Melanoma detection by enzyme-radioimmunoassay of L-dopa, dopamine, and 3-0-methyldopamine in urine

Abstract

This enzyme-radioimmunoassay for the measurement of L-dopa, dopamine, and 3-0-methyldopamine is based on the incubation of urine in the presence of catechol-O-methyltransferase, aromatic-L-amino-acid decarboxylase, and S-adenosylmethionine. The O-methylated dopamine metabolite formed, 3-O-methyldopamine, was characterized by radioimmunoassay. To evaluate the role of L-dopa metabolism in melanoma, we used the enzymeradioimmunoassay to assess concentrations of L-dopa, dopamine, and 3-O-methyldopamine in urine from 10 healthy subjects, 10 hospitalized patients without melanoma, and 28 patients with different degrees of melanoma. The effect of surgery for melanoma on urinary output of these catechols of melanoma patients was also evaluated. No significant difference in urinary L-dopa, dopamine, and 3-O-methyldopamine excretion rates was seen between normal subjects (L-dopa 1.3 ± 0.3, dopamine 147 ± 38, and 3-O-methyldopamine 31.4 ± 13.6 μg/24 h), hospitalized patients without melanoma, and amelanotic melanoma patients. However, the excretion rates for these metabolites in melanotic melanoma (L-dopa 5.6 ± 1.2, and 3-O-methyldopamine 178 ± 40.3 μg/24 h) were significantly (p<0.005) higher than in control or amelanotic melanoma subjects. After surgery, there was a substantial decrease in urinary output of L-dopa and its metabolites by these patients.