Alternative models for toxicity testing of xenobiotics.

The alternatives to whole-animal testing include endpoint assays, cell and tissue cultures, use of tissue slices, toxicokinetic modelling, and structure-activity relationships and databases. The use of in vitro systems (subcellular fractions, cell lines, primary cell cultures, tissue slices, organ cultures, etc.) as research tools in toxicology is widespread. In the past few years, the apoptosis phenomena were followed by very precise intracellular changes where, through programmed cell death, a cell can be removed from a population. The in vitro systems are ideally suited for investigations of the molecular, cellular and physiological mechanisms of chemically induced toxicity, which cannot readily be studied in vivo for known target organ and target species toxicity studies and for answering specific questions about toxic effects. The main justification for developing in vitro toxicity tests is that they will make toxicology a more scientifically based practice. It is increasingly apparent that the development and incorporation of stepwise testing strategies, combining experimental data from a range of alternative methods (physicochemical techniques, quantitative structure-activity relationships--QSAR, metabolic and kinetic modelling and in vitro tests), provide the most advanced way to predict toxicity, reducing at the same time the number of laboratory animals used for testing.