The biosynthetic
crossover of 5-lipoxygenase (5-LOX) and cyclooxygenase-2
(COX-2) enzymatic activities is a productive pathway to convert arachidonic
acid into unique eicosanoids. Here, we show that COX-2 catalysis with
5-LOX derived 5-hydroxy-eicosatetraenoic acid yields the endoperoxide
5-hydroxy-PGH
2
that spontaneously rearranges to 5-OH-PGE
2
and 5-OH-PGD
2
, the 5-hydroxy analogs of arachidonic
acid derived PGE
2
and PGD
2
. The endoperoxide
was identified via its predicted degradation product, 5,12-dihydroxy-heptadecatri-6
E
,8
E
,10
E
-enoic acid, and
by SnCl
2
-mediated reduction to 5-OH-PGF
2α
. Both 5-OH-PGE
2
and 5-OH-PGD
2
were unstable
and degraded rapidly upon treatment with weak base. This instability
hampered detection in biologic samples which was overcome by in situ
reduction using NaBH
4
to yield the corresponding stable
5-OH-PGF
2
diastereomers and enabled detection of 5-OH-PGF
2α
in activated primary human leukocytes. 5-OH-PGE
2
and 5-OH-PGD
2
were unable to activate EP and DP
prostanoid receptors, suggesting their bioactivity is distinct from
PGE
2
and PGD
2
.