Vitamin C activation of the biosynthesis of epoxyeicosatrienoic acids

The cardiovascular effects of vitamin C (VitC) could be mediated by epoxyeicosatrienoic acids (EETs). We aimed to study the mechanism of VitC-dependent microsomal formation of cis- and trans-EETs and the regulation of EET levels in rat isolated perfused kidneys and in vivo. VitC biphasically stimulated rat kidney microsomal cis- and trans-EET formation in a ratio of 1:2, involving the participation of lipid hydroperoxides (LOOHs), Fe2+ , and cytochrome P450 (CYP). Levels of LOOHs correlated with microsomal EET production. LOOH stimulation of CYP isoforms resulted in preferred trans- over cis-EET formation from arachidonic acid and was associated with the cleavage of LOOHs, which indicated a CYP peroxy-genase activity. EETs contributed to VitC-induced vasodilator responses in rat isolated perfused kidneys. VitC (1 mg/ml) given in the drinking water for 9 days doubled rat urinary EET excretion, increased plasma levels of EETs, mostly trans-EETs, by 40%, and reduced plasma levels of 20-hydroxyeicosatetraenoic acid. Depletion of VitC in brain cortex and kidney tissues by more than 20- and 50-fold, respectively, in gulonolactone oxidase-knockout mice was associated with mild increases in tissue EETs. These data suggest that LOOHs are a determinant factor for EET formation in vivo in which VitC exerts a key regulatory effect. VitC-activated CYP peroxygenase activity may represent a CYP interaction with lipoxygenases and cyclooxygenases to mediate the cardiovascular effects of VitC via formation of EETs.

Effects of epoxyeicosatrienoic acids on levels of eNOS phosphorylation and relevant signaling transduction pathways involved

Endothelial nitric oxide synthase (eNOS) is a key enzyme responsible for the regu-lation of vascular homeostasis. Many humor factors and mechanical forces can affect eNOS ac-tivity via phosphorylation modification but the mechanisms involved vary with stimuli applied. We have demonstrated that cytochrome P450 (CYP) epoxygenase-dependent metabolites of ara-chidonic acid, epoxyeicosatrienoic acids (EETs), can robustly up-regulate eNOS expression and its activity, however the relevant signaling pathways responsible for activity regulation are not well known. In this study, we explored the role of PI3 kinase (PI3K)/protein kinase B (Akt) sig-naling pathway in eNOS expression and its phosphorylation in response to EETs via direct addi-tion of EETs into cultured bovine aorta endothelial cells (BAECs) and recombinant adeno- asso-ciated virus-mediated transfection of CYP epoxygenase genes CYPF87V and CYP2C11 to pro-duce endogenous EETs followed by co-treatment with PI3K or Akt inhibitor. Results show that both exogenous and endogenous EETs could remarkably enhance eNOS expression and its phosphorylation at Ser1179 and Thr497 residues; PI3K inhibitor LY294002 could inhibit EETs-induced increase in eNOS-Ser(P)1179 but had no effect on the change of eNOS-Thr(P)497, while Akt inhibitor could attenuate the increase in phosphor-eNOS at both residues; both of the two inhibitors could block EETs-enhanced eNOS expression. These results lead to conclusions: (i) EETs-mediated regulation of eNOS activity may be related with the changes of phosphoryla-tion level at eNOS-Ser1179 via PI3K/Akt and eNOS-Thr497 via Akt; (ii) PI3K/Akt signaling pathway is involved in the up-regulation of eNOS expression by EETs.

P-450-dependent Epoxygenase Pathway of Arachidonic Acid Is Involved in Myeloma-induced Angiogenesis of Endothelial Cells

P-450-dependent epoxygenase pathway of arachidonic acid and the products of epoxyeicosatrienoic acids（EETs） have been demonstrated to be involved in angiogenesis and tumor progression.This study examined the expression of EETs and the role of the pathway in the angiogenesis of multiple myeloma（MM）.MM cell lines of U266 and RPMI8226 were cultured,and the EETs levels（11,12-EET and 14,15-EET） in the supernatant were determined by ELISA.Human umbilical vein endothelial cells（HUVECs） were cultured and used for analysis of the angiogenesis activity of the two MM cell lines,which was examined both in vitro and in vivo by employing MTT,chemotaxis,tube formation and matrigel plug assays.11,12-EET and 14,15-EET were found in the supernatant of the cultured MM cells.The levels of the two EETs in the supernatant of U266 cells were significantly higher than those in the RPMI8226 cell supernatant（P〈0.05）,and the levels paralleled the respective angiogenesis activity of the two different MM cell lines.17-octadecynoic acid（17-ODYA）,as a specific inhibitor of P450 enzyme,suppressed HUVECs proliferation and tube formation induced by MM cells.Furthermore,17-ODYA decreased the EET levels in the supernatant of MM cells.These results suggest that EETs may play an important role in the angiogenesis of MM,and the inhibitor 17-ODYA suppresses this effect.

Endothelium-derived hyperpolarizing factor and diabetes

In addition to its role as a barrier between blood and tissues, the vascular endothelium is responsible for the synthesis and released of a number of vasodilators including prostaglandins, nitric oxide and endotheliumderived hyperpolarizing factor (EDHF). As one of these vasodilators, the specific nature of EDHF has not been fully elucidated, although a number of roles have been proposed. Importantly, many conditions, such as hypertension, hyperlipidemia, heart failure, ischemiareperfusion and diabetes mellitus comprise vascular endothelial dysfunction with EDHF dysregulation. This article reviews reports on the role of EDHF in diabetesrelated endothelial dysfunction.

Increased Soluble Epoxide Hydrolase Activity Positively Correlates with Mortality in Heart Failure Patients with Preserved Ejection Fraction:Evidence from Metabolomics

Epoxyeicosatrienoic acids(EETs)have pleiotropic endogenous cardiovascular protective effects and can be hydrolyzed to the corresponding dihydroxyeicosatrienoic acids by soluble epoxide hydrolase(sEH).Heart failure with preserved ejection fraction(HFpEF)has shown an increased prevalence and worse prognosis over the decades.However,the role of sEH activ-ity in HFpEF remains unclear.We enrolled 500 patients with HFpEF and 500 healthy controls between February 2010 and March 2016.Eight types of sEH-related eicosanoids were measured according to target metabolomics,and their correlation with clinical endpoints was also analyzed.The primary endpoint was cardiac mortality,and the secondary endpoint was a composite of cardiac events,including heart failure(HF)readmission,cardiogenic hospitalization,and all-cause mortal-ity.Furthermore,the effect of sEH inhibitors on cardiac diastolic function in HFpEF was investigated in vivo and in vitro.Patients with HFpEF showed significantly enhanced EET degradation by the sEH enzyme compared with healthy controls.More importantly,sEH activity was positively correlated with cardiac mortality in patients with HFpEF,especially in older patients with arrhythmia.A consistent result was obtained in the multiple adjusted models.Decreased sEH activity by the sEH inhibitor showed a significant effective effect on the improvement of cardiac diastolic function by ameliorating lipid disorders in cardiomyocytes of HFpEF mouse model.This study demonstrated that increased sEH activity was associated with cardiac mortality in patients with HFpEF and suggested that sEH inhibition could be a promising therapeutic strategy to improve diastolic cardiac function.Clinical trial identifier:NCT03461107(https://clini caltr ials.gov).

Site-directed deuteration of dronedarone preserves cytochrome P4502J2 activity and mitigates its cardiac adverse effects in canine arrhythmic hearts

Cytochrome P4502J2(CYP2J2)metabolizes arachidonic acid(AA)to cardioprotective epoxyeicosatrienoic acids(EETs).Dronedarone,an antiarrhythmic drug prescribed for treatment of atrial fibrillation(AF)induces cardiac adverse effects(AEs)with poorly understood mechanisms.We previously demonstrated that dronedarone inactivates CYP2J2 potently and irreversibly,disrupts AA-EET pathway leading to cardiac mitochondrial toxicity rescuable via EET enrichment.In this study,we investigated if mitigation of CYP2J2 inhibition prevents dronedarone-induced cardiac AEs.We first synthesized a deuterated analogue of dronedarone(termed poyendarone)and demonstrated that it neither inactivates CYP2J2,disrupts AA-EETs metabolism nor causes cardiac mitochondrial toxicity in vitro.Our patch-clamp experiments demonstrated that pharmacoelectrophysiology of dronedarone is unaffected by deuteration.Next,we show that dronedarone treatment or CYP2J2 knockdown in spontaneously beating cardiomyocytes indicative of depleted CYP2J2 activity exacerbates beat-to-beat(BTB)variability reflective of proarrhythmic phenotype.In contrast,poyendarone treatment yields significantly lower BTB variability compared to dronedarone in cardiomyocytes indicative of preserved CYP2J2 activity.Importantly,poyendarone and dronedarone display similar antiarrhythmic properties in the canine model of persistent AF,while poyendarone substantially reduces beat-to-beat variability of repolarization duration suggestive of diminished proarrhythmic risk.Our findings prove that deuteration of dronedarone prevents CYP2J2 inactivation and mitigates dronedarone-induced cardiac AEs.