Neuroprostanes, Oxygenated Metabolites of DHA, are Responsible for the Anti-arrhythmic Effects of Omega-3 Fatty Acids
Jérôme Roy*, Olivia Touzet-Mercier*, Julien Roussel*, J. Thireau*, M. Shchepinov°, Camille Oger+, Jean-Marie Galano+, Thierry Durand+, Jean-Yves Le Guennec*. * Inserm U1046, Universités Montpellier-1 et Montpellier-2, France, + UMR CNRS 5247, Universités Montpellier-1 et Montpellier-2, ENSCM, France, ° Retrotop Onc. Oxford, UK.

The cardioprotective effects through prevention of cardiac arrhythmias of long-chain polyunsaturated fatty acids of the n-3 series (PUFAs) have been demonstrated over the last 40 years. The main n-3 PUFAs are eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n-3, DHA) and both are highly peroxidable due to the presence of skipped dienes. The effects of n-3 PUFA on cardiac function are still debated, notably because of the lack of information on the mechanisms involved. Particularly, it is not well understood which is the active lipid: the PUFA or one of its oxygenated metabolites. A diet enriched in n-3 PUFAs (mainly fish-based), leads to enrichment in these fatty acids of cardiac cell membranes. Our hypothesis is that, after an infarct, the oxidative stress and the genesis of reactive oxygen species (ROS) cause an oxidation of membrane-bound PUFAs. Thus, the oxygenated metabolites generated could modulate the activity of ionic channels to exert anti-arrhythmic effects. We thus decided to investigate the influence of the peroxidation of EPA and DHA on their potentially anti-arrhythmic properties. In this study, we applied PUFAs free acid on freshly isolated mouse ventricular myocytes bathing in a pro- or antioxidant medium. Thirty sec of electrical stimulation in presence of 10 nM isoproterenol leads to the occurrence of extrasystoles. When PUFAs are applied alone, we observed that the percentage of arrhythmic cells decreases. This anti-arrhythmic effect was not observed when anti-oxidants are used, and conversely, increased in presence of pro-oxidant. The application of 4-(RS)-4F4t-neuroprostanes, a non-enzymatic oxygenated metabolite of DHA, also prevents cellular arrhythmias. Similar experiments were performed on mice having a post-myocardial infarction (PMI) induced by the ligation of the main coronary artery and challenged with norepinephrine. In that situation again, the 4-(RS)-4F4t-NeuroP prevents the occurrence of arrhythmias, mainly ventricular extrasystoles.
These results suggest thus that rather than PUFAs themselves, it is a non-enzymatic oxygenated metabolite that is potentially anti-arrhythmic, the 4-(RS)-4F4t-NeuroP.