Mode of Action: Impaired Fetal Leydig Cell Function—Effects on Male Reproductive Development Produced by Certain Phthalate Esters

Certain phthalate esters (di-2-ethylhexyl; di-n-butyl and butyl benzyl) have profound effects on the developing male reproductive system when administered orally to pregnant experimental animals during a critical window of development. These esters produce a syndrome of adverse effects that are characteristic of a disturbance in androgen-mediated development and include a variety of reproductive tract malformations and effects on developmental phenotypic markers. A testicular dysgenesis syndrome has been proposed to explain the secular increases in a number of human male reproductive deficits, including decreased semen parameters, increased incidence of cryptorchidism and hypospadias (two of the most common human birth defects), and increased incidence of testicular (germ cell derived) cancer. The rodent phthalate data lend support to the hypothesis. This example illustrates a number of points in the use of the Human Relevance Framework. First, chemical agents may have more than one mode of action (MOA): for example, phthalate-induced peroxisome proliferation leading to hepatocarcinogensis, compared with the induction of developmental effects via effects on androgen signaling. Second, the case demonstrates the life-stage sensitivity of the response to these compounds. Third, because humans may be exposed to multiple phthalate esters producing adverse effects on reproductive development, these compounds may be useful in testing the utility of the Human Relevance Framework (HRF) approach for evaluating cumulative and aggregate risk.     

Hazard to the developing male reproductive system from cumulative exposure to phthalate esters—dibutyl phthalate,diisobutyl phthalate,butylbenzyl phthalate,diethylhexyl phthalate,dipentyl phthalate,and diisononyl phthalate

Phthalate esters are found in a wide variety of consumer and food packing products. Hence there is widespread exposure of the human population to these chemicals. Some of the phthalate esters are known to be toxic to the developing male reproductive system. This paper derives a reference dose (RfD) for each of the phthalate esters (dibutyl phthalate, diisobutyl phthalate, butylbenzyl phthalate, diethylhexyl phthalate, dipentyl phthalate, and diisononyl phthalate) that cause these effects. As these phthalate esters cause similar adverse biological effects and have the same mechanism of action, it is appropriate in a risk assessment to consider the potential adverse effects from cumulative exposure to these chemicals using a dose addition model. This paper provides examples of a cumulative risk assessment using the hazard index and relative potency approaches from the RfDs derived from studies in laboratory animals and exposure information in people. The results of the cumulative risk assessments for both a US and a German population show that the hazard index is below one. Thus it is unlikely that humans are suffering adverse developmental effects from current environmental exposure to these phthalate esters.     

Phtalates

The phthalate esters (phthalates) represent a class of chemicals largely used, mainly as plasticisers for polyvinyl chloride in a wide range of domestic and industrial applications. Their volatility and water solubility are very limited. This paper focuses on the six most largely used phthalates. In rodents, the main toxic effects observed pertain to the liver and include hepatic tumours for di-isononyl phthalate and di-(2-ethylhexyl) phthalate. However, it is generally admitted that these effects are not relevant to humans, due to the mechanism of action of these compounds. The reproductive and developmental effects are considered to be the critical endpoints for some phthalates. Di-n-butyl phthalate, butylbenzyl phthalate, and di-(2-ethylhexyl) phthalate can produce alterations of the developing and adult male reproductive system, and an embryo/foetal toxicity. Information on their toxic effects in human is rare.     

Diisobutyl phthalate has comparable anti-androgenic effects to di-n-butyl phthalate in fetal rat testis

Phthalates are widely used as plasticizers in various consumer products and building materials. Some of the phthalates are known to interfere with male reproductive development in rats, and di-n-butyl phthalate (DBP), diethylhexyl phthalate (DEHP) and butyl benzyl phthalate (BBP) were recently banned for use in toys in the EU mainly due to their reproductive toxicity. Diisobutyl phthalate (DiBP) has similar structural and application properties as DBP, and is being used as a substitute for DBP. However, knowledge on male reproductive effects of DiBP in experimental animals is lacking. METHODS: In the current study, four groups of pregnant Wistar rats were exposed to either 0mg/kg bw/day or 600 mg/kg bw/day of DiBP from gestation day (GD) 7 to either GD 19 or GD 20/21. Male offspring was examined at GD 19 or GD 20/21 for effects on testicular testosterone production and testicular histopathology. Changes in anogenital distance (AGD) were evaluated as an indication of feminisation of males. RESULTS: Anogenital distance was statistically significantly reduced at GD 20/21 together with reductions in testicular testosterone production and testicular testosterone content. Histopathological effects (Leydig cell hyperplasia, Sertoli cell vacuolisation, central location of gonocytes and presence of multinuclear gonocytes) known for DBP and DEHP were observed in testes of DiBP-exposed animals at GD 20/21. Additionally, immunohistochemical expression of P450scc and StAR proteins in Leydig cells was reduced by DiBP. At GD 19, these effects on anogenital distance, testosterone levels and histopathology were less prominent. CONCLUSION: In this study, GD 20/21 rather than GD 19 appears to be the optimal time for investigating changes in anogenital distance, testosterone levels, and testicular histopathology. DiBP has similar testicular and developmental effects as DBP and DEHP, and although more developmental and especially postnatal studies are needed to clearly identify the reproductive effects of DiBP, this study indicates a reason for concern about the use of DiBP as a substitute for DBP.     

Phthalate ester toxicity in Leydig cells: developmental timing and dosage considerations

Humans have significant exposures to phthalates, as these chemical plasticizers are ubiquitously present in flexible plastics. Recent epidemiological evidence indicates that boys born to women exposed to phthalates during pregnancy have an increased incidence of congenital genital malformations and spermatogenic dysfunction, signs of a condition referred to as testicular dysgenesis syndrome (TDS). TDS is thought to develop as a result of environmental factors that cause a testicular disturbance at an early fetal stage with a resultant spectrum of clinical testicular dysfunction, ranging from impaired spermatogenesis and genital malformations to increased risk for development of testicular cancer. Proposed environmental factors in the etiology of TDS include endocrine disrupting compounds such as the phthalates. Leydig cells have been classified as one of the main targets for phthalate ester toxicity in the body based on studies in rodents. In support of this hypothesis, two Leydig cell products - insulin-like growth factor 3 (INSL3) and testosterone (T) - are both suppressed after phthalate exposures. Both fetal and adult generations of Leydig cells are affected by phthalate esters, although their sensitivities may differ. In rodent models, when pregnant dams are exposed to phthalate esters, fetal Leydig cells form enlarged clusters that are retained in the testis even after birth, in contrast to untreated controls. Despite the retention of fetal Leydig cells, however, their numbers and average cell volume of total in exposed males are reduced, as are INSL3 production and steroidogenic competence. These alterations are directly associated with clinical features of TDS, including cryptorchidism and impaired spermatogenesis.     

Reproductive toxicity of di(2-ethylhexyl) phthalate in selenium-supplemented and selenium-deficient rats

Phthalates are abundantly produced plasticizers, and di(ethylhexyl) phthalate (DEHP) is the most widely used derivative in various consumer products and medical devices. Animal studies show that DEHP and various other phthalates cause reproductive and developmental toxicity. Although the evidences are limited, it seems reasonable that DEHP may have a potential for similar adverse effects in humans. Such concerns are increasing, particularly for the developing reproductive system of male infants and children. By taking into account the essentiality of selenium (Se) in testicular structure and functions and the high prevalence of inadequate Se intake in various part of the world, this study was designed to investigate the testicular toxicity of DEHP in Se-deficient male rats and to examine the possible preventive effects of Se supplementation on phthalate toxicity. Se deficiency was generated by feeding 3-week-old Sprague-Dawley rats with a ≤0.05 Se mg/kg diet for 5 weeks. Supplementation groups were on a 1 mg Se/kg diet, and DEHP-treated groups received a 1,000 mg/kg dose by gavage during the last 10 days of the feeding period. Testicular histopathology, sperm count and motility, and sperm morphology were examined, and plasma levels of sex hormones were measured. Toxicity and antiandrogenic effects of DEHP were evidenced by disturbed testicular histology and spermatogenesis, diminished testosterone, leutinizing hormone (LH) and follicle stimulating hormone (FSH) levels, and sperm motility. The effects of DEHP were much more pronounced in Se-deficient rats, whereas Se supplementation was found to be protective, reflecting its regulating role in cellular redox equilibrium.     

Mode of action: reduction of testosterone availability--molinate-induced inhibition of spermatogenesis

Molinate is a preemergent herbicide that has been demonstrated to affect reproduction in the rat via alterations in sperm production. A wealth of standard toxicological studies and targeted research efforts relating to this adverse effect is available, and these were used to evaluate the utility of the Human Relevance Framework (HRF) for noncancer health effects. The hypothesized mode of action involved inhibition of the hydrolysis of cholesterol from high-density lipoprotein in the rat testes, followed by an androgen withdrawal syndrome on spermatogenesis. Some evidence is available that a similar mode of action would not be operable in humans. Despite the wealth of studies conducted in the rat, the weight of evidence is insufficient to define the mode of action for reproductive toxicity in the male rat. A principal deficiency in the database was discordance between the exposure levels observed to cause biochemical disturbances in the testes related to the hypothesized mode of action and the dose levels observed to induce the adverse outcome on spermatogenesis. For this reason, a complete MOA/human relevance analysis is not possible and, based on traditional risk assessment principles, any toxic effects are assumed to be relevant for human risk assessment.     

Mode of Action: Reduction of Testosterone Availability—Molinate-Induced Inhibition of Spermatogenesis

Molinate is a preemergent herbicide that has been demonstrated to affect reproduction in the rat via alterations in sperm production. A wealth of standard toxicological studies and targeted research efforts relating to this adverse effect is available, and these were used to evaluate the utility of the Human Relevance Framework (HRF) for noncancer health effects. The hypothesized mode of action involved inhibition of the hydrolysis of cholesterol from high-density lipoprotein in the rat testes, followed by an androgen withdrawal syndrome on spermatogenesis. Some evidence is available that a similar mode of action would not be operable in humans. Despite the wealth of studies conducted in the rat, the weight of evidence is insufficient to define the mode of action for reproductive toxicity in the male rat. A principal deficiency in the database was discordance between the exposure levels observed to cause biochemical disturbances in the testes related to the hypothesized mode of action and the dose levels observed to induce the adverse outcome on spermatogenesis. For this reason, a complete MOA/human relevance analysis is not possible and, based on traditional risk assessment principles, any toxic effects are assumed to be relevant for human risk assessment.     

The effect of mono-(2-ethylhexyl) phthalate and other phthalate esters on lactate production by Sertoli cells in vitro

Sertoli cells produce lactate and pyruvate as energy substrates for the developing germ cells in the testis. Since the Sertoli cells are thought to be the initial target for phthalate esters causing testicular atrophy, the effect of some phthalates on lactate and pyruvate production by primary Sertoli cell-enriched cultures was studied. Mono-(2-ethylhexyl) phthalate (0.1-200 microM) produced a concentration-dependent stimulation of lactate, but not pyruvate production over a 24 h treatment period and an increase in the ratio of lactate/pyruvate concentration in the culture medium. Di-(2-ethylhexyl) phthalate and 2-ethylhexanol (200 microM) had no such effects. Other phthalate monoesters known to cause testicular atrophy also increased Sertoli cell lactate production and the lactate/pyruvate ratio, whereas monoesters not associated with testicular damage in vivo had no such effects. The results suggest that loss of germ cells in phthalate-induced testicular atrophy is not due to inhibition of energy substrate production by the Sertoli cells and that stimulation of lactate production may be a useful in vitro marker for phthalate esters and related compounds that cause testicular injury.     

Reproductive and Developmental Toxicity of Phthalates

The purposes of this review are to (1) evaluate human and experimental evidence for adverse effects on reproduction and development in humans, produced by exposure to phthalates, and (2) identify knowledge gaps as for future studies. The widespread use of phthalates in consumer products leads to ubiquitous and constant exposure of humans to these chemicals. Phthalates were postulated to produce endocrine-disrupting effects in rodents, where fetal exposure to these compounds was found to induce developmental and reproductive toxicity. The adverse effects observed in rodent models raised concerns as to whether exposure to phthalates represents a potential health risk to humans. At present, di(2-ethylhexyl) phthalate (DEHP), di-n-butyl phthalate (DBP), and butyl benzyl phthalate (BBP) have been demonstrated to produce reproductive and developmental toxicity; thus, this review focuses on these chemicals. For the general population, DEHP exposure is predominantly via food. The average concentrations of phthalates are highest in children and decrease with age. At present, DEHP exposures in the general population appear to be close to the tolerable daily intake (TDI), suggesting that at least some individuals exceed the TDI. In addition, specific high-risk groups exist with internal levels that are several orders of magnitude above average. Urinary metabolites used as biomarkers for the internal levels provide additional means to determine more specifically phthalate exposure levels in both general and high-risk populations. However, exposure data are not consistent and there are indications that secondary metabolites may be more accurate indicators of the internal exposure compared to primary metabolites. The present human toxicity data are not sufficient for evaluating the occurrence of reproductive effects following phthalate exposure in humans, based on existing relevant animal data. This is especially the case for data on female reproductive toxicity, which are scarce. Therefore, future research needs to focus on developmental and reproductive endpoints in humans. It should be noted that phthalates occur in mixtures but most toxicological information is based on single compounds. Thus, it is concluded that it is important to improve the knowledge of toxic interactions among the different chemicals and to develop measures for combined exposure to various groups of phthalates.     

Reproductive and developmental effects of phthalate diesters in males

Phthalate diesters are a diverse group of chemicals used to make plastics flexible and are found in personal care products, medical equipment, and medication capsules. Ubiquitous in the environment, human exposure to phthalates is unavoidable; however, the clinical relevance of low concentrations in human tissues remains uncertain. The epidemiological literature was inadequate for prior reviews to conclusively evaluate the effects of phthalates on male reproductive tract development and function, but recent studies have expanded the literature. Therefore, we conducted a systematic review of the literature focused on the effects of phthalate exposure on the developing male reproductive tract, puberty, semen quality, fertility, and reproductive hormones. We conclude that although the epidemiological evidence for an association between phthalate exposure and most adverse outcomes in the reproductive system, at concentrations to which general human populations are exposed, is minimal to weak, the evidence for effects on semen quality is moderate. Results of animal studies reveal that, although DEHP was the most potent, different phthalates have similar effects and can adversely affect development of the male reproductive tract with semen quality being the most sensitive outcome. We also note that developmental exposure in humans was within an order of magnitude of the adverse effects documented in several animal studies. While the mechanisms underlying phthalate toxicity remain unclear, the animal literature suggests that mice are less sensitive than rats and potentially more relevant to estimating effects in humans. Potential for chemical interactions and effects across generations highlights the need for continued study.     

Cumulative effects of dibutyl phthalate and diethylhexyl phthalate on male rat reproductive tract development: altered fetal steroid hormones and genes.

Exposure to plasticizers di(n-butyl) phthalate (DBP) and diethylhexyl phthalate (DEHP) during sexual differentiation causes male reproductive tract malformations in rats and rabbits. In the fetal male rat, these two phthalate esters decrease testosterone (T) production and insulin-like peptide 3 (insl3) gene expression, a hormone critical for gubernacular ligament development. We hypothesized that coadministered DBP and DEHP would act in a cumulative dose-additive fashion to induce reproductive malformations, inhibit fetal steroid hormone production, and suppress the expression of insl3 and genes responsible for steroid production. Pregnant Sprague Dawley rats were gavaged on gestation days (GD) 14-18 with vehicle control, 500 mg/kg DBP, 500 mg/kg DEHP, or a combination of DBP and DEHP (500 mg/kg each chemical; DBP+DEHP); the dose of each individual phthalate was one-half of the effective dose predicted to cause a 50% incidence of epididymal agenesis. In experiment one, adult male offspring were necropsied, and reproductive malformations and androgen-dependent organ weights were recorded. In experiment two, GD18 testes were incubated for T production and processed for gene expression by quantitative real-time PCR. The DBP+DEHP dose increased the incidence of many reproductive malformations by >or=50%, including epididymal agenesis, and reduced androgen-dependent organ weights in cumulative, dose-additive manner. Fetal T and expression of insl3 and cyp11a were cumulatively decreased by the DBP+DEHP dose. These data indicate that individual phthalates with a similar mechanism of action, but with different active metabolites (monobutyl phthalate versus monoethylhexyl phthalate), can elicit dose-additive effects when administered as a mixture.     

Decreased anogenital distance and increased incidence of undescended testes in fetuses of rats given monobenzyl phthalate,a major metabolite of butyl benzyl phthalate

The objective of this study was to determine the adverse effects of monobenzyl phthalate (MBeP), a major metabolite of butyl benzyl phthalate (BBP), on the development of the reproductive system, and to assess the role of MBeP in the antiandrogenic effects of BBP. Pregnant rats were given MBeP by gavage at 167, 250, or 375 mg/kg on days 15-17 of pregnancy. Fetuses were examined on day 21 of pregnancy. Maternal body weight gain and food consumption were significantly decreased at 167 mg/kg and higher. Fetal weight was significantly decreased at 375 mg/kg. A significant increase in the incidence of undescended testes and decrease in the anogenital distance (AGD) and ratio of AGD to the cube root of body weight was found in male fetuses at 250 mg/kg and higher. The AGD and ratio of AGD to the cube root of body weight of female fetuses in the MBeP-treated groups were comparable to those in the control group. The present data indicate that MBeP produces adverse effects on the development of the reproductive system in male offspring and suggest that MBeP may be responsible for the antiandrogenic effects of BBP.     

In utero phthalate effects in the female rat: A model for MRKH syndrome

Mayer–Rokitansky–Kuster–Hauser (MRKH) syndrome is characterized by uterine and vaginal canal aplasia in normal karyotype human females and is a syndrome with poorly defined etiology. Reproductive toxicity of phthalate esters (PEs) occurs in rat offspring exposed in utero, a phenomenon that is better studied in male offspring than females. The current study reports female reproductive tract malformations in the Sprague–Dawley rat similar to those characteristic of MRKH syndrome, following in utero exposure to a mixture of 5 PEs. We determined that females are ∼2-fold less sensitive to the effects of the 5-PE mixture than males for reproductive tract malformations. We were not fully successful in defining the critical exposure period for females; however, incidence of malformations was 88% following dosing from GD8 to 19 versus 22% and 0% for GD8–13 and GD14–19, respectively. Overall, this study provides valuable information regarding female vulnerability to in utero phthalate exposure and further characterizes a potential model for the human MRKH syndrome.     

Reproductive and developmental effects of phthalate diesters in females

Abstract

Phthalate diesters, widely used in flexible plastics and consumer products, have become prevalent contaminants in the environment. Human exposure is ubiquitous and higher phthalate metabolite concentrations documented in patients using medications with phthalate-containing slow release capsules raises concerns for potential health effects. Furthermore, animal studies suggest that phthalate exposure can modulate circulating hormone concentrations and thus may be able to adversely affect reproductive physiology and the development of estrogen sensitive target tissues. Therefore, we conducted a systematic review of the epidemiological and experimental animal literature examining the relationship between phthalate exposure and adverse female reproductive health outcomes. The epidemiological literature is sparse for most outcomes studied and plagued by small sample size, methodological weaknesses, and thus fails to support a conclusion of an adverse effect of phthalate exposure. Despite a paucity of experimental animal studies for several phthalates, we conclude that there is sufficient evidence to suggest that phthalates are reproductive toxicants. However, we note that the concentrations needed to induce adverse health effects are high compared to the concentrations measured in contemporary human biomonitoring studies. We propose that the current patchwork of studies, potential for additive effects and evidence of adverse effects of phthalate exposure in subsequent generations and at lower concentrations than in the parental generation support the need for further study.     

Adverse effects on development of the reproductive system in male offspring of rats given monobutyl phthalate, a metabolite of dibutyl phthalate, during late pregnancy

The objective of this study was to determine the adverse effects of monobutyl phthalate (MBuP), a major metabolite of dibutyl phthalate (DBP), on development of the reproductive system in offspring following maternal administration during late pregnancy, and to assess the role of MBuP in the antiandrogenic effects of DBP. Pregnant rats were given MBuP by gastric intubation at 250, 500, or 750 mg/kg on days 15 through 17 of pregnancy. Maternal body weight gain and food consumption during the administration period were significantly decreased at 500 mg/kg and higher and at 750 mg/kg, respectively. A significant increase in the incidence of postimplantation embryonic loss was found at 500 mg/kg and higher. The body weights of male and female fetuses were significantly lower at 750 mg/kg. A significant increase in the incidence of fetuses with undescended testes was found at 250 mg/kg and higher. A significant decrease in the anogenital distance (AGD) of male fetuses was observed at 250 mg/kg and higher. The AGD/body weight ratio and AGD/cube root of body weight ratio in male fetuses was also significantly reduced at 250 mg/kg and higher. The AGD, AGD/body weight ratio and AGD/cube root of body weight ratio in female fetuses in the MBuP-treated groups were comparable to those in the control group. The present study indicates that MBuP on days 15 to 17 of pregnancy produced adverse effects on the development of reproductive system in male offspring and suggest that MBuP may be responsible for the induction of the antiandrogenic effects of DBP.     

Mode of Action: Inhibition of Androgen Receptor Function—Vinclozolin-Induced Malformations in Reproductive Development

Vinclozolin is a fungicide that has been shown to cause Leydig cell tumors and atrophy of the accessory sex glands in adult rodents. In addition, exposure of rats during pregnancy causes a pattern of malformations in the male urogenital tract. A wealth of standard toxicological studies and targeted research efforts is available related to this adverse effect, and these were used to evaluate the Human Relevance Framework (HRF) for noncancer health effects. Vinclozolin and two of its metabolites, designated M1 and M2, have been shown to bind and inhibit the function of the rat and human androgen receptor. Other means of interfering with androgen receptor function (e.g., by exposure to the pharmaceutical agent flutamide) lead to similar adverse health outcomes. There is direct in vivo evidence in the rat prostate that androgen-dependent gene expression changes occur after exposure to vinclozolin. There are no proposed alternatives to the androgen receptor-mediated mode of action. Based on what is known about kinetic and dynamic factors, confidence is high that the animal mode of action (MOA) for vinclozolin-induced malformation of the male reproductive tract is highly plausible in humans.     

Mode of action: inhibition of androgen receptor function--vinclozolin-induced malformations in reproductive development

Vinclozolin is a fungicide that has been shown to cause Leydig cell tumors and atrophy of the accessory sex glands in adult rodents. In addition, exposure of rats during pregnancy causes a pattern of malformations in the male urogenital tract. A wealth of standard toxicological studies and targeted research efforts is available related to this adverse effect, and these were used to evaluate the Human Relevance Framework (HRF) for noncancer health effects. Vinclozolin and two of its metabolites, designated M1 and M2, have been shown to bind and inhibit the function of the rat and human androgen receptor. Other means of interfering with androgen receptor function (e.g., by exposure to the pharmaceutical agent flutamide) lead to similar adverse health outcomes. There is direct in vivo evidence in the rat prostate that androgen-dependent gene expression changes occur after exposure to vinclozolin. There are no proposed alternatives to the androgen receptor-mediated mode of action. Based on what is known about kinetic and dynamic factors, confidence is high that the animal mode of action (MOA) for vinclozolin-induced malformation of the male reproductive tract is highly plausible in humans.     

Prenatal developmental toxicity studies on di-n-heptyl and di-n-octyl phthalates in Sprague-Dawley rats

This study evaluates the developmental toxicity of two dialkyl phthalate esters, di-n-heptyl phthalate (DHPP) and di-n-octyl (DnOP) phthalate, which have straight-alkyl side chains of seven and eight carbons, respectively. Sprague-Dawley rats were administered 0, 0.25, 0.50, or 1g/kg/day of DHPP or DnOP, by gavage, on gestation days 6-20. DHPP and DnOP had no adverse effect on maternal feed consumption and body weight gain, or on the incidence of post-implantation loss and fetal body weight. There was no increase in the incidence of fetal malformations or external and visceral variations, whatever treatment. A significant increase in rudimentary lumbar ribs was observed at all doses of DHPP and DnOP. The anogenital distance of the male fetuses was significantly decreased at the highest dose of DHPP. This parameter was not affected by DnOP. Thus, the lowest-observed-adverse-effect level (LOAEL) for developmental toxicity was 0.25 g/kg/day for DHPP and DnOP.     

The steroidogenic acute regulatory protein as a target of endocrine disruption in male reproduction

Development of the adult male reproductive tract requires proper spatial-temporal expression of the sex hormones testosterone and estrogen during fetal developmental stages and at puberty. Exogenous agents that disrupt the production and/or actions of the testosterone and estrogen and cause aberrant reproductive tract development can be thought of as endocrine disruptors (ED). This review will focus on the impact of ED on testosterone production by Leydig cells during fetal development and in the adult. In particular, the genes encoding the steroidogenic acute regulatory protein (StAR) and cytochrome P450 17 alpha hydroxylase/17,20 lyase (CYP17A1) within the steroid hormone biosynthetic pathway are highlighted as ED targets. We begin with an overview of steroidogenesis and regulation of StAR then summarize the published literature on the effects of diethylstibesterol, phthalate esters, and arsenite on male reproduction with a focus on the expression and function of StAR.