GM1-ganglioside beta-galactosidase in leukocytes and cultured fibroblasts

Leukocyte lysosomal enzymes in Alzheimer's disease and Down's syndrome

Previous studies suggested the possibility of accelerated lysosomal degradation of brain gangliosides in Alzheimer's disease (AD). As AD pathology affects both neural and nonneural tissues, the aim of this study was to determine possible changes of glycosphingolipid metabolism in available peripheral cells in AD and Down's syndrome (DS). The activities of several lysosomal enzymes involved in catabolism of gangliosides and sulfatides were measured in leukocytes from subjects with dementia of the Alzheimer type, DS, and age-matched controls, by fluorimetry and spectrophotometry using specific substrates. The results showed a statistically significant increase of beta-galactosidase activity in both dementia of the Alzheimer type and DS leukocytes when compared with age-matched controls (p <.01 and p <.05, respectively; Student's t test). Not significantly increased activities of beta-galactosidase, beta-hexosaminidase, beta-hexosaminidase A, and slightly decreased activity of arylsulfatase A were observed in control leukocytes with aging. Our results indicate that a metabolic dysfunction and the acceleration of at least some lysosomal catabolic pathways are present in AD and DS nonneural cells.

Effect of collection, transport, processing and storage of blood specimens on the activity of lysosomal enzymes in plasma and leukocytes

This study was designed to evaluate the effect of different conditions of collection, transport and storage on the quality of blood samples from normal individuals in terms of the activity of the enzymes ss-glucuronidase, total hexosaminidase, hexosaminidase A, arylsulfatase A and ss-galactosidase. The enzyme activities were not affected by the different materials used for collection (plastic syringes or vacuum glass tubes). In the evaluation of different heparin concentrations (10% heparin, 5% heparin, and heparinized syringe) in the syringes, it was observed that higher doses resulted in an increase of at least 1-fold in the activities of ss-galactosidase, total hexosaminidase and hexosaminidase A in leukocytes, and ss-glucuronidase in plasma. When the effects of time and means of transportation were studied, samples that had been kept at room temperature showed higher deterioration with time (72 and 96 h) before processing, and in this case it was impossible to isolate leukocytes from most samples. Comparison of heparin and acid citrate-dextrose (ACD) as anticoagulants revealed that ss-glucuronidase and hexosaminidase activities in plasma reached levels near the lower normal limits when ACD was used. In conclusion, we observed that heparin should be used as the preferable anticoagulant when measuring these lysosomal enzyme activities, and we recommend that, when transport time is more than 24 h, samples should be shipped by air in a styrofoam box containing wet ice.

Characterization of beta-galactosidase in leukocytes and fibroblasts of GM1 gangliosidosis heterozygotes compared to normal subjects

OBJECTIVES

Characterization of beta-galactosidase in leukocytes and fibroblasts of heterozygotes for GM1 type I.

DESIGN AND METHODS

Leukocyte and fibroblast beta-galactosidase activity was determined fluorimetrically using 4-methylumbelliferyl-beta-D-galactoside as an artificial substrate. Optimum pH, Km, Vmax and thermostability of the enzyme at 42 degrees C were determined.

RESULTS

The leukocyte and fibroblast enzyme of heterozygotes have an optimum pH of 4.0 and 4.2, respectively. In normal subjects, the optimum pH was 4.2 in both cells, according to previous studies. The Km of the enzyme of heterozygotes was determined to be 0.65 mM in leukocytes and 0.59 mM in fibroblasts. The Vmax was determined in 167.21 nmol/h/mg of protein in heterozygotes leukocytes and 541.2 nmol/h/mg of protein in heterozygotes fibroblasts compared to 291.7 and 1768.1 nmol/h/mg of protein in controls leukocytes and fibroblasts, respectively. When leukocyte and fibroblast heterozygote beta-galactosidase was preincubated at 42 degrees C, after 80 min the residual activity was determined to be 25 to 30% of the initial activity. These results are similar to the control group.

CONCLUSIONS

We have found significant differences between the two groups in some investigated parameters. Both fibroblasts and leukocytes showed a virtually similar level of reliability as source of enzyme for the detection of heterozygotes.

A case of GM1 gangliosidosis type I

A six-month-old female gypsy child, the daughter of second degree cousins, born after a full-term pregnancy and normal delivery, is described. There was generalized neonatal edema. Abnormalities included psychomotor retardation from birth and progressive appearance of facial dysmorphism, organ enlargement, axial hypotonia, hypertonia in limbs, myoclonic jerks, optic atrophy and bilateral cherry-red spots. The diagnosis of GM1 type 1 gangliosidosis was confirmed by biochemical, enzymatic and ultrastructural findings.

Neurovisceral and skeletal GM1-gangliosidosis in dogs with beta-galactosidase deficiency

Beta-galactosidase-deficient siblings in two litters of English springer spaniel puppies showed a progressive neurological impairment, dwarfism, orbital hypertelorism, and dysostosis multiplex. An excess of GM1-ganglioside was found in the brain. Three abnormal oligosaccharides were present in samples of urine, brain, liver, and cartilage. Light microscopy of selected tissue specimens revealed cytoplasmic vacuoles in neurons, circulating blood cells, macrophages, and chondrocytes. Ultrastructural studies demonstrated that these membrane-bound vacuoles were of two types--one containing lamellated membranes and the other, finely granular material. These clinical and pathological findings are similar to those observed in human patients affected by the infantile form of GM1-gangliosidosis.

A fluorometric microassay procedure for monitoring the enzymatic activity of GM1-ganglioside beta-galactosidase by use of high-performance liquid chromatography

For the measurement of the enzymatic activity of GM1-ganglioside (II3 NeuAcGgOse4Cer, galactosyl-N-acetylgalactosaminyl-(N-acetylneuraminosyl) galactosyl-glucosylceramide) beta-galactosidase in crude enzyme samples, a microassay using nonradioisotopic GM1-ganglioside was devised. To reduce the volume of the reaction mixture and eliminate the interferences due to the fluorescent contaminants in the reaction mixture, NADH, a product after the oxidation of the released galactose with NAD and beta-galactose dehydrogenase, was fluorometrically estimated by use of high-performance liquid chromatography. By this method, as little as 10 pmol of galactose can be detected. Using rat brain homogenates as an enzyme sample, the several parameters were reexamined to define the optimal conditions for the assay. This assay method was also applied to human cultured skin fibroblast homogenates, and it was found that this method can be used for the diagnosis of GM1-gangliosidosis, instead of the usual method using the radioisotope-labeled natural substrate.

Diagnosis of Tay-Sachs disease using [3H]N-acetylneuraminic acid labelled GM2 ganglioside as substrate

GM2 ganglioside labelled with tritium in the N-acetylneuraminic acid moiety was prepared and used to measure beta-hexosaminidase A activity in cultured humans skin fibroblasts extracts. The latter convert this substrate to the correspondingly labelled GM3 ganglioside which can easily be separated from the substrate by thin-layer chromatography. No cleavage of the N-acetylneuraminic acid group was observed under our conditions. Two methods are described for the determination of GM2-beta-hexosaminidase A activity in fibroblasts. The application of these methods to the diagnosis of Tay-Sachs disease is discussed.

GM1 gangliosidosis: phenotypic variation in a single family

Infantile, juvenile, and adult forms of GM1 gangliosidosis have been well characterized. Certain genetic and biochemical studies have suggested that the phenotypic variation found in GM1 gangliosidosis results from different allelic mutations affecting the GM1 ganglioside beta-galactosidase locus and that different combinations of these mutations accounts for the clinical heterogeneity of this illness. A family in which both the infantile and juvenile forms of GM1 gangliosidosis occurred, the children sharing a common mutation of their acid beta-galactosidase activity, supports the allelic nature of these different clinical forms of the disease. From the observations made in this unique family, additional phenotypes of GM1 gangliosidosis might be anticipated.

Biochemistry and genetics of gangliosidoses

The gangliosidoses comprise an-ever increasing number of biochemically and phenotypically variant diseases. In most of them an autosomal recessive inherited deficiency of a lysosomal hydrolase results in the fatal accumulation of glucolipids (predominantly in the nervous tissue) and of oligosaccharides. The structure, substrate specificity, immunological properties of and genetic studies on the relevant glycosidases, ganglioside GM1 beta-galactosidase and beta-hexosaminidase isoenzymes, are reviewed in this paper. Contrary to general expectation, only a poor correlation is observed between the severity of the disease and residual activity of the defective enzyme when measured with synthetic or natural substrates in the presence of detergents. For the understanding of variant diseases and for their pre- and postnatal diagnosis, the necessity of studying the substrate specificity of normal and mutated enzymes under conditions similar to the in vivo situation, e.g., with natural substrates in the presence of appropriate activator proteins, is stressed. The possibility that detergents may have adverse affects on the substrate specificity of the enzymes is discussed for the beta-hexosaminidases. The significance of activator proteins for the proper interaction of lipid substrates and water-soluble hydrolases is illustrated by the fatal glycolipid storage resulting from an activator protein deficiency in the AB variant of GM2-gangliosidosis. Recent somatic complementation studies have revealed the existence of a presumably post-translational modification factor necessary for the expression of ganglioside GM1 beta-galactosidase activity. This factor is deficient in a group of variants of GM1-glangliosidosis. Among the possible reasons for the variability of enzyme activity levels in heterozygotes and patients, allelic mutations, formation of hybrid enzymes, and the existence of patients as compound heterozygotes are discussed. All these may result in the production of mutant enzymes with an altered specificity for a variety of natural substrates.