**2. The concept of EDCs**

Originally articulated in the early 1990s by Colbron [2], the theory of *endocrine disruption* referes to exogenous chemicals present in the environment and/or diet that interfere and disrupt physiological hormonal systems, inducing adverse effects on human and wildlife health. The term "endocrine disruptor" was first used at the Wingspread Conference in Wisconsin, USA in 1991 for those EDCs, which may lead to an adverse health effect [3]. Initially the term focused on chemicals with estrogenic activity that would alter reproductive function, commonly referred to as environmental estrogens or xenoestrogens; it has expanded to compounds with androgenic activity, as well as thyroid-active chemicals [4]. Consequently, different variable terms appeared, e.g. endocrine disrupter or endocrine disruptor, hormone mimics, hormone inhibitors or endocrine modulators [5]. Today, these compounds are commonly referred to as EDCs.

Various attempts to set up a scientific definition of an EDC have been made. Today is generally wide acceptance of using the WHO definition [6], which is similar with the EU definition [7]: "*An endcorine disruptor is an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub)populations".*

EDCs interfere and disrupt physiological hormonal balance inducing adverse effects on human health through different mechanisms including direct interaction with hormone receptors, competition on binding and transport proteins or interference with hormone metabolism (blocking or inducing the synthesis of the hormones). Starting from this definition there are clearly two requirements for a substance to be defined as an EDCs, namely the demonstration of an adverse effect and an endocrine disruption mode-of-action. Additionally, the definition implies proof of causality between the observed adverse effect and the endocrine disruption mode-of-action.

It is important to underline that the definition of EDC includes the term "adverse" which was considered as a key criterion to differentiate a genuine EDC from a mere endocrine modulator (that elicits an adaptative reversible response in endocrine homeostasis). According to WHO the term "adversity" means: "*a change in morphology, physiology, growth, reproduction, develop‐ ment or lifespan of an organism which results in impairment of functional capacity or impairment of capacity to compensate for additional stress or increased susceptibility to the harmful effects of other environmental influences*." [8].

This definition is not covering the potential or indicates EDC. A potential (or suspected) EDC may alter function(s) of the endocrine system and consequently may cause adverse health effects, while a substance with indication of endocrine disrupting properties (called indicated EDC) might be expected to lead to endocrine disruption in an intact organism, or its progeny, or (sub)populations.

The need for an expansion of the general term to potential EDCs is reflected on the new Guidance document on Standardised Test Guidelines for Evaluating Chemicals for Endocrine Disruption (OECD 2011) [9]: "*A possible endocrine disrupter is a chemical that is able to alter the* *functioning of the endocrine system but for which information about possible adverse consequences of that alteration in an intact organism is uncertain*".

**2. The concept of EDCs**

220 Treatment of Type 2 Diabetes

EDCs.

*(sub)populations".*

disruption mode-of-action.

*environmental influences*." [8].

or (sub)populations.

Originally articulated in the early 1990s by Colbron [2], the theory of *endocrine disruption* referes to exogenous chemicals present in the environment and/or diet that interfere and disrupt physiological hormonal systems, inducing adverse effects on human and wildlife health. The term "endocrine disruptor" was first used at the Wingspread Conference in Wisconsin, USA in 1991 for those EDCs, which may lead to an adverse health effect [3]. Initially the term focused on chemicals with estrogenic activity that would alter reproductive function, commonly referred to as environmental estrogens or xenoestrogens; it has expanded to compounds with androgenic activity, as well as thyroid-active chemicals [4]. Consequently, different variable terms appeared, e.g. endocrine disrupter or endocrine disruptor, hormone mimics, hormone inhibitors or endocrine modulators [5]. Today, these compounds are commonly referred to as

Various attempts to set up a scientific definition of an EDC have been made. Today is generally wide acceptance of using the WHO definition [6], which is similar with the EU definition [7]: "*An endcorine disruptor is an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or*

EDCs interfere and disrupt physiological hormonal balance inducing adverse effects on human health through different mechanisms including direct interaction with hormone receptors, competition on binding and transport proteins or interference with hormone metabolism (blocking or inducing the synthesis of the hormones). Starting from this definition there are clearly two requirements for a substance to be defined as an EDCs, namely the demonstration of an adverse effect and an endocrine disruption mode-of-action. Additionally, the definition implies proof of causality between the observed adverse effect and the endocrine

It is important to underline that the definition of EDC includes the term "adverse" which was considered as a key criterion to differentiate a genuine EDC from a mere endocrine modulator (that elicits an adaptative reversible response in endocrine homeostasis). According to WHO the term "adversity" means: "*a change in morphology, physiology, growth, reproduction, develop‐ ment or lifespan of an organism which results in impairment of functional capacity or impairment of capacity to compensate for additional stress or increased susceptibility to the harmful effects of other*

This definition is not covering the potential or indicates EDC. A potential (or suspected) EDC may alter function(s) of the endocrine system and consequently may cause adverse health effects, while a substance with indication of endocrine disrupting properties (called indicated EDC) might be expected to lead to endocrine disruption in an intact organism, or its progeny,

The need for an expansion of the general term to potential EDCs is reflected on the new Guidance document on Standardised Test Guidelines for Evaluating Chemicals for Endocrine Disruption (OECD 2011) [9]: "*A possible endocrine disrupter is a chemical that is able to alter the* Recently, the Endocrine Society published a statement of principles on endocrine disruptors [10] in which another definition of an EDC has been proposed: *"An EDC is an exogenous chemical, or mixture of chemicals, that interferes with any aspect of hormone action."* This definition empha‐ sizes that the ability of a chemical to interfere with hormone action is of itself a reliable predictor for adverse outcomes.

A wide variety of chemicals act as EDCs. The Endocrine Disruption Exchange List (TEDX) to date lists almost 1000 endocrine disruptors [11]. The group of EDCs is highly heterogeneous and includes synthetic chemicals used as industrial solvents/lubricants and their by-products (persistent organic pollutants – POPs, dioxins like 2,3,7,8-tetrachlorodibenzo-p-dioxin – TCDD), plastics (bisphenol A – BPA), pesticides (as dichlorodiphenyltrichloroethane – DDT), plasticizers (phthalates like diethylhexyl phthalate – DEHP), heavy metals (arsenic, cadmium), tributyl tin (TBT), fungicides (vinclozolin) and pharmaceutical agents (diethylstilbestrol – DES). POPs comprise a broad class of organohalides, including polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs) and organochlorine pesticides.

However, one should keep in mind that there is also a large number of EDCs of natural origin occurring in plants consumed as food and also some secondary metabolites from fungi that may contaminate food. Examples of EDCs with oestrogenic activity are present in soy (e.g. genistein and daidzein), mycotoxins in cereals (e.g. zearalenone), goitrogens in cabbage (with the potential to inhibit iodine uptake) and glycirrhizine in liquorice (with the potential to disturb the mineralocorticoid system) [12].

EDCs are widely dispersed in the environment. Some are persistent, having long half-lives [13], while others are rapidly degraded in the environment or human body or may be present for only short periods of time but at critical periods of development, considered windows of susceptibility.

The effects of EDCs are observed especially on sensitive groups (foetus and child), based on their susceptibility to hormonal effects [14]. Therefore, for these groups the adverse effects may occur at concentrations that are far below levels that would be considered harmful in the adult [15]

Of a special concern are EDCs such as phthalates [16], PBBs [17] and BPA, detected in pregnant women, fetuses and newborns, taking into account that exposure occuring early in pregnancy can have short-term health effects, while exposure later or during early childhood may induce cognitive and developmental deficiencies [18].

Published studies illustrate that *in utero* developmental period is a critically sensitive window of vulnerability. Disruptions during this time-frame can lead to subtle functional changes that may not emerge until later in life [19] or even later to the next generation.

Actually, is considered that *in utero* and early postnatal exposures play an important role in the development of reproductive defects, obesity and metabolic syndrome as a result of inheritable chemical-induced epigenetic changes [20, 21, 22]. As an example of epigenetic change involved in reproductive defects one can note the developmental exposure to vinclo‐ zolin causing an increase in spermatogenic cell apoptosis in the adult rats [23]. This sperma‐ togenic defect was found to be transgenerational at least to F4 generation due to a permanent altered DNA methylation of the male germ-line [21].


**Table 1.** Classification of EDCs based on Danish criteria

Many other chemicals have also been implicated in promoting toxicity for multiple genera‐ tions, including BPA [24] or pesticides [25], but in these cases the multigenerational effects involved direct exposures, therefore are not considered transgenerational because they are not transmitted solely through the germ cells. Only effects appearing in the F3 generation are considered to be truly transgenerational [26].

There are multiple classifications of EDCs, based on their mechanisms of action (on enzymes, transport proteins or receptors), the pathways modulated (e.g., xenoestrogens/antiestrogens, xenoandrogens/antiandrogens), or the biological outcomes (simulation or inhibition) [27]. However, the best classification is the Danish criteria, based on available data (*in vitro, in vivo* and epidemiological studies), which is scientifically legitimated by Hass et al. [28]. Using this approach, EDCs are divided into 3 categories: *category 1,* for substances known to produce endocrine disrupting adverse effects in humans or animal species, *category 2a* for suspected EDCs, and *category 2b* for indicated EDC. Details regarding classification criteria are included in Table 1.
