Quantitative assessment of the exposure-efficacy relationship of glucocerebrosidase using Markovian elements in Gaucher patients treated with enzyme replacement therapy.

AIMS: The aims of this study are (i) to develop a population pharmacokinetic model of enzyme activity in Gaucher-type 1 (GD1) patients after intravenous administration of enzyme replacement therapy (ERT), and (ii) to establish an exposure-efficacy relationship for bone marrow infiltration to propose dose adjustments according to patient covariate values. METHODS: A prospective follow-up, semi-experimental multi-centre study was conducted in four hospitals to evaluate the pharmacokinetics, efficacy and safety of ERT in GD1 patients. Twenty-five individuals with 266 glucocerebrosidase (GCase) observations in plasma and leukocytes and 14 individuals with 68 Spanish magnetic resonance imaging (S-MRI) observations were enrolled. RESULTS: A two concatenated compartment model with zero-order endogenous production and first-order distribution (CL1 = 3.85 × 10-1 L/d) and elimination (CL2 = 1.25 L/d) allowed GCase observations in plasma and leukocytes to be described, respectively. An exponential time dependency (kT = 6.14 × 10-1 d-1 ) effect on CL1 was incorporated. The final exposure-efficacy model was a longitudinal logistic regression model with a first-order Markov element. An Emax function (EC50 = 15.73 U/L and Emax = 2.33) linked steady-state concentrations of GCase in leukocytes to the probability of transition across the different S-MRI stages. CONCLUSION: A population pharmacokinetic model successfully characterized the leukocyte activity-time profiles of GCase following intravenous administration of ERT in GD1 patients together with an exposure-efficacy relationship in bone marrow using Markovian elements. The information obtained from this study could be of high clinical relevance in individualization of ERT in GD1 patients, as this could lead to anticipative decision-making regarding clinical response in bone and optimal dosing strategy.

Acid ceramidase inhibition ameliorates α-synuclein accumulation upon loss of GBA1 function.

GBA1 encodes the lysosomal enzyme ß-glucocerebrosidase (GCase) which converts glucosylceramide into ceramide and glucose. Mutations in GBA1 lead to Gaucher's disease and are a major risk factor for Parkinson's disease (PD) and Dementia with Lewy bodies (DLB), synucleinopathies characterized by accumulation of intracellular α-synuclein. In this study, we examined whether decreased ceramide that is observed in GCase-deficient cells contributes to α-synuclein accumulation. We demonstrated that deficiency of GCase leads to a reduction of C18-ceramide species and altered intracellular localization of Rab8a, a small GTPase implicated in secretory autophagy, that contributed to impaired secretion of α-synuclein and accumulation of intracellular α-synuclein. This secretory defect was rescued by exogenous C18-ceramide or chemical inhibition of lysosomal enzyme acid ceramidase that converts lysosomal ceramide into sphingosine. Inhibition of acid ceramidase by carmofur resulted in increased ceramide levels and decreased glucosylsphingosine levels in GCase-deficient cells, and also reduced oxidized α-synuclein and levels of ubiquitinated proteins in GBA1-PD patient-derived dopaminergic neurons. Together, these results suggest that decreased ceramide generation via the catabolic lysosomal salvage pathway in GCase mutant cells contributes to α-synuclein accumulation, potentially due to impaired secretory autophagy. We thus propose that acid ceramidase inhibition which restores ceramide levels may be a potential therapeutic strategy to target synucleinopathies linked to GBA1 mutations including PD and DLB.

The production of human glucocerebrosidase in glyco-engineered Nicotiana benthamiana plants.

For the production of therapeutic proteins in plants, the presence of ß1,2-xylose and core α1,3-fucose on plants' N-glycan structures has been debated for their antigenic activity. In this study, RNA interference (RNAi) technology was used to down-regulate the endogenous N-acetylglucosaminyltransferase I (GNTI) expression in Nicotiana benthamiana. One glyco-engineered line (NbGNTI-RNAi) showed a strong reduction of plant-specific N-glycans, with the result that as much as 90.9% of the total N-glycans were of high-mannose type. Therefore, this NbGNTI-RNAi would be a promising system for the production of therapeutic glycoproteins in plants. The NbGNTI-RNAi plant was cross-pollinated with transgenic N. benthamiana expressing human glucocerebrosidase (GC). The recombinant GC, which has been used for enzyme replacement therapy in patients with Gaucher's disease, requires terminal mannose for its therapeutic efficacy. The N-glycan structures that were presented on all of the four occupied N-glycosylation sites of recombinant GC in NbGNTI-RNAi plants (GC(gnt1) ) showed that the majority (ranging from 73.3% up to 85.5%) of the N-glycans had mannose-type structures lacking potential immunogenic ß1,2-xylose and α1,3-fucose epitopes. Moreover, GC(gnt1) could be taken up into the macrophage cells via mannose receptors, and distributed and taken up into the liver and spleen, the target organs in the treatment of Gaucher's disease. Notably, the NbGNTI-RNAi line, producing GC, was stable and the NbGNTI-RNAi plants were viable and did not show any obvious phenotype. Therefore, it would provide a robust tool for the production of GC with customized N-glycan structures.

Role of LIMP-2 in the intracellular trafficking of ß-glucosidase in different human cellular models.

Acid ß-glucosidase (GCase), the enzyme deficient in Gaucher disease (GD), is transported to lysosomes by the lysosomal integral membrane protein (LIMP)-2. In humans, LIMP-2 deficiency leads to action myoclonus-renal failure (AMRF) syndrome. GD and AMRF syndrome share some clinical features. However, they are different from clinical and biochemical points of view, suggesting that the role of LIMP-2 in the targeting of GCase would be different in different tissues. Besides, the role of LIMP-2 in the uptake and trafficking of the human recombinant (hr)GCase used in the treatment of GD is unknown. Thus, we compared GCase activity and intracellular localization in immortalized lymphocytes, fibroblasts, and a neuronal model derived from multipotent adult stem cells, from a patient with AMRF syndrome, patients with GD, and control subjects. In fibroblasts and neuronlike cells, GCase targeting to the lysosomes is completely dependent on LIMP-2, whereas in blood cells, GCase is partially targeted to lysosomes by a LIMP-2-independent mechanism. Although hrGCase cellular uptake is independent of LIMP-2, its trafficking to the lysosomes is mediated by this receptor. These data provide new insights into the mechanisms involved in the intracellular trafficking of GCase and in the pathogeneses of GD and AMRF syndrome.

Plant-based oral delivery of ß-glucocerebrosidase as an enzyme replacement therapy for Gaucher's disease.

Gaucher's disease (GD), a lysosomal storage disorder caused by mutations in the gene encoding glucocerebrosidase (GCD), is currently treated by enzyme replacement therapy (ERT) using recombinant GCD that is administered intravenously every 2 weeks. However, intravenous administration includes discomfort or pain and might cause local and systemic infections that may lead to low patient compliance. An orally administered drug has the potential to alleviate these problems. In this study, we describe the potential use of plant cells as a vehicle for the oral delivery of recombinant human GCD (prGCD) expressed in carrot cells. The in vitro results demonstrate that the plant cells protect the recombinant protein in the gastric fluids and may enable absorption into the blood. Feeding experiments, with rat and pig as model animals, using carrot cells containing prGCD, show that active recombinant prGCD was found in the digestive tract and blood system and reached both, liver and spleen, the target organs in GD. These results demonstrate that the oral administration of proteins encapsulated in plant cells is feasible. Specifically, carrot cells containing recombinant human prGCD can be used as an oral delivery system and are a feasible alternative to intravenous administration of ERT for GD.

A phase 2 multi-center, open-label, switch-over trial to evaluate the safety and efficacy of Abcertin® in patients with type 1 Gaucher disease.

Gaucher disease is a lysosomal storage disease for which enzyme replacement therapy has proven to be effective. A switch-over clinical trial was performed to evaluate the efficacy and safety of Abcertin® (ISU Abxis, Seoul, Korea) in subjects with type 1 Gaucher disease who were previously treated with imiglucerase. Five Korean patients with type 1 Gaucher disease were enrolled. Previous doses of imiglucerase ranged from 30 to 55 U/kg every other week. The same dose of Abcertin® was administered to all patients for 24 weeks. Primary efficacy endpoints were changes in hemoglobin levels and platelet counts, and the secondary efficacy endpoints included changes in liver and spleen volumes, serum biomarkers, skeletal status and bone mineral density (BMD). During the study period, no statistically significant changes were observed in all parameters including hemoglobin levels and platelet counts, liver and spleen volumes, skeletal status and BMD. Abcertin® administration was continued in three patients for another 24 weeks as an extension of the study. Hemoglobin levels and platelet counts were maintained in all three patients. In conclusion, the efficacy and safety of Abcertin® are similar to those of imiglucerase, and Abcertin® is an effective therapeutic agent for patients with type 1 Gaucher disease (Clinical Trial Registry No. NCT02053896 at www.clinicaltrials.gov).

Taliglucerase alfa: an enzyme replacement therapy using plant cell expression technology.

Gaucher disease (GD) is a rare, genetic lysosomal storage disorder caused by functional defects of acid ß-glucosidase that results in multiple organ dysfunction. Glycosylation of recombinant acid human ß-glucosidase and exposure of terminal mannose residues are critical to the success of enzyme replacement therapy (ERT) for the treatment of visceral and hematologic manifestations in GD. Three commercially available ERT products for treatment of GD type 1 (GD1) include imiglucerase, velaglucerase alfa, and taliglucerase alfa. Imiglucerase and velaglucerase alfa are produced in different mammalian cell systems and require production glycosylation modifications to expose terminal α-mannose residues, which are needed for mannose receptor-mediated uptake by target macrophages. Such modifications add to production costs. Taliglucerase alfa is a plant cell-expressed acid ß-glucosidase approved in the United States and other countries for ERT in adults with GD1. A plant-based expression system, using carrot root cell cultures, was developed for production of taliglucerase alfa and does not require additional processing for postproduction glycosidic modifications. Clinical trials have demonstrated that taliglucerase alfa is efficacious, with a well-established safety profile in adult, ERT-naïve patients with symptomatic GD1, and for such patients previously treated with imiglucerase. These included significant improvements in organomegaly and hematologic parameters as early as 6months, and maintenance of achieved therapeutic values in previously treated patients. Ongoing clinical trials will further characterize the long-term efficacy and safety of taliglucerase alfa in more diverse patient populations, and may help to guide clinical decisions for achieving optimal outcomes for patients with GD1.

Imaging of enzyme replacement therapy using PET.

Direct enzyme replacement therapy (ERT) has been introduced as a means to treat a number of rare, complex genetic conditions associated with lysosomal dysfunction. Gaucher disease was the first for which this therapy was applied and remains the prototypical example. Although ERT using recombinant lysosomal enzymes has been shown to be effective in altering the clinical course of Gaucher disease, Fabry disease, Hurler syndrome, Hunter syndrome, Maroteaux-Lamy syndrome, and Pompe disease, the recalcitrance of certain disease manifestations underscores important unanswered questions related to dosing regimes, tissue half-life of the recombinant enzyme and the ability of intravenously administered enzyme to reach critical sites of known disease pathology. We have developed an innovative method for tagging acid beta-glucocerebrosidase (GCase), the recombinant enzyme formulated in Cerezyme(R) used to treat Gaucher disease, using an (18)F-labeled substrate analogue that becomes trapped within the active site of the enzyme. Using micro-PET we show that the tissue distribution of injected enzyme can be imaged in a murine model and that the PET data correlate with tissue (18)F counts. Further we show that PET imaging readily monitors pharmacokinetic changes effected by receptor blocking. The ability to (18)F-label GCase to monitor the enzyme distribution and tissue half-life in vivo by PET provides a powerful research tool with an immediate clinical application to Gaucher disease and a clear path for application to other ERTs.

Intra-monocyte Pharmacokinetics of Imiglucerase Supports a Possible Personalized Management of Gaucher Disease Type 1.

BACKGROUND AND OBJECTIVES: Intravenous imiglucerase enzyme replacement therapy for Gaucher disease type 1 administered every 2 weeks is at variance with the imiglucerase plasma half-life of a few minutes. We hypothesized that studying the pharmacokinetics of imiglucerase in blood Gaucher disease type 1 monocytes would be more relevant for understanding enzyme replacement therapy responses. METHODS: Glucocerebrosidase intra-monocyte activity was studied by flow cytometry. The pharmacokinetics of imiglucerase was analyzed using a population-pharmacokinetic model from a cohort of 31 patients with Gaucher disease type 1 who either started or were receiving long-term treatment with imiglucerase. RESULTS: A pharmacokinetic analysis of imiglucerase showed a two-compartment model with a high peak followed by a two-phase exponential decay (fast phase half-life: 0.36 days; slow phase half-life: 9.7 days) leading to a median 1.4-fold increase in glucocerebrosidase intra-monocyte activity from the pre-treatment activity (p = 0.04). In patients receiving long-term treatment, for whom the imiglucerase dose per infusion was chosen on the basis of disease aggressiveness/response, imiglucerase clearance correlated with the administered dose. However, the residual glucocerebrosidase intra-monocyte activity value was dose independent, suggesting that the maintenance of imiglucerase residual activity is patient specific. Endogenous pre-treatment glucocerebrosidase intra-monocyte activity was the most informative single parameter for distinguishing patients without (n = 10) and with a clinical indication (n = 17) for starting enzyme replacement therapy (area under the receiver operating characteristic curve: 0.912; 95% confidence interval 0.8-1; p < 0.001), as confirmed also by a factorial analysis of mixed data. CONCLUSION: This study provides novel pharmacokinetic data that support current imiglucerase administration regimens and suggests the existence of a glucocerebrosidase activity threshold related to Gaucher disease type 1 aggressiveness. These findings can potentially improve Gaucher disease type 1 management algorithms and clinical decision making.

A multicenter, open-label, phase III study of Abcertin in Gaucher disease.

BACKGROUND: Gaucher disease (GD) is caused by a deficiency in the lysosomal enzyme glucocerebrosidase. Enzyme replacement therapy (ERT) is recommended for clinical improvement. METHODS: The efficacy and safety of a new imiglucerase, Abcertin, were assessed in 7 Egyptian patients with treatment-naïve type 1 GD. Each patient was administered a biweekly 60 U/kg dose of Abcertin for 6 months. The primary endpoint was the change in hemoglobin concentration. The secondary endpoints were changes from baseline in platelet counts, spleen and liver volumes, biomarker levels, skeletal parameters, and bone mineral density. RESULTS: The hemoglobin concentration increased by a mean of 1.96 ±â€Š0.91 g/dL (range 1.11-2.80 g/dL) or 20.6% (P = .001). Statistically significant increases in the platelet count and decreases in the spleen volume and biomarker levels were also observed. There were no severe drug-related adverse events. One patient developed anti-imiglucerase antibodies without neutralizing activity. CONCLUSION: Our study results demonstrate the efficacy and safety of Abcertin in patients with type 1 GD. This suggests that Abcertin can be an alternative ERT option for type 1 GD.

Cellular Uptake of Glucocerebrosidase in Gaucher Patients Receiving Enzyme Replacement Treatment.

BACKGROUND: Enzyme replacement therapy (ERT) is currently the standard treatment for patients with Gaucher disease type I (GD1), but the pharmacokinetics have hardly been studied. This study aimed to quantify in vivo enzyme activity in peripheral leukocytes from patients receiving long-term treatment with imiglucerase or velaglucerase for GD1, and set out to assess the process of enzymatic uptake by peripheral leukocytes. METHODS: A prospective semi-experimental study was conducted. Four time points for blood withdrawal were planned per patient to quantify the intra-leukocyte enzymatic activity. In order to assess the uptake process, the rate of enzyme uptake by leukocytes (Rupt) and the rate of enzyme disappearance from the plasma (Rdis) were estimated. RESULTS: Eight GD1 patients were included. Intra-leukocyte activity was 24.31 mU/mL [standard deviation (SD) 6.32 mU/mL; coefficient of variation (CV) 25.96 %] at baseline and 27.14 mU/mL (SD  6.96 mU/mL; CV 25.65 %) at 15 min post-perfusion. The relationships with the administered dose were linear. The Rupt value was 37.73 mU/mL/min [95 % confidence interval (CI) 25.63-49.84] and showed a linear correlation with the administered enzyme dose (p < 0.05), and the Rdis value was 189.43 mU/mL/min (95 % CI 80.31-298.55) and also showed a linear correlation with the dose (p < 0.05). CONCLUSION: This was the first in vivo study to quantify the accumulated enzymatic activity in patients receiving ERT for GD1. It showed that intra-leukocyte activity at baseline and at 15 min post-perfusion could be used as a possible marker for therapeutic individualization in patients receiving ERT for GD1.

Slow internal release of bioactive compounds under the effect of skin enzymes.

A new strategy for the skin delivery of bioactive compounds has been developed, using enzymes involved in the maintenance of the epidermal barrier function and the enzymatic transformation of corresponding precursors. This new strategy has been tested with regard to two enzymatic activities of the skin barrier: extracellular glucosidase and esterase/lipase. An analysis of the requirements for the glycosidic bond hydrolysis of any glycoconjugate by beta-glucocerebrosidase indicates that the release of the moiety linked to the glucose unit is obtained as long as the glycosidic bond being broken is not hindered, and as long as the leaving group property of the released moiety is good enough. This strategy was first applied to the release of the antioxidant delta-tocopherol. It was then extended to retinoic acid by introducing a spacer between the glucose unit and the bioactive moiety. This spacer was either a good leaving group such as hydroquinone, or a structure akin to a ceramide, namely glycerol. In these conditions, beta-glucocerebrosidase releases the complex spacer-active compound that is cleaved by an esterase. One of the advantages of this strategy lies in the slow release of the bioactive compound, extending in time its effect and most likely its tolerance, as is the case for retinoic acid.

Significance of immune response to enzyme-replacement therapy for patients with a lysosomal storage disorder.

Lysosomal storage disorders are collectively important because they cause significant morbidity and mortality. Patients can present with severe symptoms that include somatic tissue and bone pathology, developmental delay and neurological impairment. Enzyme-replacement therapy has been developed as a treatment strategy for patients with a lysosomal storage disorder, and for many of these disorders this treatment is either in clinical trial or clinical practice. One major complication arising from enzyme infusion into patients with a lysosomal storage disorder is an immune response to the replacement protein. From clinical trials, it is clear that there is considerable variability in the level of immune response to enzyme-replacement therapy, dependent upon the replacement protein being infused and the individual patient. Hypersensitivity reactions, neutralizing antibodies to the replacement protein and altered enzyme targeting or turnover are potential concerns for patients exhibiting an immune response to enzyme-replacement therapy. The relative occurrence and significance of these issues have been appraised.

Pharmacokinetics of Novel Plant Cell-Expressed Taliglucerase Alfa in Adult and Pediatric Patients with Gaucher Disease.

UNLABELLED: Taliglucerase alfa is a beta-glucocerebrosidase enzyme replacement therapy approved in the United States, Israel, and other countries for treatment of Type 1 Gaucher disease in adults, and is the first approved plant cell--expressed recombinant protein. In this report, taliglucerase alfa pharmacokinetics were assessed in adult and pediatric patients with Gaucher disease from separate multicenter trials of 30 Units/kg and 60 Units/kg doses infused every 2 weeks. Serial blood samples were obtained from adult patients following single-dose administration on day 1 (n = 26) and multiple doses at week 38 (n = 29), and from pediatric patients following administration of multiple doses of taliglucerase alfa for 10-27 months (n = 10). In both adult and pediatric patients, maximum plasma concentration (Cmax), area under the plasma concentration-time curve from time zero to last measureable concentration (AUC0-t), and from time zero to infinity (AUC0-∞) were higher after 60 Units/kg dose than 30 Units/kg dose. No tendency for accumulation or change in taliglucerase alfa pharmacokinetic parameters over time from day 1 to week 38 was observed with repeated doses of 30 or 60 Units/kg in adults. After multiple doses, mean (range) dose-normalized pharmacokinetic parameters were similar for adult versus pediatric patients receiving 60 Units/kg: Cmax expressed in ng/mL/mg was 42.4 (14.5-95.4) in adults and 46.6 (34.4-68.4) in pediatric patients, AUC0 t expressed in ng • h/mL/mg was 63.4 (26.3-156) in adults and 63.9 (39.8-85.1) in pediatric patients, t1/2 expressed in minutes was 34.8 (11.3-104) in adults and 31.5 (18.0-42.9) in pediatric patients and total body clearance expressed in L/h was 19.9 (6.25-37.9) in adults and 17.0 (11.7-24.9) in pediatric patients. These pharmacokinetic data extend the findings of taliglucerase alfa in adult and pediatric patients. TRIAL REGISTRATION: ClinicalTrials.gov. NCT00376168 (in adults); NCT01411228 (in children).

Long-term expression, systemic delivery, and macrophage uptake of recombinant human glucocerebrosidase in mice transplanted with genetically modified primary myoblasts.

A critical requirement for treatment of Gaucher disease via systemic delivery of recombinant GC is that secreted enzyme be in a form available for specific takeup by macrophages in vivo. In this article we investigated if transplanted primary myoblasts can sustain expression of human GC in vivo and if the secreted transgene product is taken up by macrophages. Transduced primary murine myoblasts were implanted into syngeneic C3H/HeJ mice. The results demonstrated that transplanted mice sustained long-term expression of transferred human GC gene in vivo. Furthermore, human GC is secreted into the circulation of mice transplanted with syngeneic primary myoblasts retrovirally transduced with human GC cDNA. The transplanted primary myoblasts differentiate and fuse with adjacent mature myofibers, and express the transgene product for up to 300 days. Human GC in the circulation reaches levels of 20-280 units/ml of plasma. Immunohistochemical studies of the target organs revealed that the secreted human GC is taken up by macrophages in liver and bone marrow. Immunochemical identification of reisolated myoblasts from transplanted mice showed that MFG-GC-transduced cells also survived as muscle stem cells in the implanted muscle. These results present in encouraging prospect for the treatment of Gaucher disease.

Enzyme therapy for Gaucher disease: the first 5 years.

Gaucher disease was first described by Philippe Gaucher in his 1882 medical thesis. Gaucher's original concept was of an unusual epithelioma of the spleen. By the early 1900s, Mandelbaum recognized the systemic nature of the disease. Several children with Gaucher disease were described at the turn of the century, but Rusca described a rapidly progressive fatal neurodegenerative type of disease, i.e. type 2, in the 1920s. The 'juvenile' form (type 3) of the disease was described in Sweden in the 1950s. In 1965, the deficient enzyme, acid beta-glucosidase, was discovered and the lysosomal nature of the disease was elucidated. Currently, three variants of Gaucher disease have been defined clinically and are distinguished by the presence and severity of neuronopathic involvement (Table 1). Each of these clinical types has substantial phenotypic variation, but types 1 and 3 have significantly heterogeneous rates of disease progression and degrees of visceral organs involvement. The neuronopathic involvement in type 3 also has substantial variation in the age of onset and disease progression even within relatively isolated communities. An extensive review of the clinical and pathologic involvement by Gaucher disease is available.

Immunoelectron microscopic localization of mannose-terminal glucocerebrosidase in lysosomes of rat liver Kupffer cells.

Knowledge of the cellular distribution and subcellular localization of mannose-terminal glucocerebrosidase after intravenous infusion is necessary for understanding the efficacy of targeted enzyme replacement therapy for Gaucher's disease. Selective uptake of mannose-terminal glucocerebrosidase by Kupffer cells in rat liver has been previously demonstrated biochemically. In this study we used immunohistochemical and immunogold labeling techniques to provide direct visual proof for the localization of the delivered enzyme. Light microscopy confirmed biochemical data identifying non-parenchymal cells as the primary target of the modified glucocerebrosidase. Using a primary antibody specific for glucocerebrosidase and a secondary gold-conjugated antibody, we used immunoelectron microscopy to quantify the extent and distribution of exogenous enzyme in various cell types in rat liver and its localization within their respective subcellular organelles. Thirty minutes after intravenous administration of mannose-terminal glucocerebrosidase, enzyme was localized primarily in lysosomes of Kupffer cells. Of eight intact Kupffer cells counted, 16 of 21 lysosomes (78%) contained immunogold conjugates (average concentration 293 gold particles/micron 2). Of 589 particles counted in these lysosomes, 485 (82%) were localized within the lumen of the lysosome; only 104 (18%) were membrane-associated. Five of the 21 lysosomes counted were negative for gold. No gold particles were found in the mitochondria of Kupffer cells and very few particles (8.2/microns 2) were found over the nucleus. The density of gold particles was also low over the nucleus (7.2/microns 2), mitochondria (8.8/microns 2), and lysosomes (7.9/microns 2) of hepatocytes. No specific labeling was observed in erythrocytes, platelets, lymphocytes, pit cells, fat-storing cells, or bile duct. Background labeling of control liver sections from rats receiving saline injection was 8.2 +/- 1.4 gold particles/microns 2. We conclude that mannose-terminal glucocerebrosidase is delivered to the lysosomes of Kupffer cells in liver and that it is distributed both within the lumen (82%) and over the membrane (18%) of the lysosome, with a slight preferential association with the membrane. These findings may provide insights into the design of more effective therapeutic enzyme preparations for the treatment of Gaucher's disease.

Miglustat.

Miglustat is an orally administered ceramide glucosyltransferase inhibitor which prevents the lysosomal accumulation of glucocerebroside that occurs in patients with Gaucher's disease. In noncomparative trials in patients with type 1 Gaucher's disease, miglustat (50 or 100mg three times daily) for 6-12 months significantly reduced baseline liver and spleen volumes. At both 6 and 12 months, the reductions in organ volumes were greater with the higher dosage. Miglustat 50 or 100mg three times daily for 6-12 months had no significant effect on haemoglobin concentrations. Baseline platelet counts were not significantly improved by either dosage at 6 months, although the higher dosage significantly increased platelet counts at 12 months. In an open extension phase, patients continued to show further reductions in organ volume as well as significant improvements in haematological parameters at 24 and 36 months. black triangle In a 6-month randomised study in patients with type 1 Gaucher's disease who had previously received long-term enzyme replacement therapy (ERT), liver volume reduction was greater with miglustat plus ERT than with ERT alone. Diarrhoea and weight loss were the most frequent adverse events associated with miglustat therapy. Fine tremor has been reported in approximately 30% of miglustat-treated patients.

Alglucerase. A review of its therapeutic use in Gaucher's disease.

Alglucerase is a mannose-terminated form of human placental glucocerebrosidase, developed to treat patients with Gaucher's disease. Functional glucocerebrosidase is deficient in Gaucher's disease, an autosomal recessive lipid storage disorder that affects people of all ethnic backgrounds, but has a higher incidence among East European Jews (Ashkenazim). Gaucher's disease manifests with hepatosplenomegaly, bleeding disorders and bone disease, with the more rare subtypes (types 2 and 3) featuring neurological dysfunction. Prior to the development of enzyme replacement therapy, treatment for Gaucher's disease was mainly symptomatic relief. Primary treatment with glucocerebrosidase focuses on removal of the lipid metabolite that causes the pathology. Because of the rarity of Gaucher's disease clinical trials are small, and much of the data investigating alglucerase therapy have been obtained from studies of patients with type 1 disease, the prevalent subtype. Nonetheless, after intravenous administration of alglucerase, improvements are evident within 6 months of therapy. Patients have increased haemoglobin levels and platelet counts, and decreased incidences of epistaxis and bruising. Spleen and liver size are reduced, and skeletal parameters improve. Children gain height and most patients receiving alglucerase therapy are able to resume work and daily activities. Alglucerase is well tolerated, with few mild adverse reactions reported. Although the pharmacokinetic and pharmacodynamic information for alglucerase is limited, its unequivocal efficacy justifies enzyme replacement therapy with this compound as first-line treatment for patients with Gaucher's disease, for whom treatment options are limited.