Cytotoxicity and Induction of Proinflammatory Cytokines from Human Monocytes Exposed to Fine (PM_2.5) and Coarse Particles (PM_10–2.5) in Outdoor and Indoor Air

Abstract

Increased incidence of mortality and morbidity due to cardiopulmonary complications has been found to associate with elevated levels of particulate air pollution (particulate matter with an aerodynamic diameter < 10 μm, PM₁₀and <2.5 μm, PM_2.5). Lung injury and an imbalance of inflammatory mediators are proposed causative mechanisms, while the toxic constituents may be acidity, transition metals, organic, and biogenic materials. To compare the ability of inhalable fine particles (PM_2.5), and coarse particles (PM_10–2.5) to cause cell injury and cytokine production in monocytes, dichotomous Andersen samplers were used to collect size-fractionated PM₁₀forin vitrotesting of the particle extracts. Particles from both outdoor and indoor air were collected onto Teflon filters, on nine separate occasions. Each filter was water extracted and each extract assessed for ability to cause cell death, as well as interleukin (IL)-6 and IL-8 production in human monocytes. Significant toxicity and cytokine production was induced by outdoor PM_10–2.5, but not by outdoor PM_2.5or the particles collected indoors. Outdoor PM_10–2.5induced 20 times the amounts of IL-6 and IL-8 than the fine particles. Cytotoxicity was inhibited by deferoxamine, a chelator of transition metals, while cytokine production was not. On the other hand, lipopolysaccharide binding protein (LBP) completely inhibited cytokine induction by PM_10–2.5, suggesting that gram-negative bacteria and/or endotoxins are components of PM_10–2.5. The effective proinflammatory effects of endotoxin on macrophages may upset lung homeostasis while metals-induced cytotoxicity/necrosis may set up inflammation independent of macrophage-derived cytokines.