Nontargeted lipidomics reveals blood biomarkers of acute and chronic docosahexaenoic acid (DHA) feeding in rats

Abstract: Contradictory results regarding the dietary intake of omega-3 PUFA and associated health benefits are not uncommon in the literature. Blood total fatty acid measurements by GC-FID or GC-MS are useful in monitoring compliance/adherence, but structural information about the parent species structures (e.g., intact glycerophospholipids) is often lost due to sample processing. In this study, Sprague-Dawley rats (n = 4/group) were placed on one of three groups: (1) a Total Western Diet (control group, TWD-) for nine weeks, (2) Total Western Diet with DHA (TWD+) for nine weeks (chronic DHA group), and (3) TWD- for nine weeks followed by 5 days on TWD+ (acute DHA group). Whole blood samples were collected and stored for analysis. Lipids were extracted using chloroform/methanol in the presence of isotopically-labeled internal standards. Nontargeted lipidomics was performed using a Waters Acuity UPLC system with a Waters Synapt G2Si QToF mass spectrometer. Data were acquired using a polarity-switching method with top-5 data-dependent acquisition. Notably, the three groups (acute, chronic, control) had distinct global lipidomes as evident from tight clusters which were formed in a PCA scores plot. We identified 6 markers of general DHA intake, including species such as PC 18:1_22:6 which was significantly higher in the acute and chronic groups as compared with control. Additionally, 13 lipids were identified as markers of chronic DHA intake, including species such as PE P-18:0_22:6 which was significantly higher in the chronic group as compared with both acute and control groups. Finally, 9 markers of acute intake were identified, with significantly different values than in the control and chronic groups but that fell in between (i.e., suggesting a transition from control towards chronic levels). These findings highlight the potential of lipidomic investigations in furthering our understanding of the relationship between diet and blood levels of omega-3 polyunsaturated fatty acids.