CHAPTER TWO
Agricultural Pesticides and Precocious Puberty Samim Ozen1, Damla Goksen, Sukran Darcan Department of Pediatric Endocrinology, Ege University School of Medicine, Izmir, Turkey 1 Corresponding author: e-mail address: [email protected]
Contents 1. Introduction 2. Puberty 3. Precocious Puberty 4. The Effects of EDs on Puberty 5. Organochlorine Pesticides and Puberty 6. DDT and DDE 7. Methoxychlor 8. Endosulfans 9. Vinclozolin 10. Acetochlor 11. Conclusion References
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Abstract The onset and course of puberty is under the control of the neuroendocrine system. Factors affecting the regulation of timing and order of this system's functions may alter the onset and course of puberty. Several environmental endocrine disruptors (EDs) with significant influences on the normal course of puberty have been identified. Despite the numerous animal and human studies on EDs that may extensively affect human health, there are still several issues that need to be clarified. This chapter discusses the effects of pesticides, which constitute a significant portion of disruptors and have been increasingly used in agriculture, on precocious puberty.
1. INTRODUCTION Recent studies have shown that there is a trend toward earlier onset of puberty in children. Although reasons for this trend remain unclear, the prevailing view involves a complex interaction between genetic, endocrine, Vitamins and Hormones, Volume 94 ISSN 0083-6729 http://dx.doi.org/10.1016/B978-0-12-800095-3.00002-X
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2014 Elsevier Inc. All rights reserved.
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and environmental factors. The ever-increasing industrialization has caused a rapid and significant increase in environmental pollutants. A proportion of these environmental pollutants are natural and synthetic chemicals that have certain effects on the endocrine system. These chemicals that have negative effects on the endocrine system are called endocrine disruptors (EDs). EDs exert their effects by binding to relevant hormone receptors, disturbing cell signaling pathways, directly affecting the central neuroendocrine system, inhibiting hormone synthesis, or causing toxic effects to relevant organs. Certain EDs that affect pubertal development in humans have been identified, such as phytoestrogens, topical and natural estrogens, pesticides, industrial chemicals, and phthalates. It has first been noticed in 1990 that EDs can cause precocious puberty (PP) in humans (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; Jacobson-Dickman & Lee, 2009; McLachlan, Simpson, & Martin, 2006; Nebesio & Pescovitz, 2007; Schoeters, Den Hond, Dhooge, Van Larebeke, & Leijs, 2008). Subsequently, numerous studies with animals and humans were conducted on the effects of EDs on the onset and course of puberty, which lead to the banning of certain chemicals. This chapter will discuss the effects of agricultural pesticides, which constitute a significant portion of EDs and have been increasingly used in recent years in parallel to the industrialization in agriculture, on PP development.
2. PUBERTY Puberty is a complex developmental process characterized by rapid physiological alterations that lead to maturation of sexual characteristics, acceleration of growth, and attainment of reproductive capacity. This sensitive developmental interval constitutes the transition from a nonreproductive to a reproductive state. Puberty is initiated during late childhood with maturation of the hypothalamic–pituitary–gonadal axis and requires extensive interplay among a variety of hormones. There are a number of dramatic changes in reproductive hormones during this period, particularly estrogen in females and androgens in males. Considering that most EDs act as estrogen or may exhibit antagonistic effects to estrogen or androgen receptors, such exposure has been implicated as provoking pubertal abnormalities in humans by interrupting normal hormonal activity (Nebesio & Pescovitz, 2007; Schoeters et al., 2008).
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3. PRECOCIOUS PUBERTY PP is characterized by the early development of secondary sexual characteristics at the age of 8 in girls and 9 in boys. It is also defined as the onset of puberty symptoms at an earlier age, that is, 2.5 standard deviations below the expected mean age, exhibiting persistent and progressive characteristics. PP includes the development of secondary sexual characteristics at an earlier age than expected, rapid bone growth, decrease in predicted final height, changes in body fat distribution, and psychosocial changes (Berberoglu, 2009; Carel & Leger, 2008). A number of studies have shown that the onset of puberty could be as early as 7.7 years in girls and 7.6 years in boys. Although there is still no consensus on this matter, the age range of 7–8 years can be defined as the gray area. The onset of puberty in girls within this age range is described with terms such as “early normal puberty,” “rapid progressive thelarche variant,” and “premature puberty” (Berberoglu, 2009; Carel & Leger, 2008; Herman-Giddens, 2007; Parent et al., 2003). Observed more frequently in girls, PP can cause significant problems, such as psychosocial issues, short stature, and increased risk of breast cancer in adulthood. Therefore, early diagnosis and treatment is necessary. PP is diagnosed by determining early secondary sexual characteristics, accelerated body growth, and advanced bone age, as well as increased levels of gonadotropins and/or sex steroids. Cases in which breast development alone is observed without advanced bone age or accelerated body growth are referred to as isolated early thelarche. Even though these cases are regarded as variants of norms, they might still develop PP later on (Berberoglu, 2009; Carel & Leger, 2008; Herman-Giddens, 2007; Parent et al., 2003). In a population study conducted in Denmark, PP was determined at a rate of 0.2% in girls and 0.01–0.02% in boys. Only half of these were determined to be actual early puberty cases. When evaluated according to the definition of early puberty, considering that puberty symptoms by PP are observed with 2.5 standard deviations below the mean age, the expected frequency should have been 0.6%. This difference may be due to insufficient determination of patients (Teilman, Pedersen, Jensen, Skakkebaek, & Jull, 2005). PP can be categorized as either gonadotropin-dependent (central/true) or gonadotropin-independent (peripheral/pseudopuberty). In gonadotropindependent PP, the hypothalamic–pituitary–gonadal (HPG) axis is activated, as also observed in physiological puberty. On the other hand, in gonadotropin-independent puberty, the HPG axis is suppressed, and PP
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is not dependent on gonadotropin secretion. This group of PP is dependent on endogenous and/or exogenous sex steroids (Berberoglu, 2009; Carel & Leger, 2008).
4. THE EFFECTS OF EDs ON PUBERTY Recent studies have shown that while the menarcheal age in girls remains unchanged, onset of puberty shifted 1–2 years earlier compared to the past years. The triggering mechanism of the early onset of puberty remains unclear. However, it is believed that this early onset is due to a complex interaction between genetic, hormonal, and environmental factors. EDs, one of the environmental factors, are blamed more intensely in the recent years (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; Jacobson-Dickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). Theoretically, hormones or substances with hormone-disrupting capability may interfere with pubertal development by actions at different levels, including the neuroendocrine hypothalamic–pituitary axis, the gonads, and peripheral target organs such as breasts, hair follicles, and genitals. In the brain, EDs may act by the stimulation of estrogen-sensitive nuclei, including hypothalamic neurons, thereby releasing kisspeptin and promoting the maturation of the hypothalamus causing earlier onset of puberty, or even PP. However, other compounds could act by gonadotropin inhibition through negative feedback. It is also possible that EDs have direct effects on both the body weight and the endocrine system of the HPG axis (Stahlhut, Van Wijngaarden, Dye, Cook, & Swan, 2007). Steroids from the adrenal glands also play a role for normal progression of puberty, including pubic hair development. Potentially, a dysfunction of the adrenal gland caused by EDs may influence the estrogenic hormonal milieu and thereby also influence pubertal development (Ulleras, Ohlsson, & Oskarsson, 2008). A potential mechanism of ED action at the HPG axis has been described in rats (Rasier, Parent, Gerard, Lebrethon, & Bourguignon, 2007). Animals were exposed to DDT or beta-estradiol, and GnRH pulsatile secretion was increased. Furthermore, an in vitro study showed amplification of the glutamate-evoked secretion of GnRH after exposure to DDT and E2 (Rasier et al., 2008). A significant portion of environmental EDs consist of pesticides used in agriculture. Pesticides have a long history of global use and have a broad spectrum of applications in agricultural and commercial pest control. Insecticides are one of the most widely used classes of pesticides. Other classes of
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pesticides include herbicides and fungicides, which target unwanted plants and fungi, respectively. While these agents have been useful for eradicating undesirable pests and disease vectors, pesticides also have unintended actions on nontargeted species, including humans, and recent studies have shown that even extremely low levels of exposure can cause damage to the developing reproductive axis (McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). Table 2.1 shows the major pesticides that can affect the endocrine system. Certain pesticides can accumulate in the environment over time and can enter the human body through water, air, food sources, and objects used in work and home settings. In addition, studies have also shown that pesticides can pass from the mother to the fetus through the placenta and to the baby through the mother’s milk (Buck Louis et al., 2008; JacobsonDickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). The effects of pesticides on the endocrine system are agonistic or antagonistic due to their hormone-like characteristics. Their effects on puberty are estrogenic, antiestrogenic, androgenic, and antiandrogenic and directly on the GnRH system (Buck Louis et al., 2008; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). These chemicals exert their estrogenic effects by directly binding to estrogen receptors, increasing aromatase activity and sensitivity to estrogen or increasing endogenous estrogen production through the GnRH system, which can eventually cause PP. The antiestrogenic and androgenic effects of these chemicals are often expressed through the inhibition of aromatase enzyme activity and the steroidogenic enzyme production system. Lastly, they exert their antiandrogenic effects by suppressing testicular steroidogenesis and blocking androgen receptors. Ultimately, depending on the types of effects they exert, pesticides can cause PP, delayed puberty, and disorders of sexual differentiation (Abaci, Demir, Bober, & Buyukgebiz, 2009; Buck Louis et al., 2008; Kandarakis et al., 2009; Massart, Parrino, Seppia, Table 2.1 Major pesticides that affect the endocrine system
Pesticides Dichlorodiphenyltrichloroethane (DDT), methoxychlor, endosulfan, 2,4-dichlorophenoxyacetic acid, alachlor, aldicarb, amitrole, atrazine, benomyl, dibromochloropropane, carbaryl, chlordane, ethyl parathion, heptachlor, kepone, ketoconazole, lindane, methomyl, permethrin, malathion, trifluralin, vinclozolin
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Federico, & Saggese, 2006; Roy, Chakraborty, & Chakraborty, 2009). The classification of some pesticides in terms of their effects on puberty is presented in Table 2.2. Most of these substances cannot be broken down and rendered ineffective by the body and are generally accumulated in fat tissue, which causes them to remain in the body for long periods of time exerting harmful effects. The period of time that the body is exposed to EDs during lifetime is crucial in terms of their harmful effects. Furthermore, the dosage and exposure duration are also important with regard to the consequences of these negative effects. As exposure duration and dosage increase, the negative effects can be more severe (Buck Louis et al., 2008; Den Hond & Schoeters, 2006;
Table 2.2 Classification of some pesticides according to their effects on the reproductive system Type of effect Pesticide References
Estrogenic
Dichlorodiphenyltrichloroethane (DDT) and its metabolites
Nebesio and Pescovitz (2007)
Methoxychlor
Gray, Ostby, Cooper, and Kelce (1999)
Methoprene
Roy et al. (2009) and Kandarakis et al. (2009)
Endosulfan
Jørgensen et al. (2000)
Antiestrogenic Prochloraz
Androgenic
Vinggaard, Nellemann, Dalgaard, Jørgensen, and Andersen (2002)
Unknown
Antiandrogenic Dichlorodiphenyldichloroethylene Kelce et al. (1995) and Wolf (DDE) et al. (1999)
Inhibition of aromatase
Vinclozolin
Gray et al. (2001) and Eustache et al. (2009)
Endosulfan
Eroschenko and Cooke (1990) and Wade, Desaulniers, Leingartner, and Foster (1997)
Prochloraz
Vinggaard et al. (2002)
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Jacobson-Dickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). There are still a very limited number of studies with animals and humans on the role of pesticides in PP. These chemicals cause PP symptoms by exerting estrogenic effects, which might be accomplished through increasing estrogenic effects, antiandrogenic effects, and GnRH production (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; Jacobson-Dickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). In a study by Wohlfahrt-Veje et al. (2012) conducted in Denmark, it was shown that breast development was earlier in individuals exposed to nonpersistent pesticides prenatally compared to the control group. In the same study, it was also revealed that endogenous gonadotropin levels were normal and androgen levels were increased in early breast development cases. The authors suggested that pesticides accelerated the formation of estrogens from androgens by increasing aromatase activity, which in turn caused early breast development. Ozen et al. (2012) evaluated the effects of pesticides on premature breast development. Forty-five girls with premature breast development, living in a rural area where greenhouse cultivation is the main income; 16 girls with early puberty, living in the city center; and 33 girls who had no signs of puberty were included in the study. Endosulfan 1, endosulfan 2, endosulfan sulfate, methoxychlor, vinclozolin, 4,4-dichlorodiphenyldichloroethylene (DDE), 4,4-dichlorodiphenyltrichloroethane (DDT), and 2,4-DDT were evaluated in the serum and adipose tissues of the groups using gas chromatography–mass spectrometry. With the exception of 4,40 -DDE, the pesticides studied were undetectable in the serum and adipose tissue samples. The levels of basal luteinizing hormone (LH), stimulated LH, and follicle-stimulating hormone and the long axis of the uterus and both ovaries were significantly different in the girls who had premature thelarche and detectable 4,40 -DDE levels compared to the girls who had premature thelarche and undetectable 4,40 -DDE levels in the serum and adipose tissues. The presence and levels of pesticides in serum and adipose tissues were not related to PP. The mechanisms that lead to PP may also result in obesity, and obesity may be the underlying cause for PP in this group (Ozen et al., 2012).
5. ORGANOCHLORINE PESTICIDES AND PUBERTY Organochlorine pesticides are lipophilic, accumulating in fatty tissues and remaining in the body for years. Organochlorine pesticides include
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certain agents, such as DDT, methoxychlor, dicofol, heptachlor, chlordane, endosulfan, aldrin, dieldrin, endrin, and mirex. Humans are predominantly exposed to organochlorine pesticides as residues on produce or through pest control. Individuals working directly with insecticides come into direct contact through inhalation and skin (Dickerson, Cunningham, & Gore, 2012).
6. DDT AND DDE DDT and similar chemicals have been long known to have estrogenic effects. In a study by Gellert, Heinrichs, and Swerdloff (1972), DDT homologues were shown to cause early puberty through their estrogenic effects in female mice. In the 1980s, after a vast quantity of DDT and dicofol was accidentally spilled into Lake Apopka in Florida, the male crocodiles were observed to have smaller phalli, lower serum testosterone levels, abnormal gonad structures, and higher concurrent serum DDT levels (Semenza, Tolbert, Rubin, Guillette, & Jackson, 1997). Numerous studies have been conducted on the effects of DDT, of which the estrogenic effects have already been proven, and its metabolite DDE on the pubertal development in children. The use of DDT, a pesticide, and its metabolites, which have been used extensively in agriculture, has been banned in many countries after determining their negative effects. In their study, Vasiliu et al. (2004) had determined that menarche occurred 1 year earlier in girls who had been exposed to high levels of DDT/DDE during the intrauterine period. In another study, Krstevska-Konstantinova et al. (2001) determined that the PP rate was 80 times higher in girls who immigrated to Belgium compared to the natives and that these girls had significantly high serum DDE levels. Ouyang et al. (2005) studied newly married female textile workers in China by measuring serum DDT/DDE concentrations. A 10 ng/g increase in exposure was associated with 0.2 years earlier onset of menarche. Because exposure occurred after pubertal development was complete, the causal order of exposure–puberty cannot be established since pubertal development may have affected the metabolism/distribution of DDT or other behaviors that influenced DDT exposure. Denham et al. (2005) conducted a cross-sectional study among girls who were aged 10–17 years and resided in the Mohawk Nation along the United States/Canadian border to assess serum concentrations and self-reported menarcheal status. No association was observed between DDT exposure and menarche despite the authors’ assumption that current serum concentrations were indicative of in utero and lactational exposures, given the long-standing concern
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regarding consumption of contaminated fish among this population. Gladen, Ragan, and Rogan (2000) conducted a prospective cohort study of boys and girls who resided in North Carolina in relation to DDE concentrations that were previously measured in their mothers’ serum, the cord serum, and the placenta (averaged for in utero exposure). Concentrations in breast milk were also determined (lactational exposure). Puberty-timing measures, Tanner stages (boys and girls), and menarche were assessed by annual questionnaires. For boys, no association was observed for either in utero or lactational DDE exposure. Among girls, there was no association with age at menarche; however, there was a suggestion of an association of higher in utero or lactational exposure and earlier breast and pubic hair development that was not statistically significant. Gaspari, Paris, Jeandel, and Sultan (2011) reported breast development and menstruation alongside enlargement of the uterus in a 4-month-old girl. Along with the patient, gas chromatography results revealed p.p0 DDD, p.p0 DDT, lindane, and endosulfan in the plasma of the parents, who had a dramatic decrease in libido, and early sexual maturation in this case, whose parents were farmers, was associated with estrogenic pesticides. It was hypothesized that early and temporary exposure to weakly estrogenic DDT in developing countries, where the exposure is still high, could stimulate hypothalamic maturation, while the pituitary gonadotropins are inhibited via negative feedback that prevents manifestation of central maturation. Migration causes withdrawal from the EDC, and the consequent pituitary inhibition disappears, allowing the hypothalamic maturation to turn on the pituitary–ovarian cascade of pubertal events, that is, central puberty (Rasier, Toppari, Parent, & Bourguignon, 2006).
7. METHOXYCHLOR Methoxychlor, a chemical that belongs to the organochlorine group, is still being extensively used in agriculture as a pesticide. It has been shown to exert estrogenic effects in a number of animal studies (Ashby & Lefevre, 2000; Eroschenko & Cooke, 1990; Gray et al., 1999; Masutomi et al., 2003). Early vaginal dilatation was observed in female mice administered with methoxychlor following the termination of receiving breast milk. PP was also observed in female mice that received methoxychlor, an antiandrogenic and estrogenic agent (Ashby & Lefevre, 2000). It has been proven to disrupt reproductive behavior and functions due to its estrogenic effects in male mice (Gray et al., 1999). In their study, conducted in a region where
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greenhouse cultivation and methoxychlor use were extensive, Ozen et al. (2012) did not detect this pesticide in the fatty tissue and serum samples of girls with early breast development. The authors suggested that this may be due to the fact that methoxychlor is a water-soluble chemical that does not accumulate in the body.
8. ENDOSULFANS It has been known that endosulfan and its derivatives, which are widely used in agriculture, have antiandrogenic and estrogenic effects (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; JacobsonDickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). Studies with animals have revealed that endosulfan exerted estrogenic effects and inhibited FSH, LG, and testosterone levels (Singh & Pandley, 1990; Wade et al., 1997). Studies on the relationship between endosulfan-group pesticides, which have been banned in many developed countries due to their toxic effects, and puberty in humans are still insufficient. In the first human study on this matter, conducted by Ozen et al. (2012), levels of the endosulfan-group pesticides endosulfan 1 (endosulfan-alpha), endosulfan 2 (endosulfan-beta), and endosulfan sulfate were measured in the serum and fatty tissue samples of girls with early breast development. While the rate of early breast development was determined to be 10% in this region, there was no evidence of the aforementioned endosulfan-group pesticides in the serum and/or fatty tissue samples. The authors suggested that the absence of these pesticides in the samples may be due to the fact that they were not being used extensively in this region at the time of the study and that these pesticides do not have significant accumulation properties as DDT and its metabolites have. There is a need for further studies on this matter. In a different study conducted in India with a total of 117 boys aged between 10 and 19 years, significant retardation of pubertal development and five times higher rate of testicular abnormalities (undescended testes, congenital hydrocele, and congenital inguinal hernia) were observed in boys, who were exposed to high levels of endosulfan, compared to the control group. The authors suggested that endosulfans exerted these effects by disrupting sex hormone synthesis (Saiyed et al., 2003). This pesticide is highly likely to cause PP in girls while exerting antiandrogenic effects in boys. There is a need for wide-population study on this matter.
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9. VINCLOZOLIN The antiandrogenic effects of vinclozolin have mostly been observed in male animals (Blystone et al., 2009). Although the estrogenic effects of this chemical used extensively in agriculture remain unclear, it has been reported that it can exert estrogen-like effects through antiandrogenic effects and estrogen receptor-alpha (Khurana, Ranmal, & Ben-Jonathan, 2000). Ozen et al. (2012) found no relationship between vinclozolin and PP in their study. However, pubertal disorders may develop through changes in sex hormone synthesis and effects due to frequent and intensive exposure to this nonpersistent pesticide.
10. ACETOCHLOR In a study with female Wistar rats and the herbicide called acetochlor, it has been shown that acetochlor can cause earlier vaginal dilatation through estrogen receptors. Researchers noted that this persistent pollutant might be an ED with estrogenic effects (Rollerova, Wsolova, & Urbancikova, 2011). In a similar study by Rollerova, Gasparova, Wsolova, and Urbancikova (2000), an increased estrogen receptor binding activity was observed in the uterus of rats that were given with acetochlor. There are no human studies with this herbicide.
11. CONCLUSION Animal and human studies on the relationship between PP and pesticides that have been increasingly used in recent years are still insufficient. It is still unclear through which mechanisms these chemicals cause PP. However, these chemicals can indirectly affect and change the normal physiological functions of the HPG axis by directly disrupting gonadotropin secretion or feedback mechanisms. It should be kept in mind that the time of exposure is as important as exposed dose, duration of exposure, and age for pesticides to be able to disrupt endocrine functions. Many other pesticides that have not been discussed in this chapter can potentially have harmful effects on pubertal development. There is a need for advanced population studies on this topic. Conflict of Interest: The authors declare there is no conflict of interest in this chapter.
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Jacobson-Dickman, E., & Lee, M. M. (2009). The influence of endocrine disruptors on pubertal timing. Current Opinion in Endocrinology, Diabetes, and Obesity, 16, 25–30. Jørgensen, M., Vendelbo, B., Skakkebaek, N. E., & Leffers, H. (2000). Assaying estrogenicity by quantitating the expression levels of endogenous estrogen-regulated genes. Environmental Health Perspectives, 108(5), 403–412. Kandarakis, E. D., Bourguignon, J. P., Giudice, L. C., Hauser, R., Prins, G. S., Soto, A. M., et al. (2009). Endocrine-disrupting chemicals: An Endocrine Society scientific statement. Endocrine Reviews, 30, 293–342. Kelce, W. R., Stone, C. R., Laws, S. C., Gray, L. E., Kemppainen, J. A., & Wilson, E. M. (1995). Persistent DDT metabolite p,p’-DDE is a potent androgen receptor antagonist. Nature, 375(6532), 581–585. Khurana, S., Ranmal, S., & Ben-Jonathan, N. (2000). Exposure of newborn male and female rats to environmental estrogens: Delayed and sustained hyperprolactinemia and alterations in estrogen receptor expression. Endocrinology, 141, 4512–4517. Krstevska-Konstantinova, M., Charlier, C., Craen, M., Du Caju, M., Heinrichs, C., de Beaufort, C., et al. (2001). Sexual precocity after immigration from developing countries to Belgium: Evidence of previous exposure to organochlorine pesticides. Human Reproduction, 16, 1020–1026. Massart, F., Parrino, R., Seppia, P., Federico, G., & Saggese, G. (2006). How do environmental estrogen disruptors induce precocious puberty? Minerva Pediatrica, 58, 247–254. Masutomi, N., Shibutani, M., Takagi, H., Uneyama, C., Takahashi, N., & Hirose, M. (2003). Impact of dietary exposure to methoxychlor, genistein, or diisononyl phthalate during the perinatal period on the development of the rat endocrine/reproductive systems in later life. Toxicology, 192(2–3), 149–170. McLachlan, J. A., Simpson, E., & Martin, M. (2006). Endocrine disrupters and female reproductive health. Best Practice & Research Clinical Endocrinology & Metabolism, 20, 63–75. Nebesio, T. D., & Pescovitz, O. H. (2007). The role of endocrine disruptors in pubertal development. In O. H. Pescovitz & E. C. Walvoord (Eds.), When puberty is precocious: Scientific and clinical aspects (p. 468). Totowa, NJ: Humana press. Ouyang, F., Perry, M. J., Venners, S. A., Chen, C., Wang, B., Yang, F., et al. (2005). Serum DDT, age at menarche, and abnormal menstrual cycle length. Occupational and Environmental Medicine, 62, 878–884. Ozen, S., Darcan, S., Bayindir, P., Karasulu, E., Simsek, D. G., & Gurler, T. (2012). Effects of pesticides used in agriculture on the development of precocious puberty. Environmental Monitoring and Assessment, 184(7), 4223–4232. Parent, A. S., Teilmann, G., Juul, A., Skakkebaek, N. E., Toppari, J., & Bourguignon, J. P. (2003). The timing of normal puberty and the age limits of sexual precocity: Variations around the world, secular trends, and changes after migration. Endocrine Reviews, 24, 668–693. Rasier, G., Parent, A. S., Gerard, A., Denooz, R., Lebrethon, M. C., Charlier, C., et al. (2008). Mechanisms of interaction of endocrine-disrupting chemicals with glutamateevoked secretion of gonadotropin-releasing hormone. Toxicological Sciences, 102, 33–41. Rasier, G., Parent, A. S., Gerard, A., Lebrethon, M. C., & Bourguignon, J. P. (2007). Early maturation of gonadotropin-releasing hormone secretion and sexual precocity after exposure of infant female rats to estradiol or dichlorodiphenyltrichloroethane. Biology of Reproduction, 77, 734–742. Rasier, G., Toppari, J., Parent, A. S., & Bourguignon, J. P. (2006). Female sexual maturation and reproduction after prepubertal exposure to estrogens and endocrine disrupting chemicals: A review of rodent and human data. Molecular and Cellular Endocrinology, 254–255, 187–201. Rollerova, E., Gasparova, Z., Wsolova, L., & Urbancikova, M. (2000). Interaction of acetochlor with estrogen receptor in the rat uterus. Acetochlor—Possible endocrine modulator? General Physiology and Biophysics, 19(1), 73–84.
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Rollerova, E., Wsolova, L., & Urbancikova, M. (2011). Neonatal exposure to herbicide acetochlor alters pubertal development in female wistar rats. Toxicology Mechanisms and Methods, 21(5), 406–417. Roy, J. R., Chakraborty, S., & Chakraborty, T. R. (2009). Estrogen-like endocrine disrupting chemicals affecting puberty in humans—A review. Medical Science Monitor, 15, 137–145. Saiyed, H., Dewan, A., Bhatnagar, V., Shenoy, U., Shenoy, R., Rajmohan, H., et al. (2003). Effect of endosulfan on male reproductive development. Environmental Health Perspectives, 111(16), 1958–1962. Schoeters, G., Den Hond, E., Dhooge, W., Van Larebeke, N., & Leijs, M. (2008). Endocrine disruptors and abnormalities of pubertal development. Basic & Clinical Pharmacology & Toxicology, 102, 168–175. Semenza, J. C., Tolbert, P. E., Rubin, C. H., Guillette, L. J., Jr., & Jackson, R. J. (1997). Reproductive toxins and alligator abnormalities at Lake Apopka, Florida. Environmental Health Perspectives, 105, 1030–1032. Singh, S. K., & Pandley, R. S. (1990). Effect of sub-chronic endosulfan exposures on plasma gonadotrophins, testosterone, testicular testosterone and enzymes of androgen biosynthesis in rat. Indian Journal of Experimental Biology, 28, 953–956. Stahlhut, R. W., Van Wijngaarden, E., Dye, T. D., Cook, S., & Swan, S. H. (2007). Concentrations of urinary phthalate metabolites are associated with increased waist circumference and insulin resistance in adult U.S. males. Environmental Health Perspectives, 115, 876–882. Teilman, G., Pedersen, C. B., Jensen, T. K., Skakkebaek, N. E., & Jull, A. (2005). Prevalence and incidence of precocious pubertal development in Denmark: An epidemiologic study based on national registries. Pediatrics, 116, 1323–1328. Ulleras, E., Ohlsson, A., & Oskarsson, A. (2008). Secretion of cortisol and aldosterone as a vulnerable target for adrenal endocrine disruption—Screening of 30 selected chemicals in the human H295R cell model. Journal of Applied Toxicology, 28, 1045–1053. Vasiliu, O., Muttineni, J., & Karmaus, W. (2004). In utero exposure to organochlorines and age at menarche. Human Reproduction, 19, 1506–1512. Vinggaard, A. M., Nellemann, C., Dalgaard, M., Jørgensen, E. B., & Andersen, H. R. (2002). Antiandrogenic effects in vitro and in vivo of the fungicide prochloraz. Toxicological Sciences, 69(2), 344–353. Wade, M. G., Desaulniers, D., Leingartner, K., & Foster, W. G. (1997). Interaction between endosulphan and dieldrin on estrogen-mediated processes in vitro and in vivo. Reproductive Toxicology, 11, 791–798. Wohlfahrt-Veje, C., Andersen, H. R., Schmidt, I. M., Aksglaede, L., Sørensen, K., Juul, A., et al. (2012). Early breast development in girls after prenatal exposure to non-persistent pesticides. International Journal of Andrology, 35(3), 273–282. Wolf, C., Jr., Lambright, C., Mann, P., Price, M., Cooper, R. L., Ostby, J., et al. (1999). Administration of potentially antiandrogenic pesticides (procymidone, linuron, iprodione, chlozolinate, p,p’-DDE, and ketoconazole) and toxic substances (dibutyland diethylhexyl phthalate, PCB 169, and ethane dimethane sulphonate) during sexual differentiation produces diverse profiles of reproductive malformations in the male rat. Toxicology and Industrial Health, 15(1-2), 94–118.
Agricultural Pesticides and Precocious Puberty Samim Ozen1, Damla Goksen, Sukran Darcan Department of Pediatric Endocrinology, Ege University School of Medicine, Izmir, Turkey 1 Corresponding author: e-mail address: [email protected]
Contents 1. Introduction 2. Puberty 3. Precocious Puberty 4. The Effects of EDs on Puberty 5. Organochlorine Pesticides and Puberty 6. DDT and DDE 7. Methoxychlor 8. Endosulfans 9. Vinclozolin 10. Acetochlor 11. Conclusion References
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Abstract The onset and course of puberty is under the control of the neuroendocrine system. Factors affecting the regulation of timing and order of this system's functions may alter the onset and course of puberty. Several environmental endocrine disruptors (EDs) with significant influences on the normal course of puberty have been identified. Despite the numerous animal and human studies on EDs that may extensively affect human health, there are still several issues that need to be clarified. This chapter discusses the effects of pesticides, which constitute a significant portion of disruptors and have been increasingly used in agriculture, on precocious puberty.
1. INTRODUCTION Recent studies have shown that there is a trend toward earlier onset of puberty in children. Although reasons for this trend remain unclear, the prevailing view involves a complex interaction between genetic, endocrine, Vitamins and Hormones, Volume 94 ISSN 0083-6729 http://dx.doi.org/10.1016/B978-0-12-800095-3.00002-X
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2014 Elsevier Inc. All rights reserved.
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and environmental factors. The ever-increasing industrialization has caused a rapid and significant increase in environmental pollutants. A proportion of these environmental pollutants are natural and synthetic chemicals that have certain effects on the endocrine system. These chemicals that have negative effects on the endocrine system are called endocrine disruptors (EDs). EDs exert their effects by binding to relevant hormone receptors, disturbing cell signaling pathways, directly affecting the central neuroendocrine system, inhibiting hormone synthesis, or causing toxic effects to relevant organs. Certain EDs that affect pubertal development in humans have been identified, such as phytoestrogens, topical and natural estrogens, pesticides, industrial chemicals, and phthalates. It has first been noticed in 1990 that EDs can cause precocious puberty (PP) in humans (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; Jacobson-Dickman & Lee, 2009; McLachlan, Simpson, & Martin, 2006; Nebesio & Pescovitz, 2007; Schoeters, Den Hond, Dhooge, Van Larebeke, & Leijs, 2008). Subsequently, numerous studies with animals and humans were conducted on the effects of EDs on the onset and course of puberty, which lead to the banning of certain chemicals. This chapter will discuss the effects of agricultural pesticides, which constitute a significant portion of EDs and have been increasingly used in recent years in parallel to the industrialization in agriculture, on PP development.
2. PUBERTY Puberty is a complex developmental process characterized by rapid physiological alterations that lead to maturation of sexual characteristics, acceleration of growth, and attainment of reproductive capacity. This sensitive developmental interval constitutes the transition from a nonreproductive to a reproductive state. Puberty is initiated during late childhood with maturation of the hypothalamic–pituitary–gonadal axis and requires extensive interplay among a variety of hormones. There are a number of dramatic changes in reproductive hormones during this period, particularly estrogen in females and androgens in males. Considering that most EDs act as estrogen or may exhibit antagonistic effects to estrogen or androgen receptors, such exposure has been implicated as provoking pubertal abnormalities in humans by interrupting normal hormonal activity (Nebesio & Pescovitz, 2007; Schoeters et al., 2008).
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3. PRECOCIOUS PUBERTY PP is characterized by the early development of secondary sexual characteristics at the age of 8 in girls and 9 in boys. It is also defined as the onset of puberty symptoms at an earlier age, that is, 2.5 standard deviations below the expected mean age, exhibiting persistent and progressive characteristics. PP includes the development of secondary sexual characteristics at an earlier age than expected, rapid bone growth, decrease in predicted final height, changes in body fat distribution, and psychosocial changes (Berberoglu, 2009; Carel & Leger, 2008). A number of studies have shown that the onset of puberty could be as early as 7.7 years in girls and 7.6 years in boys. Although there is still no consensus on this matter, the age range of 7–8 years can be defined as the gray area. The onset of puberty in girls within this age range is described with terms such as “early normal puberty,” “rapid progressive thelarche variant,” and “premature puberty” (Berberoglu, 2009; Carel & Leger, 2008; Herman-Giddens, 2007; Parent et al., 2003). Observed more frequently in girls, PP can cause significant problems, such as psychosocial issues, short stature, and increased risk of breast cancer in adulthood. Therefore, early diagnosis and treatment is necessary. PP is diagnosed by determining early secondary sexual characteristics, accelerated body growth, and advanced bone age, as well as increased levels of gonadotropins and/or sex steroids. Cases in which breast development alone is observed without advanced bone age or accelerated body growth are referred to as isolated early thelarche. Even though these cases are regarded as variants of norms, they might still develop PP later on (Berberoglu, 2009; Carel & Leger, 2008; Herman-Giddens, 2007; Parent et al., 2003). In a population study conducted in Denmark, PP was determined at a rate of 0.2% in girls and 0.01–0.02% in boys. Only half of these were determined to be actual early puberty cases. When evaluated according to the definition of early puberty, considering that puberty symptoms by PP are observed with 2.5 standard deviations below the mean age, the expected frequency should have been 0.6%. This difference may be due to insufficient determination of patients (Teilman, Pedersen, Jensen, Skakkebaek, & Jull, 2005). PP can be categorized as either gonadotropin-dependent (central/true) or gonadotropin-independent (peripheral/pseudopuberty). In gonadotropindependent PP, the hypothalamic–pituitary–gonadal (HPG) axis is activated, as also observed in physiological puberty. On the other hand, in gonadotropin-independent puberty, the HPG axis is suppressed, and PP
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is not dependent on gonadotropin secretion. This group of PP is dependent on endogenous and/or exogenous sex steroids (Berberoglu, 2009; Carel & Leger, 2008).
4. THE EFFECTS OF EDs ON PUBERTY Recent studies have shown that while the menarcheal age in girls remains unchanged, onset of puberty shifted 1–2 years earlier compared to the past years. The triggering mechanism of the early onset of puberty remains unclear. However, it is believed that this early onset is due to a complex interaction between genetic, hormonal, and environmental factors. EDs, one of the environmental factors, are blamed more intensely in the recent years (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; Jacobson-Dickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). Theoretically, hormones or substances with hormone-disrupting capability may interfere with pubertal development by actions at different levels, including the neuroendocrine hypothalamic–pituitary axis, the gonads, and peripheral target organs such as breasts, hair follicles, and genitals. In the brain, EDs may act by the stimulation of estrogen-sensitive nuclei, including hypothalamic neurons, thereby releasing kisspeptin and promoting the maturation of the hypothalamus causing earlier onset of puberty, or even PP. However, other compounds could act by gonadotropin inhibition through negative feedback. It is also possible that EDs have direct effects on both the body weight and the endocrine system of the HPG axis (Stahlhut, Van Wijngaarden, Dye, Cook, & Swan, 2007). Steroids from the adrenal glands also play a role for normal progression of puberty, including pubic hair development. Potentially, a dysfunction of the adrenal gland caused by EDs may influence the estrogenic hormonal milieu and thereby also influence pubertal development (Ulleras, Ohlsson, & Oskarsson, 2008). A potential mechanism of ED action at the HPG axis has been described in rats (Rasier, Parent, Gerard, Lebrethon, & Bourguignon, 2007). Animals were exposed to DDT or beta-estradiol, and GnRH pulsatile secretion was increased. Furthermore, an in vitro study showed amplification of the glutamate-evoked secretion of GnRH after exposure to DDT and E2 (Rasier et al., 2008). A significant portion of environmental EDs consist of pesticides used in agriculture. Pesticides have a long history of global use and have a broad spectrum of applications in agricultural and commercial pest control. Insecticides are one of the most widely used classes of pesticides. Other classes of
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pesticides include herbicides and fungicides, which target unwanted plants and fungi, respectively. While these agents have been useful for eradicating undesirable pests and disease vectors, pesticides also have unintended actions on nontargeted species, including humans, and recent studies have shown that even extremely low levels of exposure can cause damage to the developing reproductive axis (McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). Table 2.1 shows the major pesticides that can affect the endocrine system. Certain pesticides can accumulate in the environment over time and can enter the human body through water, air, food sources, and objects used in work and home settings. In addition, studies have also shown that pesticides can pass from the mother to the fetus through the placenta and to the baby through the mother’s milk (Buck Louis et al., 2008; JacobsonDickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). The effects of pesticides on the endocrine system are agonistic or antagonistic due to their hormone-like characteristics. Their effects on puberty are estrogenic, antiestrogenic, androgenic, and antiandrogenic and directly on the GnRH system (Buck Louis et al., 2008; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). These chemicals exert their estrogenic effects by directly binding to estrogen receptors, increasing aromatase activity and sensitivity to estrogen or increasing endogenous estrogen production through the GnRH system, which can eventually cause PP. The antiestrogenic and androgenic effects of these chemicals are often expressed through the inhibition of aromatase enzyme activity and the steroidogenic enzyme production system. Lastly, they exert their antiandrogenic effects by suppressing testicular steroidogenesis and blocking androgen receptors. Ultimately, depending on the types of effects they exert, pesticides can cause PP, delayed puberty, and disorders of sexual differentiation (Abaci, Demir, Bober, & Buyukgebiz, 2009; Buck Louis et al., 2008; Kandarakis et al., 2009; Massart, Parrino, Seppia, Table 2.1 Major pesticides that affect the endocrine system
Pesticides Dichlorodiphenyltrichloroethane (DDT), methoxychlor, endosulfan, 2,4-dichlorophenoxyacetic acid, alachlor, aldicarb, amitrole, atrazine, benomyl, dibromochloropropane, carbaryl, chlordane, ethyl parathion, heptachlor, kepone, ketoconazole, lindane, methomyl, permethrin, malathion, trifluralin, vinclozolin
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Federico, & Saggese, 2006; Roy, Chakraborty, & Chakraborty, 2009). The classification of some pesticides in terms of their effects on puberty is presented in Table 2.2. Most of these substances cannot be broken down and rendered ineffective by the body and are generally accumulated in fat tissue, which causes them to remain in the body for long periods of time exerting harmful effects. The period of time that the body is exposed to EDs during lifetime is crucial in terms of their harmful effects. Furthermore, the dosage and exposure duration are also important with regard to the consequences of these negative effects. As exposure duration and dosage increase, the negative effects can be more severe (Buck Louis et al., 2008; Den Hond & Schoeters, 2006;
Table 2.2 Classification of some pesticides according to their effects on the reproductive system Type of effect Pesticide References
Estrogenic
Dichlorodiphenyltrichloroethane (DDT) and its metabolites
Nebesio and Pescovitz (2007)
Methoxychlor
Gray, Ostby, Cooper, and Kelce (1999)
Methoprene
Roy et al. (2009) and Kandarakis et al. (2009)
Endosulfan
Jørgensen et al. (2000)
Antiestrogenic Prochloraz
Androgenic
Vinggaard, Nellemann, Dalgaard, Jørgensen, and Andersen (2002)
Unknown
Antiandrogenic Dichlorodiphenyldichloroethylene Kelce et al. (1995) and Wolf (DDE) et al. (1999)
Inhibition of aromatase
Vinclozolin
Gray et al. (2001) and Eustache et al. (2009)
Endosulfan
Eroschenko and Cooke (1990) and Wade, Desaulniers, Leingartner, and Foster (1997)
Prochloraz
Vinggaard et al. (2002)
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Jacobson-Dickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). There are still a very limited number of studies with animals and humans on the role of pesticides in PP. These chemicals cause PP symptoms by exerting estrogenic effects, which might be accomplished through increasing estrogenic effects, antiandrogenic effects, and GnRH production (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; Jacobson-Dickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). In a study by Wohlfahrt-Veje et al. (2012) conducted in Denmark, it was shown that breast development was earlier in individuals exposed to nonpersistent pesticides prenatally compared to the control group. In the same study, it was also revealed that endogenous gonadotropin levels were normal and androgen levels were increased in early breast development cases. The authors suggested that pesticides accelerated the formation of estrogens from androgens by increasing aromatase activity, which in turn caused early breast development. Ozen et al. (2012) evaluated the effects of pesticides on premature breast development. Forty-five girls with premature breast development, living in a rural area where greenhouse cultivation is the main income; 16 girls with early puberty, living in the city center; and 33 girls who had no signs of puberty were included in the study. Endosulfan 1, endosulfan 2, endosulfan sulfate, methoxychlor, vinclozolin, 4,4-dichlorodiphenyldichloroethylene (DDE), 4,4-dichlorodiphenyltrichloroethane (DDT), and 2,4-DDT were evaluated in the serum and adipose tissues of the groups using gas chromatography–mass spectrometry. With the exception of 4,40 -DDE, the pesticides studied were undetectable in the serum and adipose tissue samples. The levels of basal luteinizing hormone (LH), stimulated LH, and follicle-stimulating hormone and the long axis of the uterus and both ovaries were significantly different in the girls who had premature thelarche and detectable 4,40 -DDE levels compared to the girls who had premature thelarche and undetectable 4,40 -DDE levels in the serum and adipose tissues. The presence and levels of pesticides in serum and adipose tissues were not related to PP. The mechanisms that lead to PP may also result in obesity, and obesity may be the underlying cause for PP in this group (Ozen et al., 2012).
5. ORGANOCHLORINE PESTICIDES AND PUBERTY Organochlorine pesticides are lipophilic, accumulating in fatty tissues and remaining in the body for years. Organochlorine pesticides include
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certain agents, such as DDT, methoxychlor, dicofol, heptachlor, chlordane, endosulfan, aldrin, dieldrin, endrin, and mirex. Humans are predominantly exposed to organochlorine pesticides as residues on produce or through pest control. Individuals working directly with insecticides come into direct contact through inhalation and skin (Dickerson, Cunningham, & Gore, 2012).
6. DDT AND DDE DDT and similar chemicals have been long known to have estrogenic effects. In a study by Gellert, Heinrichs, and Swerdloff (1972), DDT homologues were shown to cause early puberty through their estrogenic effects in female mice. In the 1980s, after a vast quantity of DDT and dicofol was accidentally spilled into Lake Apopka in Florida, the male crocodiles were observed to have smaller phalli, lower serum testosterone levels, abnormal gonad structures, and higher concurrent serum DDT levels (Semenza, Tolbert, Rubin, Guillette, & Jackson, 1997). Numerous studies have been conducted on the effects of DDT, of which the estrogenic effects have already been proven, and its metabolite DDE on the pubertal development in children. The use of DDT, a pesticide, and its metabolites, which have been used extensively in agriculture, has been banned in many countries after determining their negative effects. In their study, Vasiliu et al. (2004) had determined that menarche occurred 1 year earlier in girls who had been exposed to high levels of DDT/DDE during the intrauterine period. In another study, Krstevska-Konstantinova et al. (2001) determined that the PP rate was 80 times higher in girls who immigrated to Belgium compared to the natives and that these girls had significantly high serum DDE levels. Ouyang et al. (2005) studied newly married female textile workers in China by measuring serum DDT/DDE concentrations. A 10 ng/g increase in exposure was associated with 0.2 years earlier onset of menarche. Because exposure occurred after pubertal development was complete, the causal order of exposure–puberty cannot be established since pubertal development may have affected the metabolism/distribution of DDT or other behaviors that influenced DDT exposure. Denham et al. (2005) conducted a cross-sectional study among girls who were aged 10–17 years and resided in the Mohawk Nation along the United States/Canadian border to assess serum concentrations and self-reported menarcheal status. No association was observed between DDT exposure and menarche despite the authors’ assumption that current serum concentrations were indicative of in utero and lactational exposures, given the long-standing concern
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regarding consumption of contaminated fish among this population. Gladen, Ragan, and Rogan (2000) conducted a prospective cohort study of boys and girls who resided in North Carolina in relation to DDE concentrations that were previously measured in their mothers’ serum, the cord serum, and the placenta (averaged for in utero exposure). Concentrations in breast milk were also determined (lactational exposure). Puberty-timing measures, Tanner stages (boys and girls), and menarche were assessed by annual questionnaires. For boys, no association was observed for either in utero or lactational DDE exposure. Among girls, there was no association with age at menarche; however, there was a suggestion of an association of higher in utero or lactational exposure and earlier breast and pubic hair development that was not statistically significant. Gaspari, Paris, Jeandel, and Sultan (2011) reported breast development and menstruation alongside enlargement of the uterus in a 4-month-old girl. Along with the patient, gas chromatography results revealed p.p0 DDD, p.p0 DDT, lindane, and endosulfan in the plasma of the parents, who had a dramatic decrease in libido, and early sexual maturation in this case, whose parents were farmers, was associated with estrogenic pesticides. It was hypothesized that early and temporary exposure to weakly estrogenic DDT in developing countries, where the exposure is still high, could stimulate hypothalamic maturation, while the pituitary gonadotropins are inhibited via negative feedback that prevents manifestation of central maturation. Migration causes withdrawal from the EDC, and the consequent pituitary inhibition disappears, allowing the hypothalamic maturation to turn on the pituitary–ovarian cascade of pubertal events, that is, central puberty (Rasier, Toppari, Parent, & Bourguignon, 2006).
7. METHOXYCHLOR Methoxychlor, a chemical that belongs to the organochlorine group, is still being extensively used in agriculture as a pesticide. It has been shown to exert estrogenic effects in a number of animal studies (Ashby & Lefevre, 2000; Eroschenko & Cooke, 1990; Gray et al., 1999; Masutomi et al., 2003). Early vaginal dilatation was observed in female mice administered with methoxychlor following the termination of receiving breast milk. PP was also observed in female mice that received methoxychlor, an antiandrogenic and estrogenic agent (Ashby & Lefevre, 2000). It has been proven to disrupt reproductive behavior and functions due to its estrogenic effects in male mice (Gray et al., 1999). In their study, conducted in a region where
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greenhouse cultivation and methoxychlor use were extensive, Ozen et al. (2012) did not detect this pesticide in the fatty tissue and serum samples of girls with early breast development. The authors suggested that this may be due to the fact that methoxychlor is a water-soluble chemical that does not accumulate in the body.
8. ENDOSULFANS It has been known that endosulfan and its derivatives, which are widely used in agriculture, have antiandrogenic and estrogenic effects (Buck Louis et al., 2008; Den Hond & Schoeters, 2006; JacobsonDickman & Lee, 2009; McLachlan et al., 2006; Nebesio & Pescovitz, 2007; Schoeters et al., 2008). Studies with animals have revealed that endosulfan exerted estrogenic effects and inhibited FSH, LG, and testosterone levels (Singh & Pandley, 1990; Wade et al., 1997). Studies on the relationship between endosulfan-group pesticides, which have been banned in many developed countries due to their toxic effects, and puberty in humans are still insufficient. In the first human study on this matter, conducted by Ozen et al. (2012), levels of the endosulfan-group pesticides endosulfan 1 (endosulfan-alpha), endosulfan 2 (endosulfan-beta), and endosulfan sulfate were measured in the serum and fatty tissue samples of girls with early breast development. While the rate of early breast development was determined to be 10% in this region, there was no evidence of the aforementioned endosulfan-group pesticides in the serum and/or fatty tissue samples. The authors suggested that the absence of these pesticides in the samples may be due to the fact that they were not being used extensively in this region at the time of the study and that these pesticides do not have significant accumulation properties as DDT and its metabolites have. There is a need for further studies on this matter. In a different study conducted in India with a total of 117 boys aged between 10 and 19 years, significant retardation of pubertal development and five times higher rate of testicular abnormalities (undescended testes, congenital hydrocele, and congenital inguinal hernia) were observed in boys, who were exposed to high levels of endosulfan, compared to the control group. The authors suggested that endosulfans exerted these effects by disrupting sex hormone synthesis (Saiyed et al., 2003). This pesticide is highly likely to cause PP in girls while exerting antiandrogenic effects in boys. There is a need for wide-population study on this matter.
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9. VINCLOZOLIN The antiandrogenic effects of vinclozolin have mostly been observed in male animals (Blystone et al., 2009). Although the estrogenic effects of this chemical used extensively in agriculture remain unclear, it has been reported that it can exert estrogen-like effects through antiandrogenic effects and estrogen receptor-alpha (Khurana, Ranmal, & Ben-Jonathan, 2000). Ozen et al. (2012) found no relationship between vinclozolin and PP in their study. However, pubertal disorders may develop through changes in sex hormone synthesis and effects due to frequent and intensive exposure to this nonpersistent pesticide.
10. ACETOCHLOR In a study with female Wistar rats and the herbicide called acetochlor, it has been shown that acetochlor can cause earlier vaginal dilatation through estrogen receptors. Researchers noted that this persistent pollutant might be an ED with estrogenic effects (Rollerova, Wsolova, & Urbancikova, 2011). In a similar study by Rollerova, Gasparova, Wsolova, and Urbancikova (2000), an increased estrogen receptor binding activity was observed in the uterus of rats that were given with acetochlor. There are no human studies with this herbicide.
11. CONCLUSION Animal and human studies on the relationship between PP and pesticides that have been increasingly used in recent years are still insufficient. It is still unclear through which mechanisms these chemicals cause PP. However, these chemicals can indirectly affect and change the normal physiological functions of the HPG axis by directly disrupting gonadotropin secretion or feedback mechanisms. It should be kept in mind that the time of exposure is as important as exposed dose, duration of exposure, and age for pesticides to be able to disrupt endocrine functions. Many other pesticides that have not been discussed in this chapter can potentially have harmful effects on pubertal development. There is a need for advanced population studies on this topic. Conflict of Interest: The authors declare there is no conflict of interest in this chapter.
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