Sulfur Mustard-Induced Increase in Intracellular Free Calcium Level and Arachidonic Acid Release from Cell Membrane

The mechanism of action of the alkylating agent bis-(2-chloroethyl)sulfide (sulfur mustard, SM) was studied using the in vitro mouse neuroblastoma-rat glioma hybrid NG108-15 clonal cell line model. Following 0.3 mM SM exposure, cell viability remained high (>80% of untreated control) up to 9 hr and then declined steadily to about 40% of control after 20-24 hr. During the early period of SM exposure, when there was no significant cell viability loss, the following effects were observed. The cellular glutathione level decreased 20% after 1 hr and 34% after 6 hr. Between 2 and 6 hr, there was a time-dependent increase (about 10 to 30%) in intracellular free calcium (Ca 2+), which was localized to the limiting membrane of swollen endoplasmic reticula and mitochondria, to euchromatin areas of the nucleus, and to areas of the cytosol and plasma membrane. Moreover, there was also a time-dependent increase in the release of isotopically labeled arachidonic acid ([ 3H]AA) from cellular membranes. Increase in [ 3H]AA release was 28% at 3 hr and about 60-80% between 6 and 9 hr. This increase in [ 3H]AA release was inhibited by quinacrine (20 μM), which is a phospholipase (PLA 2) inhibitor. At 16 hr after SM exposure, there was a large increase (about 200% of control) in [ 3H]AA release, which was coincident with a 50% loss of cell viability. These results suggest a Ca 2+-mediated toxic mechanism of SM via PLA 2 activation and arachidonate release.