Rheumatology Advance Access originally published online on May 16, 2006
Rheumatology 2006 45(7):922-923; doi:10.1093/rheumatology/kel139
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LETTER TO THE EDITOR |
Isoprostanes as a tool to investigate oxidative stress in scleroderma spectrum disorders—advantages and limitations
Pharmacology Laboratory, HP2 Laboratory, EA 3745, Grenoble Medical School, France
Correspondence to: Jean-Luc Cracowski, MD, PhD, Inserm CIC 03, Centre d'Investigation Clinique de Grenoble, CHU de Grenoble, 38043 Grenoble Cedex 09, France. E-mail: Jean-Luc.Cracowski{at}ujf-grenoble.fr
SIR, Scleroderma spectrum disorders represent heterogeneous disease with a large variation of clinical manifestations in individual patients. At one end of the spectrum is the limited systemic sclerosis according to LeRoy [1], which includes the presence of Raynaud's phenomenon (RP) and a typical capillaroscopy scleroderma pattern or positivity for Scl-70 or anti-centromere antibodies. At the other end of the spectrum are limited and diffuse cutaneous systemic sclerosis, which associates cutaneous changes and visceral involvement. The major hallmarks of these diseases are vascular dysfunction, immunological activation and tissue fibrosis. Increased oxidative stress is one of the phenomenons that may explain the link between the three faces of the disease. Quantification of oxidative stress in vivo is an important issue that can be approached by measuring F2-isoprostanes. F2-isoprostanes are a complex family of compounds produced from arachidonic acid via a free-radical-catalysed mechanism. The first demonstration that these compounds were produced in humans was shown in 1990 by Morrow et al. [2], who reported the discovery of prostaglandin-F2-like compounds generated by free-radical-induced peroxidation of arachidonic acid. Because these compounds are isomeric to prostaglandins and have an F-type cyclopentane (prostane) ring, these compounds were termed F2-isoprostanes. Since that time, F2-isoprostanes have been used extensively as clinical markers of lipid peroxidation in vascular disorders [3]. Several favourable attributes make measurement of F2-isoprostanes a reliable biomarker of oxidative stress in vivo. Isoprostanes are stable in urine, where levels are present in detectable quantities, their formation increases in models of oxidant injury and are modulated by anti-oxidant status, but their levels are not affected by lipid content of the diet [4]. Among the numerous F2-isoprostanes stereoisomers, 15-F2t-IsoP is currently mostly used as accurate clinical biomarker of lipid peroxidation [5].
Urinary and F2-isoprostane levels are increased in patients with systemic sclerosis [6]. Their levels are increased in patients at the early stages of the disease [7], but not in patients with primary (RP) [8]. Furthermore, 15-F2t-IsoP urinary levels correlate to the lung involvement and the nailfold videocapillaroscopy pattern [9], and inversely correlate to the skin post-occlusive hyperaemia [10]. These data strongly suggest that lipid peroxidation is increased in scleroderma spectrum disorders. Lipid peroxidation level relates to the extent of pulmonary and vascular damage, and may represent a biomarker of aggressive disease. 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. The recent data from Ogawa et al. [11] appear interesting at first sight: free F2-isoprostane levels would be increased in serum as well as urine. However, several major limitations prevent drawing any conclusion from this data. The authors show that free serum F2-isoprostane levels are elevated by 75-fold compared with controls, with 99% of the patients’ values being higher than the mean + 3 S.D. of the control group. This clear-cut result would be amazing for such a non-specific biomarker. This should have risen questions about potential bias. F2-isoprostanes were initially discovered as an auto-oxidation product of plasma samples kept at –20°C [12]. There is no rationale for the use of serum samples for measuring compounds that may be produced ex vivo. Indeed, ex vivo generation of isoprostane is highly susceptible to occur during clot formation, which is why most investigators using blood samples quantify isoprostane on plasma samples. Blood is collected with anti-coagulants, and promptly centrifuged at 4°C. The half-life of F2-isoprostane is short, being <20 min in the rat. Therefore, the choice of plasma vs urinary measurement is debatable for quantifying lipid peroxidation in chronic disease. The authors also specify that serum samples were obtained over the last 7 years. This implicates that serum F2-isoprostanes are stable over this large period of time, ensuring that spontaneous auto-oxidation does not occur, and we have no evidence that this is validated. Therefore, a different time between blood sampling and storage at –80°C, and a different storage time is likely to explain the difference observed between controls and patients with scleroderma. Another hint that artefactual generation occurred is the tremendous dispersion of values, as some patients exhibited isoprostane levels more than 10 000 times higher than the control levels. Another pitfall that should have been discussed is renal failure, a common comorbidity in patients with severe systemic sclerosis. Clearance of F2-isoprostanes is due both to renal filtration and metabolism. The most commonly quantified isoprostane 15-F2t-IsoP leads to two major metabolites in humans: 2,3-dinor-15-F2t-IsoP and 2,3-dinor-5,6-dihydro-15-F2t-IsoP [13, 14], but this compound is also filtrated and quantified in urine. Therefore, renal failure, by itself may contribute to the increased plasma levels via decreased excretion. Finally, the authors specify that they followed the specifications of Cayman® enzyme immunoassay kit. However, there is no indication that any purification step was applied prior to the measurement, while the lack of purification may lead to inconsistent results.
From the previous available data on urine, there is a consistent increase in isoprostane levels in patients with scleroderma, ranging from 1.25 to 3 times compared with controls [6–10]. The 75-fold increase in serum levels does not compare with it, and is likely due in most part to an artefactual generation or a decreased clearance. Further studies are required to determine the link between oxidative stress and vascular damage in systemic sclerosis. F2-isoprostane quantification exhibits many advantages that promote it as a good tool to investigate lipid peroxidation in humans. However, urinary measurements, using an initial purification step, provide a time-integrated index of systemic F2-isoprostane formation, and do not exhibit the pitfall of blood measurements. They should be favoured by investigators in an attempt to quantify F2-isoprostane as a tool to investigate oxidative stress in patients with scleroderma.
The author has declared no conflicts of interest.
References
- LeRoy EC, Medsger TA, Jr. Criteria for the classification of early systemic sclerosis. J Rheumatol 2001;28:1573–6.
[Abstract/Free Full Text] - 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;87:9383–7.
[Abstract/Free Full Text] - Cracowski JL. Isoprostanes: an emerging role in vascular physiology and disease?. Chem Phys Lipids 2004;128:75–83.[CrossRef][Web of Science][Medline]
- Roberts LJ, Morrow JD. Measurement of F2-isoprostanes as an index of oxidative stress in vivo. Free Radic Biol Med 2000;28:505–13.[CrossRef][Web of Science][Medline]
- Cracowski JL, Durand T, Bessard G. Isoprostanes as a biomarker of lipid peroxidation in humans: physiology, pharmacology and clinical implications. Trends Pharmacol Sci 2002;23:360–6.[CrossRef][Medline]
- Stein CM, Tanner SB, Awad JA, Roberts LJ, Morrow JD. Evidence of free radical-mediated injury (isoprostane overproduction) in scleroderma. Arthritis Rheum 1996;39:1146–50.[Web of Science][Medline]
- Cracowski JL, Marpeau C, Carpentier PH et al. Enhanced in vivo lipid peroxidation in scleroderma spectrum disorders. Arthritis Rheum 2001;44:1143–8.[CrossRef][Web of Science][Medline]
- Cracowski JL, Carpentier PH, Imbert B et al. Increased urinary F2-isoprostanes in systemic sclerosis, but not in primary Raynaud's phenomenon: effect of cold exposure. Arthritis Rheum 2002;46:1319–23.[CrossRef][Web of Science][Medline]
- Volpe A, Biasi D, Caramaschi P et al. Levels of F2-isoprostanes in systemic sclerosis: correlation with clinical features. Rheumatology 2006;45:314–20.
[Abstract/Free Full Text] - Cracowski JL, Kom GD, Salvat-Melis M et al. Post occlusive reactive hyperemia inversely correlates to urinary 15-F2t-isoprostane levels in systemic sclerosis. Free Rad Biol Med 2006; in press.
- Ogawa F, Shimizu K, Muroi E et al. Serum levels of 8-isoprostane, a marker of oxidative stress, are elevated in patients with systemic sclerosis. Rheumatology 2006 [Epub ahead of print].
- Roberts J, 2nd, Durand T. Special issue on isoprostanes. Preface. Chem Phys Lipids 2004;128:1–2.
- Chiabrando C, Valagussa A, Rivalta C et al. Identification and measurement of endogenous beta-oxidation metabolites of 8-epi-prostaglandin F2
. J Biol Chem 1999;274:1313–9.[Abstract/Free Full Text] - Roberts II LJ, Moore KP, Zachert WE, Oates JA, Morrow JD. Identification of the major urinary metabolite of the F2-isoprostane 8-iso-prostaglandin F2 in humans. J Biol Chem 1996;271:20617–20.
[Abstract/Free Full Text]
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