Alpha linolenic acid decreases apoptosis and oxidized phospholipids in cardiomyocytes during ischemia/reperfusion.

Key Findings:

An important mediator of ischemic damage is oxygen derived free radicals (ODFR). Membrane phospholipids are a target for oxidation by ODFR resulting in the generation of novel bioactive oxidized phospholipids (OxPL). Since phosphatidylcholine (PC) is the major phospholipid component of biological membranes, the best described group of OxPL is the oxidized phosphatidylcholines (OxPC) several of which have pro-inflammatory properties. The objective of the present study was to determine the potential of ALA to induce a cardioprotective role in cardiomyocytes during ischemia (ISCH) and IR injury, and to determine the mechanism for this cardioprotective effect. The data demonstrate, for the first time, a direct protective effect of ALA on cardiomyocytes undergoing ISCH and/or IR challenge. This appears to be through an inhibition of apoptosis induced by ISCH and IR. Mechanistically, this cardioprotective effect of ALA is achieved through an inhibition of DNA fragmentation in apoptosis. Changes in resting intracellular Ca2 may have participated in the antiapoptotic cardioprotective action of ALA during ISCH and IR challenge.  In summary, pre-treatment of cardiomyocytes with ALA and the resultant incorporation of ALA into the phospholipid pool mitigated the apoptotic stress response within cardiomyocytes. These data add to a body of evidence supporting an important cardioprotective role of the omega-3 fatty acid ALA in cardiovascular disease. The data suggest that the long-term delivery of ALA (directly or via dietary supplementation) prior to myocardial ISCH and IR challenge represents a therapeutic treatment strategy. The present data suggest that the capacity of ALA to inhibit the generation of OxPL in ISCH and IR specifically through an inhibition of POVPC- and PGPC-induced apoptotic cell death in isolated cardiomyocytes may be an important cardioprotective mechanism.

 Abstract

The omega-3 fatty acid, alpha linolenic acid (ALA) found in plant-derived foods induces significant cardiovascular benefits when ingested. ALA may be cardioprotective during ischemia; however, the mechanism(s) responsible for this effect is unknown. Isolated adult rat cardiomyocytes were exposed to medium containing ALA for 24 h and then exposed to non-ischemic (control), simulated ischemia (ISCH), or simulated ischemia/reperfusion (IR) conditions. Cardiomyocyte phospholipids were extracted and analyzed by an HPLC/electrospray ionization tandem mass spectrometry system. Pre-treatment of cells with ALA resulted in a significant incorporation of ALA within cardiomyocyte phosphatidylcholine. Cell death, DNA fragmentation and caspase-3 activity increased during ischemia and ischemia/reperfusion. Two pro-apoptotic oxidized phosphatidylcholine (OxPC) species, 1-palmitoyl-2-(5′-oxo-valeroyl)-sn-glycero-3-phosphocholine (POVPC), and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) were significantly increased during both ischemia and ischemia/reperfusion. Pre-treatment of the cells with ALA resulted in a significant reduction in cell death during ischemia and ischemia/reperfusion challenge. Apoptosis was also inhibited during ischemia and ischemia/reperfusion as shown by reduced DNA fragmentation and decreased caspase activation. ALA pre-treatment significantly decreased the production of POVPC and PGPC during ischemia and ischemia/reperfusion. ALA pre-treatment also significantly increased in resting Ca²⁺ during ischemia or ischemia/reperfusion but did not improve Ca²⁺ transients. ALA protects the cardiomyocyte from apoptotic cell death during simulated ISCH and IR by inhibiting the production of specific pro-apoptotic OxPC species. OxPCs represent a viable interventional target to protect the heart during ischemic challenge.