DECREASES IN MOUSE-BRAIN NAD(-METHYL-4-PHENYL-1,2,3,6-TETRAHYDROPYRIDINE (MPTP) - PREVENTION BY THE POLY(ADP-RIBOSE) POLYMERASE INHIBITOR, BENZAMIDE() AND ATP INDUCED BY 1)

Inhibitors of poly(ADP-ribose) polymerase (PARP), including benzamide, protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-i nduced dopamine neurotoxicity in vivo [Cosi et al., Brain Res. 729 (19 96) 264-269]. In vitro, the activation of PARP by free radical damaged DNA has been shown to be correlated with rapid decreases in the cellu lar levels of its substrate nicotinamide adenine dinucleotide (NAD(+)) , and ATP. Here, we investigated in vivo whether MPTP acutely caused r egion- and time-dependent changes in brain levels of NAD+, ATP, ADP an d AMP in C57BL/6N mice killed by head-focused microwave irradiation, a nd whether such effects were modified by treatments with neuroprotecti ve doses of benzamide. At 1 h after MPTP injections (4 x 20 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% an d 32% in the striatum and cortex, respectively, but was unchanged in t he midbrain. All of these regional changes were prevented by co-treatm ent with benzamide (2 x 160 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 maxim al and transient increases in striatal levels of MPP+ and 3-methoxytyr amine (+540%) at 0.5-2 h, followed by maximal and coincidental decreas es in NAD(+) (-10%), ATP (-11%) and dopamine content (-39%) at 3 h. Be nzamide (1 x 640 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-methoxytyram ine, and completely prevented the losses in striatal NAD(+), ATP and d opamine content, without by itself causing any changes in these latter parameters in control mice. These results (1) confirm that MPTP reduc es striatal ATP levels [Chan et al., J. Neurochem. 57 (1991) 348-351.] ; (2) show that MPTP causes a regionally-dependent (striatal and midbr ain) loss of NAD(+); (3) indicate that the PARP inhibitor benzamide ca n prevent these losses without interfering with MPTP-induced striatal dopamine release; and (4) provide further evidence to suggest an invol vement of PARP in MPTP-induced neurotoxicity in vivo. (C) 1998 Elsevie r Science B.V. All rights reserved.