Effect of Size Fractionation on the Toxicity of Amosite and Libby Amphibole Asbestos

Abstract

Abnormally high incidences of asbestos-related pulmonary disease have been reported in residents of Libby, Montana, because of occupational and environmental exposure to asbestos-contaminated vermiculite. The mechanism by which Libby amphibole (LA) causes pulmonary injury is not known. The purpose of this study is to compare the cellular stress responses induced in primary human airway epithelial cells (HAECs) exposed to a respirable size fraction (≤ 2.5 μm) of Libby amphibole (LA(2.5)) to a similar size fraction of a reference amphibole sample amosite (AM(2.5)). HAEC were exposed to 0, 2.64, 13.2, or 26.4 μg/cm(2) AM(2.5) or LA(2.5) or to equivalent doses of unfractionated amosite (AM) or LA for 2 or 24 h. Comparable messenger RNA transcript levels were observed for interleukin-8, cyclooxygenase-2, and heme oxygenase-1 in HAEC following a 24-h exposure to AM or LA. Conversely, exposure to AM(2.5) resulted in a 4- to 10-fold greater induction in these proinflammatory mediators compared with LA(2.5) after 24 h. Evaluation of the expression of 84 additional genes involved in cellular stress and toxicity responses confirmed a more robust response for AM(2.5) compared with LA(2.5) on an equal mass basis. Differences in total surface area (TSA) by gas adsorption, total particle number, or oxidant generation by the size-fractionated particles did not account for the observed difference in response. In summary, AM(2.5) and LA(2.5) are at least as potent in stimulating production of proinflammatory cytokines as unfractionated AM and LA. Interestingly, AM(2.5) was more potent at inducing a proinflammatory response than LA(2.5). This difference could not be explained by differences in mineral contamination between the two samples, TSA, or oxidant generation by the samples.

The role of iron in Libby amphibole-induced acute lung injury and inflammation

“…BEAS-2B cells were Fe-preloaded during a 4-h pretreatment with 100 μM ferric ammonium citrate (Sigma Aldrich, St. Louis, MO) or media, and then cells were washed and incubated with media or 50 μg LA. The concentrations of LA used are consistent with previous in vitro experimentation of other asbestos samples using BEAS-2B cells (Wang et al, 2006a;Wang et al, 2006b) as well as in vitro studies examining the toxicity of LA (Duncan et al, 2010). In all experiments supernatants and cells were collected 4 h after exposure.…”

“…Because the fiber length in the LA mix used in this study is relatively shorter than other asbestos materials such as amosite and crocidolite, it is likely that over time the intracellular and extracellular processes that control the Fe binding might be different with longer fibers. It has been shown that significant quantities of fibers are internalized by BEAS-2B cells during 24 h incubation with LA collected in 2000 (Duncan et al, 2010). Because the LA sample used in the present study is similar to LA sample of 2000, it is likely that the shorter fiber fractions are readily phagocytosed by alveolar macrophages.…”

“…The fiber itself and the ROS are known to induce an inflammatory cytokine release causing the recruitment of inflammatory neutrophils in an attempt to clear the foreign fiber (Haegens et al, 2005;Haegens et al, 2007). The primary inflammogenic cytokines (IL-8 in humans and MIP-2, a human analog of IL-8, in rats) are known to be induced after asbestos exposure (Hillegass et al, 2010;Duncan et al, 2010).…”

Subchronic Pulmonary Pathology, Iron Overload, and Transcriptional Activity after Libby Amphibole Exposure in Rat Models of Cardiovascular Disease

“…In vitro studies have shown that even epithelial cells can take up relatively short LA fibers (Duncan et al 2010). In the present study, light microscopy examinations with phase contrast revealed the presence of LA fibers within alveolar macrophages at 3 months, suggesting that these fibers are taken up by macrophages and not cleared from the lung within this time frame.…”

Analysis of Tissue Mineral Fiber Content

“…A similar situation has occurred with respect to the vermiculite miners in Libby, Montana, where the vermiculite mineral is contaminated with amphibole fi bers including tremolite, winchite and richterite [ 188 , 189 ]. The latter two are not regulated as asbestos, although studies have shown that size-fractionated Libby amphibole fi bers have dimensional characteristics similar to those of commercial amphibole asbestos fi bers [ 190 ]. There has been concern regarding potential neighborhood exposure to these fi bers at vermiculite exfoliation plants located in various sites around the USA [ 191 ], and we have reported an example of a case of lung cancer and asbestosis related to such an exposure [ 62 ].…”