Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 19, 2004
Publication Date: January 1, 2005
Citation: Reeves, P.G., DeMars, L.C.S., Johnson, W.T., Lukaski, H.C. 2005. Dietary copper deficiency reduces iron absorption and duodenal enterocyte hephaestin protein in male and female rats. Journal of Nutrition. 135:92-98. Interpretive Summary: It is important to know the concentration of a mineral nutrient in the diet so we can keep track of how much we consume, and whether it meets the recommended intake. However, we also need to know whether a nutrient is available for absorption. Many factors affect absorption of minerals, and one of the most important ones is the interaction of one mineral with another that might reduce or enhance absorption and utilization. In this study, we used the laboratory rat model to determine whether low intakes of dietary copper influence the absorption and utilization of iron In addition, we wanted to see if the absorption mechanism involved a copper-dependent intestinal transporter of iron called Hephaestin. The concentration of copper in the diet was less than 1 mg/kg diet in one group (deficient copper) and 5 mg/kg (adequate copper) in another; the amount of iron was 35 mg/kg (adequate) in both groups. The diets were fed to both male and female rats. At 4 weeks, radioactive iron was fed to the rats, and the amount of iron retained in the body was determined by whole-body-counting techniques. This procedure allows us to estimate how much iron was absorbed. When dietary copper was low, both male and female rats absorbed only a little more than half as much iron as when copper was adequate. In addition, low dietary copper decreased the amount of Hephaestin protein, suggesting that this might be the reason iron was not absorbed efficiently. Copper deficiency also reduced iron utilization by the rat, which resulted in anemia. This was expressed as low serum iron, low blood hemoglobin, low red cell count, and low hematocrit. This study shows the importance of having adequate intakes of copper when considering the iron status of an individual. Supplemental dietary iron might be less beneficial if copper intakes are not adequate.
Technical Abstract: Dietary copper (Cu) deficiency reduces iron (Fe) in male rats, but whether this occurs in female rats has been questioned. The mechanism for reduced Fe absorption in Cu deficiency is unknown, but may involve the intestinal Cu-dependent ferroxidase Dephaestin (Hp). A 2 x 2 factorial experiment was designed including Cu-deficient (CuD) and Cu-adequate (CuA) male and female rats. Weanling rats of both sexes were randomly divided into two groups each and fed either an AIN-93G diet with low (<0.3 mg/kg; CuD) or adequate Cu (5.0 mg/kg; CuA). After 19 d of feeding diets, rats were fed 1.0 g each of their respective diets labeled with 59**Fe. Retained 59**Fe was monitored by whole body counting for 12 d, then rats were killed and 59**Fe and Fe were measured in various organs. Duodenal enterocytes were isolated for Hp analysis by Western blotting. Signs of Fe deficiency such as low serum Fe and low RBC count were evident in CuD male rats; however, RBC count of CuD female rats was not affected. CuD male rats absorbed only 60% as much Fe as CuA male rats (p<0.001), while CuD female rats absorbed 70% (p<0.001) as much as CuA females, but no difference was found between the sexes. Hp protein was reduced by 50% in CuD rats compared with CuA rats, suggesting that this Cu-dependent ferroxidase is an important connection between Cu deficiency and reduced Fe absorption. The biological half-life (BHL) of 59**Fe in CuD rats was only 40% (p<0.001) of that in CuA rats, suggesting the Fe turnover was faster in CuD rats than CuA rats. Serum, spleen, and kidney Fe were lower (p>0.001) in CuD rats than in CuA rats. Duodenol mucosa and liver Fe were higher (p<0.01) in CuD male rats than CuA rats. Duodenol Fe but not liver Fe was higher in CuD female rats than CuA rats. Liver Fe was much higher (<0.001) overall in females than males. CuD rats had less (p<0.001) total body Fe per unit of body weight than CuA rats. Thus, Cu deficiency reduces Fe absorption in rats, regardless of sex, through reduced expression of duodenal Hp protein. What effects Cu deficiency has on the mechanism of hemoglobin synthesis and blood cell formation remain unanswered.