Urinary and serum metabolites of di-n-pentyl phthalate in rats

8-OHdG mediates the association of co-exposure to fifty-five typical endocrine-disrupting chemicals with renal function: a cross-section investigation in Southern Chinese adults

Individual typical endocrine-disrupting chemicals (EDCs), including organophosphate triesters (OPEs), parabens, triclosan (TCS), bisphenols, benzophenones (BPs), phthalates (PAEs), and synthetic phenolic antioxidants (SPAs), are associated with renal dysfunction. However, the combined effects and underlying mechanisms of mixed EDC exposure on renal function remain unclear. Two hundred ninety-nine adult participants were enrolled in the cross-sectional survey conducted in Guangzhou, China. Urinary levels of 7 OPEs, 6 parabens, TCS, 14 bisphenols, 8 BPs, 15 PAEs, 4 SPAs, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were determined, and estimated glomerular filtration rate (eGFR) was served as the outcome index. We found elevated levels of diphenyl phosphate (DPP), bisphenol A (BPA), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), and mono-butyl phthalate (MBP) showed dose-responsive associations with eGFR decline, However, nonlinear associations were observed for bis(2-butoxyethyl) hydrogen phosphate (BBOEP), TCS, 4-hydroxybenzophenone (HBP), mono-n-pentyl phthalate (MnPP), and mono-benzyl phthalate (MBzP). The quantile-based g-computation model demonstrated that a quartile increase in the EDC mixture corresponded to a 0.383-SD decrease (95% CI - 0.658 ~  - 0.108, P = 0.007) in eGFR. Notably, BPA was identified as the primary contributor to this effect. Moreover, 8-OHdG mediated the eGFR decline associated with EDC mixtures with a mediation proportion of 25.49%. A sex-modified effect was also observed (P = 0.004), indicating that exposure to the mixture of EDC was linked to more pronounced renal dysfunction in females. Our novel findings suggest that exposure to a typical mixture of EDCs is associated with renal dysfunction in the general adult population of Southern China. Furthermore, 8-OHdG may play a role in the pathogenesis of EDC mixture-related renal dysfunction.

In utero exposure to dipentyl phthalate disrupts fetal and adult Leydig cell development

Phthalates as plasticizers are widely used in many consumer products. Dipentyl phthalate (DPeP) is one of phthalates. However, there are currently few data on whether DPeP exposure affects rat Leydig cell development. In this study, we investigated the effects of in utero DPeP exposure on Leydig cell development in the testes of male newborn and adult rats. From gestational days 14 to 21, Sprague-Dawley pregnant rats were gavaged vehicle (corn oil, control) or DPeP (10, 50, 100, and 500 mg/kg body weight/day). Testosterone and the expression of Leydig cell genes and proteins in the testis at birth and at postnatal day 56 were examined. DPeP dose-dependently reduced serum testosterone levels of male offspring at birth and at postnatal day 56 at 100 and 500 mg/kg and lowered serum luteinizing hormone levels at adult males at ≥10 mg/kg when compared with the control. In addition, DPeP increased number of fetal Leydig cells by inducing their proliferation but down-regulated the expression of Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, Hsd17b3, and Insl3 in fetal Leydig cells per se. DPeP reduced number of adult Leydig cells by inducing cell apoptosis and down-regulated the expression of Lhcgr and Star in adult Leydig cells at postnatal day 56. DPeP lowered SIRT1 and BCL2 levels in the testis of adult rats. In conclusion, DPeP adversely affects both fetal and adult Leydig cell development after in utero exposure.

Di-(2-ethylhexyl) Phthalate (DEHP) and Uterine Histological Characteristics

Phthalates have a long industrial history. It is suspected that phthalates and their metabolites have detrimental effects on reproduction and development. They are well-known for their anti-androgenic effects. Several studies have indicated that phthalates and their metabolites are reprotoxic in males and endocrine disruptors. Reproduction and embryogenesis occur in the uterus of female eutherian mammals. A horizontal analytical method is preferred to elucidate the toxic effects of phthalates on human reproduction. Nevertheless, there are vast numbers of known phthalates and not all of their modes of action have been clarified. Di-(2-ethylhexyl) phthalate (DEHP) is a commonly used plasticizer and has been the subject of numerous toxicological studies. However, few of these have reported on the toxic effects of DEHP, its metabolites, other phthalates, or mixtures on female reproduction. Acute and high doses of DEHP adversely affect uterine histology. Recently, it was disclosed that chronic exposures to low doses of DEHP have endocrine disruption efficacy. DEHP induces various cellular responses including modulation of the expression and regulation of steroid hormone receptors and transcription and paracrine factors. Uteri do not respond uniformly to DEHP exposure. The phenotypic manifestations and effects on fertility in response to DEHP and its metabolites may vary with species, developmental stage, and generation. Hence, DEHP exposure may histological alter the uterus and induce endometriosis, endometriosis, hyperplasia, myoma, and developmental and reproductive toxicity.

Unexpected, ubiquitous exposure of pregnant Brazilian women to diisopentyl phthalate, one of the most potent antiandrogenic phthalates

BACKGROUND

Human exposure to phthalates and other non-persistent chemicals in developing countries is largely unknown. A preliminary analysis of urinary samples from pregnant Brazilian women revealed the presence of metabolites of Diisopentyl phthalate (DiPeP).

OBJECTIVES

Reliably quantify DiPeP metabolites in human urine and investigate the potential antiandrogenic activity of this phthalate in rats.

METHODS

We initiated a pilot pregnancy cohort in Curitiba, Brazil, to examine phthalate exposure in urine samples collected in early pregnancy (n = 50) or pooled samples from early, mid and late pregnancy (n = 44). Our well established phthalate method was modified to include the primary DiPeP metabolite, monoisopentyl phthalate (MiPeP), and two additional secondary oxidized metabolites, 3OH-MiPeP and 4OH-MiPeP. In a parallel approach, we orally exposed pregnant rats to DiPeP or Di-n-butyl phthalate (DnBP; reference phthalate) at 0, 125, 250, and 500 mg/kg/day from gestation day 14 to 18 and measured ex vivo fetal testis testosterone production.

RESULTS

We were able to detect and quantify specific DiPeP metabolites in nearly all (98%) of the early pregnancy urine samples and in all gestational pool samples with a median concentration for MiPeP of 3.65 and 3.15 μg/L, respectively, and for the two oxidized metabolites between 1.00 and 1.70 μg/L. All three urinary DiPeP metabolites were strongly correlated (r = 0.89 to 0.99). In the rat model, the effective dose (mg/kg/day) inhibiting fetal testosterone production by 50% (ED₅₀ [95% confidence interval]) was 93.6 [62.9-139.3] for DiPeP which was significantly lower than for DnBP (220.3 [172.9-280.7]), highlighting the strong antiandrogenic potency of DiPeP within the spectrum of the phthalates.

CONCLUSIONS

We unveiled and confirmed the exposure of pregnant Brazilian women to DiPeP via specific urinary metabolites. This unexpected and ubiquitous DiPeP exposure indicates to unique DiPeP exposure sources in Brazil. These exposures spark considerable concern because DiPeP is one of the most potent antiandrogenic phthalates.

Analytical method for urinary metabolites as biomarkers for monitoring exposure to phthalates by gas chromatography/mass spectrometry

Phthalates, widely used as plasticizers, have been detected in indoor air, but there have been few reports on methods of analyzing urinary metabolites as biomarkers to monitor exposure to di-n-pentyl phthalate or di-n-hexyl phthalate. Presented here is a cost-effective and sensitive analytical method for the determination of urinary metabolites of phthalates containing these two compounds. Nine urinary phthalate metabolites were enzymatically hydrolyzed and extracted with toluene: monomethyl phthalate, monoethyl phthalate, monoisobutyl phthalate, mono-n-butyl phthalate, mono-n-pentyl phthalate, mono-n-hexyl phthalate, monocyclohexyl phthalate, monobenzyl phthalate and mono(2-ethyl-5-carboxypentyl) phthalate. After transformation to their tert-butyldimethylsilyl derivatives, they were analyzed by gas chromatography/mass spectrometry in the electron impact ionization mode. The calibration curves for the metabolites were linear at urinary concentrations of up to 30 μg/L, showing that they could be determined accurately and precisely (detection limits 0.1-0.4 μg/L, quantification limits 0.3-1.3 μg/L). The urine samples collected could be stored for up to 1 month at -20°C. The proposed analytical method was used to examine urine samples from seven healthy volunteers. This method should be useful for monitoring phthalate exposure in the general population.

Cumulative effects of antiandrogenic chemical mixtures and their relevance to human health risk assessment

Toxicological studies of defined chemical mixtures assist human health risk assessment by establishing how chemicals interact with one another to induce an effect. This paper reviews how antiandrogenic chemical mixtures can alter reproductive tract development in rats with a focus on the reproductive toxicant phthalates. The reviewed studies compare observed mixture data to mathematical mixture model predictions based on dose addition or response addition to determine how the individual chemicals in a mixture interact (e.g., additive, greater, or less than additive). Phthalate mixtures were observed to act in a dose additive manner based on the relative potency of the individual phthalates to suppress fetal testosterone production. Similar dose additive effects have been reported for mixtures of phthalates with antiandrogenic pesticides of differing mechanisms of action. Overall, data from these phthalate experiments in rats can be used in conjunction with human biomonitoring data to determine individual hazard indices, and recent cumulative risk assessments in humans indicate an excess risk to antiandrogenic chemical mixtures that include phthalates only or phthalates in combination with other antiandrogenic chemicals.

Paired Serum and Urine Concentrations of Biomarkers of Diethyl Phthalate, Methyl Paraben, and Triclosan in Rats

BACKGROUND

Exposure to environmental chemicals, including phthalates and phenols such as parabens and triclosan, is ubiquitous within the U.S. general population.

OBJECTIVE

This proof-of-concept rodent study examined the relationship between oral doses of three widely used personal care product ingredients [diethyl phthalate (DEP), methyl paraben (MPB), and triclosan] and urine and serum concentrations of their respective biomarkers.

METHODS

Using female Sprague-Dawley rats, we carried out two rounds of experiments with oral gavage doses selected in accordance with no observed adverse effect levels (NOAELs) derived from previous studies: 1,735 (DEP), 1,050 (MPB), 50 (triclosan) mg/kg/day. Administered doses ranged from 0.005 to 173 mg/kg/day, 10-100,000 times below the NOAEL for each chemical. Controls for the MPB and triclosan experiments were animals treated with olive oil (vehicle) only; controls for the DEP serum experiments were animals treated with the lowest doses of MPB and triclosan. Doses were administered for 5 days with five rats in each treatment group. Urine and blood serum, collected on the last day of exposure, were analyzed for biomarkers. Relationships between oral dose and biomarker concentrations were assessed using linear regression.

RESULTS

Biomarkers were detected in all control urine samples at parts-per-billion levels, suggesting a low endemic environmental exposure to the three chemicals that could not be controlled even with all of the precautionary measures undertaken. Among the exposed animals, urinary concentrations of all three biomarkers were orders of magnitude higher than those in serum. A consistently positive linear relationship between oral dose and urinary concentration was observed (R2 > 0.80); this relationship was inconsistent in serum.

CONCLUSIONS

Our study highlights the importance of carefully considering the oral dose used in animal experiments and provides useful information in selecting doses for future studies.

CITATION

Teitelbaum SL, Li Q, Lambertini L, Belpoggi F, Manservisi F, Falcioni L, Bua L, Silva MJ, Ye X, Calafat AM, Chen J. 2016. Paired serum and urine concentrations of biomarkers of diethyl phthalate, methyl paraben, and triclosan in rats. Environ Health Perspect 124:39-45; http://dx.doi.org/10.1289/ehp.1409586.

A short-term in vivo screen using fetal testosterone production, a key event in the phthalate adverse outcome pathway, to predict disruption of sexual differentiation

This study was designed to develop and validate a short-term in vivo protocol termed the Fetal Phthalate Screen (FPS) to detect phthalate esters (PEs) and other chemicals that disrupt fetal testosterone synthesis and testis gene expression in rats. We propose that the FPS can be used to screen chemicals that produce adverse developmental outcomes via disruption of the androgen synthesis pathway more rapidly and efficiently, and with fewer animals than a postnatal one-generation study. Pregnant rats were dosed from gestational day (GD) 14 to 18 at one dose level with one of 27 chemicals including PEs, PE alternatives, pesticides known to inhibit steroidogenesis, an estrogen and a potent PPARα agonist and ex vivo testis testosterone production (T Prod) was measured on GD 18. We also included some chemicals with "unknown" activity including DMEP, DHeP, DHEH, DPHCH, DAP, TOTM, tetrabromo-diethyl hexyl phthalate (BrDEHP), and a relatively potent environmental estrogen BPAF. Dose-response studies also were conducted with this protocol with 11 of the above chemicals to determine their relative potencies. CD-1 mice also were exposed to varying dose levels of DPeP from GD 13 to 17 to determine if DPeP reduced T Prod in this species since there is a discrepancy among the results of in utero studies of PEs in mice. Compared to the known male reproductive effects of the PEs in rats the FPS correctly identified all known "positives" and "negatives" tested. Seven of eight "unknowns" tested were "negatives", they did not reduce T Prod, whereas DAP produced an "equivocal" response. Finally, a dose-response study with DPeP in CD-1 mice revealed that fetal T Prod can be inhibited by exposure to a PE in utero in this species, but at a higher dose level than required in rats.Key words. Phthalate Syndrome, Fetal endocrine biomarkers, Phthalate adverse outcome pathway, testosterone production, fetal rat testis.

Considerations for estimating daily intake values of nonpersistent environmental endocrine disruptors based on urinary biomonitoring data

Human exposure to chemicals may be estimated by back-calculating urinary concentrations resulting from biomonitoring studies if knowledge of the chemical's toxicokinetic properties is available. In this paper, available toxicokinetic data for back-calculating urinary concentrations into daily intake values for bisphenol A (BPA), phthalates, parabens, and triclosan (TCS) are reviewed and knowledge gaps are identified. Human data is evaluated and presented with relevant animal data. Focus is on the recovery of the administered dose, the route of administration, and differences between humans and animals. Two human toxicokinetic studies are currently used to conclude that an oral dose of BPA is recoverable in urine and that no free BPA is present in plasma in spite of several contradicting biominotoring studies. Urinary recovery of an oral dose of phthalates in humans is complicated to assess due to extensive metabolism. In animals using14C-marked phthalates, near-complete recovery is observed. An oral dose of14C-marked parabens is also almost completely recovered in animals. In both humans and animals, however, two unspecific metabolites are formed, which complicates the back-calculation of parabens in humans. The recovery of both oral and dermal TCS in humans has been studied, but due to background levels of TCS, the back-calculation is difficult to perform. In conclusion, due to limited data, reasonable estimates of daily intake values based on urinary data are often not possible to obtain. Several knowledge gaps are identified and new studies are suggested. The route of administration used in toxicokinetic studies often does not match realistic scenarios.

Development and application of simple pharmacokinetic models to study human exposure to di-n-butyl phthalate (DnBP) and diisobutyl phthalate (DiBP)

In a published controlled dosing experiment, a single individual consumed 5mg each of labeled di-n-butyl phthalate (DnBP) and diisobutyl phthalate (DiBP) on separate occasions and tracked metabolites in his blood and urine over 48h. Data from this study were used to structure and calibrate simple pharmacokinetic (PK) models for these two phthalates, which predict urine and blood metabolite concentrations with a given phthalate intake scenario (times and quantities). The calibrated models were applied to a second published experiment in which 5 individuals fasted over the course of a 48-h weekend (bottled water only), and their full urine voids were captured and measured for DnBP and DiBP metabolites. One goal of this model application was to confirm the validity of the calibrated models - their validity would be demonstrated if a profile of intakes could be found which adequately duplicated the metabolite concentrations measured in the urine. A second goal was to study patterns of exposure for this group. It was found that all metabolites could be duplicated very well with individual-specific "best-fit" intake scenarios, with one exception. It appears that the model predicted much lower concentrations of the metabolite, 3carboxy-mono-propylphthalate (MCPP), than were observed in all individuals. Modeled as a metabolite of DnBP, this suggests that DnBP was not the major source of MCPP in the urine. For all 5 individuals, the reconstructed dose profiles of the two phthalates were similar: about 6 small bolus doses per day and an intake of about 0.5μg/kg-day. The intakes did not appear to be associated with diary-reported activities (personal hygiene and medication) of the participants. The modeled frequent intakes suggested one (or both) of two possibilities: ongoing exposures such as an inhalation exposure, or no exposure but rather an ongoing release of body stores of the phthalate metabolites from past exposures.

Identification of potential biomarkers of exposure to di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH), an alternative for phthalate plasticizers

Di(isononyl)cyclohexane-1,2-dicarboxylate (DINCH) is used as an alternative for some phthalate plasticizers. In rats, DINCH mostly eliminates in feces as cyclohexane-1,2-dicarboxylic acid (CHDA), mono isononyl ester (MINCH) or in urine as CHDA. However, CHDA is not a specific biomarker of DINCH and measuring MINCH in feces is impractical. To identify additional potential biomarkers, we administered DINCH (500 mg/kg body weight) in a single subcutaneous (SC) or oral dose to four adult female Sprague-Dawley rats. We collected 24-h urine samples before dosing (to be used as controls) and 24-h and 48-h after dosing, and serum at necropsy after 48 h. We positively identified and accurately quantified CHDA and cyclohexane-1,2-dicarboxylic [corrected] acid, mono hydroxyisononyl ester (MHNCH) using authentic standards. Moreover, we tentatively identified MINCH and 12 oxidative metabolites, including 4 cyclohexane ring oxidation products, based on their mass spectrometric-fragmentation patterns. CHDA and MHNCH levels were higher in the urine collected 24 h after oral than SC administration. By contrast, 48-h after dosing, CHDA urinary levels were similar regardless of the exposure route. We detected all but two of the urine metabolites also in serum. Levels of CHDA and MHNCH in serum were lower than in the two post-dose urine collections. Our results suggest that several urinary oxidative metabolites, specifically CHDA, mono oxoisononyl ester and MHNCH may be used as specific biomarkers of DINCH exposure in humans.

Circulating levels of bisphenol A (BPA) and phthalates in an elderly population in Sweden, based on the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS)

The plastic manufacture compounds, bisphenol A (BPA) and phthalates, are ubiquitous and have therefore been detected in virtually all types of analyzed human samples. The aim of this study was: (1) to investigate concentrations of serum levels of BPA and phthalate metabolites in seniors residing in the city of Uppsala, Sweden (2) to evaluate gender differences in relation to serum levels of BPA and phthalate metabolites in the subjects. In the population-based Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS), encompassing 1016 subjects, all aged 70, serum levels of BPA and phthalate metabolites were measured by Isotope Dilution-High Performance Liquid Chromatography-Tandem Mass Spectrometry. BPA and four out of ten phthalate metabolites, namely, Monoisobutyl phthalate (MiBP), Monomethyl phthalate (MMP), Monoethyl phthalate (MEP), Mono-(2-ethylhexyl) phthalate (MEHP), were detectable in almost all subjects. Of the remaining phthalate metabolites, Monobenzyl phthalate (MBzP), Mono-(2-ethyl-5-hydroxyhexyl) phthalate (MeHHP), and Mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP) were seen in some 300-700 of the subjects, whereas Monoisononyl phthalate (MINP) and Mono-n-octyl phthalate (MOP) were found in only a few and Monocyclohexyl phthalate (MCHP) was not detected in any subject. Neither the circulation levels of BPA nor those of phthalate metabolites differ between the genders in this elderly population of residents in Uppsala, Sweden.

Dipentyl phthalate dosing during sexual differentiation disrupts fetal testis function and postnatal development of the male Sprague-Dawley rat with greater relative potency than other phthalates

Phthalate esters (PEs) constitute a large class of plasticizer compounds that are widely used for many consumer product applications. Ten or more members of the PE class of compounds are known to induce male fetal endocrine toxicity and postnatal reproductive malformations by disrupting androgen production during the sexual differentiation period of development. An early study conducted in the rat pubertal model suggested that dipentyl phthalate (DPeP) may be a more potent testicular toxicant than some more extensively studied phthalates. Regulatory agencies require dose-response and potency data to facilitate risk assessment; however, very little data are currently available for DPeP. The goal of this study was to establish a more comprehensive data set for DPeP, focusing on dose-response and potency information for fetal and postnatal male reproductive endpoints. We dosed pregnant rats on gestational day (GD) 17 or GD 14-18 and subsequently evaluated fetal testicular testosterone (T) production on GD 17.5 and GD 18, respectively. We also dosed pregnant rats on GD 8-18 and evaluated early postnatal endpoints in male offspring. Comparison of these data to data previously obtained under similar conditions for di (2-ethylhexyl) phthalate indicates that DPeP is approximately eightfold more potent in reducing fetal T production and two- to threefold more potent in inducing development of early postnatal male reproductive malformations. Additionally, fetal testicular T production was more sensitive to inhibitory effects of DPeP exposure than was gene expression of target genes involved in male reproductive development, supporting the use of this endpoint as a critical effect in the risk assessment process.