The effect of ligands on the uptake of iron by cells in culture

Abstract

Uptake of iron by a mammalian epithelial cell line (CNCM I-221) was shown to be dependent on the nature of the iron complex. Iron uptake was demonstrated by cytochemical staining and determination of redox-reactive iron in cell lysates. Three classes of ligands were investigated: (i) low molecular weight hydrophilic compounds, represented by ethylenediamine-tetraacetic acid (EDTA) and other charged ligands such as adenosine phosphates (ATP, ADP, AMP) and diethylenetriaminepentaacetic acid (DTPA), (2) low-molecular weight lipophilic ligands such as 8-hydroxyquinoline (8-HQ) and (3) a high molecular mass ligand, dextran. Iron complexed to 8-HQ accumulated intracellularly, the uptake rate of iron being 4.16 fmoles cell-1 h-1 of exposure at 37 degrees C or 3.86 fmoles cell-1 h-1 at 4 degrees C. Iron-dextran was endocytosed and retained in phagosomes. The uptake rate of iron following exposure to iron dextrans was found to be 5.6 fmoles cell-1 h-1 of exposure at 37 degrees C. In contrast to iron/8-HQ, uptake of iron dextran by cells was inhibited at 4 degrees C. Iron complexed to low molecular weight hydrophilic ligands was not taken up by cells. Cytotoxicity was measured by reduction of plating efficiency or tritiated thymidine incorporation. These tests showed that toxic effects of added iron were demonstrable only in cells exposed to the complex with 8-HQ.

A Versatile Ditopic Ligand System for Sensitizing the Luminescence of Bimetallic Lanthanide Bio‐Imaging Probes

“…dextran) were taken up by endocytosis and retained in phagosomes whereas the internalization of complexes with low molecular weight ligands, such as 8-hydroxyquinoline, was much faster. [62] A similar trend is observed for lanthanide complexes, with positively charged, low molecular weight, cyclen-based complexes being taken up by the cells by an active mechanism and being preferentially localized in the nucleus of living cells. [28,29,[63][64][65] The microscopy images in these latter reports show the migration of the complexes through the cytoplasm, across the nuclear membrane and into the nucleus, and show substructures within the nucleus.…”

Reduction of Fe(III) Ions Complexed to Physiological Ligands by Lipoyl Dehydrogenase and Other Flavoenzymes in Vitro

“…This conclusion was substantiated in experiments with the strong Fe(II) chelator 1,10-phenanthroline. This ligand binds ferrous ions (contrary to the physiological ligands studied here) in a redox-inactive form (40). Thus, when 1,10-phenanthroline was used as a ligand for Fe(III), a rapid lipoyl dehydrogenase-mediated formation of ferrous 1,10-phenanthroline could be observed, even in the presence of oxygen.…”

“…Furthermore, on mixing of ferric phenanthroline with phosphate buffer, formation of a precipitate has been reported (39), which would affect the 1,10-phenanthroline-based assay for Fe(II) as used here (see below). In contrast to phosphate buffer, imidazole buffer has been reported to strongly diminish the rate of Fe(II) oxidation (40), and thus would likewise influence redox reactions of iron ions. As virtually all buffer agents contain functional groups with the potential to coordinate to iron ions, thereby affecting their redox potential, the concentration of the Tris buffer used here was kept low (10 -100 mM).…”

“…ent on the characteristics of the chelating ligand (12,25,40 (25,40,55,57,73,74). Therefore, kinetic properties of the lipoyl dehydrogenase-mediated Fe(III) reduction and NAD(P)H oxidation can be assessed only in the absence of oxygen (see below).…”

Enhancement of iron toxicity in L929 cells by d-glucose: accelerated(re-)reduction

“…Thus during cold-induced apoptosis in rat hepatocytes a pathogenetically decisive increase in the concentration of cellular chelatable iron during cold incubation was observed and caused cell injury although the production of O # − d and H # O # was even decreased [11]. To further examine and characterize the mechanisms of cell injury elicited by a primary rise in the cellular chelatable iron pool, we experimentally increased the chelatable iron pool of L929 mouse fibroblasts using a membrane-permeable iron(III) complex [12]. Surprisingly, we observed a strong enhancement of iron toxicity by the addition of -glucose to the incubation medium.…”