Disruption of iron homeostasis in mesothelial cells after talc pleurodesis

The mechanism for biological effects after exposure to particles is incompletely understood. One postulate proposed to explain biological effects after exposure to particles involves altered iron homeostasis in the host. The fibro-inflammatory properties of mineral oxide particles are exploited therapeutically with the instillation of massive quantities of talc into the pleural space, to provide sclerosis. We tested the postulates that (1) in vitro exposure to talc induces a disruption in iron homeostasis, oxidative stress, and a biological effect, and (2) talc pleurodesis in humans alters iron homeostasis. In vitro exposures of both mesothelial and airway epithelial cells to 100 μg/ml talc significantly increased iron importation and concentrations of the storage protein ferritin. Using dichlorodihydrofluorescein, exposure to talc was associated with a time-dependent and concentration-dependent generation of oxidants in both cell types. The expression of proinflammatory mediators was also increased after in vitro exposures of mesothelial and airway epithelial cells to talc. Relative to control lung tissue, lung tissue from patients treated with sclerodesis demonstrated an accumulation of iron and increased expression of iron-related proteins, including ferritin, the importer divalent metal transport-1 and the exporter ferroportin-1. Talc was also observed to translocate to the parenchyma, and changes in iron homeostasis were focally distributed to sites of retention. We conclude that exposure to talc disrupts iron homeostasis, is associated with oxidative stress, and results in a biological effect (i.e., a fibro-inflammatory response). Talc pleurodesis can function as a model of the human response to mineral oxide particle exposure, albeit a massive one.