Combined administration of PARP-1 and caspase-3 inhibitors alleviates neuronal apoptosis after spinal cord injury in rats.

BACKGROUND: Neuronal apoptosis plays a pivotal role in spinal cord injury (SCI)-induced secondary cellular events. Caspase-dependent and -independent pathways are involved in neuronal apoptosis. Caspase-3 is the final effector of caspase-dependent apoptosis, while poly-ADP-ribose polymerase-1 (PARP-1) and apoptosis-inducing factor (AIF) are key executors of caspase-independent apoptosis. However, it remains unclear whether simultaneous inhibition of the two apoptosis pathways will be more beneficial for neuronal survival. Therefore, the present study investigated the ability of co-administration of the PARP-1 inhibitor 3-aminobenzamide (3-AB) and caspase-3 inhibitor z-DEVD-fmk to attenuate apoptosis in a rat SCI model.

METHODS: The rats were subjected to moderate contusive SCI. Locomotor function was measured using the Basso, Beattie, and Bresnahan rating scales; neuronal apoptosis was detected using TUNEL; and immunohistochemistry and Western blotting were used to measure protein expression.

RESULTS: We found the locomotor function of rats was weakened within 7 days post-SCI. At day 7 post-SCI, neuronal apoptosis dramatically increased and the expression of PARP-1, AIF, and cleaved caspase-3 was significantly upregulated. Further, Bcl-2 expression was significantly downregulated. The highest locomotor function recovery was recorded following the combined administration of 3-AB and z-DEVD-fmk for 7 days post-SCI, when compared with 3-AB or z-DEVD-fmk administered alone. In addition, this combination therapy significantly reduced neuronal apoptosis by preventing upregulation of PARP-1 and AIF, inhibiting caspase-3 activation, and elevating Bcl-2 expression.

CONCLUSIONS: These results suggest that combination therapy is beneficial for neuronal function recovery in SCI rats. The underlying mechanism may be associated with co-suppression of caspase-dependent and -independent apoptosis pathways.