Studies of environmental pollutant acrolein-induced endothelial dysfunction: the role of glutathione and nf-kappab

Environmental pollutant exposure has gained considerable attention as a potential risk factor contributing towards cardiovascular diseases (CVDs). Acrolein is a highly reactive electrophilic aldehyde known for its ubiquitous presence in the atmosphere. It is generated during the burning of organic matter and fuels and gets released into the atmosphere through smoke. Acrolein has been studied in the pathology of various respiratory and neurodegenerative disorders. However, the mechanisms regulating the cardiovascular risk implications of acrolein have not been understood completely. The goal of this project was to investigate acrolein-induced cell injury and endothelial dysfunction. Acrolein, at lower concentrations of 20 and 40 µM, was shown to cause no effect in cellular viability. However, these concentrations of acrolein significantly increased monocyte-endothelial binding through increased expression of monocyte chemotactic protein-1 (MCP-1), E-selectin, and Interleukin (IL)-8. In addition, acrolein also depleted cellular and mitochondrial glutathione (GSH) and increased the levels of reactive oxygen species (ROS) in endothelial cells. Furthermore, acrolein also induced nuclear factor-kappa B (Nf-kB) transcriptional activity, degradation of inhibitor of kappa B (IkB-a), and nuclear translocation of p65 subunit. In contrast, acrolein, at higher concentrations of 80 and 120 µM, was shown to promote EA.hy926 endothelial cell death. In addition, acrolein-incurred cell death at those concentrations was classified to be necrosis, as evidenced by the increased release of lactose dehydrogenase (LDH) and increased staining of DNA-binding propidium iodide (PI). Acrolein also rapidly depleted cellular antioxidant glutathione (GSH) and phase II detoxification enzymes, glutathione-S-transferase (GST) and NAD(P)H Quinone Oxireductase-1 (NQO1), in a dose-dependent manner. To further determine the role of GSH in acrolein-mediated cytotoxicity, we pretreated the cells with buthionine sulfoximine (BSO), an inhibitor for cellular GSH biosynthesis. It was observed that depleted GSH levels significantly potentiated acrolein toxicity. Next, induction of cellular GSH levels, achieved through pre-treatment of EA.hy926 cells with CDDO-Im (1-[2-cyano-3,12 dioxooleana -1,9(11)- dien-28-oyl] imidazolide), was shown to offer cytoprotection against acrolein toxicity. It was also found that the upregulation of GSH by CDDO-Im involved the activation of the Nrf2/ARE signaling and increased expression of the modifier-subunit of ?-glumatylcysteine ligase (GCLM). In conclusion, acrolein at low concentrations induces monocyte-endothelial interactions, a key step in early atherosclerosis, through depletion of intracellular GSH and activation of Nf-kB pathway. Acrolein at high concentrations induces necrosis in endothelial cells, which can enhance the inflammatory response and increase the susceptibility of developing atherosclerosis. Upregulation of GSH can provide protection against acrolein-mediated cell death. The results, taken together, provide evidence for the cardiovascular risk posed by acrolein and the importance of GSH and Nf-kB in acrolein toxicity