Molecular circuits of resolution: Formation and actions of resolvins and protectins

The cellular events underlying the resolution of acute inflammation are not known in molecular terms. To identify anti-inflammatory and proresolving circuits, we investigated the temporal and differential changes in self-resolving murine exudates using mass spectrometry-based proteomics and lipidomics. Key resolution components were defined as resolution indices including Ψ_max, the maximal neutrophil numbers that are present during the inflammatory response; T_max, the time when Ψ_max occurs; and the resolution interval (R_i) from T_max to T₅₀ when neutrophil numbers reach half Ψ_max. The onset of resolution was at ∼12 h with proteomic analysis showing both haptoglobin and S100A9 levels were maximal and other exudate proteins were dynamically regulated. Eicosanoids and polyunsaturated fatty acids first appeared within 4 h. Interestingly, the docosahexaenoic acid-derived anti-inflammatory lipid mediator 10,17S-docosatriene was generated during the R_i. Administration of aspirin-triggered lipoxin A ₄ analog, resolvin E1, or 10,17S-docosatriene each either activated and/or accelerated resolution. For example, aspirin-triggered lipoxin A ₄ analog reduced Ψ_max, resolvin E1 decreased both Ψ_max and T_max, whereas 10,17S-docosatriene reduced Ψ_max, T_max, and shortened R_i. Also, aspirin-triggered lipexin A₄ analog markedly inhibited proinflammatory cytokines and chemokines at 4 h (20-50% inhibition), whereas resolvin E1 and 10,17S-docosatriene's inhibitory actions were maximal at 12 h (30-80% inhibition). Moreover, aspirin-triggered lipoxin A₄ analog evoked release of the antiphlogistic cytokine TGF-β. These results characterize the first molecular resolution circuits and their major components activated by specific novel lipid mediators (i.e., resolvin E1 and 10,17S-docosatriene) to promote resolution.