Macrophage-mediated endothelial inflammatory responses to airborne particulates: Impact of particulate physicochemical properties

Epidemiological studies have implicated a role for airborne particulates of <2.5 mum diameter in the development/exacerbation of chronic cardiopulmonary disease; however, specific pathogenic mechanisms and the etiological significance of particle physicochemical properties remain unresolved. Using a microporous aluminosilicate zeolite Y as a manifold, we have synthesized 1 mum particulates of pure carbon (C), carbon- iron (C/Fe), and carbon- iron/fluoro-aluminum silicate (C-Fe/F-Al-Si). We have used these particulates, as well as coal fly ash (CFA) and diesel exhaust particulates (DEP), to test the hypotheses that human macrophages treated with particulates elaborate proinflammatory cytokines in quantities sufficient to induce endothelial adhesion molecule expression and that macrophage responses to particulate exposure vary as a function of particulate physicochemical properties. Human monocyte-derived macrophages (Mphi) were exposed for 24 h to sublethal concentrations of particulates, at which time phagocytosis was evident from optical microscopy. Human arterial, microvascular, or venous endothelial cells (EC) were treated with clarified supernatants recovered from Mphi cultures, stained with fluorescein-conjugated mononclonal antibodies specific for endothelial adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, or E-selectin, and assayed by fluorescence flow cytometry. Data generated by these experiments demonstrate that while supernatants of Mphi exposed to CFA and C particulates are relatively ineffective, supernatants from DEP, C/Fe, or C-Fe/F-Al-Si strongly induced adhesion molecule expression on EC, responses which were completely attenuated by antibody with blocking specificity for tumor necrosis factor alpha. Because the only difference between C and C/Fe particulates is the presence of surface iron on C/Fe, these findings suggest particulate induced oxidative stress as a contributing factor in Mphi activation and implicate redox active iron as a major determinant of particulate bioreactivity.