Effects of methylphenylpyridinium and kainic acid on protein degradation in differentiated neuroblastoma cultures

Abstract

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 μ m-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 μ m 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 α-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.