Intermediate forms of human beta-N-acetylhexosaminidase lack activity towards 4-methylumbelliferyl beta-N-acetylglucosaminide 6-sulphate

HexA-Enzyme Coated Polymer Nanoparticles for the Development of a Drug-Delivery System in the Treatment of Sandhoff Lysosomal Storage Disease

Lysosomal storage disorders (LSDs) are a set of metabolic diseases caused by mutations in genes that are in charge of the production of lysosomal enzymes, resulting in the buildup of non-degraded substrates and the consequent systemic damage that mainly involves the Central Nervous System (CNS). One of the most widely used and studied treatments is Enzyme Replacement Therapy, which is based on the administration of the recombinant deficient enzyme. This strategy has often proved fallacious due to the enzyme instability in body fluids and its inability to reach adequate levels in the CNS. In this work, we developed a system based on nanotechnology that allows a stable enzyme to be obtained by its covalent immobilization on nanoparticles (NPs) of polylactic acid, subsequently administered to a cellular model of LSDs, i.e., Sandhoff disease, caused by the absence or deficiency of the β-d-N-acetyl-hexosaminidase A (HexA) enzyme. The HexA enzymes, loaded onto the polymeric NPs through an immobilization procedure that has already been investigated and validated, were found to be stable over time, maintain optimal kinetic parameters, be able to permeate the plasma membrane, hydrolyze HexA’s natural substrate, and restore enzyme activity close to the levels of healthy cells. These results thus lay the foundation for testing the HexA-NPs in animal models of the disease and thus obtaining an efficient drug-delivery system.

Lysosomal Ceramide Metabolism Disorders: Implications in Parkinson's Disease

Ceramides are a family of bioactive lipids belonging to the class of sphingolipids. Sphingolipidoses are a group of inherited genetic diseases characterized by the unmetabolized sphingolipids and the consequent reduction of ceramide pool in lysosomes. Sphingolipidoses include several disorders as Sandhoff disease, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann Pick disease, Farber disease, and GM2 gangliosidosis. In sphingolipidosis, lysosomal lipid storage occurs in both the central nervous system and visceral tissues, and central nervous system pathology is a common hallmark for all of them. Parkinson’s disease, the most common neurodegenerative movement disorder, is characterized by the accumulation and aggregation of misfolded α-synuclein that seem associated to some lysosomal disorders, in particular Gaucher disease. This review provides evidence into the role of ceramide metabolism in the pathophysiology of lysosomes, highlighting the more recent findings on its involvement in Parkinson’s disease.

Enhancement of Lysosomal Glycohydrolase Activity in Human Primary B Lymphocytes during Spontaneous Apoptosis

It has been shown that lysosomes are involved in B cell apoptosis but lysosomal glycohydrolases have never been investigated during this event. In this study we determined the enzymatic activities of some lysosomal glycohydrolases in human tonsil B lymphocytes (TBL) undergoing in vitro spontaneous apoptosis. Fluorimetric methods were used to evaluate the activities of β-hexosaminidases, α-mannosidase, β-mannosidase, β-galactosidase, β-glucuronidase and α-fucosidase. Results show that in TBL during spontaneous apoptosis, there is a significant increase in the activity of β-hexosaminidases, α-mannosidase, β-mannosidase and β-galactosidase. Also β-glucuronidase and α-fucosidase activities increase but not in a significant manner. Further studies on β-hexosaminidases revealed that also mRNA expression of the α- and β-subunits, which constitute these enzymes, increases during spontaneous TBL apoptosis. When TBL are protected from apoptosis by the thiol molecule N-acetyl-L-cysteine (NAC), there is no longer any increase in glycohydrolase activities and mRNA expression of β-hexosaminidase α- and β-subunits. This study demonstrates for the first time that the activities and expression of some lysosomal glycohydrolases are enhanced in TBL during spontaneous apoptosis and that these increases are prevented when TBL apoptosis is inhibited.

Hypermethylation contributes to down-regulation of lysosomal β-hexosaminidase α subunit in prostate cancer cells

β-Hexosaminidase, involved in degradation of glycoproteins and glycosphingolipids, is altered in several tumours leading to enhanced migration capacity. To date, the expression of the β-hexosaminidase isoenzymes in prostate cancer cells has not been elucidated. By using PC3, LNCaP, DUCaP, MDAPCa 2b, and hyperplasic prostate (BPH-1) cell lines, we analysed the β-hexosaminidase activity in each cell line and determined β-hexosaminidase α subunit gene expression in PC3, LNCaP, and BPH-1. We then investigated the methylation status of the gene promoter and determined the cellular responses of PC3 and LNCaP after transfection with β-hexosaminidase α subunit. We found that each prostate cancer cell line had a decrease in total hexosaminidase activity and that the lack of hexosaminidase A activity, observed in PC3 and LNCaP cells, was associated with mRNA disappearance. The HEXA promoter region in LNCaP and PC3 cell lines had methylated CpG islands, as confirmed by 5'-Aza-2'-deoxycitidine treatment, in PC3 cells, used as cell cancer model. We also tested, the involvement of hexosaminidase A in the migration capacity by migration assay using Hex α subunit-transfected PC3. Finally, we found that, after Hex α subunit transfection, both PC3 and LNCaP were less susceptible to exogenous ceramide treatment. Results indicate a likely contribution of the lysosomal enzyme to the acquisition of cancerous features.

Molecular cloning and crystal structural analysis of a novel beta-N-acetylhexosaminidase from Paenibacillus sp. TS12 capable of degrading glycosphingolipids

We report the molecular cloning and characterization of two novel beta-N-acetylhexosaminidases (beta-HEX, EC 3.2.1.52) from Paenibacillus sp. strain TS12. The two beta-HEXs (Hex1 and Hex2) were 70% identical in primary structure, and the N-terminal region of both enzymes showed significant similarity with beta-HEXs belonging to glycoside hydrolase family 20 (GH20). Interestingly, however, the C-terminal region of Hex1 and Hex2 shared no sequence similarity with the GH20 beta-HEXs or other known proteins. Both recombinant enzymes, expressed in Escherichia coli BL21(DE3), hydrolyzed the beta-N-acetylhexosamine linkage of chitooligosaccharides and glycosphingolipids such as asialo GM2 and Gb4Cer in the absence of detergent. However, the enzyme was not able to hydrolyze GM2 ganglioside in the presence or in the absence of detergent. We determined three crystal structures of Hex1; the Hex1 deletion mutant Hex1-DeltaC at a resolution of 1.8 A; Hex1-DeltaC in complex with beta-N-acetylglucosamine at 1.6 A; and Hex1-DeltaC in complex with beta-N-acetylgalactosamine at 1.9 A. We made a docking model of Hex1-DeltaC with GM2 oligosaccharide, revealing that the sialic acid residue of GM2 could hinder access of the substrate to the active site cavity. This is the first report describing the molecular cloning, characterization and X-ray structure of a procaryotic beta-HEX capable of hydrolyzing glycosphingolipids.

Widespread distribution of beta-hexosaminidase activity in the brain of a Sandhoff mouse model after coinjection of adenoviral vector and mannitol

Sandhoff disease is a severe inherited neurodegenerative disorder resulting from deficiency of the beta-subunit of hexosaminidases A and B, lysosomal hydrolases involved in the degradation of G(M2) ganglioside and related metabolites. Currently, there is no viable treatment for the disease. Here, we show that adenovirus-mediated transfer of the beta-subunit of beta-hexosaminidase restored Hex A and Hex B activity after infection of Sandhoff fibroblasts. Gene transfer following intracerebral injection in a murine model of Sandhoff disease resulted in near-normal level of enzymatic activity in the entire brain at the different doses tested. The addition of hyperosmotic concentrations of mannitol to the adenoviral vector resulted in an enhancement of vector diffusion in the injected hemisphere. Adenoviral-induced lesions were found in brains injected with a high dose of the vector, but were not detected in brains injected with 100-fold lower doses, even in the presence of mannitol. Our data underline the advantage of the adjunction of mannitol to low doses of the adenoviral vector, allowing a high and diffuse transduction efficiency without viral cytotoxicity.

Absence of metabolic cross-correction in Tay-Sachs cells: implications for gene therapy

We have investigated the ability of a receptor-mediated gene transfer strategy (cross-correction) to restore ganglioside metabolism in fibroblasts from Tay-Sachs (TS) patients in vitro. TS disease is a GM2 gangliosidosis attributed to the deficiency of the lysosomal enzyme beta-hexosaminidase A (HexA) (beta-N-acetylhexosaminidase, EC ). The hypothesis is that transduced cells overexpressing and secreting large amounts of the enzyme would lead to a measurable activity in defective cells via a secretion-recapture mechanism. We transduced NIH3T3 murine fibroblasts with the LalphaHexTN retroviral vector carrying the cDNA encoding for the human Hex alpha-subunit. The Hex activity in the medium from transduced cells was approximately 10-fold higher (up to 75 milliunits) than observed in non-transduced cells. TS cells were cultured for 72 h in the presence of the cell medium derived from the transduced NIH3T3 cells, and they were analyzed for the presence and catalytic activity of the enzyme. Although TS cells were able to efficiently uptake a large amount of the soluble enzyme, the enzyme failed to reach the lysosomes in a sufficient quantity to hydrolyze the GM2 ganglioside to GM3 ganglioside. Thus, our results showed that delivery of the therapeutic HexA was not sufficient to correct the phenotype of TS cells.

Beta-N-acetylhexosaminidase activity and isoenzyme profile in the kidney and urine of trained rats

Lysosomes play an important role in the immune system functioning and are involved in different aspects of inflammatory reaction, repair processes and tissue damage at various levels. Among various effects, it is known that physical exercise influences the release of different lysosomal components. The aim of this study was to evaluate enzyme activity and isoenzymatic profile of beta-N-acetylhexosaminidase both in kidney and urine of normal and trained rats. Enzyme activity was measured by fluorimetric assay while beta-N-acetylhexosaminidase isoenzymes were separated using DEAE-cellulose chromatography. Hexosaminidase specific activity was significantly increased in urine of trained rats whereas there was no increase in the kidneys of trained rats. Indeed, no significant differences were observed in the isoenzyme profile of kidney and urine extracts from normal and trained rats. Our findings suggest the exercise-induced release of lysosomal enzymes is a functional effect and not due to disruption of lysosomal membranes.

Relationship between plasma ammonia concentration and beta-N-acetylhexosaminidase isoenzyme activities in liver cirrhosis

Ammonia is known to increase the secretion of beta-N-acetylhexosaminidase (Hex) to the extracellular medium in cultured human fibroblasts and Hep G2 cells. We examined 35 patients with liver cirrhosis and the results revealed a significant increase for the plasma activities of total Hex and its isoenzymes Hex A and Hex B (p < 0.001). The partial correlations, with other biochemical markers of liver injury constant, between plasma ammonia concentration and the activity (r = 0.658) and the proportion in percentage of the Hex B isoenzyme (r = 0.692) were statistically significant (p < 0.001). The increased concentration of ammonia could explain, at least partially, an increased secretion of Hex B isoforms to the plasma in patients with liver disease.

beta-hexosaminidase, alpha-D-mannosidase, and beta-mannosidase expression in serum from patients with carbohydrate-deficient glycoprotein syndrome type I

The activity of beta-hexosaminidase, determined with 4-methylumbelliferyl-beta-N-acetylglucopyranoside substrate, and of beta-D-mannosidase was significantly higher in the serum of patients with carbohydrate-deficient glycoprotein (CDG) syndrome type IA (phosphomannomutase deficiency) than in controls. No significant differences were observed in the activity of beta-hexosaminidase, determined using 4-methylumbelliferyl-beta-N-acetylglucopyranoside-6-sulphate as substrate, and the activity of alpha-D-mannosidase. Using DEAE-cellulose chromatography, a greater amount of hexosaminidase B than hexosaminidase A was detected in CDG serum. In CDG serum, hexosaminidase A was eluted in a more basic position in the salt gradient. An isoenzyme of alpha-D-mannosidase and beta-D-mannosidase was identified in control and CDG sera. alpha-D-Mannosidase isoenzyme was eluted in a slightly more basic position in CDG serum than in control serum, whereas beta-D-mannosidase isoenzyme was eluted in the same position.

Elevated beta-N-acetylhexosaminidase activity in focal dystonia fibroblasts

Specific activities of beta-D-hexosaminidase, alpha-D-mannosidase, beta-D-galactosidase and beta-D-glucuronidase were determined in fibroblasts of patients with writer's cramp and torticollis. These diseases show degenerative neurological disorders similar to those observed in lysosomal diseases. Hexosaminidase specific activities, determined using 4-methylumbelliferyl-beta-N-acetylglucopyranoside and 4-methylumbelliferyl-beta-N-acetylglucopyranoside-6-sulphate as substrates, were significantly higher in the fibroblasts of patients than in controls. No significant differences were observed in the specific activities of the other lysosomal enzymes. The increased hexosaminidase specific activities in torticollis and writer's cramp may be additional markers for these diseases.

Glycosaminoglycan metabolism and cytokine release in normal and otosclerotic human bone cells interleukin-1 treated

Glycosaminoglycans (GAGs), normal components of the extracellular matrix (ECM), and the glycosidases, that degrade them, play a key role in the bone remodelling process. The effects of interleukin-1 alpha (IL-1 alpha) on GAG metabolism in normal and otosclerotic human bone cells as well as its capacity to modulate IL-1 alpha, IL-1 beta and IL-6 secretion in both populations was analyzed. The amount of radiolabeled GAGs was lower in otosclerotic than in normal bone cells. IL-1 alpha reduced newly synthesized cellular and extracellular GAGs in normal cells, but only those of the cellular compartment in otosclerotic bone cells. It depressed heparan sulphate (HS) more in normal cells and chondroitin sulphate (CS) more in otosclerotic bone cells. The HA/total sulphated GAG ratio was shifted in favour of the latter in otosclerotic cells, whereas the opposite effect was seen after IL-1 alpha treatment. There was little difference in the beta-D-glucuronidase levels of the normal and pathological cells, while beta-N-acetyl-D-glucosaminidase was significantly increased in otosclerotic bone cells. As the activity of neither enzyme was modified by treatment with IL-1 alpha, the cytokine seems to exert its influences on GAG synthesis rather than on the degradation process. IL-1 alpha, IL-1 beta and IL-6 secretion was markedly higher in otosclerotic cells. IL-1 alpha modulated the secretion of each interleukin differently, thus resulting in a cytokine cascade that may act in autocrine/paracrine manner on target cells. The authors suggest that changes in the cytokine network may have a specific, yet still unknown, role during normal and pathological osteogenesis.

Assay of β-N-acetylhexosaminidase isoenzymes in different biological specimens by means of determination of their activation energies

The activation energy (Ea) of β-N-acetylhexosaminidase (Hex, EC 3.2.1.52) was determined with 3,3′-dichlorophenylsulfonphthaleinyl-N-acetyl-β-d-glucosaminide as substrate, with a much higher value being found for the Hex B isoenzyme (Ea = 75.1 kJ/mol) than for the Hex A isoenzyme (Ea = 41.8 kJ/mol). This fact allowed for the development of a fast and reliable thermodynamic method to determine the isoenzyme composition of Hex in different biological specimens (serum/plasma, saliva, cerebrospinal fluid, seminal plasma, urine, and leukocyte lysates). The results in serum given by the proposed method may be superimposed upon those obtained by the heat inactivation assay of O’Brien et al. (N Engl J Med 1970;273:15–20), and the catalytic activity calculated for Hex A offers a good correlation with that obtained by using the specific substrate 4-methylumbelliferyl-N-acetyl-β-d-glucosaminide-6 sulfate (n = 25, r = 0.953).

Beta-N-acetylhexosaminidase: a target for the design of antifungal agents

This review provides biochemical, analytical, and biological background information relating to beta-N-acetylhexosaminidase (HexNAc'ase; EC 3.2.1.52) as an emerging target for the design of low-molecular-weight antifungals. The article includes the following: (1) a biochemical description of HexNAc'ase (reaction catalyzed, nomenclature, and mechanism of action) that sets it apart from other, similar enzymes; (2) an overview and a critical evaluation of methods to assay the enzyme, including in crude extracts (photo- and fluorometric procedures with model substrates; HPLC/pulsed amperometric detection of N-acetylglucosamine and chito-oligomers; end-point vs. rate measurements); (3) a summary of some general characteristics of HexNAc'ases from fungi and organisms of other types (Km values, substrate preference, and glycoconjugation); (4) an hypothesis of a specific target function of wall-associated HexNAc'ase (a component of the assembly of surface-located enzymes effecting a continuous turnover and remodelling of the wall fabric through its combined hydrolytic and transglycosylating activities, and a mediator enzyme acting in concert with chitinase and chitin synthase to provide for the controlled lysis and synthesis of chitin during growth); (5) a tabulation of the structural formulae of reaction-based HexNAc'ase inhibitors with Ki values < or = 100 microM (some of them representing transition state mimics that could serve as leads for the development of new antifungals); and (6) an outline of approaches towards the establishment of a three-dimensional model of HexNAc'ase suitable for a truly rational design of antimycotics as well as agricultural fungicides.

Constitutive expression of beta-N-acetylhexosaminidase in a microglial cell line: transcriptional modulation by lipopolysaccharide and serum factors

We investigated the expression of the alpha- and beta-subunits of the lysosomal enzyme beta-N-acetylhexosaminidase in the BV-2 microglial cell line under different culture conditions. Beta-N-acetylhexosaminidase from BV-2 microglia cells was separated into its constituent isoenzymes on diethylaminoethyl (DEAE) cellulose, and its activity was monitored with 4-methylumbelliferyl-beta-N-acetylglucosamine and 4-methylumbelliferyl-beta-N-acetylglucosamine-6-sulphate substrates. Forms corresponding to the mouse isoenzymes A and B were present in the cells incubated in serum-supplemented medium as well as in serum-free medium. Lipopolysaccharide, a well-known activator of microglia in vitro, added to the BV-2 cells in serum-supplemented medium induced a decrease in the specific enzymatic activity determined with the 4-methylumbelliferyl-beta-N-acetylglucosamine substrate. Lipopolysaccharide had no effect on hexosaminidase isoenzyme pattern of BV-2 cells in serum-supplemented medium. The level of alpha-subunit mRNA was increased and the level of beta-subunit mRNA was decreased in BV-2 cells incubated in serum-supplemented medium plus lipopolysaccharide. In the cells incubated in a serum-free medium no significant changes in the hexosaminidase-specific activities towards the above substrates were observed. Interestingly, increased expression of alpha- and beta-subunit mRNA was evident in comparison with cultures in serum-supplemented medium. The present results suggest that the BV-2 cell line may be a useful tool to study the possible role of microglia in the metabolism of brain glycolipids.

Distribution of active alpha- and beta-subunits of beta-N-acetylhexosaminidase as a function of leukaemic cell types

beta-N-Acetylhexosaminidase isoenzymes, and the distribution of the alpha- and beta-subunits forming the enzyme in a representative series of fresh leukaemic cells and in established leukaemic cell lines, were obtained by using a combination of DEAE-cellulose chromatography and assay with the fluorogenic substrates 4-methylumbelliferyl-beta-N-acetylglucosaminide hydrolyzed by both alpha and beta subunits, and 4-methylumbelliferyl-beta-N-acetylglucosaminide-6-SO4 hydrolyzed only by hexosaminidase isoenzymes containing alpha-subunits. The presence of hexosaminidase S (the alpha alpha dimer), was found in all the leukaemic cell populations we surveyed, but not in normal human cells. The presence of this isoenzyme can therefore be considered as an additional marker of leukaemic cells. A prevalence of hexosaminidase A and A-like intermediate forms (alpha beta structure), characterize leukaemic cells of myeloid origin, whereas greater amounts of hexosaminidase B and B-like intermediate forms (beta beta structure), were consistent attributes of leukaemic cells of lymphoid origin. An over-expression of beta-subunits in blasts might be related to their undifferentiated status. These changes in the isoenzymes of hexosaminidase may prove informative about a variety of changes in the biology of leukaemic cells that could range from chromosomal alterations to changes in the proteolytic processing and glycosylation.

Metal substrates influence the release of glycosaminoglycan and transforming growth factor beta by human bone cells

Bone cells derived from human jaw were isolated from explants and grown in vitro. Subcultures were cultured on plastic (control) and metal substrates for 24 and 48 hours in medium containing 3H-glucosamine and labeled glycosaminoglycan (GAG) accumulation was measured. In bone cells cultured on metal substrates there was an evident reduction in the synthesis and secretion of radiolabeled macromolecules compared to bone cells cultured on plastic. Moreover, the accumulation of single GAG classes was specific for each substrate tested. The results showed that titanium was the only metal substrate studied in which the percentage of individual GAG classes remained the same as control cultures. GAG reduction was due to a decreased synthesis and not to an increased degradation as shown by the decrement of exoglycosidase activity. The metals also reduced the activity of transforming growth factor beta (TGF beta), measured using interleukin-1 assay method, a factor involved in the various phases of bone remodeling; in this case, too, cells grown on titanium showed the highest TGF beta activity compared to the other metal substrates studied. The results indicate that the substrate to which the cells adhere do exhibit specific differences in GAG composition and TGF beta activity. The differences observed may be important during in vivo events such as guided tissue regeneration and bone deposition.

Lysosomal hydrolases in serum from human immunodeficiency virus-infected patients

beta-Hexosaminidase isoenzymes were separated by DEAE-cellulose chromatography in the serum of 23 patients infected with human immunodeficiency virus at different stage of the disease. Forms corresponding to hexosaminidase B, I and A were present in pathological sera. There is an increase in the percentage of hexosaminidase I in pathological sera, that could be used as an additional marker to monitor the clinical stage of the disease. Furthermore, total activities of some lysosomal enzymes were determined in these sera. Activities of beta-hexosaminidase, determined with 4-methylumbelliferyl-beta-N-acetylglucopyranoside substrate, alpha-mannosidase and beta-mannosidase were significantly higher in the serum of patients at the C3 stage of disease than in controls. No significant differences were observed in the activity of beta-hexosaminidase, determined with 4-methylumbelliferyl-beta-N-acetylglucopyranoside-6-sulphate substrate, beta-glucuronidase and beta-galactosidase.

Clinical, enzymatic, and molecular characterisation of a Portuguese family with a chronic form of GM2-gangliosidosis B1 variant

Mutations in the hexosaminidase A gene (HEXA) causing the B1 variant of GM2-gangliosidosis result in the presence of a mutant enzyme protein with a catalytically defective alpha subunit. A rare and panethnically distributed mutation, transition G533A (Arg178His), is known to be a common allele among Portuguese patients with the subacute phenotype. We now report the presence of an Arg178His allele in three Portuguese sibs with a chronic form of the disease, who carry the transition G755A (Arg252His) on the second allele. This novel mutation is the first B1 allele to be associated with an adult phenotype.

N-acetyl-beta-D-glucosaminidase (NAG) isoenzymes in primary cultures of rabbit kidney proximal tubule cells: a cellular model for studies on nephrotoxicity?

N-Acetyl-beta-D-glucosaminidase (NAG) isoenzyme profile in primary cultures of rabbit kidney proximal tubule cells was studied. Confluent cells had high levels of NAG activity, but ion exchange chromatography showed that the NAG isoenzyme profile in cultured cells was different from that of rabbit renal cortex homogenates and freshly isolated cells. Confluent cultured cells contained an atypical acidic isoform, absent in homogenates and freshly isolated cells in which the predominant isoform is NAG-A (a heterodimer alpha beta). The fact that this atypical isoform was able to hydrolyse the synthetic substrate 4-methylumbelliferyl-beta-N-acetylglucosaminide-6-sulphate indicated that it probably was an alpha-subunit homodimer. These results suggest subunit rearrangement within NAG polypeptide chains linked to down-regulation of beta-subunit production in cultured rabbit proximal cells. The change in isoenzyme profile in cultured cells may make it difficult to use primary cultures of rabbit proximal tubule cells to establish correlations between in vitro and in vivo studies using NAG isoenzymes as a nephrotoxicity index, as illustrated by the effects of gentamicin.

Prenatal diagnosis of GM2-gangliosidosis B1 variant

Prenatal diagnosis in a pregnancy at risk for a juvenile B1 variant of GM2-gangliosidosis was carried out. The biochemical study of the cultured amniocytes and the affected fetal brain is reported. The results obtained show that the sulphated artificial substrate can be used in the diagnosis of B1 variant, but not the neutral one. The accumulation of GM2-ganglioside in the fetal brain of the B1 juvenile form and an infantile form of GM2-gangliosidosis (0 variant) was compared.

Beta-N-acetylhexosaminidases A and S have similar sub-cellular distributions in HL-60 cells

In HL-60 cells the most abundant isoenzymes of beta-N-acetyl-hexosaminidase are A (alpha beta) and S (alpha alpha). Sub-cellular fractionation of HL-60 cells by differential centrifugation showed that both A and S forms were present in the lysosomal and post-lysosomal (soluble) fractions in approximately equal abundance. Ion-exchange chromatography showed that a fraction enriched with plasma membranes had the A form, and a form of beta-N-acetylhexosaminidase less acidic than A, but there was no S. Analysis of the alpha-subunits of beta-N-acetylhexosaminidases A and S using Western blotting and immuno-detection with antisera raised to synthetic peptides showed that mature alpha-subunits were present in both A and S isolated from the lysosomal fraction. This observation establishes that the alpha alpha-dimer of beta-N-acetyl-hexosaminidase (S) can be transported to lysosomes in HL-60 cells whereas there is good evidence that this does not take place in fibroblasts. HL-60 cells were not stimulated to secrete lysosomal enzymes by incubating them with NH4Cl and, unlike fibroblasts, are unlikely to use mannose-6-phosphate mediated transport of beta-N-acetylhexosaminidases to lysosomes. Comparison of the sequence of the beta-N-acetylhexosaminidase alpha-subunit with a 43 amino acid sequence of cathepsin D, though to function in the mannose-6-phosphate independent targeting of this enzyme to lysosomes, showed alignment in a region towards the C-terminus in which 21% of the residues were identical with the interposition of a one amino acid gap.

Modulation of phenotypic expression of fibroblasts by alteration of the cytoskeleton

Several studies indicate that the cytoskeleton may be involved in modulating the cellular response to environmental signals. We have studied the role of the cytoskeleton in regulating glycosaminoglycan (GAG) synthesis and secretion, hyaluronate (HA) endocytosis, the activities of hexoglycosidases, protein synthesis and secretion. Fibroblasts were treated with colchicine (1-8 microM) and nocodazole (1 or 4 microM) to alter microtubules or cytochalasin B (0.5-4 microM) to alter microfilaments. Colchicine inhibited GAG synthesis and secretion in a concentration-dependent manner. It reduced protein and sulphated GAG secretion, while HA secretion was not affected. Concentration-dependent disruption of microtubules from the periphery toward the cellular centre with nocodazole inhibited only the secretion of GAG. Centrosomal microtubles appeared to be required to promote GAG synthesis; intact microtubules promoted the transport of secretory products, intercompatmental transport of lysosomal enzymes and lysosome maturation, but not protein synthesis and HA secretion. Cytochalasin B treatment inhibited, in a concentration-dependent manner, the synthesis and secretion of GAGs and proteins, and the endocytosis of HA. Intact microfilament meshworks appeared to be required to promote synthesis and secretion of proteins and proteoglycans and to contribute to the transmembrane control of receptor-mediated endocytosis. Drug treatment of concanavalin A (Con A)-stimulated fibroblasts inhibited the stimulation of GAG synthesis. It is probable that this effect may result, in part, from drug-induced effects on Con A-mediated endocytosis.

Platelet glycohydrolase activities: characterization and release

Granules containing acid hydrolases have been detected in human platelets but have not been thoroughly characterized. We have studied the activity and characteristics of glycohydrolases present in normal human platelets, evaluated their release upon stimulation with thrombin, and assessed the contribution of platelet - released lysosomal contents to the glycohydrolase activity present in normal serum. Platelets contained a remarkable glycohydrolase activity with a prevalence of beta - N-acetylhexosaminidase. All glycohydrolases were released to some extent upon stimulation with thrombin and contributed to the glycohydrolase activity found in human serum. alpha-Mannosidase and alpha-galactosidase were partially inactivated after release by a mechanism as yet undefined. In addition, thrombin stimulation affects the intraplatelet isoenzyme pattern of beta-N-acetylhexosaminidase by producing the appearance of a new form.

Tay-Sachs disease: intron 7 splice junction mutation in two Portuguese patients

A single nucleotide transversion (G-->C) in the 5' donor site of intron 7 of the beta-hexosaminidase alpha-chain gene was identified in two Portuguese patients with infantile Tay-Sachs disease. One patient was found to be homozygous and the other a compound heterozygote with the four-base insertion in exon 11 on the other allele. In fibroblasts from the homozygous patient the beta-hexosaminidase alpha mRNA was observed as a nearly undetectable fast migrating band. Through cDNA-PCR amplification and hybridization with full length alpha cDNA several fragments of smaller size than the normal transcript were detected, most of them lacking exon 7. We propose that this point mutation in the 5' donor site of intron 7 of the beta-hexosaminidase alpha-chain gene is responsible for an inefficient and abnormal processing of the mutant transcript, resulting in functional abnormality.

Two new mutations in a late infantile Tay-Sachs patient are both in exon 1 of the beta-hexosaminidase alpha subunit gene

We have identified two new point mutations in the beta-hexosaminidase alpha subunit (HEX A) gene in a non-Jewish Tay-Sachs disease patient with an unusual late infantile onset disease phenotype. The patient was a compound heterozygote with each allele of the HEX A gene containing a different mutation in exon 1. One of these is a T to C transition in the initiation codon, expected to produce no alpha subunit and therefore a classical infantile phenotype. The unusual clinical aspects and later onset in the patient must therefore be a result of residual hexosaminidase A activity associated with a mutant alpha subunit containing the second mutation, substitution of serine for proline at amino acid 25 owing to a C to T change at nucleotide 73. Western blotting and DE-52 ion exchange chromatography have been used to examine the behaviour of this mutant alpha subunit.

Pregnancy modulates the expression of beta-N-acetylhexosaminidase in rat serum and tissues

1. beta-N-Acetylhexosaminidases in maternal rat serum were separated by DEAE-cellulose chromatography and compared with those of adult rat serum. 2. In pregnant serum there is an increase of the isoenzymes which are entirely composed of beta-subunits (B and intermediate forms). 3. These alterations could be compared to those already described in human pregnancy. 4. The levels of beta-N-acetylhexosaminidase and the relative expression of alpha- and beta-subunits in normal and pregnant serum correlate with the above isoenzyme expression. 5. The increase of B and intermediate forms as well as the increase of specific activity during pregnancy was not peculiar to maternal serum but was also demonstrated in several foetal tissues and in maternal tissues, in which cases the beta-N-acetylhexosaminidase isoenzyme patterns closely resemble the foetal ones rather than those of the adult rat tissues. 6. These analogies strongly suggest that the expression of beta-subunit of beta-N-acetylhexosaminidase is regulated by hormones or other factors related to pregnancy.

Beta-N-acetylhexosaminidase in the urine, kidney and serum of bromobenzene-intoxicated mice

beta-N-Acetylhexosaminidase isoenzymes were separated from the kidney, serum and urine of normal mice and mice intoxicated with bromobenzene, using DEAE-cellulose chromatography. Both mouse serum and urine showed hexosaminidase profiles similar to the human counterparts with the presence of B (basic), I (intermediate) and A (acidic) isoenzymes. A notable feature was the presence of a high proportion of an intermediate form in mouse urine which is not always present in human urine. Hexosaminidase activity increased significantly in urine of mice intoxicated with bromobenzene. Its increase was time-dependent and due to kidney damage with a release in the urine of hexosaminidase A, I and, in higher proportion, B. No significant differences were observed in mouse kidney and serum profiles following intoxication with bromobenzene. The total activity of hexosaminidase, using 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside as substrate, did not increase in the serum of mice intoxicated with bromobenzene. Both hexosaminidase activity and the isoenzyme pattern in urine can be used as indicators of kidney damage by bromobenzene intoxication.

An evaluation of the mechanisms developmentally involved on cellular and extracellular glycosaminoglycans accumulation in chick embryo skin fibroblasts

1. Ammonium chloride, a lysosomotropic amine known to inhibit lysosomal function, was administered to 7-day cultured and 14-day chick embryo skin fibroblasts to evaluate the relationship between synthesis, degradation and uptake of glycosaminoglycans (GAG). 2. Following amine treatment, the amount of 3H-glucosamine and 35SO4 labelled cellular GAG increased, was more at 14 days than at 7 days. Hyaluronic acid (HA) incorporation was mainly interested at 7 days and that of sulphated GAG at 14 days. 3. The extracellular accumulation declined proportionally to the cellular increase of undegraded GAG. HA was mainly affected at 7 days and sulphated GAG at 14 days. 4. The amine did not change 3H-HA uptake and it was unable to inhibit its degradation. 5. The products of degradation of uptaken 3H-HA were retained inside the cell. Those released by degradation of newly synthesized GAG flowed out of the cell.

Relation between hyaluronan and sulphated glycosaminoglycan synthesis and degradation in cultured embryonic fibroblasts. Effect of concanavalin A and ammonium chloride administration

In order to evaluate the relationship between glycosaminoglycan (GAG) synthesis and degradation, the effect of NH4Cl, which inhibits lysosomal degradation, on GAG production was analysed in vitro in concanavalin A (Con A) stimulated fibroblasts from 7 and 14-day-old chick embryos. 35SO4 incorporation into total proteoglycan (PG), 3H incorporation into individual GAG classes, beta-N-acetyl-D-glucosaminidase and beta-D-glucuronidase activity were determined. The results indicate a correlation between Con A and NH4Cl effects: NH4Cl induced a reduction principally in the GAG classes most stimulated by Con A. Thus HA and DS are much more stimulated by Con A and inhibited by NH4Cl than are CS and HS.

beta-N-acetylhexosaminidases in human cerebrospinal fluid and serum of patients with multiple sclerosis

Beta-N-Acetylhexosaminidase activity and isoenzyme have been investigated in normal human cerebrospinal fluid and that of patients with multiple sclerosis. beta-N-acetylhexosaminidase activity in normal cerebrospinal fluids has been resolved into five components. The major component was in a form that eluted from DEAE cellulose at the same salt concentration as hexosaminidase As, the isoenzyme previously identified in human serum. Cerebrospinal fluid from patients exhibited a different isoenzyme profile, showing a remarkable increase in a form having a pI which was more acidic than that of As. These changes have a potential use in the diagnosis and further biochemical characterization of multiple sclerosis.

Increase of intermediate forms of beta-N-acetylhexosaminidase during rat liver development and regeneration

1. Rat liver beta-N-acetylhexosaminidase was separated into several different molecular forms by DEAE-cellulose chromatography. 2. The subunit composition of the isoenzymes, as well as the similarities to human hexosaminidases, were determined by using the specific active alpha subunit substrate 4-methylumbelliferyl-beta-N-acetylglucosamine-6-sulphate. 3. As in human tissues, the intermediate form lacked the active alpha subunit and resembled hexosaminidase B rather than A. 4. The intermediate form was markedly increased in foetal liver and in regenerating liver after partial hepatectomy. 5. The variations in isoenzyme expression were accompanied by variations in specific activity of hexosaminidase. 6. Sulphated substrate analysis and thermal stability experiments indicated that the rapid cell proliferation had a greater effect on the formation of beta-subunit of hexosaminidase than on that of alpha-subunit.

Biochemical characterization of beta-hexosaminidase in different biological specimens from eleven patients with GM2-gangliosidosis B1 variant

GM2-gangliosidosis B1 variant is thought to be a rare disorder with a wide geographical and ethnic distribution. We report the biochemical findings obtained in different specimens from a group of 11 B1 variant patients originating from the north of Portugal. The biochemical data obtained seem to indicate that only one of these patients is a genetic compound presenting a clinical and biochemical pattern similar to the majority of B1 variant patients described in the literature, but somewhat different from the profile presented by the other patients reported here, who are homozygous for the 'DN-allele'.

beta-Hexosaminidase expression in chick embryo fibroblasts in vitro

1. Two forms of beta-hexosaminidase, similar to hexosaminidase A and hexosaminidase C, were separated by DEAE-cellulose chromatography in chick embryo skin fibroblasts in vitro. 2. beta-Hexosaminidase specific activity increases during development in cultured chick embryo skin fibroblasts in vitro. 3. Concanavalin-A treatment determines the increase of the neutral form, hexosaminidase C, during development. 4. Concanavalin-A reduces the specific activity of beta-hexosaminidase during development.

First trimester prenatal diagnosis of Tay-Sachs disease using the sulfated synthetic substrate for hexosaminidase A

Uncultured and cultured embryonic trophoblastic tissue obtained by chorionic villus sampling (CVS) displays enzyme activity towards 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranosyl-6-sulfate (MUGS), a specific substrate for Hexosaminidase A (Hex A), the enzyme deficient in Tay-Sachs disease (TSD). Specific activity is comparable to that found in cultured amniocytes and fibroblasts. The enzyme activity has a pH optimum of 4.1 and an apparent Km of 6 x 10(-4) mol/L. Thirteen pregnancies in eight families at risk for TSD were monitored by CVS using MUGS as the Hex A substrate. Four fetuses were proven affected by enzyme analysis of fetal tissues and cultured fetal fibroblasts obtained at the time of termination of the pregnancies. Nine fetuses were judged to be unaffected. Eight babies were clinically normal while the other pregnancy is continuing. The use of MUGS as substrate for Hex A makes prenatal diagnosis by CVS of families at risk for TSD simple, direct and accurate.

Treatment of HL-60 cells with dimethyl sulphoxide inhibits the formation of beta-N-acetylhexosaminidase S

beta-N-Acetylhexosaminidase of HL-60 cells was separated into two main forms, A and S, by chromatography on DEAE-cellulose. Analysis of developmental changes in the isoenzyme pattern was complicated by the fact that the specific activity of beta-N-acetylhexosaminidase underwent a 6-fold change during the normal growth cycle. Two other lysosomal enzymes, beta-galactosidase and alpha-mannosidase, behaved similarly. Induction of differentiation of HL-60 cells with dimethyl sulphoxide at a low cell density (3 x 10(5) cells/ml) had a greater effect on the abundance of alpha-subunits of beta-N-acetylhexosaminidase, measured with 4-methylumbelliferyl-beta-N-acetylglucosaminide 6-sulphate, than of beta-subunits, measured with 4-methylumbelliferyl-beta-N-acetylglucosamine, and resulted in an isoenzyme profile in which A and B were the major forms, with the levels of form S greatly decreased.

Identification of an intermediate form of beta-N-acetylhexosaminidase in chorionic villi

A minor form of beta-N-acetylhexosaminidase has been found in chorionic villi, in addition to the major forms A and B. This form does not hydrolyze the 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside-6-sulpha te substrate, is thermostable, has a higher mol mass (120,000) than A and B (100,000) and on analytical isoelectric focusing, it shows a microheterogeneity with values ranging between 6.3 and 7.0. For these characteristics, it resembles beta-N-Acetylhexosaminidase P from pregnancy serum, from which is chromatographically indistinguishable.

An enzyme with properties similar to those of beta-N-acetylhexosaminidase S is expressed in the promyelocytic cell line HL-60

Extracts of the human promyelocytic cell line HL-60 contain a form of beta-N-acetylhexosaminidase that is not retained on columns of benzeneboronate-agarose ('phenylboronate-agarose') and has a pI value lower than that of beta-N-acetylhexosaminidase A. It is clearly distinct from beta-N-acetylhexosaminidase A in its behaviour on DEAE-cellulose columns, and it requires a higher concentration of salt for its elution. This 'extra' form has a higher ratio of activity towards 4-methylumbelliferyl beta-N-acetylglucosaminide 6-sulphate and 4-methylumbelliferyl beta-N-acetylglucosaminide than has beta-N-acetylhexosaminidase A and is less stable when heated at 50 degrees C. It has a pH optimum of 4.5 and is therefore not beta-N-acetylglucosaminidase C. Anti-(human beta-N-acetylhexosaminidase alpha-subunit) serum precipitated both beta-N-acetylhexosaminidase A and the 'extra' form, whereas an anti-(beta-subunit) serum precipitated beta-N-acetylhexosaminidase A but not the 'extra' form. Western blotting and immunodetection of polypeptides derived from the 'extra' form revealed a band corresponding in size to mature alpha-subunits. On the basis of this and of its behaviour on isoelectric focusing, chromatofocusing and its kinetic properties, we conclude that the 'extra' form is composed of alpha-subunits and resembles beta-N-acetylhexosaminidase S, the residual form in Sandhoff's disease.

beta-N-acetylhexosaminidases in the spleen of a patient with hairy-cell leukaemia

The spleen from a patient with hairy-cell leukaemia had beta-N-acetylhexosaminidase activity that could be resolved into three isoenzymes by chromatography on phenyl boronate agarose. Two of these were the major forms, A and B, found in normal tissues but, in addition, there was an 'extra' form that accounted for 15% of total activity. The 'extra' form hydrolysed the synthetic substrate 4-methylumbelliferyl-beta-N-acetylglucosamine 6-sulphate, indicating the presence of alpha-subunits. It was more acidic than A, was less heat-stable and showed no generation of B on denaturation under a variety of conditions. These findings and the immunoblot (Western blotting) analysis demonstrate that the 'extra' form is entirely composed of alpha-subunits, and most closely resembles S, the residual activity in Sandhoff's disease.

beta-N-acetylhexosaminidase isoenzymes during chick embryo development

1. Two forms (I and II) with acidic pH optima and a neutral form of beta-hexosaminidase has been separated by DEAE-cellulose chromatography and characterized in skin and lung of 7, 9, 11, 14 day chick embryos and 1 day old chicken. 2. Forms I and II are similar to hexosaminidase A and B for their behaviour on DEAE-cellulose chromatography, Concanavalin A-Sepharose column and thermal stability. 3. Neutral form has a neutral pH optimum and higher molecular weight and a more acidic I. P. than forms I and II, a low beta-N-acetylgalactosaminidase activity and it is not bound by a Concanavalin A-Sepharose column and in that resemble hexosaminidase C and/or other neutral hexosaminidases. 4. We have found differences in the percentage of neutral form and in the specific activities of the extracts in the skin in different stages of development. 5. No significant differences were observed in the lung.

Identification of beta-N-acetylhexosaminidase A in mouse tissues with the fluorigenic substrate 4-methylumbelliferyl-beta-N-acetylglucosamine 6-sulphate

beta-N-Acetylhexosaminidase from mouse tissue was separated into its constituent isoenzymes on DEAE-cellulose and its activity was monitored with 4-methylumbelliferyl-beta-N-acetylglucosamine and 4-methylumbelliferyl-beta-N-acetylglucosamine 6-sulphate. Forms corresponding to the human isoenzymes A (acidic), B (basic) and an 'intermediate' form were present in mouse liver and spleen, whereas in kidney the B and 'intermediate' forms predominated, with A present only as a minor component. In brain the 'intermediate', A and C activities were detected. Testis had predominantly A activity, whereas epididymis, the tissue with the highest specific activity of beta-N-acetylhexosaminidase, had an abundance of the 'intermediate' form, but was almost entirely lacking in the A form.