Hepoxilin B3 and its enzymatically formed derivative trioxilin B3 are incorporated into phospholipids in psoriatic lesions

In previous studies we observed that normal human epidermis forms 12-oxo-eicosatetraenoic acid (12-oxo-ETE) and hepoxilin B-3 (HxB(3)) as major eicosanoids, both being elevated in psoriasis. We also observed that normal epidermis, in a reaction probably catalyzed by 12-lipoxygenase, only synthesize one of the two possible 10-hydroxy epimers of HxB(3). We have now extended these previous studies investigating further transformation of HxB(3) into trioxilin B-3 (TrXB3) and esterification of both into phospholipids. Phospholipids were extracted from normal epidermis and from psoriatic scales. A combination of high performance liquid chromatography and gas chromatography-mass spectrometry analysis demonstrated the occurrence of HxB(3) and TrXB3 in the phospholipids of psoriatic lesions. Alkaline- and phospholipase-A(2)-mediated hydrolysis of the phospholipids yielded similar quantities of both HxB(3) and TrXB3 indicating their preference for the sn-2 position of glycerophospholipids. The thin layer chromatography analysis of the phospholipid classes after incubation of epidermal cells with [C-14]-labeled HxB(3), TrXB3, 12-hydroxy-eicosatetraenoic acid (12-HETE), 12-oxo-ETE, or 15-HETE showed that 12-HETE was the most esterified (12-HETE > 15-HETE > TrXB3 > 12-oxo-ETE > HxB(3)). HxB(3) and TrXB3 were mainly esterified in phosphatidyl-choline and phosphatidyl-ethanolamine. HxB(3) was also enzymatically converted into TrXB3 in vitro. HxB(3) epoxide hydrolase-like activity was not observed when boiled tissue was incubated with [C-14]-HxB(3), this activity being located in the cytosol fraction (100,000 x g supernatant) of fresh tissue. These findings suggest that in vivo some part of HxB(3) is transformed into TrXB3 and both compounds are partially incorporated into the phospholipids.