3-amino-1-4-dimethyl-5h-pyrido(4-3-b)indole and Pheochromocytoma

A carcinogenic, food-derived heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido(4,3-b)indole (Trp-P-1) was found to reduce the enzymatic activity of tyrosine hydroxylase in clonal rat pheochromocytoma PC12h cells, by its supplement to the culture medium. The reduction was observed with 10 microM Trp-P-1, and at this concentration the amount of cell protein and the activity of a non-specific enzyme, beta-galactosidase, were not affected. The mechanism of the reduction of the enzyme activity was clarified by kinetical studies. The amine reduced the affinity of tyrosine hydroxylase to a cofactor, tetrahydrobiopterin. The alteration of the enzymatic properties by Trp-P-1 was discussed in relation to the possible effect on catecholamine metabolism in the brain.

Topics: 3,4-Dihydroxyphenylacetic Acid; Adrenal Gland Neoplasms; Animals; Biopterins; Carbolines; Cell Line; Dihydroxyphenylalanine; Dopamine; Kinetics; Mutagens; Pheochromocytoma; Protein Binding; Rats; Tyrosine 3-Monooxygenase

Heterocyclic amines, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), are known to be produced in food by cooking and are carcinogenic. These amines were found to be accumulated in clonal rat pheochromocytoma PC12h cells and to reduce enzyme activity related to catecholamine synthesis. The mechanism of uptake of these heterocyclic amines into PC12h cells was studied. The uptake was dependent on the incubation time, the amount of the cells, and the concentrations of Trp-P-1 and Trp-P-2 in the incubation mixture. The uptake of these amines was saturable with their concentrations, and the uptake velocity followed the Michaelis-Menten equation, indicating that the uptake was mediated by a transporting protein. The uptake was inhibited by dopamine and serotonin, but not by noradrenaline. Involvement of the dopamine uptake system in uptake of the heterocyclic amines was further indicated by the fact that nomifensine and mazindol, specific inhibitors of dopamine uptake, reduced the uptake, but sulpiride, an antagonist of D2 receptor, did not. The significance of the uptake of the carcinogenic heterocyclic amines was discussed in relation to their possible neurotoxicity in the human brain.

Topics: Adrenal Gland Neoplasms; Animals; Carbolines; Chromatography, High Pressure Liquid; Dopamine; Kinetics; Mazindol; Mutagens; Nomifensine; Norepinephrine; Pheochromocytoma; Rats; Receptors, Dopamine; Receptors, Dopamine D2; Serotonin; Spectrometry, Fluorescence; Sulpiride

Out of carcinogenic heterocyclic amines, which are produced by pyrolysis of tryptophan in food, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) were found to reduce the activity of enzymes related to catecholamine metabolism in clonal rat pheochromocytoma PC12h cells. By 6 days' culture in the presence of 10 nM to 10 microM Typ-P-1 and -2, these heterocyclic amines were accumulated in the cells, and activity of tyrosine hydroxylase (TH) and aromatic L-aminoacid decarboxylase (AADC) were reduced markedly. Reduction of these enzyme activity was observed with Trp-P-1 and -2 at the concentrations lower than 1 microM, while cell protein and enzyme activity of a non-specific enzyme, beta-galactosidase were reduced only with 10 microM Trp-P-1. These results show that these heterocyclic amines are neurotoxins specific for dopaminergic neurons.

Topics: Animals; Aromatic-L-Amino-Acid Decarboxylases; beta-Galactosidase; Carbolines; Catecholamines; Monoamine Oxidase; Nerve Tissue Proteins; Neurons; Pheochromocytoma; Rats; Tumor Cells, Cultured; Tyrosine 3-Monooxygenase