Improved quantification of 8-epi-prostaglandin F2 alpha and F2-isoprostanes by gas chromatography/triple-stage quadrupole mass spectrometry: partial cyclooxygenase-dependent formation of 8-epi-prostaglandin F2 alpha in humans

The F2-isoprostane 8-iso-PGF2α attenuates atherosclerotic lesion formation in Ldlr-deficient mice - Potential role of vascular thromboxane A2 receptors

The F2-isoprostane 8-iso-PGF_2α (also known as 15-F_2t-isoprostane, iPF_2α-III, 8-epi PGF_2α, 15(S)-8-iso-PGF_2α, or 8-Isoprostane), a thromboxane A₂ receptor (TP) agonist, stable biomarker of oxidative stress, and risk marker of cardiovascular disease, has been proposed to aggravate atherogenesis in genetic mouse models of atherosclerotic vascular disease. Moreover, the TP plays an eminent role in the pathophysiology of endothelial dysfunction, atherogenesis, and cardiovascular disease. Yet it is unknown, how the TP expressed by vascular cells affects atherogenesis or 8-iso-PGF_2α-related effects in mouse models of atherosclerosis. We studied Ldlr-deficient vascular endothelial-specific (EC) and vascular smooth muscle cell (VSMC)-specific TP knockout mice (TP^ECKO/Ldlr KO; TP^VSMCKO/Ldlr KO) and corresponding wild-type littermates (TP^WT/Ldlr KO). The mice were fed a Western-type diet for eight weeks and received either 8-iso-PGF_2α or vehicle infusions via osmotic pumps. Subsequently, arterial blood pressure, atherosclerotic lesion formation, and lipid profiles were analyzed. We found that VSMC-, but not EC-specific TP deletion, attenuated atherogenesis without affecting blood pressure or plasma lipid profiles of the mice. In contrast to a previous report, 8-iso-PGF_2α tended to reduce atherogenesis in TP^WT/Ldlr KO and TP^{EC KO}/Ldlr KO mice, again without significantly affecting blood pressure or lipid profiles of these mice. However, no further reduction in atherogenesis was observed in 8-iso-PGF_2α-treated TP^{VSMC KO}/Ldlr KO mice. Our work suggests that the TP expressed in VSMC but not the TP expressed in EC is involved in atherosclerotic lesion formation in Ldlr-deficient mice. Furthermore, we report an inhibitory effect of 8-iso-PGF_2α on atherogenesis in this experimental atherosclerosis model, which paradoxically appears to be related to the presence of the TP in VSMC.

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.

Strategies to decrease oxidative stress biomarker levels in human medical conditions: A meta-analysis on 8-iso-prostaglandin F2α

The widespread detection of elevated oxidative stress levels in many medical conditions has led to numerous efforts to design interventions to reduce its effects. Efforts have been wide-ranging, from dietary changes to administration of antioxidants, supplements, e.g., omega-3-fatty acids, and many medications. However, there is still no systemic assessment of the efficacy of treatments for oxidative stress reduction across a variety of medical conditions. The goal of this meta-analysis is, by combining multiple studies, to quantitate the change in the levels of the popular oxidative stress biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) after a variety of treatment strategies in human populations. Nearly 350 unique publications with 180 distinct strategies were included in the analysis. For each strategy, the difference between pre- or placebo and post-treatment levels calculated using Hedges' g value of effect. In general, administration of antibiotics, antihyperlipidemic agents, or changes in lifestyle (g = - 0.63, - 0.54, and 0.56) had the largest effect. Administration of supplements, antioxidants, or changes in diet (g = - 0.09, - 0.28, - 0.12) had small quantitative effects. To fully interpret the effectiveness of these treatments, comparisons to the increase in g value for each medical condition is required. For example, antioxidants in populations with coronary artery disease (CAD) reduce the 8-iso-PGF2α levels by g = - 0.34 ± 0.1, which is quantitatively considered a small effect. However, CAD populations, in comparison to healthy populations, have an increase in 8-iso-PGF2α levels by g = 0.38 ± 0.04; therefore, the overall reduction of 8-iso-PGF2α levels is ≈ 90% by this treatment in this specific medical condition. In conclusion, 8-iso-PGF2α levels can be reduced not only by antioxidants but by many other strategies. Not all strategies are equally effective at reducing 8-iso-PGF2α levels. In addition, the effectiveness of any strategy can be assessed only in relation to the medical condition investigated.

Elevated plasma 8-iso-prostaglandin F2α levels in human smokers originate primarily from enzymatic instead of non-enzymatic lipid peroxidation

It is widely accepted that free radicals in tobacco smoke lead to oxidative stress and generate the popular lipid peroxidation biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α). However, 8-iso-PGF2α can simultaneously be produced in vivo by the prostaglandin-endoperoxide synthases (PGHS) induced by inflammation. This inflammation-dependent mechanism has never been considered as a source of elevated 8-iso-PGF2α in tobacco smokers. The goal of this study is to quantify the distribution of chemical- and PGHS-dependent 8-iso-PGF2α formation in the plasma of tobacco smokers and non-smokers. The influences of gender and hormonal contraceptive use were accounted for. The distribution was determined by measuring the 8-iso-PGF2α/prostaglandin F2α (PGF2α) ratio. When comparing smokers (n = 28) against non-smokers (n = 30), there was a statistically significant increase in the 8-iso-PGF2α concentration. The source of this increased 8-iso-PGF2α was primarily from PGHS. When stratifying for gender, the increase in 8-iso-PGF2α in male smokers (n = 9) was primarily from PGHS. Interestingly, female smokers on hormonal contraceptives had increased 8-iso-PGF2α in both pathways, whereas those not on hormonal contraceptives did not have increased 8-iso-PGF2α. In conclusion, increased plasma 8-iso-PGF2α in tobacco smokers has complex origins, with PGHS-dependent formation as the primary source. Accounting for both pathways provides a definitive measurement of both oxidative stress and inflammation.

Development of an LC-ESI(-)-MS/MS method for the simultaneous quantification of 35 isoprostanes and isofurans derived from the major n3- and n6-PUFAs

Misregulation of oxidative and antioxidative processes in the organism - oxidative stress - contributes to the pathogenesis of different diseases, e.g. inflammatory or neurodegenerative diseases. Oxidative stress leads to autoxidation of polyunsaturated fatty acids giving rise to prostaglandin-like isoprostanes (IsoP) and isofurans (IsoF). On the one hand they could serve as biomarker of oxidative stress and on the other hand may act as lipid mediators, similarly as the enzymatically formed oxylipins. In the present paper we describe the development of an LC-ESI(-)-MS/MS method allowing the parallel quantification of 27 IsoP and 8 IsoF derived from 6 different PUFA (ALA, ARA, EPA, AdA, n6-DPA, DHA) within 12 min. The chromatographic separation was carried out on an RP-C18 column (2.1 × 150 mm, 1.8 μm) yielding narrow peaks with an average width at half maximum of 3.3-4.2 s. Detection was carried out on a triple quadrupole mass spectrometer operating in selected reaction monitoring mode allowing the selective detection of regioisomers. The limit of detection ranged between 0.1 and 1 nM allowing in combination with solid phase extraction the detection of IsoP and IsoF at subnanomolar concentrations in biological samples. The method was validated for human plasma showing high accuracy and precision. Application of the approach on the investigation of oxidative stress in cultured cells indicated a distinct pattern of IsoP and IsoF in response to reactive oxygen species which warrants further investigation. The described method is not only the most comprehensive approach for the simultaneous quantification of IsoP and IsoF, but it was also integrated in a targeted metabolomics method (Ostermann et al. (2015) Anal Bioanal Chem) allowing the quantification of in total 164 oxylipins formed enzymatically and non-enzymatically within 30.5 min.

Classifying oxidative stress by F2-isoprostane levels across human diseases: A meta-analysis

The notion that oxidative stress plays a role in virtually every human disease and environmental exposure has become ingrained in everyday knowledge. However, mounting evidence regarding the lack of specificity of biomarkers traditionally used as indicators of oxidative stress in human disease and exposures now necessitates re-evaluation. To prioritize these re-evaluations, published literature was comprehensively analyzed in a meta-analysis to quantitatively classify the levels of systemic oxidative damage across human disease and in response to environmental exposures.

In this meta-analysis, the F₂-isoprostane, 8-iso-PGF_2α, was specifically chosen as the representative marker of oxidative damage. To combine published values across measurement methods and specimens, the standardized mean differences (Hedges’ g) in 8-iso-PGF_2α levels between affected and control populations were calculated.

The meta-analysis resulted in a classification of oxidative damage levels as measured by 8-iso-PGF_2α across 50 human health outcomes and exposures from 242 distinct publications. Relatively small increases in 8-iso-PGF_2α levels (g<0.8) were found in the following conditions: hypertension (g=0.4), metabolic syndrome (g=0.5), asthma (g=0.4), and tobacco smoking (g=0.7). In contrast, large increases in 8-iso-PGF_2α levels were observed in pathologies of the kidney, e.g., chronic renal insufficiency (g=1.9), obstructive sleep apnoea (g=1.1), and pre-eclampsia (g=1.1), as well as respiratory tract disorders, e.g., cystic fibrosis (g=2.3).

In conclusion, we have established a quantitative classification for the level of 8-iso-PGF_2α generation in different human pathologies and exposures based on a comprehensive meta-analysis of published data. This analysis provides knowledge on the true involvement of oxidative damage across human health outcomes as well as utilizes past research to prioritize those conditions requiring further scrutiny on the mechanisms of biomarker generation.

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Oxidative damage is highly variable in human conditions as measured by F₂-isoprostanes.

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Respiratory tract and urogenital diseases have the highest F₂-isoprostanes.

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Cancer and cardiovascular diseases have surprisingly low F₂-isoprostanes.

Reinterpreting the best biomarker of oxidative stress: The 8-iso-prostaglandin F2α/prostaglandin F2α ratio shows complex origins of lipid peroxidation biomarkers in animal models

Oxidative stress is elevated in numerous environmental exposures and diseases. Millions of dollars have been spent to try to ameliorate this damaging process using anti-oxidant therapies. Currently, the best accepted biomarker of oxidative stress is the lipid oxidation product 8-iso-prostaglandin F2α (8-iso-PGF2α), which has been measured in over a thousand human and animal studies. 8-iso-PGF2α generation has been exclusively attributed to nonenzymatic chemical lipid peroxidation (CLP). However, 8-iso-PGF2α can also be produced enzymatically by prostaglandin-endoperoxide synthases (PGHS) in vivo. When failing to account for PGHS-dependent generation, 8-iso-PGF2α cannot be interpreted as a selective biomarker of oxidative stress. We investigated the formation of 8-iso-PGF2α in rats exposed to carbon tetrachloride (CCl4) or lipopolysaccharide (LPS) using the 8-iso-PGF2α/PGF2α ratio to quantitatively determine the source(s) of 8-iso-PGF2α. Upon exposure to a 120mg/kg dose of CCl4, the contribution of CLP accounted for only 55.6±19.4% of measured 8-iso-PGF2α, whereas in the 1200mg/kg dose, CLP was the predominant source of 8-iso-PGF2α (86.6±8.0% of total). In contrast to CCl4, exposure to 0.5mg/kg LPS was characterized by a significant increase in both the contribution of PGHS (59.5±7.0) and CLP (40.5±14.0%). In conclusion, significant generation of 8-iso-PGF2α occurs through enzymatic as well as chemical lipid peroxidation. The distribution of the contribution is dependent on the exposure agent as well as the dose. The 8-iso-PGF2α/PGF2α ratio accurately determines the source of 8-iso-PGF2α and provides an absolute measure of oxidative stress in vivo.

Reinterpreting the best biomarker of oxidative stress: The 8-iso-PGF(2α)/PGF(2α) ratio distinguishes chemical from enzymatic lipid peroxidation

The biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) is regarded as the gold standard for detection of excessive chemical lipid peroxidation in humans. However, biosynthesis of 8-iso-PGF2α via enzymatic lipid peroxidation by prostaglandin-endoperoxide synthases (PGHSs), which are significantly induced in inflammation, could lead to incorrect biomarker interpretation. To resolve the ambiguity with this biomarker, the ratio of 8-iso-PGF2α to prostaglandin F2α (PGF2α) is established as a quantitative measure to distinguish enzymatic from chemical lipid peroxidation in vitro, in animal models, and in humans. Using this method, we find that chemical lipid peroxidation contributes only 3% to the total 8-iso-PGF2α in the plasma of rats. In contrast, the 8-iso-PGF2α levels in plasma of human males are generated >99% by chemical lipid peroxidation. This establishes the potential for an alternate pathway of biomarker synthesis, and draws into question the source of increases in 8-iso-PGF2α seen in many human diseases. In conclusion, increases in 8-iso-PGF2α do not necessarily reflect increases in oxidative stress; therefore, past studies using 8-iso-PGF2α as a marker of oxidative stress may have been misinterpreted. The 8-iso-PGF2α/PGF2α ratio can be used to distinguish biomarker synthesis pathways and thus confirm the potential change in oxidative stress in the myriad of disease and chemical exposures known to induce 8-iso-PGF2α.

Optimized method for quantification of total F(2)-isoprostanes using gas chromatography-tandem mass spectrometry

F2-isoprostanes are produced from the oxidative degradation of arachidonic acid and are considered the gold standard marker of lipid peroxidation in biological samples. We developed a liquid-liquid extraction method for the determination of total isoprostanes using negative chemical ionization gas chromatography-tandem mass spectrometry in plasma and tissue homogenates. Incorporating liquid-liquid extraction allows for greater sample through-put than current approaches. Here we describe the protocol and include numerous trouble-shooting suggestions. The method found healthy individuals with 150-250 pg of isoprostanes per ml of plasma and end stage kidney disease patients to have the highest measured values of up to 1100 pg/ml. This assay has an accurate working linear range of 40-1000 pg of isoprostanes (100-2500 pg/ml) and an average coefficient of variance of 7%. Tissue values for healthy mice liver were 50-70 pg/μg protein. This method provides increased ion selectivity and detection capabilities with economical sample through-put.

Glycaemic variability in paediatric patients with type 1 diabetes on continuous subcutaneous insulin infusion (CSII) or multiple daily injections (MDI): a cross-sectional cohort study

OBJECTIVE

This cross-sectional observational cohort study was designed to investigate i) whether glycaemic variability in paediatric patients with type 1 diabetes is lower in those using an insulin pump (CSII) compared with those using multiple daily insulin injections (MDI) and ii) whether urinary F2 -isoprostanes and/or urinary prostaglandin F2 excretion as surrogate marker of oxidative stress and cyclooxygenase activity are associated with glycaemic variability.

METHODS

48 paediatric patients with type 1 diabetes (22 using an insulin pump) underwent an ambulatory 3-day continuous glucose monitoring. All patients continued with normal daily activities and collected urine for two consecutive 24 h periods. The glucose pentagon was used to calculate the glycaemic risk parameter.

RESULTS

Insulin requirements, HDL-cholesterol, the mean of glycaemic excursions (P < 0·01) and the standard deviation of mean glucose concentration (P < 0·05) were significantly lower in patients with CSII compared with those using MDI. By contrast, averaged HbA1c during the last twelve months as well as at the time of sensor insertion did not differ significantly between both groups. Summarizing characteristic parameter of acute and long-term metabolic control into the glucose pentagon revealed a significantly lower glycaemic risk parameter in CSI patients compared with both, healthy subjects and patients using MDI (P < 0·05).

CONCLUSIONS

Paediatric patients with type 1 diabetes using an insulin pump presented with lower glycaemic variability and a concomitantly lower glycaemic risk parameter compared with those using MDII. Whether these findings translate into a lower risk of diabetes associated cardiovascular complications remains to be elucidated.

Development and validation of a liquid chromatography/electrospray ionization tandem mass spectrometry method for the quantification of latanoprost free acid in rabbit aqueous humor and ciliary body

A rapid, selective and sensitive method for quantification of latanoprost free acid in rabbit aqueous humor (AH) and ciliary body (CB) using reverse phase-high performance liquid chromatography coupled with electrospray ionization (ESI)-mass spectrometry/mass spectrometry has been developed and validated. Quantification in AH and CB was achieved by stable isotope dilution employing tetra-deuterated analog of latanoprost free acid, used as internal standard. Sample preparation was based on protein precipitation with methanol in AH, and on liquid extraction with a mixture of ethyl acetate and isopropanol 60:40 (v/v) in CB. Elution was achieved on an octylsilica (C8) column, using an isocratic elution method. Detection was performed on a triple quadrupole mass spectrometer, using ESI in positive ion selected reaction monitoring mode. Calibration curves were linear in the validated concentration ranges of 10-160 ng/mL in AH and 80-1280 ng/g in CB. The accuracy and precision values, obtained from three different sets of quality control samples, each analyzed in triplicate on three different days, were within the generally accepted criteria for analytical methods (< 15%). The limit of detection was 30.66 pg/mL in AH and 237.75 pg/g in CB. The assay proved to be accurate and precise when applied to the in vivo study of latanoprost free acid in rabbit AH and CB after single administration of an eye drops containing latanoprost.

Beyond prostaglandins--chemistry and biology of cyclic oxygenated metabolites formed by free-radical pathways from polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are important constituents in all organisms. They fulfil many functions, ranging from modulating the structure of membranes to acting as precursors of physiologically important molecules, such as the prostaglandins, which for a long time were the most prominent cyclic PUFA metabolites. However, since the beginning of the 1990s a large variety of cyclic metabolites have been discovered that form under autoxidative conditions in vivo to a much larger extent than do prostaglandins. These compounds--isoprostanes, neuroprostanes, phytoprostanes, and isofurans--proved subsequently to be ubiquitous in nature. They display a wide range of biological activities, and isoprostanes have become the currently most reliable indicators of oxidative stress in humans. In a relatively short time, the structural variety, properties, and applications of the autoxidatively formed cyclic PUFA derivatives have been uncovered.

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.

Urinary prostaglandin F2alpha is generated from the isoprostane pathway and not the cyclooxygenase in humans

Prostaglandins (PGs) derived from the enzymatic oxidation of arachidonic acid by the cyclooxygenases (COXs) are potent lipid mediators involved in human physiology and pathophysiology. Structurally similar compounds, the isoprostanes (IsoPs), are generated from the free radical-catalyzed oxidation of arachidonic acid independent of COX. IsoPs exhibit significant bioactivity and play a role in the pathogenesis of diseases associated with oxidant injury. As one of the major PGs, prostaglandin F(2alpha) (PGF(2alpha)) is present in human urine in significant concentrations and is presumed to be derived from COX activity. We determined, however, that levels of putative PGF(2alpha) in urine cannot be suppressed by nonsteroidal anti-inflammatory agents, suggesting that it is generated via another mechanism(s). An important difference between COX-derived PGF(2alpha) and the IsoPs is that the former is an optically pure compound, whereas IsoPs are racemic. Utilizing a rodent model of oxidative stress, we now show that significant amounts of compounds identical in all respects to PGF(2alpha) and its enantiomer, ent-PGF(2alpha), are formed in equal amounts esterified in tissue phospholipids, suggesting that these compounds are derived via the IsoP pathway. Further, employing liquid chromatography/mass spectrometry, the vast majority of putative PGF(2alpha) in human urine is derived from the free radical-initiated peroxidation of arachidonate independent of COX and is composed of PGF(2alpha) and its enantiomer, although the latter compound is approximately 2-fold more abundant. Thus, quantification of urinary PGF(2alpha) actually reflects oxidative stress status as opposed to COX activity. Indeed, levels of this compound are elevated in urine from cigarette smokers and in humans with hypercholesterolemia, two conditions associated with oxidant stress. The elucidation that urinary PGF(2alpha) in humans is derived from the IsoP pathway has implications regarding PG formation and inhibition in vivo.

Renal cortical regulation of COX-1 and functionally related products in early renovascular hypertension (rat)

Renal volume regulation is modulated by the action of cyclooxygenases (COX) and the resulting generation of prostanoids. Epithelial expression of COX isoforms in the cortex directs COX-1 to the distal convolutions and cortical collecting duct, and COX-2 to the thick ascending limb. Partly colocalized are prostaglandin E synthase (PGES), the downstream enzyme for renal prostaglandin E(2) (PGE(2)) generation, and the EP receptors type 1 and 3. COX-1 and related components were studied in two kidney-one clip (2K1C) Goldblatt hypertensive rats with combined chronic ANG II or bradykinin B(2) receptor blockade using candesartan (cand) or the B(2) antagonist Hoechst 140 (Hoe). Rats (untreated sham, 2K1C, sham + cand, 2K1C + cand, sham + Hoe, 2K1C + Hoe) were treated to map expression of parameters controlling PGE(2) synthesis. In 2K1C, cortical COX isoforms did not change uniformly. COX-2 changed in parallel with NO synthase 1 (NOS1) expression with a raise in the clipped, but a decrease in the nonclipped side. By contrast, COX-1 and PGES were uniformly downregulated in both kidneys, along with reduced urinary PGE(2) levels, and showed no clear relations with the NO status. ANG II receptor blockade confirmed negative regulation of COX-2 by ANG II but blunted the decrease in COX-1 selectively in nonclipped kidneys. B(2) receptor blockade reduced COX-2 induction in 2K1C but had no clear effect on COX-1. We suggest that in 2K1C, COX-1 and PGES expression may fail to oppose the effects of renovascular hypertension through reduced prostaglandin signaling in late distal tubule and cortical collecting duct.

Non-steroidal anti-inflammatory drug (NSAID) use and levels of a lipid oxidation marker in plasma and nipple aspirate fluids

Non-steroidal anti-inflammatory drugs (NSAIDs) are thought to reduce cancer risk by inhibiting cyclo-oxygenases, resulting in deceased formation of inflammatory mediators and oxidative stress. We examined whether the level of one oxidative stress marker, 15-F(2t)-isoprostane, was affected by NSAID use in plasma and breast nipple aspirate fluids (NAF) of pre-menopausal women who were participating in a dietary intervention trial (n=121). Baseline levels of 15-F(2t)-isoprostane were lower in NSAID users than non-users in both NAF and plasma, although the differences did not persist after intervention. Over the duration of the study, information on NSAID use was collected five times, and average 15-F(2t)-isoprostane levels in both NAF and plasma exhibited a statistically significant trend for decreases with increased frequency of NSAID use. These results indicate that NSAID use can result in lower levels of 15-F(2t)-isoprostane, which may have implications for the effects of NSAID use on breast cancer risk.

Kinetics of biomarkers: biological and technical validity of isoprostanes in plasma

Isoprostanes, non-enzymatic peroxidation products of arachidonic acid, are attractive biomarkers of oxidative stress in research in biology, medicine and nutrition. For the appropriate use of biomarkers it is required that these are both biologically and technically valid. Whereas the biological validity of isoprostanes is well-established, it is technically quite complicated to measure isoprostanes and its metabolites in body fluids, and its rapid disappearance from plasma may hamper practical application. This paper shortly introduces isoprostanes as a biomarker for studies with humans, describes a novel fast and sensitive method for measuring isoprostanes in plasma by high-performance liquid chromatography and tandem mass spectrometry, and provides several examples of the use of the method in studies in humans. By taking care of the biological and technical validity of this biomarker it is possible to establish the antioxidant effects of some food ingredients in studies with human volunteers.

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.

Cyclooxygenase-mediated prostaglandin F2alpha is decreased in an elderly population treated with low-dose aspirin

Low-dose aspirin (acetylsalicylic acid) is used as prophylaxis against cardiovascular diseases. The effect of aspirin on inflammation and oxidative stress, processes known to be involved in cardiovascular diseases, are not fully known. The cyclooxygenase(COX)-mediated inflammatory indicator prostaglandin F2alpha (PGF2alpha) (15-keto-dihydro-PGF2alpha), cytokine-mediated inflammatory indicators (interleukin-6, high-sensitivity C-reactive protein, serum amyloid A protein), and oxidative stress indicators (8-iso-PGF2alpha, tocopherols) were quantified in men with daily 75 mg of aspirin (n=175) and control men (n=464), all of age 77, in a cross-sectional study. Men treated with aspirin had decreased levels of urinary 15-keto-dihydro-PGF2alpha than controls (P<0.01), independent of possible cardiovascular risk factors. Aspirin-treated men had increased levels of alpha-tocopherol than controls (P<0.05). This is the first study to indicate that low-dose aspirin treatment is associated with decreased levels of PGF2alpha. This observation suggests a possible COX-mediated anti-inflammatory effect of low-dose aspirin, which should be further confirmed by intervention studies.

Biomarkers of oxidative stress study III. Effects of the nonsteroidal anti-inflammatory agents indomethacin and meclofenamic acid on measurements of oxidative products of lipids in CCl4 poisoning

Plasma and urinary levels of malondialdehyde-like products (MDA) and isoprostanes were identified as markers of in vivo lipid peroxidation in an animal model of CCl4 poisoning. We sought to determine the extent to which the formation of these oxidation products is influenced by inhibition of the cyclooxygenase enzymes which catalytically generate proinflammatory lipid peroxidation products known as prostaglandins and thromboxane. In the present studies, after induction of oxidant stress in rats with CCl4, lipid peroxidation products measured in plasma and urine demonstrate that isoprostanes and MDA can be partially inhibited by cyclooxygenase inhibitors, albeit to different extents. The lowering of isoprostane and MDA formation, however, may not to due primarily to the diminution of catalytic generation of isoprostanes or MDA by the cyclooxygenases but, rather, may be the result of the suppression of nonenzymatic lipid peroxidation. This is suggested since 8,12-iso-iPF2alpha-VI is also reduced by indomethacin, yet, unlike other isoprostanes and MDA, it is not generated catalytically by the cyclooxygenase. Thus, although the two cyclooxygenase inhibitors we tested have statistically significant effects on the measurements of both isoprostanes and MDA in this study, the results provide evidence that these lipid-degradation products primarily constitute markers of oxidative stress.

Rapid preparation of human urine and plasma samples for analysis of F2-isoprostanes by gas chromatography-mass spectrometry

Reliable MS-based methods have been developed for the measurement of free and esterified F2-isoprostanes. However, prior to sample analysis several steps of purification, including solid-phase extraction followed by TLC or HPLC, are usually required, making it tedious to analyze large sample numbers, e.g., for population studies. We report a quick sample purification method using anion exchange solid phase extraction (SPE), which is highly selective for acidic compounds. Urine and hydrolyzed plasma of healthy individuals were acidified before SPE extraction, washed with 4 different solvent mixtures and finally eluted with ethyl acetate. The eluted samples were first derivatized with pentafluorobenzyl bromide followed by a second derivatization with bis-(trimethylsilyl)trifluoroacetamide. F2-isoprostanes were analyzed by GC-MS-NCI. The method was highly sensitive; the limit of detection at 5:1 signal-to-noise ratio was 0.037 ng/ml and 0.007 ng/mg creatinine for plasma and urine, respectively. Anion exchange SPE extraction for F2-isoprostane showed recovery of 55-65% and high linearity for concentration 0-1.0 ng/ml for urine (CV=4.08%, r2=0.990) and 0-0.5 ng/ml for plasma (CV=4.07%, r2=0.998). Fasting for 6h significantly increased plasma F2-isoprostanes levels, which has implications for the design of intervention studies using this biomarker.

Divergence in urinary 8-iso-PGF(2alpha) (iPF(2alpha)-III, 15-F(2t)-IsoP) levels from gas chromatography-tandem mass spectrometry quantification after thin-layer chromatography and immunoaffinity column chromatography reveals heterogeneity of 8-iso-PGF(2alpha). Possible methodological, mechanistic and clinical implications

Free radical-catalysed oxidation of arachidonic acid esterified to lipids leads to the formation of the F(2)-isoprostane family which may theoretically comprise up to 64 isomers. We have previously shown that the combination of TLC and GC-tandem MS (referred to as method A) allows for the accurate and highly specific quantification of 8-iso-PGF(2alpha) (iPF(2alpha)-III, 15-F(2t)-IsoP) in human urine. Immunoaffinity column chromatography (IAC) with immobilized antibodies raised against 8-iso-PGF(2alpha) (i.e. 15(S)-8-iso-PGF(2alpha)) has been shown by others to be highly selective and specific for this 8-iso-PGF(2alpha) isomer when quantified by GC-MS. In the present study we established IAC for urinary 8-iso-PGF(2alpha) for subsequent quantification by GC-tandem MS (referred to as method B). This method was fully validated and found to be highly accurate and precise for urinary 15(S)-8-iso-PGF(2alpha). 8-iso-PGF(2alpha) was measured in urine of 10 young healthy humans by both methods. 8-iso-PGF(2alpha) was determined to be 291+/-102 pg/mg creatinine by method A and 141+/-41 pg/mg creatinine by method B. Analysis of the combined through and wash phases of the IAC step, i.e. of the unretained compounds, by method A showed the presence of non-immunoreactive 8-iso-PGF(2alpha) at 128+/-55 pg/mg creatinine. This finding suggests that urinary 8-iso-PGF(2alpha) is heterogenous, with 15(S)-8-iso-PGF(2alpha) contributing by approximately 50%. PGF(2alpha) and other 8-iso-PGF(2alpha) isomers including 15(R)-8-iso-PGF(2alpha) are not IAC-immunoreactive and are chromatographically separated from 15(S)-8-iso-PGF(2alpha). We assume that ent-15(S)-8-iso-PGF(2alpha) is also contributing by approximately 50% to urinary 8-iso-PGF(2alpha). This finding may have methodological, mechanistic and clinical implications.

Inhibition of COX-2 prevents hypertension and proteinuria associated with a decrease of 8-iso-PGF2alpha formation in L-NAME-treated rats

BACKGROUND

The inhibition of nitric oxide (NO) exerts injurious effects on the cardiovascular system by several mechanisms, such as the activation of the renin-angiotensin system, oxidative stress, and inflammatory cytokines. We examined whether COX-2, an inducible isoform of cyclooxygenase, is associated with the pathogenesis observed in N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats.

METHODS

Three groups of 8-week-old male Sprague-Dawley rats were studied (n = 6 in each group): group 1, untreated controls; group 2, treated with L-NAME (1 g/l for 3 weeks, p.o.); and group 3, L-NAME co-treated with COX-2 inhibitor NS-398 (5 mg/kg per day, i.p.). The L-NAME-induced expression of COX-2 mRNA and protein was semi-quantified in the kidneys and the thoracic aorta. Urinary excretion of the prostaglandin 6-keto PGF(1alpha), thromboxane B2 (TXB2), and prostaglandin E2 (PGE2) was measured in the three groups. Moreover, urinary excretion of 8-iso-PGF(2alpha), a potent vasoconstricting arachidonic acid metabolite acting through thromboxane A (TXA) receptor activation, proposed recently as a marker of oxidative stress, was also measured.

RESULTS

L-NAME induced significant increases in systolic blood pressure (P< 0.01), urinary protein (P< 0.05), and renal excretion of 8-iso-PGF(2alpha)(P< 0.01), compared with the control. In L-NAME-treated rats, the levels of COX-2 mRNA and protein were more than 50% higher in the kidneys (P< 0.05), and six-fold higher in the thoracic aorta (P< 0.01) than in control rats. NS-398 significantly ameliorated an increase in systolic blood pressure (P< 0.01) and urinary protein (P< 0.05) induced by L-NAME.

CONCLUSIONS

These data indicate that an increase in COX-2 expression might have a hypertensive effect, partly associated with 8-iso-PGF(2alpha) formation in l-NAME-treated rats.

Derivatization of F2-isoprostanes with 1-pyrenyldiazomethane and their subsequent determination by fluorescence high-performance liquid chromatography

F(2)-isoprostanes are produced during free radical oxidation of cell phospholipids and are considered reliable biomarkers of oxidative stress. Currently, mass spectroscopy is the method of choice to detect F(2)-isoprostanes. However, due to numerous isomeric forms, analysis of F(2)-isoprostanes using MS detectors requires preliminary chromatographic separation. The current study was undertaken to develop a method of HPLC separation and quantification of different isomers of prostaglandin F(2alpha), including 8-iso-PGF(2alpha), following derivatization with 1-pyrenyldiazomethane (PDAM) to a highly fluorescent 1-pyrenylmethyl ester. HPLC separation and quantification of 1-pyrenylmethyl esters of PGF(2alpha) isomers at picogram level are complicated by numerous interfering products of the degradation of 1-pyrenyldiazomethane. A procedure of derivatization and purification was developed to reduce these interfering contaminants. The procedure of derivatization includes sorption of PGF(2alpha) isomers from solution in a hexane:ethyl acetate mixture (10:1) on a cellulose support prepared in the form of small (4 x 4mm) filter paper squares. Bound PGF(2alpha) isomers are derivatized by 1-pyrenyldiazomethane dissolved in the same hexane:ethyl acetate mixture. During subsequent washing of the cellulose squares by the hexane:ethyl acetate mixture (10:1), fluorescent derivatives of PGF(2alpha) remain bound to cellulose while a significant portion of the contaminants are washed out. The 1-pyrenylmethyl esters of PGF(2alpha) can be quantitatively extracted from cellulose by an ethyl acetate:methanol (1:1) mixture. The next step in eliminating interference is a solid-phase extraction on silica cartridges using ethyl acetate for application of the sample and an ethyl acetate:methanol (1:1) mixture for elution. Final purification is achieved by normal-phase HPLC with wet ethyl acetate as the mobile phase. This chromatographic method displays remarkable resolution in the separation of different PGF(2alpha) isomers and can be used not only for sample purification but also for pre-MS separation. The purified 1-pyrenylmethyl esters of PGF(2alpha) were quantitatively analyzed by reverse-phase HPLC with fluorescent detection, with a detection limit of 5-10 pg.

Diclofenac-induced embryotoxicity is associated with increased embryonic 8-isoprostaglandin F2alpha level in rat whole embryo culture

Diclofenac is embryotoxic in animals but the mechanism of its embryotoxicity is not fully understood. We postulated that diclofenac-induced embryotoxicity might be related to free oxygen radical damage. Rat embryos were explanted at 9.5 days gestation and cultured in medium containing various concentrations of diclofenac. The direct effect of diclofenac on embryonic free oxygen radical content was evaluated by measuring the 8-isoprostaglandin F2alpha level. We found that embryos exposed to high concentrations of diclofenac (7.5 and 15.0 micro g/ml) had significantly higher levels of 8-isoprostaglandin F2alpha (2.85 and 3.50 pg/mm embryonic crown-rump length, respectively) than the control group (1.73 pg/mm, P<0.05), while the 8-isoprostaglandin F2alpha level in embryos exposed to low concentration of diclofenac (1.5 micro g/ml) was 2.54 pg/mm, which was not significantly different from the control group. Median embryo morphologic score was also lower in the high concentration group compared to the control group (39.0 versus 44.0, P<0.05). These results suggest that diclofenac-induced embryopathy may be related to free oxygen radical damage.

Respiratory syncytial virus induces prostaglandin E2, IL-10 and IL-11 generation in antigen presenting cells

Bronchiolitis caused by respiratory syncytial virus (RSV) infection is a major cause of hospitalization in children under 1 years of age. The disease characteristically does not induce protective immunity. However, a mononuclear peribronchiolar and perivascular infiltrate during RSV infection is suggestive of an immune-mediated pathogenesis. Macrophages and dendritic cells (DCs) play an essential role in the initiation and maintenance of immune response to pathogens. To analyse interactions of RSV and immune cells, human cord blood derived macrophages and dendritic cells were infected with RSV. Both cells were found to be infected with RSV resulting in the activation of macrophages and maturation of dendritic cells as reflected by enhanced expression of several surface antigens. In the next set of experiments, generation of mediators was compared between cells infected with RSV, parainfluenza (PIV3) and influenza virus as well as ultracentrifuged virus free supernatant. Whereas the supernatant did not induce release of mediators, all three live virus infections induced IL-6 production from macrophages and DC. Influenza virus infection induced predominantly IL-12 p75 generation in DC. In contrast, RSV induced strong IL-11 and prostaglandin E2 release from both macrophages and DCs. In addition, RSV but not influenza and parainfluenza virus induced a strong IL-10 generation particularly from macrophages. Since IL-10, IL-11 and PGE2 are known to act immunosuppressive rather than proinflammatory, these mediators might be responsible for the delayed protective RSV specific immune response.

Determination of travoprost and travoprost free acid in human plasma by electrospray HPLC/MS/MS

A quantitative method for the analysis of AL-5848, the (+)-enantiomer of fluprostenol (FP), in human plasma is described. Plasma was spiked with a tetradeuterated analog of travoprost free acid (AL-5848X) as internal standard (IS) and acidified with 0.1 M formic acid. Sample clean up was performed using reversed phase solid-phase extraction. Following elution of the compounds of interest and evaporation to dryness, the residue was reconstituted in methanol:water (1:1) and chromatographed on an octadecylsilica (C18) column with negative ion electrospray ionization tandem mass spectrometry. The [M[bond]H](-) ions at m/z 457 and 461 for the analyte and IS, respectively, were subjected to collisional fragmentation with argon to yield the same intense 3-trifluoromethylphenolate (m/z 161) product ion. The validated concentration range was 0.010-3.00 ng/ml based on a 1.0 ml plasma aliquot. Fully adequate accuracy, precision, specificity, recovery and stability for routine use in clinical pharmacokinetic studies were demonstrated. Analysis of a second plasma aliquot following incubation with rabbit esterase allows the isopropyl ester pro-drug, travoprost (AL-6221), to be determined by difference.

Mouse cerebral prostaglandins, but not oxidative damage, change with age and are responsive to indomethacin treatment

Epidemiological and clinical trial data indicate that at least some non-steroidal anti-inflammatory drugs (NSAIDs) reduce the risk of developing Alzheimer's disease (AD). Advancing age is the most robust risk factor for AD. If NSAIDs mitigate the initiation of AD by affecting processes of aging, and if the target of NSAIDs are cyclooxygenases (COX), then COX activity would be hypothesized to increase with advancing age in brain regions affected by AD. We tested this hypothesis in mouse cerebrum by measuring two outcomes of increased COX activity, prostaglandin (PG) levels and markers of oxidative damage. Our results showed that frontal cortical PGE(2) and 6-keto-PGF(1alpha) levels were significantly increased at 14 months compared to 2 months, but that frontal cortical levels of these PGs at 26 months returned to levels observed at 2 months of age. At all ages, 2-week treatment with indomethacin (14 microg/ml drinking water, or approximately 2.2 mg/kg per day) equally suppressed frontal cortical levels of both PGs. In contrast, basal levels of oxidative damage to cerebral cortex did not increase in mice aged up to 26 months, and indomethacin treatment did not significantly alter basal levels of oxidative damage as assayed by F(2)-isoprostanes or protein carbonyls. These results suggest that indomethacin may influence the initiation of AD by reducing cerebral PG elevation that may occur in middle age, but that it is unlikely to have a direct effect on levels of oxidative damage.

Overexpression of cytochrome P450 CYP2J2 protects against hypoxia-reoxygenation injury in cultured bovine aortic endothelial cells

CYP2J2 is abundant in human heart and its arachidonic acid metabolites, the epoxyeicosatrienoic acids (EETs), have potent vasodilatory, antiinflammatory and cardioprotective properties. This study was designed to examine the role of CYP2J2 in hypoxia-reoxygenation-induced injury in cultured bovine aortic endothelial cells (BAECs). Early passage BAECs were exposed to 24-h hypoxia followed by 4-h reoxygenation (HR). HR resulted in cell injury, as indicated by significant increases in lactate dehydrogenase (LDH) release and trypan blue stained cells (p < 0.01) and was associated with a decrease in CYP2J2 protein expression. Transfection of BAECs with the CYP2J2 cDNA resulted in increased CYP2J2 expression and arachidonic acid epoxygenase activity, compared with cells transfected with an irrelevant green fluorescent protein (GFP) cDNA. HR induced significant injury in GFP-transfected BAECs, as indicated by increases in LDH release and trypan blue-stained cells (p < 0.01); however, the HR-induced injury was markedly attenuated in CYP2J2-transfected cells (p < 0.01). HR increased cellular 8-iso-prostaglandin F(2alpha) (p < 0.05), and decreased eNOS expression, L-arginine uptake and conversion, and nitrite production (p < 0.01) in GFP-transfected BAECs. CYP2J2 transfection attenuated the HR-induced increase in 8-iso-prostaglandin F(2alpha) (p < 0.05) and decreased the amount of extracellular superoxide detected by cytochrome c reduction under normoxic conditions (p < 0.05) but did not significantly affect HR-induced decreases in eNOS expression, L-arginine uptake and conversion, and nitrite production. Treatment of BAECs with synthetic EETs and/or epoxide hydrolase inhibitors also showed protective effects against HR injury (p < 0.05). These observations suggest: (1) HR results in endothelial injury and decreased CYP2J2 expression; (2) transfection with the CYP2J2 cDNA protects against HR injury; and (3) the cytoprotective effects of CYP2J2 may be mediated, at least in part, by antioxidant effects.

Isoprostanes: an overview and putative roles in pulmonary pathophysiology

Isoprostanes are produced during peroxidation of membrane lipids by free radicals and reactive oxygen species. Initially, they were recognized as being valuable markers of oxidative stress, and in the past 10 years, dozens of disease states and experimental conditions with diverse etiologies have been shown to be associated with marked increases in urinary, plasma, and tissue levels of isoprostanes. However, they are not just mere markers; they evoke important biological responses on virtually every cell type found within the lung, and these responses exhibit compound-, tissue-, and species-related variations. In fact, the isoprostanes may mediate many of the features of the disease states for which they are used as indicators. In this review, I describe the chemistry, metabolism, and pharmacology of isoprostanes, with a particular emphasis on pulmonary cell types, and the possible roles of isoprostanes in pulmonary pathophysiology.

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.

Vascular biology of the isoprostanes

Isoprostanes are a family of compounds produced from polyunsaturated fatty acids via a free-radical-catalysed mechanism. F(2)-isoprostanes are prostaglandin F(2alpha) isomers derived from arachidonic acid. These compounds induce potent vasoconstriction, mediated primarily by TP receptor stimulation, and in some vessels by the release of cyclooxygenase products. This vasoconstriction may be modulated by the endothelium through the release of NO. Potent vasoconstriction is also observed with E(2)-isoprostanes. Experimental and clinical data suggest a role for F(2)-isoprostanes in atherogenesis. These compounds can be detected in free forms in biological fluids as well as esterified in low-density lipoproteins or cell membranes. Their quantification represents a reliable marker of lipid peroxidation. Elevated levels of F(2)-isoprostanes in biological fluids in pathological conditions including atherosclerosis, ischaemia-reperfusion injury, and inflammatory vascular diseases, suggest a relationship between lipid peroxidation and such diseases. F(2)-isoprostanes are currently being investigated as non-invasive quantitative markers to monitor the response to anti-oxidant treatment.

Effect of preterm formula with and without long-chain polyunsaturated fatty acids on the urinary excretion of F2-isoprostanes and 8-epi-prostaglandin F2alpha

BACKGROUND

The objective of this study was to evaluate the effect of conventional and long-chain polyunsaturated fatty acids (LCP)-enriched preterm formula on the endogenous formation of F2-isoprostanes and 8-epi-prostaglandin (PG) F2alpha as possible markers of lipid peroxidation in preterm infants during their first weeks of life.

METHODS

In a prospective, randomized, double-blind study, infants received either formula enriched with LCP (n = 8), standard preterm formula (n = 7), or (expressed) breast milk (n = 8). Urine was sampled at study entry and after the study period of 3 weeks. The formation of F2-isoprostanes and 8-epi-PGF2alpha was evaluated by measuring the urinary excretion by gas chromatography-mass spectrometry.

RESULTS

No differences in the urinary excretion of F2-isoprostanes and 8-epi-PGF2alpha were observed at the end of the study period.

CONCLUSIONS

This result suggests that supplementation of a preterm formula with LCP for a period of 3 weeks does not stimulate lipid peroxidation in preterm infants.

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).

An improved method for the measurement of urinary and plasma F2-isoprostanes using gas chromatography-mass spectrometry

We have developed an improved method for the measurement of F2-isoprostanes using stable isotope dilution capillary gas chromatography/electron capture negative ionization mass spectrometry (GC-ECNI-MS). The F2-isoprostane family consists of a series of chemically stable prostaglandin F2 (PGF2)-like compounds generated during peroxidation of arachidonic acid in phospholipids. There is evidence that measurement of F2-isoprostanes represents a reliable and useful index of lipid peroxidation and oxidant stress in vivo. Furthermore, 8-epi-PGF2alpha, which is one of the more abundant F2-isoprostanes, is biologically active, being a potent mitogen and vasoconstrictor of rat and rabbit lung and kidney, as well as a partial agonist of platelet aggregation. Measurement of F2-isoprostanes in biological samples is complex and has involved methods which utilize multiple chromatographic steps, including separation by thin-layer chromatography, leading to poor sample recovery. We now present an improved method for the measurement of plasma and urinary F2-isoprostanes using a combination of silica and reverse-phase extraction cartridges, high-performance liquid chromatography (HPLC), and GC-ECNI-MS. Different approaches to the derivatization of the F2-isoprostanes prior to GC-ECNI-MS are also addressed. The overall recovery of F2-isoprostanes is improved (approx 70% for urine) and the within and between assay reproducibility is 6.7% (n = 23) and 3.7% (n = 3), respectively. The mean urinary excretion of F2-isoprostanes in eight healthy males was 365 +/- 5 pmol/mmol creatinine and in three smokers 981 +/- 138 pmol/mmol creatinine. The mean total (free + esterified) plasma F2-isoprostane concentration was 952 +/- 38 pmol/liter, with a within and between assay reproducibility of 8% (n = 13) and 5.6% (n = 3), respectively. This improved method for the measurement of F2-isoprostanes represents a significant advance in terms of the rapidity and yield in the purification of biological samples. The inclusion of HPLC separation enables improved analysis of F2-isoprostanes by GC-MS. This methodology will assist in defining the role of F2-isoprostanes as in vivo markers of oxidant stress in clinical and experimental settings.

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.

Oxidized phospholipids and isoprostanes in atherosclerosis

Lipid oxidation has been shown to be a prominent feature of atherosclerosis. The presence of isoprostanes and other lipid oxidation products has been clearly demonstrated in lesions. Furthermore, antibodies to oxidized phospholipids have been identified in animal and human models. Recent evidence suggests that oxidized phospholipids may activate all vascular cell types. The identification and isolation of particular oxidative products has provided some important information about the receptors for these active lipids.

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.