The detection of cytotoxicity produced by short-lived reactive intermediates: a study with bromobenzene

The Development and Evaluation of In Vitro Tests by the FRAME Alternatives Laboratory

This review outlines the work which has been conducted in the FRAME Alternatives Laboratory during the first ten years of the FRAME Research Programme. A number of in vitro tests, including the kenacid blue, neutral red release and fluorescein leakage assay methods, have been evaluated and have subsequently been included in validation schemes organised by the US Soap and Detergent Association, the US Cosmetic, Toiletry and Fragrance Association, the European Commission and the European Cosmetic, Toiletry and Perfumery Association, as well as in the Scandinavian multicentre evaluation of in vitro cytotoxicity testing scheme. More recently, research has been undertaken in the areas of phototoxicity, immunotoxicity, dermal toxicity and intercellular communication, in addition to investigations into fundamental mechanisms of toxicity.

The FRAME Alternatives Laboratory Database. 1. In Vitro Basal Cytotoxicity determined by the Kenacid Blue Total Protein Assay

A database of over 280 chemicals has been compiled by using a mouse 3T3-L1 fibroblast-like cell line in exponential growth, exposed to chemicals for 72 hours in a 96-well tissue culture plate format, and determining cell number via the Kenacid blue (KB) assay for total protein. Ranking the chemicals according to their basal cytotoxicity, expressed as the concentration (mM) that inhibits increase in total cellular protein over 72 hours by 50% (the ID50 value) shows a wide range of ID50 values, from 0.00003mM to 10,096mM. This information includes the results for MEIC chemicals 1–50, and we have now added basal cytotoxicity data for 23 of the next 25 MEIC chemicals. When the neutral red uptake (NRU) assay was performed with the same cell cultures, before the KB assay, very similar indications of basal cytotoxicity were obtained. Comparisons between the results with 3T3-L1 cells and with a human fibroblast-like cell line, BCL-D1 showed a significant difference in order of magnitude of the ID50 value for only 5 of 52 chemicals. However, there was a difference in ID50 value of more than one order of magnitude for 8 of 24 chemicals tested with an undifferentiated teratocarcinoma cell line, F9.

Influence of sample preparation on cellular glutathione recovery from adherent cells in culture

During the last decade, the unbound glutathione content of cultured adherent cells has become a very important biological marker for many pharmacological and toxicological in vitro studies with regard to the protective role of the tripeptide in its reduced form (GSH). However, the literature does not provide extensive information on the influence of sample preparation on cellular GSH and thiol analyses. Using the fibroblast-like V79 cell line as model, we undertook a comparative study of the efficiency of different procedures reported in the literature with respect to GSH recovery. Depending on the preanalytical step, up to 10-fold discrepancies could be observed in the recovery of intracellular GSH. Different parameters that must be controlled in order to maximize GSH recovery are discussed. The optimal strategy consisted in rapid perchloric acid deproteinization performed directly in the dish, which was extremely valuable for preparing GSH samples from adherent cells, and especially from cells expressing elevated gamma-glutamyl transferase activity.

An in vitro study of the microsomal metabolism and cellular toxicity of phenytoin, sorbinil and mianserin

1. The cytotoxicity of metabolites generated from phenytoin, sorbinil and mianserin by human and mouse liver microsomes was assessed by co-incubation with human mononuclear leucocytes as target cells. Cytotoxicity was determined by trypan blue dye exclusion. 2. Phenytoin and sorbinil were metabolised by NADPH-dependent murine microsomal enzymes to cytotoxic metabolites. Cytotoxicity produced by both drugs was significantly enhanced by the epoxide hydrolase inhibitor trichloropropane oxide (TCPO). No significant cytotoxicity was observed in the presence of human liver microsomes. 3. Mianserin was metabolised by both human and mouse liver microsomes to a cytotoxin. Cytotoxicity was greater in the presence of human liver microsomes (13.7 +/- 2.2%; mean +/- s.d. for four livers, compared with 6.0 +/- 2.4%, mean +/- s.d., n = 4, with mouse liver microsomes), and was unaffected by pretreatment with TCPO. 4. Stable metabolites were quantified by radiometric high performance liquid chromatography. Phenytoin and sorbinil were metabolised to 5-(p-hydroxyphenyl)-5-phenyl-hydantoin (0.3-0.5% of incubated radioactivity) and 2-hydroxysorbinil (0.4-2.7% of incubated radioactivity), respectively, by both human and mouse liver microsomes. 5. Mianserin was metabolised to 8-hydroxymianserin and desmethylmianserin by both human and mouse liver microsomes. Desmethylmianserin was the major product in incubations with human liver microsomes (32.3 +/- 12%, mean +/- s.d. for four livers), whereas 8-hydroxymianserin was the predominant metabolite generated by mouse liver microsomes (25.9 +/- 1.5%, mean +/- s.d., n = 4). 6. Generation of electrophilic metabolites was assessed by determination of the amount of radiolabelled material which became irreversibly bound to protein. Only mouse liver microsomes activated phenytoin to a chemically reactive metabolite, whereas both mouse and human liver microsomes generated reactive metabolites from sorbinil and mianserin. 7. These studies show that drug cytotoxicity can be mediated by low concentrations (circa microM) of metabolites generated by NADPH-dependent hepatic microsomal enzymes; however demonstration of cytotoxicity in vitro has not been established as a means of predicting in vivo toxicity.

The Detection of Reactive Metabolites Generated by the Microsomal Mixed Function Oxidase System

It is recognised that the cytotoxicity of a number of xenobiotics is mediated through the production of reactive metabolites (1). Given this, and the current emphasis on the development of in vitro tests for assessment of xenobiotic cytotoxicity (2), it is of considerable interest to develop systems for the detection in vitro of cytotoxic reactive metabolites. Indeed, it would seem appropriate to employ a limited battery of tests for detection of xenobiotic-mediated cytotoxicity, some of which would be dedicated to assessment of the role of metabolism in such toxicity. The aim of this review is to identify and discuss the approaches currently being employed to this end, and to suggest some possible future trends.