1
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Shi H, Xia Y. Shotgun Lipidomic Profiling of Sebum Lipids via Photocatalyzed Paternò-Büchi Reaction and Ion Mobility-Mass Spectrometry. Anal Chem 2024; 96:5589-5597. [PMID: 38556723 DOI: 10.1021/acs.analchem.4c00141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/02/2024]
Abstract
Sebum lipids are composed of nonpolar lipids, and they pose challenges for mass spectrometry-based analysis due to low ionization efficiency and the existence of numerous isomers and isobars. To address these challenges, we have developed ethyl 2-oxo-2-(pyridine-3-yacetate as a charge-tagging Paternò-Büchi reagent and Michler's ketone as a highly efficient photocatalyst, achieving ∼90% conversion for C═C derivatization under 440 nm LED irradiation. This derivatization, when coupled with electrospray ionization-tandem mass spectrometry, boosts the detection of sebum lipids and pinpoints C═C location in a chain-specific fashion. Identification and quantitation of isomers are readily achieved for wax esters, a class of underexplored sebum lipids, which have C═C bonds distributed in fatty alcohol and fatty acyl chains. A shotgun analysis workflow has been developed by pairing the offline PB derivatization with cyclic ion mobility spectrometry-mass spectrometry. Besides the dominant n-10 C═C location in unsaturated wax esters, profiling of low abundance isomers, including the rarely reported n-7 and n-13 locations, is greatly enhanced due to separations of C═C diagnostic ions by ion mobility. Over 900 distinct lipid structures from human sebum lipid extract have been profiled at the chain-specific C═C level, including wax esters (500), glycerolipids (393), and cholesterol esters (22), far more exceeding previous reports. Overall, we have developed a fast and comprehensive lipidomic profiling tool for sebum samples, a type of noninvasive biofluids holding potential for the discovery of disease markers in distal organs.
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Affiliation(s)
- Hengxue Shi
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Department of Chemistry, Tsinghua University, Beijing 10084, China
| | - Yu Xia
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Department of Chemistry, Tsinghua University, Beijing 10084, China
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2
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Tie C, Cui X, Zhang Z, Geng Y, Liu T, Rong X, Zheng X. Novel Structure-Driven Predict-to-Hit Strategy for PC Double Bond Positional Isomer Identification Based on Negative LC-MRM Analysis. Anal Chem 2024. [PMID: 38330201 DOI: 10.1021/acs.analchem.3c04032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
As the predominant phospholipids in mammalian cells, phosphatidylcholines (PCs) have been demonstrated to play a crucial role in a multitude of vital biological processes. Research has highlighted the significance of the diversity in PC isomers as instigators of both physiological and pathological responses, particularly those with variations in the position of double bonds within their fatty chains. Profiling these PC isomers is paramount to advancing our understanding of their biological functions. Despite the availability of analytical methods utilizing high-resolution secondary mass spectrometry (MS2) fragmentation, a novel approach was imperative to facilitate large-scale profiling of PC isomers while ensuring accessibility, facility, and reliability. In this study, an innovative strategy centered around structure-driven predict-to-hit profiling of the double bond positional isomers for PCs was meticulously developed, employing negative reversed-phase liquid chromatography-multiple reaction monitoring (RPLC-MRM). This novel methodology heightened the sensitivity. The analysis of rat lung tissue samples resulted in the identification of 130 distinct PC isomers. This approach transcended the confines of available PC isomer standards, thereby broadening the horizons of PC-related biofunction investigations. By optimizing the quantitation reliability, the scale of sample analysis was judiciously managed. This work pioneers a novel paradigm for the exploration of PC isomers, distinct from the conventional methods reliant on high-resolution mass spectrometry (HRMS). It equips researchers with potent tools to further explore the biofunctional aspects of lipids.
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Affiliation(s)
- Cai Tie
- State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources, Ding 11 Xueyuan Road, Beijing 100083, China
- School of Chemical and Environmental Engineering, China University of Mining and Technology-Beijing, Ding 11 Xueyuan Road, Beijing 100083, China
| | - Xinge Cui
- Clinical Pharmacology Research Center, Peking Union Medical College Hospital, State Key Laboratory of Complex Severe and Rare Diseases, NMPA Key Laboratory for Clinical Research and Evaluation of Drug, Beijing Key Laboratory of Clinical PK & PD Investigation for Innovative Drugs, Chinese Academy of Medical Sciences & Peking Union Medical College, No.1 Shuaifuyuan Wangfujing, Dongcheng District, Beijing 100730, China
| | - Zhijun Zhang
- School of Chemical and Environmental Engineering, China University of Mining and Technology-Beijing, Ding 11 Xueyuan Road, Beijing 100083, China
| | - Yicong Geng
- School of Chemical and Environmental Engineering, China University of Mining and Technology-Beijing, Ding 11 Xueyuan Road, Beijing 100083, China
| | - Ting Liu
- SCIEX, Analytical Instrument Trading Co., Ltd., 518 North Fuquan Road, Shanghai 200335, China
| | - Xiaojuan Rong
- Xinjiang Institute of Material Medica, 140 North Xinhua Road, Urumqi, Xinjiang 830004, China
| | - Xin Zheng
- Clinical Pharmacology Research Center, Peking Union Medical College Hospital, State Key Laboratory of Complex Severe and Rare Diseases, NMPA Key Laboratory for Clinical Research and Evaluation of Drug, Beijing Key Laboratory of Clinical PK & PD Investigation for Innovative Drugs, Chinese Academy of Medical Sciences & Peking Union Medical College, No.1 Shuaifuyuan Wangfujing, Dongcheng District, Beijing 100730, China
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3
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Kedia K, Harris R, Ekroos K, Moser KW, DeBord D, Tiberi P, Goracci L, Zhang NR, Wang W, Spellman DS, Bateman K. Investigating Performance of the SLIM-Based High Resolution Ion Mobility Platform for Separation of Isomeric Phosphatidylcholine Species. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:2176-2186. [PMID: 37703523 DOI: 10.1021/jasms.3c00157] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/15/2023]
Abstract
Lipids are structurally diverse molecules that play a pivotal role in a plethora of biological processes. However, deciphering the biological roles of the specific lipids is challenging due to the existence of numerous isomers. This high chemical complexity of the lipidome is one of the major challenges in lipidomics research, as the traditional liquid chromatography-mass spectrometry (LC-MS) based approaches are often not powerful enough to resolve these isomeric and isobaric nuances within complex samples. Thus, lipids are uniquely suited to the benefits provided by multidimensional liquid chromatography-ion mobility-mass spectrometry (LC-IM-MS) analysis. However, many forms of lipid isomerism, including double-bond positional isomers and regioisomers, are structurally similar such that their collision cross section (CCS) differences are unresolvable via conventional IM approaches. Here we evaluate the performance of a high resolution ion mobility (HRIM) system based on structures for lossless ion manipulation (SLIM) technology interfaced to a high resolution quadrupole time-of-flight (QTOF) analyzer to address the noted lipidomic isomerism challenge. SLIM implements the traveling wave ion mobility technique along an ∼13 m ion path, providing longer path lengths to enable improved separation of isomeric features. We demonstrate the power of HRIM-MS to dissect isomeric PC standards differing only in double bond (DB) and stereospecific number (SN) positions. The partial separation of protonated DB isomers is significantly enhanced when they are analyzed as metal adducts. For sodium adducts, we achieve close to baseline separation of three different PC 18:1/18:1 isomers with different cis-double bond locations. Similarly, PC 18:1/18:1 (cis-9) can be resolved from the corresponding PC 18:1/18:1 (trans-9) form. The separation capacity is further enhanced when using silver ion doping, enabling the baseline separation of regioisomers that cannot be resolved when measured as sodium adducts. The sensitivity and reproducibility of the approach were assessed, and the performance for more complex mixtures was benchmarked by identifying PC isomers in total brain and liver lipid extracts.
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Affiliation(s)
- Komal Kedia
- Merck & Co., Inc., West Point, Pennsylvania 19486, United States
| | - Rachel Harris
- MOBILion Systems, Inc., Chadds Ford, Pennsylvania 19317, United States
| | - Kim Ekroos
- Lipidomics Consulting Ltd, Irisviksvägen 31D, 02230 Esbo, Finland
| | - Kelly W Moser
- MOBILion Systems, Inc., Chadds Ford, Pennsylvania 19317, United States
| | - Daniel DeBord
- MOBILion Systems, Inc., Chadds Ford, Pennsylvania 19317, United States
| | - Paolo Tiberi
- Molecular Discovery Ltd., Centennial Park, Borehamwood, Hertfordshire WD6 3FG United Kingdom
| | - Laura Goracci
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy
| | | | - Weixun Wang
- Merck & Co., Inc., West Point, Pennsylvania 19486, United States
| | | | - Kevin Bateman
- Merck & Co., Inc., West Point, Pennsylvania 19486, United States
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4
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Vondrackova M, Kopczynski D, Hoffmann N, Kuda O. LORA, Lipid Over-Representation Analysis Based on Structural Information. Anal Chem 2023; 95:12600-12604. [PMID: 37584663 PMCID: PMC10469370 DOI: 10.1021/acs.analchem.3c02039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Accepted: 08/01/2023] [Indexed: 08/17/2023]
Abstract
With the increasing number of lipidomic studies, there is a need for an efficient and automated analysis of lipidomic data. One of the challenges faced by most existing approaches to lipidomic data analysis is lipid nomenclature. The systematic nomenclature of lipids contains all available information about the molecule, including its hierarchical representation, which can be used for statistical evaluation. The Lipid Over-Representation Analysis (LORA) web application (https://lora.metabolomics.fgu.cas.cz) analyzes this information using the Java-based Goslin framework, which translates lipid names into a standardized nomenclature. Goslin provides the level of lipid hierarchy, including information on headgroups, acyl chains, and their modifications, up to the "complete structure" level. LORA allows the user to upload the experimental query and reference data sets, select a grammar for lipid name normalization, and then process the data. The user can then interactively explore the results and perform lipid over-representation analysis based on selected criteria. The results are graphically visualized according to the lipidome hierarchy. The lipids present in the most over-represented terms (lipids with the highest number of enriched shared structural features) are defined as Very Important Lipids (VILs). For example, the main result of a demo data set is the information that the query is significantly enriched with "glycerophospholipids" containing "acyl 20:4" at the "sn-2 position". These terms define a set of VILs (e.g., PC 18:2/20:4;O and PE 16:0/20:4(5,8,10,14);OH). All results, graphs, and visualizations are summarized in a report. LORA is a tool focused on the smart mining of epilipidomics data sets to facilitate their interpretation at the molecular level.
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Affiliation(s)
- Michaela Vondrackova
- Institute
of Physiology, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czechia
| | - Dominik Kopczynski
- Institute
of Analytical Chemistry, University of Vienna, 1090 Vienna, Austria
| | - Nils Hoffmann
- Forschungszentrum
Jülich, Institute of Bio- and Geosciences
(IBG-5), 52428 Jülich, Germany
| | - Ondrej Kuda
- Institute
of Physiology, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czechia
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5
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Zhang D, Lin Q, Xia T, Zhao J, Zhang W, Ouyang Z, Xia Y. LipidOA: A Machine-Learning and Prior-Knowledge-Based Tool for Structural Annotation of Glycerophospholipids. Anal Chem 2022; 94:16759-16767. [DOI: 10.1021/acs.analchem.2c03505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- Donghui Zhang
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing100084, China
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Department of Chemistry, Tsinghua University, Beijing10084, China
| | - Qiaohong Lin
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Department of Chemistry, Tsinghua University, Beijing10084, China
| | - Tian Xia
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Department of Chemistry, Tsinghua University, Beijing10084, China
| | - Jing Zhao
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Department of Chemistry, Tsinghua University, Beijing10084, China
| | - Wenpeng Zhang
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing100084, China
| | - Zheng Ouyang
- State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing100084, China
| | - Yu Xia
- MOE Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology, Department of Chemistry, Tsinghua University, Beijing10084, China
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6
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Cerrato A, Capriotti AL, Cavaliere C, Montone CM, Piovesana S, Laganà A. Novel Aza-Paternò-Büchi Reaction Allows Pinpointing Carbon-Carbon Double Bonds in Unsaturated Lipids by Higher Collisional Dissociation. Anal Chem 2022; 94:13117-13125. [PMID: 36121000 PMCID: PMC9523615 DOI: 10.1021/acs.analchem.2c02549] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The evaluation of double bond positions in fatty acyl
chains has
always been of great concern given their significance in the chemical
and biochemical role of lipids. Despite being the foremost technique
for lipidomics, it is difficult in practice to obtain identification
beyond the fatty acyl level by the sole high-resolution mass spectrometry.
Paternò–Büchi reactions of fatty acids (FAs)
with ketones have been successfully proposed for pinpointing double
bonds in FAs in combination with the collision-induced fragmentation
technique. In the present paper, an aza-Paternò–Büchi
(aPB) reaction of lipids with 6-azauracil (6-AU) was proposed for
the first time for the determination of carbon–carbon double
bonds in fatty acyl chains using higher collisional dissociation in
the negative ion mode. The method was optimized using free FA and
phospholipid analytical standards and compared to the standard Paternò–Büchi
reaction with acetone. The introduction of the 6-AU moiety allowed
enhancing the ionization efficiency of the FA precursor and diagnostic
product ions, thanks to the presence of ionizable sites on the derivatizing
agent. Moreover, the aPB derivatization allowed the obtention of deprotonated
ions of phosphatidylcholines, thanks to an intramolecular methyl transfer
from the phosphocholine polar heads during ionization. The workflow
was finally applied for pinpointing carbon–carbon double bonds
in 77 polar lipids from an yeast (Saccharomyces cerevisiae) extract.
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Affiliation(s)
- Andrea Cerrato
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy
| | - Anna Laura Capriotti
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy
| | - Chiara Cavaliere
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy
| | - Carmela Maria Montone
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy
| | - Susy Piovesana
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy
| | - Aldo Laganà
- Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, Rome 00185, Italy
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7
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Yoon JH, Seo Y, Jo YS, Lee S, Cho E, Cazenave-Gassiot A, Shin YS, Moon MH, An HJ, Wenk MR, Suh PG. Brain lipidomics: From functional landscape to clinical significance. SCIENCE ADVANCES 2022; 8:eadc9317. [PMID: 36112688 PMCID: PMC9481132 DOI: 10.1126/sciadv.adc9317] [Citation(s) in RCA: 71] [Impact Index Per Article: 35.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Accepted: 08/01/2022] [Indexed: 05/23/2023]
Abstract
Lipids are crucial components of cellular function owing to their role in membrane formation, intercellular signaling, energy storage, and homeostasis maintenance. In the brain, lipid dysregulations have been associated with the etiology and progression of neurodegeneration and other neurological pathologies. Hence, brain lipids are emerging as important potential targets for the early diagnosis and prognosis of neurological diseases. This review aims to highlight the significance and usefulness of lipidomics in diagnosing and treating brain diseases. We explored lipid alterations associated with brain diseases, paying attention to organ-specific characteristics and the functions of brain lipids. As the recent advances in brain lipidomics would have been impossible without advances in analytical techniques, we provide up-to-date information on mass spectrometric approaches and integrative analysis with other omic approaches. Last, we present the potential applications of lipidomics combined with artificial intelligence techniques and interdisciplinary collaborative research for treating brain diseases with clinical heterogeneities.
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Affiliation(s)
- Jong Hyuk Yoon
- Neurodegenerative Diseases Research Group, Korea Brain Research Institute, Daegu 41062, Republic of Korea
| | - Youngsuk Seo
- Neurodegenerative Diseases Research Group, Korea Brain Research Institute, Daegu 41062, Republic of Korea
| | - Yeon Suk Jo
- Neurodegenerative Diseases Research Group, Korea Brain Research Institute, Daegu 41062, Republic of Korea
- Department of Brain Sciences, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Daegu 42988, Republic of Korea
| | - Seulah Lee
- Neurodegenerative Diseases Research Group, Korea Brain Research Institute, Daegu 41062, Republic of Korea
| | - Eunji Cho
- Neurodegenerative Diseases Research Group, Korea Brain Research Institute, Daegu 41062, Republic of Korea
| | - Amaury Cazenave-Gassiot
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119077, Singapore
- Singapore Lipidomics Incubator (SLING), Life Sciences Institute, National University of Singapore, Singapore 119077, Singapore
| | - Yong-Seung Shin
- Laboratory Solutions Sales, Agilent Technologies Korea Ltd., Seoul, 06621, Republic of Korea
| | - Myeong Hee Moon
- Department of Chemistry, Yonsei University, Seoul 03722, Republic of Korea
| | - Hyun Joo An
- Graduate School of Analytical Science and Technology, Chungnam National University, Daejeon 34134, Republic of Korea
| | - Markus R. Wenk
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119077, Singapore
- Singapore Lipidomics Incubator (SLING), Life Sciences Institute, National University of Singapore, Singapore 119077, Singapore
| | - Pann-Ghill Suh
- Korea Brain Research Institute, Daegu 41062, Republic of Korea
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8
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Shields SWJ, Sanders JD, Brodbelt JS. Enhancing the Signal-to-Noise of Diagnostic Fragment Ions of Unsaturated Glycerophospholipids via Precursor Exclusion Ultraviolet Photodissociation Mass Spectrometry (PEx-UVPD-MS). Anal Chem 2022; 94:11352-11359. [PMID: 35917227 PMCID: PMC9484799 DOI: 10.1021/acs.analchem.2c02128] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding and elucidating the diverse structures and functions of lipids has motivated the development of many innovative tandem mass spectrometry (MS/MS) strategies. Higher-energy activation methods, such as ultraviolet photodissociation (UVPD), generate unique fragment ions from glycerophospholipids that can be used to perform in-depth structural analysis and facilitate the deconvolution of isomeric lipid structures in complex samples. Although detailed characterization is central to the correlation of lipid structure to biological function, it is often impeded by the lack of sufficient instrument sensitivity for highly bioactive but low-abundance phospholipids. Here, we present precursor exclusion (PEx) UVPD, a simple yet powerful technique to enhance the signal-to-noise (S/N) of informative low-abundance fragment ions produced from UVPD of glycerophospholipids. Through the exclusion of the large population of undissociated precursor ions with an MS3 strategy, the S/N of diagnostic fragment ions from PC 18:0/18:2(9Z, 12Z) increased up to an average of 13x for PEx-UVPD compared to UVPD alone. These enhancements were extended to complex mixtures of lipids from bovine liver extract to confidently identify 35 unique structures using liquid chromatography PEx-UVPD. This methodology has the potential to advance lipidomics research by offering deeper structure elucidation and confident identification of biologically active lipids.
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Affiliation(s)
- Samuel W J Shields
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - James D Sanders
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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9
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Need for more focus on lipid species in studies of biological and model membranes. Prog Lipid Res 2022; 86:101160. [DOI: 10.1016/j.plipres.2022.101160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2021] [Accepted: 03/06/2022] [Indexed: 11/23/2022]
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10
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Baumann A, Denninger AR, Domin M, Demé B, Kirschner DA. Metabolically-incorporated deuterium in myelin localized by neutron diffraction and identified by mass spectrometry. Curr Res Struct Biol 2022; 4:231-245. [PMID: 35941866 PMCID: PMC9356250 DOI: 10.1016/j.crstbi.2022.06.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 06/10/2022] [Indexed: 11/25/2022] Open
Abstract
Myelin is a natural and dynamic multilamellar membrane structure that continues to be of significant biological and neurological interest, especially with respect to its biosynthesis and assembly during its normal formation, maintenance, and pathological breakdown. To explore the usefulness of neutron diffraction in the structural analysis of myelin, we investigated the use of in vivo labeling by metabolically incorporating non-toxic levels of deuterium (2H; D) via drinking water into a pregnant dam (D-dam) and her developing embryos. All of the mice were sacrificed when the pups (D-pups) were 55 days old. Myelinated sciatic nerves were dissected, fixed in glutaraldehyde and examined by neutron diffraction. Parallel samples that were unfixed (trigeminal nerves) were frozen for mass spectrometry (MS). The diffraction patterns of the nerves from deuterium-fed mice (D-mice) vs. the controls (H-mice) had major differences in the intensities of the Bragg peaks but no appreciable differences in myelin periodicity. Neutron scattering density profiles showed an appreciable increase in density at the center of the lipid-rich membrane bilayer. This increase was greater in D-pups than in D-dam, and its localization was consistent with deuteration of lipid hydrocarbon, which predominates over transmembrane protein in myelin. MS analysis of the lipids isolated from the trigeminal nerves demonstrated that in the pups the percentage of lipids that had one or more deuterium atoms was uniformly high across lipid species (97.6% ± 2.0%), whereas in the mother the lipids were substantially less deuterated (60.6% ± 26.4%) with levels varying among lipid species and subspecies. The mass distribution pattern of deuterium-containing isotopologues indicated the fraction (in %) of each lipid (sub-)species having one or more deuteriums incorporated: in the D-pups, the pattern was always bell-shaped, and the average number of D atoms ranged from a low of ∼4 in fatty acid to a high of ∼9 in cerebroside. By contrast, in D-dam most lipids had more complex, overlapping distributions that were weighted toward a lower average number of deuteriums, which ranged from a low of ∼3–4 in fatty acid and in one species of sulfatide to a high of 6–7 in cerebroside and sphingomyelin. The consistently high level of deuteration in D-pups can be attributed to their de novo lipogenesis during gestation and rapid, postnatal myelination. The widely varying levels of deuteration in D-dam, by contrast, likely depends on the relative metabolic stability of the particular lipid species during myelin maintenance. Our current findings demonstrate that stably-incorporated D label can be detected and localized using neutron diffraction in a complex tissue such as myelin; and moreover, that MS can be used to screen a broad range of deuterated lipid species to monitor differential rates of lipid turnover. In addition to helping to develop a comprehensive understanding of the de novo synthesis and turnover of specific lipids in normal and abnormal myelin, our results also suggest application to studies on myelin proteins (which constitute only 20–30% by dry mass of the myelin, vs. 70–80% for lipid), as well as more broadly to the molecular constituents of other biological tissues. Deuterium metabolically assimilated into gestating mouse pups via drinking water. Neutron diffraction localized deuterium to middle of myelin membrane bilayers. Mass spectrometry identified 26 deuterated lipid species as myelinic. Myelin of pups substantially more deuterated than that of their dam. Deuterium differentially distributed among lipid species and subspecies. De novo lipid biogenesis vs. steady-state maintenance readily distinguished. Novel paradigm suggests application to animal models of human myelinopathies.
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