Fish embryo models

Scholz S., Fisher S., Gundel U., Kuster E., Luckenbach T. Voelker D. (2008) The zebra fish embryo model in environmental risk assessment - application beyond acute toxicity testing. Environmental Science and Pollution Research International 15 394-404. 

Fish embryos as alternative models for drug safety evaluation... 

In the present chapter we suggest the use of fish embryos as a powerful screening system that could be used to prioritize compounds for later testing using rodent or other mammalian models and clinical trials. We describe the peculiarities of the model, provide examples that show promising applications, and discuss potential limitations and future research perspectives. 

Many possible alternative models have been explored during the last decades (e.g., whole rate embryo culture and primary or permanent embryonic stem cells54). Furthermore, different attempts have been made to develop QSAR approaches for the prediction of teratogenic effects.55-57 Fish embryos also appear to be a promising alternative test system for the reliable and cost-effective identification of potential human teratogenic compounds.58 An experimental advantage is their extracorporal development and the transparency of the eggs of... 

Early life stages of zebrafish have also been proposed as models to study the immune response. The innate immune response or components of the underpinning signaling pathways are already established in zebrafish embryos, and proinflammatory responses provoked by pathogens have been observed.90-93 However, immune modulation by drugs has yet not been addressed in fish embryos. 

Embryonic zebra fish model was employed to study fullerene toxicity. This model is quite convenient because the embryos are transparent in the first week of life and their rate of development is rather fast. C60, C70, and C60(OH)24 have been tested on early embryogenesis (Usenko et al., 2007), presenting effects on this process with malformations, pericardial edema, and mortality. The results for fullerols are milder, but it is difficult to attribute this effect to the presence of the functionalizations themselves or to the easier solubilization, implying diminished cluster formations and avoiding the use of solvents as toluene or THF, the presence of which can play an important role in toxicity, as already demonstrated. 

Zebrafish Brachydanio/Danio rerio) embryos can be produced in large numbers and carry sufficient nutrients within the egg sack to allow development within micro plate volumes [52, 53]. Mutation frequency has been estimated indirectly using transgenic fish [54[ and UDS, comet, MNT and alkaline filter elution methods have been used effectively [55]. At present, there has been insufficient study of the model to understand predictivity of mammalian genotoxicity, and none of the methods has been demonstrated at throughputs sufficient for hit and lead screening. 

By far the most comprehensive research into AHR-related effects of PCDD/Fs on fish was a retrospective analysis of Lake Ontario lake trout reproductive impairment due to AHR-mediated early life stage mortality [16]. This includes blue sac disease as well as sublethal effects, which may increase susceptibility of sac fry and alevins to increased mortality and predation during swim-up. Lake trout are more susceptible to AHR-mediated toxic effects than any other Great Lakes species, with the possible exception of mink. WHO TEFs for fish were used to calculate the 2378-TCDD equivalent (TECegg or TEQ) concentrations in lake trout eggs. The validity of the additive toxicity equivalence model was established through early life stage trout toxicity tests. The WHO fish TEFs are likely to be fairly robust for lake trout, since they were determined primarily from relative potency values for effects in embryos of a related salmonid, rainbow trout, even if the relative sensitivity of the species to 2378-TeCDD toxicity may be different. 

The medaka (Oryzias latipes) is a teleost native to Japan, Korea, China, and Taiwan23. Similar to the zebrafish, it produces transparent embryos that allow easy observation and manipulation. Medaka is a popular model organism in Japan and the first fish species in which stable transgenesis was established, it provides some complimentary features to the zebrafish such as adaptation to a wide range of temperatures.22 The identification of sex specific markers, secondary sex characters and a sex determination gene have lead to increasing attraction of the medaka as a model for research on sex determination and differentiation23-28 (photo Andre Kunzelmann, UFZ). 

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