LIQUID-CHROMATOGRAPHIC PROFILING OF AROMATIC METABOLITES IN NEURAL CREST TUMORS
Abstract
The merits of liquid chromatography with electrochemical detection have been examined for their utility in the clinical analysis of important tyrosine metabolites. Primary emphasis was placed on the catecholamines--norepinephrine, epinephrine, dopamine--and their respective O-methylated metabolites--normetanephrine, metanephrine, and 3-methoxytyramine. The latter group of compounds is formed from the catecholamines through the action of the enzyme catechol-O-methyltransferase and S-adenosylmethionine. Mutually optimized conditions for both the separation of these amines on reverse phase media and their detection amperometrically are presented. The hybrid combination of liquid chromatography and electrochemical detection offered the advantages of highly efficient separations for improved selectivity, subpicomole sensitivity for the biogenic amines, and the convenience of direct detection. Reverse phase separations for the catecholamines required long chain sulfates or sulfonates; retention under these "ion pairing" conditions operated under a dynamic ion exchange mechanism. An analytical method for the determination of urinary metanephrines is described. The procedure employs small ion-exchange columns for the selective isolation of the amines before instrumental analysis. The combination of this method with a similar one for the urinary catecholamine precursors proved suitable for the metabolic profiling of several patients afflicted with pheochromocytoma and neuroblastoma. These nervous system tumors could be easily differentiated on the basis of the excretion profiles. For neuroblastoma, the differences in norepinephrines and epinephrine excretion between healthy and diseased patients were negligible. Dopamine, however, was grossly elevated in neuroblastoma. The benefits of multicomponent analysis in these specimens proved fruitful. Postoperative metabolic profiles were also run periodically to ascertain patient progress; the amines acted as appropriate markers in predicting the patient's eventual fate. The applicability of LCEC to enzyme assays was also investigated in a study of COMT activity in various physiological matrices. The ability to simultaneously quantitate the multiple isomers produced in the reaction enabled the examination of different tissues for both absolute activities and product preferences.
Degree
Ph.D.
Subject Area
Analytical chemistry
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