s an acute phase MedChemExpress Debio1347 reactant, may be involved in CE-induced apoptosis, probably via the CRP/ROS cascade. HO-1 and/or CORM-2 protect against CE-induced inflammation, ROS production and apoptosis induction We next investigated whether there is any change in HO-1 expression in zebrafish gills or human respiratory epithelial cells following CE exposure and the functional significance of induction of HO-1 by CE. Zebrafish and human epithelial cells were exposed to different concentrations of CE. IHC analysis clearly indicated an increased expression of HO-1 in CE challenged cells. Western blot analysis also confirmed that CE exposure was associated with a marked increase in HO-1 protein level compared to controls. The peak induction concentration was 50 ppm. We further examined evidence for HO activity. As shown in Fig. 5D, the treatment with CE dramatically increased HO enzyme activity, which correlated well with the observed increase in HO-1 protein levels. These data suggest that overexpression of HO-1 may be a crucial defense mechanism in response to an oxidative stress such as CE exposure. As previously reported, we confirmed increased apoptosis in CE exposed epithelial cells. However, pre-treatment with HO-1 inhibitor, ZnPP resulted in a significant increase in apoptosis and in dead cells . We also detected intracellular ROS generation in epithelial cells by measuring DCFDA, an indicator of H2O2, which is a major component of ROS. We found that DCFDA levels were significantly higher at baseline in the absence of CE when compared to ZnPP treatment cells with and without DCFDA treated cells. CE exposure induced more ROS production and adherens junctional proteins. Cell lysates from BEAS-2B cells were analyzed by western blotting with anti-ZO-1, ZO-2 and Occludin and E-cadherin and FAK antibodies at different concentration of CE for 4 hours. The densities of protein bands were determined by densitometry and the data represent a fold change from the control density. The data are representative of three independent experiments. Data are shown as a mean SD. p < 0.05, p < 0.01 vs control by a oneway ANOVA with HSD test. doi:10.1371/journal.pone.0122275.g003 and ~20 fold with CE 300 ppm). Importantly, the ROS levels induced by CE markedly increased if HO-1 activity was inhibited using ZnPP, while decreased if cells were pretreated with PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19761586 CORM-2. These data indicate that epithelial cells are more susceptible to CE-induced oxidant generation and cell apoptosis when HO-1 activity is inhibited and CORM-2 may protect against CE-induced ROS production. To further investigate the role of HO-1 in cellular protection, we evaluated the effect of CE exposure in vivo in HO-1 KO mice. CE-induced acute lung injury was associated with increased inflammation and alveolar-capillary permeability, as measured by BAL cell counts and protein content, respectively. Compared to HO-1 WT mice, HO-1 KO mice had significantly more alterations in permeability, and higher number 
of lymphocytes, neutrophils and eosinophils as well as PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19763404 more protein in their BAL fluid in the presence of CE, which is consistent with an increase in lung inflammation and permeability. More accumulation of 12 / 23 HO-1 Protects against Corexit-Induced Apoptosis Fig 4. Both HO-1 and CORM-2 protect against CE-induced ROS production. BREA-2B cells pretreated with 10 M ZnPP or 10 M CORM-2 were either unlabeled or labeled with 20 M DCFDA for 30 minutes and then cultured for an additional 3 hours with or wi