Development and improvement of tests for identification of hormone disrupting drugs

30 Apr 2022

Swim bladder inflation in zebrafish larvae is inhibited by chemicals that affect the thyroid hormones T4 and T3. Here the effect is seen after four days of exposure to the polycyclic aromatic hydrocarbon, phenanthrene. Source: Vergauwen et al., 2015.

Our ERGO Coordinator, Henrik Holbech and Project Manager, Helle Lyngborg both from SDU contributed an informative article to promote ERGO and its valuable research of endocrine disruptors. The article featured in the April 2022 issue of Dansk Kemi. Dansk Kemi translated as ‘Danish Chemistry’ in English, is a journal for chemical engineers and other related topics. Below are some translated extracts from the article.

In recent decades, there has been a strong focus on the fact that chemicals can affect human and animal hormonal systems in a way that can cause serious health effects, including development and reproduction. Therefore, for the next 20 years, work will be done internationally (the EU and the OECD) to develop and validate tests that can identify endocrine disrupting chemicals so that they can be better regulated by law. There are still big gaps in the tests that are available today and legally, one is not quite in place yet in the EU. That is why, under the Horizon 2020 research programme, the EU has funded €50 million to eight European projects, known as the EURION Cluster. The eight projects are researching how to develop and validate tests that can identify endocrine disruptors. One of these projects is ERGO (EndocRine Guideline Optimisation), coordinated by the Ecotoxicology research group in the Department of Biology, SDU.

Both in humans and in animals in the wild, there have been signs of gender development problems since the 1970s. For human health, it can be very difficult to prove effects of specific substances. However, several studies have seen an association between exposure to chemicals and effects on male sex development and reproduction, particular examples include declining sperm count and increased risk of testicular cancer, but also effects in girls and women such as breast cancer and early menstruation are associated with chemical exposure. In relation to the environment, there is clear evidence for effects of specific substances. For example, it has been shown that fish can become hermaphrodites due to the presence of estrogen-like substances such as nonylphenol and octylphenol in wastewater, and female snails developing male genitals due to tributyltin (TBT) which is present in ships’ hull paint.

In order to be able to identify endocrine disrupting chemicals, it is required, as previously mentioned, that you have suitable tests for it. The current test guidelines, which are validated by the OECD and thus accepted by all OECD member countries, identify some effects, especially for chemicals that affect the sex hormone system (where the hormones are estrogens like 17ÿ-estradiol and androgens like testosterone). However, many other types of effects still lack tests. An example is the thyroid hormone system, where thyroid hormones (T4 and T3) are important for, among other things, the development of all mammals’ brains and later for metabolism. In amphibians and fish, thyroid hormones are crucial for the transition from tadpole/fish larva to frog/fish. The thyroid hormone system in mammals is similar to the system in fish and in amphibians, and so we use this in ERGO, where we develop so-called biomarkers for effects on the thyroid hormone system in fish. One of the promising markers is the inflation of the fish swim bladder, which is controlled by thyroid hormones. Strange as it may sound, a lack of inflation of the swim bladder in a zebrafish larva after exposure to a chemical could in many cases predict effects in humans with the same chemical. Unfortunately (for historical reasons), regulatory procedures for hazard assessment of chemicals are separate for human health (where mammals (rodents) are used) and for the environment (where fish and amphibians are used). This means that useful data from tests with vertebrates other than mammals have so far been ignored in human health research. ERGO‘s hypothesis is that results from experiments with fish and amphibians can predict harmful effects on hormonal systems in mammals and vice versa. We use zebrafish, frog spawn, mice and a variety of cell-based tests to demonstrate this. New markers are developed using advanced analysis methods for changes in gene
expression, protein expression and metabolism (transcriptomics, proteomics, metabolomics). The goal is to develop and improve OECD tests, both so that we get a more effective identification of endocrine disruptors and thus a better protection of consumers and the environment, and also so that we eventually reduce the use of animal testing.

Read the original article