Environmental pollutants as
Importance of Thyroid
Thyroid hormones are essential for:
Normal brain development in fetus.
For the control of metabolism,
For normal adult physiology.
What Happens in the presence
of Endocrine Disruptors?
Environmental pollutants Interfere with
the normal functioning of thyroid
hormone and produce hazaderous
Disturbed Thyroid Harmone signalling
How Pollutants act?
Structural Similarity with THs:
Several Thyroid Disruptors have high degree
structural resemblance to the thyroxine (T4)
and triiodothyronine (T3) due to which they
get attach to receptor sites instead of THs.
Interference with regulation:
Many industrial chemicals and pollutants can
interfere with thyroid function by acting on
different points of regulation of thyroid
hormone synthesis, release, transport
through the blood, metabolism of thyroid
Major Thyroid Disruptors And
It block uptake of Iodide in thyroid cells.As a
result T3 and T4 synthesis decreased.Higher
in smoker Women.
These are lipophilic in nature and accumulate
in fatty tissues.PCBs inhibit TSH receptors
and decrease production of T3 and T4. It
reduce T4 circulation in blood.
It enhance hepatic(liver) metabolism results
in increase metabolism of T3 and T4
T4 transport to target tissues via serum
transport proteins e.g Transthyretin(TTR)
but if pentachlorophenol competitively
binds to serum transport proteins then
T4 would not be transported to target
At high temprature BPA leach out of
plastics into food.
In Human embryonic kidney cell and
hepatoblastoma cells BPA inhibit T3
binding to TR .
especially those found in soy protein
(e.g., genistein, coumesterol) cause
goiter in Human infants.
Abnormalities due to Thyroid
Goiter and thyroid diseases are
associated with TH disruption.
It results in impaired intellectual
development in childrens or
permanent cognitive deficiencies.
Perchlorates as Thyroid
Perchlorate is a known competitive
inhibitor of the sodium-iodide in
humans and can inhibit iodide
uptake, leading to the suppression of
T3 and T4.
It has been related to lower levels of
iodine in breast milk.As a result of
iodine deficiency neurodevelopmental
disorders occur in utero.
In an environment with perchlorate
exposure may have a significant effect on
thyroid hormone production particularly in
the environment of dietary iodine
PCBs as Thyroid Disruptors
The concept that PCBs can exert a
neurotoxic effect on the developing brain
by causing a state of relative
Polychlorinated biphenyls belong to the
class of organochlorine compounds
classified as persistent
organohalogenated pollutants (POPs)
(1)It reducing the ability of thyroid
hormones to bind to transport proteins in
(2)It enhance hepatic metabolism by
up-regulating the sulfotransferases
that break down thyroid hormones in
(3)It inhibit the production of
deiodinases that allow T4 to be
converted to T3
(4)it act as either an agonist or
antagonist at the site of the cellular
The role of TSH in activating growth and
differentiation of follicular cells have
shown that a prolonged disruption of the
pituitary-thyroid axis is linked to thyroid
neoplasia. Two mechanisms involved in
the disruption of the pituitary thyroid axis
are chemically-induced blocking of
thyroid peroxidase and inhibition of T4
deiodinases, which are known to occur
with TD exposure