Structural analysis of the major urinary oligosaccharides in feline alpha-mannosidosis

Oligosaccharide analysis in urine by maldi-tof mass spectrometry for the diagnosis of lysosomal storage diseases

BACKGROUND

There are 45 known genetic diseases that impair the lysosomal degradation of macromolecules. The loss of a single lysosomal hydrolase leads to the accumulation of its undegraded substrates in tissues and increases of related glycoconjugates in urine, some of which can be detected by screening of free oligosaccharides (FOS) in urine. Traditional 1-dimensional TLC for urine oligosaccharide analysis has limited analytical specificity and sensitivity. We developed fast and robust urinary FOS and glycoaminoacid analyses by MALDI-time-of-flight/time-of-flight (MALDI-TOF/TOF) mass spectrometry for the diagnosis of oligosaccharidoses and other lysosomal storage diseases.

METHODS

The FOS in urine equivalent to 0.09 mg creatinine were purified through sequential passage over a Sep-Pak C18 column and a carbograph column and were then permethylated. MALDI-TOF/TOF was used to analyze the permethylated FOS. We studied urine samples from individuals in 7 different age groups ranging from 0-1 months to ≥ 17 years as well as urine from known patients with different lysosomal storage diseases.

RESULTS

We identified diagnostic urinary FOS patterns for α-mannosidosis, galactosialidosis, mucolipidosis type II/III, sialidosis, α-fucosidosis, aspartylglucosaminuria (AGU), Pompe disease, Gaucher disease, and GM1 and GM2 gangliosidosis. Interestingly, the increase in urinary FOS characteristic of lysosomal storage diseases relative to normal FOS appeared to correlate with the disease severity.

CONCLUSIONS

The analysis of urinary FOS by MALDI-TOF/TOF is a powerful tool for first-tier screening of oligosaccharidoses and lysosomal storage diseases.

Cerebral Magnetic Resonance Spectroscopy Demonstrates Long-Term Effect of Bone Marrow Transplantation in α-Mannosidosis

α-Mannosidosis, OMIM #248500, is an autosomal recessive lysosomal storage disease caused by acidic α-mannosidase deficiency. Treatment options include bone marrow transplantation (BMT) and, possibly in the future, enzyme replacement therapy. Brain magnetic resonance spectroscopy (MRS) enables non-invasive monitoring of cerebral treatment effect. Accumulated cerebral mannose-containing oligosaccharides were demonstrated by MRS in a patient who at age 2 years and 11 months received a BMT from a haploidentical non-carrier sibling. The cerebral mannose-containing oligosaccharides had disappeared as early as 9½ months after BMT. MRS furthermore demonstrated the persistent treatment effect at regular intervals up to 5½ years after BMT. MRS is a non-invasive tool that can demonstrate the effect of BMT treatment. Likewise, MRS may be used to demonstrate the cerebral effect of other potential treatments such as enzyme replacement therapy.

Magnetic resonance spectroscopy of the occipital cortex and the cerebellar vermis distinguishes individual cats affected with alpha-mannosidosis from normal cats

A genetic deficiency of lysosomal alpha-mannosidase causes the lysosomal storage disease alpha-mannosidosis (AMD), in which oligosaccharide accumulation occurs in neurons and glia. The purpose of this study was to evaluate the role of magnetic resonance spectroscopy (MRS) in detecting the oligosaccharide accumulation in AMD. Five cats with AMD and eight age-matched normal cats underwent in vivo MRS studies with a single voxel short echo time (20 ms) STEAM spectroscopy sequence on a 4.7T magnet. Two voxels were studied in each cat, from the cerebellar vermis and the occipital cortex. Metabolites of brain samples from these regions were extracted with perchloric acid and analyzed by high resolution NMR spectroscopy. A significantly elevated unresolved resonance signal between 3.4 and 4. ppm was observed in the cerebellar vermis and occipital cortex of all AMD cats, which was absent in normal cats. This resonance was shown to be from carbohydrate moieties by high resolution NMR of tissue extracts. Resonances from the Glc-NAc group (1.8-2.2 ppm) along with anomeric proton signals (4.6-5.4 ppm) from undigested oligosaccharides were also observed in the extract spectra from AMD cats. This MRS spectral pattern may be a useful biomarker for AMD diagnosis as well as for assessing responses to therapy.

Glycoprotein lysosomal storage disorders: alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency

Glycoproteinoses belong to the lysosomal storage disorders group. The common feature of these diseases is the deficiency of a lysosomal protein that is part of glycan catabolism. Most of the lysosomal enzymes involved in the hydrolysis of glycoprotein carbohydrate chains are exo-glycosidases, which stepwise remove terminal monosaccharides. Thus, the deficiency of a single enzyme causes the blockage of the entire pathway and induces a storage of incompletely degraded substances inside the lysosome. Different mutations may be observed in a single disease and in all cases account for the nonexpression of lysosomal glycosidase activity. Different clinical phenotypes generally characterize a specific disorder, which rather must be described as a continuum in severity, suggesting that other biochemical or environmental factors influence the course of the disease. This review provides details on clinical features, genotype-phenotype correlations, enzymology and biochemical storage of four human glycoprotein lysosomal storage disorders, respectively alpha- and beta-mannosidosis, fucosidosis and alpha-N-acetylgalactosaminidase deficiency. Moreover, several animal disorders of glycoprotein metabolism have been found and constitute valuable models for the understanding of their human counterparts.

Isolation and characterization of the gene encoding the mouse broad specificity lysosomal alpha-mannosidase1

A genomic clone encoding the mouse lysosomal alpha-mannosidases was isolated and the gene was found to be encoded by 24 exons spanning approximately 14.5 kb of genomic DNA. The intron-exon boundaries were conserved between the mouse, human, and bovine lysosomal alpha-mannosidase genes as well as being partially conserved in several other species. In order to define the promoter of the mouse mannosidase gene, >1 kb of DNA sequence was obtained upstream from the respective initiation codon. The transcription start site was identified by a 5'-RACE procedure and putative promoter elements were identified by expression of promoter/reporter constructs. Fluorescence in situ hybridization analysis using the mouse and human mannosidase genomic clones as probes, localized the mouse gene to chromosome 8, at band position 8C2, and the human gene to chromosome 19p13.2, a region syntenic to the lysosomal mannosidase gene on mouse chromosome 8.

Substrate specificity of the bovine and feline neutral alpha-mannosidases

Neutral alpha-mannosidases were prepared from bovine and cat liver. The activities were distinguished from lysosomal and Golgi alpha-mannosidases by their neutral pH optima, relatively low Km for their synthetic substrate p-nitrophenyl alpha-D-mannoside, inhibition by Zn2+ and absence of inhibition by Co2+, EDTA, low concentrations of swainsonine, or deoxymannojirimycin. The cytosolic alpha-mannosidases were not retained by concanavalin A-Sepharose. They were able to degrade efficiently a variety of oligosaccharides with structures corresponding to certain high-mannose glycans or the oligomannosyl parts of hybrid and complex glycans. However, unlike lysosomal alpha-mannosidases from the same species these enzymes were not able to degrade Man9GlcNAc2 efficiently, and the bovine neutral alpha-mannosidase was not able to degrade a hexasaccharide with a structure analogous to Man5GlcNAc2-PP-dolichol. Sharp differences were noted for the bovine and cat enzymes with regard to the specificity of degradation. The bovine neutral alpha-mannosidase degraded the substrates by defined pathways, but the cat neutral alpha-mannosidase often produced complex mixtures of products, especially from the larger oligosaccharides. Therefore the bovine enzyme resembled the rat and human cytosolic alpha-mannosidases, but the cat enzyme did not. The bovine and cat neutral alpha-mannosidases, unlike the corresponding lysosomal activities, did not show specificity for the hydrolysis of the (1----3)- and (1----6)-linked mannose residues in the N-linked glycan pentasaccharide core.

Different oligosaccharides accumulate in the brain and urine of a cat with alpha-mannosidosis: structure determination of five brain-derived and seventeen urinary oligosaccharides

Five brain-derived and 17 urinary oligomannose-type oligosaccharides were isolated by ion-exchange chromatography on Mono Q or Dowex, followed by HPLC on Lichrosorb-NH2 from a Persian cat suffering from alpha-mannosidosis. The structures of the carbohydrate chains were determined by 500- or 600-MHz 1H-NMR spectroscopy. Different oligosaccharide patterns were found in brain and urine. 99% of the urinary oligosaccharides possess an alpha(1-6)-linked mannose residue attached to beta-mannose, whereas only 5% of the brain-derived oligosaccharides contain such a residue. Furthermore, of the urinary carbohydrate chains 71% end with Man beta 1-4GlcNAc beta 1-4GlcNAc and 29% end with Man beta 1-4GlcNAc, whereas the corresponding amounts are 23% and 77%, respectively, for the brain-derived oligosaccharides.

Rat liver chitobiase: purification, properties, and role in the lysosomal degradation of Asn-linked glycoproteins

Chitobiase, the lysosomal glycosidase responsible for splitting the GlcNAc beta-D-(1-4)GlcNAc moiety in Asn-linked glycoproteins, was purified over 600-fold from frozen rat livers utilizing an assay with di-N-acetylchitobiose as the substrate. The final preparation showed a major polypeptide of Mr 43,000 (sodium dodecylsulfate-polyacrylamide gel electrophoresis) that was determined to be the chitobiase by an immunological method. The purified chitobiase also hydrolyzed tri- and tetrasaccharides of chitin, which like di-N-acetylchitobiose were not substrates if first reduced by NaBH4. The initial products formed during hydrolysis of the tetrasaccharide were trisaccharide and GlcNAc. These results imply that chitobiase is a "reducing-end exohexosaminidase" which cleaves single GlcNAc units only from the reducing end of oligosaccharides. Fucose, typically found linked to the reducing-end GlcNAc in complex oligosaccharide chains, was found to block this reaction. Additional substrates that were hydrolyzed included GlcNAc beta-D-(1-4)MurNAc, the repeating structure from bacterial cell wall peptidoglycan, and the Man beta-D-(1-4)GlcNAc reducing-end component of glycoproteins. Km and Vm for hydrolysis of these substrates were of similar magnitude as for di-N-acetylchitobiose (6.3 mM and 15 mumol/min/mg protein, respectively). Liver tissues from nin mammalian species were surveyed for the presence of chitobiase activity. The activity was found in rat, mouse, rabbit, and guinea pig liver (Stirling [(1974) FEBS Lett. 39, 171-175] previously observed the enzyme in human liver), but not in dog, sheep, pig, cat, and cow liver. The presence or absence of chitobiase so far observed was found to exactly correlate with the type of oligosaccharide fragments found to accumulate in animals containing genetic or inhibitor-induced lysosomal storage pathologies. The presence of the chitobiase corresponds to the occurrence of one GlcNAc unit at the reducing end of stored oligosaccharides, while the absence of this glycosidase yields fragments with an intact GlcNAc beta-D-(1-4)GlcNAc moiety. These results verify our previous proposal that lysosomal disassembly of glycoproteins to free amino acids and sugars is an ordered, bidirectional pathway in which chitobiase (when present) catalyzes the last step during digestion of the protein-oligosaccharide linkage region.

The accumulation of oligosaccharides in tissues and body fluids of cats with alpha-mannosidosis

Oligosaccharides were extracted from tissues and body fluids of five kittens with alpha-mannosidosis, three being from the same litter. The kittens were all of different ages at death and were compared to normal and heterozygote cats. The oligosaccharides were analyzed by high-pressure liquid chromatography after perbenzoylation and were identified by comparison with compounds of known structure. This provided a detailed picture of the distribution of oligosaccharides in each tissue, and a method for quantitation of the total oligosaccharides. With the exception of the youngest animal (death at day 2), the oligosaccharide elution profiles were broadly similar for all tissues and fluids, and were typical of feline alpha-mannosidosis. In contrast, concentrations of total oligosaccharides diverged widely from one source to another, from a high of 17.3 mumol/g to a low of 0.04 mumol/g. The results are interpreted in the context of glycoprotein catabolism.

Characterization of alpha-mannosidase in feline mannosidosis

Acidic alpha-mannosidase deficiency has been identified in a family of Blue Persian cats. Characterization of the residual activity revealed that the Km for the substrate, 4-methylumbelliferyl-alpha-D-mannoside, increased approximately three-fold with a severe deficiency in Vmax (1-2%) in homogenates of liver and brain of affected cats compared with controls. The residual activity at pH 4.0 in liver homogenates from affected cats is very thermolabile at 51 degrees C while the control activity is stable at this temperature for 1 h. Subcellular fractionation of liver was performed from a control and diseased cat in order to compare the properties of the different alpha-mannosidases localized in these fractions. The residual activity present in the lysosomal fraction from diseased cat liver showed altered pH optimum, two-fold increase in Km with a severely reduced Vmax and increased thermolability compared with the activity in the lysosomal fraction from control liver. The thermal inactivation pattern and Km of the residual activity in the lysosomal fraction is different from the non-lysosomal alpha-mannosidase in the liver of the affected cat. This suggests that the residual activity in the lysosomal fraction of the liver from the affected cat is not due to contamination of non-lysosomal alpha-mannosidase in this fraction. Whether this residual activity represents the properties of the mutant enzyme or yet another minor normal component of lysosomes different from the major inactive mutant or absent lysosomal enzyme remains to be elucidated.

Biochemical, ultrastructural and histochemical studies of cat placentae deficient in activity of lysosomal alpha-mannosidase

Lysosomal alpha-mannosidase activity, oligosaccharide profiles, light and electron microscopy and lectin histochemistry studies were performed on full-term placentae obtained from five litters of cats. They resulted from breeding related cats who are obligate heterozygotes for lysosomal alpha-mannosidase deficiency. alpha-Mannosidase activity in placentae from affected kittens was less than 10 per cent of control, while in placentae from presumptive heterozygotes the activity was less than 50 per cent of control. High-pressure liquid chromatographic analysis of oligosaccharides revealed massive accumulation of undegraded oligosaccharides in placentae of affected kittens. A small elevation was found in placentae from presumptive heterozygous kittens, and none was detected in placentae of normal kittens. Light and electron microscopic examinations revealed vacuolization of fetal endothelial and mesenchymal cells only in placentae of affected kittens. Succinylated wheat germ agglutinin and concanavalin A stained the fetal fibroblasts only in placentae of affected kittens.