Using the human hepatoma cell line, HepG2, and the BALB/c mouse fibroblast cell line, 3T3, as the bioindicators in the neutral red cytotoxicity assay, the effect of hydroxyl substitution on the toxicity of 1,4naphthoquinone was studied. The sequence of potency for the quinones was 5,8-dihydroxy-1,4-naphthoquinone > 5-hydroxy-1.4-naphthoquinone > 1,4-naphthoquinone * 2-hydroxy-1,4-naphthoquinone. Pretreatment of the cells with dicoumarol, an inhibitor of DT-diaphorase, enhanced the cytotoxicity of 1,4-naphthoquinone but not of the hydroxylated naphthoquinones. Pretreatment of the BALB/c cells with buthionine sulfoximine, an inhibitor of glutathione synthesis, enhanced the sensitivity of the cells to all the hydroxylated naphthoquinones but not to 1,4-naphthoquinone. A similar pretreatment of the HepG2 cells with buthionine sulfoximine enhanced the toxicity of the 2-hydroxy-and 5,8-dihydroxy-1,4-naphthoquinones but not of 5-hydroxy-1,4naphthoquinone or of 1,4-naphthoquinone.
Some differences were noted in the responses to the hydroxylated 1,4-naphthoquinones between buthionine sulfoximine-treated replicating cells and buthionine sulfoximine-treated isolated rat hepatocytes, a nonreplicating cell in culture. The use of a replicating cell system in studying the mechanisms of the cytotoxicity of quinones may be a n important adjunct to studies using the isolated rat hepatocytes, which is the standard model system.