Isoprostanes, emerging biomarkers and potential mediators in cardiovascular diseases

Jean-Luc Cracowskia,* and Olivier Ormezzanob

a Laboratoire de Pharmacologie, Faculté de Médecine de Grenoble, HP2 EA 3745, France
b Department of Cardiology, Grenoble University Hospital, France

* Correspondence to: Laboratoire de Pharmacologie, Faculté de Médecine de Grenoble, HP2 EA 3745, 38700 La Tronche, France. Tel.: +33 4 76 76 92 60; fax: +33 4 76 76 92 62 (E-mail: jean-luc.cracowski{at}ujf-grenoble.fr).

Arachidonic acid is an essential unsaturated fatty acid and is the most abundant in cell membranes. Its metabolism leads to the formation of the well known prostaglandins and thromboxanes, which are implicated in the modulation of vascular tone and growth and play an important role on the blood-vessel interface. The discovery of their pharmacological activity led to the development of some potent drugs such as the prostacyclin analogues, while thromboxane A2-receptor antagonists are currently under development. While research on arachidonic acid metabolites focused for decades on the enzymatic pathway, Morrow and Roberts 1 described in 1990 another pathway of arachidonic acid metabolism, i.e., a free radical pathway, leading to a large series of compounds termed isoprostanes.

A first level of complexity is that, unlike the enzymatic formation of prostaglandins, F2-isoprostanes derive from a non-specific free radical attack of arachidonic acid, i.e., that four different series of compounds, called regioisomers, differing in the nature of their side chains, are formed (Fig. 1). The second level of complexity is that eight isomers may be formed among each of these four regioisomers, i.e., 64 different F2-isoprostanes are formed. The third level of complexity is man-made: three different nomenclatures co-exist2. Given the potential number of compounds, this can lead to a nightmare for the non-specialist, and a puzzle for novices to determine which is which. For clarity, the nomenclature validated by the International Union of Pure and Applied Chemistry3 should be used. The fourth level of complexity is that F2-isoprostanes are only one family of the myriad of compounds produced through free radical peroxidation of arachidonic acid, including two recent families of compounds termed isoketals and isofurans (Fig. 1)4.



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Fig. 1 The isoprostane pathway.

 
Most currently available data concerns the isoprostanes from the 15-series, especially 15-F2t-IsoP (formerly named 8-iso-PGF2). 15-F2t-IsoP is a vasoconstrictor in most species and vascular beds5. These constrictor properties are not restricted to blood vessels, and have been demonstrated in the lymphatic vessels, the bronchi, the gastrointestinal tract and the uterus. In addition, 15-F2t-IsoP stimulates mitogenesis6, enhances monocytes and polymorphonuclear adhesion to endothelial cells7, and induces endothelial cell necrosis8. While most of these effects are mediated by thromboxane A2-prostaglandin H2 (TP) receptor stimulation, other effects such as PPAR activation9 is TP receptor independent. However, there is no evidence to date that a specific isoprostane receptor exists. Acting as a partial agonist, 15-F2t-IsoP inhibits platelet aggregation in human whole blood10.

15-F2t-IsoP is released in conditions associated with free radical generation, such as cardiac ischaemia–reperfusion, and is the most sensitive and specific biomarker of lipid peroxidation in vascular disorders11. Several authors have tried to answer an important question: are these compounds merely biomarkers, or do they act as mediators in pathological conditions12,13? As we do not possess a pharmacological agent that may specifically inhibit the biological effects of 15-F2t-IsoP, the answer cannot be straightforward. Basal plasma concentrations of 15-F2t-IsoP have been found to range from approximately 1x10–10 to 5x10–10 moll–1 in plasma samples. These concentrations are unlikely to induce a systemic vasoactive effect considering the EC50 values of 15-F2t-IsoP observed in vitro5 However, F2-isoprostanes are released at the site of free radical injury and then diluted in the circulation and therefore local concentrations might be sufficiently high to induce regional vasoconstriction. Indeed, the concentrations of 15-F2t-IsoP and 5-F2t-IsoP were increased markedly (from basal levels) in the coronary sinus and plasma following coronary angioplasty14,15. 15-F2t-IsoP concentrations were in the nanomolar range, and thus unlikely to contribute to epicardial coronary artery vasoconstriction16. However, the concentration of 15-F2t-IsoP might be sufficiently high to induce a vasoconstriction in the microcirculation because the potency of 15-F2t-IsoP seems to be higher in these arteries compared with conductance arteries17. Considering 5-F2t-IsoP, this compound does not possess any vasomotor activity18,19, and is therefore unlikely to play a pathogenic role on the coronary vasculature.

No specific inhibition of 15-F2t-IsoP or other isoprostane vascular effects can currently be achieved. However, TP receptor antagonists but not aspirin, are effective in the inhibition of atherosclerosis in apo E-KO (knock-out) mice, showing that TP receptor blockade by S18886 is effective by a mechanism independent of platelet-derived thromboxane A220, whereas isoprostane suppression with vitamin E retards atherogenesis in the same animal model21. Similarly, TP receptor antagonism by L670596, but not COX-2 inhibition, prevented pulmonary hypertension and endothelin-1 upregulation in 60% O2-mediated pulmonary hypertension in newborns rats22. In addition to these animal data, a study showed that in patients suffering from coronary artery disease, S18886 (a TP receptor antagonist) improved acetylcholine-induced and flow-mediated vasodilation in patients treated with aspirin23. An hypothesis is that endogenous TP receptor activation induced by 15-F2t-IsoP or other isoprostanes may be involved in the COX-independent effects of TP receptor antagonists24. However, because TP receptors share other endogenous ligands such as prostaglandin H2 or HETEs, such data give strength to the hypothesis that isoprostanes are involved in the vascular physiology and pathogenesis, but does not enable a definitive conclusion.

Given that many isomeric isoprostanes exist, one should not focus only on 15-F2t-IsoP. Other isoprostanes possess potent pharmacological activity, the most potent ones being the isoprostanes from the E series. For example, 15-E2t-IsoP is 10 times more potent than 15-F2t-IsoP in systemic as well as pulmonary vessels25,26. Furthermore, in a recent report Hou et al.,19 showed that many other regioisomers, including those from the 12-series, constricted retinal and brain microvessels. These regioisomers are likely to be produced under the same conditions as 15-F2t-IsoP, but no data is currently available concerning their production in cardiac ischaemia–perfusion. Finally, other potential physiological mediators of the isoprostane pathway include the isothromboxanes27 and the receptor independent effects of isoketals, that rapidly adduct to membrane proteins28.

Isoprostanes are currently the more valuable biomarkers of lipid peroxidation11. They have been measured in biological fluids such as urine, plasma, exhaled breath condensate, bronchoalveolar lavage fluid, bile, cerebrospinal, seminal and pericardial fluids. They were also detectable in normal tissues, including umbilical cords29. Their measurement in biological fluids has prompted clinical investigations on the pathophysiological role of lipid peroxidation in cardiovascular diseases (see 30,31). Among the biological fluids available, most studies were performed on urine because of the non-invasiveness of the procedure and the lack of artefactual generation. A strong link between lipid peroxidation and vascular diseases associated with ischaemia–reperfusion, atherosclerosis and inflammation has been suggested by the elevated levels of lipid peroxidation observed in such diseases.

In addition to being a pathophysiological marker, the quantification of F2-isoprostanes might represent a prognostic marker. F2-isoprostane levels consistently correlate to the severity of heart failure32,33,34, and correlate to the haemodynamic response to NO in pulmonary hypertension35. Furthermore, Schwedhelm et al., showed in a recent case-control study that urinary 15-F2t-IsoP was a strong independent concentration-dependent risk marker of coronary heart disease36. There are currently no published clinical studies aimed at testing isoprostanes as a long-term prognostic marker, with strong endpoints such as mortality or morbidity, but at least two cohort studies are currently on-going.

In conclusion, we are just beginning to explore the wilderness of arachidonic acid metabolism leading to isoprostane formation. While the available data provides fuel for discussion concerning the potential implication of 15-F2t-IsoP in vascular disorders, the unknown physiological and pathological significance of the myriad of compounds produced from arachidonic acid in conditions of enhanced free radical generation, observed in many vascular diseases, leaves scope for many more investigations.

References

  1. Morrow JD, Hill KE, Burk RF, et al. A series of prostaglandin F2-like compounds are produced in vivo in humans by a non-cyclooxygenase, free radical-catalyzed mechanism Proc Natl Acad Sci USA 1990;87:9383-9387.[Abstract]
  2. Cracowski JL, Durand T, Bessard G. Isoprostanes as a biomarker of lipid peroxidation in humans: physiology, pharmacology and clinical implications Trends Pharmacol Sci 2002;23:360-366.[CrossRef][Medline]
  3. Taber DF, Morrow JD, Robert II LJ. A nomenclature system for the isoprostanes Prostaglandins 1997;53:63-67.[CrossRef][Medline]
  4. Roberts 2nd LJ, Fessel JP. The biochemistry of the isoprostane, neuroprostane, and isofuran pathways of lipid peroxidation Chem Phys Lipids 2004;128:173-186.[CrossRef][Medline]
  5. Cracowski JL, Devillier P, Durand T, et al. Vascular biology of the isoprostanes J Vasc Res 2001;38:93-103.[CrossRef][Medline]
  6. Miggin SM, Kinsella BT. Thromboxane A2 receptor mediated activation of the mitogen activated protein kinase cascades in human uterine smooth muscle cells Biochim Biophys Acta 2001;1539:147-162.[CrossRef][Medline]
  7. Leitinger N, Huber J, Rizza C, et al. The isoprostane 8-iso-PGF stimulates endothelial cells to bind monocytes: differences from thromboxane-mediated endothelial activation FASEB J 2001;15:1254-1256.[Abstract/Free Full Text]
  8. Brault S, Martinez-Bermudez AK, Marrache AM, et al. Selective neuromicrovascular endothelial cell death by 8-Iso-prostaglandin F2α: possible role in ischemic brain injury Stroke 2003;34:776-782.[Abstract/Free Full Text]
  9. McNamara P, Lawson JA, Rokach J, et al. Isoprostane activation of the nuclear hormone receptor PPAR Adv Exp Med Biol 2002;507:351-355.[Medline]
  10. Cranshaw JH, Evans TW, Mitchell JA. Characterization of the effects of isoprostanes on platelet aggregation in human whole blood Br J Pharmacol 2001;132:1699-1706.[Abstract/Free Full Text]
  11. Roberts LJ, Morrow JD. Measurement of F2-isoprostanes as an index of oxidative stress in vivo Free Radic Biol Med 2000;28:505-513.[CrossRef][Medline]
  12. Iuliano L, Pratico D, Greco C, et al. Angioplasty increases coronary sinus F2-isoprostane formation: evidence for in vivo oxidative stress during PTCA J Am Coll Cardiol 2001;37:76-80.[CrossRef][Medline]
  13. Cracowski JL, Marliere S, Bessard G. Vasomotor effects and pathophysiologic relevance of F2-isoprostane formation in vascular diseases J Am Coll Cardiol 2002;39:554.[Medline]
  14. Iuliano L, Pratico D, Ferro D, et al. Enhanced lipid peroxidation in patients positive for antiphospholipid antibodies Blood 1997;90:3931-3935.[Abstract/Free Full Text]
  15. Greave K, Dixon SR, O'Brien Coker I, et al. The influence of isoprostane F2a-III on reflow after myocardial infarction Eur Heart J 2004;25:847-853.[Abstract/Free Full Text]
  16. Kromer B, Tippins JR. Coronary artery constriction by the isoprostane 8-epi-prostaglandin F Br J Pharmacol 1996;119:1276-1280.[Abstract]
  17. Hou X, Gobeil Jr. F, Peri K, et al. Augmented vasoconstriction and thromboxane formation by 15-F2t-isoprostane (8-iso-prostaglandin F(2α)) in immature pig periventricular brain microvessels Stroke 2000;31:516-524discussion 525.[Abstract/Free Full Text]
  18. Marlière S, Cracowski JL, Durand T, et al. The 5-series F2-isoprostanes possess no vasomotor effects in the rat thoracic aorta, the human internal mammary artery and the human saphenous vein Br J Pharmacol 2002;135:1276-1280.[Abstract/Free Full Text]
  19. Hou X, Roberts 2nd LJ, Gobeil Jr. F, et al. Isomer-specific contractile effects of a series of synthetic f2-isoprostanes on retinal and cerebral microvasculature Free Radic Biol Med 2004;36:163-172.[CrossRef][Medline]
  20. Cayatte AJ, Du Y, Oliver-Krasinski J, et al. The thromboxane receptor antagonist S18886 but not aspirin inhibits atherogenesis in apo E-deficient mice : evidence that eicosanoids other than thromboxane contribute to atherosclerosis Arterioscler Thromb Vasc Biol 2000;20:1724-1728.[Abstract/Free Full Text]
  21. Pratico D, Tangirala RK, Rader DJ, et al. Vitamin E suppresses isoprostane generation in vivo and reduces atherosclerosis in ApoE-deficient mice Nat Med 1998;4:1189-1192.[CrossRef][Medline]
  22. Jankov RP, Belcastro R, Ovcina E, et al. Thromboxane A(2) receptors mediate pulmonary hypertension in 60% oxygen-exposed newborn rats by a cyclooxygenase-independent mechanism Am J Respir Crit Care Med 2002;166:208-214.[Abstract/Free Full Text]
  23. Belhassen L, Pelle G, Dubois-Rande JL, et al. Improved endothelial function by the thromboxane A2 receptor antagonist S 18886 in patients with coronary artery disease treated with aspirin J Am Coll Cardiol 2003;41:1198-1204.[CrossRef][Medline]
  24. Pratico D, Cheng Y, FitzGerald GA. TP or not TP: primary mediators in a close runoff? Arterioscler Thromb Vasc Biol 2000;20:1695-1698.[Free Full Text]
  25. Janssen LJ, Tazzeo T. Involvement of TP and EP3 receptors in vasoconstrictor responses to isoprostanes in pulmonary vasculature J Pharmacol Exp Ther 2002;301:1060-1066.[Abstract/Free Full Text]
  26. Cracowski JL, Devillier P, Chavanon O, et al. Isoprostaglandin E2 type III (8-iso-prostaglandin E2) evoked contractions in human internal mammary artery Life Sci 2001;68:2405-2413.[CrossRef][Medline]
  27. Morrow JD, Awad JA, Wu A, et al. Nonenzymatic free radical-catalyzed generation of thromboxane-like compounds (isothromboxanes) in vivo J Biol Chem 1996;271:23185-23190.[Abstract/Free Full Text]
  28. Brame CJ, Boutaud O, Davies SS, et al. Modification of proteins by isoketal-containing oxidized phospholipids J Biol Chem 2004;279:13447-13451.[Abstract/Free Full Text]
  29. Obwegeser R, Oguogho A, Ulm M, et al. Maternal cigarette smoking increases F2-isoprostanes and reduces prostacyclin and nitric oxide in umbilical vessels Prostaglandins Other Lipid Mediat 1999;57:269-279.[CrossRef][Medline]
  30. Cracowski JL. Isoprostanes: an emerging role in vascular physiology and disease Chem Phys Lipids 2004;128:75-83.[CrossRef][Medline]
  31. Davi G, Falco A, Patrono C. Determinants of F2-isoprostane biosynthesis and inhibition in man Chem Phys Lipids 2004;128:149-163.[CrossRef][Medline]
  32. Mallat Z, Philip I, Lebret M, et al. Elevated levels of 8-iso-prostaglandin F in pericardial fluid of patients with heart failure: a potential role for in vivo oxidant stress in ventricular dilatation and progression to heart failure Circulation 1998;97:1536-1539.[Abstract/Free Full Text]
  33. Cracowski JL, Tremel F, Marpeau C, et al. Increased formation of F2-isoprostanes in patients with severe heart failure Heart 2000;84:439-440.[Free Full Text]
  34. Nonaka-Sarukawa M, Yamamoto K, Aoki H, et al. Increased urinary isoprostane excretion in patients with non-ischemic congestive heart failure: a marker of oxidative stress Heart 2003.
  35. Cracowski JL, Cracowski C, Bessard G, et al. Increased lipid peroxidation in patients with pulmonary hypertension Am J Respir Crit Care Med 2001;164:1038-1042.[Abstract/Free Full Text]
  36. Schwedhelm E, Bartling A, Lenzen H, et al. Urinary 8-iso-prostaglandin F2α as a risk marker in patients with coronary heart disease: a matched case-control study Circulation 2004;109:843-848.[Abstract/Free Full Text]




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