Epoxide hydrolases are involved in the metabolism of 5(6)-epoxyeicosatrienoic acid.

Epoxyeicosatrienoic acids (EETs) have garnered extensive research interest as crucial signaling mediators that regulate key biological processes, including inflammation, pain and angiogenesis. While the metabolism of 8(9)-, 11(12)-, and 14(15)-EET has been well established to be metabolized in the presence of epoxide hydrolases, primarily soluble epoxide hydrolase (sEH) and microsomal epoxide hydrolase (mEH), the fate of 5(6)-EET was previously thought to be limited to its spontaneous chemical conversion into 5,6-dihydroxyeicosatrienoic acid (5,6-DHET) lactone. Here, we reported that the metabolism of 5(6)-EET is also enzymatically regulated by both sEH and mEH, occurring in parallel with its chemical formation to 5,6-DHET lactone. Specifically, in an epoxide hydrolases-free system, 5(6)-EET was rapidly converted to 5,6-DHET lactone, whereas 14(15)-EET remained relatively stable. In contrast, in a cellular system, EPHX2 (encodes sEH) knockout and EPHX1 (encodes mEH) knockout significantly attenuated 5(6)-EET degradation, indicating that both sEH and mEH actively mediate the metabolism of 5(6)-EET. Moreover, we observed that 5(6)-EET underwent conversion to 5,6-DHET lactone within the cellular environment as well. This study provides direct evidence that enzymatic metabolism of 5(6)-EET by epoxide hydrolases occurs concurrently with its spontaneous chemical transformation. This study expands our understanding of 5(6)-EET metabolism and reveals a previously unrecognized role of epoxide hydrolases in modulating relevant biological fate.