Thimerosal-induced apoptosis in human SCM1 gastric cancer cells: Activation of p38 MAP kinase and caspase-3 pathways without involvement of [Ca²⁺]_i elevation

Thimerosal is a mercury-containing preservative in some vaccines. The effect of thimerosal on human gastric cancer cells is unknown. This study shows that in cultured human gastric cancer cells (SCM1), thimerosal reduced cell viability in a concentration- and time-dependent manner. Thimerosal caused apoptosis as assessed by propidium iodide-stained cells and caspase-3 activation. Although immunoblotting data revealed that thimerosal could activate the phosphorylation of extracellular signal-regulated kinase, c-Jun NH₂-terminal protein kinase, and p38 mitogen-activated protein kinase (p38 MAPK), only SB203580 (a p38 MAPK inhibitor) partially prevented cells from apoptosis. Thimerosal also induced [Ca²⁺]_i increases via Ca²⁺ influx from the extracellular space. However, pretreatment with (bis(o-aminophenoxy)ethane-N,N,N′, N′-tetraacetate)/AM, a Ca²⁺ chelator, to prevent thimerosal-induced [Ca²⁺]_i increases did not protect cells from death. The results suggest that in SCM1 cells, thimerosal caused Ca²⁺-independent apoptosis via phosphorylating p38 MAPK resulting in caspase-3 activation.