Tebuconazole disrupts steroidogenesis in Xenopus laevis.

A 27-day controlled exposure study of adult male African clawed frogs (Xenopus laevis) was conducted to examine the mechanism by which tebuconazole may disrupt steroidogenesis. The fungicide was measured by LC-MS/MS in tank water and in target tissues (adipose, kidney, liver, and brain), and we observed tissue-specific bioconcentration with BCF up to 238. Up to 10 different steroid hormones were quantified in gonads using LC-MS/MS and in plasma using GC-MS/MS and a radioimmunoassay was performed for further measurement of androgens. In order to assess whether effects increased with exposure or animals adapted to the xenobiotic, blood samples were collected 12 days into the study and at termination (day 27). After 12 days of exposure to 100 and 500μgL(-1) tebuconazole, plasma levels of testosterone (T) and dihydrotestosterone (DHT) were increased, while plasma 17β-estradiol (E2) concentrations were greatly reduced. Exposure to 0.1μgL(-1), on the other hand, resulted in decreased levels of T and DHT, with no effects observed for E2. After 27 days of exposure, effects were no longer observed in circulating androgen levels while the suppressive effect on E2 persisted in the two high-exposure groups (100 and 500μgL(-1)). Furthermore, tebuconazole increased gonadal concentrations of T and DHT as well as expression of the enzyme CYP17 (500μgL(-1), 27 days). These results suggest that tebuconazole exposure may supress the action of CYP17 at the lowest exposure (0.1μgL(-1)), while CYP19 suppression dominates at higher exposure concentrations (increased androgens and decreased E2). Increased androgen levels in plasma half-way into the study and in gonads at termination may thus be explained by compensatory mechanisms, mediated through increased enzymatic expression, as prolonged exposure had no effect on circulating androgen levels.