Decreases in mouse brain NAD+ and ATP induced by 1-methyl-4-phenyl-1, 2,3,6-tetrahydropyridine (MPTP): prevention by the poly(ADP-ribose) polymerase inhibitor, benzamide.

Inhibitors of poly(ADP-ribose) polymerase (PARP), including benzamide, protect against 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP)-induced dopamine neurotoxicity in vivo [Cosi et al., Brain Res. 729 (1996) 264-269]. In vitro, the activation of PARP by free radical damaged DNA has been shown to be correlated with rapid decreases in the cellular levels of its substrate nicotinamide adenine dinucleotide (NAD+), and ATP. Here, we investigated in vivo whether MPTP acutely caused region- and time-dependent changes in brain levels of NAD+, ATP, ADP and AMP in C57BL/6N mice killed by head-focused microwave irradiation, and whether such effects were modified by treatments with neuroprotective doses of benzamide. At 1 h after MPTP injections (4x20 mg/kg i.p.), NAD+ was reduced by 11-13% in the striatum and ventral midbrain, but not in the frontal cortex. The ATP/ADP ratio was reduced by 10% and 32% in the striatum and cortex, respectively, but was unchanged in the midbrain. All of these regional changes were prevented by co-treatment with benzamide (2x160 mg/kg i.p.), which by itself did not alter regional levels of NAD+, ATP, ADP or AMP in control mice. In a time-course study, a single dose of MPTP (30 mg/kg i.p.) resulted in maximal and transient increases in striatal levels of MPP+ and 3-methoxytyramine (+540%) at 0.5-2 h, followed by maximal and coincidental decreases in NAD+ (-10%), ATP (-11%) and dopamine content (-39%) at 3 h. Benzamide (1x640 mg/kg i. p., 30 min before MPTP) partially reduced MPP+ levels by 30% with little or no effect on MPTP or MPDP+ levels, did not affect or even slightly potentiated the increase in 3-methoxytyramine, and completely prevented the losses in striatal NAD+, ATP and dopamine content, without by itself causing any changes in these latter parameters in control mice. These results (1) confirm that MPTP reduces striatal ATP levels [Chan et al., J. Neurochem. 57 (1991) 348-351.]; (2) show that MPTP causes a regionally-dependent (striatal and midbrain) loss of NAD+; (3) indicate that the PARP inhibitor benzamide can prevent these losses without interfering with MPTP-induced striatal dopamine release; and (4) provide further evidence to suggest an involvement of PARP in MPTP-induced neurotoxicity in vivo.