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Endocrine System and Endocrine Disrupting Chemicals
Endocrine system consists of a set of glands disseminated throughout the body.
Hormones are the chemicals secreted by the glands and transferred through bloodstream to the target tissues. At the target site, these hormones stimulate action by
another hormone production, alteration in metabolism or any other action depending upon the targeted receptor. Almost 50 different types of hormones manage the
normal human physiology throughout life. EDCs possess similar properties as hormones and thus interfere with conventional endocrine mechanism leading to deleterious effects in both human beings and wildlife [10].
The general disrupting mechanisms of EDCs were anticipated through animal
studies. The main mechanism by which EDCs interrupt cell programming is through
epigenetic alterations [11]. Epigenetic alterations are referred as hereditary modifications in gene expression irrespective of any change in underlying DNA sequence.
Epigenetics can modify gene expression and transcription through various pathways such as cytosine residues methylation, post-translation alteration of histones,
and modification of expression on microRNA [12]. Furthermore, these epigenetic
alterations may irreversibly alter the epigenome in germline resulting in the transfer
of changes to successive generations. These transgenerational effects of EDCs only
exist when the exposure occurs during developmental phase [13]. For instance,
when a pregnant female gets exposed to EDCs, the germline of fetus (F1) also gets
exposed to it. This exposed germline serves as the gametes for the next generation
(F2). The successive generation (F3) will also be affected by the EDCs but through
indirect exposure. The continuation of EDCs effect in F3 is considered as transgenerational [7]. Figure 10.1 illustrates the epigenetic alterations caused by EDCs [14].
Endocrine Disrupting Chemicals as Obesogens
Obesogens
Conventionally, the increase in the rate of obesity is ascribed with enhanced fat
consumption and a subsequent decrease in physical activities. However, there are
certain chemicals in environment that contribute towards escalating obesity rates
[15]. Obesogens are referred as such chemicals that cause increase in weight either
due to the direct stimulation of fat cells or through the indirect modification of the
pathways that modulates appetite, satiation, metabolism, and energy balance that
promotes the storage of calories [16]. Numerous known obesogens are EDCs that
act through disrupting hormone receptors [17]. Several obesogenic EDCs have been
involved in the development of diabetes, cardiovascular diseases, metabolic syndrome, non-fatty liver, infertility, and cancer [18]. The most common obesogenic
EDCs include bisphenols, phthalates, polychlorinated biphenyls (PCBs), parabens,
T. H. Mallhi et al.
Endocrine System and Endocrine Disrupting Chemicals
Endocrine system consists of a set of glands disseminated throughout the body.
Hormones are the chemicals secreted by the glands and transferred through bloodstream to the target tissues. At the target site, these hormones stimulate action by
another hormone production, alteration in metabolism or any other action depending upon the targeted receptor. Almost 50 different types of hormones manage the
normal human physiology throughout life. EDCs possess similar properties as hormones and thus interfere with conventional endocrine mechanism leading to deleterious effects in both human beings and wildlife [10].
The general disrupting mechanisms of EDCs were anticipated through animal
studies. The main mechanism by which EDCs interrupt cell programming is through
epigenetic alterations [11]. Epigenetic alterations are referred as hereditary modifications in gene expression irrespective of any change in underlying DNA sequence.
Epigenetics can modify gene expression and transcription through various pathways such as cytosine residues methylation, post-translation alteration of histones,
and modification of expression on microRNA [12]. Furthermore, these epigenetic
alterations may irreversibly alter the epigenome in germline resulting in the transfer
of changes to successive generations. These transgenerational effects of EDCs only
exist when the exposure occurs during developmental phase [13]. For instance,
when a pregnant female gets exposed to EDCs, the germline of fetus (F1) also gets
exposed to it. This exposed germline serves as the gametes for the next generation
(F2). The successive generation (F3) will also be affected by the EDCs but through
indirect exposure. The continuation of EDCs effect in F3 is considered as transgenerational [7]. Figure 10.1 illustrates the epigenetic alterations caused by EDCs [14].
Endocrine Disrupting Chemicals as Obesogens
Obesogens
Conventionally, the increase in the rate of obesity is ascribed with enhanced fat
consumption and a subsequent decrease in physical activities. However, there are
certain chemicals in environment that contribute towards escalating obesity rates
[15]. Obesogens are referred as such chemicals that cause increase in weight either
due to the direct stimulation of fat cells or through the indirect modification of the
pathways that modulates appetite, satiation, metabolism, and energy balance that
promotes the storage of calories [16]. Numerous known obesogens are EDCs that
act through disrupting hormone receptors [17]. Several obesogenic EDCs have been
involved in the development of diabetes, cardiovascular diseases, metabolic syndrome, non-fatty liver, infertility, and cancer [18]. The most common obesogenic
EDCs include bisphenols, phthalates, polychlorinated biphenyls (PCBs), parabens,
T. H. Mallhi et al.