Assessing and influencing the fractional contribution of erythrocyte-bound 59Fe to individual 59Fe tissue content in murine 59Fe distribution studies

59Fe-distribution in conditional ferritin-H-deleted mice

The objective was to explore how ferritin-H deletion influences (59)Fe-distribution and excretion-kinetics in mice. Kinetics of (59)Fe-release from organs, whole-body excretion, and distribution-kinetics of intravenously injected (59)Fe trace amounts were compared in iron-deficient and iron-replete mice with (Fth(Δ/Δ)) and without (Fth(lox/lox)) conditional Mx-Cre-induced ferritin-H deletion. (59)Fe was released from spleen and liver beginning on day 2 and day 5 after ferritin-H deletion, respectively, but was not excreted from the body. Plasma-(59)Fe was cleared significantly faster in iron-deficient Fth(Δ/Δ)-mice than in iron-adequate Fth(lox/lox)-controls. (59)Fe-distribution showed a transient peak (e.g., in heart, kidney, muscle) in Fth(lox/lox) control mice, but not in ferritin-H-deleted Fth(Δ/Δ) mice 24 hours after (59)Fe injection. (59)Fe uptake into the liver and spleen was significantly lower in iron-deficient Fth(Δ/Δ) than in Fth(lox/lox) mice 24 hours and 7 days after injection, respectively, and rapidly appeared in circulating erythrocytes instead. The rate of (59)Fe release after ferritin-H deletion supports earlier data on ferritin turnover in mammals; released (59)Fe is not excreted from the body. Instead, (59)Fe is channeled into erythropoiesis and circulating erythrocytes significantly more extensively and faster. Along with a lack of transient interim (59)Fe storage (e.g., in the heart and kidney), this finding is evidence for ferritin-related iron storage-capacity affecting rate and extent of iron utilization.

Iron absorption and distribution in TNF(DeltaARE/+) mice, a model of chronic inflammation

Hemizygous TNF(DeltaARE/+) mice are a murine model for chronic inflammation. We utilized these animals to study iron-kinetics and corresponding protein expression in an iron-deficient and iron-adequate setting. (59)Fe-absorption was determined in ligated duodenal loops in vivo. Whole body distribution of i.v. injected (59)Fe was analysed, and the organ specific expression of ferroportin, transferrin receptor-1, hepcidin and duodenal DMT-1 was quantified by real-time PCR and Western blotting. Duodenal (59)Fe-lumen-to-body transport was not affected by the genotype. Duodenal (59)Fe-retention was increased in TNF(DeltaARE/+) mice, suggesting higher (59)Fe-losses with defoliated enterocytes. Iron-deficiency increased duodenal (59)Fe-lumen-to-body transport, and higher duodenal (59)Fe-tissue retention went along with higher duodenal DMT-1, ferroportin, and liver hepcidin expression. TNF(DeltaARE/+) mice significantly increase their (59)Fe-content in inflamed joints and ilea, and correspondingly reduce splenic (59)Fe-content. Leukocyte infiltrations in the joints suggest a substantial shift of iron-loaded RES cells to inflamed tissues as the underlying mechanism. This finding was paralleled by increased non-haem iron content in joints and reduced haemoglobin and haematocrit concentrations in TNF(DeltaARE/+) mice. In conclusion, erythropoiesis in inflamed TNF(DeltaARE/+) mice could be iron-limited due to losses with exfoliated iron-loaded enterocytes and/or to increased iron-retention in RES cells that shift from the spleen to inflamed tissues.