Choose the Appropriate Tests To Conduct a Research

How and why we should use a certain cell test or animal test when investigating on chemicals present in our foods/drinks?

First of all, each one has advantages and disadvantages, requires more or less work and can be more or less costly. Second, there is not a single test that answers all questions. So, researchers and monitoring agencies have to apply those tests that are informative and reliable, depending on the question.

If the question is Does this chemical accelerate fat accumulation in cells? then a cell test is quick and reliable (see step 3.3).

If the question is Is there a link between phytoestrogens in soybeans and early menarche? then cell tests are uninformative and we need to choose the appropriate embryo or larva biotest that gives us the answer. (see step 3.4)

Another example: do you remember the DeepWater oil spill in the Caribean sea? Two questions can be asked, requiring different schemes for their answers:

A. Are we really exposed to contaminants harmful to our health? We need to sample water at the beach where people go, at the time when they go (months later after the spill), and look for biological impact.

B. How does the environment react and tolerate contamination? Then we need to collect samples at different distances and at different times from the day and place of the spill, compare them and monitor the chemical decay.

Time is an important issue. In the laboratory we can easily mimic the dose of a single chemical or mix of chemicals. We can mimic variations in the dose and decide the time of exposure. But it is very difficult to mimic long exposure times while at the same time examining the full organism development and physiology – from fertilization to adult.

Cell tests are not better or worse than embryo tests. It really depends on the question being asked and on the tools and methods that are currently available. We have to make choices: either we use cells or we use organisms; either we look at embryo development or we look at adult physiology; either we focus on the chemicals (the doses, the mixes) or we examine organism effects (genes, metabolism, hormones, fertility, adipogenesis, feeding behaviour, etc…). To do all at once is nearly impossible for a single laboratory, and even for partnerships of laboratories.

The effects of EDCs are not easily modeled by cell tests. Appropriate animal models are required to attempt to recapitulate the human experience and to ensure translational utility. Honestly, we are still far from these tests. While conventional toxicology relies on selected strains of rodents and focuses on endpoints such as tumor-formation or birth defects, EDC research needs a diversity of species to model subtle endocrine outcomes.

New tests are likely to come up and be validated in the near future, due to advances in genomics, live imaging and other branches of experimental science. An expanding range of tests could soon be available to EDC researchers, and this is good news.

Animal Models to Study EDCs

The fish model Zebrafish larvae are ideal for studying the outcomes in the developmental process, physiology, and behavior in vertebrates, following exposure to EDCs and xenobiotics. Zebrafishes are a low-cost model, consent to scale up the analyses or to combine exogenous effects with gene expression analyses or even gene modification. Zebrafish should be incorporated into regulatory testing strategies for EDC.

The amphibian model Xenopus leavis is an ideal model to test thyroid axis disruption across vertebrate after already some days of exposure protocol. It is especially useful for studies of plant protection products on thyroid homeostasis.

Bird models Birds have been used mostly in ecotoxicological studies to predict the fate of environmental contaminants in the environment, rather than examine the population effect of chemicals. Also mention studies that altered feeding behavior. Hence, this kind of screening program can be also harnessed in legislative frameworks. Since avian embryos can be easily visualized, birds tend to be appreciated also for toxicology or developmental studies.

Rodent models In classical toxicology, this model has been widely used for human risk assessment and focuses mostly on birth defects and tumor formation. However, for EDCs studies the strains to be used need to be selected carefully, since the aims are the changes of pubertal timing, mammary gland development, or even social behaviors.

Organisms that can be used as biotest have to be easily obtained from the environment and/or their breeding has to be uncomplicated. The genetic structure of the organism and its sensitivity to various classes of xenobiotics should be known. The organism should react similarly (as compared to humans) to the dose of the chemical. Finally, the latency and appropriate critical period of a given species for EDCs should be kept into consideration.

In conclusion, to conduct serious research we have to make choices, and reasonably teams of scientists with specialized competencies and tools have to cooperate to device new tests and methods to correctly estimate the entity of EDCs action.