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

Gaucher Disease: A Glance from a Medicinal Chemistry Perspective

Rare diseases are particular pathological conditions affecting a limited number of people and few drugs are known to be effective as therapeutic treatment. Gaucher disease, caused by a deficiency of the lysosomal enzyme glucocerebrosidase, belongs to this class of disorders, and it is considered the most common among the Lysosomal Storage Diseases. The two main therapeutic approaches are the Enzyme Replacement Therapy (ERT) and the Substrate Reduction Therapy (SRT). ERT, consisting in replacing the defective enzyme by administering a recombinant enzyme, is effective in alleviating the visceral symptoms, hallmarks of the most common subtype of the disease whereas it has no effects when symptoms involve CNS, since the recombinant protein is unable to significantly cross the Blood Brain Barrier. The SRT strategy involves inhibiting glucosylceramide synthase (GCS), the enzyme responsible for the production of the associated storage molecule. The rational design of new inhibitors of GCS has been hampered by the lack of either the crystal structure of the enzyme or an in-silico model of the active site which could provide important information regarding the interactions of potential inhibitors with the target, but, despite this, interesting results have been obtained and are herein reviewed.

Inhibition of cysteine protease cathepsin L increases the level and activity of lysosomal glucocerebrosidase

The glucocerebrosidase (GCase) encoded by the GBA1 gene hydrolyzes glucosylceramide (GluCer) to ceramide and glucose in lysosomes. Homozygous or compound heterozygous GBA1 mutations cause the lysosomal storage disease Gaucher disease (GD) due to severe loss of GCase activity. Loss-of-function variants in the GBA1 gene are also the most common genetic risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Restoring lysosomal GCase activity represents an important therapeutic approach for GBA1-associated diseases. We hypothesized that increasing the stability of lysosomal GCase protein could correct deficient GCase activity in these conditions. However, it remains unknown how GCase stability is regulated in the lysosome. We found that cathepsin L, a lysosomal cysteine protease, cleaves GCase and regulates its stability. In support of these data, GCase protein was elevated in the brain of cathepsin L-KO mice. Chemical inhibition of cathepsin L increased both GCase levels and activity in fibroblasts from patients with GD. Importantly, inhibition of cathepsin L in dopaminergic neurons from a patient GBA1-PD led to increased GCase levels and activity as well as reduced phosphorylated α-synuclein. These results suggest that targeting cathepsin L-mediated GCase degradation represents a potential therapeutic strategy for GCase deficiency in PD and related disorders that exhibit decreased GCase activity.

Cation-independent mannose 6-phosphate receptor: From roles and functions to targeted therapies

The cation-independent mannose 6-phosphate receptor (CI-M6PR) is a ubiquitous transmembrane receptor whose main intracellular role is to direct enzymes carrying mannose 6-phosphate moieties to lysosomal compartments. Recently, the small membrane-bound portion of this receptor has appeared to be implicated in numerous pathophysiological processes. This review presents an overview of the main ligand partners and the roles of CI-M6PR in lysosomal storage diseases, neurology, immunology and cancer fields. Moreover, this membrane receptor has already been noted for its strong potential in therapeutic applications thanks to its cellular internalization activity and its ability to address pathogenic factors to lysosomes for degradation. A number of therapeutic delivery approaches using CI-M6PR, in particular with enzymes, antibodies or nanoparticles, are currently being proposed.

Green Biologics: Harnessing the Power of Plants to Produce Pharmaceuticals

Plants are increasingly used for the production of high-quality biological molecules for use as pharmaceuticals and biomaterials in industry. Plants have proved that they can produce life-saving therapeutic proteins (Elelyso™-Gaucher's disease treatment, ZMapp™-anti-Ebola monoclonal antibodies, seasonal flu vaccine, Covifenz™-SARS-CoV-2 virus-like particle vaccine); however, some of these therapeutic proteins are difficult to bring to market, which leads to serious difficulties for the manufacturing companies. The closure of one of the leading companies in the sector (the Canadian biotech company Medicago Inc., producer of Covifenz) as a result of the withdrawal of investments from the parent company has led to the serious question: What is hindering the exploitation of plant-made biologics to improve health outcomes? Exploring the vast potential of plants as biological factories, this review provides an updated perspective on plant-derived biologics (PDB). A key focus is placed on the advancements in plant-based expression systems and highlighting cutting-edge technologies that streamline the production of complex protein-based biologics. The versatility of plant-derived biologics across diverse fields, such as human and animal health, industry, and agriculture, is emphasized. This review also meticulously examines regulatory considerations specific to plant-derived biologics, shedding light on the disparities faced compared to biologics produced in other systems.

Glycosylation shapes the efficacy and safety of diverse protein, gene and cell therapies

Over recent decades, therapeutic proteins have had widespread success in treating a myriad of diseases. Glycosylation, a near universal feature of this class of drugs, is a critical quality attribute that significantly influences the physical properties, safety profile and biological activity of therapeutic proteins. Optimizing protein glycosylation, therefore, offers an important avenue to developing more efficacious therapies. In this review, we discuss specific examples of how variations in glycan structure and glycoengineering impacts the stability, safety, and clinical efficacy of protein-based drugs that are already in the market as well as those that are still in preclinical development. We also highlight the impact of glycosylation on next generation biologics such as T cell-based cancer therapy and gene therapy.

Plant glycoengineering for designing next-generation vaccines and therapeutic proteins

Protein glycosylation has a huge impact on biological processes in all domains of life. The type of glycan present on a recombinant glycoprotein depends on protein intrinsic features and the glycosylation repertoire of the cell type used for expression. Glycoengineering approaches are used to eliminate unwanted glycan modifications and to facilitate the coordinated expression of glycosylation enzymes or whole metabolic pathways to furnish glycans with distinct modifications. The formation of tailored glycans enables structure-function studies and optimization of therapeutic proteins used in different applications. While recombinant proteins or proteins from natural sources can be in vitro glycoengineered using glycosyltransferases or chemoenzymatic synthesis, many approaches use genetic engineering involving the elimination of endogenous genes and introduction of heterologous genes to cell-based production systems. Plant glycoengineering enables the in planta production of recombinant glycoproteins with human or animal-type glycans that resemble natural glycosylation or contain novel glycan structures. This review summarizes key achievements in glycoengineering of plants and highlights current developments aiming to make plants more suitable for the production of a diverse range of recombinant glycoproteins for innovative therapies.

Product safety aspects of plant molecular farming

Plant molecular farming (PMF) has been promoted since the 1990s as a rapid, cost-effective and (most of all) safe alternative to the cultivation of bacteria or animal cells for the production of biopharmaceutical proteins. Numerous plant species have been investigated for the production of a broad range of protein-based drug candidates. The inherent safety of these products is frequently highlighted as an advantage of PMF because plant viruses do not replicate in humans and vice versa. However, a more nuanced analysis of this principle is required when considering other pathogens because toxic compounds pose a risk even in the absence of replication. Similarly, it is necessary to assess the risks associated with the host system (e.g., the presence of toxic secondary metabolites) and the production approach (e.g., transient expression based on bacterial infiltration substantially increases the endotoxin load). This review considers the most relevant host systems in terms of their toxicity profile, including the presence of secondary metabolites, and the risks arising from the persistence of these substances after downstream processing and product purification. Similarly, we discuss a range of plant pathogens and disease vectors that can influence product safety, for example, due to the release of toxins. The ability of downstream unit operations to remove contaminants and process-related toxic impurities such as endotoxins is also addressed. This overview of plant-based production, focusing on product safety aspects, provides recommendations that will allow stakeholders to choose the most appropriate strategies for process development.

High accumulation of the Man5GlcNAc2 structure by combining N-acetylglucosaminyltransferase I gene suppression and mannosidase I gene overexpression in Nicotiana tabacum SR1

High accumulation of a single high-mannose glycan structure is important to ensure the quality of therapeutic proteins. We developed a glyco-engineering strategy for ensuring high accumulation of the Man₅GlcNAc₂ structure by combining N-acetylglucosaminyltransferase I (GnT I) gene suppression and mannosidase I (Man I) gene overexpression. Nicotiana tabacum SR1 was used as the glyco-engineered host owing to the lower risk of pathogenic contamination than that in mammalian cells. We generated three glyco-engineered plant strains (gnt, gnt-MANA1, and gnt-MANA2) with suppression of GnT I or the combined suppression of GnT I and overexpression of Man I A1 or A2. The quantitative reverse transcriptase-PCR analysis showed a higher level of upregulation of Man I expression in gnt-MANA1/A2 plants than in the wild-type plants. Man I activity assay showed that the gnt-MANA1 plants had a higher Man I activity than did the wild-type and gnt-MANA2 plants. N-glycan analysis independently performed on two plants of each plant strain showed that gnt-MANA1 plants had a low abundance of the Man_6-9GlcNAc₂ structure (2.8%, 7.1%) and high abundance of the Man₅GlcNAc₂ structure (80.0%, 82.8%) compared with those in the wild-type and gnt plants. These results indicated that GnT I knockdown suppressed further modification of the Man₅GlcNAc₂ structure, and Man I overexpression enhanced the conversion of Man_6-9GlcNAc₂ structures to the Man₅GlcNAc₂ structure. The developed glyco-engineered plants have potential for serving as novel expression hosts for therapeutic proteins.

Osteonecrosis in Gaucher disease in the era of multiple therapies: Biomarker set for risk stratification from a tertiary referral center

Background

A salutary effect of treatments for Gaucher disease (GD) has been a reduction in the incidence of avascular osteonecrosis (AVN). However, there are reports of AVN in patients receiving enzyme replacement therapy (ERT) , and it is not known whether it is related to individual treatments, GBA genotypes, phenotypes, biomarkers of residual disease activity, or anti-drug antibodies. Prompted by development of AVN in several patients receiving ERT, we aimed to delineate the determinants of AVN in patients receiving ERT or eliglustat substrate reduction therapy (SRT) during 20 years in a tertiary referral center.

Methods

Longitudinal follow-ups of 155 GD patients between 2001 and 2021 were analyzed for episodes of AVN on therapy, type of therapy, GBA1 genotype, spleen status, biomarkers, and other disease indicators. We applied mixed-effects logistic model to delineate the independent correlates of AVN while receiving treatment.

Results

The patients received cumulative 1382 years of treatment. There were 16 episodes of AVN in 14 patients, with two episodes, each occurring in two patients. Heteroallelic p.Asn409Ser GD1 patients were 10 times (95% CI, 1.5-67.2) more likely than p.Asn409Ser homozygous patients to develop osteonecrosis during treatment. History of AVN prior to treatment initiation was associated with 4.8-fold increased risk of AVN on treatment (95% CI, 1.5-15.2). The risk of AVN among patients receiving velaglucerase ERT was 4.68 times higher compared to patients receiving imiglucerase ERT (95% CI, 1.67-13). No patient receiving eliglustat SRT suffered AVN. There was a significant correlation between GlcSph levels and AVN. Together, these biomarkers reliably predicted risk of AVN during therapy (ROC AUC 0.894, p<0.001).

Conclusions

There is a low, but significant risk of AVN in GD in the era of ERT/SRT. We found that increased risk of AVN was related to GBA genotype, history of AVN prior to treatment initiation, residual serum GlcSph level, and the type of ERT. No patient receiving SRT developed AVN. These findings exemplify a new approach to biomarker applications in a rare inborn error of metabolism to evaluate clinical outcomes in comprehensively followed patients and will aid identification of GD patients at higher risk of AVN who will benefit from closer monitoring and treatment optimization.

Funding

LSD Training Fellowship from Sanofi to MB.

Virus-like nanoparticles as enzyme carriers for Enzyme Replacement Therapy (ERT)

Enzyme replacement therapy (ERT) has been used to treat a few of the many existing diseases which are originated from the lack of, or low enzymatic activity. Exogenous enzymes are administered to contend with the enzymatic activity deficiency. Enzymatic nanoreactors based on the enzyme encapsulation inside of virus-like particles (VLPs) appear as an interesting alternative for ERT. VLPs are excellent delivery vehicles for therapeutic enzymes as they are biodegradable, uniformly organized, and porous nanostructures that transport and could protect the biocatalyst from the external environment without much affecting the bioactivity. Consequently, significant efforts have been made in the production processes of virus-based enzymatic nanoreactors and their functionalization, which are critically reviewed. The use of virus-based enzymatic nanoreactors for the treatment of lysosomal storage diseases such as Gaucher, Fabry, and Pompe diseases, as well as potential therapies for galactosemia, and Hurler and Hunter syndromes are discussed.

A universal GlycoDesign for lysosomal replacement enzymes to improve circulation time and biodistribution

Currently available enzyme replacement therapies for lysosomal storage diseases are limited in their effectiveness due in part to short circulation times and suboptimal biodistribution of the therapeutic enzymes. We previously engineered Chinese hamster ovary (CHO) cells to produce α-galactosidase A (GLA) with various N-glycan structures and demonstrated that elimination of mannose-6-phosphate (M6P) and conversion to homogeneous sialylated N-glycans prolonged circulation time and improved biodistribution of the enzyme following a single-dose infusion into Fabry mice. Here, we confirmed these findings using repeated infusions of the glycoengineered GLA into Fabry mice and further tested whether this glycoengineering approach, Long-Acting-GlycoDesign (LAGD), could be implemented on other lysosomal enzymes. LAGD-engineered CHO cells stably expressing a panel of lysosomal enzymes [aspartylglucosamine (AGA), beta-glucuronidase (GUSB), cathepsin D (CTSD), tripeptidyl peptidase (TPP1), alpha-glucosidase (GAA) or iduronate 2-sulfatase (IDS)] successfully converted all M6P-containing N-glycans to complex sialylated N-glycans. The resulting homogenous glycodesigns enabled glycoprotein profiling by native mass spectrometry. Notably, LAGD extended the plasma half-life of all three enzymes tested (GLA, GUSB, AGA) in wildtype mice. LAGD may be widely applicable to lysosomal replacement enzymes to improve their circulatory stability and therapeutic efficacy.

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.

Production of recombinant β-glucocerebrosidase in wild-type and glycoengineered transgenic Nicotiana benthamiana root cultures with different N-glycan profiles

Gaucher disease is an inherited lysosomal storage disorder caused by an insufficiency of active β-glucocerebrosidase (GCase). Exogenous recombinant GCase via enzyme replacement therapy is considered the most practical treatment for Gaucher disease. Mannose receptors mediate the efficient uptake of exogenous GCase into macrophages. Thus, terminal mannose residues on N-glycans are essential for the delivery of exogenous GCase. In this study, recombinant GCase was produced in root cultures of wild-type (WT) and glycoengineered transgenic Nicotiana benthamiana with downregulated N-acetylglucosaminyltransferase I expression. Root cultures of WT and glycoengineered transgenic N. benthamiana plants were successfully generated by the induction of plant hormones. Recombinant GCases produced in both root cultures possessed GCase enzyme activity. Purified GCases derived from both root cultures revealed different N-glycan profiles. The WT-derived GCase possessed the predominant plant-type N-glycans, which contain plant-specific sugars-linkages, specifically β1,2-xylose and α1,3-fucose residues. Notably, the mannosidic-type N-glycans with terminal mannose residues were abundant in the purified GCase derived from glycoengineered N. benthamiana root culture. This research provides a promising plant-based system for the production of recombinant GCase with terminal mannose residues on N-glycans.

Strategies for Glycoengineering Therapeutic Proteins

Almost all therapeutic proteins are glycosylated, with the carbohydrate component playing a long-established, substantial role in the safety and pharmacokinetic properties of this dominant category of drugs. In the past few years and moving forward, glycosylation is increasingly being implicated in the pharmacodynamics and therapeutic efficacy of therapeutic proteins. This article provides illustrative examples of drugs that have already been improved through glycoengineering including cytokines exemplified by erythropoietin (EPO), enzymes (ectonucleotide pyrophosphatase 1, ENPP1), and IgG antibodies (e.g., afucosylated Gazyva^®, Poteligeo^®, Fasenra™, and Uplizna^®). In the future, the deliberate modification of therapeutic protein glycosylation will become more prevalent as glycoengineering strategies, including sophisticated computer-aided tools for “building in” glycans sites, acceptance of a broad range of production systems with various glycosylation capabilities, and supplementation methods for introducing non-natural metabolites into glycosylation pathways further develop and become more accessible.

Improving Protein Quantity and Quality—The Next Level of Plant Molecular Farming

Plants offer several unique advantages in the production of recombinant pharmaceuticals for humans and animals. Although numerous recombinant proteins have been expressed in plants, only a small fraction have been successfully put into use. The hugely distinct expression systems between plant and animal cells frequently cause insufficient yield of the recombinant proteins with poor or undesired activity. To overcome the issues that greatly constrain the development of plant-produced pharmaceuticals, great efforts have been made to improve expression systems and develop alternative strategies to increase both the quantity and quality of the recombinant proteins. Recent technological revolutions, such as targeted genome editing, deconstructed vectors, virus-like particles, and humanized glycosylation, have led to great advances in plant molecular farming to meet the industrial manufacturing and clinical application standards. In this review, we discuss the technological advances made in various plant expression platforms, with special focus on the upstream designs and milestone achievements in improving the yield and glycosylation of the plant-produced pharmaceutical proteins.

Long-term safety and effectiveness of velaglucerase alfa in Gaucher disease: 6-year interim analysis of a post-marketing surveillance in Japan

BACKGROUND

Gaucher disease (GD) is caused by reduced lysosomal enzyme β-glucocerebrosidase activity. Heterogeneous genotypes and phenotypes have been observed within GD types and across ethnicities. Enzyme replacement therapy is generally recommended for patients with type 1 GD, the least severe form of GD. In Japan, velaglucerase alfa has a broad indication covering type 1, 2 or 3 GD.  METHODS: All patients with type 1, 2, or 3 GD administered velaglucerase alfa 60 U/kg every 2 weeks via intravenous infusion after its launch date in Japan in 2014, were enrolled in a non-interventional, observational post-marketing surveillance (PMS). Individual patient data were reported via case report forms (CRFs). Key safety endpoints investigated included the incidence of infusion-related reactions (IRRs), the safety of velaglucerase alfa in patients with types 2 and 3 GD, from patients under one year of age to elderly patients (≥ 65 years of age). Long-term efficacy was also assessed.  RESULTS: In total, 53 patients with GD were registered. CRFs were available for 41 (77.4%) patients at the 6-year interim analysis. Fourteen adverse drug reactions (ADRs) were reported in seven patients. All reported ADRs occurred in patients with type 2 GD. ADRs were reported by 63.6% (7/11) of patients with type 2 GD. Ten ADRs were reported in five patients aged < 4 years. No elderly patients experienced any ADR during the surveillance period. Five ADRs occurring in three (10.0%) patients were classified as IRRs, with one case of vomiting (moderate severity) resulting in treatment discontinuation. Ten serious adverse events were reported in five (16.7%) patients. Three fatal events were considered to be unrelated to treatment with velaglucerase alfa. Platelet counts increased after the administration of velaglucerase alfa and were generally maintained within the normal range over the administration period. Among eleven patients tested for neutralizing anti-velaglucerase alfa antibodies, two (18.2%) were assessed as positive results.  CONCLUSION: PMS data from patients with types 1-3 GD in Japan indicate that long-term treatment with velaglucerase alfa was well-tolerated and associated with increased platelet counts, which is consistent with observations made in studies outside of Japan.

TRIAL REGISTRATION

NCT03625882 registered July 2014.

Histomorphometric analysis of liver biopsies of treated patients with Gaucher disease type 1

Gaucher disease (GD) is an autosomal recessive lysosomal disorder caused by a disturbance in the metabolism of glucocerebroside in the macrophages. Most of its manifestations – hepatosplenomegaly, anemia, thrombocytopenia, and bone pain – are amenable to a macrophage-target therapy such as enzyme replacement. However, there is increasing evidence that abnormalities of the liver persist despite the specific GD treatment. In this work, we adapted histomorphometry techniques to the study of hepatocytes in GD using liver tissue of treated patients, developing the first morphometrical method for canalicular quantification in immunohistochemistry-stained liver biopsies, and exploring histomorphometric characteristics of GD. This is the first histomorphometric technique developed for canalicular analysis on histological liver biopsy samples.

Plant-made immunotoxin building blocks: A roadmap for producing therapeutic antibody-toxin fusions

Molecular farming in plants is an emerging platform for the production of pharmaceutical proteins, and host species such as tobacco are now becoming competitive with commercially established production hosts based on bacteria and mammalian cell lines. The range of recombinant therapeutic proteins produced in plants includes replacement enzymes, vaccines and monoclonal antibodies (mAbs). But plants can also be used to manufacture toxins, such as the mistletoe lectin viscumin, providing an opportunity to express active antibody-toxin fusion proteins, so-called recombinant immunotoxins (RITs). Mammalian production systems are currently used to produce antibody-drug conjugates (ADCs), which require the separate expression and purification of each component followed by a complex and hazardous coupling procedure. In contrast, RITs made in plants are expressed in a single step and could therefore reduce production and purification costs. The costs can be reduced further if subcellular compartments that accumulate large quantities of the stable protein are identified and optimal plant growth conditions are selected. In this review, we first provide an overview of the current state of RIT production in plants before discussing the three key components of RITs in detail. The specificity-defining domain (often an antibody) binds cancer cells, including solid tumors and hematological malignancies. The toxin provides the means to kill target cells. Toxins from different species with different modes of action can be used for this purpose. Finally, the linker spaces the two other components to ensure they adopt a stable, functional conformation, and may also promote toxin release inside the cell. Given the diversity of these components, we extract broad principles that can be used as recommendations for the development of effective RITs. Future research should focus on such proteins to exploit the advantages of plants as efficient production platforms for targeted anti-cancer therapeutics.

Transient Production of Human β-Glucocerebrosidase With Mannosidic-Type N-Glycan Structure in Glycoengineered Nicotiana benthamiana Plants

Gaucher disease is an inherited lysosomal storage disorder caused by a deficiency of functional enzyme β-glucocerebrosidase (GCase). Recombinant GCase has been used in enzyme replacement therapy to treat Gaucher disease. Importantly, the terminal mannose N-glycan structure is essential for the uptake of recombinant GCase into macrophages via the mannose receptor. In this research, recombinant GCase was produced using Agrobacterium-mediated transient expression in both wild-type (WT) and N-acetylglucosaminyltransferase I (GnTI) downregulated Nicotiana benthamiana (ΔgntI) plants, the latter of which accumulates mannosidic-type N-glycan structures. The successfully produced functional GCase exhibited GCase enzyme activity. The enzyme activity was the same as that of the conventional mammalian-derived GCase. Notably, N-glycan analysis revealed that a mannosidic-type N-glycan structure lacking plant-specific N-glycans (β1,2-xylose and α1,3-fucose residues) was predominant in all glycosylation sites of purified GCase produced from ΔgntI plants. Our research provides a promising alternative plant line as a host for the production of recombinant GCase with a mannosidic-type N-glycan structure. This glycoengineered plant might be applicable to the production of other pharmaceutical proteins, especially mannose receptor targeted protein, for therapeutic uses.

The interplay between Glucocerebrosidase, α-synuclein and lipids in human models of Parkinson's disease

Mutations in the gene GBA, encoding glucocerebrosidase (GCase), are the highest genetic risk factor for Parkinson's disease (PD). GCase is a lysosomal glycoprotein responsible for the hydrolysis of glucosylceramide into glucose and ceramide. Mutations in GBA cause a decrease in GCase activity, stability and protein levels which in turn lead to the accumulation of GCase lipid substrates as well as α-synuclein (αS) in vitro and in vivo. αS is the main constituent of Lewy bodies found in the brain of PD patients and an increase in its levels was found to be associated with a decrease in GCase activity/protein levels in vitro and in vivo. In this review, we describe the reported biophysical and biochemical changes that GBA mutations can induce in GCase activity and stability as well as the current overview of the levels of GCase protein/activity, αS and lipids measured in patient-derived samples including post-mortem brains, stem cell-derived neurons, cerebrospinal fluid, blood and fibroblasts as well as in SH-SY5Y cells. In particular, we report how the levels of αS and lipids are affected by/correlated to significant changes in GCase activity/protein levels and which cellular pathways are activated or disrupted by these changes in each model. Finally, we review the current strategies used to revert the changes in the levels of GCase activity/protein, αS and lipids in the context of PD.

Overexpression of a multifunctional β-glucosidase gene from thermophilic archaeon Sulfolobus solfataricus in transgenic tobacco could facilitate glucose release and its use as a reporter

The β-glucosidase, which hydrolyzes the β(1-4) glucosidic linkage of disaccharides, oligosaccharides and glucose-substituted molecules, has been used in many biotechnological applications. The current commercial source of β-glucosidase is mainly microbial fermentation. Plants have been developed as bioreactors to produce various kinds of proteins including β-glucosidase because of the potential low cost. Sulfolobus solfataricus is a thermoacidophilic archaeon that can grow optimally at high temperature, around 80 °C, and pH 2-4. We overexpressed the β-glucosidase gene from S. solfataricus in transgenic tobacco via Agrobacteria-mediated transformation. Three transgenic tobacco lines with β-glucosidase gene expression driven by the rbcS promoter were obtained, and the recombinant proteins were accumulated in chloroplasts, endoplasmic reticulum and vacuoles up to 1%, 0.6% and 0.3% of total soluble protein, respectively. By stacking the transgenes via crossing distinct transgenic events, the level of β-glucosidase in plants could further increase. The plant-expressed β-glucosidase had optimal activity at 80 °C and pH 5-6. In addition, the plant-expressed β-glucosidase showed high thermostability; on heat pre-treatment at 80 °C for 2 h, approximately 70% residual activity remained. Furthermore, wind-dried leaf tissues of transgenic plants showed good stability in short-term storage at room temperature, with β-glucosidase activity of about 80% still remaining after 1 week of storage as compared with fresh leaf. Furthermore, we demonstrated the possibility of using the archaebacterial β-glucosidase gene as a reporter in plants based on alternative β-galactosidase activity.

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 baculoviral system for the production of human β-glucocerebrosidase enables atomic resolution analysis

The lysosomal glycoside hydrolase β-glucocerebrosidase (GBA; sometimes called GBA1 or GCase) catalyses the hydrolysis of glycosphingolipids. Inherited deficiencies in GBA cause the lysosomal storage disorder Gaucher disease (GD). Consequently, GBA is of considerable medical interest, with continuous advances in the development of inhibitors, chaperones and activity-based probes. The development of new GBA inhibitors requires a source of active protein; however, the majority of structural and mechanistic studies of GBA today rely on clinical enzyme-replacement therapy (ERT) formulations, which are incredibly costly and are often difficult to obtain in adequate supply. Here, the production of active crystallizable GBA in insect cells using a baculovirus expression system is reported, providing a nonclinical source of recombinant GBA with comparable activity and biophysical properties to ERT preparations. Furthermore, a novel crystal form of GBA is described which diffracts to give a 0.98 Å resolution unliganded structure. A structure in complex with the inactivator 2,4-dinitrophenyl-2-deoxy-2-fluoro-β-D-glucopyranoside was also obtained, demonstrating the ability of this GBA formulation to be used in ligand-binding studies. In light of its purity, stability and activity, the GBA production protocol described here should circumvent the need for ERT formulations for structural and biochemical studies and serve to support GD research.

Multiplexed Comparative Analysis of Intact Glycopeptides Using Electron-Transfer Dissociation and Synchronous Precursor Selection Based Triple-Stage Mass Spectrometry

A recently developed synchronous precursor selection (SPS) mass spectrometry to the third (MS3) protocol enables more accurate multiplexed quantification of proteins/peptides using tandem mass tags (TMT) through comparison of reporter ion intensities at the MS3 level. However, challenges still exist for TMT-based simultaneous quantification and identification of intact glycopeptides due to inefficient peptide backbone fragmentation when using collision-induced dissociation (CID). To overcome this limitation, here we report an improved SPS/ETD workflow for TMT-based intact glycopeptide quantification and identification. The SPS/ETD approach was implemented on an Orbitrap Tribrid mass spectrometer and begins with selection of a parent ion in the MS scan, followed by tandem mass spectrometry (MS2) fragmentation by CID in the ion trap. Following MS2 fragmentation, SPS enables simultaneous isolation of the top 10 MS2 fragment ions for further higher energy collisional dissociation (HCD) fragmentation with the resulting MS3 fragments detected in an Orbitrap analyzer. Here, in addition to the standard SPS workflow, an electron-transfer dissociation (ETD) MS2 was performed and analyzed in the ion trap. The resultant ETD and CID spectra were used for the identification of the intact glycopeptides, while the quantitative comparison of site-specific glycans was achieved utilizing TMT reporter ions from HCD MS3 spectra. For intact glycopeptides, through systematic optimization and evaluation using a glycoprotein interference model, the SPS/ETD approach was demonstrated to offer improved accuracy, precision, and sensitivity compared to traditional data-dependent MS2 quantification, while maintaining the glycopeptide identification capability. Finally, this workflow was applied for the site-specific quantitative comparison of the glycoforms for two therapeutic enzymes (Cerezyme and VPRIV) and their different lots. The results demonstrate that this workflow is suitable for TMT-based intact glycopeptide characterization of glycoproteins.

Molecular farming - The slope of enlightenment

Molecular farming can be defined as the use of plants to produce recombinant protein products. The technology is now >30 years old. The early promise of molecular farming was based on three perceived advantages: the low costs of growing plants, the immense scalability of agricultural production, and the inherent safety of plants as hosts for the production of pharmaceuticals. This resulted in a glut of research publications in which diverse proteins were expressed in equally diverse plant-based systems, and numerous companies were founded hoping to commercialize the new technology. There was a moderate degree of success for companies producing non-pharmaceutical proteins, but in the pharmaceutical sector the anticipation raised by promising early research was soon met by the cold hard reality of industrial pragmatism. Plants did not have a track record of success in pharmaceutical protein manufacturing, lacked a regulatory framework, and did not perform as well as established industry platforms. Negative attitudes towards genetically modified plants added to the mix. By the early 2000s, major industry players started to lose interest and pharmaceutical molecular farming fell from a peak of expectation into a trough of disillusionment, just as predicted by the Gartner hype cycle. But many of the pioneers of molecular farming have refocused their activities and have worked to address the limitations that hampered the first generation of technologies. The field has now consolidated around a smaller number of better-characterized platforms and has started to develop standardized methods and best practices, mirroring the evolution of more mature industry sectors. Likewise, attention has turned from proof-of-principle studies to realistic techno-economic modeling to capture significant niche markets, replicating the success of the industrial molecular farming sector. Here we argue that these recent developments signify that pharmaceutical molecular farming is now climbing the slope of enlightenment and will soon emerge as a mature technology.

Sialoglycans and genetically engineered plants

Plants express N-glycosylation pathways and produce N-glycosylated proteins but differ from the mammalian-type proteins. Therefore attempts are made to design and engineer plant glycosylation pathways that can produce mammalian-type glycosylated moieties so that large quantities of biopharmaceuticals compatible to the human body can be produced. Most of the studies of plant expression systems for molecular farming have been conducted on Nicotiana sp. and genetic engineering and molecular biology tools have enabled the generation of glycoengineered plant for human use in the production of therapeutic recombinant proteins. We have discussed in this chapter the advances of glycoengineering in plants with special reference to the reconstruction of silaylation pathways in plants and the latest application in the production of antibody and therapeutics in plants.

Toward Engineering the Mannose 6-Phosphate Elaboration Pathway in Plants for Enzyme Replacement Therapy of Lysosomal Storage Disorders

Mucopolysaccharidosis (MPS) I is a severe lysosomal storage disease caused by α-L-iduronidase (IDUA) deficiency, which results in accumulation of non-degraded glycosaminoglycans in lysosomes. Costly enzyme replacement therapy (ERT) is the conventional treatment for MPS I. Toward producing a more cost-effective and safe alternative to the commercial mammalian cell-based production systems, we have produced recombinant human IDUA in seeds of an Arabidopsis mutant to generate the enzyme in a biologically active and non-immunogenic form containing predominantly high mannose N-linked glycans. Recombinant enzyme in ERT is generally thought to require a mannose 6-phosphate (M6P) targeting signal for endocytosis into patient cells and for intracellular delivery to the lysosome. Toward effecting in planta phosphorylation, the human M6P elaboration machinery was successfully co-expressed along with the recombinant human IDUA using a single multi-gene construct. Uptake studies using purified putative M6P-IDUA generated in planta on cultured MPS I primary fibroblasts indicated that the endocytosed recombinant lysosomal enzyme led to substantial reduction of glycosaminoglycans. However, the efficiency of the putative M6P-IDUA in reducing glycosaminoglycan storage was comparable with the efficiency of the purified plant mannose-terminated IDUA, suggesting a poor in planta M6P-elaboration by the expressed machinery. Although the in planta M6P-tagging process efficiency would need to be improved, an exciting outcome of our work was that the plant-derived mannose-terminated IDUA yielded results comparable to those obtained with the commercial IDUA (Aldurazyme^® (Sanofi, Paris, France)), and a significant amount of the plant-IDUA is trafficked by a M6P receptor-independent pathway. Thus, a plant-based platform for generating lysosomal hydrolases may represent an alternative and cost-effective strategy to the conventional ERT, without the requirement for additional processing to create the M6P motif.

Quality Control and Downstream Processing of Therapeutic Enzymes

Therapeutic enzymes are a commercially minor but clinically important area of biopharmaceuticals. An array of therapeutic enzymes has been developed for a variety of human diseases, including leukaemia and enzyme-deficiency diseases such as Gaucher's disease. Production and testing of therapeutic enzymes is strictly governed by regulatory bodies in each country around the world, and batch-to-batch consistency is crucially important. Manufacture of a batch starts with the fermentation or cell culture stage. After expression of the therapeutic enzyme in a cell culture bioreactor, robust and reproducible protein purification, or downstream processing (DSP) of the target product, is critical to ensuring safe delivery of these medicines. Modern processing technology, including the use of disposable processing equipment, has greatly improved the DSP development pathway in terms of robustness and speed to clinic. Once purified, the drug substance undergoes rigorous quality control (QC) testing according to current regulatory guidance, to enable release to the clinic and patient. QC testing is conducted to ensure the safety, purity, identity, potency and strength of the medicinal product, requiring multiple analytical methods that are rigorously validated and monitored for robust performance. Several case studies, including L-asparaginase and asfotase alfa, are discussed to illustrate the methods described herein.

Genetic engineering approaches to improve posttranslational modification of biopharmaceuticals in different production platforms

The number of approved biopharmaceuticals, where product quality attributes remain of major importance, is increasing steadily. Within the available variety of expression hosts, the production of biopharmaceuticals faces diverse limitations with respect to posttranslational modifications (PTM), while different biopharmaceuticals demand different forms and specifications of PTMs for proper functionality. With the growing toolbox of genetic engineering technologies, it is now possible to address general as well as host- or biopharmaceutical-specific product quality obstacles. In this review, we present diverse expression systems derived from mammalians, bacteria, yeast, plants, and insects as well as available genetic engineering tools. We focus on genes for knockout/knockdown and overexpression for meaningful approaches to improve biopharmaceutical PTMs and discuss their applicability as well as future trends in the field.

Low binding affinity and reduced complement-dependent cell death efficacy of ofatumumab produced using a plant system (Nicotiana benthamiana L.)

The plant protein production system is a platform that can not only reduce production costs but also produce monoclonal antibodies that do not have the risk of residual proteins from the host. However, due to the difference between post-translational processes in plants and animals, there may be a modification in the Fab region of the monoclonal antibody produced in the plant; thus, it is necessary to compare the antigen affinity of this antibody with that of the prototype. In this study, ofatumumab, a fully human anti-CD20 IgG1κ monoclonal antibody used for its non-cross resistance to rituximab, was expressed in Nicotiana benthamiana, and its affinities and efficacies were compared with those of native ofatumumab produced from CHO cells. Two forms of plant ofatumumab (with or without HDEL-tag) were generated and their production yields were compared. The HDEL-tagged ofatumumab was more expressed in plants than the form without HDEL-tag. The specificity of the target recognition of plant-derived ofatumumab was confirmed by mCherry-CD20-expressing HEK cells via immuno-staining, and the capping of CD20 after ofatumumab binding was also confirmed using Ramos B cells. In the functional equivalence tests, the binding affinities and complement-dependent cell cytotoxicity efficacy of plant-ofatumumab-HDEL and plant-ofatumumab without HDEL were significantly reduced compared to those of CHO-derived ofatumumab. Therefore, we suggest that although ofatumumab is not a good candidate as a template for plant-derived monoclonal antibodies because of its decreased affinity when produced in plants, it is an interesting target to study the differences between post-translational modifications in mammals and plants.

Characterization of a GDP-Fucose Transporter and a Fucosyltransferase Involved in the Fucosylation of Glycoproteins in the Diatom Phaeodactylum tricornutum

Although Phaeodactylum tricornutum is gaining importance in plant molecular farming for the production of high-value molecules such as monoclonal antibodies, little is currently known about key cell metabolism occurring in this diatom such as protein glycosylation. For example, incorporation of fucose residues in the glycans N-linked to protein in P. tricornutum is questionable. Indeed, such epitope has previously been found on N-glycans of endogenous glycoproteins in P. tricornutum. Meanwhile, the potential immunogenicity of the α(1,3)-fucose epitope present on plant-derived biopharmaceuticals is still a matter of debate. In this paper, we have studied molecular actors potentially involved in the fucosylation of the glycoproteins in P. tricornutum. Based on sequence similarities, we have identified a putative P. tricornutum GDP-L-fucose transporter and three fucosyltransferase (FuT) candidates. The putative P. tricornutum GDP-L-fucose transporter coding sequence was expressed in the Chinese Hamster Ovary (CHO)-gmt5 mutant lacking its endogenous GDP-L-fucose transporter activity. We show that the P. tricornutum transporter is able to rescue the fucosylation of proteins in this CHO-gmt5 mutant cell line, thus demonstrating the functional activity of the diatom transporter and its appropriate Golgi localization. In addition, we overexpressed one of the three FuT candidates, namely the FuT54599, in P. tricornutum and investigated its localization within Golgi stacks of the diatom. Our findings show that overexpression of the FuT54599 leads to a significant increase of the α(1,3)-fucosylation of the diatom endogenous glycoproteins.

Pharmacokinetics, pharmacodynamics, and safety of moss-aGalactosidase A in patients with Fabry disease

Moss-aGalactosidase A (moss-aGal) is a moss-derived version of human α-galactosidase developed for enzyme replacement therapy in patients with Fabry disease. It exhibits a homogenous N-glycosylation profile with >90% mannose-terminated glycans. In contrast to mammalian cell produced α-galactosidase, moss-aGal does not rely on mannose-6-phosphate receptor mediated endocytosis but targets the mannose receptor for tissue uptake. We conducted a phase 1 clinical trial with moss-aGal in six patients with confirmed diagnosis of Fabry disease during a 28-day schedule. All patients received a single dose of 0.2 mg/kg moss-aGal by i.v.-infusion. Primary endpoints of the trial were safety and pharmacokinetics; secondary endpoints were pharmacodynamics by analyzing urine and plasma Gb3 and lyso-Gb3 concentrations. In all patients, the administered single dose was well tolerated. No safety issues were observed. Pharmacokinetic data revealed a stable nonlinear profile with a short plasma half-life of moss-aGal of 14 minutes. After one single dose of moss-aGal, urinary Gb3 concentrations decreased up to 23% 7 days and up to 60% 28 days post-dose. Plasma concentrations of lyso-Gb3 decreased by 3.8% and of Gb3 by 11% 28 days post-dose. These data reveal that a single dose of moss-aGal was safe, well tolerated, and led to a prolonged reduction of Gb3 excretion. As previously shown, moss-aGal is taken up via the mannose receptor, which is expressed on macrophages but also on endothelial and kidney cells. Thus, these data indicate that moss-aGal may target kidney cells. After these promising results, phase 2/3 clinical trials are in preparation.

Characterization of Human Recombinant N-Acetylgalactosamine-6-Sulfate Sulfatase Produced in Pichia pastoris as Potential Enzyme for Mucopolysaccharidosis IVA Treatment

Mucopolysaccharidosis IVA (MPS IVA or Morquio A syndrome) is a lysosomal storage disease caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to lysosomal storage of keratan sulfate and chondroitin-6-sulfate. Currently, enzyme replacement therapy using an enzyme produced in CHO cells represents the main treatment option for MPS IVA patients. As an alternative, we reported the production of an active GALNS enzyme produced in the yeast Pichia pastoris (prGALNS), which showed internalization by cultured cells through a potential receptor-mediated process and similar post-translational processing as human enzyme. In this study, we further studied the therapeutic potential of prGALNS through the characterization of the N-glycosylation structure, in vitro cell uptake and keratan sulfate reduction, and in vivo biodistribution and generation of anti-prGALNS antibodies. Taken together, these results represent an important step in the development of a P. pastoris-based platform for production of a therapeutic GALNS for MPS IVA enzyme replacement therapy.

Brassica rapa hairy root based expression system leads to the production of highly homogenous and reproducible profiles of recombinant human alpha-L-iduronidase

The Brassica rapa hairy root based expression platform, a turnip hairy root based expression system, is able to produce human complex glycoproteins such as the alpha-L-iduronidase (IDUA) with an activity similar to the one produced by Chinese Hamster Ovary (CHO) cells. In this article, a particular attention has been paid to the N- and O-glycosylation that characterize the alpha-L-iduronidase produced using this hairy root based system. This analysis showed that the recombinant protein is characterized by highly homogeneous post translational profiles enabling a strong batch to batch reproducibility. Indeed, on each of the 6 N-glycosylation sites of the IDUA, a single N-glycan composed of a core Man3 GlcNAc2 carrying one beta(1,2)-xylose and one alpha(1,3)-fucose epitope (M3XFGN2) was identified, highlighting the high homogeneity of the production system. Hydroxylation of proline residues and arabinosylation were identified during O-glycosylation analysis, still with a remarkable reproducibility. This platform is thus positioned as an effective and consistent expression system for the production of human complex therapeutic proteins.

CRISPR/Cas9-mediated knockout of six glycosyltransferase genes in Nicotiana benthamiana for the production of recombinant proteins lacking β-1,2-xylose and core α-1,3-fucose

Plants offer fast, flexible and easily scalable alternative platforms for the production of pharmaceutical proteins, but differences between plant and mammalian N-linked glycans, including the presence of β-1,2-xylose and core α-1,3-fucose residues in plants, can affect the activity, potency and immunogenicity of plant-derived proteins. Nicotiana benthamiana is widely used for the transient expression of recombinant proteins so it is desirable to modify the endogenous N-glycosylation machinery to allow the synthesis of complex N-glycans lacking β-1,2-xylose and core α-1,3-fucose. Here, we used multiplex CRISPR/Cas9 genome editing to generate N. benthamiana production lines deficient in plant-specific α-1,3-fucosyltransferase and β-1,2-xylosyltransferase activity, reflecting the mutation of six different genes. We confirmed the functional gene knockouts by Sanger sequencing and mass spectrometry-based N-glycan analysis of endogenous proteins and the recombinant monoclonal antibody 2G12. Furthermore, we compared the CD64-binding affinity of 2G12 glycovariants produced in wild-type N. benthamiana, the newly generated FX-KO line, and Chinese hamster ovary (CHO) cells, confirming that the glyco-engineered antibody performed as well as its CHO-produced counterpart.

Changes of the peripheral blood mononuclear cells membrane fluidity from type 1 Gaucher disease patients: an electron paramagnetic resonance study

Gaucher disease (GD) is a lysosomal storage disorder, caused by an impaired function of β-glucocerebrosidase, which results in accumulation of glucocerebroside in cells, and altered membrane ordering. Using electron paramagnetic resonance spin labeling, a statistically significant difference in the order parameter between the peripheral blood mononuclear cell membranes of GD patients and healthy controls was observed. Moreover, the results show that the introduction of the enzyme replacement therapy leads to the restoration of the physiological membrane fluidity. Accordingly, this simple method could serve as a preliminary test for GD diagnosis and therapy efficiency.

Pharmacological treatment of pediatric Gaucher disease

INTRODUCTION

Gaucher disease (GD) is an autosomal recessive disorder resulting from the deficiency of the lysosomal enzyme glucocerebrosidase (b-glucosidase), associated with varying degrees of visceral, bone and central nervous system pathology, leading to wide phenotypic diversity. Response to therapy and clinical outcomes are very different between the three clinical subtypes - non-neuronopathic, acute neuronopathic, and chronic neuronopathic forms; hence a definitive clinical diagnosis is essential. The availability of two therapeutic options, i.e. enzyme replacement and substrate reduction, has transformed the natural course of the disease. As pre-treatment disease severity clearly impacts results of therapy, early diagnosis and initiation of treatment especially in the pediatric population are keys to achieving an optimal outcome. Areas covered: We reviewed the literature concerning the treatment of GD focusing on pediatric presentations, various pharmacological treatment options and recommendations for management goals. A PubMed literature search was performed for relevant publications between 1991 and September 2018. Expert commentary: The approval of enzyme replacement therapy (ERT) for GD in the pediatric age group has significantly altered the course of the disease, especially for non-neuronopathic and chronic neuronopathic forms, as ERT does not cross the blood-brain barrier. Early diagnosis, regular follow-up and early initiation of treatment can thus prevent some irreversible complications and improve patient quality of life.

The Lysosomal Protein Arylsulfatase B Is a Key Enzyme Involved in Skeletal Turnover

Skeletal pathologies are frequently observed in lysosomal storage disorders, yet the relevance of specific lysosomal enzymes in bone remodeling cell types is poorly defined. Two lysosomal enzymes, ie, cathepsin K (Ctsk) and Acp5 (also known as tartrate-resistant acid phosphatase), have long been known as molecular marker proteins of differentiated osteoclasts. However, whereas the cysteine protease Ctsk is directly involved in the degradation of bone matrix proteins, the molecular function of Acp5 in osteoclasts is still unknown. Here we show that Acp5, in concert with Acp2 (lysosomal acid phosphatase), is required for dephosphorylation of the lysosomal mannose 6-phosphate targeting signal to promote the activity of specific lysosomal enzymes. Using an unbiased approach we identified the glycosaminoglycan-degrading enzyme arylsulfatase B (Arsb), mutated in mucopolysaccharidosis type VI (MPS-VI), as an osteoclast marker, whose activity depends on dephosphorylation by Acp2 and Acp5. Similar to Acp2/Acp5^-/- mice, Arsb-deficient mice display lysosomal storage accumulation in osteoclasts, impaired osteoclast activity, and high trabecular bone mass. Of note, the most prominent lysosomal storage accumulation was observed in osteocytes from Arsb-deficient mice, yet this pathology did not impair production of sclerostin (Sost) and Fgf23. Because the influence of enzyme replacement therapy (ERT) on bone remodeling in MPS-VI is still unknown, we additionally treated Arsb-deficient mice by weekly injection of recombinant human ARSB from 12 to 24 weeks of age. We found that the high bone mass phenotype of Arsb-deficient mice and the underlying bone cell deficits were fully corrected by ERT in the trabecular compartment. Taken together, our results do not only show that the function of Acp5 in osteoclasts is linked to dephosphorylation and activation of lysosomal enzymes, they also provide an important proof-of-principle for the feasibility of ERT to correct bone cell pathologies in lysosomal storage disorders. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

The Production of Human β-Glucocerebrosidase in Nicotiana benthamiana Root Culture

Gaucher disease is caused by a deficiency of the enzyme glucocerebrosidase (GCase). Currently, enzyme-replacement therapy using recombinant GCase produced in mammalian cells is considered the most effective treatment. Plants are an attractive alternative host for recombinant protein production due to the low cost of large-scale production and lack of risk of contamination by human pathogens. Compared to whole plants, root cultures can grow faster. Therefore, this study aimed to produce recombinant GCase in a Nicotiana benthamiana root culture. Root culture of a GCase-producing transgenic plant was induced by indole-3-acetic acid at the concentration of 1 mg/L. Recombinant GCase was successfully produced in roots as a functional protein with an enzyme activity equal to 81.40 ± 17.99 units/mg total protein. Crude proteins were extracted from the roots. Recombinant GCase could be purified by concanavalin A and phenyl 650C chromatography. The productivity of GCase was approximately 1 µg/g of the root. A N-glycan analysis of purified GCase was performed using nano LC/MS. The Man₃XylFucGlcNAc₂ structure was predominant in purified GCase with two plant-specific glycan residues. This study presents evidence for a new, safe and efficient system of recombinant GCase production that might be applied to other recombinant proteins.

Green Therapeutic Biocapsules: Using Plant Cells to Orally Deliver Biopharmaceuticals

The use of innovative platforms to produce biopharmaceuticals cheaply and deliver them through noninvasive routes could expand their social benefits. Coverage should increase as a consequence of lower cost and higher patient compliance due to painless administration. For more than two decades of research, oral therapies that rely on genetically engineered plants for the production of biopharmaceuticals have been explored to treat or prevent high-impact diseases. Recent reports on the successful oral delivery of plant-made biopharmaceuticals raise new hopes for the field. Several candidates have shown protection in animal models, and efforts to establish their production on an industrial scale are ongoing. These advances and perspectives for the field are analyzed.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

How we manage Gaucher Disease in the era of choices

Treatment of Gaucher Disease (GD) is now beset with the abundance of therapeutic options for an individual patient, making the choice of therapy complex for both expert and non-expert clinicians. The pathogenesis of all disease manifestations is a gene mutation-driven deficiency of glucocerebrosidase, but the clinical expression and response of each of the clinical manifestations to different therapies can be difficult to predict. Enzyme replacement therapy has been available since 1991 and is well-established, with known efficacy and minimal toxicity. Of interest, the three available enzymes are distinct molecules and were registered as new products, not biosimilars. Oral substrate reduction therapy has undergone a revitalisation with a newly approved agent in this class for which some efficacy and toxicity questions have been raised. Herein we present our approach to the management of GD in the era of choices, including a new algorithm for how to manage a newly diagnosed patient.

Pharmacotherapy of Gaucher Disease: Current and Future Options

The clinical manifestations of Gaucher disease, a rare genetic lysosomal storage disorder, are debilitating, and the neuronopathic forms of the disease are fatal. The authors describe the current and investigational therapies for treatment.

Taliglucerase alfa: safety and efficacy across 6 clinical studies in adults and children with Gaucher disease

Taliglucerase alfa is an enzyme replacement therapy (ERT) approved for treatment of adult and paediatric patients with Type 1 Gaucher disease (GD) in several countries and the first plant cell-expressed recombinant therapeutic protein approved by the US Food and Drug Administration for humans. Here, we review the findings across six key taliglucerase alfa clinical studies. A total of 33 treatment-naïve adult patients were randomized to taliglucerase alfa 30 U/kg or 60 U/kg in a 9-month, multicentre, randomized, double-blind, parallel-group, dose-comparison pivotal study, after which eligible patients continued into two consecutive extension studies; 17 treatment-naïve adult patients completed 5 total years of treatment with taliglucerase alfa. In the only ERT study focused on exclusively paediatric patients with GD, 11 treatment-naïve children were randomized to taliglucerase alfa 30 U/kg or 60 U/kg in a 12-month, multicentre, double-blind study; nine completed 3 total years of treatment in a dedicated paediatric extension study. The effect of switching patients from imiglucerase to taliglucerase alfa was also investigated in a separate 9-month study that included 26 adults and five children; 10 adults completed a total of 3 years and two children completed a total of 2.75 years of taliglucerase alfa treatment in the extension studies. All studies evaluated safety and spleen volume, liver volume, platelet count, haemoglobin concentration, and biomarkers as measures of efficacy. Detailed results from baseline through the end of these studies are presented. Taliglucerase alfa was well tolerated, and adverse events were generally mild/moderate in severity and transient. Treatment with taliglucerase alfa resulted in improvements (treatment-naïve patients) or stability (patients switched from imiglucerase) in visceral, haematologic, and biomarker parameters. Together, this comprehensive data set supports the treatment of adult and paediatric patients with GD who are naïve to ERT or who have previously been treated with imiglucerase.

Immunogenicity of glycans on biotherapeutic drugs produced in plant expression systems-The taliglucerase alfa story

Plants are a promising alternative for the production of biotherapeutics. Manufacturing in-planta adds plant specific glycans. To understand immunogenic potential of these glycans, we developed a validated method to detect plant specific glycan antibodies in human serum. Using this assay, low prevalence of pre-existing anti-plant glycan antibodies was found in healthy humans (13.5%) and in glucocerebrosidase-deficient Gaucher disease (GD) patients (5%). A low incidence (9% in naïve patient and none in treatment experienced patients) of induced anti-plant glycan antibodies was observed in GD patients after up to 30 months replacement therapy treatment with taliglucerase alfa, a version of human glucocerebrosidase produced in plant cells. Detailed evaluation of clinical safety and efficacy endpoints indicated that anti-plant glycan antibodies did not affect the safety or efficacy of taliglucerase alfa in patients. This study shows the benefit of using large scale human trials to evaluate the immunogenicity risk of plant derived glycans, and indicates no apparent risk related to anti-plant glycan antibodies.

Insights into the structural biology of Gaucher disease

Gaucher disease, the most common lysosomal storage disorder, is caused by mutations in the gene encoding the acid-β-glucosidase lysosomal hydrolase enzyme that cleaves glucocerebroside into glucose and ceramide. Reduced enzyme activity and impaired structural stability arise due to >300 known disease-causing mutations. Several of these mutations have also been associated with an increased risk of Parkinson disease (PD). Since the discovery of the acid-β-glucosidase X-ray structure, there have been major advances in our understanding of the structural properties of the protein. Analysis of specific residues has provided insight into their functional and structural importance and provided insight into the pathogenesis of Gaucher disease and the contribution to PD. Disease-causing mutations are positioned throughout the acid-β-glucosidase structure, with many located far from the active site and thus retaining some enzymatic activity however, thus far no clear relationship between mutation location and disease severity has been established. Here, we review the crystal structure of acid-β-glucosidase, while highlighting important structural aspects of the protein in detail. This review discusses the structural stability of acid-β-glucosidase, which can be altered by pH and glycosylation, and explores the relationship between known Gaucher disease and PD mutations, structural stability and disease severity.

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.

Reduced paucimannosidic N-glycan formation by suppression of a specific β-hexosaminidase from Nicotiana benthamiana

Plants are attractive hosts for the production of recombinant glycoproteins for therapeutic use. Recent advances in glyco-engineering facilitate the elimination of nonmammalian-type glycosylation and introduction of missing pathways for customized N-glycan formation. However, some therapeutically relevant recombinant glycoproteins exhibit unwanted truncated (paucimannosidic) N-glycans that lack GlcNAc residues at the nonreducing terminal end. These paucimannosidic N-glycans increase product heterogeneity and may affect the biological function of the recombinant drugs. Here, we identified two enzymes, β-hexosaminidases (HEXOs) that account for the formation of paucimannosidic N-glycans in Nicotiana benthamiana, a widely used expression host for recombinant proteins. Subcellular localization studies showed that HEXO1 is a vacuolar protein and HEXO3 is mainly located at the plasma membrane in N. benthamiana leaf epidermal cells. Both enzymes are functional and can complement the corresponding HEXO-deficient Arabidopsis thaliana mutants. In planta expression of HEXO3 demonstrated that core α1,3-fucose enhances the trimming of GlcNAc residues from the Fc domain of human IgG. Finally, using RNA interference, we show that suppression of HEXO3 expression can be applied to increase the amounts of complex N-glycans on plant-produced human α1-antitrypsin.