Minje Han

Use of Tandem Mass Spectrometry for Newborn Screening of 6 Lysosomal Storage Disorders in a Korean Population

Background We evaluated the performance of multiplex tandem mass spectrometry (MS/MS) in newborn screening for detection of 6 lysosomal storage disorders (LSDs), namely, Niemann-Pick A/B, Krabbe, Gaucher, Fabry, and Pompe diseases and Hurler syndrome. Methods We revised the conditions and procedures of multiplex enzyme assay for the MS/MS analysis and determined the precision of our enzyme assay and the effects of sample amounts and incubation time on the results. We also measured the degree of correlation between the enzyme activities in the dried blood spots (DBSs) and those in the leukocytes. DBSs of 211 normal newborns and 13 newborns with various LSDs were analyzed using our revised methods. Results The intra- and inter-assay precisions were 2.9-18.7% and 8.1-18.1%, respectively. The amount of product obtained was proportional to the DBS eluate volume, but a slight flattening was observed in the product vs. sample volume curve at higher sample volumes. For each enzyme assay, the amount of product obtained increased linearly with the incubation period (range, 0-24 hr). Passing and Bablok regression analysis revealed that the enzyme activities in the DBSs and those in the leukocytes were favorably correlated. The enzyme activities measured in the DBSs were consistently lower in patients with LSDs than in normal newborns. Conclusions The performance of our revised techniques for MS/MS detection and enzyme assays was of the generally acceptable standard. To our knowledge, this is the first report on the use of MS/MS for newborn screening of LSDs in an Asian population.

Method for simultaneous analysis of nine second-line anti-tuberculosis drugs using UPLC-MS/MS

OBJECTIVES Therapeutic drug monitoring (TDM) of anti-tuberculosis (TB) drugs is beneficial for patients responding slowly to treatment and those with multidrug-resistant TB. We used ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to develop a rapid method for simultaneously measuring the blood concentrations of nine second-line anti-TB drugs: streptomycin, kanamycin, clarithromycin, cycloserine, moxifloxacin, levofloxacin, para-aminosalicylic acid, prothionamide and linezolid. METHODS Serum samples were extracted with acidified methanol and neutralized with NaOH. A Waters Acquity HSS T3 column and gradients of ammonium formate and acetonitrile in 0.1% formic acid were used for UPLC separation. Drug concentrations were determined by multiple reaction monitoring in positive ion mode, and assay performance was evaluated. We applied this method to TDM, analysing random serum samples from 85 patients treated with second-line drugs. RESULTS Sample preparation using acidified methanol extraction followed by neutralization yielded good recovery and ionization efficiency, with chromatographic separation achieved within 3 min per sample. Within-run and between-run precisions were 1.7%-7.5% and 1.7%-12.4%, respectively, at concentrations representing low and high levels for the nine drugs. Lower limits of detection and quantification were 0.025-0.5 and 0.25-5.0 μg/mL, respectively. Linearity was acceptable at five concentrations for each drug. No ion suppression was observed at the retention time for most compounds, except for streptomycin, kanamycin and cycloserine, which were eluted close to the void volume of the column. In a limited pilot study, all quantifiable human samples had values within the validated assay ranges. CONCLUSIONS The performance of our MS/MS detection technique was generally acceptable. The method provided rapid, sensitive and reproducible quantification of nine second-line anti-TB drugs and should facilitate drug monitoring during treatment.

Ultra‐performance liquid chromatography/tandem mass spectrometry for determination of sulfatides in dried blood spots from patients with metachromatic leukodystrophy

RATIONALE Metachromatic leukodystrophy (MLD) is a genetic autosomal recessive disease caused by a deficiency in arylsulfatase A. Accumulated sulfatides can be detected in the urine and detection of sulfatiduria is a useful test for diagnosis and monitoring. To our knowledge, no studies have explored the accumulation of sulfatides in dried blood spots (DBSs). We developed an ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method for measuring sulfatides in DBSs from patients with MLD. METHODS DBSs were eluted with internal standard. After mixing and centrifugation, the organic layer was transferred to a 96-well microplate and dried, then resuspended in methanol/propanol solution. Samples were analyzed on an UPLC system. Total running time was 4 min. Quantification was achieved by multiple reaction monitoring using a tandem mass spectrometer. We evaluated the precision, linearity, and ion suppression of the method and analyzed sulfatide concentrations in DBS specimens from MLD patients (n = 9), pseudodeficiency (PD) patient (n = 1), obligate heterozygotes (OH) (n = 2) and normal controls (n = 124). RESULTS In negative-ion mode, sulfatides species subjected to collision-induced dissociation readily fragment to produce an intense ion at m/z 96.8 (HSO4(-)). The precisions of low and high concentration controls ranged from 5.4 to 19.9%. The sulfatides produced linear responses. Molecular species of sulfatides were barely detected in DBSs from normal individuals and the PD-OH group [mean (range), 0.07 (<0.05-0.34) and 0.13 (<0.05-0.22) µg/mL, respectively]. In contrast, the DBSs from MLD patients showed a marked increase in several molecular species of sulfatide [mean (range), 2.02 (1.18-3.89) µg/mL]. CONCLUSIONS Simultaneous detection for sulfatides using UPLC/MS/MS can be successfully applied to DBS analysis. This method provides a fast and effective screening and monitoring tool for the diagnosis and treatment of MLD.

Comparison of Three Multiple Allergen Simultaneous Tests: RIDA Allergy Screen, MAST Optigen, and Polycheck Allergy

We compared the performances of 3 Multiple Allergen Simultaneous Test (MAST) assays: RIDA Allergy Screen (R-Biopharm, Darmstadt, Germany), MAST Optigen allergy system (Hitachi Chemical Diagnostics, Mountain View, CA), and Polycheck Allergy (Biocheck GmbH, Munster, Germany). Forty sera that tested positive with the RIDA Allergy Screen (20 for food and 20 for inhalant panel) were subjected to MAST Optigen and Polycheck Allergy. For 26 available sera with discrepant results, 62 ImmunoCAP allergen-specific IgE tests (Pharmacia Diagnostics, Uppsala, Sweden) were performed. Percent agreements (kappa value) were 87.6% (0.59) and 91.3% (0.60) between RIDA and MAST; 89.9% (0.55) and 88.3% (0.46) between RIDA and Polycheck; and 86.8% (0.51) and 90.6% (0.61) between MAST and Polycheck. Compared with ImmunoCAP, agreements (kappa value) of inhalant and food panels were 51.7% (0.04) and 33.3% (−0.38) for RIDA; 60.7% (0.27) and 81.8% (0.59) for MAST; and 65.5% (0.26) and 45.5% (0.07) for Polycheck. The agreements between RIDA, MAST, and Polycheck and ImmunoCAP-positivity were 45.7%, 88.2%, and 28.6%, respectively, and the agreements for ImmunoCAP-negativity were 37.0%, 51.9%, and 88.9%. MAST Optigen showed better agreement with ImmunoCAP than other assays in the food panel. Better sensitivity of MAST Optigen and better specificity of Polycheck Allergy were suspected.

Biochemical and Genetic Analysis of Seven Korean Individuals With Suspected Metachromatic Leukodystrophy

Metachromatic leukodystrophy (MLD) is an autosomal recessive disease caused by a deficiency in arylsulfatase A (ARSA). However, decreased ARSA activity is also observed in pseudodeficiency (PD). To distinguish between MLD and PD, we performed gene mutation and sulfatide analyses by using dried blood spots (DBSs) from seven Korean individuals who underwent an analysis of ARSA activity. DNA was extracted from DBSs, and PCR-direct sequencing of ARSA was performed. The cDNA obtained was analyzed to confirm a novel mutation. Of the seven subjects, three were confirmed as having MLD, one was confirmed as having MLD-PD, one was confirmed as having PD, and the remaining two were obligate heterozygotes. We verified the novel pathogenic variant c.1107+1delG by performing familial and cDNA analyses. Sulfatide concentrations in DBSs were analyzed and were quantified by using ultra-performance liquid chromatography and tandem mass spectrometry, respectively. Total sulfatide concentration was inversely correlated with ARSA activity (Spearmans coefficient of rank correlation, P=0.929, P=0.0025). The results of this mutational and biochemical study on MLD will increase our understanding of the genetic characteristics of MLD in Koreans.

Performance evaluation of SD A1cCare as a HbA1c analyzer for point-of-care testing.

OBJECTIVES Some studies have shown that a rapid feedback of HbA1c results is helpful for controlling plasma glucose levels. Point-of-care (POC) instruments that are fast, portable, and easy to use are suitable for rapid determination of HbA1c levels. Here, we evaluated the analytical performance of a newly developed POC HbA1c analyzer, SD A1cCare (SD Biosensor, Inc.). DESIGN AND METHODS The precision, linearity, and correlation with the Variant II Turbo instrument (Bio-Rad Laboratories, Inc.) were evaluated according to CLSI guidelines for SD A1cCare. All tests were performed according to the manufacturer instructions, and statistical analyses, including linear regression and Passing-Bablok regression, were performed. Bias from the IFCC reference targets was also evaluated with 12 duplicate specimens (n=24 in total). RESULTS The coefficients of variation based on EP9-A2 protocol were 2.6% in SI unit and 1.8% in NGSP unit. The calibration curve was linear, with R(2)=0.9911 in the range of 23.5 to 125.1 mmol/mol in SI units (4.3% to 13.6% in NGSP units). The results of the SD A1cCare correlated with those of the Variant II Turbo (r=0.986). Deviations from IFCC targets at 30, 60, and 90 mmol/mol IFCC levels were -1.95, -1.85, and -1.74 mmol/mol, respectively. CONCLUSIONS The SD A1cCare analyzer showed excellent precision, linearity, correlation with the Variant II Turbo analyzer, and accuracy with IFCC targets. Therefore, it may be suitable for HbA1c assays in the POC setting and in small laboratories.

Multiplex Assay of Second-Line Anti-Tuberculosis Drugs in Dried Blood Spots Using Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

As dried blood spots (DBSs) have various advantages over conventional venous blood sampling, some assays for detection of one or two anti-tuberculosis (TB) drugs in DBSs have been developed. However, there are no assays currently available for the simultaneous measurement of three or more anti-TB drugs in DBSs. In this study, we developed and evaluated a multiplex method for detecting nine anti-TB drugs including streptomycin, kanamycin, clarithromycin, cycloserine, moxifloxacin, levofloxacin, para-aminosalicylic acid, prothionamide, and linezolid in DBSs by using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Seventy-nine patient samples of DBS were analyzed on the UPLC-MS/MS system. All drug concentrations were determined within 4 min, and assay performance was evaluated. All drugs were clearly separated without ion suppression. Within-run and between-run precisions were 1.7-13.0% and 5.7-17.0%, respectively, at concentrations representing low and high levels for the nine drugs. Lower limits of detection and quantification were 0.06-0.6 and 0.5-5.0 µg/mL, respectively. Linearity was acceptable at five level concentrations for each drug. Correlations between drug concentrations in plasma and DBSs by using Passing-Bablock regression and Pearsons rho (ρ, 0.798-0.989) were acceptable. In conclusion, we developed a multiplex assay to measure nine second-line anti-TB drugs in DBSs successfully. This assay provided convenient and rapid drug quantification and could have applications in drug monitoring during treatment.

Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry Measurement of Leukocyte Arylsulfatase A Activity Using a Natural Substrate

Biochemical diagnosis of metachromatic leukodystrophy (MLD) is usually performed by measuring arylsulfatase A (ARSA; EC3.1.6.8) activity with artificial substrates (p-nitrocatechol sulfate or 4-methylumbelliferyl sulfate) in leukocytes or cultured skin fibroblasts [1, 2]. Unfortunately, these artificial substrates are also substrates for several other enzymes, including arylsulfatase B [3, 4]. Thus, quantitation of residual activity could be inaccurate, especially in the context of MLD variants and ARSA pseudodeficiency. In this study, we evaluated the feasibility of ultra-performance liquid chromatography (UPLC)-tandem mass spectrometry (MS/MS) in a leukocyte ARSA assay using a natural sulfatide substrate, and we compared this approach with a traditional spectrophotometric assay using a synthetic substrate. The substrate and internal standard (IS) were N-octadecanoyl-sulfatide and N-octadecanoyl-D35-psychosine (Matreya LLC, Pleasant Gap, PA, USA), respectively. We used C18 β-D-glucosyl ceramide (Avanti Polar Lipids Inc., Alabaster, AL, USA) instead of C18 β-D-galactosyl ceramide as the standard because of commercial availability. The enzyme reaction cocktail contained 2.08 g/L sodium taurodeoxycholate, 33 mmol/L MnCl2, 0.08 mol/L sodium acetate buffer (pH 4.5), and 6.20 µmol/L substrate. Seventy microliters of reaction cocktail and 30 µL of sonicated leukocyte solution were incubated at 37℃ for 1 hr and were quenched with 100 µL of ethyl acetate-methanol solution. Ten microliters of 1 µmol/L IS solution and 300 µL of both ethyl acetate and water were added to the reaction vial and centrifuged at 15,700 g for 10 min. Two hundred microliters of the top organic layer was dried under N2 gas and resuspended in 70 µL of methanol. And 7 µL was injected into a Waters ACQUITY UPLC system (Waters, Milford, MA, USA). The mobile phase was a mixture that was 97% methanol containing 3% of 0.05 mol/L ammonium formate solution in water at a flow rate of 0.5 mL/min. A Quattro Premier XE MS/MS (Waters) was operated by using the following settings: cone voltage, 25, 30, and 25 V; collision energy, 35, 40, and 35 V; and multiple reaction monitoring transition in positive ion mode, m/z 808.5→264.3, m/z 763.7→265.3, and m/z 728.5→264.3 for the substrate, IS, and product, respectively. The amount of product was calculated from the calibration curves constructed with five concentrations of C18 s-D-glucosyl ceramide (0-687 nmol/L), and the enzyme activities were expressed in nmol/min/mg protein. Substrates, products, and IS were fully separated by using UPLC with an HSS T3 1.8-µm column (2.1×50 mm) with a 3 min chromatographic separation time (Fig. 1). The amount of product obtained was proportional to the volume of leukocytes used in the assay (10, 20, 30, 40, and 50 µL of leukocyte extract) and increased linearly with the incubation period (0, 0.5, 1, 2, and 3 hr). We chose a 30 µL leukocyte volume and a 1 hr incubation time for all subsequent enzymatic assays. The within- and between-run imprecision (CVs), as determined by 10 replicated analyses and 5 consecutive runs using a normal control sample, were 7.7% and 14.5%, respectively. Fig. 1 Representative ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) multiple reaction monitoring (MRM) chromatograms from the mixture of S, IS and standard (A) and the mixture of ARSA enzyme reactions in the leukocyte samples ... To validate the capability of our system to detect MLD patients, three MLD patients, one pseudodeficiency, one obligate heterozygote and 38 normal adults were examined. All patients exhibited reduced enzyme activity using synthetic substrates, confirmed by mutation analysis. As expected, the leukocytes of MLD patients exhibited consistently lower enzyme activities than those of the obligate heterozygote, pseudodeficiency, and normal adults without overlapping values (Fig. 2A). The provisional cut-off value was estimated as 1.23 mmol/min/mg protein. Passing-Bablok regression analysis revealed that the UPLC-MS/MS method and the traditional colorimetric assay [1] compared favorably (r=0.8019) (Fig. 2B). Fig. 2 Comparison of arylsufatase A activities measured by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in leukocytes samples from three patients with MLD (all 2-yr-old females) and one patient with pseudodeficiency (PD, a 47-yr-old ... Recently, reports on multiplex enzyme assay screening of dried blood spots (DBS) for lysosomal storage disorders have engendered interest in the use of MS/MS for newborn screening [5, 6]. Although assays using natural sulfatide substrates are more complicated because of the poor water solubility of sulfatides [7], utilization of natural substrates is increasingly required becausethe ARSA assay may soon be incorporated into newborn screening programs. In this regard, mass spectrometry is accepted as a valuable tool for the analysis of lipids and lipid-metabolizing enzymes using a natural substrate system. In this study, we investigated the feasibility of UPLC-MS/MS for use in a leukocyte ARSA assay using a natural sulfatide substrate. To the best of our knowledge, this is the first study to report the feasibility of UPLC-MS/MS for diagnosing MLD. The assay performance for our devised method in terms of precision and correlation with a traditional spectrophotometric method was within the generally acceptable standard and could be adopted for newborn screening of DBSs for MLD. More experiments would be needed to develop the assay for routine application.