Sex and dietary ALA and DHA effects on rat heart phospholipase A2 activity mediating fatty acid release and oxylipin formation have cardiovascular implications

Abstract

The ways in which diet and sex influence heart phospholipase A₂ (PLA₂) activities are underexplored, particularly with respect to effects on oxylipin formation. Therefore, male and female Sprague-Dawley rats were provided diets with 1.3 % α-linolenic acid (ALA) or docosahexaenoic acid (DHA) for 6 weeks, and heart homogenates were incubated with inhibitors for secreted (s)PLA₂ (Varespladib) or calcium-independent (i)PLA₂ (methyl arachidonyl fluorophosphonate). Non-esterified polyunsaturated fatty acids (PUFA) and oxylipins were determined by HPLC-MS/MS and data were analyzed using 3-way repeated measures ANOVA. sPLA₂ activity was selective for DHA release and DHA oxylipin formation, and contributed to ∼50 % of arachidonic acid (ARA) release, but only ∼30 % of ARA oxylipin formation. Eicosapentaenoic acid (EPA) release and oxylipin formation was minor but primarily mediated by iPLA₂. iPLA₂ activity was less selective, with activity towards all measured PUFA and oxylipins, with the primary PUFA released depending on diet. For both sPLA₂ and iPLA₂, there was more activity towards DHA and its oxylipins with the DHA diet, and towards ALA and ARA and their oxylipins with the ALA diet. Sex effects on fatty acids and oxylipins differed, as DHA, EPA and ALA release were higher in females, while DGLA and cyclooxygenase-derived ARA oxylipin formation were higher in males. Interestingly, the sex effect on cyclooxygenase ARA oxylipins was attenuated with dietary DHA. These findings provide further rationale for the simultaneous measurement of PUFA and oxylipins since they are not always congruent, and shed new light on diet and sex effects on PLA₂ types in cardiovascular oxylipin biology.