Corrective effect on Fabry mice of yeast recombinant human α-galactosidase with N-linked sugar chains suitable for lysosomal delivery

Urinary mulberry bodies as a potential biomarker for early diagnosis and efficacy assessment of enzyme replacement therapy in Fabry nephropathy

BACKGROUND

The inability of enzyme replacement therapy (ERT) to prevent progression of Fabry nephropathy (FN) in the presence of >1 g/day proteinuria underscores the necessity of identifying effective biomarkers for early diagnosis of FN preceding proteinuria. Here we attempted to identify biomarkers for early detection of FN.

METHODS

Fifty-one Fabry disease (FD) patients were enrolled. Urinary mulberry bodies (uMBs) were immunostained for globotriaosylceramide (Gb3) and renal cell markers to determine their origin. The association between semiquantitative uMB excretion and the histological severity of podocyte vacuolation was investigated in seven patients using the vacuolated podocyte:glomerular average area ratio. The association between the semiquantitative estimate of uMB excretion and duration of ERT was analyzed. A longitudinal study was conducted to assess the effect of ERT on uMB excretion.

RESULTS

Thirty-two patients (63%) had uMBs, while only 31% showed proteinuria. The uMBs were positive for Gb3, lysosomal-associated membrane protein 1 and podocalyxin, suggesting they were derived from lysosomes with Gb3 accumulation in podocytes. We observed more severe podocyte vacuolation with increased uMB excretion (P = 0.03 for trend); however, the same was not observed with increased proteinuria. The percentage of patients with substantial uMB excretion increased with shorter ERT duration (P = 0.018). Eighteen-month-long ERT reduced uMB excretion (P = 0.03) without affecting proteinuria.

CONCLUSIONS

uMB excretion, implying ongoing podocyte injury, preceded proteinuria in most patients. Semiquantitative uMB estimates can serve as novel biomarkers for early FN diagnosis and for monitoring the efficacy of FD-specific therapies.

Single enzyme nanoparticle, an effective tool for enzyme replacement therapy

The term "single enzyme nanoparticle" (SEN) refers to a chemically or biologically engineered single enzyme molecule. SENs are distinguished from conventional protein nanoparticles in that they can maintain their individual structure and enzymatic activity following modification. Furthermore, SENs exhibit enhanced properties as biopharmaceuticals, such as reduced antigenicity, and increased stability and targetability, which are attributed to the introduction of specific moieties, such as poly(ethylene glycol), carbohydrates, and antibodies. Enzyme replacement therapy (ERT) is a crucial therapeutic option for controlling enzyme-deficiency-related disorders. However, the unfavorable properties of enzymes, including immunogenicity, lack of targetability, and instability, can undermine the clinical significance of ERT. As shown in the cases of Adagen®, Revcovi®, Palynziq®, and Strensiq®, SEN can be an effective technology for overcoming these obstacles. Based on these four licensed products, we expect that additional SENs will be introduced for ERT in the near future. In this article, we review the concepts and features of SENs, as well as their preparation methods. Additionally, we summarize different types of enzyme deficiency disorders and the corresponding therapeutic enzymes. Finally, we focus on the current status of SENs in ERT by reviewing FDA-approved products.

Glucosylceramide synthase inhibition with lucerastat lowers globotriaosylceramide and lysosome staining in cultured fibroblasts from Fabry patients with different mutation types

Fabry disease is an X-linked lysosomal storage disorder caused by mutations in the GLA gene coding for α-galactosidase A (α-GalA). The deleterious mutations lead to accumulation of α-GalA substrates, including globotriaosylceramide (Gb3) and globotriaosylsphingosine. Progressive glycolipid storage results in cellular dysfunction, leading to organ damage and clinical disease, i.e. neuropathic pain, impaired renal function and cardiomyopathy. Many Fabry patients are treated by bi-weekly intravenous infusions of replacement enzyme. While the only available oral therapy is an α-GalA chaperone, which is indicated for a limited number of patients with specific 'amenable' mutations. Lucerastat is an orally bioavailable inhibitor of glucosylceramide synthase (GCS) that is in late stage clinical development for Fabry disease. Here we investigated the ability of lucerastat to lower Gb3, globotriaosylsphingosine and lysosomal staining in cultured fibroblasts from 15 different Fabry patients. Patients' cells included 13 different pathogenic variants, with 13 cell lines harboring GLA mutations associated with the classic disease phenotype. Lucerastat dose dependently reduced Gb3 in all cell lines. For 13 cell lines the Gb3 data could be fit to an IC50 curve, giving a median IC50 [interquartile range (IQR)] = 11 μM (8.2-18); the median percent reduction (IQR) in Gb3 was 77% (70-83). Lucerastat treatment also dose dependently reduced LysoTracker Red staining of acidic compartments. Lucerastat's effects in the cell lines were compared to those with current treatments-agalsidase alfa and migalastat. Consequently, the GCS inhibitor lucerastat provides a viable mechanism to reduce Gb3 accumulation and lysosome volume, suitable for all Fabry patients regardless of genotype.

Valuation of agro-industrial wastes as substrates for heterologous production of α-galactosidase

Background

The recycling of agro-industrial wastes is at present limited by the availability of efficient and low-cost enzyme cocktails. The use of these materials as culture media to produce the enzymes can contribute to the profitability of the recycling process and to the circular economy. The aim of this work is the construction of a recombinant yeast strain efficient to grow in mixed whey (residue of cheese making) and beet molasses (residue of sugar manufacture) as culture medium, and to produce heterologous α-galactosidase, an enzyme with varied industrial applications and wide market.

Results

The gene MEL1, encoding the α-galactosidase of Saccharomyces cerevisiae, was integrated (four copies) in the LAC4 locus of the Kluyveromyces lactis industrial strain GG799. The constructed recombinant strain produces high levels of extracellular α-galactosidase under the control of the LAC4 promoter, inducible by lactose and galactose, and the native MEL1 secretion signal peptide. K. lactis produces natively beta-galactosidase and invertase thus metabolizing the sugars of whey and molasses. A culture medium based on whey and molasses was statistically optimized, and then the cultures scaled-up at laboratory level, thus obtaining 19 U/mL of heterologous α-galactosidase with a productivity of 0.158 U/L h, which is the highest value reported hitherto from a cheap waste-based medium.

Conclusions

A K. lactis recombinant strain was constructed and a sustainable culture medium, based on a mixture of cheese whey and beet molasses, was optimized for high productivity of S. cerevisiae α-galactosidase, thus contributing to the circular economy by producing a heterologous enzyme from two agro-industrial wastes.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0988-6) contains supplementary material, which is available to authorized users.

Lucerastat, an Iminosugar for Substrate Reduction Therapy: Tolerability, Pharmacodynamics, and Pharmacokinetics in Patients With Fabry Disease on Enzyme Replacement

Lucerastat is a glucosylceramide synthase inhibitor aimed at reducing production of glycosphingolipids (GSLs), including those accumulating in Fabry disease. The safety, tolerability, pharmacodynamics, and pharmacokinetics of oral lucerastat were evaluated in an exploratory study in patients with Fabry disease. In this single-center, open-label, randomized study, 10 patients received lucerastat 1,000 mg b.i.d. for 12 weeks in addition to enzyme replacement therapy (ERT; the lucerastat group). Four patients with Fabry disease received ERT only. Eight patients reported 17 adverse events (AEs) in the lucerastat group. No clinically relevant safety abnormalities were observed. The mean (SD) levels of the plasma GSLs, glucosylceramide, lactosylceramide, and globotriaosylceramide, were significantly decreased from baseline in the lucerastat group (-49.0% (16.5%), -32.7% (13.0%), and -55.0% (10.4%), respectively). Lucerastat 1,000 mg b.i.d. was well tolerated in patients with Fabry disease over 12 weeks. A marked decrease in plasma GSLs was observed, suggesting clinical potential for lucerastat in patients with Fabry disease.

Human recombinant lysosomal enzymes produced in microorganisms

Lysosomal storage diseases (LSDs) are caused by accumulation of partially degraded substrates within the lysosome, as a result of a function loss of a lysosomal protein. Recombinant lysosomal proteins are usually produced in mammalian cells, based on their capacity to carry out post-translational modifications similar to those observed in human native proteins. However, during the last years, a growing number of studies have shown the possibility to produce active forms of lysosomal proteins in other expression systems, such as plants and microorganisms. In this paper, we review the production and characterization of human lysosomal proteins, deficient in several LSDs, which have been produced in microorganisms. For this purpose, Escherichia coli, Saccharomyces cerevisiae, Pichia pastoris, Yarrowia lipolytica, and Ogataea minuta have been used as expression systems. The recombinant lysosomal proteins expressed in these hosts have shown similar substrate specificities, and temperature and pH stability profiles to those produced in mammalian cells. In addition, pre-clinical results have shown that recombinant lysosomal enzymes produced in microorganisms can be taken-up by cells and reduce the substrate accumulated within the lysosome. Recently, metabolic engineering in yeasts has allowed the production of lysosomal enzymes with tailored N-glycosylations, while progresses in E. coli N-glycosylations offer a potential platform to improve the production of these recombinant lysosomal enzymes. In summary, microorganisms represent convenient platform for the production of recombinant lysosomal proteins for biochemical and physicochemical characterization, as well as for the development of ERT for LSD.

Carboxyl-terminal truncations alter the activity of the human α-galactosidase A

Fabry disease is an X-linked inborn error of glycolipid metabolism caused by deficiency of the human lysosomal enzyme, α-galactosidase A (αGal), leading to strokes, myocardial infarctions, and terminal renal failure, often leading to death in the fourth or fifth decade of life. The enzyme is responsible for the hydrolysis of terminal α-galactoside linkages in various glycolipids. Enzyme replacement therapy (ERT) has been approved for the treatment of Fabry disease, but adverse reactions, including immune reactions, make it desirable to generate improved methods for ERT. One approach to circumvent these adverse reactions is the development of derivatives of the enzyme with more activity per mg. It was previously reported that carboxyl-terminal deletions of 2 to 10 amino acids led to increased activity of about 2 to 6-fold. However, this data was qualitative or semi-quantitative and relied on comparison of the amounts of mRNA present in Northern blots with αGal enzyme activity using a transient expression system in COS-1 cells. Here we follow up on this report by constructing and purifying mutant enzymes with deletions of 2, 4, 6, 8, and 10 C-terminal amino acids (Δ2, Δ4, Δ6, Δ8, Δ10) for unambiguous quantitative enzyme assays. The results reported here show that the k_cat/K_m approximately doubles with deletions of 2, 4, 6 and 10 amino acids (0.8 to 1.7-fold effect) while a deletion of 8 amino acids decreases the k_cat/K_m (7.2-fold effect). These results indicate that the mutated enzymes with increased activity constructed here would be expected to have a greater therapeutic effect on a per mg basis, and could therefore reduce the likelihood of adverse infusion related reactions in Fabry patients receiving ERT treatment. These results also illustrate the principle that in vitro mutagenesis can be used to generate αGal derivatives with improved enzyme activity.

Enzyme replacement therapy partially prevents invariant Natural Killer T cell deficiency in the Fabry disease mouse model

Fabry disease is a lysosomal storage disease caused by deficient activity of the α-Galactosidase A (α-Gal A) enzyme, which leads to abnormal accumulation of glycosphingolipids, mainly globotriaosylceramide (Gb3), in the lysosome. Glycosphingolipids are known to be invariant Natural Killer T (iNKT) cell antigens. Several animal models of lysosomal storage diseases, including Fabry disease, present a defect in iNKT cell selection by the thymus. We have studied the effect of age and the impact of enzyme replacement therapy on Gb3 accumulation and iNKT cells of Fabry knockout mice. At 4 weeks of age, Fabry knockout mice already showed Gb3 accumulation and a reduction in the percentage of iNKT cells. In older mice (12-week old), we observed an accentuated peripheral iNKT deficiency. 12-week old animals also showed a reduced splenic CD4+/CD4- iNKT cell ratio due to greater loss in the iNKT CD4+ subset. Treatment of Fabry knockout mice with α-Gal A replacement therapy efficiently reduced Gb3 deposition in the liver and spleen. Moreover, enzyme replacement therapy had a positive effect on the number of iNKT cells in an organ-dependent fashion. Indeed, treatment of Fabry knockout mice with α-Gal A did not alter iNKT cell percentage in the thymus and liver but increased splenic iNKT cell percentage when compared to untreated mice. Study of animals prior to treatment indicates that enzyme replacement therapy stabilized iNKT cell percentage in the spleen. This stabilization is due to a specific effect on the iNKT CD4+ subset, preventing the decrease on the number of these cells that occurs with age in Fabry knockout mice. This study reveals that enzyme replacement therapy has a positive organ and subset-dependent effect in iNKT cells of Fabry knockout mice.

Efficient uptake of recombinant α-galactosidase A produced with a gene-manipulated yeast by Fabry mice kidneys

To economically produce recombinant human α-galactosidase A (GLA) with a cell culture system that does not require bovine serum, we chose methylotrophic yeast cells with the OCH1 gene, which encodes α-1,6-mannosyltransferase, deleted and over-expressing the Mnn4p (MNN4) gene, which encodes a positive regulator of mannosylphosphate transferase, as a host cell line. The enzyme (yr-hGLA) produced with the gene-manipulated yeast cells has almost the same enzymological parameters as those of the recombinant human GLA produced with cultured human fibroblasts (agalsidase alfa), which is currently used for enzyme replacement therapy for Fabry disease. However, the basic structures of their sugar chains are quite different. yr-hGLA has a high content of phosphorylated N-glycans and is well incorporated into the kidneys, the main target organ in Fabry disease, where it cleaves the accumulated glycosphingolipids. A glycoprotein production system involving this gene-manipulated yeast cell line will be useful for the development of a new enzyme replacement therapy for Fabry disease.

Molecular mechanism for stabilization of a mutant α-galactosidase A involving M51I amino acid substitution by imino sugars

Small molecules including imino sugars are expected to act as chaperones for a mutant α-galactosidase A (GLA), which will be useful for pharmacological chaperone therapy for Fabry disease. However, there is little detailed information about the molecular mechanism. We paid attention to an M51I mutant GLA which had been reported to strongly react to an imino sugar. The predicted structural change caused by this amino acid substitution is very small and located on the surface of the molecule. We produced the mutant enzyme in yeast, and determined its enzymological characteristics. The enzymological parameter values are almost the same as those of the wild-type GLA, although the mutant enzyme is unstable not only under neutral pH conditions but also under acidic ones. Then, we directly examined the effect of imino sugars including 1-deoxygalactonojirimycin and galactostatin bisulfite on the purified mutant enzyme. The imino sugars apparently improved the stability of the mutant enzyme under both neutral and acidic pH conditions. The results of surface plasmon resonance biosensor assaying suggested that the imino sugars retained their binding activity as to the mutant enzyme under both neutral and acidic pH conditions. This information will facilitate improvement of pharmacological chaperone therapy for Fabry disease.

Contributions of Saccharomyces cerevisiae to understanding mammalian gene function and therapy

Due to its genetic tractability and ease of manipulation, the yeast Saccharomyces cerevisiae has been extensively used as a model organism to understand how eukaryotic cells grow, divide, and respond to environmental changes. In this chapter, we reasoned that functional annotation of novel genes revealed by sequencing should adopt an integrative approach including both bioinformatics and experimental analysis to reveal functional conservation and divergence of complexes and pathways. The techniques and resources generated for systems biology studies in yeast have found a wide range of applications. Here we focused on using these technologies in revealing functions of genes from mammals, in identifying targets of novel and known drugs and in screening drugs targeting specific proteins and/or protein-protein interactions.

Structural analysis of Saccharomyces cerevisiae alpha-galactosidase and its complexes with natural substrates reveals new insights into substrate specificity of GH27 glycosidases

Alpha-galactosidases catalyze the hydrolysis of terminal alpha-1,6-galactosyl units from galacto-oligosaccharides and polymeric galactomannans. The crystal structures of tetrameric Saccharomyces cerevisiae alpha-galactosidase and its complexes with the substrates melibiose and raffinose have been determined to 1.95, 2.40, and 2.70 A resolution. The monomer folds into a catalytic (alpha/beta)(8) barrel and a C-terminal beta-sandwich domain with unassigned function. This pattern is conserved with other family 27 glycosidases, but this enzyme presents a unique 45-residue insertion in the beta-sandwich domain that folds over the barrel protecting it from the solvent and likely explaining its high stability. The structure of the complexes and the mutational analysis show that oligomerization is a key factor in substrate binding, as the substrates are located in a deep cavity making direct interactions with the adjacent subunit. Furthermore, docking analysis suggests that the supplementary domain could be involved in binding sugar units distal from the scissile bond, therefore ascribing a role in fine-tuning substrate specificity to this domain. It may also have a role in promoting association with the polymeric substrate because of the ordered arrangement that the four domains present in one face of the tetramer. Our analysis extends to other family 27 glycosidases, where some traits regarding specificity and oligomerization can be formulated on the basis of their sequence and the structures available. These results improve our knowledge on the activity of this important family of enzymes and give a deeper insight into the structural features that rule modularity and protein-carbohydrate interactions.

Crystallization and preliminary X-ray diffraction data of alpha-galactosidase from Saccharomyces cerevisiae

Saccharomyces cerevisiae alpha-galactosidase is a highly glycosylated extracellular protein that catalyzes the hydrolysis of alpha-galactosidic linkages in various glucids. Its enzymatic activity is of interest in many food-related industries and has biotechnological applications. Glycosylated and in vitro deglycosylated protein samples were both assayed for crystallization, but only the latter gave good-quality crystals that were suitable for X-ray crystallography. The crystals belonged to space group P42(1)2, with unit-cell parameters a = b = 101.24, c = 111.52 A. A complete diffraction data set was collected to 1.95 A resolution using a synchrotron source.

Use of a modified alpha-N-acetylgalactosaminidase in the development of enzyme replacement therapy for Fabry disease

A modified alpha-N-acetylgalactosaminidase (NAGA) with alpha-galactosidase A (GLA)-like substrate specificity was designed on the basis of structural studies and was produced in Chinese hamster ovary cells. The enzyme acquired the ability to catalyze the degradation of 4-methylumbelliferyl-alpha-D-galactopyranoside. It retained the original NAGA's stability in plasma and N-glycans containing many mannose 6-phosphate (M6P) residues, which are advantageous for uptake by cells via M6P receptors. There was no immunological cross-reactivity between the modified NAGA and GLA, and the modified NAGA did not react to serum from a patient with Fabry disease recurrently treated with a recombinant GLA. The enzyme cleaved globotriaosylceramide (Gb3) accumulated in cultured fibroblasts from a patient with Fabry disease. Furthermore, like recombinant GLA proteins presently used for enzyme replacement therapy (ERT) for Fabry disease, the enzyme intravenously injected into Fabry model mice prevented Gb3 storage in the liver, kidneys, and heart and improved the pathological changes in these organs. Because this modified NAGA is hardly expected to cause an allergic reaction in Fabry disease patients, it is highly promising as a new and safe enzyme for ERT for Fabry disease.

Establishment of immortalized Schwann cells from Fabry mice and their low uptake of recombinant alpha-galactosidase

Peripheral neuropathy is one of the important manifestations of Fabry disease. Enzyme replacement therapy with presently available recombinant alpha-galactosidases does not always improve the Fabry neuropathy. But the reason has not been determined yet. We established a Schwann cell line from Fabry mice, characterized it, and then examined the uptake of alpha-galactosidase by cells and its effect on the degradation of accumulated substrate. The cells exhibited a distinct Schwann cell morphology and biochemical phenotype (alpha-Galactosidase activity was deficient, and numerous cytoplasmic inclusion bodies were present in the cells). A recombinant alpha-galactosidase added to the culture medium was incorporated into the cultured Fabry Schwann cells dose dependently. But the increase in cell-associated enzyme activity was less than that in the cases of human and mouse Fabry fibroblasts. The administration of a high dose of the enzyme improved the pathological changes in cells, although a low dose of it did not. Cellular uptake of the enzyme was strongly inhibited in the presence of mannose 6-phosphate. This suggests that the enzyme is incorporated via cation-independent mannose 6-phosphate receptors in Schwann cells. The low expression of cation-independent mannose 6-phosphate receptors in Schwann cells must be one of the reasons their uptake of the present enzymes was low. The administration of a high dose of the enzyme or the development of an enzyme containing many mannose 6-phosphate residues is required to improve Fabry neuropathy.

Production of recombinant beta-hexosaminidase A, a potential enzyme for replacement therapy for Tay-Sachs and Sandhoff diseases, in the methylotrophic yeast Ogataea minuta

Human beta-hexosaminidase A (HexA) is a heterodimeric glycoprotein composed of alpha- and beta-subunits that degrades GM2 gangliosides in lysosomes. GM2 gangliosidosis is a lysosomal storage disease in which an inherited deficiency of HexA causes the accumulation of GM2 gangliosides. In order to prepare a large amount of HexA for a treatment based on enzyme replacement therapy (ERT), recombinant HexA was produced in the methylotrophic yeast Ogataea minuta instead of in mammalian cells, which are commonly used to produce recombinant enzymes for ERT. The problem of antigenicity due to differences in N-glycan structures between mammalian and yeast glycoproteins was potentially resolved by using alpha-1,6-mannosyltransferase-deficient (och1Delta) yeast as the host. Genes encoding the alpha- and beta-subunits of HexA were integrated into the yeast cell, and the heterodimer was expressed together with its isozymes HexS (alphaalpha) and HexB (betabeta). A total of 57 mg of beta-hexosaminidase isozymes, of which 13 mg was HexA (alphabeta), was produced per liter of medium. HexA was purified with immobilized metal affinity column for the His tag attached to the beta-subunit. The purified HexA was treated with alpha-mannosidase to expose mannose-6-phosphate (M6P) residues on the N-glycans. The specific activities of HexA and M6P-exposed HexA (M6PHexA) for the artificial substrate 4MU-GlcNAc were 1.2 +/- 0.1 and 1.7 +/- 0.3 mmol/h/mg, respectively. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis pattern suggested a C-terminal truncation in the beta-subunit of the recombinant protein. M6PHexA was incorporated dose dependently into GM2 gangliosidosis patient-derived fibroblasts via M6P receptors on the cell surface, and degradation of accumulated GM2 ganglioside was observed.