Isotopic Distribution Calibration for Mass Spectrometry.

Mass spectrometry (MS) is widely used in science and industry. It allows accurate, specific, sensitive, and reproducible detection and quantification of a huge range of analytes. Across MS applications, quantification by MS has grown most dramatically, with >50 million experiments/year in the USA alone. However, quantification performance varies between instruments, compounds, different samples, and within- and across runs, necessitating normalization with analyte-similar internal standards (IS) and use of IS-corrected multipoint external calibration curves for each analyte, a complicated and resource-intensive approach, which is particularly ill-suited for multi-analyte measurements. We have developed an internal calibration method that utilizes the natural isotope distribution of an IS for a given analyte to provide internal multipoint calibration. Multiple isotope distribution calibrators for different targets in the same sample facilitate multiplex quantification, while the emerging random-access automated MS platforms should also greatly benefit from this approach. Finally, isotope distribution calibration allows mathematical correction for suboptimal experimental conditions. This might also enable quantification of hitherto difficult, or impossible to quantify, targets, if the distribution is adjusted in silico to mimic the analyte. The approach works well for high resolution, accurate mass MS for analytes with at least a modest-sized isotopic envelope. As shown herein, the approach can also be applied to lower molecular weight analytes, but the reduction in calibration points does reduce quantification performance.

Bioinformatics analysis of targeted metabolomics--uncovering old and new tales of diabetic mice under medication.

Metabolomics is a powerful tool for identifying both known and new disease-related perturbations in metabolic pathways. In preclinical drug testing, it has a high potential for early identification of drug off-target effects. Recent advances in high-precision high-throughput mass spectrometry have brought the metabolomic field to a point where quantitative, targeted, metabolomic measurements with ready-to-use kits allow for the automated in-house screening for hundreds of different metabolites in large sets of biological samples. Today, the field of metabolomics is, arguably, at a point where transcriptomics was about 5 yr ago. This being so, the field has a strong need for adapted bioinformatics tools and methods. In this paper we describe a systematic analysis of a targeted quantitative characterization of more than 800 metabolites in blood plasma samples from healthy and diabetic mice under rosiglitazone treatment. We show that known and new metabolic phenotypes of diabetes and medication can be recovered in a statistically objective manner. We find that concentrations of methylglutaryl carnitine are oppositely impacted by rosiglitazone treatment of both healthy and diabetic mice. Analyzing ratios between metabolite concentrations dramatically reduces the noise in the data set, allowing for the discovery of new potential biomarkers of diabetes, such as the N-hydroxyacyloylsphingosyl-phosphocholines SM(OH)28:0 and SM(OH)26:0. Using a hierarchical clustering technique on partial eta(2) values, we identify functionally related groups of metabolites, indicating a diabetes-related shift from lysophosphatidylcholine to phosphatidylcholine levels. The bioinformatics data analysis approach introduced here can be readily generalized to other drug testing scenarios and other medical disorders.

A rapid HPLC-MS/MS method for the simultaneous quantification of cyclosporine A, tacrolimus, sirolimus and everolimus in human blood samples.

In the past few years, high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) has matured to a true alternative to antibody-based immunoassays in routine therapeutic drug monitoring. In transplantation medicine, mass spectrometry-based assessment of immunosuppressant drug levels is considered a gold standard diagnostic procedure. We describe a fast state-of-the-art routine online solid-phase extraction (SPE) HPLC-MS/MS analysis platform that allows monitoring of cyclosporine A, tacrolimus, sirolimus and everolimus from 50-microl aliquots of EDTA whole blood specimens within 3.4 min total analysis time. Sample purification is done by offline protein precipitation followed by two automated chromatographic separation steps. Mass spectrometry-based analyte quantification relies on selected reaction monitoring experiments. The assay underwent complete validation and performance evaluation studies and performs very well in several international proficiency testing schemes. In daily routine, it allows reporting of about 75 patient sample results per work shift with a typical total individual sample turnaround time of less than 3 h.

Isotope correction of mass spectrometry profiles.

Isotope correction of a profile is an important step in the analysis of mass spectrometry derived data. The problem is mathematically formulated as a system of linear equations which is general enough to include previous correction methods. For the solution of these equations when applied to the whole profile an efficient algorithm is developed. In experimental tests the resulting algorithm corrected the profile fast and successfully.

Rapid sample preparation and simultaneous quantitation of prostaglandins and lipoxygenase derived fatty acid metabolites by liquid chromatography-mass spectrometry from small sample volumes.

BACKGROUND: Fatty acid metabolites play a key role in numerous physiological and pathological processes. A rapid liquid chromatography-mass spectrometry assay for the simultaneous determination of prostanoids, isoprostane and lipoxygenase (LOX) derived fatty acid metabolites in a small biological sample of only 20 microL was developed. METHODS: Human plasma samples were applied to a filter spot, extracted without prior derivatization and analyzed within 13 min. Detection of metabolites was performed on a triple quadrupole mass spectrometer in negative multiple-reaction monitoring detection mode. Application of this assay to various biological matrices was performed. RESULTS: The validated assay was linear over the concentration range of 5-500 nmol/L for prostanoids and isoprostane, 50-5000 nmol/L for LOX-derived metabolites and 400-40,000 nmol/L for fatty acids. Limits of quantitation were 0.4-233 nmol/L, depending on the metabolite. Plasma samples from diabetic patients and controls showed significant increases in (+/-)9-HODE and 15(S)-HETE with p-values of 0.019 and 0.024, respectively. CONCLUSIONS: The small amount of 20 microL sample volume used in this assay and the demonstrated application to various sample types makes it an ideal routine analysis method for fatty acid metabolites. The resulting values for LOX-derived metabolites in diabetes mellitus type 2 samples support earlier findings about the role of lipid oxidation products in diabetes.

Profiling oligosaccharidurias by electrospray tandem mass spectrometry: quantifying reducing oligosaccharides.

A method to semiquantify urinary oligosaccharides from patients suffering from oligosaccharidurias is presented. 1-Phenyl-3-methyl-5-pyrazolone has been used to derivatize urinary oligosaccharides prior to analysis by electrospray ionization-tandem mass spectrometry (ESI-MS/MS). Disease-specific oligosaccharides were identified for several oligosaccharidurias, including GM1 gangliosidosis, GM2 gangliosidosis, sialic acid storage disease, sialidase/neuraminidase deficiency, galactosialidosis, I-cell disease, fucosidosis, Pompe and Gaucher diseases, and alpha-mannosidosis. The oligosaccharides were referenced against the internal standard, methyl lactose, to produce ratios for comparison with control samples. Elevations in specific urinary oligosaccharides were indicative of lysosomal disease and the defective catabolic enzyme. This method has been adapted to enable assay of large sample numbers and could readily be extended to other oligosaccharidurias and to monitor oligosaccharide levels in patients receiving treatment. It also has immediate potential for incorporation into a newborn screening program.

Determination of monosaccharides and disaccharides in mucopolysaccharidoses patients by electrospray ionisation mass spectrometry.

The mucopolysaccharidoses are a group of lysosomal storage disorders characterised by the storage of glycosaminoglycans. With the exception of Hunters syndrome (MPS II), which is X-linked, they are autosomal recessively inherited resulting in a defect in any one of 10 lysosomal enzymes needed to catabolise glycosaminoglycans. The type and size of the glycosaminoglycans stored in lysosomes are determined by the particular enzyme deficiency. These glycosaminoglycan elevations are subsequently observed in tissue, circulation, and urine. A method has been developed for the derivatisation and quantification of sulfated N-acetylhexosamine-containing mono- and disaccharides from patient samples by electrospray ionisation tandem mass spectrometry. Urine from most mucopolysaccharidoses types had significant increases in di- and monosulfated N-acetylhexosamines (GalNAc4,6S, GalNAc6S, GalNAc4S, or GlcNAc6S) and monosulfated N-acetylhexosamine-uronic acid disaccharides (GalNAc6S-UA, GalNAc4S-UA, or GlcNAc6S-UA). Analysis of plasma and dried blood spots on filter paper collected from mucopolysaccharidoses patients showed elevations of total monosulfated N-acetylhexosamines but less than that seen in urine. Urine samples from bone marrow transplant recipients, mucopolysaccharidosis IVA and mucopolysaccharidosis VI patients, showed decreases in HexNAcS, HexNAcS(2)/GalNAc4,6S, and HexNAcS-UA post-transplant. This decrease correlated with clinical improvement to levels comparable with those identified in patients with less severe phenotypes. These metabolic markers therefore have potential applications in diagnosis, phenotype prediction and monitoring of current and future therapies, particularly for the mucopolysaccharidosis IIID, IVA, VI, and multiple sulfatase deficiency. This paper reports a sensitive and simple method for the measurement of sulfated N-acetylhexosamines and sulfated disaccharides shown to be elevated in some mucopolysaccharidosis and multiple sulfatase deficient patients.

Monitoring dose response of enzyme replacement therapy in feline mucopolysaccharidosis type VI by tandem mass spectrometry.

Mucopolysaccharidosis type VI is an inherited disorder of glycosaminoglycan metabolism characterized by organomegaly, corneal clouding, and skeletal dysplasia. Recent developments in the use of tandem mass spectrometry to measure sulfated mono- and disaccharides have enabled us to perform noninvasive, biochemical monitoring during therapy regimes in mucopolysaccharidosis type VI cats in addition to established methods of disease evaluation. In this study, mucopolysaccharidosis type VI animals were given high-dose (20 mg/kg) enzyme replacement therapy for the first month after birth followed by low doses (1 mg/kg) for a further 2 mo and were compared with animals maintained on 1 mg/kg enzyme replacement therapy for 3 mo. A sulfated monosaccharide (N-acetylhexosamine) and a sulfated disaccharide (N-acetylhexosamine-uronic acid) were elevated in MPS VI cat urine and blood. These markers showed a clear discrimination between the treatment groups during the first 4 wk of therapy: values in the high-dose group were close to normal whereas those in the low-dose group were only slightly lower than the untreated mucopolysaccharidosis type VI cats. However, within 2 mo of cessation of the high-dose therapy there was minimal difference in the oligosaccharide levels, with both groups lying between the untreated and unaffected cats. At the completion of the trial, subjective minor improvement was noted in overall physical disease features and also in lysosomal vacuolation in tissues from animals on the initial high-dose enzyme replacement therapy compared to the low-dose therapy animals. Initial high-dose therapy reduced storage load in the animals but had no lasting clinical benefit over continuous low-dose therapy.

Disease-specific markers for the mucopolysaccharidoses.

Unprecedented demands are now placed on clinicians for early diagnosis as we enter into an era of advancing treatment opportunities for the mucopolysaccharidoses (MPS). Biochemical monitoring of any therapeutic avenue will also be prerequisite. To this end, we aimed to identify a range of urinary oligosaccharides that could be used to identify and characterize patients with MPS. We analyzed 94 urine samples from 68 patients with MPS and 26 control individuals for oligosaccharides derived from glycosaminoglycans using electrospray ionization-tandem mass spectrometry. The oligosaccharide profile for each patient group was compared with that of the control group. The Mann-Whitney U test was used to measure the difference between each patient group and the controls for each analyte. Urine samples from patients before and at successive times after bone marrow transplantation were also evaluated. A number of oligosaccharides were identified in the urine of each MPS subtype, and for each of these, specific oligosaccharide profiles were formulated. These profiles enabled the identification of all 68 patients and their subtypes with the exception of MPS IIIB and IIIC. Selected oligosaccharides were used to assess three individuals after a bone marrow transplant, and, in each case, a substantial reduction in the level of diagnostic oligosaccharides, posttransplantation, was observed. The identification and measurement of glycosaminoglycan-derived oligosaccharides in urine provides a sensitive and specific screen for the early identification of individuals with MPS. The resulting oligosaccharide profiles not only characterize subtype but also provide a disease-specific fingerprint for the biochemical monitoring of current and proposed therapies.

Determination of oligosaccharides in Pompe disease by electrospray ionization tandem mass spectrometry.

BACKGROUND: The development of therapies for lysosomal storage disorders has created a need for biochemical markers to monitor the efficacy of therapy and methods to quantify these markers in biologic samples. In Pompe disease, the concentration of a tetrasaccharide, consisting of four glucose residues, is reputedly increased in urine and plasma, but faster and more sensitive methods are required for the analysis of this, and other oligosaccharides, from biologic fluids. METHODS: We optimized the derivatization of storage oligosaccharides with 1-phenyl-3-methyl-5-pyrazolone for the measurement, by electrospray ionization tandem mass spectrometry, of oligosaccharide concentrations in urine (n = 6), plasma (n = 11), and dried-blood spots (n = 17) from Pompe-affected individuals. Age-matched control samples of urine (n = 10), plasma (n = 28), and blood spots (n = 369) were also analyzed. RESULTS: The mean tetrasaccharide concentration was increased in urine from infantile-onset (0.69-12 mmol/mol of creatinine) and adult-onset (0.22-3.0 mmol/mol of creatinine) Pompe individuals compared with age-matched controls. In plasma samples, an increased tetrasaccharide concentration was observed in some infantile patients (up to 22 micromol/L) compared with age-matched controls (mean, 2.2 micromol/L). The method developed was sensitive enough to determine oligosaccharide concentrations in a single 3-mm blood spot, but no differences were observed between blood spots from control and Pompe-affected individuals. CONCLUSIONS: Measurements of oligosaccharide concentrations in urine by this new method have potential application for the diagnosis and monitoring of patients with Pompe disease. Plasma analysis may have limited application for infantile patients, but analysis of blood spots does not discriminate between controls and affected individuals.

Determination of oligosaccharides and glycolipids in amniotic fluid by electrospray ionisation tandem mass spectrometry: in utero indicators of lysosomal storage diseases.

Prenatal diagnosis is available for many lysosomal storage disorders (LSD) using chorionic villus samples or amniocytes. Such diagnoses can be problematical if sample transport and culture are required prior to analysis. The purpose of this study was to identify useful biochemical markers for the diagnosis of lysosomal storage disorders from amniotic fluid. Amniotic fluid samples from control (n=49) and LSD affected (n=36) pregnancies were analysed for the protein markers LAMP-1 and saposin C by ELISA, and for oligosaccharide and lipid metabolite markers by electrospray ionisation-tandem mass spectrometry. Lysosomal storage disorder samples include; aspartylglucosaminuria, galactosialidosis, Gaucher disease, GM1 gangliosidosis, mucopolysaccharidosis types I, II, IIIC, IVA, VI, and VII, mucolipidosis type II, multiple sulfatase deficiency, and sialidosis type II. Each disorder produced a unique signature metabolic profile of protein, oligosaccharide, and glycolipid markers. Some metabolite elevations directly related to the disorder whilst others appeared unrelated to the primary defect. Many lysosomal storage disorders were clearly distinguishable from control populations by the second trimester and in one case in the first trimester. Samples from GM1 gangliosidosis and mucopolysaccharidosis type VII displayed a correlation between gestational age and amount of stored metabolite. These preliminary results provide proof of principal for the use of biomarkers contained in amniotic fluid as clinical tests for some of the more frequent lysosomal storage disorders causal for hydrops fetalis.