Isolation and measurement of urinary 8-iso-prostaglandin F2alpha by high-performance liquid chromatography and gas chromatography-mass spectrometry

Mass Spectrometry in Advancement of Redox Precision Medicine

Redox (portmanteau of reduction-oxidation) reactions involve the transfer of electrons between chemical species in biological processes fundamental to life. It is of outmost importance that cells maintain a healthy redox state by balancing the action of oxidants and antioxidants; failure to do so leads to a multitude of diseases including cancer, diabetes, fibrosis, autoimmune diseases, and cardiovascular and neurodegenerative diseases. From the perspective of precision medicine, it is therefore beneficial to interrogate the redox phenotype of the individual-similar to the use of genomic sequencing-in order to design tailored strategies for disease prevention and treatment. This chapter provides an overview of redox metabolism and focuses on how mass spectrometry (MS) can be applied to advance our knowledge in redox biology and precision medicine.

Simultaneous quantification of F2-isoprostanes and prostaglandins in human urine by liquid chromatography tandem-mass spectrometry

A specific and sensitive LC-MS/MS method for analysis of F(2)-isoprostanes (F(2)-IsoPs) and prostaglandins (PGs) in urine was developed and validated to examine the levels of F(2)-IsoPs and prostaglandin F(2α) (PGF(2α)), in human urine in patients undergoing cardiac surgery. The rapid extraction for F(2)-IsoPs and PGs from urine was achieved using a polymeric weak anion solid phase extraction cartridge. The base-line separation of 8-iso-PGF(2α), 8-iso-15(R)-PGF(2α), PGF(2α), and 15(R)-PGF(2α) was carried out on a Hydro-RP column (250mm×2.0mm i.d., Phenomenex, CA) using a linear gradient of methanol:acetonitrile (1:1, v/v) in 0.1% formic acid at a flow rate of 0.2mL/min. The method was proved to be accurate and precise for simultaneous quantification of each analyte over a linear dynamic range of 0.05-50ng/mL with correlation coefficients greater than 0.99. The intra-day and inter-day assay precision at the lowest quality control (0.07ng/mL) level were less than 17%. The mean extraction recoveries of F(2)-IsoPs and PGs were in a range of 79-100%. In applications of this method to patients undergoing cardiac surgery, post-surgery urinary concentrations of 8-iso-PGF(2α) increased significantly in patients (n=14) who did not develop acute kidney (AKI) (pre-surgery 0.344±0.039 vs. post-surgery 0.682±0.094ng/mg creatinine, p<0.01), whereas there was no significant change in this isoprostane in the patients (n=4) who developed AKI (pre-surgery 0.298±0.062 vs. post-surgery 0.383±0.117ng/mg creatinine, NS). Therefore, the method is suitable for the analysis of individual F(2)-IsoPs and PGF(2α)'s in both clinical and research studies.

Quantification of urinary 8-iso-prostaglandin F2alpha using liquid chromatography-tandem mass spectrometry during cardiac valve surgery

Oxidative stress is an unavoidable event during many complex surgical procedures. 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) is a reliable biomarker for the evaluation of oxidative stress in vivo. The aim of this study is to develop simple and accurate liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for the detection of urinary 8-iso-PGF(2alpha) in samples collected from patients who received a cardiopulmonary bypass (CPB) during cardiac valve surgery. Urine samples of 14 patients with cardiac valve diseases were collected before, during, and after CPB. The level of 8-iso-PGF(2alpha) was detected via selected-reaction monitoring triple quadrupole MS/MS and the result was compared with 12 healthy volunteers. The method's detection limit (3S/N) was 0.25 pg for 8-iso-PGF(2alpha), with a linear working range of 0.25-20 ng/ml. For patients with cardiac valve disease, the 8-iso-PGF(2alpha) levels before the bypasses were the same as those of healthy individuals (P>0.05) and the 8-iso-PGF(2alpha) levels during and after CPB were significantly higher than those before the bypasses (P<0.05). In conclusion, we present a simple and specific protocol for LC-MS/MS quantification of urinary 8-iso-PGF(2alpha) collected during CPB. Using this technique, it would be feasible to assess the levels of oxidative stress during cardiac surgery and thereby helpful for the management of oxidative injury.

Determination of F2-isoprostanes in urine by online solid phase extraction coupled to liquid chromatography with tandem mass spectrometry

F(2)-isoprostanes are a unique class of prostaglandin-like compounds formed in vivo, which have been established as biomarkers of oxidative stress. Accurate analysis has been challenging due to lack of specificity for the isoforms of isoprostanes and lengthy sample preparation procedures to enable trace quantitative analysis. A quantitative analytical method was developed for the determination of F(2)-isoprostanes in rat and hamster urine by online solid phase extraction (SPE) coupled with liquid chromatography and tandem mass spectrometry (LC-MS/MS). The online SPE LC-MS/MS procedure has significant advantages over alternative methods with respect to specificity, sensitivity, simplicity, and speed. The assay enables the detection of iPF(2alpha)-III, iPF(2alpha)-IV, and iPF(2alpha)-VI over a linear dynamic range of 0.1-50 ng/mL in rat urine samples. This range covers the basal levels of these F(2)-isoprostanes. The limit of quantitation (LOQ) for the standard isoprostanes was about 0.3 ng/mL. The average recoveries ranged from 73 to 115% depending upon the individual F(2)-isoprostane isomers in rat urine. Additionally, the method was used to determine increases of endogenous urine iPF(2alpha)-VI and iPF(2alpha)-III in hamsters challenged with either low-fat or high-fat diets.

Key issues in F2-isoprostane analysis

A large body of evidence indicates that measurement of F2-isoprostanes, specific prostaglandin F2-like compounds derived from the non-enzymatic peroxidation of arachidonic acid, is a reliable biomarker of oxidant stress in the human body. Since the discovery of F2-isoprostanes in the early 1990s, a variety of analytical approaches has been introduced for the quantification of these novel compounds. The aim of the present review is to shed light on the available gas chromatographic–mass spectrometric assays for the measurement of plasma or urinary F2-isoprostanes and to highlight a number of issues which need to be addressed in order to implement F2-isoprostane measurement as a gold-standard biomarker of oxidative stress in biological samples.

Quantitation of isoprostane isomers in human urine from smokers and nonsmokers by LC-MS/MS

A simple, rapid liquid chromatography-tandem mass spectrometry method was developed to identify and quantitate in human urine the isoprostanes iPF(2 alpha)-III, 15-epi-iPF(2 alpha)-III, iPF(2 alpha)-VI, and 8,12-iso-iPF(2 alpha)-VI along with the prostaglandin PGF(2 alpha) and 2,3-dinor-iPF(2 alpha)-III, a metabolite of iPF(2 alpha)-III. Assay specificity, linearity, precision, and accuracy met the required criteria for most analytes. The urine sample storage stability and standard solution stability were also tested. The methodology was applied to analyze 24 h urine samples collected from smokers and nonsmokers on controlled diets. The results for iPF(2 alpha)-III obtained by our method were significantly correlated with results by an ELISA, although an approximately 2-fold high bias was observed for the ELISA data. For iPF(2 alpha)-III and its metabolite 2,3-dinor-iPF(2 alpha)-III, smokers had significantly higher concentrations than nonsmokers (513 +/- 275 vs. 294 +/- 104 pg/mg creatinine; 3,030 +/- 1,546 vs. 2,046 +/- 836 pg/mg creatinine, respectively). The concentration of iPF(2 alpha)-VI tended to be higher in smokers than in nonsmokers; however, the increase was not statistically significant in this sample set. Concentrations of the other three isoprostane isomers showed no trends toward differences between smokers and nonsmokers. Among smokers, the daily output of two type VI isoprostanes showed a weak correlation with the amount of tobacco smoke exposure, as determined by urinary excretion of total nicotine equivalents.

Benefits of prolonged gradient separation for high-performance liquid chromatography-tandem mass spectrometry quantitation of plasma total 15-series F-isoprostanes

The F(2)-isoprostanes are products of free-radical-induced oxidation of arachidonic acid (AA) that are stereoisomers of prostaglandin F(2alpha) (PGF(2alpha)). We describe a method for quantitation of several 15-series PGF isomers (15-PGFs) and AA by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS). Plasma samples were subjected to alkaline hydrolysis and acidified, and total (free + esterified) 15-PGFs and AA were extracted with organic solvents. The analytes were separated by gradient reverse-phase HPLC and detected by multiple reaction monitoring on a triple-quadrupole mass spectrometer, using deuterated internal standards for quantitation. The assay had a linear range of 1-40 pg of 8-iso-PGF(2alpha) on column and can quantify as little as 40 pg/mL (0.11 nM) in plasma. Outcomes significantly correlated (p < 0.0001) with data obtained by gas chromatography-mass spectrometry GC-MS or enzyme-linked immunosorbent assay. All plasma 15-PGF isomers increased over time with in vitro cigarette smoke exposure and correlated (p < 0.0001) with each other. The same strong inter-15-PGF correlations were observed in plasma from healthy young adult subjects. The coefficients of variation of HPLC-MS-MS measurements (24-32%) were smaller than those obtained by GC-MS (53%). Thus, HPLC-MS-MS potentially offers greater precision and allows quantitation of more compounds with simpler sample preparation than existing methods. Ours is the first validated quantitative assay using HPLC-tandem MS applied to plasma total 15-PGFs.

Les isoprostanes, biomarqueurs de peroxydation lipidique chez l'homme. Partie 2 : méthodes de quantification

The isoprostanes are a new class of natural products produced in vivo by a non-enzymatic free-radical-induced peroxidation of polyunsaturated fatty acids. The quantification of these compounds represents a reliable and useful index of lipid peroxidation and oxidant stress in vivo. Then, a large amount of works has been done in the field of isoprostane analysis, but till now, no standardized method seems to emerge. Indeed, described methodologies differ either in the sample preparation steps or in the detection techniques or both. Extraction and purification procedures are often critical and time-consuming, requiring successive chromatographic steps and these procedures lead to a substantial loose of target compounds. Moreover, two main analytical approaches have been adopted for IsoP measurement: immunological methods or mass spectrometry. Some discussion about the methodology used for measurement of isoprostane is important. This review will aim to present and compare different methods developed nowadays for extraction, purification and analysis of F(2)-iPs in various biological samples.

Application of gas chromatography-mass spectrometry for analysis of isoprostanes: their role in cardiovascular disease

Cardiovascular disease (CVD) is the major cause of death in the Western hemisphere. Oxidative stress is involved in the pathophysiology of cancer, neurodegenerative conditions and CVD. Lipid peroxidation is one of the oxidative modifications possible in biological systems. The isoprostanes are derivatives of one specific lipid, i.e., arachidonic acid, after lipid peroxidation. Several isoprostanes have been identified in biological tissues and fluids, among them 8-iso prostaglandin F2alpha (8-iso-PGF2alpha, 8-epi-PGF2alpha, iPF2alpha-III, 15-F2t-IsoP) and its metabolite, 2,3-dinor-4,5-dihydro-8-iso-PGF2alpha. The isoprostanes are reliable in vivo markers of lipid peroxidation in humans: they are endogenously formed, characteristic in structure, ubiquitous in nature, stable in- and ex vivo and reliably quantitatable. In this Review, different analytical approaches will be discussed including immunologic, chromatographic and spectrometric techniques with the main emphasis on mass spectrometry. Analysis of isoprostanes applying radio immunoassay (RIA), enzyme immunoassay (EIA), high performance-liquid chromatography (HPLC), liquid chromatography-tandem mass spectrometry (LC-tandem MS), gas chromatography-mass spectrometry (GC-MS) and GC-tandem MS will be exemplified in the field of cardiovascular research. Results from several clinical studies are included indicating the validity of isoprostanes as surrogate parameters of oxidative stress in cardiovascular disease.

Quantifying F2-isoprostanes in umbilical cord blood of newborn by gas chromatography-mass spectrometry

We attempted to improve the extraction procedures to determine the F(2)-isoprostanes in plasma of umbilical cord arterial and venous blood by gas chromatography mass spectrometry. Plasma samples were deproteinized and hydrolyzed; free and esterified F(2)-isoprostanes were extracted by solid-phase extraction columns with citric acid/methanol/cyclohexane and ammonia solution/methanol and then derivatized by PFBBr and BSTFA. Concentrations of total plasma F(2)-isoprostanes eluted at the retention time of an internal standard of 8-iso-prostaglandin F(2alpha)-D(4) were quantified. The absolute recovery was 83+/-1.9% (95% confidence). Intraassay precision and interassay precision were lower than 1.0%. Analytical accuracy was 99.0+/-0.4% (95% confidence). Linearity, r(2), over the concentration range of 10 to 5000 pg/ml of spiked 8-iso-prostaglandin F(2alpha) in plasma was 0.9985. The method detection limit was 21 pg/ml (99% confidence) and the limit of quantitation was approximately 4 pg/ml. Analysis of 200 neonatal cord blood samples revealed few overlapping peaks causing interference in the elution of the F(2)-isoprostanes. With the use of an autosampler and one technician, 48 samples can be completed within 24h with 6h of actual hands-on work. This method could be potentially employed for routine analysis of plasma F(2)-isoprostanes in clinical laboratories.

Determination of isoprostaglandin F2alpha type III in human urine by gas chromatography-electronic impact mass spectrometry. Comparison with enzyme immunoassay

F2-Isoprostanes are stable lipid peroxidation products of arachidonic acid, the quantification of which provides an index of oxidative stress in vivo. We describe a method for analysing isoprostaglandin F2alpha type III (15-F2t-IsoP) in biological fluids. The method involves solid-phase extraction on octadecyl endcapped and aminopropyl cartridges. After conversion to trimethylsilyl ester trimethylsilyl ether derivatives, isoprostaglandin F2alpha type III is analysed by mass spectrometry, operated in electronic impact selected ion monitoring mode. We have compared enzyme immunoassay (EIA; Cayman, Ann Arbor, MI, USA) to this method with 30 human urine aliquots following the same extraction procedure in order to determine the agreement between both methods. Isoprostaglandin F2alpha type III concentrations determined with gas chromatography-mass spectrometry (GC-MS) did not agree with those determined with EIA. Our results suggest that GC-MS and EIA do not measure the same compounds. As a consequence, comparison of clinical results using GC-MS and EIA should be avoided.

Urinary F2-isoprostanes formation in kidney transplantation

BACKGROUND

Oxygen free-radical mediated lipid peroxidation has been implicated in many diseases such as chronic renal failure, hemodialysis and chronic kidney transplant rejection. However, insight into the role of free radical generation in kidney transplantation has been constrained by the limitations of current indexes of oxidant stress in vivo. Isoprostaglandin F2alpha type-III (iPF2alpha-III, formerly known as 8-iso-prostaglandin F2alpha) is emerging as a reliable marker of oxidant stress in vivo. The purpose of our study was to investigate iPF2alpha-III formation as an index of lipid peroxidation in the 5 d following kidney transplantation.

METHODS

Urinary iPF2alpha-III measurements were performed by enzyme immunoassay from day I to 5 in 11 patients undergoing kidney transplantation. Results were compared with 11 healthy volunteers matched in sex, age and cigarette smoking.

RESULTS

Urinary excretion of iPF2alpha-III at day 1 did not significantly differ between control and transplant group (111 +/- 17 vs. 92 +/- 10 pM/ mM creatinine, respectively, NS). Urinary iPF2alpha-III levels did not differ between day 1 to 5, and were not correlated to cold ischaemia time.

CONCLUSION

Our study shows no evidence of enhanced lipid peroxidation in the first 5 d following kidney transplantation.

Rapid and sensitive quantification of 8-isoprostaglandin F2alpha in human plasma and urine by liquid chromatography-electrospray ionization mass spectrometry

The isoprostane, 8-isoprostaglandin F2alpha (8-iso-PGF2alpha), is produced non-enzymatically by direct oxidation of arachidonic acid on the cell surface by oxygen radicals. We developed a new assay method for 8-iso-PGF2alpha using 2H4-8-iso-PGF2alpha as the internal standard (I.S.) by high-performance liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). For this assay, we established a very simple and rapid pretreatment method using a membrane filter-type solid-phase extraction column (Empore disk cartridge) for human urine extracts or intact plasma. LC-ESI-MS was performed in the selected ion monitoring (SIM) mode using target ions at m/z 353.24 (8-iso-PGF2alpha) and m/z 357.26 (I.S.) with a resolution of 1,500. The imprecision for this method was below 13.7%. Mean inaccuracy was 8.7% for added levels of 8-iso-PGF2alpha up to 5,000 pg/ml of urine and 500 pg/ml of plasma. Determination of plasma and urinary 8-iso-PGF2alpha concentrations in healthy subjects by the present method revealed that its urinary concentration in smokers tends to be higher than that in nonsmokers.

Tandem mass spectrometric quantification of 8-iso-prostaglandin F2alpha and its metabolite 2,3-dinor-5,6-dihydro-8-iso-prostaglandin F2alpha in human urine

Whole body synthesis of F2-isoprostanes, a family of cyclooxygenase-independent eicosanoids formed by free-radical catalysed peroxidation, should be best assessed by quantifying their urinary metabolites. Two methods for the quantitative determination of F2-isoprostane metabolites in human urine performing either thin-layer chromatography (TLC) (method A) or high-performance liquid chromatography (HPLC) (method B) prior to GC-tandem MS are described. Method A allows for simultaneous quantification of 8-iso-PGF2alpha, one prominent member of the F2-isoprostane family, and its major urinary metabolite, 2,3-dinor-5,6-dihydro-8-iso-PGF2alpha. Mean excretion was found to be 223 and 506 pg/mg creatinine of 8-iso-PGF2alpha and 2,3-dinor-5,6-dihydro-8-iso-PGF2alpha, respectively (n=14). A tight correlation existed between the urinary excretion of these two isoprostanes (r=0.86). Method B enables quantification of dinor-dihydro metabolites of various F2-isoprostanes including 8-iso-PGF2alpha. 2,3-Dinor-5,6-dihydro-8-iso-PGF2alpha was found to be an abundant dinor-dihydro F2-isoprostane metabolite. Validity of method A was proven by a combination of HPLC with TLC prior to GC-tandem MS analysis. A correlation was observed between the urinary concentrations of 2,3-dinor-5,6-dihydro-8-iso-PGF2alpha measured by GC-MS and GC-tandem MS (r=0.84).

Methods for assessing the biological effects of specific plant components

Until very recently, phytonutrient research was the province of natural product chemists and consisted of primarily anecdotal clinical references. In recent years, an extensive set of qualitative and semi-quantitative dietary epidemiologic data has been developed. This developing base of epidemiologic data is now being supplemented by biochemical, mechanistic, and genetic epidemiology of a more quantitative nature. As we seek to understand the mechanisms that explain a large body of epidemiologic evidence, newer laboratory methods continue to be developed. Though there is a continuing need for even more discriminating nutrition epidemiology to drive the basic research in this area forward, the focus of in vitro, animal and clinical (human) studies must continue to be refined, and appropriate biomarkers for chronic and acute (death) disease end-points must be developed.

Dietary carotenoids and lung cancer: a review of recent research

Several hundred carotenoid research studies have been published since 1996, when two major intervention trials showed a lack of protective effect of beta-carotene supplements against lung cancer. Recent epidemiologic studies continue to show an association between high dietary intake of beta-carotene and lower risk of lung cancer. New research is attempting to clarify the apparently contradictory results of intervention and epidemiologic studies. Promising areas of investigation include characterizing biologic activities of carotenoids and gaining further insight into whether they may serve primarily as markers for a healthy lifestyle or diet.

Application of gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry to assess in vivo synthesis of prostaglandins, thromboxane, leukotrienes, isoprostanes and related compounds in humans

Prostaglandins, thromboxane, leukotrienes, isoprostanes and other arachidonic acid metabolites are structurally closely related, potent, biologically active compounds. One of the most challenging tasks in eicosanoids research has been to define the role of the various eicosanoids in human health and disease, and to monitor the effects of drugs on the in vivo synthesis of these lipid mediators in man. Great advances in instrumentation and ionization techniques, in particular the development of tandem mass spectrometry and negative-ion chemical ionization (NICI), in gas chromatography and also advances in methodologies for solid-phase extraction and sample purification by thin-layer chromatography and high-performance liquid chromatography have been made. Now gas chromatography-mass spectrometry (GC-MS) and GC-tandem MS in the NICI mode are currently indispensable analytical tools for reliable routine quantitation of eicosanoid formation in vivo in humans. In this article analytical methods for eicosanoids based on GC-MS and GC-tandem MS are reviewed emphasizing the quantitative measurement of specific index metabolites in human urine and its importance in clinical studies in man. Aspects of method validation and quality control are also discussed.

Specific and rapid quantification of 8-iso-prostaglandin F2alpha in urine of healthy humans and patients with Zellweger syndrome by gas chromatography-tandem mass spectrometry

8-iso-Prostaglandin F2alpha (8-iso-PGF2alpha) is currently discussed as a potential index parameter of oxidative stress in vivo. We describe in this article a fully validated gas chromatographic-tandem mass spectrometric method for the quantitative determination of 8-iso-PGF2alpha in human urine. The method is highly specific and requires a single thin-layer chromatographic step for sample purification. Inter- and intraday imprecision were below 8%. Mean inaccuracy was 5.3% for added levels of 8-iso-PGF2alpha up to 2000 pg/ml of urine. We measured highly elevated excretion of 8-iso-PGF2alpha in the urine of children with peroxisomal beta-oxidation deficiency, i.e. Zellweger syndrome, (63.3+/-16.6 ng/mg creatinine) compared to that of healthy children (0.51+/-0.16 ng/mg creatinine) (mean+/-S.D., both n=5). The method could be useful for diagnosing Zellweger syndrome and for investigating the utility of 8-iso-PGF2alpha as a novel marker for oxidative stress in vivo in man.