Review of miglustat for clinical management in Gaucher disease type 1

Development of iminosugar-based glycosidase inhibitors as drug candidates for SARS-CoV-2 virus via molecular modelling and in vitro studies

We developed new iminosugar-based glycosidase inhibitors against SARS-CoV-2. Known drugs (miglustat, migalastat, miglitol, and swainsonine) were chosen as lead compounds to develop three classes of glycosidase inhibitors (α-glucosidase, α-galactosidase, and mannosidase). Molecular modelling of the lead compounds, synthesis of the compounds with the highest docking scores, enzyme inhibition tests, and in vitro antiviral assays afforded rationally designed inhibitors. Two highly active α-glucosidase inhibitors were discovered, where one of them is the most potent iminosugar-based anti-SARS-CoV-2 agent to date (EC90 = 1.94 µM in A549-ACE2 cells against Omicron BA.1 strain). However, galactosidase inhibitors did not exhibit antiviral activity, whereas mannosidase inhibitors were both active and cytotoxic. As our iminosugar-based drug candidates act by a host-directed mechanism, they should be more resilient to drug resistance. Moreover, this strategy could be extended to identify potential drug candidates for other viral infections.

Mysterious sphingolipids: metabolic interrelationships at the center of pathophysiology

Metabolic pathways are complex and intertwined. Deficiencies in one or more enzymes in a given pathway are directly linked with genetic diseases, most of them having devastating manifestations. The metabolic pathways undertaken by sphingolipids are diverse and elaborate with ceramide species serving as the hubs of sphingolipid intermediary metabolism and function. Sphingolipids are bioactive lipids that serve a multitude of cellular functions. Being pleiotropic in function, deficiency or overproduction of certain sphingolipids is associated with many genetic and chronic diseases. In this up-to-date review article, we strive to gather recent scientific evidence about sphingolipid metabolism, its enzymes, and regulation. We shed light on the importance of sphingolipid metabolism in a variety of genetic diseases and in nervous and immune system ailments. This is a comprehensive review of the state of the field of sphingolipid biochemistry.

A zebrafish model of combined saposin deficiency identifies acid sphingomyelinase as a potential therapeutic target

Sphingolipidoses are a subcategory of lysosomal storage diseases (LSDs) caused by mutations in enzymes of the sphingolipid catabolic pathway. Like many LSDs, neurological involvement in sphingolipidoses leads to early mortality with limited treatment options. Given the role of myelin loss as a major contributor toward LSD-associated neurodegeneration, we investigated the pathways contributing to demyelination in a CRISPR-Cas9-generated zebrafish model of combined saposin (psap) deficiency. psap knockout (KO) zebrafish recapitulated major LSD pathologies, including reduced lifespan, reduced lipid storage, impaired locomotion and severe myelin loss; loss of myelin basic protein a (mbpa) mRNA was progressive, with no changes in additional markers of oligodendrocyte differentiation. Brain transcriptomics revealed dysregulated mTORC1 signaling and elevated neuroinflammation, where increased proinflammatory cytokine expression preceded and mTORC1 signaling changes followed mbpa loss. We examined pharmacological and genetic rescue strategies via water tank administration of the multiple sclerosis drug monomethylfumarate (MMF), and crossing the psap KO line into an acid sphingomyelinase (smpd1) deficiency model. smpd1 mutagenesis, but not MMF treatment, prolonged lifespan in psap KO zebrafish, highlighting the modulation of acid sphingomyelinase activity as a potential path toward sphingolipidosis treatment.

Glucosylceramide Synthase Inhibitors Induce Ceramide Accumulation and Sensitize H3K27 Mutant Diffuse Midline Glioma to Irradiation

H3K27M mutant (mut) diffuse midline glioma (DMG) is a lethal cancer with no effective cure. The glycosphingolipids (GSL) metabolism is altered in these tumors and could be exploited to develop new therapies. We tested the effect of the glucosylceramide synthase inhibitors (GSI) miglustat and eliglustat on cell proliferation, alone or in combination with temozolomide or ionizing radiation. Miglustat was included in the therapy protocol of two pediatric patients. The effect of H3.3K27 trimethylation on GSL composition was analyzed in ependymoma. GSI reduced the expression of the ganglioside GD2 in a concentration and time-dependent manner and increased the expression of ceramide, ceramide 1-phosphate, sphingosine, and sphingomyelin but not of sphingosine 1-phosphate. Miglustat significantly increased the efficacy of irradiation. Treatment with miglustat according to dose recommendations for patients with Niemann-Pick disease was well tolerated with manageable toxicities. One patient showed a mixed response. In ependymoma, a high concentration of GD2 was found only in the presence of the loss of H3.3K27 trimethylation. In conclusion, treatment with miglustat and, in general, targeting GSL metabolism may offer a new therapeutic opportunity and can be administered in close proximity to radiation therapy. Alterations in H3K27 could be useful to identify patients with a deregulated GSL metabolism.

Glucosylceramide is essential for Heartland and Dabie bandavirus glycoprotein-induced membrane fusion

Due to climate changes, there has been a large expansion of emerging tick-borne zoonotic viruses, including Heartland bandavirus (HRTV) and Dabie bandavirus (DBV). As etiologic agents of hemorrhagic fever with high fatality, HRTV and DBV have been recognized as dangerous viral pathogens that likely cause future wide epidemics. Despite serious health concerns, the mechanisms underlying viral infection are largely unknown. HRTV and DBV Gn and Gc are viral surface glycoproteins required for early entry events during infection. Glycosphingolipids, including galactosylceramide (GalCer), glucosylceramide (GlcCer) and lactosylceramide (LacCer), are a class of membrane lipids that play essential roles in membrane structure and viral lifecycle. Here, our genome-wide CRISPR/Cas9 knockout screen identifies that glycosphingolipid biosynthesis pathway is essential for HRTV and DBV infection. The deficiency of UDP-glucose ceramide glucosyltransferase (UGCG) that produces GlcCer resulted in the loss of infectivity of recombinant viruses pseudotyped with HRTV or DBV Gn/Gc glycoproteins. Conversely, exogenous supplement of GlcCer, but not GalCer or LacCer, recovered viral entry of UGCG-deficient cells in a dose-dependent manner. Biophysical analyses showed that GlcCer targeted the lipid-head-group binding pocket of Gc to form a stable protein-lipid complex, which allowed the insertion of Gc protein into host lysosomal membrane lipid bilayers for viral fusion. Mutagenesis showed that D841 residue at the Gc lipid binding pocket was critical for GlcCer interaction and thereby, viral entry. These findings reveal detailed mechanism of GlcCer glycosphingolipid in HRTV and DBV Gc-mediated membrane fusion and provide a potential therapeutic target for tickborne virus infection.

Miglustat, a glucosylceramide synthase inhibitor, mitigates liver fibrosis through TGF-β/Smad pathway suppression in hepatic stellate cells

Transforming growth factor (TGF)-β/Smad pathway is implicated in the pathogenesis of liver fibrosis, a condition characterized by excessive deposition of extracellular matrix (ECM) proteins such as collagen in response to chronic inflammation. It has been reported that ceramide regulates collagen production through TGF-β/Smad pathway activation. In this study, we examined whether miglustat, an inhibitor of glucosylceramide synthase, can suppress liver fibrosis by reducing TGF-β/Smad pathway activity. Human hepatic stellate cells (HHSteCs) were cultured with TGF-β and multiple miglustat concentrations to examine dose-dependent effects on the expression levels of ECM-related genes and Smad proteins. To evaluate the efficacy of miglustat for fibrosis mitigation, C57BL/6 mice were treated with carbon tetrachloride (CCl₄) for 4 weeks to induce liver fibrosis, followed by combined CCl₄ plus miglustat for a further 2 weeks. To examine if miglustat can also prevent fibrosis, mice were treated with CCl₄ for 2 weeks, followed by CCl₄ plus miglustat for 2 weeks. Miglustat dose-dependently downregulated expression of α-smooth muscle actin and ECM components in TGF-β-treated HHSteCs. Both phosphorylation and nuclear translocation of Smad2 and Smad3 were also suppressed by miglustat treatment. Sirius-Red staining and hydroxyproline assays of model mouse liver samples revealed that miglustat reduced fibrosis, an effect accompanied by decreased expression of ECM. Our findings suggest that miglustat can both prevent and reverse liver fibrosis by inhibiting TGF-β/Smad pathway.

Sphingolipids in neurodegenerative diseases

Neurodegenerative Diseases (NDDs) are a group of disorders that cause progressive deficits of neuronal function. Recent evidence argues that sphingolipid metabolism is affected in a surprisingly broad set of NDDs. These include some lysosomal storage diseases (LSDs), hereditary sensory and autonomous neuropathy (HSAN), hereditary spastic paraplegia (HSP), infantile neuroaxonal dystrophy (INAD), Friedreich's ataxia (FRDA), as well as some forms of amyotrophic lateral sclerosis (ALS) and Parkinson's disease (PD). Many of these diseases have been modeled in Drosophila melanogaster and are associated with elevated levels of ceramides. Similar changes have also been reported in vertebrate cells and mouse models. Here, we summarize studies using fly models and/or patient samples which demonstrate the nature of the defects in sphingolipid metabolism, the organelles that are implicated, the cell types that are initially affected, and potential therapeutics for these diseases.

From Lysosomal Storage Disorders to Parkinson's Disease - Challenges and Opportunities

Lysosomes are specialized organelles with an acidic pH that act as recycling hubs for intracellular and extracellular components. They harbour numerous different hydrolytic enzymes to degrade substrates like proteins, peptides, and glycolipids. Reduced catalytic activity of lysosomal enzymes can cause the accumulation of these substrates and loss of lysosomal integrity, resulting in lysosomal dysfunction and lysosomal storage disorders (LSDs). Post-mitotic cells, such as neurons, seem to be highly sensitive to damages induced by lysosomal dysfunction, thus LSDs often manifest with neurological symptoms. Interestingly, some LSDs and Parkinson's disease (PD) share common cellular pathomechanisms, suggesting convergence of aetiology of the two disease types. This is further underlined by genetic associations of several lysosomal genes involved in LSDs with PD. The increasing number of lysosome-associated genetic risk factors for PD makes it necessary to understand functions and interactions of lysosomal proteins/enzymes both in health and disease, thereby holding the potential to identify new therapeutic targets. In this review, we highlight genetic and mechanistic interactions between the complex lysosomal network, LSDs and PD, and elaborate on methodical challenges in lysosomal research.

Glycosphingolipids in Diabetes, Oxidative Stress, and Cardiovascular Disease: Prevention in Experimental Animal Models

Diabetes contributes to about 30% morbidity and mortality world-wide and has tidal wave increases in several countries in Asia. Diabetes is a multi-factorial disease compounded by inflammation, dyslipidemia, atherosclerosis, and is sometimes accompanied with gains in body weight. Sphingolipid pathways that interplay in the enhancement of the pathology of this disease may be potential therapeutic targets. Thus, the application of advanced sphingolipidomics may help predict the progression of this disease and therapeutic outcomes in man. Pre-clinical studies using various experimental animal models of diabetes provide valuable information on the role of sphingolipid signaling networks in diabetes and the efficacy of drugs to determine the translatability of innovative discoveries to man. In this review, we discuss three major concepts regarding sphingolipids and diabetes. First, we discuss a possible involvement of a monosialodihexosylceramide (GM3) in insulin-insulin receptor interactions. Second, a potential role for ceramide (Cer) and lactosylceramide (LacCer) in apoptosis and mitochondrial dysfunction is proposed. Third, a larger role of LacCer in antioxidant status and inflammation is discussed. We also discuss how inhibitors of glycosphingolipid synthesis can ameliorate diabetes in experimental animal models.

A novel mouse model of CMT1B identifies hyperglycosylation as a new pathogenetic mechanism

Mutations in the Myelin Protein Zero gene (MPZ), encoding P0, the major structural glycoprotein of peripheral nerve myelin, are the cause of Charcot-Marie-Tooth (CMT) type 1B neuropathy, and most P0 mutations appear to act through gain-of-function mechanisms. Here, we investigated how misglycosylation, a pathomechanism encompassing several genetic disorders, may affect P0 function. Using in vitro assays, we showed that gain of glycosylation is more damaging for P0 trafficking and functionality as compared with a loss of glycosylation. Hence, we generated, via CRISPR/Cas9, a mouse model carrying the MPZD61N mutation, predicted to generate a new N-glycosylation site in P0. In humans, MPZD61N causes a severe early-onset form of CMT1B, suggesting that hyperglycosylation may interfere with myelin formation, leading to pathology. We show here that MPZD61N/+ mice develop a tremor as early as P15 which worsens with age and correlates with a significant motor impairment, reduced muscular strength and substantial alterations in neurophysiology. The pathological analysis confirmed a dysmyelinating phenotype characterized by diffuse hypomyelination and focal hypermyelination. We find that the mutant P0D61N does not cause significant endoplasmic reticulum stress, a common pathomechanism in CMT1B, but is properly trafficked to myelin where it causes myelin uncompaction. Finally, we show that myelinating dorsal root ganglia cultures from MPZD61N mice replicate some of the abnormalities seen in vivo, suggesting that they may represent a valuable tool to investigate therapeutic approaches. Collectively, our data indicate that the MPZD61N/+ mouse represents an authentic model of severe CMT1B affirming gain-of-glycosylation in P0 as a novel pathomechanism of disease.

New therapeutic approaches to Parkinson's disease targeting GBA, LRRK2 and Parkin

Parkinson's disease (PD) is defined as a complex disorder with multifactorial pathogenesis, yet a more accurate definition could be that PD is not a single entity, but rather a mixture of different diseases with similar phenotypes. Attempts to classify subtypes of PD have been made based on clinical phenotypes or biomarkers. However, the most practical approach, at least for a portion of the patients, could be to classify patients based on genes involved in PD. GBA and LRRK2 mutations are the most common genetic causes or risk factors of PD, and PRKN is the most common cause of autosomal recessive form of PD. Patients carrying variants in GBA, LRRK2 or PRKN differ in some of their clinical characteristics, pathology and biochemical parameters. Thus, these three PD-associated genes are of special interest for drug development. Existing therapeutic approaches in PD are strictly symptomatic, as numerous clinical trials aimed at modifying PD progression or providing neuroprotection have failed over the last few decades. The lack of precision medicine approach in most of these trials could be one of the reasons why they were not successful. In the current review we discuss novel therapeutic approaches targeting GBA, LRRK2 and PRKN and discuss different aspects related to these genes and clinical trials.

GM1 Gangliosidosis-A Mini-Review

GM1 gangliosidosis is a progressive, neurosomatic, lysosomal storage disorder caused by mutations in the GLB1 gene encoding the enzyme β-galactosidase. Absent or reduced β-galactosidase activity leads to the accumulation of β-linked galactose-containing glycoconjugates including the glycosphingolipid (GSL) GM1-ganglioside in neuronal tissue. GM1-gangliosidosis is classified into three forms [Type I (infantile), Type II (late-infantile and juvenile), and Type III (adult)], based on the age of onset of clinical symptoms, although the disorder is really a continuum that correlates only partially with the levels of residual enzyme activity. Severe neurocognitive decline is a feature of Type I and II disease and is associated with premature mortality. Most of the disease-causing β-galactosidase mutations reported in the literature are clustered in exons 2, 6, 15, and 16 of the GLB1 gene. So far 261 pathogenic variants have been described, missense/nonsense mutations being the most prevalent. There are five mouse models of GM1-gangliosidosis reported in the literature generated using different targeting strategies of the Glb1 murine locus. Individual models differ in terms of age of onset of the clinical, biochemical, and pathological signs and symptoms, and overall lifespan. However, they do share the major abnormalities and neurological symptoms that are characteristic of the most severe forms of GM1-gangliosidosis. These mouse models have been used to study pathogenic mechanisms, to identify biomarkers, and to evaluate therapeutic strategies. Three GLB1 gene therapy trials are currently recruiting Type I and Type II patients (NCT04273269, NCT03952637, and NCT04713475) and Type II and Type III patients are being recruited for a trial utilizing the glucosylceramide synthase inhibitor, venglustat (NCT04221451).

Milestones in treatments for inborn errors of metabolism: Reflections on Where chemistry and medicine meet

From Sir Archibald Garrod's initial description of the tetrad of albinism, alkaptonuria, cystinuria, and pentosuria to today, the field of medicine dedicated to inborn errors of metabolism has evolved from disease identification and mechanistic discovery to the development of therapies designed to subvert biochemical defects. In this review, we highlight major milestones in the treatment and diagnosis of inborn errors of metabolism, starting with dietary therapy for phenylketonuria in the 1950s and 1960s, and ending with current approaches in genetic manipulation.

n-Propyl 6-amino-2,6-dideoxy-2,2-difluoro-β-d-glucopyranoside is a good inhibitor for the β-galactosidase from E. coli

A convenient route has been developed for the synthesis of novel 6-amino-2,2-(or 3,3-difluoro)-2-(or 3),6-dideoxy-hexopyranoses. Biological screening showed these compounds as good inhibitors for several glycosidases. Especially n-propyl 6-amino-2,6-dideoxy-2,2-difluoro-β-d-glucopyranoside (8) was an excellent competitive inhibitor for the β-galactosidase from E. coli holding a K_i of 0.50 μM.

Substrate reduction therapy with Miglustat in pediatric patients with GM1 type 2 gangliosidosis delays neurological involvement: A multicenter experience

BACKGROUND

In GM1 gangliosidosis the lack of function of β-galactosidase results in an accumulation of GM1 ganglioside and related glycoconjugates in visceral organs, and particularly in the central nervous system, leading to severe disability and premature death. In the type 2 form of the disease, early intervention would be important to avoid precocious complications. To date, there are no effective therapeutic options in preventing progressive neurological deterioration. Substrate reduction therapy with Miglustat, a N-alkylated sugar that inhibits the enzyme glucosylceramide synthase, has been proposed for the treatment of several lysosomal storage disorders such as Gaucher type 1 and Niemann Pick Type C diseases. However, data on Miglustat therapy in patients with GM1 gangliosidosis are still scarce.

METHODS

We report here the results of Miglustat administration in four Italian children (average age: 55 months, range 20-125) affected by GM1 gangliosidosis type 2 treated in three different Italian pediatric hospitals specialized in metabolic diseases.

CONCLUSION

This treatment was safe and relatively well tolerated by all patients, with stabilization and/or slowing down of the neurological progression in three subjects.

Cheminformatics Tools for Analyzing and Designing Optimized Small-Molecule Collections and Libraries

Libraries of well-annotated small molecules have many uses in chemical genetics, drug discovery, and therapeutic repurposing. Multiple libraries are available, but few data-driven approaches exist to compare them and design new libraries. We describe an approach to scoring and creating libraries based on binding selectivity, target coverage, and induced cellular phenotypes as well as chemical structure, stage of clinical development, and user preference. The approach, available via the online tool http://www.smallmoleculesuite.org, assembles sets of compounds with the lowest possible off-target overlap. Analysis of six kinase inhibitor libraries using our approach reveals dramatic differences among them and led us to design a new LSP-OptimalKinase library that outperforms existing collections in target coverage and compact size. We also describe a mechanism of action library that optimally covers 1,852 targets in the liganded genome. Our tools facilitate creation, analysis, and updates of both private and public compound collections.

Chain-Branched Polyhydroxylated Octahydro-1H-Indoles as Potential Leads against Lysosomal Storage Diseases

Here, the synthesis and glycosidase inhibition properties of the two first known 3-ethyloctahydro-1H-indole-4,5,6-triols are reported. This study shows the transformation of d-glucose into polyhydroxylated 1-(2-nitrocyclohexane) acetaldehydes, followed by a protocol involving the formation of the azacyclopentane ring. Results of inhibitory potency assays and docking calculations show that at least one of them could be a lead for optimization in the search for compounds that behave like folding chaperones in lysosomal storage diseases.

Targeting Glucosylceramide Synthesis in the Treatment of Rare and Common Renal Disease

Sphingolipids, including ceramides, glycosphingolipids, sphingomyelin, and sphingosine-1-phosphate, have been recognized as important molecules that regulate critical cellular functions. Although originally studied in the context of lysosomal storage diseases, the roles of these compounds in more common disorders involving metabolism, vascular disease, and aberrant growth has been the focus of recent studies, including in disorders that affect the kidneys. These efforts have led to new insights into Fabry disease, a classic disorder of lysosomal function that results in renal failure as well as in more common renal diseases including diabetic nephropathy and polycystic kidney disease. Pathways for glycosphingolipid synthesis can be targeted with orally available small-molecule inhibitors, creating new opportunities for the treatment of both rare and common kidney diseases.

Budget Impact Analysis of Eliglustat for the Treatment of Gaucher Disease Type 1 in the United States

BACKGROUND

Gaucher disease type 1 (GD1) is a rare, genetic, lysosomal storage disease with no cure. Current treatment options include intravenous (IV) enzyme replacement therapy ([ERT]; imiglucerase, velaglucerase alfa, or taliglucerase alfa) or oral substrate reduction therapy ([SRT]; eliglustat or miglustat). The cost to U.S. payers of an IV-administered drug can vary depending on the site of care (i.e., home, outpatient clinic, or hospital setting). Treatment with oral eliglustat may present an opportunity for cost savings.

OBJECTIVE

To evaluate the budget impact from a U.S. payer perspective associated with transitioning patients receiving ERTs to the oral SRT eliglustat for the treatment of adults with GD1.

METHODS

A budget impact model estimated the change in pharmaceutical and administration costs resulting from increasing the market share of eliglustat from 12% (current) to 44% (new). The market share for eliglustat was drawn equally from existing shares of imiglucerase (40%) and velaglucerase alfa (40%) and assumed to be static over the analysis period. ERT costs were adjusted to account for site of care-based markup and the proportion of patients receiving infusions in each site of care (home, infusion center, or hospital outpatient). Annual ERT costs were calculated assuming a biweekly dose of 47.4 U per kg, a 72-kg patient weight, and 24 infusions per year. The effect of key variables was tested in the sensitivity analyses. All costs are expressed in 2017 U.S. dollars.

RESULTS

In a new plan with 5 million members and 25 GD1 treated patients, increased use of eliglustat resulted in an annual savings of $1,526,710 and a total savings of $4,580,130 (13.6%) over 3 years. The corresponding annual per member per month savings was $0.025. This is further illustrated in the sensitivity and scenario analyses where the use of eliglustat was cost saving in all cases. Shifting more patients receiving ERT in the hospital outpatient setting to eliglustat resulted in increased savings.

CONCLUSIONS

Based on these analyses, increased use of eliglustat resulted in meaningful cost savings to a payer's overall budget. Cost savings are highest among patients switching from ERT administered in a hospital outpatient setting. The results suggest that cost savings are also likely achievable from initiating patients on oral eliglustat instead of infusion-based therapy from the outset of treatment.

DISCLOSURES

This study was sponsored by Sanofi Genzyme. Evidera received funding from Sanofi Genzyme to conduct this study and prepare the manuscript. The sponsor collaborated on the study design, analysis, interpretation of results, and writing of the manuscript. Nalysnyk is an employee of and shareholder in Sanofi Genzyme. Ward, Cele, and Uyei are employees of Evidera, which provides consulting and other research services to biopharmaceutical companies. Sugarman was also an Evidera employee when the study was being conducted and the manuscript written. This study was presented as a poster at the Academy of Managed Care Pharmacy Nexus 2016, October 3-6, 2016; National City, MD, and at the International Society for Pharmacoeconomics and Outcomes Research, 22nd Annual International Meeting; May 20-24, 2017; Boston, MA.

Design of a New α-1-C-Alkyl-DAB Derivative Acting as a Pharmacological Chaperone for β-Glucocerebrosidase Using Ligand Docking and Molecular Dynamics Simulation

Some point mutations in β-glucocerebrosidase cause either improper folding or instability of this protein, resulting in Gaucher disease. Pharmacological chaperones bind to the mutant enzyme and stabilize this enzyme; thus, pharmacological chaperone therapy was proposed as a potential treatment for Gaucher disease. The binding affinities of α-1-C-alkyl 1,4-dideoxy-1,4-imino-d-arabinitol (DAB) derivatives, which act as pharmacological chaperones for β-glucocerebrosidase, abruptly increased upon elongation of their alkyl chain. In this study, the primary causes of such an increase in binding affinity were analyzed using protein–ligand docking and molecular dynamics simulations. We found that the activity cliff between α-1-C-heptyl-DAB and α-1-C-octyl-DAB was due to the shape and size of the hydrophobic binding site accommodating the alkyl chains, and that the interaction with this hydrophobic site controlled the binding affinity of the ligands well. Furthermore, based on the aromatic/hydrophobic properties of the binding site, a 7-(tetralin-2-yl)-heptyl-DAB compound was designed and synthesized. This compound had significantly enhanced activity. The design strategy in consideration of aromatic interactions in the hydrophobic pocket was useful for generating effective pharmacological chaperones for the treatment of Gaucher disease.

Characterization of the PLP-dependent transaminase initiating azasugar biosynthesis

Biosynthesis of the azasugar 1-deoxynojirimycin (DNJ) critically involves a transamination in the first committed step. Here, we identify the azasugar biosynthetic cluster signature in Paenibacillus polymyxa SC2 (Ppo), homologous to that reported in Bacillus amyloliquefaciens FZB42 (Bam), and report the characterization of the aminotransferase GabT1 (named from Bam). GabT1 from Ppo exhibits a specific activity of 4.9 nmol/min/mg at 30°C (pH 7.5), a somewhat promiscuous amino donor selectivity, and curvilinear steady-state kinetics that do not reflect the predicted ping-pong behavior typical of aminotransferases. Analysis of the first half reaction with l-glutamate in the absence of the acceptor fructose 6-phosphate revealed that it was capable of catalyzing multiple turnovers of glutamate. Kinetic modeling of steady-state initial velocity data was consistent with a novel hybrid branching kinetic mechanism which included dissociation of PMP after the first half reaction to generate the apoenzyme which could bind PLP for another catalytic deamination event. Based on comparative sequence analyses, we identified an uncommon His-Val dyad in the PLP-binding pocket which we hypothesized was responsible for the unusual kinetics. Restoration of the conserved PLP-binding site motif via the mutant H119F restored classic ping-pong kinetic behavior.

Neural stem cells for disease modeling and evaluation of therapeutics for infantile (CLN1/PPT1) and late infantile (CLN2/TPP1) neuronal ceroid lipofuscinoses

BACKGROUND

Infantile and late infantile neuronal ceroid lipofuscinoses (NCLs) are lysosomal storage diseases affecting the central nervous system (CNS). The infantile NCL (INCL) is caused by mutations in the PPT1 gene and late-infantile NCL (LINCL) is due to mutations in the TPP1 gene. Deficiency in PPT1 or TPP1 enzyme function results in lysosomal accumulation of pathological lipofuscin-like material in the patient cells. There is currently no small-molecular drug treatment for NCLs.

RESULTS

We have generated induced pluripotent stem cells (iPSC) from three patient dermal fibroblast lines and further differentiated them into neural stem cells (NSCs). Using these new disease models, we evaluated the effect of δ-tocopherol (DT) and hydroxypropyl-β-cyclodextrin (HPBCD) with the enzyme replacement therapy as the control. Treatment with the relevant recombinant enzyme or DT significantly ameliorated the lipid accumulation and lysosomal enlargement in the disease cells. A combination therapy of δ-tocopherol and HPBCD further improved the effect compared to that of either drug used as a single therapy.

CONCLUSION

The results demonstrate that these patient iPSC derived NCL NSCs are valid cell- based disease models with characteristic disease phenotypes that can be used for study of disease pathophysiology and drug development.

A new framework for evaluating the health impacts of treatment for Gaucher disease type 1

Background

The Disease Severity Scoring System (DS3) is a validated measure for evaluating Gaucher disease type 1 (GD1) severity. We developed a new framework, consisting of health states, transition probabilities between those states, and preferences for those states (utilities) based on the DS3 to predict long-term outcomes of patients starting treatment. We defined nine mutually exclusive (alive) health states based on three DS3 categories: mild (0 ≤ DS3 ≤ 3.5) without symptoms of bone disease; mild with bone pain, mild with severe skeletal complications (SSC) defined as lytic lesions, avascular necrosis, or fracture; moderate (3.5 < DS3 ≤ 6.5) without SSC; moderate with SSC; marked (6.5 < DS3 ≤ 9.5) without SSC; marked with SSC; severe (9.5 < DS3 ≤ 19) without SSC; and severe with SSC. Health-state transition probabilities and utilities were estimated from a longitudinal sample of patients with GD1 who started enzyme replacement therapy (the DS3 Score Study). Age dependent GD1-specific mortality was derived from published data. We used a Markov state-transition model to illustrate how to estimate time spent in each health state.

Results

The average predicted utilities for each health state ranged from 0.76 for mild disease with no clinical symptoms of bone disease to 0.52 with severe disease with SSC. Transition probabilities depended on disease severity (DS3 score) at treatment initiation and whether patients had undergone a total splenectomy or had an intact spleen/partial splenectomy prior to starting treatment. Patients who started treatment with intact or residual spleens spent more time in better health states than those who started treatment with total splenectomy.

Conclusions

This new framework, which is based on the DS3, can be used to project the long-term outcomes of GD1 patients starting treatment. The framework could also be used to compare the long-term outcomes of different GD1 treatment options.

Trial registration

NCT01136304. Registered: May 31, 2010 (retrospectively registered).

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-017-0592-6) contains supplementary material, which is available to authorized users.

Induced Pluripotent Stem Cells for Disease Modeling and Evaluation of Therapeutics for Niemann-Pick Disease Type A

Niemann-Pick disease type A (NPA)-induced pluripotent stem cells from patient dermal fibroblasts were differentiated into neural stem cells. By using the differentiated NPA neuronal cells as a cell-based disease model system, α-tocopherol, δ-tocopherol, and hydroxypropyl-β-cyclodextrin significantly reduced sphingomyelin accumulation in these NPA neuronal cells. This cell-based NPA model can be used for further study of disease pathophysiology and for high-throughput screening of compound libraries to identify lead compounds for drug development.

Niemann-Pick disease type A (NPA) is a lysosomal storage disease caused by mutations in the SMPD1 gene that encodes acid sphingomyelinase (ASM). Deficiency in ASM function results in lysosomal accumulation of sphingomyelin and neurodegeneration. Currently, there is no effective treatment for NPA. To accelerate drug discovery for treatment of NPA, we generated induced pluripotent stem cells from two patient dermal fibroblast lines and differentiated them into neural stem cells. The NPA neural stem cells exhibit a disease phenotype of lysosomal sphingomyelin accumulation and enlarged lysosomes. By using this disease model, we also evaluated three compounds that reportedly reduced lysosomal lipid accumulation in Niemann-Pick disease type C as well as enzyme replacement therapy with ASM. We found that α-tocopherol, δ-tocopherol, hydroxypropyl-β-cyclodextrin, and ASM reduced sphingomyelin accumulation and enlarged lysosomes in NPA neural stem cells. Therefore, the NPA neural stem cells possess the characteristic NPA disease phenotype that can be ameliorated by tocopherols, cyclodextrin, and ASM. Our results demonstrate the efficacies of cyclodextrin and tocopherols in the NPA cell-based model. Our data also indicate that the NPA neural stem cells can be used as a new cell-based disease model for further study of disease pathophysiology and for high-throughput screening to identify new lead compounds for drug development.

Significance

Currently, there is no effective treatment for Niemann-Pick disease type A (NPA). To accelerate drug discovery for treatment of NPA, NPA-induced pluripotent stem cells were generated from patient dermal fibroblasts and differentiated into neural stem cells. By using the differentiated NPA neuronal cells as a cell-based disease model system, α-tocopherol, δ-tocopherol, and hydroxypropyl-β-cyclodextrin significantly reduced sphingomyelin accumulation in these NPA neuronal cells. Therefore, this cell-based NPA model can be used for further study of disease pathophysiology and for high-throughput screening of compound libraries to identify lead compounds for drug development.

Progress and potential of non-inhibitory small molecule chaperones for the treatment of Gaucher disease and its implications for Parkinson disease

Gaucher disease, caused by pathological mutations GBA1, encodes the lysosome-resident enzyme glucocerebrosidase, which cleaves glucosylceramide into glucose and ceramide. In Gaucher disease, glucocerebrosidase deficiency leads to lysosomal accumulation of substrate, primarily in cells of the reticulo-endothelial system. Gaucher disease has broad clinical heterogeneity, and mutations in GBA1 are a risk factor for the development of different synucleinopathies. Insights into the cell biology and biochemistry of glucocerebrosidase have led to new therapeutic approaches for Gaucher disease including small chemical chaperones. Such chaperones facilitate proper enzyme folding and translocation to lysosomes, thereby preventing premature breakdown of the enzyme in the proteasome. This review discusses recent progress in developing chemical chaperones as a therapy for Gaucher disease, with implications for the treatment of synucleinopathies. It focuses on the development of non-inhibitory glucocerebrosidase chaperones and their therapeutic advantages over inhibitory chaperones, as well as the challenges involved in identifying and validating chemical chaperones.

A peptide-linked recombinant glucocerebrosidase for targeted neuronal delivery: Design, production, and assessment

Although recombinant glucocerebrosidase (GCase) is the standard therapy for the inherited lysosomal storage disease Gaucher's disease (GD), enzyme replacement is not effective when the central nervous system is affected. We created a series of recombinant genes/proteins where GCase was linked to different membrane binding peptides including the Tat peptide, the rabies glycoprotein derived peptide (RDP), the binding domain from tetanus toxin (TTC), and a tetanus like peptide (Tet1). The majority of these proteins were well-expressed in a mammalian producer cell line (HEK 293F). Purified recombinant Tat-GCase and RDP-GCase showed similar GCase protein delivery to a neuronal cell line that genetically lacks the functional enzyme, and greater delivery than control GCase, Cerezyme (Genzyme). This initial result was unexpected based on observations of superior protein delivery to neurons with RDP as a vector. A recombinant protein where a fragment of the flexible hinge region from IgA (IgAh) was introduced between RDP and GCase showed substantially enhanced GCase neuronal delivery (2.5 times over Tat-GCase), suggesting that the original construct resulted in interference with the capacity of RDP to bind neuronal membranes. Extended treatment of these knockout neuronal cells with either Tat-GCase or RDP-IgAh-GCase resulted in an >90% reduction in the lipid substrate glucosylsphingosine, approaching normal levels. Further in vivo studies of RDP-IgAh-GCase as well as Tat-GCase are warranted to assess their potential as treatments for neuronopathic forms of GD. These peptide vectors are especially attractive as they have the potential to carry a protein across the blood-brain barrier, avoiding invasive direct brain delivery.

Amino-functionalized iminocyclitols: synthetic glycomimetics of medicinal interest

A review on the syntheses and biological activities of unnatural glycomimetics highlighting the effect of replacement of hydroxyl groups of natural iminosugars by amino functionalities is presented.

Effect of oral eliglustat on splenomegaly in patients with Gaucher disease type 1: the ENGAGE randomized clinical trial

IMPORTANCE

Gaucher disease type 1 is characterized by hepatosplenomegaly, anemia, thrombocytopenia, and skeletal disease. A safe, effective oral therapy is needed.

OBJECTIVE

To determine whether eliglustat, a novel oral substrate reduction therapy, safely reverses clinical manifestations in untreated adults with Gaucher disease type 1.

DESIGN, SETTING, AND PARTICIPANTS

Phase 3, randomized, double-blind, placebo-controlled trial conducted at 18 sites in 12 countries from November 2009 to July 2012 among eligible patients with splenomegaly plus thrombocytopenia and/or anemia. Of 72 patients screened, 40 were enrolled.

INTERVENTIONS

Patients were stratified by spleen volume and randomized 1:1 to receive eliglustat (50 or 100 mg twice daily; n = 20) or placebo (n = 20) for 9 months.

MAIN OUTCOMES AND MEASURES

The primary efficacy end point was percentage change in spleen volume in multiples of normal from baseline to 9 months; secondary efficacy end points were change in hemoglobin level and percentage changes in liver volume and platelet count.

RESULTS

All patients had baseline splenomegaly and thrombocytopenia (mostly moderate or severe), most had mild or moderate hepatomegaly, and 20% had mild anemia. Least-square mean spleen volume decreased by 27.77% (95% CI, -32.57% to -22.97%) in the eliglustat group (from 13.89 to 10.17 multiples of normal) vs an increase of 2.26% (95% CI, -2.54% to 7.06%) in the placebo group (from 12.50 to 12.84 multiples of normal) for an absolute treatment difference of -30.03% (95% CI, -36.82% to -23.24%; P < .001). For the secondary end points, the least-square mean absolute differences between groups all favored eliglustat, with a 1.22-g/dL increase in hemoglobin level (95% CI, 0.57-1.88 g/dL; P < .001), 6.64% decrease in liver volume (95% CI, -11.37% to -1.91%; P = .007), and 41.06% increase in platelet count (95% CI, 23.95%-58.17%; P < .001). No serious adverse events occurred. One patient in the eliglustat group withdrew (non-treatment related); 39 of the 40 patients transitioned to an open-label extension study.

CONCLUSIONS AND RELEVANCE

Among previously untreated adults with Gaucher disease type 1, treatment with eliglustat compared with placebo for 9 months resulted in significant improvements in spleen volume, hemoglobin level, liver volume, and platelet count. The clinical significance of these findings is uncertain, and more definitive conclusions about clinical efficacy and utility will require comparison with the standard treatment of enzyme replacement therapy as well as longer-term follow-up.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00891202.

Sphingolipids and lysosomal pathologies

Endocytosed (glyco)sphingolipids are degraded, together with other membrane lipids in a stepwise fashion by endolysosomal enzymes with the help of small lipid binding proteins, the sphingolipid activator proteins (SAPs), at the surface of intraluminal lysosomal vesicles. Inherited defects in a sphingolipid-degrading enzyme or SAP cause the accumulation of the corresponding lipid substrates, including cytotoxic lysosphingolipids, such as galactosylsphingosine and glucosylsphingosine, and lead to a sphingolipidosis. Analysis of patients with prosaposin deficiency revealed the accumulation of intra-endolysosmal vesicles and membrane structures (IM). Feeding of prosaposin reverses the storage, suggesting inner membrane structures as platforms of sphingolipid degradation. Water soluble enzymes can hardly attack sphingolipids embedded in the membrane of inner endolysosomal vesicles. The degradation of sphingolipids with few sugar residues therefore requires the help of the SAPs, and is strongly stimulated by anionic membrane lipids. IMs are rich in anionic bis(monoacylglycero)phosphate (BMP). This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Remodeling the proteostasis network to rescue glucocerebrosidase variants by inhibiting ER-associated degradation and enhancing ER folding

Gaucher’s disease (GD) is characterized by loss of lysosomal glucocerebrosidase (GC) activity. Mutations in the gene encoding GC destabilize the protein’s native folding leading to ER-associated degradation (ERAD) of the misfolded enzyme. Enhancing the cellular folding capacity by remodeling the proteostasis network promotes native folding and lysosomal activity of mutated GC variants. However, proteostasis modulators reported so far, including ERAD inhibitors, trigger cellular stress and lead to induction of apoptosis. We show herein that lacidipine, an L-type Ca²⁺ channel blocker that also inhibits ryanodine receptors on the ER membrane, enhances folding, trafficking and lysosomal activity of the most severely destabilized GC variant achieved via ERAD inhibition in fibroblasts derived from patients with GD. Interestingly, reprogramming the proteostasis network by combining modulation of Ca²⁺ homeostasis and ERAD inhibition remodels the unfolded protein response and dramatically lowers apoptosis induction typically associated with ERAD inhibition.

Induced pluripotent stem cell technology for disease modeling and drug screening with emphasis on lysosomal storage diseases

The recent derivation of disease-specific induced pluripotent stem cells (iPSCs) from somatic cells of patients with familial and sporadic forms of diseases and the demonstration of their ability to give rise to disease-relevant cell types provide an excellent opportunity to gain further insights into the mechanisms responsible for the pathophysiology of these diseases and develop novel therapeutic drugs. Here, we review the recent advances in iPSC technology for modeling of various lysosomal storage diseases (LSDs) and discuss possible strategies through which LSD-iPSCs can be exploited to identify novel drugs and improve future clinical treatment of LSDs.

Radiological aspects of Gaucher disease

Advances in imaging and the development of commercially available enzyme therapy have significantly altered the traditional radiology of Gaucher disease. The cost of treatment and need for monitoring response to therapy have magnified the importance of imaging. There are no recent comprehensive reviews of the radiology of this relatively common lysosomal storage disease. This article describes the modern imaging, techniques and radiological manifestations of Gaucher disease.

Evaluation of miglustat treatment in patients with type III mucopolysaccharidosis: a randomized, double-blind, placebo-controlled study

OBJECTIVE

To evaluate the efficacy and safety of oral miglustat treatment in patients with mucopolysaccharidosis type III. The primary outcome was efficacy with improvement or stabilization in at least two domains of Vineland Adaptative Behavior Scales at 6 months. The secondary outcome measured the evolution of other cognitive tests at 12 months. The safety and tolerability were assessed throughout the study.

STUDY DESIGN

This was a randomized, double-blind, placebo-controlled, monocenter, institutional, phase IIb to III study. In case of efficacy at 6 months, the study would go on for another 6 months on an open design with all patients receiving miglustat. In the absence of efficacy at 6 months, the trial had to be continued for 6 more months with the initial design.

RESULTS

After 6 months, efficacy was not superior in patients with miglustat. The independent review board confirmed continuing the study until 12 months.

CONCLUSION

Miglustat treatment was not associated with any improvement/stabilization in behavior problems in patients with mucopolysaccharidosis type III. Miglustat has an acceptable safety profile. However, the study has confirmed that miglustat is able to pass through the blood-brain barrier without significantly decreasing ganglioside levels.

Ca2+ homeostasis modulation enhances the amenability of L444P glucosylcerebrosidase to proteostasis regulation in patient-derived fibroblasts

Gaucher's disease is caused by deficiency of lysosomal glucocerebrosidase (GC) activity and accumulation of GC substrate, glucosylceramide. A number of point mutations in GC encoding gene have been reported to destabilize the enzyme native structure, resulting in protein misfolding and degradation. Particularly, the L444P GC variant, often associated with neuropathic manifestations of the disease, is severely destabilized and immediately degraded, resulting in complete loss of enzymatic activity. In addition, glucosylceramide accumulation causes Ca(2+) efflux from the endoplasmic reticulum (ER) through ryanodine receptors (RyRs) in the neurons of Gaucher's disease patients. We hypothesized that excessive [Ca(2+)](ER) efflux impairs ER folding and studied how modulation of [Ca(2+)](ER) affects folding of L444P GC in patient-derived fibroblasts. We report that RyRs blockers mediated [Ca(2+)] modulation, recreating a "wild type-like" folding environment in the ER, more amenable to rescuing the folding of mutated L444P GC through proteostasis regulation. Treating patient-derived fibroblasts with a RyRs blocker and a proteostasis modulator, MG-132, results in enhanced folding, trafficking, and activity of the severely destabilized L444P GC variant. Global gene expression profiling and mechanistic studies were conducted to investigate the folding quality control expression pattern conducive to native folding of mutated L444P GC and revealed that the ER-lumenal BiP/GRP78 plays a key role in the biogenesis of this GC variant.

Pathology and current treatment of neurodegenerative sphingolipidoses

Sphingolipidoses constitute a large subgroup of lysosomal storage disorders (LSDs). Many of them are associated with a progressive neurodegeneration. As is the case for LSDs in general, most sphingolipidoses are caused by deficiencies in lysosomal hydrolases. However, accumulation of sphingolipids can also result from deficiencies in proteins involved in the transport or posttranslational modification of lysosomal enzymes, transport of lipids, or lysosomal membrane proteins required for transport of lysosomal degradation end products. The accumulation of sphingolipids in the lysosome together with secondary changes in the concentration and localization of other lipids may cause trafficking defects of membrane lipids and proteins, affect calcium homeostasis, induce the unfolded protein response, activate apoptotic cascades, and affect various signal transduction pathways. To what extent, however, these changes contribute to the pathogenesis of the diseases is not fully understood. Currently, there is no cure for sphingolipidoses. Therapies like enzyme replacement, pharmacological chaperone, and substrate reduction therapy, which have been shown to be efficient in non-neuronopathic LSDs, are currently evaluated in clinical trials of neuronopathic sphingolipidoses. In the future, neural stem cell therapy and gene therapy may become an option for these disorders.

ELIGLUSTAT TARTRATE: Glucosylceramide Synthase Inhibitor Treatment of Type 1 Gaucher Disease

Eliglustat tartrate (Genz-112638) is a novel, orally administered agent currently in development for the treatment of lysosomal storage disorders, including type 1 Gaucher disease and Fabry disease. This glucosylceramide analogue acts as an inhibitor of glucosylceramide synthase, a Golgi complex enzyme that catalyzes the formation of glucosylceramide from ceramide and UDP-glucose and is the first step in the formation of glucocerebroside-based glycosphingolipids. Pre-clinical pharmacological studies demonstrate that the agent has a high therapeutic index, excellent oral bioavailability and limited toxicity. Phase I studies in healthy volunteers revealed limited toxicity with an excellent pharmacodynamic response, as measured by decreased plasma glucosylceramide concentrations. Phase II studies in patients with type 1 Gaucher disease have demonstrated promising clinical responses, as measured by decreases in spleen size, improvement in hemoglobin concentrations and increased platelet counts. Two randomized phase III trials testing the efficacy and safety of eliglustat tartrate are currently in progress.

Cystic fibrosis transmembrane conductance regulator modulators for personalized drug treatment of cystic fibrosis: progress to date

This article considers the issue of personalized drug discovery for the orphan disease cystic fibrosis (CF) to deliver a candidate for therapeutic development. CF is a very complicated disease due to numerous anomalies of the gene leading to progressive severity and morbidity. Despite extensive research efforts, 20 years after the cloning of the CF gene, CF patients are still waiting for a curative treatment as prescribed medications still target the secondary manifestations of the disease rather than the gene or the CF transmembrane conductance regulator (CFTR) protein. New therapeutics aimed at improving mutant CFTR functions, also known as 'protein repair therapy' are nevertheless hoped and predicted to replace some of the currently used therapy, while improving the quality of life as well as life expectancy of CF patients. Although there is substantial variability in the cost of treating CF between countries, a protein repair therapy should also alleviate the financial burden of medical costs for CF patients and their families. Finding new drugs or rediscovering old ones for CF is critically dependent on the delivery of molecular and structural information on the CFTR protein, on its mutated version and on the network of CFTR-interacting proteins. The expertise needed to turn compounds into marketable drugs for CF will depend on our ability to provide biological information obtained from pertinent models of the disease and on our success in transferring safe molecules to clinical trials. Predicting a drug-induced response is also an attractive challenge that could be rapidly applied to patients.

Therapy for lysosomal storage disorders

In the last years, much progress has been achieved in the field of lysosomal storage disorders. In the past, no specific treatment was available for the affected patients; management mainly consisted of supportive care and treatment of complications. As orphan drug regulations, however, encouraged development of drugs for these disorders by granting marketing exclusivity for 10 years and other commercial benefits, enzyme replacement therapy became available for lysosomal storage disorders, such as Gaucher disease, Fabry disease, mucopolysaccharidoses type I, II, and VI, and Pompe disease. This review will summarize the efficacy and clinical status of hematopoietic stem cell transplantation, enzyme replacement, and substrate deprivation therapy, and describe new therapeutic perspectives currently under preclinical investigations such as chaperone-mediated therapy, stop-codon read-through therapy, and gene therapy.