Increased concentration of ferrous iron in the gastrointestinal tract increases the number of various pathogens and induces inflammation. LPS and/or high-fat diet-associated metaflammation is mediated through a quaternary receptor signaling complex containing iron-regulated pathway, IL-6/STAT inflammatory signaling pathway, hepcidin regulatory pathway, and common TLR4/NF-κB signaling pathway. We, therefore, investigated whether bifidobacteria directly or indirectly ameliorate LPS- and/or high-fat diet-associated metaflammation by reduction of intestinal iron concentration and/or the above-mentioned pathways. MATERIAL & METHODS We used a triple co-culture model of HT-29/B6, HMDM and HepG2 cells with apically added Bifidobacterium pseudolongum (DSMZ 20099), in the absence or presence of iron, LPS or oleate. Expressions of the biomarkers of interest were determined after 24 h incubation by TaqMan qRT-PCR, cell-based ELISA or Western blot. RESULTS Bifidobacteria inhibited LPS- and oleate-induced protein expression of inflammatory cytokines (IL-6, TNF-α) concomitantly with decreases in cellular TG and iron concentration. Exposure of co-cultured cells to bifidobacteria blocked NF-kB activity through inhibition of IκBα, p38 MAPK, and phosphorylation of NF-kB 65 subunit. TaqMan qRT-PCR and Western blot analysis revealed that bifidobacteria downregulated mRNA and protein expression of BMP6, DMT1, hepcidin, l-ferritin, ferroportin, IL-6, TfR1, Stat3, and TLR4 following exposure to excessive extracellular LPS, oleate and iron. However, the patterns of TLR2 mRNA and protein expression were quite the opposite of those of TLR4. CONCLUSION Commensal bifidobacteria ameliorate metaflammation/inflammatory responses to excessive extracellular LPS, oleate and iron through at least two molecular/signaling mechanisms: i. modulation of interactions of the hepcidin- and iron-signaling pathways via reduction of excess iron; ii. reduction of pro-inflammatory cytokines and hepcidin production through inhibition of the TLR4/NF-kB pathway. This may be a molecular basis by which commensal bifidobacteria enhance intrinsic cellular tolerance against excess consumption of energy-yielding substrates and/or free iron.

中文翻译：

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共生双歧杆菌对铁调素/铁信号通路相互作用的调节在抑制与炎症相关的生物标志物中起重要作用。

胃肠道中亚铁的浓度增加会增加各种病原体的数量并诱发炎症。LPS和/或高脂饮食相关的发炎通过包含铁调节途径，IL-6 / STAT炎性信号传导途径，铁调素调节途径和常见TLR4 /NF-κB信号传导途径的四级受体信号传导复合物介导。因此，我们研究了双歧杆菌是否通过降低肠铁浓度和/或上述途径来直接或间接改善与LPS和/或高脂饮食相关的发炎。材料与方法我们在没有铁，LPS或油酸盐的情况下，使用HT-29 / B6，HMDM和HepG2细胞与顶端添加的假双歧杆菌（DSMZ 20099）的三重共培养模型。通过TaqMan qRT-PCR，基于细胞的ELISA或Western blot孵育24小时后，即可确定目标生物标志物的表达。结果双歧杆菌可抑制LPS和油酸酯诱导的炎症细胞因子（IL-6，TNF-α）的蛋白表达，同时降低细胞的TG和铁浓度。共培养细胞暴露于双歧杆菌通过抑制IκBα，p38 MAPK和NF-kB 65亚基的磷酸化来阻断NF-kB活性。TaqMan qRT-PCR和Western blot分析表明，暴露于过量的细胞外LPS，油酸和铁后，双歧杆菌下调了BMP6，DMT1，hepcidin，l-铁蛋白，铁转运蛋白，IL-6，TfR1，Stat3和TLR4的mRNA和蛋白质表达。但是，TLR2 mRNA和蛋白质表达的模式与TLR4相反。结论共生双歧杆菌通过至少两种分子/信号传导机制改善了对过量细胞外脂多糖，油酸盐和铁的发炎/炎症反应：通过减少过量铁来调节铁调素和铁信号通路的相互作用；ii。通过抑制TLR4 / NF-kB途径减少促炎性细胞因子和铁调素的产生。这可能是共生双歧杆菌增强内在的细胞耐受性的分子基础，该耐受性是针对过量消耗能量的底物和/或游离铁的。通过抑制TLR4 / NF-kB途径减少促炎性细胞因子和铁调素的产生。这可能是共生双歧杆菌增强内在的细胞耐受性的分子基础，该耐受性是针对过量消耗能量的底物和/或游离铁的。通过抑制TLR4 / NF-kB途径减少促炎性细胞因子和铁调素的产生。这可能是共生双歧杆菌增强内在的细胞耐受性的分子基础，该耐受性是针对过量消耗能量的底物和/或游离铁的。