Sensitivity to dioxin decreases as zebrafish mature

Area of Science:

• Environmental Toxicology
• Developmental Biology
• Aquatic Toxicology

Background:

• Teleost fish embryos show extreme sensitivity to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).
• Adult fish exhibit reduced sensitivity to TCDD, indicating a developmental difference in toxic response.

Purpose of the Study:

• To investigate and characterize the differential sensitivity of zebrafish (Danio rerio) to TCDD across various developmental stages.
• To understand the age-dependent toxicological effects and molecular responses to TCDD exposure.

Main Methods:

• Zebrafish were exposed to graded concentrations of TCDD at different ages, from 1 day post-fertilization (dpf) to 30 dpf.
• LD(50) values, latency of response, and specific toxicological endpoints (cardiovascular, growth, skeletal, pigmentation) were assessed.
• Transcriptional profiles in heart tissue were analyzed to compare molecular responses at different exposure ages.

Main Results:

• Embryos exposed at 1 dpf had significantly lower LD(50) values compared to juveniles exposed at 30 dpf.
• Embryo toxicity involved cardiovascular collapse and heart malformations; juvenile toxicity included stunted growth, altered pigmentation, and skeletal issues, with no observed cardiovascular effects.
• Transcriptional changes in hearts differed substantially between embryonic and juvenile TCDD exposures, with cardiotoxicity linked to pre-metamorphic stages (around 14 dpf).

Conclusions:

• The developmental stage of zebrafish at the time of TCDD exposure is a critical determinant of the toxicological outcome.
• TCDD elicits distinct organ-specific toxicities and molecular responses depending on the developmental phase of the fish.
• Understanding these stage-specific responses is crucial for accurate risk assessment of TCDD in aquatic environments.