Adaptive responses and apoptosis in endothelial cells exposed to carbon monoxide

Prior studies have shown that exposure to carbon monoxide (CO) will elevate the steady-state concentration of nitric oxide (NO) in several cell types and body organs and that some toxic effects of CO are directed toward endot helial cells. Studies reported in this paper were conducted with bovine pul monary artery endothelial cells exposed to 10 to 100 ppm CO to achieve conc entrations between 11 and 110 nM in air-saturated buffer. Exposure to 11 nM CO increased synthesis of manganous superoxide dismutase and conferred res istance against the lethal effects of 110 nM CO. At concentrations of 88 nM CO or more, exposures for 1 h or longer caused cell death that became appa rent 18 h after the exposure ceased. Caspase-1 was activated in response to CO, and cell death was inhibited by a caspase-1 inhibitor. Alteration of p roteolytic pathways by CO was indicated by the presence of ubiquitin-contai ning intracellular inclusion bodies. Morphological changes and caspase acti vation indicated that cell death was an apoptotic process. Cells exposed to 110 nM CO had higher concentrations of manganous superoxide dismutase and heme oxygenase-1 but no changes in glutathione peroxidase, glucose-6-phosph ate dehydrogenase, thiols, or catalase, Elevated levels of antioxidant enzy mes and apoptosis were inhibited by the nitric oxide synthase inhibitor, S- isopropylisothiourea, and the peroxynitrite scavenger, selenomethionine. Th ese results show that biochemical effects of CO occur at environmentally re levant concentrations, that apoptotic cell death follows exposure to relati vely high concentrations of CO, and that these actions of CO are mediated b y nitric oxide.