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

Isoprostanes in Veterinary Medicine: Beyond a Biomarker

Oxidative stress has been associated with many pathologies, in both human and animal medicine. Damage to tissue components such as lipids is a defining feature of oxidative stress and can lead to the generation of many oxidized products, including isoprostanes (IsoP). First recognized in the early 1990s, IsoP are formed in numerous biological fluids and tissues, chemically stable, and easily measured by noninvasive means. Additionally, IsoP are highly specific indicators of lipid peroxidation and thereby are regarded as excellent biomarkers of oxidative stress. Although there have been many advancements in the detection and use of IsoP as a biomarker, there is still a paucity of knowledge regarding the biological activity of these molecules and their potential roles in pathology of oxidative stress. Furthermore, the use of IsoP has been limited in veterinary species thus far and represents an avenue of opportunity for clinical applications in veterinary practice. Examples of clinical applications of IsoP in veterinary medicine include use as a novel biomarker to guide treatment recommendations or as a target to mitigate inflammatory processes. This review will discuss the history, biosynthesis, measurement, use as a biomarker, and biological action of IsoP, particularly in the context of veterinary medicine.

Cardiovascular pharmacology and physiology of the isoprostanes

F(2)-isoprostanes are a complex family of compounds produced from arachidonic acid via a free radical-catalyzed mechanism. Their quantification as a pathophysiological biomarker provides a unique opportunity to investigate lipid peroxidation in vascular diseases. Their measurement also provides an interesting biomarker for the rational dose selection of antioxidants in vascular diseases where oxidative stress might be involved. In addition to their use as biomarkers, some isoprostanes possess a biological activity. The 15-series F(2)- and E(2)-isoprostanes mediate vasoconstriction in different vascular beds and species. In addition, 15-F(2t)-IsoP induces smooth muscle cells mitogenesis and monocyte adhesion to endothelial cells. The data available supports but does not prove the hypothesis that isoprostanes are involved in vascular physiology and pathogenesis.

Les isoprostanes, biomarqueurs de peroxydation lipidique chez l'homme. Partie 3 : biomarqueurs et médiateurs en physiologie et pathologie vasculaire

The 15-series F(2)-isoprostanes mediate vasoconstriction in different vascular beds and species. This contraction is mediated by the thromboxane receptors stimulation, and may be modulated by the endothelium. Furthermore, 15-F(2t)-IsoP induces smooth muscle cells mitogenesis and monocyte adhesion to endothelial cells. Some 15-series E(2)-isoprostanes are more potent than F(2)-isoprostanes. In clinical studies, 15-F(2t)-IsoP levels are increased in vascular disorders involving atherosclerosis, ischemia-reperfusion and inflammation. F(2)-isoprostane levels correlate to the severity of heart failure and pulmonary hypertension, raising the potential prognostic interest of these biomarkers. Whether the effects observed in vitro are observed consistently in vivo at physiological concentrations and whether these effects contribute to pathological states in vivo is still debated.

Increased platelet CD63 and P-selectin expression persist in atherosclerotic ischemic stroke

Platelet activation is an important process in the pathogenesis of atherothrombosis. However, the serial changes of platelet activation in atherosclerotic ischemic stroke have not been determined. In this study, we measured serially platelet expression of CD63 and P-selectin and platelet aggregability to ADP and collagen. Measurements were made 24 and 72 h and 7 and 90 days after the ischemic event in 29 patients with atherosclerotic ischemic stroke. Platelet aggregability was significantly decreased after 72 h compared to that at 24 h of stroke onset. However, platelet CD63 and P-selectin expression remained high even 90 days after the events. These findings suggest that platelet hyperactivation in atherosclerotic ischemic stroke may be sustained for a considerable period.

Les isoprostanes : un rôle physiopathologique potentiel en pathologie vasculaire

PURPOSE

Isoprostanes are arachidonic acid metabolites produced by a free-radical-dependent mechanism.

CURRENT KNOWLEDGE AND KEY POINTS

The 15-series F2-isoprostanes and some 15-series E2-isoprostanes mediate vasoconstriction in different vascular beds and species. Furthermore, 15-F2t-IsoP induces smooth muscle cells mitogenesis and monocyte adhesion to endothelial cells. In clinical studies, 15-F2t-IsoP levels are increased in vascular disorders involving atherosclerosis, ischemia-reperfusion and inflammation.

FUTURE PROSPECTS AND PROJECTS

Whether the effects observed in vitro are observed consistently in vivo at physiological concentrations and whether these effects contribute to pathological states in vivo is still debated.

Isoprostanes: an emerging role in vascular physiology and disease?

Among the isoprostanes, the 15-series F2-isoprostanes and 15-E2t-IsoP mediate vasoconstriction in different vascular beds and species. In addition, 15-F2t-IsoP induces smooth muscle cells mitogenesis and monocyte adhesion to endothelial cells. In clinical studies, 15-F2t-IsoP levels are increased in some vascular disorders involving atherosclerosis, ischemia-reperfusion and inflammation. Whether the same effects observed in vitro are observed consistently in vivo at physiological concentrations and whether these effects contribute to pathological states in vivo is still debated.

Stereodivergent synthesis of all 15-F(2) isoprostanes

Isoprostanes, lipid metabolites generated from free radical oxidation of membrane-bound arachidonic acid, have been detected in organisms subjected to oxidative stress; however, the function and cellular targets of the isoprostanes are unclear. As an initial step toward studying the biological role of these molecules, we report the preparation of all known and anticipated 15-F2 isoprostanes. The stereodivergent strategy to the complete isoprostane library features a ring-opening metathesis to introduce the cis-alkyl side chains that are characteristic of this class of molecules. Resolution to the individual stereoisomers can be accomplished by either a catalytic asymmetric reduction or an auxiliary-based separation protocol. In either case, the individual isomers can be converted to the corresponding 15-F2 isoprostanes through a straightforward functionalization of the carboxylic acid-containing side chain. The availability of this complete 15-F2 isoprostane library, containing both known and anticipated lipid metabolites, allows for the first time the side-by-side evaluation of these compounds in a variety of biological assays.

Production of 8-epi prostaglandin F(2alpha) in human platelets during administration of organic nitrates

OBJECTIVES

The objective of this study was, using isolated platelets as a surrogate for vascular cells, to examine the effect of nonintermittent organic nitrate administration on 8-epi prostaglandin F(2alpha) (8-epi PGF(2alpha)) content and the effect of concurrent oral ascorbate administration.

BACKGROUND

The long-term efficacy of organic nitrates is hampered by hemodynamic tolerance, which develops during continuous administration. This has been associated with altered production of superoxide and nitric oxide, as well as oxidative stress. This effect may be ameliorated by the co-administration of antioxidants.

METHODS

Ten healthy male subjects received nitroglycerin (NTG) transdermally at a dosage of 0.4 mg/h for 3 days with ascorbate or lactose (1.2 g/day). After two weeks washout, the treatment was repeated with reversed ascorbate/lactose. Platelets were prepared by centrifugation and esterified 8-epi PGF(2alpha) measured at the start and finish of each treatment by immunoassay.

RESULTS

Nitroglycerin, in the absence of supplemental ascorbate, was associated with a significant increase in platelet-esterified 8-epi PGF(2alpha), from 32.9 (95% confidence interval [CI] 11.8 to 54.0) to 51.0 (95% CI 16.3 to 85.7) pg/mg protein (p < 0.05). Co-administration of ascorbate with NTG resulted in a significant decrease in 8-epi PGF(2alpha) production, from 38.8 (95% CI 24.9 to 52.7) to 19.0 (95% CI 13.5 to 24.5) pg/mg protein (p < 0.05).

CONCLUSIONS

Continuous NTG administration results in an increase in platelet-esterified 8-epi PGF(2alpha), a free radical and cyclooxygenase-dependent compound. This is reversed by co-administration of the free radical scavenger ascorbate. Whether this increase is merely a marker for increased oxidative stress or a mediator of oxidative injury contributing to the hemodynamic changes observed in nonintermittent organic nitrate treatment has yet to be resolved.

Isoprostanes as a biomarker of lipid peroxidation in humans: physiology, pharmacology and clinical implications

Isoprostanes are a complex family of compounds produced from arachidonic acid via a free-radical-catalyzed mechanism. They can be quantified as reliable markers of lipid peroxidation. Among the isoprostanes, 15-F(2t)-IsoP and 15-E(2t)-IsoP are biologically active and mediate vasoconstriction and bronchoconstriction and augment nociception. These effects are thought to be mediated via the activation of prostanoid TP receptors, with isoprostanes acting as full or partial agonists. A strong link between lipid peroxidation and diseases associated with ischaemia-reperfusion, atherosclerosis and inflammation has been suggested by elevated levels of F(2)-isoprostanes observed in such diseases. Thus, quantification of F(2)-isoprostanes as a pathophysiological marker provides a unique opportunity to investigate lipid peroxidation in human diseases and provides an interesting biomarker for rational dose selection of antioxidants in diseases where oxidative stress might be involved.

The 5-series F(2)-isoprostanes possess no vasomotor effects in the rat thoracic aorta, the human internal mammary artery and the human saphenous vein

1. Among the F(2)-isoprostanes, the 15- and the 5-series are currently used as markers of lipid peroxidation in vascular diseases. 15-F(2t)-IsoP (also named iPF(2 alpha)-III) exerts a vasoconstriction in most vessels, whereas no data is available concerning 5-F(2t)-IsoP (also named iPF(2 alpha)-VI), which is more abundant in plasma. 2. The aim of this study was to determine whether 5-F(2t)-IsoP possess any vascular effects on various vessels including the isolated rat thoracic aorta, the human internal mammary artery and the saphenous vein. 3. In organ baths, 5-F(2t)-IsoP and its 5-epimer did not affect the basal tone of any vessel, unlike 15-F(2t)-IsoP. These compounds possessed no antagonist effects on 15-F(2t)-IsoP-induced contractions, No dilator effect was observed in comparison with sodium nitroprusside and acetylcholine on the rat aorta. 4. In conclusion, we show that unlike 15-F(2t)-IsoP, 5-F(2t)-IsoP and its 5-epimer possess no vasomotor effects and as such are unlikely to be involved in the pathogenesis of vascular diseases. Further studies are required to test whether these mediators may have effects on systems not being measured in the current study.