Cellular non-heme iron content is a determinant of nitric oxide-mediated apoptosis, necrosis, and caspase inhibition

In this report, we tested the hypothesis that cellular content of non-heme iron determined whether cytotoxic levels of nitric oxide (NO) resulted in a poptosis versus necrosis, The consequences of NO exposure on cell viability were tested in RAW264.7 cells (a cell type with low non-heme iron levels) and hepatocytes (cells with high non-heme iron content). Whereas micromolar concentrations of the NO donor S-nitroso;N-acetyl-DL-penicillamine induced apoptosis in RAW264.7 cells, millimolar concentrations were required to in duce necrosis in hepatocytes. Caspase-3 activation and cytochrome c release were evident in RAW264.7 cells, but only cytochrome c release was detectab le in hepatocytes following high dose S-nitroso-N-acetyl-DL-penicillamine e xposure. Pretreating RAW264.7 cells with FeSO4 increased intracellular non- heme iron to levels similar to those measured in hepatocytes and delayed NO -induced cell death, which then occurred in the absence of caspase-3 activa tion. Iron loading was also associated with the formation of intracellular dinitrosyl-iron complexes (DNIC) upon NO exposure. Cytosolic preparations c ontaining DNIC as well as pure preparations of DNIC suppressed caspase acti vity. These data suggest that non-heme iron content is a key factor in dete rmining the consequence of NO on cell viability by regulating the chemical fate of NO.