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The response in the blood of piglets to oral doses of galactose and glucose and intravenous administration of galactose.

The kinetics of the response in the blood of piglets to physiological oral intakes of galactose and glucose, and intravenous administration of galactose are described. Following the intravenous administration of galactose to 2- and 10-d-old piglets (n 7), the half-life was 7.98 (SD 0.75) and 7.99 (SD 1.89) min respectively, and efficient elimination rate was 9.09 (SD 2.15) and 8.75 (SD 0.79)% per min respectively. The turnover of galactose in the piglets was 100.3 micrograms/min per kg body weight. These observations demonstrate that galactose was rapidly removed from the blood of the piglets. While the dosing and sampling procedures stimulated hyperglycaemia, they had no effect on the concentration of galactose in the peripheral plasma. The galactose area under the curve (adjusted to the plasma volume of the animal) following a dose of either galactose or galactose plus glucose was 1.75 (SD 0.15) and 1.95 (SD 0.14) arbitrary units respectively in 2-d-old piglets and 1.96 (SD 0.26) and 1.98 (SD 0.10) arbitrary units respectively in 10-d-old piglets. Since the presence of glucose did not lower the adjusted area under the curve for galactose in the peripheral blood, the effect of glucose on the metabolism of galactose in piglets was more like that reported for rats than that for man, guinea-pigs or mice. It is suggested that the galactose moiety of lactose may make an important contribution to the replenishment of liver glycogen in the neonatal piglet.

Administration, Oral↗

Galactose breath testing distinguishes variant and severe galactose-1-phosphate uridyltransferase genotypes.

A galactose breath test that quantitates [1-(13)C]galactose conversion to 13CO2 provides information on the whole body galactose oxidative capacity. As there is little information on the relationship between whole body oxidation and the genotype in patients with galactosemia, we measured the 13CO2 excretion for 2 h after administration of [1-(13)C]galactose in 37 patients (3-48 y old) with galactose-1-phosphate uridyltransferase (GALT) deficiency and 20 control subjects (3-37 y old). Eleven patients with the common Q188R/Q188R genotype and no detectable erythrocyte GALT activity eliminated <2% of a bolus of [1-(13)C]galactose as 13CO2 compared with 8.47 to 28.23% in controls. This defines a severe metabolic phenotype. Seven patients with one Q188R allele and a second mutant allele such as L195P, E308K, V151A, M142K, or Q344K and one patient with a K285N/unknown genotype also released <2% as 13CO2 in 2 h. The presence of N314D or S135L as the second mutant allele does not impair total body galactose oxidation, as individuals with the GALT genotype of Q188R/N314D, K285N/N314D, and Q188R/S135L had normal 2-h galactose breath tests. Subjects with S135L/S135L, N314D/N314D, S135L/deltaT2359 as well as other rarer genotypes such as R258C/Y209C, E203K/IVSC-N314D, K285N/T138M, Q188R/D113N, S135L/F171S, R148W/N314D, and IVSC-N314D/N314D oxidized galactose comparable to controls. The dissociation of residual erythrocyte GALT activity and whole body galactose oxidative capacity is exemplified by blacks with a S135L/S135L genotype and absent erythrocyte GALT activity. An oral 2-h [1-(13)C]galactose breath test distinguishes severe and variant GALT genotypes and enables delineation of the extent of impaired galactose metabolism in an array of patients who possess diverse GALT mutations. It may prove to be useful in establishing whether a patient is capable of manifesting disease similar to patients with a Q188R/Q188R genotype.

Adolescent↗

Catalytic properties of galactose oxidase to liposome-forming amphiphiles which have many pendent galactose residues.

A galactose-carrying vinyl monomer [2-(methacryloyloxy)ethyl beta-D-galactopyranoside, MEGal] was polymerized by using a lipophilic radical initiator. The amphiphiles obtained (DODA-PMEGal) formed stable liposomes by mixing with phospholipids, and the galactose residues on the liposome surface were effectively recognized and oxidized by galactose oxidase. The affinity (estimated by the 1/Km value) of galactose oxidase for the galactose residues on the liposomes was higher than those for free galactose and MEGal and dependent on the length of galactose-carrying polymer chains on the liposome surface and the fluidity of the membranes, whereas not significantly influenced by the surface density of galactose residues on the liposomes. The affinity of galactose oxidase for the galactose-carrying linear polymers, which were prepared by using an ordinary azo-type radical initiator and a chain-transfer reagent, was also higher than those for free galactose and MEGal and dependent on the degree of polymerization of MEGal. The affinity was, however, relatively much smaller than those for DODA-PMEGals incorporated in liposomes.

Amides↗

Evidence for alternate galactose oxidation in a patient with deletion of the galactose-1-phosphate uridyltransferase gene.

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.

Blotting, Southern↗

Effect of 5% galactose diet on galactose and dulcitol in plasma and lens of male and female pigs.

The study was performed to compare the galactose tolerance of male and female pigs to 5% galactose and 25% hydrolysed whey (HW; containing 5% galactose) diets. Plasma galactose and dulcitol levels were measured throughout the diet period and correlated with the lens dulcitol contents at the end of the period. On the first day of the diet there was no significant difference between male and female blood galactose levels after galactose ingestion. The consumption of HW resulted in a significant 30% decrease in the blood galactose peak in females; there was no parallel difference in males on the HW diet. The 30-day diet induced a significant decrease in galactosaemia peaks resulting from galactose ingestion in both males and females, indicating an activation of galactose metabolism. The HW diet resulted in an equivalent decrease in peak galactosaemia only in males, cancelling the initial differences observed between males and females. The final dulcitol content in the lenses appeared to be correlated with plasma galactose but not with plasma dulcitol. However, the differences in plasma galactose between males and females, or between the two diets, resulted in smaller and often non-significant differences in lens dulcitol.

Analysis of Variance↗

Insights into the role of the aromatic residue in galactose-binding sites: MP2/6-311G++** study on galactose- and glucose-aromatic residue analogue complexes.

The presence of an aromatic residue (Trp, Phe, Tyr) facing the nonpolar face of galactose is a common feature of galactose-specific lectins. The interactions such as those between the C-H groups of galactose and the pi-electron cloud of aromatic residues have been characterized as weak hydrogen bonds between soft acids and soft bases, largely governed by dispersive and charge transfer interactions. An analysis of the binding sites of several galactose-specific lectins revealed that the spatial position-orientation of galactose relative to the binding site aromatic residue varies substantially. The effect of variations in position-orientations of galactose on the interaction energies of galactose-aromatic residue complexes has not been determined so far. In view of this, MP2/6-311G++** calculations were performed on galactose- and glucose-aromatic residue analogue complexes in eight position-orientations. The results show that the strength of the C-H...pi interactions in galactose-aromatic residue complexes is comparable to that of a hydrogen bond. Rather than the type of aromatic residue, the position-orientation of the saccharide appears to be more critical in determining the strength of their interactions. Earlier studies have found the binding site aromatic residue to be critical, but its role was not clear. This study shows that the aromatic residue is important for discriminating galactose from glucose, in addition to its contribution to binding energy.

Amino Acid Sequence↗

Galactose transport in Saccharomyces cerevisiae. 3. Characteristics of galactose uptake in transferaseless cells: evidence against transport-associated phosphorylation.

The characteristics of the inducible galactose transport system in bakers' yeast were studied in uridine diphosphate, galactose-1-phosphate uridylyl-transferaseless cells. Transferaseless cells transport galactose at the same initial rate as wild-type cells and accumulate a mixture of free galactose and galactose-1-phosphate. The addition of (14)C-labeled galactose to cells preloaded with unlabeled galactose and galactose-1-phosphate results in a higher rate of labeling of the free-sugar pool than of the galactose-1-phosphate pool. These results support other evidence that galactose uptake in bakers' yeast is a carrier-mediated, facilitated diffusion and that phosphorylation is an intracellular event after uptake of the free sugar.

Biological Transport↗

Lactose Uptake Driven by Galactose Efflux in Streptococcus thermophilus: Evidence for a Galactose-Lactose Antiporter.

Galactose-nonfermenting (Gal) Streptococcus thermophilus TS2 releases galactose into the extracellular medium when grown in medium containing excess lactose. Starved and de-energized Gal cells, however, could be loaded with galactose to levels approximately equal to the extracellular concentration (0 to 50 mM). When loaded cells were separated from the medium and resuspended in fresh broth containing 5 mM lactose, galactose efflux occurred. De-energized, galactose-loaded cells, resuspended in buffer or medium, accumulated [C]lactose at a greater rate and to significantly higher intracellular concentrations than unloaded cells. Uptake of lactose by loaded cells was inhibited more than that by unloaded cells in the presence of extracellular galactose, indicating that a galactose gradient was involved in the exchange system. When de-energized, galactose-loaded cells were resuspended in carbohydrate-free medium at pH 6.7, a proton motive force (Deltap) of 86 to 90 mV was formed, whereas de-energized, nonloaded cells maintained a Deltap of about 56 mV. However, uptake of lactose by loaded cells occurred when the proton motive force was abolished by the addition of an uncoupler or in the presence of a proton-translocating ATPase inhibitor. These results support the hypothesis that galactose efflux in GalS. thermophilus is electrogenic and that the exchange reaction (lactose uptake and galactose efflux) probably occurs via an antiporter system.

Journal Article↗

Clinical significance of plasma galactose and erythrocyte galactose-1-phosphate measurements in transferase-deficient galactosemia and in individuals with below-normal transferase activity.

We correlated the clinical symptoms of transferase-deficient galactosemia with the plasma galactose and erythrocyte galactose-1-phosphate concentrations in six galactosemic patients during dietary treatment, in a child before treatment, and in 12 individuals with below-normal erythrocyte hexose-1-phosphate uridylyltransferase activity. All the treated patients were asymptomatic. Normal galactose and either normal or above-normal galactose-1-phosphate concentrations were found. Three of these patients were clinically normal as newborns while ingesting galactose-containing foods and may resemble the asymptomatic Negro galactosemic. The clinical symptoms of galactosemia were observed in the untreated patient, who showed markedly above-normal concentrations of galactose and galactose-1-phosphate, protein and reducing substances in the urine, above-normal bilirubin and alkaline phosphatase in the plasma, with normal values for glucose, aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyltransferase. Clinical improvement in this patient paralleled the decline in erythrocyte galactose-1-phosphate. The individuals with below-normal hexose-1-phosphate uridylyltransferase activity (range 7--17 U/g of hemoglobin) had normal galactose and galactose-1-phosphate concentrations and were asymptomatic.

Adolescent↗

Simultaneous quantitative estimation of galactose-1-phosphate and galactose in blood for the diagnosis of galactosemia.

A new microfluorometrical simultaneous assay method of galactose-1-phosphate and galactose in blood discs was devised by use of alkaline phosphatase and beta-galactose dehydrogenase. Our method statistically corresponded well with the Kirkman's method. It can detect 1 X 10(-10) mole of minimal concentration of galactose-1-phosphate and galactose in one blood disc paper (3 mm in diameter), and this means the sensitivity of assay of galactose-1-phosphate was 0.1 mg%. Assay range in our method was very broad (0-2 mM or 0-10 mM). The accuracy and reproducibility of galactose-1-phosphate assay were 3.4 +/- 0.1 mg%, 8.0 +/- 0.4 mg% or 15.1 +/- 0.6 mg%. Mean values of galactose-1-phosphate and galactose in blood on normal infants were 0.8 mg% and 0.3 mg%, respectively. We applied this method to mass screening of galactosemia and could accurately distinguish many positive and false positive cases detected by Paigen's and Beutler's methods. This method gave us an easy and accurate assay system for the diagnosis of uridyl transferase and galactokinase deficiencies.

Alkaline Phosphatase↗

The effect of pH on incorporation of galactose by a normal human cell line and cell lines from patients with defective galactose metabolism.

Incorporation of radioactive galactose into TCA-insoluble material of galactosemic fibroblasts is more sensitive to low pH than is the incorporation by normal human fibroblasts. This study was undertaken to determine (1) whether there was any pH which could correct or counteract the galactosemic defect relative to galactose incorporation, and (2) whether the low pH effect was specific for galactose metabolism or whether general cellular metabolism in galactosemic cells was more sensitive to low pH than that in normal cells. The pH dependencies of incorporation of radioactive galactose and glucose into cellular macromolecules were investigated in galactosemic and normal cells. Normal cells have a biphasic curve with respect to galactose incorporation with peaks at pH 7.0 and 8.5. Galactosemic cells have only the high pH peak. The maximum incorporation by galactosemic cells was never more than about 30% that seen by normal cells under the conditions of these experiments. Thus manipulation of the pH alone cannot correct the galactosemic defect. The rate of incorporation of radioactive galactose was studied in normal, galactosemic and galactokinase deficient cells, at pH 7.2 and at pH 6.3. At pH 7.2, galactosemic cells incorporate galactose at a linear rate which is 30 to 40% that of normal cells while incorporation by kinase-deficient cells is between 5 and 10% of normal. At pH 6.3, the incorporation is also linear. However, galactosemic cells now exhibit the same rate as kinase-deficient cells in which the low level of incorporation is unaffected by pH. These results suggest that incorporation of galactose by galactosemic cells at low pH is not due to metabolic death of the cells, but may be due to the inhibition of some specific step or steps along a metabolic route of galactose metabolism other than the Leloir pathway.

Cell Line↗

Pathways of galactose metabolism by galactosemics: evidence for galactose conversion to hepatic UDPglucose.

To determine if classic galactosemics have residual galactose-1-phosphate uridyltransferase (GALT) activity to explain their considerable ability to oxidize galactose over 24 h, we devised a method for assessing their ability to form hepatic UDPglucose (UDPglu), an intermediate in the normal Leloir pathway of galactose metabolism. The protocol involved the single oral administration of 7 mg/kg [2-13C]galactose concomitant with multiple small doses of acetaminophen with measurement of the extent of labeling of urinary acetaminophen glucuronide, the glucuronide moiety being formed from hepatic UDPglu. We performed the study lasting 24 h in two normal subjects and three classic galactosemics, two homozygous for the Q188R mutation and one compound for the Q188R/K258N mutation. The labeling and total excretion of acetaminophen glucuronide was measured in urine by nuclear magnetic resonance techniques. Concomitant with determination of label in the glucuronide measurement was made of galactose oxidation to 13CO2 and the 13C enrichment of plasma glucose. All of the galactosemic patients formed 13C enriched acetaminophen glucuronide indicating that they had converted the labeled galactose to [13C]UDPglu and that residual GALT or another pathway that forms UDPglu is present in hepatic tissue. Compared to the normal whose glucuronide labeling was rapid and short-lived that of the galactosemics was delayed and extended for a long period over 10 h. The extent of isotopic enrichment of glucuronide by galactosemics was comparable to the normals, resulting in a much greater conversion of galactose to UDPglu by the galactosemics. The labeling of the UDPglu pool was reflected by the rate of 13CO2 formation being rapid in the normal with peak labeling at 2-3 h with total oxidation of over 70% in 24 h. The oxidation of the galactosemics was slow with a broad peak of 13CO2 at 10 h and a total excretion of 25-39% of the [13C]galactose administered. The normal subjects formed highly enriched plasma glucose within 30 min while no enrichment of plasma glucose was detected until after 300 min in galactosemics. The exact pathway(s) of galactose metabolism by galactosemics to UDPglu remain to be determined. Their delineation may contribute to new approaches to therapeutic strategies for this enigmatic disorder.

Acetaminophen↗

Mediators of galactose sensitivity in UDP-galactose 4'-epimerase-impaired mammalian cells.

UDP-galactose 4'-epimerase (GALE) catalyzes the final step in the Leloir pathway of galactose metabolism, interconverting UDP-galactose and UDP-glucose. Unlike its Escherichia coli counterpart, mammalian GALE also interconverts UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. Considering the key roles played by all four of these UDP-sugars in glycosylation, human GALE therefore not only contributes to the Leloir pathway, but also functions as a gatekeeper overseeing the ratios of important substrate pools required for the synthesis of glycosylated macromolecules. Defects in human GALE result in the disorder epimerase-deficiency galactosemia. To explore the relationship among GALE activity, substrate specificity, metabolic balance, and galactose sensitivity in mammalian cells, we employed a previously described GALE-null line of Chinese hamster ovary cells, ldlD. Using a transfection protocol, we generated ldlD derivative cell lines that expressed different levels of wild-type human GALE or E. coli GALE and compared the phenotypes and metabolic profiles of these lines cultured in the presence versus absence of galactose. We found that GALE-null cells accumulated abnormally high levels of Gal-1-P and UDP-Gal and abnormally low levels of UDP-Glc and UDP-GlcNAc in the presence of galactose and that human GALE expression corrected each of these defects. Comparing the human GALE- and E. coli GALE-expressing cells, we found that although GALE activity toward both substrates was required to restore metabolic balance, UDP-GalNAc activity was not required for cell proliferation in the presence of otherwise cytostatic concentrations of galactose. Finally, we found that uridine supplementation, which essentially corrected UDP-Glc and, to a lesser extent UDP-GlcNAc depletion, enabled ldlD cells to proliferate in the presence of galactose despite the continued accumulation of Gal-1-P and UDP-Gal. These data offer important insights into the mechanism of galactose sensitivity in epimerase-impaired cells and suggest a potential novel therapy for patients with epimerase-deficiency galactosemia.

Animals↗

Blood-brain transfer of galactose in experimental galactosemia, with special reference to the competitive interaction between galactose and glucose.

The interaction between glucose and galactose during transport across the cerebral capillary endothelium was studied in anesthetized rats. Although galactose is present in the diet of suckling mammals and is a potential substrate for brain metabolism in adult mammals, its effect on glucose transport in adult rats is unknown. A kinetic model was formulated to analyze the effect of chronically elevated galactose levels on glucose transport in adult rats. The analysis indicated that galactose and glucose compete for the same transport mechanism in the cerebral capillary endothelium. The Tmax of glucose and galactose were both about 380 mumol 100 g-1 min-1 and the Kt of galactose (30 mM) was about three times that of glucose (10 mM). During prolonged galactosemia in adult rats, neither the Tmax, nor the Kt of either competitor changed substantially when compared with rats subjected to acute galactosemia. At 10 mM galactose in plasma in rats with acute galactosemia, the inhibition of glucose transport, simulated a 25% reduction of plasma glucose, and in rats with chronic galactosemia a 20% reduction. This moderate effect is in contrast to the effect of galactose in suckling rats in which 10 mM galactose in plasma reduced the glucose transport to a level corresponding to a 50% reduction of the plasma glucose concentration.

Animals↗

Galactose transport in Saccharomyces cerevisiae. II. Characteristics of galactose uptake and exchange in galactokinaseless cells.

The characteristics of the inducible galactose system in Saccharomyces cerevisiae were studied by using the nonmetabolized galactose analogues, l-arabinose and d-fucose, and galactokinaseless and transportless mutants. Induced wild-type cells transport l-arabinose by facilitated diffusion. Transportless cells transport neither galactose nor l-arabinose above the noninduced rate, whereas galactokinaseless cells transport galactose l-arabinose and d-fucose by facilitated diffusion. Determination of unidirectional rate of (14)C-labeled galactose uptake by preloaded galactokinaseless cells, containing a large unlabeled free-galactose pool, showed that the rate of galactose uptake by facilitated diffusion is greater than the rate of galactose metabolism at similar external galactose concentrations.

Arabinose↗

Effect of prolonged galactose consumption on galactose tolerance in young healthy humans.

This study was carried out on two groups of healthy young subjects. One group (n = 8) was given a single oral dose of galactose (0.5 g/kg body weight), and a single measurement of blood galactose was made 40 min later. A second group (n = 16) was given a daily supplement of 0.5 g/kg galactose for 15 days, and blood galactose and galactitol were measured. On the first day of the test period, some subjects seemed to tolerate galactose less well than others: galactitol appeared in their plasmas and could be related to a significantly higher galactosaemia than that of subjects without detectable galactitol in the plasma. However, after 15 days of galactose intake, the less galactose-tolerant subjects appeared to have adapted, as indicated by the significant decrease in the blood galactose and the disappearance of galactitol. No change was found in the galactose-tolerant subjects. No significant difference was found between males and females.

Adult↗

Effect of galactose diet removal on the progression of retinal vessel changes in galactose-fed dogs.

PURPOSE: Feeding dogs a diet containing 30% galactose induces experimental galactosemia and results in the formation of diabetes-like microvascular lesions of the retina. The appearance and progression of these retinal lesions can be arrested in a dose-dependent manner by treating these dogs with aldose reductase inhibitors from the onset of galactosemia. To determine whether the elimination of galactosemia can also reduce the progression of retinal lesions, the galactose diet was removed from the galactosemic dogs after either the appearance of pericyte ghosts or formation of microaneurysms. METHODS: Ten control dogs were fed a normal diet, and 50 dogs were fed a diet containing 30% galactose. The galactose diet was removed from 15 dogs after 24 months, the time at which pericyte ghosts had previously been observed to develop, and from another 15 dogs after 31 months, when microaneurysms had previously been observed to develop. Eighteen dogs were continued on a galactose diet. Beginning at 24 months, eyes from each group were enucleated at approximately 6-month intervals. Changes in retinal lesions were quantified by computer image analyses. RESULTS: Significant (P < 0.05-0.01) increases in the endothelium-pericyte (E-P) ratio and decreases in pericyte density were observed with increased duration of galactose feeding. Although no reversal of retinal lesions occurred, differences in the progression of retinal lesions between the galactose-fed and galactose-deprived groups became evident after 12 to 24 months. CONCLUSIONS: Discontinuation of galactose in the diet at the initial stages of background retinopathy beneficially delays the progression of retinal lesions.

Animals↗

Identification of a region of UDP-galactose:N-acetylglucosamine beta 4-galactosyltransferase involved in UDP-galactose binding by differential labeling.

The location of regions in the primary structure of UDP-galactose:N-acetylglucosamine beta 4-galactosyl-transferase (GT) that are involved in binding UDP-galactose has been investigated by differential chemical modification with two different reagents in the presence and absence of UDP-galactose. Treatment with periodate-cleaved UDP and NaCNBH3 resulted in a loss of 80% of GT activity, which was largely prevented by UDP-galactose. Stoichiometry of labeling and peptide maps of the modified enzyme samples indicated partial labeling at many sites. A major site of reaction in the absence of UDP-galactose that was essentially unmodified in its presence was found to correspond to Lys341 in the cDNA sequence of GT. As a second approach, the reactivities of the amino groups of GT were compared in the presence and absence of saturating levels of UDP-galactose by trace acetylation with [3H]acetic anhydride. UDP-galactose binding was found to perturb the reactivities of a number of lysines in the C-terminal region of GT, the most pronounced effect being a reduction in the reactivity of Lys351. The two procedures thus identified a region between residues 341 and 351 as being associated with UDP-galactose binding. This region overlaps a small section in the sequence of GT that was previously noted to be similar to part of bovine alpha-1,3-galactosyltransferase (Joziasse, D. H., Shaper, J. H., Van den Eijnden, D. H., Van Tunen, A. J., and Shaper, N. L. (1989) J. Biol. Chem. 264, 14290-14297). Sequence comparisons indicate that extended regions at the C terminus of each enzyme encompassing this area may represent homologous UDP-galactose-binding domains.

Amino Acid Sequence↗