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) cel ls under different experimental conditions including the composition of the test medium (DMEM at pH 7.35 and 7.0, and in LeBoeufs modified DMEM at pH 6.7) 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 pr imary active metabolite in vivo, mono(2-ethylhexyl)phthalate (MEHP). SHE ce lls were exposed to the HPP tested either alone, or in sequential treatment s 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-st age exposure assay was applied with DMEM at pH 7.35 and 7.0. Structural ana logues did nor give similar results using the same experimental conditions. Indeed, while MCP was more potent at acidic pH, the transforming potency o f clofibrate was higher at pH 7.0 and 7.35. DEHP and MEHP also behaved diff erently: in contrast to DEHP, MEHP was more active at pH 6.7 than at pn 7.0 . The MT induction, resulting from the interaction between MCP and BaP or T PA, appeared pH-dependent and higher at pH 7.0 than at pH 7.35. This study showed that: ii) pH actually influences SHE cell response to HPPs, iii) the use of acidic medium (pH 6.7) does not guarantee a better detection of HPP s' transforming effects and (iii) repeated applications of the test-medium within the 7 days of the assay are more efficient in detecting a transformi ng potency. (C) 1999 Elsevier Science Ltd. All rights reserved.