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

Abstract

Background: Surface-available iron (Fe) is proposed to contribute to asbestos-induced toxicity through the production of reactive oxygen species.Objective: Our goal was to evaluate the hypothesis that rat models of cardiovascular disease with coexistent Fe overload would be increasingly sensitive to Libby amphibole (LA)-induced subchronic lung injury.Methods: Male healthy Wistar Kyoto (WKY), spontaneously hypertensive (SH), and SH heart failure (SHHF) rats were intratracheally instilled with 0.0, 0.25, or 1.0 mg LA (with saline as the vehicle). We examined bronchoalveolar lavage fluid (BALF) and histological lung sections after 1 week, 1 month, or 3 months for pulmonary biomarkers and pathology. SHHF rats were also assessed at 6 months for pathological changes.Results: All animals developed concentration- and time-dependent interstitial fibrosis. Time-dependent Fe accumulation occurred in LA-laden macrophages in all strains but was exacerbated in SHHF rats. LA-exposed SHHF rats developed atypical hyperplastic lesions of bronchiolar epithelial cell origin at 3 and 6 months. Strain-related baseline differences existed in gene expression at 3 months, with persistent LA effects in WKY but not SH or SHHF rats. LA exposure altered genes for a number of pathways, including inflammation, immune regulation, and cell-cycle control. Cell-cycle control genes were inhibited after LA exposure in SH and SHHF but not WKY rats, whereas tumor suppressor genes were induced only in WKY rats. The inflammatory gene expression also was apparent only in WKY rats.Conclusion: These data show that in Fe-overload conditions, progressive Fe accumulation occurs in fiber-laden macrophages within LA-induced lesions. Fe overload does not appear to contribute to chronic inflammation, and its role in hyperplastic lesion development requires further examination.

Vascular and Thrombogenic Effects of Pulmonary Exposure to Libby Amphibole

“…Furthermore, asbestos in general is known to induce chronic inflammation and oxidative stress within the lung, which may be responsible for chronic changes in prothrombotic markers that were noted in our studies. In a previous study, Shannahan et al (2012) demonstrated that WKY display alterations in pulmonary genes related to inflammation through 3 mo while SH and SHHF remained unchanged due to LA. Data indicate that the chronic pulmonary inflammation seen in the LA-exposed WKY may result in the long-term systemic alterations that are similar to baseline changes in SH and SHHF.…”

“…Analysis of gene array data from our recent study addressing the pulmonary adverse health effects of LA at 3 mo postexposure (Shannahan et al 2012) depicted changes in the transcription of genes related to pathways involving coagulation and the complement system in the Values are mean ± SE (n = 6/group). Asterisk indicates significant difference within strain with respect to saline controls (p < .05); # indicates significant difference from WKY at the same exposure concentration (p < .05).…”

“…To determine possible coagulatory effects in the lung, data from Affymetrix gene arrays from lungs of WKY, SH and SHHF rats exposed to saline or 1 mg LA/rat (n = 6/group) at 3 month time point (Shannahan et al 2012) were used to construct a functional list of genes. Briefly, biotin-labeled cRNA was produced from 15 µg total lung tissue RNA using an Affymetrix IVT-express labeling kit (catalog number 901228).…”

“…Pulmonary tissue gene array data from 3 mo post saline or LA exposure in WKY, SH, and SHHF (Shannahan et al 2012, study 1) were examined for exposure-and strainrelated differences in thrombogenic response. KEGG pathway analysis identified coagulation pathway as one among several inflammogenic pathways to be different at baseline and/or affected by LA exposure.…”

Antioxidant Defenses in the Lung

“…Other air pollutants that induce oxidative stress include PM with variable size and dimensions originating from, for example, industrial sources, diesel exhaust, or asbestos mining, which generate ROS largely due to their contained redox-active transition metal ions (iron, copper, etc.) (Shannahan et al, 2012). In addition to their common exposure to an oxidative environment, lung cells are also continuously subjected to ROS generation as by-product of various enzymatic reactions, including production of O 2 À and H 2 O 2 at complex I and III in the mitochondrial respiratory chain, the major site of cellular O 2 consumption, and by other enzymatic sources within mitochondria, such as p66shc, amine oxidases, a-ketoglutarate dehydrogenase, and pyruvate dehydrogenase (Drose and Brandt, 2012;Lenaz, 2012).…”