| dc.description.abstract | Eicosanoids, such as prostaglandins, leukotrienes, hydroxy- and epoxy-derivatives of arachidonic acid (AA), are lipid autacoids that regulate constitutive as well as inflammatory processes. Prostaglandins (PGs) and leukotrienes (LTs), two well-characterized families of eicosanoids, are produced through separate pathways downstream of cytosolic phospholipase A2 (cPLA2), and require the enzymatic oxygenation of arachidonic acid (AA) by cyclooxygenase-2 (COX-2) or 5-lipoxygenase (5-LOX), respectively. Our recent discovery that the consecutive oxygenation of AA by 5-LOX and COX-2 leads to the formation of novel bioactive lipid autacoids provides a novel paradigm for investigating possible mechanisms of regulation of inflammation.
The consecutive oxygenation of AA first by 5-LOX to 5S-HETE (a byproduct of leukotriene formation) and then by COX-2 leads to the formation of an unstable diendoperoxide (diEP). The diEP rearranges enzymatically (through hematopoietic prostaglandin D synthase [HPGDS] to the eicosanoid product hemiketal D2 (HKD2). Non-enzymatic rearrangement of the diEP can also occur. The non-enzymatic rearrangement yields a mixture of hemiketal E2 (HKE2) and HKD2. Both HKE2 and HKD2 are newly characterized, biologically active lipid autacoids.
The HKE2 methyl ester recently became available through chemical synthesis. My work involved cleavage of the HKE2 methyl ester to free HKE2. I also examined HKE2 formation and localization in cell culture models, as well as possible receptor targets of HKE2.
Using the synthetic HKE2, my project tested the hypothesis that HKE2 modulates inflammation in settings where HKE2 might be formed, for example (1) in phagocytosis, proliferation, and COX-2/PGE2 levels in stimulated versus unstimulated macrophages, (2) in tubulogenesis of human umbilical vein endothelial cells (HUVECs) and (3) COX-2/PGE2 and chemokine levels in primary human synovial fibroblasts isolated from patients with rheumatoid arthritis.
Experiments designed to test the biological activity of HKE2 using the chemically derived HKE2, yielded insignificant positive results. While the experimental paradigms were designed to reflect physiological events in which one might expect HKE2 to be formed, and thus act, the targets tested are by no means comprehensive. Since the HKE2 is a novel compound, that is produced endogenously, showing its failure to act at a target is still progress in understanding its physiological role. | |
