Thallium induces PC12 cells apoptosis through alterations in cells redox state and lysosomal labilization

HANZEL, C. E.; VERSTRAETEN, S. V.

Montevideo, Uruguay

Congreso; V Reunión de la Sociedad de Radicales Libres en Biología y Medicina, Grupo Sudamericano y V Conferencia Internacional de Peroxinitrito y Especies Reactivas del Nitrógeno; 2007

Sociedad de Radicales Libres en Biología y Medicina, Grupo Sudamericano

Thallium (Tl) is a non-redox heavy metal, with two oxidation states (Tl+ and Tl3+). Tl is a highly neurotoxic agent whose molecular mechanisms of action are poorly understood. Working with PC12 cells, we previously demonstrated that both Tl+ and Tl3+ decreased mitochondrial membrane potential, effect that was accompanied by an increase in H2O2 content, a significant decrease in GSH content, and an increase in cytoplasmic oxidants and lipid oxidation products content. Considering these results, we aim to elucidate the possible mechanisms of cell death involved in Tl toxicity. PC12 cells were incubated for 24 or 48 h in the presence of Tl+ or Tl3+ (10-100 uM) and nuclear morphology was microscopically characterized using the probes acridine orange and ethidium bromide. After 48 h of cells exposure to Tl, a significant increase in the number of apoptotic nuclei was found (26% at 100 uM for Tl+ and Tl3+). Western blot analysis after 24 h of incubation in the presence of Tl+ or Tl3+ (50 or 100 uM) showed high PARP cleavage (70 % at 100 uM for Tl+ and Tl3+), the release of cytochrome c into the cytosol (60 % sy 100 uM for Tl+), and an unaffected Bcl-2 content. Phosphatidylserine externalization was only found when PC12 cells were treated with 100 uM Tl+. Besides, an increase in caspase 8 activity was observed when cells were incubated in the presence of 50 uM Tl3+. A significant lysosomal labilization as determined by cathepsin D activity in the cytosol was observed in cells treated for 24 h with 50 or 100 uM Tl+ or Tl3+. Neither autophagic cell death as evaluated by the incorporation of the probe MDC into autophagic vacuoles, nor necrosis as evaluated by LDH activity, were involved in Tl toxicity. In summary, Tl induces apoptosis in PC12 cells through the activation of the intrinsic pathway. In addition, Tl causes an imbalance in cells redox state and lysosomal labilization, effects that could be in part responsible for the apoptotic cell death. This work was supported by grants of UBA (072) and CONICET (PIP 5536), Argentina.