edema significantly compared with those of groups I (p<0.05, p<0.05, respectively). Moreover, KCL-440 significantly improved neurological symptoms (posture and hemiplegia).
Conclusions
These results demonstrate that a newly synthesized PARP inhibitor, KCL-440 prevents neuronal cell death, compared to a free radical scavenger, edaravone. Furthermore, it is suggested that this PARP inhibitor may be a candidate for new neuroprotectant for the treatment of acute stroke in future.