The Effect of Vitamin D3 on Hepcidin and IL-8 Expression in Monocytes

Abstract

Background: It has been shown that optimal levels of vitamin D3 offer many health benefits and confer resistance to many diseases, notably those related to metabolic syndrome. Vitamin D3 status is of particular relevance in elderly populations wherein deficiency of this vitamin is increasingly being reported. Anaemia is also a common finding with approximately 10 percent of persons older than 65 years of age suffering from mild to moderate anaemia. In about 1/3 of these patients, the type of anaemia observed is anaemia of inflammation (AI) and is linked to the presence of high levels of the iron regulatory peptide hormone hepcidin. Hepcidin is antimicrobial peptide (AMP) structurally similar to other members of this family, in particular the defensins. Hepcidin negatively regulates iron absorption in the intestine and inhibits reticuloendothelial macrophages from releasing recycled iron. During periods of infection and inflammation, hepcidin levels increase due to the action of many cytokines including IL-8. Hepcidin has therefore a dual role in the immune response. It has been demonstrated that in monocytes, vitamin D3 is also able to induce the expression of the AMP cathelicidin due to the presence of a vitamin D3 response element (VDRE) in promoter regions of the cathelicidin ( Camp ) gene. It is however currently unknown whether vitamin D3 also plays a role in the signalling pathway that controls hepcidin expression. Methods: In the present work, we address the possibility that vitamin D3 is able to modulate hepcidin expression by stimulating monocytic THP-1 cells with varying concentrations of vitamin D3, extracting mRNA and ascertaining hepcidin expression by RT-PCR and gel electrophoresis. We also postulate that vitamin D3 stimulation in these cells is able to regulate the expression of IL-8 and use the supernatant from cell culture to explore this hypothesis. Results: The results presented here confirm previous reports that these cells constitutively express hepcidin mRNA and extend these observations by demonstrating that vitamin D3 can indeed modulate hepcidin expression. Modulation was dependent on the concentration of vitamin D3 used with maximal effect at 10 nM under the conditions used. Results also demonstrate that non-stimulated THP-1 supernatants release low levels of IL-8 and treatment with vitamin D3 at all concentrations tested reduced the levels of IL-8. A further observation was that IL-8 levels were very similar after 4 and 20 hours of vitamin D3 treatment, suggesting that the production and secretion of IL-8 happened at relatively early time points. Conclusion : The present work has demonstrated that THP-1 cells when stimulated with higher concentrations of vitamin D3 (10 and 100 nM) decrease their expression of hepcidin mRNA while no change in the housekeeping gene GAPDH was observed. This downregulation of hepcidin mRNA expression may be translated in vivo with increases in serum iron and therefore may be potentially relevant in the treatment of AI/ACD. The present work also confirms previous reports that stimulation with vitamin D3 causes THP-1 cells to decrease the production of the pro-inflammatory cytokine IL-8, suggesting that vitamin D3 insufficiency may play a role in inflammatory disease and may offer new therapeutic options. doi: http://dx.doi.org/10.4021/jh71e