S288: differential recovery of macrophage iron deficiency by oral iron formulations determines cell inflammatory activation in anemic conditions

Background: Recently, exposure of macrophages to free iron has been implicated in sterile inflammation through ROS-dependent cell pro-inflammatory activation. Here we asked whether oral iron formulations administered to correct anemia in iron-deficient individuals alter macrophage plasticity and promote cell inflammatory activation. Aims: To investigate this, we assessed the impact of the most commonly used oral iron salt, iron sulfate (FeSO4), and an innovative oral iron formulation, sucrosomial iron (SI), on macrophage inflammatory response in conditions of iron deficiency anemia (IDA). FeSO4 is absorbed via the canonical DMT1/FPN inorganic iron pathway, and generates higher levels of free non-transferrin-bound iron (NTBI) to which macrophages can be exposed, leading to cell iron accumulation. By contrast, SI is - at least in part - absorbed intact through para/trans-cellular intestinal routes and, once in the circulation, is likely internalized by reticulo-endothelial macrophages, which recycle iron from the sucrosomial matrix to support erythropoiesis. Methods: We analyzed the iron status and inflammatory response of hepatic and splenic macrophages in iron-deficient anemic wild-type mice daily treated with SI or FeSO4 for 2 weeks to correct their anemia. Results: Iron-deficient mice treated with SI showed an efficient but slightly slower recovery of anemia as monitored by blood parameters (e.g. Hb, RBC, HCT), compared to FeSO4-treated ones. The gradual anemia recovery by SI likely reflects the additional macrophage-dependent processing needed to recycle iron from the intact SI shell, which is not required following FeSO4 absorption. Indeed, the quick absorption of FeSO4 triggered higher levels of Tf saturation and NTBI than SI. As a result, FeSO4 corrected intracellular iron deficiency in macrophages more rapidly than SI, as indicated by a more pronounced TfR1 suppression and bigger labile iron pool. This induced higher ROS levels and increased apoptosis in macrophages from FeSO4-treated compared to SI-treated mice. Importantly, the faster cell iron deficiency recovery was associated with TNFa, IL1b and IL-6 release in hepatic macrophages from FeSO4-treated mice, which remained almost negligible in cells from SI-treated animals. In vivo findings were fully recapitulated in vitro in iron-deficient bone marrow-derived macrophages (BMDM). FeSO4 corrected BMDM iron status faster than SI, as suggested by a quick rise in labile iron pool and suppression of TfR1 after 2h treatment. By contrast, SI showed a slower and progressive ability to improve cell iron deficiency, modulating LIP and TfR1 after 5h of treatment, in agreement with a longer recycling process of iron from the sucrester shell. While FeSO4 exposure caused a massive increase in ROS levels and a significant elevation of inflammatory cytokines, SI minimally affected ROS and inflammation in BMDMs. Interestingly, metabolome data suggest that iron sulfate but not SI suppressed lipid metabolism in macrophages, indicating a reduced fatty acid b-oxidation and limited reliance on mitochondrial metabolism in iron sulfate-treated macrophages, hallmark of pro-inflammatory cell rewiring. Summary/Conclusion: Our data indicate that the gradual cell iron deficiency correction by SI likely exerts a protective effect in macrophages against iron-mediated inflammatory activation by limiting ROS formation. Overall, these studies show that SI is a superior oral iron formulation than iron salts in terms of reduced pro-oxidant and inflammatory action, with relevance for IDA treatment in individuals with pre-existing inflammatory conditions. Keywords: Iron deficiency anemia