Metabolite Monobutyl Phthalate Research Articles

Development of fluorescence polarization immunoassay to detect dibutylphthalate (dbp) and its active metabolite monobutylphthalate (mbp) in environmental samples

Development of fluorescence polarization immunoassay to detect dibutylphthalate (dbp) and its active metabolite monobutylphthalate (mbp) in environmental samples

Monobutyl phthalate (MBP) can dysregulate the antioxidant system and induce apoptosis of zebrafish liver

In this paper, the acute toxicity of monobutyl phthalate (MBP), the main hydrolysis product of dibutyl phthalate, on adult zebrafish liver antioxidant system was studied. Compared the toxicity effect of MBP and DBP by histopathology and apoptosis experiments, we speculated that the toxic effects of DBP on animals may be caused by its metabolite MBP. The results indicated that the antioxidant Nrf2-Keap1 pathway was insufficient to resist MBP-induced hepatotoxicity and led to an imbalance of membrane ion homeostasis and liver damage. Decreased cell viability, significant tissue lesions and early hepatocyte apoptosis were observed in the zebrafish liver in MBP exposure at high concentration (10 mg/L). The activities of antioxidant enzymes and ATPases in zebrafish liver were inhibited with increased malondialdehyde (MDA) content and alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. Integrated biomarker response (IBR) calculation results indicated that MBP mainly inhibited catalase (CAT) activity. Simultaneously, the expression of antioxidant-related genes (SOD, CAT, GPx, Nrf2, HO-1) was down-regulated, while apoptosis-related genes (p53, bax, cas3) were significantly up-regulated.

Early life exposure to phthalates in the Canadian Healthy Infant Longitudinal Development (CHILD) study: a multi-city birth cohort.

Few studies have examined phthalate exposure during infancy and early life, critical windows of development. The Canadian Healthy Infant Longitudinal Development (CHILD) study, a population-based birth cohort, ascertained multiple exposures during early life. To characterize exposure to phthalates during infancy and early childhood. Environmental questionnaires were administered, and urine samples collected at 3, 12, and 36 months. In the first 1578 children, urine was analyzed for eight phthalate metabolites: mono-methyl phthalate (MMP), mono-ethyl phthalate (MEP), mono-butyl phthalate (MBP), mono-benzyl phthalate (MBzP), mono-2-ethylhexyl phthalate (MEHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), and mono-3-carboxypropyl phthalate (MCPP). Geometric mean (GM) concentrations were calculated by age, together with factors that may influence concentrations. Trends with age were examined using mixed models and differences within factors examined using ANOVA. The highest urinary concentration was for the metabolite MBP at all ages (GM: 15-32 ng/mL). Concentrations of all phthalate metabolites significantly increased with age ranging from GM: 0.5-15.1 ng/mL at 3 months and 1.9-32.1 ng/mL at 36 months. Concentrations of all metabolites were higher in the lowest income categories except for MEHP at 3 months, among children with any breastfeeding at 12 months, and in urine collected on dates with warmer outdoor temperatures (>17 °C), except for MBzP at 3 months and MEHP at 3 and 12 months. No consistent differences were found by gender, study site, or maternal age. Higher phthalate metabolite concentrations were observed among children in lower income families. Examination of factors associated with income could inform interventions aimed to reduce infant phthalate exposure.

RhoG-ELMO1-RAC1 is involved in phagocytosis suppressed by mono-butyl phthalate in TM4 cells.

Di-n-butyl phthalate (DBP) is one of the most dominant phthalate esters and is ubiquitous in the environment. Male reproductive toxicity of DBP and its active metabolite mono-butyl phthalate (MBP) has been demonstrated in in vivo and in vitro studies. The objective of this study was to explore the roles of RhoG-ELMO1-RAC1 in phagocytosis disrupted by MBP in TM4 cells. Mouse Sertoli cell lines (TM4 cells) were maintained and treated by various levels of MBP (1, 10, and 100μM) for 24h. Then, cells were harvested for further experiments. Phagocytic capacity of TM4 cells was detected by flow cytometry, immunofluorescence, and oil red O staining. RAC1 activity (GTP-RAC1) was measured by RAC1 pull-down assay. Expression of mRNA and protein related to phagocytosis including ELMO1, RhoG, and RAC1 was analyzed by qRT-PCR and Western blots, respectively. MBP inhibited phagocytosis of TM4 cells and downregulated GTP-RAC1 expression and movement to membrane markedly. Furthermore, ELMO1 protein expression was downregulated in a dose-dependent manner after MBP treatments. Additionally, expression of proteins relating to phagocytosis, including RhoG and GTP-RAC1, was decreased significantly, but expression of total-RAC1 remained unchanged. GTP-RAC1 expression increased dramatically after TM4 cells were transfected with ELMO1 or RhoG plasmid, but restored under co-treatments with MBP and ELMO1/RhoG plasmid. This study suggests that MBP can reduce the phagocytosis of Sertoli cells through RhoG-ELMO1-RAC1 pathway.

Effects of dibutyl phthalate and di(2-ethylhexyl) phthalate with their metabolites on CYP2C9*1 and CYP2C19*1 activities in vitro

The aim of this article is to assess the effect of phthalates on the activities of CYP2C9 and CYP2C19 in vitro. In this study, recombinant CYP2C9*1 and CYP2C19*1 microsomes were used to investigate the effects of phthalates and their metabolites on corresponding enzyme activities in vitro. 2–100 μM substrate of enzyme was incubated with series concentration of phthalates for 30 min at 37 °C. The metabolic products were detected using ultra-high performance liquid chromatography (UHPLC) and ultra-high performance liquid chromatography–mass spectrometry (UHPLC–MS/MS) methods. The results showed dibutyl phthalate (DBP) significantly inhibited CYP2C9*1 with an activity inhibition rate of 67.3% and half-maximal inhibitory concentration (IC50) of 29.63 μmol L–1, but its metabolite monobutyl phthalate (MBP) had no significant effect. On the other hand, di(2-ethylhexyl)phthalate (DEHP) had no effect on CYP2C9*1, but its metabolite monoethylhexyl phthalate (MEHP) significantly inhibited the enzyme activity with an activity inhibition rate of 90.6% and IC50 of 6.37 μmol L–1. With regards to CYP2C19*1, DBP completely inhibited the enzyme activity with an activity inhibition rate of 100% and IC50 of 2.63 μmol L–1, but its metabolite MBP had no effect on it. DEHP and MEHP also inhibited the activity of CYP2C19*1. Further investigation showed MEHP was a competitive inhibitor of CYP2C9*1 (Ki = 7.063 μmol L–1), and DBP was a competitive inhibitor of CYP2C19*1 (Ki = 7.013 μmol L–1) against their substrates, both phthalates were non-competitive inhibitors of the cofactor NADPH. Our results suggested that DBP, DEHP, and their metabolites exhibited significant inhibitory effects toward either CYP2C9*1 or CYP2C19*1. These findings provided valuable information for a potentially toxic mechanism of DEHP and DBP on endocrine disruption and a useful guidance for safe and effective usage of drugs in patients with long-term DEHP and DBP exposure.

Degradation of dibutyl phthalate in two contrasting agricultural soils and its long-term effects on soil microbial community

Due to its widespread application and large-scale production, dibutyl phthalate (DBP) has become one of the most frequently identified phthalic acid esters (PAEs) in soils. The fate of DBP and its effects on microbial communities in soils with contrasting properties have seldom been studied. In this study, the degradation of DBP and its long-term effects on the soil microbial community were investigated in aquic cambisols and udic ferrosols. The half-lives of DBP in aquic cambisols and udic ferrosols were found to be 0.286–1.41 days and 0.870–20.4 days, respectively, indicating that DBP was degraded faster in aquic cambisols. In addition, the degradation of DBP in aquic cambisols was less vulnerable to adverse incubation conditions, including high DBP concentration, low temperature and low moisture. These results can be ascribed to the higher microbial abundance and activity in aquic cambisols than in udic ferrosols. During DBP degradation, the toxic metabolite monobutyl phthalate (MBP) was present only transiently and did not accumulate in the two soils. After 60 days of incubation, the degradation-resistant DBP residue concentrations were as high as 1.10 and 1.34 mg/kg, and the relative abundance of 8.51%–12.9% of bacterial genera and 5.59%–6.02% of fungal genera was significantly disturbed by DBP in both test soils. The results from this study highlight the need to comprehensively evaluate the environmental risks of degradation-resistant DBP residues and the impact of DBP contamination on soil microbial functions.

Effects of in vitro exposure to dibutyl phthalate, mono-butyl phthalate, and acetyl tributyl citrate on ovarian antral follicle growth and viability.

Dibutyl phthalate (DBP) is present in consumer products and the coating of some oral medications. Acetyl tributyl citrate (ATBC) has been proposed as an alternative to DBP because DBP causes endocrine disruption in animal models. Following ingestion, DBP is converted to its main metabolite mono-butyl phthalate (MBP) which has been detected in >90% of human follicular fluid samples. Previous studies show that DBP reduces the number of antral follicles present in the ovaries of mice. Thus, this study was designed to evaluate the effects of DBP, MBP, and ATBC on in vitro growth and viability of mouse ovarian antral follicles. Antral follicles were isolated from CD-1 females (PND32-37) and treated with vehicle, DBP, MBP, or ATBC (starting at 0.001 and up to 1000 μg/ml for DBP; 24-72 h). Follicle diameter, ATP production, qPCR, and TUNEL were used to measure follicle growth, viability, cell cycle and apoptosis gene expression, and cell death-associated DNA fragmentation, respectively. While MBP did not cause toxicity, DBP exposure at ≥10 μg/ml resulted in growth inhibition followed by cytoxicity at ≥500 μg/ml. ATBC increased the number of nongrowing follicles at 0.01 μg/ml and did not affect ATP production, but increased TUNEL positive area in treated follicles. Gene expression results suggest that cytotoxicity in DBP-treated follicles occurs via activation of cell cycle arrest prior to follicular death. These findings suggest that concentrations of DBP ≥10 μg/ml are detrimental to antral follicles and that ATBC should be examined further as it may disrupt antral follicle function at low concentrations.

Development of physiologically based pharmacokinetic model of di-butyl phthalate and its toxic metabolite mono-butyl phthalate in rats

Development of physiologically based pharmacokinetic model of di-butyl phthalate and its toxic metabolite mono-butyl phthalate in rats

MiRNA-200c mediates mono-butyl phthalate-disrupted steroidogenesis by targeting vimentin in Leydig tumor cells and murine adrenocortical tumor cells.

The reproductive toxicity of plasticizer di-n-butyl phthalate (DBP) and its active metabolite monobutyl phthalate (MBP) has been demonstrated in rodents. The objective of this study was to explore roles of vimentin and miRNA-200c in steroidogenesis interfered by MBP. Mouse Leydig tumor cells (MLTC-1) and murine adrenocortical tumor cells (Y1) were employed and exposed to various levels of MBP (10(-7), 10(-6), 10(-5) and 10(-4)M). Steroid hormone production was increased significantly when MLTC-1 and Y1 cells were exposed to MBP at 10(-7)M. Additionally, vimentin and steroidogenic acute regulatory protein (StAR) expressions were upregulated at the same dose. It was found that MBP increased the steroidogenesis by facilitating the cholesterol transfer process by vimentin. In contrast, miRNA-200c expression was depressed at doses of MBP (10(-7)M) in both cells. Moreover, vimentin expression and progesterone production were increased in both MLTC-1 and Y1 cells after miRNA-200c expression was artificially inhibited. These results strongly suggested that MBP raised steroid hormone synthesis via upregulated vimentin by miRNA-200c.

Neurological Toxicity of Individual and Mixtures of Low Dose Arsenic, Mono and Di (n-butyl) Phthalates on Sub-Chronic Exposure to Mice

The objective of this study was to evaluate the toxicity of individual and mixtures of di(n-butyl) phthalates (DBP) and their active metabolite monobutyl phthalate (MBP) and arsenic (As) on spatial cognition associated with hippocampal apoptosis in mice. Mice were exposed, individually or in combination, to DBP (50mg/kg body weight, intragastrically), MBP (50mg/kg body weight, intragastrically), and As (10mg/L, per os) for 8weeks. The Morris water maze test showed that mice exposed to DBP/MBP combined with As exhibited longer escape latencies and the lower average number of crossing the platform. The As content in the hippocampus after As exposure increased as compared to those without As exposure. In mice exposed to DBP/MBP combined with As, pathological alterations and oxidative damage to the hippocampus were found. Expression of apoptosis-related protein: Bax and caspase-3 were significantly increased in the hippocampus, while there was no significant change in expression of Bcl-2. The results suggested that DBP and MBP combined with As can induce spatial cognitive deficits through altering the expression of apoptosis-related protein and As played a critical role in cognition impairments. And the joint exposure has antagonistic effect.

Effects of di(n-butyl) and monobutyl phthalate on steroidogenesis pathways in the murine Leydig tumor cell line MLTC-1

Di(n-butyl) phthalate (DBP) and its active metabolite monobutyl phthalate (MBP) have been shown to disrupt reproductive organ growth. The objective of this study was to evaluate the effects of DBP/MBP on steroidogenesis in the murine Leydig tumor cell line MLTC-1 in vitro. MLTC-1 cells were incubated with various concentrations of DBP (100, 1, 0.01, and 0μmol/l in DMSO) and MBP (1000, 10, 0.1, and 0μmol/l in DMSO) for 24h. Testosterone secretion was stimulated at the lowest doses and inhibited at higher treatment doses of DBP and MBP. The mRNA levels of the side-chain cleavage enzyme (P450scc), cytochrome p450c17 (P450c17) and 3β-hydroxy-steroid dehydrogenase (3βHSD) were significantly reduced in the phthalate-exposed groups, whereas, the transcription and translation of insulin-like hormone 3 (INSL3) was affected by DBP and MBP. Alterations of the steroidogenic enzymes and INSL3 in MLTC-1 cells may be involved in the biphasic effects of DBP/MBP on androgen production.

Effects of mono and di(n-butyl) phthalate on superoxide dismutase

Di(n-butyl) phthalate (DBP) is a plasticizer used in the manufacture of several industrial and household articles. They get easily released to the environment and may cause adverse effects to living organisms. Effects of DBP and its metabolite monobutyl phthalate (MBP) on superoxide dismutase (SOD), an antioxidant enzyme, have been studied. When SOD was incubated with varying amount of DBP the activity of the enzyme was decreased proportionate to the concentration of the phthalates added. A similar result was observed with MBP also. These indicate that the DBP and MBP possess concentration dependent inhibitory effect on SOD. The mode of interaction of DBP and MBP has also been investigated using modeling and docking studies. The docking results showed that both DBP and MBP can bind in the active site of SOD and can make hydrogen bonds with the active site residue R143. This residue is crucial in the binding of reactive oxygen species (ROS) during its conversion to hydrogen peroxide and molecular oxygen. This may perhaps explain the inhibitory effect of DBP and MBP on SOD.

Cryptorchidism at birth in Nice area (France) is associated with higher prenatal exposure to PCBs and DDE, as assessed by colostrum concentrations

Since fetal exposure to anti-androgenic and/or estrogenic compounds has adverse effect on animal reproduction, such exposure could be harmful to human fetus. Data are scarce on cryptorchidism and human exposure to endocrine disruptors. We performed a prospective case-control study to assess the incidence of cryptorchidism and fetal exposure to selected chemicals in the Nice area. One hundred and fifty-one cord bloods (67 cryptorchid, 84 tightly matched controls) and 125 colostrums (56 for cryptorchid and 69 for controls) were screened for xenobiotics, including anti-androgenic dichloro-diphenyl-trichloro-ethylene (DDE), polychlorinated biphenyls (PCBs), and dibutylphthalate (and metabolite monobutylphthalate, mBP). Median concentrations in colostrum were higher, although not statistically significantly, in cryptorchid versus controls. Cryptorchid boys were more likely to be classified in the most contaminated groups in colostrum for DDE, Sigma PCBs and the composite score PCB + DDE. The same trend, but again not statistically significantly was observed for mBP. Odds ratio for cryptorchidism was increased for the highest score of Sigma PCB, with a trend only for DDE and Sigma PCB + DDE versus the lowest score of those components. Our results support an association between congenital cryptorchidism and fetal exposure to PCBs and possibly DDE. Higher concentrations in milk could be a marker of higher exposure or for an impaired detoxification pattern in genetically predisposed individuals.

Fetal Mouse Phthalate Exposure Shows that Gonocyte Multinucleation is Not Associated with Decreased Testicular Testosterone

The rat has been explored in detail for its in utero susceptibility to male reproductive tract malformation following phthalate exposure. Few other species have been studied in detail, and it is important for both mechanistic and risk assessment purposes to understand the species specificity of this response. We investigated the response of the fetal mouse testis to phthalate exposure and compared these results with those previously obtained from the rat. Initial experiments using a variety of phthalate congeners (monobutyl phthalate, di-(n-butyl) phthalate, or mono (2-ethylhexyl) phthalate) and exposure paradigms did not reduce fetal mouse testis testosterone levels. Pharmacokinetic data after a single 500 mg/kg di-(n-butyl)-phthalate (DBP) exposure on mouse gestation day (gd) 18 demonstrated that the concentrations and kinetics of the active metabolite monobutyl phthalate (MBP) in fetal and maternal plasma were similar to the rat. After a single 500 mg/kg or multiple day 250 mg/kg fetal mouse DBP exposure, rapid and dynamic changes in testis gene expression were observed, including induction of immediate early genes. Unlike the rat, expression of genes involved in cholesterol homeostasis and steroidogenesis were not decreased and were increased in a few cases. Similar to the rat, however, a 250- or 500-mg DBP/kg/day mouse exposure from gd 16 through 18 significantly increased seminiferous cord diameter, the number of multinucleated gonocytes per cord, and the number of nuclei per multinucleated gonocyte. Together, these results demonstrate that fetal mouse and rat phthalate exposure both induce immediate early gene expression and disrupt seminiferous cord and gonocyte development. This response in the mouse occurs without a measurable decrease in testicular testosterone, suggesting that altered seminiferous cord formation and gonocyte multinucleation may not be mechanistically linked to lowered testosterone.

The Testosterone Test: Phthalate Inhibits Leydig Cell Aggregation

Vol. 115, No. 3 EnvironewsOpen AccessThe Testosterone Test: Phthalate Inhibits Leydig Cell Aggregation Julia R. Barrett Julia R. Barrett Search for more papers by this author Published:1 March 2007https://doi.org/10.1289/ehp.115-a153aCited by:1AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Testicular cancer and low sperm count are adult disorders, but evidence increasingly suggests they have a fetal origin. Cryptorchidism and hypospadias, apparent at birth, also appear linked to prebirth events. According to the testicular dysgenesis syndrome (TDS) hypothesis, all four disorders, which by some reports have become more common in recent decades, partially stem from fetal abnormalities in testosterone-producing Leydig cells. An investigation now reveals that di(n-butyl) phthalate (DBP) and its metabolite monobutyl phthalate (MBP) suppress testosterone production in rats and primates [EHP 115:390–396; Hallmark et al.]. Attempts to establish in vitro models were unsuccessful, however.In rats, prenatal exposure to DBP can induce Leydig cell changes and TDS-like effects. Chronic, low-level exposure to DBP and other phthalates, widely used as plasticizers, is common among humans, but it is unknown if it causes the same effects. The primary goal of the current study was to determine whether effects seen in rats could be replicated in vitro with fetal rat and human testis explants (extracted tissue maintained in culture). The team also conducted experiments in male infant marmosets, whose neonatal testosterone production mirrors that of human males.Preliminary work revealed that rats with prenatal DBP exposure produced significantly less testosterone and had more medium or large Leydig cell clusters. This is notable because larger clusters are associated with defective testicular development. Rat fetal testis explants, however, showed only minor MBP-related effects, and results from comparable human explants were even less conclusive.Because known in vivo reactions could not be replicated in vitro—indicating either a problem with the method or misidentification of the active metabolite—the team tested MBP in marmosets. In five sets of marmoset twins, one twin was exposed to MBP for two weeks while the other served as a control. Blood testosterone levels did not differ significantly, but Leydig cell numbers and size were consistently increased in the MBP group.Because low testosterone triggers increased secretion of luteinizing hormone, which stimulates Leydig cell testosterone production, the researchers checked whether there was an initial MBP-associated suppression in testosterone production. They found that a single dose of MBP in newborn marmosets significantly reduced testosterone levels within hours. This finding led to the hypothesis that increased luteinizing hormone secretion compensates for an initial MBP-associated inhibition of testosterone production, which the researchers conclude should be considered in future animal studies. They also conclude that in vivo marmoset research represents the best current means for investigating the steroidogenic effects of DBP relevant to humans.Testicular effectThe numbers and size of Leydig cells (in brown, above) increased in MBP-treated marmosets.FiguresReferencesRelatedDetailsCited by Orsi A, Rees D, Andreini I, Venturella S, Cinelli S and Oberto G (2011) Overview of the marmoset as a model in nonclinical development of pharmaceutical products, Regulatory Toxicology and Pharmacology, 10.1016/j.yrtph.2010.12.003, 59:1, (19-27), Online publication date: 1-Feb-2011. Vol. 115, No. 3 March 2007Metrics About Article Metrics Publication History Originally published1 March 2007Published in print1 March 2007 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.

Effects of Monobutyl and Di( n -butyl) Phthalate in Vitro on Steroidogenesis and Leydig Cell Aggregation in Fetal Testis Explants from the Rat: Comparison with Effects in Vivo in the Fetal Rat and Neonatal Marmoset and in Vitro in the Human

BackgroundCertain phthalates can impair Leydig cell distribution and steroidogenesis in the fetal rat in utero, but it is unknown whether similar effects might occur in the human.ObjectivesOur aim in this study was to investigate the effects of di(n-butyl) phthalate (DBP), or its metabolite monobutyl phthalate (MBP), on testosterone production and Leydig cell aggregation (LCA) in fetal testis explants from the rat and human, and to compare the results with in vivo findings for DBP-exposed rats. We also wanted to determine if DBP/MBP affects testosterone production in vivo in the neonatal male marmoset.MethodsFetal testis explants obtained from the rat [gestation day (GD)19.5] and from the human (15–19 weeks of gestation) were cultured for 24–48 hr with or without human chorionic gonadotropin (hCG) or 22R-hydroxycholesterol (22R-OH), and with or without DBP/MBP. Pregnant rats and neonatal male marmosets were dosed with 500 mg/kg/day DBP or MBP.ResultsExposure of rats in utero to DBP (500 mg/kg/day) for 48 hr before GD21.5 induced major suppression of intratesticular testosterone levels and cytochrome P450 side chain cleavage enzyme (P450scc) expression; this short-term treatment induced LCA, but was less marked than longer term (GD13.5–20.5) DBP treatment. In vitro, MBP (10−3 M) did not affect basal or 22R-OH-stimulated testosterone production by fetal rat testis explants but slightly attenuated hCG-stimulated steroidogenesis; MBP induced minor LCA in vitro. None of these parameters were affected in human fetal testis explants cultured with 10−3 M MBP for up to 48 hr. Because the in vivo effects of DBP/MBP were not reproduced in vitro in the rat, the absence of MBP effects in vitro on fetal human testes is inconclusive. In newborn (Day 2–7) marmosets, administration of a single dose of 500 mg/kg MBP significantly (p = 0.019) suppressed blood testosterone levels 5 hr later. Similar treatment of newborn co-twin male marmosets for 14 days resulted in increased Leydig cell volume per testis (p = 0.011), compared with co-twin controls; this is consistent with MBP-induced inhibition of steroidogenesis followed by compensatory Leydig cell hyperplasia/hypertrophy.ConclusionsThese findings suggest that MBP/DBP suppresses steroidogenesis by fetal-type Leydig cells in primates as in rodents, but this cannot be studied in vitro.

Urinary and amniotic fluid levels of phthalate monoesters in rats after the oral administration of di(2-ethylhexyl) phthalate and di- n-butyl phthalate

Two studies were designed to examine amniotic fluid and maternal urine concentrations of the di(2-ethylhexyl) phthalate (DEHP) metabolite mono(2-ethylhexyl) phthalate (MEHP) and the di- n-butyl phthalate (DBP) metabolite monobutyl phthalate (MBP) after administration of DEHP and DBP during pregnancy. In the first study, pregnant Sprague–Dawley rats were administered 0, 11, 33, 100, or 300 mg DEHP/kg/day by oral gavage starting on gestational day (GD) 7. In the second study, DBP was administered by oral gavage to pregnant Sprague–Dawley rats at doses of 0, 100, or 250 mg/kg/day starting on GD 13. Maternal urine and amniotic fluid were collected and analyzed to determine the free and glucuronidated levels of MEHP and MBP. In urine, MEHP and MBP were mostly glucuronidated. By contrast, free MEHP and free MBP predominated in amniotic fluid. Statistically significant correlations were found between maternal DEHP dose and total maternal urinary MEHP ( p = 0.0117), and between maternal DEHP dose and total amniotic fluid MEHP levels ( p = 0.0021). Total maternal urinary MEHP and total amniotic fluid MEHP levels were correlated (Pearson correlation coefficient = 0.968). Statistically significant differences were found in amniotic MBP levels between animals within the same DBP dose treatment group ( p < 0.0001) and between animals in different dose treatment groups ( p < 0.0001). Amniotic fluid MBP levels increased with increasing DBP doses, and high variability in maternal urinary levels of MBP between rats was observed. Although no firm conclusions could be drawn from the urinary MBP data, the MEHP results suggest that maternal urinary MEHP levels may be useful surrogate markers for fetal exposure to DEHP.

Pharmacokinetics of monobutylphthalate, the active metabolite of di- n-butylphthalate, in pregnant rats

Di- n -butylphthalate (DBP) is a phthalic acid ester used as a plasticizer and solvent. DBP is a developmental toxicant in rats and mice, with adverse effects arising from the monoester metabolite monobutyl phthalate (MBP). The objective of this study was to evaluate the pharmacokinetics of MBP and monobutyl phthalate glucuronide (MBP-G) in pregnant rats following intravenous (i.v.) dosing with MBP. Pregnant dams were i.v. dosed with aqueous MBP (10, 30, or 50 mg MBP/kg body weight) on gestation day (GD) 19. The pharmacokinetics of MBP and MBP-G were rapid: MBP was metabolized to MBP-G within 5 min, and MBP and MBP-G disappeared from maternal and fetal plasma within 24 h of dosing. Results were consistent with two previous studies that utilized oral doses of DBP, suggesting that chemical (DBP versus MBP), vehicle (oil versus aqueous), dose level, and route (oral versus i.v.) have minimal effects on the maternal pharmacokinetics of MBP and MBP-G. This study provides direct pharmacokinetic analysis for MBP and MBP-G in pregnant rats during fetal male reproductive development, and indicates that future pharmacokinetic or toxicology studies can reliably utilize oral dosing with DBP.