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Stanton Segal - One of the best experts on this subject based on the ideXlab platform.
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Evidence for function of UDP galactose pyrophosphorylase in mice with absent Galactose-1-Phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2007Co-Authors: Suzanne L. Wehrli, Robert Reynolds, Stanton SegalAbstract:Abstract Mice with deletion of the Galactose-1-Phosphate Uridyltransferase (GALT) gene were examined for their ability to form 13 C labeled hepatic UDP glucose from administered 1- 13 C galactose. NMR analysis of urinary acetaminophen glucuronide, which is derived from hepatic UDP glucose showed 13 C enrichment after concomitant administration of 13 C galactose and acetaminophen. The finding is consistent with the function of UDP galactose pyrophosphorylase as an alternate pathway of galactose metabolism.
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UDP-galactose pyrophosphorylase in mice with Galactose-1-Phosphate Uridyltransferase deficiency.
Molecular Genetics and Metabolism, 2005Co-Authors: Nancy D Leslie, Claire Yager, Robert Reynolds, Stanton SegalAbstract:Abstract UDP-glucose pyrophosphorylase (E.C. 2.7.7.9), encoded by ugp , provides UDP-glucose which is critical to the synthesis of glycogen, and also catalyzes the reaction between UTP and Galactose-1-Phosphate, yielding UDP-galactose. This activity of UDP-gal pyrophosphorylase (UDP-galPP) suggests a role in an alternate pathway for galactose metabolism in patients with deficiency of Galactose-1-Phosphate Uridyltransferase (GALT). We examined the effects of GALT deficiency and dietary galactose on UDP-glucose pyrophosphorylase (UDP-gluPP) and UDP-galactose pyrophosphorylase activity and ugp expression in liver of mice with homozygous deletion of the critical regions of galt. Activity with glucose-1-phosphate as substrate was significantly higher than that with Galactose-1-Phosphate. In liver from mice with GALT deficiency (G/G), UDP-galPP activity appeared to be lower than that measured in liver from control (N/N) animals. This difference disappeared when the N/N tissue homogenate was dialyzed to remove residual UDP-glucose, confirming that careful elimination of residual GALT activity is necessary, since GALT has 1000-fold greater activity toward Galactose-1-Phosphate than that of UDP-galPP in liver homogenates. Prior exposure to conventional mouse chow, high galactose chow, and high glucose chow did not alter UDP-glu PP or UDP-galPP activity. Steady state UGP mRNA levels were determined in tissues from normal and G/G animals. UGP expression was highest in liver, and did not differ by genotype or exposure to high galactose chow. UDP-galPP activity may account for unexplained ability to oxidize galactose in animals with no GALT activity, but is insufficient to alter accumulation of galactose metabolites.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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The rate of de novo galactose synthesis in patients with Galactose-1-Phosphate Uridyltransferase deficiency
Molecular genetics and metabolism, 2004Co-Authors: Gerard T Berry, Claire Yager, Cong Ning, Robert Reynolds, Peter J. Moate, Raymond C. Boston, Stanton SegalAbstract: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.
Gerard T Berry - One of the best experts on this subject based on the ideXlab platform.
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Quantification of Galactose-1-Phosphate Uridyltransferase Enzyme Activity by Liquid Chromatography–Tandem Mass Spectrometry
Clinical chemistry, 2010Co-Authors: Adam S. Ptolemy, Lauren Harmonay, Mark D. Kellogg, Gerard T BerryAbstract:Background: The diagnosis of galactosemia usually involves the measurement of Galactose-1-Phosphate Uridyltransferase (GALT) activity. Traditional radioactive and fluorescent GALT assays are nonspecific, laborious, and/or lack sufficient analytical sensitivity. We developed a liquid chromatography–tandem mass spectrometry (LC-MS/MS)–based assay for GALT enzyme activity measurement. Method: Our assay used stable isotope-labeled α- Galactose-1-Phosphate ([13C6]-Gal-1-P) as an enzyme substrate. Sample cleanup and separation were achieved by reversed-phase ion-pair chromatography, and the enzymatic product, isotope-labeled uridine diphosphate galactose ([13C6]-UDPGal), was detected by MS/MS at mass transition (571 > 323) and quantified by use of [13C6]-Glu-1-P (265 > 79) as an internal standard. Results: The method yielded a mean (SD) GALT enzyme activity of 23.8 (3.8) μmol · (g Hgb)−1 · h−1 in erythrocyte extracts from 71 controls. The limit of quantification was 0.04 μmol · (g Hgb)−1 · h−1 (0.2% of normal control value). Intraassay imprecision was determined at 4 different levels (100%, 25%, 5%, and 0.2% of the normal control values), and the CVs were calculated to be 2.1%, 2.5%, 4.6%, and 9.7%, respectively (n = 3). Interassay imprecision CVs were 4.5%, 6.7%, 8.2%, and 13.2% (n = 5), respectively. The assay recoveries at the 4 levels were higher than 90%. The apparent K m of the 2 substrates, Gal-1-P and UDPGlc, were determined to be 0.38 mmol/L and 0.071 mmol/L, respectively. The assay in erythrocytes of 33 patients with classical galactosemia revealed no detectable activity. Conclusions: This LC-MS/MS–based assay for GALT enzyme activity will be useful for the diagnosis and study of biochemically heterogeneous patients with galactosemia, especially those with uncommon genotypes and detectable but low residual activities.
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The rate of de novo galactose synthesis in patients with Galactose-1-Phosphate Uridyltransferase deficiency
Molecular genetics and metabolism, 2004Co-Authors: Gerard T Berry, Claire Yager, Cong Ning, Robert Reynolds, Peter J. Moate, Raymond C. Boston, Stanton SegalAbstract: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.
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Galactose Metabolism in Mice with Galactose-1-Phosphate Uridyltransferase Deficiency: Sucklings and 7-Week-Old Animals Fed a High-Galactose Diet
Molecular Genetics and Metabolism, 2001Co-Authors: Cong Ning, Claire Yager, Robert Reynolds, Nancy D Leslie, Gerard T Berry, Jie Chen, Stanton SegalAbstract:Abstract Mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) demonstrate abnormal galactose metabolism but no obvious clinical phenotype. To further dissect the pathways of galactose metabolism in these animals, galactose oxidation and metabolite levels were studied in 16-day-old sucklings and the effect of a 4 week prior exposure to a 40% glucose or 40% galactose diet was determined in 7-week-old mice. Suckling GALT-deficient (G/G) mice slowly oxidized [1- 14 C]galactose to 14 CO 2 , 4.0% of the dose when fed and 7.9% when fasted compared to normal animals 38.3 and 36.4% in 4 h, respectively. Plasma of G/G sucklings contained 11.1 mM galactose and erythrocyte galactose 1-phosphate levels were 28.2 and 31.9 mg/dl packed cells. Galactose, galactitol, galactonate, and galactose 1-phosphate were found in G/G suckling mouse tissues. The tissue galactose concentrations were 10% or less of that in plasma, suggesting that there was limited cellular entry of galactose. In 7-week-old fasted mice with 4 weeks prior exposure to glucose or galactose-containing diet, 4-h oxidation was 12.9 and 15.0% of the administered radiolabeled galactose, respectively. Normal animals oxidized 33.9 and 37.9% of the dose when fed the same diets, respectively. The ability of G/G mice to oxidize galactose in the absence of GALT activity suggests the presence of alternate metabolic pathways for galactose disposition. G/G mice fed the galactose-free 40% glucose diet had erythrocyte galactose 1-phosphate levels ranging from 6.4 to 17.7 mg/dl packed cells and detectable galactose and galactose metabolites in tissues, suggesting that these animals endogenously produced galactose. The plasma of 40% galactose-fed G/G mice contained 9.1 mM galactose with red blood cell galactose 1-phosphate averaging 43.6 mg/dl. Tissues of these animals also contained high levels of galactose and galactose 1-phosphate. Liver contained over 4 μmol/g galactonate but little galactitol. Despite the elevated galactose and galactose 1-phosphate, the animals tolerated the high-galactose diet and were indistinguishable from normal animals, exhibiting no manifestations of galactose toxicity seen in human GALT-deficient galactosemia. The data suggest that high galactose 1-phosphate levels do not cause galactose toxicity and that high galactitol in combination with galactose 1-phosphate may be a prerequisite. Absence of GALT appears necessary but insufficient to produce human galactosemic phenotype.
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Evidence for Alternate Galactose Oxidation in a Patient with Deletion of the Galactose-1-Phosphate Uridyltransferase Gene
Molecular Genetics and Metabolism, 2001Co-Authors: Gerard T Berry, Claire Yager, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract The persistent, dietary-independent elevation of galactose metabolites in patients with Galactose-1-Phosphate Uridyltransferase (GALT) deficiency is probably secondary to de novo synthesis of galactose. Relatively constant steady-state levels of galactose metabolites in patients also suggest that non-GALT metabolic pathways must function to dispose of the galactose synthesized each day. The discovery of a patient with a rare deletion of the GALT gene provided a unique opportunity to examine the availability of any alternate galactose oxidative capacity both in vivo and in vitro. Utilizing genomic DNA from the patient, Southern blot data demonstrated that 10 of the 11 GALT exons were homozygously deleted. By measurement of 13CO2 in expired air for up to 24 h after an oral bolus of [1-13C]galactose, it was demonstrated that 17% of the galactose was metabolized, a value comparable to the 3-h elimination rate in a control subject. Furthermore, lymphoblasts prepared from the patient could also convert [1-14C]galactose to 14CO2. This unique study provides the first unambiguous evidence that another pathway exists in man that can be responsible for galactose disposal. Further knowledge of this alternate galactose oxidative route and its regulation may aid in formulating new strategies for the treatment of galactosemia.
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in vivo evidence of brain galactitol accumulation in an infant with galactosemia and encephalopathy
The Journal of Pediatrics, 2001Co-Authors: Gerard T Berry, Alice T Mazur, Cong Ning, Jill V Hunter, Zhiyue J Wang, Steffi F Dreha, David G Brooks, R A Zimmerman, Stanton SegalAbstract:Abstract In a newborn infant with Galactose-1-Phosphate Uridyltransferase deficiency and encephalopathy, brain magnetic resonance imaging revealed cytotoxic edema in white matter. Using in vivo proton magnetic resonance spectroscopy, we detected ~8 mmol galactitol per kilogram of brain tissue, an amount potentially relevant to the pathogenesis of brain edema. (J Pediatr 2001;138:260-2)
Robert Reynolds - One of the best experts on this subject based on the ideXlab platform.
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Evidence for function of UDP galactose pyrophosphorylase in mice with absent Galactose-1-Phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2007Co-Authors: Suzanne L. Wehrli, Robert Reynolds, Stanton SegalAbstract:Abstract Mice with deletion of the Galactose-1-Phosphate Uridyltransferase (GALT) gene were examined for their ability to form 13 C labeled hepatic UDP glucose from administered 1- 13 C galactose. NMR analysis of urinary acetaminophen glucuronide, which is derived from hepatic UDP glucose showed 13 C enrichment after concomitant administration of 13 C galactose and acetaminophen. The finding is consistent with the function of UDP galactose pyrophosphorylase as an alternate pathway of galactose metabolism.
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UDP-galactose pyrophosphorylase in mice with Galactose-1-Phosphate Uridyltransferase deficiency.
Molecular Genetics and Metabolism, 2005Co-Authors: Nancy D Leslie, Claire Yager, Robert Reynolds, Stanton SegalAbstract:Abstract UDP-glucose pyrophosphorylase (E.C. 2.7.7.9), encoded by ugp , provides UDP-glucose which is critical to the synthesis of glycogen, and also catalyzes the reaction between UTP and Galactose-1-Phosphate, yielding UDP-galactose. This activity of UDP-gal pyrophosphorylase (UDP-galPP) suggests a role in an alternate pathway for galactose metabolism in patients with deficiency of Galactose-1-Phosphate Uridyltransferase (GALT). We examined the effects of GALT deficiency and dietary galactose on UDP-glucose pyrophosphorylase (UDP-gluPP) and UDP-galactose pyrophosphorylase activity and ugp expression in liver of mice with homozygous deletion of the critical regions of galt. Activity with glucose-1-phosphate as substrate was significantly higher than that with Galactose-1-Phosphate. In liver from mice with GALT deficiency (G/G), UDP-galPP activity appeared to be lower than that measured in liver from control (N/N) animals. This difference disappeared when the N/N tissue homogenate was dialyzed to remove residual UDP-glucose, confirming that careful elimination of residual GALT activity is necessary, since GALT has 1000-fold greater activity toward Galactose-1-Phosphate than that of UDP-galPP in liver homogenates. Prior exposure to conventional mouse chow, high galactose chow, and high glucose chow did not alter UDP-glu PP or UDP-galPP activity. Steady state UGP mRNA levels were determined in tissues from normal and G/G animals. UGP expression was highest in liver, and did not differ by genotype or exposure to high galactose chow. UDP-galPP activity may account for unexplained ability to oxidize galactose in animals with no GALT activity, but is insufficient to alter accumulation of galactose metabolites.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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The rate of de novo galactose synthesis in patients with Galactose-1-Phosphate Uridyltransferase deficiency
Molecular genetics and metabolism, 2004Co-Authors: Gerard T Berry, Claire Yager, Cong Ning, Robert Reynolds, Peter J. Moate, Raymond C. Boston, Stanton SegalAbstract: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.
Cong Ning - One of the best experts on this subject based on the ideXlab platform.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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The rate of de novo galactose synthesis in patients with Galactose-1-Phosphate Uridyltransferase deficiency
Molecular genetics and metabolism, 2004Co-Authors: Gerard T Berry, Claire Yager, Cong Ning, Robert Reynolds, Peter J. Moate, Raymond C. Boston, Stanton SegalAbstract: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.
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Galactose Metabolism in Mice with Galactose-1-Phosphate Uridyltransferase Deficiency: Sucklings and 7-Week-Old Animals Fed a High-Galactose Diet
Molecular Genetics and Metabolism, 2001Co-Authors: Cong Ning, Claire Yager, Robert Reynolds, Nancy D Leslie, Gerard T Berry, Jie Chen, Stanton SegalAbstract:Abstract Mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) demonstrate abnormal galactose metabolism but no obvious clinical phenotype. To further dissect the pathways of galactose metabolism in these animals, galactose oxidation and metabolite levels were studied in 16-day-old sucklings and the effect of a 4 week prior exposure to a 40% glucose or 40% galactose diet was determined in 7-week-old mice. Suckling GALT-deficient (G/G) mice slowly oxidized [1- 14 C]galactose to 14 CO 2 , 4.0% of the dose when fed and 7.9% when fasted compared to normal animals 38.3 and 36.4% in 4 h, respectively. Plasma of G/G sucklings contained 11.1 mM galactose and erythrocyte galactose 1-phosphate levels were 28.2 and 31.9 mg/dl packed cells. Galactose, galactitol, galactonate, and galactose 1-phosphate were found in G/G suckling mouse tissues. The tissue galactose concentrations were 10% or less of that in plasma, suggesting that there was limited cellular entry of galactose. In 7-week-old fasted mice with 4 weeks prior exposure to glucose or galactose-containing diet, 4-h oxidation was 12.9 and 15.0% of the administered radiolabeled galactose, respectively. Normal animals oxidized 33.9 and 37.9% of the dose when fed the same diets, respectively. The ability of G/G mice to oxidize galactose in the absence of GALT activity suggests the presence of alternate metabolic pathways for galactose disposition. G/G mice fed the galactose-free 40% glucose diet had erythrocyte galactose 1-phosphate levels ranging from 6.4 to 17.7 mg/dl packed cells and detectable galactose and galactose metabolites in tissues, suggesting that these animals endogenously produced galactose. The plasma of 40% galactose-fed G/G mice contained 9.1 mM galactose with red blood cell galactose 1-phosphate averaging 43.6 mg/dl. Tissues of these animals also contained high levels of galactose and galactose 1-phosphate. Liver contained over 4 μmol/g galactonate but little galactitol. Despite the elevated galactose and galactose 1-phosphate, the animals tolerated the high-galactose diet and were indistinguishable from normal animals, exhibiting no manifestations of galactose toxicity seen in human GALT-deficient galactosemia. The data suggest that high galactose 1-phosphate levels do not cause galactose toxicity and that high galactitol in combination with galactose 1-phosphate may be a prerequisite. Absence of GALT appears necessary but insufficient to produce human galactosemic phenotype.
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in vivo evidence of brain galactitol accumulation in an infant with galactosemia and encephalopathy
The Journal of Pediatrics, 2001Co-Authors: Gerard T Berry, Alice T Mazur, Cong Ning, Jill V Hunter, Zhiyue J Wang, Steffi F Dreha, David G Brooks, R A Zimmerman, Stanton SegalAbstract:Abstract In a newborn infant with Galactose-1-Phosphate Uridyltransferase deficiency and encephalopathy, brain magnetic resonance imaging revealed cytotoxic edema in white matter. Using in vivo proton magnetic resonance spectroscopy, we detected ~8 mmol galactitol per kilogram of brain tissue, an amount potentially relevant to the pathogenesis of brain edema. (J Pediatr 2001;138:260-2)
Claire Yager - One of the best experts on this subject based on the ideXlab platform.
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UDP-galactose pyrophosphorylase in mice with Galactose-1-Phosphate Uridyltransferase deficiency.
Molecular Genetics and Metabolism, 2005Co-Authors: Nancy D Leslie, Claire Yager, Robert Reynolds, Stanton SegalAbstract:Abstract UDP-glucose pyrophosphorylase (E.C. 2.7.7.9), encoded by ugp , provides UDP-glucose which is critical to the synthesis of glycogen, and also catalyzes the reaction between UTP and Galactose-1-Phosphate, yielding UDP-galactose. This activity of UDP-gal pyrophosphorylase (UDP-galPP) suggests a role in an alternate pathway for galactose metabolism in patients with deficiency of Galactose-1-Phosphate Uridyltransferase (GALT). We examined the effects of GALT deficiency and dietary galactose on UDP-glucose pyrophosphorylase (UDP-gluPP) and UDP-galactose pyrophosphorylase activity and ugp expression in liver of mice with homozygous deletion of the critical regions of galt. Activity with glucose-1-phosphate as substrate was significantly higher than that with Galactose-1-Phosphate. In liver from mice with GALT deficiency (G/G), UDP-galPP activity appeared to be lower than that measured in liver from control (N/N) animals. This difference disappeared when the N/N tissue homogenate was dialyzed to remove residual UDP-glucose, confirming that careful elimination of residual GALT activity is necessary, since GALT has 1000-fold greater activity toward Galactose-1-Phosphate than that of UDP-galPP in liver homogenates. Prior exposure to conventional mouse chow, high galactose chow, and high glucose chow did not alter UDP-glu PP or UDP-galPP activity. Steady state UGP mRNA levels were determined in tissues from normal and G/G animals. UGP expression was highest in liver, and did not differ by genotype or exposure to high galactose chow. UDP-galPP activity may account for unexplained ability to oxidize galactose in animals with no GALT activity, but is insufficient to alter accumulation of galactose metabolites.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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galactitol and galactonate accumulation in heart and skeletal muscle of mice with deficiency of galactose 1 phosphate Uridyltransferase
Molecular Genetics and Metabolism, 2004Co-Authors: Claire Yager, Cong Ning, Robert Reynolds, Nancy D Leslie, Stanton SegalAbstract:Abstract Under conditions of dietary galactose loading, mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) accumulate large amounts of galactitol and galactonate in heart and skeletal muscle. In contrast to liver, brain, and kidney, which form little galactitol when GALT-deficient animals (G/G) ingest a 40% galactose diet, heart and skeletal muscle galactitol reaches 22.90±1.62 (M±SE) and 38.88±2.62μmol/g tissue, respectively, levels 40–100 times that of Galactose-1-Phosphate (Gal-1-P). Sixteen-day-old suckling G/G mice accumulate galactitol in heart and to a lesser extent, in skeletal muscle. Heart and skeletal muscle of G/G mice also form galactonate, with levels comparable to that of liver, which was presumed previously to be the only tissue capable of converting galactose to galactonate under conditions of loading. The data suggest that heart and skeletal muscle play a role in disposition of galactose when GALT activity is impaired, contributing a large share to urinary galactitol and galactonate excretion. The ability of heart and muscle to form galactonate may also contribute to the G/G mouse's ability to slowly oxidize galactose to CO 2 , since the compound is an intermediate in an alternate route for galactose disposition.
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The rate of de novo galactose synthesis in patients with Galactose-1-Phosphate Uridyltransferase deficiency
Molecular genetics and metabolism, 2004Co-Authors: Gerard T Berry, Claire Yager, Cong Ning, Robert Reynolds, Peter J. Moate, Raymond C. Boston, Stanton SegalAbstract: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.
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Galactose Metabolism in Mice with Galactose-1-Phosphate Uridyltransferase Deficiency: Sucklings and 7-Week-Old Animals Fed a High-Galactose Diet
Molecular Genetics and Metabolism, 2001Co-Authors: Cong Ning, Claire Yager, Robert Reynolds, Nancy D Leslie, Gerard T Berry, Jie Chen, Stanton SegalAbstract:Abstract Mice deficient in Galactose-1-Phosphate Uridyltransferase (GALT) demonstrate abnormal galactose metabolism but no obvious clinical phenotype. To further dissect the pathways of galactose metabolism in these animals, galactose oxidation and metabolite levels were studied in 16-day-old sucklings and the effect of a 4 week prior exposure to a 40% glucose or 40% galactose diet was determined in 7-week-old mice. Suckling GALT-deficient (G/G) mice slowly oxidized [1- 14 C]galactose to 14 CO 2 , 4.0% of the dose when fed and 7.9% when fasted compared to normal animals 38.3 and 36.4% in 4 h, respectively. Plasma of G/G sucklings contained 11.1 mM galactose and erythrocyte galactose 1-phosphate levels were 28.2 and 31.9 mg/dl packed cells. Galactose, galactitol, galactonate, and galactose 1-phosphate were found in G/G suckling mouse tissues. The tissue galactose concentrations were 10% or less of that in plasma, suggesting that there was limited cellular entry of galactose. In 7-week-old fasted mice with 4 weeks prior exposure to glucose or galactose-containing diet, 4-h oxidation was 12.9 and 15.0% of the administered radiolabeled galactose, respectively. Normal animals oxidized 33.9 and 37.9% of the dose when fed the same diets, respectively. The ability of G/G mice to oxidize galactose in the absence of GALT activity suggests the presence of alternate metabolic pathways for galactose disposition. G/G mice fed the galactose-free 40% glucose diet had erythrocyte galactose 1-phosphate levels ranging from 6.4 to 17.7 mg/dl packed cells and detectable galactose and galactose metabolites in tissues, suggesting that these animals endogenously produced galactose. The plasma of 40% galactose-fed G/G mice contained 9.1 mM galactose with red blood cell galactose 1-phosphate averaging 43.6 mg/dl. Tissues of these animals also contained high levels of galactose and galactose 1-phosphate. Liver contained over 4 μmol/g galactonate but little galactitol. Despite the elevated galactose and galactose 1-phosphate, the animals tolerated the high-galactose diet and were indistinguishable from normal animals, exhibiting no manifestations of galactose toxicity seen in human GALT-deficient galactosemia. The data suggest that high galactose 1-phosphate levels do not cause galactose toxicity and that high galactitol in combination with galactose 1-phosphate may be a prerequisite. Absence of GALT appears necessary but insufficient to produce human galactosemic phenotype.
