EVALUATION OF TOXICITY INDICATORS IN RAT PRIMARY ASTROCYTES, C6 GLIOMA AND HUMAN 1321N1 ASTROCYTOMA-CELLS - CAN GLIOTOXICITY BE DISTINGUISHED FROM CYTOTOXICITY

A comparison was made of rat primary astrocytes, C6 glioma cells pre-t reated with dibutyryl cyclic AMP, and the human astrocyte 132N1 cell l ine using a range of 40 compounds and the neutral red (NR) assay. The 40 chemicals included substances known to be toxic to astrocytes or ne urons, to be generally cytotoxic or not thought to be toxic to nervous tissue. For those compounds which were toxic, changes in glial fibril lary acidic protein (GFAP) levels were measured in the primary and C6 cultures, and changes in vimentin and S-100 measured in the C6 cells. The number of compounds with EC50 values < 2000 mu g/ml for the NR ass ay for the different cell cultures were as follows: primary astrocytes , 19; C6 cells, 15, and 1321N1 cells, 11. The log of the EC50 values f or the NR assay for the test compounds between the three cell types wa s not significantly different at the 5% level by paired Student's t-te st. For the toxic substances the correlation coefficients of the EC50 values between primary cells and the C6 or 1321N1 cells were r > 0.5, and between the C6 and 1321N1 cells r > 0.9. For GFAP there was a simi lar degree of correlation in EC50 values between the different cell ty pes. The GFAP, vimentin and S-100 levels showed similar EC50 values fo r the toxicants, but were not as sensitive as the NR assay. The toxic substances caused altered morphology in the primary, C6 and 1321N1 cel ls, with increased branching of cell processes. The combined astrocyte systems identified 8 out of 9 substances reported to be toxic to astr ocytes in vivo, together with substances which have general cytotoxic properties. A number of substances (including the 1 out of 9 reported gliotoxic substances), which may primarily affect neurons, which may a ffect nervous tissue after long-term exposure, or which are not though t to be toxic to nervous tissue, were not detected. The astrocyte syst ems positively identify gliotoxic and cytotoxic substances and will al low detailed mechanistic studies to be made on the different underlyin g mechanisms.