Low concentrations of 1-methyl-4-phenylpyridinium ion induce caspase-mediated apoptosis in human SH-SY5Y neuroblastoma cells

There is growing evidence that apoptotic mechanisms underlie the neurodegen eration leading to Parkinson's disease. 1-Methyl-4-phenylpyridinium ion (MP P+), the active metabolite of the parkinsonism-inducing drug MPTP, induced apoptosis in cultures of human SH-SY5Y neuroblastoma cells. Nuclear fragmen tation, DNA laddering, and a 20% decrease in viability were seen after a 4- day incubation with 5 muM MPP+. Cell viability decreased by 40% at 100 muM MPP+, but the degree of apoptosis was not correlatively increased. The MPP-induced apoptosis was completely prevented by the broad caspase inhibitor zVAD.fmk but not by the caspase-8 inhibitor IETD.fmk. Furthermore, MPP+ had no effect on the levels of Fas or Fas-L, suggesting lack of activation of the Fas-V/Fas/caspase-8 pathway of apoptosis. There was no evidence of mito chondrial dysfunction at 5 muM MPP+: NO differences were seen in transmembr ane potential or in cytochrome c release from controls. At 100 muM MPP+, th e mitochondrial potential decreased, and cytoplasmic cytochrome c and caspa se-9 activation increased slightly. At both low and high concentrations of MPP+, VDVADase and DEVDase activities increased. We conclude that MPP+ can induce caspase-mediated apoptosis, which is prevented by caspase inhibition , at concentrations lower than those needed to trigger mitochondrial dysfun ction and closer to those found in the brains of MPTP-treated animals. (C) 2001 Wiley-Liss, Inc.