Libby amphibole exposure in rat models of cardiovascular disease [see Supplemental Material, Figure 3 (http:// dx.doi.org/10.1289/ehp.1103990)]. These genes remained unchanged in WKY rats but tended to be inhibited from their already low baseline in SH and SHHF rats after LA exposure. These genes included those for chemokines such as CXCL-14 [chemokine (C-X-C motif) ligand 14] and CCL-5 [chemokine (C-C motif) ligand 5], suggesting that some genes that regulate inflam- matory response to LA tend to be inhibited in SH and SHHF rats but not in WKY rats. Strain differences at baseline and after LA exposure were noted in the genes involved in cell-cycle control (Figure 5). Genes expressed at high levels in the lungs of control SH and SHHF rats, including the gene for matrix metal- loproteinase-9 and some oncogenes, are grouped in cluster 1. These genes appear to be induced in WKY rats after LA but inhibited in SH and SHHF rats. A few cell-cycle control and growth arrest genes are expressed at lower levels at baseline in SH and SHHF rats compared with WKY saline-treated controls (Figure 5, cluster 2). These genes are inhibited in SH and SHHF rats after LA exposure. Finally, tumor suppres- sor and growth receptors genes are induced WKY Saline WKY LA SH Saline SH LA SHHF Saline SHHF LA only in WKY rats 3 months after LA exposure (Figure 5, cluster 3). Discussion Asbestos-associated Fe has been postulated to play a role in the inflammatory process; how- ever, its influence on chronic pathology in humans is unknown. The accumulation of Fe at tumor sites has been shown to be a conse- quence of tumor-associated inflammation and oxidative stress (Kukulj et al. 2010). In contrast, other studies suggest that Fe promotes tumor progression through generation of ROS, lead- ing to cancer through oxidation and damage of DNA (Toyokuni 2011). Recently, we have shown that rat models of CVD-associated Fe overload do not show an exacerbation of acute LA-induced inflammation and furthermore that this acute inflammatory response is reduced by Fe despite its ability to generate ROS in syn- thetic media (Shannahan et al. 2011a, 2011b). Here we show that pulmonary fibrosis pro- gresses to a similar degree in all three rat strains over a 3-month period following LA exposure. Fe accumulation in fiber-laden macrophages was primarily noted in SHHF rats with Fe 1 r e t s u l C Hierarchical clustering within selected KEGG pathways was performed to understand the strain-related directional changes in gene expression belonging to specific processes. As indicated in Figure 4, many genes related to inflammation were induced at baseline in SH rats and to some degree in SHHF rats com- pared with WKY controls. The expression levels of these same genes were increased more read- ily after LA exposure in WKY rats, and to a lesser extent in SHHF rats, but had a tendency to be inhibited in SH rats. Notable examples included genes for nuclear factor κB (NFκB), tumor necrosis factor, and a variety of inter- leukins. Genes expressed at high levels in WKY rats at baseline compared with baseline in SH and SHHF rats are shown in cluster 2 e n i l e LA YKW lin _SSH L_SHA F_aSSHH LF_SHHA _ a Figure 3. Heat map of KEGG pathways showing significant difference in LA-exposed WKY, SH, and SHHF rats and control SH and SHHF rats com- pared with control WKY rats. Black indicates that no genes in the pathway have altered transcrip- tion compared with control (WKY saline). Green indicates that the pathway has too few genes with altered transcription compared with control (WKY saline) to be significant by the Fisher exact test. Red indicates that the pathway contains a suf- ficient number of transcriptionally altered genes to be significant (p ≤ 0.05) by the Fisher exact test. Figure 4. Hierarchical clustering of inflammation genes comparing WKY, SH, and SHHF rats at 3 months after saline or 1.0 mg LA exposure. DEGs related to inflammation were assembled from KEGG pathways 4060, 4062, 4070, 4310, 4510, 4514, 4520, 4620, 4621, and 4670. Clusters 1 and 2 with genes up-regulated in WKY rats exposed to LA were separated [cluster 2 heat map is shown in the Supplemental Materials, Figure 3 (http:// dx.doi.org/10.1289/ehp.1103990)]. Red indicates genes that have high expression values, green indicates genes that have low expression values across all groups, and black indicates median expression. Environmental Health Perspectives • volume 120 | number 1 | January 2012 89