Human lymphocytes as target cells in a metabolizing test system in vitro for detecting potential mutagens

A metabolizing test system is presented that comprises mouse liver microsomes for metabolic activation of the test compound, NADPH as co-factors, dimethylnitrosamine (DMN) as model mutagen and human peripheral lymphocytes as target cells. Lymphocytes were cultured in RPMI 1640 medium in the presence of phytohemagglutinin for 48 h before being used in the system. Incubation of the lymphocytes for 45 min in the metabolically active system reduced thymidine incorporation by 50%, whereas in the metabolically inactive system without NADPH thymidine incorporation was reduced by 15%. The latter reduction was due to the cytotoxic effects of the mouse liver microsomes and of DMN. When the lymphocytes were cultured for another 24 h after exposure to the metabolizing system and DMN, significant increased formation of chromosomal aberrations such as gaps were observed, cross-overs and breaks being less frequent.