Long-lived enzymatic metabolites of thromboxane B 2 in the human circulation

Abstract

Thromboxane A 2, a potent vasoconstrictor and platelet agonist, is an evanescent cyclooxygenase product of arachidonic acid. Assessment of thromboxane biosynthesis commonly relies upon analysis of the stable but biologically inactive hydration product, thromboxane B 2. However, measurement of this compound in plasma is readily confounded by platelet activation ex vivo. We have identified 11-dehydro-thromboxane B 2, 11-dehydro-13,14-dihydro-15-keto-thromboxane B 2, and 2,3-dinor-thromboxane B 2 as enzymatic products of infused thromboxane B 2 in the human circulation. Biosynthesis of deuterated standards permitted the development of quantitative analyses for these compounds, employing capillary gas chromatography-negative ion chemical ionization-mass spectrometry. We thus established that the postinfusion half-lives of 11-dehydrothromboxane B 2 and the keto-dihydro metabolite approximated 1 hour, while that of the dinor metabolite ranged from 15 to 17 min. Combined analysis of short- and long-lived enzymatic metabolites of thromboxane B 2 promises to bypass the problem of ex vivo platelet activation and enhance the likelihood of relating a discreet clinical event to an alteration in the biosynthesis of thromboxane A 2 in the human circulation.