Vitamin C activation of the biosynthesis of epoxyeicosatrienoic acids

Houli Jiang,Samantha Benjamin,Darryl C Zeldin,John R Falck,John C Mcgiff,Kavita Jain,Joan P Graves,James M May,Fiona E Harrison,Bruce D Hammock

doi:10.4236/abb.2012.33029

Abstract

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 peroxygenase 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.

Highlights

Vitamin C (VitC, ascorbic acid) is an antioxidant with implicated antihypertensive, antiinflammatory, antiatherogenic, antiarrhythmic, antiapoptotic and natriuretic functions [1,2,3,4,5,6]
epoxyeicosatrienoic acids (EETs) contributed to vitamin C (VitC)-induced vasodilator responses in rat isolated perfused kidneys
cytochrome P450 (CYP) inhibitors, methylsulphonylpropargyloxyphenyl hexanamide (MSPPOH) and 17-octadecynoic acid (ODYA), lipid hydroperoxides, hydroperoxyeicosatetraenoic acids (HPETEs), d6-20-hydroxyeicosatrienoic acid (20-HETE), d11DHETs, (±)13-hydroperoxy-9Z, 11E-octadecadienoic acid (13-HPODE) and 13S-hydroperoxy-9Z, 11E, 15Z-octadecatrienoic acid (13-HPOTrE), as well as other eicosanoid standards were from Cayman, while deuterated (d8) EETs were from Enzo Life Sciences

Summary

Introduction

Vitamin C (VitC, ascorbic acid) is an antioxidant with implicated antihypertensive, antiinflammatory, antiatherogenic, antiarrhythmic, antiapoptotic and natriuretic functions [1,2,3,4,5,6]. Epoxyeicosatrienoic acids (EETs), cytochrome P450 (CYP) products from arachidonic acid (AA), have potent functions similar to the cardiovascular effects of VitC. EETs are vasodilatory, antiinflammatory and natriuretic lipid mediators [8,9]. They activate K+ channels and are proposed to function as endothelium-derived hyperpolarizing factors (EDHF). EETs exert potent antiinflammatory effects [11]. EETs possess fibrinolytic, angiogenic, analgesic, antiapoptotic and antiatherosclerotic functions. EETs protect the heart from ischemic damage and postischemic electrocardiogram abnormalities [12]

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