Analysis of aspartylglucosamine at the picomole level by high-performance liquid chromatography

Aspartylglycosaminuria: a review

Aspartylglucosaminuria (AGU), a recessively inherited lysosomal storage disease, is the most common disorder of glycoprotein degradation with a high prevalence in the Finnish population. It is a lifelong condition affecting on the patient's appearance, cognition, adaptive skills, physical growth, personality, body structure, and health. An infantile growth spurt and development of macrocephalia associated to hernias and respiratory infections are the key signs to an early identification of AGU. Progressive intellectual and physical disability is the main symptom leading to death usually before the age of 50 years.The disease is caused by the deficient activity of the lysosomal enzyme glycosylasparaginase (aspartylglucosaminidase, AGA), which leads to a disorder in the degradation of glycoasparagines - aspartylglucosamine or other glycoconjugates with an aspartylglucosamine moiety at their reducing end - and accumulation of these undegraded glycoasparagines in tissues and body fluids. A single nucleotide change in the AGA gene resulting in a cysteine to serine substitution (C163S) in the AGA enzyme protein causes the deficiency of the glycosylasparaginase activity in the Finnish population. Homozygosity for the single nucleotide change causing the C163S mutation is responsible for 98% of the AGU cases in Finland simplifying the carrier detection and prenatal diagnosis of the disorder in the Finnish population. A mouse strain, which completely lacks the Aga activity has been generated through targeted disruption of the Aga gene in embryonic stem cells. These Aga-deficient mice share most of the clinical, histopathologic and biochemical characteristics of human AGU disease. Treatment of AGU mice with recombinant AGA resulted in rapid correction of the pathophysiologic characteristics of AGU in non-neuronal tissues of the animals. The accumulation of aspartylglucosamine was reduced by up to 40% in the brain tissue of the animals depending on the age of the animals and the therapeutic protocol. Enzyme replacement trials on human AGU patients have not been reported so far. Allogenic stem cell transplantation has not proved effective in curing AGU.

Human leukocyte glycosylasparaginase: cell-to-cell transfer and properties in correction of aspartylglycosaminuria

Aspartylglycosaminuria (AGU), a severe lysosomal storage disease, is caused by the deficiency of the lysosomal enzyme, glycosylasparaginase (GA), and accumulation of aspartylglucosamine (GlcNAc-Asn) in tissues. Here we show that human leukocyte glycosylasparaginase can correct the metabolic defect in Epstein-Barr virus (EBV)-transformed AGU lymphocytes rapidly and effectively by mannose-6-phosphate receptor-mediated endocytosis or by contact-mediated cell-to-cell transfer from normal EBV-transformed lymphocytes, and that 2-7% of normal activity is sufficient to correct the GlcNAc-Asn metabolism in the cells. Cell-to-cell contact is obligatory for the transfer of GA since normal transformed lymphocytes do not excrete GA into extracellular medium. The combined evidence indicates that cell-to-cell transfer of GA plays a main role in enzyme replacement therapy of AGU by normal lymphocytes.

A mouse model for the human lysosomal disease aspartylglycosaminuria

Aspartylglycosaminuria (AGU), the most common disorder of glycoprotein degradation in humans, is caused by mutations in the gene encoding the lysosomal enzyme glycosylasparaginase (Aga). The resulting enzyme deficiency allows aspartylglucosamine (GlcNAc-Asn) and other glycoasparagines to accumulate in tissues and body fluids, from early fetal life onward. The clinical course is characterized by normal early development, slowly progressing to severe mental and motor retardation in early adulthood. The exact pathogenesis of AGU in humans is unknown and neither therapy nor an animal model for this debilitating and ultimately fatal disease exists. Through targeted disruption of the mouse Aga gene in embryonic stem cells, we generated mice that completely lack Aga activity. At the age of 5-10 months a massive accumulation of GlcNAc-Asn was detected along with lysosomal vacuolization, axonal swelling in the gracile nucleus and impaired neuromotor coordination. A significant number of older male mice had massively swollen bladders, which was not caused by obstruction, but most likely related to the impaired function of the nervous system. These findings are consistent with the pathogenesis of AGU and provide further data explaining the impaired neurological function in AGU patients.

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)

Use of dabsylation, column switching and chiral separation for the determination of a renin inhibitor in rat, marmoset and human plasma

A high-performance liquid chromatographic method with column switching was developed for the determination of the renin inhibitor Ro 42-5892/001, (S)-alpha-[(S)-alpha-[(tert.-butylsulphonyl)methyl]hydrocinnama mido]-N- [(1S,2R,3S)-1-(cyclohexylmethyl)-3-cylcopropyl-2, 3-dihydroxypropyl]imidazole-4-propionamide methanesulphonate (1:1), in rat, marmoset and human plasma, using a Nucleosil C8 120 (3 microns) stationary phase. Since the analyte and the internal standard are optical isomers, beta-cyclodextrin was used as a mobile phase constituent for their chiral separation. The method took advantage of the characteristics of dabsyl chloride derivatives, namely sensitivity, specificity and, particularly, stability, providing a quantification limit of 5 ng/ml. The accuracy (range of inaccuracy 1-13%) and the inter-assay precision (coefficient of variation range 1.8-9.1%) were acceptable. The method was successfully applied to toxicokinetic studies in rats and marmosets.