Poly(ADP-ribose) polymerase inhibitors protect against MPTP-induced depletions of striatal dopamine and cortical noradrenaline in C57B1/6 mice

Treatment of C57Bl/6 mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) reduced striatal dopamine and cortical noradrenaline levels by 77-83% and 43-46%, respectively, at 7 days post-treatment. Co-treatments with five different inhibitors of poly(ADP-ribose) polymerase (PARP), including benzamide, significantly prevented the MPTP-induced catecholamine depletions. Benzamide was present in the striatum, 30 min after single i.p. injection, at low millimolar concentrations known to selectively inhibit PARP in vitro. The protective activities of benzamide and its derivatives paralleled their in vitro efficacies and potencies both as neuroprotective agents and as inhibitors of PARP, while the activity of 1,5-dihydroxyisoquinoline, a structurally-unrelated compound, did not. In naive animals, the PARP inhibitors by themselves did not alter striatal dopamine levels at 7 days post-treatment. However, in acute studies, 1,5-dihydroxyisoquinoline and nicotinamide caused marked alterations in striatal dopamine metabolite levels; on the contrary, benzamide and its amino-derivatives showed little or no effect on dopamine metabolism. These results indicate that, although these compounds might act at other sites in addition to PARP, PARP inhibitors possess neuroprotective potential in vivo and suggest a role for PARP in MPTP neurotoxicity.