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Male Pubertal Development: Are Endocrine-Disrupting Compounds Shifting the Norms?

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Male Pubertal Development: Are Endocrine-Disrupting Compounds Shifting the Norms? W ZAWATSKI and M M LEE Puberty and EDCs 218:2 R1–R12 Review Male pubertal development: are endocrine-disrupting compounds shifting the norms? Correspondence 1 William Zawatski and Mary M Lee should be addressed to M M Lee Pediatric Endocrine Division, 1Department of Pediatrics, University of Massachusetts Medical School, 55 Lake Email Avenue North, Worcester, Massachusetts 01655, USA [email protected] Abstract Endocrine-disrupting compounds (EDCs) are synthetic or natural compounds that interfere Key Words with endogenous endocrine action. The frequent use of chemicals with endocrine active " testosterone properties in household products and contamination of soil, water, and food sources by " development persistent chemical pollutants result in ubiquitous exposures. Wildlife observations and " puberty animal toxicological studies reveal adverse effects of EDCs on reproductive health. " endocrine-disrupting In humans, a growing number of epidemiological studies report an association with compounds altered pubertal timing and progression. While these data are primarily reported in females, " sexual development this review will focus on the small number of studies performed in males that report an association of polychlorinated biphenyls with earlier sexual maturity rating and confirm subtle effects of lead, dioxins, and endosulfan on delaying pubertal onset and progression in boys. Recent studies have also demonstrated that EDC exposure may affect pubertal Journal of Endocrinology testosterone production without having a noticeable effect on sexual maturity rating. A limitation to understand the effects of EDCs in humans is the potential for confounding due to the long temporal lag from early-life exposures to adult outcomes. The complex interplay of multiple environmental exposures over time also complicates the interpretation of human studies. These studies have identified critical windows of vulnerability during development when exposures to EDCs alter critical pathways and affect postnatal reproductive health. Contemporaneous exposures can also disrupt the hypothalamic–pituitary–gonadal axis. This paper will review the normal process of puberty in males and summarize human data that suggest potential perturbations in pubertal onset and tempo with early-life exposures to EDCs. Journal of Endocrinology (2013) 218, R1–R12 Introduction While earlier onset of thelarche and pubarche in females pubertal timing is the significant improvement in overall has been consistently observed in recent decades (Euling public health over the past century. Multiple reports, et al. 2008a), the trends in male pubertal timing are however, also emphasize the potential role of environ- less clear. Some studies report an earlier age of onset for mental chemicals, specifically endocrine-disrupting pubic hair and testicular development in males, whereas compounds (EDCs; Acerini & Hughes 2006, Euling et al. others dispute such temporal shifts (Euling et al. 2008a). 2008b, Mouritsen et al. 2010, Toppari & Juul 2010). EDCs An important contributor to the secular trend in female are hormonally active compounds that are speculated to http://joe.endocrinology-journals.org Ñ 2013 Society for Endocrinology Published by Bioscientifica Ltd. DOI: 10.1530/JOE-12-0449 Printed in Great Britain Downloaded from Bioscientifica.com at 10/02/2021 07:50:10AM via free access Review W ZAWATSKI and M M LEE Puberty and EDCs 218:2 R2 have a causative role in the recent decline in sperm counts pulsatile GNRH release from the hypothalamus that and impaired fertility worldwide, as well as the region- stimulates pituitary LH secretion, which in turn drives specific changes in the prevalence of hypospadias and testosterone production by testicular Leydig cells (see Fig. 1). cryptorchidism, and reproductive tract cancers (Sharpe & Short bursts of LH release occur nocturnally early in puberty, Skakkebaek 1993). This review explains pubertal develop- accompanied by nighttime elevations in serum testoster- ment in males, summarizes the reproductive effects of one. GNRH also increases FSH secretion, which promotes EDCs in animal models and their connection to human maturation of the seminiferous tubules and spermatogonia. health, and reviews the available human data relating to Serum concentrations of LH, testosterone, and inhibin B are EDC exposure and male pubertal timing. positively associated with age and pubertal progression (Anderson et al.2003, Crofton et al.2004). A large, cross- sectional study measured LH, testosterone, and inhibin B Male pubertal development levels in 828 boys aged 6–11 years in an effort to understand Puberty is an important parameter of reproductive health, the relationship between hormone concentrations and marking the sexual maturation of the hypothalamic– pubertal staging (Lee et al.2010b). The increment in LH pituitary–gonadal (HPG) axis that culminates in adult and testosterone concentrations was greatest from ages hormonal profiles and physical changes that are essential 9 through 11 years, whereas a progressive rise in serum for reproductive fitness. The reawakening of the HPG axis inhibin B was seen from age 6 years onward. While these stimulates gonadal sex steroid production, which leads to hormones increase with advancing age and progressive development of secondary sexual characteristics, acceler- pubic hair and genital stages, individual hormone levels ated growth, and achievement of fertility. Pubertal status significantly overlap between Tanner stages, making it and progression are evaluated using a sexual maturity difficult to establish distinct criteria to delineate pubertal scale developed by Tanner and now adopted widely onset and stages (Fig. 2). For example, while the mean (Marshall & Tanner 1970). testosterone values increase from 0.87 to 0.97 nmol/l The GNRH pulse generator and the HPG axis are in genital stage 1 vs 2, the confidence limits overlap functional by the end of the first trimester of gestation extensively (0.67–1.07 for stage 1 vs 0.76–1.25 for stage 2; (Grumbach 2002). After birth, the HPG axis is active until Lee et al.2010b). w6 months of life, with gonadotropin and sex steroid The critical determinants of pubertal activation of the HPG axis have not been fully identified, but somatic Journal of Endocrinology concentrations peaking between 4 and 12 weeks of life (Forest et al.1973, Anderson et al.2003), representing the growth, body fat, diet, stress, photoperiod, circadian ‘mini-puberty’ of infancy. Subsequently, GNRH pulsatility rhythm, gonadal steroids, energy expenditure, and olfac- is markedly reduced and the HPG axis is relatively quiescent tory cues influence the neuronal network to modulate throughout childhood. Onset of puberty is characterized by pubertal onset (Ebling 2005). Kisspeptins are a family of peptides encoded by the KISS1 gene on chromosome 1q32 that bind to GPR54 (KiSS-1 receptor), a member of the Physiologic Environmental rhodopsin family of G-protein-coupled receptors factors: stress, Neuronal factors: nutrition and energy network temperature and (reviewed in Roseweir & Millar (2009) and Kauffman expenditure photoperiod (2010)). Kisspeptin is produced as a 145 amino acid Hypothalamus propeptide that is cleaved to generate the bioactive DDT GNRH DDE kisspeptin-54. Analysis of expression reveals that KiSS-1 PCBs Phthalates axon terminals densely innervate the infundibular stalk Pituitary and lamina terminalis in the hypothalamus while KiSS-1-ir LH and FSH axon varicosities are found in a number of hypothalamic Lead Dioxin regions, including the ventral periventricular, supraoptic, PCBs Inhibin Testes Endosulfan preoptic, paraventricular, and infundibular nuclei. Testosterone KiSS-1-ir fibers are also present in the ventromedial and Environmental chemicals dorsomedial hypothalamus, the medial septum, and stria terminalis. KiSS-1 and GNRH have overlapping expression in circumventricular organs, and KiSS-1-containing axon Figure 1 Schematic of the HPG axis and the potential endocrine targets for EDC varicosities are contiguous to GNRH neuronal dendrites, perturbation of puberty. while GPR54 is expressed on GNRH neurons as well as in http://joe.endocrinology-journals.org Ñ 2013 Society for Endocrinology Published by Bioscientifica Ltd. DOI: 10.1530/JOE-12-0449 Printed in Great Britain Downloaded from Bioscientifica.com at 10/02/2021 07:50:10AM via free access Review W ZAWATSKI and M M LEE Puberty and EDCs 218:2 R3 2.0 2.0 100 1.5 1.5 80 60 1.0 1.0 40 LH (IU/l) 0.5 0.5 20 0 0 Inhibin B (ng/l) 0 0123 (nmol/l) Testosterone 0123 0 123 Tanner stage Tanner stage Tanner stage Figure 2 Graph of changes in LH, testosterone, and inhibin values during genital testosterone and inhibin B levels in the peripubertal period and stages 1, 2, and 3. Mean and 95% confidence limits are depicted (generated racial/ethnic differences among boys aged 6–11 years: analyses from with permission using data in Table 2 from Lee PA, Gollenberg AL, NHANES III, 1988–1994. Clinical Endocrinology 73 744–751). Hediger ML, Himes JH, Zhang Z & Louis GM 2010b Luteinizing hormone, the adenohypophysis (Oakley et al. 2009). The intimate androgens, DHEA, DHEAS, and androstenedione. The connection between neurons expressing KiSS-1 and adrenal androgens start to increase at ages 6–8 years, 2 or GNRH, established via KiSS-1 binding to GPR54, supports more years before gonadarche, and are responsible for the the crucial role of the kisspeptin/GPR54 ligand receptor mid-childhood growth spurt and initial stages of pubic hair complex in pubertal activation
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