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Updated: Jul 14, 2026
Rapid Evaluation of Toxicity of Chemical Compounds Using Zebrafish Embryos
Published on: August 25, 2019
Toxicity and cardiac effects of carbaryl in early developing zebrafish (Danio rerio) embryos
C C Lin1, Michelle N Y Hui, S H Cheng
1Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Hong Kong.
Abstract:
Carbaryl, an acetylcholinesterase inhibitor, is known to be moderately toxic to adult zebrafish and has been reported to cause heart malformations and irregular heartbeat in medaka. We performed experiments to study the toxicity of carbaryl, specifically its effects on the heart, in early developing zebrafish embryos. LC50 and EC50 values for carbaryl at 28 h post-fertilization were 44.66 microg/ml and 7.52 microg/ml, respectively, and 10 microg/ml carbaryl was used in subsequent experiments. After confirming acetylcholinesterase inhibition by carbaryl using an enzymatic method, we observed red blood cell accumulation, delayed hatching and pericardial edema, but not heart malformation as described in some previous reports. Our chronic exposure data also demonstrated carbaryl-induced bradycardia, which is a common effect of acetylcholinesterase inhibitors due to the accumulation of acetylcholine, in embryos from 1 day post-fertilization (dpf) to 5 dpf. The distance between the sinus venosus, the point where blood enters the atrium, and the bulbus arteriosus, the point where blood leaves the ventricle, indicated normal looping of the heart tube. Immunostaining of myosin heavy chains with the ventricle-specific antibody MF20 and the atrium-specific antibody S46 showed normal development of heart chambers. At the same time, acute exposure resulted in carbaryl-induced bradycardia. Heart rate dropped significantly after a 10-min exposure to 100 microg/ml carbaryl but recovered when carbaryl was removed. The novel observation of carbaryl-induced bradycardia in 1- and 2-dpf embryos suggested that carbaryl affected cardiac function possibly through an alternative mechanism other than acetylcholinesterase inhibition such as inhibition of calcium ion channels, since acetylcholine receptors in zebrafish are not functional until 3 dpf. However, the exact nature of this mechanism is currently unknown, and thus further studies are required.
Insights
Carbaryl exposure in zebrafish embryos caused bradycardia (slow heart rate) and other developmental issues. This suggests potential alternative toxicity mechanisms beyond acetylcholinesterase inhibition in early development.
Area of Science:
- Environmental toxicology
- Developmental biology
- Cardiovascular toxicology
Background:
- Carbaryl is an acetylcholinesterase inhibitor with known toxicity to aquatic organisms.
- Previous studies reported heart malformations in medaka exposed to carbaryl.
- Zebrafish embryos offer a model for studying early developmental toxicity.
Purpose of the Study:
- To investigate the cardiotoxicity of carbaryl in early developing zebrafish embryos.
- To determine the effects of carbaryl on heart rate and cardiac development.
- To explore potential mechanisms of carbaryl toxicity in zebrafish embryos.
Main Methods:
- Determined lethal concentration (LC50) and effect concentration (EC50) values for carbaryl.
- Exposed zebrafish embryos to carbaryl and observed developmental endpoints.
- Confirmed acetylcholinesterase inhibition using enzymatic assays.
- Monitored heart rate and performed immunostaining for cardiac structures.
Main Results:
- LC50 and EC50 values were established; 10 microg/ml carbaryl was used for further experiments.
- Observed red blood cell accumulation, delayed hatching, and pericardial edema.
- Carbaryl induced bradycardia in zebrafish embryos during both chronic and acute exposures.
- Normal heart tube looping and chamber development were observed, contradicting some previous reports of malformations.
- Bradycardia in very early embryos (1-2 dpf) suggests a mechanism independent of functional acetylcholine receptors.
Conclusions:
- Carbaryl exposure causes significant cardiotoxicity, primarily manifesting as bradycardia, in developing zebrafish embryos.
- Observed developmental effects like edema and delayed hatching indicate broader toxicity.
- The early onset of bradycardia suggests carbaryl may affect cardiac function via mechanisms other than acetylcholinesterase inhibition, possibly involving ion channels.
- Further research is needed to elucidate the precise molecular mechanisms underlying carbaryl's cardiotoxic effects in zebrafish embryos.
