Non-animal testing methodologies appropriate for regulatory toxicology
Ultimately, and not surprisingly, the best model for the study of humans is the human being. What follows are examples of non- invasive, human-based methodologies for toxicity testing. It is these, and similar systems, that should become the focus of attention and investment for industry and regulators. It is both noteworthy and disturbing to see how far behind the US the UK position is, in terms of progress towards regulatory acceptance of these methodologies (22, 23). There are, however, signs that some cooperation is taking place across the Atlantic on the issue of database development (24).
Toxicogenomics is a modern scientific discipline that combines knowledge of toxicology and gene function. It can be used to obtain species-specific data that can be applied to any living cell system (plant, animal or human). In addition, toxicogenomics can be employed to study any chemical, whether it is a food additive, a pesticide, or a medical drug. When used in combination with high throughput screening methods, it is possible to study a large number of chemicals and to generate vast quantities of data with respect to possible cell damage. The results of these tests can be obtained in 24 - 48 hours. Animal tests often require up to two years to complete. Toxicogenomics is already recognised as an important adjunct for the assessment of toxic risk in humans in the USA and in Japan (25).
"Toxicogenomics applies genomics (the study of genes) concepts and technologies to study the adverse effects of chemicals. These studies use global gene expression analyses to detect expression changes that influence, predict, or help define drug toxicity. Technological advances have enabled scientists to simultaneously analyse thousands of genes of several species, including humans and rodents, quickly and in a reproducible manner. In short, the technology now exists to potentially revolutionise toxicity testing" (26).
Pharmacogenetics is the study of genetic factors that influence an organism's reaction to a drug. It takes advantage of knowledge from the human genome project and modern gene screening techniques. A report published by the Nuffield Council on Bioethics in September 2003 provides a good insight into this non-animal methodology and its specific application to humans:'People often respond differently to the same medicine. Few medicines are effective for everyone;all may cause adverse reactions and occasionally death. Research in pharmacogenetics investigates how differences in our genes can affect the way in which we respond to medicines' (27).
Quantitative structure-activity relationships (QSAR) correlate the structure or property of a chemical compound with its potential biological activities. For example, novel substances can be rapidly screened on the basis of their chemical structure, and compared with known existing compounds already in use. With the help of modern computers, QSAR currently are being applied in many disciplines, with many pertaining to drug design and environmental risk assessment (28).
Microdosing, or 'Phase 0' studies,involves the administration to human subjects of tiny amounts (sub-therapeutic or 'nanodose' concentrations) of an experimental drug. The fate of the drug in the human body can be tracked by means of radioactive labelling. The tiny dose of drug given is approximately one million fold lower than the recommended daily dose in patients and therefore significantly reduces the risk of adverse drug reactions (29).
Donated human tissues
There are more than 200 different cell types in the human body, all of which are available from UK human tissue banks, making it possible to focus our research on human cells,instead of animal cells. In addition to cell cultures, the use of human organ slices (in particular, the human liver) represents another important adjunct to the field of modern toxicology (30). Studying human organs brings scientists another step closer to understanding human health and disease. Although the isolated organ still falls short of a whole, living system, it nevertheless yields information relevant to the species in question - human beings. In addition, human patients can be studied non-invasively to reveal whole body function, and post-mortem examinations of deceased individuals can yield significant amounts of additional information.