Changes of the Expressions of the Genes Involved in Iron Metabolism by the Iron Chelation Therapy in the Iron Overloaded Mouse Model.

[Introduction and aim] Iron chelation therapy has been applied for iron overload. Desferrioxamine (DFO) must have been the most used iron chelator in the world. DFO has been thought to chelate iron from the liver and reticuloendotherial systems in that iron is accumulated, and accelerate iron excretion from the body. On the other hand, many new molecules involved in iron metabolism have been discovered in these 10 years, and the understanding of the molecular mechanisms of iron metabolism has progressed. However, the changes of the genes involved in iron metabolism in iron chelating therapy have not been fully investigated. Therefore, the aim of this study is to clarify the responses of the body to the iron chelation therapy and the mechanisms of iron removal by iron chelator DFO. We investigated the changes of genes involved in iron metabolism in the important organs, such as the liver and the gastrointestinal tract, at the early stage of iron chelation therapy by treating the iron overloaded mouse with DFO.

[Methods] Iron overloaded mouse model was made by giving iron dextran interperitonealy (the iron-loaded group). DFO was given for the iron overloaded mice regularly by the interperitoneal (The iron-loaded + DFO treated group). The iron chelation by DFO had continued for 4 weeks. Mice without any treatment were participated as the control. After 4 weeks, mice were sacrificed, and the liver, small intestine, heart, and blood were collected from all mice. Total RNA was then purified, and quantitative RT-PCR (qRT-PCR) was performed for genes involved in iron metabolism. The genes investigated in this study were HFE, transferrin receptor 1 (TfR1), transferrin receptor 2 (TfR2), hepcidin-1 (HAMP1), hepcidin-2 (HAMP2), ferroportin 1 (FPN1), divalent metal transporter 1 (DMT1), duodenal cytochrome b (Dcytb), hephasetin and ferritin. Protein isolated from collected organ was applied for western blot.

[Results] There was no significant difference in the physique, the weight of the liver and spleen, hemoglobin, serum iron concentration among all groups of mice. The serum ferritin was remarkably increased in iron-loaded group, and there was no decline of serum ferritin in the iron-loaded + DFO treated group. Although the expressions of HFE, TfR2, HAMP1, HAMP2 in the liver didn’t show significant difference among each of the groups by qRT-PCR, the ferritin mRNA and FPN1 mRNA were decreased significantly in the iron-loaded + DFO treated group compared to the iron-loaded group. In the duodenum, there was no difference in the expressions of DMT1, Dcytb, hephasetin, but the expressions of ferritin mRNA and FPN1 mRNA were significantly decreased in the iron-loaded + DFO treated group.

[Discussion and conclusions] In addition to removal of iron from the organ that iron is accumulated, our data showed that iron chelation therapy had the effect on the expressions of the genes involved in iron metabolism. The decreases of ferritin mRNA at both of the liver and the duodenum might imply that intracellular free iron was chelated by DFO. Concerning the decline of FPN1 mRNA, there might be a possibility that intracellular iron depletion by DFO cause the inhibition of translation of FPN1 mRNA via iron responsive element which exists in 5’-untranslated region of FPN1 mRNA. FPN1 in duodenum functions for iron transfer from the enterocyte to blood, so that the decrease of body iron likely increase the expression of FPN1 in the duodenum because body would like to increase iron uptake from duodenum. However, our result indicated that iron chelation therapy did not upregulate FPN1 mRNA expression. Our data rather showed that FPN1 is downregurated, and this indicated that iron chelation would lead to decreased iron uptake from the duodenum, and this would be preferable effect of DFO in the view of iron chelation therapy for iron overload.