INVESTIGATION OF THE MECHANISM OF BIOSYNTHESIS OF 8-HYDROXYEICOSATETRAENOIC ACID IN MOUSE SKIN

One of the many changes induced by topical application of phorbol ester or calcium ionophore A23187 to mouse skin is the appearance of an enzymic activity which will convert arachidonic acid to its 8-hydroxyeicosatetraenoic acid metabolite (8-HETE) (Gschwendt, M., et al (1986) Carcinogenesis 7, 449-455). Induction of this activity is lower in strains of mice with a weak inflammatory response to TPA, and the 8-HETE may be involved in the inflammation or hyperplasia. To further characterize the activity, we first measured the chirality of the product; it is almost exclusively the 8D(S)-hydroxy enantiomer (8S-HETE). The 8(S)-HETE is formed from octadeuterated arachidonic acid with complete retention of deuterium labels, indicating that a keto intermediate is not involved in the biosynthesis. Using arachidonic acids labeled with a prochiral tritium in either the 10D(R) or 10L(S) positions, we found that the biosynthesis of 8S-HETE is associated with the stereoselective abstraction of the 10D(R) hydrogen from the 10-carbon of the substrate. This stereoselective hydrogen removal conforms to the properties of an 8S-lipoxygenase. This is the only lipoxygenase known to catalyze solely 8S-oxygenation of arachidonic acid. The recent characterization of stereoselective biological effects for other HETEs serve as strong precedents to suggest that 8S-HETE has a specific role in the cellular tissue response to TPA.