Protection of dopaminergic neurons with a novel astrocyte modulating agent (R)-(-)-2-propyloctanoic acid (ONO-2506) in an MPTP-mouse model of Parkinson's disease

We examined the neuroprotective effects of a novel astrocyte-modulating agent, (R)-(-)-2-propyloctanoic acid (ONO-2506), in a mouse model of Parkinson's disease. Male C57BL/6 mice received four intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (10 mg/kg) at 1-h intervals. Dopamine content in the striatum, measured with HPLC 3 days after MPTP injection, was reduced to 23% of control. But this dopamine depletion was dose-dependently prevented by repeated treatments with ONO-2506 (3, 10 and 30 mg/kg, i.p.) administered 1, 6, 24 and 48 h after MPTP injection (51% of control in 30 mg/kg group, p<0.01). ONO-2506 treatment (30 mg/kg) started after 6 h, followed by treatments at 24 and 48 h, also prevented the reduction of dopamine content (42% of control vs. 11% of control in the saline-treated group, p<0.01). We also performed immunohistochemistry for tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP). The MPTP injection resulted in a loss of TH-positive dopaminergic neurons (42% of control, p<0.01) in the substantia nigra after 7 days, but ONO-2506 treatment prevented this neuronal loss (70% of control, p<0.01). The MPTP injection led to reactive astrocytosis in the striatum after 7 days, but ONO-2506 induced earlier, moderate astrocytic activation after 3-7 days. These findings show that ONO-2506 protects dopaminergic neurons against MPTP neurotoxicity probably through facilitating astrocytic support for neuronal recovery from injury. Pharmacological modulation of astrocytes may offer a novel therapeutic strategy for Parkinson's disease.