Determination of [U-13C]glucose turnover into various metabolite pools for the differential diagnosis of lactic acidemias.
Stable-isotope tracer experiments performed in vitro are evaluated for their utility in differentiating between pyruvate dehydrogenase and cytochrome oxidase deficiencies, two of several enzyme defects commonly associated with the lactic acidemias. Fibroblasts of enzyme-deficient individuals and of age-matched controls are grown in medium containing [U-13C]glucose. Direct analysis of cells and conditioned culture medium provides only minor differences in the organic acid/amino acid GC-MS profiles, making differentiation of enzyme defects difficult by this method. However, differences have been found in the glucose turnover into various cell metabolites, making differentiation of these two enzyme defects possible. The cellular pool of glutamic acid experiences 13C-enrichment in both the control and cytochrome oxidase deficient lines, but not in the pyruvate dehydrogenase-deficient line. The cellular pool of an unknown, possibly an aminopentose sugar, on the other hand, experiences 13C-enrichment in the pyruvate dehydrogenase and control lines, but not in the cytochrome oxidase line. These observations, as well as other differences in the extent of enrichment into various metabolite pools, suggest that this stable-isotope approach, in vitro, is feasible and may allow these two enzyme defects to be differentiated in a definitive manner. Such stable-isotope experiments are easy to carry out with cultured cells and are inexpensive. Applications of the technique to other genetic disorders might be appropriate.
Kassel
D B
DB
Department of Chemistry, Michigan State University, East Lansing 48824.
Glerum
M
M
Robinson
B H
BH
Sweeley
C C
CC
D000596:Amino Acids / Q000032:analysis; D002247:Carbon Isotopes; D002478:Cells, Cultured; D030401:Cytochrome-c Oxidase Deficiency; D003937:Diagnosis, Differential; D003576:Electron Transport Complex IV / Q000032:analysis; D005347:Fibroblasts / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007223:Infant; D007773:Lactates / Q000097:blood*; D015325:Pyruvate Dehydrogenase Complex Deficiency Disease / Q000175:diagnosis*; D015323:Pyruvate Metabolism, Inborn Errors / Q000175:diagnosis*
D000596:Amino Acids; D002247:Carbon Isotopes; D007773:Lactates; D003576:Electron Transport Complex IV; D005947:Glucose