Effects of methylphenylpyridinium and kainic acid on protein degradation in differentiated neuroblastoma cultures.
Cultured neuroblastoma cells were used to study the toxic effects of the two neurotoxins methylphenylpyridinium (MPP(+)) and kainic acid. Degradation of cellular proteins (as an indicator of toxin-induced protein damage) and cell death were measured after incubation for 24 hr with a range of doses of MPP(+) and kainic acid. One-way analysis of variance tests showed that the two neurotoxins had highly significant dose-related effects on protein degradation in the differentiated human neuroblastoma cells (P = 0.0003 and P = 0.004, respectively) and in the mouse neuroblastoma cells (P = 0.002 and P = 0.0004, respectively). The dose-response relationship was similar for both toxins, an increase in protein degradation was observed at some low doses but higher doses caused a decrease in degradation often to below control levels. Levels of neurotoxin that increased protein degradation had no statistically significant effect on cell death; however, 50 mum-MPP(+) significantly decreased protein degradation and caused a concomitant increase in cell deaths in mouse neuroblastoma cells in a low-glutamate medium. Neither toxin at concentrations of 10 mum or less had any effect on undifferentiated mouse neuroblastoma cells. Changes in protein degradation in differentiated mouse neuroblastoma cells, induced by kainic acid, were not observed in low-glutamate medium; however, MPP(+) significantly decreased protein degradation in low-glutamate medium. Pre-incubation of these cells with alpha-tocopherol prevented these MPP(+)-induced changes. Protein degradation in human neuroblastoma cells was enhanced by both dopamine and iron when added with either MPP(+) or kainic acid using a low-glutamate medium. Both toxins under study cause dose-dependent changes in intracellular protein degradation similar to those found using known free-radical generators.
Thomas
S M
SM
Department of Immunology, St George's Hospital Medical School, Tooting, London SW17 0RE, UK.
Anderton
B H
BH