THE EFFECT OF PARAOXONASE 1 ON ENDOTHELIAL CELL HYPERPOLARIZATION MEDIATED BY EICOSAPENTAENOIC ACID AND DOCOSAHEXAENOIC ACID DERIVATIVES

Abstract

Objective: It has been claimed that Paraoxonase 1 (PON1), an antiatherogenic high-density lipoprotein (HDL)-associated enzyme, protects against cardiovascular disease (CVD), for which hypertension is a major risk factor. On the other hand, an increasing number of studies associate heightened PON1 activity with increased risk of hypertension and CVD. Our previous findings revealed that 5,6-EET, a cytochrome P450 (CYP)-derived arachidonic acid (AA) metabolite is unstable, transforming into a new derivative, which is a potential endothelium-derived hyperpolarizing factor (EDHF). This derivative mediates calcium influx, leading to endothelial hyperpolarization and vasodilation and has also been shown to be hydrolyzed by PON1. Based on the similarity between the chemical structure of CYP-derived metabolites of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) to those of AA, we hypothesized that the analogous EPA and DHA derivatives could potentially induce endothelial hyperpolarization and elicit vascular dilation. The aim of this study is to explore hyperpolarization of endothelial cells induced by derivatives of EPA and DHA and PON1's role in hypertension via its effect on this process. Design and method: Human umbilical vein endothelial cells pre-incubated with recombinant PON1 (re-PON1) or human PON1-HDL purified from serum of hypertensive and normotensive patients before the experiment. The endothelial hyperpolarization was monitored by measuring calcium influx via confocal microscopy analysis. Results: Confocal microscopy experiments revealed that endothelial cells incubated with re-PON1 exhibited impaired calcium influx as mediated by EPA and DHA derivatives. Further experiments demonstrated that incubation with human PON1-HDL also reduced calcium influx. However, 1-hour incubation with re-PON1 followed by 3-hour incubation without re-PON1 did not interfere with calcium influx mediated by the EPA derivative. Conclusions: This data suggests that specific EPA and DHA derivatives are potential EDHFs, by regulating calcium influx in the endothelium and that PON1 activity interferes with this process. Therefore, PON1 and those derivatives represent novel targets for future treatment for hypertension.