Effects of Select PM-Associated Metals on Alveolar Macrophage Phosphorylated ERK1 and -2 and iNOS Expression During Ongoing Alteration in Iron Homeostasis

Abstract

It was hypothesized that relative mass relationships among select constituent metals and iron (Fe³⁺) govern the pulmonary immunotoxic potential of any PM_2.5 sample, as these determine the extent to which Fe³⁺ binding by transferrin is affected (resulting in altered alveolar macrophage [AM] Fe status and subsequent antibacterial function). Iron response protein (IRP) binding activity is a useful indirect measurement of changes in Fe status, as reductions in cell Fe levels lead to increases in IRP binding. However, AM IRP activity can be affected by an increased presence of nitric oxide generated by inducible nitric oxide synthase (iNOS). This study sought to determine if any changes in AM IRP activity induced by PM_2.5 constituents V, Mn, or Al were independent from effects of the metals on cell NO formation. NR8383 rat AM were exposed to Fe³⁺ alone or combined with V, Mn, or Al at metal:Fe ratios representative of those in PM_2.5 collected in New York City, Los Angeles, and Seattle during fall 2001. Cells were then assessed for changes in IRP activity and iNOS expression. Phosphorylated extracellular signal-regulated kinase (ERK) 1 and 2 levels were also measured since activated ERKs are involved in signaling pathways that lead to increased iNOS expression. The results indicate that V and Al, and to a lesser extent Mn, altered IRP activity, though the effects were not consistently concentration dependent. Furthermore, while V and Mn treatments did not induce iNOS expression, Al did. These results confirmed our hypothesis that certain metals associated with PM_2.5 might alter the pulmonary immunocompetence of exposed hosts by affecting the Fe status of AM, a major class of deep lung defense cells.

This study was supported by funds from the USEPA/PM Center Grant R82735101. The authors are also grateful to services/assistance provided, in part, by the Center Program in the NYU Department of Environmental Medicine that is supported by NIEHS (grant ES00260). The authors also acknowledge the support provided from the U.S. EPA/PM Center Grant R82735501 at the Northwest Center for Particulate Matter and Health in Seattle, WA, and by U.S. EPA grants R82735201 and CR8280260-01-0 at the Southern California Particle Center and Supersite in Los Angeles.

Notes

This study was supported by funds from the USEPA/PM Center Grant R82735101. The authors are also grateful to services/assistance provided, in part, by the Center Program in the NYU Department of Environmental Medicine that is supported by NIEHS (grant ES00260). The authors also acknowledge the support provided from the U.S. EPA/PM Center Grant R82735501 at the Northwest Center for Particulate Matter and Health in Seattle, WA, and by U.S. EPA grants R82735201 and CR8280260-01-0 at the Southern California Particle Center and Supersite in Los Angeles.