Effects of copper and ceruloplasmin on iron transport in the Caco 2 cell intestinal model

Previous studies have implicated copper proteins, including ceruloplasmin, in intestinal iron transport. Polarized Caco2 cells with tight junctions were used to examine the possibilities that (a) ceruloplasmin promotes iron absorption by enhancing release at the basolateral cell surface and (b) copper deficiency reduces intestinal iron transport. Iron uptake and overall transport were followed for 90 min with 1 μM 59Fe(II) applied to the apical surface of Caco2 cell monolayers. Apotransferrin (38 μM) was in the basolateral chamber. Induction of iron deficiency with desferrioxamine (100 μM; 18 h) markedly increased uptake and overall transport of iron. Uptake increased from about 20% to about 65% of dose, and overall 59Fe transport from <1% to 60% of dose. On the basis of actual iron released into the basal chamber (measured with bathophenanthroline), transport increased 8-fold. Desferrioxamine pretreatment reduced cellular Fe by 55%. The addition of freshly isolated, enzymatically active human ceruloplasmin to the basolateral chamber during absorption had no effect on uptake or transport of iron by the cells. Unexpectedly, pretreatment with three different chelators of copper (18 h), which reduced cellular levels about 40%, more than doubled iron uptake and raised overall transport to 20%. This was so, whether or not cells were also made iron deficient with desferrioxamine. Acute addition of 1 μM Cu(II) to the apical chamber had no significant effect upon iron uptake, retention, or transport in iron deficient or normal cells, in the presence of absence of ascorbate. We conclude that intestinal absorption of Fe(II) is unlikely to depend upon plasma ceruloplasmin, and that cuproproteins involved in this form of iron transport must be binding copper tightly.