Detection of Changes in Alveolar Macrophage Iron Status Induced by Select PM_2.5-Associated Components Using Iron-Response Protein Binding Activity

Abstract

The extent of adverse health effects, including induction/exacerbation of infectious lung disease, arising from entrainment of equivalent amounts (or exposure to a fixed increment) of fine particulate matter (PM_2.5) can vary from region to region or city to city in a region. To begin to explain how differing effects on host resistance might arise after exposure to PM_2.5 from various sites, we hypothesized that select metals (e.g., V, Al, and Mn) in each PM_2.5 caused changes in alveolar macrophage (AM) Fe status that, ultimately, would lead to altered antibacterial function. To test this, iron-response protein (IRP) binding activity in a rat AM cell line was assessed after exposure to Fe alone and in conjunction with V, Mn, and/or Al at ratios of V:Fe, Al:Fe, or Mn:Fe encountered in PM_2.5 samples from New York City, Los Angeles, and Seattle. Results indicated that V and Al each significantly altered IRP activity, though effects were not consistently ratio-(i.e., dose-) dependent; Mn had little impact on activity. We conclude that the reductions in Fe status detected here via the IRP assay arose, in part, from effects on transferrin-mediated Fe^{3 +} delivery to the AM. Ongoing studies using this assay are allowing us to better determine: (1) whether mass (and/or molar) relationships between Fe and V, Al, and/or Mn in any PM_2.5 sample consistently govern the extent of change in AM Fe status; (2) how much any specified PM_2.5 constituent (metal or nonmetal) contributes to the overall disruption of Fe status found induced by an intact parent sample; and (3) whether induced changes in binding activity are relatable to other changes expected to occur in the AM, that is, in IRP-dependent mRNA/levels of ferritin/transferrin receptor and Fe-dependent functions. These studies demonstrate that pollutant-induced effects on lung cell Fe status can be assessed in a reproducible manner using an assay that can be readily performed by investigators who might otherwise have no access to other very costly analytical equipment, such as graphite atomic absorption or x-ray fluorescence spectro(photo)meters.