The pulmonary biology of isoprostanes

Polyunsaturated fatty acids and fatty acid-derived lipid mediators: Recent advances in the understanding of their biosynthesis, structures, and functions

Polyunsaturated fatty acids (PUFAs) are structural components of membrane phospholipids, and influence cellular function via effects on membrane properties, and also by acting as a precursor pool for lipid mediators. These lipid mediators are formed via activation of pathways involving at least one step of dioxygen-dependent oxidation, and are consequently called oxylipins. Their biosynthesis can be either enzymatically-dependent, utilising the promiscuous cyclooxygenase, lipoxygenase, or cytochrome P450 mixed function oxidase pathways, or nonenzymatic via free radical-catalyzed pathways. The oxylipins include the classical eicosanoids, comprising prostaglandins, thromboxanes, and leukotrienes, and also more recently identified lipid mediators. With the advent of new technologies there is growing interest in identifying these different lipid mediators and characterising their roles in health and disease. This review brings together contributions from some of those at the forefront of research into lipid mediators, who provide brief introductions and summaries of current understanding of the structure and functions of the main classes of nonclassical oxylipins. The topics covered include omega-3 and omega-6 PUFA biosynthesis pathways, focusing on the roles of the different fatty acid desaturase enzymes, oxidized linoleic acid metabolites, omega-3 PUFA-derived specialized pro-resolving mediators, elovanoids, nonenzymatically oxidized PUFAs, and fatty acid esters of hydroxy fatty acids.

Measurement of Enzymatic and Nonenzymatic Polyunsaturated Fatty Acid Oxidation Products in Plasma and Urine of Macular Degeneration Using LC-QTOF-MS/MS

Oxidized polyunsaturated fatty acids (PUFA) are associated to pathogenesis of diseases including cardiovascular and neurodegeneration. The novel products are not only biomarkers but also lipid mediators in gene regulation and signaling pathways. Herein, simultaneous quantitation of 28 products derived from nonenzymatic and enzymatic oxidation of PUFA i.e. 5-, 15-F_2t -isoprostanes, 7-, 17-F_2t -dihomo-isoprostanes, 7-, 17-F_2t -dihomo-isofurans, 5-, 8-, 18-F_3t -isoprostanes, 4-, 10-, 13-, 14-, 20-F_4t -neuroprostanes, 5-, 8-, 9-, 11-,12-, 15-, 20-HETE, 4-, 7-, 11-, 14-, 17-HDHA, RvE1, and NPD1 using LC-(ESI)-QTOF-MS/MS was developed. These products were measurable in a single sample and the analytical time was relative short (~15 min). Furthermore, we showed that the use of internal standards is a requisite to normalize matrix effects and preparation loss for the quantitation. Validation assays indicated the method to be robust for plasma and mid-stream urine sample analysis in particular from those of age-related macular degeneration subjects, where the accuracy of quantitation displayed good repeatability.

Increase in omega-6 and decrease in omega-3 polyunsaturated fatty acid oxidation elevates the risk of exudative AMD development in adults with Chinese diet

Appropriate diet is essential for the regulation of age-related macular degeneration (AMD). In particular the type of dietary polyunsaturated fatty acids (PUFA) and poor antioxidant status including carotenoid levels concomitantly contribute to AMD risk. Build-up of oxidative stress in AMD induces PUFA oxidation, and a mix of lipid oxidation products (LOPs) are generated. However, LOPs are not comprehensively evaluated in AMD. LOPs are considered biomarkers of oxidative stress but also contributes to inflammatory response. In this cross-sectional case-control study, plasma omega-6/omega-3 PUFA ratios and antioxidant status (glutathione, superoxide dismutase and catalase), and plasma and urinary LOPs (41 types) were determined to evaluate its odds-ratio in the risk of developing exudative AMD (n = 99) compared to age-gender-matched healthy controls (n = 198) in adults with Chinese diet. The odds ratio of developing exudative AMD increased with LOPs from omega-6 PUFA and decreased from those of omega-3 PUFA. These observations were associated with a high plasma omega-6/omega-3 PUFA ratio and low carotenoid levels. In short, poor PUFA and antioxidant status increased the production of omega-6 PUFA LOPs such as dihomo-isoprostane and dihomo-isofuran, and lowered omega-3 PUFA LOPs such as neuroprostanes due to the high omega-6/omega-3 PUFA ratios; they were also correlated to the risk of AMD development. These findings indicate the generation of specific LOPs is associated with the development of exudative AMD.

Outdoor air pollution, exhaled 8-isoprostane and current asthma in adults: the EGEA study

Associations between outdoor air pollution and asthma in adults are still scarce, and the underlying biological mechanisms are poorly understood. Our aim was to study the associations between 1) long-term exposure to outdoor air pollution and current asthma, 2) exhaled 8-isoprostane (8-iso; a biomarker related to oxidative stress) and current asthma, and 3) outdoor air pollution and exhaled 8-iso.Cross-sectional analyses were conducted in 608 adults (39% with current asthma) from the first follow-up of the French case-control and family study on asthma (EGEA; the Epidemiological study of the Genetic and Environmental factors of Asthma). Data on nitrogen dioxide, nitrogen oxides, particulate matter with a diameter ≤10 and ≤2.5 µm (PM₁₀ and PM_2.5), road traffic, and ozone (O₃) were from ESCAPE (European Study of Cohorts for Air Pollution Effects) and IFEN (French Institute for the Environment) assessments. Models took account of city and familial dependence.The risk of current asthma increased with traffic intensity (adjusted (a)OR 1.09 (95% CI 1.00-1.18) per 5000 vehicles per day), with O₃ exposure (aOR 2.04 (95% CI 1.27-3.29) per 10 µg·m^-3) and with exhaled 8-iso concentration (aOR 1.50 (95% CI 1.06-2.12) per 1 pg·mL^-1). Among participants without asthma, exhaled 8-iso concentration increased with PM_2.5 exposure (adjusted (a)β 0.23 (95% CI 0.005-0.46) per 5 µg·m^-3), and decreased with O₃ and O_3-summer exposures (aβ -0.20 (95% CI -0.39- -0.01) and aβ -0.52 (95% CI -0.77- -0.26) per 10 µg·m^-3, respectively).Our results add new insights into a potential role of oxidative stress in the associations between outdoor air pollution and asthma in adults.

Identification of potential erythrocyte phospholipid fatty acid biomarkers of advanced lung adenocarcinoma, squamous cell lung carcinoma, and small cell lung cancer

New biomarkers for lung cancer would be valuable. Our aim was to analyze the fatty acid profiles of the main phospholipid species in erythrocytes from patients with advanced squamous cell lung carcinoma (SCC), lung adenocarcinoma (ADC), and small cell lung cancer (SCLC) and benign lung diseases (chronic obstructive pulmonary disease (COPD) and asthma) to determine the fatty acids that could be use as lung cancer markers. Twenty-eight, 18, 14, 16, and 15 patients with, respectively, SCC, ADC, SCLC, asthma, and COPD and 50 healthy subjects were enrolled in the study. Fatty acid profiles were investigated using gas chromatography/mass spectrometry followed by receiver operating characteristic (ROC) curve analysis. The fatty acid profiles changed significantly in the different pathologies analyzed. Based on the diagnostic yields and operating characteristics, the most significant fatty acids that might be used as biomarkers were as follows: ADC--arachidonic acid (20:4n6) in phosphatidylcholine and oleic acid (18:1n9) in phosphatidylethanolamine (PE); SCC--eicosapentaenoic acid (20:5n3) in PE and palmitic acid (16:0) in phosphatidylserine + phosphatidylinositol (PS+PI); SCLC--eicosadienoic acid (20:2n6) in PS+PI and lignoceric acid (24:0) in sphingomyelin. In conclusion, fatty acids from erythrocyte phospholipid species might serve as biomarkers in the diagnosis, and probably in other aspects related to clinical disease management, of ADC, SCC, and SCLC.

Relationship between oxidative stress-related biomarkers and antioxidant status with asthma and atopy in young adults: a population-based study

BACKGROUND AND AIM

Enhanced oxidative stress has been described in adults who suffer from symptoms of asthma and poor lung function. This study assessed the relation between markers of oxidative stress and antioxidant status and lung function, symptoms of asthma, atopy and bronchial hyperresponsiveness (BHR) in young adults.

METHODS

A sub-sample of 589 individuals aged 22-28 years, selected from a total of 1232 included in a survey assessing early and current risk factors for chronic diseases, participated in the study. Participants were from an agricultural area of Chile, responded to a Spanish version of the European Community Respiratory Health Survey questionnaire, were skin tested to eight allergens, and challenged with methacholine to assess BHR. Five hundred and eighty-five individuals had measures of plasma biomarkers ferric reducing ability of plasma, uric acid, protein carbonyls and 564 had 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) assessed.

RESULTS

All participants had detectable plasma 8-iso-PGF(2alpha) and carbonyl levels. There was no indication for an association between markers of antioxidant status or oxidative stress with any of the outcomes studied.

CONCLUSION

The levels of oxidative stress-related biomarkers and antioxidant status in plasma may not be related to asthma in the general population in the absence of more severe symptoms or exacerbations.

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.

Direct eicosanoid profiling of the hypoxic lung by comprehensive analysis via capillary liquid chromatography with dual online photodiode-array and tandem mass-spectrometric detection

Eicosanoids are arachidonic acid-derived mediators, with partly contradictory, incompletely elucidated actions. Thus, epoxyeicosatrienoic acids (EETs) are controversially discussed as putative vasodilatative endothelium-derived hyperpolarizing factors in the cardiovascular compartment but reported as vasoconstrictors in the lung. Inconsistent findings concerning eicosanoid physiology may be because previous methods were lacking sensitivity, identification reliability, and/or have focused on special eicosanoid groups only, ignoring the overall mediator context, and thus limiting the correlation accuracy between autacoid formation and bioactivity profile. Therefore, we developed an approach which enables the simultaneous assessment of 44 eicosanoids, including all representatives of the arachidonic acid cascade, i.e., cytochrome P450, lipoxygenase, cyclooxygenase products, and free isoprostanes as in vivo markers of oxidative stress, in one 50-minute chromatographic run. The approach combines (i) source-specific sample extraction, (ii) rugged isocratic and high-sensitivity capillary liquid-chromatographic separation, and (iii) reliable dual online photodiode-array and electrospray ionization tandem mass-spectrometric identification and quantitation. High sensitivity with limits of quantification in the femtogram range was achieved by use of capillary columns with typical high peak efficiency, due to small inner diameters, and virtually complete substance transfer to the mass spectrometer, due to flow rates in the low microliter range, instead of large inner diameter columns with low chromatographic signal and only partial analyte transfer employed by previous methods. This expeditious, global and sensitive technique provides the prerequisite for new, accurate insights regarding the physiology of specific mediators, for example EETs, in the context of all relevant vasoactive autacoids under varying conditions of oxidative stress by direct comparison of all eicosanoid generation profiles. Indeed, application of comprehensive "eicoprofiling" to hypoxically ventilated rabbit lungs revealed at a glance the enhanced biosynthesis of free EETs in the overall mediator generation context, thus suggesting their hypothetical contribution to hypoxic pulmonary vasoconstriction.

Oxidative stress and lipid-derived inflammatory mediators during acute exacerbations of cystic fibrosis

BACKGROUND AND OBJECTIVE

In cystic fibrosis (CF) very few studies have assessed sputum 8-iso-PGF2alpha levels during pulmonary exacerbations as a direct measure of airway oxidative stress. The role of other lipid-derived inflammatory mediators, such as the cysteinyl leukotrienes (cys-LTs) and prostaglandin (PG)-E2, during exacerbations is also poorly defined and the effect of conventional antibiotic therapy on these components of the inflammatory process is unclear.

METHODS

Sputum 8-iso-PGF2alpha, total cys-LT and PGE2 levels were measured in 17 CF patients experiencing a pulmonary exacerbation and repeated analysis were performed in 15 of these patients after antibiotic treatment. Eight stable CF and nine healthy subjects provided control data.

RESULTS

Sputum 8-iso-PGF2alpha was significantly elevated in acute, but not stable CF patients versus healthy controls (P < 0.001). Similarly, sputum cys-LT and PGE2 levels were increased in acute compared with stable CF patients and healthy controls (P <or= 0.001). Although substantially lower than in acute patients, sputum cys-LT levels in stable patients were also significantly higher than in normal controls (P = 0.01). There were strong associations between cys-LT levels and sputum total cell counts, and blood neutrophils in acute patients (r2 = 0.53, P = 0.001 and r2 = 0.33, P < 0.05, respectively). Overall in the CF patients, FEV1% predicted was strongly and negatively correlated with sputum 8-iso-PGF2alpha (r2 = 0.34, P = 0.006), cys-LT (r2 = 0.40, P = 0.002) and PGE2 (r2 = 0.52, P < 0.001) levels. Antibiotic treatment reduced sputum total cell count (P = 0.03), but did not affect 8-iso-PGF2alpha, cys-LT or PGE2 levels.

CONCLUSIONS

CF exacerbations are characterized by increased oxidative stress and sputum concentrations of bioactive lipid mediators. Treatment does not modulate these aspects of inflammation and more targeted therapy needs further study.

Aspirin induces the production of the inflammatory mediator 8-epi-PGF in mast cells

Recently it has been shown that mast cells, through release of their pro-inflammatory mediators, are involved in aspirin attacks in aspirin-sensitive patients. To date, little information is available concerning 8-isoprostane (8-epi-prostaglandin F) production by mast cells. Therefore, we examined whether exposure of mast cells to aspirin can lead to isoprostane production. In this study we show that in mast cells, IgE and antigen stimulates an intracellular oxidative burst inducing H(2)O(2) and 8-epi-PGF production. Moreover, we show that exposure of mast cells to aspirin directly induces the production of 8-epi-PGF. Our study suggests that production of 8-epi-PGF by mast cells could contribute to the inflammatory response in e.g. aspirin-sensitive asthma patients.

8-isoprostaglandin E(2) activates Ca(2+)-dependent K(+) current via cyclic AMP signaling pathway in murine renal artery

The inhibitory pathway of 8-isoprostaglandin E(2) was investigated in murine renal arterial smooth muscle. K(+) current was augmented in a concentration-dependent fashion, with an average increase of 123+/-28% (n=6) following application of 10(-5) M 8-iso PGE(2). This augmentation was observed in the presence of 4-aminopyridine (4-AP, 10(-3) M) but not that of charybdotoxin (Ch Tx, 10(-7) M). Fluorimetric recordings showed marked concentration-dependent increase of cytosolic Ca(2+) levels by 8-iso PGE(2), while an enzyme-linked immunosorbent assay (ELISA)-based cyclic AMP assay showed increased cAMP levels by 10(-7) M 8-iso PGE(2) challenge. The isoprostane-induced augmentation was prevented by the ryanodine receptor blocker ruthenium red (10(-5) M) or the adenylate cyclase blocker SQ 22536 (10(-4) M). The protein kinase A (PKA) inhibitor H 89 (10(-5) M) inhibited resting K(+) currents (78+/-5%, n=5) but did not prevent 8-iso PGE(2) from augmenting the remaining K(+) current. We conclude that 8-iso PGE(2) enhances Ca(2+)-dependent K(+) currents in murine renal artery through a cAMP-dependent pathway which may involve internally sequestered Ca(2+).

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.

B1-phytoprostanes trigger plant defense and detoxification responses

Phytoprostanes are prostaglandin/jasmonate-like products of nonenzymatic lipid peroxidation that not only occur ubiquitously in healthy plants but also increase in response to oxidative stress. In this work, we show that the two naturally occurring B(1)-phytoprostanes (PPB(1)) regioisomers I and II (each comprising two enantiomers) are short-lived stress metabolites that display a broad spectrum of biological activities. Gene expression analysis of Arabidopsis (Arabidopsis thaliana) cell cultures treated with PPB(1)-I or -II revealed that both regioisomers triggered a massive detoxification and defense response. Interestingly, expression of several glutathione S-transferases, glycosyl transferases, and putative ATP-binding cassette transporters was found to be increased by one or both PPB(1) regioisomers, and hence, may enhance the plant's capacity to inactivate and sequester reactive products of lipid peroxidation. Moreover, pretreatment of tobacco (Nicotiana tabacum) suspension cells with PPB(1) considerably prevented cell death caused by severe CuSO(4) poisoning. Several Arabidopsis genes induced by PPB(1), such as those coding for adenylylsulfate reductase, tryptophan synthase beta-chain, and PAD3 pointed to an activation of the camalexin biosynthesis pathway that indeed led to the accumulation of camalexin in PPB(1) treated leaves of Arabidopsis. Stimulation of secondary metabolism appears to be a common plant reaction in response to PPB(1). In three different plant species, PPB(1)-II induced a concentration dependent accumulation of phytoalexins that was comparable to that induced by methyl jasmonate. PPB(1)-I was much weaker active or almost inactive. No differences were found between the enantiomers of each regioisomer. Thus, results suggest that PPB(1) represent stress signals that improve plants capacity to cope better with a variety of stresses.

Archetype signals in plants: the phytoprostanes

The paradox of aerobic life, or the 'Oxygen Paradox', is that animals and plants cannot exist without oxygen, yet oxygen is inherently dangerous to their existence. The reductive environment of cells provides ample opportunities for oxygen to undergo unscheduled reduction events, yielding free radicals that catalyze lipid peroxidation. Oxidized lipids are constitutively present in higher organisms and, notably, their levels increase in response to a variety of stresses. Recent results suggest that products of non-enzymatic lipid peroxidation pathways, such as the isoprostanes/phytoprostanes in animals and plants, might have an evolutionarily ancient function in host defense.