Characterization of cardiolipin from Escherichia coli by electrospray ionization with multiple stage quadrupole ion-trap mass spectrometric analysis of [M - 2H + Na]- ions

Application and potential of multifrequency ultrasound in juice industry: Comprehensive analysis of inactivation and germination of Alicyclobacillus acidoterrestris spores

The majority of acidic fruits are perishable owing to their high-water activity, which promotes microbial activity, thus exhibiting metabolic functions that cause spoilage. Along with sanitary practices, several treatments are used during processing and/or storage to inhibit the development of undesirable bacteria. To overcome the challenges caused by mild heat treatment, juice manufacturers have recently increased their involvement in developing novel non-thermal processing procedures. Ultrasonication alone or in combination with other hurdle technologies may be used to pasteurize processed fruit juices. Multifrequency ultrasound has gained popularity due to the fact that mono-frequency ultrasound has less impact on bacterial inactivation and bioactive compound enhancement of fruit juice. Here, we present and discuss the fundamental information and technological knowledge of how spoilage bacteria, specifically Alicyclobacillus acidoterrestris, assemble resistant spores and inactivate and germinate dormant spores in response to nutrient germinants and physical treatments such as heat and ultrasound. To the authors' knowledge, no prior review of ultrasonic inactivation and germination of A. acidoterrestris in fruit juice exists. Therefore, this article aims to provide a review of previously published research on the inactivation and germination of A. acidoterrestris in fruit juice by ultrasound and heat.

Sex Differences of Cardiolipin in Tissue Distribution Based on Targeted Lipidomic Analysis by UHPLC-QTOF-MS/MS

Cardiolipins (CLs) are involved in ATP production, mitochondria biogenesis, apoptosis and mitophagy. Their tissue distribution can provide insight into the function of mitochondria and related diseases. However, the reports on tissue distribution of CLs remain limited. In this research, CLs were identified from heart, liver, kidney, spleen, lung, skeletal muscle, and brain using ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS/MS). Then, the distribution and sex difference of CLs in seven tissues were compared by a targeted lipidomic approach. A total of 88 CLs were identified, of which 58, 51, 57, 58, 50, 61 and 52 CLs were found in heart, liver, kidney, spleen, lung, skeletal muscle, and brain, respectively. Compared with the distribution of CLs in heart, liver, kidney, and skeletal muscle, the CLs in spleen, lung, and brain showed significant differences. Moreover, the results indicated that there were sex differences of CLs in liver and kidney. A total of 16 CLs in liver tissue and 21 CLs in kidney tissue, with significant sex differences, were screened. Our findings in the targeted lipidomic analysis demonstrated that tissue distribution of CLs was essential in the dynamic states and sex differences of CLs, which might provide evidence for the mitochondrial-related mechanism under physiological and pathological conditions.

Enhanced Characterization of Cardiolipins via Hybrid 193 nm Ultraviolet Photodissociation Mass Spectrometry

Cardiolipins (CLs) constitute a structurally complex class of glycerophospholipids with a unique tetraacylated structure accompanied by distinctive functional roles. Aberrations in the composition of this lipid class have been associated with disease states, spurring interest in the development of new approaches to differentiate the structures of diverse CLs in complex mixtures. The structural characterization of these complex lipids using conventional methods, however, suffers from limited resolution and frequently proves unable to discern subtle yet biologically significant features such as unsaturation sites or acyl chain position assignments. Here, we describe the synergistic use of chemical derivatization and hybrid dissociation techniques to characterize CL from complex biological mixtures with both double bond and sn positional isomer resolution in a shotgun mass spectrometry strategy. Utilizing (trimethylsilyl)diazomethane (TMSD), CL phosphate groups were methylated to promote positive-mode ionization by the production of metal-cationized lipids, enabling structural interrogation via hybrid higher-energy collisional activation/ultraviolet photodissociation (HCD/UVPD). This combination of TMSD derivatization and HCD/UVPD fragmentation results in diagnostic product ions that permit distinction and relative quantitation of sn-stereoisomers and the localization of double bonds. Applying this strategy to a total lipid extract from a thyroid carcinoma revealed a previously unreported 18:2/18:1 motif, elucidating a structural feature unique to the lipid class.

Localization of Carbon-Carbon Double Bond and Cyclopropane Sites in Cardiolipins via Gas-Phase Charge Inversion Reactions

Cardiolipins (CLs) are comprised of two phosphatic acid moieties bound to a central glycerol backbone and are substituted with four acyl chains. Consequently, a vast number of distinct CL structures are possible in different biological contexts, representing a significant analytical challenge. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) has become a widely used approach for the detection, characterization, and quantitation of complex lipids, including CLs. Central to this approach is fragmentation of the [CLs - H]- or [CL - 2H]2- anions by collision-induced dissociation (CID). Product ions in the resulting tandem mass spectra confirm the CL subclass assignment and reveal the numbers of carbons and degrees of unsaturation in each of the acyl chains. Conventional CID, however, affords limited structural elucidation of the fatty acyl chains, failing to discriminate isomers arising from different site(s) of unsaturation or cyclopropanation and potentially obscuring their metabolic origins. Here, we report the application of charge inversion ion/ion chemistry in the gas phase to enhance the structural elucidation of CLs. Briefly, CID of [CL - H]2- anions generated via negative ion ESI allowed for the assignment of individual fatty acyl substituents and phosphatidic acid moieties. Next, gas-phase derivatization of the resulting CL product ions, including fatty acyl carboxylate anions, was effected with gas-phase ion/ion charge inversion reactions with tris-phenanthroline magnesium reagent dications. Subsequent isolation and activation of the charge-inverted fatty acyl complex cations permitted the localization of both carbon-carbon double bond and cyclopropane motifs within each of the four acyl chains of CLs. This approach was applied to the de novo elucidation of unknown CLs in a biological extract revealing distinct isomeric populations and regiochemical relationships between double bonds and carbocyles.

Cationic π-Conjugated Polyelectrolyte Shows Antimicrobial Activity by Causing Lipid Loss and Lowering Elastic Modulus of Bacteria

Cationic, π-conjugated oligo-/polyelectrolytes (CCOEs/CCPEs) have shown great potential as antimicrobial materials to fight against antibiotic resistance. In this work, we treated wild-type and ampicillin-resistant (amp-resistant) Escherichia coli (E. coli) with a promising cationic, π-conjugated polyelectrolyte (P1) with a phenylene-based backbone and investigated the resulting morphological, mechanical, and compositional changes of the outer membrane of bacteria in great detail. The cationic quaternary amine groups of P1 led to electrostatic interactions with negatively charged moieties within the outer membrane of bacteria. Using atomic force microscopy (AFM), high-resolution transmission electron microscopy (TEM), we showed that due to this treatment, the bacterial outer membrane became rougher, decreased in stiffness/elastic modulus (AFM nanoindentation), formed blebs, and released vesicles near the cells. These evidences, in addition to increased staining of the P1-treated cell membrane by lipophilic dye Nile Red (confocal laser scanning microscopy (CLSM)), suggested loosening/disruption of packing of the outer cell envelope and release and exposure of lipid-based components. Lipidomics and fatty acid analysis confirmed a significant loss of phosphate-based outer membrane lipids and fatty acids, some of which are critically needed to maintain cell wall integrity and mechanical strength. Lipidomics and UV-vis analysis also confirmed that the extracellular vesicles released upon treatment (AFM) are composed of lipids and cationic P1. Such surface alterations (vesicle/bleb formation) and release of lipids/fatty acids upon treatment were effective enough to inhibit further growth of E. coli cells without completely disintegrating the cells and have been known as a defense mechanism of the cells against cationic antimicrobial agents.

Proton Transfer Reactions for the Gas-Phase Separation, Concentration, and Identification of Cardiolipins

Cardiolipin (CL) analysis demands high specificity, due to the extensive diversity of CL structures, and high sensitivity, due to their low relative abundance within the lipidome. While electrospray ionization mass spectrometry (ESI-MS) is the most widely used technology in lipidomics, the potential for multiple charging presents unique challenges for CL identification and quantification. Depending on the conditions, ESI-MS of lipid extracts in negative ion mode can give rise to cardiolipins ionized as both singly and doubly deprotonated anions. This signal degeneracy diminishes the signal-to-noise ratio, while in addition (for direct infusion), the dianion population falls within a m/z range already heavily congested with monoanions from more abundant glycerophospholipid subclasses. Herein, we describe a direct infusion strategy for CL profiling from total lipid extracts utilizing gas-phase proton-transfer ion/ion reactions. In this approach, lipid extracts are ionized by negative ion ESI generating both singly deprotonated phospholipids and doubly deprotonated CL anions. Charge reduction of the negative ion population by ion/ion reactions leads to an enhancement in singly deprotonated [CL - H]- species via proton transfer to the corresponding [CL - 2H]2-̅ dianions. To concentrate the [CL - H]- anion signal, multiple iterations of ion accumulation and proton-transfer ion/ion reaction can be performed prior to subsequent interrogation. Mass selection and collisional activation of the enriched population of [CL - H]- anions facilitates the assignment of individual fatty acyl substituents and phosphatidic acid moieties. Demonstrated advantages of this new approach derive from the improved performance in complex mixture analysis affording detailed characterization of low abundant CLs directly from a total biological extract.

Fast and Quantitative Phospholipidomic Analysis of SH-SY5Y Neuroblastoma Cell Cultures Using Liquid Chromatography-Tandem Mass Spectrometry and 31P Nuclear Magnetic Resonance

Global lipid analysis still lags behind proteomics with respect to the availability of databases, experimental protocols, and specialized software. Determining the lipidome of cellular model systems in common use is of particular importance, especially when research questions involve lipids directly. In Parkinson's disease research, there is a growing awareness for the role of the biological membrane, where individual lipids may contribute to provoking α-synuclein oligomerisation and fibrillation. We present an analysis of the whole cell and plasma membrane lipid isolates of a neuroblastoma cell line, SH-SY5Y, a commonly used model system for research on this and other neurodegenerative diseases. We have used two complementary lipidomics methods. The relative quantities of PC, PE, SMs, CL, PI, PG, and PS were determined by ³¹P NMR. Fatty acid chain composition and their relative abundances within each phospholipid group were evaluated by liquid chromatography-tandem mass spectrometry. For this part of the analysis, we have developed and made available a set of Matlab scripts, LipMat. Our approach allowed us to observe several deviations of lipid abundances when compared to published reports regarding phospholipid analysis of cell cultures or brain matter. The most striking was the high abundance of PC (54.7 ± 1.9%) and low abundance of PE (17.8 ± 4.8%) and SMs (2.7 ± 1.2%). In addition, the observed abundance of PS was smaller than expected (4.7 ± 2.7%), similar to the observed abundance of PG (4.5 ± 1.8%). The observed fatty acid chain distribution was similar to the whole brain content with some notable differences: a higher abundance of 16:1 PC FA (17.4 ± 3.4% in PC whole cell content), lower abundance of 22:6 PE FA (15.9 ± 2.2% in plasma membrane fraction), and a complete lack of 22:6 PS FA.

Hybrid 193 nm Ultraviolet Photodissociation Mass Spectrometry Localizes Cardiolipin Unsaturations

Developing alternative MS/MS strategies to distinguish isomeric lipids has become a high impact goal in shotgun lipidomics. Novel approaches have been developed to resolve structural features that are not discernible by traditional shotgun methods and have consequently promoted the discovery of new disease biomarkers. However, these methods have largely been limited to characterizing lipids with low structural complexity. Here, ultraviolet photodissociation (UVPD) strategies for phospholipid characterization are expanded for analysis of cardiolipins (CL), a class of phospholipids that exhibits a higher degree of structural complexity. A hybrid collision induced dissociation/193 nm UVPD (CID/UVPD) approach was implemented to pinpoint the location of both double bond and cyclopropyl unsaturations on the four acyl chains of CLs. This strategy was complemented with CID for the de novo elucidation of unknown CLs in biological extracts.

Evaluation of cardiolipin nanodisks as lipid replacement therapy for Barth syndrome

Barth syndrome (BTHS) is a mitochondrial disorder characterized by cardiomyopathy and skeletal muscle weakness. Disease results from mutations in the tafazzin (TAZ) gene, encoding a phospholipid transacylase. Defective tafazzin activity results in an aberrant cardiolipin (CL) profile. The feasibility of restoring the intracellular CL profile was tested by in vivo administration of exogenous CL in nanodisk (ND) delivery particles. Ninety mg/kg CL (as ND) was administered to doxycycline-inducible taz shRNA knockdown (KD) mice once a week. After 10 weeks of CL-ND treatment, the mice were sacrificed and tissues harvested. Liquid chromatography-mass spectrometry of extracted lipids revealed that CL-ND administration failed to alter the CL profile of taz KD or WT mice. Thus, although CL-ND were previously shown to be an effective means of delivering CL to cultured cells, this effect does not extend to an in vivo setting. We conclude that CL-ND administration is not a suitable therapy option for BTHS.

Lipidomics by ultrahigh performance liquid chromatography-high resolution mass spectrometry and its application to complex biological samples

An improved approach for selective and sensitive identification and quantitation of lipid molecular species using reversed phase chromatography coupled to high resolution mass spectrometry was developed. The method is applicable to a wide variety of biological matrices using a simple liquid-liquid extraction procedure. Together, this approach combines multiple selectivity criteria: Reversed phase chromatography separates lipids according to their acyl chain length and degree of unsaturation and is capable of resolving positional isomers of lysophospholipids, as well as structural isomers of diacyl phospholipids and glycerolipids. Orbitrap mass spectrometry delivers the elemental composition of both positive and negative ions with high mass accuracy. Finally, automatically generated tandem mass spectra provide structural insight into numerous glycerolipids, phospholipids, and sphingolipids within a single run. Calibration showed linearity ranges of more than four orders of magnitude, good values for accuracy and precision at biologically relevant concentration levels, and limits of quantitation of a few femtomoles on column. Hundreds of lipid molecular species were detected and quantified in three different biological matrices, which cover well the wide variety and complexity of various model organisms in lipidomic research. Together with a software package, this method is a prime choice for global lipidomic analysis of even the most complex biological samples.

Greazy: Open-Source Software for Automated Phospholipid Tandem Mass Spectrometry Identification

Lipid identification from data produced with high-throughput technologies is essential to the elucidation of the roles played by lipids in cellular function and disease. Software tools for identifying lipids from tandem mass (MS/MS) spectra have been developed, but they are often costly or lack the sophistication of their proteomics counterparts. We have developed Greazy, an open source tool for the automated identification of phospholipids from MS/MS spectra, that utilizes methods similar to those developed for proteomics. From user-supplied parameters, Greazy builds a phospholipid search space and associated theoretical MS/MS spectra. Experimental spectra are scored against search space lipids with similar precursor masses using a peak score based on the hypergeometric distribution and an intensity score utilizing the percentage of total ion intensity residing in matching peaks. The LipidLama component filters the results via mixture modeling and density estimation. We assess Greazy's performance against the NIST 2014 metabolomics library, observing high accuracy in a search of multiple lipid classes. We compare Greazy/LipidLama against the commercial lipid identification software LipidSearch and show that the two platforms differ considerably in the sets of identified spectra while showing good agreement on those spectra identified by both. Lastly, we demonstrate the utility of Greazy/LipidLama with different instruments. We searched data from replicates of alveolar type 2 epithelial cells obtained with an Orbitrap and from human serum replicates generated on a quadrupole-time-of-flight (Q-TOF). These findings substantiate the application of proteomics derived methods to the identification of lipids. The software is available from the ProteoWizard repository: http://tiny.cc/bumbershoot-vc12-bin64 .

Enzymatic measurement of phosphatidylglycerol and cardiolipin in cultured cells and mitochondria

Phosphatidylglycerol (PG) and cardiolipin (CL) are synthesized in mitochondria and regulate numerous biological functions. In this study, a novel fluorometric method was developed for measuring PG and CL using combinations of specific enzymes and Amplex Red. This assay quantified the sum of PG and CL (PG + CL) regardless of the species of fatty acyl chain. The calibration curve for PG + CL measurement was linear, and the detection limit was 1 μM (10 pmol in the reaction mixture). This new method was applied to the determinations of PG + CL content in HEK293 cells and CL content in purified mitochondria, because the mitochondrial content of PG is negligible compared with that of CL. We demonstrated that the PG+CL content was greater at low cell density than at high cell density. The overexpression of phosphatidylglycerophosphate synthase 1 (PGS1) increased the cellular contents of PG + CL and phosphatidylcholine (PC), and reduced that of phosphatidic acid. PGS1 overexpression also elevated the mitochondrial contents of CL and PC, but had no effect on the number of mitochondria per cell. In addition to the enzymatic measurements of other phospholipids, this simple, sensitive and high-throughput assay for measuring PG + CL can be used to understand cellular, physiological and pathological processes.

Characterization of polar lipids of Listeria monocytogenes by HCD and low-energy CAD linear ion-trap mass spectrometry with electrospray ionization

Listeria monocytogenes (L. monocytogenes) is a facultative, Gram-positive, food-borne bacterium, which causes serious infections. Although it is known that lipids play important roles in the survival of Listeria, the detailed structures of these lipids have not been established. In this contribution, we described linear ion-trap multiple-stage mass spectrometric approaches with high-resolution mass spectrometry toward complete structural analysis including the identities of the fatty acid substituents and their position on the glycerol backbone of the polar lipids, mainly phosphatidylglycerol, cardiolipin (CL), and lysyl-CL from L. monocytogenes. The location of the methyl side group along the fatty acid chain in each lipid family was characterized by a charge-switch strategy. This is achieved by first alkaline hydrolysis to release the fatty acid substituents, followed by tandem mass spectrometry on their N-(4-aminomethylphenyl) pyridinium (AMPP) derivatives as the M+ ions. Several findings in this study are unique: (1) we confirm the presence of a plasmalogen PG family that has not been previous reported; (2) an ion arising from a rare internal loss of lysylglycerol residue was observed in the MS(2) spectrum of lysyl-CL, permitting its distinction from other CL subfamilies.

Glycerophospholipids

Glycerophospholipids are phosphodiesters of glycerol and an alcohol referred to as the polar headgroup. The two glycerol carbinol groups are typically esterified with long chain fatty acyl groups which impart hydrophobic character to these otherwise polar molecules. The simplest glycerophospholipid is phosphatidic acid which is a monophosphoester of diacylglycerol. The common polar headgroups are choline, ethanolamine, serine, inositol, and glycerol which divide the phospholipids into different classes. This chapter discusses glycerophosphocholine lipids (PC), glycerophosphoethanolamine lipids (PE), phosphatidylserine (PS), phosphatidic acid (PA), phosphatidylinositol (PI), phosphatidylglycerol (PG), bis(acyl-lysophosphatidyl)glycerol (BMP) and cardiolipin.

Evaluation of the interplay among the charge of porphyrinic photosensitizers, lipid oxidation and photoinactivation efficiency in Escherichia coli

Photodynamic inactivation (PDI) is a simple and controllable method to destroy microorganisms based on the production of reactive oxygen species (ROS) (e.g., free radicals and singlet oxygen), which irreversibly oxidize microorganism's vital constituents resulting in lethal damage. This process requires the combined action of oxygen, light and a photosensitizer (PS), which absorbs and uses the energy from light to produce ROS. For a better understanding of the photoinactivation process, the knowledge on how some molecular targets are affected by PDI assumes great importance. The aim of this work was to study the relation between the number and position of positive charges on porphyrinic macrocycles and the changes observed on bacterial lipids. For that, five porphyrin derivatives, bearing one to four positive charges, already evaluated as PS on Escherichia coli inactivation, have been tested on lipid extracts from this bacterium, and also on a simple liposome model. The effects were evaluated by the quantification of lipid hydroperoxides and by analysis of the variation of fatty acyl profiles. E. coli suspensions and liposomes were irradiated with white light in the presence of each PS (5.0 μM). Afterwards, total E. coli lipids were extracted and quantified by phosphorus assay. Lipid oxidation on bacteria and on liposomes was quantified by ferrous oxidation in xylenol orange (FOX2 assay) and the analysis of the fatty acid profile was done by gas chromatography (GC). As previously observed for E. coli viability, an overall increase in the lipid hydroperoxides content, depending on the PS charge and on its distribution on the macrocycle, was observed. Analysis of the fatty acid profile has shown a decrease of the unsaturated fatty acids, corroborating the relation between lipid oxidation and PDI efficiency. Bacterial membrane phospholipids are important molecular targets of photoinactivation and the number of charges of the PS molecule, as well as their distribution, have a clear effect on the lipid oxidation and on the efficiency of PDI. The distinct extent of the formation of lipid hydroperoxy derivatives, depending on the PS used, is a good indicator of this process. The FOX2 assay allowed the detection of lipid peroxidation of E. coli membrane after PDI with all the five porphyrins, however, it was not the most appropriated method to quantify the relative lipid oxidation caused by PS with different efficiencies. The fatty acid analysis used to quantify the extent of lipid oxidation by the different PS provided better results. The same results were observed for the liposome model. Consequently, the model system based on liposomes is a fast and simple method that can be used for the screening of the efficiency of new PS, before proceeding with the more complex studies on bacterial models.

Insect endosymbiont proliferation is limited by lipid availability

Spiroplasma poulsonii is a maternally transmitted bacterial endosymbiont that is naturally associated with Drosophila melanogaster. S. poulsonii resides extracellularly in the hemolymph, where it must acquire metabolites to sustain proliferation. In this study, we find that Spiroplasma proliferation specifically depletes host hemolymph diacylglyceride, the major lipid class transported by the lipoprotein, Lpp. RNAi-mediated knockdown of Lpp expression, which reduces the amount of circulating lipids, inhibits Spiroplasma proliferation demonstrating that bacterial proliferation requires hemolymph-lipids. Altogether, our study shows that an insect endosymbiont acquires specific lipidic metabolites from the transport lipoproteins in the hemolymph of its host. In addition, we show that the proliferation of this endosymbiont is limited by the availability of hemolymph lipids. This feature could limit endosymbiont over-proliferation under conditions of host nutrient limitation as lipid availability is strongly influenced by the nutritional state.

DOI:http://dx.doi.org/10.7554/eLife.02964.001

All animals host a large number of harmless microbes. Often the two partners involved in these interactions will depend on each other to thrive: microbes support important host functions and in return the host provides a safe place to live and a continuous supply of food. Many microbes that are intimately associated with animals have lost the ability to gain nutrients from sources other than their host and are unable to survive on their own. However, in many cases, the source and the type of nutrients provided to the microbes are unknown.

One of the most common microbial species found in insects is Spiroplasma. This microbe lives in very large numbers in the fluid that fills the body cavities of insects, called the hemolymph. The microbes are transmitted from mother to offspring, and in some circumstances can provide benefits to the insects; for instance, Spiroplasma-infested flies appear to be protected against infection by some parasites. Unfortunately, as it is difficult to study insect–microbe relationships, little else is known about the physiological interactions between these two species.

Herren et al. studied the association between Spiroplasma and the fly Drosophila melanogaster. Under normal conditions, Spiroplasma only reduces the life span of the infested fly. This indicates that Spiroplasma has a low impact on the general fitness of its host, only negatively affecting the survival and egg laying ability of old flies. When flies had limited access to nutrients, the number of Spiroplasma they carried was reduced, without the flies losing fitness. This suggests that Spiroplasma growth is dependent on something in the flies' diet.

To understand which nutrients are important for the growth of Spiroplasma in Drosophila, Herren et al. analyzed the hemolymph of flies and found that there are fewer fatty-molecules, called lipids, when nutrients are limited. Healthy flies carrying Spiroplasma also have fewer lipids in their hemolymph, suggesting that these are what Spiroplasma feed on. Indeed, inactivating a protein required by the fly to transport lipids to the hemolymph reduced the growth of Spiroplasma in these flies.

Herren et al. concluded that the growth of Spiroplasma inside its host is limited by the availability of lipids in the hemolymph. Since this is dependent on diet, the dependence on lipids couples the growth of Spiroplasma to the nutritional state of its host. Herren et al. speculate that this mechanism reduces the fitness cost of harboring the microbes and prevents the damaging consequence of an uncontrolled proliferation of the microbes. Moreover, Spiroplasma's preference for lipids may explain why it helps to protect flies against parasitic infection, as many parasites also rely on lipids for their growth. Herren et al. suggest this strategy could also be used in other animal–microbe associations.

DOI:http://dx.doi.org/10.7554/eLife.02964.002

PhoPQ regulates acidic glycerophospholipid content of the Salmonella Typhimurium outer membrane

Gram-negative bacteria have two lipid membranes separated by a periplasmic space containing peptidoglycan. The surface bilayer, or outer membrane (OM), provides a barrier to toxic molecules, including host cationic antimicrobial peptides (CAMPs). The OM comprises an outer leaflet of lipid A, the bioactive component of lipopolysaccharide (LPS), and an inner leaflet of glycerophospholipids (GPLs). The structure of lipid A is environmentally regulated in a manner that can promote bacterial infection by increasing bacterial resistance to CAMP and reducing LPS recognition by the innate immune system. The gastrointestinal pathogen, Salmonella Typhimurium, responds to acidic pH and CAMP through the PhoPQ two-component regulatory system, which stimulates lipid A remodeling, CAMP resistance, and intracellular survival within acidified phagosomes. Work here demonstrates that, in addition to regulating lipid A structure, the S. Typhimurium PhoPQ virulence regulators also regulate acidic GPL by increasing the levels of cardiolipins and palmitoylated acylphosphatidylglycerols within the OM. Triacylated palmitoyl-PG species were diminished in strains deleted for the PhoPQ-regulated OM lipid A palmitoyltransferase enzyme, PagP. Purified PagP transferred palmitate to PG consistent with PagP acylation of both lipid A and PG within the OM. Therefore, PhoPQ coordinately regulates OM acidic GPL with lipid A structure, suggesting that GPLs cooperate with lipid A to form an OM barrier critical for CAMP resistance and intracellular survival of S. Typhimurium.

Photodynamic oxidation of Escherichia coli membrane phospholipids: new insights based on lipidomics

RATIONALE

The irreversible oxidation of biological molecules, such as lipids, can be achieved with a photosensitizing agent and subsequent exposure to light, in the presence of molecular oxygen. Although lipid peroxidation is an important toxicity mechanism in bacteria, the alterations caused by the photodynamic therapy on bacterial phospholipids are still unknown. In this work, we studied the photodynamic oxidation of Escherichia coli membrane phospholipids using a lipidomic approach.

METHODS

E. coli ATCC 25922 were irradiated for 90 min with white light (4 mW cm(-2), 21.6 J cm(-2)) in the presence of a tricationic porphyrin [(5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin triiodide, Tri-Py(+)-Me-PF]. Lipids were extracted and separated by thin-layer chromatography. Phospholipid classes were quantified by phosphorus assay and analyzed by electrospray ionization tandem mass spectrometry. Fatty acids were analyzed by gas chromatography. Quantification of lipid hydroperoxides was performed by FOX2 assay. Analysis of the photodynamic oxidation of a phospholipid standard was also performed.

RESULTS

Our approach allowed us to see that the photodynamic treatment induced the formation of a high amount of lipid hydroperoxides in the E. coli lipid extract. Quantification of fatty acids revealed a decrease in the unsaturated C16:1 and C18:1 species suggesting that oxidative modifications were responsible for their variation. It was also observed that photosensitization induced the oxidation of phosphatidylethanolamines with C16:1, C18:1 and C18:2 fatty acyl chains, with formation of hydroxy and hydroperoxy derivatives.

CONCLUSIONS

Membrane phospholipids of E. coli are molecular targets of the photodynamic effect induced by Tri-Py(+) -Me-PF. The overall change in the relative amount of unsaturated fatty acids and the formation of PE hydroxides and hydroperoxides evidence the damages in bacterial phospholipids caused by this lethal treatment.

Matrix-assisted laser desorption/ionization mass spectrometry imaging of cardiolipins in rat organ sections

Cardiolipin (CL) is a class of phospholipid tightly associated with the mitochondria functions and a prime target of oxidative stress. Peroxidation of CL dissociates its bound cytochrome C, a phenomenon that reflects oxidative stress sustained by the organ and a trigger for the intrinsic apoptotic pathway. However, CL distribution in normal organ tissues has yet to be documented. Fresh rat organs were snap-frozen, cut into cryosections that were subsequently desalted with ammonium acetate solution, and vacuum-dried. CL distribution in situ was determined using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) technique on sections sublimed with 2,5-dihydroxybenzoic acid. CL images in rat cardiac ventricular section showed a homogeneous distribution of a single m/z 1447.9 ion species that was confirmed as the (18:2)4 CL by tandem mass spectrometry. The presence of low abundant (18:2)3(18:1) CL with the bulk (18:2)4 CL in quadriceps femoris rendered the muscle CL exhibiting a slightly deviated isotopic pattern from that of cardiac muscle. In rat liver, MALDI-MSI unveiled three CL-containing mass ranges, each with a unique in situ distribution pattern. Co-registration of the CL ion images with its stained liver section image further revealed the association of CLs in each mass range with the functional zones in the liver parenchyma and suggests the participation of in situ CLs with localized hepatic functions such as oxidation, conjugation, and detoxification. The advances in CL imaging offer an approach with molecular accuracy to reveal potentially dysregulated metabolic machineries in acute and chronic diseased states.

Structural studies on archaeal phytanyl-ether lipids isolated from membranes of extreme halophiles by linear ion-trap multiple-stage tandem mass spectrometry with electrospray ionization

The structures of archaeal glycerophospholipids and glycolipids are unique in that they consist of phytanyl substituents ether linked to the glycerol backbone, imparting stability to the molecules. In this contribution, we described multiple-stage linear ion-trap combined with high resolution mass spectrometry toward structural characterization of this lipid family desorbed as lithiated adduct ions or as the [M-H](-) and [M-2H](2-) ions by ESI. MS(n) on various forms of the lithiated adduct ions yielded rich structurally informative ions leading to complete structure identification of this lipid family, including the location of the methyl branches of the phytanyl chain. By contrast, structural information deriving from MS(n) on the [M-H](-) and [M-2H](2-) ions is not complete. The fragmentation pathways in an ion-trap, including unusual internal loss of glycerol moiety and internal loss of hexose found for this lipid family were proposed. This mass spectrometric approach provides a simple tool to facilitate confident characterization of this unique lipid family.

Bioinformatics tools and challenges in structural analysis of lipidomics MS/MS data

Lipidomics, the systematic study of the lipid composition of a cell or tissue, is an invaluable complement to knowledge gained by genomics and proteomics research. Mass spectrometry provides a means to detect hundreds of lipids in parallel, and this includes low abundance species of lipids. Nevertheless, frequently occurring isobaric and isomeric lipid species complicate lipidomics analyses from an analytical and bioinformatics perspective. Various MS/MS strategies have evolved to resolve ambiguous identifications of lipid species, and these strategies have been supported by corresponding bioinformatics analysis tools. This review intends to familiarize readers with available bioinformatics MS/MS analysis tools and databases, the structural information obtainable from these, and their applicability to different MS/MS strategies. Finally, future challenges in detecting double bond positions are investigated from a bioinformatics perspective.

Simultaneous analysis of cardiolipin and lipid A from Helicobacter pylori by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Cardiolipin (CL) is an anionic tetraacylphospholipid found in mammalian tissues, inner membrane of mitochondria and in the cytoplasmic membrane of Gram-positive and -negative bacteria. Lipid A is the principal structural component responsible for the range of biological activities of lipopolysaccharides. Here we report a MALDI-MS-based method for the sensitive simultaneous analysis of CL and lipid A from Helicobacter pylori cells. The sensitivity was demonstrated by the analysis of CL and lipid A from a single bacterial colony of in vitro grown H. pylori strain NCTC 11637 (ATCC 43504). We then characterized the CL and lipid A structures in H. pylori cells grown under three different conditions, on agar-horse blood plates, in liquid culture and ex vivo. The results revealed the presence of high amounts of myristic (C14:0) and 19-carbon cyclopropane (C19:0cyc) fatty acids. Alterations in CL structure were observed in H. pylori cells cultivated on plates as compared with the bacteria grown in broth culture. Furthermore, significant changes in lipid A acylation pattern were detected in H. pylori cells during formation of coccoids. In contrast, structural analysis of CL from ex vivo H. pylori cells recovered from the stomachs of infected Mongolian gerbils demonstrated only minor changes in acyl chain combination. This is the first report of simultaneous analysis of CL and lipid A from ex vivo cells of H. pylori.

Hydrophilic interaction liquid chromatography: ESI-MS/MS of plasmalogen phospholipids from Pectinatus bacterium

Liquid chromatography-electrospray tandem mass spectrometry (LC/ESI-MS/MS) was used to analyze phospholipids from three species of the anaerobic beer-spoilage bacterial genus Pectinatus. Analysis of total lipids by HILIC (Hydrophilic Interaction Liquid Chromatography) column succeeded in separating diacyl- and plasmalogen phospholipids. Plasmalogens were then analyzed by means of the ESI-MS/MS and more than 220 molecular species of four classes of plasmalogens (PlsCho (choline plasmalogen), PlsEtn (ethanolamine plasmalogen), PlsGro (glycerol plasmalogen), and PlsSer (serine plasmalogen)) were identified. Major molecular species were c-p19:0/15:0 PlsEtn and PlsSer, which accounted for more than 4% of the total lipids.

Liquid chromatography/tandem mass spectrometry analysis of long-chain oxidation products of cardiolipin induced by the hydroxyl radical

The anionic phospholipid cardiolipin (CL) is found almost exclusively in the inner membrane of mitochondria, playing an important role in energy metabolism. Oxidation of CL has been associated with apoptotic events and various pathologies. In this study, electrospray ionization mass spectrometry coupled with liquid chromatography (LC/ESI-MS) was used to identify tetralinoleoyl-cardiolipin (TLCL) modifications induced by the OH(·) radical generated under Fenton reaction conditions (H(2)O(2) and Fe(2+)). The identified oxidation products of TLCL contained 2, 4, 6 and 8 additional oxygen atoms. These long-chain oxidation products were characterized by LC/ESI-MS/MS as doubly [M-2H](2-) and singly charged [M-H](-) ions. A detailed analysis of the fragmentation pathways of these precursor ions allowed the identification of hydroperoxy derivatives of CL. MS/MS analysis indicated that CL oxidation products with 4, 6 and 8 oxygen atoms have one fatty acyl chain bearing 4 oxygen atoms ([RCOO+4O](-)). Even when the TLCL molecule was oxidized by the addition of eight oxygen atoms, one of the acyl chains remained non-modified and one fatty acyl chain contained three or four oxygen atoms. This led us to conclude that under oxidative conditions by the OH(·) radical, the distribution of oxygens/peroxy groups in the CL molecule is not random, even when CL has the same fatty acyl chains in all the positions. Using mass spectrometry, the oxidation products have been unequivocally assigned, which may be useful for their detection in biological samples.

Toward total structural analysis of cardiolipins: multiple-stage linear ion-trap mass spectrometry on the [M - 2H + 3Li]+ ions

ESI multiple-stage linear ion-trap (LIT) mass spectrometric approaches for a near-complete structural characterization of cardiolipins (CLs), including identification of the fatty acyl substituents, assignment of the fatty acid substituents on the glycerol backbone, and location of the double-bond(s) or cyclopropyl group along the fatty acid chain are described. Upon collisionally activated dissociation (CAD) on the [M - 2H + 3Li](+) ions of CL in an ion-trap (MS(2)), two sets of fragment ions (designated as (a + 136) and (b + 136) ions) analogous to those previously reported for the [M - 2H + 3Na](+) ions were observed, leading to assignment of the phosphatidyl moieties attached to 1'- or 3'-position of the central glycerol. Further dissociation of the (a + 136) (or (b + 136)) ions (MS(3)) gives rise to the (a + 136 - R(1(or 2))CO(2)Li) (or b + 136 - R(1(or 2))CO(2)Li) ion pairs that identify the fatty acid moieties and their position on the glycerol backbone. This is followed by MS(4) on the (a + 136 - R(1(or 2))CO(2)Li) (or b + 136 - R(1(or 2))CO(2)Li) ion to eliminate a tricyclic glycerophosphate ester residue (136 Da) to yield the (a - R(1(or 2))CO(2)Li) ion, which is then subjected to MS(5). The MS(5) spectrum contains the structural information that locates the double-bond(s) or cyclopropyl group of the fatty acid substituents. Finally, the subsequent MS(6) on the dilithiated fatty acid ions generated from MS(5) also yields feature ions that confirm the assignment.

Oxidative lipidomics of apoptosis: quantitative assessment of phospholipid hydroperoxides in cells and tissues

Oxidized phospholipids play essential roles in execution of mitochondrial stage of apoptosis and clearance of apoptotic cells. The identification and quantification of oxidized phospholipids generated during apoptosis can be successfully achieved by oxidative lipidomics. With this approach, diverse molecular species of phospholipids and their hydroperoxides are identified and characterized by soft-ionization mass-spectrometry techniques such as electrospray ionization (ESI). Quantitative assessment of lipid hydroperoxides is performed by fluorescence HPLC-based protocol. The protocol is based on separation of phospholipids using two-dimensional-high-performance thin-layer chromatography (2-D-HPTLC). Phospholipids are hydrolyzed using phospholipase A(2). The fatty acid hydroperoxides (FA-OOH) released is quantified by a fluorometric assay using Amplex red reagent and microperoxidase-11 (MP-11). Detection limit of this protocol is 1-2 pmol of lipid hydroperoxides. Lipid arrays vs. oxidized lipid arrays can be performed by comparing the abundance of phospholipids with the abundance of oxidized phospholipids. Using oxidative lipidomics approach we show that the pattern of phospholipid oxidation during apoptosis is nonrandom and does not follow their abundance in several types of cells undergoing apoptosis and a variety of disease states. This has important implications for evaluation of apoptosis in vivo. The anionic phospholipids, cardiolipin (CL) and phosphatidylserine (PS), are the preferred peroxidation substrates.

The glycerophosphoinositols: cellular metabolism and biological functions

The glycerophosphoinositols are cellular products of phospholipase A(2) and lysolipase activities on the membrane phosphoinositides. Their intracellular concentrations can vary upon oncogenic transformation, cell differentiation and hormonal stimulation. Specific glycerophosphodiester phosphodiesterases are involved in their catabolism, which, as with their formation, is under hormonal regulation. With their mechanisms of action including modulation of adenylyl cyclase, intracellular calcium levels, and Rho-GTPases, the glycerophosphoinositols have diverse effects in multiple cell types: induction of cell proliferation in thyroid cells; modulation of actin cytoskeleton organisation in fibroblasts; and reduction of the invasive potential of tumour cell lines. More recent investigations include their effects in inflammatory and immune responses. Indeed, the glycerophosphoinositols enhance cytokine-dependent chemotaxis in T-lymphocytes induced by SDF-1alpha-receptor activation, indicating roles for these compounds as modulators of T-cell signalling and T-cell responses.

Electrospray ionization with low-energy collisionally activated dissociation tandem mass spectrometry of glycerophospholipids: mechanisms of fragmentation and structural characterization

This review describes the use of low-energy collisionally activated dissociation (CAD) with both tandem quadrupole and ion-trap mass spectrometry toward structural characterization of glycerophospholipids (GPLs), including classes of glycerophosphocholine, glycerophosphoethanolamine, glycerophosphoserine, glycerophosphoglycerol glycerophosphoinositol and glycerophosphatidic acid, as well as their lyso-, plasmanyl-, and plasmenylphospholipid subclasses. The mechanisms underlying the fragmentation processes leading to structural characterization of GPLs in various ion forms desorbed by electrospray ionization in the positive-ion and negative-ion modes are also discussed. The tandem mass spectrometric approaches afford the identification of the polar head group, the fatty acid substituents and the location of the radyl groups on the glycerol backbone of all the GPLs.

Determination of cellular lipids bound to human CD1d molecules

CD1 molecules are glycoproteins that present lipid antigens at the cell surface for immunological recognition by specialized populations of T lymphocytes. Prior experimental data suggest a wide variety of lipid species can bind to CD1 molecules, but little is known about the characteristics of cellular ligands that are selected for presentation. Here we have molecularly characterized lipids bound to the human CD1d isoform. Ligands were eluted from secreted CD1d molecules and separated by normal phase HPLC, then characterized by mass spectroscopy. A total of 177 lipid species were molecularly identified, comprising glycerophospholipids and sphingolipids. The glycerophospholipids included common diacylglycerol species, reduced forms known as plasmalogens, lyso-phospholipids (monoacyl species), and cardiolipins (tetraacyl species). The sphingolipids included sphingomyelins and glycosylated forms, such as the ganglioside GM3. These results demonstrate that human CD1d molecules bind a surprising diversity of lipid structures within the secretory pathway, including compounds that have been reported to play roles in cancer, autoimmune diseases, lipid signaling, and cell death.

Mass spectrometry analysis of oxidized phospholipids

The evidence that oxidized phospholipids play a role in signaling, apoptotic events and in age-related diseases is responsible for the increasing interest for the study of this subject. Phospholipid changes induced by oxidative reactions yield a huge number of structurally different oxidation products which difficult their isolation and characterization. Mass spectrometry (MS), and tandem mass spectrometry (MS/MS) using the soft ionization methods (electrospray and matrix-assisted laser desorption ionization) is one of the finest approaches for the study of oxidized phospholipids. Product ions in tandem mass spectra of oxidized phospholipids, allow identifying changes in the fatty acyl chain and specific features such as presence of new functional groups in the molecule and their location along the fatty acyl chain. This review describes the work published on the use of mass spectrometry in identifying oxidized phospholipids from the different classes.

Oxidative lipidomics of gamma-irradiation-induced intestinal injury

Although gamma-irradiation-induced tissue injury has been associated with lipid peroxidation, the individual phospholipid molecular targets have not been identified. We employed oxidative lipidomics to qualitatively and quantitatively characterize phospholipid peroxidation in a radiosensitive tissue, the small intestine, of mice exposed to total body irradiation (TBI) (10 and 15 Gy). Using electrospray ionization mass spectrometry we found that the major classes of intestine phospholipids-phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol-included clusters with highly oxidizable molecular species containing docosahexaenoic fatty acid. Molecular species of cardiolipin were represented by only two major less oxidizable individual molecular species-tetralinoleoylcardiolipin and trilinoleoyl-mono-oleoylcardiolipin. Selective and robust oxidation of two anionic phospholipids-cardiolipin in mitochondria and phosphatidylserine outside of mitochondria-was observed 24 h after gamma-irradiation. MS analysis detected several TBI-induced molecular species of oxidized cardiolipin: (C(18:2))(3)(C(18:2)-OOH), (C(18:2))(2)(C(18:2)-OOH)(2), (C(18:2))(1)(C(18:2)-OOH)(3), and (C(18:2)-OOH)(4). The major molecular species involved in TBI-triggered peroxidation of phosphatidylserine included C(18:0)/C(22:6)-OOH, C(18:0)/C(22:5)-OOH, and C(18:0)/C(22:4)-OOH. More abundant phospholipids-phosphatidylcholine and phosphatidylethanolamine-did not reveal any oxidative stress responses despite the presence of highly oxidizable docosahexaenoic fatty acid residues in their molecular species. A marked activation of caspases 3/7 that was detected in the intestine of gamma-irradiated mice indicates the involvement of apoptotic cell death in the TBI injury. Given that oxidized molecular species of cardiolipin and phosphatidylserine accumulate during apoptosis of different cells in vitro we speculate that cardiolipin and phosphatidylserine oxidation products may be useful as potential biomarkers of gamma-irradiation-induced intestinal apoptosis in vivo and may represent a promising target for the discovery of new radioprotectors and radiosensitizers.

Oxidative lipidomics of programmed cell death

Oxidized phospholipids play an important role in execution of the mitochondrial stage of apoptosis and clearance of apoptotic cells by macrophages. Therefore, the identification and quantification of oxidized phospholipids generated during apoptosis are very important. These can be achieved successfully by a newly developed approach--oxidative lipidomics, including a combination of electrospray ionization/mass spectrometry (ESI-MS) and fluorescence high-performance liquid chromatography techniques. Using oxidative lipidomics allows the quantification of specific phospholipids and their hydroperoxides. We characterized selective oxidation of two anionic phospholipids: cardiolipin (CL) in mitochondria and phosphatidylserine (PS) outside of mitochondria. ESI-MS analysis of cytochrome c/H(2)O(2)-driven tetralinoleoyl-CL (TLCL) oxidized molecular species demonstrated accumulation of products monohydroxy-TLCL; monohydroxy-monohydroperoxy-TLCL, monohydroxy-dihydroperoxy-TLCL, monohydroxy-trihydroperoxy-TLCL; and monohydroxy-tetrahydroperoxy-TLCL. We explored the application of oxidative lipidomics in a number of conditions in both in vitro and in vivo models where there is a known contribution of apoptosis and/or inflammation. Accumulation of CL hydroperoxides, originated from molecular species of CL containing C(22:6) after experimental traumatic brain injury, was shown. ESI-MS analysis of intestine CL in mouse after gamma-irradiation detected several CL oxidized molecular species: (C(18:2))(3)/(C(18:2+OOH)); (C(18:2))(2)/(C(18:2+OOH))(2); (C(18:2))(1)/(C(18:2+OOH))(3); and (C(18:2+OOH))(4). ESI-MS analysis and tandem MS/MS experiments revealed that PS with oxidized C(22:6) [m/z866 (C(18:0)/C(22:6+OOH)) originated from the ion at m/z 834 (C(18:0)/C(22:6))] was the major oxidized molecular species in the tested models in vitro and in vivo, including (1) cytochrome c/H(2)O(2) catalyzed oxidation of rat brain PS; (2) after experimental traumatic rat brain injury in rats, (3) in postmortem brain samples from patients with Alzheimer's disease, and (4) in the small intestine in gamma-irradiated mouse. We conclude that oxidative lipidomics is a powerful technique to study lipid oxidation and its role in cell death across a spectrum of tissues and insults.

Algorithm for processing raw mass spectrometric data to identify and quantitate complex lipid molecular species in mixtures by data-dependent scanning and fragment ion database searching

We developed the Lipid Qualitative/Quantitative Analysis (LipidQA) software platform to identify and quantitate complex lipid molecular species in biological mixtures. LipidQA can process raw electronic data files from the TSQ-7000 triple stage quadrupole and LTQ linear ion trap mass spectrometers from Thermo-Finnigan and the Q-TOF hybrid quadrupole/time-of-flight instrument from Waters-Micromass and could readily be modified to accommodate data from others. The program processes multiple spectra in a few seconds and includes a deisotoping algorithm that increases the accuracy of structural identification and quantitation. Identification is achieved by comparing MS(2) spectra obtained in a data-dependent manner to a library of reference spectra of complex lipids that we have acquired or constructed from established fragmentation rules. The current form of the algorithm can process data acquired in negative or positive ion mode for glycerophospholipid species of all major head-group classes.

Selective early cardiolipin peroxidation after traumatic brain injury: an oxidative lipidomics analysis

OBJECTIVE

Enhanced lipid peroxidation is well established in traumatic brain injury. However, its molecular targets, identity of peroxidized phospholipid species, and their signaling role have not been deciphered.

METHODS

Using controlled cortical impact as a model of traumatic brain injury, we employed a newly developed oxidative lipidomics approach to qualitatively and quantitatively characterize the lipid peroxidation response.

RESULTS

Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry analysis of rat cortical mitochondrial/synaptosomal fractions demonstrated the presence of highly oxidizable molecular species containing C(22:6) fatty acid residues in all major classes of phospholipids. However, the pattern of phospholipid oxidation at 3 hours after injury displayed a nonrandom character independent of abundance of oxidizable species and included only one mitochondria-specific phospholipid, cardiolipin (CL). This selective CL peroxidation was followed at 24 hours by peroxidation of other phospholipids, most prominently phosphatidylserine, but also phosphatidylcholine and phosphatidylethanolamine. CL oxidation preceded appearance of biomarkers of apoptosis (caspase-3 activation, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positivity) and oxidative stress (loss of glutathione and ascorbate).

INTERPRETATION

The temporal sequence combined with the recently demonstrated role of CL hydroperoxides (CL-OOH) in in vitro models of apoptosis suggest that CL-OOH may be both a key in vivo trigger of apoptotic cell death and a therapeutic target in experimental traumatic brain injury.

Direct MALDI-MS analysis of cardiolipin from rat organs sections

Cardiolipins (CL) are mitochondria specific lipids. They play a critical role in ATP synthesis mediated by oxidative phosphorylation. Abnormal CL distribution is associated with several disease states. MALDI-MS and MALDI-MS/MS were used to demonstrate in situ analysis and characterization of CL from tissue sections of organs containing high concentrations of mitochondria. Once the experimental parameters were established, a survey of CL distribution in heart, liver, kidney, leg muscle, and testis was undertaken. The major CL specie in the heart muscle, leg muscle, liver, and kidney is the (18:2)(4) CL, while liver and kidney also contain a minor specie, (18:2)(3)/(18:1) CL. The major CL specie in testis is the (16:0)(4) CL. The CL species distribution in various organs appeared to be in agreement with prior reports. Overall, proper matrix selection, tissue section handling, instrument tuning, and the inclusion of cesium ion in matrix ensured successful in situ MALDI-MS and MALDI-MS/MS analysis of CL. Upon modification and standardization, this method could be streamlined for rapid pathological diagnosis with short turnaround time in clinical settings.

Current literature in mass spectrometry

In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (6 Weeks journals ‐ Search completed at 4th. Oct. 2006)

Characterization of cardiolipin as the sodiated ions by positive-ion electrospray ionization with multiple stage quadrupole ion-trap mass spectrometry

The application of multiple-stage ion-trap (IT) mass spectrometric methods for the structural characterization of cardiolipin (CL), a 1,3-bisphosphatidyl-sn-glycerol that consists of four fatty acyl chains and three glycerol backbones (designated as A, B, and central glycerol, respectively), as the sodiated adduct ions in the positive-ion mode was evaluated. Following collisionally activated dissociation (CAD), the [M - 2H + 3Na]+ ions of CL yield two prominent fragment ion pairs that consist of the phosphatidyl moieties attached to the 1'- and 3'-position of the central glycerol, respectively, resulting from the differential losses of the diacylglycerol moieties containing A and B glycerol, respectively. The results are consistent with those previously described for the [M - H]- and [M - 2H + Na]- ions in the negative-ion mode, thus permitting assignment of the two phosphatidyl moieties attached to the 1'- or 3'-position of the central glycerol. The identities of the fatty acyl substituents and their positions on the glycerol backbones (glycerol A and B) are deduced from further degradation of the above ion pairs that give the fragment ions reflecting the fatty acid substituents at the sn-1 (or sn-1') and sn-2 (or sn-2') positions. The ions that arise from losses of the fatty acid substituents at sn-1 and sn-1', respectively, are prominent, but the analogous ions from losses of the fatty acid substituents at sn-2 and sn-2', respectively, are of low abundance in the MS2 product-ion spectra. This feature further confirms the assignment of the positions of the fatty acid substituents. The similar IT multiple-stage mass spectrometric approaches including MS2 and MS3 for structural characterization of CL using its [M + Na]+ and the [M - H + 2Na]+ ions are also readily applicable. However, their uses for structural characterization are less desirable because formation of the [M + Na]+ and the [M - H + 2Na]+ ions for CL is not predictable.