W3 AM Toxicogenomics in Environmental Studies
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in Ballroom 3

(VOL-1117-677203) Dynamic gene expression changes precede dioxin-induced liver pathogenesis in medaka.

Volz, D¹, Hinton, D¹, Law, J², Kullman, S¹, ¹ Duke University, Durham, North Carolina, USA² North Carolina State University, Raleigh, North Carolina, USA

ABSTRACT- A major challenge for toxicogenomics is predicting chemically induced morphological alterations from wide-scale gene expression changes. In this study, we exploited the aryl hydrocarbon receptor agonist dioxin (2,3,7,8-TCDD) as a model compound with well-defined toxicities and biomarkers of response (CYP1A). Adult orange-red male medaka were ip-injected once with vehicle (DMSO) or dioxin (0.1, 1.0, or 10 g/kg) and recovered for 13-d post-exposure. Subsets of fish within each treatment were sampled at days 1, 5, 9, and 13 for histologic evaluation, real-time PCR (CYP1A), and liver-specific gene expression changes using 175-gene arrays. Hepatic gene expression patterns were analyzed using mixed linear models and principal component analysis, and described relative to morphological alterations in the liver. Fish survival was >85% across all treatments during the 13-d exposure period. No histological changes were observed in livers from vehicle-treated fish at all time-points and day-1 dioxin-treated fish. However, overall hepatic transcript induction was most pronounced on day 1 in dioxin-treated fish. Relative to day 1 controls, there were 78, 161, and 158 significant transcript responses in fish treated with 0.1, 1.0, and 10.0 g/kg respectively. Following this strong day 1 response, fish exposed to 0.1 g/kg exhibited mild hepatocellular atrophy on day 5 with no adverse histological changes and minimal gene expression changes at the remaining time-points. However, moderate fatty liver and atrophy was observed on day 9 in fish exposed to 1.0 g/kg, and severe fatty liver (day 5), atrophy (day 9), and perivascular inflammation (day 13) was observed in fish exposed to 10 g/kg dioxin. While gene expression patterns approached controls after day 1 in fish exposed to 0.1 and 1.0 g/kg dioxin, transcript profiles in the highest dose were dynamic and preceded atrophy and inflammation at later time-points. CYP1A transcript levels measured by real-time PCR corroborated these dose- and time-dependent trends. In the highest dose, we also identified a gene (ependymin) that may be involved in hepatic injury repair. Overall, this study addresses complexities related to chemically induced hepatic gene expression responses, and illustrated an initial stress response followed by cytologic and adaptive changes.

Key words: toxicogenomics, medaka, liver, dioxin