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Triclosan and anuran metamorphosis: no effect on thyroid-mediated metamorphosis in Xenopus laevis
Douglas J Fort1, Robert L Rogers, Joseph W Gorsuch
1Fort Environmental Laboratories, Stillwater, Oklahoma 74074, USA. djfort@fortlabs.com
Abstract:
Nieuwkoop and Faber stage 51 Xenopus laevis larvae were exposed for 21 days to four different concentrations of triclosan (TCS): <0.2 (control), 0.6, 1.5, 7.2, or 32.3 microg TCS/l. Primary endpoints were survival, hind limb length, body length (whole; snout to vent), developmental stage, wet whole body weight, and thyroid histology. Thyroid hormone (TH) concentrations were determined in whole thyroid and plasma samples from stage-matched exposure day 21 specimens. TH receptor-beta (TRbeta) expression was measured in stage-matched tail fin tissue samples collected at exposure days 0 and 21. Reduced larval growth occurred at exposure day 21 with 1.5 microg/l treatment. Larval developmental stage at exposure day 21 was not significantly different from controls based on observed parameters. Thyroid histology was not affected by TCS, and thyroxine (T4) levels in thyroid glands or plasma were not different from controls. A concentration-dependent increase in TRbeta expression in exposure day 21 larvae was not detected. However, increased expression was found in stage-matched larvae exposed to 1.5 or 7.2 microg TCS/l. Our study indicates that environmentally relevant TCS concentrations do not alter the normal course of thyroid-mediated metamorphosis in this standard anuran model.
Insights
Environmentally relevant triclosan (TCS) concentrations did not disrupt thyroid hormone-mediated metamorphosis in Xenopus laevis frog larvae. While some growth reduction and altered thyroid receptor-beta expression occurred, overall development remained unaffected.
Area of Science:
- Environmental toxicology
- Endocrinology
- Developmental biology
Background:
- Triclosan (TCS) is a widely used antimicrobial agent with potential endocrine-disrupting properties.
- Thyroid hormones (TH) are critical regulators of amphibian metamorphosis.
Purpose of the Study:
- To investigate the effects of environmentally relevant triclosan concentrations on thyroid hormone regulation and metamorphosis in Xenopus laevis.
- To assess potential impacts on growth, development, thyroid histology, and thyroid hormone receptor expression.
Main Methods:
- Xenopus laevis larvae (Nieuwkoop and Faber stage 51) were exposed to varying concentrations of triclosan (0.6–32.3 microg/l) for 21 days.
- Endpoints included survival, morphometrics, developmental stage, body weight, thyroid histology, plasma and thyroid TH levels, and TH receptor-beta (TRbeta) expression.
Main Results:
- Reduced larval growth was observed at 1.5 microg/l TCS.
- No significant alterations in developmental stage, thyroid histology, or thyroxine (T4) levels were detected.
- Increased TRbeta expression was noted at 1.5 and 7.2 microg/l TCS, but not in a concentration-dependent manner.
Conclusions:
- Environmentally relevant triclosan concentrations do not appear to significantly disrupt thyroid-mediated metamorphosis in Xenopus laevis.
- While minor effects on growth and receptor expression were observed, the overall metamorphic process remained intact.
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