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 8DS)-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 10DR or 10LS positions, we found that the biosynthesis of 8S-
HETE is associated with the stereoselective abstraction of the 10DR
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.