Comparison of injectable iron complexes in their ability to iron load tissues and to induce oxidative stress

Abstract

Iron and copper homeostasis have been studied in various tissues after iron-loading with the polynuclear ferric hydroxide carbohydrate complexes, iron dextran, iron polymaltose, iron sucrose and iron gluconate for four weeks. There were significant increases in the iron content of the different rat tissues compared to controls, with the exception of the brain, which showed no change in its iron content following iron loading. However, the level of iron loading in the different tissues varied according to the preparation administered and only iron dextran was able to significantly increase the iron content of both broncho-alveolar macrophages and heart. The hepatic copper content decreased with iron loading, although this did not reach significance. However the copper content did not alter in the iron loaded broncho-alveolar macrophages. Despite such increases in hepatic iron content, there was little evidence of changes in oxidative stress, the activities of cytosolic (apart from iron dextran) or mitochondrial hepatic superoxide dismutase, SOD, were similar to that of the control rats, confirming the fact that the low reduction potential of these compounds prevents the reduction of the ferric moiety. It was not necessary for macrophages to significantly increase their iron content to initiate changes in NO^. release. Iron gluconate and iron sucrose increased NO^. release, while iron polymaltose and iron dextran decreased NO^. release although only the latter iron preparation significantly increased their iron content. It may be that the speciation of iron within the macrophage is an important determinant in changes in NO^. release after ex vivo stimulation. We conclude that tissues loaded with iron by such polynuclear iron complexes have variable loading despite the comparable iron dose. However, there was little evidence for participation of the accumulated iron in free radical reactions although there was some evidence for alteration in immune function of broncho-alveolar macrophages.