Cytotoxicity of MEIC Chemicals Nos. 11-30 in 3T3 Mouse Fibroblasts with and without Microsomal Activation.

The cytotoxicity of MEIC chemicals Nos. 11-30 was evaluated by determination of neutral red uptake in Balb/c 3T3 mouse fibroblasts with and without the addition of a microsomal activation mixture. The use of microsomes significantly decreased the cytotoxicity of malathion, 2,4-dichlorophenoxyacetic acid, propranolol, thioridazine, lithium sulfate, copper sulfate and thallium sulfate, whereas the cytotoxicity of 1,1,1-trichloroethylene, phenol, nicotine, and paraquat was significantly increased by use of the microsomal activation mixture. These cytotoxicity data are in line with observations in other studies on microsomal modulation of the cytotoxicity of the test substances. Moderate to good correlations were found between the cytotoxicity data and rodent lethality data, and the addition of microsomes slightly improved the in vitro/in vivo concordance. The evidence to support the relevance of the in vitro/in vivo correlations obtained in the MEIC project is limited due to a high variability on the in vivo lethality data and a large interlaboratory variation on the in vitro data.