A metabolomic map of Zellweger spectrum disorders reveals novel disease biomarkers

PURPOSE

Peroxisome biogenesis disorders-Zellweger spectrum disorders (PBD-ZSD) are metabolic diseases with multisystem manifestations. Individuals with PBD-ZSD exhibit impaired peroxisomal biochemical functions and have abnormal levels of peroxisomal metabolites, but the broader metabolic impact of peroxisomal dysfunction and the utility of metabolomic methods is unknown.

METHODS

We studied 19 individuals with clinically and molecularly characterized PBD-ZSD. We performed both quantitative peroxisomal biochemical diagnostic studies in parallel with untargeted small molecule metabolomic profiling in plasma samples with detection of >650 named compounds.

RESULTS

The cohort represented intermediate to mild PBD-ZSD subjects with peroxisomal biochemical alterations on targeted analysis. Untargeted metabolomic profiling of these samples revealed elevations in pipecolic acid and long-chain lysophosphatidylcholines, as well as an unanticipated reduction in multiple sphingomyelin species. These sphingomyelin reductions observed were consistent across the PBD-ZSD samples and were rare in a population of >1,000 clinical samples. Interestingly, the pattern or "PBD-ZSD metabolome" was more pronounced in younger subjects suggesting studies earlier in life reveal larger biochemical changes.

CONCLUSION

Untargeted metabolomics is effective in detecting mild to intermediate cases of PBD-ZSD. Surprisingly, dramatic reductions in plasma sphingomyelin are a consistent feature of the PBD-ZSD metabolome. The use of metabolomics in PBD-ZSD can provide insight into novel biomarkers of disease.

Utility of amniotic fluid chitotriosidase in the prenatal diagnosis of lysosomal storage disorders

OBJECTIVE

Plasma chitotriosidase is a documented biomarker for certain lysosomal storage disorders. However, its clinical utility for prenatal samples is not elucidated yet.

METHODS

We have established Reference intervals for amniotic fluid chitotriosidase using control amniotic fluids (n = 47) and compared the activity with amniotic fluids affected by lysosomal storage disorders (n = 25).

RESULTS

The reference interval established was 0-6.76 nmol/h/ml. The amniotic fluids affected with LSDs exhibited elevation of chitotriosidase. The area under the curve (AUC) of receiver operating characteristic curve for affected vs. healthy was 0.987 indicating 98.6% accuracy of chitotriosidase in identifying pregnancies affected with LSDs. Among the different LSDs, Gaucher (202.00 ± 35.27 nmol/h/ml) and Niemann-pick A/B (60.33 ± 21.59 nmol/h/ml) showed very high levels of chitotriosidase.

CONCLUSION

Amniotic fluid chitotriosidase has the potential to serve as a diagnostic marker for lysosomal storage disorders, more specifically for Gaucher and Niemann-Pick A/B.

Detection of mucopolysaccharidosis III-A (Sanfilippo Syndrome-A) in dried blood spots (DBS) by tandem mass spectrometry

BACKGROUND

With ongoing efforts to develop improved treatments for Sanfilippo Syndrome Type A (MPS-IIIA), a disease caused by the inability to degrade heparan sulfate in lysosomes, we sought to develop an enzymatic activity assay for the relevant enzyme, sulfamidase, that uses dried blood spots (DBS).

METHODS

We designed and synthesized a new sulfamidase substrate that can be used to measure sulfamidase activity in DBS using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

RESULTS

Sulfamidase activity was readily detected in DBS using the new substrate and LC-MS/MS. Sulfamidase activity showed acceptable linearity proportional to the amount of enzyme and reaction time. Sulfamidase activity in 238 random newborns was well elevated compared to the range of activities measured in DBS from 8 patients previously confirmed to have MPS-IIIA.

CONCLUSIONS

This is the first report of an assay capable of detecting sulfamidase in DBS. The new assay could be useful in diagnosis and potentially for newborn screening of MPS-IIIA.

Deep characterization of the anti-drug antibodies developed in Fabry disease patients, a prospective analysis from the French multicenter cohort FFABRY

BACKGROUND

Fabry disease (OMIM #301500) is an X-linked disorder caused by alpha-galactosidase A deficiency with two major clinical phenotypes: classic and non-classic of different prognosis. From 2001, enzyme replacement therapies (ERT) have been available. We aimed to determine the epidemiology and the functional characteristics of anti-drug antibodies. Patients from the French multicenter cohort FFABRY (n = 103 patients, 53 males) were prospectively screened for total anti-agalsidase IgG and IgG subclasses with a home-made enzyme-linked immunosorbent assay (ELISA), enzyme-inhibition assessed with neutralization assays and lysoGb3 plasma levels, and compared for clinical outcomes.

RESULTS

Among the patients exposed to agalsidase, 40% of men (n = 18/45) and 8% of women (n = 2/25) had antibodies with a complete cross-reactivity towards both ERTs. Antibodies developed preferentially in men with non-missense GLA mutations (relative risk 2.88, p = 0.006) and classic phenotype (58.6% (17/29) vs 6.7% (1/16), p = 0.0005). Specific anti-agalsidase IgG1 were the most frequently observed (16/18 men), but the highest concentrations were observed for IgG4 (median 1.89 μg/ml, interquartile range (IQR) [0.41-12.24]). In the men exposed to agalsidase, inhibition was correlated with the total IgG titer (r = 0.67, p < 0.0001), especially IgG4 (r = 0.75, p = 0.0005) and IgG2 (r = 0.72, p = 0.001). Inhibition was confirmed intracellularly in Fabry patient leucocytes cultured with IgG-positive versus negative serum (median: 42.0 vs 75.6%, p = 0.04), which was correlated with IgG2 (r = 0.67, p = 0.017, n = 12) and IgG4 levels (r = 0.59, p = 0.041, n = 12). Plasma LysoGb3 levels were correlated with total IgG (r = 0.66, p = 0.001), IgG2 (r = 0.72, p = 0.004), IgG4 (r = 0.58, p = 0.03) and IgG1 (r = 0.55, p = 0.04) titers. Within the classic group, no clinical difference was observed but lysoGb3 levels were higher in antibody-positive patients (median 33.2 ng/ml [IQR 20.6-55.6] vs 12.5 [10.1-24.0], p = 0.005).

CONCLUSION

Anti-agalsidase antibodies preferentially develop in the severe classic Fabry phenotype. They are frequently associated with enzyme inhibition and higher lysoGb3 levels. As such, they could be considered as a hallmark of severity associated with the classic phenotype. The distinction of the clinical phenotypes should now be mandatory in studies dealing with Fabry disease and its current and future therapies.

Clinical characteristics and surgical history of Taiwanese patients with mucopolysaccharidosis type II: data from the hunter outcome survey (HOS)

BACKGROUND

Mucopolysaccharidosis type II (MPS II) is the most frequently occurring MPS in Taiwan, with an incidence of 2.05 per 100,000 live male births, but little is known about clinical characteristics and surgical history in Taiwanese patients.

METHODS

Medical history, demographics, signs and symptoms, and surgical history were analysed in all patients from Taiwanese centres in the Hunter Outcome Survey (HOS; NCT 03292887), a global, multicentre registry that collects real-world data on patients with MPS II.

RESULTS

As of January 2016, 61 male Taiwanese patients were enrolled; 49% (24/49) had received at least one infusion of idursulfase. Median (10th, 90th percentiles) ages at signs and symptom onset and at diagnosis were 2.5 (0.2, 5.5) years (n = 55) and 3.5 (1.2, 11.9) years (n = 56), respectively. Hernia, facial features consistent with MPS II and claw hands were the earliest presenting signs and symptoms (median ages of 3.2 [0.4, 12.0] years, 4.3 [1.1, 12.0] years and 4.7 [2.5, 12.2] years [n = 45, 53 and 50], respectively). More than 75% of patients had undergone a surgical procedure, most commonly hernia repair (57% of patients). Median age at first surgery for hernia repair was 4.2 (0.5, 9.8) years (n = 35). Almost one-third (31.1%) of patients had at least one surgical procedure before diagnosis, and of the 20 procedures before diagnosis, 16 were hernia repair.

CONCLUSIONS

This information from patients in HOS highlights the importance of both medical and surgical history in diagnosing MPS II in Taiwanese patients.

Mitochondrial adventures at the organelle society

Mitochondria are constantly communicating with the rest of the cell. Defects in mitochondria underlie severe pathologies, whose mechanisms remain poorly understood. It is becoming increasingly evident that mitochondrial malfunction resonates in other organelles, perturbing their function and their biogenesis. In this manuscript, we review the current knowledge on the cross-talk between mitochondria and other organelles, particularly lysosomes, peroxisomes and the endoplasmic reticulum. Several organelle interactions are mediated by transcriptional programs, and other signaling mechanisms are likely mediating organelle dysfunction downstream of mitochondrial impairments. Many of these organelle crosstalk pathways are likely to have a role in pathological processes.

Subcellular Nanorheology Reveals Lysosomal Viscosity as a Reporter for Lysosomal Storage Diseases

We describe a new method to measure viscosity within subcellular organelles of a living cell using nanorheology. We demonstrate proof of concept by measuring viscosity in lysosomes in multiple cell types and disease models. The lysosome is an organelle responsible for the breakdown of complex biomolecules. When different lysosomal proteins are defective, they are unable to break down specific biological substrates, which get stored within the lysosome, causing about 70 fatal diseases called lysosomal storage disorders (LSDs). Although the buildup of storage material is critical to the pathology of these diseases, methods to monitor cargo accumulation in the lysosome are lacking for most LSDs. Using passive particle tracking nanorheology and fluorescence recovery after photobleaching, we report that viscosity in the lysosome increases significantly during cargo accumulation in several LSD models. In a mammalian cell culture model of Niemann Pick C, lysosomal viscosity directly correlates with the levels of accumulated cholesterol. We also observed increased viscosity in diverse LSD models in Caenorhabditis elegans, revealing that lysosomal viscosity is a powerful reporter with which to monitor substrate accumulation in LSDs for new diagnostics or to assay therapeutic efficacy.

Functional Analysis of the Ser149/Thr149 Variants of Human Aspartylglucosaminidase and Optimization of the Coding Sequence for Protein Production

Aspartylglucosaminidase (AGA) is a lysosomal hydrolase that participates in the breakdown of glycoproteins. Defects in the AGA gene result in a lysosomal storage disorder, aspartylglucosaminuria (AGU), that manifests mainly as progressive mental retardation. A number of AGU missense mutations have been identified that result in reduced AGA activity. Human variants that contain either Ser or Thr in position 149 have been described, but it is unknown if this affects AGA processing or activity. Here, we have directly compared the Ser149/Thr149 variants of AGA and show that they do not differ in terms of relative specific activity or processing. Therefore, Thr149 AGA, which is the rare variant, can be considered as a neutral or benign variant. Furthermore, we have here produced codon-optimized versions of these two variants and show that they are expressed at significantly higher levels than AGA with the natural codon-usage. Since optimal AGA expression is of vital importance for both gene therapy and enzyme replacement, our data suggest that use of codon-optimized AGA may be beneficial for these therapy options.

Presumptive Spontaneous Lysosomal Storage-Like Disease in a Crl:CD1(ICR) Mouse

A clinically unremarkable 4.5-mo-old female Crl:CD1(ICR) VAF/Elite mouse was euthanized for scheduled sentinel processing. Gross necropsy findings included significant hepatosplenomegaly and visceral lymphadenomegaly, resulting in a preliminary gross diagnosis of lymphoma. Histology revealed florid accumulations of large, 'foamy' macrophages present in the bone marrow, small intestines, and viscera including liver, spleen, lymph nodes, thymus, uterus, and ovaries. The cytoplasm of these cells was abundant, stained pale blue with Wright-Giemsa and was periodic acid-Schiff positive. Given these characteristic gross and histologic findings, a spontaneous lysosomal storage-like disease was diagnosed in this mouse. Cholesterol ester storage disease is likely, because of the visceral involvement with sparing of the CNS, but could not be diagnosed definitively. To our knowledge, this report is the first to describe a case of spontaneous lysosomal storage disease in an outbred mouse of the CD1(ICR) background.

Carbohydrate-Processing Enzymes of the Lysosome: Diseases Caused by Misfolded Mutants and Sugar Mimetics as Correcting Pharmacological Chaperones

Lysosomal storage diseases are hereditary disorders caused by mutations on genes encoding for one of the more than fifty lysosomal enzymes involved in the highly ordered degradation cascades of glycans, glycoconjugates, and other complex biomolecules in the lysosome. Several of these metabolic disorders are associated with the absence or the lack of activity of carbohydrate-processing enzymes in this cell compartment. In a recently introduced therapy concept, for susceptible mutants, small substrate-related molecules (so-called pharmacological chaperones), such as reversible inhibitors of these enzymes, may serve as templates for the correct folding and transport of the respective protein mutant, thus improving its concentration and, consequently, its enzymatic activity in the lysosome. Carbohydrate-processing enzymes in the lysosome, related lysosomal diseases, and the scope and limitations of reported reversible inhibitors as pharmacological chaperones are discussed with a view to possibly extending and improving research efforts in this area of orphan diseases.

Patients' perspectives on newborn screening for later-onset lysosomal storage diseases

Lysosomal storage diseases (LSDs) are an individually rare but collectively common group of hereditary, progressive, multi-systemic disorders. Recent technological advances have brought newborn screening (NBS) for LSDs to attention in the United States. However, many LSD symptoms present in later childhood or adulthood, with a wide spectrum of severity. Because late-onset symptoms stray from the traditional NBS model, healthcare providers have expressed concerns about potential harm to patients and/or their families. In this study, 47 individuals with Fabry disease (FD), 22 with Gaucher disease (GD), and 22 with late-onset Pompe disease (LOPD) were surveyed regarding how their life might have been impacted by NBS. Of the 91 participants, none had symptoms at birth and 42 (46.7%) were symptom-free until adulthood. Over half (52.8%) were diagnosed ≥5years from symptom onset; of these, significantly more had FD (60%) or LOPD (63.6%) than GD (23.8%). However, length of diagnostic odyssey was not significantly correlated with opinion on NBS. Most participants either strongly agreed (45%) or agreed (33.3%) with NBS for their condition, with no significant differences between diseases. Opinions on NBS were correlated with participants' opinions on whether NBS would have resulted in better current health, but uncorrelated with disease severity or current life satisfaction. Significantly more participants with FD (42.6%) and LOPD (63.6%) than GD (13.6%) felt they would have greater life satisfaction had they been diagnosed as a newborn (p=0.007). Almost half (41%) of participants would have made different life decisions, including lifestyle, financial, and reproductive decisions. Regarding potential harm, participants were most concerned about insurability and least concerned about removal of children's autonomy. In conclusion, NBS is highly approved of among individuals with LSDs themselves, as it would significantly eliminate diagnostic odysseys and potentially alter life planning.

Neonatal tolerance induction enables accurate evaluation of gene therapy for MPS I in a canine model

High fidelity animal models of human disease are essential for preclinical evaluation of novel gene and protein therapeutics. However, these studies can be complicated by exaggerated immune responses against the human transgene. Here we demonstrate that dogs with a genetic deficiency of the enzyme α-l-iduronidase (IDUA), a model of the lysosomal storage disease mucopolysaccharidosis type I (MPS I), can be rendered immunologically tolerant to human IDUA through neonatal exposure to the enzyme. Using MPS I dogs tolerized to human IDUA as neonates, we evaluated intrathecal delivery of an adeno-associated virus serotype 9 vector expressing human IDUA as a therapy for the central nervous system manifestations of MPS I. These studies established the efficacy of the human vector in the canine model, and allowed for estimation of the minimum effective dose, providing key information for the design of first-in-human trials. This approach can facilitate evaluation of human therapeutics in relevant animal models, and may also have clinical applications for the prevention of immune responses to gene and protein replacement therapies.

Pilot study of newborn screening for six lysosomal storage diseases using Tandem Mass Spectrometry

BACKGROUND

There is current expansion of newborn screening (NBS) programs to include lysosomal storage disorders because of the availability of treatments that produce an optimal clinical outcome when started early in life.

OBJECTIVE

To evaluate the performance of a multiplex-tandem mass spectrometry (MS/MS) enzymatic activity assay of 6 lysosomal enzymes in a NBS laboratory for the identification of newborns at risk for developing Pompe, Mucopolysaccharidosis-I (MPS-I), Fabry, Gaucher, Niemann Pick-A/B, and Krabbe diseases.

METHODS AND RESULTS

Enzyme activities (acid α-glucosidase (GAA), galactocerebrosidase (GALC), glucocerebrosidase (GBA), α-galactosidase A (GLA), α-iduronidase (IDUA) and sphingomyeline phosphodiesterase-1 (SMPD-1)) were measured on ~43,000 de-identified dried blood spot (DBS) punches, and screen positive samples were submitted for DNA sequencing to obtain genotype confirmation of disease risk. The 6-plex assay was efficiently performed in the Washington state NBS laboratory by a single laboratory technician at the bench using a single MS/MS instrument. The number of screen positive samples per 100,000 newborns were as follows: GAA (4.5), IDUA (13.6), GLA (18.2), SMPD1 (11.4), GBA (6.8), and GALC (25.0).

DISCUSSION

A 6-plex MS/MS assay for 6 lysosomal enzymes can be successfully performed in a NBS laboratory. The analytical ranges (enzyme-dependent assay response for the quality control HIGH sample divided by that for all enzyme-independent processes) for the 6-enzymes with the MS/MS is 5- to 15-fold higher than comparable fluorimetric assays using 4-methylumbelliferyl substrates. The rate of screen positive detection is consistently lower for the MS/MS assay compared to the fluorimetric assay using a digital microfluidics platform.

Less Is More: Substrate Reduction Therapy for Lysosomal Storage Disorders

Lysosomal storage diseases (LSDs) are a group of rare, life-threatening genetic disorders, usually caused by a dysfunction in one of the many enzymes responsible for intralysosomal digestion. Even though no cure is available for any LSD, a few treatment strategies do exist. Traditionally, efforts have been mainly targeting the functional loss of the enzyme, by injection of a recombinant formulation, in a process called enzyme replacement therapy (ERT), with no impact on neuropathology. This ineffectiveness, together with its high cost and lifelong dependence is amongst the main reasons why additional therapeutic approaches are being (and have to be) investigated: chaperone therapy; gene enhancement; gene therapy; and, alternatively, substrate reduction therapy (SRT), whose aim is to prevent storage not by correcting the original enzymatic defect but, instead, by decreasing the levels of biosynthesis of the accumulating substrate(s). Here we review the concept of substrate reduction, highlighting the major breakthroughs in the field and discussing the future of SRT, not only as a monotherapy but also, especially, as complementary approach for LSDs.

Effect of Readthrough Treatment in Fibroblasts of Patients Affected by Lysosomal Diseases Caused by Premature Termination Codons

Aminoglycoside antibiotics, such as gentamicin, may induce premature termination codon (PTC) readthrough and elude the nonsense-mediated mRNA decay mechanism. Because PTCs are frequently involved in lysosomal diseases, readthrough compounds may be useful as potential therapeutic agents. The aim of our study was to identify patients responsive to gentamicin treatment in order to be used as positive controls to further screen for other PTC readthrough compounds. With this aim, fibroblasts from 11 patients affected by 6 different lysosomal diseases carrying PTCs were treated with gentamicin. Treatment response was evaluated by measuring enzymatic activity, abnormal metabolite accumulation, mRNA expression, protein localization, and cell viability. The potential effect of readthrough was also analyzed by in silico predictions. Results showed that fibroblasts from 5/11 patients exhibited an up to 3-fold increase of enzymatic activity after gentamicin treatment. Accordingly, cell lines tested showed enhanced well-localized protein and/or increased mRNA expression levels and/or reduced metabolite accumulation. Interestingly, these cell lines also showed increased enzymatic activity after PTC124 treatment, which is a PTC readthrough-promoting compound. In conclusion, our results provide a proof-of-concept that PTCs can be effectively suppressed by readthrough drugs, with different efficiencies depending on the genetic context. The screening of new compounds with readthrough activity is a strategy that can be used to develop efficient therapies for diseases caused by PTC mutations.

Autophagic vacuolar pathology in desminopathies

Autophagic vacuolar myopathies are an emerging group of muscle diseases with common pathologic features. These include autophagic vacuoles containing both lysosomal and autophagosomal proteins sometimes lined with sarcolemmal proteins such as dystrophin. These features have been most clearly described in patients with Danon's disease due to LAMP2 deficiency and X-linked myopathy with excessive autophagy (XMEA) due to mutations in VMA21. Disruptions of these proteins lead to lysosomal dysfunction and subsequent autophagic vacuolar pathology. We performed whole exome sequencing on two families with autosomal dominantly inherited myopathies with autophagic vacuolar pathology and surprisingly identified a p.R454W tail domain mutation and a novel p.S6W head domain mutation in desmin, DES. In addition, re-evaluation of muscle tissue from another family with a novel p.I402N missense DES mutation also identified autophagic vacuoles. We suggest that autophagic vacuoles may be an underappreciated pathology present in desminopathy patient muscle. Moreover, autophagic vacuolar pathology can be due to genetic etiologies unrelated to primary defects in the lysosomes or autophagic machinery. Specifically, cytoskeletal derangement and the accumulation of aggregated proteins such as desmin may activate the autophagic system leading to the pathologic features of an autophagic vacuolar myopathy.

Genetic convergence of Parkinson's disease and lysosomal storage disorders

Parkinson's disease is a common progressive neurodegenerative disorder characterized by predominant degeneration of the dopaminergic neurons in the substantia nigra pars compacta and the presence of intracellular inclusions enriched in α-synuclein, resulting in a variety motor and nonmotor symptoms. Lysosomal storage disorders are a group of disorders including Gaucher disease, Niemann-Pick disease, and neuronal ceroid lipofuscinoses caused by the defective activity of lysosomal and nonlysosomal proteins. In addition to an overlap in some clinical features between lysosomal storage disorders and Parkinson's disease, the two disorders may be also linked pathogenically. There is growing support for the notion that mutations in genes causing lysosomal storage disorders including the glucocerebrosidase gene, the sphingomyelin phosphodiesterase 1 gene, and the NPC1 gene may increase risk for developing Parkinson's disease. In this review, we discuss the recent advances in the genetic convergence of Parkinson's disease and lysosomal storage disorders, shedding new light on the understanding of shared pathogenic pathways.

[A family with two children diagnosed with aspartylglucosaminuria-case report and literature review]

OBJECTIVE

The authors sought to investigate the clinical features and characteristics of genetic mutation in patients with aspartylglucosaminuria.

METHOD

Clinical data of two pediatric siblings in a family were analyzed retrospectively and relative literature was reviewed in order to study the clinical features, imaging and enzymatic characteristics and genetic mutations.

RESULT

Case 1, the proband, male, he was hospitalized at 20 months of age because of fever and hepatosplenomegaly for nine days. This child was of moderate nutritional status and normal development. Blood tests showed hemoglobin 78.0 g/L, RBC3.18 × 10¹²/L, WBC 4.06 × 10⁹/L, neutrophils 0.236, lymphocytes 0.631, platelets 34 × 10⁹/L, C-reactive protein 17 mg/L. Blood biochemistry showed alanine aminotransferase 67.1 U/L, aspartate aminotransferase 74.1 U/L, serum albumin 32.8 g/L, direct bilirubin 10.5 µmol/L, lactate dehydrogenase 301.7 U/L. Bone marrow cytology showed reactive morphological changes in bone marrow cells. Atypical lymphocytes could be seen in both peripheral blood and bone marrow smears. Cranial MRI showed poor myelination. Aspartylglucosaminidase activity in peripheral leucocytes of the proband 5.7 nmol/(g × min) vs. normal control>26.6 nmol/(g × min). On his AGA gene and that of his parents, a heterozygous mutation site located in exon 3, c.392C>T (p.S131L), was identified as a novel mutation inherited from his father. The mutation from his mother has not been detected. The proband was not responsive to the anti-infectious medication, nutritional intervention and symptomatic treatment.He died one month after diagnosis.His elder brother, Case 2, showed fever, recurrent respiratory tract infection and progressive psychomotor regression with hepatosplenomegaly from the age of four years. Cranial MRI revealed extensive symmetrical leukodystrophy in bilateral cerebra, cerebellum and brainstem.He died at the age of six years.Related literature was summarized, and no Chinese AGU cases had been reported; 221 foreign cases were collected. The clinical and imaging characteristics were summarized. Delay in language development was one of the clinical symptoms that the majority of parents of AGU children first noted.

CONCLUSION

Patients with aspartylglucosaminuria lack of specific symptoms.For children with unexplained delayed speech and progressive mental retardation, the possibility of AGU should be considered, and efforts be made for enzymatic and genetic diagnosis. c.392C> T (p.S131L) was identified as a novel mutation of AGA gene.

Evaluation of butyrate-induced production of a mannose-6-phosphorylated therapeutic enzyme using parallel bioreactors

Bioreactor process changes can have a profound effect on the yield and quality of biotechnology products. Mannose-6-phosphate (M6P) glycan content and the enzymatic catalytic kinetic parameters are critical quality attributes (CQAs) of many therapeutic enzymes used to treat lysosomal storage diseases (LSDs). Here, we have evaluated the effect of adding butyrate to bioreactor production cultures of human recombinant β-glucuronidase produced from CHO-K1 cells, with an emphasis on CQAs. The β-glucuronidase produced in parallel bioreactors was quantified by capillary electrophoresis, the catalytic kinetic parameters were measured using steady-state analysis, and mannose-6-phosphorylation status was assessed using an M6P-specific single-chain antibody fragment. Using this approach, we found that butyrate treatment increased β-glucuronidase production up to approximately threefold without significantly affecting the catalytic properties of the enzyme. However, M6P content in β-glucuronidase was inversely correlated with the increased enzyme production induced by butyrate treatment. This assessment demonstrated that although butyrate dramatically increased β-glucuronidase production in bioreactors, it adversely impacted the mannose-6-phosphorylation of this LSD therapeutic enzyme. This strategy may have utility in evaluating manufacturing process changes to improve therapeutic enzyme yields and CQAs.

A somatic cell defect is associated with the onset of neurological symptoms in a lysosomal storage disease

Mutations in individuals with the lysosomal storage disorder Niemann-Pick disease, type C1 (NPC1) are heterogeneous, not localized to specific protein domains, and not correlated to time of onset or disease severity. We demonstrate direct correlation of the time of neurological symptom onset with the severity of lysosomal defects in NPC1 patient-derived fibroblasts. This is a novel assay for NPC1 individuals that may be predictive of NPC1 disease progression and broadly applicable to other lysosomal disorders.

Glycomics using mass spectrometry

Mass spectrometry plays an increasingly important role in structural glycomics. This review provides an overview on currently used mass spectrometric approaches such as the characterization of glycans, the analysis of glycopeptides obtained by proteolytic cleavage of proteins and the analysis of glycosphingolipids. The given examples are demonstrating the application of mass spectrometry to study glycosylation changes associated with congenital disorders of glycosylation, lysosomal storage diseases, autoimmune diseases and cancer.

A shortcut to the lysosome: the mannose-6-phosphate-independent pathway

Lysosomal hydrolases have long been known to be responsible for the degradation of different substrates in the cell. These acid hydrolases are synthesized in the rough endoplasmic reticulum and transported through the Golgi apparatus to the trans-Golgi network (TGN). From there, they are delivered to endosomal/lysosomal compartments, where they finally become active due to the acidic pH characteristic of the lysosomal compartment. The majority of the enzymes leave the TGN after modification with mannose-6-phosphate (M6P) residues, which are specifically recognized by M6P receptors (MPRs), ensuring their transport to the endosomal/lysosomal system. Although M6P receptors play a major role in the intracellular transport of newly synthesized lysosomal enzymes in mammalian cells, several lines of evidence suggest the existence of alternative processes of lysosomal targeting. Among them, the two that are mediated by the M6P alternative receptors, lysosomal integral membrane protein (LIMP-2) and sortilin, have gained unequivocal support. LIMP-2 was shown to be implicated in the delivery of beta-glucocerebrosidase (GCase) to the lysosomes, whereas sortilin has been suggested to be a multifunctional receptor capable of binding several different ligands, including neurotensin and receptor-associated protein (RAP), and of targeting several proteins to the lysosome, including sphingolipid activator proteins (prosaposin and GM2 activator protein), acid sphingomyelinase and cathepsins D and H. Here, we review the current knowledge on these two proteins: their discovery, study, structural features and cellular function, with special attention to their role as alternative receptors to lysosomal trafficking. Recent studies associating both LIMP2 and sortilin to disease are also extensively reviewed.

Identification of drugs inducing phospholipidosis by novel in vitro data

Drug-induced phospholipidosis (PLD) is a lysosomal storage disorder characterized by the accumulation of phospholipids within the lysosome. This adverse drug effect can occur in various tissues and is suspected to impact cellular viability. Therefore, it is important to test chemical compounds for their potential to induce PLD during the drug design process. PLD has been reported to be a side effect of many commonly used drugs, especially those with cationic amphiphilic properties. To predict drug-induced PLD in silico, we established a high-throughput cell-culture-based method to quantitatively determine the induction of PLD by chemical compounds. Using this assay, we tested 297 drug-like compounds at two different concentrations (2.5 μM and 5.0 μM). We were able to identify 28 previously unknown PLD-inducing agents. Furthermore, our experimental results enabled the development of a binary classification model to predict PLD-inducing agents based on their molecular properties. This random forest prediction system yields a bootstrapped validated accuracy of 86 %. PLD-inducing agents overlap with those that target similar biological processes; a high degree of concordance with PLD-inducing agents was identified for cationic amphiphilic compounds, small molecules that inhibit acid sphingomyelinase, compounds that cross the blood-brain barrier, and compounds that violate Lipinski's rule of five. Furthermore, we were able to show that PLD-inducing compounds applied in combination additively induce PLD.