In vitro cytotoxicity testing: 24-hour and 72-hour studies with cultured lung cells

By Hopkinson, D. - Bourne, R. - Barile, F.A.

This study was designed to evaluate the potential of an in vitro cell culture method for its ability to determine cytotoxicity and to compare the cytotoxic concentrations with established LD50 values for the same chemicals. Rat lung epithelial cells (L2) were incubated in the absence or presence of increasing concentrations of the test chemical for 24 hours, and the inhibition of incorporation of radio-labelled amino acids into newly synthesised proteins was used as a marker for toxicity. In addition, cultured cells were exposed to the test chemicals for 72 hours, and cell proliferation experiments were performed as parallel measures of toxicity. Inhibitory concentrations were extrapolated from concentration-effect curves after linear regression analysis. The biological significance of the results of testing 20 chemicals shows that the experimental IC50 values are as accurate as predictors of human toxicity as are equivalent toxic blood concentrations derived from rodent LD50s. Results obtained from 72-hour growth studies reveal a greater sensitivity to cytotoxicity than from the 24-hour protein synthesis experiments. Statistically, however, the differences between the two protocols are inconclusive. It is anticipated that these procedures, together with a related battery of tests, may supplement or replace animal protocols currently used for human risk assessment.