Hemoglobin precipitation greatly improves 4-methylumbelliferone-based diagnostic assays for lysosomal storage diseases in dried blood spots

Enzymatic diagnosis of Pompe disease: lessons from 28 years of experience

Pompe disease is a lysosomal and neuromuscular disorder caused by deficiency of acid alpha-glucosidase (GAA), and causes classic infantile, childhood onset, or adulthood onset phenotypes. The biochemical diagnosis is based on GAA activity assays in dried blood spots, leukocytes, or fibroblasts. Diagnosis can be complicated by the existence of pseudodeficiencies, i.e., GAA variants that lower GAA activity but do not cause Pompe disease. A large-scale comparison between these assays for patient samples, including exceptions and borderline cases, along with clinical diagnoses has not been reported so far. Here we analyzed GAA activity in a total of 1709 diagnostic cases over the past 28 years using a total of 2591 analyses and we confirmed the clinical diagnosis in 174 patients. We compared the following assays: leukocytes using glycogen or 4MUG as substrate, fibroblasts using 4MUG as substrate, and dried blood spots using 4MUG as substrate. In 794 individuals, two or more assays were performed. We found that phenotypes could only be distinguished using fibroblasts with 4MUG as substrate. Pseudodeficiencies caused by the GAA2 allele could be ruled out using 4MUG rather than glycogen as substrate in leukocytes or fibroblasts. The Asian pseudodeficiency could only be ruled out in fibroblasts using 4MUG as substrate. We conclude that fibroblasts using 4MUG as substrate provides the most reliable assay for biochemical diagnosis and can serve to validate results from leukocytes or dried blood spots.

Emerging Approaches for Fluorescence-Based Newborn Screening of Mucopolysaccharidoses

Interest in newborn screening for mucopolysaccharidoses (MPS) is growing, due in part to ongoing efforts to develop new therapies for these disorders and new screening assays to identify increased risk for the individual MPSs on the basis of deficiency in the cognate enzyme. Existing tests for MPSs utilize either fluorescence or mass spectrometry detection methods to measure biomarkers of disease (e.g., enzyme function or glycosaminoglycans) using either urine or dried blood spot (DBS) samples. There are currently two approaches to fluorescence-based enzyme function assays from DBS: (1) manual reaction mixing, incubation, and termination followed by detection on a microtiter plate reader; and (2) miniaturized automation of these same assay steps using digital microfluidics technology. This article describes the origins of laboratory assays for enzyme activity measurement, the maturation and clinical application of fluorescent enzyme assays for MPS newborn screening, and considerations for future expansion of the technology.

Digital microfluidics comes of age: high-throughput screening to bedside diagnostic testing for genetic disorders in newborns

INTRODUCTION

Digital microfluidics (DMF) is an emerging technology with the appropriate metrics for application to newborn and high-risk screening for inherited metabolic disease and other conditions that benefit from early treatment. Areas covered: This review traces the development of electrowetting-based DMF technology toward the fulfillment of its promise to provide an inexpensive platform to conduct enzymatic assays and targeted biomarker assays at the bedside. The high-throughput DMF platform, referred to as SEEKER®, was recently authorized by the United States Food and Drug Administration to screen newborns for four lysosomal storage disorders (LSDs) and is deployed in newborn screening programs in the United States. The development of reagents and methods for LSD screening and results from screening centers are reviewed. Preliminary results from a more compact DMF device, to perform disease-specific test panels from small volumes of blood, are also reviewed. Literature for this review was sourced using principal author and subject searches in PubMed. Expert commentary: Newborn screening is a vital and highly successful public health program. DMF technology adds value to the current testing platforms that will benefit apparently healthy newborns with underlying genetic disorders and infants at-risk for conditions that present with symptoms in the newborn period.

Methods for Determination of α-Glycosidase, β-Glycosidase, and α-Galactosidase Activities in Dried Blood Spot Samples

The lysosomal storage diseases (LDSs) are a heterogeneous group of inherited genetic disorders caused by defects of lysosomal proteins. The accumulation of undigested substrates from different catabolic pathways leads to cellular dysfunction. LSDs generally presents during early childhood and have a devastating impact on the families and on public health. Over the years, approaches for treatment of some LSDs have been developed with different strategies. Increasing availability of treatments of these diseases has accelerated the development of new methods and techniques for rapid diagnosis in patients with clinical indication.The use of dried blood spot (DBS) test has been proposed as a first tier test to identify patients with Gaucher, Pompe, and Fabry diseases. DBS usage is advantageous for the purpose of screening as it is non-invasive, sensitive, has low-cost and fast turnaround time compared to measurements in leucocyte and/or fibroblast culture. This chapter focuses on the activity measurement of three lysosomal enzymes (α-glucosidase, β-glucosidase, and α galactosidase) in DBS samples by using fluorescent substrates and by the LC-MS/MS (liquid chromatography-mass spectrometry) method. All steps of the methods, from preparation of the solutions to calculation of the enzyme activity, will be explained in detail.

An Improved Helferich Method for the α/β-Stereoselective Synthesis of 4-Methylumbelliferyl Glycosides for the Detection of Microorganisms

An improved Helferich method is presented. It involves the glycosylation of 4-methyl-umbelliferone with glycosyl acetates in the presence of boron trifluoride etherate combined with triethylamine, pyridine, or 4-dimethylaminopyridine under mild conditions, followed by deprotection to give fluorogenic 4-methylumbelliferyl glycoside substrates. Due to the use of base, the glycosylation reaction proceeds more easily, is uncommonly α- or β-stereoselective, and affords the corresponding products in moderate to excellent yields (51%-94%) under appropriate conditions.

Enzymatic diagnosis of Fabry disease using a fluorometric assay on dried blood spots: An alternative methodology

Fabry disease (FD, OMIM#301500) is an X-linked lysosomal storage disorder caused by the functional deficiency of α-galactosidase A, a lysosomal enzyme. A method to screen for FD in large populations has been developed using a fluorometric assay of α-galactosidase A activity in dried blood spots (DBS) on filter paper. However, results can be influenced by quenching of fluorescence by haemoglobin which, together with small sample size, may result in a low light emission signal. An alternative, simple and sensitive fluorometric assay was developed for the determination of α-galactosidase A activity in DBS. The assay uses 4-methylumbelliferyl-α-d-galactose as an artificial substrate. To minimize the risk of false-positives, zinc sulfate was used for protein precipitation to stop the enzymatic reaction and eliminate interfering species (hemoglobin). Samples from 209 individuals (60 hemizygotes, 68 heterozygotes, and 81 controls) were tested to establish reference values for the assay. The mean α-galactosidase A activity of the 81 controls was 9.1 ± 3.3 μmol h(-1) L(-1) (mean ± SD). All 60 hemizygotes affected with FD had AGAL activities below 1.7 μmol h(-1) L(-1) (0.2 ± 0.3 μmol h(-1) L(-1)). For the 68 heterozygous females, AGAL activity ranged from 0 to 12.6 μmol h(-1) L(-1) (3.5 ± 2.7 μmol h(-1) L(-1)). Two-thirds of the female patients could be identified using the enzymatic assay and a cut-off level of 40% of the median control value (<3.4 μmol h(-1) L(-1)). Our fluorometric assay using zinc sulfate protein precipitation was shown to have similar sensitivity and robustness while reducing the risk of false positive results due to quenching of 4-MU fluorescence by haemoglobin.

Hematopoiesis toxicity induced by 4-methylumbelliferon determined in an invertebrate model organism

Umbelliferone has potential value as it has an inhibitory effect on tumor cells; however, its impact on an animal's circulatory system and hematopoietic function has not been reported. In this study, 4-methylumbelliferon (4-MU), an umbelliferone derivative, was used as a model drug, and its potential toxicity on hemocytes and hematopoietic organs (HOs) was investigated using an invertebrate animal model, the silkworm, Bombyx mori. The results showed that the level of reactive oxygen species in HOs increased when larvae (third day of the fifth instar) were orally exposed to 4 mM 4-MU for 8 min, followed by the induction of improved antioxidative metabolism of coenzymes in hemolymph. Exposure to 4-MU also significantly upregulated the expression levels of several genes in the hemolymph and fat body (a detoxification tissue similar to the liver in mammals) including antimicrobial peptide gene cecropinA and moricin, and a phagocytosis-related gene, tetraspanin E, suggesting an increased antioxidant level and antimicrobial ability of the circulatory system. However, the percentage of dead hemocytes increased and hematopoiesis significantly decreased in HOs, indicating the toxic effect of 4-MU on hemocytes and hematopoiesis, despite it inducing enhanced antioxidant and antimicrobial activity in the circulatory system.

Improving arylsulfatase activity determination in dried blood spots: Screening and diagnostic approaches for Maroteaux-Lamy syndrome (MPS VI)

BACKGROUND

Mucopolysaccharidosis type VI can be screened by measuring the lysosomal arylsulfatase B (ARSB) residual enzyme activity in dried blood spots (DBS) using synthetic substrates. However, we have found experimental obstacles when determining ARSB activity with the fluorescent method due to the significant quenching effect rendered by DBS components.

METHODS

We adapted the methods originally described by Chamoles et al. [1] and Civallero et al. [2] and put forward 2 distinct approaches for ARSB activity quantification from DBS samples by measuring the 4-methylumbelliferone (β-MU) fluorescence generated from the ARSB 4-methylumbelliferone sulfate (β-MUS) substrate.

RESULTS

We demonstrate the high throughput feasibility of a novel approach for measuring ARSB activities by incorporating tailor-made calibration curves according to each patient's DBS sample quenching properties. The second method is used to calculate ARSB activities by measuring the fluorescence and absorbance parameters in each reaction sample with a single DBS-free calibration curve.

CONCLUSIONS

The quantitative correlation between the DBS sample absorbance and its quenching effect can be used to calculate predictive ARSB activities and would serve as an affordable first tier screening test. The method described herein demonstrates the critical importance of adapting the β-MU calibration curves to each patient's unique DBS sample matrix and its positive impact on the accuracy and reliability of ARSB activity measurements.

Extended use of dried-leukocytes impregnated in filter paper samples for detection of Pompe, Gaucher, and Morquio A diseases

BACKGROUND

Lysosomal storage diseases (LSD) are a group of genetic conditions which could present a vast spectrum of abnormalities that may include skeletal abnormalities, organ dysfunction, neuronal involvement, and tissue accumulation of complex molecules, among other manifestations. Definitive diagnosis of LSD is generally obtained by specific enzyme assays performed in leukocytes, fibroblasts, or more recently, dried-blood filter paper (DBFP) samples.

METHODS

We recently introduced dried-leukocytes filter paper (DLFP) as an alternative source of enzyme to assay heparan sulfamidase and galactocerebrosidase activities, which could not be measured in DBFP samples using fluorometric methods. We present a new fluorometric methods on DLFP samples, for evaluation of α-glucosidase (GAA), β-glucosidase (GBA), and N-acetylgalactosamine-6-sulfatase (GALNS) activities, key enzyme assays for the identification of patients with Pompe disease (PD), Gaucher disease (GD), and Morquio A disease (MD), respectively.

RESULTS

We show a clear discrimination between confirmed PD, GD, and MD patients and healthy controls.

CONCLUSIONS

We conclude that the assays of GAA, GBA, and GALNS on DLFP are reliable and useful methods for the identification of PD, GD, and MD diseases, respectively. As sample preparation is feasible in standard biochemical laboratories and transportation is very simple, it could enable patients living in remote areas to be investigated, diagnosed and eventually treated with the specific therapies available for these diseases.

Antioxidative properties of 4-methylumbelliferone are related to antibacterial activity in the silkworm (Bombyx mori) digestive tract

Umbelliferones have gained significant attention due to their tumor-inhibitory effects in vitro. This study was undertaken to examine the impact of umbelliferones in an invertebrate model organism, Bombyx mori, to assess the underlying antimicrobial activities via antioxidation in vivo. Oral administration of 4 mM 4-methylumbelliferone (4-MU), a model umbelliferone drug, in B. Mori larvae caused a rapid increase in reactive oxygen species, such as hydrogen peroxide (H2O2) and antimicrobial activity in the digestive tract. In addition, a significant increase in total antioxidant capacity as well as superoxide anion radical-inhibiting activity and reduced glutathione were detected. The antioxidant defense system was activated following induction of H2O2, resulting in a significant rise in catalase (50-66 %) and glutathione peroxidase (175 %) activities, which were helpful in defending digestive tract cells against oxidative injury. These results help in understanding the anticancer mechanism of 4-MU based on its antioxidation in organisms.

Antioxidative capacity in the fat body of Bombyx mori is increased following oral administration of 4-methylumbelliferone

Plant sources of umbelliferones have tumor-inhibitory effects at the cellular level. However, their physiological functions in animals are largely unresolved. In this study, we provide evidence to show that 4-methylumbelliferone (4-MU) participates in the regulation of antioxidative capacity in the fat body of Bombyx mori, a tissue similar to mammalian liver in this model invertebrate. Larvae (3rd day of the 5th instar) were orally exposed to 4 mM 4-MU, an umbelliferone, which swiftly induced the generation of a large number of ROS (e.g. H2O2 increased 6 to 8-fold), and 4-MU was detected in the fat body 8 min after administration. In addition, the activities of CAT and GPx were up-regulated 4 to 11-fold and 2 to 16-fold, respectively, and were helpful in defending fat body cells against oxidative injury in combination with NADPH. Furthermore, significant increases in the contents of T-AOC (up to approx. 2-fold), antioxidants of ASAFR (by 2 to 4-fold) and GSH were detected.

Newborn screening for hunter disease: a small-scale feasibility study

Hunter disease (Mucopolysaccharidosis type II, MPS II) is an X-linked lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase (IDS). Two main therapies have been reported for MPS II patients: enzyme-replacement therapy (ERT) and hematopoietic stem-cell transplantation (HSCT). Both treatment modalities have been shown to improve some symptoms, but the results with regard to cognitive functioning have been poor. Early initiation of therapy, i.e., before neurological symptoms have manifested, may alter cognitive outcome. The need for early identification makes Hunter disease a candidate for newborn screening (NBS). Our objective was to explore the use of a fluorometric assay that could be applicable for high-throughput analysis of IDS activity in dried blood spots (DBS). The median IDS activity in DBS samples from 1,426 newborns was 377 pmol/punch/17 h (range 78-1111). The IDS activity in one sample was repeatedly under the cutoff value (set at 20% of the median value), which would imply a recall rate of 0.07%. A sample from a clinically diagnosed MPS II individual, included in each 96-well test plate, had IDS activities well below the 20% cutoff value. Coefficients of variation in quality control samples with low, medium, and high IDS activities (190, 304, and 430 pmol/punch/17 h, respectively) were 12% to 16%. This small-scale pilot study shows that newborn screening for Hunter disease using a fluorometric assay in DBS is technically feasible with a fairly low recall rate. NBS may allow for identification of infants with Hunter disease before clinical symptoms become evident enabling early intervention.

Selective screening for lysosomal storage diseases with dried blood spots collected on filter paper in 4,700 high-risk colombian subjects

Lysosomal storage disorders (LSDs) are a very heterogeneous group of hereditary disorders. The diagnostic process usually involves complex sampling, processing, testing, and validation procedures, performed by specialized laboratories only, which causes great limitations in reaching a diagnosis for patients affected by these diseases.There are few studies about LSDs in Colombia. The diagnostic limitations often make medical practitioners disregard the possibility of these disorders while diagnosing their patients. The current study documents the results of a 7-year screening in high-risk patients, aimed to detect LSDs using dried blood spots (DBS) collected on filter paper, with a micromethodology that facilitates diagnosis even with a large number of samples.The activities of α-galactosidase A, α glucosidase, α-L-iduronidase, arylsulfatase B, β-galactosidase, β-glucosidase, total hexosaminidase, iduronate sulfatase, and chitotriosidase were analyzed in high-risk patients for lysosomal disease. The catalytic activity was evaluated with fluorometric micromethods using artificial substrates marked with 4-methylumbelliferone.The reference values for a control population were established for the enzymes listed above, and 242 patients were found to have an enzyme deficiency, guiding to the following diagnoses: Fabry disease (n = 31), Pompe disease (n = 16), Hurler Syndrome (n = 15), Maroteaux-Lamy Syndrome (n = 34), GM1 Gangliosidosis (n = 10), Morquio B (n = 1), Gaucher disease (n = 101), Sandhoff disease (n = 1), Mucolipidosis (n = 2), and Hunter Syndrome (n = 31). In conclusion, this protocol provides a comprehensive diagnostic approach which could be carried out in Colombia and made it available to medical services spread around the country, enabling the identification of a large number of patients affected by LSDs, which could potentially benefit from the therapeutic tools already available for many of these diseases.

Determination of Acid β-Galactosidase Activity: Methodology and Perspectives

Early, accurate diagnosis of lysosomal storage disorders is a major challenge, even for trained specialists. Finding innovative, accurate diagnostic methods, and high throughput, cost-effective tools are crucial to medical progress and will contribute to improved quality of life. The goal of this work was to improve currently used protocols to determine activity of acid β-galactosidase, and discuss the possibility analysing lysosomal enzymes with microfluidic systems. A principle of the determination of β-galactosidase activity was fluorometric measurement of a deprotonated form of 4-methylumbelliferone released in the enzymatic reaction. Measurements were performed using Jurkat T cells as a source of the enzyme. We observed the temperature-dependent substrate inhibition effect and determined the substrate (4-MU-β-d-galactopyranoside) concentration which should be used to determine acid β-galactosidase activity at 37 °C (0.8 mM) and at room temperature (0.6 mM). We proved that the sample incubation time may be significantly reduced to only a few minutes. We also showed that the amount of alkaline buffer used to stop the enzymatic reaction may be minimized and even, in some cases, eliminated. The presented results show how the sensitivity of the available methods to diagnose patients suffer from gangliosidosis GM1 or Morquio B disease can be improved. The proposed method may be easily implemented with microfluidic systems, which currently are promising tools for point-of-care applications.

Dried blood spots for the enzymatic diagnosis of lysosomal storage diseases in dogs and cats

BACKGROUND

In people, lysosomal storage diseases (LSD) can be diagnosed by assaying enzyme activities in dried blood spots (DBS).

OBJECTIVE

The aim of this study was to evaluate the feasibility of using DBS samples from dogs and cats to measure lysosomal enzymatic activities and diagnose LSD.

METHODS

Drops of fresh whole blood collected in EDTA from dogs and cats with known or suspected LSD and from clinically healthy dogs and cats were placed on neonatal screening cards, dried, and mailed to the Metabolic Laboratory, University Children's Hospital, Frankfurt, Germany. Activities of selected lysosomal enzymes were measured using fluorescent substrates in a 2-mm diameter disk (~2.6 μL blood) punched from the DBS. Results were expressed as nmol substrate hydrolyzed per mL of blood per minute or hour.

RESULTS

Reference values were established for several lysosomal enzyme activities in DBS from dogs and cats; for most enzymes, activities were higher than those published for human samples. Activities of β-glucuronidase, N-acetylglucosamine-4-sulfatase (arylsulfatase B), α-mannosidase, α-galactosidase, α-fucosidase, and hexosaminidase A were measureable in DBS from healthy cats and dogs; α-iduronidase activity was measureable only in cats. In samples from animals with LSD, markedly reduced activity of a specific enzyme was found. In contrast, in samples from cats affected with mucolipidosis II, activities of lysosomal enzymes were markedly increased.

CONCLUSIONS

Measurement of lysosomal enzyme activities in DBS provides an inexpensive, simple, and convenient method to screen animals for suspected LSD and requires only a small sample volume. For diseases in which the relevant enzyme activity can be measured in DBS, a specific diagnosis can be made.

Algorithm for Pompe disease newborn screening: results from the Taiwan screening program

BACKGROUND

Pompe disease is caused by a deficiency in acid α-glucosidase (GAA) and results in progressive, debilitating, and often life-threatening symptoms. Newborn screening has led to the early diagnosis of Pompe disease, but the best algorithm for screening has not yet been established.

MATERIALS AND METHODS

GAA and neutral α-glucosidase (NAG) activities in dried blood spots (DBSs) were assayed using 4-methylumbelliferyl-β-d-glucopyranoside as the substrate. We also measure α-galactosidase A (GLA) activity in DBSs for comparison. A total of 473,738 newborns were screened for Pompe disease, and the data were analyzed retrospectively to determine the best screening algorithm.

RESULTS

The fluorescence assay used in the screening possessed good reproducibility, but the NAG/GAA ratio was superior in separating the true-positive from the false-positive cases. An NAG/GAA cutoff ratio≥60 produces a positive predictive value (PPV) of 63.4%, and in our sample, only two cases of later-onset Pompe disease would have been missed. The GLA/GAA ratio is not as effective as the NAG/GAA ratio.

CONCLUSION

A suitable control enzyme can improve the performance of newborn screening. Newborn screening for Pompe disease can be performed using the NAG/GAA ratio as a cutoff even in the presence of GAA partial deficiency.

The use of dried blood spot samples in the diagnosis of lysosomal storage disorders--current status and perspectives

Dried blood spot (DBS) methods are currently available for identification of a range of lysosomal storage disorders (LSDs). These disorders are generally characterized by a deficiency of activity of a lysosomal enzyme and by a broad spectrum of phenotypes. Diagnosis of LSD patients is often delayed, which is of particular concern as therapeutic outcomes (e.g. enzyme replacement therapy) are generally more favorable in early disease stages. Experts in the field of LSDs diagnostics and screening programs convened and reviewed experiences with the use of DBS methods, and discuss the diagnostic challenges, possible applications and quality programs in this paper. Given the easy sampling and shipping and stability of samples, DBS has evident advantages over other laboratory methods and can be particularly helpful in the early identification of affected LSD patients through neonatal screening, high-risk population screening or family screening.

Digital microfluidic platform for multiplexing enzyme assays: implications for lysosomal storage disease screening in newborns

BACKGROUND

Newborn screening for lysosomal storage diseases (LSDs) has been gaining considerable interest owing to the availability of enzyme replacement therapies. We present a digital microfluidic platform to perform rapid, multiplexed enzymatic analysis of acid α-glucosidase (GAA) and acid α-galactosidase to screen for Pompe and Fabry disorders. The results were compared with those obtained using standard fluorometric methods.

METHODS

We performed bench-based, fluorometric enzymatic analysis on 60 deidentified newborn dried blood spots (DBSs), plus 10 Pompe-affected and 11 Fabry-affected samples, at Duke Biochemical Genetics Laboratory using a 3-mm punch for each assay and an incubation time of 20 h. We used a digital microfluidic platform to automate fluorometric enzymatic assays at Advanced Liquid Logic Inc. using extract from a single punch for both assays, with an incubation time of 6 h. Assays were also performed with an incubation time of 1 h.

RESULTS

Assay results were generally comparable, although mean enzymatic activity for GAA using microfluidics was approximately 3 times higher than that obtained using bench-based methods, which could be attributed to higher substrate concentration. Clear separation was observed between the normal and affected samples at both 6- and 1-h incubation times using digital microfluidics.

CONCLUSIONS

A digital microfluidic platform compared favorably with a clinical reference laboratory to perform enzymatic analysis in DBSs for Pompe and Fabry disorders. This platform presents a new technology for a newborn screening laboratory to screen LSDs by fully automating all the liquid-handling operations in an inexpensive system, providing rapid results.