Objective: Previous in vitro studies have suggested that beta-carotene 15,15'-dioxygenase is an iron-dependent enzyme. However, in vivo, it is difficult to alter iron tissue concentration by varying dietary iron because of homeostatic control. On the other hand, an interaction between iron and copper has been shown, i.e., copper-deficiency results in an increase of iron in rat liver. Therefore, we hypothesized that intestinal iron concentration could be increased by copper-deficiency. Our objective was to examine the effects of iron as affected by dietary copper on beta-carotene 15,15'-dioxygenase activity in the small intestine.
Methods: Weanling male Sprague-Dawley rats (40 to 45g) were divided into four dietary groups: two copper-adequate groups (6.0 microg Cu/g diet) and two copper-deficient groups (0.6 microg Cu/g) combined with either normal iron (44 microg Fe/g) or high iron (87 microg Fe/g). Iron and copper concentrations were determined by atomic absorption spectrophotometry and the dioxygenase activity by reverse phase HPLC.
Results: Intestinal copper concentration was significantly reduced (40%) by the consumption of the copper-deficient diets, but intestinal iron was not changed by doubling dietary iron in rats fed either copper-adequate or copper-deficient diets. However, as hypothesized, the two copper-deficient groups exhibited higher intestinal iron concentration (> or =137%, p<0.001) than the copper-adequate controls. In addition, intestinal beta-carotene 15,15'-dioxygenase activity was increased by 27% and 106%, respectively, for copper-deficient rats fed either normal or high iron diets, compared to the respective copper-adequate controls (p<0.01). The dioxygenase activity was not significantly affected by dietary iron in either copper-adequate or copper-deficient groups. Finally, the enzyme activity was positively correlated (r=0.67, p<0.0001) with iron concentration and negatively correlated (r=-0.49, p<0.01) with copper concentration in small intestine.
Conclusions: Intestinal beta-carotene 15,15'-dioxygenase may be an iron-dependent enzyme sensitive to copper status in vivo.