Data from: Crystalline silica-induced proinflammatory eicosanoid storm in novel alveolar macrophage model quelled by docosahexaenoic acid

Introduction: Workplace exposure to respirable crystalline silica (cSiO₂) is associated with chronic inflammatory and autoimmune diseases. At the mechanistic level, cSiO₂ particles are quickly phagocytosed by resident alveolar macrophages (AMs) in the lung, causing a robust cycle of proinflammatory cytokine release, lysosomal rupture, mitochondrial toxicity, and immunogenic cell death if the particle is not efficiently cleared by the lung. We and others have demonstrated in bone marrow-derived and transformed macrophage models that supplementation with the ω-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) contributes to increased membrane phospholipid content of DHA and subsequent suppression of cSiO₂-triggered inflammatory responses. However, mechanistic exploration of ω-3 PUFA effects in AMs is challenging due to reliance on short-lived primary AMs derived from lung lavage fluid.

Methods: To address these limitations, we have employed a recently developed novel self-renewing AM model from C57BL/6 mice, fetal liver-derived alveolar-like macrophages (FLAMs), that is phenotypically representative of primary lung AM populations. We found that incubation of FLAMs with 25 µM  DHA as ethanolic suspensions or as complexes with bovine serum albumin were equally effective at increasing ω-3 PUFA content of phospholipids at the expense of the ω-6 PUFA arachidonic acid (ARA) and the ω-9 monounsaturated fatty acid oleic acid. Based on these findings, FLAMs were treated with 25 µM DHA in EtOH or EtOH vehicle (VEH) for 24 h, with or without LPS for 2 h, and with or without cSiO₂ for 1.5 or 4 h then proinflammatory cytokine release, lysosomal membrane permeabilization, and mitochondrial depolarization assessed. In addition, oxylipin metabolites were measured using a targeted LC-MS lipidomics panel of 156 metabolites.

Results: Regardless of whether FLAMs were LPS-primed, cSiO₂-triggered lysosomal permeability, mitochondrial toxicity, and cell death were not impacted by DHA. LPS+cSiO₂ elicited marked IL-1α, IL-1β, and TNF-α release after 1.5 and 4 h of cSiO₂ exposure, which was significantly inhibited by DHA. In VEH-treated cells, cSiO₂ alone and LPS+cSiO2 induced synthesis of ARA-derived proinflammatory oxylipins including prostaglandins, leukotrienes, and thromboxanes that was suppressed by DHA. In addition, DHA promoted synthesis of pro-resolving DHA-derived oxylipins at the expense of ARA-derived oxylipins.

Discussion:  FLAMs were amenable to lipidome modulation by DHA, which suppressed cSiO₂-triggered proinflammatory cytokine responses and ARA-derived oxylipins that potentially contribute to the particle's toxicity in the lung. FLAMs are a promising in vitro alternative to primary AMs for investigating interventions against toxicant-triggered inflammation and autoimmunity in the lung.