NOBILETIN TREATMENT IMPROVES MOTOR AND COGNITIVE DEFICITS SEEN IN MPTP-INDUCED PARKINSON MODEL MICE

摘要

Nobiletin, a polymethoxylated flavonoid found in citrus fruit peel, reportedly improves memory impairment in rodent models. Here we report its effect on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced motor and cognitive deficits. Nobiletin administration (50 mg/kg i.p.) for 2 consecutive weeks improved motor deficits seen in MPTP-induced Parkinson model mice by 2 weeks, an effect that continued until 2 weeks after drug withdrawal. Drug treatment promoted similar rescue of MPTP-induced cognitive impairment at equivalent time points. Nonetheless, nobiletin treatment did not block loss of dopaminer-gic neurons seen in the MPTP-treated mouse midbrain, nor did it rescue decreased tyrosine hydroxylase (TH) protein levels seen in the striatum or hippocampal CA1 region of these mice. Interestingly, nobiletin administration (50 mg/kg i.p.) rescued reduced levels of Ca~(2+)/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and phosphorylation at Thr-34 of dopamine- and cAMP-regulated phosphoprotein-32 (DARPP-32) in striatum and hippocampal CA1 to levels seen in sham-operated mice. Likewise, CaMKII- and cAMP kinase-dependent TH phosphorylation was significantly restored by nobiletin treatment. MPTP-induced reduction of dopamine contents in the striatum and hippocampal CA1 region was improved by nobiletin administration (50 mg/kg i.p.). Acute intraperi-toneal administration of nobiletin also enhanced dopamine release in striatum and hippocampal CA1, an effect partially inhibited by treatment with nifedipine (a L-type Ca~(2+) channel inhibitor) or NNC 55-0396 (a T-type Ca~(2+) channel inhibitor) and completely abolished by combined treatment with both. Overall, our study describes a novel nobiletin activity in brain and suggests that nobiletin rescues motor and cognitive dysfunction in MPTP-induced Parkinson model mice, in part by enhancing dopamine release.