Key Event Title
|Level of Biological Organization|
|male reproductive system|
Key Event Components
|male reproductive organ||morphological change|
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP|
|PPARα activation leading to impaired fertility||AdverseOutcome|
Key Event Description
Male reproductive tract malformations (congenital malformation of male genitalia) comprise any physical abnormality of the male internal or external genitalia present at birth. Some result from excessive or deficient androgen effect, others result from teratogenic effects, or are associated with anomalies of other parts of the body in a recognizable pattern (i.e., a syndrome). The cause of many of these birth defects is unknown.
Hypospadias is a defect of the urogenital system, a malformation in which the urethra opens on the underside of the penis instead of the tip. It results from an incomplete closure of the urethral folds, leaving a split on the penis (Kalfa, Philibert, and Sultan 2009). When the urethra opens to the glans or corona of the penis, it is called distal, whereas opening to the shaft or penoscrotal area defines hypospadias as proximal. Androgens regulate the masculinization of external genitalia. Therefore any defects in androgen biosynthesis, metabolism or action during foetal development can cause hypospadias. Gene defects causing disorders of testicular differentiation, conversion of testosterone to dihydrotestosterone or mutations in the androgen receptor can also result in hypospadias (Kalfa et al. 2008). In about 20% of patients with isolated hypospadias there are signs of endocrine abnormalities by the time of diagnosis (Rey et al. 2005). The majority of hypospadias are believed to have a multifactorial etiology, although a small percentage do result from single gene mutations (Baskin, Himes, and Colborn 2001). The only treatment of hypospadias is surgery, thus, prevention is imperative.
Biological compartments: reproductive system
How It Is Measured or Detected
Malformations are detected by macroscopically for any structural abnormality or pathological change. The Congenital malformation of the genitalia is a medical term referring to a broad category of conditions that for humans is classified by International Classification of Diseases (ICD) in chapter "Congenital malformations of genital organs" (Q50-Q56) e.g.Q54 Hypospadias, Q53 Undescended testicle. Hypospadias is usually diagnosed during the routine examination after birth. The hypospadias belongs to the category of "Congenital malformation of the genitalia" - a medical term referring to a broad category of conditions as classified in the International Classification of Diseases (ICD) in chapter "Congenital malformations of genital organs" (Q50-Q56) e.g. Q54 Hypospadias.
The anogenital distance (AGD) is a sexual dimorphism that results from the sex difference in foetal androgen (DHT) levels (Rhees et al., 1997). The AGD, the distance from the anus to the genitals, is widely used as biomarker of prenatal androgen exposure during a reproductive programming window (Wolf et al. 1999), (McIntyre, Barlow, and Foster 2001), (Macleod et al. 2010). The AGD is a marker of perineal growth and caudal migration of the genital tubercle. It is androgen-dependent in male rodents (Bowman et al. 2003). Measurement of AGD has also been proposed as a quantitative biomarker of foetal endocrine disruptor exposure in humans (Arbuckle et al. 2008), (Dean and Sharpe 2013). A longer (more “masculine”) AGD is typically associated with favourable health outcomes, while a shorter AGD is associated with adverse health outcomes. The AGD in males is approximately double that of females. Less is known about clinical correlates of AGD in females, although one study found that in women a longer AGD was associated with increased odds of multifollicular ovaries (Mendiola et al. 2012). The AGD is reflecting the prenatal hormonal milieu and in addition a biomarker for the risk of reproductive health problems linked to that early hormonal environment (Barrett et al. 2014). In animal studies, AGD measured from the genital tubercle to the anus is a sensitive marker of in utero exposure to androgens and anti-androgens, and is used extensively in animal reproductive toxicology studies (McIntyre, Barlow, and Foster 2001). AGD of each pup should be measured on at least one occasion from pre natal day postnatal day (PND) 0 through PND 4. Pup body weight should be collected on the day the AGD is measured and the AGD should be normalized to a measure of pup size, preferably the cube root of body weight (12). AGD is influenced by the body weight of the animal and therefore, this should be taken into account when evaluating the data (Gallavan et al, 1999). Body weight as a covariable may also be used (Howdeshell et al. 2007). Decreased AGD in male rats is a hallmark of exposure to antiandrogenic substances (Noriega et al, 2009; Christiansen et al, 2010). A statistically significant change in AGD that cannot be explained by the size of the animal indicates an adverse effect of exposure and should be considered in setting the NOAEL (OECD, 2008).
The extended one-generation in vivo reproductive toxicity study OECD TG 443 is used to investigate adverse effects of chemical substances on fertility and developmental toxicity in the rat, in which AGD is measured.
Domain of Applicability
Rodents (Gray et al. 2001) Human (Manson and Carr 2003) Wildlife species (Hayes et al. 2002)
AGD Across numerous species, including humans, AGD is longer in males compared to females; for review see (Barrett et al. 2014).
Regulatory Significance of the Adverse Outcome
In regulatory hazard identification and risk assessment of chemicals malformations of male genitalia are considered as a chemically induced adverse outcome that is used for risk assessment and management purposes. The prenatal developmental toxicity study (TG 414) is the method for examining embryo-foetal toxicity as a consequence of exposure during pregnancy. Parental and offspring growth, development and viability are the relevant endpoints in generation studies (OECD TG 415/416/443). These guidelines are implemented in a number of occasions where the reproductive /developmental toxicity have to be assessed in order to comply with relevant EU regulations.
Under REACH, information on reproductive toxicity is required for chemicals with an annual production/importation volume of 10 metric tonnes or more. Standard information requirements include a screening study on reproduction toxicity (OECD TG 421/422) at Annex VIII (10-100 t.p.a), a prenatal developmental toxicity study (OECD 414) on a first species at Annex IX (100-1000 t.p.a), and from March 2015 the OECD 443(Extended One-Generation Reproductive Toxicity Study) is reproductive toxicity requirement instead of the two generation reproductive toxicity study (OECD TG 416). If not conducted already at Annex IX, a prenatal developmental toxicity study on a second species at Annex X (≥ 1000 t.p.a.).
Under the Biocidal Products Regulation (BPR), information is also required on reproductive toxicity for active substances as part of core data set and additional data set (EU 2012, ECHA 2013). As a core data set, prenatal developmental toxicity study (EU TM B.31) in rabbits as a first species and a two-generation reproduction toxicity study (EU TM B.31) are required. OECD TG 443 (Extended One-Generation Reproductive Toxicity Study) shall be considered as an alternative approach to the multi-generation study.
According to the Classification, Labelling and Packaging (CLP) regulation (EC, 200; Annex I: 220.127.116.11): a) “reproductive toxicity” includes adverse effects on sexual function and fertility in adult males and females, as well as developmental toxicity in the offspring; b) “effects on fertility” includes adverse effects on sexual function and fertility; and c) “developmental toxicity” includes adverse effects on development of the offspring.
AGD is a reproductive endpoint, assessment of AGD is mandatory in OECD TG 443, 415/416 (OECD 2012).
Arbuckle, Tye E, Russ Hauser, Shanna H Swan, Catherine S Mao, Matthew P Longnecker, Katharina M Main, Robin M Whyatt, et al. 2008. “Meeting Report: Measuring Endocrine-Sensitive Endpoints within the First Years of Life.” Environmental Health Perspectives 116 (7) (July): 948–51. doi:10.1289/ehp.11226.
Barrett, Emily S, Lauren E Parlett, J Bruce Redmon, and Shanna H Swan. 2014. “Evidence for Sexually Dimorphic Associations between Maternal Characteristics and Anogenital Distance, a Marker of Reproductive Development.” American Journal of Epidemiology 179 (1) (January 1): 57–66. doi:10.1093/aje/kwt220.
Baskin, L S, K Himes, and T Colborn. 2001. “Hypospadias and Endocrine Disruption: Is There a Connection?” Environmental Health Perspectives 109 (11) (November): 1175–83.
Bowman, Christopher J, Norman J Barlow, Katie J Turner, Duncan G Wallace, and Paul M D Foster. 2003. “Effects of in Utero Exposure to Finasteride on Androgen-Dependent Reproductive Development in the Male Rat.” Toxicological Sciences : An Official Journal of the Society of Toxicology 74 (2) (August): 393–406. doi:10.1093/toxsci/kfg128.
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Kalfa, Nicolas, Benchun Liu, Ophir Klein, Ming-Hsieh Wang, Mei Cao, and Laurence S Baskin. 2008. “Genomic Variants of ATF3 in Patients with Hypospadias.” The Journal of Urology 180 (5) (November): 2183–8; discussion 2188. doi:10.1016/j.juro.2008.07.066.
Kalfa, Nicolas, Pascal Philibert, and Charles Sultan. 2009. “Is Hypospadias a Genetic, Endocrine or Environmental Disease, or Still an Unexplained Malformation?” International Journal of Andrology 32 (3) (June): 187–97. doi:10.1111/j.1365-2605.2008.00899.x.
Macleod, D J, R M Sharpe, M Welsh, M Fisken, H M Scott, G R Hutchison, A J Drake, and S van den Driesche. 2010. “Androgen Action in the Masculinization Programming Window and Development of Male Reproductive Organs.” International Journal of Andrology 33 (2) (April): 279–87. doi:10.1111/j.1365-2605.2009.01005.x.
Manson, Jeanne M, and Michael C Carr. 2003. “Molecular Epidemiology of Hypospadias: Review of Genetic and Environmental Risk Factors.” Birth Defects Research. Part A, Clinical and Molecular Teratology 67 (10) (October): 825–36. doi:10.1002/bdra.10084.
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Mendiola, Jaime, Manuela Roca, Lidia Mínguez-Alarcón, Maria-Pilar Mira-Escolano, José J López-Espín, Emily S Barrett, Shanna H Swan, and Alberto M Torres-Cantero. 2012. “Anogenital Distance Is Related to Ovarian Follicular Number in Young Spanish Women: A Cross-Sectional Study.” Environmental Health : A Global Access Science Source 11 (January): 90. doi:10.1186/1476-069X-11-90.
OECD. 2012. Test No. 443: Extended One-Generation Reproductive Toxicity Study. OECD Guidelines for the Testing of Chemicals, Section 4. OECD Publishing. doi:10.1787/9789264185371-en.
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