an overview of scientific advances on neurotoxicological impacts
of EDCs, click here.]
A, TM Meerts, JJ van Zanden, EAC Luijks, I van Leeuwen-Bol, G Marsh,
E Jakobsson , Å Bergman and A Brouwer. 2000. Potent Competitive
Interactions of Some Brominated Flame Retardants and Related Compounds
with Human Transthyretin in Vitro. Toxicological
Sciences 56: 95-104.
PDBEs common in sewage
Michigan salmon contaminated by PBDEs
research article elevates concern about flame retardants
dramatically, especially given independent information about the
of flame retardant contamination and the potential impact of thyroid
disruptions on brain development.
bottom line is that some widespread flame retardants are more
powerful than the natural hormones themselves at binding with
transthyretin, a protein crucial to normal thyroid hormone function.These
retardants are present. They are powerful. And their impact could
did Ilonka et al. study?
authors examined the ability of certain polybrominated diphenyl
ethers (PBDEs), pentabromophenol (PBP), and tetrabromobisphenol
A (TBBPA) to prevent natural human thyroid hormone, thyroxine (or
T4), from binding with human transthryetin in test tube experiments.
logic was simple. Ilonka et al. were motivated by the observation
that these flame retardants are similar in chemical form to natural
human thyroid hormone T4. This raised concerns that if these compounds
were present in people, then they might interfere with the natural
binding of T4 to transthryetin, thus potentially leading to disruption
of the thyroid control over brain development.
tube experiments like this, called competitive binding experiments,
are well-accepted, indeed classic experiments used to assess the
potency of interaction among natural and synthetic compounds. In
the experiments, natural and synthetic compounds are mixed together
in a way that allows the experimenters to measure whether the synthetic
materials displaced the natural compounds from binding.
compounds that compete effectively with the natural hormone are
thought to be riskier than those that don't (all other things being
equal), because if present they are more likely to interfere with
natural hormone function. In most systems studied, e.g., estrogen
(as opposed to thyroid) mimics, the synthetic compound is significantly
less powerful on a molecule by molecule basis than the natural compound.
did they find?
One of the striking results found by Ilonka et al. is
that several of the flame retardants studied are more powerful
than the natural hormone, T4, in binding with transthryetin:
results presented in this study clearly demonstrate for the
first time that hydroxylated brominated flame retardants of
several different classes are able to bind to human transthyretin
in vitro, some with extremely high potency, e.g., TBBPA
and PBP. This is an important finding, as brominated flame
retardants are used extensively at present for a large variety
of applications and can be detected in wildlife and humans.
The results of this paper thus indicate the possible capability
of a large group of particularly brominated industrial chemicals
to interfere with and potentially disrupt the thyroid hormone
transport and metabolism."