A novel mechanism of ascorbate direct modulation of soluble epoxide hydrolase.

To test the hypothesis that VitC downregulates soluble epoxide hydrolase (sEH, responsible for converting EETs to DHETs) to stabilize tissue EETs, the heart, lung, liver, kidney, and mesenteric arteries isolated from normal rats were incubated with VitC (1000μM) for 72h, and tissue sEH expression, along with EET and DHET profiles were assessed. VitC caused significant reductions in sEH mRNA and protein content in the liver, heart and vessels, but had no effect on renal and pulmonary sEH expression, revealing a tissue-specific regulatory mechanism. The functional consequence of reduced sEH expression was validated by LC/MS/MS-based analysis, indicating that in VitC-treated tissues that displayed downregulation of sEH mRNA and protein expression, total DHETs were significantly lower, accompanied with a greater ratio of EETs/DHETs than those in VitC-untreated groups. Thus, VitC elicits a transcriptional downregulation of sEH in normal liver, heart, and vessels to reduce EET degradation and increase EET bioavailability.