Extended [13C]galactose oxidation studies in patients with galactosemia.

Since patients with galactose-1-phosphate uridyltransferase (GALT) deficiency have considerable endogenous galactose formation and only limited urinary excretion of galactose metabolites, there must be mechanisms for disposal of the sugar. Otherwise, a steady-state could not be maintained and there would be continuous body accumulation of galactose and alternate pathway products. Previous studies quantitating the amount of galactose handled by oxidation to CO2 focused on short collection periods of expired air after administering isotopically labeled galactose mainly designed for discerning differences in the capacity to oxidize the sugar in relation to genotype. Assuming that there may be more extensive oxidation than that observed in short-term studies in order to dispose the daily galactose burden, we have examined the amount of [1-13C]galactose oxidized to 13CO2 over a 24-h period after either a single bolus or continuous IV administration by 11 patients with classic galactosemia including patients homozygous for the Q188R gene mutation. As much as 58% of the administered galactose was oxidized to 13CO2 in 24 h. The pathways involved remain to be determined but a significant amount may be metabolized by non-GALT pathways since a patient homozygous for gene deletion had an oxidative capability. We conclude that classic patients have the ability to slowly oxidize galactose to CO2 in 24 h in amounts comparable to that which a normal handles in approximately one-fifth the time. This capacity enables the galactosemic to maintain a balance of galactose disposal with the galactose burden imposed by endogenous formation and dietary intake.

The rate of de novo galactose synthesis in patients with galactose-1-phosphate uridyltransferase deficiency.

Using both a continuous infusion of isotopically labeled [1-13C]galactose with a steady-state analysis and a single injection kinetic approach, we have calculated the apparent galactose appearance rate (GAR) in patients with galactose-1-phosphate uridyltransferase deficiency and control subjects. With the steady-state protocol, the GAR in 18 patients less than 18 years of age was 1.34+/-0.53 mg/kg/h (mean+/-SD) and was significantly greater than the mean of 0.56+/-0.01 mg/kg/h (p=0.004) in five patients above 18 years of age. Patients who were given a priming dose of [1-13C]galactose had a reduced GAR compared to those without a priming dose, 0.73+/-0.05 (n=9) vs 1.46+/-0.62 (n=14)mg/kg/h (p=0.005). The GAR in controls was lower than in patients ranging from 0.58 to 0.68 mg/kg/h in children and 0.07-0.09 mg/kg/h in adults. In the single bolus studies the plasma [13C]galactose enrichment decreased in a biexponential pattern suggesting at least a two-compartment system. The calculated GAR in three adult patients was similar to that found in them by the continuous infusion technique. The GAR in patients suggests the source of galactose for the continued elevation of galactose metabolites as well as the basis for the long-term complications in galactosemia despite restricted dietary galactose intake.

Identification of galactitol and galactonate in red blood cells by gas chromatography/mass spectrometry.

BACKGROUND: Because the products of alternate pathways of galactose metabolism, galactitol and galactonate are important in galactosemia, we sought to identify these compounds in red blood cells (RBC). METHODS: RBC extracts were trimethylsilylated (TMS) and analyzed by gas chromatography/mass spectrometry (GC/MS). RESULTS: The presence of both galactitol and galactonate was identified in RBC of 15 galactosemic and 13 normal subjects by their mass spectra and chromatographic comparisons with both unlabeled and 13C labeled standards. The levels in RBC of galactosemics appear to be much higher than those of normal subjects. CONCLUSION: The determination of these compounds in RBC along with galactose-1-phosphate (gal-1-P) in the same procedure provides the potential for their use in better monitoring of diet therapy in galactosemic patients.