Specialized pro-resolving mediators (SPMs)

When the body sustains an injury or infection, it launches inflammation — but equally important, and far less understood, is how that inflammation is switched off. This review covers a family of molecules called specialized pro-resolving mediators (SPMs), which are small lipid-based signals the body manufactures from dietary fats (primarily the omega-3 fatty acids EPA and DHA, and the omega-6 arachidonic acid). Rather than simply suppressing inflammation the way anti-inflammatory drugs do, SPMs actively instruct the immune system to clean up debris, stop sending in more inflammatory cells, and begin tissue repair. The review maps out four distinct SPM families — lipoxins, E-series resolvins, D-series resolvins, protectins, and maresins — each with partially overlapping but biochemically distinct roles. A striking feature is that SPMs appear effective at extraordinarily low concentrations, far below typical drug doses, suggesting they work through high-affinity receptor signaling rather than bulk pharmacology. Most current clinical strategies focus on raising SPM production indirectly by increasing omega-3 intake rather than administering SPMs directly, though early-phase trials with RvE1 in ocular inflammation represent a direct-administration exception. Understanding SPMs reframes chronic inflammatory disease: the problem may not just be too much pro-inflammatory signaling, but too little pro-resolution signaling.

• Four biochemically distinct SPM families have been characterized: lipoxins (from arachidonic acid via LOX enzymes), E-series resolvins (from EPA), D-series resolvins (from DHA), protectins (from DHA), and maresins (from DHA via macrophage-specific enzymatic routes) — each acting through different receptors and effector programs.
• RvE1 (an E-series resolvin) exerts its neutrophil-halting effect by binding the ChemR23 receptor, providing one of the clearest receptor-level mechanistic accounts of SPM action; RvD1 and RvD2 have attracted the most clinical development interest among the D-series.
• SPMs appear active at doses substantially smaller than conventional pharmacological agents, a finding the review flags as an unresolved mechanistic question — likely reflecting unusually high receptor affinity or signal amplification — and maresins are distinguished from other SPM families by their specific capacity to drive M2 macrophage polarization and tissue regeneration rather than primarily

This is a mechanism review article synthesizing the primary literature on SPM biochemistry, receptor pharmacology, and early clinical translation. No original experimental data or patient cohort is reported; the article is structured as a narrative taxonomy covering biosynthetic pathways, receptor targets, and functional roles for each SPM family. Clinical translation evidence is drawn from early-phase human trials, with RvE1 in ocular inflammation cited as the most advanced example of direct SPM administration.

As a narrative mechanism review rather than a systematic review or meta-analysis, the article does not quantitatively pool evidence or formally assess study quality, so the relative strength of support across SPM families is difficult to judge. Key biological gaps acknowledged in the article include incomplete tissue- and time-point-specific SPM production data, unresolved questions about functional redundancy versus specificity among family members, and no mechanistic explanation for the unusually low effective doses. The next clarifying experiments would likely be tissue-resolved lipidomic time-course studies in human disease cohorts and controlled trials directly comparing SPM administration against omega-3 substrate loading. Translational confidence for most SPMs beyond RvE1 remains preclinical.

This review directly extends [§19], which frames resolution as an active programmed process rather than passive decay of inflammation — the SPM families described here constitute the molecular effectors of exactly that active program. It also extends [§23], because the omega-3 index (a validated clinical biomarker of EPA and DHA status) directly quantifies the substrate pool from which E-series and D-series resolvins, protectins, and maresins are biosynthesized, making SPM production capacity measurable in real patients. The efferocytosis-focused work in [§77] runs parallel to this article: maresins and D-series resolvins promote the macrophage clearance behavior (efferocytosis) that [§77] examines in the context of atherosclerotic plaque stability, linking SPM biology to a specific high-stakes clinical phenotype.

• Resolution as an active process
  Provides the conceptual framework — resolution as an active biological process — that this SPM taxonomy mechanistically populates; reading both together links the 'why' of resolution biology to the 'how' at the molecular level.
• The omega-3 index as biomarker
  The omega-3 index article offers a clinically validated tool for measuring the EPA and DHA substrate levels that directly determine a patient's SPM biosynthetic capacity, bridging this mechanistic review to bedside measurement.
• Comprehensive analysis of efferocytosis-related genes in diagnosis and immune infiltration in atherosclerosis: based on bulk and single-cell RNA sequencing data
  Examines efferocytosis — the macrophage-driven debris-clearance behavior that maresins and D-series resolvins specifically promote — in atherosclerosis, providing a disease-specific context for the tissue-regeneration roles described here.