Galactose metabolism and cell "sociology"

Coordinated movement, neuromuscular synaptogenesis and trans-synaptic signaling defects in Drosophila galactosemia models

The multiple galactosemia disease states manifest long-term neurological symptoms. Galactosemia I results from loss of galactose-1-phosphate uridyltransferase (GALT), which converts galactose-1-phosphate + UDP-glucose to glucose-1-phosphate + UDP-galactose. Galactosemia II results from loss of galactokinase (GALK), phosphorylating galactose to galactose-1-phosphate. Galactosemia III results from the loss of UDP-galactose 4'-epimerase (GALE), which interconverts UDP-galactose and UDP-glucose, as well as UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. UDP-glucose pyrophosphorylase (UGP) alternatively makes UDP-galactose from uridine triphosphate and galactose-1-phosphate. All four UDP-sugars are essential donors for glycoprotein biosynthesis with critical roles at the developing neuromuscular synapse. Drosophila galactosemia I (dGALT) and II (dGALK) disease models genetically interact; manifesting deficits in coordinated movement, neuromuscular junction (NMJ) development, synaptic glycosylation, and Wnt trans-synaptic signalling. Similarly, dGALE and dUGP mutants display striking locomotor and NMJ formation defects, including expanded synaptic arbours, glycosylation losses, and differential changes in Wnt trans-synaptic signalling. In combination with dGALT loss, both dGALE and dUGP mutants compromise the synaptomatrix glycan environment that regulates Wnt trans-synaptic signalling that drives 1) presynaptic Futsch/MAP1b microtubule dynamics and 2) postsynaptic Frizzled nuclear import (FNI). Taken together, these findings indicate UDP-sugar balance is a key modifier of neurological outcomes in all three interacting galactosemia disease models, suggest that Futsch homolog MAP1B and the Wnt Frizzled receptor may be disease-relevant targets in epimerase and transferase galactosemias, and identify UGP as promising new potential therapeutic target for galactosemia neuropathology.

Developmental defects in a Caenorhabditis elegans model for type III galactosemia

Type III galactosemia is a metabolic disorder caused by reduced activity of UDP-galactose-4-epimerase, which participates in galactose metabolism and the generation of various UDP-sugar species. We characterized gale-1 in Caenorhabditis elegans and found that a complete loss-of-function mutation is lethal, as has been hypothesized for humans, whereas a nonlethal partial loss-of-function allele causes a variety of developmental abnormalities, likely resulting from the impairment of the glycosylation process. We also observed that gale-1 mutants are hypersensitive to galactose as well as to infections. Interestingly, we found interactions between gale-1 and the unfolded protein response.

Transcriptome sequencing and profiling of expressed genes in phloem and xylem of ramie (Boehmeria nivea L. Gaud)

Ramie (Boehmeria nivea L. Gaud) is a highly versatile herbaceous plant which is widely cropped in southern China. The success of this herbaceous plant relies on wide use in modern industry. Understanding the profiling of expressed genes in phloem and xylem of ramie is crucial for improving its industrial performance. Herein, we uncover the transcriptome profile in phloem and xylem in present study. Using Illumina paired-end sequencing technology, 57 million high quality reads were generated. De novo assembly yielded 87,144 unigenes with an average length of 635 bp. By sequence similarity searching for public databases, a total of 32,541 (41.77%) unigenes were annotated for their function. Among these genes, 57,873 (66.4%) and 28,678 (32.9%) unigenes were assigned to categories of Gene Ontology and Orthologous Groups database, respectively. By searching against the Kyoto Encyclopedia of Genes and Genomes Pathway database (KEGG), 18,331 (21.0%) unigenes were mapped to 125 pathways. The metabolic pathways were assigned the most unigene (4,793, 26.2%). Furthermore, Pol II and Pol III subunits as well as the genes of Galactose metabolism pathway had higher expression in phloem compared to xylem. In addition, fatty acid metabolism pathway genes showed more abundant in xylem than phloem. These results suggest that high activities of RNA synthesis and Galactose metabolism pathway promises fiber synthesis in phloem. The present study is the initial exploration to uncover the fiber biosynthesis difference between phloem and xylem in ramie through the analysis of deep sequencing data.

Self-recognition of high-mannose type glycans mediating adhesion of embryonal fibroblasts

High-mannose type N-linked glycan with 6 mannosyl residues, termed "M6Gn2", displayed clear binding to the same M6Gn2, conjugated with ceramide mimetic (cer-m) and incorporated in liposome, or coated on polystyrene plates. However, the conjugate of M6Gn2-cer-m did not interact with complex-type N-linked glycan with various structures having multiple GlcNAc termini, conjugated with cer-m. The following observations indicate that hamster embryonic fibroblast NIL-2 K cells display homotypic autoadhesion, mediated through the self-recognition capability of high-mannose type glycans expressed on these cells: (i) NIL-2 K cells display clear binding to lectins capable of binding to high-mannose type glycans (e.g., ConA), but not to other lectins capable of binding to other carbohydrates (e.g. GS-II). (ii) NIL-2 K cells adhere strongly to plates coated with M6Gn2-cer-m, but not to plates coated with complex-type N-linked glycans having multiple GlcNAc termini, conjugated with cer-m; (iii) degree of NIL-2 K cell adhesion to plates coated with M6Gn2-cer-m showed a clear dose-dependence on the amount of M6Gn2-cer-m; and (iv) the degree of NIL-2 K adhesion to plates coated with M6Gn2-cer-m was inhibited in a dose-dependent manner by α1,4-L-mannonolactone, the specific inhibitor in high-mannose type glycans addition. These data indicate that adhesion of NIL-2 K is mediated by self-aggregation of high mannose type glycan. Further studies are to be addressed on auto-adhesion of other types of cells based on self interaction of high mannose type glycans.

The poor growth of Rhodospirillum rubrum mutants lacking RubisCO is due to the accumulation of ribulose-1,5-bisphosphate

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) catalyzes the first step of CO(2) fixation in the Calvin-Benson-Bassham (CBB) cycle. Besides its function in fixing CO(2) to support photoautotrophic growth, the CBB cycle is also important under photoheterotrophic growth conditions in purple nonsulfur photosynthetic bacteria. It has been assumed that the poor photoheterotrophic growth of RubisCO-deficient strains was due to the accumulation of excess intracellular reductant, which implied that the CBB cycle is important for maintaining the redox balance under these conditions. However, we present analyses of cbbM mutants in Rhodospirillum rubrum that indicate that toxicity is the result of an elevated intracellular pool of ribulose-1,5-bisphosphate (RuBP). There is a redox effect on growth, but it is apparently an indirect effect on the accumulation of RuBP, perhaps by the regulation of the activities of enzymes involved in RuBP regeneration. Our studies also show that the CBB cycle is not essential for R. rubrum to grow under photoheterotrophic conditions and that its role in controlling the redox balance needs to be further elucidated. Finally, we also show that CbbR is a positive transcriptional regulator of the cbb operon (cbbEFPT) in R. rubrum, as seen with related organisms, and define the transcriptional organization of the cbb genes.

The metabolism of d-galactosamine and N-acetyl-d-galactosamine in rat liver

d-[1-(14)C]Galactosamine appears to be utilized mainly by the pathway of galactose metabolism in rat liver, as evidenced by the products isolated from the acid-soluble fraction of perfused rat liver. These products were eluted in the following order from a Dowex 1 (formate form) column and were characterized as galactosamine 1-phosphate, sialic acid, UDP-glucosamine, UDP-galactosamine, N-acetylgalactosamine 1-phosphate, N-acetylglucosamine 6-phosphate, UDP-N-acetylglucosamine, UDP-N-acetylgalactosamine and an unidentified galactosamine-containing compound. In addition, [1-(14)C]glucosamine was found in the glycogen, an incorporation previously shown to result from the substitution of UDP-glucosamine for UDP-glucose in the glycogen synthetase reaction. Analysis of the [1-(14)C]glucosamine-containing disaccharides released from glycogen by beta-amylase provided additional evidence that they consist of a mixture of glucose and glucosamine in a 1:1 ratio, but with glucose predominating on the reducing end. UDP-N-acetylgalactosamine was shown to result from the reaction of UTP with N-acetylgalactosamine 1-phosphate in the presence of a rat liver extract.

UDP-galactose 4' epimerase (GALE) is essential for development of Drosophila melanogaster

UDP-galactose 4' epimerase (GALE) catalyzes the interconversion of UDP-galactose and UDP-glucose in the final step of the Leloir pathway; human GALE (hGALE) also interconverts UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine. GALE therefore plays key roles in the metabolism of dietary galactose, in the production of endogenous galactose, and in maintaining the ratios of key substrates for glycoprotein and glycolipid biosynthesis. Partial impairment of hGALE results in the potentially lethal disorder epimerase-deficiency galactosemia. We report here the generation and initial characterization of a first whole-animal model of GALE deficiency using the fruit fly Drosophila melanogaster. Our results confirm that GALE function is essential in developing animals; Drosophila lacking GALE die as embryos but are rescued by the expression of a human GALE transgene. Larvae in which GALE has been conditionally knocked down die within days of GALE loss. Conditional knockdown and transgene expression studies further demonstrate that GALE expression in the gut primordium and Malpighian tubules is both necessary and sufficient for survival. Finally, like patients with generalized epimerase deficiency galactosemia, Drosophila with partial GALE loss survive in the absence of galactose but succumb in development if exposed to dietary galactose. These data establish the utility of the fly model of GALE deficiency and set the stage for future studies to define the mechanism(s) and modifiers of outcome in epimerase deficiency galactosemia.

Galactose toxicity in animals

In most organisms, productive utilization of galactose requires the highly conserved Leloir pathway of galactose metabolism. Yet, if this metabolic pathway is perturbed due to congenital deficiencies of the three associated enzymes, or an overwhelming presence of galactose, this monosaccharide which is abundantly present in milk and many non-dairy foodstuffs, will become highly toxic to humans and animals. Despite more than four decades of intense research, little is known about the molecular mechanisms of galactose toxicity in human patients and animal models. In this contemporary review, we take a unique approach to present an overview of galactose toxicity resulting from the three known congenital disorders of galactose metabolism and from experimental hypergalactosemia. Additionally, we update the reader about research progress on animal models, as well as advances in clinical management and therapies of these disorders.

Structure and function of glycosphingolipids and sphingolipids: recollections and future trends

Based on development of various methodologies for isolation and characterization of glycosphingolipids (GSLs), we have identified a number of GSLs with globo-series or lacto-series structure. Many of them are tumor-associated or developmentally regulated antigens. The major question arose, what are their functions in cells and tissues? Various approaches to answer this question were undertaken. While the method is different for each approach, we have continuously studied GSL or glycosyl epitope interaction with functional membrane components, which include tetraspanins, growth factor receptors, integrins, and signal transducer molecules. Often, GSLs were found to interact with other carbohydrates within a specific membrane microdomain termed "glycosynapse", which mediates cell adhesion with concurrent signal transduction. Future trends in GSL and glycosyl epitope research are considered, including stem cell biology and epithelial-mesenchymal transition (EMT) process.

Epimerase-deficiency galactosemia is not a binary condition

Epimerase-deficiency galactosemia results from the impairment of UDP-galactose 4'-epimerase (GALE), the third enzyme in the Leloir pathway of galactose metabolism. Originally identified as a clinically benign "peripheral" condition with enzyme impairment restricted to circulating blood cells, GALE deficiency was later demonstrated also to exist in a rare but clinically severe "generalized" form, with enzyme impairment affecting a range of tissues. Isolated cases of clinically and/or biochemically intermediate cases of epimerase deficiency have also been reported. We report here studies of 10 patients who, in the neonatal period, received the diagnosis of hemolysate epimerase deficiency. We have characterized these patients with regard to three parameters: (1) GALE activity in transformed lymphoblasts, representing a "nonperipheral" tissue, (2) metabolic sensitivity of those lymphoblasts to galactose challenge in culture, and (3) evidence of normal versus abnormal galactose metabolism in the patients themselves. Our results demonstrate two important points. First, whereas some of the patients studied exhibited near-normal levels of GALE activity in lymphoblasts, consistent with a diagnosis of peripheral epimerase deficiency, many did not. We detected a spectrum of GALE activity levels ranging from 15%-64% of control levels, demonstrating that epimerase deficiency is not a binary condition; it is a continuum disorder. Second, lymphoblasts demonstrating the most severe reduction in GALE activity also demonstrated abnormal metabolite levels in the presence of external galactose and, in some cases, also in the absence of galactose. These abnormalities included elevated galactose-1P, elevated UDP-galactose, and deficient UDP-glucose. Moreover, some of the patients themselves also demonstrated metabolic abnormalities, both on and off galactose-restricted diet. Long-term follow-up studies of these and other patients will be required to elucidate the clinical significance of these biochemical abnormalities and the potential impact of dietary intervention on outcome.

Molecular mechanism for cancer-associated induction of sialyl Lewis X and sialyl Lewis A expression-The Warburg effect revisited

Cell adhesion mediated by selectins and their carbohydrate ligands, sialyl Lewis X and sialyl Lewis A, figures heavily in cancer metastasis. Expression of these carbohydrate determinants is markedly enhanced in cancer cells, but the molecular mechanism that leads to cancer-associated expression of sialyl Lewis X/A has not been well understood. Results of recent studies indicated involvement of two principal mechanisms in the accelerated expression of sialyl Lewis X/A in cancers; 'incomplete synthesis' and ' neo synthesis.' As to 'incomplete synthesis,' we have recently found further modified forms of sialyl Lewis X and sialyl Lewis A in non-malignant colonic epithelium, which have additional 6-sulfation or 2 --> 6 sialylation. The impairment of GlcNAc 6-sulfation and 2 --> 6 sialylation upon malignant transformation leads to accumulation of sialyl Lewis X/A in colon cancer cells. Epigenetic changes such as DNA methylation and/or histone deacetylation are suggested to lie behind such incomplete synthesis. As to the mechanism called ' neo synthesis,' recent studies have indicated that cancer-associated alterations in the sugar transportation and intermediate carbohydrate metabolism play important roles. Cancer cells are known to exhibit a metabolic shift from oxidative to elevated anaerobic glycolysis (Warburg effect), which is correlated with the increased gene expression of sugar transporters and glycolytic enzymes induced by common cancer-specific genetic alterations. The increased sialyl Lewis X/A expression in cancer is a link in the chains of these events because our recent results indicated that these events accompany transcriptional induction of a set of genes closely related to its expression.

Hypoxia induces adhesion molecules on cancer cells: A missing link between Warburg effect and induction of selectin-ligand carbohydrates

Cancer cells undergo distinct metabolic changes to cope with their hypoxic environment. These changes are achieved at least partly by the action of transcriptional factors called hypoxia-inducible factors (HIFs). We investigated gene expression in cultured human colon cancer cells induced by hypoxic conditions with special reference to cell-adhesion molecules and carbohydrate determinants having cell-adhesive activity by using DNA-microarray and RT-PCR techniques. Hypoxic culture of colon cancer cells induced a marked increase in expression of selectin ligands, the sialyl Lewis x and sialyl Lewis a determinants at the cell surface, which led to a definite increase in cancer cell adhesion to endothelial E-selectin. The transcription of genes for fucosyltransferase VII (FUT7), sialyltransferase ST3Gal-I (ST3O), and UDP-galactose transporter-1 (UGT1), which are all known to be involved in the synthesis of the carbohydrate ligands for E-selectin, was significantly induced in cancer cells by hypoxic culture. In addition, a remarkable induction was detected in the genes for syndecan-4 (SDC4) and alpha5-integrin (ITGA5), the cell-adhesion molecules involved in the enhanced adhesion of cancer cells to fibronectin. The transcriptional induction by hypoxia was reproduced in the luciferase-reporter assays for these genes, which were significantly suppressed by the co-transfection of a dominant-negative form of HIF. These results indicate that the metabolic shifts of cancer cells partly mediated by HIFs significantly enhance their adhesion to vascular endothelial cells, through both selectin- and integrin-mediated pathways, and suggest that this enhancement further facilitates hematogenous metastasis of cancers and tumor angiogenesis.

Characterization of the O-GlcNAc protein modification in Xenopus laevis oocyte during oogenesis and progesterone-stimulated maturation

Little information exists about single N-acetylglucosamine modifications on proteins in growth and developmental model systems. To explore these phenomena, Xenopus laevis oocytes from stages I-VI of oogenesis were isolated and proteins analyzed on SDS-PAGE. The proteins were probed with antibodies specific for O-GlcNAc. Levels of the O-GlcNAc protein modification were highest in stages I and II, while decreasing in stages III-VI. The reduction in amount of O-GlcNAc-modified proteins was correlated to increases in apparent O-GlcNAcase (streptozotocin-inhibitable neutral hexosaminidase), activity involved in removing protein monoglycosylations. The O-GlcNAc modification was also characterized during progesterone-stimulated oocyte maturation. Although O-GlcNAcase activity appeared relatively constant between quiescent and matured stage VI oocytes, a small decrease in the levels of both total and specific O-GlcNAc-modified proteins was observed. Investigating the function of O-GlcNAc during maturation, oocytes were incubated with compounds known to modulate the levels of the O-GlcNAc protein modification and then stimulated to mature. Oocytes treated with compounds known to increase O-glycosylation consistently matured slower than non-treated controls, while oocytes treated with compounds that decrease O-glycosylation matured slightly faster than controls. The O-GlcNAc modification may play important roles in both the developmental and cell division processes of X. laevis oocytes.

The glycosynapse

Physically distinguishable microdomains associated with various functional membrane proteins are one of the major current topics in cell biology. Glycosphingolipids present in such microdomains have been used as "markers;" however, the functional role of glycosyl epitopes in microdomains has received little attention. In this review, I have tried to summarize the evidence that glycosyl epitopes in microdomains mediate cell adhesion and signal transduction events that affect cellular phenotypes. Molecular assemblies that perform such functions are hereby termed "glycosynapse" in analogy to "immunological synapse," the membrane assembly of immunocyte adhesion and signaling. Three types of glycosynapses are so far distinguishable: (i) Glycosphingolipids organized with cytoplasmic signal transducers and proteolipid tetraspanin with or without growth factor receptors; (ii) transmembrane mucin-type glycoproteins with clustered O-linked glycoepitopes for cell adhesion and associated signal transducers at lipid domain; and (iii) N-glycosylated transmembrane adhesion receptors complexed with tetraspanin and gangliosides, as typically seen with the integrin-tetraspanin-ganglioside complex. The possibility is discussed that glycosynapses give rise to a high degree of diversity and complexity of phenotypes.

Classical galactosemia and mutations at the galactose-1-phosphate uridyl transferase (GALT) gene

Classical galactosemia is caused by a deficiency in activity of the enzyme galactose-1-phosphate uridyl transferase (GALT), which, in turn, is caused by mutations at the GALT gene. The disorder exhibits considerable allelic heterogeneity and, at the end of 1998, more than 150 different base changes were recorded in 24 different populations and ethnic groups in 15 countries worldwide. The mutations most frequently cited are Q188R, K285N, S135L, and N314D. Q188R is the most common mutation in European populations or in those predominantly of European descent. Overall, it accounts for 60-70% of mutant chromosomes, but there are significant differences in its relative frequency in individual populations. Individuals homoallelic for Q188R tend to have a severe phenotype and this is in keeping with the virtually complete loss of enzyme activity observed in in vitro expression systems. Globally, K285N is rarer, but in many European populations it can be found on 25-40% of mutant chromosomes. It is invariably associated with a severe phenotype. S135L is found almost exclusively in African Americans. In vitro expression results are discrepant, but some individuals carrying S135L appear to exhibit GALT activity in some tissues. Duarte 1 (or Los Angeles) and Duarte 2 (or Duarte) variants carry the same amino acid substitution, N314D, even though D1 is associated with increased erythrocyte GALT activity and D2 with reduced activity. N314D is in linkage disequilibrium with other base changes that differ on the D1 and D2 alleles. N314D does not impair GALT activity in in vitro expression systems. However, there are differences in the abundance of GALT protein in lymphoblastoid cells lines from D2 and D1 individuals. It is unclear whether the specific molecular changes that distinguish the D1 and D2 alleles account for the different activities. The considerable genetic heterogeneity documented to date undoubtedly contributes to the phenotypic heterogeneity that is observed in galactosemia. The additional effects of nonallelic variation and other constitutional factors on phenotypic variability remain to be elucidated.

Histopathological and electron microscopical observations on rainbow trout fry syndrome

Rainbow trout (Oncorhynchus mykiss) fry and fingerlings with clinical signs of rainbow trout fry syndrome, and rainbow trout (0.5 to 3.5 g) with experimentally induced infections with Flavobacterium psychrophilum, were examined histopathologically and electron microscopically. Severe hypertrophy of the spleen and cellular degeneration were consistently observed. Distinctive features of the disease were the loss of definition of the splenic border and its replacement by a loosely structured eosinophilic layer, fibrinous inflammation and intercellular oedema within the spleen, and the presence of numerous filamentous bacteria interspersed throughout the organ.

The fundamental importance of human galactose metabolism: lessons from genetics and biochemistry

Cloning and characterization of all three human galactose-metabolic genes (GALK, GALT and GALE) has led to the identification of a number of mutations which are generally of the missense type in patients with galactosemia, an inborn error of metabolism. The predominance of missense mutations is interesting, considering the general importance of galactose metabolism for cellular energy production and proper modification of glycoproteins and glycolipids. Abnormalities in both of these macromolecules have been described in transferase-deficiency galactosemia, the most common and best-studied form of galactosemia. Thus, the parallel biochemical and molecular genetic analyses of human galactose metabolism are shedding light on this under-appreciated metabolic pathway that is critical for cellular energy production, modification of cellular macromolecules and normal human development.

2-Deoxy-2-[18F]fluoro-D-galactose as an in vivo tracer for imaging galactose metabolism in tumors with positron emission tomography

The feasibility of 2-deoxy-2-[18F]fluoro-D-galactose ([ 18F]FdGal) for imaging galactose metabolism in tumors with positron emission tomography (PET), was investigated using two hepatomas, Yoshida sarcoma, or glioma in rats, and mouse mammary carcinoma. In hepatoma-bearing rats the highest uptake of [18F]FdGal was observed in the liver followed by the kidney and tumor. The tumor uptake increased with time, and the high uptake ratios of tumor to organ were observed except for the liver and kidney. Tumor uptake was also measured in all tumors. As main metabolites in all tumors, [18F]FdGal 1-phosphate and UDP-[18F]FdGal were found by HPLC. Two hepatomas showed a slightly higher uptake and a larger percentage of UDP derivative than the other three tumors. By autoradiography the brain tumor was visualized clearly. These results indicate that [18F]FdGal has potential as a tracer for imaging galactose metabolism in tumors with PET.

Analogs of cell surface carbohydrates. Synthesis of D-galactose derivatives having an ethynyl, vinyl or epoxy residue at C-5

Compounds derived from D-galactose having an ethynyl, vinyl, or epoxide residue at C-5, as well as 7,7-dibromo olefinic, isomeric 7,7-gem-bromofluoro olefinic, and 6,6-gem-difluoro derivatives were obtained from 1,2:3,4-di-O-iso-propylidene-alpha-D-galacto-hexodialdo-1,5- pyranose.

Accumulation of 2-deoxy-2-[18F]fluoro-D-galactose in the liver by phosphate and uridylate trapping

To investigate the highest accumulation of 2-deoxy-2-[18F]fluoro-D-galactose ([18F]FdGal) in the liver, metabolic studies with [18F]FdGal were carried out in Wistar rats for 120 min after i.v. injection. As main metabolites 2-deoxy-2-[18F]fluoro-D-galactose 1-phosphate ([18F]FdGal-1-P) and UDP-2-deoxy-2-[18F]-fluoro-D-galactose (UDP-[18F]FdGal) were identified in the liver and other tissues. The [18F]FdGal was phosphorylated by galactokinase. The phosphorylation rate was very rapid in the liver, in which at 5 min after injection 81% of 18F was detected as [18F]FdGal-1-P. After this time the phosphate form decreased with time, which was explained by conversion of [18F]FdGal-1-P to UDP-[18F]FdGal by UDP-glucose: galactose-1-phosphate uridyltransferase. At 120 min after injection 77% of the 18F was measured in the UDP-[18F]FdGal. In the brain both reaction rates were slower than in the liver. Both phosphate and uridylate derivates were also observed as main metabolites in the heart, lung, spleen and small intestine. On the other hand, a small amount of [18F]FdGal-1-P was detected in the plasma, in which the percentage of phosphate increased gradually and was 6% at 120 min. These results show that the [18F]FdGal metabolism in tissue results in phosphate and uridylate trapping and that the [18F]FdGal has potential for measuring in vivo galactose metabolism with positron emission tomography.

r-Galactonolactone in experimental galactosemic animals

An accumulation of galactose-1,4-lactone, an oxidation product of galactose, was observed in various tissues of galactosemic guinea pigs fed a 40% galactose diet for 6 weeks. In addition, an accumulation of the two galactose metabolites varied among organs. The highest content of the lactone was observed in the liver and the content of the lactone exceeded that of the reduced counterpart. The lens gave the highest galactitol content. In the serum the level of the lactone was very low. A trace amount of the lactone was detected in the kidney while it was mostly excreted into urine within 54 h upon withdrawal of the diet. On the other hand, in the animals kept on a high galactose diet for only 2 days, urinary lactone rapidly decreased. These observations indicated that a high galactose level in the circulation was associated with the production of the lactone in various tissues and that the accumulated lactone was released into the circulation very slowly and then excreted into the urine. Suppression of galactitol production by administration of an aldose reductase inhibitor resulted in the accumulation of the lactone in the lens, the testis, and the muscle, as well as in the circulation. The lactone thus produced was excreted exclusively into the urine. This observation indicates a close relationship between the oxidative and reductive metabolisms of galactose at a toxic level.

A case of uridine diphosphate galactose-4-epimerase deficiency detected by neonatal screening for galactosaemia

An infant with a deficiency of the enzyme uridine diphosphate galactose-4-epimerase was detected during galactosaemia screening of the Queensland newborn population. No case of epimerase deficiency has been reported previously in Australia and the incidence in our population is unknown. A deficiency of this enzyme is usually quite benign although two cases with a galactosaemia-like syndrome have been reported. This infant is developing normally, both intellectually and physically, in spite of extremely high levels of red blood cell galactose-1-phosphate. The introduction of newer methods of galactosaemia screening in Australia will probably result in the detection of other cases of this enzyme deficiency.

Finding of a galactose-oxidation-product in lens of galactose-fed guinea pig

From studies on polyols in lens of galactose-fed guinea pigs, r-galactono-1,4-lactone was found, which proves the presence of galactonic acid as a product of galactose oxidation, by gas liquid chromatography and mass spectrometry. The content of this component was one tenth of that of galactitol. In vitro culture of rat lens in 30 mM galactose-loaded media demonstrated the formation of the lactone. The significance of the lactone was discussed with respect to the galactose metabolism in lens.

Biosynthesis of galactocerebrosides and glucocerebrosides in glial cell lines

UDP-galactose:ceramide galactosyltransferase (CGalT, EC 2.4.1.45) and UDP-glucose:ceramide glucosyltransferase (CGlcT, EC 2.4.1.80) were determined in the glial cell lines G26-20, G26-24, C6, and C6TK-. The enzymatic assay for CGalT in cultured glial cells was complicated by a rapid conversion of UDP-galactose to UDP-glucose, due to the elevated UDP-galactose-4'-epimerase activity in certain glial cell clones. It seems that mechanisms regulating UDP-galactose-4'-epimerase activity and levels of UDP sugars in the glial cell lines differ from those in brain tissue. Compared with the maximum activity of CGalT in the myelinating rat brain, the enzyme activities in the oligodendroglioma clonal cell lines G26-20 and G26-24 were 16-30 times lower. On the other hand, CGalT levels in G26-20 and G26-24 cells were comparable to the values found in young rat brain before myelination starts. No CGalT activity could be detected in C6 or C6TK- cells by the method used in this study, whereas CGlcT activity was found in all glial cell lines tested and its levels were close to the values observed in the young rat brain.

Natural cytotoxic cells against solid tumors in mice: blocking of cytotoxicity by D-mannose

Natural cytotoxic (NC) and natural killer (NK) cells have been defined by their ability to lyse certain solid or lymphoid tumor targets in vitro, without prior sensitization. Our present studies describe an attempt to characterize the structures involved in the effector-target recognition leading to tumor cell lysis. Addition of the monosaccharide D-mannose to the NC cell assay significantly blocked cytotoxicity of the fibrosarcoma Meth A target by the effector cells at 50 mM and lower concentrations. D-Galactose showed blocking activity in one of five experiments, only at 50 mM. L-Fucose, D-glucose, and N-acetyl-D-glucosamine did not affect NC cell cytotoxicity at similar concentrations. All of the sugars tested inhibited NK cell lysis of the lymphoma YAC-I target. None of the sugars affected killing of the appropriate target by allosensitized cytotoxic T lymphocytes. The blocking of NC-mediated cytotoxicity was not due to a direct toxic action of the sugars on the effector cells. These findings suggest that, in the NC system, recognition involves lectin-like structures with a specificity for D-mannose (or D-galactose, or both), whereas, in the NK system, such lectin-like structures are less restricted. Such structures appear not to be involved in the specific cytotoxicity mediated by T cells.

The A and B blood group substances on odontogenic epithelium

The presence of glycoprotein-associated blood group substances on various types of odontogenic epithelium has been demonstrated through enzyme histochemistry. The sporadic nature of their appearance would preclude speculation about these substances and the development of odontogenic neoplasms.

Structural studies on branched fucosphingolipids of hog gastric mucosa

A structural studies have been performed on new complex glycolipids extracted from hog gastric mucosa by 0.4 M sodium acetate in methanol-chloroform-water, and which were purified to homogeneity by DEAE-Sephadex and Florisil column chromatography and by preparative thin-layer chromatography in three solvent systems. Five branched fucolipids have been purified from this extract, three of which have been characterized previously [1] and remaining two were subject of this investigations. Based on the results of partial acid hydrolyses, oxidation with periodate and chromium trioxide, permethylation and serological activities following structures were proposed.

Immunologic and chemical studies on mucopolysaccharide derived from murine lymphosarcoma

Mucopolysaccharide was prepared from media in which the Gardner's lymphosarcoma cells were cultured. Multiple intraperitoneal injections of the preparation into syngeneic mice resulted in enhancement of the tumors which were inoculated prior to the injections. Sera of these hosts contained antibodies reacting with antigens of the outer layer of the tumor cells. Chemical analyses of the preparation showed that the mucopolysaccharide is composed of hexosamine, uronic, acid, hexose, and proteins. The mucopolysaccharide was shown to possess unique migration rate on electrophoresis and thin layer chromatography.

CO2 production from galactose in galactose-1-phosphate uridyl transferase-deficient Escherichia coli

Escherichia coli K-12 deficient in galactose-1-phosphate uridyl transferase is capable of converting significant amounts of d-[1-(14)C]galactose to (14)CO(2), whereas strains deficient in other enzymes of the Leloir pathway cannot do so.

Galactose and glucose metabolism in galactokinase deficient, galactose-1-P-uridyl transferase deficient and normal human fibroblasts

Despite the genetic interruption of the Leloir pathway both galactosemic patients and galactosemic fibroblasts can convert galactose to CO2 and TCA precipitable products, although at less than the normal rate. These observations stimulated investigations into the identity of the alternative metabolic routes which allows for galactose metabolism in the absence of in vitro galactose-1-P-uridyl transferase. Four lines of galactosemic cells, each without detectable gal-transferase, produced 14CO2 from [1-14C]-galactose (0.094 mumoles in 20 cc of medium) at approximately 39% +/- 16% the rate of transferase positive cells over a 48-hour period. However, galactokinase deficient fibroblasts produced 14CO2 and TCA precipitable products from [1-14C]-galactose or [U-14C]-galactose at only 3% to 9% the rate of normal fibroblasts. Therefore it seems likely that gal-transferase deficient fibroblasts must first synthesize galactose-1-P for further metabolism of galactose.

Biosynthesis of glycosaminoglycans: uridine diphosphate glucose 4'-epimerase from cornea and epiphysial-plate cartilage

UDP-glucose 4'-epimerase (EC 5.1.3.2.) was extracted from newborn-pig epiphysial-plate cartilage and whole bovine cornea. The formation of radioactive UDP-galactose from UDP[U-14C]glucose was demonstrated by radioautography after separation of the sugar nucleotides by paper chromatography or t.l.c. The pH optimum and the Km values for UDP-glucose, UDP-galactose and NAD+ were determined in both tissues. UDP-galactose and UDP-glucuronic acid formation after incubation with different UDP-glucose concentrations was followed; the same experiment was carried out using different UDP-galactose concentrations and following the formation of UDP-glucose and UDP-glucuronic acid. At equilibrium, the ratio UDP-glucose/UDP-galactose reaches a value of about 3.5. The results obtained seem to indicate that UDP-glucose 4'-epimerase activity is strongly dependent on that of UDP-glucose dehydrogenase. The physiological meaning of UDP-glucose 4'-epimerase in glycosaminoglycan biosynthesis in the two tissues under study is discussed on the basis of the Km values of UDP-glucose 4'-epimerase and UDP-glucose dehydrogenase and on the basis of the rate of UDP-glucose and UDP-galactose utilization.

Orosomucoid content of pleural and peritoneal effusions

22 nonneoplastic, noninflammatory effusions (cirrhosis and congestive heart failure), 12 non-neoplastic inflammatory effusions (tuberculosis, lupus erythematosus, rheumatoid arthritis, and idiopathic pleuropericarditis), and 58 neoplastic effusions (cancer of lung, breast, ovary, and pancreas, and lymphoma) were analyzed by radial immunodiffusion for orosomucoid concentration. The average concentration +/-SE was 35+/-4, 65+/-17, and 130+/-13 mg/100 ml in the three types of effusion, respectively. By gel filtration and ion exchange chromatography, orosomucoid was isolated from 12 nonmalignant and 14 malignant fluids. The orosomucoid preparations reacted as single components in acrylamide gel electrophoresis at pH 9.0, and in immunodiffusion and immunoelectrophoresis against antisera to human serum and to human plasma orosomucoid. In radial immunodiffusion, the slope of the line relating concentration to the square of the diameter of the precipitate area was identical for orosomucoid isolated from normal human plasma and from nonneoplastic effusions, but was subnormal for orosomucoid isolated from neoplastic fluids. All orosomucoid preparations had normal amino acid composition. Orosomucoid from the nonmalignant effusions had normal carbohydrate content. 11 of 14 samples of orosomucoid isolated from neoplastic fluids had abnormalities in carbohydrate composition, consisting of subnormal content of sialic acid (11 of 14), hexose (10 of 14), and hexosamine (3 of 14), and abnormally high content of hexosamine (4 of 14). Discriminant analysis showed that concentration of orosomucoid distinguished between neoplastic and nonneoplastic noninflammatory effusions more effectively than concentration of total protein, albumin, alpha(1), alpha(2), beta, or gamma-globulin.