α-Pyrrolidinononanophenone provokes apoptosis of neuronal cells through alterations in antioxidant properties

In this study, we found that exposure to alpha-pyrrolidinononanophenone (alpha-PNP), a highly lipophilic synthetic cathinone, provokes apoptosis of human neuronal SK-N-SH cells. The drug sensitivity of the cells (50% lethal concentration of 12 mu M) was similar to those of aortic endothelial and smooth muscle cells, and was higher than those of cells derived from colon, liver, lung and kidney, suggesting that alpha-PNP overdose and abuse cause serious damage in central nervous and vascular systems. SK-N-SH cell treatment with lethal concentrations (20 and 50 mu M) of alpha-PNP facilitated the reactive oxygen species (ROS) production. The treatment also prompted elevation of Bax/Bcl-2 ratio, lowering of mitochondrial membrane potential, release of cytochrome-c into cytosol, and resultant activation of caspase-9 and caspase-3. The apoptotic events (caspase-3 activation and DNA fragmentation) were abolished by pretreatment with antioxidants, N-acetyl-L-cysteine and polyethyleneglycol-conjugated catalase. These results suggest that ROS production, mitochondrial dysfunction and caspase activation are potential events in the mechanism underlying the alpha-PNP-triggered neuronal cell apoptosis. Intriguingly, the alpha-PNP treatment of SK-N-SH cells was found to promote formation of 4-hydroxynonenal, a reactive aldehyde generated from lipid peroxidation. The alpha-PNP treatment also decreased cellular levels of total and reduced glutathiones, expression of gamma-glutamylcysteine synthetase mRNA and glutathione reductase activity. Furthermore, the alpha-PNP treatment resulted in both decrease in proteasomal activities and increase in expression of autophagy-related factors, which were significantly prevented by pretreating with N-acetyl-L-cysteine. Therefore, the ROS formation by alpha-PNP treatment may be ascribable to the decrease in glutathione level through its consumption during 4-hydroxynonenal detoxification and dysfunction of both de novo synthesis and regeneration of glutathione, in addition to impairments in proteasomal and autophagic systems that degrade cellular oxidized components.