Actions of the E2-isoprostane, 8-ISO-PGE2, on the platelet thromboxane/endoperoxide receptor in humans and rats: additional evidence for the existence of a unique isoprostane receptor

Analysis of Lipid Peroxidation by UPLC-MS/MS and Retinoprotective Effects of the Natural Polyphenol Pterostilbene

The loss of redox homeostasis induced by hyperglycemia is an early sign and key factor in the development of diabetic retinopathy. Due to the high level of long-chain polyunsaturated fatty acids, diabetic retina is highly susceptible to lipid peroxidation, source of pathophysiological alterations in diabetic retinopathy. Previous studies have shown that pterostilbene, a natural antioxidant polyphenol, is an effective therapy against diabetic retinopathy development, although its protective effects on lipid peroxidation are not well known. Plasma, urine and retinas from diabetic rabbits, control and diabetic rabbits treated daily with pterostilbene were analyzed. Lipid peroxidation was evaluated through the determination of derivatives from arachidonic, adrenic and docosahexaenoic acids by ultra-performance liquid chromatography coupled with tandem mass spectrometry. Diabetes increased lipid peroxidation in retina, plasma and urine samples and pterostilbene treatment restored control values, showing its ability to prevent early and main alterations in the development of diabetic retinopathy. Through our study, we are able to propose the use of a derivative of adrenic acid, 17(RS)-10-epi-SC-Δ¹⁵-11-dihomo-IsoF, for the first time, as a suitable biomarker of diabetic retinopathy in plasmas or urine.

ROS in Platelet Biology: Functional Aspects and Methodological Insights

Reactive oxygen species (ROS) and mitochondria play a pivotal role in regulating platelet functions. Platelet activation determines a drastic change in redox balance and in platelet metabolism. Indeed, several signaling pathways have been demonstrated to induce ROS production by NAPDH oxidase (NOX) and mitochondria, upon platelet activation. Platelet-derived ROS, in turn, boost further ROS production and consequent platelet activation, adhesion and recruitment in an auto-amplifying loop. This vicious circle results in a platelet procoagulant phenotype and apoptosis, both accounting for the high thrombotic risk in oxidative stress-related diseases. This review sought to elucidate molecular mechanisms underlying ROS production upon platelet activation and the effects of an altered redox balance on platelet function, focusing on the main advances that have been made in platelet redox biology. Furthermore, given the increasing interest in this field, we also describe the up-to-date methods for detecting platelets, ROS and the platelet bioenergetic profile, which have been proposed as potential disease biomarkers.

Enantioselective high-performance liquid chromatography analysis of oxygenated polyunsaturated fatty acids

Oxygenated polyunsaturated fatty acids (PUFAs)play an outstanding role in the physiological and pathological regulation of several biological processes. These oxygenated metabolites can be produced both enzimatically, yielding almost pure enantiomers, and non-enzymatically. The free radical-mediated non-enzymatic oxidation commonly produces racemic mixtures which are used as biomarkers of oxidative stress and tissue damage. The biological activity of oxygenated PUFAs is often associated with only one enantiomer, making it necessary of availing of lipidomics platforms allowing to disclose the role of single enantiomers in health and disease. Polysaccharide-based chiral stationary phases (CSPs) play a dominating part in this setting. As for the cellulose backbone, 4-methylbenzoate derivatives exhibit very high chiral recognition ability towards this class of compounds. Concerning the phenylcarbamate derivatives of cellulose and amylose, the tris(3,5-dimethylphenylcarbamate) variants show the best enantioresolving ability for a variety of oxygenated PUFAs. Moreover, also the amylose tris(5-chloro-2-methylphenylcarbamate)-based selector produces relevant chromatographic performances. The extreme versatility of those CSPs mostly depends on their compatibility with the most relevant elution modes: normal- and reversed-phase, as well as polar organic/ionic-mode. In this review article, a selection of enantioseparation studies of different oxygenated PUFAs is reported, with both tris(benzoates) and tris(phenylcarbamates) of cellulose and amylose.

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.

Isoprostanes as potential cerebral vasospasm biomarkers

Despite enormous progress in medicine, symptomatic cerebral vasospasm (CVS), remains an unexplained clinical problem, which leaves both physicians and patients helpless and relying on chance, due to the lack of specific marker indicative of imminent danger as well as the lack of specific treatment. In our opinion CVS occurrence depends on dynamic disbalance between free radicals' formation (oxidative stress) and antioxidant activity. Isoprostanes are products of free-radical peroxidation of polyunsaturated fatty acids, and seem to mark a promising path for the research aiming to unravel its possible mechanism. Not only are they the biomarkers of oxidative stress in vivo and in vitro, but also have manifold biological effects (including vasoactive, inflammatory and mitogenic) via activation of the thromboxane A2 receptor (TBXA2R), both in physiological and pathophysiological processes. This review addresses the importance of isoprostanes in CVS in quest of appropriate biomarkers.

Ultra-weak photon emission as a dynamic tool for monitoring oxidative stress metabolism

In recent years, excessive oxidative metabolism has been reported as a critical determinant of pathogenicity in many diseases. The advent of a simple tool that can provide a physiological readout of oxidative stress would be a major step towards monitoring this dynamic process in biological systems, while also improving our understanding of this process. Ultra-weak photon emission (UPE) has been proposed as a potential tool for measuring oxidative processes due to the association between UPE and reactive oxygen species. Here, we used HL-60 cells as an in vitro model to test the potential of using UPE as readout for dynamically monitoring oxidative stress after inducing respiratory burst. In addition, to probe for possible changes in oxidative metabolism, we performed targeted metabolomics on cell extracts and culture medium. Lastly, we tested the effects of treating cells with the NADPH oxidase inhibitor diphenyleneiodonium chloride (DPI). Our results show that UPE can be used as readout for measuring oxidative stress metabolism and related processes.

Eicosanoid Mediators in the Airway Inflammation of Asthmatic Patients: What is New?

Lipid mediators contribute to inflammation providing both pro-inflammatory signals and terminating the inflammatory process by activation of macrophages. Among the most significant biologically lipid mediators, these are produced by free-radical or enzymatic oxygenation of arachidonic acid named "eicosanoids". There were some novel eicosanoids identified within the last decade, and many of them are measurable in clinical samples by affordable chromatography-mass spectrometry equipment or sensitive immunoassays. In this review, we present some recent advances in understanding of the signaling by eicosanoid mediators during asthmatic airway inflammation. Eicosanoid profiling in the exhaled breath condensate, induced sputum, or their metabolites measurements in urine is complementary to the cellular phenotyping of asthmatic inflammation. Special attention is paid to aspirin-exacerbated respiratory disease, a phenotype of asthma manifested by the most profound changes in the profile of eicosanoids produced. A hallmark of this type of asthma with hypersensitivity to non-steroid anti-inflammatory drugs (NSAIDs) is to increase biosynthesis of cysteinyl leukotrienes on the systemic level. It depends on transcellular biosynthesis of leukotriene C₄ by platelets that adhere to granulocytes releasing leukotriene A₄. However, other abnormalities are also reported in this type of asthma as a resistance to anti-inflammatory activity of prostaglandin E₂ or a robust eosinophil interferon-γ response resulting in cysteinyl leukotrienes production. A novel mechanism is also discussed in which an isoprostane structurally related to prostaglandin E₂ is released into exhaled breath condensate during a provoked asthmatic attack. However, it is concluded that any single eicosanoid or even their complex profile can hardly provide a thorough explanation for the mechanism of asthmatic inflammation.

Pathophysiology of isoprostanes in the cardiovascular system: implications of isoprostane-mediated thromboxane A2 receptor activation

Isoprostanes are free radical-catalysed PG-like products of unsaturated fatty acids, such as arachidonic acid, which are widely recognized as reliable markers of systemic lipid peroxidation and oxidative stress in vivo. Moreover, activation of enzymes, such as COX-2, may contribute to isoprostane formation. Indeed, formation of isoprostanes is considerably increased in various diseases which have been linked to oxidative stress, such as cardiovascular disease (CVD), and may predict the atherosclerotic burden and the risk of cardiovascular complications in the latter patients. In addition, several isoprostanes may directly contribute to the functional consequences of oxidant stress via activation of the TxA2 prostanoid receptor (TP), for example, by affecting endothelial cell function and regeneration, vascular tone, haemostasis and ischaemia/reperfusion injury. In this context, experimental and clinical data suggest that selected isoprostanes may represent important alternative activators of the TP receptor when endogenous TxA2 levels are low, for example, in aspirin-treated individuals with CVD. In this review, we will summarize the current understanding of isoprostane formation, biochemistry and (patho) physiology in the cardiovascular context.

A fast one-step extraction and UPLC-MS/MS analysis for E2/D 2 series prostaglandins and isoprostanes

Prostaglandins (PG) and isoprostanes (iso-PG) may be derived through cyclooxygenase or free radical pathways and are important signaling molecules that are also robust biomarkers of oxidative stress. Their quantification is important for understanding many biological processes where PG, iso-PG, or oxidative stress are involved. One of the common methods for PG and iso-PG quantifications is LC-MS/MS that allows a highly selective, sensitive, simultaneous analysis for prostanoids without derivatization. However, the currently used LC-MS/MS methods require a multi-step extraction and a long (within an hour) LC separation to achieve simultaneous separation and analysis of the major iso-PG. The developed and validated for brain tissue analysis one-step extraction protocol and UPLC-MS/MS method significantly increases the recovery of the PG extraction up to 95 %, and allows for a much faster (within 4 min) major iso-PGE2 and -PGD2 separation with 5 times narrower chromatographic peaks as compared to previously used methods. In addition, it decreases the time and cost of analysis due to the one-step extraction approach performed in disposable centrifuge tubes. All together, this significantly increases the sensitivity, and the time and cost efficiency of the PG and iso-PG analysis.

Eicosanoids and adipokines in breast cancer: from molecular mechanisms to clinical considerations

Chronic inflammation is one of the foremost risk factors for different types of malignancies, including breast cancer. Additional risk factors of this pathology in postmenopausal women are weight gain, obesity, estrogen secretion, and an imbalance in the production of adipokines, such as leptin and adiponectin. Various signaling products of transcription factor, nuclear factor-kappaB, in particular inflammatory eicosanoids, reactive oxygen species (ROS), and cytokines, are thought to be involved in chronic inflammation-induced cancer. Together, these key components have an influence on inflammatory reactions in malignant tissue damage when their levels are deregulated endogenously. Prostaglandins (PGs) are well recognized in inflammation and cancer, and they are solely biosynthesized through cyclooxygenases (COXs) from arachidonic acid. Concurrently, ROS give rise to bioactive isoprostanes from arachidonic acid precursors that are also involved in acute and chronic inflammation, but their specific characteristics in breast cancer are less demonstrated. Higher aromatase activity, a cytochrome P-450 enzyme, is intimately connected to tumor growth in the breast through estrogen synthesis, and is interrelated to COXs that catalyze the formation of both inflammatory and anti-inflammatory PGs such as PGE(2), PGF(2α), PGD(2), and PGJ(2) synchronously under the influence of specific mediators and downstream enzymes. Some of the latter compounds upsurge the intracellular cyclic adenosine monophosphate concentration and appear to be associated with estrogen synthesis. This review discusses the role of COX- and ROS-catalyzed eicosanoids and adipokines in breast cancer, and therefore ranges from their molecular mechanisms to clinical aspects to understand the impact of inflammation.

Reduction of 8-iso-prostaglandin F2α in the first week after Roux-en-Y gastric bypass surgery

Obesity is associated with increased markers of oxidative stress. We examined whether oxidative stress is reduced within the first week after Roux-en-Y gastric bypass (RYGB) surgery and could be related to changes in adipose tissue depots. The reactive oxygen species (ROS) marker 8-iso-prostaglandin F2α (8-iso-PGF2α) and activity of antioxidant glutathione peroxidases (GPX) in plasma were compared before and ~1 week after RYGB. The effects of RYGB on subcutaneous adipose tissue and interstitial fluid 8-iso-PGF2α levels and subcutaneous adipose tissue expression of GPX-3 were also assessed. Levels of 8-iso-PGF2α in subcutaneous and visceral adipose tissue were determined. Plasma 8-iso-PGF2α levels decreased (122 ± 75 to 56 ± 15 pg/ml, P = 0.001) and GPX activity increased (84 ± 18 to 108 ± 25 nmol/min/ml, P = 0.003) in the first week post-RYGB. RYGB also resulted in reductions of 8-iso-PGF2α in subcutaneous adipose tissue (1,742 ± 931 to 1,132 ± 420 pg/g fat, P = 0.046) and interstitial fluid (348 ± 118 to 221 ± 83 pg/ml, P = 0.046) that were comparable to plasma (26-33%, P = 0.74). Adipose GPX-3 expression was increased (6.7 ± 4.7-fold, P = 0.004) in the first postoperative week. The improvements in oxidative stress occurred with minimal weight loss (2.4 ± 3.4%, P = 0.031) and elevations in plasma interleukin-6 (18.0 ± 46.8 to 28.0 ± 58.9 pg/ml, P = 0.004). Subcutaneous and visceral adipose tissues express comparable 8-iso-PGF2α levels (1,204 ± 470 and 1,331 ± 264 pg/g fat, respectively; P = 0.34). These data suggest that RYGB affects adipose tissue leading to the restoration of adipose redox balance within the first postoperative week and that plasma 8-iso-PGF2α is primarily derived from subcutaneous adipose tissue.

Role of prostanoid production and receptors in the regulation of retinal endogenous amino acid neurotransmitters by 8-isoprostaglandin E2, ex vivo

The role of enzymes and receptors of the prostanoid pathway in the inhibitory effect of 8-isoprostaglandin E2 (8-isoPGE2) on endogenous amino acid neurotransmitter levels was examined, ex vivo. Freshly isolated bovine eyeballs were injected intravitreally with IsoPs, incubated in Krebs buffer for 30 min and retina prepared for HPLC-ECD detection of amino acids. 8-isoPGE2 attenuated retinal glutamate and its metabolite, glutamine and glycine in a concentration-dependent manner. The nonselective cyclooxygenase (COX)-inhibitor, flurbiprofen, COX-2 selective inhibitor, NS-398 and thromboxane (Tx) synthase inhibitor, furegrelate had no effect on both basal amino acid levels and the inhibitory effects of 8-isoPGE2 (1-100 μM) on the retinal amino acids. Whereas the TP-receptor antagonist SQ-29548(10 μM) exhibited no effect, SC-19220(EP1; 30 μM), AH-6809(EP(1-3); 30 μM) and AH-23848(EP4; 30 μM) reversed the inhibitory effects of 8-isoPGE2 (0.01-100 μM) on glutamate, glutamine and glycine levels. We conclude that prostanoid EP-receptors regulate the inhibitory effect of 8-isoPGE2 on basal levels of endogenous amino acids in bovine retina, ex vivo.

Role of superoxide and thromboxane receptors in acute angiotensin II-induced vasoconstriction of rabbit vessels

This study explored the hypothesis that a portion of angiotensin II-induced contractions is dependent on superoxide generation and release of a previously unidentified arachidonic acid metabolite that activates vascular smooth muscle thromboxane receptors. Treatment of rabbit aorta or mesentery artery with the thromboxane receptor antagonist SQ29548 (10 μM) reduced angiotensin II-induced contractions (maximal contraction in aorta; control vs. SQ29548: 134 ± 16 vs. 93 ± 10%). A subset of rabbits deficient in vascular thromboxane receptors also displayed decreased contractions to angiotensin II. The superoxide dismutase mimetic Tiron (30 mM) attenuated angiotensin II-induced contractions only in rabbits with functional vascular thromboxane receptors (maximal contraction in aorta; control vs. Tiron: 105 ± 5 vs. 69 ± 11%). Removal of the endothelium or treatment with a nitric oxide synthase inhibitor, nitro-l-arginine (30 μM) did not alter angiotensin II-induced contractions. Tiron and SQ29548 decreased angiotensin II-induced contractions in the denuded aortas by a similar percentage as that observed in intact vessels. The cyclooxygenase inhibitor indomethacin (10 μM) or thromboxane synthase inhibitor dazoxiben (10 μM) had no effect on angiotensin II-induced contractions indicating that the vasoconstrictor was not thromboxane. Angiotensin II increased the formation of a 15-series isoprostane. Isoprostanes are free radical-derived products of arachidonic acid. The unidentified isoprostane increased when vessels were incubated with the superoxide-generating system xanthine/xanthine oxidase. Pretreatment of rabbit aorta with the isoprostane isolated from aortic incubations enhanced angiotensin II-induced contractions. Results suggest the factor activating thromboxane receptors and contributing to angiotensin II vasoconstriction involves the superoxide-mediated generation of a 15-series isoprostane.

LC/MS/MS method for analysis of E₂ series prostaglandins and isoprostanes

15-series prostaglandins (PGE₂s) and isoprostanes (isoPGE₂s) are robust biomarkers of oxidative stress, possess potent biological activity, and may be derived through cyclooxygenase or free radical pathways. Thus, their quantification is critical in understanding many biological processes where PG, isoPG, or oxidative stress are involved. LC/MS/MS methods allow a highly selective, sensitive, simultaneous analysis for prostanoids without derivatization. However, the LC/MS/MS methods currently used do not allow for simultaneous separation of the major brain PGE₂/D₂) and isoPGE₂ without derivatization and multiple HPLC separations. The developed LC/MS/MS method allows for the major brain PGE₂/PGD₂/isoPGE₂ such as PGE₂, entPGE₂, 8-isoPGE₂, 11β-PGE₂, PGD₂, and 15(R)-PGD₂ to be separated and quantified without derivatization. The method was validated by analyzing free and esterified isoPGE₂ in mouse brains fixed with head-focused microwave irradiation before or after global ischemia. Using the developed method, we report for the first time the esterified isoPGE₂ levels in brain tissue under basal conditions and upon global ischemia and demonstrate a nonreleasable pool of esterified isoPG upon ischemia. In addition, we demonstrated that PGE₂s found esterified in the sn-2 position in phospholipids are derived from a free radical nonenzymatic pathway under basal conditions. Our method for brain PG analysis provides a high level of selectivity to detect changes in brain PG and isoPG mass under both basal and pathological conditions.

Platelet function and Isoprostane biology. Should isoprostanes be the newest member of the orphan-ligand family?

While there have been many reports investigating the biological activity and signaling mechanisms of isoprostanes, their role in biology, particularly in platelets, appears to still be underestimated. Moreover, whether these lipids have their own receptors is still debated, despite multiple reports that discrete receptors for isporpstanes do exist on platelets, vascular tissues, amongst others. This paper provides a review of the important literature of isoprostanes and provides reasoning that isoprostanes should be classified as orphan ligands until their receptor(s) is/are identified.

Quantification of F2-isoprostanes as a reliable index of oxidative stress in vivo using gas chromatography-mass spectrometry (GC-MS) method

Free radical-induced lipid peroxidation has been implicated in a number of human diseases including atherosclerosis, cancer, and neurodegenerative diseases. F(2)-Isoprostanes (IsoPs) are isomers of prostaglandin PGF(2alpha) that are generated in vivo from the free radical-initiated peroxidation of arachidonic acid independent of cyclooxygenase enzymes. Since the discovery of the IsoPs in the early 1990s, a large body of evidence has been accumulated to indicate that quantification of these F(2)-IsoPs represents the most reliable biomarker to assess oxidative stress in vivo. A variety of analytical approaches have been developed for the quantification of these novel compounds; these methods include mass spectrometry (MS) detection coupled to gas chromatography (GC) or liquid chromatography (LC) separation, and detection using immunological approaches. This article summarizes our current methodology to quantify F(2)-IsoPs in biological fluids and tissues using GC-MS. This method includes solid-phase extraction (SPE), thin-layer chromatography (TLC) purification, chemical derivatization, and MS detection using negative ion chemical ionization (NICI) coupled with GC. The protocol described herein has been optimized and validated to provide the best sensitivity and selectivity for quantification of F(2)-IsoPs from a variety of biological sources.

Identification of intact oxidation products of glycerophospholipids in vitro and in vivo using negative ion electrospray iontrap mass spectrometry

Free radical-induced oxidation products of polyunsaturated fatty acids esterified to phospholipids have been implicated in a number of human diseases including atherosclerosis and neurodegenerative diseases. Some of these phospholipid oxidation products have potent biological activities and likely contribute to human pathophysiological conditions. Oxidation products have also been used as markers of oxidative stress in vivo. Identification and quantification of phospholipid oxidation products are often performed by analyzing the oxidized free fatty acid moieties after hydrolysis from the phospholipids head groups by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS). We now describe the definitive identification of intact oxidized products of glycerophospholipids including glycerophosphatidylcholine (GPC), glycerophosphatidylethanolamine (GPE), and glycerophosphatidylserine (GPS) in vitro and in vivo using iontrap MS. For these analyses, the negative ions of the oxidation products of phospholipids are fragmented to MS(n) and unequivocal structural characterization is obtained based on collision-induced dissociation (CID) of the sn-2 carboxylate ion. This technique overcomes the need to hydrolyze fatty acids from phospholipids in the analysis. The method has been used to identify a number of oxidation products of glycerophospholipids including hydroxyeicosatetraenoates (HETEs) and isoprostanes (IsoPs) esterified to different classes of glycerophospholipids in vitro and in vivo. These studies thus provide a new approach to identify the intact oxidation products of glycerolphospholipids.

Lipid metabolites as regulators of airway smooth muscle function

Compelling evidence identifies airway smooth muscle (ASM) not only as a target but also a cellular source for a diverse range of mediators underlying the processes of airway narrowing and airway hyperresponsiveness in diseases such as asthma. These include the growing family of plasma membrane phospholipid-derived polyunsaturated fatty acids broadly characterised by the prostaglandins, leukotrienes, lipoxins, isoprostanes and lysophospholipids. In this review, we describe the enzymatic and non-enzymatic biosynthetic pathways of these lipid mediators and how these are influenced by drug treatment, oxidative stress and airways disease. Additionally, we outline their cognate receptors, many of which are expressed by ASM. We describe potential deleterious and protective roles for these lipid mediators in airway inflammatory and remodelling processes by describing their effects on diverse functions of ASM in asthma that have the potential to contribute to asthma pathogenesis and symptoms. These functions include contractile tone development, cytokine and extracellular matrix production, and cellular proliferation and migration.

F2-isoprostanes in human health and diseases: from molecular mechanisms to clinical implications

Oxidative stress is implicated as one of the major underlying mechanisms behind many acute and chronic diseases, and involved in normal aging. However, the measurement of free radicals or their end products is complicated. Thus, proof of association of free radicals in pathologic conditions has been absent. Isoprostanes are prostaglandin-like bioactive compounds that are biosynthesized in vivo independent of cyclooxygenases, principally through free-radical catalyzation of arachidonic acid. Isoprostanes are now considered to be reliable biomarkers of oxidative stress, as evidenced by an autonomous study organized recently by the National Institutes of Health (NIH) in the United States. A number of these compounds have potent biologic activities such as vasoconstrictive and certain inflammatory properties. Isoprostanes are involved in many human diseases. Additionally, elevated levels of F(2)-isoprostanes have been seen in normal human pregnancy and after intake of some fatty acids, but their physiologic assignments have not yet been distinctive. This evidence indicates that measurement of bioactive F(2)-isoprostanes in body fluids offers a unique noninvasive analytic utensil to study the role of free radicals in physiology, oxidative stress-related diseases, experimental acute or chronic inflammatory conditions, and also in the assessment of various antioxidants, radical scavengers, and drugs.

Characterization of isoprostane signaling: evidence for a unique coordination profile of 8-iso-PGF(2alpha) with the thromboxane A(2) receptor, and activation of a separate cAMP-dependent inhibitory pathway in human platelets

Since isoprostanes are thought to participate in the pathogenesis of thrombosis, presumably through their interaction with thromboxane receptors (TPRs), we examined the ability of 8-iso-PGF(2alpha) to bind/signal through TPRs. Using TPR expressing HEK cells, it was found that 8-iso-PGF(2alpha) mobilized calcium and bound TPRs with a dissociation constant (K(d)) of 57 nM. Interestingly, site-directed-mutagenesis revealed that 8-iso-PGF(2alpha) has a unique coordination profile with TPRs. Thus, while Phe184 and Asp193 are shared by both 8-iso-PGF(2alpha) and classical TPR ligands, Phe196 was found to be required only for 8-iso-PGF(2alpha) binding. Functional studies also revealed interesting results. Namely, that 8-iso-PGF(2alpha) signals in human platelets through both a stimulatory (TPR-dependent) and an inhibitory (cAMP-dependent) pathway. Consistent with the existence of two signaling pathways, platelets were also found to possess two separate binding sites for 8-iso-PGF(2alpha). While the stimulatory site is represented by TPRs, the second cAMP inhibitory site is presently unidentified, but does not involve receptors for PGI(2), PGD(2) or PGE(2). In summary, these studies provide the first documentation that: (1) 8-iso-PGF(2alpha) coordinates with Phe184, Asp193 and Phe196 on platelet TPRs; (2) Phe196 serves as a unique TPR binding site for 8-iso-PGF(2alpha); (3) 8-iso-PGF(2alpha) signals through both stimulatory and inhibitory pathways in platelets; (4) 8-iso-PGF(2alpha) inhibits human platelet activation through a cAMP-dependent mechanism; (5) 8-iso-PGF(2alpha) interacts with platelets at two separate binding sites. Collectively, these results provide evidence for a novel isoprostane function in platelets which is mediated through a cAMP-coupled receptor.

New techniques to detect oxidative stress markers: mass spectrometry-based methods to detect isoprostanes as the gold standard for oxidative stress in vivo

Free radical-induced lipid oxidation under oxidative stress has been implicated in a number of human diseases. Isoprostanes (IsoPs), isomers of prostaglandins, are one of the major classes of oxidation products derived from this oxidation process. Measurement of the levels of IsoPs by Mass Spectrometry-based methods has become the "gold standard" biomarker of oxidative stress in vivo. Significant advances have been made in understanding this important pathway of lipid peroxidation since the discovery of IsoP formation in vivo 18 years ago. Studies from our laboratory and others are discussed that have provided insights into the mechanism of formation. Furthermore, new independent studies have demonstrated that IsoPs are the most reliable available marker of lipid peroxidation in vivo, and recent work examining IsoP formation has provided valuable information about the pathogenesis of numerous human diseases. Thus, the complexity of the IsoP pathway has expanded, providing novel insights into mechanisms of lipid peroxidation in vivo and allowing investigators to explore the role of oxidative stress in human disease.

E-ring isoprostane augments cholinergic neurotransmission in bovine trachealis via FP prostanoid receptors

Isoprostanes are prostaglandin-like molecules that accumulate in oxidative stress and also exert powerful biological effects on a wide variety of tissues. We investigated the effects of several different isoprostanes on contractions evoked by electrical field stimulation (EFS) in bovine trachealis, finding only 15-E2t-IsoP to augment those responses. Many others have shown that isoprostanes act on prostanoid receptors, usually those of the thromboxane-selective prostanoid receptor (TP) subtype, although some describe actions through prostaglandin E2-selective prostanoid receptor (EP) or less frequently through prostaglandin F2alpha-selective prostanoid receptors (FP). We used an extensive panel of highly selective agonists and antagonists of prostanoid receptors to characterize the ones through which 15-E2t-IsoP was acting here. Pretreatment with the FP-selective AL-8810 significantly inhibited the augmentation, whereas TP- and EP-selective blockers did not. On the other hand, the augmentation exerted by 15-E2t-IsoP was mimicked by submicromolar concentrations of the FP-selective agonists PGF2alpha and fluprostenol, as well as by micromolar concentrations of the TP-selective agonist U46619. The concentration-response relationship for exogenously added acetylcholine was not significantly affected by 15-E2t-IsoP, confirming that the effect of the latter on EFS-evoked responses was exerted prejunctionally (i.e., to enhance release of Ach from nerve endings), rather than a direct postjunctional effect via a receptor on the smooth muscle. Finally, we investigated whether the inhibitory (adrenergic) innervation was also modulated by 15-E2t-IsoP, finding EFS-evoked relaxations to be unaffected by the isoprostane. We conclude that 15-E2t-IsoP acts upon an FP receptor on the cholinergic nerve endings, leading to enhanced neurotransmission.

The bronchodilators 8-iso-prostaglandin E2 and prostaglandin E2 induce K+ current suppression via thromboxane A2 receptors in porcine tracheal smooth muscle

We examined relaxations and changes in K(+) current evoked by 8-iso-prostaglandin E(2) and prostaglandin E(2) in porcine tracheal smooth muscle. Both autacoids completely reversed cholinergic tone; blockade of thromboxane A(2) receptors had no effect on relaxations to either compound. 8-iso-prostaglandin E(2) and prostaglandin E(2) suppressed outward K(+) currents while the thromboxane A(2) receptor agonist U46619 (9, 11-dideoxy-9a,11a-methanoepoxy prostaglandin F(2alpha)) had no significant effect. During thromboxane A(2) receptor antagonism, however, 8-iso-prostaglandin E(2) markedly augmented K(+) currents while prostaglandin E(2) no longer suppressed K(+) currents, indicating that the inhibition of K(+) currents by both compounds was thromboxane A(2) receptor-mediated. Furthermore, the observation that K(+) currents were augmented by 8-iso-prostaglandin E(2) but not by prostaglandin E(2) suggests that the salutory effect is not exerted through a prostaglandin E receptor. Additionally, our observations argue against any causal role for K(+) current activation in mediating relaxations evoked by isoprostanes or by prostaglandin E(2). We conclude that 8-iso-prostaglandin E(2) relaxes porcine tracheal smooth muscle independent of K(+) current activity, and that 8-iso-prostaglandin E(2) may also act at a non-thromboxane A(2)/non-prostaglandin E receptor to augment K(+) currents.

The isoprostane 8-iso-PGF2alpha suppresses monocyte adhesion to human microvascular endothelial cells via two independent mechanisms

Isoprostanes, produced in vivo by non-enzymatic free-radical-induced lipid peroxidation, are markers of oxidative stress. Elevated serum and urine levels of 8-iso-PGF2alpha have been reported in a variety of diseases, many of which are characterized by early perivascular inflammatory infiltrates. It has been suggested that, in addition to being markers of oxidative stress, isoprostanes may have pathogenic functions. In this study, we investigated the potential role of 8-iso-PGF2alpha in inflammation, focusing on its effects on adhesion of monocytes to microvascular endothelial cells, an early event in the inflammatory response. In monocyte adhesion assays, 8-iso-PGF2alpha (>10(-8) M) suppressed both basal and TNF-alpha-induced monocyte adhesion to quiescent or proliferating human dermal (HMEC) and rat renal microvascular endothelial cells. In contrast, 8-iso-PGF2alpha stimulated monocyte adhesion to human umbilical vein endothelial cells (HUVEC) as also reported by others. 8-Iso-PGF2alpha had no effect on the viability (Trypan Blue exclusion) of U937 monocytes or HMEC. 8-Iso-PGF2alpha also had no effect on HMEC surface expression of ICAM-1 or VCAM-1. Exposure of HMEC to 8-iso-PGF2alpha for 1-2 h was sufficient to reduce monocyte adhesion to the cell surface, and this effect was independent of de novo protein synthesis by HMEC. The effect of 8-iso-PGF2alpha was mimicked by a thromboxane receptor (TP) agonist (U46619) and blocked by a TP antagonist (SQ29548), indicating a TP-mediated process. Signal transduction pathway inhibitors (SB203580, curcumin, and PD98059) implicated p38 and JNK, but not ERK, in 8-iso-PGF2alpha-induced suppression of monocyte adhesion. In addition to a direct effect, conditioned medium (CM) transfer experiments suggest that 8-iso-PGF2alpha induces a secondary mediator, which also suppresses monocyte adhesion but via an alternative mechanism initiated between 3-4 h, which is TP-independent, requires new protein synthesis, and is primarily dependent on activation of p38. The data show that 8-iso-PGF2alpha can suppress the attachment of monocytes to HMECs via two independent pathways, indicating a potential anti-inflammatory effect of 8-iso-PGF2alpha in the microvasculature.

Effects of isoprostane on tubuloglomerular feedback: roles of TP receptors, NOS, and salt intake

A thromboxane prostanoid receptor (TP-R) agonist U-46,619 enhances tubuloglomerular feedback (TGF). Glomerular expression of TP-R and enhancement of TGF by U-46,619 increase with salt intake. We investigated the hypothesis that 8-isoprostaglandin F(2alpha) (8-Iso) activates TGF via TP-R. The maximal TGF response in rats was assessed from the fall in proximal stop flow pressure (PSF; an index of glomerular capillary pressure) during loop of Henle (LH) microperfusion of artificial tubular fluid (ATF) at 40 nl/min. Microperfusion of 8-Iso (10(-4) M) into the efferent arteriole (EA) enhanced TGF responses by 20 +/- 3% (P < 0.01). TGF response to 8-Iso was independent of dietary salt [DeltaTGF%, low salt (LS): 21 +/- 5%; normal salt (NS): 17 +/- 4%; high salt (HS): 29 +/- 8%, not significant (ns)], unlike the salt-dependent effect of U-46,619 (DeltaTGF%, LS: 41 +/- 5%; NS: 52 +/- 4%; HS: 112 +/- 21%). Ifetroban, the TP-R antagonist, abolished TGF responses to 8-Iso and U-46,619 at all levels of salt intake. During luminal perfusion of N-monomethyl-l-arginine (l-NMA), the effect of 8-Iso on TGF was enhanced in NS and HS but not in LS (LS: 22 +/- 6 vs. LS + l-NMA: 28 +/- 6%, ns; NS: 18 +/- 4 vs. NS + l-NMA: 40 +/- 4, P < 0.01; HS: 27 +/- 3 vs. HS + l-NMA: 65 +/- 6, P < 0.01). However, U-46,619 did not further increase TGF after l-NMA in all salt groups (LS: 43 +/- 7 vs. LS + l-NMA: 51 +/- 6, ns; NS: 52 +/- 7 vs. NS + l-NMA: 48 +/- 8, ns; HS: 114 +/- 21 vs. HS + l-NMA: 74 +/- 22, ns). In conclusion, activation of TP receptors by U-46,619 and 8-Iso-PGF(2alpha) enhances TGF. In addition, the effect of U-46,619 was salt dependent, whereas the effect of 8-Iso-PGF(2alpha) was salt independent. However, stimulation of NO by 8-isoprostanes masks its salt-sensitive effect on TGF.

Isoprostanes: novel bioactive products of lipid peroxidation

Isoprostanes, are a novel group of prostaglandin-like compounds that are biosynthesised from esterified polyunsaturated fatty acid (PUFA) through a non-enzymatic free radical-catalysed reaction. Several of these compounds possess potent biological activity, as evidenced mainly through their pulmonary and renal vasoconstrictive effects, and have short half-lives. It has been shown that isoprostanes act as full or partial agonists through thromboxane receptors. Both human and experimental studies have indicated associations of isoprostanes and severe inflammatory conditions, ischemia-reperfusion, diabetes and atherosclerosis. Reports have shown that F2-isoprostanes are authentic biomarkers of lipid peroxidation and can be used as potential in vivo indicators of oxidant stress in various clinical conditions, as well as in evaluations of antioxidants or drugs for their free radical-scavenging properties. Higher levels of F2-isoprostanes have been found in the normal human pregnancy compared to non-pregnancy, but their physiological role has not been well studied so far. Since bioactive F2-isoprostanes are continuously formed in various tissues and large amounts of these potent compounds are found unmetabolised in their free acid form in the urine in normal basal conditions with a wide inter-individual variation, their role in the regulation of normal physiological functions could be of further biological interest, but has yet to be disclosed. Their potent biological activity has attracted great attention among scientists, since these compounds are found in humans and animals in both physiological and pathological conditions and can be used as reliable biomarkers of lipid peroxidation.

Vasoconstrictor effects of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F2α on human umbilical vein

The present study was undertaken to determine whether 8-iso-prostaglandin E2 and 8-iso-prostaglandin F(2alpha) posses contractile action on human umbilical vein and to evaluate the possible involvement of prostanoid TP receptors in this effect. Human umbilical vein rings were mounted in organ baths and concentration-response curves to 8-iso-prostaglandin E2 or 8-iso-prostaglandin F(2alpha) were constructed. Both isoprostanes evoked concentration-dependent contraction. 8-iso-prostaglandin E2 (pEC50=6.90+/-0.03) was significantly more potent than 8-iso-prostaglandin F(2alpha) (pEC50=6.10+/-0.04). However, both isoprostanes were equieffective. The prostanoid TP receptor antagonists, ICI-192,605 (4-(Z)-6-(2-o-Chlorophenyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl)hexenoic acid) and SQ-29548 (7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-[1S(1alpha,2alpha(Z),3alpha,4alpha)]-5-Heptenoic acid) produced a competitive rightward shift of 8-iso-prostaglandin E2 concentration-response curves with pKB values of 8.91+/-0.04 and 8.07+/-0.07, respectively. When ICI-192,605 (1 nM) and SQ-29548 (10 nM) were evaluated against 8-iso-prostaglandin F(2alpha) they produced a parallel rightward displacement of 8-iso-prostaglandin F(2alpha) concentration-response curves without affecting the maximum responses giving pA2 values of 9.02+/-0.12 and 8.26+/-0.13, respectively. In conclusion, the present study describes for the first time the vasoconstrictor action of 8-iso-prostaglandin E2 and 8-iso-prostaglandin F(2alpha) in human umbilical vein. Furthermore, the affinity values obtained with ICI-192,605 and SQ-29548 provide strong pharmacological evidence of prostanoid TP receptors involvement in this effect.

Formation of prostaglandins E2 and D2 via the isoprostane pathway: a mechanism for the generation of bioactive prostaglandins independent of cyclooxygenase

It has heretofore been assumed that the cyclooxygenases (COXs) are solely responsible for peostaglandin (PG) synthesis in vivo. An important structural feature of PGH2 formed by COX is the trans-configuration of side chains relative to the prostane ring. Previously, we reported that a series of PG-like compounds termed isoprostanes (IsoPs) are formed in vivo in humans from the free radical-catalyzed peroxidation of arachidonate independent of COX. A major difference between these compounds and PGs is that IsoPs are formed from endoperoxide intermediates, the vast majority of which contain side chains that are cis relative to the prostane ring. In addition, unlike the formation of eicosanoids from COX, IsoPs are formed as racemic mixtures because they are generated nonenzymatically. IsoPs containing E- and D-type prostane rings (E2/D2-IsoPs) are one class of IsoPs formed, and we have reported previously that one of the major IsoPs generated is 15-E2t-IsoP (8-iso-PGE2). Unlike PGE2, 15-E2t-IsoP is significantly more unstable in buffered solutions in vitro and undergoes epimerization to PGE2. Analogously, the D-ring IsoP (15-D2c-IsoP) would be predicted to rearrange to PGD2. We now report that compounds identical in all respects to PGE2 and PGD2 and their respective enantiomers are generated in vivo via the IsoP pathway, presumably by epimerization of racemic 15-E2t-IsoP and 15-D2c-IsoP, respectively. Racemic PGE2 and PGD2 were present esterified in phospholipids derived from liver tissue from rats exposed to oxidant stress at levels of 24 +/- 16 and 37 +/- 12 ng/g of tissue, respectively. In addition, racemic PGs, particularly PGD2, were present unesterified in urine from normal animals and humans and represented up to 10% of the total PG detected. Levels of racemic PGD2 increased 35-fold after treatment of rats with carbon tetrachloride to induce oxidant stress. In this setting, PGD2 and its enantiomer generated by the IsoP pathway represented approximately 30% of the total PGD2 present in urine. These findings strongly support the contention that a second pathway exists for the formation of bioactive PGs in vivo that is independent of COX.

Isoprostane-mediated secretion from human airway epithelial cells

Isoprostanes are liberated when reactive oxygen species (ROS) mediate the peroxidation of arachidonic acid or other polyunsaturated fatty acids. Because exposure to ROS is associated with tissue damage in the lung, we examined whether exposure to isoprostanes elicited a response in airway epithelial cells, potentially implicating isoprostane production in the epithelial response to oxidant stress. Application of the isoprostane 8-iso-prostaglandin E2 (8-iso-PGE2) produced an increase in transepithelial anion secretion across monolayers of the human airway epithelial cell line Calu-3, measured as an increase in short circuit current (Isc). This increase in Isc was greater when 8-iso-PGE2 was applied to the basolateral rather than the apical face of the Calu-3 monolayers and was almost entirely abolished by the addition of diphenylamine-2-carboxylate, implicating the cystic fibrosis transmembrane conductance regulator Cl- channel in the response. Experiments with electrically isolated apical and basolateral membrane preparations revealed that 8-iso-PGE2 stimulated both apical Cl- and basolateral K+ conductances. Using reverse transcription-polymerase chain reaction, we found that Calu-3 cells express the TPalpha, but not the TPbeta, isoform of the receptor, and that these cells secrete in response to the thromboxane A2 (TP) receptor agonist 9,11-dideoxy-9alpha,11alpha-methanoepoxy-prostaglandin F2alpha (U-46619). However, although part of the response seems to mediated via TP receptors, there are significant non-TP receptor-mediated effects on both the apical and basolateral membranes of Calu-3 cells. This is the first report of an isoprostane eliciting an effect in airway epithelial cells and suggests a potential role for this class of molecules in pulmonary host defense.

Regulation of activator protein-1 by 8-iso-prostaglandin E2 in a thromboxane A2 receptor-dependent and -independent manner

The thromboxane (TX) A(2) receptor (TP) encompasses two alternatively spliced forms, termed the platelet/placental (TP-P) and endothelial (TP-E) type receptors. Experimental evidence suggests that TP activity may be modulated by novel ligands, termed the isoprostanes, that paradoxically act as TP agonists in smooth muscle and TP antagonists in platelet preparations. Here we have investigated whether prototypical isoprostanes 8-iso-prostaglandin (PG)F(2 alpha) and 8-iso-PGE(2) regulate the activity of TP isoforms expressed in Chinese hamster ovary (CHO) cells using activator protein-1 (AP-1)-luciferase activity as a reporter. AP-1-luciferase activity was increased by a TP agonist [9,11-dideoxy-9 alpha,11 alpha-methanoepoxy PGF(2 alpha) (U46619)] in CHO cells transfected with the human TP-P and TP-E receptors, and this response was fully inhibited by TP antagonists [1S-[1 alpha,2 beta(Z),3 alpha,5 alpha]]-7-[3-[[4-iodophenyl)sulfonyl]amino]-6,6-dimethylbicyclo[3.1.1]hept-2-yl]-5-heptenoic acid (I-SAP) and [1S-[1 alpha,2 alpha(Z),3 alpha,4 alpha]]-7-[[2-[(phenylamino) carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1] hept-2-yl]-5-heptenoic acid (SQ 29,548)]. AP-1-luciferase activity was potently (nanomolar concentrations) increased by 8-iso-PGE(2) in CHO TP-P and TP-E cells, and this response was partially inhibited by cotreatment of cells with TP antagonists, whereas 8-iso-PGF(2 alpha) was without effect. Cyclooxygenase inhibitors did not abolish 8-iso-PGE(2) mediated AP-1-luciferase activity, indicating that this response is not dependent on de novo TXA(2) biosynthesis. Interestingly, 8-iso-PGE(2)-mediated AP-1-luciferase activity was near maximal in naive cells between 1 and 10 nM concentrations, and this response was not inhibited by TP antagonist or reproduced by agonists for TP or EP(1)/EP(3) receptors. These observations 1) support a role for novel ligands in the regulation of TP-dependent signaling, 2) indicate that TP-P and TP-E couple to AP-1, 3) provide further evidence that isoprostanes function as TP agonists in a cell-type specific fashion, and 4) indicate that additional targets regulated by 8-iso-PGE(2) couple to AP-1.

Modulation of JB6 mouse epidermal cell transformation response by the prostaglandin F2alpha receptor

Prostaglandin F(2alpha) (PGF(2alpha)) modulates clonal selection processes in the mouse skin model of carcinogenesis. In this study we investigated whether JB6 mouse epidermal cells expressed a functional PGF(2alpha) receptor (FP) coupled with a cell-transformation response. Treatment of JB6 cells with an FP agonist (fluprostenol) potently (pM-nM) increased anchorage-dependent and anchorage-independent growth. Inositol phospholipid accumulation and extracellular signal-regulated kinase (Erk) activity were increased in cells treated with FP agonists, consistent with established FP-related signal transduction. FP mRNA was detected by reverse transcription-polymerase chain reaction, and the average specific [(3)H]PGF(2alpha) binding was 8.25 +/- 0.95 fmol/mg protein. Erk activity and colony size were increased by cotreatment of JB6 cells with epidermal growth factor (EGF) and fluprostenol to a greater extent than with either treatment alone, whereas the cotreatment effect on colony number appeared to be simply additive. Collectively, our data indicated that JB6 cells expressed a functional FP coupled with transformation-related signal transduction and the regulation of clonal selection processes. Erk activity appears to be a convergence point in the EGF and FP pathways. The data raise the possibility that the FP contributes to clonal selection processes but probably plays a more important role as a response modifier.

Involvement of TP and EP3 receptors in vasoconstrictor responses to isoprostanes in pulmonary vasculature

Although isoprostanes generally act on smooth muscle via TXA(2)-selective prostanoid receptors (TPs), some suggest other prostanoid receptors or possibly even a novel isoprostane-selective receptor might be involved. We studied contractions to several isoprostanes in porcine pulmonary vasculature using organ bath techniques. 8-iso-prostaglandin E(2) (PGE(2)) was the most potent and efficacious of the isoprostanes, with a log EC(50) of -7.0 +/- 0.2 in the pulmonary artery and -6.8 +/- 0.2 in the pulmonary vein. The responses to all the isoprostanes were essentially completely blocked by the TP receptor antagonist ICI 192605 [4(Z)-6-[(2,4,5-cis)2-(2-chlorophenyl)-4-(2-hydroxyphenyl)1,3-dioxan-5-yl]hexenoic acid], and the equilibrium dissociation constants for ICI 192605 competing with U46619 or 8-iso-PGE(2) were both approximately 2 nM, indicating that isoprostane-evoked responses involve primarily TP receptors. Only 8-iso-PGE(2) was able to evoke substantial contractions in the presence of ICI 192605 and only in the pulmonary vein. The EC(50) of these ICI 192605-insensitive responses was -6.1 +/- 0.2. Using a variety of prostanoid agonists, we found the pulmonary vein lacked excitatory PGF(2alpha)-selective prostanoid receptor (FP) or PGD(2)-selective prostanoid receptor (DP) but expressed excitatory EP(3) receptors. The ICI 192605-insensitive responses to 8-iso-PGE(2) were unaffected by the EP(1) antagonist SC-19220 [8-chloro-debenz[b,f][1,4]oxazepine-10(11H)-carboxy-(2-acetyl) hydrazine; 10(-5) M] but were antagonized by the less selective DP/EP(1)/EP(2) antagonist AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid; 10(-5) M) or by cyclopiazonic acid (10(-5) M; depletes the internal Ca(2+) store). Our data indicate that, whereas 8-iso-PGE(2) constricts pulmonary vasculature primarily through TP receptors, a substantial portion of this response is also directed through EP(3) receptors or possibly a novel isoprostane receptor.

Are endothelium-derived hyperpolarizing and contracting factors isoprostanes?

The endothelium releases many vasoactive substances, including prostacyclin, nitric oxide and endothelin, in addition to several other factors about which little is known. The latter are referred to as 'endothelium-derived hyperpolarizing factors' (EDHFs) and 'endothelium-derived contracting factors' (EDCFs). Although there is much debate about the identities of EDHFs and EDCFs, a prevailing hypothesis is that they are cyclooxygenase-independent metabolites of arachidonic acid and many researchers associate them with free radicals. These properties are shared with isoprostanes. In this article, I compare the properties of EDHFs and EDCFs with those of the isoprostanes and propose novel experiments that might identify isoprostanes as candidate molecules for EDHFs and EDCFs.

Prohemorrhagic potential of dipyrone, ibuprofen, ketorolac, and aspirin: mechanisms associated with blood flow and erythrocyte deformability

Dipyrone, ibuprofen, ketorolac, and aspirin were tested in a well-defined perfusion system (shear rates: 300/s, 800/s, and 1,800/s). Whole blood samples were treated with the drugs at analgesic doses and platelet interaction with damaged subendothelium was measured. All the drugs fully inhibited platelet cyclooxygenase, as assessed by classic aggregometry. Perfusion studies showed that there was a general tendency to reduce the percentage of large aggregates (thrombus; %T), to increase the percentage of adhered platelets (adhesion; %A), and to reduce the height of thrombi with respect to control. Aspirin significantly increased %A and reduced %T at all shear rates tested, whereas dipyrone had the same effect at 800/s, and ketorolac and ibuprofen at 1,800/s. In addition, aspirin significantly reduced erythrocyte deformability with respect to the other drugs. In conclusion, under our experimental conditions, aspirin showed the most remarkable effects on platelet function, closely followed by dipyrone. The effects of ketorolac were moderate, whereas ibuprofen had a minor impact on platelet function.

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.

Characterization of the effects of isoprostanes on platelet aggregation in human whole blood

We tested the effects of 11 commercially-available isoprostanes on platelet aggregation directly or when triggered by the thromboxane receptor agonist U46619 or collagen in healthy human citrated blood using a whole blood aggregometer. None of the isoprostanes tested triggered aggregation alone, nor facilitated aggregation by a sub-threshold dose of U46619 or collagen. Five isoprostanes inhibited aggregation (rank order of potency 8-iso PGE(1)>8-iso PGE(2)>8-iso PGF(2alpha)>8-iso PGF(3alpha)>8-iso-13,14-dihydro-15-keto PGF(2alpha)). Blood incubated with LPS to induce a gross inflammatory response exhibited a time dependent (2 - 12 h) reduction in aggregation to U46619 but maintained a consistent response to collagen. Under these conditions, as in control blood, none of the isoprostanes tested induced aggregation. In fact, the inhibitory actions of isoprostanes on U46619-induced aggregation were enhanced in blood treated with LPS. L-NAME inhibited aggregation induced by U46619 in fresh blood and in blood treated with LPS. In the presence of L-NAME, (with or without LPS) none of the isoprostanes tested induced aggregation but retained their inhibitory action. Thus, in human whole blood the action of 8-iso PGE(1), 8-iso PGE(2), 8-iso PGF(2alpha), 8-iso PGF(3alpha), and 8-iso-13,14-dihydro-15-keto PGF(2alpha) is antiaggregatory. Moreover, this inhibitory capacity is still apparent and may be enhanced in blood subjected to inflammatory stimulation.

Total synthesis of the four enantiomerically pure diastereomers of 8-F(2t)-isoprostane

Syntheses of the four enantiomerically pure diastereomers of 8-F(2t)-isoprostane (5-8) are described. The key to this approach was to prepare the racemic alcohol 9 in high diastereomeric purity and then resolve 9 by lipase-mediated acetylation to yield the enantiomerically pure alcohols 30 and 32.

Isoprostanes: generation, pharmacology, and roles in free-radical-mediated effects in the lung

Isoprostanes are produced during peroxidation of membrane lipids by free radicals and reactive oxygen species, and are currently used as markers of many disease states and experimental conditions in which oxidative stress is a prominent feature. A small number of reports have described the ability of some isoprostanes to evoke important biological effects in smooth muscle and other cell types. However, most of these studies were done using rat tissues, and only two specific isoprostanes - 8-iso-PGE(2)and 8-iso-PGF(2alpha)- were tested. In this review, we describe the generation of isoprostanes during oxidative stress, and their effects on smooth muscle, including our novel findings of their effects on human airway, pulmonary artery and pulmonary vein smooth muscles. Collectively, the data suggest that isoprostanes may not only be markers, but may in fact mediate the effects of free radicals and reactive oxygen species.

Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysis

BACKGROUND

Haptoglobin knockout (Hp-/-) mice are more sensitive to phenylhydrazine-induced hemolysis than Hp+/+ mice.

METHODS

Hemolysis was induced in Hp-/- and Hp+/+ mice using phenylhydrazine. Relative renal tissue damage and function were then assessed.

RESULTS

Hp-/- mice had higher basal levels of renal lipid peroxidation, as evidenced by levels of malonaldehyde and 4-hydroxy-2(E)-nonenal (MDA/HNE). After the administration of phenylhydrazine, levels of 8-hydroxyguanine (but not other products of oxidative DNA damage) were significantly elevated in the renal DNA. There was also increased induction of heme oxygenase-1. The more severe renal damage in Hp-/- mice was also evident in the delayed erythropoietin gene expression and poorer renal clearance of 3H-inulin. This reduction in glomerular filtration function in Hp+/+ and Hp-/- mice could be restored to baseline by vasodilators (prazosin or diazoxide), implicating renal vasoconstriction as a major mechanism of acute renal failure during induced hemolysis. Precipitation of hemoglobin in the kidney was not increased in Hp-/- mice.

CONCLUSIONS

Haptoglobin appears to play an important physiological role as an antioxidant, particularly during hemolysis.

Characterization of prostanoid receptors mediating actions of the isoprostanes, 8-iso-PGE(2) and 8-iso-PGF(2alpha), in some isolated smooth muscle preparations

We investigated the contracting actions of the isoprostanes (isoPs), 8-iso-prostaglandin (PG) F(2alpha) and 8-iso-PGE(2), in comparison to the effects of the thromboxane (TX) A(2)-mimetic U 46619 and the traditional prostaglandin PGE(2) in the isolated rat aorta, isolated rat gastric fundus and the isolated guinea-pig ileum. U 46619 and 8-iso-PGF(2alpha) caused contractions in the rat aorta and rat gastric fundus in a concentration-dependent manner, whereas these agonists showed no effects in the guinea-pig ileum. However, 8-iso-PGE(2) and PGE(2) caused contractions in all isolated organs used. The prostanoid TP-receptor antagonist SQ 29,548 (10 nM) significantly antagonized vasoconstrictions induced by the agonists used in the rat aorta. SQ 29,548 at a final concentration of 3 microM, but not at lower concentrations, significantly inhibited contractions induced by U 46619, 8-iso-PGF(2alpha) and 8-iso-PGE(2) in the rat fundus. Responses to PGE(2) were unchanged. The prostanoid EP(1)-receptor antagonist SC 51089 (3 microM) significantly inhibited contractions induced by 8-iso-PGE(2) and PGE(2) in the rat fundus and in the guinea-pig ileum. SC 51089 had no effect on responses to any of the agonists tested. Our results show that 8-iso-PGE(2), in contrast to 8-iso-PGF(2alpha), can also cause contractions by activation of the EP(1)-receptors in the rat gastric fundus and the guinea-pig ileum. The findings of the present study do not support the existence of a unique isoP-receptor in the tissues used.

C-nociceptor sensitization by isoprostanes is cyclooxygenase dependent

Isoprostane E(2) (8-iso-PGE) and F(2alpha) (8-iso-PGF) sensitize nociceptors and capsaicin-sensitive DRG neurons. In this study we investigated the cyclooxygenase-dependence of isoprostane-induced C-nociceptor sensitization. Systemic pretreatment of rats with ketorolac (1 and 10 mg/kg) abolished 8-iso-PGF sensitization and reduced the effects of 8-iso-PGE. Ibuprofen (30 mg/kg) blocked all sensitizing effects. These data suggest that some algesic properties of isoprostanes are mediated via prostanoid synthesis.

DDM-PGE(2)-mediated cytoprotection in renal epithelial cells by a thromboxane A(2) receptor coupled to NF-kappaB

The present studies were conducted to determine the pharmacological nature of a cytoprotective 11-deoxy-16,16-dimethyl-PGE(2) (DDM-PGE(2)) receptor in LLC-PK(1) cells. DDM-PGE(2)-mediated cytoprotection against 2,3,5-(trisglutathion-S-yl)hydroquinone (TGHQ)-mediated cytotoxicity can be reproduced using thromboxane A(2) (TXA(2)) receptor (TP) agonists (U46619 and IBOP), and the cytoprotective response to DDM-PGE(2) and TP agonists is inhibited by TP antagonists (SQ-29,548 and ISAP). Western blot analysis using an antipeptide antibody against the human platelet TP receptor (55 kDa) identified a particulate associated 54-kDa protein. DDM-PGE(2)-mediated 12-O-tetradecanoyl phorbol-13-acetate (TPA) responsive element (TRE) binding activity is not inhibited by cyclooxygenase inhibitors (aspirin and indomethacin) or a TXA(2) synthase inhibitor (sulfasalazine), suggesting that the biological response to DDM-PGE(2) is not dependent on de novo TXA(2) biosynthesis. Peak DDM-PGE(2)- and U46619-mediated TRE binding activity and nuclear factor-kappaB (NF-kappaB) binding activity are inhibited by SQ-29,548. The full cytoprotective response to DDM-PGE(2) requires an 8-h pulse with agonist. DDM-PGE(2)-mediated TRE and NF-kappaB binding activity remain elevated in the presence of agonist and rapidly decay following agonist washout, suggesting a direct correlation between DDM-PGE(2)-mediated cytoprotection and persistent DNA binding activities. TPA, a protein kinase C activator, induces cytoprotection and a persistent increase of NF-kappaB binding activity. DDM-PGE(2)-mediated cytoprotection and NF-kappaB binding activity but not TRE binding activity are inhibited by sulfasalazine. We conclude that the DDM-PGE(2) receptor is a TP receptor and that the cytoprotective response may be mediated in part by NF-kappaB.