Dexamethasone-Mediated Up-Regulation of the Mannose Receptor Improves the Delivery of Recombinant Glucocerebrosidase to Gaucher Macrophages

Targeted Enzymatic VLP-Nanoreactors with β-Glucocerebrosidase Activity as Potential Enzyme Replacement Therapy for Gaucher's Disease

Gaucher disease is a genetic disorder and the most common lysosomal disease caused by the deficiency of enzyme β-glucocerebrosidase (GCase). Although enzyme replacement therapy (ERT) is successfully applied using mannose-exposed conjugated glucocerebrosidase, the lower stability of the enzyme in blood demands periodic intravenous administration that adds to the high cost of treatment. In this work, the enzyme β-glucocerebrosidase was encapsulated inside virus-like nanoparticles (VLPs) from brome mosaic virus (BMV), and their surface was functionalized with mannose groups for targeting to macrophages. The VLP nanoreactors showed significant GCase catalytic activity. Moreover, the Michaelis-Menten constants for the free GCase enzyme (KM =0.29 mM) and the functionalized nanoreactors (KM =0.32 mM) were similar even after chemical modification. Importantly, the stability of enzymes under physiological conditions (pH 7.4, 37 °C) was enhanced by ≈11-fold after encapsulation; this is beneficial for obtaining a higher blood circulation half-life, which may decrease the cost of therapy by reducing the requirement of multiple intravenous injections. Finally, the mannose receptor targeted enzymatic nanoreactors showed enhanced internalization into macrophage cells. Thus, the catalytic activity and cell targeting suggest the potential of these nanoreactors in ERT of Gaucher's disease.

Therapeutic effect of pH-Responsive dexamethasone prodrug nanoparticles on acute lung injury

Acute lung injury/inflammation (ALI) is usually caused by various injury factors inside and outside the lung, which can be transformed into acute respiratory distress syndrome (ARDS) in severe cases. Alveolar macrophages play a key role in the pathogenesis of ALI, which regulate inflammatory responses by secreting inflammatory mediators. Therefore, we prepared dexamethasone (DXM)/mannose co-modified branched polyethyleneimine (PEI) (DXM-PEI-mannose, DPM) prodrug nanopartcales, which could effectively target the mannose receptor (MR) on the surface of alveolar macrophages and be used for the treatment of ALI. The DXM-PEI (DP) prodrug was obtained by linking DXM with branched PEI through Schiff base reaction. Subsequently, the pH-responsive DPM prodrug was obtained by using mannose-targeted head modification. The DPM prodrug NPs with a particle size of 115 ± 1 nm, a polydispersity index (PDI) value of 0.054 ± 0.018, and a zeta potential of 31 ± 1 mV were obtained by cross-linking. The drug loading of DPM prodrug NPs measured by the acid hydrolysis method was 51.88%, which had good serum stability and biocompatibility. By comparing the stability and property release of prodrug NPs under different pH (7.4 and 5.0) conditions, it showed that DPM prodrug NPs had certain sensitivity to the micro-acid environment. To study the targeting of mouse mononuclear macrophages, mannose-modified prodrug NPs showed significant in vitro targeting. Moreover, prodrug NPs showed good anti-inflammatory activity in vitro, which was significantly different from free drugs. In vivo biodistribution experiments also showed that it had a long-term lung targeting effect. DPM prodrug NPs also had a good therapeutic effect on ALI. In conclusion, the mannose-modified DXM prodrug NPs delivery system could specifically target lung tissues and have a good therapeutic effect, which might be useful for the treatment of lung diseases.

Advances in receptor modulation strategies for flexible, efficient, and enhanced antitumor efficacy

Tumor-sensitivity, effective transport, and precise delivery to tumor cells of nano drug delivery systems (NDDs) have been great challenges to cancer therapy in recent years. The conventional targeting approach involves actively installing the corresponding ligand on the nanocarriers, which is prone to recognize the antigen blasts overexpressed on the surface of tumor cells. However, there are some probable limitations for the active tumor-targeting systems in vivo as follows: a. the limited ligand amount of modifications; b. possible steric hindrance, which was likely to prevent ligand-receptor interaction during the delivery process. c. the restrained antigen saturation highly expressed on the cell membrane, will definitely decrease the specificity and often lead to "off-target" effects of NDDs; and d. water insolubility of nanocarriers due to excess of ligands modification. Obviously, any regulation of receptors on surface of tumor cells exerted an important influence on the delivery of targeting systems. Herein, receptor upregulation was mostly desired for enhancing targeted therapy from the cellular level. This technique with the amplification of receptors has the potential to enhance tumor sensitivity towards corresponding ligand-modified nanoparticles, and thereby increasing the effective therapeutic concentration as well as improving the efficacy of chemotherapy. The enhancement of positively expressed receptors on tumor cells and receptor-dependent therapeutic agents or NDDs with an assembled "self-promoting" effect contributes to increasing cell sensitivity to NPs, and will provide a basic platform for clinical therapeutic practice. In this review, we highlight the significance of modulating various receptors on different types of cancer cells for drug delivery and therapeutic benefits.

Targeted enzyme delivery systems in lysosomal disorders: an innovative form of therapy for mucopolysaccharidosis

Mucopolysaccharidoses (MPSs), which are inherited lysosomal storage disorders caused by the accumulation of undegraded glycosaminoglycans, can affect the central nervous system (CNS) and elicit cognitive and behavioral issues. Currently used enzyme replacement therapy methodologies often fail to adequately treat the manifestations of the disease in the CNS and other organs such as bone, cartilage, cornea, and heart. Targeted enzyme delivery systems (EDSs) can efficiently cross biological barriers such as blood-brain barrier and provide maximal therapeutic effects with minimal side effects, and hence, offer great clinical benefits over the currently used conventional enzyme replacement therapies. In this review, we provide comprehensive insights into MPSs and explore the clinical impacts of multimodal targeted EDSs.

Enzyme replacement therapies: what is the best option?

Despite many beneficial outcomes of the conventional enzyme replacement therapy (ERT), several limitations such as the high-cost of the treatment and various inadvertent side effects including the occurrence of an immunological response against the infused enzyme and development of resistance to enzymes persist. These issues may limit the desired therapeutic outcomes of a majority of the lysosomal storage diseases (LSDs). Furthermore, the biodistribution of the recombinant enzymes into the target cells within the central nervous system (CNS), bone, cartilage, cornea, and heart still remain unresolved. All these shortcomings necessitate the development of more effective diagnosis and treatment modalities against LSDs. Taken all, maximizing the therapeutic response with minimal undesired side effects might be attainable by the development of targeted enzyme delivery systems (EDSs) as a promising alternative to the LSDs treatments, including different types of mucopolysaccharidoses ( MPSs ) as well as Fabry, Krabbe, Gaucher and Pompe diseases.

Lysosomal enzyme replacement therapies: Historical development, clinical outcomes, and future perspectives

Lysosomes and lysosomal enzymes play a central role in numerous cellular processes, including cellular nutrition, recycling, signaling, defense, and cell death. Genetic deficiencies of lysosomal components, most commonly enzymes, are known as "lysosomal storage disorders" or "lysosomal diseases" (LDs) and lead to lysosomal dysfunction. LDs broadly affect peripheral organs and the central nervous system (CNS), debilitating patients and frequently causing fatality. Among other approaches, enzyme replacement therapy (ERT) has advanced to the clinic and represents a beneficial strategy for 8 out of the 50-60 known LDs. However, despite its value, current ERT suffers from several shortcomings, including various side effects, development of "resistance", and suboptimal delivery throughout the body, particularly to the CNS, lowering the therapeutic outcome and precluding the use of this strategy for a majority of LDs. This review offers an overview of the biomedical causes of LDs, their socio-medical relevance, treatment modalities and caveats, experimental alternatives, and future treatment perspectives.

Investigations on therapeutic glucocerebrosidases through paired detection with fluorescent activity-based probes

Deficiency of glucocerebrosidase (GBA) causes Gaucher disease (GD). In the common non-neuronopathic GD type I variant, glucosylceramide accumulates primarily in the lysosomes of visceral macrophages. Supplementing storage cells with lacking enzyme is accomplished via chronic intravenous administration of recombinant GBA containing mannose-terminated N-linked glycans, mediating the selective uptake by macrophages expressing mannose-binding lectin(s). Two recombinant GBA preparations with distinct N-linked glycans are registered in Europe for treatment of type I GD: imiglucerase (Genzyme), contains predominantly Man(3) glycans, and velaglucerase (Shire PLC) Man(9) glycans. Activity-based probes (ABPs) enable fluorescent labeling of recombinant GBA preparations through their covalent attachment to the catalytic nucleophile E340 of GBA. We comparatively studied binding and uptake of ABP-labeled imiglucerase and velaglucerase in isolated dendritic cells, cultured human macrophages and living mice, through simultaneous detection of different GBAs by paired measurements. Uptake of ABP-labeled rGBAs by dendritic cells was comparable, as well as the bio-distribution following equimolar intravenous administration to mice. ABP-labeled rGBAs were recovered largely in liver, white-blood cells, bone marrow and spleen. Lungs, brain and skin, affected tissues in severe GD types II and III, were only poorly supplemented. Small, but significant differences were noted in binding and uptake of rGBAs in cultured human macrophages, in the absence and presence of mannan. Mannan-competed binding and uptake were largest for velaglucerase, when determined with single enzymes or as equimolar mixtures of both enzymes. Vice versa, imiglucerase showed more prominent binding and uptake not competed by mannan. Uptake of recombinant GBAs by cultured macrophages seems to involve multiple receptors, including several mannose-binding lectins. Differences among cells from different donors (n = 12) were noted, but the same trends were always observed. Our study suggests that further insight in targeting and efficacy of enzyme therapy of individual Gaucher patients could be obtained by the use of recombinant GBA, trace-labeled with an ABP, preferably equipped with an infrared fluorophore or other reporter tag suitable for in vivo imaging.

Monocytes/Macrophages Upregulate the Hyaluronidase HYAL1 and Adapt Its Subcellular Trafficking to Promote Extracellular Residency upon Differentiation into Osteoclasts

Osteoclasts are giant bone-resorbing cells originating from monocytes/macrophages. During their differentiation, they overexpress two lysosomal enzymes, cathepsin K and TRAP, which are secreted into the resorption lacuna, an acidified sealed area in contact with bone matrix where bone degradation takes place. Here we report that the acid hydrolase HYAL1, a hyaluronidase able to degrade the glycosaminoglycans hyaluronic acid (HA) and chondroitin sulfate, is also upregulated upon osteoclastogenesis. The mRNA expression and protein level of HYAL1 are markedly increased in osteoclasts differentiated from RAW264.7 mouse macrophages or primary mouse bone marrow monocytes compared to these precursor cells. As a result, the HYAL1-mediated HA hydrolysis ability of osteoclasts is strongly enhanced. Using subcellular fractionation, we demonstrate that HYAL1 proteins are sorted to the osteoclast lysosomes even though, in contrast to cathepsin K and TRAP, HYAL1 is poorly mannose 6-phosphorylated. We reported previously that macrophages secrete HYAL1 proforms by constitutive secretion, and that these are recaptured by the cell surface mannose receptor, processed in endosomes and sorted to lysosomes. Present work highlights that osteoclasts secrete HYAL1 in two ways, through lysosomal exocytosis and constitutive secretion, and that these cells promote the extracellular residency of HYAL1 through downregulation of the mannose receptor. Interestingly, the expression of the other main hyaluronidase, HYAL2, and of lysosomal exoglycosidases involved in HA degradation, does not increase similarly to HYAL1 upon osteoclastogenesis. Taken together, these findings point out the predominant involvement of HYAL1 in bone HA metabolism and perhaps bone remodeling via the resorption lacuna.

Strategies for delivery of therapeutics into the central nervous system for treatment of lysosomal storage disorders

Lysosomal storage disorders (LSDs) are a group of about fifty life-threatening conditions caused by genetic defects affecting lysosomal components. The underscoring molecular deficiency leads to widespread cellular dysfunction through most tissues in the body, including peripheral organs and the central nervous system (CNS). Efforts during the last few decades have rendered a remarkable advance regarding our knowledge, medical awareness, and early detection of these genetic defects, as well as development of several treatment modalities. Clinical and experimental strategies encompassing enzyme replacement, gene and cell therapies, substrate reduction, and chemical chaperones are showing considerable potential in attenuating the peripheral pathology. However, a major drawback has been encountered regarding the suboptimal impact of these approaches on the CNS pathology. Particular anatomical and biochemical constraints of this tissue pose a major obstacle to the delivery of therapeutics into the CNS. Approaches to overcome these obstacles include modalities of local administration, strategies to enhance the blood-CNS permeability, intranasal delivery, use of exosomes, and those exploiting targeting of transporters and transcytosis pathways in the endothelial lining. The later two approaches are being pursued at the time by coupling therapeutic agents to affinity moieties and drug delivery systems capable of targeting these natural transport routes. This approach is particularly promising, as using paths naturally active at this interface may render safe and effective delivery of LSD therapies into the CNS.

Glycosylation and functionality of recombinant β-glucocerebrosidase from various production systems

The glycosylation of recombinant β-glucocerebrosidase, and in particular the exposure of mannose residues, has been shown to be a key factor in the success of ERT (enzyme replacement therapy) for the treatment of GD (Gaucher disease). Macrophages, the target cells in GD, internalize β-glucocerebrosidase through MRs (mannose receptors). Three enzymes are commercially available for the treatment of GD by ERT. Taliglucerase alfa, imiglucerase and velaglucerase alfa are each produced in different cell systems and undergo various post-translational or post-production glycosylation modifications to expose their mannose residues. This is the first study in which the glycosylation profiles of the three enzymes are compared, using the same methodology and the effect on functionality and cellular uptake is evaluated. While the major differences in glycosylation profiles reside in the variation of terminal residues and mannose chain length, the enzymatic activity and stability are not affected by these differences. Furthermore, the cellular uptake and in-cell stability in rat and human macrophages are similar. Finally, in vivo studies to evaluate the uptake into target organs also show similar results for all three enzymes. These results indicate that the variations of glycosylation between the three regulatory-approved β-glucocerebrosidase enzymes have no effect on their function or distribution.

Characterization of functional mannose receptor in a continuous hybridoma cell line

Background

The mannose receptor is the best described member of the type I transmembrane C-type lectins; however much remains unanswered about the biology of the receptor. One difficulty has been the inability to consistently express high levels of a functional full length mannose receptor cDNA in mammalian cells. Another difficulty has been the lack of a human macrophage cell line expressing a fully functional receptor. Commonly used human macrophage cell lines such as U937, THP-1, Mono-Mac and HL60 do not express the mannose receptor. We have developed a macrophage hybridoma cell line (43^MR cells) created by fusion of U937 cells with primary human monocyte-derived macrophages, resulting in a non-adherent cell line expressing several properties of primary macrophages. The purpose of this study was to identify and select mannose receptor-expressing cells using fluorescence-activated cell sorting and to characterize the expression and function of the receptor.

Results

In the current study we show that the mannose receptor found on this novel cell has endocytic characteristics consistent with and similar to the mannose receptor found on the surface of monocyte-derived human macrophages and rat bone marrow-derived macrophages. In addition, we demonstrate that these cells engage and internalize pathogen particles such as S. aureus and C. albicans. We further establish the transfectability of these cells via the introduction of a plasmid expressing influenza A hemagglutinin.

Conclusions

The 43^MR cell line represents the first naturally expressed MR-positive cell line derived from a human macrophage background. This cell line provides an important cell model for other researchers for the study of human MR biology and host-pathogen interactions.

Biotherapeutic target or sink: analysis of the macrophage mannose receptor tissue distribution in murine models of lysosomal storage diseases

Lysosomal storage diseases (LSDs) are metabolic disorders caused by enzyme deficiencies that lead to lysosomal accumulation of undegraded substrates. Enzyme replacement therapies (ERT) have been developed as treatments for patients with Gaucher, Niemann-Pick, Fabry, and Pompe diseases. Depending on the disease, the corresponding therapeutic enzyme is designed to be internalized by diseased cells through receptor-mediated endocytosis via macrophage mannose receptors (MMR) or mannose-6-phosphate receptors (M6PR). Enzymes developed to treat Gaucher and Niemann-Pick diseases are meant to target MMR-expressing cells, and in the case of Cerezyme [recombinant human β-glucocerebrosidase (rhβGC)] for treating Gaucher disease, glycans on the enzyme are modified to increase specificity toward this receptor. Due to heterogeneity in glycosylation on enzymes intended to target the M6PR, however, there may also be some unintended targeting to MMR-expressing cells, which could act as unwanted sinks. Examples include Fabrazyme [recombinant human α-galactosidase A (rhαGal)] for treating Fabry disease and Myozyme [recombinant human acid α-glucosidase (rhGAA)] for treating Pompe disease. It is therefore of great interest to better understand the cell type and tissue distribution of MMR in murine LSD models used to evaluate ERT efficacy and mechanism of action. In this study, we generated affinity-purified polyclonal antibody against murine MMR and used it to carry out a systematic examination of MMR protein localization in murine models of Gaucher, Niemann-Pick, Fabry, and Pompe diseases. Using immunohistochemistry, immunofluorescence, and confocal microscopy, we examined MMR distribution in liver, spleen, lung, kidney, heart, diaphragm, quadriceps, and triceps in these animal models and compared them with MMR distribution in wild-type mice.

Use of direct fluorescence labeling and confocal microscopy to determine the biodistribution of two protein therapeutics, Cerezyme and Ceredase

Efficient targeting of therapeutic reagents to tissues and cell types of interest is critical to achieving therapeutic efficacy and avoiding unwanted side effects due to offtarget uptake. To increase assay efficiency and reduce the number of animals used per experiment during preclinical development, we used a combination of direct fluorescence labeling and confocal microscopy to simultaneously examine the biodistribution of two therapeutic proteins, Cerezyme and Ceredase, in the same animals. We show that the fluorescent tags do not interfere with protein uptake and localization. We are able to detect Cerezyme and Ceredase in intact cells and organs and demonstrate colocalization within target cells using confocal microscopy. In addition, the relative amount of protein internalized by different cell types can be quantified using cell type-specific markers and morphometric analysis. This approach provides an easy and straightforward means of assessing the tissue and cell type-specific biodistribution of multiple protein therapeutics in target organs using a minimal number of animals.

New biotechnological and nanomedicine strategies for treatment of lysosomal storage disorders

This review discusses the multiple bio- and nanotechnological strategies developed in the last few decades for treatment of a group of fatal genetic diseases termed lysosomal storage disorders. Some basic foundation on the biomedical causes and social and clinical relevance of these diseases is provided. Several treatment modalities, from those currently available to novel therapeutic approaches under development, are also discussed; these include gene and cell therapies, substrate reduction therapy, chemical chaperones, enzyme replacement therapy, multifunctional chimeras, targeting strategies, and drug carrier approaches.

Effect of mannose chain length on targeting of glucocerebrosidase for enzyme replacement therapy of Gaucher disease

Recombinant human glucocerebrosidase (imiglucerase, Cerezyme) is used in enzyme replacement therapy for Gaucher disease. Complex oligosaccharides present on Chinese hamster ovary cell-expressed glucocerebrosidase (GCase) are enzymatically remodeled into a mannose core, facilitating mannose receptor-mediated uptake into macrophages. Alternative expression systems could be used to produce GCase containing larger oligomannose structures, offering the possibility of an improvement in targeting to macrophages. A secondary advantage of these expression systems would be to eliminate the need for carbohydrate remodeling. Here, multiple expression systems were used to produce GCase containing primarily terminal oligomannose, from Man2 to Man9. GCase from these multiple expression systems was compared to Cerezyme with respect to affinity for mannose receptor and serum mannose-binding lectin (MBL), macrophage uptake, and intracellular half-life. In vivo studies comparing clearance and targeting of Cerezyme and the Man9 form of GCase were carried out in a Gaucher mouse model (D409V/null). Mannose receptor binding, macrophage uptake, and in vivo targeting were similar for all forms of GCase. Increased MBL binding was observed for all forms of GCase having larger mannose structures than those of Cerezyme, which could influence pharmacokinetic behavior. These studies demonstrate that although alternative cell expression systems are effective for producing oligomannose-terminated glucocerebrosidase, there is no biochemical or pharmacological advantage in producing GCase with an increased number of mannose residues. The display of alternative carbohydrate structures on GCase expressed in these systems also runs the risk of undesirable consequences, such as an increase in MBL binding or a possible increase in immunogenicity due to the presentation of non-mammalian glycans.

Glucosylceramide transfer from lysosomes--the missing link in molecular pathology of glucosylceramidase deficiency: a hypothesis based on existing data

Gaucher disease (GD), deficiency of acid glucosylceramidase (GlcCer-ase) is characterized by deficient degradation of beta-glucosylceramide (GlcCer). It is well known that, in GD, the lysosomal accumulation of uncleaved GlcCer is limited to macrophages, which are gradually converted to storage cells with well known cytology--Gaucher cells (GCs). On the basis of previous studies of the disorder and of a comparison with other lysosomal enzymopathies affecting degradation of the GlcCer-based glycosphingolipid series, it is hypothesized that in other cell types (i.e. non-macrophage cells) the uncleaved GlcCer, in GlcCer-ase deficiency, is transferred to other cell compartments, where it may be processed and even accumulated to various degrees. The consequence of the abnormal extralysosomal load may differ according to the cell type and compartment targeted and may be influenced by genetically determined factors, by a number of acquired conditions, including the current metabolic situation. The sequelae of the uncleaved GlcCer extralysosomal transfer may range from probably innocent or positive stimulatory, to the much more serious, in which it interferes with a variety of cell functions, and in extreme cases, can lead to cell death. This alternative processing of uncleaved GlcCer may help to explain tissue alterations seen in GD that have, so far, resisted explanation based simply on the presence of GCs. Paralysosomal alternative processing may thus go a long way towards filling a long-standing gap in the understanding of the molecular pathology of the disorder. The impact of this alternative process will most likely be inversely proportional to the level of residual GlcCer-ase activity. Lysosomal sequestration of GlcCer in these cells is either absent or in those exceptional cases where it does occur, it is exceptional and rudimentary. It is suggested that paralysosomal alternative processing of uncleaved GlcCer is the main target for enzyme replacement therapy. The mechanism responsible for GlcCer transfer remains to be elucidated. It may also help in explaining the so far unclear origin of glucosylsphingosine (GlcSph) and define the mutual relation between these two processes.

Lysosomal enzyme delivery by ICAM-1-targeted nanocarriers bypassing glycosylation- and clathrin-dependent endocytosis

Enzyme replacement therapy, a state-of-the-art treatment for many lysosomal storage disorders, relies on carbohydrate-mediated binding of recombinant enzymes to receptors that mediate lysosomal delivery via clathrin-dependent endocytosis. Suboptimal glycosylation of recombinant enzymes and deficiency of clathrin-mediated endocytosis in some lysosomal enzyme-deficient cells limit delivery and efficacy of enzyme replacement therapy for lysosomal disorders. We explored a novel delivery strategy utilizing nanocarriers targeted to a glycosylation- and clathrin-independent receptor, intercellular adhesion molecule (ICAM)-1, a glycoprotein expressed on diverse cell types, up-regulated and functionally involved in inflammation, a hallmark of many lysosomal disorders. We targeted recombinant human acid sphingomyelinase (ASM), deficient in types A and B Niemann-Pick disease, to ICAM-1 by loading this enzyme to nanocarriers coated with anti-ICAM. Anti-ICAM/ASM nanocarriers, but not control ASM or ASM nanocarriers, bound to ICAM-1-positive cells (activated endothelial cells and Niemann-Pick disease patient fibroblasts) via ICAM-1, in a glycosylation-independent manner. Anti-ICAM/ASM nanocarriers entered cells via CAM-mediated endocytosis, bypassing the clathrin-dependent pathway, and trafficked to lysosomes, where delivered ASM displayed stable activity and alleviated lysosomal lipid accumulation. Therefore, lysosomal enzyme targeting using nanocarriers targeted to ICAM-1 bypasses defunct pathways and may improve the efficacy of enzyme replacement therapy for lysosomal disorders, such as Niemann-Pick disease.

Carbohydrate-remodelled acid alpha-glucosidase with higher affinity for the cation-independent mannose 6-phosphate receptor demonstrates improved delivery to muscles of Pompe mice

To enhance the delivery of rhGAA (recombinant GAA, where GAA stands for acid alpha-glucosidase) to the affected muscles in Pompe disease, the carbohydrate moieties on the enzyme were remodelled to exhibit a high affinity ligand for the CI-MPR (cation-independent M6P receptor, where M6P stands for mannose 6-phosphate). This was achieved by chemically conjugating on to rhGAA, a synthetic oligosaccharide ligand bearing M6P residues in the optimal configuration for binding the receptor. The carbonyl chemistry used resulted in the conjugation of approx. six synthetic ligands on to each enzyme. The resulting modified enzyme [neo-rhGAA (modified recombinant human GAA harbouring synthetic oligosaccharide ligands)] displayed near-normal specific activity and significantly increased affinity for the CI-MPR. However, binding to the mannose receptor was unaffected despite the introduction of additional mannose residues in neo-rhGAA. Uptake studies using L6 myoblasts showed neo-rhGAA was internalized approx. 20-fold more efficiently than the unmodified enzyme. Administration of neo-rhGAA into Pompe mice also resulted in greater clearance of glycogen from all the affected muscles when compared with the unmodified rhGAA. Comparable reductions in tissue glycogen levels in the Pompe mice were realized using an approx. 8-fold lower dose of neo-rhGAA in the heart and diaphragm and an approx. 4-fold lower dose in the skeletal muscles. Treatment of older Pompe mice, which are more refractory to enzyme therapy, with 40 mg/kg neo-rhGAA resulted in near-complete clearance of glycogen from all the affected muscles as opposed to only partial correction with the unmodified rhGAA. These results demonstrate that remodelling the carbohydrate of rhGAA to improve its affinity for the CI-MPR represents a feasible approach to enhance the efficacy of enzyme replacement therapy for Pompe disease.

Enhancement of antibacterial superoxide-anion generation in human monocytes by fumaric acid esters

Fumaric acid esters (FAE) are used for the systemic therapy of psoriasis with high clinical efficacy. Among the potential side effects of FAE therapy, lymphocytopenia is sometimes observed. We have investigated the effect of dimethylfumarate (DMF) and its main metabolite methylhydrogenfumarate (MHF) as well as dexamethasone on superoxide anion generation by human monocytes and neutrophils after stimulation with bacteria (Staphylococcus aureus and Escherichia coli) and the yeast Candida albicans in addition with zymosan particles and with the tripeptide fMLP. Expression of mannose receptors on monocytes and neutrophils was also analyzed. The results showed that dexamethasone significantly inhibited superoxide anion generation from monocytes in response to bacteria and C. albicans, whereas DMF as well as MHF dose dependently increased the production of superoxide anion in monocytes in response to zymosan, fMLP and bacteria. Dexamethasone, DMF or MHF did not modulate superoxide anion generation of neutrophils. Expression of mannose receptors on monocytes was not regulated by DMF or MHF. Our data provide evidence that DMF and MHF do not alter the production of superoxide anions as an important mechanism of innate defense against microorganisms.

Gaucher disease: pathological mechanisms and modern management

Gaucher disease, the most common lysosomal storage disorder, is caused by the defective activity of the lysosomal enzyme, acid-beta-glucosidase (GlcCerase), leading to accumulation of glucosylceramide (GlcCer), particularly in cells of the macrophage lineage. Nearly 200 mutations in GlcCerase have been described, but for the most part, genotype-phenotype correlations are weak, and little is known about the down-stream biochemical changes that occur upon GlcCer accumulation that result in cell and tissue dysfunction. In contrast, the clinical course of Gaucher disease has been well described, and at least one treatment is available, namely enzyme replacement therapy. One other treatment, substrate reduction therapy, has recently been marketed, and others are in early stages of development. This review, after discussing pathological mechanisms, evaluates the advantages and disadvantages of existing therapies.