Resolution biology — SPMs (resolvins, protectins, maresins)

This mechanism review synthesizes the biology of specialized pro-resolving mediators (SPMs) — a family of lipid molecules including resolvins, protectins, and maresins — that actively drive the resolution of inflammation rather than simply allowing it to fade. The central paradigm shift, pioneered by Charles Serhan's group at Harvard, is that resolution is a biochemically programmed phase, not a passive default. SPMs are made from omega-3 fatty acids (EPA and DHA) via the same enzymatic machinery (COX and LOX) that initially produces pro-inflammatory eicosanoids — but only when sufficient omega-3 substrate is present in cell membranes. When omega-3 status is low, as is typical in Western diets, this enzymatic class-switch fails, and the system remains locked in pro-inflammatory signaling. This provides a mechanistic explanation for chronic, non-resolving inflammation: the resolution program is substrate-limited. The omega-3 index — percentage of EPA+DHA in red blood cell phospholipids — is a standardized, clinically available test that directly measures this substrate availability, with levels above 8% considered optimal versus the 3–5% typical of Western populations. Direct pharmacological administration of specific resolvins (e.g., Resolvin E1, Resolvin D2) is an active area of translational research, though largely preclinical.

• Resolution of inflammation is an active, biochemically driven process mediated by SPMs (resolvins, protectins, maresins) — not a passive cessation of pro-inflammatory signaling.
• The enzymatic class-switch from pro-inflammatory eicosanoid production (PGE2, LTB4) to resolvin biosynthesis requires sufficient EPA and DHA in cell membranes; inadequate omega-3 substrate prevents this switch and sustains inflammation.
• The omega-3 index (% EPA+DHA in red blood cell phospholipids) is a clinically measurable proxy for SPM biosynthetic capacity, with optimal levels reported as >8% versus the 3–5% observed in most Western populations.
• SPM families map to distinct omega-3 precursors: lipoxins derive from arachidonic acid, E-series resolvins from EPA, and D-series resolvins, protectins, and maresins from DHA.
• Direct SPM administration (Resolvin E1, Resolvin D2) is under preclinical investigation as a pharmacological strategy, representing one of the most active translational areas in inflammation biology.

This is a narrative mechanism review synthesizing foundational and translational research on SPM biology, primarily from the Serhan laboratory at Harvard and associated groups. No original experimental data or clinical trial data are presented; the article integrates preclinical (cell and animal model) findings with biochemical pathway characterization and emerging translational evidence. It functions as a conceptual framework article rather than a primary study, and therefore carries no defined sample size, intervention arm, or follow-up period.

As a mechanism review without original data, the article cannot establish causality between omega-3 index levels and clinical resolution outcomes in human mucosal disease — that link remains inferential. The SPM pharmacology section is explicitly described as mostly preclinical, meaning therapeutic efficacy and safety in humans are unestablished. The review does not address inter-individual variability in SPM biosynthetic enzyme activity (ALOX5, COX-2 polymorphisms), which could confound the substrate-availability model. The critical next experiment is a randomized trial pairing omega-3 index measurement at baseline with mucosal SPM quantification and clinical resolution endpoints in an inflammatory bowel disease or mucosal inflammation cohort.

This review establishes the SPM framework as a unifying resolution biology lens that contextualizes several other articles in the corpus. It parallels [§146], which demonstrates that lithocholic acid-mediated macrophage reprogramming resolves colitis via a distinct lipid-signaling axis — both articles converge on the principle that active biochemical programs, not passive mediator withdrawal, determine inflammatory resolution in the gut. It also parallels [§147], where vitamin D signaling modulates mucosal immune tone, representing another substrate-dependent immunomodulatory system where Western populations are commonly deficient — a structural analogy to the omega-3 substrate-limitation argument central to SPM biology. The framework extends meaningfully to [§120], where Eubacterium rectale modulates glutamine metabolism and NF-κB signaling in IBD, since microbiota-derived metabolic shifts could alter the fatty acid membrane composition that determines SPM biosynthetic capacity. Finally, the review's mechanistic logic provides interpretive scaffolding for [§119], which targets pyroptosis and pro-inflammatory polarization in ulcerative colitis — SPM deficiency would be expected to amplify exactly the sustained innate activation phenotype that pyroptosis-targeting strategies attempt to suppress.

• Intermittent fasting alleviates ulcerative colitis via lithocholic acid-mediated macrophage reprogramming
  Both articles identify active lipid-mediated biochemical programs that resolve rather than merely suppress gut inflammation — comparing them clarifies how bile acid and omega-3 pathways may converge or complement each other at the macrophage level.
• The Role of Vitamin D in Inflammatory Bowel Disease: Clinical Relevance and Therapeutic Potential
  Vitamin D, like omega-3 fatty acids, is a fat-soluble substrate commonly deficient in Western populations that modulates mucosal immune resolution — comparing these articles reveals a pattern of multiple substrate-dependent immunomodulatory systems failing in parallel.
• Eubacterium rectale Mitigates Inflammatory Bowel Disease via Modulation of Glutamine Metabolism Through the GLS2 and NF-κB Pathway
  Eubacterium rectale's modulation of glutamine metabolism and NF-κB in IBD represents a microbiota-driven route to resolution that could interact with SPM biosynthesis through effects on membrane lipid composition and innate cell polarization.
• Emapunil attenuates ulcerative colitis by suppressing Z-DNA binding protein 1 driven pyroptosis and pro-inflammatory polarization in macrophages
  Emapunil targets Z-DNA binding protein 1-driven pyroptosis and pro-inflammatory polarization in ulcerative colitis — the SPM framework predicts that resolution failure (due to omega-3 insufficiency) would amplify this exact sustained innate activation phenotype, making these mechanistically complementary.
• Saccharomyces Boulardii CNCM I-745 on Intestinal Barrier Function
  Saccharomyces boulardii's effects on intestinal barrier function represent a parallel non-lipid route to mucosal protection; comparing with SPM biology highlights whether barrier restoration and active resolution are independent or sequentially coupled processes.