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Ferumoxytol Attenuates the Function of MDSCs to Ameliorate LPS-Induced Immunosuppression in Sepsis.

ABSTRACT: Sepsis-induced immunosuppression is recognized as one of the main features responsible for therapeutic failures. Myeloid-derived suppressor cells (MDSCs), which are mainly characterized by their suppressive properties, have been reported to be expanded in sepsis. Ferumoxytol (FMT), an FDA-approved iron supplement, has been shown to possess immune-modulatory properties in tumors. However, it is unclear whether FMT alters the functions of MDSCs to reduce late-sepsis immunosuppression. Here, we showed an immunomodulatory effect of FMT on MDSCs to ameliorate lipopolysaccharide (LPS)-induced immunosuppression in the late stage of sepsis. Separation of cells with internalized FMT and detection of the intracellular iron content showed that MDSCs could uptake FMT. Low doses of FMT had no effects on the cell viability of MDSCs, but FMT inhibited the expansion of MDSCs in vitro. Moreover, FMT significantly downregulated the expression levels of Arg-1, S100A8, S100A9, and p47phox as well as ROS production in MDSCs. FMT decreased the percentage of granulocytic MDSCs (G-MDSCs) and promoted the differentiation of MDSCs into macrophages. Furthermore, FMT reduced white blood cell recruitment and alveolar wall thickening in the lungs and areas of necrosis in the liver as well as some biochemical markers of liver dysfunction. FMT decreased the percentage of G-MDSCs and monocytic MDSCs (M-MDSCs) in the spleens of LPS-induced septic mice. Of note, FMT reduced the T cell immunosuppressive functions of both G-MDSCs and M-MDSCs. Expectedly, FMT also significantly reduced Arg-1 and p47phox gene expression in splenic CD11b⁺Gr-1⁺ cells isolated from LPS-challenged mice. These data indicate that FMT decreased the immunosuppressive functions of MDSCs by decreasing Arg-1 and ROS production, suggesting that FMT may reduce long-term immunosuppression in the late stage of sepsis.

SUBMITTER: Xue Y

PROVIDER: S-EPMC6915194 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In patients with active lupus, spontaneous endotoxemia and possibly tolerance to lipopolysaccharide (LPS) is a potentially adverse complication. Similarly, previous reports have demonstrated that FcGRIIb deficient mice (FcGRIIb-/-; a lupus mouse model) are susceptible to LPS tolerance-induced decreased cytokine responses that inadequate for the organismal control. Thus, understanding the relationship between FcGRIIb and LPS tolerance could improve the therapeutic strategy for lupus. LPS tolerance can be induced through sequential LPS stimulations in either cells or a model organism. In RAW264.7 (a mouse macrophage cell-line), sequential LPS stimulation induced the secretion of Lipocalin-2 (Lcn-2) despite reduced cytokine secretion and severe energy depletion, as measured by the extracellular flux analysis, typical of LPS tolerance. In contrast, treatment with recombinant Lcn-2 (rLcn-2) attenuated LPS tolerance, as shown by an increase in secreted cytokines and altered macrophage polarization toward M1 (increased iNOS and TNF-α) in RAW264.7 cells. These results suggest a role of Lcn-2 in LPS tolerance attenuation. In bone marrow derived macrophages, Lcn-2 level was similar in LPS tolerant FcGRIIb-/- and wild-type (WT) cells despite the increased LPS tolerance of FcGRIIb-/- cells, suggesting relatively low basal levels of Lcn-2 produced in FcGRIIb-/- cells. In addition, attenuation of LPS tolerance effectuated by granulocyte-monocyte colony stimulating factor (GM-CSF) reduced Lcn-2 in both cell types, implying an inverse correlation between Lcn-2 and the severity of LPS tolerance. Consequently, rLcn-2 improved LPS tolerance only in FcGRIIb-/- macrophages and attenuated disease severity of cecal ligation and puncture (CLP) sepsis pre-conditioning with sequential LPS injection (LPS-CLP model) only in FcGRIIb-/- mice, but not in WT mice. To summarize, inadequate Lcn-2 production in FcGRIIb-/- macrophage might, at least in part, be responsible for the inordinate LPS tolerance compared with WT cells. Additionally, supplementation of rLcn-2 attenuates LPS tolerance in FcGRIIb-/- macrophages in vitro, and in FcGRIIb-/- mice with LPS-CLP sepsis in vivo. In conclusion, Lcn-2 secreted by macrophages is possibly an autocrine signal to counter the reduced cytokine secretion in LPS tolerance.

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Ferumoxytol Attenuates the Function of MDSCs to Ameliorate LPS-Induced Immunosuppression in Sepsis.

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