Biosynthetic Crossover of 5-Lipoxygenase and Cyclooxygenase-2 Yields 5-Hydroxy-PGE₂ and 5-Hydroxy-PGD₂

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-PGH₂ that spontaneously rearranges to 5-OH-PGE₂ and 5-OH-PGD₂, the 5-hydroxy analogs of arachidonic acid derived PGE₂ and PGD₂. The endoperoxide was identified via its predicted degradation product, 5,12-dihydroxy-heptadecatri-6E,8E,10E-enoic acid, and by SnCl₂-mediated reduction to 5-OH-PGF_2α. Both 5-OH-PGE₂ and 5-OH-PGD₂ 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 NaBH₄ to yield the corresponding stable 5-OH-PGF₂ diastereomers and enabled detection of 5-OH-PGF_2α in activated primary human leukocytes. 5-OH-PGE₂ and 5-OH-PGD₂ were unable to activate EP and DP prostanoid receptors, suggesting their bioactivity is distinct from PGE₂ and PGD₂.