In vitro inhibition and intracellular enhancement of lysosomal alpha-galactosidase A activity in Fabry lymphoblasts by 1-deoxygalactonojirimycin and its derivatives

Tripeptidyl-peptidase I in health and disease

The lysosomal lumen contains numerous acidic hydrolases involved in the degradation of carbohydrates, lipids, proteins, and nucleic acids, which are basic cell components that turn over continuously within the cell and/or are ingested from outside of the cell. Deficiency in almost any of these hydrolases causes accumulation of the undigested material in secondary lysosomes, which manifests itself as a form of lysosomal storage disorder (LSD). Mutations in tripeptidyl-peptidase I (TPP I) underlie the classic late-infantile form of neuronal ceroid lipofuscinoses (CLN2), the most common neurodegenerative disorders of childhood. TPP I is an aminopeptidase with minor endopeptidase activity and Ser475 serving as an active-site nucleophile. The enzyme is synthesized as a highly glycosylated precursor transported by mannose-6-phosphate receptors to lysosomes, where it undergoes proteolytic maturation. This review summarizes recent progress in understanding of TPP I biology and molecular pathology of the CLN2 disease process, including distribution of the enzyme, its biosynthesis, glycosylation, transport and activation, as well as catalytic mechanisms and their potential implications for pathogenesis and treatment of the underlying disease. Promising data from gene and stem cell therapy in laboratory animals raise hope that CLN2 will be the first neurodegenerative LSD for which causative treatment will become available for humans.

Fabry disease: identification of 50 novel alpha-galactosidase A mutations causing the classic phenotype and three-dimensional structural analysis of 29 missense mutations

Fabry disease, an X-linked recessive inborn error of glycosphingolipid catabolism, results from the deficient activity of the lysosomal exoglycohydrolase, α-galactosidase A (EC 3.2.1.22; α-Gal A). The molecular lesions in the α-Gal A gene causing the classic phenotype of Fabry disease in 66 unrelated families were determined. In 49 families, 50 new mutations were identified, including: 29 missense mutations (N34K, T41I, D93V, R112S, L166G, G171D, M187T, S201Y, S201F, D234E, W236R, D264Y, M267R, V269M, G271S, G271V, S276G, Q283P, A285P, A285D, M290I, P293T, Q312H, Q321R, G328V, E338K, A348P, E358A, Q386P); nine nonsense mutations (C56X, E79X, K127X, Y151X, Y173X, L177X, W262X, Q306X, E338X); five splicing defects (IVS4-1G > A, IVS5-2A > G, IVS5 + 3A > G, IVS5 + 4A > G, IVS6-1G > C); four small deletions (18delA, 457delGAC, 567delG, 1096delACCAT); one small insertion (996insC); one 3.1 kilobase Alu-Alu deletion (which included exon 2); and one complex mutation (K374R, 1124delGAG). In 18 families, 17 previously reported mutations were identified, with R112C occurring in two families. In two classically affected families, affected males were identified with two mutations: one with two novel mutations, D264Y and V269M and the other with one novel (Q312H) and one previously reported (A143T) mutation. Transient expression of the individual mutations revealed that D264Y and Q312H were localised in the endoplasmic reticulum and had no detectable or markedly reduced activity, whereas V269M and A143T were localised in lysosomes and had approximately 10 per cent and approximately 35 per cent of expressed wild-type activity, respectively. Structural analyses based on the enzyme's three-dimensional structure predicted the effect of the 29 novel missense mutations on the mutant glycoprotein's structure. Of note, three novel mutations (approximately 10 per cent) were predicted not to significantly alter the glycoprotein's structure; however, they were disease causing. These studies further define the molecular heterogeneity of the α-Gal A mutations in classical Fabry disease, permit precise heterozygote detection and prenatal diagnosis, and provide insights into the structural alterations of the mutant enzymes that cause the classic phenotype.

Pharmacological chaperone corrects lysosomal storage in Fabry disease caused by trafficking-incompetent variants

Fabry disease is a lysosomal storage disorder caused by deficiency of alpha-galactosidase A (alpha-Gal A) resulting in lysosomal accumulation of glycosphingolipid globotriosylceramide Gb3. Misfolded alpha-Gal A variants can have residual enzyme activity but are unstable. Their lysosomal trafficking is impaired because they are retained in the endoplasmic reticulum (ER) by quality control. Subinhibitory doses of the competitive inhibitor of alpha-Gal A, 1-deoxygalactonojirimycin (DGJ), stabilize mutant alpha-Gal A in vitro and correct the trafficking defect. We showed by immunolabeling that the chaperone-like action of DGJ significantly reduces the lysosomal Gb3 storage in human Fabry fibroblasts harboring the novel mutations T194I and V390fsX8. The specificity of the DGJ effect was proven by RNA interference. Electron microscopic morphometry demonstrated a reduction of large-size, disease-associated lysosomes and loss of characteristic multilamellar lysosomal inclusions on DGJ treatment. In addition, the pre-Golgi intermediates were decreased. However, the rough ER was not different between DGJ-treated and untreated cells. Pulse-chase experiments revealed that DGJ treatment resulted in maturation and stabilization of mutant alpha-Gal A. Genes involved in cell stress signaling, heat shock response, unfolded protein response, and ER-associated degradation show no apparent difference in expression between untreated and DGJ-treated fibroblasts. The DGJ treatment has no apparent cytotoxic effects. Thus our data show the usefulness of a pharmacological chaperone for correction of the lysosomal storage in Fabry fibroblasts harboring different mutations with residual enzyme activity. Pharmacological chaperones acting on misfolded, unstable mutant proteins that exhibit residual biological activity offer a convenient and cost-efficient therapeutic strategy.

Chemical chaperones and permissive temperatures alter localization of Gaucher disease associated glucocerebrosidase variants

Point mutations in the lysosomal hydrolase, glucocerebrosidase (GC), can cause Gaucher disease, a common lysosomal storage disease. Several clinically important GC mutations impede folding in the endoplasmic reticulum (ER) and target these enzymes for ER-associated degradation (ERAD). The removal of these misfolded proteins decreases the lysosomal concentration of GC, which results in glucosylceramide accumulation. The most common GC variant, N370S, and other clinically relevant variants, G202R and L444P, exhibit different cellular localization patterns in patient-derived fibroblasts. We show that these distributions can be altered by manipulation of the ER folding environment, either by chemical chaperones or by temperature shifts. N370S, L444P, and G202R GC are destabilized in the neutral pH environment of the ER, rendering them prone to ERAD. Fibroblasts harboring the G202R and L444P GC mutations grown at 30 degrees C localize the mutant proteins to the lysosome, and this increases total GC activity. Both of these temperature-sensitive mutants appear to be stable at 37 degrees C once they are trafficked to the low pH environment of the lysosome. Chemical chaperones correct the ER instability and significant ER retention of G202R GC. N370S is also destabilized under ER simulating conditions, a deficiency that is corrected by chemical chaperone binding. These data clearly show manipulating the ER environment with chemical chaperones increases the lysosomal concentration of partially active GC variants and suggest that small molecules could be used to treat Gaucher disease.

Storage solutions: treating lysosomal disorders of the brain

Many neurodegenerative diseases are characterized by the accumulation of undegradable molecules in cells or at extracellular sites in the brain. One such family of diseases is the lysosomal storage disorders, which result from defects in various aspects of lysosomal function. Until recently, there was little prospect of treating storage diseases involving the CNS. However, recent progress has been made in understanding these conditions and in translating the findings into experimental therapies. We review the developments in this field and discuss the similarities in pathological features between these diseases and some more common neurodegenerative disorders.

A lipid analogue that inhibits sphingomyelin hydrolysis and synthesis, increases ceramide, and leads to cell death

We report the synthesis and characterization of a novel thiourea derivative of sphingomyelin (AD2765). In vitro assays using pure enzyme and/or cell extracts revealed that this compound inhibited the hydrolysis of BODIPY-conjugated or 14C-labeled sphingomyelin by acid sphingomyelinase and Mg2+-dependent neutral sphingomyelinase. Studies in normal human skin fibroblasts further revealed that AD2765 was taken up by cells and inhibited the hydrolysis of BODIPY-conjugated sphingomyelin in situ. In situ and in vitro studies also showed that this compound inhibited the synthesis of sphingomyelin from BODIPY-conjugated ceramide. The specificity of AD2765 for enzymes involved in sphingomyelin metabolism was demonstrated by the fact that it had no effect on the hydrolysis of BODIPY-conjugated ceramide by acid ceramidase or on the synthesis of BODIPY-conjugated glucosylceramide from BODIPY-conjugated ceramide. The overall effect of AD2765 on sphingomyelin metabolism was concentration-dependent, and treatment of normal human skin fibroblasts or cancer cells with this compound at concentrations > 10 microM led to an increase in cellular ceramide and cell death. Thus, AD2765 might be used to manipulate sphingomyelin metabolism in various ways, potentially to reduce substrate accumulation in cells from types A and B Niemann-Pick disease patients, and/or to affect the growth of human cancer cells.

Lysosomal leukocyte β-d-glucuronidase during enzyme replacement therapy in Fabry disease

OBJECTIVE

Fabry disease results from a deficiency in the activity of alpha-d-galactosidase A and subsequent accumulation of neutral glycosphingolipids in lysosomes. This study investigated whether lysosomal enzymes can indicate biochemical changes in the lysosomal apparatus induced by enzyme replacement therapy (ERT).

DESIGN AND METHODS

Eight patients were monitored by clinical and biochemical tests and several lysosomal glycohydrolases were measured in plasma and leucocytes.

RESULTS

Before starting ERT, beta-d-glucuronidase in leukocytes was markedly increased. After 1 month of therapy, enzyme levels dropped in all patients. In the patients who regularly followed the therapy, the enzyme levels remained stable for the next 20 months. In one patient who interrupted therapy for 2 months, the enzyme levels rose again.

CONCLUSIONS

Lysosomal enzymes can be useful for monitoring biochemical changes in patients with Fabry disease receiving ERT. Though these findings refer to only a small number of patients, the correlation between beta-d-glucuronidase levels and ERT is interesting and might serve as a basis for further studies to define the potential of this enzyme in monitoring the effects of ERT in lysosomal storage disorders.

ER retention and degradation as the molecular basis underlying Gaucher disease heterogeneity

Gaucher disease (GD), an autosomal recessive disease, is characterized by accumulation of glucosylceramide mainly in cells of the reticuloendothelial system, due to mutations in the acid beta-glucocerebrosidase gene. Some of the patients suffer from neurological symptoms (type 2 and type 3 patients), whereas patients with type 1 GD do not present neurological signs. The disease is heterogeneous even among patients with the same genotype, implicating that a mutation in the glucocerebrosidase gene is required to cause GD but other factors play an important role in the manifestation of the disease. Glucocerebrosidase is a lysosomal enzyme, synthesized on endoplasmic reticulum (ER)-bound polyribosomes and translocated into the ER. Following N-linked glycosylations, it is transported to the Golgi apparatus, from where it is trafficked to the lysosomes. In this study, we tested glucocerebrosidase protein levels, N-glycans processing and intracellular localization in skin fibroblasts derived from patients with GD. Our results strongly suggest that mutant glucocerebrosidase variants present variable levels of ER retention and undergo ER-associated degradation in the proteasomes. The degree of ER retention and proteasomal degradation is one of the factors that determine GD severity.

Imino sugar inhibitors for treating the lysosomal glycosphingolipidoses

The inherited metabolic disorders of glycosphingolipid (GSL) metabolism are a relatively rare group of diseases that have diverse and often neurodegenerative phenotypes. Typically, a deficiency in catabolic enzyme activity leads to lysosomal storage of GSL substrates and in many diseases, several other glycoconjugates. A novel generic approach to treating these diseases has been termed substrate reduction therapy (SRT), and the discovery and development of N-alkylated imino sugars as effective and approved drugs is discussed. An understanding of the molecular mechanism for the inhibition of the key enzyme in GSL biosynthesis, ceramide glucosyltransferase (CGT) by N-alkylated imino sugars, has also lead to compound design for improvements to inhibitory potency, bioavailability, enzyme selectivity, and biological safety. Following a successful clinical evaluation of one compound, N-butyl-deoxynojirimycin [(NB-DNJ), miglustat, Zavesca], for treating type I Gaucher disease, issues regarding the significance of side effects and CNS access have been addressed as exposure of drug to patients has increased. An alternative experimental approach to treat specific glycosphingolipid (GSL) lysosomal storage diseases is to use imino sugars as molecular chaperons that assist protein folding and stability of mutant enzymes. The principles of chaperon-mediated therapy (CMT) are described, and the potential efficacy and preclinical status of imino sugars is compared with substrate reduction therapy (SRT). The increasing use of imino sugars for clinical evaluation of a group of storage diseases that are complex and often intractable disorders to treat has considerable benefit. This is particularly so given the ability of small molecules to be orally available, penetrate the central nervous system (CNS), and have well-characterized biological and pharmacological properties.

A novel enzymatic technique for limiting drug mobility in a hydrogel matrix

An oral colon specific drug delivery platform has been developed to facilitate targetted release of therapeutic proteins as well as small molecule drugs. A simple enzymatic procedure is used to modify the molecular architecture of a lightly chemically crosslinked galactomannan hydrogel as well as a model drug-galactomannan oligomer conjugate, fluoroisocynate (FITC) tagged guar oligomer, to entrap the model drug. The enzyme-modified hydrogel retains the drug until it reaches the colonic environment where bacteria secrete enzymes (namely beta-mannanase) to degrade the gel and release the drug molecule. Laser scanning confocal microscopy combined with fluorescence recovery after photobleaching is used to quantify the diffusion of the drug conjugate. The diffusion coefficient of solutes in the lightly crosslinked galactomannan hydrogel is approximately equal to the diffusion coefficient in the guar solution for simple diffusional drug loading. After drug loading, alpha-galactosidase treatment generates additional physical crosslinks in the hydrogel matrix as well as between the drug-oligomer conjugate and the hydrogel, which reduces diffusion of the drug-oligomer conjugate significantly. Degradation of the hydrogel by beta-mannanase results in a slow and controlled rate of FITC-guar oligomer diffusion, which generates an extended release profile for the model drug.

A Madagascar Sponge Batzella sp. as a source of alkylated iminosugars

Three new C-alkylated iminosugars, batzellasides A (3), B (4), and C (5), along with the known halitoxin (2) polymer were isolated from a Batzella sp. sponge, collected off the west coast of Madagascar. Although this class of azasugars is well known from terrestrial sources, our report represents the first examples of iminosugars from a marine organism. Comparison with the properties of known natural and synthetic iminosugars assisted in the structure determinations. Compounds 3-5 inhibited the growth of Staphylococcus epidermidis with MICs of < or =6.3 microg/mL.

Transgenic mouse expressing human mutant alpha-galactosidase A in an endogenous enzyme deficient background: a biochemical animal model for studying active-site specific chaperone therapy for Fabry disease

Fabry disease is an inborn error of glycosphingolipid metabolism caused by the deficiency of lysosomal alpha-galactosidase A (alpha-Gal A). We have established transgenic mice that exclusively express human mutant alpha-Gal A (R301Q) in an alpha-Gal A knock-out background (TgM/KO mice). This serves as a biochemical model to study and evaluate active-site specific chaperone (ASSC) therapy for Fabry disease, which is specific for those missense mutations that cause misfolding of alpha-Gal A. The alpha-Gal A activities in the heart, kidney, spleen, and liver of homozygous TgM/KO mice were 52.6, 9.9, 29.6 and 44.4 unit/mg protein, respectively, corresponding to 16.4-, 0.8-, 0.6- and 1.4-fold of the endogenous enzyme activities in the same tissues of non-transgenic mice with a similar genetic background. Oral administration of 1-deoxygalactonojirimycin (DGJ), a competitive inhibitor of alpha-Gal A and an effective ASSC for Fabry disease, at 0.05 mM in the drinking water of the mice for 2 weeks resulted in 13.8-, 3.3-, 3.9-, and 2.6-fold increases in enzyme activities in the heart, kidney, spleen and liver, respectively. No accumulation of globotriaosylceramide, a natural substrate of alpha-Gal A, could be detected in the heart of TgM/KO mice after DGJ treatment, indicating that degradation of the glycolipid in the heart was not inhibited by DGJ at that dosage. The alpha-Gal A activity in homozygous or heterozygous fibroblasts established from TgM/KO mice (TMK cells) was approximately 39 and 20 unit/mg protein, respectively. These TgM/KO mice and TMK cells are useful tools for studying the mechanism of ASSC therapy, and for screening ASSCs for Fabry disease.

α-1-C-Alkyl-1-deoxynojirimycin derivatives as potent and selective inhibitors of intestinal isomaltase: remarkable effect of the alkyl chain length on glycosidase inhibitory profile

A series of alpha- and beta-1-C-alkyl-1-deoxynojirimycin derivatives was prepared and evaluated as glycosidase inhibitors. Biological assays showed a marked dependence of the selectivity and potency of the inhibitors upon the position of the alkyl chain (alpha-1-C-, beta-1-C- or N-alkyl derivatives). In addition, the efficiency of alpha-1-C-alkyl-1-deoxynojirimycin derivatives as intestinal isomaltase inhibitors increases with the length of the alkyl chain. The strongest inhibition was found for alpha-1-C -nonyl-1-deoxynojirimycin with an IC50=3.5 nM (25x more potent inhibitor than the shorter chain homologue carrying a C8 chain). These results demonstrate that subtle changes in the aglycon fragment may result in remarkable enzyme specificity.

Recent advances in the biochemistry and genetics of sphingolipidoses

Sphingolipidoses are a subgroup of lysosomal storage diseases. They are defined as disorders caused by a genetic defect in catabolism of sphingosine-containing lipids. Catabolism of these lipids involves enzymes and activator proteins. After the discovery of lysosomes by de Duve and the demonstration of the first defective lysosomal enzyme by Hers in 1963, the first enzyme deficiency for sphingolipidoses was characterized in 1965 and all the defective enzymes were demonstrated in the last three decades. In 1984, the first activator protein was found and it expanded the concept of sphingolipidoses. In the following years, many researches have been undertaken to understand the molecular basis of these diseases, the mechanism of pathogenesis, the mechanism of lysosomal digestion of glycosphingolipids (GSLs) and the functional domains of lysosomal enzymes. New hypotheses and theories have been put forward for the mechanism of lysosomal digestion and pathogenesis. However, although much has been done, the pathogenesis of sphingolipidoses has not been fully elucidated. Mouse models of these diseases have facilitated the elucidation of pathogenesis and the development of therapeutic strategies for these diseases, which are not treatable at present except for Fabry and type 1 Gaucher disease. The purpose of this review is to collect information on the recent researches related to sphingolipidoses. The review includes the hydrolysis of GSLs in lysosome, mechanism of hydrolysis, pathogenesis and genetics of sphingolipidoses, a brief mouse model and therapeutic strategies of these diseases.

Biological Properties of d- and l-1-Deoxyazasugars

L-Enantiomers of 1-deoxynojirimycin (DNJ), 1-deoxymannojirimycin (manno-DNJ), 1-deoxyallonojirimycin (allo-DNJ), 1-deoxyaltronojirimycin (altro-DNJ), 1-deoxygalactonojirimycin (galacto-DNJ), 1-deoxygulonojirimycin (gulo-DNJ), and 1-deoxyidonojirimycin (ido-DNJ) were prepared according to prior methods for the d-enantiomers. These enantiospecific syntheses established unambiguously the absolute configuration of naturally occurring DNJ, manno-DNJ, allo-DNJ, altro-DNJ, and gulo-DNJ. Although d-DNJ and d-galacto-DNJ are known to be powerful competitive inhibitors of alpha-glucosidase and alpha-galactosidase, respectively, with K(i) values in the nM range, l-DNJ and l-galacto-DNJ were noncompetitive inhibitors of alpha-glucosidase and alpha-galactosidase, respectively, with K(i) values in the muM range. However, the azasugar mimicking the structure of the terminal sugar moiety of the natural substrate is not always an inhibitor of the glycosidase responsible for the hydrolysis. d-manno-DNJ is known as a much better inhibitor of alpha-l-fucosidase than alpha-mannosidase, while l-allo-DNJ was a better inhibitor than d-manno-DNJ of alpha-mannosidase. l-galacto-DNJ can be regarded as the 6-hydroxylated derivative of deoxyfuconojirimycin (DFJ), which is a powerful inhibitor of alpha-l-fucosidase with a K(i) value in the nM range. However, this replacement of the methyl group in DFJ by a hydroxymethyl group reduced its affinity by about 50-fold. This suggests that there is a hydrophobic region in or around the active site of alpha-l-fucosidase. It has been found that inhibitors of human lysosomal glycosidases have therapeutic potential for the corresponding lysosomal storage diseases (Nat. Med. 1999, 5, 112; Proc. Natl. Acad. Sci. USA, 2002, 99, 15428). Inhibition of human lysosomal glycosidases by the 1-deoxyazasugars synthesized was investigated. d-galacto-DNJ is a potent inhibitor of lysosomal alpha-galactosidase (IC(50) = 90 nM) and is now being evaluated preclinically for its potential use in Fabry disease, while d-DNJ inhibiting alpha-glucosidase (IC(50) = 40 nM) potently does not appear to become a potential therapeutic agent because of additional inhibitory activity toward glycoprotein processing alpha-glucosidases. On the other hand, although l-allo-DNJ is a moderate inhibitor of alpha-mannosidase (IC(50) = 64 microM), it may become a key compound for the drug design of potential therapeutic agents for alpha-mannosidosis.

Design and synthesis of 2-acetamidomethyl derivatives of isofagomine as potential inhibitors of human lysosomal β-hexosaminidases

As part of a program towards the development of specific inhibitors of human lysosomal beta-hexosaminidase for use as chemical chaperones in therapy of G(M2) gangliosidosis related diseases, the synthesis of 2-acetamidomethyl derivatives of isofagomine has been undertaken. Key event in this synthesis is the conversion of a C-2 substituted gluconolactone derivative into the corresponding lactam, followed by reduction to the corresponding amine. The 1-N-imino-2 acetamidomethyl derivative 5 proved to be a rather selective inhibitor with a K(i) of 2.4 microM for homogenate of human spleen lysosomal beta-hexosaminidase.

Enzyme replacement and enhancement therapies for lysosomal diseases

Although first suggested by de Duve in 1964, enzyme replacement therapy (ERT) for lysosomal storage diseases did not become a reality until the early 1990s when its safety and effectiveness were demonstrated in type 1 Gaucher disease. Today, ERT is a reality for Gaucher disease, Fabry disease and mucopolysaccharidosis type I (MPS I), and clinical trials with recombinant human enzymes are ongoing in Pompe disease, MPS II and MPS VI, and are about to begin in Neimann-Pick B disease. In addition to ERT, enzyme enhancement therapy (EET) offers a novel therapeutic strategy to increase the residual function of mutant proteins. EET employs small molecules as 'pharmacological chaperones' to rescue misfolded and/or unstable mutant enzymes or proteins that have residual function. EET also offers the possibility of treating neurodegenerative lysosomal disorders since these small therapeutic molecules may cross the blood-brain barrier. The current status of ERT and the prospects for EET for lysosomal storage diseases are reviewed.

Enzyme replacement therapy in Fabry disease: clinical implications

PURPOSE OF REVIEW

Fabry disease is an X-linked lysosomal storage disorder caused by a deficiency of the enzyme alpha-galactosidase A. The lack of enzyme activity results in an intracellular accumulation of glycosphingolipids, mainly globotriaosylceramide, in various tissues. Significant morbidity is caused by progressive effects on the vascular endothelium, heart, brain and kidney leading to end-stage renal disease. In this review we would like to give a current overview on recent advances in therapy and an outlook on future aspects in the management of Fabry disease.

RECENT FINDINGS

Besides symptomatic management, enzyme replacement therapy with recombinant alpha-galactosidase A is the only specific treatment currently available. Clinical trials using recombinant alpha-galactosidase A showed safety and efficacy in reversing substrate storage in different tissues. Short-term response on clinical manifestations such as impaired kidney function demonstrates a clear potential to improve and stabilize symptoms of the disease. In patients with residual enzyme activity enzyme enhancement therapy with pharmacological chaperones seems to be an attractive approach. Enzyme replacement therapy mediated by gene transfer may become a promising alternative treatment strategy in the future.

SUMMARY

Remarkable advances in the treatment of patients with Fabry disease have been made with the introduction of enzyme replacement therapy in clinical use. Although lysosomal globotriaosylceramide deposits are cleared very effectively, longer term experience on clinical outcome in patients with severe vital organ involvement is still limited.

N-hydroxyethyl-piperidine and -pyrrolidine homoazasugars: preparation and evaluation of glycosidase inhibitory activity

An efficient and practical strategy for the synthesis of N-hydroxyethyl-1-deoxy-homonojirimycins 4 and 5 and N-hydroxyethyl-pyrrolidine homoazasugars 6 and 7 with full stereocontrol is being reported. The key step involved is the intermolecular Michael addition of benzylamine to D-glucose derived alpha,beta-unsaturated ester 8 followed by N-alkylation with ethyl bromoacetate. Reduction with LAH, acetylation, hydrogenation and protection with -Cbz group afforded compounds 14a and 14b. Removal of 1,2-acetonide functionality, hydrogenation and deacetylation afforded N-hydroxyethyl-D-gluco-1-deoxyhomonojirimycin (4) and N-hydroxyethyl-L-ido-1-deoxyhomonojirimycin (5), respectively. Compounds 14a and 14b on acetylation followed by removal of 1,2-acetonide functionality, sodium metaperiodate oxidation, hydrogenation and deacetylation gave 1,4,5-trideoxy-1,4-imino-N-hydroxyethyl-D-arabino-hexitol (6) and 1,4,5-trideoxy-1,4-imino-N-hydroxyethyl-L-xylo-hexitol (7), respectively. The glycosidase inhibition activity of compounds 4, 5, 6, 7, 16a and 16b was evaluated using sweet almond seed as a rich source of different glycosidases.

Concise and highly stereocontrolled synthesis of 1-deoxygalactonojirimycin and its congeners using dioxanylpiperidene, a promising chiral building block

[reaction: see text] A concise and stereoselective synthesis of the chiral building block, dioxanylpiperidene 4 as a precursor for deoxyazasugars, starting from the Garner aldehyde 5 using catalytic ring-closing metathesis (RCM) for the construction of the piperidine ring is described. The asymmetric synthesis of 1-deoxygalactonojirimycin and its congeners 1-3 was carried out via the use of 4 in a highly stereocontrolled mode.

Asymmetric synthesis of the four possible fagomine isomers

The asymmetric synthesis of fagomine and its congeners 1-4 has been achieved by catalytic ring-closing metathesis (RCM). The synthesis involved the construction of the piperidene-type chiral building block 5 followed by dihydroxylation, starting from the d-serine-derived Garner aldehyde 6.

Enzyme replacement and enhancement therapies: lessons from lysosomal disorders

The past decade has witnessed remarkable advances in our ability to treat inherited metabolic disorders, especially the lysosomal storage diseases, a group of more than 40 disorders, each of which is caused by the deficiency of a lysosomal enzyme or protein. During the past few years, both enzyme replacement and enhancement therapies have been developed to treat these disorders. This review discusses the successes and shortcomings of these therapeutic strategies, and the contributions that they have made to treating lysosomal storage diseases.

Chemical chaperones increase the cellular activity of N370S beta -glucosidase: a therapeutic strategy for Gaucher disease

Gaucher disease is a lysosomal storage disorder caused by deficient lysosomal beta-glucosidase (beta-Glu) activity. A marked decrease in enzyme activity results in progressive accumulation of the substrate (glucosylceramide) in macrophages, leading to hepatosplenomegaly, anemia, skeletal lesions, and sometimes CNS involvement. Enzyme replacement therapy for Gaucher disease is costly and relatively ineffective for CNS involvement. Chemical chaperones have been shown to stabilize various proteins against misfolding, increasing proper trafficking from the endoplasmic reticulum. We report herein that the addition of subinhibitory concentrations (10 microM) of N-(n-nonyl)deoxynojirimycin (NN-DNJ) to a fibroblast culture medium for 9 days leads to a 2-fold increase in the activity of N370S beta-Glu, the most common mutation causing Gaucher disease. Moreover, the increased activity persists for at least 6 days after the withdrawal of the putative chaperone. The NN-DNJ chaperone also increases WT beta-Glu activity, but not that of L444P, a less prevalent Gaucher disease variant. Incubation of isolated soluble WT enzyme with NN-DNJ reveals that beta-Glu is stabilized against heat denaturation in a dose-dependent fashion. We propose that NN-DNJ chaperones beta-Glu folding at neutral pH, thus allowing the stabilized enzyme to transit from the endoplasmic reticulum to the Golgi, enabling proper trafficking to the lysosome. Clinical data suggest that a modest increase in beta-Glu activity may be sufficient to achieve a therapeutic effect.

Purification and characterization of alpha-galactosidase from a thermophilic fungus Thermomyces lanuginosus

An extracellular alpha-galactosidase was purified to electrophoretic homogeneity from a locust bean gum-spent culture fluid of a mannanolytic strain of the thermophilic fungus Thermomyces lanuginosus. Molecular mass of the enzyme is 57 kDa. The pure enzyme which has a glycoprotein nature, afforded several forms on IEF, indicating its microheterogeneity. Isoelectric point of the major form was 5.2. Enzyme is the most active against aryl alpha-D-galactosides but efficiently hydrolyzed alpha-glycosidically linked non-reducing terminal galactopyranosyl residues occurring in natural substrates such as melibiose, raffinose, stachyose, and fragments of galactomannan. In addition, the enzyme is able to catalyze efficient degalactosylation of polymeric galactomannans leading to precipitation of the polymers. Stereochemical course of hydrolysis of two substrates, 4-nitrophenyl alpha-galactopyranoside and galactosyl(1)mannotriose, followed by (1)H NMR spectroscopy, pointed out the alpha-anomer of D-galactose was the primary product of hydrolysis from which the beta-anomer was formed by mutarotation. Hence the enzyme is a retaining glycosyl hydrolase. In accord with its retaining character the enzyme catalyzed transgalactosylation from 4-nitrophenyl alpha-galactopyranoside as a glycosyl donor. Amino acid sequence alignment of N-terminal and two internal sequences suggested that the enzyme is a member of family 27 of glycosyl hydrolases.

Enzyme replacement and beyond

During the last decade, enzyme replacement therapy for lysosomal storage diseases became a reality with the demonstration of its safety and effectiveness in type 1 Gaucher disease. Currently, enzyme replacement and several other potential therapeutic strategies are being developed for selected lysosomal storage diseases, including Fabry disease due to the deficient activity of alpha-galactosidase A (alpha-Gal A). The development and clinical evaluation of these new therapies require a stepwise process, each step being rigorously reviewed and approved by national or international regulatory agencies. For lethal disorders that affect small populations, such as many inherited metabolic diseases, this process can be accelerated by 'orphan drug' and 'fast track' regulations. As an example of the drug development process, the development of recombinant human alpha-Gal A (r-halphaGal A) replacement for Fabry disease is presented, including the preclinical studies in the 'Fabry mouse' model, and the clinical phase 1/2, phase 3, and phase 3 extension studies, which demonstrate the safety and efficacy of this new therapy.

Novel alpha-L-fucosidase inhibitors from the bark of Angylocalyx pynaertii (Leguminosae)

The extract of bark of Angylocalyx pynaertii (Leguminosae) was found to potently inhibit mammalian alpha-L-fucosidases. A thorough examination of the extract resulted in the discovery of 15 polyhydroxylated alkaloids, including the known alkaloids from seeds of this plant, 1,4-dideoxy-1,4-imino-D-arabinitol (DAB), 1-deoxymannojirimycin (DMJ) and 2,5-imino-1,2,5-trideoxy-D-mannitol (6-deoxy-DMDP). Among them, eight sugar-mimic alkaloids showed the potent inhibitory activity towards bovine epididymis alpha-L-fucosidase and their Ki values are as follows: 6-deoxy-DMDP (83 microM), 2,5-imino-1,2,5-trideoxy-L-glucitol (0.49 microM), 2,5-dideoxy-2,5-imino-D-fucitol (17 microM), 2,5-imino-1,2,5-trideoxy-D-altritol (3.7 microM), DMJ (4.7 microM), N-methyl-DMJ (30 microM), 6-O-alpha-L-rhamnopyranosyl-DMJ (Rha-DMJ, 0.06 microM), and beta-L-homofuconojirimycin (beta-HFJ, 0.0053 microM). We definitively deduced the structural requirements of inhibitors of alpha-L-fucosidase for the piperidine alkaloids (DMJ derivatives). The minimum structural feature of alpha-L-fucosidase inhibitors is the correct configuration of the three hydroxyl groups on the piperidine ring corresponding to C2, C3 and C4 of L-fucose. Furthermore, the addition of a methyl group in the correct configuration to the ring carbon atom corresponding to C5 of L-fucose generates extremely powerful inhibition of alpha-L-fucosidase. The replacement of the methyl group of beta-HFJ by a hydroxymethyl group reduced its inhibitory potential about 80-fold. This suggests that there may be a hydrophobic region in or around the active site. The existence or configuration of a substituent group on the ring carbon atom corresponding to the anomeric position of L-fucose does not appear to be important for the inhibition. Interestingly, Rha-DMJ was a 70-fold more potent inhibitor of alpha-L-fucosidase than DMJ. This implies that the lysosomal alpha-L-fucosidase may have subsites recognizing oligosaccharyl structures in natural substrates.