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The article discusses a study in which samples of bronchoalveolar-lavage (BAL) fluid from 51 patients with vaping, product use-associated lung injury (EVALI) were analyzed. It is suggested that vitamin E acetate may play a role in the cause of EVALI. Topics mentioned include analytic limit of detection (LOD) and tetrahydrocannabinol (THC) biomarkers.

Background: Lipid profiling is central for coronary artery disease (CAD) risk assessment. Nonadherence or unreported use of lipid-lowering drugs, particularly statins, can significantly complicate the association between lipid profile measures and CAD clinical outcomes. By combining medication history evaluation with statin analysis in plasma, we determined the effects of inaccurately reported statin use on lipid profile measures and their association with CAD risk., Methods: We compared medication history of statin use with statin concentration measurements, by liquid chromatography-tandem mass spectrometry, in 690 participants undergoing coronary angiography (63 ± 11 years of age). Nominal logistic regression was employed to model CAD diagnosis with statin measurements, phenotypic, and lipid profile characteristics., Results: Medication history of statin use was confirmed by statin assay for 81% of the patients. Surprisingly, statins were detected in 46% of patients without statin use records. Nonreported statin use was disproportionately higher among older participants. Stratifying samples by statin history resulted in underestimated LDL-lipid measures. Apolipoprotein B concentrations had a significant inverse CAD association, which became nonsignificant upon re-stratification using the statin assay data., Conclusions: Our study uncovered prominent discrepancies between medication records and actual statin use measured by mass spectrometry. We showed that inaccurate statin use assessments may lead to overestimation and underestimation of LDL levels in statin user and nonuser categories, exaggerating the reverse epidemiology association between LDL levels and CAD diagnosis. Combining medication history and quantitative statin assay data can significantly improve the design, analysis, and interpretation of clinical and epidemiological studies., (© Association for Diagnostics & Laboratory Medicine 2024.)

Designing studies for lipid-metabolism-related biomarker discovery is challenging because of the high prevalence of various statin and fibrate usage for lipid-lowering therapies. When the statin and fibrate use is determined based on self-reports, patient adherence to the prescribed statin dose regimen remains unknown. A potentially more accurate way to verify a patient's medication adherence is by direct analytical measurements. Current analytical methods are prohibitive because of the limited panel of drugs per test and large sample volume requirement that is not available from archived samples. A 4-min-long method was developed for the detection of seven statins and three fibrates using 10 µL of plasma analyzed via reverse-phase liquid chromatography and tandem mass spectrometry. The method was applied to the analysis of 941 archived plasma samples collected from patients before cardiac catheterization. When statin use was self-reported, statins were detected in 78.6% of the samples. In the case of self-reported atorvastatin use, the agreement with detection was 90.2%. However, when no statin use was reported, 42.4% of the samples had detectable levels of statins, with a similar range of concentrations as the samples from the self-reported statin users. The method is highly applicable in population studies designed for biomarker discovery or diet and lifestyle intervention studies, where the accuracy of statin or fibrate use may strongly affect the statistical evaluation of the biomarker data.

Background: Medical results generated by European CE Marking for In Vitro Diagnostic or in-house tests should be traceable to higher order reference measurement systems (RMS), such as International Federation of Clinical Chemistry and Laboratory Medicine (IFCC)-endorsed reference measurement procedures (RMPs) and reference materials. Currently, serum apolipoprotein (a) [apo(a)] is recognized as a novel risk factor for cardiovascular risk assessment and patient management. The former RMS for serum apo(a) is no longer available; consequently, an International System of Units (SI)-traceable, ideally multiplexed, and sustainable RMS for apo(a) is needed., Methods: A mass spectrometry (MS)-based candidate RMP (cRMP) for apo(a) was developed using quantitative bottom-up proteomics targeting 3 proteotypic peptides. The method was provisionally validated according to ISO 15193 using a single human serum based calibrator traceable to the former WHO-IFCC RMS., Results: The quantitation of serum apo(a) was by design independent of its size polymorphism, was linear from 3.8 to 456 nmol/L, and had a lower limit of quantitation for apo(a) of 3.8 nmol/L using peptide LFLEPTQADIALLK. Interpeptide agreement showed Pearson Rs of 0.987 and 0.984 for peptides GISSTVTGR and TPENYPNAGLTR, and method comparison indicated good correspondence (slopes 0.977, 1.033, and 1.085 for LFLEPTQADIALLK, GISSTVTGR, and TPENYPNAGLTR). Average within-laboratory imprecision of the cRMP was 8.9%, 11.9%, and 12.8% for the 3 peptides., Conclusions: A robust, antibody-independent, MS-based cRMP was developed as higher order RMP and an essential part of the apo(a) traceability chain and future RMS. The cRMP fulfils predefined analytical performance specifications, making it a promising RMP candidate in an SI-traceable MS-based RMS for apo(a)., (©American Association for Clinical Chemistry 2023.)

We propose the hypothesis that small high-density lipoprotein (HDL) particles reduce the risk of Alzheimer's disease (AD) by virtue of their capacity to exchange lipids, affecting neuronal membrane composition and vascular and synaptic functions. Concentrations of small HDLs in cerebrospinal fluid (CSF) and plasma were measured in 180 individuals ≥60 years of age using ion mobility methodology. Small HDL concentrations in CSF were positively associated with performance in three domains of cognitive function independent of apolipoprotein E (APOE) ε4 status, age, sex, and years of education. Moreover, there was a significant correlation between levels of small HDLs in CSF and plasma. Further studies will be aimed at determining whether specific components of small HDL exchange across the blood, brain, and CSF barriers, and developing approaches to exploit small HDLs for therapeutic purposes., (© 2022 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)

Background: Genetic variants in apolipoprotein L1 (APOL1), a protein that protects humans from infection with African trypanosomes, explain a substantial proportion of the excess risk of chronic kidney disease affecting individuals with sub-Saharan ancestry. The mechanisms by which risk variants damage kidney cells remain incompletely understood. In preclinical models, APOL1 expressed in podocytes can lead to significant kidney injury. In humans, studies in kidney transplant suggest that the effects of APOL1 variants are predominantly driven by donor genotype. Less attention has been paid to a possible role for circulating APOL1 in kidney injury., Methods: Using liquid chromatography-tandem mass spectrometry, the concentrations of APOL1 were measured in plasma and urine from participants in the Seattle Kidney Study. Asymmetric flow field-flow fractionation was used to evaluate the size of APOL1-containing lipoprotein particles in plasma. Transgenic mice that express wild-type or risk variant APOL1 from an albumin promoter were treated to cause kidney injury and evaluated for renal disease and pathology., Results: In human participants, urine concentrations of APOL1 were correlated with plasma concentrations and reduced kidney function. Risk variant APOL1 was enriched in larger particles. In mice, circulating risk variant APOL1-G1 promoted kidney damage and reduced podocyte density without renal expression of APOL1., Conclusions: These results suggest that plasma APOL1 is dynamic and contributes to the progression of kidney disease in humans, which may have implications for treatment of APOL1-associated kidney disease and for kidney transplantation., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: We appreciate receiving BAC/APOL1 mice from Merck, Kenilworth, NJ. We appreciate receiving APOL1 antibodies from Genentech, South San Francisco, CA. Dr. Ian de Boer reports consulting fees from AstraZeneca, Bayer, Boehringer-Ingelheim, Cyclerion Therapeutics, George Clinical, Gilead, Goldfinch Bio, and Ironwood. This does not alter our adherence to PLOS ONE policies on sharing data and materials. Interested researchers are able to obtain BAC/APOL1 mice from Merck (contact is Lisa Gentile), APOL1 antibodies from Genentech (contact is Suzie Scales, PhD), and Alb/APOL1 transgenic mice from NIDDK, NIH (contact is Jeffrey Kopp, MD), under an appropriate material transfer agreement.

Aberrations in lipid and lipoprotein metabolic pathways can lead to numerous diseases, including cardiovascular disease, diabetes, neurological disorders, and cancer. The integration of quantitative lipid and lipoprotein profiling of human plasma may provide a powerful approach to inform early disease diagnosis and prevention. In this study, we leveraged data-driven quantitative targeted lipidomics and proteomics to identify specific molecular changes associated with different metabolic risk categories, including hyperlipidemic, hypercholesterolemic, hypertriglyceridemic, hyperglycemic, and normolipidemic conditions. Based on the quantitative characterization of serum samples from 146 individuals, we have determined individual lipid species and proteins that were significantly up- or down-regulated relative to the normolipidemic group. Then, we established protein-lipid topological networks for each metabolic category and linked dysregulated proteins and lipids with defined metabolic pathways. To evaluate the differentiating power of integrated lipidomics and proteomics data, we have built an artificial neural network model that simultaneously and accurately categorized the samples from each metabolic risk category based on the determined lipidomics and proteomics profiles. Together, our findings provide new insights into molecular changes associated with metabolic risk conditions, suggest new condition-specific associations between apolipoproteins and lipids, and may inform new biomarker discovery in lipid metabolism-associated disorders.

Background: Inducing brain ATP-binding cassette 1 (ABCA1) activity in Alzheimer's disease (AD) mouse models is associated with improvement in AD pathology. The purpose of this study was to investigate the effects of the ABCA1 agonist peptide CS-6253 on amyloid-β peptides (Aβ) and lipoproteins in plasma and cerebrospinal fluid (CSF) of cynomolgus monkeys, a species with amyloid and lipoprotein metabolism similar to humans., Methods: CS-6253 peptide was injected intravenously into cynomolgus monkeys at various doses in three different studies. Plasma and CSF samples were collected at several time points before and after treatment. Levels of cholesterol, triglyceride (TG), lipoprotein particles, apolipoproteins, and Aβ were measured using ELISA, ion-mobility analysis, and asymmetric-flow field-flow fractionation (AF4). The relationship between the change in levels of these biomarkers was analyzed using multiple linear regression models and linear mixed-effects models., Results: Following CS-6253 intravenous injection, within minutes, small plasma high-density lipoprotein (HDL) particles were increased. In two independent experiments, plasma TG, apolipoprotein E (apoE), and Aβ42/40 ratio were transiently increased following CS-6253 intravenous injection. This change was associated with a non-significant decrease in CSF Aβ42. Both plasma total cholesterol and HDL-cholesterol levels were reduced following treatment. AF4 fractionation revealed that CS-6253 treatment displaced apoE from HDL to intermediate-density- and low density-lipoprotein (IDL/LDL)-sized particles in plasma. In contrast to plasma, CS-6253 had no effect on the assessed CSF apolipoproteins or lipids., Conclusions: Treatment with the ABCA1 agonist CS-6253 appears to favor Aβ clearance from the brain., (© 2022. The Author(s).)

Large epidemiological studies often require sample transportation and storage, presenting unique considerations when applying advanced lipidomics techniques. The goal of this study was to acquire lipidomics data on plasma and serum samples stored at potential preanalytical conditions (e.g., thawing, extracting, evaporating), systematically monitoring lipid species for a period of one month. Split aliquots of 10 plasma samples and 10 serum samples from healthy individuals were kept in three temperature-related environments: refrigerator, laboratory benchtop, or heated incubator. Samples were analyzed at six different time points over 28 days using a Bligh & Dyer lipid extraction protocol followed by direct infusion into a lipidomics platform using differential mobility with tandem mass spectrometry. The observed concentration changes over time were evaluated relative to method and inter-individual biological variability. In addition, to evaluate the effect of lipase enzyme levels on concentration changes during storage, we compared corresponding fasting and post-prandial plasma samples collected from 5 individuals. Based on our data, a series of low abundance free fatty acid (FFA), diacylglycerol (DAG), and cholesteryl ester (CE) species were identified as potential analytical markers for degradation. These FFA and DAG species are typically produced by endogenous lipases from numerous triacylglycerols (TAGs), and certain high abundance phosphatidylcholines (PCs). The low concentration CEs, which appeared to increase several fold, were likely mass-isobars from oxidation of other high concentration CEs. Although the concentration changes of the high abundant TAG, PC, and CE precursors remained within method variability, the concentration trends of FFA, DAG, and oxidized CE products should be systematically monitored over time to inform analysts about possible pre-analytical biases due to degradation in the study sample sets., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Human high-density lipoproteins (HDLs) are a complex mixture of structurally related nanoparticles that perform distinct physiological functions. We previously showed that human HDL containing apolipoprotein A-I (APOA1) but not apolipoprotein A-II (APOA2), designated LpA-I, is composed primarily of two discretely sized populations. Here, we isolated these particles directly from human plasma by antibody affinity chromatography, separated them by high-resolution size-exclusion chromatography and performed a deep molecular characterization of each species. The large and small LpA-I populations were spherical with mean diameters of 109 Å and 91 Å, respectively. Unexpectedly, isotope dilution MS/MS with [ 15 N]-APOA1 in concert with quantitation of particle concentration by calibrated ion mobility analysis demonstrated that the large particles contained fewer APOA1 molecules than the small particles; the stoichiometries were 3.0 and 3.7 molecules of APOA1 per particle, respectively. MS/MS experiments showed that the protein cargo of large LpA-I particles was more diverse. Human HDL and isolated particles containing both APOA1 and APOA2 exhibit a much wider range and variation of particle sizes than LpA-I, indicating that APOA2 is likely the major contributor to HDL size heterogeneity. We propose a ratchet model based on the trefoil structure of APOA1 whereby the helical cage maintaining particle structure has two "settings"-large and small-that accounts for these findings. This understanding of the determinants of HDL particle size and protein cargo distribution serves as a basis for determining the roles of HDL subpopulations in metabolism and disease states., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The composition-function relationship of HDL particles and its effects on the mechanisms driving coronary heart disease (CHD) is poorly understood. We tested the hypothesis that the functionality of HDL particles is significantly influenced by their lipid composition. Using a novel 3D-separation method, we isolated five different-sized HDL subpopulations from CHD patients who had low preβ-1 functionality (low-F) (ABCA1-dependent cholesterol-efflux normalized for preβ-1 concentration) and controls who had either low-F or high preβ-1 functionality (high-F). Molecular numbers of apoA-I, apoA-II, and eight major lipid classes were determined in each subpopulation by LC-MS. The average number of lipid molecules decreased from 422 in the large spherical α-1 particles to 57 in the small discoid preβ-1 particles. With decreasing particle size, the relative concentration of free cholesterol (FC) decreased in α-mobility but not in preβ-1 particles. Preβ-1 particles contained more lipids than predicted; 30% of which were neutral lipids (cholesteryl ester and triglyceride), indicating that these particles were mainly remodeled from larger particles not newly synthesized. There were significant correlations between HDL-particle functionality and the concentrations of several lipids. Unexpectedly, the phospholipid:FC ratio was significantly correlated with large-HDL-particle functionality but not with preβ-1 functionality. There was significant positive correlation between particle functionality and total lipids in high-F controls, indicating that the lipid-binding capacity of apoA-I plays a major role in the cholesterol efflux capacity of HDL particles. Functionality and lipid composition of HDL particles are significantly correlated and probably both are influenced by the lipid-binding capacity of apoA-I.

CDC, the Food and Drug Administration (FDA), state and local health departments, and multiple public health and clinical partners are investigating a national outbreak of e-cigarette, or vaping, product use-associated lung injury (EVALI). Based on data collected as of October 15, 2019, 86% of 867 EVALI patients reported using tetrahydrocannabinol (THC)-containing products in the 3 months preceding symptom onset (1). Analyses of THC-containing product samples by FDA and state public health laboratories have identified potentially harmful constituents in these products, such as vitamin E acetate, medium chain triglyceride oil (MCT oil), and other lipids (2,3) (personal communication, D.T. Heitkemper, FDA Forensic Chemistry Center, November 2019). Vitamin E acetate, in particular, might be used as an additive in the production of e-cigarette, or vaping, products; it also can be used as a thickening agent in THC products (4). Inhalation of vitamin E acetate might impair lung function (5-7).

Progress toward better diagnosis and treatment of lipid metabolism-related diseases requires high throughput approaches for multiplexed quantitative analysis of structurally diverse lipids, including phospholipids (PLs). This work demonstrates a simplified "one-pot" phospholipid extraction protocol, as an alternative to conventional liquid-liquid extraction. Performed in a 96-well format, the extraction was coupled with high throughput UPLC and multiplexed tandem mass spectrometry (MS/MS) detection, allowing non-targeted quantification of phosphatidylcholines (PC), sphingomyelins (SM), lysophosphatidylcholines (LPC), phosphatidylethanolamines (PE), and phosphatidylinositols (PI). Using 50 μL aliquots of serum samples from 110 individuals, lipoproteins were fractionated by size, and analyzed for phospholipids and non-polar lipids including free cholesterol (FC), cholesteryl esters (CEs) and triglycerides (TGs). Analysis of serum samples with wide range of Total-TG levels showed significant differences in PL composition. The correlations of molar ratios in lipoprotein size fractions, SM/PL with FC/PL, PE/PL with TG/CE, and PE/PL with PI/PL, demonstrate the applicability of the method for quantitative composition analysis of high, low and very-low density lipoproteins (HDL, LDL and VLDL), and characterization of lipid metabolism related disease states., (Copyright © 2019. Published by Elsevier B.V.)

Inhalation of Bacillus anthracis spores can cause a rapidly progressing fatal infection. B. anthracis secretes three protein toxins: lethal factor (LF), edema factor (EF), and protective antigen (PA). EF and LF may circulate as free or PA-bound forms. Both free EF (EF) and PA-bound-EF (ETx) have adenylyl cyclase activity converting ATP to cAMP. We developed an adenylyl cyclase activity-based method for detecting and quantifying total EF (EF+ETx) in plasma. The three-step method includes magnetic immunocapture with monoclonal antibodies, reaction with ATP generating cAMP, and quantification of cAMP by isotope-dilution HPLC-MS/MS. Total EF was quantified from 5PL regression of cAMP vs ETx concentration. The detection limit was 20 fg/mL (225 zeptomoles/mL for the 89 kDa protein). Relative standard deviations for controls with 0.3, 6.0, and 90 pg/mL were 11.7-16.6% with 91.2-99.5% accuracy. The method demonstrated 100% specificity in 238 human serum/plasma samples collected from unexposed healthy individuals, and 100% sensitivity in samples from 3 human and 5 rhesus macaques with inhalation anthrax. Analysis of EF in the rhesus macaques showed that it was detected earlier post-exposure than B. anthracis by culture and PCR. Similar to LF, the kinetics of EF over the course of infection were triphasic, with an initial rise (phase-1), decline (phase-2), and final rapid rise (phase-3). EF levels were ~ 2-4 orders of magnitude lower than LF during phase-1 and phase-2 and only ~ 6-fold lower at death/euthanasia. Analysis of EF improves early diagnosis and adds to our understanding of anthrax toxemia throughout infection. The LF/EF ratio may also indicate the stage of infection and need for advanced treatments.

Protein digestion coupled to liquid chromatography and tandem mass spectrometry (LC-MS/MS) detection enables multiplexed quantification of proteins in complex biological matrices. However, the reproducibility of enzymatic digestion of proteins to produce proteotypic target peptides is a major limiting factor of assay precision. Online digestion using immobilized trypsin addresses this problem through precise control of digestion conditions and time. Because online digestion is typically for a short time, the potential for peptide degradation, a major source of measurement bias, is significantly reduced. Online proteolysis requires minimal sample preparation and is easily coupled to LC-MS/MS systems, further reducing potential method variability. We describe herein a method optimized for the multiplexed quantification of several apolipoproteins in human serum using on-column digestion. We highlight key features of the method that enhance assay accuracy and precision. These include the use of value-assigned serum as calibrators and stable isotope-labeled (SIL) peptide analogs as internal standards. We also comment on practical aspects of column switching valve design, instrument maintenance, tandem mass spectrometry data acquisition, and data processing.

In clinical trials, inhibition of cholesteryl ester transfer protein (CETP) raises HDL cholesterol levels but does not robustly improve cardiovascular outcomes. Approximately two-thirds of trial participants are obese. Lower plasma CETP activity is associated with increased cardiovascular risk in human studies, and protective aspects of CETP have been observed in mice fed a high-fat diet (HFD) with regard to metabolic outcomes. To define whether CETP inhibition has different effects depending on the presence of obesity, we performed short-term anacetrapib treatment in chow- and HFD-fed CETP transgenic mice. Anacetrapib raised HDL cholesterol and improved aspects of HDL functionality, including reverse cholesterol transport, and HDL's antioxidative capacity in HFD-fed mice was better than in chow-fed mice. Anacetrapib worsened the anti-inflammatory capacity of HDL in HFD-fed mice. The HDL proteome was markedly different with anacetrapib treatment in HFD- versus chow-fed mice. Despite benefits on HDL, anacetrapib led to liver triglyceride accumulation and insulin resistance in HFD-fed mice. Overall, our results support a physiologic importance of CETP in protecting from fatty liver and demonstrate context selectivity of CETP inhibition that might be important in obese subjects., (© 2018 by the American Diabetes Association.)

Background: Despite the usefulness of standard lipid parameters for cardiovascular disease risk assessment, undiagnosed residual risk remains high. Advanced lipoprotein testing (ALT) was developed to provide physicians with more predictive diagnostic tools. ALT methods separate and/or measure lipoproteins according to different parameters such as size, density, charge, or content, and equivalence of results across methods has not been demonstrated., Methods: Through a split-sample study, 25 clinical specimens (CSs) were assayed in 10 laboratories before and after freezing using the major ALT methods for non-HDL particles (non-HDL-P) or apolipoprotein B-100 (apoB-100) measurements with the intent to assess their comparability in the current state of the art., Results: The overall relative standard deviation (CV) of non-HDL-P and apoB-100 concentrations measured by electrospray differential mobility analysis, nuclear magnetic resonance, immunonephelometry, LC-MS/MS, and vertical autoprofile in the 25 frozen CSs was 14.1%. Within-method comparability was heterogeneous, and CV among 4 different LC-MS/MS methods was 11.4% for apoB-100. No significant effect of freezing and thawing was observed., Conclusions: This study demonstrates that ALT methods do not yet provide equivalent results for the measurement of non-HDL-P and apoB-100. The better agreement between methods harmonized to the WHO/IFCC reference material suggests that standardizing ALT methods by use of a common commutable calibrator will improve cross-platform comparability. This study provides further evidence that LC-MS/MS is the most suitable candidate reference measurement procedure to standardize apoB-100 measurement, as it would provide results with SI traceability. The absence of freezing and thawing effect suggests that frozen serum pools could be used as secondary reference materials., (© 2018 American Association for Clinical Chemistry.)

Lipoproteins are complex molecular assemblies that are key participants in the intricate cascade of extracellular lipid metabolism with important consequences in the formation of atherosclerotic lesions and the development of cardiovascular disease. Multiplexed mass spectrometry (MS) techniques have substantially improved the ability to characterize the composition of lipoproteins. However, these advanced MS techniques are limited by traditional pre-analytical fractionation techniques that compromise the structural integrity of lipoprotein particles during separation from serum or plasma. In this work, we applied a highly effective and gentle hydrodynamic size based fractionation technique, asymmetric flow field-flow fractionation (AF4), and integrated it into a comprehensive tandem mass spectrometry based workflow that was used for the measurement of apolipoproteins (apos A-I, A-II, A-IV, B, C-I, C-II, C-III and E), free cholesterol (FC), cholesterol esters (CE), triglycerides (TG), and phospholipids (PL) (phosphatidylcholine (PC), sphingomyelin (SM), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and lysophosphatidylcholine (LPC)). Hydrodynamic size in each of 40 size fractions separated by AF4 was measured by dynamic light scattering. Measuring all major lipids and apolipoproteins in each size fraction and in the whole serum, using total of 0.1 ml, allowed the volumetric calculation of lipoprotein particle numbers and expression of composition in molar analyte per particle number ratios. Measurements in 110 serum samples showed substantive differences between size fractions of HDL and LDL. Lipoprotein composition within size fractions was expressed in molar ratios of analytes (A-I/A-II, C-II/C-I, C-II/C-III. E/C-III, FC/PL, SM/PL, PE/PL, and PI/PL), showing differences in sample categories with combinations of normal and high levels of Total-C and/or Total-TG. The agreement with previous studies indirectly validates the AF4-LC-MS/MS approach and demonstrates the potential of this workflow for characterization of lipoprotein composition in clinical studies using small volumes of archived frozen samples.

As the lipidomics field continues to advance, self-evaluation within the community is critical. Here, we performed an interlaboratory comparison exercise for lipidomics using Standard Reference Material (SRM) 1950-Metabolites in Frozen Human Plasma, a commercially available reference material. The interlaboratory study comprised 31 diverse laboratories, with each laboratory using a different lipidomics workflow. A total of 1,527 unique lipids were measured across all laboratories and consensus location estimates and associated uncertainties were determined for 339 of these lipids measured at the sum composition level by five or more participating laboratories. These evaluated lipids detected in SRM 1950 serve as community-wide benchmarks for intra- and interlaboratory quality control and method validation. These analyses were performed using nonstandardized laboratory-independent workflows. The consensus locations were also compared with a previous examination of SRM 1950 by the LIPID MAPS consortium. While the central theme of the interlaboratory study was to provide values to help harmonize lipids, lipid mediators, and precursor measurements across the community, it was also initiated to stimulate a discussion regarding areas in need of improvement., (Copyright © 2017 by the American Society for Biochemistry and Molecular Biology, Inc.)

We demonstrate the application of in-source nitrogen collision-induced dissociation (CID) that eliminates the need for ester hydrolysis before simultaneous analysis of esterified cholesterol (EC) and triglycerides (TG) along with free cholesterol (FC) from human serum, using normal phase liquid chromatography (LC) coupled to atmospheric pressure chemical ionization (APCI) tandem mass spectrometry (MS/MS). The analysis requires only 50 μL of 1:100 dilute serum with a high-throughput, precipitation/evaporation/extraction protocol in one pot. Known representative mixtures of EC and TG species were used as calibrators with stable isotope labeled analogs as internal standards. The APCI MS source was operated with nitrogen source gas. Reproducible in-source CID was achieved with the use of optimal cone voltage (declustering potential), generating FC, EC, and TG lipid class-specific precursor fragment ions for multiple reaction monitoring (MRM). Using a representative mixture of purified FC, CE, and TG species as calibrators, the method accuracy was assessed with analysis of five inter-laboratory standardization materials, showing -10% bias for Total-C and -3% for Total-TG. Repeated duplicate analysis of a quality control pool showed intra-day and inter-day variation of 5% and 5.8% for FC, 5.2% and 8.5% for Total-C, and 4.1% and 7.7% for Total-TG. The applicability of the method was demonstrated on 32 serum samples and corresponding lipoprotein sub-fractions collected from normolipidemic, hypercholesterolemic, hypertriglyceridemic, and hyperlipidemic donors. The results show that in-source CID coupled with isotope dilution UHPLC-MS/MS is a viable high precision approach for translational research studies where samples are substantially diluted or the amounts of archived samples are limited. Graphical Abstract ᅟ.

Purpose: Apolipoprotein A-I (ApoA-I) and apolipoprotein B-100 (ApoB-100) are amphipathic proteins that are strong predictors of cardiovascular disease risk. The traceable calibration of apolipoprotein assays is a persistent challenge, especially for ApoB-100, which cannot be solubilized in purified form., Experimental Design: A simultaneous quantitation method for ApoA-I and ApoB-100 was developed using tryptic digestion without predigestion reduction and alkylation, followed by LC separation coupled with isotope dilution MS analysis. The accuracy of the method was assured by selecting structurally exposed signature peptides, optimal choice of detergent, protein:enzyme ratio, and incubation time. Peptide calibrators were value assigned by isobaric tagging isotope dilution MS amino acid analysis., Results: The method reproducibility was validated in technical repeats of three serum samples, giving 2-3% intraday CVs (N = 5) and <7% interday CVs (N = 21). The repeated analysis of interlaboratory harmonization standards showed -1% difference for ApoA-I and -12% for ApoB-100 relative to the assigned value. The applicability of the method was demonstrated by repeated analysis of 24 patient samples with a wide range of total cholesterol and triglyceride levels., Conclusions and Clinical Relevance: The method is applicable for simultaneous analysis of ApoA-I and ApoB-100 in patient samples, and for characterization of serum pool calibrators for other analytical platforms., (Published 2017. This article is a U.S. Government work and is in the public domain in the USA.)

Tandem mass spectrometry (MS/MS)-based proteomic workflows with a bottom-up approach require enzymatic digestion of proteins to peptide analytes, usually by trypsin. Online coupling of trypsin digestion of proteins, using an immobilized enzyme reactor (IMER), with liquid chromatography (LC) and MS/MS is becoming a frequently used approach. However, finding IMER digestion conditions that allow quantitative analysis of multiple proteins with wide range of endogenous concentration requires optimization of multiple interactive parameters: digestion buffer flow rate, injection volume, sample dilution, and surfactant type/ concentration. In this report, we present a design of experiment approach for the optimization of an integrated IMER-LC-MS/MS platform. With bovine serum albumin as a model protein, the digestion efficacy and digestion rate were monitored based on LC-MS/MS peak area count versus protein concentration regression. The optimal parameters were determined through multivariate surface response modeling and consideration of diffusion controlled immobilized enzyme kinetics. The results may provide guidance to other users for the development of quantitative IMER-LC-MS/MS methods for other proteins.

Apolipoproteins measured in plasma or serum are potential biomarkers for assessing metabolic irregularities that are associated with the development of cardiovascular disease (CVD). LC-MS/MS allows quantitative measurement of multiple apolipoproteins in the same sample run. However, the accuracy and precision of the LC-MS/MS measurement depends on the reproducibility of the enzymatic protein digestion step. With the application of an immobilized enzyme reactor (IMER), the reproducibility of the trypsin digestion can be controlled with high precision via flow rate, column volume and temperature. In this report, we demonstrate the application of an integrated IMER-LC-MS/MS platform for the simultaneous quantitative analysis of eight apolipoproteins. Using a dilution series of a characterized serum pool as calibrator, the method was validated by repeated analysis of pooled sera and individual serum samples with a wide range of lipid profiles, all showing intra-assay CV<4.4% and inter-assay CV<8%. In addition, the method was compared with traditional homogeneous digestion coupled LC-MS/MS for the quantification of apoA-I and apoB-100. Applied in large scale human population studies, this method can serve the translation of a wider panel of apolipoprotein biomarkers from research to clinical application., Significance: Currently, the translation of apolipoprotein biomarkers to clinical application is impaired because of the high cost of large cohort studies using traditional single-analyte immunoassays. The application of on-line tryptic digestion coupled with LC-MS/MS analysis is an effective way to address this problem. In this work we demonstrate a high throughput, multiplexed, automated proteomics workflow for the simultaneous analysis of multiple proteins., (Published by Elsevier B.V.)

HDL cholesterol (HDL-C) efflux function may be a more robust biomarker of coronary artery disease risk than HDL-C. To study HDL function, apoB-containing lipoproteins are precipitated from serum. Whether apoB precipitation affects HDL subspecies composition and function has not been thoroughly investigated. We studied the effects of four common apoB precipitation methods [polyethylene glycol (PEG), dextran sulfate/magnesium chloride (MgCl2), heparin sodium/manganese chloride (MnCl2), and LipoSep immunoprecipitation (IP)] on HDL subspecies composition, apolipoproteins, and function (cholesterol efflux and reduction of LDL oxidation). PEG dramatically shifted the size distribution of HDL and apolipoproteins (assessed by two independent methods), while leaving substantial amounts of reagent in the sample. PEG also changed the distribution of cholesterol efflux and LDL oxidation across size fractions, but not overall efflux across the HDL range. Dextran sulfate/MgCl2, heparin sodium/MnCl2, and LipoSep IP did not change the size distribution of HDL subspecies, but altered the quantity of a subset of apolipoproteins. Thus, each of the apoB precipitation methods affected HDL composition and/or size distribution. We conclude that careful evaluation is needed when selecting apoB depletion methods for existing and future bioassays of HDL function.

The seeds of the Ricinus communis (Castor bean) plant are the source of the economically important commodity castor oil. Castor seeds also contain the proteins ricin and R. communis agglutinin (RCA), two toxic lectins that are hazardous to human health. Radial immunodiffusion (RID) and the enzyme linked immunosorbent assay (ELISA) are two antibody-based methods commonly used to quantify ricin and RCA; however, antibodies currently used in these methods cannot distinguish between ricin and RCA due to the high sequence homology of the respective proteins. In this study, a technique combining antibody-based affinity capture with liquid chromatography and multiple reaction monitoring (MRM) mass spectrometry (MS) was used to quantify the amounts of ricin and RCA independently in extracts prepared from the seeds of eighteen representative cultivars of R. communis which were propagated under identical conditions. Additionally, liquid chromatography and MRM-MS was used to determine rRNA N-glycosidase activity for each cultivar and the overall activity in these cultivars was compared to a purified ricin standard. Of the cultivars studied, the average ricin content was 9.3 mg/g seed, the average RCA content was 9.9 mg/g seed, and the enzymatic activity agreed with the activity of a purified ricin reference within 35% relative activity., Competing Interests: The authors declare that there are no conflicts of interest., (Published by Elsevier Ltd.)