One-Year Plasma N-linked Glycome Intra-individual and Inter-individual Variability in the Chicken Model of Spontaneous Ovarian Adenocarcinoma

Development of a hydrophilic interaction liquid chromatography coupled with matrix-assisted laser desorption/ionization-mass spectrometric imaging platform for N-glycan relative quantitation using stable-isotope labeled hydrazide reagents

In this work, the capability of newly developed hydrophilic interaction liquid chromatography (HILIC) coupled with matrix-assisted laser desorption/ionization-mass spectrometric imaging (MALDI-MSI) platform for quantitative analysis of N-glycans has been demonstrated. As a proof-of-principle experiment, heavy and light stable-isotope labeled hydrazide reagents labeled maltodextrin ladder were used to demonstrate the feasibility of the HILIC-MALDI-MSI platform for reliable quantitative analysis of N-glycans. MALDI-MSI analysis by an Orbitrap mass spectrometer enabled high-resolution and high-sensitivity detection of N-glycans eluted from HILIC column, allowing the re-construction of LC chromatograms as well as accurate mass measurements for structural inference. MALDI-MSI analysis of the collected LC traces showed that the chromatographic resolution was preserved. The N-glycans released from human serum was used to demonstrate the utility of this novel platform in quantitative analysis of N-glycans from a complex sample. Benefiting from the minimized ion suppression provided by HILIC separation, comparison between MALDI-MS and the newly developed platform HILIC-MALDI-MSI revealed that HILIC-MALDI-MSI provided higher N-glycan coverage as well as better quantitation accuracy in the quantitative analysis of N-glycans released from human serum. Graphical abstract Reconstructed chromatograms based on HILIC-MALDI-MSI results of heavy and light labeled maltodextrin enabling quantitative glycan analysis.

Polarity switching mass spectrometry imaging of healthy and cancerous hen ovarian tissue sections by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI)

Mass spectrometry imaging (MSI) is a rapidly evolving field for monitoring the spatial distribution and abundance of analytes in biological tissue sections. It allows for direct and simultaneous analysis of hundreds of different compounds in a label-free manner. In order to obtain a comprehensive metabolite and lipid data, a polarity switching MSI method using infrared matrix assisted laser desorption electrospray ionization (IR-MALDESI) was developed and optimized where the electrospray polarity was alternated from one voxel to the next. Healthy and cancerous ovarian hen tissue sections were analyzed using this method. Distribution and relative abundance of different metabolites and lipids within each tissue section were discerned, and differences between the two were revealed. Additionally, the utility of using mass spectrometry concepts such as spectral accuracy and sulfur counting for confident identification of analytes in an untargeted method are discussed.

The chicken model of spontaneous ovarian cancer

The chicken is a unique experimental model for studying the spontaneous onset and progression of ovarian cancer (OVC). The prevalence of OVC in chickens can range from 5 to 35% depending on age, genetic strain, reproductive history, and diet. Furthermore, the chicken presents epidemiological, morphological, and molecular traits that are similar to human OVC making it a relevant experimental model for translation research. Similarities to humans include associated increased risk of OVC with the number of ovulations, common histopathological subtypes including high-grade serous, and molecular-level markers or pathways such as CA-125 expression and p53 mutation frequency.  Collectively, the similarities between chicken and human OVC combined with a tightly controlled genetic background and predictable onset window provides an outstanding experimental model for studying the early events and progression of spontaneous OVC tumors under controlled environmental conditions. This review will cover the existing literature on OVC in the chicken and highlight potential opportunities for further exploitation (e.g. biomarkers, prevention, treatment, and genomics).

Individuality Normalization when Labeling with Isotopic Glycan Hydrazide Tags (INLIGHT): a novel glycan-relative quantification strategy

The Individuality Normalization when Labeling with Isotopic Glycan Hydrazide Tags (INLIGHT) strategy for the sample preparation, data analysis, and relative quantification of N-linked glycans is presented. Glycans are derivatized with either natural (L) or stable-isotope labeled (H) hydrazide reagents and analyzed using reversed phase liquid chromatography coupled online to a Q Exactive mass spectrometer. A simple glycan ladder, maltodextrin, is first used to demonstrate the relative quantification strategy in samples with negligible analytical and biological variability. It is shown that after a molecular weight correction attributable to isotopic overlap and a post-acquisition normalization of the data to account for any systematic bias, a plot of the experimental H:L ratio versus the calculated H:L ratio exhibits a correlation of unity for maltodextrin samples mixed in different ratios. We also demonstrate that the INLIGHT approach can quantify species over four orders of magnitude in ion abundance. The INLIGHT strategy is further demonstrated in pooled human plasma, where it is shown that the post-acquisition normalization is more effective than using a single spiked-in internal standard. Finally, changes in glycosylation are able to be detected in complex biological matrices, when spiked with a glycoprotein. The ability to spike in a glycoprotein and detect change at the glycan level validates both the sample preparation and data analysis strategy, making INLIGHT an invaluable relative quantification strategy for the field of glycomics.

The use of a xylosylated plant glycoprotein as an internal standard accounting for N-linked glycan cleavage and sample preparation variability

RATIONALE

Traditionally, free oligosaccharide internal standards are used to account for variability in glycan relative quantification experiments by mass spectrometry. However, a more suitable internal standard would be a glycoprotein, which could also control for enzymatic cleavage efficiency, allowing for more accurate quantitative experiments.

METHODS

Hydrophobic, hydrazide N-linked glycan reagents (both native and stable-isotope labeled) are used to derivatize and differentially label N-linked glycan samples for relative quantification, and the samples are analyzed by a reversed-phase liquid chromatography chip system coupled online to a Q-Exactive mass spectrometer. The inclusion of two internal standards, maltoheptaose (previously used) and horseradish peroxidase (HRP) (novel), is studied to demonstrate the effectiveness of using a glycoprotein as an internal standard in glycan relative quantification experiments.

RESULTS

HRP is a glycoprotein containing a xylosylated N-linked glycan, which is unique from mammalian N-linked glycans. Thus, the internal standard xylosylated glycan could be detected without interference to the sample. Additionally, it was shown that differences in cleavage efficiency can be detected by monitoring the HRP glycan. In a sample where cleavage efficiency variation is minimal, the HRP glycan performs as well as maltoheptaose.

CONCLUSIONS

Because the HRP glycan performs as well as maltoheptaose but is also capable of correcting and accounting for cleavage variability, it is a more versatile internal standard and will be used in all subsequent biological studies. Because of the possible lot-to-lot variation of an enzyme, differences in biological matrix, and variable enzyme activity over time, it is a necessity to account for glycan cleavage variability in glycan relative quantification experiments.

Multi-peptide nLC-PC-IDMS-SRM-based assay for the quantification of biomarkers in the chicken ovarian cancer model

A novel form of ovomacroglobulin/ovostatin (OVOS2) predicted from EST data was previously identified in the chicken ovarian cancer model using a mass spectrometry-based shotgun label-free proteomics strategy. The quantitative label-free data from plasma showed a significant increase over time with the spontaneous onset and progression of ovarian cancer making it a potential protein biomarker for further study. Two other proteins of interest identified from this initial study included vitellogenin-1 (Vit-1), a lipid-transport protein tied to egg production, and transthyretin (TTR), a retinol binding transport protein currently used in the clinical management of ovarian cancer. A multiplexed protein cleavage isotope dilution mass spectrometry (PC-IDMS) assay was developed to quantify OVOS2, Vit-1, and TTR by selected reaction monitoring (SRM). A total of 6 stable isotope labeled (SIL) peptide standards were used in the assay with three tryptic peptides from OVOS2, one for Vit-1, and two for TTR. The assay was developed for use with un-depleted raw plasma combined with the filter assisted sample preparation (FASP) method and its use was also demonstrated for matched ovary tissue samples. The PC-IDMS data for the two TTR peptides did not correlate with each other with more than a 10-fold difference in concentration for all 5 time points measured. The PC-IDMS data from the longitudinal plasma samples correlated well for OVOS2 and Vit-1 whereas TTR was inconclusive. Interestingly, the absolute amount for one of the OVOS2 SIL peptides was 2-fold less compared with the other two SIL peptides. These data illustrate the successes and challenges of qualifying quantitative levels of proteins from an in-gel digestion sample preparation followed by LC-MS/MS (GeLC) label-free discovery-based approach to a targeted SRM-based quantitative assay in plasma and tissues.

Systematic comparison of reverse phase and hydrophilic interaction liquid chromatography platforms for the analysis of N-linked glycans

Due to the hydrophilic nature of glycans, reverse phase chromatography has not been widely used as a glycomic separation technique coupled to mass spectrometry. Other approaches such as hydrophilic interaction chromatography and porous graphitized carbon chromatography are often employed, though these strategies frequently suffer from decreased chromatographic resolution, long equilibration times, indefinite retention, and column bleed. Herein, it is shown that, through an efficient hydrazone formation derivatization of N-linked glycans (~4 h of additional sample preparation time which is carried out in parallel), numerous experimental and practical advantages are gained when analyzing the glycans by online reverse phase chromatography. These benefits include an increased number of glycans detected, increased peak capacity of the separation, and the ability to analyze glycans on the identical liquid chromatography-mass spectrometry platform commonly used for proteomic analyses. The data presented show that separation of derivatized N-linked glycans by reverse phase chromatography significantly out-performs traditional separation of native or derivatized glycans by hydrophilic interaction chromatography. Furthermore, the movement to a more ubiquitous separation technique will afford numerous research groups the opportunity to analyze both proteomic and glycomic samples on the same platform with minimal time and physical change between experiments, increasing the efficiency of "multiomic" biological approaches.

Stable-isotope labeled hydrophobic hydrazide reagents for the relative quantification of N-linked glycans by electrospray ionization mass spectrometry

This study presents the development of stable-isotope labeled hydrophobic, hydrazide reagents for the relative quantification of N-linked glycans. The P2GPN "light" ((12)C) and "heavy" ((13)C(6)) pair are used to differentially label two N-linked glycan samples. The samples are combined 1:1, separated using HILIC, and then mass differentiated and quantified using mass spectrometry. These reagents have several benefits: (1) impart hydrophobic character to the glycans affording an increase in electrospray ionization efficiency and MS detection; (2) indistinguishable chromatographic, MS, and MS/MS performance of the "light" and "heavy" reagents affording relative quantification; and (3) analytical variability is significantly reduced due to the two samples being mixed together after sample preparation. Obtaining these analytical benefits only requires ~4 h of sample preparation time. It is shown that these reagents are capable of quantifying changes in glycosylation in simple mixtures, and the analytical variability of the reagents in pooled plasma samples is shown to be less than ±30%. Additionally, the incorporation of an internal standard allows one to account for the difference in systematic error between the two samples due to the samples being processed in parallel and not mixed until after derivatization.