Multiple glycosidase deficiencies in a case of juvenile (type 3) Gaucher disease

Molecular cloning of Chinese hamster ceramide glucosyltransferase and its enhanced expression in peroxisome-defective mutant Z65 cells

To clarify the metabolic bases of characteristic increases in the concentrations of glucosylceramide (CMH) and GM3 in peroxisome-defective mutant Chinese hamster ovary (CHO) cells (Z65), we measured the ceramide glucosyltransferase (CGT) and beta-glucosidase activities in Z65 and CHO-K1 cells, and found that the former enzyme was responsible for the accumulation of CMH in Z65 cells. Inhibition of CGT by D,L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) caused a marked reduction in a incorporation of [3-14C]serine to CMH in both CHO-K1 and Z65 cells, but resulted in the accumulation of ceramide in Z65 cells in a concentration higher than that in CHO-K1 cells. Then, we cloned the cDNA encoding CGT from CHO-K1 cells, which exhibited sequence homology with the human gene product (98.7%). Northern blot analysis of CGT revealed increased expression of it in Z65 cells compared with that in CHO-K1 cells, which probably caused the simultaneous increase in GM3. With an immunohistochemical procedure, GM3 was found to be more strongly expressed in the cell membrane of Z65 cells than in CHO-K1 cells.

Increased activity of lysosomal glycohydrolases in glioma tissue and surrounding areas from human brain

Increased metabolic activity represented by an increase in both anabolism and catabolism in tumours, including gliomas, is a well known phenomenon and utilised in positron emission tomography imaging of tumours. In this study lysosomal enzyme activities of some glycohydrolases were investigated in glioma tissue from human brain. Tumour tissue (ten cases) and brain tissue surrounding the tumour tissue (seven cases) from patients with a histopathological diagnosis of glioblastoma multiforme or anaplastic astrocytoma were analysed for activity of the lysosomal enzymes galactosylceramidase, glucosylceramidase, beta-galactosidase, beta-N-acetyl-glucosaminidase, beta-glucuronidase and acid phosphatase. All of the investigated lysosomal enzymes except galactosylceramidase showed increased activity compared with that in normal brain tissue. Moreover, despite sparsity of tumour cells the specimens taken from surrounding areas showed elevated activities of the same enzymes. The findings indicate an upregulation of the activity not only in tumour but also in normal cells of the surrounding area.

Human glucocerebrosidase catalyses transglucosylation between glucocerebroside and retinol

The basal activity of human placental glucocerebrosidase is elevated 16-fold by n-pentanol when assayed using p-nitrophenyl beta-D-glucopyranoside (pNPGlc) as the beta-glucosidase substrate. This enhancement of activity is the result of the formation of a transglucosylation product, n-pentyl beta-D-glucoside, in rate-determining competition with the hydrolytic reaction. The transglucosylation product accounts for approximately 80% of the reaction product generated in the presence of n-pentanol (0.18 M) when either glucocerebroside or pNPGlc was used as the substrate. This stimulatory effect can be increased an additional 3-fold by the inclusion of phosphatidylserine (20 micrograms/ml) or sodium taurodeoxycholate (0.3%, w/v) in the incubation medium. In the presence of retinol, glucocerebrosidase also catalyses the synthesis of a novel lipid glucoside, retinyl glucoside, when either glucocerebroside or pNPGlc serves as the substrate. The reaction product was identified as retinyl beta-D-glucoside, based on its susceptibility to hydrolysis by almond beta-D-glucosidase and the subsequent release of equimolar amounts of retinol and glucose. The rate of retinyl-beta-glucoside formation is dependent on the concentration of retinol in the incubation medium, reaching saturation at approximately 0.3 mM retinol. Retinyl beta-D-glucoside is a substrate for two broad-specificity mammalian beta-glucosidases, namely the cytosolic and membrane-associated beta-glucosidases of guinea pig liver. However, retinyl beta-D-glucoside is not hydrolysed by placental glucocerebrosidase. These data indicate that the glucocerebrosidase-catalysed transfer of glucose from glucocerebroside to natural endogenous lipid alcohols, followed by the action of a broad-specificity beta-glucosidase on the transglucosylation product, could provide mammals with an alternative pathway for the breakdown of glucocerebroside to glucose and ceramide.

Mutations causing Gaucher disease

Glucocerebrosidase is a lysosomal enzyme responsible for hydrolysis of glucosylceramide to ceramide and glucose. Mutations disrupting the function of this enzyme cause autosomal recessive Gaucher disease. This disease is very heterogeneous. The clinical heterogeneity is due to a large number of mutations within the gene encoding glucocerebrosidase. To date 36 mutations have been described in Gaucher disease. In this part we present the mutations and review the more common ones. We also review the glucocerebrosidase natural activator, designated saposin C and mutations in its gene, associated with Gaucher disease.

Hydrocephalus, corneal opacities, deafness, valvular heart disease, deformed toes and leptomeningeal fibrous thickening in adult siblings: a new syndrome associated with beta-glucocerebrosidase deficiency and a mosaic population of storage cells

We describe three adult siblings with communicating hydrocephalus, corneal opacities, deafness, valvular heart disease, and deformed toes associated with glucosylceramide (glc-cer)-beta-glucosidase deficiency. The common manifestations of Gaucher disease were not evident. Supranuclear gaze palsies characteristic of type 3 were noted from early childhood, although the major signs were undeveloped until early adult life. Autopsy disclosed thickened leptomeninges with perivascular fibrosis, non-rheumatic calcified aortic and mitral stenosis with marked fibrosis, and mild infiltration of Gaucher cells in the reticuloendothelial organs. In contrast to the slight accumulation of glc-cer in the liver and spleen, the activity of glc-cer-beta-glucosidase was markedly decreased in the tissues, as much as in a patient with type 2 Gaucher disease. Common mutations were not found in the glucocerebrosidase gene.

Amniotic tissue transplantation: clinical and biochemical evaluations for some lysosomal storage diseases

Amniotic epithelial cells has been used for transplantation in patients with lysosomal storage diseases as an enzyme replacement therapy. But its clinical effect is still the question under debate. We performed amniotic tissue transplantation on patients with different lysosomal storage diseases: one with Tay-Sachs disease, one with juvenile Gaucher disease and one with juvenile metachromatic leukodystrophy. The patient having juvenile Gaucher disease received this grafting twice. Objective clinical improvement was observed in the first trial where this patient showed an increase of soluble beta-glucosidase one week after implantation. No clinical or biochemical changes were seen in the other patients. Although there are some advantages to amniotic tissue transplantation, original methods should be modified to cell transplantation in order to avoid graft-versus-host reaction which could happen in repeated implantation.

The occurrence of two immunologically distinguishable beta-glucocerebrosidases in human spleen

The beta-glucosidase activity in spleen from control subjects and patients with different clinical phenotypes of Gaucher's disease was characterized. The occurrence of a soluble non-specific beta-glucosidase with a neutral pH optimum and two membrane-associated beta-glucocerebrosidases with an acid pH optimum was demonstrated. The two beta-glucocerebrosidases can be distinguished on the basis of their ability to react with anti-(placental beta-glucocerebrosidase) antibodies bound to protein-A--Sepharose 4B beads. One of the splenic beta-glucocerebrosidases (form I) is precipitated by the immobilized antibodies and the other (form II) is not. The two forms also differ in binding affinity to concanavalin A, degree of stimulation of enzymic activity by taurocholate and isoelectric point. In contrast, the Km values of the two beta-glucocerebrosidases for natural and artificial substrates are similar and both are inhibited by conduritol B-epoxide. In spleen from three patients with type 1, one patient with type 2 and one patient with type 3 Gaucher's disease form I beta-glucocerebrosidase was found to be clearly deficient, whereas the activity of form II was 25-50% of that in control spleen. The non-specific, neutral beta-glucosidase was not deficient in these Gaucher spleens. The distinct biochemical and immunological properties of non-specific beta-glucosidase and the fact that normal levels of the enzyme are present in patients with Gaucher's disease indicate, in confirmation of previous reports, that non-specific beta-glucosidase is not related to beta-glucocerebrosidase.

Gaucher disease: the effects of phosphatidylserine on glucocerebrosidase from normal and Gaucher fibroblasts

Glucocerebroside beta-glucosidase (glucocerebrosidase) activity was assayed from cultured fibroblasts of normal individuals, and patients with type 1 (non-neuropathic), type 2 (acute neuropathic), and type 3 (subacute neuropathic) form of Gaucher disease. Residual glucocerebrosidase activity of patients was 8.9 to 17.4% of normal controls, and there was no clear correlation between the level of residual enzyme activity and the different clinical subtypes of the disease. When membrane-bound glucocerebrosidase activity was assayed in the presence of crude brain lipid extracts or purified phosphatidylserine, enzyme from both the normal and type 1 Gaucher fibroblasts was stimulated dramatically (35-60% by crude extracts, 85-90% by phosphatidylserine). This stimulation was not observed with fibroblast glucocerebrosidase of an infantile type 2 and two juvenile type 3 Gaucher patients. The presence of inhibitors of glucocerebrosidase in these type 2 and type 3 Gaucher cells was not detected. Contrary to the mutant enzyme from these Gaucher fibroblasts, glucocerebrosidase from fibroblasts of two adult type 3 Gaucher patients with cerebral involvement was stimulated substantially (72-85%) by phosphatidylserine. When membrane-bound glucocerebrosidase from fibroblasts of the infantile type 2 and juvenile type 3 patients was solubilized with sodium cholate (1% w/v) and delipidated, the phospholipid stimulation of enzyme activity was restored. These findings suggest that considerable clinical and biochemical heterogeneity exists among patients with neuropathic Gaucher disease and that phosphatidylserine activation cannot be used as a reliable indicator in predicting future onset of neurodegeneration in Gaucher patients. The possibility of an aberrant binding of mutant glucocerebrosidase to the lysosomal membrane in juvenile type 3 form of Gaucher disease is discussed.

Multiple forms of membrane-bound beta-glucosidase in Gaucher's disease

Two forms of membrane-bound beta-glucosidase in the spleen of normal individuals were distinguished by their thermostability properties. The heat-labile form A predominates; it catalyzes the hydrolysis of the natural substrate, glucosylceramide, and is activated by the detergent, sodium taurocholate. The minor heat-stable form B is inactive against glucosylceramide and is inhibited by taurocholate. The activity of form A increases from childhood to adult life, as does the activity of the soluble beta-glucosidase and of glucosylceramide beta-glucosidase. In the spleen of nine patients with different types of Gaucher's disease the residual membrane-bound beta-glucosidase was predominantly heat-stable and inhibited by taurocholate. There was no clear correlation between the properties of the residual enzyme in the different types of the disorder and their respective clinical severity. The results are discussed in relation to the biochemical pathogenesis and the enzymatic diagnosis of Gaucher's disease.

Gaucher disease. III. Substrate specificity of glucocerebrosidase and the use of nonlabeled natural substrates for the investigation of patients

A reproducible and convenient method for assaying glucocerebrosidase activity using the natural substrates has been developed. From the insoluble pellet fraction of cultured skin fibroblast homogenates, released glucose was measured enzymically using hexokinase coupled with the glucose-6-phosphate dehydrogenase (G6PD) and nicotinamide adenine dinucleotide phosphate (NADP) system. Optimal enzyme assay conditions required both Triton X-100 and sodium taurocholate, pH 4.8. Glucocerebrosidase activities from three patients with type 1 Gaucher disease were 17.5%, 15.8%, and 11.2% of normal (normal = 198 +/- 14 nmol/hr per mg protein, n = 3). The first patient had normal beta-glucosidase activity with the artificial fluorogenic umbelliferone substrate. Interference with the accuracy of the glucose-dependent assay system by either glycolytic or gluconeogenic enzyme activites was not detected under these experimental conditions, and when substrates with long fatty-acid chain lengths (C = 22) were used, markedly decreased glucocerebrosidase activity occurred in both normal individuals and patients. The apparent Km's for the natural substrates were 0.56 +/- 0.05 mM for controls and 2.2-3.3 mM for Gaucher fibroblasts. These data further support the hypothesis that a structurally altered and catalytically deficient enzyme is synthesized in patients with type 1 Gaucher disease and illustrate the value of the natural substrate in investigating patients.