Padilla-Carlin, DJ; Schladweiler, MCJ; Kodavanti, UP; Shannahan, JH; Bern, AM; Lowers, HA; Meeker, GP; Gavett, SH
Rationale: An increased incidence of asbestos-related diseases (ARD) in Libby, Montana has prompted toxicological investigations into the potential mechanism(s) of Libby amphibole (LA) asbestos that induce ARD. Asbestos exposure, in general, results in a potent pulmonary inflammatory response which stimulates cell proliferation and fibrosis of the lung. We hypothesized that the F344 rat would demonstrate an increase in mRNA expression of inflammatory cytokines, hemeoxygenase-1 (HO-1), and growth factors in the lung after a single exposure to LA or Amosite (Amo; positive control) asbestos.
Methods: Water elutriation was conducted to prepare a rat respirable fraction of LA and Amo equivalent to airborne particulate matter ≤ 2.5 μm mass median aerodynamic diameter (PM ). Male F344 rats 2.5 (~250 g) were exposed to a single bolus (250 μl) of either saline (SAL), amosite (0.65 mg/rat), or LA (0.65 or 6.5 mg/rat) by intratracheal instillation (n = 6/group). Real-Time Polymerase Chain Reaction (RT-PCR) was used to evaluate the time-course of inflammatory (cytokines and HO-1) and growth factor gene expression in the accessory lung lobe from rats euthanized at 1d, 3d, 7d, 2wk, and 3mo post-exposure.
Results: Interleukin (IL-1) expression was unchanged among the groups at all timepoints, but both the high dose LA and Amo groups exhibited increased tumor necrosis factor-alpha (TNF-α) expression by ~2-fold at 1d when compared to SAL. Interleukin-6 (IL-6) was increased in the high-dose LA and Amo at 1d by ~15 and 25-fold, respectively, and at 7d, both groups were 2-fold higher than SAL. HO-1 expression in the Amo group was increased at 1d and 7d by 7- and 2-fold, respectively, whereas the high-dose LA group exhibited higher mRNA expression at 1d, 7d, and 3mo (2 to 3-fold increase) compared to SAL. The growth factors (platelet-derived growth factor-A polypeptide, connective tissue growth factor, and Pro-Collagen I) were unchanged in the exposed groups with respect to SAL at all timepoints, but transforming growth factor-1 beta (TGF-1β) appeared down-regulated at 3mo in all asbestos-exposed groups.
Conclusions: Amo and LA induced an acute inflammatory cytokine and HO-1 mRNA response (up to 7d) which subsided by 2wk. However, except for down-regulation of TGF-1β at 3mo, growth factor mRNA expression was not changed up to 3mo after exposure. Future studies will examine these inflammatory and growth factor responses to these two types of amphibole fibers using immunohistochemical analysis to evaluate the distribution of inflammation and potential mechanisms of fibrosis. This abstract does not reflect USEPA policy.
