| One of the primary goals in toxicity testing is to define the deleterious effects of new chemical compounds (pharmaceuticals, etc.) before they are released into the market. Currently, toxicity studies have relied on the use of animal bioassays to determine acute, subacute and subchronic toxicity, as well as carcinogenic, and reproductive toxicity. Several problems inherent in these tests, including: cost (millions per chemical), time (up to 4 years) and the sheer number of animals required, are recognized by the Environmental Protection Agency (EPA), the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program. To alleviate these problems these groups are committed to improving toxicity testing by developing more efficient and cost effective methodologies. Several new methods (Big Blue and the Ames Test) have been developed for carcinogen testing and are designed to quickly identify genotoxic compounds. These tests are advantageous in that they require few animals and are not particularly time consuming. Unlike standard bioassays, however, they do not identify carcinogens that are nongenotoxic and therefore do not completely replace the standard carcinogen bioassay.; Another recent technological advance, DNA microarrays, have been recognized for their potential use in toxicity testing. As outlined in several symposia, microarrays may provide a method to quickly categorize chemicals and improve the efficiency of standard toxicity bioassays. However, the limited use of this technology in toxicology and whole animal studies requires that the quantitative aspects of the technology and the parameters critical for toxicant prediction be examined.; Hence, this dissertation describes the development of a gene array for use in toxicological studies as well as identifying and defining parameters critical for its successful utilization. The studies conclude that, DNA arrays are more sensitive and have similar dynamic range to standard methodology (Northern Blots). Additionally, in whole animal studies, the variability introduced in DNA arrays by spotting and hybridization is less than the interanimal variability. This dissertation also demonstrates the ability of DNA arrays to categorize several distinct classes of chemicals as well as illustrating the importance of time, dose and tissue parameters in successfully classifying novel toxicants based on gene expression. |
