metabolism-mediated toxicity

/Tag:metabolism-mediated toxicity

A Preliminary Comparison of LiverBeadsTM with a Conventional Rat Hepatocyte Culture Preparation: Some Aspects of Xenobiotic Metabolism and Related Toxicity

Alison H. Hammond, Michael J. Garle and Jeffrey R. Fry

LiverBeadsTM are made of hepatocytes that are immobilised and cryopreserved in alginate gel. They have great potential as an easily transportable and easily handled source of hepatocytes for use in in vitro pharmacotoxicology. In this study, we compared the drug metabolising capacity of LiverBeads in culture with that of conventional cultures and of cultures derived from cryopreserved cells. Trypan blue exclusion, lactate dehydrogenase and DNA content were measured in LiverBead cultures. The levels were all similar to those of the conventional cultures, as were the toxicities of precocene II and allyl alcohol, although more variability was seen in the LiverBeads than in the conventional cultures. The cytochrome P450-dependent activity 3,4-dimethyl-7-ethoxycoumarin-O-dealkylase, was reduced in the LiverBeads when compared to the conventional cultures, although the pattern of conjugation was very similar. In addition, the inducibility of cytochrome P4504A was demonstrated in LiverBeads. Cultures from cryopreserved cells were more susceptible to the toxicants tested, and contained less lactate dehydrogenase and DNA than the conventional cultures. Overall, in terms of the aspects of drug metabolism measured, the cultures from LiverBeads appeared to be equivalent to conventional cultures, and superior to cultures from cryopreserved cells.
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A Genetically Engineered Cell-based System for Detecting Metabolism-mediated Toxicity

Sarah Bull, Ingrid Langezaal, Richard Clothier and Sandra Coecke

Xenobiotics undergong bioactivation by CYP450 enzymes form reactive metabolites that may exert direct metabolism-mediated toxicity. An in vitro model was developed to study the direct toxic effects that follow the metabolic activation of chemicals. The model uses monolayer cultures of genetically engineered NIH-3T3 or V79 cells that express individual human or rat CYP450 isoforms, respectively. Following exposure to 1,3-dichloropropanol or cyclophosphamide, basal cytotoxicity endpoints, including neutral red uptake and Alamar Blue™ reduction were used to assess changes in cell number and functional viability resulting from the formation of metabolites. Cell lines that express cytochrome P450 enzymes metabolised the test compounds, leading to increased toxicity compared with that observed in the control cell line. The use of specific inhibitors confirmed that the formation of reactive metabolites was CYP450-isoform dependent. These results indicate that a panel of genetically engineered cell lines expressing various cytochrome P450 enzyme isoforms can be used to reveal measurable etabolising capabilities, and could become a useful tool for the detection and possible determination of CYP450 isoforms in human liver metabolism-mediated toxicity.
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