Certain chemicals, such as BPA, are potential endocrine disruptors - compounds that interrupt the processes of natural hormones. Based on rodent studies, the US Food and Drug Administration say that exposure to such compounds is safe at low levels. But new research has found that rodents and humans have different responses to these chemicals, suggesting that current exposure recommendations need to be evaluated.
Potential endocrine disruptors (EDs) can be found in pesticides, flame retardants and food and drink packaging. Exposure to such chemicals, including BPA (bisphenol A), has been associated with an array of health problems, particularly reproductive disorders, male impotence and developmental disorders.
Past research has suggested that infants, children and pregnant women are most vulnerable to the effects of ED exposure. Most recently, Medical News Today reported on a study suggesting that male fetus exposure to BPA may increase the risk of prostate cancer.
At present, researchers commonly use rodent models to assess how ED exposure affects human health. Once scientists have seen how certain EDs affect rodents, they reduce the observed safety threshold by 100 to work out the safety levels for humans.
But in a new study, researchers from France found that human and rat testes responded differently to EDs in two thirds of cases - a finding that questions current ED safety levels for humans.
Human testes over 100 times more susceptible to some EDs than rodents
To reach their findings, published in the journal Reproduction, the team used a new vitro culture technique, called FeTA, to simulate normal testicular development in rats, mice and humans. The effects of six potential EDs on the three species were assessed at different stages of development.
From this, the researchers found that response to EDs was similar in humans and rodents in only one third of cases. Human testes were found to be over 100 times more susceptible to the effects of certain chemicals, such as BPA, than the testes of rodents.
Commenting on the findings, lead study author Prof. René Habert, of the University of Paris-Diderot, says:
"Our work suggests that for some compounds, human and rat cells show different susceptibilities. For others, there appear to be fundamental differences in the way these compounds act in humans and rodents.
We think that these differences between species are even more pronounced for reproductive functions. This means we really have to question how relevant animal data is to assessing risk in humans."
Effects of EDs 'should be tested on both human and rodent cells'
These findings suggest that going forward, the effects of EDs should be tested on both human and rodent cells to ensure the safety risk of chemicals is accurate, according to the research team. They note that the FeTA method is a reliable tool for conducting such testing.
Researchers found that rodent and human testes respond differently to endocrine-disrupting chemicals, such as BPA.
"The FeTA system is a great tool for comparing effects of endocrine disruptors on testis development in different species," adds Prof. Habert. "However, the limitation is that we cannot use it to study long-term effects, as testis development can only be maintained for up to 10 days, depending on the species."
The researchers now plan to assess the safety risks of BPA substitutes, including BPS (bisphenol S) and BPF (bisphenol F).
In addition, they want to see how these compounds connect with both human and rodent cells in a molecular sense in order to determine why different species experience different effects.
Prof. Habert concludes:
"We need to develop specific tools to study chemical toxicity in human reproductive cells; this will allow us to accurately assess safety thresholds for different compounds, and re-evaluate the acceptable daily intake levels to protect human health for some of them."
In a recent feature, we looked at the impact of industrial chemicals on infant brain development and whether a change in US chemical policy is needed.