Disposition of orally administered di-(2-ethylhexyl) phthalate and mono-(2-ethylhexyl) phthalate in the rat

Exposure to Di-(2-Ethylhexyl) phthalate drives ovarian dysfunction by inducing granulosa cell pyroptosis via the SLC39A5/NF-κB/NLRP3 axis

Endocrine-disrupting chemicals (EDCs) have been reported to affect populations by disrupting the human endocrine system. Di-(2-ethylhexyl) phthalate (DEHP) is an EDC that is present in various consumer products. Exposure to DEHP could contribute to reproductive system dysfunction, with subsequent adverse female reproductive outcomes. Granulosa cells (GCs) play essential roles in ovarian function and fertility. To further reveal the underlying mechanism by which DEHP impairs female fertility and affects the normal function of GCs, in vivo and in vitro experiments were performed. Transcript sequencing was used to identify genes that were differentially expressed in GCs after DEHP treatment. SLC39A5 was shown to be overexpressed in the DEHP group compared to the normal control group. DEHP treatment and overexpression of SLC39A5 activated NF-κB-related factors, followed by an increase in the transcript expression level of NLRP3. NLRP3 inflammasomes play crucial roles in pyroptosis by acting as sensors. Pyroptosis is a type of inflammation-related cell death associated with various diseases, including ovarian cancer and polycystic ovary syndrome. Activation of NF-κB contributed to the upregulation of pyroptosis in GCs, while pyroptosis factors were downregulated after the inhibition of NF-κB with JSH-23. The same phenomenon was also observed in a mouse model in which DEHP-treated mice had higher expression levels of NF-κB and pyroptosis markers in GCs. Moreover, this phenomenon could be partially reversed by the NF-κB inhibitor JSH-23. DEHP treatment also disrupted the normal expression of ovarian function-related genes and inhibited the proliferation of GCs. Reproductive system impairment was observed in mice exposed to DEHP. DEHP-treated mice had a lower body weight, smaller reproductive organs, fewer healthy follicles, and diminished ovarian reserve. Thus, DEHP contributes to ovarian dysfunction by inducing pyroptosis via the SLC39A5/NF-κB/NLRP3 axis in GCs.

Toxicokinetics of mono-(2-ethylhexyl) phthalate with low-dose exposure applying fluorescence tracing technique

Di(2-ethylhexyl) phthalate (DEHP) belongs to environmental endocrine disrupting chemicals (EEDCs) and can be rapidly hydrolyzed into the ultimate toxicant mono-2-ethylhexyl phthalate (MEHP). In this study, we used 5-aminofluorescein modified MEHP (MEHP-AF) as a fluorescence tracer to explore the toxicokinetics, including toxicokinetic parameters, absorption and transport across the intestinal mucosal barrier, distribution and pathological changes of organs. While the dose was as lower than 10 mg/kg by intragastric administration, the toxicokinetic parameters obtained by fluorescence microplate method were similar to those with the literatures by chromatography. MEHP-AF can be rapidly absorbed through the intestinal mucosal barrier in rats. In situ organ distribution in mice showed that MEHP-AF was mainly concentrated in the liver, kidney and testis. Our results suggested that the fluorescence tracing technique had the advantages with easy processing, less time-consuming, higher sensitivity for the quantitative determination, In addition, this technology also avoids the interference of exogenous or endogenous DEHP and MEHP in the experimental system. It also can be utilized to the visualization detection of MEHP in situ localization in the absorption organ and the toxic target organ. The results show that this may be a more feasible MEHP toxicological research method.

Phthalate metabolites: Characterization, toxicities, global distribution, and exposure assessment

Phthalates are plasticizers in various products and regarded as endocrine disruptors due to their anti-androgen effects. Environmental occurrence and toxicities of parent phthalates have been widely reported, while the current state of knowledge on their metabolites is rarely summarized. Based on the available literature, the present review mainly aims to 1) characterize the potential metabolites of phthalates (mPAEs) using the pharmacokinetics evidences acquired via animal or human models; 2) examine the molecular and cellular mechanism involved in toxicity for mPAEs; 3) investigate the exposure levels of mPAEs in different human specimens (e.g., urine, blood, seminal fluid, breast milk, amniotic fluid and others) across the globe; 4) discuss the models and related parameters for phthalate exposure assessment. We suggest there is subtle difference in toxic mechanisms for mPAEs compared to their parent phthalates due to their alternative chemical structures. Human monitoring studies performed in Asia, America and Europe have provided the population exposure baseline levels for typical phthalates in different regions. Urine is the preferred matrix than other specimens for phthalate exposure study. Among ten urinary mPAEs, the largest proportions of di-(2-ethylhexyl) phthalate (DEHP) metabolites (40%), monoethyl phthalate (mEP) (43%) and DEHP metabolites/mEP (both 29%) were observed in Asia, America and Europe respectively, and mono-5-carboxy-2-ethypentyl phthalate was the most abundant compounds among DEHP metabolites. Daily intakes of phthalates can be accurately calculated via urinary mPAEs if the proper exposure parameters were determined. Further work should focus on combining epidemiological and biological evidences to establish links between phthalates exposure and biological phenotypes. More accurate molar fractions (F_UE) of the urinary excreted monoester related to the ingested diesters should be collected in epidemiological or pharmacokinetic studies for different population.

Toxicology and carcinogenesis studies of di(2-ethylhexyl) phthalate administered in feed to Sprague Dawley (Hsd:Sprague Dawley SD) rats

Di(2-ethylhexyl) phthalate (DEHP) is a member of the phthalate ester chemical class that occurs commonly in the environment and to which humans are widely exposed. Lifetime exposure to DEHP is likely to occur, including during the in utero and early postnatal windows of development. To date, no carcinogenicity assessments of DEHP have used a lifetime exposure paradigm that includes the perinatal period (gestation and lactation). The National Toxicology Program (NTP) tested the hypothesis that exposure during the perinatal period would alter the DEHP carcinogenic response quantitatively (more neoplasms) or qualitatively (different neoplasm types). Two chronic carcinogenicity assessments of DEHP were conducted in which Sprague Dawley (Hsd:Sprague Dawley SD) rats were exposed to dosed feed containing 0, 300, 1,000, 3,000, or 10,000 ppm DEHP for 2 years using different exposure paradigms. In Study 1, groups of 45 F0 time-mated females were provided dosed feed beginning on gestation day (GD) 6 through lactation. On postnatal day (PND) 21, groups of 50 F1 rats per sex continued on the study and were provided dosed feed containing the same DEHP concentration as their respective dam for 2 years. In Study 2, groups of 50 rats per sex, aged 6 to 7 weeks at study start, were provided dosed feed containing DEHP for 2 years. (Abstract Abridged).

Effects of pubertal exposure to low doses of di-(2-ethylexyl)phthalate on reproductive behaviors in male mice

Reproductive behaviors are tightly regulated by sex steroid hormones. Interference with these hormones or their neural signaling pathways leads to behavioral alterations. We have previously shown that oral exposure of adult male mice to di(2-ethylhexyl) phthalate (DEHP), an organic environmental endocrine disruptor, altered sexual behavior. In this study, we examined the effects of pubertal exposure to DEHP and analyzed whether pubertal and adult exposures to DEHP trigger long-term effects. For pubertal exposure, male mice were exposed orally to the vehicle or DEHP at 5 or 50 μg/kg/d from postnatal day (PND) 30 to PND60. Exposure was arrested and animals were analyzed on PND120. They exhibited normal olfactory preference but showed modified emission of ultrasonic vocalizations. DEHP exposure also affected partner preference and mating components. These modifications were associated with normal circulating testosterone levels and weight of androgen-sensitive tissues. In contrast, androgen receptor (AR) protein amount was reduced in the hypothalamic preoptic area in particular for the DEHP-50 group. Pubertal exposure also increased the anxiety-state level without changing circadian activity. When adult male mice were exposed to DEHP at the same doses from PND60 to PND105 and analyzed two months later, no effects of treatment on reproductive and anxiety-related behaviors or hypothalamic AR protein amount were seen. Our data show that pubertal exposure of male mice to DEHP induces long-term behavioral changes in contrast to the adult exposure. This highlights the sensitivity of the nervous system to low doses of DEHP during the critical period of puberty.

Determination of Selected Phthalates in Some Commercial Cosmetic Products by HPLC-UV

Aim and scope:

Due to the serious toxicological risks and their widespread use, quantitative determination of phthalates in cosmetic products have importance for public health. The aim of this study was to develop a validated simple, rapid and reliable high-performance liquid chromatography (HPLC) method for the determination of phthalates which are; dimethyl phthalate (DMP), diethyl phthalate (DEP), benzyl butyl phthalate (BBP), di-n-butyl phthalate (DBP), di(2- ethylhexyl) phthalate (DEHP), in cosmetic products and to investigate these phthalate (PHT) levels in 48 cosmetic products marketing in Sivas, Turkey.

Materials and Methods:

Separation was achieved by a reverse-phase ACE-5 C18 column (4.6 x 250 mm, 5.0 μm). As the mobile phase, 5 mM KH2PO4 and acetonitrile were used gradiently at 1.5 ml min-1. All PHT esters were detected at 230 nm and the run time was taking 21 minutes.

Results:

This method showed the high sensitivity value the limit of quantification (LOQ) values for which are below 0.64 μg mL-1 of all phthalates. Method linearity was ≥0.999 (r2). Accuracy and precision values of all phthalates were calculated between (-6.5) and 6.6 (RE%) and ≤6.2 (RSD%), respectively. Average recovery was between 94.8% and 99.6%. Forty-eight samples used for both babies and adults were successfully analyzed by the developed method. Results have shown that, DMP (340.7 μg mL-1 ±323.7), DEP (1852.1 μg mL-1 ± 2192.0), and DBP (691.3 μg mL-1 ± 1378.5) were used highly in nail polish, fragrance and cream products, respectively.

Conclusion:

Phthalate esters, which are mostly detected in the content of fragrance, cream and nail polish products and our research in general, are DEP (1852.1 μg mL-1 ± 2192.0), DBP (691.3 μg mL-1 ± 1378.5) and DMP (340.7 μg mL-1 ±323.7), respectively. Phthalates were found in the content of all 48 cosmetic products examined, and the most detected phthalates in general average were DEP (581.7 μg mL-1 + 1405.2) with a rate of 79.2%. The unexpectedly high phthalate content in the examined cosmetic products revealed a great risk of these products on human health. The developed method is a simple, sensitive, reliable and economical alternative for the determination of phthalates in the content of cosmetic products, it can be used to identify phthalate esters in different products after some modifications.

Physiologically Based Pharmacokinetic Models Predicting Renal and Hepatic Concentrations of Industrial Chemicals after Virtual Oral Doses in Rats

Recently developed high-throughput in vitro assays in combination with computational models could provide alternatives to animal testing. The purpose of the present study was to model the plasma, hepatic, and renal pharmacokinetics of approximately 150 structurally varied types of drugs, food components, and industrial chemicals after virtual external oral dosing in rats and to determine the relationship between the simulated internal concentrations in tissue/plasma and their lowest-observed-effect levels. The model parameters were based on rat plasma data from the literature and empirically determined pharmacokinetics measured after oral administrations to rats carried out to evaluate hepatotoxic or nephrotic potentials. To ensure that the analyzed substances exhibited a broad diversity of chemical structures, their structure-based location in the chemical space underwent projection onto a two-dimensional plane, as reported previously, using generative topographic mapping. A high-throughput in silico one-compartment model and a physiologically based pharmacokinetic (PBPK) model consisting of chemical receptor (gut), metabolizing (liver), central (main), and excreting (kidney) compartments were developed in parallel. For 159 disparate chemicals, the maximum plasma concentrations and the areas under the concentration-time curves obtained by one-compartment models and modified simple PBPK models were closely correlated. However, there were differences between the PBPK modeled and empirically obtained hepatic/renal concentrations and plasma maximal concentrations/areas under the concentration-time curves of the 159 chemicals. For a few compounds, the lowest-observed-effect levels were available for hepatotoxicity and nephrotoxicity in the Hazard Evaluation Support System Integrated Platform in Japan. The areas under the renal or hepatic concentration-time curves estimated using PBPK modeling were inversely associated with these lowest-observed-effect levels. Using PBPK forward dosimetry could provide the plasma/tissue concentrations of drugs and chemicals after oral dosing, thereby facilitating estimates of nephrotoxic or hepatotoxic potential as a part of the risk assessment.

Plasma and Hepatic Concentrations of Chemicals after Virtual Oral Administrations Extrapolated Using Rat Plasma Data and Simple Physiologically Based Pharmacokinetic Models

Only a small fraction of chemicals possesses adequate in vivo toxicokinetic data for assessing potential hazards. The aim of the present study was to model the plasma and hepatic pharmacokinetics of more than 50 disparate types of chemicals and drugs after virtual oral administrations in rats. The models were based on reported pharmacokinetics determined after oral administration to rats. An inverse relationship was observed between no-observed-effect levels after oral administration and chemical absorbance rates evaluated for cell permeability ( r = -0.98, p < 0.001, n = 17). For a varied selection of more than 30 chemicals, the plasma concentration curves and the maximum concentrations obtained using a simple one-compartment model (recently recommended as a high-throughput toxicokinetic model) and a simple physiologically based pharmacokinetic (PBPK) model (consisting of chemical receptor, metabolizing, and central compartments) were highly consistent. The hepatic and plasma concentrations and the hepatic and plasma areas under the concentration-time curves of more than 50 chemicals were roughly correlated; however, differences were evident between the PBPK-modeled values in livers and empirically obtained values in plasma. Of the compounds selected for analysis, only seven had the lowest observed effect level (LOEL) values for hepatoxicity listed in the Hazard Evaluation Support System Integrated Platform in Japan. For these seven compounds, the LOEL values and the areas under the hepatic concentration-time curves estimated using PBPK modeling were inversely correlated ( r = -0.78, p < 0.05, n = 7). This study provides important information to help simulate the high hepatic levels of potent hepatotoxic compounds. Using suitable PBPK parameters, the present models could estimate the plasma/hepatic concentrations of chemicals and drugs after oral doses using both PBPK forward and reverse dosimetry, thereby indicating the potential value of this modeling approach in predicting hepatic toxicity as a part of risk assessments of chemicals absorbed in the human body.

Mono-(2-ethylhexyl) phthalate induces apoptosis through miR-16 in human first trimester placental cell line HTR-8/SVneo

Phthalates have been linked to adverse pregnancy complications. Mono-(2-ethylhexyl) phthalate, an active metabolite of di-(2-ethylhexyl) phthalate and an endocrine disruptor, has been shown to induce apoptosis in various cell types including placental cells. However, the mechanism of action of MEHP induced apoptosis is still unknown. We hypothesized that apoptosis may be mediated in part through altered microRNA(s) in placenta under MEHP exposure. In the present study, we report that MEHP increases miR-16 expression in a time- and dose-dependent manner (p<0.05), while inducing apoptosis in HTR-8/SVneo. Cells treated with MEHP showed a dose-dependent increase in cytotoxicity and reactive oxygen species along with decreased cell viability. Consistent with significant increase in apoptosis analyzed by flow cytometry, we detected decreased anti-apoptotic BCL-2 at transcriptional and translational levels with MEHP (p<0.05). Knockdown of miR-16 did not decrease the BCL-2/BAX protein expression ratio in the presence of MEHP when compared to negative control demonstrating that MEHP induces apoptosis directly through miR-16. In conclusion, our study demonstrates for the first time that MEHP induces miR-16, which in turn, alters BCL-2/BAX ratio leading to increased apoptosis. This study provides a novel insight into MEHP induced epigenetic regulation in placental apoptosis which may lead to pregnancy complications.

Determination and pharmacokinetics of di-(2-ethylhexyl) phthalate in rats by ultra performance liquid chromatography with tandem mass spectrometry

Di-(2-ethylhexyl) phthalate (DEHP) is used to increase the flexibility of plastics for industrial products. However, the illegal use of the plasticizer DEHP in food and drinks has been reported in Taiwan in 2011. In order to assess the exact extent of the absorption of DEHP via the oral route, the aim of this study is to develop a reliable and validated ultra performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) method to evaluate the oral bioavailability of DEHP in rats. The optimal chromatographic separation of DEHP and butyl benzyl phthalate (BBP; used as internal standard) were achieved on a C₁₈ column. The mobile phase was consisted of 5 mM ammonium acetate-methanol (11:89, v/v) with a flow rate of 0.25 mL/min. The monitoring ion transitions were m/z 391.4 → 149.0 for DEHP and m/z 313.3 → 149.0 for BBP. The mean matrix effects of DEHP at low, medium and high concentrations were 94.5 ± 5.7% and 100.1 ± 2.3% in plasma and feces homogenate samples, respectively. In conclusion, the validated UPLC-MS/MS method is suitable for analyzing the rat plasma sample of DEHP and the oral bioavailability of DEHP was about 7% in rats.

Disappearance of vimentin in Sertoli cells: a mono(2-ethylhexyl) phthalate effect

The effects of mono(2-ethylhexyl) phthalate (MEHP) on 21-day-old C57Bl/6N mice and their Sertoli cell cultures were studied. Mice were given a single dose of 800 mg/kg MEHP by oral gavage and sacrificed 24 h later. At the same time, testes were harvested from another batch of mice for Sertoli cell cultures. Cultures were subsequently exposed to 0, 1, and 100 nmol/ml MEHP for 0, 3, 6, 12, and 24 h. An antivimentin antibody was used to detect intermediate filament changes in Sertoli cells. Meanwhile, detection of preapoptotic signals and presence of apoptotic cells were done using annexin V-FITC (fluorescein isothiocyanate) and TUNEL (deoxynucleotidyltransferase-mediated dUTP nick end labeling) analyses, respectively. In vivo results showed a correlation between the increase in TUNEL-positive cells and the vimentin disruption in treated mice. Toluidine blue staining of the Sertoli cell cultures showed the increased number and size of vacuoles in Sertoli cell cytoplasm. Vimentin immunohistochemistry showed gradual disappearance of vimentin in Sertoli cell cultures as time and dose increased. Some Sertoli cells were found to be annexin V-FITC positive, but no TUNEL-positive cells were found. Taken together, these results show that the appearance of vacuoles and the vimentin disappearance caused by MEHP in the Sertoli cells are related with each other and can be observed in relation to time. This can be used as an indicator of the loss of mechanical support for spermatogenic cells, which in the end causes apoptosis of spermatogenic cells.

An ultrastructural study on the effects of mono(2-ethylhexyl) phthalate on mice testes: cell death and sloughing of spermatogenic cells

Mono(2-ethylhexyl) phthalate (MEHP) is a well-characterized testicular toxicant. In this study, morphological alterations of mice testes caused by repeated administrations of MEHP were examined by light and transmission electron microscopy. Prepubertal male mice were given a range of MEHP doses (600-900 mg/kg/day) for 3 consecutive days in corn oil by oral gavage. Control animals were given only corn oil. Thereafter, the testes were excised, fixed in 4% paraformaldehyde for light microscopy and/or 5% glutaraldehyde for transmission electron microscopy. Then, they were embedded, and sectioned. TUNEL analysis was done to quantify the occurrence of apoptosis in the testis. Cellular damages were also observed. Results showed that administration of 700 mg/kg of MEHP caused a significant increase in TUNEL-positive cells. At the same time, mice treated with higher doses of MEHP showed presence of degenerating (apoptotic and necrotic) spermatogenic cells. Appearance of small vacuoles in the Sertoli cell cytoplasm and displacement of spermatogenic cells were also observed. Sloughed and shed spermatogenic cells found in the tubular lumen were identified to be necrotic and apoptotic in appearance, respectively.

Testicular toxicity of DEHP, but not DEHA, is elevated under conditions of thioacetamide-induced liver damage

As part of an investigation of possible enhancement by liver disease of testicular toxicity caused by phthalates, we tested the effects of di(2-ethylhexyl)phthalate (DEHP) and di(2-ethylhexyl)adipate (DEHA) in a thioacetamide (TAA)-induced rat liver damage model. Male, 6-week-old, F344 rats (n=60) were divided into ten groups. Animals of groups 1-5 received TAA (200 mg/kg, intraperitoneal, three times per week) for 4 weeks, and groups 6-10 served as controls without TAA. After a 1 week interval, at week 5, powder diet containing DEHP or DEHA was provided to the animals of groups 1 and 6 (DEHP 25000 ppm), groups 2 and 7 (DEHP 6000 ppm), groups 3 and 8 (DEHA 25000 ppm) and groups 4 and 9 (DEHA 6000 ppm), while groups 5 and 10 received basal diet. All animals were sacrificed at week 9. Significant decrease in sperm numbers and motility and increase in morphology abnormalities were evident in group 1 as compared to groups 5 and 6 (p<0.01). However, DEHA treatment was not associated with any apparent testicular toxicity in either TAA- or vehicle-treated animals. Histopathological examination of the testes revealed severe atrophy and degeneration of testicular tubules in all animals given TAA and DEHP at high dose, only mild to moderate lesions being found with DEHP alone. We conclude that liver toxicity induced by TAA is associated with the enhancement of testicular toxicity of DEHP, but not DEHA, in rats.

Determination of di(2-ethylhexyl)phthalate and mono(2-ethylhexyl)phthalate in human serum using liquid chromatography-tandem mass spectrometry

Concentrations of mono(2-ethylhexyl)phthalate (MEHP), and di(2-ethylhexyl)phthalate (DEHP), in serum of healthy volunteers were determined by high performance liquid chromatography (HPLC) with tandem mass spectrometry (LC/MS/MS). The serum was extracted with acetone, followed by hexane extraction under acidic conditions, and then applied to the LC/MS/MS. Recoveries of 20 ng/ml of MEHP and DEHP were 101+/-5.7 (n=6) and 102+/-6.5% (n=6), respectively. The limits of quantification (LOQ) of MEHP and DEHP in the method were 5.0 and 14.0 ng/ml, respectively. The concentration of MEHP in the serum was at or less than the LOQ. The concentration of DEHP in the serum was less than the LOQ. Contaminations of MEHP and DEHP from experimental reagents, apparatus and air during the procedure were less than the LOQ and were estimated to be <1.0 and 2.2+/-0.6 ng/ml, respectively. After subtraction of the contamination, the net concentrations of MEHP and DEHP in the serum were estimated at or <5 and <2 ng/ml, respectively. To decrease contamination by DEHP, the cleanup steps and the apparatus and solvent usage were minimized in the sample preparation procedures. The high selectivity of LC/MS/MS is the key for obtaining reliable experimental data from in the matrix-rich analytical samples and for maintaining a low level contamination of MEHP and DEHP in this experimental system. This method would be a useful tool for the detection of MEHP and DEHP in serum.

Blood burden of di(2-ethylhexyl) phthalate and its primary metabolite mono(2-ethylhexyl) phthalate in pregnant and nonpregnant rats and marmosets

A comparison of the dose-dependent blood burden of di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP) in pregnant and nonpregnant rats and marmosets is presented. Sprague-Dawley rats and marmosets were treated orally with 30 or 500 mg DEHP/kg per day, nonpregnant animals on 7 (rats) and 29 (marmosets) consecutive days, pregnant animals on gestation days 14-19 (rats) and 96-124 (marmosets). In addition, rats received a single dose of 1000 mg DEHP/kg. Blood was collected up to 48 h after dosing. Concentrations of DEHP and MEHP in blood were determined by GC/MS. In rats, normalized areas under the concentration-time curves (AUCs) of DEHP were two orders of magnitude smaller than the normalized AUCs of the first metabolite MEHP. Metabolism of MEHP was saturable. Repeated DEHP treatment and pregnancy had only little influence on the normalized AUC of MEHP. In marmosets, most of MEHP concentration-time courses oscillated. Normalized AUCs of DEHP were at least one order of magnitude smaller than those of MEHP. In pregnant marmosets, normalized AUCs of MEHP were similar to those in nonpregnant animals with the exception that at 500 mg DEHP/kg per day, the normalized AUCs determined on gestation days 103, 117, and 124 were distinctly smaller. The maximum concentrations of MEHP in blood of marmosets were up to 7.5 times and the normalized AUCs up to 16 times lower than in rats receiving the same daily oral DEHP dose per kilogram of body weight. From this toxicokinetic comparison, DEHP can be expected to be several times less effective in the offspring of marmosets than in that of rats if the blood burden by MEHP in dams can be regarded as a dose surrogate for the MEHP burden in their fetuses.

Hepatocarcinogenic potential of di(2-ethylhexyl)phthalate in rodents and its implications on human risk

The plasticizer di(2-ethylhexyl) phthalate (DEHP), to which humans are extensively exposed, was found to be hepatocarcinogenic in rats and mice. DEHP is potentially set free from objects made of synthetic materials (e.g., those used in medicine). Chronically, the greatest amounts are transferred to persons undergoing hemodialysis (up to 3.1 mg/kg b.w. per day) who would thus be considered the individuals most endangered by tumorigenesis. Although toxicokinetics seem to play a certain unclear role in the course of DEHP-related toxicity, toxicodynamic factors appear more decisive. DEHP is a representative of "peroxisome proliferators" (PP), a distinct group of substances that, in rodents, do not only induce peroxisomes but also specific enzymes in other organelles, organ growth, and DNA synthesis. The cluster of the characteristic effects of PP is generally, although perhaps not quite appropriately summarized as "peroxisome proliferation," and is strongest in the liver. The lowest observed effect level (LOEL) and the no observed effect level (NOEL) of peroxisome proliferation in the rat, as determined by the induction of specific enzymes (peroxisomal beta-oxidation, carnitine-acetyl-transferase, cytochrome P-452), DNA synthesis, and hepatomegaly, may be assumed as 50 and 25 mg/kg b.w. per day, respectively. DEHP and other carcinogenic PP are neither genotoxic nor tumor initiators, but they appear to be tumor promoters, also implicating a threshold level for the carcinogenic effect. Although a causal relationship between a particular effect of peroxisome proliferation and hepatocarcinogenesis is as yet unknown, peroxisome proliferation as a whole phenomenon appears to be associated with the potential of tumor induction, as shown by comparison of the relative strength of individual PP and by comparison of species and organ specificities. Likewise, LOEL and NOEL of rodent carcinogenesis, that is, 300 and 50 to 100 mg/kg b.w. per day, respectively, are above but not too far from the corresponding values for the investigated parameters of peroxisome proliferation. Thus, with respect to dose alone, worst-case exposure in hemodialysis patients is at least 16-fold below the LOEL of any characterized PP-specific effect of DEHP and approximately 100-fold below that of DEHP-related tumorigenesis. Also, primates are less responsive to PP than rats with respect to the investigated biochemical and morphological parameters. If this lower primate responsiveness is extrapolated to estimate carcinogenicity in humans, we might thus arrive at an even larger safety margin than when based on exposure alone. Doses of PP hypolipidemics that had clearly induced several indicators of peroxisome proliferation in rats did not cause any clear-cut enhancements in the peroxisomes of patients, even though most of these hypolipidemics were considerably stronger PP than DEHP. Thus, an actual threat to humans by DEHP seems rather unlikely. Accordingly, hepatocarcinogenesis was neither enhanced in workers exposed to DEHP nor in patients treated with hypolipidemics.

Studies on Se incorporation in selenoproteins; effects of peroxisome proliferators and hydrogen peroxide generating system

The objective of this study was to characterize the influence of peroxisome proliferation on the metabolism of physiological concentrations of Se. In an initial series of experiments hepatocytes in primary cultures and isolated from ordinary-fed rats, were used. The cells were exposed to 75Se-selenite (30 nM) and after 24 h the labelling of selenoproteins was analysed with SDS-PAGE. Treatments with mono(2-ethylhexyl)phthalate (MEHP; a metabolite of di(2-ethylhexyl)phthalate (DEHP)), nafenopin, decreased oxygen tension and a H2O2 generating system decreased the labelling of a 23-kDa and a 15-kDa protein. The decreased labelling of the 23- and the 15-kDa proteins was usually accompanied by an increased labelling of a 58-kDa protein. Increased oxygen tension induced uncertain effects, possibly due to toxicity. In order to further evaluate the validity of the model, the labelling was also studied in hepatocytes isolated from Se-deficient and torula yeast-fed rats. In these cells there was a decreased labelling of the 23-kDa protein as compared to cells from Se-supplemented controls when 100 nM selenite was used. In in vivo experiments it was found that a DEHP-induced decrease in glutathione peroxidase (GSH-Px) activity was potentiated by high doses of selenite. To a large extent, the labelling data are compatible with enzyme activity data and in vivo data. For example, the decreased labelling of the 23-kDa protein may reflect the decreased GSH-Px activity. It is concluded that the effects induced by MEHP on Se-labelling can be explained by an increase in the steady state level of H2O2.

Effects of co-administration of di(2-ethylhexyl)phthalate and testosterone on several parameters in the testis and pharmacokinetics of its mono-de-esterified metabolite

The administration of 1 g/kg di(2-ethylhexyl)phthalate (DEHP) or 5 mg/kg testosterone for 1 week did not affect the testicular and prostatic gland weights in rats. However, co-administration of DEHP and testosterone induced severe testicular atrophy accompanied by a decrease of zinc concentration in the testis and reduction of the activity of testicular specific lactate dehydrogenase isozyme. These changes were similar to the results of high dose administration of DEHP alone. Values of biological half-life and area under the concentration-time curve (AUC) of mono(2-ethylhexyl)phthalate, the main metabolite of DEHP, in testes after a single co-administration of DEHP (p.o.) and testosterone (i.p.) were higher than those after DEHP administration alone. Results suggest that the co-administration of DEHP and testosterone enhanced the adverse effects of DEHP on testes as the result of changes in pharmacokinetic values of MEHP.

Testicular toxicity induced by single dosing of di- and mono-(2-ethylhexyl) phthalate in the rat

The testicular toxicity of di-(2-ethylhexyl) phthalate (DEHP), a widely used plasticizer, and of its major metabolite, mono-(2-ethylhexyl) phthalate (MEHP), was assessed after a single dose in rats. Treatment with a single dose of 2.8 g/kg DEHP or 0.8 g/kg MEHP was sufficient to induce testicular atrophy as observed 7 days after dosing. Such a treatment had no effect on plasma FSH levels, and had varying effects on testicular zinc concentrations. After a single dose of 0.8 g/kg MEHP the testicular toxicity was age-dependent, in that only prepubertal rats were susceptible.

Transfer of di(2-ethylhexyl) phthalate through rat milk and effects on milk composition and the mammary gland

Five daily oral doses of di(2-ethylhexyl) phthalate (DEHP) (2 g/kg) given to rats on Days 2-6, 6-10, or 14-18 of lactation caused significant decreases in body weight and increases in hepatic peroxisomal enzymes palmitoyl CoA oxidase and carnitine acetyltransferase in the dams and their suckling pups. Plasma cholesterol and triglyceride levels were decreased in the lactating dams. Decreased food consumption, as indicated by pair-fed rats, accounted for the decreased body weight in the pups but not the increases in enzyme activities. To determine whether DEHP and mono(2-ethylhexyl) phthalate (MEHP) were transferred through the milk, milk and plasma were collected from lactating rats 6 hr after the third dose of DEHP. The milk contained 216 +/- 23 micrograms/ml DEHP and 25 +/- 6 micrograms/ml MEHP (mean +/- SE), while the plasma contained less than 0.5 micrograms/ml DEHP and 75 +/- 12 micrograms/ml MEHP. The high milk/plasma ratio for DEHP (greater than 200) indicates efficient extraction of DEHP from the plasma into the milk. DEHP dosing during lactation also caused a decrease in mammary gland weight and a decrease in mammary gland RNA content which reflects synthetic activity. The water content of the milk was reduced, which probably accounted for the increase in lipid in the milk. Milk lactose was decreased in DEHP-treated and pair-fed rats, consistent with the decrease in milk production. The results show that exposure to high doses of DEHP during lactation in rats can result in changes in milk quality and quantity and can lead to DEHP and MEHP exposure in the suckling rat pups.