Stereochemical analysis and biological activity of 3-hydroxy-leukotriene B₄: A metabolite from ethanol-treated rat hepatocytes

Leukotriene B₄ (LTB₄), a biologically active metabolite derived from arachidonic acid by the 5-lipoxygenase cascade, is inactivated by cytochrome P-450-dependent ω-hydroxylation followed by second oxidation into a ω- carboxyl group. In many tissues, this second step is mediated by alcohol dehydrogenase. Isolated rat hepatocytes metabolized LTB₄ in the presence of ethanol and ethoxyresorufin into substantial quantities of 3-hydroxy-LTB₄ as determined by mass spectrometry. The absolute configuration of this metabolite was found to be greater than 98% 3(S)-hydroxy-LTB₄ by comparison to synthetic standards. Investigation of the pharmacologic properties of the 3(S)- and 3(R)-hydroxy-LTB₄ revealed that both caused a significant increase in intracellular free calcium in human neutrophils at 1 μM. Both enantiomers also induced thromboxane A₂ release from the isolated guinea pig lung in a dose-dependent manner. This activity was fully blocked by a specific LTB₄ receptor antagonist, LY223982, with an IC₅₀ of 0.21 μM for LTB₄. These results suggested that activation of the LTB₄ receptor does not involve significant recognition of the carbon atoms close to the carboxyl moiety of LTB₄. The failure of the hepatocyte to metabolically inactivate LTB₄ in the presence of ethanol may be of importance to humans, particularly because the bioactive metabolite 3(S)-hydroxy-LTB₄ was further metabolized by human neutrophils significantly more slowly than LTB₄.