Determination of bioactive eicosanoids in brain tissue by a sensitive reversed-phase liquid chromatographic method with fluorescence detection

The variation in the levels of 18 amino acids in the cortex and plasma of cerebral ischemia C57BL/6 mice

Emerging evidence suggests that amino acid (AA) neurotransmitters play important roles in the pathophysiological processes of cerebral ischemia. In this work, an HPLC with fluorescence detection (HPLC-FLR) method was developed for the simultaneous determination of 18 AAs in the cortex and plasma after cerebral ischemia in mice. The ischemia model was prepared by bilateral common carotid artery occlusion, and then the cortex and plasma of the sham, ischemia, and naringenin groups were collected. Based on the protein precipitation method, a simple and effective sample preparation method was developed. The treated sample contained minimal proteins and lipids. The analysis of the sample was performed by the proposed HPLC-FLR method in combination with o-phthalaldehyde. The results showed a statistically significant increase in excitatory AAs (aspartic acid and glutamic acid), inhibitory AAs (glycine and 4-aminobutyric acid), phenylalanine, citrulline, isoleucine, and leucine levels, and a decrease of glutathione and phenylalanine levels when compared with the sham group in the cortex. Besides, the administration of naringenin had significant effects on excitatory AAs, inhibitory AA (glycine), glutamine, tyrosine, phenylalanine, and leucine levels when compared with the sham group in the cortex. These findings could be utilized in studying and clarifying the mechanisms of ischemia.

Tissue pretreatment for LC-MS/MS analysis of PUFA and eicosanoid distribution in mouse brain and liver

Polyunsaturated fatty acids (PUFAs) and eicosanoids are important mediators of inflammation. The functional role of eicosanoids in metabolic-syndrome-related diseases has been extensively studied. However, their role in neuroinflammation and the development of neurodegenerative diseases is still unclear. The aim of this study was the development of a sample pretreatment protocol for the simultaneous analysis of PUFAs and eicosanoids in mouse liver and brain. Liver and brain samples of male wild-type C57BL/6J mice (11-122 mg) were used to investigate conditions for tissue rinsing, homogenization, extraction, and storage. A targeted liquid chromatography-negative electrospray ionization tandem mass spectrometry method was applied to quantify 7 PUFAs and 94 eicosanoids. The final pretreatment protocol consisted of a 5-min homogenization step by sonication in 650 μL n-hexane/2-propanol (60:40 v/v) containing 2,6-di-tert-butyl-4-methylphenol at 50 μg/mL. Homogenates representing 1 mg tissue were extracted in a single step with n-hexane/2-propanol (60:40 v/v) containing 0.1% formic acid. Autoxidation was prevented by addition of 2,6-di-tert-butyl-4-methylphenol at 50 μg/mL and keeping the samples at 4 °C during sample preparation. Extracts were dried under nitrogen and reconstituted in liquid chromatography eluent before analysis. Recovery was determined to range from 45% to 149% for both liver and brain tissue. Within-run and between-run variability ranged between 7% and 18% for PUFAs and between 1% and 24% for eicosanoids. In liver, 7 PUFAs and 15 eicosanoids were quantified; in brain, 6 PUFAs and 21 eicosanoids had significant differences within the brain substructures. In conclusion, a robust and reproducible sample preparation protocol for the multiplexed analysis of PUFAs and eicosanoids by liquid chromatography-tandem mass spectrometry in liver and discrete brain substructures was developed.

Methods of the Analysis of Oxylipins in Biological Samples

Oxylipins are derivatives of polyunsaturated fatty acids and due to their important and diverse functions in the body, they have become a popular subject of studies. The main challenge for researchers is their low stability and often very low concentration in samples. Therefore, in recent years there have been developments in the extraction and analysis methods of oxylipins. New approaches in extraction methods were described in our previous review. In turn, the old analysis methods have been replaced by new approaches based on mass spectrometry (MS) coupled with liquid chromatography (LC) and gas chromatography (GC), and the best of these methods allow hundreds of oxylipins to be quantitatively identified. This review presents comparative and comprehensive information on the progress of various methods used by various authors to achieve the best results in the analysis of oxylipins in biological samples.

Lipidomic methodologies for biomarkers of chronic inflammation in nutritional research: ω-3 and ω-6 lipid mediators

The evolutionary history of hominins has been characterized by significant dietary changes, which include the introduction of meat eating, cooking, and the changes associated with plant and animal domestication. The Western pattern diet has been linked with the onset of chronic inflammation, and serious health problems including obesity, metabolic syndrome, and cardiovascular diseases. Diets enriched with ω-3 marine PUFAs have revealed additional improvements in health status associated to a reduction of proinflammatory ω-3 and ω-6 lipid mediators. Lipid mediators are produced from enzymatic and non-enzymatic oxidation of PUFAs. Interest in better understanding the occurrence of these metabolites has increased exponentially as a result of the growing evidence of their role on inflammatory processes, control of the immune system, cell signaling, onset of metabolic diseases, or even cancer. The scope of this review has been to highlight the recent findings on: a) the formation of lipid mediators and their role in different inflammatory and metabolic conditions, b) the direct use of lipid mediators as antiinflammatory drugs or the potential of new drugs as a new therapeutic option for the synthesis of antiinflammatory or resolving lipid mediators and c) the impact of nutritional interventions to modulate lipid mediators synthesis towards antiinflammatory conditions. In a second part, we have summarized methodological approaches (Lipidomics) for the accurate analysis of lipid mediators. Although several techniques have been used, most authors preferred the combination of SPE with LC-MS. Advantages and disadvantages of each method are herein addressed, as well as the main LC-MS difficulties and challenges for the establishment of new biomarkers and standardization of experimental designs, and finally to deepen the study of mechanisms involved on the inflammatory response.

Modern Methods of Sample Preparation for the Analysis of Oxylipins in Biological Samples

Oxylipins are potent lipid mediators derived from polyunsaturated fatty acids, which play important roles in various biological processes. Being important regulators and/or markers of a wide range of normal and pathological processes, oxylipins are becoming a popular subject of research; however, the low stability and often very low concentration of oxylipins in samples are a significant challenge for authors and continuous improvement is required in both the extraction and analysis techniques. In recent years, the study of oxylipins has been directly related to the development of new technological platforms based on mass spectrometry (LC–MS/MS and gas chromatography–mass spectrometry (GC–MS)/MS), as well as the improvement in methods for the extraction of oxylipins from biological samples. In this review, we systematize and compare information on sample preparation procedures, including solid-phase extraction, liquid–liquid extraction from different biological tissues.

A sensitive and improved throughput UPLC-MS/MS quantitation method of total cytochrome P450 mediated arachidonic acid metabolites that can separate regio-isomers and cis/trans-EETs from human plasma

A method for the detection and quantification of hydroxyl and epoxy arachidonic acid (AA) metabolites in human plasma was developed using liquid-liquid extraction, phospholipid saponification followed by derivatization of the acid moiety and liquid chromatographic tandem mass spectrometric detection. Derivatization with a pyridinium analog allowed for detection in the positive ion mode, greatly improving sensitivity and the stability of the more labile AA metabolites. The entire method utilizes a 96-well plate format, increasing sample throughput, and was optimized to measure 5-, 8-, 9-, 11-, 12-, 15-, 19-, and 20- hydroxyeicosatetraenoic acid (HETE), 5,6-, 8,9-, 11,12-, and 14,15- dihydroxyeicosatrienoic acid (DHET), and the regio- and cis-/ trans- isomers of 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acid (EET). The method was validated for its applicability over the FA concentration range found in human plasma. Using 100 μL aliquots of pooled human plasma, EET levels, particularly 5,6-EET, were observed to be higher than previously reported, with measured concentrations of 23.6 ng/ml for 5,6-EET, 5.6 ng/mL for 5,6-trans-EET, 8.0 ng/mL for 8,9-EET, 1.9 ng/mL for 8,9-trans-EET, 8.8 ng/mL for 11,12-EET, 3.4 ng/mL for 11,12-trans-EET, 10.7 ng/mL for 14,15-EET, and 1.7 ng/mL 14,15-trans- EET. This method is suitable for large population studies to elucidate the complex interactions between the eicosanoids and various disease states and may be used for quantitation of a wide variety of fattyacids beyond eicosanoids from small volumes of human plasma.

Detection of Lipid Mediators of Inflammation in the Human Tear Film

PURPOSE

Lipid mediators of inflammation are a group of signaling molecules produced by various cells under physiological conditions and modulate the inflammatory process during various pathologic conditions. Although eicosanoids and F2-isoprostanes are recognized lipid mediators of inflammation, there is no consensus yet on the extraction and mass spectrometry (MS) method for their analysis in individual human tear samples. Thus, the aim of this study was to develop an optimal method for extraction of lipid mediators of inflammation in the tear film and evaluate MS techniques for their analysis.

METHODS

Basal tears were collected from each eye of 19 subjects using glass microcapillaries. Lipid extraction was performed using either varying concentrations of acidified methanol, a modified Folch method, or solid-phase extraction. Initially, an untargeted analysis of the extracts was performed using SCIEX TripleTOF 5600 mass spectrometer to identify any lipid mediators of inflammation (eicosanoids) and later a targeted analysis was performed using the SCIEX 6500 Qtrap to identify and quantify prostaglandins and isoprostanes. Mass spectra and chromatograms were analyzed using Peakview, XCMS, and Multiquant software.

RESULTS

Prostaglandins and isoprostanes were observed and quantified using the Qtrap mass spectrometer under multiple reaction monitoring (MRM) mode after solid-phase extraction. Extraction with acidified methanol along with the Folch method produced cleaner spectra during MS with the Triple time of flight (TOF) mass spectrometer. Lipid mediators of inflammation were not observed in any of the tear samples using the Triple TOF mass spectrometer.

CONCLUSIONS

Solid-phase extraction may be the method of choice for extraction of prostaglandins and isoprostanes in low volumes of tears. The SCIEX Qtrap 6500 in MRM mode may be suitable to identify and quantify similar lipid mediators of inflammation.

Simultaneous LC-MS/MS analysis of eicosanoids and related metabolites in human serum, sputum and BALF

The differences among individual eicosanoids in eliciting different physiological and pathological responses are largely unknown because of the lack of valid and simple analytical methods for the quantification of individual eicosanoids and their metabolites in serum, sputum and bronchial alveolar lavage fluid (BALF). Therefore, a simple and sensitive LC-MS/MS method for the simultaneous quantification of 34 eicosanoids in human serum, sputum and BALF was developed and validated. This method is valid and sensitive with a limit of quantification ranging from 0.2 to 3 ng/mL for the various analytes, and has a large dynamic range (500 ng/mL) and a short run time (25 min). The intra- and inter-day accuracy and precision values met the acceptance criteria according to US Food and Drug Administration guidelines. Using this method, detailed eicosanoid profiles were quantified in serum, sputum and BALF from a pilot human study. In summary, a reliable and simple LC-MS/MS method to quantify major eicosanoids and their metabolites was developed and applied to quantify eicosanoids in human various fluids, demonstrating its suitability to assess eicosanoid biomarkers in human clinical trials.

Shotgun lipidomics in substantiating lipid peroxidation in redox biology: Methods and applications

Multi-dimensional mass spectrometry-based shotgun lipidomics (MDMS-SL) has made profound advances for comprehensive analysis of cellular lipids. It represents one of the most powerful tools in analyzing lipids directly from lipid extracts of biological samples. It enables the analysis of nearly 50 lipid classes and thousands of individual lipid species with high accuracy/precision. The redox imbalance causes oxidative stress, resulting in lipid peroxidation, and alterations in lipid metabolism and homeostasis. Some lipid classes such as oxidized fatty acids, 4-hydroxyalkenal species, and plasmalogen are sensitive to oxidative stress or generated corresponding to redox imbalance. Therefore, accurate assessment of these lipid classes can provide not only the redox states, but also molecular insights into the pathogenesis of diseases. This review focuses on the advances of MDMS-SL in analysis of these lipid classes and molecular species, and summarizes their recent representative applications in biomedical/biological research. We believe that MDMS-SL can make great contributions to redox biology through substantiating the aberrant lipid metabolism, signaling, trafficking, and homeostasis under oxidative stress-related condition.

Quantitative analysis of lipids: a higher-throughput LC-MS/MS-based method and its comparison to ELISA

Aim:

Lipids such as prostaglandins, leukotrienes and thromboxanes are released as a result of an inflammatory episode in pain (central and peripheral).

Methodology & results:

To measure these lipids as potential mechanistic biomarkers in neuropathic pain models, we developed a higher-throughput LC–MS/MS-based method with simultaneous detection of PGE2, PGD2, PGF2α, LTB4, TXB2 and 2-arachidonoyl glycerol in brain and spinal cord tissues. We also demonstrate that the LC–MS/MS method was more sensitive and specific in differentiating PGE2 levels in CNS tissues compared with ELISA.

Conclusion:

The ability to modify the LC–MS/MS method to accommodate numerous other lipids in one analysis, demonstrates that the presented method offers a cost–effective and more sensitive alternative to ELISA method useful in drug discovery settings.

In humans, lipids carry out various functions such as energy production and storage, insulation, digestion and absorption and hormone production. Out of the several lipids, prostaglandins, thromboxanes and leukotrienes play a critical role in cardiovascular diseases, allergic reactions and inflammation. Thus, it is important to monitor their levels as potential mechanistic biomarkers to effectively diagnose and treat the underlying diseases. We have successfully used a highly specific and higher-throughput mass spectrometric method to quantify these lipids in brain cells as well as in brain and spinal cord tissues from rats (pain model) and compared the data obtained in the traditional ELISA.

Analysis of cytochrome P450 metabolites of arachidonic acid by stable isotope probe labeling coupled with ultra high-performance liquid chromatography/mass spectrometry

Cytochrome P450 metabolites of arachidonic acid (AA) belong to eicosanoids and are potent lipid mediators of inflammation. It is well-known that eicosanoids play an important role in numerous pathophysiological processes. Therefore, quantitative analysis of cytochrome P450 metabolites of AA, including hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatreinoic acids (EETs), and dihydroxyeicosatrienoic acids (DHETs) can provide crucial information to uncover underlying mechanisms of cytochrome P450 metabolites of AA related diseases. Herein, we developed a highly sensitive method to identify and quantify HETEs, EETs, and DHETs in lipid extracts of biological samples based on stable isotope probe labeling coupled with ultra high-performance liquid chromatography/mass spectrometry. To this end, a pair of stable isotope probes, 2-dimethylaminoethylamine (DMED) and d4-2-dimethylaminoethylamine (d4-DMED), were utilized to facilely label eicosanoids. The heavy labeled eicosanoid standards were prepared and used as internal standards for quantification to minimize the matrix and ion suppression effects in mass spectrometry analysis. In addition, the detection sensitivities of DMED labeled eicosanoids improved by 3-104 folds in standard solution and 5-138 folds in serum matrix compared with unlabeled analytes. Moreover, a good separation of eicosanoids isomers was achieved upon DMED labeling. The established method provided substantial sensitivity (limit of quantification at sub-picogram), high specificity, and broad linear dynamics range (3 orders of magnitude). We further quantified cytochrome P450 metabolites of AA in rat liver, heart, brain tissues and human serum using the developed method. The results showed that 19 eicosanoids could be distinctly detected and the contents of 11-, 15-, 16-, 20-HETE, 5,6-EET, and 14,15-EET in type 2 diabetes mellitus patients and 5-, 11-, 12-, 15-, 16-, 20-HETE, 8,9-EET, and 5,6-DHET in myeloid leukemia patients had significant changes, demonstrating that these eicosanoids may have important roles on the pathogenesis of type 2 diabetes mellitus and myeloid leukemia.

Simultaneous quantification of leukotrienes and hydroxyeicosatetraenoic acids in cell culture medium using liquid chromatography/tandem mass spectrometry

Leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are important bioactive lipid mediators that participate in various pathophysiological processes. To advance understanding of the mechanisms that regulate these mediators in physiological and pathological processes, an analytical method using liquid chromatography/tandem mass spectrometry for the simultaneous quantification of LTB4, LTC4, LTD4, LTE4, 5-HETE, 8-HETE, 12-HETE and 15-HETE in cell culture media was developed. A Supel™-Select HLB solid-phase extraction cartridge was used for sample preparation. The compounds were separated on a C18 column using gradient elution with acetonitrile-water-formic acid (20:80:0.1, v/v/v) and acetonitrile-formic acid (100:0.1, v/v). The calibration curves of LTB4, LTD4, LTE4 and HETEs were linear in the range of 0.025-10 ng/mL, and the calibration curve of LTC4 was linear in the range of 0.25-10 ng/mL. Validation assessment showed that the method was highly reliable with good accuracy and precision. The stability of LTs and HETEs was also investigated. Using the developed method, we measured LTs and HETEs in the culture supernatant of the human mast cell line HMC-1. The present method could facilitate investigations of the mechanisms that regulate the production, release and signaling of LTs and HETEs.

Method for measuring lipid mediators, proteins, and messenger RNAs from a single tissue specimen

This article describes a new method for extracting RNA, protein, and lipid mediators from a single tissue specimen. Specifically, mouse bone fracture callus specimens were extracted into a single solution that was processed using three different procedures to measure messenger RNA (mRNA) levels by reverse transcription-quantitative polymerase chain reaction (RTqPCR), cytokines and growth factors using an xMAP method, and lipid mediators by liquid chromatography-tandem mass spectrometry (LC-MS/MS). This method has several advantages because it decreases the number of animals necessary for experimentation, allows division of the sample from a homogeneous mixture that reduces sample variability, and uses a solution that protects the integrity of the macromolecules during storage.

A review of analytical methods for eicosanoids in brain tissue

Eicosanoids are potent lipid mediators of inflammation and are known to play an important role in numerous pathophysiological processes. Furthermore, inflammation has been proven to be a mediator of diseases such as hypertension, atherosclerosis, Alzheimer's disease, cancer and rheumatoid arthritis. Hence, these lipid mediators have gained significant attention in recent years. This review focuses on chromatographic and mass spectrometric methods that have been used to analyze arachidonic acid and its metabolites in brain tissue. Recently published analytical methods such as LC-MS/MS and GC-MS/MS are discussed and compared in terms of limit of quantitation and sample preparation procedures, including solid phase extraction and derivatization. Analytical challenges are also highlighted.

Liquid chromatography-tandem mass spectrometry for the analysis of eicosanoids and related lipids in human biological matrices: a review

Today, there is an increasing number of liquid chromatography tandem-mass spectrometric (LC-MS/MS) methods for the analysis of eicosanoids and related lipids in biological matrices. An overview of currently applied LC-MS/MS methods is given with attention to sample preparation strategies, chromatographic separation including ultra high performance liquid chromatography (UHPLC) and chiral separation, as well as to mass spectrometric detection using multiple reacting monitoring (MRM). Further, the application in recent clinical research is reviewed with focus on preanalytical aspects prior to LC-MS/MS analysis as well as applications in major diseases of Western civilization including respiratory diseases, diabetes, cancer, liver diseases, atherosclerosis, and neurovascular diseases.

Exploratory investigation reveals parallel alteration of plasma fatty acids and eicosanoids in coronary artery disease patients

Fatty acids and eicosanoids are two important classes of signaling lipid molecules involved in the pathogenesis of cardiovascular diseases. To investigate the physiological functions and interplay between fatty acids and eicosanoids in coronary artery disease (CAD) patients, we developed an analytical approach for parallel quantitative analysis of plasma fatty acids and eicosanoids, using gas chromatography-tandem mass spectrometry (GC-MS/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). In this study, 26 fatty acids and 12 eicosanoids were confidently detected in 12 patients with confirmed coronary artery disease and 11 healthy subjects. Pattern recognition analysis (principal components analysis, orthogonal partial least-square discriminate analysis, and hierarchical clustering analysis) demonstrated that the plasma lipid profile of fatty acids and eicosanoids enabled robust discrimination of CAD patients versus healthy subjects. Significant differences in six fatty acids and five eicosanoids were noted among CAD patients and healthy subjects. The development of cardiovascular disease-induced metabolic change of fatty acids and eicosanoids, such as eicosapentaenoic acid, docosahexaenoic acid, arachidonic acid, hydroxyeicosatetraenoic acids and hydroxyoctadecadienoic acid, were consistent with previous isolated observations. Moderate-strong correlations between three plasma fatty acids and three eicosanoids from arachidonic acid metabolism were also observed. In brief, findings from this exploratory study offered a new insight on the roles of various bioactive lipid molecules in the development of coronary artery disease biomarkers.

Upregulation of cytochrome P450 2J3/11,12-epoxyeicosatrienoic acid inhibits apoptosis in neonatal rat cardiomyocytes by a caspase-dependent pathway

Short, nonlethal ischemic episodes administered to hearts directly after ischemic events (ischemic postconditioning, IPost) have an advantage over ischemic preconditioning (IPC). The endogenous cytochrome P450 2J3/11,12-epoxyeicosatrienoic acid (CYP2J3/11,12-EET) is upregulated by IPost, but not IPC, in the rat heart. The CYP epoxygenase inhibitor N-methylsulphonyl-6-(2-propargyloxyphenyl) hexanamide (MS-PPOH) reduces the cardioprotective effects of IPost, but not IPC. We proposed that upregulation of CYP2J3/11,12-EET during IPost induces cardioprotection by inhibiting cardiomyocyte apoptosis and that multiple apoptotic signals, including changes in mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore (mPTP) opening, mitochondrial cytochrome c leakage, caspase-3 levels, and levels of protective kinases such as Bcl-2 and Bax, are involved in the process. Neonatal rat cardiomyocytes underwent 3-h hypoxia followed by 2-, 5-, or 6-h reoxygenation (H/R) or three cycles of 5-min reoxygenation followed by 5-min hypoxia before 90-min reoxygenation (HPost); or were transfected with pcDNA3.1-CYP2J3 for 48 h before H/R; or were treated with MS-PPOH for 10 min before HPost. For HPost alone, pcDNA3.1-CYP2J3 transfection attenuated cardiomyocyte apoptosis to 68.4% (p<0.05) of that with H/R. pcDNA3.1-CYP2J3 transfection significantly decreased MMP and inhibited mPTP opening induced by H/R, reduced mitochondrial cytochrome c leakage, cleaved caspase-3 protein expression, and increased the ratio of Bcl-2 to Bax expression. MS-PPOH abolished this effect. Therefore, upregulation of CYP2J3/11,12-EET during HPost is involved in cardioprotection by inhibiting apoptosis via a caspase-dependent pathway, and the apoptosis-suppressive effect may have important clinical implications during HPost.

Enhancement of the capabilities of liquid chromatography-mass spectrometry with derivatization: general principles and applications

The integration of liquid chromatography-mass spectrometry (LC-MS) with derivatization is a relatively new and unique strategy that could add value and could enhance the capabilities of LC-MS-based technologies. The derivatization process could be carried out in various analytical steps, for example, sampling, storage, sample preparation, HPLC separation, and MS detection. This review presents an overview of derivatization-based LC-MS strategy over the past 10 years and covers both the general principles and applications in the fields of pharmaceutical and biomedical analysis, biomarker and metabolomic research, environmental analysis, and food-safety evaluation. The underlying mechanisms and theories for derivative reagent selection are summarized and highlighted to guide future studies.

Rapid simultaneous analysis of cyclooxygenase, lipoxygenase and cytochrome P-450 metabolites of arachidonic and linoleic acids using high performance liquid chromatography/mass spectrometry in tandem mode

Eicosanoids are oxidized arachidonate-derived lipid products generated by cyclooxygenase, lipoxygenase and cytochrome P-450 pathways. They are involved in diverse processes in health and disease and they are highly bioactive. Gas chromatography and enzyme immunoassays were used to quantify these mediators in the past. However, the recent availability of high-sensitivity liquid chromatography-mass spectrometry has provided a new approach for quantification that minimizes the sample size and the required preparation. This paper describes a rapid and simple technique for the simultaneous quantitative analysis of prostaglandin (PG) E(2) and PGJ(2); leukotrienes (LT) B(4) and D(4); 5-, 12-, 15- and 20-hydroxyeicosatetraenoic acids (HETEs); 13-hydroxyoctadecadienoic acid (13-HODE); 5,6-, 8,9-, 11,12- and 14,15-epoxyeicosatrienoic acids (EETs); and 11,12- and 14,15-dihydroxieicosatrienoic acids (DHETs) in cell culture supernatants and urine. We simultaneously analyzed 14 arachidonic acid metabolites representative from the three pathways, together with 13-HODE, a linoleic-derived product. Solid phase extraction was used for the sample preparation. The recoveries obtained ranged from 25% to 100%, depending on the metabolites. The LC/MS/MS method used the gradient on a C(18) column and electrospray ionization in negative ion detection mode. The method was optimized for sensitivity and for separation within 20 min. The linear ranges of the calibration curves were 0.1-200 ng/ml for PGE(2), PGJ(2), LTB(4), 5-HETE, 12-HETE, 15-HETE, 13-HODE, 11,12-EET, 11,12-DHET and 14,15-DHET, and 1-200ng/ml for LTD(4), 20-HETE, 5,6-EET, 8,9-EET and 14,15-EET. The advantages of this method include minimal sample preparation, high sensitivity and elimination of the problem associated with thermal instability in gas chromatography analysis.

Ultra-pressure liquid chromatography/tandem mass spectrometry targeted profiling of arachidonic acid and eicosanoids in human colorectal cancer

Cumulative evidence shows that eicosanoids such as prostaglandins, leukotrienes, thromboxanes and hydroxy eicosatetraenoic acids play an important role in associating inflammation with human colorectal cancer (CRC). In this study an ultra-pressure liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed and validated for the targeted profiling of eight relevant eicosanoids and the major metabolic precursor, arachidonic acid (AA), in human colon. Multiple reaction monitoring (MRM) experiments were performed in negative electrospray ionization mode. The metabolites were separated using a C(18) column consisting of 1.7 µm ethylene-bridged hybrid particles (100 × 2.1 mm i.d.) and gradient elution (50 to 95% of solvent B) with a mobile phase comprising water (0.1% formic acid) [solvent A] and acetonitrile (0.1% formic acid) [solvent B] at a flow rate of 0.4 mL/min. The analysis time for each sample was 5.5 min. Our UPLC/MS/MS method demonstrated satisfactory validation results in terms of selectivity, sensitivity, matrix effect, linearity, extraction efficiency, intra- and inter-day precision, accuracy and autosampler stability. The method was applied for the clinical profiling of matched pairs of cancerous and normal colon mucosae obtained from eight colorectal cancer patients. Endogenous levels of AA and selected eicosanoids such as prostaglandin E(2) (PGE(2)), prostacyclin (PGI(2)) [assayed as its stable hydrolytic product 6-keto-prostaglandin(1α) (6-k PGF(1α))] and 12-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12-HETE) were found to be significantly different (p <0.05; paired t-test) between cancerous and normal mucosae.

Analysis of bioactive eicosanoids in equine plasma by stable isotope dilution reversed-phase liquid chromatography/multiple reaction monitoring mass spectrometry

Oxidative metabolites of arachidonic acid (AA) are implicated in inflammation. Thus, we evaluated cycloxygenases (COXs) and lipoxygenases (LOs) mediated metabolism of AA to eicosanoids in equine plasma. Eicosanoids were extracted from plasma by two liquid-liquid extraction (LLE) steps; first was by chloroform/isopropanol and second by methyl-tert-butyl ether. For identification and quantification of 25 eicosanoids, a highly specific, selective and sensitive stable isotope dilution liquid chromatography (LC) multiple reaction monitoring (MRM) mass spectrometric (MS) method was developed. To avoid artifact formation of eicosanoids, deferoxamine was added to plasma to chelate residual transition metal ions. The calibration curve showed excellent linearity within 0.1 to 10 ng/mL. Slopes of the calibration curves generated by adding known quantities of eicosanoids in plasma were higher than those prepared in methanol/mobile phase A. Addition of deferoxamine decreased the slope of calibration curves generated using plasma. Limit of detection (LOD) was 1-10 pg on-column for 25 different eicosanoids. Inter-day accuracy was 86-111%, whereas intra-day accuracy was from 88-110%, and precision did not exceed 15% for all quality control (QC) samples. To evaluate the formation of eicosanoids, AA was exogenously added or endogenous AA was released from esterified lipids by calcium ionophore (CI) A23187 treatment of equine whole blood. Pre-treatment of equine whole blood with dexamethasone (DEX) significantly inhibited AA or CI A23187- mediated formation of eicosanoids. The validated method is now employed in studies undertaken to better understand the mechanism of action and pharmacokinetics/pharmacodynamics of eicosanoids after administration of glucocorticoids to horses. This method is reliably reproducible.

Cyclooxygenase (COX)-1 activity precedes the COX-2 induction in Aβ-induced neuroinflammation

Two different isoforms of cyclooxygenases, COX-1 and COX-2, are constitutively expressed under normal physiological conditions of the central nervous system, and accumulating data indicate that both isoforms may be involved in different pathological conditions. However, the distinct role of COX-1 and COX-2 and the probable interaction between them in neuroinflammatory conditions associated with Alzheimer's disease are conflicting issues. The aim of this study was to elucidate the comparable role of each COX isoform in neuroinflammatory response induced by β-amyloid peptide (Aβ). Using histological and biochemical methods, 13 days after stereotaxic injection of Aβ into the rat prefrontal cortex, hippocampal neuroinflammation and neuronal injury were confirmed by increased expression of tumor necrosis factor-alpha (TNF-α) and COX-2, elevated levels of prostaglandin E2 (PGE2), astrogliosis, activation of caspase-3, and neuronal cell loss. Selective COX-1 or COX-2 inhibitors, SC560 and NS398, respectively, were chronically used to explore the role of COX-1 and COX-2. Treatment with either COX-1 or COX-2 selective inhibitor or their combination equally decreased the level of TNF-α, PGE2, and cleaved caspase-3 and attenuated astrogliosis and neuronal cell loss. Interestingly, treatment with COX-1 selective inhibitor or the combined COX inhibitors prevented the induction of COX-2. These results indicate that the activity of both isoforms is detrimental in neuroinflammatory conditions associated with Aβ, but COX-1 activity is necessary for COX-2 induction and COX-2 activity seems to be the main source of PGE2 increment.

A LC-MS-based method for quantification of biomarkers from serum of allergic rats

Allergies are highly complex disorders with clinical manifestations ranging from mild oral, gastrointestinal, recurrent wheezing, and cutaneous symptoms to life-threatening systemic conditions. The levels of arachidonic acid, eicosanoids, histamine, organic acids and valine are considered to have a variety of physiological functions in connection with allergies. In this research, we have developed a RP-LC/MS method to separate and quantitate six different potential endogenous biomarkers, including leukotrieneB₄ (LTB₄), prostaglandinD₂ (PGD₂), arachidonic acid (AA), histamine (HI), lactic acid (LA) and valine (VAL), from serum of rats with ovalbumin (OVA)-induced allergy and normal rats, and the discrepancies between the model group and the control group were compared. The separation was performed on a Prevail C₁₈ column (250 mm × 4.6 mm, 5 μm) with a gradient elution of acetonitrile with 0.1% formic acid (v/v) and 10 mM ammonium formate (adjusted to pH 4.0 with formic acid) at a flow rate of 0.5 mL min⁻¹ The method was validated and shown to be sensitive, accurate (recovery values 76.16–92.57%) and precise (RSD < 10% for all compounds) with a linear range over several orders of magnitude. The method was successfully applied to rat serum and shown to be indicative of the endogenous levels of biomarkers within the rat body. The analysis of the biomarkers can provide insight into the allergic mechanisms associated with related diseases.

Prostanoid extraction and measurement

Prostanoids are involved in numerous physiological and pathophysiological processes in all body organs. Therefore, measurement of the concentration of the prostanoids has always been of importance for research and drug development purposes as a measure of cyclooxygenase (COX) activities. Techniques used for the measurement of prostanoids have been described decades ago. These techniques have come a long way and improvements have been reported, especially with the specificity in competition immunoassays that rely on the use of specific antibodies against a given prostanoid. These assays are relatively fast and do not involve the use of radioactive isotopes as radioimmunoassay. However, prior extraction is required in order to concentrate the prostanoids and remove interfering substances such as proteins. In this chapter, we describe two protocols for the extraction and measurement of prostanoids using C18 columns and commercial enzyme immunoassays, which do not require specialized equipments and can be performed in any laboratory with standard equipments.

Rapid, simultaneous quantitation of mono and dioxygenated metabolites of arachidonic acid in human CSF and rat brain

Currently, there are few biomarkers to predict the risk of symptomatic cerebral vasospasm (SV) in subarachnoid hemorrhage (SAH) patients. Mono and dioxygenated arachidonic acid metabolites, involved in the pathogenesis of ischemic injury, may serve as indicators of SV. This study developed a quantitative UPLC-MS/MS method to simultaneously measure hydroxyeicosatetraenoic acid (HETE), dihydroxyeicosatrienoic acid (DiHETrE), and epoxyeicosatrienoic acid (EET) metabolites of arachidonic acid in cerebrospinal fluid (CSF) samples of SAH patients. Additionally, we determined the recovery of these metabolites from polyvinylchloride (PVC) bags used for CSF collection. Linear calibration curves ranging from 0.208 to 33.3 ng/ml were validated. The inter-day and intra-day variance was less than 15% at most concentrations with extraction efficiency greater than 73%. The matrix did not affect the reproducibility and reliability of the assay. In CSF samples, peak concentrations of 8,9-DiHETrE, 20-HETE, 15-HETE, and 12-HETE ranged from 0.293 to 24.9 ng/ml. In rat brain cortical tissue samples, concentrations of 20-, 15-, 12-HETE, 8,9-EET, and 14,15-, 11,12-DiHETrE ranged from 0.57 to 23.99 pmol/g wet tissue. In rat cortical microsomal incubates, all 10 metabolites were measured with formation rates ranging from 0.03 to 7.77 pmol/mg/min. Furthermore, 12-HETE and EET metabolites were significantly altered by contact with PVC bags at all time points evaluated. These data demonstrate that the simultaneous measurement of these compounds in human CSF and rat brain can be achieved with a UPLC-MS/MS system and that this method is necessary for evaluation of these metabolites as potential quantitative biomarkers in future clinical trials.

Targeted quantitative analysis of eicosanoid lipids in biological samples using liquid chromatography-tandem mass spectrometry

The eicosanoids are a large family of arachidonic acid oxidation products that contain 20 carbon atoms. Cyclooxygenase (COX)-derived eicosanoids have important roles as autacoids involved in the regulation of cardiovascular function and tumor progression. Lipoxygenase (LO)-derived eicosanoids have been implicated as important mediators of inflammation, asthma, cardiovascular disease and cancer. Cytochrome P-450 (P450)-derived eicosanoids are both vasodilators and vasoconstrictors. There is intense interest in the analysis of reactive oxygen species (ROS)-derived isoprostanes (isoPs) because of their utility as biomarkers of oxidative stress. Enzymatic pathways of eicosanoid formation are regioselective and enantioselective, whereas ROS-mediated eicosanoid formation proceeds with no stereoselectivity. Many of the eicosanoids are also present in only pM concentrations in biological fluids. This presents a formidable analytical challenge because methodology is required that can separate enantiomers and diastereomers with high sensitivity and specificity. However, the discovery of atmospheric pressure ionization (API)/MS methodology of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and electron capture (EC) APCI has revolutionized our ability to analyze endogenous eicosanoids. LC separations of eicosanoids can now be readily coupled with API ionization, collision induced dissociation (CID) and tandem MS (MS/MS). This makes it possible to efficiently conduct targeted eicosanoid analyses using LC-multiple reaction motoring (MRM)/MS. Several examples of targeted eicosanoid lipid analysis using conventional LC-ESI/MS have been discussed and some new data on the analysis of eicosanoids using chiral LC-ECAPCI/MS has been presented.

Lipidomic analysis of prostanoids by liquid chromatography-electrospray tandem mass spectrometry

Lipidomics aim to generate qualitative and quantitative information on different classes of lipids and their species, and when applied in conjunction with proteomic and genomic assays, facilitate the comprehensive study of lipid metabolism in cellular, organ, or body systems. Advances in mass spectrometry have underpinned the expansion of lipidomic methodologies. Prostanoids are potent autacoids present in a plethora of cellular systems, known best for their intimate role in inflammation. Electrospray ionisation (ESI) allows the efficient ionisation of prostanoids in aqueous systems. ESI can be readily coupled to liquid chromatography (LC) followed by tandem mass spectrometry (MS/MS)-based detection, thus allowing the development of a potent and selective LC/ESI-MS/MS quantitative assays. The protocol we describe in this chapter outlines the steps we follow to (a) extract prostanoids from solid or liquid samples, (b) semi-purify the metabolites using solid phase extraction (c) set-up the HPLC separation using reverse phase chromatography and (d) set-up the MS/MS assay using a triple quadrupole mass spectrometer. The experimental details and notes presented here are based on the detailed protocols followed in our group.

UVB light upregulates prostaglandin synthases and prostaglandin receptors in mouse keratinocytes

Prostaglandins belong to a class of cyclic lipid-derived mediators synthesized from arachidonic acid via COX-1, COX-2 and various prostaglandin synthases. Members of this family include prostaglandins such as PGE(2), PGF(2alpha), PGD(2) and PGI(2) (prostacyclin) as well as thromboxane. In the present studies we analyzed the effects of UVB on prostaglandin production and prostaglandin synthase expression in primary cultures of undifferentiated and calcium-differentiated mouse keratinocytes. Both cell types were found to constitutively synthesize PGE(2), PGD(2) and the PGD(2) metabolite PGJ(2). Twenty-four hours after treatment with UVB (25 mJ/cm(2)), production of PGE(2) and PGJ(2) increased, while PGD(2) production decreased. This was associated with increased expression of COX-2 mRNA and protein. UVB (2.5-25 mJ/cm(2)) also caused marked increases in mRNA expression for the prostanoid synthases PGDS, mPGES-1, mPGES-2, PGFS and PGIS, as well as expression of receptors for PGE(2) (EP1 and EP2), PGD(2) (DP and CRTH2) and prostacyclin (IP). UVB was more effective in inducing COX-2 and DP in differentiated cells and EP1 and IP in undifferentiated cells. UVB readily activated keratinocyte PI-3-kinase (PI3K)/Akt, JNK and p38 MAP signaling pathways which are known to regulate COX-2 expression. While inhibition of PI3K suppressed UVB-induced mPGES-1 and CRTH2 expression, JNK inhibition suppressed mPGES-1, PGIS, EP2 and CRTH2, and p38 kinase inhibition only suppressed EP1 and EP2. These data indicate that UVB modulates expression of prostaglandin synthases and receptors by distinct mechanisms. Moreover, both the capacity of keratinocytes to generate prostaglandins and their ability to respond to these lipid mediators are stimulated by exposure to UVB.

Soluble epoxide hydrolase gene deletion is protective against experimental cerebral ischemia

BACKGROUND AND PURPOSE

Cytochrome P450 epoxygenase metabolizes arachidonic acid to epoxyeicosatrienoic acids (EETs). EETs are produced in the brain and perform important biological functions, including vasodilation and neuroprotection. However, EETs are rapidly metabolized via soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs). We tested the hypothesis that sEH gene deletion is protective against focal cerebral ischemia through enhanced collateral blood flow.

METHODS

sEH knockout (sEHKO) mice with and without EETs antagonist 14, 15 epoxyeicosa-5(Z)-enoic acid (EEZE) were subjected to 2-hour middle cerebral artery occlusion (MCAO), and infarct size was measured at 24 hours of reperfusion and compared to wild-type (WT) mice. Local CBF rates were measured at the end of MCAO using iodoantipyrine (IAP) autoradiography, sEH protein was analyzed by Western blot and immunohistochemistry, and hydrolase activity and levels of EETs/DHETs were measured in brain and plasma using LC-MS/MS and ELISA, respectively.

RESULTS

sEH immunoreactivity was detected in WT, but not sEHKO mouse brain, and was localized to vascular and nonvascular cells. 14,15-DHET was abundantly present in WT, but virtually absent in sEHKO mouse plasma. However, hydrolase activity and free 14,15-EET in brain tissue were not different between WT and sEHKO mice. Infarct size was significantly smaller, whereas regional cerebral blood flow rates were significantly higher in sEHKO compared to WT mice. Infarct size reduction was recapitulated by 14,15-EET infusion. However, 14,15-EEZE did not alter infarct size in sEHKO mice.

CONCLUSIONS

sEH gene deletion is protective against ischemic stroke by a vascular mechanism linked to reduced hydration of circulating EETs.

Development and validation of a high-performance liquid chromatography-electrospray mass spectrometry method for the simultaneous determination of 23 eicosanoids

Inflammation is implicated in the pathogenesis of a number of diseases, including cardiovascular disease. Current research is focused on developing assays to search for biomarkers for inflammation. Eicosanoids are the oxidative metabolites of arachidonic acid (eicosatetraenoic acid, AA), a long chain polyunsaturated fatty acid common in Western diets. AA can be oxidized by one of three pathways to form prostaglandins (PGs), leukotrienes (LTs), or a number of hydroxyl and epoxy compounds. These eicosanoids have a variety of physiological functions, including regulating inflammation. We have developed a method utilizing LC-MS to separate and quantitate 23 different eicosanoids from all the three oxidative pathways. The eicosanoids were separated using a gradient elution of acetonitrile with 0.1% formic acid (v/v) and water with 0.1% formic acid (v/v) at a flow rate of 1 mL/min with a Symmetry C18 column (250 mm x 4.6 mm). Deuterated eicosanoids were used as internal standards for quantitation. Mass spectrometric detection was carried out using an Agilent 1100-series LC-MSD with an electrospray ionization interface. Electrospray ionisation (ESI) mass spectra were acquired using negative ionization and selective ion monitoring. The method was validated and shown to be sensitive (LOQ at pg levels for most compounds), accurate (recovery values 75-120%) and precise (R.S.D.<20 for all compounds) with a linear range over several orders of magnitude. The method was applied to rat kidney tissue and shown to be indicative of the eicosanoid levels within a specific organ. The analysis of eicosanoids can provide insight into the inflammatory mechanisms associated with cardiovascular disease.

Fast and simple online sample preparation coupled with capillary LC-MS/MS for determination of prostaglandins in cell culture supernatants

An online 2-D strong cation exchange (SCX)-RP capillary liquid chromatographic (cLC) method with IT mass spectrometric (IT-MS/MS) detection for the simultaneous determination of prostaglandin (PG) A(1), PGD(2), PGE(1), PGE(2), PGF(2a), 6-keto-(6k)PGF(1a), and 15-Delta(12,14)-deoxy-PGJ(2) (15dPGJ(2)) in cell culture supernatants was developed and validated. Pretreatment of the cell culture supernatants included dilution and filtration, and the analysis time including all sample preparation steps was less than 50 min per sample. Peptides/proteins contained in the matrix were removed by the SCX column. LODs in the range of 0.4-2.2 ng/mL cell culture supernatant, recoveries higher than 80% and within- and between-day precisions of less than 30% RSDs were obtained. Human mesenchymal stem cells (hMSCs) were stimulated with cytokine-containing supernatants derived from activated T lymphocytes, and PG production was analyzed using the developed method. PGE(2 )was found in cultures from both untreated and stimulated hMSCs, while PGE(1) was present above the detection limit only in stimulated cells.

Quantitative profiling of epoxyeicosatrienoic, hydroxyeicosatetraenoic, and dihydroxyeicosatetraenoic acids in human intrauterine tissues using liquid chromatography/electrospray ionization tandem mass spectrometry

A reversed-phase liquid chromatography negative ion electrospray tandem mass spectrometry (LC/ESI-MS/MS) method was developed and validated to quantify a range of physiologically relevant eicosanoids, including 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs); 5-, 8-, 9-, 12-, and 15-hydroxyeicosatetraenoic acids (HETEs), and 5,6-, 8,15-, and 12,20-dihydroxyeicosatetraenoic acids (DiHETEs) in human intrauterine tissues. A solid-phase extraction method was employed to extract the eicosanoids, and gradient LC separation was performed on a Kromasil C(18) column. Mass spectrometric detection was performed by multiple reaction monitoring over a 31-min run time. The calibration curves were linear over the range of 4-400pmol/g tissue, and the intra- and interday precision and accuracy were within a coefficient of variation of 2.0 to 27.4% and 4.6 to 17.9%, respectively. The lower limit of quantitation was 1.0pmol/g tissue. The method was applied successfully to the characterization and quantitation of eicosanoids in the different compartments of human intrauterine tissues. Our results demonstrate significantly greater amounts of HETEs than of either the EETs or DiHETEs (P<0.001), irrespective of tissue type. Specifically, the metabolite 12-HETE was significantly more abundant (P<0.001) than all other HETEs. Of the EET metabolites, 5,6-EET predominated (P<0.001). A significant negative correlation between EETs and HETEs for all tissues (rho=-0.390, P<0.001) was identified, implying a biological feedback mechanism between these two arachidonate metabolite classes.

A liquid chromatography/mass spectrometric method for simultaneous analysis of arachidonic acid and its endogenous eicosanoid metabolites prostaglandins, dihydroxyeicosatrienoic acids, hydroxyeicosatetraenoic acids, and epoxyeicosatrienoic acids in rat brain tissue

A sensitive, specific, and robust liquid chromatography/mass spectrometric (LC/MS) method was developed and validated that allows simultaneous analysis of arachidonic acid (AA) and its cyclooxygenase, cytochrome P450, and lipoxygenase pathway metabolites prostaglandins (PGs), dihydroxyeicosatrienoic acids (DiHETrEs), hydroxyeicosatetraenoic acids (HETEs) and epoxyeicosatrienoic acids (EETs), including PGF(2alpha), PGE(2), PGD(2), PGJ(2), 14,15-DiHETrE, 11,12-DiHETrE, 8,9-DiHETrE, 5,6-DiHETrE, 20-HETE, 15-HETE, 12-HETE, 9-HETE, 8-HETE, 5-HETE, 14,15-EET, 11,12-EET, 8,9-EET, and 5,6-EET in rat brain tissues. Deuterium labeled PGF(2alpha)-d(4), PGD(2)-d(4), 15(S)-HETE-d(8), 14,15-EET-d(8), 11,12-EET-d(8), 8,9-EET-d(8), and AA-d(8) were used as internal standards. Solid phase extraction was used for sample preparation. A gradient LC/MS method using a C18 column and electrospray ionization source under negative ion mode was optimized for the best sensitivity and separation within 35 min. The method validation, including LC/MS instrument qualification, specificity, calibration model, accuracy, precision (without brain matrix and with brain matrix), and extraction efficiency were performed. The linear ranges of the calibration curves were 2-1000 pg for PGs, DiHETrEs, HETEs, and EETs, 10-2400 pg for PGE(2) and PGD(2), and 20-2000 ng for AA, respectively.

Identification and quantification of metabolites of arachidonic acid from cultures of endothelial cells by HPLC-MS2

Epoxyeicosatrienoic acids (EETs) and hydroxyeicosatetraenoic acids (HETEs) are oxidative products of arachidonic acid, some of which participate in the regulation of vascular tone. Little is known about the production of EETs and HETEs in cultures of endothelial cells. This paper reports an assay for the simultaneous quantification of isomers of EETs and HETEs from endothelial cell culture supernatants by employing solid-phase extraction and liquid chromatography-mass spectrometry. The method enabled measurement of 5,6-EET, 8,9-EET, 11,12-EET, 14,15-EET, 5-HETE, 8-HETE, 11-HETE, 12-HETE and 15-HETE. The metabolites were chromatographically separated by reversed-phase HPLC and identified by negative ESI tandem mass spectrometry and this method was used to investigate the metabolism of arachidonic acid with an endothelial cell line. For quantification, the sum of signal intensities of characteristic fragment ions was used. The detection limits for 5,6-EET and of other EET and HETE isomers were 2.0, 0.64 and 8 ng ml(-1) culture medium, respectively. The precision of the method was determined with spiked culture medium (three concentrations, n = 5) and the average RSD ranged from 6.0 to 24.2%. The dynamic range was 0.6-23.5 ng ml(-1) culture medium for EETs and 8.0-200 ng ml(-1) for HETEs. Arachidonic acid was mainly metabolised to HETEs with product levels ranging from 59.3 to 460 ng 10(-6) cells. The median of 8,9-EET and 14,15-EET was 14.5 and 17.7 ng 10(-6) cells, respectively, whereas 5,6-EET and 11,12-EET were below 2 ng 10(-6) cells in a 5-min incubation assay at a 30 microM arachidonic acid substrate concentration.

A role for 5,6-epoxyeicosatrienoic acid in calcium entry by de novo conformational coupling in human platelets

A major pathway for Ca(2+) entry in non-excitable cells is activated following depletion of intracellular Ca(2+) stores. A de novo conformational coupling between elements in the plasma membrane (PM) and Ca(2+) stores has been proposed as the most likely mechanism to activate this capacitative Ca(2+) entry (CCE) in several cell types, including platelets. Here we report that a cytochrome P450 metabolite, 5,6-EET, might be a component of the de novo conformational coupling in human platelets. In these cells, 5,6-EET induces divalent cation entry without having any detectable effect on Ca(2+) store depletion. 5,6-EET-induced Ca(2+) entry was sensitive to the CCE blockers 2-APB, lanthanum, SKF-96365 and nickel and impaired by incubation with anti-hTRPC1 antibody. Ca(2+) entry stimulated by low concentrations of thapsigargin, which selectively depletes the dense tubular system and induces EET production, was impaired by the cytochrome P450 inhibitor 17-ODYA, which has no effect on CCE mediated by depletion of the acidic stores using 2,5-di-(tert-butyl)-1,4-hydroquinone. We have found that 5,6-EET-induced Ca(2+) entry requires basal levels of H(2)O(2), which might maintain a redox state favourable for this event. Finally, our results indicate that 5,6-EET induces the activation of tyrosine kinase proteins and the reorganization of the actin cytoskeleton, which might provide a support for the transport of portions of the Ca(2+) store towards the PM to facilitate de novo coupling between IP(3)R type II and hTRPC1 detected by coimmunoprecipitation. We propose that the involvement of 5,6-EET in TG-induced coupling between IP(3)R type II and hTRPC1 and subsequently CCE is compatible with the de novo conformational coupling in human platelets.

Liquid chromatography–mass spectrometric analysis of buprenorphine and its N-dealkylated metabolite norbuprenorphine in rat brain tissue and plasma

INTRODUCTION

A specific, accurate, and reproducible liquid chromatography-mass spectrometric (LC/MS) method was developed and validated that allows simultaneous measurement of the centrally acting analgesic buprenorphine and its major metabolite, norbuprenorphine, in rat brain and plasma samples.

METHODS

A 96-well plate solid phase extraction (SPE) procedure was developed for buprenorphine and norbuprenorphine using mixed-mode cation-exchange reversed-phase sorbent. An LC method using a C8 column with isocratic mobile phase (80:20 water/acetonitrile with 20 mM ammonium acetate and 0.1% acetic acid) was developed for reproducible and selective separation. A quadrupole mass spectrometer with atmospheric electrospray ionization source under positive ion mode was used for detection. d4-Buprenorphine and d3-norbuprenorphine were used as internal standards.

RESULTS

The calibration curves for buprenorphine and norbuprenorphine in plasma and brain tissue were linear within the range of 7 to 8333 ng/ml (plasma) and 5 to 5000 ng/g (brain). The lower limit of quantification for both buprenorphine and norbuprenorphine from brain tissue was 5 ng/g, and from plasma was 7 ng/ml. Assay accuracy and precision of back-calculated standards were within +/-15%.

DISCUSSION

This method will be useful for investigation of buprenorphine's mechanism of action and clinical profile.

Contribution of 20-HETE to augmented myogenic constriction in coronary arteries of endothelial NO synthase knockout mice

Previous studies suggested an important role for 20-HETE in the regulation of myogenic responses. Thus, pressure-diameter relationships were investigated in isolated, cannulated coronary arteries (approximately 100 microm) from male endothelial NO synthase knockout (eNOS-KO) and wild-type (WT) mice. All arteries constricted in response to step increases in perfusate pressure from 20 to 100 mm Hg. This constriction was significantly enhanced from 40 to 100 mm Hg in arteries of eNOS-KO compared with those of WT mice. For example, at 60 and 100 mm Hg, respectively, the normalized diameter (expressed as a percentage of the corresponding passive diameter) of arteries of eNOS-KO mice was 10% and 12% smaller than that of WT mice. Removal of the endothelium did not significantly affect the responses of vessels from either strain of mice. However, N-methylsulfonyl-12,12-dibromododec-11-enamide (5x10(-6) M), an inhibitor of cytochrome P-450 (CYP)/omega-hydroxylase, significantly attenuated the greater myogenic constriction of arteries from eNOS-KO mice by approximately 12% at each pressure step but did not significantly affect responses of those from WT mice, leading to a comparable myogenic response in the 2 strains. Western blot analysis demonstrated a comparable CYP4A protein content in coronary arteries of the 2 strains of mice. However, production of 20-HETE, measured by fluorescent high-performance liquid chromatography assay was approximately 2.7-fold greater in eNOS-KO compared to WT mice. Thus, as a function of eNOS deficiency, the enhanced coronary artery constriction to pressure is attributable to an increased activity of omega-hydroxylase, which, consequently, increases the synthesis of 20-HETE in vascular smooth muscle.

Cyclooxygenase-2-specific inhibitor improves functional outcomes, provides neuroprotection, and reduces inflammation in a rat model of traumatic brain injury

OBJECTIVE

Increases in brain cyclooxygenase-2 (COX2) are associated with the central inflammatory response and with delayed neuronal death, events that cause secondary insults after traumatic brain injury. A growing literature supports the benefit of COX2-specific inhibitors in treating brain injuries.

METHODS

DFU [5,5-dimethyl-3(3-fluorophenyl)-4(4-methylsulfonyl)phenyl-2(5)H)-furanone] is a third-generation, highly specific COX2 enzyme inhibitor. DFU treatments (1 or 10 mg/kg intraperitoneally, twice daily for 3 d) were initiated either before or after traumatic brain injury in a lateral cortical contusion rat model.

RESULTS

DFU treatments initiated 10 minutes before injury or up to 6 hours after injury enhanced functional recovery at 3 days compared with vehicle-treated controls. Significant improvements in neurological reflexes and memory were observed. DFU initiated 10 minutes before injury improved histopathology and altered eicosanoid profiles in the brain. DFU 1 mg/kg reduced the rise in prostaglandin E2 in the brain at 24 hours after injury. DFU 10 mg/kg attenuated injury-induced COX2 immunoreactivity in the cortex (24 and 72 h) and hippocampus (6 and 72 h). This treatment also decreased the total number of activated caspase-3-immunoreactive cells in the injured cortex and hippocampus, significantly reducing the number of activated caspase-3-immunoreactive neurons at 72 hours after injury. DFU 1 mg/kg amplified potentially anti-inflammatory epoxyeicosatrienoic acid levels by more than fourfold in the injured brain. DFU 10 mg/kg protected the levels of 2-arachidonoyl glycerol, a neuroprotective endocannabinoid, in the injured brain.

CONCLUSION

These improvements, particularly when treatment began up to 6 hours after injury, suggest exciting neuroprotective potential for COX2 inhibitors in the treatment of traumatic brain injury and support the consideration of Phase I/II clinical trials.