The arsenic in mice as experimental model for risk modifiers.

Studies on the relevance of host factors in modulating the physiological responses following chronic exposure to xenobiotics were carried out according to a “Toxicogenomic Model on Arsenic in Mice” developed at thte JRC. This model is focused on chronic exposure to arsenate given alone or in combination with other xenobiotics, to assess potential “cocktail effects” and related cumulative risks. DNA-macroarrays technology is applied to evaluate physiological responses at transcriptional level and assessing possible biochemical responses. A cluster of 1200 cancer genes was used for screening purposes, while quantitative PCR on selected genes applied for validation. The exposure varied from in-utero and post-lactation up to adult age (4 months), the chemical forms (arsenate and dimethylarsenate) and doses from 0.1 up to 10 mg As/L in drinking water. Comparison between acute single doses and chronic exposure was also performed. Chronic exposure to arsenate and atrazine in drinking water was selected as an example of multiple chronic exposure. The liver, kidney, lung, bone marrow, adrenals, uterus, and testis were the tissues considered. In the tissues of mice chronically exposed to arsenate, the modulation of gene expression was not only depending on the levels, types and length of exposure, while differently regulated also by the sex, age and diet. The main gene functional families modulated were covering a wide range of biochemical and physiological regulations, like cell cycle modulation, cell adhesion, apoptosis, xenobiotic metabolism, DNA repair, protein turnover, and proto-oncogenes. The patterns of gene expression were strongly influenced by co-exposure to other xenobiotics like atrazine and naphthalene, particularly for genes involved in the metabolism and in neuroendocrine regulation. These effects varied according to the tissue considered, supporting the needs for coherent and specifically designed studies to assess relevant biomarkers of long-term exposure to low levels of xenobiotics and their mixtures.