Iron uptake and toxicity in Caco-2 cells

The differences between the in vitro effects of iron attributed to valence, chelation, and complexation are known in terms of markers of oxidative stress. Few studies, however, describe the effects of iron on general markers of toxicity used in the testing of cell cultures. The aim of the present study was to determine the toxicity and uptake of different salts and iron complexes in the human intestinal cell line, Caco-2.Cells were incubated with 1.5 mM of different species of iron FeCl₃/nitrilotriacetic acid (NTA) (1:2), FeCl₃/citric acid (1:2), FeCl₃ and FeSO₄] for 22–24 h. Thereafter, toxicological and uptake experiments were performed.The iron uptake, viability (via MTT assay), and membrane stability (via LDH release) of Caco-2 cells incubated with various iron forms differed significantly from untreated controls which showed no detrimental effects on cells and less iron uptake. The lowest signal for cell viability (MTT assay) was found after the incubation of the cells with FeCl₃/citric acid, being significantly different to treatment with FeCl₃, where the highest MTT signal was detected (p=0.002). No differences between the tested iron species could be found regarding cell proliferation (via serial cell counting) and viability using the trypan blue exclusion test. The lowest membrane damage (via LDH release) was registered in cells treated with FeCl₃/citric acid (1:2), whereas the highest LDH release could be found in cells incubated with FeCl₃/NTA (1:2). The highest intracellular iron concentration (measured via GFAAS) was detected after the treatment of Caco-2 cells with FeCl₃ and FeCl₃/NTA (1:2).This study substantiates the importance of the choice of complexes, as NTA seemed to enhance the toxicity of iron, while citric acid inhibited iron uptake and toxicity.