CsCl as an auxiliary reagent for the analysis of phosphatidylcholine mixtures by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS)

Matrix-assisted laser-desorption/ionization-mass spectrometric imaging of psilocybin and its analogues in psychedelic mushrooms using a cesium chloride-coated target plate

Fungi with hallucinogenic properties and neurotoxicity have been listed as prohibited drugs in recent years, but there is a lack of in situ quantification of psilocybin and analogues in these samples to avoid the decomposition of these psychoactive tryptamines in time-consuming sample preparation. In this study, matrix-assisted laser-desorption/ionization (MALDI)-Fourier transform ion cyclotron resonance (FT ICR) mass spectrometric imaging (MSI) was used to analyze the distribution of psilocybin and its analogues in hallucinogenic Psilocybe mushrooms. A cesium chloride (CsCl)-coated target plate was prepared to improve the detection sensitivity and reduce the interference of other compounds or decomposition products with very similar m/z values in MALDI-FT ICR MS analysis. Psilocybin and other tryptamines with structurally similar compounds, including psilocin, baeocystin, tryptophan, tryptamine, and aeruginascin, were identified and imaged in the psilocybe tissue section; the semiquantitative analysis of the distribution of psilocybin was also investigated using a homemade 75-well CsCl-coated plate; and the target plate can be placed on the mass spectrometry target carrier along with the indium-tin oxide (ITO) conductive slide, which can simultaneously carry out matrix vapor deposition, thus ensuring the parallelism between the standards and samples in the pretreatment experiment and MSI. The contents of psilocybin and its analogues in the psilocybe tissue section can be evaluated from the color changes corresponding to different concentration standard curves. Furthermore, a comprehensive comparison between MALDI-FT ICR MS and ultra-performance liquid chromatography-quadrupole time of flight mass spectrometry (UPLC-Q/TOF MS) analysis was performed for quantification and validation. This study reduces the decomposition in time-consuming sample pretreatment and provides a powerful tool for drug abuse control and forensic analysis.

Analytical Platforms for the Determination of Phospholipid Turnover in Breast Cancer Tissue: Role of Phospholipase Activity in Breast Cancer Development

Altered lipid metabolism has been associated with the progression of various cancers, and aberrant expression of enzymes involved in the lipid metabolism has been detected in different stages of cancer. Breast cancer (BC) is one of the cancer types known to be associated with alterations in the lipid metabolism and overexpression of enzymes involved in this metabolism. It has been demonstrated that inhibition of the activity of certain enzymes, such as that of phospholipase A₂ in BC cell lines sensitizes these cells and decreases the IC₅₀ values for forthcoming therapy with traditional drugs, such as doxorubicin and tamoxifen. Moreover, other phospholipases, such as phospholipase C and D, are involved in intracellular signal transduction, which emphasizes their importance in cancer development. Finally, BC is assumed to be dependent on the diet and the composition of lipids in nutrients. Despite their importance, analytical approaches that can associate the activity of phospholipases with changes in the lipid composition and distribution in cancer tissues are not yet standardized. In this review, an overview of various analytical platforms that are applied on the study of lipids and phospholipase activity in BC tissues will be given, as well as their association with cancer diagnosis and tumor progression. The methods that are applied to tissues obtained from the BC patients will be emphasized and critically evaluated, regarding their applicability in oncology.

Relative quantitation of phosphatidylcholines with interfered masses of protonated and sodiated molecules by tandem and Fourier-transform ion cyclotron resonance mass spectrometry

The present work deals with deconvolution of interfered peaks of protonated and sodiated phosphatidylcholines to solve the problem of relative quantitation of these compounds. The method was developed based on the fact that adducts of phosphatidylcholines with proton and sodium ion give unique characteristic peaks in tandem mass spectrometry. Ultra-high-resolution Fourier-transform ion cyclotron resonance mass spectrometry was used to resolve interfered peaks and thus validate the results of tandem mass spectrometry-based deconvolution. Applicability of the method was tested with synthesized phosphatidylcholines and applied for tissue-spray analysis of the clinical samples and demonstrated good correlation (0.996) between MS/MS and Fourier-transform ion cyclotron resonance mass spectrometry results.

Swimming at different temperatures: The lipid composition of sperm from three freshwater fish species determined by mass spectrometry and nuclear magnetic resonance spectroscopy

The spawning behavior of different fish species is as diverse as their habitats. A lot of factors influence the (phospho)lipid composition of fish sperm, including the water temperature at which spawning takes place. Therefore, this study aimed on the elucidation of the phospholipid composition of sperm from three fish species from different orders (common carp - Cyprinus carpio, northern pike - Esox lucius and burbot - Lota lota) with different spawning temperatures by nuclear magnetic resonance spectroscopy (NMR), matrix-assisted laser desorption/ionization mass spectrometry and thin-layer chromatography (TLC) coupled to electrospray ionization mass spectrometry as well as gas chromatography. Next to the lipid composition that was different for carp, northern pike and burbot, regarding the moieties of the different (phospho)lipid classes (particularly sphingomyelin and acidic phospholipids) and the saturation degree of the fatty acyl residues, there were differences observed depending on the analytical method that was used. The results from TLC and NMR investigations differed regarding the amounts of the different phospholipids. Reasons for these discrepancies are discussed in detail.

Recent Developments of Useful MALDI Matrices for the Mass Spectrometric Characterization of Lipids

Matrix-assisted laser desorption/ionization (MALDI) is one of the most successful “soft” ionization methods in the field of mass spectrometry and enables the analysis of a broad range of molecules, including lipids. Although the details of the ionization process are still unknown, the importance of the matrix is commonly accepted. Both, the development of and the search for useful matrices was, and still is, an empirical process, since properties like vacuum stability, high absorption at the laser wavelength, etc. have to be fulfilled by a compound to become a useful matrix. This review provides a survey of successfully used MALDI matrices for the lipid analyses of complex biological samples. The advantages and drawbacks of the established organic matrix molecules (cinnamic or benzoic acid derivatives), liquid crystalline matrices, and mixtures of common matrices will be discussed. Furthermore, we will deal with nanocrystalline matrices, which are most suitable to analyze small molecules, such as free fatty acids. It will be shown that the analysis of mixtures and the quantitative analysis of small molecules can be easily performed if the matrix is carefully selected. Finally, some basic principles of how useful matrix compounds can be “designed” de novo will be introduced.

A Comparison of Tissue Spray and Lipid Extract Direct Injection Electrospray Ionization Mass Spectrometry for the Differentiation of Eutopic and Ectopic Endometrial Tissues

Recent research revealed that tissue spray mass spectrometry enables rapid molecular profiling of biological tissues, which is of great importance for the search of disease biomarkers as well as for online surgery control. However, the payback for the high speed of analysis in tissue spray analysis is the generally lower chemical sensitivity compared with the traditional approach based on the offline chemical extraction and electrospray ionization mass spectrometry detection. In this study, high resolution mass spectrometry analysis of endometrium tissues of different localizations obtained using direct tissue spray mass spectrometry in positive ion mode is compared with the results of electrospray ionization analysis of lipid extracts. Identified features in both cases belong to three lipid classes: phosphatidylcholines, phosphoethanolamines, and sphingomyelins. Lipids coverage is validated by hydrophilic interaction liquid chromatography with mass spectrometry of lipid extracts. Multivariate analysis of data from both methods reveals satisfactory differentiation of eutopic and ectopic endometrium tissues. Overall, our results indicate that the chemical information provided by tissue spray ionization is sufficient to allow differentiation of endometrial tissues by localization with similar reliability but higher speed than in the traditional approach relying on offline extraction. Graphical Abstract ᅟ.

Endometriosis foci differentiation by rapid lipid profiling using tissue spray ionization and high resolution mass spectrometry

Obtaining fast screening information on molecular composition of a tissue sample is of great importance for a disease biomarkers search and for online surgery control. In this study, high resolution mass spectrometry analysis of eutopic and ectopic endometrium tissues (90 samples) is done using direct tissue spray mass spectrometry in both positive and negative ion modes. The most abundant peaks in the both ion modes are those corresponding to lipids. Species of three lipid classes are observed, phosphatidylcholines (PC), sphingomyelins (SM) and phosphoethanolamines (PE). Direct tissue analysis gives mainly information on PC and SM lipids (29 species) in positive ion mode and PC, SM and PE lipids (50 species) in negative ion mode which gives complementary data for endometriosis foci differentiation. The biggest differences were found for phospholipids with polyunsaturated acyls and alkils. Although, tissue spray shows itself as appropriate tool for tissue investigation, caution should be paid to the interpretation of mass spectra because of their higher complexity with more possible adducts formation and multiple interferences must be taken into account. The present work extends the application of direct tissue analysis for the rapid differentiation between endometriotic tissues of different foci.

Addition of CsCl reduces ion suppression effects in the matrix-assisted laser desorption/ionization mass spectra of triacylglycerol/phosphatidylcholine mixtures and adipose tissue extracts

RATIONALE

Ion suppression is a known disadvantage in mixture analysis. Matrix-assisted laser desorption/ionization (MALDI) mass spectra of crude adipose tissue extracts are dominated by triacylglycerol (TAG) signals while less abundant phospholipids such as phosphatidylcholines (PC) and particularly phosphatidylethanolamines (PE) are suppressed. It is suggested that addition of an excess of cesium (Cs) ions helps to overcome this problem.

METHODS

Selected lipid mixtures of known compositions and organic adipose tissue extracts were investigated by positive ion MALDI-time-of-flight mass spectrometry (TOF MS). 2,5-Dihydroxybenzoic acid (DHB) in methanol was used as the matrix. In selected cases the methanolic DHB solution was saturated by the addition of different solid alkali chlorides (such as NaCl, KCl, RbCl and CsCl). Studies on the solubilities of these salts in methanol and the interaction with DHB (by ¹³ C NMR) were also performed.

RESULTS

Saturation of the DHB matrix with solid CsCl leads to tremendous intensity differences, i.e. the intensities of the TAG signals (which otherwise dominate the mass spectra) are significantly reduced. In contrast, the intensity of small signals of phospholipids increases considerably. Decrease in the TAG signal intensity is particularly caused by the considerable size of the Cs⁺ ion which prevents successful analyte ionization.

CONCLUSIONS

The addition of CsCl improves the detectability of otherwise invisible or weak phospholipid ions. This is a simple approach to detect small amounts of phospholipids in the presence of an excess of TAG. No laborious and time-consuming separation of the total lipid extract into the individual lipid classes is required. Copyright © 2016 John Wiley & Sons, Ltd.

2,5-dihydroxybenzoic acid salts for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric lipid analysis: simplified spectra interpretation and insights into gas-phase fragmentation

RATIONALE

In the last decades the interest in lipids as important components of membranes has considerably increased. Nowadays, lipids are often routinely analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). In this regard, many relevant aspects are so far unknown, e.g., gas-phase stabilities, adduct formation and fragmentation. To fill this gap, MALDI matrix salts are presented which allow for simplified lipid analysis and elucidation of the underlying gas-phase fragmentation mechanisms.

METHODS

MALDI-TOF MS was used due to its beneficial properties for lipid investigations, e.g., high sensitivity, simple sample preparations, and a high tolerance to contaminants. The lipid hydrolysis, ionization and fragmentation properties of synthesized near neutral Na(+) and NH4 (+) salts of the commonly used MALDI matrix 2,5-dihydroxybenzoic acid were compared to that of DHB free acid itself as well as to base addition to DHB during dried-droplet sample preparation.

RESULTS

Many lipid classes such as sterols, triacylglycerols, phosphatidylcholines and -ethanolamines undergo initial protonation with subsequent prompt partial up to quantitative fragmentation when analyzed with classical acidic matrices by MALDI-TOF MS. Neutral matrix salts can prevent initial analyte fragmentation by suppression of analyte protonation. Additionally, intramolecular gas-phase fragmentation reactions can be inhibited due to analyte stabilization by cation chelation. Base addition during sample preparation leads not only to in situ generation of matrix salts but also to analyte hydrolysis.

CONCLUSIONS

Neutral DHB salts avoid separation of lipid species into several ionization states when used as matrices in MALDI-TOF MS. This allows for simplified lipid spectra interpretation. Due to the high cationization efficiency of DHB matrix salts, certain lipid classes become detectable which cannot be analyzed easily using standard acidic DHB.

Changes of murine sperm phospholipid composition during epididymal maturation determined by MALDI-TOF mass spectrometry

After leaving the testis, spermatozoa undergo several important steps of biochemical maturation during the passage through the epididymis, increasing their motility and fertilizing ability. These changes comprise (among others) the modification of the phospholipid composition of the sperm membrane. This process is thought to be important for the achievement of motility and fertilizing capacity. The lipids of the sperm membrane are characterized by a significant content of unsaturated fatty acyl residues, resulting in a high sensitivity against oxidative stress. This is evidenced by the appearance of lysolipids, for example, lysophosphatidylcholine, which acts like a detergent and is normally present in only very small amounts in biological membranes. The epididymis represents a tubular system comprising three main parts (caput, corpus, and cauda), through which the spermatozoa are consecutively transported undergoing distinct maturation stages. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, we established three striking differences in the lipid composition of murine spermatozoa from the different epididymal regions: in comparison to the caput sperm, sperm from the cauda are characterized by (1) a higher degree of unsaturation (PC 18:0/22:5 and 18:0/22:6 vs. 18:0/20:4 and 18:0/18:1), (2) an enhanced plasmalogen content, and (3) an enhanced content of lysolipids. These changes are likely to be of physiological relevance and potentially useful as diagnostic markers of sperm maturation and acquisition of motility.

Zebrafish brain lipid characterization and quantification by ¹H nuclear magnetic resonance spectroscopy and MALDI-TOF mass spectrometry

Lipids play an important role in many neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. Zebrafish models for these diseases have been recently developed. The detailed brain lipid composition of the adult zebrafish is not known, and therefore, the representativeness of these models cannot be properly evaluated. In this study, we characterized the total lipid composition of healthy adult zebrafish using (1)H nuclear magnetic resonance spectroscopy. A close resemblance of the zebrafish brain composition is shown in comparison to the human brain. Moreover, several lipids involved in the pathogenesis of neurodegenerative diseases (i.e., cholesterol, phosphatidylcholine, docosahexaenoic acid, and further, polyunsaturated fatty acids) are detected and quantified. These lipids might represent useful biomarkers in future research toward human therapies. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry coupled with high-performance thin-layer chromatography was used for further characterization of zebrafish brain lipids. Our results show that the lipid composition of the zebrafish brain is rather similar to the human brain and thus confirms that zebrafish represents a good model for studying various brain diseases.

Conservation of honey bee (Apis mellifera) sperm phospholipids during storage in the bee queen--a TLC/MALDI-TOF MS study

The honey bee (Apis mellifera) is characterized by a high degree of phenotypic plasticity of senescence-related processes, and has therefore become a model organism of gerontological research. Sperm of honey bee drones can remain fertile for several years within the storage organ of queens. The reason for this longevity is unknown, but the suppression of lipid peroxidation seems to play a decisive role. Here, we examined the questions of whether spermatheca- and in vitro-stored honey bee sperm are indeed resistant to lipid peroxidation, and whether the nature of sperm lipids could explain this resistance. The lipid composition of bee sperm was determined by matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) combined with thin-layer chromatography (TLC). The positive ion mass spectra of drone sperm lipids are dominated by two glycerophosphocholine (GPC) species, although small amounts of sphingomyelins (SM) and glycerophosphoethanolamines (GPE) are also detectable after TLC. Alkyl/acyl and alkenyl/acyl compounds of GPC, and alkyl/acyl as well as diacyl compounds of GPE were detected containing oleyl, oleoyl, palmityl and palmitoyl as the most abundant residues. Assignments of all compounds have been additionally verified by enzymatic digestion and exposition to HCl. During incubation of sperm in the presence of air, characteristic lipid oxidation products such as lysophosphatidylcholine (LPC) appear. Inside the spermatheca, however, sperm lipids are obviously protected from oxidation and their composition does not change, even if they are stored over years. Our data support the view that the membrane composition of honey bee sperm could help to explain the extraordinary longevity of these cells.

A survey of useful salt additives in matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry of lipids: introducing nitrates for improved analysis

RATIONALE

Matrix-assisted laser desorption/ionization (MALDI) is a powerful technique for the direct analysis of lipids in complex mixtures and thin tissue sections, making it an extremely attractive method for profiling lipids in health and disease. Lipids are readily detected as [M+H](+), [M+Na](+) and [M+K](+) ions in positive ion MALDI mass spectrometry (MS) experiments. This not only decreases sensitivity, but can also lead to overlapping m/z values of the various adducts of different lipids. Additives can be used to promote formation of a particular adduct, improving sensitivity, reducing spectral complexity and enhancing structural characterization in collision-induced dissociation (CID) experiments.

METHODS

Li(+), Na(+), K(+), Cs(+) and NH(4)(+) cations were considered as a range of salt types (acetates, chlorides and nitrates) incorporated into DHB matrix solutions at concentrations between 5 and 80 mM. The study was extended to evaluate the effect of these additives on CID experiments of a lipid standard, after optimization of collision energy parameters. Experiments were performed on a hybrid quadrupole time-of-flight (QqTOF) instrument.

RESULTS

The systematic evaluation of new and existing additives in MALDI-MS and MS/MS of lipids demonstrated the importance of additive cation and anion choice and concentration for tailoring spectral results.

CONCLUSIONS

The recommended choice of additive depends on the desired outcomes of the experiment to be performed (MS or MS/MS). Nitrates are found to be particularly useful additives for lipid analysis.

Phosphatidylcholine dimers can be easily misinterpreted as cardiolipins in complex lipid mixtures: a matrix-assisted laser desorption/ionization time-of-flight mass spectrometric study of lipids from hepatocytes

The liver is an important organ that is particularly involved in the lipid metabolism of the organism. Thus, high interest is nowadays focused on the lipid composition of the liver and particularly the liver parenchymal cells, the hepatocytes. Hepatocytes contain common phospholipids (PL) such as phosphatidylcholines, -ethanolamines and -inositols, for instance, that can be easily analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) even without previous separation of the PL mixture. However, in addition to common PL, hepatocytes possess also significant amounts of cardiolipin (CLP). The MS analysis of this PL is quite challenging because it (a) has a higher mass than common lipids and (b) possesses a higher negative charge. We will show here that caution is required if CLP is analyzed directly from the total lipid extract because PC dimers may be interpreted as cardiolipins if the positive ion MALDI mass spectra are analyzed.

Quantitative analysis of phospholipids using nanostructured laser desorption ionization targets

Since its introduction as an ionization technique in mass spectrometry, matrix-assisted laser desorption ionization (MALDI) has been applied to a wide range of applications. Quantitative small molecule analysis by MALDI, however, is limited due to the presence of intense signals from the matrix coupled with non-homogeneous surfaces. The surface used in nano-structured laser desorption ionization (NALDI) eliminates the need for a matrix and the resulting interferences, and allows for quantitative analysis of small molecules. This study was designed to analyze and quantitate phospholipid components of liposomes. Here we have developed an assay to quantitate the DPPC and DC(8,9)PC in liposomes by NALDI following various treatments. To test our method we chose to analyze a liposome system composed of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DC(8,9)PC (1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine), as DC(8,9)PC is known to undergo cross-linking upon treatment with UV (254 nm) and this reaction converts the monomer into a polymer. First, calibration curves for pure lipids (DPPC and DC(8,9)PC) were created using DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) as an internal standard. The calibration curve for both DPPC and DC(8,9)PC showed an R(2) of 0.992, obtained using the intensity ratio of analyte and internal standard. Next, DPPC:DC(8,9)PC liposomes were treated with UV radiation (254 nm). Following this treatment, lipids were extracted from the liposomes and analyzed. The analysis of the lipids before and after UV exposure confirmed a decrease in the signal of DC(8,9)PC of about 90%. In contrast, there was no reduction in DPPC signal.

Laser desorption and ionization time-of-flightversus matrix-assisted laser desorption and ionization time-of-flight mass spectrometry of and metal complexes

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been recently established as a powerful, "soft" ionization technique for the analysis of both transition metal complexes, which are used as metallo-drugs in the therapy of various types of tumors, and biomolecules. Since some metal complexes absorb light in the UV range, it should be possible to analyse them without additional matrices, i.e. using LDI-TOF MS. In this study, the matrix-free approach was tested for the analysis of [PtCl2(dach)] (dichloride(1,2-diamincyclohexane) platinum(ii)), [RuCl2(en)2]Cl (dichloridobis(ethylenediamine) ruthenium(iii) chloride) and [RuCl2(bipy)2]Cl (bis(bipyridine)dichloridoruthenium(iii) chloride) and the detection limit for these compounds was determined. In summary, the LDI-TOF mass spectra of [PtCl2(dach)] and [RuCl2(en)2]Cl are rather simple, whereas in the presence of 2,5-DHB as a matrix, additional peaks are generated. On the other hand, the standard MALDI-TOF mass spectrum of [RuCl2(bipy)2]Cl exhibits only one peak arising from the complex, in contrast to six peaks detectable in the LDI-TOF mass spectrum. The detection limit in the MALDI-TOF MS analysis of [PtCl2(dach)] and [RuCl2(bipy)2]Cl complexes was lower than that determined in LDI-TOF MS. Taking all into account, in this paper, we have demonstrated some advantages and drawbacks of the matrix-free LDI-TOF mass spectrometric analysis of transition metal complexes.

A simple desalting method for direct MALDI mass spectrometry profiling of tissue lipids

Direct MALDI-mass spectrometry (MALDI-MS) profiling of tissue lipids often observes isobaric phosphatidylcholine (PC) species caused by the endogenous alkali metal ions that bias the relative abundance of tissue lipids. Fresh rat brain cryosections were washed with 70% ethanol (EtOH), water (H₂O), or 150 mM ammonium acetate (NH₄Ac), and the desalting effectiveness of each fluid was evaluated by MALDI-MS profiling of PC and sphingomyelin (SM) species in tissue and in the washing runoff. The results indicated that EtOH and H₂O only partially desalted the tissue lipids, yet both substantially displaced the tissue lipids to the washing runoffs. On the other hand, NH₄Ac effectively desalted the tissue lipids and produced a runoff containing no detectable PCs or SMs. NH₄Ac wash also unveiled the underlying changes of PCs and SMs in the infarcted rat cortex previously masked by edema-caused increase of tissue sodium. The MS/MS of an isobaric PC in the infarcted cortex revealed the precursor change as the result of NH₄Ac wash and confirmed the desalting effectiveness of such wash. Other than desalting, NH₄Ac wash also removes contaminants in tissue, enhances the overall spectral quality, and benefits additionally in profiling of biological molecules in tissue.

Direct profiling of phospholipids and lysophospholipids in rat brain sections after ischemic stroke

Stroke, a deleterious cerebrovascular event, is caused by a critical reduction in the blood flow to the brain parenchyma that leads to brain injury and loss of brain functions. The inflammatory responses following ischemia often aggravate the neurological damage. Several pro-inflammatory mediators released after stroke are closely related to the metabolism of phospholipids. In this study we directly profiled the changes in phospholipids in the infarcted rat cerebral cortex 24 hours after middle cerebral artery occlusion (MCAO) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Several phosphatidylcholine (PC) species and sphingomyelin (SM) were significantly decreased after infarction. The cationization pattern of the remaining PCs showed a prominent shift from a mostly potassiated or protonated form to a predominantly sodiated pattern. Stroke also elevated the lysophosphatidylcholines (LPCs) and heme in tissue. The isobaric pairs in PC and LPC classes were resolved by masses through their respective alkali metal adducts in the presence of CsCl. The major fatty acyl LPC species were also structurally confirmed by MALDI-MS/MS. Overall, the results described the changes in PC and LPC species in the infarcted rat cortex. The elevated tissue levels of LPCs and heme signify the ongoing pathological lipid breakdown and the state of parenchymal inflammation. The elevated LPC level in tissue suggests a means of intervention through lysophospholipid metabolism that could potentially benefit the management of stroke and other acute neurological injuries.

Analysis of Lipids Using 2,4,6-Trihydroxyacetophenone as a Matrix for MALDI Mass Spectrometry

Lipids exhibit a broad range of chemical properties that make their analysis quite demanding. Today, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) represents a versatile tool in the field of lipid analysis, also offering the possibility for molecular structural identification using novel MALDI tandem time-of-flight (TOF/TOF) instrumentation. In this study, we evaluated 2,4,6-trihydroxyacetophenone (THAP) for the analysis of various lipid classes including neutral storage lipids (triacylglycerols), polar membrane lipids (glycerophospho- and sphingolipids), and glycosphingolipids. THAP proved to be a versatile matrix for the routine analysis of various lipids from biological samples ("lipidomics"). A sample preparation methodology was established using selective alkali salt doping for subsequent MS/MS experiments. Sodiated and lithiated molecules provided superior structural information on lipids (i.e., acyl group identification); thus, following this approach, both selective peak detection with high sensitivity and more reliable structural information were obtained simultaneously.

Colloidal Graphite-Assisted Laser Desorption/Ionization Mass Spectrometry and MSnof Small Molecules. 1. Imaging of Cerebrosides Directly from Rat Brain Tissue

Graphite-assisted laser desorption/ionization (GALDI) mass spectrometry (MS) was investigated for analysis of cerebrosides in a complex total brain lipid extract. Conventional MALDI MS and GALDI MS were compared regarding lipid analysis by using high-vacuum (HV, <10-6 Torr) LDI time-of-flight mass spectrometry and intermediate-pressure (IP, 0.17 Torr) linear ion trap mass spectrometry. Cerebrosides were not detected or detected with low sensitivity in MALDI MS because of other dominant phospholipids. By using GALDI, cerebrosides were detected as intense mass peaks without prior separation from other lipid species while mass peaks corresponding to phosphatidylcholines (PCs) were weak. The signal increase for cerebrosides and the signal decrease for PCs in GALDI MS were more significant in HV than in IP. MSn experiments of precursor ions corresponding to cerebrosides and PCs in brain lipid extract were performed to identify the detected species and distinguish isobaric ions. Twenty-two cerebroside species were detected by GALDI whereas eight cerebroside species were detected by MALDI. Sulfatides in brain lipid extract were also easily detected by GALDI MS in the negative ion mode. By forming a colloidal graphite thin film on rat brain tissue, direct lipid profiling by imaging mass spectrometry (IMS) was performed. Chemically selective images for cerebrosides and sulfatides were successfully obtained. Imaging tandem mass spectrometry (IMS/MS) was performed to generate images of specific product ions from isobaric species.

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.

Lipid composition of membranes of Escherichia coli by liquid chromatography/tandem mass spectrometry using negative electrospray ionization

A liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method using reversed-phase chromatography was developed for the analysis of phospholipids from bacterial extracts of a wild-type strain of Escherichia coli. Product ion mass spectra from [M--H](-) precursor ions allowed an identification of individual phospholipid species that includes both fatty acid composition and fatty acyl location on the glycerol backbone using diagnostic product ions. Thus, complete assignment, including sn-1/sn-2 fatty acyl position, was achieved for this strain of E. coli. In addition, the phospholipids were quantified relative to one another using an internal standard method.

The phosphatidylcholine/lysophosphatidylcholine ratio in human plasma is an indicator of the severity of rheumatoid arthritis: investigations by 31P NMR and MALDI-TOF MS

OBJECTIVES

Lipid second messengers, e.g. lysophosphatidylcholines (LPC) are involved in the pathogenesis of inflammatory diseases, for instance, rheumatoid arthritis (RA). Unfortunately, the analysis of LPC in complex mixtures as present in body fluids is still challenging.

DESIGN AND METHODS

Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) was applied for phospholipid (PL) analysis of organic extracts of synovial fluids from patients with RA as well as the corresponding plasma. These data were compared with results obtained by high resolution 31P NMR spectroscopy.

RESULTS

Synovial fluids may be replaced by plasma since the analysis of both body fluids gives very similar results. Patients undergoing treatment with TNF-alpha inhibitors (ADALIMUMAB (HUMIRA)) were examined in order to investigate whether the clinically-significant attenuation of disease activity is accompanied by changes of the PL composition of plasma. It will be shown that especially the PC/LPC ratios of plasma represent a reliable measure of inflammation and increase upon therapy.

CONCLUSIONS

Since plasma samples are readily available, our approach might be useful to draw conclusions before puncture of the affected joints is necessary and the PC/LPC ratio detected in plasma may serve as an indicator of RA in early stages.

Cholesterol esterase action on human high density lipoproteins and inhibition studies: detection by MALDI-TOF MS

The modification of lipoproteins by lipolytic enzymes such as cholesterol esterase (CEase) is assumed to play an important role in the pathogenesis of atherosclerosis. However, details of the activation and inhibition of CEase are still unknown. In this study, matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to investigate the extracts of human lipoproteins after treatment with CEase and to monitor the effects of the inhibitor 2-(diethylamino)-6,7-dihydro-4H,5H-cyclopenta[4,5] thieno[2,3-d][1,3]oxazin-4-one (DOT-3). This approach has the advantage that all lipid classes can be independently detected; therefore, conclusions on the mechanism of the applied enzyme are possible. Besides the expected decrease of cholesteryl esters (CEs) in HDL, a significantly enhanced content of lysophosphatidylcholine (LPC) was also detected, confirming the broad substrate specificity of CEase. It was also demonstrated that DOT-3 significantly inhibited the CEase-catalyzed cleavage of CEs in HDL. Phospholipid (PL) vesicles prepared from phosphatidylcholine (PC) or PC and cholesteryl linoleate were treated with CEase, and the changes in lipid composition were investigated. From the analysis of the generated LPC species in HDL and in the isolated lipid mixtures, it is evident that CEase catalyzes the cleavage of the fatty acid residues in both the sn-1 and sn-2 positions of the PLs. These effects are obvious in the absence as well as in the presence of detergents.

Radiation-induced free-radical transformation of phospholipids: MALDI-TOF MS study

Under the action of free-radical reaction initiators on membrane phospholipids, complex processes are taking place in both hydrophobic and hydrophilic parts of the phospholipids. Realization of these processes results in a mixture consisting of the initial lipids and their peroxidation and fragmentation products. Identification of compounds in such mixtures requires analytical methods of high sensitivity, reproducibility and accuracy to be applied. These properties are characteristic of the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method. In the studies of radiation-induced free-radical transformations of phosphatidylglycerol, the MALDI-TOF MS in combination with thin layer chromatography (TLC) has been shown to be able to detect and identify products of free-radical transformations taking place in both hydrophilic and hydrophobic parts of the phospholipid. Thus, the MALDI-TOF MS can serve as a suitable analytical tool to investigate free-radical transformations of lipids.

Matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectrometry in lipid and phospholipid research

The interest in the analysis of lipids and phospholipids is continuously increasing due to the importance of these molecules in biochemistry (e.g. in the context of biomembranes and lipid second messengers) as well as in industry. Unfortunately, commonly used methods of lipid analysis are often time-consuming and tedious because they include previous separation and/or derivatization steps. With the development of "soft-ionization techniques" like electrospray ionization (ESI) or matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF), mass spectrometry became also applicable to lipid analysis. The aim of this review is to summarize so far available experiences in MALDI-TOF mass spectrometric analysis of lipids. It will be shown that MALDI-TOF MS can be applied to all known lipid classes and the characteristics of individual lipids will be discussed. Additionally, some selected applications in medicine and biology, e.g. mixture analysis, cell and tissue analysis and the determination of enzyme activities will be described. Advantages and disadvantages of MALDI-TOF MS in comparison to other established lipid analysis methods will be also discussed.

Analysis of the phospholipid composition of bronchoalveolar lavage (BAL) fluid from man and minipig by MALDI-TOF mass spectrometry in combination with TLC

Surfaces of lungs are covered by the surfactant, an aqueous mixture of different phospholipids (PL) and proteins. Although the surfactant represents a relatively simple mixture of only a few PL (primarily phosphatidylcholine (PC) and phosphatidylglycerol (PG)), reliable methods of routine lipid analysis of the surfactant are still lacking. It will be shown that matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS) represents a suitable technique for the differentiation of the apolar components of the surfactant of different species. Samples of man and minipig are used in this study since both are known to vary in their PL composition. PL of surfactant were separated by thin-layer chromatography (TLC) and the obtained subfractions subjected to MALDI-TOF MS analysis in order to monitor the presence of even minor PL species. It will be shown that besides PG and PC, also phosphatidylethanolamine, -inositol and sphingomyelin can be detected in surfactant of man, whereas only sphingomyelin could be detected in the minipig sample.

Mass spectrometric detection of protein, lipid and heme components of cytochrome c oxidase from R. sphaeroides and the stabilization of non-covalent complexes from the enzyme

The cytochrome c oxidase enzyme from the Rhodobacter sphaeroides bacteria exists as a complex of four peptide subunits, two hemes, and a variety of lipids and metal ions held together by non-covalent forces. While the native enzyme functions as an associated unit, this complex usually dissociates during MALDI- TOF analysis. Through the use of matrix additives such as sucrose, the complete complex and partial complexes can be stabilized in the MALDI-TOF experiment. The dissociation of the complex allows for the detection of the components of the enzyme. The direct detection of associated lipids from an aqueous solution of the intact enzyme may eliminate the need for enzyme disruption and lipid extraction. The partial dissociation of multisubunit enzymes in such experiments may allow for the determination of subunit-subunit and subunit-lipid interactions

Influence of tidal volume on pulmonary NO release, tissue lipid peroxidation and surfactant phospholipids

Mechanical stress during ventilation may cause or aggravate acute lung injury. This study investigates the influence of low vs. high tidal volume (V(t)) on factors known to play key roles in acute lung injury: nitric oxide release, eNOS and iNOS gene expression, lipid peroxidation (LPO), and surfactant phospholipids (PL). Isolated rabbit lungs were subjected to one of three ventilation patterns for 135 min (V(t)-PEEP): 6 ml/kg-0 cm H(2)O. 12 ml/kg-0 cm H(2)O 6 ml/kg-5 cm H(2)O, 12 ml/kg-0 cm H(2)O, and 6 ml/kg-5 cm H(2)O resulted in comparable peak inspiratory pressure (PIP). This allowed comparing low and high V(t) without dependence on PIP. Ventilatory patterns did not induce changes in pulmonary artery pressure, vascular permeability (K(f,c)), PIP or pulmonary compliance. High V(t) in comparison with both of the low V(t) groups caused an increase in BALF-nitrite (30.6+/-3.0* vs. 21.4+/-2.2 and 16.2+/-3.3 microM), BALF-PL (1110+/-19* vs. 750+/-68 and 634+/-82 microg/ml), and tissue LPO product accumulation (0.62+/-0.051* vs. 0.48+/-0.052 and 0.43+/-0.031 nmol/mg), *P<0.05 each. Perfusate nitrite and BALF-PL composition (assessed by use of 31P-NMR spectroscopy and MALDI-TOF mass spectrometry) did not differ among the groups. High V(t) ventilation reduced eNOS gene expression but did not affect iNOS expression. The increased release of NO and the accumulation of LPO products may represent early lung injury while elevated BALF-PL may reflect distension-induced surfactant secretion.

Application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for monitoring the digestion of phosphatidylcholine by pancreatic phospholipase A(2)

Different methods were established for monitoring the phospholipase A(2)(PLA(2)) activity but all of them are rather cumbersome and time consuming. In this paper we have investigated the suitability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the determination of the PLA(2) activity. Phosphatidylcholine (PC) was digested with pancreatic PLA(2) under different conditions, i.e., various Ca(2+), PC, and PLA(2) concentrations. The digestion products were analyzed by MALDI-TOF MS and the concentration of lysophosphatidylcholine (LPC)-generated upon PLA(2) digestion-was determined by the application of an internal standard (known concentration) and by a comparison of their signal-to-noise ratios. The results clearly demonstrate that the LPC concentration determined from the MALDI-TOF mass spectra correlates directly with the activity of the applied enzyme. Additionally, LPC concentration increased with an increase in Ca(2+), as well as in the PC concentration. A single MALDI-TOF mass spectrum provides immediate information on the digestion products as well as on the residual substrate without requirements for any previous derivatization. MALDI-TOF MS can be easily and simply applied for monitoring the PLA(2) activity and we assume that this method might also be useful for other types of phospholipases.

Investigations of the lysophospholipid composition of human neutrophils under different stimulation conditions by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF MS) is usually used for the analyses of proteins carbohydrates and oligonucleotides. In spite of the number of advantages that MALDI-TOF MS exhibits for lipid analysis, this method has not often been applied in this field. In this paper we have extended our previous studies on the suitability of MALDI-TOF MS for the investigation of changes in the content of lipid-derived second messengers in organic extracts of human neutrophils. Qualitative differences in the lysophospholipid composition in organic extracts of the human neutrophils under different stimulation conditions could be easily observed by MALDI-TOF MS. Although there are still some methodological problems to be solved before this method can be routinely applied for the quantification of different lipid classes in complex biological mixtures (such as organic extracts of human neutrophils) it is shown here that MALDI-TOF MS possesses the capability to be used as a simple screening method for the investigation of the content of lipid-derived second messengers and of signalling pathways in cells.