Transepithelial heme-iron transport: effect of heme oxygenase overexpression

Heme iron is found in the diet mainly in the form of hemoglobin and myoglobin. It is known that heme iron (heme-Fe) and inorganic iron are absorbed differently. Intracellularly, heme oxygenase-1 (HO1) participates in the cleavage of the heme ring producing biliverdin, CO and ferrous iron. Iron released from heme becomes part of labile iron pool, and it can be stored in ferritin or released through the basolateral membrane. The mechanism by which heme-Fe is metabolized within cells is not completely understood.

This study focused on the uptake and transport of heme iron and on the role of heme oxygenase-1 on heme iron metabolism.

Caco-2 cells were incubated with different concentrations of heme-Fe. A full-length heme oxygenase-1 cDNA was expressed in Caco-2 cells and intracellular iron and heme-Fe content, heme uptake, heme and iron transport and heme oxygenase-1 immunolocalization were assessed in these cells.

Heme-Fe was bioavailable and induced an intracellular increase in iron, ferritin and HO1 levels and a decrease in DMT1 expression. In cells overexpressing HO1, heme-Fe uptake and transepithelial Fe transport was higher than in controls. Most heme-Fe was metabolized to free iron, most of which was found mainly in the basolateral chamber. However, there is a fraction of heme that is delivered intact to the basolateral side. In a high heme-Fe condition, HO1 is found near the plasma membrane.

These results suggest that heme oxygenase-1 catabolizes most of the heme-Fe and favors iron influx and efflux in intestinal cells.