PARENT SESSION

2P Modelling ecotoxic effects
Poster Hall
8:30 AM - Monday, 28 April 2003

(MOP/147) Correlation between in vitro and in vivo toxicity of uncoupling compounds.

Schreiber, Zachariah^{1, 2}, Escher, Beate¹, Schwarzenbach, Rene^{1, 2}, ¹ EAWAG Swiss Federal Institute for Environ. Sci. and Technol., Duebendorf, Switzerland² ETH Swiss Federal Institute of Technology, Zuerich, Switzerland

ABSTRACT- In vitro mechanistic ecotoxicity tests offer information about the specific toxicity of environmental contaminants and can contribute to better risk assessment. However, before these tests are established and can partially replace conventional assays, the relevance of a chemical′s mechanism of toxicity established in the in vitro assay needs to be verified in vivo . As well, the relative sensitivity of the in vitro and in vivo assays must be systematically compared to determine if the in vitro systems are adequately sensitive. The work presented here uses a specific mechanism of toxicity, uncoupling of the chemiosmotic proton gradient in energy transducing membranes, to develop the methods and tools required to extend an in vitro membrane toxicity assay to an in vivo toxicity assay (in Rhodobacter sphaeroides GA). It has been shown in photosynthetically growing Rh. sphaeroides that uptake of dicarboxylic acid carbon sources (in this work succinic acid) is sensitive to specifically uncoupling chemicals. Therefore uptake of succinic acid was chosen as the in vivo endpoint for examination. First, the mechanism of action leading to impaired succinic acid uptake was examined with radioactive uptake experiments (¹⁴C-succinic acid) in the presence of known uncouplers (CCCP and FCCP), other toxicants with specific mechanisms of toxic action (antimycin, N,N′-dicyclohexylcarbodiimide, myxothiazol, nigericin, valinomycin and vanadate), a baseline toxicant (1-hexanol), and general stress conditions (acid, alkaline and osmotic shock). Secondly, a test set of four phenolic compounds (2,4-dinitrophenol; 2,6-Dibromo-4-cyanophenol; 3,4,5-trichlorophenol and 3,5-dibromocresol) identified as uncouplers in the in vitro system, were tested in the in vivo system. Third, in order to compare the two systems, an in vivo toxicokinetic (TK)/toxicodynamic (TD) model was developed. Modelled are the target-site concentration (TK), and the uncoupling disturbance of substrate uptake (TD). This is compared with the existing in vitro membrane potential model.

Key words: Rhodobacter Sphaeroides, uncoupling, mechanism of toxicity, toxicokinetic/toxicodynamicmodel