Peroxisome Proliferator-induced Transformation of Syrian Hamster Embryo Cells: Influence of Experimental Procedures

We compared the ability of four hepatic peroxisome proliferators (HPPs) to induce morphological transformation (MT) in Syrian hamster embryo (SHE) cells under different experimental conditions including the composition of the test medium (DMEM at pH7.35 and 7.0, and in LeBoeuf's modified DMEM at pH6.7) and the modalities of exposure. The HPPs studied were two structurally-related hypolipidaemic agents, clofibrate and methyl clofenapate (MCP), an industrial plasticizer, di(2-ethylhexyl)phthalate (DEHP) and one of its primary active metabolite in vivo, mono(2-ethylhexyl)phthalate (MEHP). SHE cells were exposed to the HPP tested either alone, or in sequential treatments with other carcinogens such as benzo[a]pyrene (BaP) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) in order to study possible interactions. A two-stage exposure assay was applied with DMEM at pH7.35 and 7.0. Structural analogues did not give similar results using the same experimental conditions. Indeed, while MCP was more potent at acidic pH, the transforming potency of clofibrate was higher at pH7.0 and 7.35. DEHP and MEHP also behaved differently: in contrast to DEHP, MEHP was more active at pH6.7 than at pH7.0. The MT induction, resulting from the interaction between MCP and BaP or TPA, appeared pH-dependent and higher at pH7.0 than at pH7.35. This study showed that: (i) pH actually influences SHE cell response to HPPs, (ii) the use of acidic medium (pH6.7) does not guarantee a better detection of HPPs' transforming effects and (iii) repeated applications of the test-medium within the 7 days of the assay are more efficient in detecting a transforming potency.