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A semi-automated, high throughput approach for O-glycosylation profiling of in vitro established cancer cell lines by MALDI-FT-ICR MS. Glycoconj J 2021; 38:747-756. [PMID: 34283362 PMCID: PMC8821499 DOI: 10.1007/s10719-021-10003-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 05/04/2021] [Accepted: 06/02/2021] [Indexed: 12/30/2022]
Abstract
The study of protein O-glycosylation is important in biological research as O-glycans have been reported to regulate a multitude of molecular and cell biology processes occurring in cancer. It is known that alterations in O-glycosylation are involved in the development and progression of cancer. Their easy accessibility makes in vitro established cell lines suitable and useful models for studying biological mechanisms in disease. However, the O-glycosylation analysis of large numbers of samples, as required in systems biology and biomarker discovery studies, is often challenging. In the present study, O-glycans from three human colorectal cancer cell lines and two human pancreatic cancer cell lines were released by semi-automated, high throughput reductive β-elimination and analysed using ultrahigh resolution MALDI-FT-ICR MS. Automated data integration and processing was performed using MassyTools, where the analyte was automatically included for relative quantitation based on a range of selection criteria including signal-to-noise ratio, mass error and isotopic pattern quality scores. A total of 126 O-glycan compositions, ranging from a single monosaccharide to large oligosaccharides exhibiting complex glycan motifs, were detected. The use of ultrahigh resolution MALDI-FTICR MS enabled glycan identification and quantitation in the matrix region of the spectrum. This approach has the potential to be used for O-glycosylation analysis of large numbers of samples, such as patient sample cohorts.
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Wang W, Kałuża A, Nouta J, Nicolardi S, Ferens-Sieczkowska M, Wuhrer M, Lageveen-Kammeijer GSM, de Haan N. High-throughput glycopeptide profiling of prostate-specific antigen from seminal plasma by MALDI-MS. Talanta 2020; 222:121495. [PMID: 33167210 DOI: 10.1016/j.talanta.2020.121495] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 07/27/2020] [Accepted: 07/30/2020] [Indexed: 11/28/2022]
Abstract
An altered total seminal plasma glycosylation has been associated with male infertility, and the highly abundant seminal plasma glycoprotein prostate-specific antigen (PSA) plays an important role in fertilization. However, the exact role of PSA glycosylation in male fertility is not clear. To understand the involvement of PSA glycosylation in the fertilization process, analytical methods are required to study the glycosylation of PSA from seminal plasma with a high glycoform resolution and in a protein-specific manner. In this study, we developed a novel, high-throughput PSA glycopeptide workflow, based on matrix-assisted laser desorption/ionization-mass spectrometry, allowing the discrimination of sialic acid linkage isomers via the derivatization of glycopeptides. The method was successfully applied on a cohort consisting of seminal plasma from infertile and fertile men (N = 102). Forty-four glycopeptides were quantified in all samples, showing mainly complex-type glycans with high levels of fucosylation and sialylation. In addition, N,N-diacetyllactosamine (LacdiNAc) motives were found as well as hybrid-type and high mannose-type structures. Our method showed a high intra- and interday repeatability and revealed no difference in PSA glycosylation between fertile and infertile men. Next to seminal plasma, the method is also expected to be of use for studying PSA glycopeptides derived from other biofluids and/or in other disease contexts.
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Affiliation(s)
- Wei Wang
- Leiden University Medical Center, Center for Proteomics and Metabolomics, 2300, RC, Leiden, the Netherlands
| | - Anna Kałuża
- Wrocław Medical University, Department of Chemistry and Immunochemistry, Curie-Skłodowska Str. 50, 50-369, Wrocław, Poland
| | - Jan Nouta
- Leiden University Medical Center, Center for Proteomics and Metabolomics, 2300, RC, Leiden, the Netherlands
| | - Simone Nicolardi
- Leiden University Medical Center, Center for Proteomics and Metabolomics, 2300, RC, Leiden, the Netherlands
| | - Mirosława Ferens-Sieczkowska
- Wrocław Medical University, Department of Chemistry and Immunochemistry, Curie-Skłodowska Str. 50, 50-369, Wrocław, Poland
| | - Manfred Wuhrer
- Leiden University Medical Center, Center for Proteomics and Metabolomics, 2300, RC, Leiden, the Netherlands
| | | | - Noortje de Haan
- Leiden University Medical Center, Center for Proteomics and Metabolomics, 2300, RC, Leiden, the Netherlands.
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Tsypin M, Asmellash S, Meyer K, Touchet B, Roder H. Extending the information content of the MALDI analysis of biological fluids via multi-million shot analysis. PLoS One 2019; 14:e0226012. [PMID: 31815946 PMCID: PMC6901224 DOI: 10.1371/journal.pone.0226012] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Accepted: 11/18/2019] [Indexed: 12/31/2022] Open
Abstract
INTRODUCTION Reliable measurements of the protein content of biological fluids like serum or plasma can provide valuable input for the development of personalized medicine tests. Standard MALDI analysis typically only shows high abundance proteins, which limits its utility for test development. It also exhibits reproducibility issues with respect to quantitative measurements. In this paper we show how the sensitivity of MALDI profiling of intact proteins in unfractionated human serum can be substantially increased by exposing a sample to many more laser shots than are commonly used. Analytical reproducibility is also improved. METHODS To assess what is theoretically achievable we utilized spectra from the same samples obtained over many years and combined them to generate MALDI spectral averages of up to 100,000,000 shots for a single sample, and up to 8,000,000 shots for a set of 40 different serum samples. Spectral attributes, such as number of peaks and spectral noise of such averaged spectra were investigated together with analytical reproducibility as a function of the number of shots. We confirmed that results were similar on MALDI instruments from different manufacturers. RESULTS We observed an expected decrease of noise, roughly proportional to the square root of the number of shots, over the whole investigated range of the number of shots (5 orders of magnitude), resulting in an increase in the number of reliably detected peaks. The reproducibility of the amplitude of these peaks, measured by CV and concordance analysis also improves with very similar dependence on shot number, reaching median CVs below 2% for shot numbers > 4 million. Measures of analytical information content and association with biological processes increase with increasing number of shots. CONCLUSIONS We demonstrate that substantially increasing the number of laser shots in a MALDI-TOF analysis leads to more informative and reliable data on the protein content of unfractionated serum. This approach has already been used in the development of clinical tests in oncology.
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Affiliation(s)
- Maxim Tsypin
- Biodesix Inc., Boulder, Colorado, United States of America
| | | | - Krista Meyer
- Biodesix Inc., Boulder, Colorado, United States of America
| | | | - Heinrich Roder
- Biodesix Inc., Boulder, Colorado, United States of America
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Fleurbaaij F, Kraakman MEM, Claas ECJ, Knetsch CW, van Leeuwen HC, van der Burgt YEM, Veldkamp KE, Vos MC, Goessens W, Mertens BJ, Kuijper EJ, Hensbergen PJ, Nicolardi S. Typing Pseudomonas aeruginosa Isolates with Ultrahigh Resolution MALDI-FTICR Mass Spectrometry. Anal Chem 2016; 88:5996-6003. [PMID: 27123572 DOI: 10.1021/acs.analchem.6b01037] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The introduction of standardized matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) platforms in the medical microbiological practice has revolutionized the way microbial species identification is performed on a daily basis. To a large extent, this is due to the ease of operation. Acquired spectra are compared to profiles obtained from cultured colonies present in a reference spectra database. It is fast and reliable, and costs are low compared to previous diagnostic approaches. However, the low resolution and dynamic range of the MALDI-TOF profiles have shown limited applicability for the discrimination of different bacterial strains, as achieved with typing based on genetic markers. This is pivotal in cases where certain strains are associated with, e.g., virulence or antibiotic resistance. Ultrahigh resolution MALDI-FTICR MS allows the measurement of small proteins at isotopic resolution and can be used to analyze complex mixtures with increased dynamic range and higher precision than MALDI-TOF MS, while still generating results in a similar time frame. Here, we propose to use ultrahigh resolution 15T MALDI-Fourier transform ion cyclotron resonance (FTICR) MS to discriminate clinically relevant bacterial strains after species identification performed by MALDI-TOF MS. We used a collection of well characterized Pseudomonas aeruginosa strains, featuring distinct antibiotic resistance profiles, and isolates obtained during hospital outbreaks. Following cluster analysis based on amplification fragment length polymorphism (AFLP), these strains were grouped into three different clusters. The same clusters were obtained using protein profiles generated by MALDI-FTICR MS. Subsequent intact protein analysis by electrospray ionization (ESI)-collision-induced dissociation (CID)-FTICR MS was applied to identify protein isoforms that contribute to the separation of the different clusters, illustrating the additional advantage of this analytical platform.
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Affiliation(s)
- Frank Fleurbaaij
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Margriet E M Kraakman
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Eric C J Claas
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Cornelis W Knetsch
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Hans C van Leeuwen
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Yuri E M van der Burgt
- Center for Proteomics and Metabolomics, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Karin Ellen Veldkamp
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Margreet C Vos
- Department of Medical Microbiology and Infectious Disease, Erasmus MC , 3015 CN Rotterdam, The Netherlands
| | - Wil Goessens
- Department of Medical Microbiology and Infectious Disease, Erasmus MC , 3015 CN Rotterdam, The Netherlands
| | - Bart J Mertens
- Department of Medical Statistics, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Ed J Kuijper
- Department of Medical Microbiology, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Paul J Hensbergen
- Center for Proteomics and Metabolomics, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
| | - Simone Nicolardi
- Center for Proteomics and Metabolomics, Leiden University Medical Center , 2333 ZA Leiden, The Netherlands
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Nicolardi S, Bogdanov B, Deelder AM, Palmblad M, van der Burgt YEM. Developments in FTICR-MS and Its Potential for Body Fluid Signatures. Int J Mol Sci 2015; 16:27133-44. [PMID: 26580595 PMCID: PMC4661870 DOI: 10.3390/ijms161126012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2015] [Revised: 11/03/2015] [Accepted: 11/05/2015] [Indexed: 01/01/2023] Open
Abstract
Fourier transform mass spectrometry (FTMS) is the method of choice for measurements that require ultra-high resolution. The establishment of Fourier transform ion cyclotron resonance (FTICR) MS, the availability of biomolecular ionization techniques and the introduction of the Orbitrap™ mass spectrometer have widened the number of FTMS-applications enormously. One recent example involves clinical proteomics using FTICR-MS to discover and validate protein biomarker signatures in body fluids such as serum or plasma. These biological samples are highly complex in terms of the type and number of components, their concentration range, and the structural identity of each species, and thus require extensive sample cleanup and chromatographic separation procedures. Clearly, such an elaborate and multi-step sample preparation process hampers high-throughput analysis of large clinical cohorts. A final MS read-out at ultra-high resolution enables the analysis of a more complex sample and can thus simplify upfront fractionations. To this end, FTICR-MS offers superior ultra-high resolving power with accurate and precise mass-to-charge ratio (m/z) measurement of a high number of peptides and small proteins (up to 20 kDa) at isotopic resolution over a wide mass range, and furthermore includes a wide variety of fragmentation strategies to characterize protein sequence and structure, including post-translational modifications (PTMs). In our laboratory, we have successfully applied FTICR “next-generation” peptide profiles with the purpose of cancer disease classifications. Here we will review a number of developments and innovations in FTICR-MS that have resulted in robust and routine procedures aiming for ultra-high resolution signatures of clinical samples, exemplified with state-of-the-art examples for serum and saliva.
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Affiliation(s)
- Simone Nicolardi
- Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC Leiden, The Netherlands.
| | - Bogdan Bogdanov
- Perkin Elmer, San Jose Technology Center, San Jose, CA 95134, USA.
| | - André M Deelder
- Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC Leiden, The Netherlands.
| | - Magnus Palmblad
- Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC Leiden, The Netherlands.
| | - Yuri E M van der Burgt
- Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC Leiden, The Netherlands.
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Fleurbaaij F, van Leeuwen HC, Klychnikov OI, Kuijper EJ, Hensbergen PJ. Mass Spectrometry in Clinical Microbiology and Infectious Diseases. Chromatographia 2015. [DOI: 10.1007/s10337-014-2839-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Nicolardi S, Velstra B, Mertens BJ, Bonsing B, Mesker WE, Tollenaar RA, Deelder AM, van der Burgt YE. Ultrahigh resolution profiles lead to more detailed serum peptidome signatures of pancreatic cancer. TRANSLATIONAL PROTEOMICS 2014. [DOI: 10.1016/j.trprot.2013.12.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
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Nicolardi S, van der Burgt YEM, Wuhrer M, Deelder AM. Mapping O-glycosylation of apolipoprotein C-III in MALDI-FT-ICR protein profiles. Proteomics 2013; 13:992-1001. [PMID: 23335445 DOI: 10.1002/pmic.201200293] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 08/29/2012] [Accepted: 10/23/2012] [Indexed: 01/10/2023]
Abstract
Ultrahigh resolution MALDI-FT-ICR profiles were obtained from human serum samples that were processed using a fully automated RPC18-based magnetic bead method. Proteins were profiled from m/z value 6630 with a resolving power of 73 000 up to m/z value 12 600 with a resolving power of 37 000. In this study, a detailed evaluation was performed of the isoforms of apolipoprotein C-III, i.e. the different mucin-type core 1 O-glycans with the addition of one or two sialic acid residues. The MALDI-FT-ICR profiles are discussed with regard to reproducibility of the signal intensities as well as the accurate mass measurements. ESI-FT-ICR-MS/MS analyses of the same serum samples were performed to confirm the identity of apolipoprotein C-III glycoforms.
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Affiliation(s)
- Simone Nicolardi
- Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), Leiden, The Netherlands
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Gianazza E, Chinello C, Mainini V, Cazzaniga M, Squeo V, Albo G, Signorini S, Di Pierro SS, Ferrero S, Nicolardi S, van der Burgt YE, Deelder AM, Magni F. Alterations of the serum peptidome in renal cell carcinoma discriminating benign and malignant kidney tumors. J Proteomics 2012; 76 Spec No.:125-40. [DOI: 10.1016/j.jprot.2012.07.032] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Revised: 07/16/2012] [Accepted: 07/19/2012] [Indexed: 01/21/2023]
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Clinical metabolomics: the next stage of clinical biochemistry. BLOOD TRANSFUSION = TRASFUSIONE DEL SANGUE 2012; 10 Suppl 2:s19-24. [PMID: 22890264 DOI: 10.2450/2012.005s] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Temperature-dependent instability of the cTnI subunit in NIST SRM2921 characterized by tryptic peptide mapping. J Chromatogr B Analyt Technol Biomed Life Sci 2012; 902:147-50. [PMID: 22771105 DOI: 10.1016/j.jchromb.2012.06.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Revised: 06/11/2012] [Accepted: 06/17/2012] [Indexed: 11/20/2022]
Abstract
In this study temperature-dependent instability of the cTnI subunit of the three-protein complex NIST SRM2921 was demonstrated using a mass spectrometric tryptic peptide mapping approach. The results were compared to the cTnI subunit obtained as a protein standard from Calbiochem with identical amino acid sequence. Both the three-protein complex from NIST as well as the cTnI subunit were incubated at elevated temperatures and then evaluated with respect to the primary sequence. The corresponding peptide maps were analyzed using LC-MS/MS. From a Mascot database search in combination with "semiTrypsin" tolerance it was found that two peptide backbone cleavages had occurred in subunit cTnI in NIST SRM2921 material upon incubation at 37°C, namely between amino acids at 148/149 and 194/195. The Calbiochem standard did not show increased levels of "unexpected" peptides in tryptic peptide maps. One of the two peptide backbone cleavages could also be monitored using a "single-step" MALDI-MS approach, i.e. without the need for peptide separation. The amount of degradation appeared rather constant in replicate temperature-instability experiments. However, for accurate quantification internal labelled standards are needed.
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Bladergroen MR, Derks RJE, Nicolardi S, de Visser B, van Berloo S, van der Burgt YEM, Deelder AM. Standardized and automated solid-phase extraction procedures for high-throughput proteomics of body fluids. J Proteomics 2012; 77:144-53. [PMID: 22842157 DOI: 10.1016/j.jprot.2012.07.023] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 07/04/2012] [Accepted: 07/16/2012] [Indexed: 01/17/2023]
Abstract
In order to balance the speed of analytical sample preparation procedures with mass spectrometry (MS)-based clinical proteomics the application of high-throughput robotic systems for body fluid workup is essential. In this paper we describe the implementation of various solid-phase extraction (SPE) sample preparation protocols on two different platforms, namely: 1) Magnetic bead-based SPE of peptides and proteins from body fluids on a Hamilton liquid handling workstation; 2) Cartridge-based SPE on a SPARK Symbiosis system. All SPE protocols were optimized for MS-based proteomics and compared with respect to obtained peptide- and protein profiles. Throughput numbers that were achieved in a 24 hour time frame for the sample workup procedures were more than 700 samples for the magnetic bead-based method and over 1000 samples for the cartridge-based method.
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Affiliation(s)
- Marco R Bladergroen
- Leiden University Medical Center (LUMC), Department of Parasitology, Biomolecular Mass Spectrometry Unit, Albinusdreef 2, 2300 RC, Leiden, The Netherlands
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Velstra B, van der Burgt YEM, Mertens BJ, Mesker WE, Deelder AM, Tollenaar RAEM. Improved classification of breast cancer peptide and protein profiles by combining two serum workup procedures. J Cancer Res Clin Oncol 2012; 138:1983-92. [PMID: 22763645 PMCID: PMC3491194 DOI: 10.1007/s00432-012-1273-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 06/15/2012] [Indexed: 12/22/2022]
Abstract
Purpose Detection of breast cancer at early stage increases patient’s survival. Mass spectrometry-based protein analysis of serum samples is a promising approach to obtain biomarker profiles for early detection. A combination of commonly applied solid-phase extraction procedures for clean-up may increase the number of detectable peptides and proteins. In this study, we have evaluated whether the classification performance of breast cancer profiles improves by using two serum workup procedures. Methods Serum samples from 105 breast cancer patients and 202 healthy volunteers were processed according to a standardized protocol implemented on a high-end liquid-handling robot. Peptide and protein enrichments were carried out using weak-cation exchange (WCX) and reversed-phase (RP) C18 magnetic beads. Profiles were acquired on a matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer. In this way, two different biomarker profiles were obtained for each serum sample, yielding a WCX- and RPC18-dataset. Results The profiles were statistically evaluated with double cross-validation. Classification results of WCX- and RPC18-datasets were determined for each set separately and for the combination of both sets. Sensitivity and specificity were 82 and 87 % (WCX) and 73 and 93 % (RPC18) for the individual workup procedures. These values increased up to 84 and 95 %, respectively, upon combining the data. Conclusion It was found that MALDI-TOF peptide and protein profiles can be used for classification of breast cancer with high sensitivity and specificity. The classification performance even improved when two workup procedures were applied, since these provide a greater number of features (proteins). Electronic supplementary material The online version of this article (doi:10.1007/s00432-012-1273-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Berit Velstra
- Department of Surgery, Leiden University Medical Center (LUMC), Albinusdreef 2, 2333 ZA, Leiden, The Netherlands.
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Identification of human serum peptides in fourier transform ion cyclotron resonance precision profiles. INTERNATIONAL JOURNAL OF PROTEOMICS 2012; 2012:804036. [PMID: 22685657 PMCID: PMC3364581 DOI: 10.1155/2012/804036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Accepted: 03/21/2012] [Indexed: 12/31/2022]
Abstract
The continuous efforts to find new prognostic or diagnostic biomarkers have stimulated the use of mass spectrometry (MS) profiles in a clinical setting. In the early days (about one decade ago), a single low-resolution mass spectrum derived from an individual's body fluid was used for comparative studies. However, a peptide profile of a complex mixture is most informative when recorded on an ultrahigh resolution instrument such as a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. In this study we show the benefits of the ultrahigh resolving power and the high mass accuracy and precision provided by an FTICR mass spectrometer equipped with a 15-tesla magnet. The ultrahigh-resolution data not only allow assignment of fragment ions with high charge states (4+, 5+) but also enhance confidence of human serum peptide identifications from tandem MS experiments. This is exemplified with collision-induced dissociation (CID) and electron transfer dissociation (ETD) data of middle-down-sized endogenous or protein-breakdown peptides that are of interest in biomarker discovery studies.
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