Effect of 1-methyl-4-phenylpyridinium ion (MPP +) on catecholamine levels and activity of related enzymes in clonal rat pheochromocytoma PC12h cells

Abstract

1-Methyl-4-phenylpyridinium ion (MPP +), a metabolite of a neurotoxin, 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine, was found to reduce dopamine (DA) level and the activity of enzymes related to its metabolism in clonal rat pheochromocytoma PC12h cells. After 6 days' culture in the presence of 1 mM and 100 μM MPP +, DA content in PC12h cells was reduced markedly, but with MPP + at concentrations lower than 10 μM, DA levels in the cells did not change. The amounts of 3, 4-dihydrophenylacetic acid (DOPAC), a metabolite of DA were reduced markedly in culture medium and in PC12h cells cultured with MPP + at concentrations higher than 1 μM. MPP + was found to reduce the enzyme activity of tyrosine hydroxylase (TH), monoamine oxidase (MAO) and aromatic L-aminoacid decarboxylase (AADC). In the presence of MPP + at concentrations higher than 10 μM, reduction of TH activity in the cells was more pronounced than reduction of cell protein or of the activity of a non-specific enzyme, β-galactosidase. With 1 mM and 100 μM MPP +, MAO activity was reduced to about 30% of that in control cells. Reduction was observed with MPP + at concentrations higher than 1 μM. AADC was the most sensitive to MPP + and its activity was reduced markedly in the cells cultured with 100 nM MPP +. These results indicate that MPP + inhibits not only the biosynthesis of catecholamines, but also the enzyme participating in their catabolism in cells, and may thus perturb catecholamine levels in the brain.