Caco-2 cells were grown onto trans-well inserts of 0.4 μm pore size for 3 weeks to reach maximum confluency. Cells were subsequently pre-incubated with different concentrations of retinoids (0.01, 0.1, 1.0 and 5.0 μg/mL) for 48 h. Caco-2 monolayers were washed once with PBS and fluorescein isothiocyanate (FITC)-labeled 10 kDA dextran (Sigma–Aldrich, St. Louis, USA) and added to the apical chambers at a final concentration of 0.2 mg/mL. Ethylenediaminetetraacetic acid (EDTA) 0.1 mM was used in parallel as a positive control. Following overnight incubation, media from the basal chambers were collected

and analyzed for FITC-dextran leakage using spectrofluorometric analysis (Biotek, Winooski, USA). Data are provided based on mean values from two independent representative experiments. Based on a paired analysis of LPS-induced responses, statistical significance was determined using a one-way analysis of variance with Tukey’s multi-comparison post-test Ferroptosis activation using OSI-744 solubility dmso Graph Pad Prism 5 software (GraphPad Software, La Jolla, California, USA). In the presence of LPS, ATRA significantly inhibited the LPS-induced release

of pro-inflammatory cytokines such as TNF, IL-6, macrophage inflammatory protein (MIP)-1α and MIP-1β from ivDCs ( Fig. 1); data were consistent across all retinoid concentrations tested (0.01, 0.1, 1.0 and 5.0 μg/mL) and, for clarity, only 1 μg/mL data are shown. Additionally, ATRA and its derivatives significantly stimulated the

production of monocyte chemotactic protein (MCP)-1 and vascular endothelial growth factor (VEGF), and also the anti-inflammatory cytokine IL-10 ( Fig. 1). Although incubation of ivDCs with retinoids affected the LPS-induced release of several other cytokine targets implicated in the inflammatory response, none of these changes were significant ( Supplementary Fig. I). In the absence of LPS, incubation with ATRA and 13-cis-RA each induced increases in GM-CSF, MCP-1 and VEGF from ivDCs, which were significant at the highest doses tested; a similar but non-significant trend being evident for 4-oxo-13-cis-RA ( Fig. 2). There was little or no change in the cytokine response for IL-1α, IL-1 receptor antagonist Chorioepithelioma (IL-1RA), IL-4, and IL-18. Although there was a tendency for the retinoids tested to induce the release of intercellular adhesion molecule-1 (ICAM-1), interferon (IFN)-γ, IL-1β, lymphotoxin-α, matrix metalloproteinase (MMP)-2 and stem cell factor, and to also inhibit the release of IL-10, IL-6, MIP-1α, MIP-1β and TNF, these changes were modest and in all cases not statistically significant ( Supplementary Fig. II). In the presence of LPS, similarly significant increases were seen in the release of MCP-1, eotaxin-1, and VEGF following incubation of ivMACs with each retinoid ( Fig. 3, consistent responses were again evident across all retinoid concentrations and, for clarity, only 1 μg/mL data are shown).