Search

Dithiocarbamates (DTCs) have a wide variety of applications in diverse fields ranging from agriculture to medicine. DTCs are teratogenic to vertebrates but the mechanisms by which they exert these effects are poorly understood. Here, we show that low nanomolar exposure to three DTCs, tetraethylthiuram (thiram), tetramethylthiuram (disulfiram), and sodium metam (metam), leads to craniofacial abnormalities in developing zebrafish embryos that are reminiscent of DTC-induced abnormalities found in higher vertebrates. In order to better understand the molecular events underlying DTC teratogenesis, we exposed embryonic zebrafish (PAC2) cells to thiram and disulfiram and measured changes in gene expression with microarrays. We found differential expression of 166 genes that were specific for exposure to DTCs and identified a network of genes related to connective tissue development and function. Additionally, we found eight downregulated genes related to transforming growth factor beta-1 (TGF-beta1) signaling, including an essential transcription factor for zebrafish craniofacial development, SRY-box-containing gene 9a (sox9a). Finally, we show that sox9a expression is perturbed in the ceratobranchial arches of DTC-exposed zebrafish, suggesting that this is an important event in the development of DTC-induced craniofacial abnormalities. Together, we provide evidence for a novel teratogenic endpoint and a molecular basis for a better understanding of DTC-induced teratogenesis in vertebrates.

Identification of nuclear receptor-mediated endocrine activities is important in a variety of fields, ranging from pharmacological and clinical screening, to food and feed safety, toxicological monitoring, and risk assessment. Traditionally animal studies such as the Hershberger and Allen-Doisy tests are used for the assessment of androgenic and estrogenic potencies, respectively. To allow fast analysis of the activities of new chemicals, food additives, and pharmaceutical compounds, high-throughput screening strategies have been developed. Here, a panel of mainly steroidal compounds, screened in different in vitro assays, was compared with two human U2-OS cell line-based CALUX (Chemically Activated LUciferase eXpression) reporter gene assays for androgens (AR CALUX) and estrogens (ERalpha CALUX). Correlations found between the data of these two CALUX reporter gene assays and data obtained with other in vitro screening assays measuring receptor binding or reporter gene activation (CHO cell line-based) were good (correlation coefficients (r2) between 0.54 and 0.76; p < 0.0001). Good correlations were also found between the in vitro and in vivo data (correlation coefficient r2 = 0.46 for the AR CALUX vs. Hershberger assay and r2 = 0.87 for the ERalpha CALUX vs. Allen-Doisy assay). The variations in the results obtained with the reporter gene assays (CALUX vs. CHO cell line based) were relatively small, showing the robustness of these types of assays. Using hierarchical clustering, bioactivity relationships between compounds but also relationships between various bioassays were determined. The in vitro assays were found to be good predictors of in vivo androgenic or estrogenic activity of a range of compounds, allowing prescreen and/or possible reduction of animal studies.