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

Fast and reliable quantification of aldosterone, cortisol and cortisone via LC-MS/MS to study 11β-hydroxysteroid dehydrogenase activities in primary cell cultures

Cell culture experiments can support characterization of enzymatic activities in healthy and tumorous human tissues. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) enables simultaneous measurement of several steroids from a single sample, facilitating analysis of molecular pathways involved in steroid biosynthesis. We developed a reliable but fast method for quantification of cortisol, cortisone and aldosterone in cell culture supernatant. Validation, including investigation of matrix-matched calibration, was performed for two different cell types. Utility of the method was demonstrated in the study of 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) activity under conditions of glucocorticoid and mineralocorticoid excess in different cell types. Aldosterone, cortisol and cortisone were extracted by liquid-liquid extraction (LLE) with methyl tert-butyl ether from 1 mL of cell culture supernatant. Steroids were separated on a Kinetex biphenyl column (50 ×2.1 mm, 2.6 µm) with gradient elution of water and methanol containing 2 mM ammonium format and analysed in multiple reaction monitoring mode after positive electrospray ionization. Application of the method included cell culture experiments with two different primary cell types, human coronary artery smooth muscle cells (HCSMC) and human coronary artery endothelial cells (EC). Cells were treated with different concentrations of cortisol, aldosterone and mifepristone, a glucocorticoid receptor antagonist and quantitative PCR was performed. The method exhibits high precision (CV ≤ 6 %) and accuracy (deviation from nominal concentration ≤ 6 %) for concentrations above the limit of quantification (LoQ) which is 0.11, 0.56 and 0.69 nmol/L for aldosterone, cortisone and cortisol, respectively. Calibration curves did not differ when prepared in media or solvent. The method enabled us to confirm activity of HSD11B2 and concentration dependent conversion of cortisol to cortisone in HCSMC (median conversion ratio at 140 nM cortisol = 1.46 %). In contrast we did not observe any HSD11B2 activity in EC. Neither addition of high aldosterone, nor addition of 1 µM mifepristone had impact on glucocorticoid concentrations. Quantitative PCR revealed expression of HSD11B1 and HSD11B2 in HCSMC but not in EC. We present a fast and reliable method for quantification of cortisol, cortisone and aldosterone in cell culture supernatants. The method enabled us to study HSD11B2 activity in two different cell types and will support future experiments investigating mechanisms of target organ damage in conditions of glucocorticoid and mineralocorticoid excess.

Quantitative profiling of prostaglandins as oxidative stress biomarkers in vitro and in vivo by negative ion online solid phase extraction - Liquid chromatography-tandem mass spectrometry

Free radical-mediated oxidation of arachidonic acid to prostanoids has been implicated in a variety of pathophysiological conditions such as oxidative stress. Here, we report on the development of a liquid chromatography-mass spectrometry method to measure several classes of prostaglandin derivatives based on regioisomer-specific mass transitions down to levels of 20 pg/ml applied to the measurement of prostaglandin biomarkers in primary hepatocytes. The quantitative profiling of prostaglandin derivatives in rat and human hepatocytes revealed the increase of several isomers on stress response. In addition to the well-established markers for oxidative stress such as 8-iso-prostaglandin F2α and the prostaglandin isomers PE2 and PD2, this method revealed a significant increase of 15R-prostaglandin D2 from 236.1 ± 138.0 pg/1E6 cells in untreated rat hepatocytes to 2001 ± 577.1 pg/1E6 cells on treatment with ferric NTA (an Fe(3+) chelate with nitrilotriacetic acid causing oxidative stress in vitro as well as in vivo). Like 15R-prostaglandin D2, an unassigned isomer that revealed a more significant increase than commonly analyzed prostaglandin derivatives was identified. Mass spectrometric detection on a high-resolution instrument enabled high-quality quantitative analysis of analytes in plasma levels from rat experiments, where increased concentrations up to 23-fold change treatment with Fe(III)NTA were observed.

Determining cyclooxygenase-2 activity in three different test systems utilizing online-solid phase extraction-liquid chromatography-mass spectrometry for parallel quantification of prostaglandin E(2), D(2) and thromboxane B(2)

Cyclooxygenase-2 (COX-2) catalyzes the formation of PGH2 from arachidonic acid. PGH2 is further converted to different prostaglandins (PG), such as PGE2, PGD2 and TxB2. In this study a rapid online-SPE-LC-MS method for the simultaneous quantification of PGE2, PGD2 and TxB2 streamlined for COX-2 enzyme assays is presented. Baseline separation of all analytes was achieved in only 7.1 min per sample, including sample preparation by online SPE. The method showed high sensitivity (LODs of 0.65-1.25 fmol on column) and accuracy (89-113%) in protein containing media. Because of online-SPE, no manual sample preparation was required, except for addition of IS solution, allowing to use the approach as rapid read-out in COX-2 activity assays. This was demonstrated by applying the method on three in vitro test systems: a cell-free enzyme assay, an assay using HCA-7 cells constitutively expressing COX-2 and primary human monocytes. In these assays, the potency of three popular drugs celecoxib, indomethacin and dexamethasone was successfully characterized with the new online-LC-MS method. The comparison of the results showed that the inhibitory effects of PG formation strongly depend on the test system. Thus we suggest that the modulation of COX-2 activity of a test compound should be at least characterized in two assay systems. With the online-SPE-LC-MS described in here we present a versatile tool as read-out for these types of assays.

Liquid chromatography-tandem mass spectrometry analysis of eicosanoids and related compounds in cell models

Enzyme- and free radical-catalyzed oxidation of polyunsaturated fatty acids (PUFAs) produces the eicosanoids, docosanoids and octadecanoids. This large family of potent bioactive lipids is involved in many biochemical and signaling pathways which are implicated in physiological and pathophysiological processes and can be viable therapeutic targets. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers selectivity, sensitivity, robustness and high resolution and is able to analyze a large number of eicosanoids in biological samples in a short time. The present article reviews and discusses reported LC-MS/MS methods and the results obtained from their application in cell models. Reliable analytical outcomes are critically important for understanding physiological and pathophysiological cellular processes, such as inflammation, diseases with inflammatory components (e.g., cardiovascular disease, diabetes, metabolic syndrome), as well as cancer. Reported findings obtained by using the LC-MS/MS methodology in cell systems may have important predictive as well as nutritional and pharmacological implications. We conclude that the LC-MS/MS methodology is a versatile and reliable analytical tool for the simultaneous analysis of multiple PUFA-derived metabolites including the eicosanoids in cell culture samples at concentrations on the pM/nM threshold, i.e. at baseline and after stimulation.

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.

LC-MS/MS profiling for detection of endogenous steroids and prostaglandins in tissue samples

Roles of steroid hormones, and compounds that can influence their levels in cells, are of increasing interest in e.g. cancer research, partly because resistance to hormone therapies often complicates treatment. To elucidate the processes involved, the hormones and related compounds need to be accurately measured. Reversed-phase liquid chromatography with dynamic multiple reaction monitoring mass spectrometric detection in electrospray mode is capable of providing such measurements. Therefore, LC-MS/MS was developed for sensitive, selective analysis of 11 steroid hormones, cholesterol and two prostaglandins. The effects of the tissue matrix, and solid-phase extraction (SPE) sample clean-up, on the LC-MS/MS signals of the hormones were also investigated. The results show that the developed LC-MS/MS method, following SPE clean-up to reduce matrix interference, can detect selected steroids in extracts of mouse tissues. The method provides linear measurements of the steroids at concentrations up to few ng/μL, and limits of detection in the range 0.03-0.2 pg/μL (for some compounds lower than those of previously reported methods).

Profiling the regulatory lipids: another systemic way to unveil the biological mystery

PURPOSE OF REVIEW

The regulatory lipids are a class of bioactive lipids which regulate various important biological processes. Profiling these regulatory lipids is an attractive method to understand the role of these metabolites. This is especially true because most of these regulatory lipids are derived from several important pharmacological targets: cyclooxygenase, lipoxygenase, and cytochrome P450 enzymes. This review highlights the development of methods to profile these regulatory lipids and the recent publications employing these profiling methods.

RECENT FINDINGS

The recent development of methods for the profiling of regulatory lipids target two different directions: to expand coverage for discovery studies (fingerprinting) and to make the quantitative method more accurate, sensitive, and faster for diagnostic or more detailed studies. Recent applications of these profiling methods including assessment of in-vivo drug engagement, pathways crosstalk, and possible mechanisms for side-effects of a withdrawn anti-inflammatory drug rofecoxib are also reviewed here.

SUMMARY

The profiling of regulatory lipids is a useful tool for many investigations. The breadth of coverage, throughput limits with detection, and reproducibility of quantitation are being improved. The resulting data will assist with fundamental investigation, disease biomarker discovery, drug discovery, and drug development.

Quantitative profiling method for oxylipin metabolome by liquid chromatography electrospray ionization tandem mass spectrometry

Cyclooxygenase, lipoxygenase, and epoxygenase derived oxylipins, especially eicosanoids, play important roles in many physiological processes. Assessment of oxidized fatty acid levels is important for understanding their homeostatic and pathophysiological roles. Most reported methods examine these pathways in isolation. The work described here employed a solid phase extraction-liquid chromatography-electrospray ionization MS/MS (SPE-LC-ESI MS/MS) method to monitor these metabolites. In 21 min, 39 oxylipins were quantified along with eight corresponding internal standards. The limits of quantification were between 0.07 and 32 pg (20 pM-10 nM). Finally, the validated method was used to evaluate oxylipin profiles in lipopolysaccharide-exposed mice, an established septic inflammatory model. The method described here offers a useful tool for the evaluation of complex regulatory oxylipin responses in in vitro or in vivo studies.

Determination of thromboxanes, leukotrienes and lipoxins using high-temperature capillary liquid chromatography-tandem mass spectrometry and on-line sample preparation

An on-line strong cation-exchange (SCX)-reversed-phase (RP) capillary liquid chromatographic (cLC) method with ion-trap tandem mass spectrometric (IT-MS/MS) detection for the simultaneous determination of thromboxane (TX) B(2), TXB(3), leukotriene (LT) B(4), LTD(4) and lipoxin (LX) A(4) in cell culture supernatants was developed and validated. In the present method, a high temperature (70 degrees C) was used for the separation on the analytical column to obtain efficient chromatography of the thromboxanes. An on-line sample preparation was performed, where peptides/proteins contained in the matrix were removed by the SCX column. Sample pre-treatment included dilution and filtration, and the analysis time including all sample preparation steps was 60min per sample. Limits of detection in the range of 1-4ng/mL cell culture supernatant, recoveries between 30% and 100%, within day precisions of less than 20% RSD and between day precisions of less than 30% RSD were obtained. Human mesenchymal stem cells (hMSCs) were stimulated with cytokine-containing supernatants derived from activated human T lymphocytes, and thromboxane, leukotriene and lipoxin production was analysed using the developed method. TXB(2) was found in cultures from both non-differentiated and differentiated hMSCs that were stimulated with a cytokine-containing supernatant obtained from activated T-cells.