Vitamin D supplementation ameliorates anemia of inflammation by reducing hepcidin levels and inactivating inflammatory signaling pathways.

Background: Anemia of inflammation (AI) is a mild form of anemia. Vitamin D deficiency has been linked to an increased risk of AI. This study aims to investigate the potential molecular mechanisms underlying the protective role of vitamin D in AI.

Methods: HepG2 cells were stimulated with lipopolysaccharide (LPS) to induce an inflammatory model in vitro. Cell counting kit-8 assays were conducted to assess vitamin D's cytotoxicity to HepG2 cells. RT-qPCR analysis was conducted to evaluate hepcidin mRNA levels. A rat AI model was established by subcutaneous injection of complete Freund's adjuvant (CFA). Hematoxylin-eosin staining was performed for synovial histopathological analysis. The concentrations of inflammatory cytokines were determined by ELISA. Western blotting was used to evaluate the protein levels of hepcidin, ferroportin, and markers associated with signaling pathways.

Results: Vitamin D dose-dependently reduced hepcidin expression in LPS-treated HepG2 cells. Vitamin D inactivated NF-κB, JAK2/STAT3, and BMP6/SMAD pathways to reduce hepcidin levels in LPS-treated HepG2 cells. Vitamin D ameliorated CFA-induced synovial injury and inflammatory response in rats. Vitamin D reduced hepcidin expression and improved anemia in CFA-injected rats. Vitamin D inactivated NF-κB, JAK2/STAT3, and BMP6/SMAD pathways in the liver of CFA-injected rats.

Conclusion: Vitamin D supplementation ameliorates experimental AI by downregulating hepcidin expression through NF-κB, JAK2/STAT3, and BMP6/SMAD pathways.