Author: Gianpiero Pescarmona
Chelator of divalent ions
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Susser susser 1996
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Inviato da Samsung Mobile.
Phthalate esters (esters of phthalic acid) are a group of chemicals used to make plastics more flexible and harder to break.
They are often called plasticizer.
These compounds are synthetized by reacting phthalic anhydride with alcohol.
Most common are:
# DEHP di(2-ethylhexyl) phthalate
# DIDP diisodecyl phthalate
# DINP diisononyl phthalate
# BBzP benzylbutylphthalate
Phthalates are used widely in polyvinyl chloride plastics PVC , which are used to make products such as plastic packaging, garden hoses, medical device, children's toys.
Phthalates with small R and R' groups are also used as solvents in pesticides and personal-care items like perfume, eye shadow, nail polish, liquid soap, and hair spray.
Phthalates are easily released into the environment.
Because phthalate plasticizers are not chemically bound to PVC, they can easily leach into the environment and comes into contact with humans mainly through dermal exposure, oral ingestion and inhalation.
It is possible to come into contact with phthalates by:
ingestion: people are exposed to phthalates by eating and drinking foods that have been in contact with containers and products containing phthalates. Young children may have a greater risk of being exposed to phthalate because of their hand-to-mouth behaviors
absorption: phthalates are found in many scented and cosmetic products, where they stabilize the fragrance, increase spreadability, and enhance absorption. Low-molecular-weight phthalates such as DEP, DBP, BBzP can be absorbed through the skin and into the bloodstream
inhalation: phthalates can be breathed in from dust or fumes from any products that contain vinyl, such as vinyl flooring, vinyl seating (in cars, for example), and some diaper-changing mats. The production of fumes by these products is called off-gassing.
Maternal exposure to phthalate provides the first source of fetal exposure.
This exposure to phthalates continues after birth through breast feeding, baby and infant food sources and contact to the environment.
Diet is believed to be the main source of DEHP and other phthalates in the general population.
Fatty foods such as milk, butter, and meats are a major source.
In general, children's exposure to phthalates is greater than on adults.
In a 1990s Canadian study that modeled ambient exposures, it was estimated that daily exposure to DEHP was:
* 9 μg/kg bodyweight/day in infants,
* 19 μg/kg bodyweight/day in toddlers,
* 14 μg/kg bodyweight/day in children,
* 6 μg/kg bodyweight/day in adults.
Infants and toddlers are at the greatest risk of exposure, because of their mouthing behavior.
People are commonly exposed to phthalates, and most people in the US tested by the Centers for Disease Control and Prevention have metabolites of multiple phthalates in their urine:
“In the Fourth National Report on Human Exposure to Environmental Chemicals (Fourth Report), CDC scientists measured 13 phthalate metabolites in the urine of 2,636 or more participants aged six years and older who took part in the National Health and Nutrition Examination Survey (NHANES) during 2003–2004.
For several phthalate metabolites, results from the prior survey periods of 1999–2000 and 2001–2002 are also included in the Fourth Report.
By measuring phthalate metabolites in urine, scientists can estimate the amount of phthalates that have entered people's bodies.
??CDC researchers found measurable levels of many phthalate metabolites in the general population.
This finding indicates that phthalate exposure is widespread in the U.S. population.??
Research has found that adult women have higher levels of urinary metabolites than men for those phthalates that are used in soaps, body washes, shampoos, cosmetics, and similar personal care products.
Finding a detectable amount of phthalate metabolites in urine does not imply that the levels of one or more will cause an adverse health effect.
Biomonitoring studies on levels of phthalate metabolites provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of these chemicals than are found in the general population.
Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.”
Once phthalates enter a person's body, they are converted into breakdown products (metabolites) that pass out quickly in urine.
DEHP is a high molecular weight compound that is first hydrolyzed by pancreatic lipases, liver esterases, and nonspecific esterases in the blood. Further degradation produces more than 15 short branch derivatives.
MEHP (Mono(2-ethylhexyl) phthalate) is formed after the first hydrolysis of DEHP, and is ten-times more potent than DEHP in vitro. In humans, MEHP is excreted in the urine mostly conjugated with glucuronic acid, and is used as a biomarker to estimate DEHP exposure.
DEHP and its metabolites are rapidly cleared from the circulation.
MEHP acts as potent activator of the peroxisome proliferator-activated receptor (PPAR) α and γ nuclear receptors, which are involved in lipid metabolism and adipocyte differentiation and development, respectively. PPAR α has also been linked with inflammatory response.
A man who voluntarily swallowed 10 g of DEHP had stomach irritation and diarrhea.
DEHP, at the levels found in the environment, is not expected to cause adverse health effects in humans.
Most of what we know about the health effects of DEHP comes from studies of rats and mice that appear to be particularly sensitive to some of the effects of DEHP.
Studies of long-term exposures in rats and mice have shown that high oral doses of DEHP cause health effects mainly in the liver and testes.
These effects are induced by levels of DEHP that are much higher than those received by humans from environmental exposures.
Toxicity of DEHP in other tissues is less well characterized, although effects in the thyroid, ovaries and blood has been reported in a few animal studies.
Phthalates are endocrine disruptor, chemicals that in certain doses can interfere with the endocrine system.
Epidemiological studies have suggested an association between phthalate exposures and human reproductive effects in infant and adult populations.
In male, exposure to DEHP in rodents was found to be an endocrine disruptor, and in humans there are correlations between phthalate exposure and:
decreased anogenital distance
reduced testosterone levels
poor semen quality
These clinical findings, together with cryptorchidism, hypospadias, and testicular cancer , are grouped under the term testicular dysgenesis syndrome (TDS), which is thought to originate from an insult to Sertoli or Leydig cell function during development.
DEHP exposures occurring before the maturity of the rats, and particularly during the fetal period results in reduced testosterone formation by the fetal testis due to reduced expression of enzymes and proteins involved in steroidogenesis.
The testosterone decrease is triggered when exposure levels are between 50 and 100 mg/kg/day.
The decrease is in the presence of near normal Leydig cell numbers, as well as near normal proteins and enzymes involved in the transport of cholesterol into the mitochondria and in downstream steroidogenic enzymes, which suggested that the classical steroidogenic pathway is not affected in the adult offspring.
These long-term anti-androgenic effects also are observed with the phthalate DBP, suggesting a similar mechanism of action between phthalates.
In the adult male offspring, exposed in utero to DEHP, the decreased testosterone levels are surprising because the adult population of Leydig cells is not present at the time of exposure in the fetus, and DEHP and its metabolites are cleared soon after birth.
This suggests that DEHP may have targeted the stem cells of the adult-type Leydig cells, which most likely are present in utero, or cells from other organs that subsequently affect testosterone formation by adult Leydig cells.
Another effect of DEHP is the decreased mineralcorticoid receptor (MR) levels in Leydig cells.
No effect of DEHP is seen on receptors for androgen, estrogen, progesterone, glucocorticoid or steroidogenic factor 1.
This decrease in MR closely correlated with reduction in serum testosterone levels.
In addition, Leydig cells expressed 11βHSD2, a corticosterone-inactivating enzyme which allows for specific MR activation by the endogenous ligand aldosterone, suggesting that the action of MR is aldosterone-mediated.
As with testosterone and MR levels, serum levels of aldosterone are decreased, suggesting the adrenal gland as another long-term target of DEHP.
DEHP targets the adrenal gland steroid production and that it is most sensitive before maturity.
Interestingly, angiotensin II, potassium, corticosterone, and ACTH levels are not affected by DEHP, suggesting that its effect is confined to the zona glomerulosa of the adrenal gland.
Dissection of the renin–angiotensin pathway showed that the angiotensin II receptors, in particular ATIIR-IIb, are decreased by the exposure to DEHP.
This could results in under-stimulation of the adrenal gland to produce aldosterone.
Similar to the testes, a mechanism not involving the classical steroidogenic pathway is likely to be responsible for the decrease in aldosterone biosynthesis since expression of the protein and enzymes involved in steroidogenesis are not affected.
Adult aldosterone levels remained similar to those in puberty, corresponding to half of the adult levels, suggesting that DEHP targets genes involves in the maturation of the zona glomerulosa or genes that increase the capacity to produce more aldosterone.
In addition, despite the lower levels of aldosterone, there is no compensation from the renin–angiotensin system to increase angiotensin II and ultimately aldosterone.
This was similar to the testes where decreased testosterone levels don’t result in an increase of LH levels, although this appears to depend on the time of exposure.
It is likely that the feedback loops regulating aldosterone and testosterone production are reset to accommodate for the lower levels of the steroidogenic hormones present during development.
The reduced levels of aldosterone resultes in decreases of systemic blood pressure.
Fetal origin of endocrine dysfunction in the adult: The phthalate model
"Endocrine susceptibility of the human testis to phthalates”:male
In the female, DEHP also targets the reproductive system, but data on the mechanisms have lagged compared to the male.
New data from studies of female offspring exposed in utero to DEHP is suggesting sex-specific effects of phthalates, and that DEHP has a multi-organ effects that depends on the time of exposure.
In humans, studies have shown an association between high levels of MEHP and an increase in:
early pregnancy loss
decreased gestation times
In rodents, exposure to phthalates has shown effects on steroidogenesis and dysregulation of the reproductive system.
The outcome of these effects is dependent on the time of exposure with long lasting impact occurring before maturity.
The ovary is identified as a target of high dose of DEHP (2 gr/kg/ml) showed suppression of estradiol levels, absence of the LH surge, anovulation, increased estrous cycles, and polycystic ovaries.
Interestingly, DEHP is the only phthalate shown to decrease estradiol levels by directly affecting the granulosa cells while other phthalates, such as DBP, increased the degradation rate of estradiol through up-regulation of liver-metabolizing enzymes.
DEHP reduces estradiol levels by decreasing the expression of aromatase in granulosa cells, in a dose dependent manner by a mechanism mediated by the PPARs.
"Effects of phthalate exposure on reproductive development and PPARs in prepubertal female rats”:http://www-ncbi-nlm-nih-gov.offcampus.dam.unito.it/pubmed/22279657
Fetal origin of endocrine dysfunction in the adult: The phthalate model
A link between altered thyroid function and phthalate exposure has been reported in humans but there is no experimental evidence for this.
In utero exposure to DEHP increase Thyroid stimulating hormone (TSH) levels but this increased is in contrast to free triiodothyronine(T3) levels.
Di(2-ethylhexyl) phthalate metabolites may alter thyroid hormone levels in men
Fetal origin of endocrine dysfunction in the adult: The phthalate model
Chronic dietary administration of DEHP has been shown to produce liver tumors in rats and mice.
Treatment with DEHP produced a pleiotropic response including:
*hyperplasia and hypertrophy
*induction of several metabolic enzymes
*elevation of the relative liver weight
*inhibition of gap-junctional communication
*enhanced peroxisomal β oxidation (PPAR α receptor)
*increased replicative DNA synthesis.
Increased cell replication produced by peroxisomal proliferators may enhance the growth of hepatic lesions from spontaneously initiated cells into hepatic focal lesions.
During the last decades more than 100.000 new chemicals have been introduced to the environment and during the same period of time there has been a remarkable increase in several chronic illnesses, including asthma and allergy in children.
Epidemiological data point to a possible correlation between phthalate exposure and asthma and airway diseases in children.
Experimental studies present support for an adjuvant effect on basic mechanisms in allergic sensitization by several phthalates.
Despite variations in the experimental design and reported result in the individual studies, a majority of published reports have identified adjuvant effects on Th2 differentiation, production of Th2 cytokines and enhanced levels of Th2 promoted immunoglobulins (mainly IgG1 but also IgE) in mice.
A limited amount of data do also suggest phthalate-induced enhancement of mast cell degranulation and eosinophilic infiltration which are important parts in the early inflammation phase.
Phthalate exposure and asthma in children
The use of some phthalates has been restricted in the European Union and in United States for use in children's toys since 1999.
DEHP, BBP, and DBP are restricted for all toys; DINP, DIDP, and DNOP are restricted only in toys that can be taken into the mouth.
The restriction states that the amount of phthalates may not be greater than 0.1% mass percent of the plasticized part of the toy.
These phthalates are allowed at any concentration in other products and other phthalates are not restricted.
Phthalates are used in some but not all PVC formulations, and there are no specific labeling requirements for phthalates.
PVC plastics are labelled "Type 3" for recycling reasons.
However, the presence of phthalates rather than other plasticizers is not marked on PVC items.
Only unplasticized PVC (uPVC), which is mainly used as a hard construction material, has no plasticizers.
If a more accurate test is needed, chemical analysis, for example by gas chromatography or liquid chromatography, can establish the presence of phthalates.
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