Respiratory Epithelial Cells Demonstrate Lactoferrin Receptors That Increase After Metal Exposure

Human airway epithelial cells can increase expression of both lactoferrin and ferritin after exposure to catalytically active metal. These proteins transport and store metal, with coordination sites fully complexed, and therefore can diminish the oxidative stress. The intracellular transport of lactoferrin results in a transfer of complexed metal to ferritin, where it is stored in a less reactive form. This effort to control the injurious properties of metals would be facilitated by lactoferrin receptors (LfRs) on airway epithelial cells. We tested the hypotheses that 1) LfRs exist on respiratory epithelial cells and 2) exposure to both an air pollution particle, which has abundant concentrations of metals, and individual metal salts increase the expression of LfRs. Before exposure to either the particle or metals, incubation of BEAS-2B cells with varying concentrations of 125I-labeled lactoferrin demonstrated lactoferrin binding that was saturable. Measurement of 125I-lactoferrin binding after the inclusion of 100 micrograms/ml of oil fly ash in the incubation medium demonstrated increased binding within 5 min of exposure, which reached a maximal value at 45 min. Inclusion of 1.0 mM deferoxamine in the incubation of BEAS-2B cells with 100 micrograms/ml of oil fly ash decreased lactoferrin binding. Comparable to the particle, exposure of BEAS-2B cells to either 1.0 mM vanadyl sulfate or 1.0 mM iron (III) sulfate, but not to nickel sulfate, for 45 min elevated LfR activity. We conclude that LfRs on respiratory epithelial cells increased after exposure to metal. LfRs could participate in decreasing the oxidative stress presented to the lower respiratory tract by complexing catalytically active metals.