Haoyue Zhang

Comparison of maltose and acarbose as inhibitors of maltase-glucoamylase activity in assaying acid α-glucosidase activity in dried blood spots for the diagnosis of infantile Pompe disease

Purpose: The study’s purpose was to compare acarbose and maltose as inhibitors of maltase-glucoamylase activity for determining acid α-glucosidase activity in dried blood spot specimens for early identification of patients with infantile Pompe disease, a severe form of acid α-glucosidase deficiency.Methods: Acid α-glucosidase activities in dried blood spot extracts were determined fluorometrically using the artificial substrate 4-methylumbelliferyl-α-D-pyranoside. Acarbose or maltose was used to inhibit maltase-glucoamylase, an enzyme present in polymorphonuclear neutrophils that contributes to the total α-glucosidase activity at acidic pH.Results: Complete discrimination between patients with proven infantile Pompe disease (n = 20), obligate heterozygotes (n = 16), and controls (n = 150) was achieved using 8 μmol/L acarbose as the inhibitor. Higher acarbose concentration (80 μmol/L) did not improve the assay. By using 4 mM maltose as the inhibitor, heterozygotes and patients were not completely separated. The results using acarbose compared well with those using the skin fibroblast assay in the same group of patients with proven infantile Pompe disease.Conclusion: Acid α-glucosidase activity measurements in dried blood spot extracts can reliably detect infantile Pompe disease in patients. The convenience of collecting and shipping dried blood specimens plus rapid turnaround time makes this assay an attractive alternative to established methods.

Immunomodulatory Gene Therapy Prevents Antibody Formation and Lethal Hypersensitivity Reactions in Murine Pompe Disease

Infantile Pompe disease progresses to a lethal cardiomyopathy in absence of effective treatment. Enzyme-replacement therapy (ERT) with recombinant human acid alpha-glucosidase (rhGAA) has been effective in most patients with Pompe disease, but efficacy was reduced by high-titer antibody responses. Immunomodulatory gene therapy with a low dose adeno-associated virus (AAV) vector (2 x 10(10) particles) containing a liver-specific regulatory cassette significantly lowered immunoglobin G (IgG), IgG1, and IgE antibodies to GAA in Pompe disease mice, when compared with mock-treated mice (P < 0.05). AAV-LSPhGAApA had the same effect on GAA-antibody production whether it was given prior to, following, or simultaneously with the initial GAA injection. Mice given AAV-LSPhGAApA had significantly less decrease in body temperature (P < 0.001) and lower anaphylactic scores (P < 0.01) following the GAA challenge. Mouse mast cell protease-1 (MMCP-1) followed the pattern associated with hypersensitivity reactions (P < 0.05). Regulatory T cells (Treg) were demonstrated to play a role in the tolerance induced by gene therapy as depletion of Treg led to an increase in GAA-specific IgG (P < 0.001). Treg depleted mice were challenged with GAA and had significantly stronger allergic reactions than mice given gene therapy without subsequent Treg depletion (temperature: P < 0.01; symptoms: P < 0.05). Ubiquitous GAA expression failed to prevent antibody formation. Thus, immunomodulatory gene therapy could provide adjunctive therapy in lysosomal storage disorders treated by enzyme replacement.

Screening for pompe disease using a rapid dried blood spot method: Experience of a clinical diagnostic laboratory

Pompe disease (acid maltase deficiency; glycogen storage disease type II) is caused by deficiency of the lysosomal enzyme acid alpha‐glucosidase (GAA). Our clinical laboratory began to offer a fluorometric dried blood spot (DBS)‐based GAA activity assay for Pompe disease in 2006 after the FDA approved GAA enzyme replacement therapy in April of that year. The purpose of this study was to examine the experience of our clinical laboratory in using this assay. Over a 2‐year period, we received samples for the DBS GAA assay from 891 patients referred for possible Pompe disease, of whom 111 (12.5%) patients across the disease spectrum who had results in the affected range. The majority of the patients were referred by neurologists and geneticists. When available, we correlated the results obtained through DBS GAA activity assay with the results from a second DBS, or a second tissue (cultured skin fibroblasts or muscle biopsy). In our experience, the DBS GAA activity assay provides a robust, rapid, and reliable first tier test for screening patients suspected of having Pompe disease. Muscle Nerve 40: 32–36, 2009

Long-term monitoring of patients with infantile-onset Pompe disease on enzyme replacement therapy using a urinary glucose tetrasaccharide biomarker.

Purpose: To investigate the correlation of the urinary glucose tetrasaccharide, Glcα1-6Glcα1-4Glcα1-4Glc, (Glc4) with skeletal muscle glycogen content and the long-term clinical response to enzyme replacement therapy with recombinant human acid alpha glucosidase in infantile Pompe disease.Methods: Eighteen patients, ≤6 months old, were enrolled in a clinical trial of enzyme replacement therapy for up to 142 weeks. Urinary Glc4, skeletal muscle glycogen, and other clinical and laboratory assessments were made at baseline and at regular intervals. Urinary Glc4 was determined using an isotope-dilution tandem mass spectrometric assay. The clinical response to treatment was defined according to the motor function response. Trends in urinary Glc4 were correlated with the clinical response and compared with serum enzyme markers of skeletal muscle damage, creatine kinase, aspartate aminotransferase, and alanine aminotransferase.Results: Urinary Glc4, in contrast to the serum markers, correlated closely with skeletal muscle glycogen content and with the clinical response. Patients with the best response to treatment maintained the lowest levels of Glc4 throughout the trial.Conclusion: The results from this study support the use of urinary Glc4 for monitoring patients with infantile-onset Pompe disease on therapy.

An improved method for glycosaminoglycan analysis by LC–MS/MS of urine samples collected on filter paper

BACKGROUND Mucopolysaccharidoses are complex lysosomal storage disorders caused by any of eleven different enzyme deficiencies resulting in the accumulation of substrates, mainly glycosaminoglycans (GAGs), in various tissues and biological fluids. METHOD We developed and validated a urine filter paper methodology for the analysis of GAGs using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for mucopolysaccharidoses type I, type II and type VI patients. We focused on 2 objectives: first, its applicability to high-risk screening, and secondly, to facilitate the collection and shipping of samples to reference centers as part of diagnostic investigation, as well as from treated patients needing to be monitored for assessment of the efficacy of treatment. GAGs in urine dried onto filter paper were extracted and subjected to methanolysis to obtain the repeating disaccharides of the molecules. We devised a multiple reaction monitoring method in positive electrospray ionization mode. RESULTS The use of deuterated internal standards for dermatan sulfate (DS) and heparan sulfate (HS) reduced a troubling matrix effect. The resulting CVs were <14%. Linearity assessment showed Pearson correlation coefficients of 0.999 and 0.997, for DS and HS, respectively. The stability on filter paper was good for DS and HS for up to 6 weeks at various temperatures. CONCLUSION We devised a robust and efficient LC-MS/MS methodology for GAGS quantification in urine dried on filter paper and subjected to environmental conditions likely to be encountered during collection, storage and shipping of specimens from referring physicians to medical centers.

Analysis of Glycosaminoglycans in Cerebrospinal Fluid from Patients with Mucopolysaccharidoses by Isotope-Dilution Ultra-Performance Liquid Chromatography–Tandem Mass Spectrometry

BACKGROUND New therapies for the treatment of mucopolysaccharidoses that target the brain, including intrathecal enzyme replacement, are being explored. Quantitative analysis of the glycosaminoglycans (GAGs) that accumulate in these disorders is required to assess the disease burden and monitor the effect of therapy in affected patients. Because current methods lack the required limit of quantification and specificity to analyze GAGs in small volumes of cerebrospinal fluid (CSF), we developed a method based on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). METHODS Samples of CSF (25 μL) were evaporated to dryness and subjected to methanolysis. The GAGs were degraded to uronic acid-N-acetylhexosamine dimers and mixed with internal standards derived from deuteriomethanolysis of GAG standards. Specific dimers derived from heparan, dermatan and chondroitin sulfates (HS, DS and CS) were separated by UPLC and analyzed by electrospray ionization MS/MS using selected reaction monitoring for each targeted GAG product and its corresponding internal standard. RESULTS CSF from control pediatric subjects (n = 22) contained <0.38 mg/L HS, 0.26 mg/L DS, and 2.8 mg/L CS, whereas CSF from patients with Hurler syndrome (n = 7) contained concentrations of DS and HS that were at least 6-fold greater than the upper control limits. These concentrations were reduced by 17.5% to 82.5% after allogeneic transplantation and treatment with intrathecal and intravenous enzyme replacement therapy. CONCLUSIONS The method described here has potential value in monitoring patients with mucopolysaccharidoses receiving treatment targeted to the brain.

Assessing disease severity in Pompe disease: the roles of a urinary glucose tetrasaccharide biomarker and imaging techniques.

Defining disease severity in patients with Pompe disease is important for prognosis and monitoring the response to therapies. Current approaches include qualitative and quantitative assessments of the disease burden, and clinical measures of the impact of the disease on affected systems. The aims of this manuscript were to review a noninvasive urinary glucose tetrasaccharide biomarker of glycogen storage, and to discuss advances in imaging techniques for determining the disease burden in Pompe disease. The glucose tetrasaccharide, Glcα1‐6Glcα1‐4Glcα1‐4Glc (Glc4), is a glycogen‐derived limit dextrin that correlates with the extent of glycogen accumulation in skeletal muscle. As such, it is more useful than traditional biomarkers of tissue damage, such as CK and AST, for monitoring the response to enzyme replacement therapy in patients with Pompe disease. Glc4 is also useful as an adjunctive diagnostic test for Pompe disease when performed in conjunction with acid alpha‐glucosidase activity measurements. Review of clinical records of 208 patients evaluated for Pompe disease by this approach showed Glc4 had 94% sensitivity and 84% specificity for Pompe disease. We propose Glc4 is useful as an overall measure of disease burden, but does not provide information on the location and distribution of excess glycogen accumulation. In this manuscript we also review magnetic resonance spectroscopy and imaging techniques as alternative, noninvasive tools for quantifying glycogen and detailing changes, such as fibrofatty muscle degeneration, in specific muscle groups in Pompe disease. These techniques show promise as a means of monitoring disease progression and the response to treatment in Pompe disease.

A straightforward, quantitative ultra-performance liquid chromatography‐tandem mass spectrometric method for heparan sulfate, dermatan sulfate and chondroitin sulfate in urine: An improved clinical screening test for the mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are complex storage disorders that result in the accumulation of glycosaminoglycans (GAGs) in urine, blood, brain and other tissues. Symptomatic patients are typically screened for MPS by analysis of GAG in urine. Current screening methods used in clinical laboratories are based on colorimetric assays that lack the sensitivity and specificity to reliably detect mild GAG elevations that occur in some patients with MPS. We have developed a straightforward, reliable method to quantify chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS) in urine by stable isotope dilution tandem mass spectrometry. The GAGs were methanolyzed to uronic acid-N-acetylhexosamine or iduronic acid-N-glucosamine dimers and mixed with stable isotope labeled internal standards derived from deuteriomethanolysis of GAG standards. Specific dimers derived from HS, DS and CS were separated by ultra-performance liquid chromatography and analyzed by electrospray ionization tandem mass spectrometry using selected reaction monitoring for each targeted GAG product and its corresponding internal standard. The method was robust with a mean inaccuracy from 1 to 15%, imprecision below 11%, and a lower limit of quantification of 0.4mg/L for CS, DS and HS. We demonstrate that the method has the required sensitivity and specificity to discriminate patients with MPS III, MPS IVA and MPS VI from those with MPS I or MPS II and can detect mildly elevated GAG species relative to age-specific reference intervals. This assay may also be used for the monitoring of patients following therapeutic intervention. Patients with MPS IVB are, however, not detectable by this method.

Urinary F2-Isoprostanes as a Biomarker of Reduced Risk of Type 2 Diabetes

OBJECTIVE We have previously reported evidence of an inverse association between a urinary F2-isoprostane and type 2 diabetes risk in a pilot case-control study nested within the Insulin Resistance Atherosclerosis Study (IRAS). Here, we report the results from the study extended to the entire IRAS cohort. RESEARCH DESIGN AND METHODS This prospective study included 138 incident type 2 diabetes case and 714 noncase subjects. Four F2-isoprostanes (iPF2α-III; 2,3-dinor-iPF2α-III; iPF2α-VI; and 8,12-iso-iPF2α-VI) were assayed in baseline urine samples using liquid chromatography–tandem mass spectrometry. RESULTS Three F2-isoprostanes showed significant inverse associations with type 2 diabetes risk: the adjusted odds ratios were 0.52 (95% CI 0.39–0.67), 0.56 (0.42–0.73), 0.62 (0.48–0.79), and 0.91 (0.72–1.12) for iPF2α-III; 2,3-dinor-iPF2α-III; iPF2α-VI; and 8,12-iso-iPF2α-VI, respectively. CONCLUSIONS Our findings indicate that urinary F2-isoprostanes are inversely associated with type 2 diabetes risk beyond the traditional risk factors and may be useful in identifying high-risk populations.

Allantoin in human urine quantified by ultra-performance liquid chromatography-tandem mass spectrometry.

Uric acid is a potent antioxidant and scavenger of singlet oxygen and other radicals in humans. Allantoin, the predominant product of free radical-induced oxidation of uric acid, is efficiently excreted in the urine and has potential as a biomarker of oxidative stress. We developed a rapid and specific assay for urinary allantoin using ultra-performance liquid chromatography-tandem mass spectrometry suitable for high-throughput clinical studies. The method required minimal sample preparation and was accurate (mean error=6%), precise (intra- and interday imprecision <8%), and sensitive (limit of detection=0.06pmol). Allantoin levels measured in control samples were comparable to literature values.