371
shown elevated nitric oxide production, cell death, lipid peroxidation, oxidative
stress as well as activation of transcription factors upon UVB exposure. This suggests that methyl paraben is generally considered as safe preservative in the cosmetics, but may give rise to undesirable effects to human skin upon sunlight exposure
[24]. This also illustrates that sunlight may potentiates the harmful effects of parabens especially methyl paraben [24].
Upon hydrolysis, parabens undergo biotransformation process and converted
into para-hydroxybenzoic acid along with alcohol in in vivo conditions. Esterases
comprising carboxylesterases catalyzes this process [25]. Humans as well as animal
studies have depicted that ester bond hydrolysis happens in small intestine and liver
microsomes. Although, increase in the length of alkyl chain usually diminishes the
process of hydrolysis in the human liver microsomes [26, 27]. Parabens are eliminated from the body mainly through the urine. Alternatively, some number of parabens are also eliminated via feces and bile. This is also advantageous in a way that
urinary metabolites are used as biomarker for evaluating paraben exposure to body
[22, 28].
Correspondingly, studies have suggested that some parabens especially of low
molecular weight or short alkyl chain excreted in unmetabolized form in the urine
[29]. For this reason, level of parabens in the urinary sample of 60 Danish men was
determined. Concentrations of 98%, 80%, 98% as well as 83% were measured in
urine samples involving methyl paraben, ethyl paraben, propyl paraben along with
butyl paraben, respectively [30].
Parabens as Endocrine Disrupting Chemicals
Influence on Thyroid Gland
Thyroidhormone has crucial role in normal development along with regulation of
metabolism in adults. This hormone has association with body weight as well as
energy expenditure. Likewise, hyperthyroidism elevates resting energy expenditure
and leads to weight loss. Conversely, hypothyroidism promotes reduced energy
expenditure and hence give rise to increased weight [31, 32]. So, thyroid hormone
has pivotal role in the cellular metabolism and participates in variety of pathways
which are involved in metabolism of lipids, proteins, and carbohydrates. Besides,
thyroid hormone is a primary regulator of mitochondrial respiration as well as biogenesis. Patients with abnormality in thyroid hormones mostly develops symptoms
of metabolic dysfunction, also having association with cancer [33, 34].
Significant decrease in T4 level is observed upon paraben’s exposure in an animal study in prepubertal female rats [35]. One study on adult females also demonstrated decrease in T3 and T4 on butyl paraben exposure, and this decrease was
different among racial/ ethnic groups. Some rodent studies also illustrated decrease
in thyroid hormone level upon paraben exposure [36]. Thyroid stimulating hormone
22 Parabens as Endocrine Disrupting Chemicals and Their Association…
shown elevated nitric oxide production, cell death, lipid peroxidation, oxidative
stress as well as activation of transcription factors upon UVB exposure. This suggests that methyl paraben is generally considered as safe preservative in the cosmetics, but may give rise to undesirable effects to human skin upon sunlight exposure
[24]. This also illustrates that sunlight may potentiates the harmful effects of parabens especially methyl paraben [24].
Upon hydrolysis, parabens undergo biotransformation process and converted
into para-hydroxybenzoic acid along with alcohol in in vivo conditions. Esterases
comprising carboxylesterases catalyzes this process [25]. Humans as well as animal
studies have depicted that ester bond hydrolysis happens in small intestine and liver
microsomes. Although, increase in the length of alkyl chain usually diminishes the
process of hydrolysis in the human liver microsomes [26, 27]. Parabens are eliminated from the body mainly through the urine. Alternatively, some number of parabens are also eliminated via feces and bile. This is also advantageous in a way that
urinary metabolites are used as biomarker for evaluating paraben exposure to body
[22, 28].
Correspondingly, studies have suggested that some parabens especially of low
molecular weight or short alkyl chain excreted in unmetabolized form in the urine
[29]. For this reason, level of parabens in the urinary sample of 60 Danish men was
determined. Concentrations of 98%, 80%, 98% as well as 83% were measured in
urine samples involving methyl paraben, ethyl paraben, propyl paraben along with
butyl paraben, respectively [30].
Parabens as Endocrine Disrupting Chemicals
Influence on Thyroid Gland
Thyroidhormone has crucial role in normal development along with regulation of
metabolism in adults. This hormone has association with body weight as well as
energy expenditure. Likewise, hyperthyroidism elevates resting energy expenditure
and leads to weight loss. Conversely, hypothyroidism promotes reduced energy
expenditure and hence give rise to increased weight [31, 32]. So, thyroid hormone
has pivotal role in the cellular metabolism and participates in variety of pathways
which are involved in metabolism of lipids, proteins, and carbohydrates. Besides,
thyroid hormone is a primary regulator of mitochondrial respiration as well as biogenesis. Patients with abnormality in thyroid hormones mostly develops symptoms
of metabolic dysfunction, also having association with cancer [33, 34].
Significant decrease in T4 level is observed upon paraben’s exposure in an animal study in prepubertal female rats [35]. One study on adult females also demonstrated decrease in T3 and T4 on butyl paraben exposure, and this decrease was
different among racial/ ethnic groups. Some rodent studies also illustrated decrease
in thyroid hormone level upon paraben exposure [36]. Thyroid stimulating hormone
22 Parabens as Endocrine Disrupting Chemicals and Their Association…