In vascular endothelium, Nitric oxide (NO) is produced by a constitutively expressed enzyme known as endothelial nitric oxide synthase (eNOS), which converts L-arginine to L-citrulline. A great amount of evidences implicate NO plays an important role in controlling vascular tone and modulating blood flow to organs . Interestingly, experimental evidences suggest that NO is involved in the pathogenesis of insulin resistance and diabetes. eNOS activity and the production of NO are chronically impaired in type 2 diabetes. Decreased eNOS activity has been observed in both aortic endothelium and cardiac tissue of fructose-treated rats, and furthermore exogenous insulin therapy appears to improve endothelial function in patients with type 2 diabetes. Our previous data indicated that fructose intake induced increased blood pressure, insulin resistance and downregulation of eNOS expression, and eNOS overexpression significantly decreased fructose-induced hypertension and insulin resistance in rats. Taken together, these data suggest that insulin resistance and diabetes are characterized partly by endothelial dysfunction and potentially by altered eNOS expression and NO production.
It is well known that cytochrome P450 (CYP) epoxygenases metabolized arachidonic acid into four different cis-epoxyeicosatrienoic acids (EETs): 5,6-, 8,9-, 11,12-, and 14,15-EET. Human P450 2J2 (CYP2J2) and its rat homolog CYP2J3 are predominant enzymes responsible for the oxidation of endogenous arachidonic acid pools in vascular endothelium, cardiac myocytes, pancreas, and other tissues where they exert regulatory effects in normal and pathophysiological processes.
Accumulating evidence suggests that EETs play crucial and diverse roles in cardiovascular homeostasis. CYP epoxygenases and EETs upregulate eNOS expression and phosphorylation in bovine aortic endothelial cells via activation of Mitogen-activated protein kinase (MAPK), protein kinase C, and phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathways[7, 8]. Our previous study indicated that CYP2J3 overexpression significantly reduced insulin resistance, decreased blood pressure and prevented eNOS downregulation induced by fructose intake, and possibly CYP2J3 gene delivery reduced blood pressure through upregulated eNOS expression and downregulated endothelin-1 (ET-1) and endothelin receptor A (ETA) expression. Furthermore, CYP2J3 overexpression significantly improved insulin resistance, at least in part through eNOS, IRS-1, and PI3K/AKT signaling pathways, as well as adenosine monophosphate-activated protein kinase (AMPK) signaling pathways in liver, muscle, heart, and kidney. Interestingly, CYP-derived eicosanoids are vasodilatory, at least in part through their ability to activate eNOS and subsequent NO release, however, whether CYP2J3 overexpression can decrease blood pressure and reduce insulin resistance induced by fructose via eNOS is still not completely clear.
In this study, we hypothesized that overexpression of CYP2J3 and the subsequent increase in production of EETs might attenuate hypertension and insulin resistance via upregulation of eNOS. Thus, the present study investigated the roles of eNOS in CYP2J3 gene delivery reducing blood pressure and improving insulin resistance in fructose-treated rats.