The profiles of actions of
lipoxin A4 (
LXA4) and
lipoxin B4 (
LXB4), two
lipoxygenase-derived
eicosanoids, were examined with human neutrophils. At nanomolar concentrations,
LXA4 and
LXB4 each stimulated the release of [1-14C]
arachidonic acid from esterified sources in neutrophils.
Lipoxin-induced release of [1-14C]
arachidonic acid was both dose- and time-dependent and was comparable to that induced by the chemotactic
peptide f-
met-leu-phe. Time-course studies revealed that
lipoxin A4 and
lipoxin B4 each induced a biphasic release of [1-14C]
arachidonic acid, which was evident within seconds (5-15 sec) in its initial phase and minutes (greater than 30 sec) in the second phase. In contrast, the all-trans isomers of
LXA4 and
LXB4 did not provoke [1-14C]AA release.
Lipoxin-induced release of
arachidonic acid was inhibited by prior treatment of the cells with
pertussis toxin but not by its beta-oligomers, suggesting the involvement of guaninine
nucleotide-binding regulatory
proteins in this event. Dual radiolabeling of neutrophil
phospholipid classes with [1-14C]
arachidonic acid and [3H]
palmitic acid showed that
phosphatidylcholine was a major source of
lipoxin-induced release of [1-14C]
arachidonic acid. They also demonstrated that
lipoxins rapidly stimulate both formation of
phosphatidic acid as well as
phospholipid remodeling. Although both
LXA4 and
LXB4 (10(-8)-10(-6) M) stimulated the release of [1-14C]
arachidonic acid, neither compound evoked its oxygenation by either the 5- or
15-lipoxygenase pathways (including the formation of
LTB4, 20-COOH-
LTB4, 5-
HETE, or 15-
HETE).
LXA4 and
LXB4 (10(-7) M) each stimulated the elevation of cytosolic Ca2+ as monitored with Fura 2-loaded cells, albeit to a lesser extent than equimolar concentrations of FMLP. Neither
lipoxin altered the binding of [3H]
LTB4 to its receptor on neutrophils. In addition, they did not stimulate aggregation or induce adhesion of neutrophils to human endothelial cells. Results indicate that both
LXA4 and
LXB4 stimulate the rapid remodeling of neutrophil
phospholipids to release
arachidonic acid without provoking either aggregation or the formation of
lipoxygenase-derived products within a similar temporal and dose range. Together they indicate that
LXA4 and
LXB4 display selective actions with human neutrophils and suggest that these
eicosanoids possess unique profiles of action which may regulate neutrophil function during
inflammation.