Blocking a specific ion channel reduces inflammation in lung cells

Silicosis caused by exposure to silica dust is a serious occupational health threat in the United States and worldwide. For example, artificial stone workers are exposed to dust that has a higher percentage of silica than natural stone, creating a more significant exposure in a shorter period of time and placing these workers at an enhanced risk of developing silicosis. Silicosis is an incurable lung disease marked by chronic inflammation. When silica dust is inhaled, the cells responsible for clearing it out of the lungs, macrophages, become damaged and initiate a cycle of chronic inflammation that results in lung and systemic diseases. Because the mechanisms leading to inflammation from silica are poorly understood, effective treatments for silicosis are not available. It is known that as the silica particle is taken up by macrophages it moves into a degradative organelle (lysosome) where it causes damage that results in leakage of lysosomal contents into the rest of the cell initiating a cycle of cell death and chronic inflammation. Therefore, determining the mechanisms of this leakage is crucial to being able to understand and prevent chronic inflammation. I propose that this early step in the initiation of inflammation can be prevented by blocking specific ion channels (in this case a K+ channel) within the organelle. To test this hypothesis, macrophages were plated in 96-well plates and pre-treated with the K+ ion channel blocker paxilline 30 minutes prior to 24-hr exposures to silica (50 ug/mL). Cell death and inflammatory activity were assessed. For comparison, macrophages were also pre-treated with an alternate K+ ion channel blocker, iberiotoxin, that only blocks ion channels at the cell surface. Lactate dehydrogenase is released when a cell membrane is damaged and was measured as an indicator of cell death in these experiments. Interleukin 1 beta (IL-1B) is a cell signaling protein that sends inflammatory signals to immune cells and is measured as an indicator of activating the inflammation pathway in macrophages. Pre-treatment of the cells with paxilline before silica exposure resulted in reduced cell death and significantly reduced inflammation in two types of macrophages. In contrast, iberiotoxin did not reduce cell death or inflammation. In conclusion, blocking a specific K+ ion channel decreases silica-caused cell death and inflammation in macrophages, offering valuable insight into the mechanisms of inflammation for further development of silicosis therapeutics and prevention