Effects of PM2.5 components in the release of amphiregulin by human airway epithelial cells.

Exposure to ambient particulate matter (PM) is responsible for airway inflammation and tissue remodeling. Urban PM(2.5) (aerodynamic diameter <2.5microm) is a complex mixture rich in soots and containing hydrosoluble and organic components. We previously showed that the exposure of airway epithelial cells to PM(2.5) triggers the release of amphiregulin (AR), ligand of the epidermal growth factor receptor (EGFR) involved in proinflammatory and repair responses. The effect of Paris PM(2.5) organic and aqueous fractions in AR expression and secretion was investigated on the bronchial epithelial cell line 16HBE and normal human nasal epithelial (NHNE) cells. Both a macroarray specific for inflammation pathways and RT-PCR showed an AR upregulation in organic extract-treated 16HBE cells. AR release is induced in 16HBE and NHNE cells grown on plastic and exposed to native PM(2.5), organic extract and to a lesser extent washed PM(2.5) (deprived of its hydrosoluble content) and aqueous extract. Furthermore, as assessed by using NHNE cells grown on Transwell inserts, this secretion is polarized toward the basolateral side where the EGFR is expressed. To conclude, both PM(2.5) organic and hydrosoluble components are involved in the expression and secretion of AR; organic compounds exhibiting a strong effect when they are easily bioavailable.

Responses of well-differentiated nasal epithelial cells exposed to particles: role of the epithelium in airway inflammation.

Numerous epidemiological studies support the contention that ambient air pollution particles can adversely affect human health. To explain the acute inflammatory process in airways exposed to particles, a number of in vitro studies have been performed on cells grown submerged on plastic and poorly differentiated, and on cell lines, the physiology of which is somewhat different from that of well-differentiated cells. In order to obtain results using a model system in which epithelial cells are similar to those of the human airway in vivo, apical membranes of well-differentiated human nasal epithelial (HNE) cells cultured in an air-liquid interface (ALI) were exposed for 24 h to diesel exhaust particles (DEP) and Paris urban air particles (PM(2.5)). DEP and PM(2.5) (10-80 microg/cm(2)) stimulated both IL-8 and amphiregulin (ligand of EGFR) secretion exclusively towards the basal compartment. In contrast, there was no IL-1beta secretion and only weak non-reproducible secretion of TNF-alpha. IL-6 and GM-CSF were consistently stimulated towards the apical compartment and only when cells were exposed to PM(2.5). ICAM-1 protein expression on cell surfaces remained low after particle exposure, although it increased after TNF-alpha treatment. Internalization of particles, which is believed to initiate oxidative stress and proinflammatory cytokine expression, was restricted to small nanoparticles (< or =40 nm). Production of reactive oxygen species (ROS) was detected, and DEP were more efficient than PM(2.5). Collectively, our results suggest that airway epithelial cells exposed to particles augment the local inflammatory response in the lung but cannot alone initiate a systemic inflammatory response.

The toxicity of H2O2 on the ionic homeostasis of airway epithelial cells in vitro.

Oxygen species may be formed in the air spaces of the respiratory tract in response to environmental pollution such as particulate matter. The mechanisms and target molecules of these oxidants are still mainly unknown but may involve modifications of the ionic homeostasis in epithelial cells. Cytosolic concentrations of Ca2+ (Fura2) and Na+ (SBFI) and short-circuit current (Isc) were followed in primary cultures of human nasal epithelial cells and in the cell line 16HBE14o- after exposure to H2O2 or *OH (H2O2 + Fe2+). Cells were grown on glass coverslips for ionic imaging or on permeable snapwell inserts for Isc studies. Exposure of the apical as well as the basal side of the cultures to H2O2 or *OH induced a concentration-dependent transient increase in Isc which is due to a transient secretion of Cl-. Cai also increased transiently with approximately the same kinetics. The response was dependent on the release of calcium from intracellular stores. Nai on the contrary increased steadily over more than an hour. When the apical membrane was permeabilized with gramicidin, *OH inhibited the Na+ current (a measure of Na(+)-K(+)-ATPase activity in the baso-lateral membrane). The arrest of the pump was significant after 30 min exposure to oxidant. On the other hand no increase in the apical or baso-lateral sodium conductances could be detected. The progressive arrest of the Na+/K(+)-pump may contribute to the sustained elevation of Nai. This strong modification in the cellular ionic homeostasis may participate in the stress response of the respiratory epithelium through alterations in signal transduction pathways.