Metabolism of iron from (3,5,5-trimethylhexanoyl)ferrocene in rats. A dietary model for severe iron overload

The feeding of diets enriched with (3,5,5-trimethylhexanoyl)ferrocene (TMH-ferrocene) has been shown recently to produce a severe experimental iron overload in rats and has been considered as an adequate animal model for hereditary haemochromatosis in humans. We synthesized three 59Fe-labelled ferrocene compounds with different lipophilic characters (ferrocene, TMH-ferrocene, and 1,1'-bis(3,5,5-trimethylhexanoyl)ferrocene [(TMH)2-ferrocene]) and studied the metabolism of iron from these compounds in comparison with the hydrophilic ferrous sulphate in rats with iron deficiency, and normal and increased iron stores. The bioavailability of iron from TMH-ferrocene (whole body retention, 48% from a 5 mg Fe dose) was twice as high as from ferrocene and six times higher than from (TMH)2-ferrocene and ferrous sulphate. In contrast to the well-known iron salts (ferrous sulphate), the intestinal absorption of TMH-ferrocene iron was independent from the dose (1 or 5 mg Fe) and similar in iron-deficient and iron-loaded rats, indicating that the intestinal absorption of the TMH-ferrocene is not regulated by the body iron stores. After intestinal absorption, TMH-ferrocene iron in the portal blood is transported to the liver independently from transferrin. In contrast to absorbed ferrocene, iron from TMH-ferrocene is almost completely released from the hydrocarbon moiety within the liver. Depending on the body iron stores, TMH-ferrocene iron is then incorporated preferentially into haemoglobin (iron-deficient rats) or added to the iron stores in the liver (iron-loaded rats). A transient storage of the 59Fe-label in fat tissue was observed only from oral ferrocene but not from TMH-ferrocene. Due to the outstandingly high bioavailability of TMH-ferrocene, the chronic feeding of this compound resulted in a fast and progressive iron overload in rats (liver iron: 16.9 mg Fe/g wet weight after 10 weeks of feeding a diet containing 0.5% TMH-ferrocene), and can be regarded as the best characterized and most useful animal model for severe hepatocellular iron overload in humans.