Do EPA-derived pro-resolving mediators help resolve inflammation, and does a low EPA/high AA:EPA ratio indicate a more pro-inflammatory balance?

The balance between pro-inflammatory lipid mediators and those that actively resolve inflammation is a critical determinant of chronic systemic inflammation and associated cardiovascular risk.

Mechanistic pathways of resolution

• Enzymatic synthesis: Eicosapentaenoic acid (EPA) is metabolized via a transcellular pathway involving endothelial cyclooxygenase-2 (COX-2)—an activity enhanced by aspirin acetylation—and leukocyte 5-lipoxygenase (5-LOX) to generate E-series specialized pro-resolving mediators (SPMs), including RvE1, RvE2, and RvE3.
• Receptor activation: RvE1 acts as a direct agonist for the G-protein coupled receptor ChemR23 on macrophages and dendritic cells, promoting non-phlogistic efferocytosis and upregulation of the anti-inflammatory cytokine IL-10.
• Leukocyte regulation: By binding to ChemR23 and antagonizing the pro-inflammatory leukotriene B4 receptor (BLT1) on neutrophils, E-series resolvins restrict neutrophil recruitment and transendothelial migration, shifting macrophages toward a tissue-restorative phenotype.

Clinical evidence and lipid balance

• Substrate competition: Arachidonic acid (AA) and EPA compete for the same enzymatic pathways. A high AA/EPA ratio (averaging 10:1 to 15:1 in Western diets compared to 1.5:1 to 3:1 in high-marine-intake cohorts) reflects a shift toward pro-inflammatory eicosanoid production.
• Inflammatory biomarkers: Higher AA/EPA ratios consistently correlate with elevated markers of systemic inflammation, including high-sensitivity C-reactive protein (hs-CRP) ($r \approx 0.18$), interleukin-6 (IL-6), and GlycA.
• Synergistic risk: Clinical evidence, including data from the Hisayama Study, demonstrates that the cardiovascular risk of a low EPA/AA ratio is compounded when paired with elevated baseline hs-CRP ($\ge 1.0$ mg/L).

Bottom line

• A high AA/EPA ratio signifies a systemic, pro-inflammatory lipid mediator imbalance that correlates with elevated hs-CRP and blunts the active, ChemR23-mediated cellular resolution pathways necessary to control chronic inflammation.