Abstract Body (Do not enter title and authors here): Background: Atherosclerosis is a chronic inflammatory disease driven by the defective resolution of inflammation. Alterations in monocyte/macrophage subtypes in the atherosclerotic plaque, particularly a shift towards inflammatory subtypes, contribute to chronic inflammation and the progression of atherosclerosis. Previous studies have documented a protective effect of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplementation on atherosclerosis, but the specific impact of specialized pro-resolving lipid mediators (SPMs) derived from EPA and DHA on modulating monocyte populations remains unclear.
Hypothesis: We tested the hypothesis that EPA/DHA supplementation would alter the monocyte landscape toward a pro-resolving phenotype in LDL receptor knockout (Ldlr^-/-) atheroprone mice, and that this effect would be blunted by the deletion of the 15-lipoxygenase gene (15Lox), which is responsible for the synthesis of most SPMs.
Methods: Ldlr^-/-/15Lox^+/+ single knockout (SKO, n=48) and Ldlr^-/-/15Lox^-/- double knockout (DKO, n=48) male and female mice were randomized to four diet groups (n=12/group): 1) low-fat diet (LFD, 4% fat and 0.02% cholesterol); 2) LFD + 1% EPA/DHA (w/w); 3) high-fat diet (HFD, 20% fat and 0.2% cholesterol); and 4) HFD + 1% EPA/DHA (w/w). The diet interventions lasted for 16 weeks. At the end of the study, mice were euthanized, fresh splenocytes were harvested, and flow cytometry was performed using the markers CD11b, Ly6G, and Ly6C to profile pro-inflammatory and pro-resolution monocytes.
Results: EPA/DHA supplementation did not affect the spleen monocyte landscape in either SKO or DKO mice fed the LFD. However, in SKO mice fed the HFD, the proportion of pro-inflammatory monocytes (CD11b⁺Ly6C^hi) was significantly lower in the EPA/DHA supplementation group (19±6% versus 12±7%, mean±SD, p=0.03), with a trend toward higher resolving monocytes (CD11b⁺Ly6C^low, 80±6% versus 87±7%; p=0.12). Strikingly, EPA/DHA supplementation did not significantly change pro-inflammatory monocytes (14±5% versus 13±6%, p=0.84) or resolving monocytes (85±5% versus 86±6%, p=0.95) in DKO mice fed the HFD.
Conclusions: Our results suggest that EPA/DHA supplementation exerts immune modulatory effects that are dependent on the expression of 15Lox. Ongoing work is focused on assessing the impact of these effects on atherosclerosis plaque burden.