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J. Biol. Chem., Vol. 279, Issue 35, 36412-36418, August 27, 2004

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Identification of 5,6-trans-Epoxyeicosatrienoic Acid in the Phospholipids of Red Blood Cells^*

Houli Jiang, John C. McGiff, John Quilley, David Sacerdoti¶, L. Manmohan Reddy||, John R. Falck||, Fan Zhang, Kenneth M. Lerea**, and Patrick Y-K Wong

From the Department of Pharmacology and the ^**Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595, the ^¶Department of Medicine, University of Padova, Padova 35128, Italy, and the ^||Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390

A novel eicosanoid, 5,6-trans-epoxy-8Z,11Z,14Z-eicosatrienoic acid (5,6-trans-EET), was identified in rat red blood cells. Characterization of 5,6-trans-EET in the sn-2 position of the phospholipids was accomplished by hydrolysis with phospholipase A₂ followed by gas chromatography/mass spectrometry as well as electrospray ionization-tandem mass spectrometry analyses. The electron ionization spectrum of 5,6-erythro-dihydroxyeicosatrienoic acid (5,6-erythro-DHET), converted from 5,6-trans-EET in the samples, matches that of the authentic standard. Hydrogenation of the extracted 5,6-erythro-DHET with platinum(IV) oxide/hydrogen resulted in an increase of the molecular mass by 6 daltons and the same retention time shift as an authentic standard in gas chromatography, suggesting the existence of three olefins as well as the 5,6-erythro-dihydroxyl structure in the metabolite. Match of retention times by chromatography indicated identity of the stereochemistry of the red blood cell 5,6-erythro-DHET vis à vis the synthetic standard. High pressure liquid chromatography-electrospray ionization-tandem mass spectrometry analysis of the phospholipase A₂-hydrolyzed lipid extracts from red blood cells revealed match of the mass spectrum and retention time of the compound with the authentic 5,6-trans-EET standard, providing direct evidence of the existence of 5,6-trans-EET in red blood cells. The presence of other trans-EETs was also demonstrated. The ability of both 5,6-trans-EET and its product 5,6-erythro-DHET to relax preconstricted renal interlobar arteries was significantly greater than that of 5,6-cis-EET. In contrast, 5,6-cis-EET and 5,6-trans-EET were equipotent in their capacity to inhibit collagen-induced rat platelet aggregation, whereas 5,6-erythro-DHET was without effect. We propose that the red blood cells serve as a reservoir for epoxides which on release may act in a vasoregulatory capacity.

Received for publication, April 9, 2004 , and in revised form, June 18, 2004.

^* This work was supported by grants from the New York Medical College Castle-Krob Research Endowment in support of the New York Medical College Intramural Research Support Program (to H. J.), National Institutes of Health Grants HL-25394 (to J. C. M.), HL-34300 (to J. C. M.), and GM31278 (to J. R. F.), the Robert A. Welch Foundation (to J. R. F.), and an American Diabetes Association grant (to J. Q.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 914-594-3117; E-mail: houli_jiang{at}nymc.edu.

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