Comparative capacities of the pig colon and duodenum for luminal iron absorption

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Abstract
Iron deficiency is the most common human nutritional disorder in the world. Iron absorptive capacity of the small intestine is known to be much limited and therefore large quantities of iron salts must be used to treat iron deficiency. As a result, significant amounts of iron may reach the large intestine. This study compared the capacities of the small and large intestine to transfer luminal iron to the venous blood in relationship with the expression in epithelial cells of proteins involved in iron absorption using a pig model. Intracaecal injection of iron sulphate corresponding with 2.5 and 5.0 mg elemental iron per kg body mass resulted in modest, transient, but significant (p<0.05) increases in iron concentration in the portal blood plasma. By comparing portal blood plasma iron concentrations following injection in the duodenal and caecal lumen, we calculated that 5 h after injection, iron colonic absorption represented approximately 14% of duodenal absorption. Caecal and proximal colon mucosa accumulated iron to a much lower extent than the duodenal mucosa. Isolated colonocytes were found to express divalent metal transporter (DMT1) and ferritin, but to a lesser extent than the duodenal enterocytes. Ferroportin was highly expressed in colonocytes. In these cells as well as in enterocytes ferroportin was found to be glycosylated. In short term experiments and at a concentration in the range of that measured in the aqueous phases recovered from the large intestine luminal content after iron injection, iron sulphate did not alter colonocyte viability. We concluded that the colonic epithelial cells that express proteins involved in iron absorption are able to transfer luminal iron to the venous blood even if its relative participation in the overall intestinal absorption appears to be modest under our experimental conditions.