Respiratory sensitizer hexamethylene diisocyanate inhibits SOD 1 and induces ERK-dependent detoxifying and maturation pathways in dendritic-like cells

• Published in: Free radical biology & medicine 2014-07, Vol.72, p.238-246
• Main Authors: Silva, Ana, Nunes, Carla, Martins, João, Dinis, Teresa C.P., Lopes, Celeste, Neves, Bruno, Cruz, Teresa
• Format: Article
• Language: English
• Subjects: Air Pollutants - toxicity; Blotting, Western; Cell Line; Dendritic Cells - drug effects; Dendritic Cells - metabolism; ERK; Free radicals; Gene Expression - drug effects; Humans; Isocyanates - toxicity; MAP Kinase Signaling System - drug effects; MDR1; Membrane Potential, Mitochondrial; Mitochondria; Real-Time Polymerase Chain Reaction; Respiratory allergy; Respiratory Hypersensitivity - metabolism; Reverse Transcriptase Polymerase Chain Reaction; ROS; SOD; Superoxide Dismutase - metabolism; Superoxide Dismutase-1; THP-1 dendritic cells
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2014.04.005

Respiratory allergy to low-molecular-weight chemicals is a current concern in the context of occupational health, and a certified method to identify respiratory allergens is still under investigation. The aim of this work was to unveil some of the poorly understood initial molecular events and toxicity pathways underlying respiratory sensitization, which might be crucial to disclosing the key building blocks of new testing strategies and may contribute to the development of a valid in vitro method for the identification of respiratory allergens. Immortalized human dendritic cell (DC)-like THP-1 cells were exposed to the respiratory allergen hexamethylene diisocyanate (HDI) for 6h, and the activation of several signaling pathways was analyzed. Mitochondrial membrane potential (MMP) alterations, superoxide anion (O2−) production, and gene expression modulation in HDI-treated cells were also evaluated. According to our results, HDI induces O2− increase (P < 0.001) through enzymatic inhibition of cytoplasmic superoxide dismutase 1 (P < 0.05), which might reduce MMP, further leading to mitochondrial O2− production. Increased O2− levels promote ERK phosphorylation (approx sixfold compared to control; P < 0.001) and downstream transcriptional increase of several genes: HMOX1 (P < 0.05), involved in the protection of chemical reactive species; MDR1 (P < 0.01), responsible for the efflux of xenobiotics in the cell; and CD83 (P < 0.05), a DC maturation marker. These results raise new perspectives on the action of respiratory allergens in DCs and point out key molecular events that are crucial for the development of the so-called adverse outcome pathways, particularly regarding O2− increase through enzymatic inhibition, and important for ERK activation. Furthermore, our results highlight the role of ERK signaling, but not p38 MAPK, in the activation of vital mechanisms in cells exposed to a respiratory allergen, such as cell detoxification, migration, and maturation. Proposed mechanism of HDI-induced DC response. HDI is internalized by DC, possibly coupled to albumin. Intracellularly, HDI might interact directly with cytoplasmic SOD 1, leading to a conformational alteration of the protein and its further inactivity. This would result in increased cytoplasmic O2-, which might account for MMP reduction and consequent increase in mitochondrial O2- level. The accumulation of O2- then activate ERK thus inducing the expression of HMOX1, MDR1 and CD83 genes. DC – dendritic