The glycoasparagines in urine of a patient with aspartylglycosaminuria

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

Identification of Monosialylated N-glycoforms in the CDG Urinome by Ion Mobility Tandem Mass Spectrometry: The Potential for Clinical Applications

Introduction

A novel approach of ion mobility tandem mass spectrometry (IMS-MS/MS) is applied to analysis of human glycourinome to obtain carbohydrate pattern data of congenital disorders of glycosylation patient. Overlapping of the complex carbohydrate mass range landscape has been highly reduced upon IMS-MS procedure, allowing more efficient identification by mapping and sequencing of glycan precursor ions, following their separation by mobility, according to difference in drift time through the traveling wave IMS cell. Intact and truncated N- and O-glycan structures modified by sialylation and fucosylation were identified according to their drift time separated molecular ions and submitted to fragmentation in a narrow mass window.

IMS CID MS/MS Analysis

The fragmentation spectra generated from the IMS separated precursor ions contain series of fragment ions maintaining the same mobility as their parent ions, and the assignment accuracy can be significantly enhanced.

Conclusion

According to the specific fragment ion patterns, carbohydrate epitopes described to be involved in pathological processes were assigned. A high potential of this glycomics-based strategy for clinical applications can be presented.

A mass spectrometric strategy for profiling glycoproteinoses, Pompe disease, and sialic acid storage diseases

Glycoproteinoses, Pompe disease, and sialic acid storage diseases are characterized by a massive accumulation of unprocessed oligosaccharides and/or glycoconjugates in urine. The identification of these glycocompounds is essential for a proper diagnosis. In this study, we investigated the potential of MALDI-TOF-MS to identify glycocompounds present in urine from patients with different inborn errors of glycan metabolism. Urinary glycocompounds were permethylated, and analyzed using GC-MS and MALDI-TOF-MS. In order to confirm tentative assignments, a second aliquot of urine was purified on a C18 Sep-Pak cartridge and glycocompounds were desalted on a column of nonporous graphitized carbon. The glycocompounds were then sequentially on-plate digested using an array of exoglycosidases. A range of disease-specific oligosaccharides as well as glycopeptides was identified for all oligosacchariduria models. In addition, free sialic acid accumulated in urine from a patient suffering from French-type sialuria, has been detected by a GC-MS approach, which could be applied to other sialic acid storage diseases. This procedure is simple, and can be performed in few simple steps in less than 24 h. This current method can be applied for newborn screening for other inherited metabolic diseases as well as for assessing treatments in clinical trials.

MALDI-QTOFMS/MS identification of glycoforms from the urine of a CDG patient

Identification of single glycoconjugate components in a complex mixture from the urine of a patient suffering from a congenital disorder of glycosylation was probed by MALDIMS analysis on a hybrid quadrupole time-of-flight instrument. In negative ion mode, complex maps containing more than 50 ionic species were obtained and a number of molecular ions directly as-signed using a previously developed computer-assisted algorithm. To confirm the data and determine the carbohydrate sequence, single molecular ions were selected and submitted to fragmentation experiments. Interpretation of fragmentation spectra was also assisted by the soft-ware using alignment with spectra generated in silico. According to fragmentation data, the majority of glycoconjugate ionic species could be assigned to free oligosaccharides along with ten species tentatively assigned to glycopeptides. Following this approach for glycan identification by a combination of MALDI-QTOFMS and MS/MS experiments, computer-assisted assignment and fragment analysis, data for a potential glycan data base are produced. Of high benefit for this approach are two main factors: low sample consumption due to the high sensitivity of ion formation, and generation of only singly charged species in MALDIMS allowing interpretation with-out any deconvolution. In this experimental set-up, sequencing of single components from the MALDI maps by low energy CID followed by computer-assisted assignment and data base search is proposed as a most efficient strategy for the rapid identification of complex carbohydrate structures in clinical glycomics.

Aspartylglucosaminuria: radiologic course of the disease with histopathologic correlation

Twelve living patients (aged 19 months to 32 years) with aspartylglucosaminuria were examined by magnetic resonance imaging (MRI), and the magnetic resonance (MR) images of 16 health volunteers (aged 4 to 32 years) were used as controls. One patient was examined twice. Postmortem MRI and histopathologic analysis were done on the brains of four additional adult patients. Signal intensities determined quantitatively on T2-weighted images differed significantly between patients and controls, being higher from the white matter (P < .0002) and lower from the thalami (P < .03) in the patients. The generally increased signal intensity of the white matter was most obvious in the young patients, with many focal areas of very high signal intensity in the subcortical white matter. The subcortical white matter showed a somewhat increased signal intensity even at the age of 32 years. In two of the four postmortem MR images, the distinction between the gray and white matter was still poor. At histopathologic analysis, the basic cortical cytoarchitecture was generally preserved but most neurons contained vacuoles, which were also found in the neurons of the deep gray matter. In two of the four autopsy cases the white matter showed diffuse pallor of myelin staining and some gliosis. Thus aspartylglucosaminuria is primarily a gray-matter disease also affecting white matter by delaying myelination.

Dissection of the molecular pathology of aspartylglucosaminuria provides the basis for DNA diagnostics and future therapeutic interventions

Aspartylglucosaminuria (AGU) is exceptional among lysosomal storage diseases since it represents the only known amidase deficiency in man, being caused by an inadequate function of aspartylglucosaminidase (AGA, E.C. 3.5.1.26.). This amidase is essential in one of the final steps in the ordered breakdown of glycoproteins since it cleaves Asn from the residual N-acetylglucosamines (for reviews see 1, 2). The deficiency of the enzyme activity results in the typical lysosomal accumulation of the abnormal degradation products (mainly aspartylglucosamine, 2-acetamido-1-beta-L-aspartamido-1,2-dideoxyglucose) in patients' cells and tissues. The diagnosis of AGU has so far been based on the detection of abnormal metabolites in urine and decreased enzyme activity in the cultured fibroblasts or isolated lymphocytes. Prenatal diagnosis has been possible by demonstrating the deficient enzyme activity of amniocytes or chorion villus biopsies. Identification of carriers has been difficult and unreliable due to the high individual variation in AGA activity and prerequisite for isolated blood lymphocytes. During the past few years we have purified the human enzyme into homogeneity, isolated the full length cDNA and characterized the majority of AGU mutations in this cDNA. This work facilitated the development of a reliable DNA diagnostic test suitable also for large scale carrier screening. The molecular pathology of the most common AGU mutation was unravelled, this being a prerequisite for the oncoming developments for therapy. Although AGU is a relatively rare disease, characterization of the AGU mutations and their cellular consequences have revealed highly interesting new phenomena in the biosynthesis of this lysosomal enzyme, some of which carry general biological significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutations causing aspartylglucosaminuria (AGU): a lysosomal accumulation disease

This article provides a review of the mutations reported so far in the lysosomal storage disease aspartylglucosaminuria (AGU). The clinical symptoms, biochemical findings, and diagnostic possibilities of the disease are introduced. The prevalence and biological consequences of the found mutations are then described, as well as the availability of a new rapid DNA test suitable for carrier screening. This test will be especially applicable in the genetically isolated Finnish population, where the carrier frequency of AGU was found to be as high as 1:36. Finally, future prospects dealing with the foreseeable therapeutic interventions of the disease are discussed.

High-performance liquid chromatography of urinary oligosaccharides in the diagnosis of glycoprotein degradation disorders

Urinary oligosaccharides can be separated by high-performance anion-exchange chromatography using a Dionex CarboPac PA1 column, elution with aqueous sodium hydroxide and sodium acetate solutions and detection by pulsed amperometry. Each of the urines of patients with glycoprotein degradation disorders yielded a pattern of oligosaccharide excretion unique for that disorder, facilitating an unambiguous diagnosis. The method is sensitive (10 microliters of urine required) and fast (40 min).

Human leucocyte aspartylglucosaminidase. Evidence for two different subunits in a more complex native structure

Human leucocyte aspartylglucosaminidase (AGA: 1-aspartamido-beta-N-acetylglucosamine amidohydrolase, EC 3.5.1.26) was purified to homogeneity by using affinity chromatography, gel filtration, chromatofocusing and reverse-phase h.p.l.c. As shown by SDS/PAGE, the homogeneous purified enzyme preparation consists of four polypeptide chains with molecular masses of 25, 24, 18 and 17 kDa. In the native polyacrylamide gel these polypeptides migrate as one active enzyme complex, and by gel filtration the peak of enzyme activity can be detected in a position of about 65 kDa. Digestion with endoproteinase Lys-C or endoproteinase Asp-N, followed by peptide analysis with reverse-phase h.p.l.c., reveals an identical peptide pattern for the 24 and 25 kDa bands as well as for the 17 and 18 kDa bands. This treatment further demonstrated a totally different peptide pattern for the 24/25 kDa versus the 17/18 kDa subunit. The N-terminal sequences of the 17 kDa and the 18 kDa peptides were identical, as determined by Edman degradation. The N-termini of the 24 kDa and the 25 kDa peptides were blocked. The enzyme was partly resistant to endoglycosidases H and F, but N-glycosidase F transformed the 24/25 kDa band into one 23 kDa band and the 17/18 kDa band into one 16 kDa band. Also, immunological data obtained with antisera produced against these subunits showed that AGA consists of two non-identical polypeptides.

Amniotic fluid glycoasparagines in fetal aspartylglycosaminuria

Midterm amniotic fluid samples from one pregnancy with the fetus affected by aspartylglycosaminuria and from 11 normal pregnancies were analysed for glycoasparagines accumulating in urine in aspartylglycosaminuria. The aspartylglucosamine concentration in the affected pregnancy was about five times higher than in the controls, but the absolute value was very low being only about one-thousandth of that in urine in aspartylglycosaminuria and one-tenth of that in urine samples from normal adults. In total monosaccharide analysis, only galactose content in the affected amniotic fluid was slightly elevated compared to controls, indicating that higher glycoasparagines typical of urine in aspartylglycosaminuria were not accumulated in significant amounts. The data demonstrate that the analysis of glycoasparagines in amniotic fluid is not likely to permit reliable prenatal diagnosis of aspartylglycosaminuria.

Urinary sialic acid screening in neurologic disorders

Urine sialic acid was measured in 246 patients evaluated for possible neurodegenerative disorders. Total, free, and bound sialic acid excretion declined significantly with patients' ages. Among 11 patients (4.5%) with age-related excretion rates greater than 2 standard deviations above the mean, 5 had the following disorders: free sialic acid storage disease, mucolipidosis type II, pseudohypoparathyroidism, sinus histiocytosis, and probable Sanfilippo syndrome. Although the remaining 6 were undiagnosed, 2 exhibited deteriorating courses and the other 4 presented variable combinations of organomegaly, developmental delay or mental retardation, seizures, facial dysmorphism, or bony abnormalities. Thus, these individuals also may have metabolic disorders with abnormal excretions of sialic acid-containing compounds. With awareness of age-related excretion rates, sialic acid screening is most useful for the sialidoses, mucolipidoses, and disorders of free sialic acid metabolism.

Prenatal diagnosis and fetal pathology of aspartylglucosaminuria

The prenatal diagnosis of aspartylglucosaminuria (AGU), a lysosomal storage disorder of glycoprotein degradation, was made by demonstrating the deficiency of N-aspartylglucosaminidase on cultured cells from a midterm amniotic fluid sample. Four other amniotic fluid studies from at-risk pregnancies gave a normal or a heterozygote level of enzyme activity. These pregnancies have gone to term and the delivery of healthy babies. The pregnancy with the affected fetus was terminated and the prenatal diagnosis was verified by enzyme assays on cord blood lymphocytes, cultured cells from skin biopsy, and from placental villi. Electron microscopic evidence of lysosomal storage was seen in several organs of the fetus with the notable exception of the central nervous system. The undifferentiated mesenchymal fibroblasts particularly were heavily loaded with cytoplasmic inclusions in skin, liver, kidney, and placenta.

Progressive neurologic deterioration and renal failure due to storage of glutamyl ribose-5-phosphate

A six-year-old boy presented with a history of seizures, progressive neurologic deterioration, and proteinuria. Physical examination revealed mildly coarse facies, failure to thrive, generalized hypotonia with muscle wasting, and optic atrophy; there was no organomegaly. The family history suggested an X-linked recessive inheritance. The electroencephalogram, electroretinogram, evoked potentials, and computed axial tomography of the brain were abnormal. Urine oligosaccharide chromatography, urine amino acids and organic acids, and results of leukocyte and fibroblast lysosomal-enzyme assays for the known storage diseases were normal; however, conjunctival and renal biopsy specimens contained enlarged lysosomes on electron microscopy. The patient had progressive neurologic deterioration and died of renal failure at eight years of age. A compound identified as glutamyl ribose-5-phosphate was purified from the brain (0.96 mumol per gram, wet weight) and kidney (0.60 mumol per gram, wet weight). This compound is the linkage group in ADP-ribosylation of proteins, an important regulatory process in gene expression and DNA repair. We believe this new disorder represents a glycoproteinosis that results in the cytoplasmic storage of glutamyl ribose-5-phosphate.

Aspartylglycosaminuria: an inborn error of glycoprotein catabolism

Aspartylglycosaminuria (AGU, McKusick 20840) is a metabolic disorder affecting the catabolism of glycoproteins. It was first described in 1967, by Jenner and Pollitt, in two mentally retarded English siblings. Subsequently several cases were reported from Finland (Palo and Mattsson, 1970; Autio, 1972; Autio et al., 1973). Today the number of known cases is about 140, most of them Finnish or of Finnish origin (Aula et al., 1980). The incidence of AGU in Finland has been estimated to be approximately 1:26000 and the disease is inherited as an autosomal recessive trait (Autio et al., 1973). Clinical manifestations include progressive mental retardation, coarse gargoyle-like facial features, skeletal abnormalities and recurrent infections. Early development of the patients is usually normal, but by the age of 5-15 years they are already severely retarded (Autio, 1972; Autio et al., 1973). Morphologically AGU is a generalized storage disease (Haltia et al., 1975). Affected tissues show enlarged lysosomes. Vacuolization is a prominent feature of liver and nerve cells (Haltia et al., 1975) and of peripheral lymphocytes (Aula et al., 1975).

Regional distribution of glycoasparagine storage material in the brain in aspartylglycosaminuria

We have studied the regional distribution of glycoasparagine storage material in the brain in aspartylglycosaminuria, a condition characterized by inherited deficiency of lysosomal N-aspartyl-beta-N-acetylglucosamine amidohydrolase. Gaschromatographic measurements of the main accumulating glycoprotein-derived metabolite, N-acetylglucosaminyl-asparagine (GlcNAc-Asn), in 12 defined cerebral areas showed that GlcNAc-Asn is rather evenly distributed in the brain. The mean concentrations ranged from 0.454 mg/g wet tissue (corpus callosum) to 0.0610 mg/g (pons). The GlcNAc-Asn concentrations tended to be higher in grey matter areas than in white matter areas. GlcNAc-Asn was identified in the isolated neuronal fraction, but not in the myelin fraction, by mass-fragmentographic techniques. Electron-microscopic reexamination of a brain biopsy specimen revealed, in addition to the abundant presence of storage lysosomes in the neuronal perikarya, numerous cytoplasmic inclusions in brain capillary endothelial cells and pericytes as well as in occasional macrophages. The results indicate that the glycoasparagine storage material is not limited to expected cortical areas in aspartylglycosaminuria, but is distributed in a rather constant fashion in all cerebral grey and white matter areas studied.

Urinary sialic acid levels in aspartylglycosaminuria

Urinary sialoglycoconjugates were studied in 22 patients with inherited deficiency of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (aspartylglycosaminuria), in eight obligate heterozygotes, and in age- and sex-matched control subjects. Total sialic acid excretion was significantly higher in the patients (38.3 +/- 17.7 mumol/mmol creatinine, mean +/- S.D.) than in the matched controls (17.7 +/- 7.3 mumol/mmol creatinine, p less than 0.001). The sialic acid output in the heterozygotes did not differ from that of the controls. Gel filtration studies revealed that the increase in urinary sialic acid in aspartylglycosaminuria is of bound type and confined to the low molecular mass region. A linear positive correlation was found between the output of sialic acid and glycoasparagine in the individual patients (r = 0.77, p less than 0.001). The amount of sialylated metabolites excreted in urine did not correlate with the severity of clinical manifestations in aspartyl-glycosaminuria.

N-Acetylglucosamine-asparagine levels in tissues of patients with aspartylglycosaminuria

The levels of the main glycoprotein-derived storage compound, N-acetylglucosamine-asparagine, in various post mortem tissues of three adult patients with inherited deficiency of lysosomal 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (aspartylglycosaminuria) were measured by gas-liquid chromatography. All aspartylglycosaminuria tissues studied contained significant amounts of N-acetylglucosamine-asparagine, whereas none of the corresponding control tissues contained detectable amounts of this compound. High levels of N-acetylglucosamine-asparagine were found in the liver (3.65 mg/g wet weight), spleen (2.24) and thyroid (2.18), and lower levels in the kidney (0.89), brain (0.53), spinal cord (0.32), sciatic nerve (0.34) and skeletal muscle (0.16). The results show that N-acetylglucosamine-asparagine accumulates chiefly in tissues with important functions in glycoprotein metabolism and/or high endocytic activity. Correlation of the results to the clinical manifestations of aspartylglycosaminuria did not reveal a direct relationship between the amount of N-acetylglucosamine-asparagine stored and the degree of organ dysfunction.

Urinary oligosaccharide excretion in disorders of glycolipid, glycoprotein and glycogen metabolism. A review of screening for differential diagnosis

In recent years great interest has centered around metabolic disorders in which excessive oligosacchariduria is a prominent feature. This review describes the methods of both structural and diagnostic investigations of oligosaccharides in a number of these diseases. Special emphasis has been laid upon simple screening methods which would avail themselves to the clinical chemistry laboratory

Variation of urinary excretion of aspartylglucosamine and associated clinical findings in aspartyglucosaminuria

The urinary excretion of aspartylglucosamine (AADG), the main accumulating glycoprotein degradation product in aspartylglucosaminuria (AGU), was studied in 40 patients at various stages of the disease. Only slight variation was found when the amount of AADG excreted by ten AGU patients under 10 years of age was compared with AADG excretion of older patients at a clinically advanced stage of the disease. The 24h AADG excretion of the younger patients was 354 mg compared with 441 mg in the group of ten patients over 20 years of age. Clinical symptoms were unrelated to AADG excretion.

Structural determination of three glycoasparagines isolated from the urine of a patient with aspartylglycosaminuria

Three different glycoasparagines have been isolated from the urine of a patient with aspartylglycosaminuria and their structures determined using sugar, amino acid and methylation analysis, enzymic degradation and measurements of the optical rotations. The structures were 2-acetamido-1-N-(4'-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (yield 135 mg/l) beta-D-galactopyranosyl-(1 leads to 4)-2-acetamido-1-N-(4'-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (yield 35 mg/l), and alpha-D-mannopyranosyl-(1 leads to 6)-beta-D-mannopyranosyl-(1 leads to 4)-2-acetamido-2-deoxy-beta-D-glucopyranosyl-(1 leads to 4)-2-acetamido-1-N-(4'-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (yield 30 mg/l). The first two compounds have previously been described, whereas the third compound is different from any of the glycoasparagines isolated before.