Quantitative Liquid Chromatography-mass Spectrometry Research Articles

Fast LC-MS quantitation of glucose and glycerol via enzymatic derivatization

Glucose and glycerol are important circulating metabolites. Due to poor ionization and/or ion suppression, the liquid chromatography-mass spectrometry (LC-MS) detection of glucose and glycerol presents challenges. Here, we propose an efficient LC-MS method of quantitative glucose and glycerol detection via enzymatic derivatization to glucose-6-phosphate and sn-glycerol-3-phosphate, respectively. This derivatization protocol can be used to measure the concentrations of glucose production in a plethora of sample types for metabolic analysis and is compatible with the general metabolomics workflow. This novel approach allows us to quantitatively study glucose and glycerol metabolism using stable isotope tracers in vivo.

Fractional laser-assisted topical delivery of bleomycin quantified by LC-MS and visualized by MALDI mass spectrometry imaging

Bleomycin exhibits antiproliferative effects desirable for use in dermato-oncology but topical use is limited by its 1415 Da molar mass. Ablative fractional laser (AFL)-assisted drug delivery has been shown to enhance drug uptake in skin. The aim of this study was with AFL to deliver bleomycin into skin, quantify uptake, and visualize biodistribution with mass spectrometry. In a Franz diffusion cell study, pig skin samples (n = 66) were treated with AFL (λ = 10,600 nm), 5% density, and 0, 5, 20, or 80 mJ/microbeam (mb) pulse energies before exposure to bleomycin for 0.5, 4, or 24 h. Bleomycin was quantified in biopsy cryosections at depths of 100, 500, and 1500 µm using high-performance liquid chromatography-mass spectrometry (LC-MS), and drug biodistribution was visualized for 80 mJ/mb samples by matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI). The pulse energies 5, 20, and 80 mJ/mb resulted in microscopic ablation zones (MAZs) reaching superficial, mid, and deep dermis respectively. Bleomycin was successfully delivered into the skin and deeper MAZs and longer exposure time resulted in higher skin concentrations. After 24 h, AFL exposure resulted in significant amounts of bleomycin throughout all skin layers (≥510 µg/cm3, p ≤ .002). In comparison, concentrations in intact skin exposed to bleomycin remained below limit of quantification. MALDI-MSI supported the quantitative LC-MS results by visualizing bleomycin biodistribution and revealing high uptake around MAZs with delivery into surrounding skin tissue. In conclusion, topical drug delivery of the large and hydrophilic molecule bleomycin is feasible, promising, and should be explored in an in vivo setting.

Quantitative LC-MS and MS/MS analysis of sialylated glycans modified by linkage-specific alkylamidation

Sialic acids (Sia) are involved in various biological and pathological processes, and are often found attached to non-reducing ends of glycans through either α2,3- or α2,6-linkages. To quantitatively analyze glycan structures with these linkage isoforms by liquid chromatography-mass spectrometry (LC-MS), we established a linkage-specific two-step alkylamidation method for N-glycans. Using this method, carboxyl groups of α2,3- and α2,6-linked Sia are derivatized with two kinds of alkylamines with different mass values in a linkage-specific manner, allowing products to be easily distinguished. The reaction efficiencies for di-, tri-, and tetra-sialyl PA-N-glycans were >94%, with few by-products. Mixtures of 2-aminopyridine (PA)-tagged N-glycans from human α1-acid glycoprotein were subjected to the method, and products were analyzed by LC-MS and MS/MS, and simultaneously monitored with a fluorescence detector. The relative content of Siaα2-3Gal and Siaα2-6Gal was estimated from the integrated fluorescence intensity of each peak. Moreover, MS/MS data clearly indicated characteristic B-ion fragments of N-glycan branches, such as the sialyl Lex sequence, with Sia linkage-specific alkylamidation, suggesting that this method also provides useful information of branch sequences. We optimized the method with the aim of (1) enabling high-throughput analysis and (2) maximizing the analysis of glycans from various types of samples, including highly heterogeneous glycans.

Urine inositol pentakisphosphate 2-kinase and changes in kidney structure in early diabetic kidney disease in type 1 diabetes.

We examined the association of urine inositol 1,3,4,5,6-pentakisphosphate 2-kinase (IPP2K) with the presence and progression of diabetic kidney disease (DKD) lesions. Urine IPP2K was measured at baseline by quantitative liquid chromatography-mass spectrometry in 215 participants from the Renin-Angiotensin System Study who had type 1 diabetes and were normoalbuminuric and normotensive with normal or increased glomerular filtration rate (GFR). Urine IPP2K was detectable in 166 participants. Participants with IPP2K below the limit of quantification (LOQ) were assigned concentrations of LOQ/√2. All concentrations were then standardized to urine creatinine (Cr) concentration. Kidney morphometric data were available from biopsies at baseline and after 5 yr. Relationships of IPP2K/Cr with morphometric variables were assessed by linear regression after adjustment for age, sex, diabetes duration, hemoglobin A1c, mean arterial pressure, treatment assignment, and, for longitudinal analyses, baseline structure. Baseline mean age was 29.7 yr, mean diabetes duration 11.2 yr, median albumin excretion rate 5.0 μg/min, and mean iohexol GFR 129 ml·min-1·1.73m-2. Higher IPP2K/Cr was associated with higher baseline peripheral glomerular total filtration surface density [Sv(PGBM/glom), tertile 3 vs. tertile 1 β = 0.527, P = 0.011] and with greater preservation of Sv(PGBM/glom) after 5 yr ( tertile 3 vs. tertile 1 β = 0.317, P = 0.013). Smaller increases in mesangial fractional volume ( tertile 3 vs. tertile 1 β = -0.578, P = 0.018) were observed after 5 yr in men with higher urine IPP2K/Cr concentrations. Higher urine IPP2K/Cr is associated with less severe kidney lesions at baseline and with preservation of kidney structure over 5 yr in individuals with type 1 diabetes and no clinical evidence of DKD at baseline.

Functional analysis of synovial fluid from osteoarthritic knee and carpometacarpal joints unravels different molecular profiles.

In this work, we aimed to elucidate the molecular mechanisms driving primary OA. By studying the dynamics of protein expression in two different types of OA joints we searched for similarities and disparities to identify key molecular mechanisms driving OA. For this purpose, human SF samples were obtained from CMC-I OA and knee joint of OA patients. SF samples were analysed by label-free quantitative liquid chromatography mass spectrometry. Disease-relevant proteins identified in proteomics studies, such as clusterin, paraoxonase/arylesterase 1 (PON1) and transthyretin were validated by enzyme-linked immunosorbent assays, and on the mRNA level by droplet digital PCR. Functional studies were performed in vitro using primary chondrocytes. Differential proteomic changes were observed in the concentration of 40 proteins including clusterin, PON1 and transthyretin. Immunoassay analyses of clusterin, PON1, transthyretin and other inflammatory cytokines confirmed significant differences in protein concentration in SF of CMC-I and knee OA patients, with primarily lower protein expression levels in CMC-I. Functional studies on chondrocytes unequivocally demonstrated that stimulation with SF obtained from knee OA, in contrast to CMC-I OA joint, caused a significant upregulation in pro-inflammatory response, cell death and hypertrophy. This study demonstrates that differential expression of molecular players in SF from different OA joints evokes diverse effects on primary chondrocytes. The pathomolecular mechanisms of OA may significantly differ in various joints, a finding that brings a new dimension into the pathogenesis of primary OA.

Protective Effect of a Locked Retinal Chromophore Analog against Light-Induced Retinal Degeneration.

Continuous regeneration of the 11-cis-retinal visual chromophore from all-trans-retinal is critical for vision. Insufficiency of 11-cis-retinal arising from the dysfunction of key proteins involved in its regeneration can impair retinal health, ultimately leading to loss of human sight. Delayed recovery of visual sensitivity and night blindness caused by inadequate regeneration of the visual pigment rhodopsin are typical early signs of this condition. Excessive concentrations of unliganded, constitutively active opsin and increased levels of all-trans-retinal and its byproducts in photoreceptors also accelerate retinal degeneration after light exposure. Exogenous 9-cis-retinal iso-chromophore can reduce the toxicity of ligand-free opsin but fails to prevent the buildup of retinoid photoproducts when their clearance is defective in human retinopathies, such as Stargardt disease or age-related macular degeneration. Here we evaluated the effect of a locked chromophore analog, 11-cis-6-membered ring-retinal against bright light-induced retinal degeneration in Abca4-/-Rdh8-/- mice. Using in vivo imaging techniques, optical coherence tomography, scanning laser ophthalmoscopy, and two-photon microscopy, along with in vitro histologic analysis of retinal morphology, we found that treatment with 11-cis-6-membered ring-retinal before light stimulation prevented rod and cone photoreceptor degradation and preserved functional acuity in these mice. Moreover, additive accumulation of 11-cis-6-membered ring-retinal measured in the eyes of these mice by quantitative liquid chromatography-mass spectrometry indicated stable binding of this retinoid to opsin. Together, these results suggest that eliminating excess of unliganded opsin can prevent light-induced retinal degeneration in Abca4-/-Rdh8-/- mice.

Mining the acidic serum proteome utilizing off-gel isoelectric focusing and label free quantitative liquid chromatography mass spectrometry

Serum remains an attractive source for the discovery of disease related biomarkers due to its intimate interaction with the majority of tissues within the body. The dynamic range of proteins present within serum has long complicated the ability to detect low level tissue leakage proteins that offer more promise as potential biomarkers due to their higher degree of specificity. Depletion strategies, using affinity based sorbents, to remove the most abundant serum proteins are routinely used for matrix simplification during discovery strategies focused on the serum proteome or glycoproteome. Glycoproteins bearing glycans with terminal sialic acid residues have been shown to be differentially expressed in a variety of cancers and are of interest due to the varied involvement of sialic acid in biological functions related to cancer development and metastasis. Herein, we describe the use of 14P serum depletion with subsequent off-gel isoelectric focusing using narrow pH range acidic strips, to facilitate simplification and enrichment of the acidic proteome and glycoproteome prior to label free liquid chromatography mass spectrometry (LC–MS) based proteomic analysis. The developed platform enabled the detection of proteins present within serum at sub-nanomolar concentrations while data analysis using a variety of bioinformatics resources suggested that many of the detected proteins were tissue leakage proteins or proteins associated with specific cellular compartments, rather than traditional secreted proteins. Comparison with theoretical isoelectric point (pI) values also revealed that some detected proteins had higher pI values than the separation range applied during the IEF step, suggesting that their presence may be due to glycans with high degrees of sialylation being attached to the protein backbone, as well as the presence of other post translational modifications. Such findings agree with offline glycomic profiling of the IEF fractions wherein increasing degrees of sialylation were detected across the pH strip from the basic towards the acidic end. Application of the platform using pooled serum from patients bearing gastric cancer, both before and after surgical intervention for tumour removal, revealed a number of differentially expressed proteins associated with cell recognition and cell signalling. The developed platform enabled excellent sensitivity and offers strong potential for application within biomarker discovery studies focused on the acidic proteome.

Endocannabinoid system in systemic lupus erythematosus: First evidence for a deranged 2-arachidonoylglycerol metabolism.

The endocannabinoid (eCB) system plays a key role in many physiological and pathological conditions and its dysregulation has been described in several rheumatological and autoimmune diseases. Yet, its possible alteration in systemic lupus erythematosus (SLE) has never been investigated. Here, we aimed filling this gap in plasma and peripheral blood mononuclear cells (PBMCs) of patients with SLE and age- and sex- matched healthy subjects (HS). Liquid chromatography-mass spectrometry quantitation of eCB levels highlighted that plasma levels of 2-arachidonoylglycerol (2-AG) were significantly increased in SLE patients compared to HS (p = 0.0059), and among SLE patients, highest 2-AG levels were associated with a lower disease activity. No differences were found in N-arachidonoylethanolamine (AEA) and its congeners N-palmitoylethanolamine (PEA) and N-oleoylethanolamine (OEA) concentrations between the two groups. Moreover, gene expression analysis of metabolic enzymes and receptor targets of eCBs and investigation of functional activity and protein expression of selected components of eCB system disclosed a deranged 2-AG metabolism in patients with SLE. Indeed, expression and functional activity of 2-AG biosynthetic enzyme DAGL were selectively enhanced in PBMCs of SLE patients compared to HS. In conclusion, our results demonstrate, for the first time, an alteration of eCB system in SLE patients. They represents the first step toward the understanding of the role of eCB system in SLE that likely suggest DAGL and 2-AG as potential biomarkers of SLE in easily accessible blood samples. Our data provides proof-of-concept to the development of cannabis-based medicine as immune-modulating agents.

Data Generated by Quantitative Liquid Chromatography-Mass Spectrometry Proteomics Are Only the Start and Not the Endpoint: Optimization of Quantitative Concatemer-Based Measurement of Hepatic Uridine-5'-Diphosphate-Glucuronosyltransferase Enzymes with Reference to Catalytic Activity.

Quantitative proteomic methods require optimization at several stages, including sample preparation, liquid chromatography-tandem mass spectrometry (LC-MS/MS), and data analysis, with the final analysis stage being less widely appreciated by end-users. Previously reported measurement of eight uridine-5'-diphospho-glucuronosyltransferases (UGT) generated by two laboratories [using stable isotope-labeled (SIL) peptides or quantitative concatemer (QconCAT)] reflected significant disparity between proteomic methods. Initial analysis of QconCAT data showed lack of correlation with catalytic activity for several UGTs (1A4, 1A6, 1A9, 2B15) and moderate correlations for UGTs 1A1, 1A3, and 2B7 (Rs = 0.40-0.79, P < 0.05; R2 = 0.30); good correlations were demonstrated between cytochrome P450 activities and abundances measured in the same experiments. Consequently, a systematic review of data analysis, starting from unprocessed LC-MS/MS data, was undertaken, with the aim of improving accuracy, defined by correlation against activity. Three main criteria were found to be important: choice of monitored peptides and fragments, correction for isotope-label incorporation, and abundance normalization using fractional protein mass. Upon optimization, abundance-activity correlations improved significantly for six UGTs (Rs = 0.53-0.87, P < 0.01; R2 = 0.48-0.73); UGT1A9 showed moderate correlation (Rs = 0.47, P = 0.02; R2 = 0.34). No spurious abundance-activity relationships were identified. However, methods remained suboptimal for UGT1A3 and UGT1A9; here hydrophobicity of standard peptides is believed to be limiting. This commentary provides a detailed data analysis strategy and indicates, using examples, the significance of systematic data processing following acquisition. The proposed strategy offers significant improvement on existing guidelines applicable to clinically relevant proteins quantified using QconCAT.

Honeybees Tolerate Cyanogenic Glucosides from Clover Nectar and Flowers.

Honeybees (Apis mellifera) pollinate flowers and collect nectar from many important crops. White clover (Trifolium repens) is widely grown as a temperate forage crop, and requires honeybee pollination for seed set. In this study, using a quantitative LC-MS (Liquid Chromatography-Mass Spectrometry) assay, we show that the cyanogenic glucosides linamarin and lotaustralin are present in the leaves, sepals, petals, anthers, and nectar of T. repens. Cyanogenic glucosides are generally thought to be defense compounds, releasing toxic hydrogen cyanide upon degradation. However, increasing evidence indicates that plant secondary metabolites found in nectar may protect pollinators from disease or predators. In a laboratory survival study with chronic feeding of secondary metabolites, we show that honeybees can ingest the cyanogenic glucosides linamarin and amygdalin at naturally occurring concentrations with no ill effects, even though they have enzyme activity towards degradation of cyanogenic glucosides. This suggests that honeybees can ingest and tolerate cyanogenic glucosides from flower nectar. Honeybees retain only a portion of ingested cyanogenic glucosides. Whether they detoxify the rest using rhodanese or deposit them in the hive should be the focus of further research.

Matrix-effect free quantitative liquid chromatography mass spectrometry analysis in complex matrices using nanoflow liquid chromatography with integrated emitter tip and high dilution factors

Matrix effects are probably the Achilles heel of most quantitative liquid chromatography mass spectrometry (LC–MS) methods based on electrospray ionization. This work reports the evaluation of matrix effects in challenging matrices such as food extracts, human urine or wastewater at different dilution factors using nanoflow liquid chromatography-high resolution mass spectrometry (LC–MS). For this purpose, a suite of representative low-molecular weight compounds such as pesticides, drugs of abuse, sport drugs or environmental contaminants were selected. The approach is based on the use of reversed-phase C18 nano columns furnished with an integrated emitter tip. The nanoflow LC system was combined with full-scan high resolution mass spectrometry using a HRMS (orbitrap) instrument operated at a resolution of 70000. The sensitivity achieved with this configuration enables the implementation of high dilution factors (e.g. 1:20, 1:50 or beyond). When combining nanoflow LC–MS analysis with such high dilution factors (e.g. 1:50), signal suppression was negligible in most cases, so that matrix-matched standards may eventually be skipped, simplifying laboratory workflows by using external calibration in demanding applications such as drug analysis in urine, environmental contaminants in wastewater or pesticide testing in food, thus, eliminating the need for standard addition, matrix-matched calibration or isotopically-labelled standards.

Abstract 2622: A LC-MS/MS method to quantify specific dietary isothiocyanates in human urine for epidemiological studies

Abstract Epidemiological studies have demonstrated an inverse relationship between the intake of cruciferous vegetables and risk of cancers. The protective effects may be attributed to glucosinolates and glucobrassicins in these vegetables. While glucosinolates and glucobrassicins are not chemopreventive, their metabolites, isothiocyanates (ITCs), indole-3-carbinol (I3C), and 3,3′-diindolylmethane (DIM), have been shown to inhibit tumorigenesis in rodent models. In the past studies the total ITCs intake was estimated through food frequency questionnaires and/or urinary total ITC by a HPLC-based method. Self-reported intake of cruciferous vegetables has inherent limitations in estimating the intake of ITCs because of differences in the contents of their precursors present in different kinds of cruciferous vegetables, different locations and methods of cultivation, or different methods of food preparation. Animal and cell culture studies have shown that different types of ITCs have different anticancer properties and potency, suggesting that they are not equal in protecting against the development of cancers. The lack of a reliable method to quantify specific ITCs derived from dietary intake of cruciferous vegetables hinders the investigation of the role of specific ITCs against the development of cancer in human populations. To address this deficiency, we developed a flexible, highly sensitive, fast and reliable quantitative liquid chromatography mass spectrometry method (LC-MS/MS) for detecting and quantifying common dietary ITCs plus DIM in human urine. Urinary ITCs are measured as mercapturic acid conjugates (ITCs-NAC), predominant metabolite of ITCs, using multiple reaction monitoring (MRM) technique and deuterated [2H3]-ITCs-NAC as internal standards. DIM is quantified in separate experiment using [2H2]-DIM internal standard. The method was validated by a small set of previously analyzed samples from Singapore Chinese Health Study. We found an excellent correlation between previously reported total ITCs levels and sum of ITCs detected by newly developed method. The combination of minimal sample preparation, ultra-performance liquid chromatography, and highly sensitive mass spectrometer resulted in a method that is fast (below 10 min for ITCs and 12 min for DIM) and sensitive (low femtomolar LOQ) amenable to population studies. Citation Format: Marcin Dyba, Jian-Min Yuan, Jennifer Adams-Haduch, Fung-Lung Chung. A LC-MS/MS method to quantify specific dietary isothiocyanates in human urine for epidemiological studies. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2622.

Abstract 3530: Hsp90-Tom70 interaction facilitates ATM localization to mitochondria and induces mitochondrial autophagy

Abstract The serine/threonine protein kinase Ataxia telangiectasia mutated (ATM), plays a critical role in DNA damage response specifically to agents that induce DNA double strand breaks. Recently, mitochondrial autophagy (mitophagy)-associated non-nuclear functions have been attributed to ATM in AT fibroblast (Valentin-Vega YA et al., Blood 119: 1490; 2012). Our investigations suggested similar role of ATM in mantle cell lymphoma (MCL) cell lines (Sarkar, A et al., Proc. AACR, 74: Abstract # 313; 2014). This is clinically important, since ATM is lost in &amp;gt;50% of primary malignant B-cells in MCL patients. To identify the role of ATM in mitophagy, using MCL cell lines, we established that a fraction of ATM protein is located within mitochondria. The proportion of mitochondrial ATM increases following mitophagy induced by mitochondrial uncoupler CCCP or FCCP in ATM proficient cell lines. This process is compromised in MCL cells lacking ATM. However how ATM enters mitochondria is not known. Using quantitative liquid chromatography mass spectrometry analysis (LC/MS), we identified new ATM interacting proteins in HEK293 cells that facilitate mitochondrial transport of ATM. These new ATM interacting proteins (Hsp90, Hsp70 and the outer mitochondrial translocation (TOM) complex, including Tom70) are unrelated to DNA damage response. The physical association of ATM with Hsp90 and Tom70 was confirmed by co-immunoprecipitation experiments while ATM-Hsp70 interaction was mostly nonspecific. Additionally, using kinase dead FLAG-ATM construct in HEK293 cells or pharmacologic (KU55933) inhibition of ATM kinase activity in ATM proficient Jeko-1 and Mino MCL cell lines, we demonstrate that ATM phosphorylation is dispensable to enforce mitophagic exclusion of nonfunctional mitochondria since non-phosphorylated ATM can still bound to Hsp90 and induce mitophagy. These MCL cell lines when treated with an Hsp90 inhibitor; 17-AAG either alone or in combination with CCCP; abolished mitochondrial ATM localization and are defective in CCCP-induced mitochondrial clearance suggesting extra-mitochondrial ATM enters mitochondria via Hsp90 interaction. Further analysis revealed ATM-Hsp90 loosely associate with outer mitochondrial import receptor Tom70 via Hsp90 interaction and this targeting preference between Hsp90-Tom70 is abolished following deletion of the cytosolic tricopeptide repeat (TPR) clamp domain of Tom70 entailing that ATM-Hsp90-Tom70 complex may be required for ATM entry inside mitochondria. Moreover, trypsin digested purified mitochondrial fraction from HeLa cells revealed the entry of C terminal ATM protein within mitochondria while N terminal part remained in the cytosolic fraction. The molecular model of ATM's role in mitophagy and its biological consequence in ATM deficient MCL will be discussed. Citation Format: Aloke K. Sarkar, Tej K. Pandita, Varsha Gandhi. Hsp90-Tom70 interaction facilitates ATM localization to mitochondria and induces mitochondrial autophagy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3530.

Generalized multiple internal standard method for quantitative liquid chromatography mass spectrometry

In this contribution, a multiplicative effects model for generalized multiple-internal-standard method (MEMGMIS) was proposed to solve the signal instability problem of LC–MS over time. MEMGMIS model seamlessly integrates the multiple-internal-standard strategy with multivariate calibration method, and takes full use of all the information carried by multiple internal standards during the quantification of target analytes. Unlike the existing methods based on multiple internal standards, MEMGMIS does not require selecting an optimal internal standard for the quantification of a specific analyte from multiple internal standards used. MEMGMIS was applied to a proof-of-concept model system: the simultaneous quantitative analysis of five edible artificial colorants in two kinds of cocktail drinks. Experimental results demonstrated that MEMGMIS models established on LC–MS data of calibration samples prepared with ultrapure water could provide quite satisfactory concentration predictions for colorants in cocktail samples from their LC–MS data measured 10days after the LC–MS analysis of the calibration samples. The average relative prediction errors of MEMGMIS models did not exceed 6.0%, considerably better than the corresponding values of commonly used univariate calibration models combined with multiple internal standards. The advantages of good performance and simple implementation render MEMGMIS model a promising alternative tool in quantitative LC–MS assays.

Validation of the Mass-Extraction-Window for Quantitative Methods Using Liquid Chromatography High Resolution Mass Spectrometry.

A paradigm shift is underway in the field of quantitative liquid chromatography-mass spectrometry (LC-MS) analysis thanks to the arrival of recent high-resolution mass spectrometers (HRMS). The capability of HRMS to perform sensitive and reliable quantifications of a large variety of analytes in HR-full scan mode is showing that it is now realistic to perform quantitative and qualitative analysis with the same instrument. Moreover, HR-full scan acquisition offers a global view of sample extracts and allows retrospective investigations as virtually all ionized compounds are detected with a high sensitivity. In time, the versatility of HRMS together with the increasing need for relative quantification of hundreds of endogenous metabolites should promote a shift from triple-quadrupole MS to HRMS. However, a current "pitfall" in quantitative LC-HRMS analysis is the lack of HRMS-specific guidance for validated quantitative analyses. Indeed, false positive and false negative HRMS detections are rare, albeit possible, if inadequate parameters are used. Here, we investigated two key parameters for the validation of LC-HRMS quantitative analyses: the mass accuracy (MA) and the mass-extraction-window (MEW) that is used to construct the extracted-ion-chromatograms. We propose MA-parameters, graphs, and equations to calculate rational MEW width for the validation of quantitative LC-HRMS methods. MA measurements were performed on four different LC-HRMS platforms. Experimentally determined MEW values ranged between 5.6 and 16.5 ppm and depended on the HRMS platform, its working environment, the calibration procedure, and the analyte considered. The proposed procedure provides a fit-for-purpose MEW determination and prevents false detections.

The Proteome of Native Adult Müller Glial Cells From Murine Retina

To date, the proteomic profiling of Müller cells, the dominant macroglia of the retina, has been hampered because of the absence of suitable enrichment methods. We established a novel protocol to isolate native, intact Müller cells from adult murine retinae at excellent purity which retain in situ morphology and are well suited for proteomic analyses. Two different strategies of sample preparation - an in StageTips (iST) and a subcellular fractionation approach including cell surface protein profiling were used for quantitative liquid chromatography-mass spectrometry (LC-MSMS) comparing Müller cell-enriched to depleted neuronal fractions. Pathway enrichment analyses on both data sets enabled us to identify Müller cell-specific functions which included focal adhesion kinase signaling, signal transduction mediated by calcium as second messenger, transmembrane neurotransmitter transport and antioxidant activity. Pathways associated with RNA processing, cellular respiration and phototransduction were enriched in the neuronal subpopulation. Proteomic results were validated for selected Müller cell genes by quantitative real time PCR, confirming the high expression levels of numerous members of the angiogenic and anti-inflammatory annexins and antioxidant enzymes (e.g. paraoxonase 2, peroxiredoxin 1, 4 and 6). Finally, the significant enrichment of antioxidant proteins in Müller cells was confirmed by measurements on vital retinal cells using the oxidative stress indicator CM-H2DCFDA. In contrast to photoreceptors or bipolar cells, Müller cells were most efficiently protected against H2O2-induced reactive oxygen species formation, which is in line with the protein repertoire identified in the proteomic profiling. Our novel approach to isolate intact glial cells from adult retina in combination with proteomic profiling enabled the identification of novel Müller glia specific proteins, which were validated as markers and for their functional impact in glial physiology. This provides the basis to allow the discovery of novel glial specializations and will enable us to elucidate the role of Müller cells in retinal pathologies — a topic still controversially discussed.

Facile synthesis of deuterium-labeled denatonium cation and its application in the quantitative analysis of Bitrex by liquid chromatography-mass spectrometry.

Quantitative analysis by liquid chromatography-mass spectrometry (LC-MS) is frequently based on the application of isotopically labeled standards which usually have to be specially synthesized. Although the synthesis of deuterated isotopologues is relatively inexpensive, they are not considered as good internal standards due to the possible deuterium effect on the retention time during LC-MS analysis. We developed a method of deuterium labeling of denatonium benzoate (Bitrex) via H/D exchange of its α-carbon hydrogen atoms in CH2 group situated between carbonyl and quaternary ammonium groups. The proposed strategy is rapid, cost-efficient, and does not require derivatization reagents or further purification. The LC-MS analysis of isotopologues revealed that the introduced deuterons do not undergo back exchange under acidic conditions, and the co-elution of deuterated and non-deuterated forms is observed. The obtained deuterated standard was applied in the quantitative LC-MS analysis of Bitrex in commercially available household products.Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-015-8815-y) contains supplementary material, which is available to authorized users.

Functional assessment of antibody oxidation by native mass spectrometry

Oxidation of methionine (Met) residues is one of several chemical degradation pathways for recombinant IgG1 antibodies. Studies using several methodologies have indicated that Met oxidation in the constant IgG1 domains affects in vitro interaction with human neonatal Fc (huFcRn) receptor, which is important for antibody half-life. Here, a completely new approach to investigating the effect of oxidative stress conditions has been applied. Quantitative ultra-performance liquid chromatography mass spectrometry (MS) peptide mapping, classical surface plasmon resonance and the recently developed FcRn column chromatography were combined with the new fast-growing approach of native MS as a near native state protein complex analysis in solution. Optimized mass spectrometric voltage and pressure conditions were applied to stabilize antibody/huFcRn receptor complexes in the gas phase for subsequent native MS experiments with oxidized IgG1 material. This approach demonstrated a linear correlation between quantitative native MS and IgG-FcRn functional analysis.In our study, oxidation of the heavy chain Met-265 resulted in a stepwise reduction of mAb3/huFcRn receptor complex formation. Remarkably, a quantitative effect of the heavy chain Met-265 oxidation on relative binding capacity was only detected for doubly oxidized IgG1, whereas IgG1 with only one oxidized heavy chain Met-265 was not found to significantly affect IgG1 binding to huFcRn. Thus, mono-oxidized IgG1 heavy chain Met-265 most likely does not represent a critical quality attribute for pharmacokinetics.

Absolute and Multiplex Quantification of Antibodies in Serum Using Psaq™ Standards and LC-MS/MS

In preclinical studies, monoclonal antibodies (mAbs) are traditionally assayed by ligand-binding-assays. Recently, quantitative liquid chromatography mass spectrometry (MS)-based assays have emerged which circumvent a number of challenges. These assays may also be multiplex, making them potentially compatible with pharmacokinetic assays for combined antibody therapies. We combined a quantitative MS-based approach with the protein standard for absolute quantification (PSAQ™) strategy to simultaneously quantify three mAb variants presenting minor sequence differences. Stable isotopically labeled mAbs were produced and used as quantification standards. Titration curves were performed to assess the analytical performances of the method. LC-MS/MS and ELISA data were cross-compared. The approach presented provides similar accuracy and precision than ELISA, while being multiplex and faster to develop. It has applications at all stages of the pharmaceutical development.

Evaluation of the Impact of Sulfobutylether7-β-Cydodextrin on the Liquid Chromatography-Mass spectrometry Analysis of Biological Samples Arising from In Vivo Pharmacokinetic Studies

The utility of cyclodextrin (CD) complexation in improving apparent solubility of drugs in parenteral formulations is well established. Administration of these formulations delivers CD directly into the systemic circulation, and it may be necessary to demonstrate unaltered in vivo disposition of a drug coadministered with a CD. Crucial to the undertaking of such a study is the need for bioanalytical assays in which CD presence does not impact drug quantitation. This is of particular importance when assessing the potential impact of in vivo CD complexation on the urinary excretion of a drug, as CDs are predominantly eliminated via glomerular filtration, and hence are present in urine at significantly higher concentration than would be present in blood and plasma. Of 23 publications (in the past 30 years) describing preclinical and clinical assessment of drug pharmacokinetics after i.v. administration of CD-enabled formulations, only two reports clearly stated that the presence of CD had no impact on assay performance. In this work, we describe the simple process involved in (1) predicting the maximum concentrations of a modified CD, sulfobutylether7 -β-CD (SBE7 -β-CD), in plasma and urine samples from preclinical studies, and (2) evaluating the impact of SBE7 -β-CD on the quantitative liquid chromatography-mass spectrometry analysis of rimantadine.