Delayed hepcidin response explains the lag period in iron absorption following a stimulus to increase erythropoiesis.

INTRODUCTION: The delay of several days between an erythropoietic stimulus and the subsequent increase in intestinal iron absorption is commonly believed to represent the time required for body signals to programme the immature crypt enterocytes and for these cells to migrate to the villus. Recent data however suggest that signals from the body to alter absorption are mediated by circulating hepcidin and that this peptide exerts its effect on mature villus enterocytes. METHODS: We have examined the delay in the absorptive response following stimulated erythropoiesis using phenylhydrazine induced haemolysis and correlated this with expression of hepcidin in the liver and iron transporters in the duodenum. RESULTS: There was a delay of four days following haemolysis before a significant increase in iron absorption was observed. Hepatic hepcidin expression did not decrease until day 3, reaching almost undetectable levels by days 4 and 5. This coincided with the increase in duodenal expression of divalent metal transporter 1, duodenal cytochrome b, and Ireg1. CONCLUSION: These results suggest that the delayed increase in iron absorption following stimulated erythropoiesis is attributable to a lag in the hepcidin response rather than crypt programming, and are consistent with a direct effect of the hepcidin pathway on mature villus enterocytes.

Changes in the expression of intestinal iron transport and hepatic regulatory molecules explain the enhanced iron absorption associated with pregnancy in the rat.

BACKGROUND: Iron absorption increases during pregnancy to cater for the increased iron requirements of the growing fetus. AIMS: To investigate the role of the duodenal iron transport molecules and hepatic regulatory molecules in coordinating the changes in iron absorption observed during pregnancy. METHODS: Rats at various days of gestation and 24-48 hours post-partum were examined for hepatic expression of hepcidin, transferrin receptors 1 and 2, and HFE (the gene mutated in the most prevalent form of hereditary haemochromatosis), and duodenal expression of divalent metal transporter 1 (DMT1), duodenal cytochrome b (Dcytb), iron regulated mRNA (Ireg1), and hephaestin (Hp) by ribonuclease protection assay, western blotting, and immunohistochemistry. RESULTS: Decreased hepatic non-haem iron and transferrin saturation and increased expression of transferrin receptor 1 in the liver indicated a progressive reduction in maternal body iron stores during pregnancy. Duodenal expression of the iron transport molecules DMT1, Dcytb, and Ireg1 increased during pregnancy, and this corresponded with a reduction in hepcidin, HFE, and transferrin receptor 2 expression in the liver. Expression of all molecules returned towards control values by 24-48 hours post-partum. CONCLUSIONS: These data indicate that increased expression of key iron transport molecules is responsible for the elevated iron absorption associated with pregnancy, and implicate hepcidin, HFE, and transferrin receptor 2 in determining how the maternal iron homeostatic machinery responds to the increased iron demands accompanying gestation.

Relationship between intestinal iron-transporter expression, hepatic hepcidin levels and the control of iron absorption.

Hepcidin is an anti-microbial peptide predicted to be involved in the regulation of intestinal iron absorption. We have examined the relationship between the expression of hepcidin in the liver and the expression of the iron-transport molecules divalent-metal transporter 1, duodenal cytochrome b, hephaestin and Ireg1 in the duodenum of rats switched from an iron-replete to an iron-deficient diet or treated to induce an acute phase response. In each case, elevated hepcidin expression correlated with reduced iron absorption and depressed levels of iron-transport molecules. These data are consistent with hepcidin playing a role as a negative regulator of intestinal iron absorption.