Proteomic analysis of proteins secreted by HepG2 cells treated with butyl benzyl phthalate

Proteomic changes in proteins secreted by human hepatocellular carcinomas (HepG2) cells exposed to butyl benzyl phthalate (BBP) were evaluated. HepG2 cells were treated with three different concentrations of BBP (0, 10, or 25 μM) for 24 or 48 h. Following incubation, the cells were subjected to proteomic analysis using two different pI ranges (4-7 and 6-9) and large-size two-dimensional gel electrophoresis. Results showed resolution of a total of 2776 protein spots. Of these, 29, including 19 upregulated and 10 downregulated proteins, were identified by electrospray ionization-mass spectrometry-mass spectrometry (ESI-MS/MS). Among these, the identities of cystatin C, Rho guanine nucleotide dissociation inhibitor, gelsolin, DEK protein, Raf kinase inhibitory protein, triose phosphate isomerase, heptaglobin-related protein, inter-alpha-trypsin inhibitor heavy chain H2, and electron transfer flavoprotein subunit beta were confirmed by Western blot analysis. These proteins were found to be involved in apoptosis, signaling, tumor progression, energy metabolism, and cell structure and motility. Therefore, these proteins have potential to be employed as biomarkers of BBP exposure and may be useful in understanding mechanisms underlying the adverse effects of BBP.

Human body burdens of chemicals used in plastic manufacture

In the last decades, the availability of sophisticated analytical chemistry techniques has facilitated measuring trace levels of multiple environmental chemicals in human biological matrices (i.e. biomonitoring) with a high degree of accuracy and precision. As biomonitoring data have become readily available, interest in their interpretation has increased. We present an overview on the use of biomonitoring in exposure and risk assessment using phthalates and bisphenol A as examples of chemicals used in the manufacture of plastic goods. We present and review the most relevant research on biomarkers of exposure for phthalates and bisphenol A, including novel and most comprehensive biomonitoring data from Germany and the United States. We discuss several factors relevant for interpreting and understanding biomonitoring data, including selection of both biomarkers of exposure and human matrices, and toxicokinetic information.

A marine sulfate-reducing bacterium producing multiple antibiotics: biological and chemical investigation

A marine sulfate-reducing bacterium SRB-22 was isolated by means of the agar shake dilution method and identified as Desulfovibrio desulfuricans by morphological, physiological and biochemical characteristics and 16S rDNA analysis. In the bioassay, its extract showed broad-spectrum antimicrobial activity using the paper disc agar diffusion method. This isolate showed a different antimicrobial profile than either ampicillin or nystatin and was found to produce at least eight antimicrobial components by bioautography. Suitable fermentation conditions for production of the active constituents were determined to be 28 day cultivation at 25 °C to 30 °C with a 10% inoculation ratio. Under these conditions, the SRB-22 was fermented, extracted and chemically investigated. So far an antimicrobial compound, mono-n-butyl phthalate, and an inactive compound, thymine, have been isolated and characterized.

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.

Skin Penetration And Lag Times Of Neat And Aqueous Diethyl Phthalate, 1,2-Dichloroethane And Naphthalene

Cutaneous exposures to occupational chemicals may cause toxic effects. For any chemical, the potential for systemic toxicity from dermal exposure depends on its ability to penetrate the skin. Most laboratory studies measure chemical penetration from an aqueous solution through isolated human or laboratory animal skin, although most exposures are not from pure aqueous solutions. The US EPA Interagency Testing Committee (ITC) mandated by the Toxic Substances Control Act, has required industry to measure the in vitro penetration of 34 chemicals in their pure or neat form (if liquid). The goal of the present study was to measure skin permeability and lag time for three neat chemicals of industrial importance, representing the general types of chemicals to be studied by the ITC (non-volatile liquids, volatile liquids, and solids), and to examine interlaboratory variation from these studies. Steady state fluxes and lag times of diethyl phthalate (DEP, slightly volatile), 1,2-dichloroethane (DCE, highly volatile), and naphthalene (NAP, solid) were studied in two different laboratories using different analytical methods. One lab also measured fluxes and lag times from saturated aqueous vehicle. Static diffusion cells, dermatomed hairless guinea pig skin, and gas chromatography were used to measure skin penetration. In the two laboratories, the steady state fluxes (mean+/-SD; microg cm(-2)hour(-1)) of DEP applied neat were: 11.8+/-4.1 and 23.9+/-7.0; fluxes of DCE (neat) were 6280+/-1380 and 3842+/-712; fluxes of NAP from powder were 30.4+/-2.0 and 7.5+/-4.7. Compared with neat fluxes measured in the same laboratory, flux from saturated aqueous solution was higher with DEP (1.9 x) but lower with DCE (0.17 x) and NAP (0.45 x). The three chemicals studied including a dry powder, demonstrate the potential for significant dermal penetration.

Environmental phthalate exposure in relation to reproductive outcomes and other health endpoints in humans

After briefly discussing human exposure to phthalates--diesters of 1,2-benzenedicarboxylic acid (phthalic acid)--this article first presents recent findings from the Study for Future Families, a multi-center pregnancy study in which the human analogue of the phthalate syndrome was first identified. This is one of an increasing number of studies that have investigated human endpoints in relation to environmental exposure to these ubiquitous compounds. This literature, which includes a range of human health endpoints following prenatal, neonatal, childhood, and adult exposures, is then summarized. At least one significant association has been reported for urinary metabolites of di-n-butyl phthalate (DBP), butylbenzyl phthalate (BzBP), diethyl phthlate (DEP), and di-isononyl phthalate (DINP) and for three of the urinary metabolites of di(2-ethylhexyl) phthalate (DEHP). Many of the findings reported in humans--most of which have been in males--are consistent with the anti-androgenic action that has been demonstrated for several phthalates. Replication of the results described here and further mechanistic studies are needed to strengthen links between phthalates and adverse health outcomes.

The transient dermal exposure: theory and experimental examples using skin and silicone membranes

A diffusion model is presented to account for the disposition of chemicals applied to skin as transient exposures. Two conditions are considered that apply to the skin surface following the exposure period, which are applicable to chemicals exhibiting two extremes of chemical volatility. For one case, representing highly volatile compounds, the solution is generalized to apply to multiple transient exposures. For both cases, algebraic expressions are derived to calculate the total amount of chemical that penetrates the skin. The theory is applied to experimental measurements of the in vitro penetration of diethyl phthalate applied to hairless guinea pig (HGP) skin and silicone rubber membranes (SRMs) as transient exposures. The transient exposure theory ably models the experimental data, with coefficients of determination greater than 0.97 (HGP) and greater than 0.99 (SRM). The ability of parameters derived from concurrent infinite dose experiments to predict the time course of absorption from transient exposures is explored. Discrepancies were found between measured cumulative penetration of chemical from transient exposure experiments and penetration predicted from parameters derived from infinite dose experiments, particularly for HGP. Possible reasons are explored. The current model may provide a realistic framework for estimating absorption from occupational, environmental and pharmaceutical dermal exposures.

Metabolite profiles of di-n-butyl phthalate in humans and rats

Di-n-butyl phthalate (DBP) is widely used in consumer products. In humans and in rats, DBP is metabolized to mono-n-butyl phthalate (MBP). MBP may also further oxidize to other metabolites of DBP. We studied the metabolic profiles of DBP in rats and humans to evaluate the similarities between the two species and between different exposure scenarios. In rats administered DBP by oral gavage, we identified MBP and three urinary oxidative metabolites of DBP: mono-3-oxo-n-butyl phthalate, mono-3-hydroxy-n-butyl phthalate (MHBP), and mono-3-carboxypropyl phthalate (MCPP). MBP, MHBP, and MCPP were also present in serum, albeit at lower levels than in urine. Statistically significant correlations (p < 0.01) existed between the concentrations of MBP and the concentrations of MHBP (Pearson correlation coefficient r = 0.82 [urine] and r = 0.96 [serum]) and MCPP (r = 0.77 [urine] and r = 0.97 [serum]). However, the concentrations of these metabolites in urine collected 6 h after dosing and in serum 24 h after dosing were not correlated, suggesting continuous metabolism of DBP and/or individual differences among rats. Serum DBP metabolite concentrations increased with the dose, whereas urinary concentrations did not. We also identified MBP, MHBP, and MCPP in the urine of four men exposed to DBP bytaking a prescription medication containing DBP, and MBP and MCPP in 94 adults with no documented exposure to DBP. In the human samples, we observed statistically significant correlations (p < 0.01) among the urinary concentrations of MBP and MCPP, although the correlation was stronger for the four exposed men (r = 0.99) than for the adults without a documented exposure to DBP (r = 0.70). Our results suggest that regardless of species and exposure scenario, MBP, the major DBP metabolite, is an optimal biomarker of exposure to DBP. In addition to MBP, MCPP and MHBP may be adequate biomarkers of exposure to DBP in occupational settings orin potential high-exposure scenarios.

Toxicity study of maternal transfer of polychlorinated biphenyls and diethyl phthalate to 21-day-old male and female weanling pups of Wistar rats

Polychlorinated biphenyls (PCBs) are environmental pollutants known to act as xenoestrogens. PCBs and diethylphthalate (DEP) are ubiquitous environmental pollutants because both are used as plasticizers and in various other industrial applications. Therefore, a study was undertaken to evaluate the interactive toxicity of DEP and PCB in 21-day-old male and female pups of Wistar rats. Healthy young male and female albino rats of Wistar strain weighing 75-100g (6-7 weeks old) were randomly assigned to four groups of six each. Group I male and female rats were fed a normal diet and water ad libitum. Group II and III male and female rats were given PCB (Clophen A60) and DEP dissolved in corn oil mixed with the diet at 50 mg/kg of the diet (2.85 mg/kg body wt) individually to each group. Group IV male and female rats received a mixture of DEP and PCB (Clophen A60), each dissolved in corn oil mixed with the diet at 50 mg/kg of the diet (2.85 mg/kg body wt). Hundred days after the treatment, females were mated with males for 10 days. Exposure to DEP and PCB was continued throughout mating, gestation until termination at weaning, which was 150 days of total treatment period of adults. The pups from each group were then segregated on the basis of their sex. Six male and female pups each (approx. 21 days old) from each group were chosen randomly and were killed for toxicity study. Liver-to-body weight ratio showed significant increase in the male and female pups of PCB- and PCB+DEP-treated rats, whereas male pups of DEP alone treated rats showed significant increase and female pups showed significant decrease as compared to controls and other treated groups. Significant increase in liver and serum lactate dehydrogenase (LDH) and acid phosphatase (ACP) activity in the male and female pups of the three treated groups was observed. Alkaline phosphatase (ALP) activity was significantly increased only in the serum of male and female pups of the three treated groups, whereas significant decrease in the liver of male pups of the three treated groups. In the female pups, significant decrease in liver ALP was observed only PCB- and PCB+DEP-treated groups. Histology of liver showed severe vacuolation and steatosis in the hepatocytes of PCB-treated male and female pups and in PCB+DEP-treated group, vacuolation, and steatosis was much more predominant as compared to the PCB and DEP alone treated groups. DEP alone treated groups, both male and female pups showed mild vacuolations in the liver. A synergistic interactive toxic effect of PCB and DEP was evident in both male and female pups in the following study.

Toxicokinetics of phthalic acid: the common final metabolite of phthalic acid esters in rats

The toxicokinetic profiles of phthalic acid (PA), which is the common final metabolite of phthalic acid esters (PAE), were studied in rats after orally administering doses 20, 100, or 500 mg/kg. Concentrations of PA were determined in serum or urine by high-performance liquid chromatography (HPLC). The plasma concentrations of PA showed a biexponential increase following oral administration of doses ranging from 20 to 500 mg/kg. The terminal elimination half-lives (t1/2) of PA at dosages of 20, 100, or 500 mg/kg were 6.46 +/- 1.13, 5.19 +/- 3.56, and 5.10 +/- 1.10 h, respectively, total clearances (Cl/F) of PA at 20, 100, or 500 mg/kg were 97.43 +/- 4.20, 215.01 +/- 55.42, and 721.07 +/- 51.81 ml/h, and apparent distribution volumes of PA in the steady state (Vz/F) at 20, 100, or 500 mg/kg were 903.28 +/- 125.28, 1419.87 +/- 527.53, and 5264.86 +/- 993.65 ml, respectively. PA was absorbed rapidly after an oral dose of 500 mg/kg with peak concentration (Cmax) in blood (3.5 +/- 0.33 microg/ml) at 30 min postadministration. After oral administration, the dose-normalized area under the curve (AUC) (146.90 +/- 9.33 microg/h/ml) for 500 mg/kg was significantly greater than at 20 mg/kg (44.69 +/- 2.56 microg/h/ml). Urine analysis indicated that 13 +/- 0.45% of the administered PA dose (at 500 mg/kg, p.o.) was recovered unchanged in urine within 24 h. Data concerning the toxicokinetic profiles of PA improve our understanding of the toxicological potential of PAE and may prove useful for risk assessments of multiple phthalates exposure.

Systemic uptake of diethyl phthalate, dibutyl phthalate, and butyl paraben following whole-body topical application and reproductive and thyroid hormone levels in humans

In vitro and animal studies have reported endocrine-disrupting activity of chemicals used commonly as additives in cosmetics and skin care products. We investigated whether diethyl phthalate (DEP), dibutyl phthalate (DBP), and butyl paraben (BP) were systemically absorbed and influenced endogenous reproductive and thyroid hormone levels in humans after topical application. In a two-week single-blinded study, 26 healthy young male volunteers were assigned to daily whole-body topical application of 2 mg/cm2 basic cream formulation each without (week one) and with (week two) the three 2% (w/w) compounds. The concentrations of BP and the main phthalate metabolites monoethyl (MEP) and monobutyl phthalate (MBP) were measured in serum together with the following reproductive hormones: follicle stimulating hormone (FSH), lutenising hormone (LH), testosterone, estradiol, and inhibin B and thyroid hormones (thyroid stimulating hormone (TSH), free thyroxine (FT4), total triiodothyroxine (T3), and total thyroxine (T4)). MEP, MBP, and BP peaked in serum a few hours after application, reaching mean +/- SEM levels of 1001 +/- 81 microg/L, 51 +/- 6 microg/ L, and 135 +/- 11 microg/L, respectively. Only MEP was detectable in serum before treatment. Minor differences in inhibin B, LH, estradiol, T4, FT4, and TSH were observed between the two weeks, but these were not related to exposure. We demonstrated for the first time that DEP, DBP, and BP could be systemically absorbed in man after topical application. The systemic absorption of these compounds did not seem to have any short-term influence on the levels of reproductive and thyroid hormones in the examined young men.

Mechanistic evaluation of factors affecting compound loading into ion-exchange fibers

Donnan theory was applied to gain mechanistic understanding on the factors affecting drug loading process, compound-fiber affinity and subsequent release from fibrous ion-exchangers. Impact of initial loading solution concentration on fiber occupancy and loading efficiency of compounds were assessed experimentally and theoretically. Relative affinity towards the anion-exchange fibers was studied by dual loading of monovalent salicylic acid and either more lipophilic 3-isopropylsalicylic acid or divalent 5-hydroxyisophthalic acid. The effect of fiber framework on compound binding was evaluated separately for weakly and strongly basic fibers of similar ion-exchange capacities. The results revealed that loading into the ion-exchange fibers can be efficiently adjusted by the concentration of loading solution, leading to improved controllability of drug release from the fiber and minimised drug loss during the loading procedure. Ion-exchange fibers can be utilised successfully in simultaneous delivery of two ionic drugs, which offers a potential drug delivery system for synergistically active drugs. However, physicochemical characteristics of the drug (lipophilicity, valence) and framework of fibrous ion-exchanger affect the relative affinity of the drug towards the fiber, and should not be neglected when selecting appropriate ion-exchange fiber or optimising the external conditions during loading/release. Application of Donnan theory in modelling calculations supported precisely the experimental observations of compound loading (fiber occupancy and loading efficiency).

Urinary metabolites of diisodecyl phthalate in rats

Diisodecyl phthalate (DiDP) is an isomeric mixture of phthalates with predominantly 10-carbon branched-dialkyl chains, widely used as a plasticizer for polyvinyl chloride. The extent of human exposure to DiDP is unknown in part because adequate biomarkers of exposure to DiDP are not available. We identified several major metabolites of DiDP in urine of adult female Sprague-Dawley rats after a single oral administration of DiDP (300 mg/kg). These metabolites can potentially be used as biomarkers of exposure to DiDP. The metabolites extracted from urine were chromatographically resolved and identified by their chromatographic behavior and full scan negative ion electrospray ionization mass spectrum. The identity of metabolites with similar molecular weights was further examined in accurate mass mode. For some metabolites, unequivocal identification was done using authentic standards. Among these were the hydrolytic monoester of DiDP, monoisodecyl phthalate (MiDP), detected as a minor metabolite, and one omega oxidation product of MiDP, mono(carboxy-isononyl) phthalate (MCiNP), which was the most abundant urinary metabolite. We also tentatively identified other secondary metabolites of MiDP, mono(hydroxy-isodecyl) phthalate, mono(oxo-isodecyl) phthalate, mono(carboxy-isoheptyl) phthalate, mono(carboxy-isohexyl) phthalate, mono(carboxy-isopentyl) phthalate, mono(carboxy-isobutyl) phthalate, and mono(carboxy-ethyl) phthalate. Oxidative metabolites of diisoundecyl phthalate (DiUdP) and diisononyl phthalate (DiNP) were also detected suggesting the presence of DiUdP and DiNP in the DiDP formulation. The urinary concentrations of all these metabolites gradually decreased in the 4 days following the administration of DiDP. MCiNP and other DiDP secondary metabolites are more abundant in urine than MiDP, suggesting that these oxidative products are better biomarkers for DiDP exposure assessment than MiDP. Additional research on the toxicokinetics of these metabolites is needed to understand the extent of human exposure to DiDP from the urinary concentrations of MCiNP and other DiDP secondary metabolites.

Metabolism of phthalates in humans

Phthalates are synthetic compounds widely used as plasticisers, solvents and additives in many consumer products. Several animal studies have shown that some phthalates possess endocrine disrupting effects. Some of the effects of phthalates seen in rats are due to testosterone lowering effects on the foetal testis and they are similar to those seen in humans with testicular dysgenesis syndrome. Therefore, exposure of the human foetus and infants to phthalates via maternal exposure is a matter of concern. The metabolic pathways of phthalate metabolites excreted in human urine are partly known for some phthalates, but our knowledge about metabolic distribution in the body and other biological fluids, including breast milk, is limited. Compared to urine, human breast milk contains relatively more of the hydrophobic phthalates, such as di-n-butyl phthalate and the longer-branched, di(2-ethylhexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DiNP); and their monoester metabolites. Urine, however, contains relatively more of the secondary metabolites of DEHP and DiNP, as well as the monoester phthalates of the more short-branched phthalates. This differential distribution is of special concern as, in particular, the hydrophobic phthalates and their metabolites are shown to have adverse effects following in utero and lactational exposures in animal studies.

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.

Can exposure characterization explain concurrence or discordance between toxicology and epidemiology?

The importance of reliable exposure assessment, as a key component of the overall risk assessment process, has been well described for some considerable time. Yet, despite this widely accepted tenet, many studies conclude significant adverse health effects, with associated public policy implications, in the absence of adequate or, in some cases, even rudimentary, exposure quantification. Moreover, it appears that epidemiological studies in humans and toxicological studies in experimental animals may both suffer from inadequate exposure assessment. In this review, we discuss the nature and quality of the exposure assessment in both epidemiologic and toxicologic studies using examples from the pesticides and phthalate literature. Each type of study has its strengths and weaknesses in how exposure is assessed and often the strength of one is also a weakness. It would appear that insufficient or incomplete information about differences in exposure assessment could explain, at least in some cases, the differences in outcome between toxicological and epidemiological studies. Research efforts should focus on improving the feasibility of including biomonitoring in both animal and human studies to facilitate comparisons between animal and human models and improve exposure assessment in epidemiologic studies. Animal and human studies should measure the same biomarkers, where possible, to facilitate human health risk assessment.

Di-iso-nonylphthalate (DINP) metabolites in human urine after a single oral dose of deuterium-labelled DINP

Di-iso-nonylphthalate (DINP), a complex mixture of predominantly nine-carbon branched chain dialkyl phthalate isomers, has replaced di-(2-ethylhexyl)phthalate (DEHP) as the major plasticiser for polyvinylchloride (PVC) polymers. Similar to DEHP, DINP is a developmental and reproductive toxicant in rodents. This study for the first time describes human metabolism and elimination of DINP in a male volunteer after we applied a single oral DINP dose of 1.27 mg/kg body-weight. To avoid interference by omnipresent background exposure we used deuterium-labelled DINP. We investigated the urinary excretion of the simple monoester mono-iso-nonylphthalate (MINP) and oxidised isomers with hydroxy (OH-MINP), oxo (oxo-MINP) and carboxy (carboxy-MINP) functional groups. We used isomeric MINP and three specific oxidised isomer standards for quantification: mono-(4-methyl-7-hydroxy-octyl)phthalate (7OH-MMeOP), mono-(4-methyl-7-oxo-octyl)phthalate (7oxo-MMeOP) and mono-(4-methyl-7-carboxyheptyl)phthalate (7carboxy-MMeHP). These specific DINP metabolites are currently the only synthetic DINP metabolite standards available. Within 48 h we recovered 43.6% of the applied dose in urine as the above DINP metabolites, 20.2% as OH-MINP, 10.7% as carboxy-MINP, 10.6% as oxo-MINP and only 2.2% as MINP. Other oxidised DINP metabolites not determined in this study probably increase the share of the DINP dose excreted via urine. Elimination followed a multi-phase pattern, elimination half-lives in the second phase (beginning 24h post-dose) can only roughly be estimated to be 12h for the OH- and oxo-MINP-metabolites and 18 h for carboxy-MINP metabolites. After 24h, the carboxy-MINP metabolites replaced the OH-MINP metabolites as the major urinary metabolites. All oxidised DINP metabolites are suitable parameters for biomonitoring human DINP exposure.

A category approach for reproductive effects of phthalates

In regulatory toxicology, the experimental assessment of reproductive toxicity is one of the most costly endpoints to perform. Categorizing chemicals is an approach that can be used to reduce animal tests in risk assessments of chemicals, for example, via REACH (Registration, Evaluation, and Authorization of Chemicals). The category approach was tested for reproductive toxicity with a group of 10 ortho-phthalate esters, with different side chain lengths. Three ortho-phthalates were used for testing the category. Phthalates with side-chain lengths C4 to C6 that are commonly known to cause reproductive effects were included, as well as the recently discovered mechanism that indicates antiandrogenic effects. The differences in physicochemical properties, absorption rates, and metabolism between the phthalates investigated could not fully explain the difference in reproductive toxicity. It was concluded that phthalates with the alkyl side-chain length from C4 to C6 produce similar severe reproductive effects in experimental animals. It is expected that phthalates included in the tight boundaries of the proposed category would all show severe reproductive effects, especially the antiandrogenic effects. Further testing might not be needed for phthalates within these boundaries. If necessary, limited testing could focus on the critical endpoints. Detailed mechanistic information is needed on phthalates to apply the categories for regulatory toxicology.

Phthalate monoesters in perfusate from a dual placenta perfusion system, the placenta tissue and umbilical cord blood

Fetal exposure to phthalates may be associated with adverse reproductive effects, including cryptorchidism and decreased semen quality. Information about human placental transfer is needed to qualify the hypotheses. A dual recirculating placenta perfusion system to monitor concentrations of eight phthalate monoesters in fetal and maternal perfusates was established. In addition to perfusate background measures of phthalate monoesters, the concentrations in umbilical cord plasma and placenta tissue were measured. Monomethyl phthalate (mMP), monoethyl phthalate (mEP), monobutyl phthalate (mBP), and mono (2-ethyl-hexyl) phthalate (mEHP) were detected in both maternal and fetal perfusate, demonstrating a release of compounds from tissue or blood to perfusates. The distribution of compounds between perfusate, umbilical cord plasma, and tissue was in accordance with the physical-chemical properties of the compounds. Results from the present study of compounds residing in the tissue are essential before studying human transplacental transfer, storage, and metabolism of selected phthalate monoesters.

Metabolism of terephthalic acid and its effects on CYP4B1 induction

OBJECTIVE

To investgate the metabolism of terephthalic acid (TPA) in rats and its mechanism. Methods Metabolism was evaluated by incubating sodium terephthalate (NaTPA) with rat normal liver microsomes, or with microsomes pretreated by phenobarbital sodium, or with 3-methycholanthrene, or with diet control following a NADPH-generating system. The determination was performed by high performance liquid chromatography (HPLC), and the mutagenic activation was analyzed by umu tester strain Salmonella typhimurium NM2009. Expression of CYP4B1 mRNA was detected by RT-PCR. Results The amount of NaTPA (12.5-200 micromol x L(-1)) detected by HPLC did not decrease in microsomes induced by NADPH-generating system. Incubation of TPA (0.025-0.1 mmol x L(-1)) with induced or noninduced liver microsomes in an NM2009 umu response system did not show any mutagenic activation. TPA exposure increased the expression of CYP4B 1 mRNA in rat liver, kidney, and bladder.

CONCLUSION

Lack of metabolism of TPA in liver and negative genotoxic data from NM2009 study are consistent with other previous short-term tests, suggesting that the carcinogenesis in TPA feeding animals is not directly interfered with TPA itself and/or its metabolites.

Mono-(3-carboxypropyl) phthalate, a metabolite of di-n-octyl phthalate

Di-n-octyl phthalate (DnOP) is found as a component of mixed C6-C10 linear-chain phthalates used as plasticizers in various polyvinyl chloride applications, including flooring and carpet tiles. Following exposure and absorption, DnOP is metabolized to its hydrolytic monoester, mono-n-octyl phthalate (MnOP), and other oxidative products. The urinary levels of one of these oxidative metabolites, mono-(3-carboxypropyl) phthalate (MCPP), were about 560-fold higher than MnOP in Sprague-Dawley rats dosed with DnOP by gavage. Furthermore, MCPP was also found in the urine of rats dosed with di-isooctyl phthalate (DiOP), di-isononyl phthalate (DiNP), di-isodecyl phthalate (DiDP), di-(2-ethylhexyl) phthalate, and di-n-butyl phthalate (DBP), although at concentrations considerably lower than in rats given similar concentrations of DnOP. The comparatively much higher urinary concentrations of MCPP than of the hydrolytic monoesters of the high-molecular-weight phthalates DiOP, DiNP, and DiDP in the exposed rats suggest that these monoesters may be poor biomarkers of exposure to their precursor phthalates and may explain the relatively low frequency of detection of these monoester metabolites in human populations. MCPP and MnOP were also measured in 267 human urine samples. The frequent detection and higher urinary concentrations of MCPP than MnOP suggest that exposure to DnOP might be higher than previously thought based on the measurements of MnOP alone. However, because MCPP is also a minor metabolite of DBP and other phthalates in rats, and the metabolism of phthalates in rodents and humans may differ, additional data on the absorption, distribution, metabolism, and elimination of MCPP are needed to completely understand the extent of human exposure to DnOP from the urinary concentrations of MCPP.

Monitoring phthalate exposure in humans

The dialkyl- or alkyl/aryl esters of 1,2-benzenedicarboxylic acid, commonly known as phthalates, are high-production-volume synthetic chemicals and ubiquitous environmental contaminants because of their use in plastics and other common consumer products. Di-(2-ethylhexyl) phthalate (DEHP) is the most abundant phthalate in the environment. Humans are exposed to these compounds through ingestion, inhalation, and dermal exposure for their whole lifetime, since the intrauterine life. Public and scientific concern has increased in recent years about the potential health risks associated with exposure to phthalates. The main focus has moved away from the hepatotoxic effects to the endocrine disrupting potency of these chemicals. To date, although the consistent toxicologic data on phthalates is suggestive, information on sources and pathways of human exposure to phthalates is limited. Recently, exposure to phthalates has been assessed by analyzing urine for their metabolites. This approach is contrary to the determination of the parent phthalates in air, water and foodstuff and not subject to contamination. Furthermore, these metabolites and the parent phthalates are considered the toxic species. However, accurate methods and models for measuring the amount of phthalates absorbed by the various pathways of exposure have to be developed. In fact, a frequent biological monitoring of phthalates in body fluids and tissues would be highly advisable, both in helping physicians to perform health risk assessments for exposure in the general population and in guiding governments to provide regulations concerning the maximum allowed concentrations in the environment, plasticized products, medications and medical equipment.

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 50mg 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 24h 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.