Incorporation of Marine Lipids into Mitochondrial Membranes Increases Susceptibility to Damage by Calcium and Reactive Oxygen Species: Evidence for Enhanced Activation of Phospholipase A2in Mitochondria Enriched with n - 3 Fatty Acids

Experiments were designed to evaluate the susceptibility of mitochondrial membranes enriched with n-3 fatty acids to damage by Ca2+and reactive oxygen species. Fatty acid content and respiratory function were assessed in renal cortical mitochondria isolated from fish-oil- and beef-tallow-fed rats. Dietary fish oils were readily incorporated into mitochondrial membranes. After exposure to Ca2+and reactive oxygen species, mitochondria enriched in n-3 fatty acids, and using pyruvate and malate as substrates, had significantly greater changes in state 3 and uncoupled respirations, when compared with mitochondria from rats fed beef tallow. Mitochondrial site 1 (NADH coenzyme Q reductase) activity was reduced to 45 and 85% of control values in fish-oil- and beef-tallow-fed groups, respectively. Exposure to Ca2+and reactive oxygen species enhanced the release of polyunsaturated fatty acids enriched at the sn-2 position of phospholipids from mitochondria of fish-oil-fed rats when compared with similarly treated mitochondria of beef-tallow-fed rats. This release of fatty acids was partially inhibited by dibucaine, the phospholipase A2inhibitor, which we have previously shown to protect mitochondria against damage associated with Ca2+and reactive oxygen species. The results indicate that phospholipase A2is activated in mitochondria exposed to Ca2+and reactive oxygen species and is responsible, at least in part, for the impairment of respiratory function. Phospholipase A2activity and mitochondrial damage are enhanced when mitochondrial membranes are enriched with n-3 fatty acids.