Chromatographic separation and quantitative determination of the metabolites of di-(2-ethylhexyl) phthalate from urine of laboratory animals

In-depth profiling of di(2-ethylhexyl) phthalate metabolic footprints in rats using click chemistry-mass spectrometry probes

Di(2-ethylhexyl) phthalate (DEHP), the most widely used plasticizers in the world, has been regarded as an endocrine disrupting chemical with serious adverse health outcomes. Accumulating evidence strongly suggests that the undesirable biological effects of DEHP are meditated by its metabolites rather than itself. However, the metabolic footprints of DEHP in vivo are still unclear. Here we developed a click chemistry-assisted mass spectrometry (CC-MS) strategy for in-depth profiling DEHP metabolites in rats. An alkyne-modified DEHP analogue (alkyne-DEHP) was synthesized as a tracer for in vivo tracing, and a pair of MS probes (4-azido-nphenylbenzamide, 4-ANPA, and its deuterated reagent d₅-4-ANPA) were prepared to specifically label the alkyne-DEHP metabolites, and prominently improve their detection sensitivity and selectivity. Using the CC-MS strategy, we successfully screened 247 alkyne-DEHP metabolites from rat urine, feces, and serum, including many unrevealed metabolites, such as oxidized phthalate diester metabolites and glucuronides of phthalate monoester metabolites. The discovery of new DEHP metabolites provides additional insights for understanding the metabolism of DEHP, which may be beneficial in exploring the mechanism underlying DEHP induced-toxicity in the future.

Prenatal exposure to phthalates is associated with decreased anogenital distance and penile size in male newborns

Reproductive effects from phthalate exposure have been documented mostly in animal studies. This study explored the association between prenatal exposure to phthalate metabolites, anogenital distance and penile measurements in male newborns in Toluca, State of Mexico. A total of 174 pregnant women provided urine samples for phthalate analysis during their last prenatal visit, and the 73 who gave birth to male infants were included in the study. The 73 male newborns were weighed and measured using standardized methods after delivery. After adjusting for creatinine and supine length at birth, significant inverse associations were observed between an index of prenatal exposure to total phthalate exposure and the distance from the anus to anterior base of the penis (β = -0.191 mm per 1 μg/l, P = 0.037), penile width (β = -0.0414, P = 0.050) and stretched length (β = -0.2137, P = 0.034); prenatal exposure to mono-2-ethylhexyl phthalate exposure was associated with a reduction in the stretched length of the penis (β = -0.2604, P = 0.050). Human exposure to phthalates is a public health concern, and the system most vulnerable to its potential effects seems to be the immature male reproductive tract.

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

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

Phthalate metabolites in obese individuals undergoing weight loss: Urinary levels and estimation of the phthalates daily intake

Human exposure to chemicals commonly encountered in our environment, like phthalates, is routinely assessed through urinary measurement of their metabolites. A particular attention is given to the specific population groups, such as obese, for which the dietary intake of environmental chemicals is higher. To evaluate the exposure to phthalates, nine phthalate metabolites (PMs) were analyzed in urine collected from obese individuals and a control population. Obese individuals lost weight through either bariatric surgery or a conservative weight loss program with dietary and lifestyle counseling. Urine samples were also collected from the obese individuals after 3, 6 and 12months of weight loss. Individual daily intakes of the corresponding phthalate diesters were estimated based on the urinary PM concentrations. A high variability was recorded for the levels of each PM in both obese and control urine samples showing the exposure to high levels of PMs in specific subgroups. The most important PM metabolite as percentage contribution to the total PM levels was mono-ethyl phthalate followed by the metabolites of di-butyl phthalate and di 2-ethyl-hexyl phthalate (DEHP). No differences in the PM levels and profiles between obese entering the program and controls were observed. Although paralleled by a significant decrease of their weight, an increase in the urinary PM levels after 3 to 6months loss was seen. Constant figures for the estimated phthalates daily intake were observed over the studied period, suggesting that besides food consumption, other human exposure sources to phthalates (e.g. air, dust) might be also important. The weight loss treatment method followed by obese individuals influenced the correlations between PM levels, suggesting a change of the intake sources with time. Except for few gender differences recorded between the urinary DEHP metabolites correlations, no other differences were observed for the urinary PM levels as a function of age, body mass index or waist circumference. Linear regression analysis showed almost no significance of the relationship between measured urinary PMs and serum free thyroxine, thyroid-stimulating hormone (TSH) for all obese individuals participating to the study, while for the control samples, several PMs were significantly associated with the serum TSH levels.

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.

Phthalate-induced Leydig cell hyperplasia is associated with multiple endocrine disturbances

The possibility that exposures to environmental agents are associated with reproductive disorders in human populations has generated much public interest recently. Phthalate esters are used most commonly as plasticizers in the food and construction industry, and di-(2-ethylhexyl) phthalate (DEHP) is the most abundant phthalate in the environment. Daily human exposure to DEHP in the U.S. is significant, and occupational and clinical exposures from DEHP-plasticized medical devices, e.g., blood bags, hemodialysis tubing, and nasogastric feeding tubes, increase body burden levels. We investigated the effects of chronic exposures to low environmentally relevant DEHP levels on testicular function. Our data show that prolonged exposures to this agent induced high levels of the gonadotropin luteinizing hormone and increased the serum concentrations of sex hormones [testosterone and 17beta-estradiol (E2)] by >50%. Increased proliferative activity in Leydig cells was evidenced by enhanced expression of cell cycle proteins, as determined by RT-PCR. The numbers of Leydig cells in the testis of DEHP-treated rats were 40-60% higher than in control rats, indicating induction of Leydig cell hyperplasia. DEHP-induced elevations in serum testosterone and E2 levels suggest the possibility of multiple crosstalks between androgen, estrogen, and steroid hormone receptors, whereas the presence of estrogen receptors in nonreproductive tissues, e.g., cardiovascular system and bones, implies that the increases in serum E2 levels have implications beyond reproduction, including systemic physiology. Analysis of the effects of phthalate exposures on gonadotropin and steroid hormone levels should form part of overall risk assessment in human populations.

Internal exposure of the general population to DEHP and other phthalates--determination of secondary and primary phthalate monoester metabolites in urine

A number of phthalates and their metabolites are suspected of having teratogenic and endocrine disrupting effects. Especially the developmental and reproductive effects of di(2-ethylhexyl)phthalate (DEHP) are under scrutiny. In this study we determined the concentrations of the secondary, chain oxidized monoester metabolites of DEHP, mono(2-ethyl-5-hydroxyhexyl)phthalate (5OH-MEHP) and mono(2-ethyl-5-oxo-hexyl)phthalate (5oxo-MEHP) in urine samples from the general population. The utilization of the secondary metabolites minimized any risk of contamination by the ubiquitously present phthalate parent compounds. Included in the method were also the simple monoester metabolites of DEHP, dioctylphthalate (DOP), di-n-butylphthalate (DnBuP), butylbenzylphthalate (BBzP) and diethylphthalate (DEP). Automated sample preparation was performed applying a column switching liquid chromatography system enabling online extraction of the urine on a restricted access material (RAM) and separation on a reversed phase analytical column. Detection was performed by negative ESI-tandem mass spectrometry in multiple reaction monitoring mode and quantification by isotope dilution. The excretion of DEHP and the other phthalates was studied by analyzing first morning urine samples from 53 women and 32 men aged 7-64 years (median: 34.2 years) living in northern Bavaria (Germany) who were not occupationally exposed to phthalates. Phthalate metabolites, secondary and primary ones, were detected in all specimens. Concentrations were found to vary strongly from phthalate to phthalate and subject to subject with differences spanning more than three orders of magnitude. Median concentrations for excretion of DEHP metabolites were 46.8 microg/L for 5OH-MEHP (range 0.5-818 microg/L), 36.5 microg/L for 5oxo-MEHP (range 0.5-544 microg/L), and 10.3 microg/L for MEHP (range:<0.5 (limit of quantification, LOQ) to 177 microg/L). A strong correlation was found between the excretion of 5OH-MEHP and 5oxo-MEHP with a correlation coefficient of r=0.991, indicating close metabolic proximity of those two parameters but also the absence of any contaminating interference. Median concentrations for the other monoester metabolites were for mono-n-butylphthalate (MnBuP) 181 microg/L, for monobenzylphthalate (MBzP) 21.0 microg/L, for monoethylphthalate (MEP) 90.2 microg/L and for mono-n-octylphthalate (MOP)<1.0 microg/L (LOQ). These results will help to perform health risk assessments for the phthalate exposure of the general population.

Phthalate esters detected in various water samples and biodegradation of the phthalates by microbes isolated from river water

Phthalate esters (PEs), especially di-n-butyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) were detected in various water samples such as river water, well water and tap water. On degradation tests of PEs, Tempaku River water degraded almost 100% of diethyl phthalate (DEP), di-isobutyl phthalate and DBP, and approximately 70% of DEHP. All eight isolates from Tempaku River water (R1-R7, D1) did not degrade dimethyl phthalate (DMP), but showed biodegrading ability for the other PEs. The DBP-degrading ability was particularly high for the isolates R1-R3 and D1 of Acinetobacter iwoffii. Crude enzyme solutions prepared from bacterial cells of these isolates showed a higher degrading activity for DEHP compared with that for microbially-degradable DBP. Particularly high DEHP-degrading activity was found for crude enzyme solutions of the isolate D1. As metabolites from the river water and bacterial isolates, DMP and an unknown diester were produced from DEP. DMP, DEP, monomethyl phthalate, monobutyl phthalate (MBP) and an unknown diester were produced from DBP. DBP, DEP, DMP and an unknown diester were produced from DEHP. As metabolites by the crude enzyme solutions, DMP, MBP and an unknown diester derivative were produced from DBP. DBP, mono-(2-ethylhexyl) phthalate and an unknown diester derivative were produced from DEHP. Diesters with shortened alkyl carbon chains were also found as metabolites by the isolates and their crude enzyme solutions. The results suggest that the alkyl chains in the diesters are also decomposed in addition to monoester formation from DBP or DEHP at the first step reported for animals and some types of bacteria.

Chromatographic fractionation and analysis by mass spectrometry of conjugated metabolites of bis(2-ethylhexyl)phthalate in urine

Mono(2-ethylhexyl)phthalate (MEHP), the primary metabolite of the plasticizer bis(2-ethylhexyl)phthalate (DEHP), was given to guinea pigs and mice and the methods for the isolation, separation and analysis of its metabolites in urine were developed. Following solid-phase extraction with octadecylsilane-bonded silica, individual metabolites were purified and separated using a combination of ion-exchange chromatography on lipophilic gels and reversed-phase high-performance liquid chromatography. Analysis of intact conjugates, as well as nonconjugated metabolites, was performed by fast atom bombardment mass spectrometry (FAB-MS) and, after derivatization, by gas chromatography-mass spectrometry. Enzymatic methods were used for further characterization. The study confirms glucuronidation as the major conjugation pathway for MEHP in the investigated species. Although less important quantitatively, glucosidation is shown to be an alternative conjugation pathway in mice. The methods developed were applied to a sample of urine from a hyperbilirubinemic newborn infant subjected to DEHP-exposure in conjunction with an exchange transfusion. It was demonstrated that metabolites of DEHP were excreted in amounts which could be analyzed by FAB-MS.

Hydrolysis, absorption and metabolism of di(2-ethylhexyl) terephthalate in the rat

1. The hydrolysis of di(2-ethylhexyl) terephthalate (DEHT) and di(2-ethylhexyl) phthalate (DEHP) were studied using rat gut homogenate fractions in vitro. Both isomers were hydrolysed by the intestinal fraction; however, DEHP was hydrolysed to 2-ethylhexanol (2-EH) and mono(2-ethylhexyl) phthalate (MEHP) in about equal proportions, whereas DEHT was hydrolysed to 2-EH and terephthalic acid (TPA). The half-lives for disappearance of the diesters were determined to be 12.6 min for DEHP and 53.3 min for DEHT. 2. The absorption and metabolism of DEHT were studied by administering [hexyl-2-14C]DEHT (in corn oil) by oral gavage at a dose level of 100 mg/kg to 10 adult male Sprague-Dawley rats. Urine, faeces and expired air were collected for 144 h and analysed for the presence of radioactivity, and faeces and urine were analysed for unlabelled metabolites. 3. Radioactivity was eliminated in faeces (56.5 +/- 12.1% of dose) primarily as unchanged DEHT, small amounts of MEHT and polar metabolites; excreted in urine (31.9 +/- 10.9% of dose) principally as MEHT and metabolic products of 2-EH; and expired as 14CO2 (3.6 +/- 0.9% of dose). Less than 2% of the administered radioactivity was found in the carcass. Small amounts of 14C were found in the tissues with the highest amounts found in liver and fat. 4. Metabolites identified in urine included terephthalic acid (equivalent to 51% of dose), oxidized metabolites of 2-EH and MEHT, and glucuronic and sulphuric acid conjugates (equivalent to about 10% of dose).(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolism of di(2-ethylhexyl)phthalate in the earthworm Lumbricus terrestris

1. Earthworms can hydrolyze di-(2-ethylhexyl) phthalate (DEHP) to mono-2-ethylhexyl phthalate (MEHP) and phthalic acid (PA). 2. They apparently cannot produce the side-chain-oxidized derivatives of MEHP that constitute the major DEHP metabolites in higher animals. 3. With the assistance of intestinal bacterial Pseudomonas, the worm-derived PA is degraded through protocatechuic and beta-carboxymuconic acids to CO2. 4. There is an indication of a second pathway for degradation of PA leading through benzoic acid.

Mono-2-ethylhexyl phthalate, a metabolite of di-(2-ethylhexyl) phthalate, causally linked to testicular atrophy in rats

Acute testicular atrophy results when appropriate dosages of di-(2-ethylhexyl) phthalate (DEHP) or its hydrolysis product mono-2-ethylhexyl phthalate (MEHP) are given to male rats. Events thought to be involved in this pathological effect also occur in cultures of testicular cells in vitro, but require MEHP rather than DEHP. Primary cultures of hepatocytes, Sertoli cells, and Leydig cells were incubated with 14C-labeled MEHP [8 microM] for up to 24 hr. No significant reduction in viability was produced under these conditions. In contrast to the hepatocytes, which extensively metabolized MEHP to a variety of products in 1 hr, the testicular cell cultures were apparently unable to metabolize MEHP (beyond a slight hydrolysis to phthalic acid by Sertoli cells) in 18-24 hr. MEHP was efficiently taken up by hepatocytes, but much less so by testicular cells. These results, combined with related observations from the literature, support the hypothesis that MEHP itself is the metabolite of DEHP responsible for testicular atrophy in rats.

The metabolism of mono-(2-ethylhexyl) phthalate (MEHP) and liver peroxisome proliferation in the hamster

This study has investigated the in vivo metabolism of mono-(2-ethylhexyl) phthalate (MEHP), the initial metabolite of di-(2-ethylhexyl) phthalate in mammals, and the hepatic peroxisome proliferation induced by this compound following multiple oral administration to hamsters. Hamsters received [14C]-MEHP, by gavage, at doses of 50 and 500 mg/kg body wt on each of three consecutive days. Urine was collected every 24 hours and metabolite profiles were determined using capillary gas-chromatography. Multiple high doses of MEHP (500 mg/kg) induced a change in the relative proportions of metabolites produced. As previously reported for the rat, metabolites derived from sequential omega- following by beta-oxidation were increased. This increase was correlated with a parallel 3-fold increase in peroxisomal beta-oxidation--a marker for peroxisome proliferation. Hamsters were less responsive than rats to peroxisome proliferation elicited by MEHP. In contrast to the rat, a large proportion of hamster omega-1 oxidation products of MEHP (metabolites 6 and 9, mono (2-ethylhexyl-5-oxohexyl) phthalate and mono (2-ethyl-5-hydroxyhexyl) phthalate, respectively) were found as their glucuronide conjugates. This metabolic species difference may relate to differences in sensitivity to MEHP as a peroxisome proliferator. The relationship between metabolite conjugation, peroxisome proliferation and production of omega-oxidation metabolites is discussed.

Analysis by fast atom bombardment mass spectrometry of conjugated metabolites of bis(2-ethylhexyl) phthalate

Mono(2-ethylhexyl) phthalate was given to guinea pigs and mice and its metabolites were isolated from urine. A procedure consisting of sorbent extraction, ion-exchange chromatography and reversed-phase high-performance liquid chromatography was used in the purification scheme. The metabolites were analysed by fast atom bombardment mass spectrometry. It is concluded that the purification procedure is very mild and that fast atom bombardment is a useful ionization technique for intact conjugates of metabolites of bis(2-ethylhexyl) phthalate.

The induction of omega and beta-oxidation of fatty acids and effect on alpha 2u globulin content in the liver and kidney of rats administered 2,2,4-trimethylpentane

The effect of daily administration of 12 mmol/kg 2,2,4-trimethylpentane for 10 d on hepatic and renal microsomal mono-oxygenase activity, peroxisomal beta-oxidation and the concentration of alpha 2u-globulin has been examined in male and female rats. 2,2,4-Trimethylpentane produces liver and, to a lesser extent, kidney enlargement. This is associated with the selective induction of cytochrome P-450-mediated omega-oxidation and peroxisomal beta-oxidation of fatty acids and proliferation of peroxisomes. Male rats show a more marked response than female rats. 2,2,4-Trimethylpentane produces an increase in alpha 2u-globulin in the kidney of male rats. The relevance of selective induction of omega- and beta-oxidation of fatty acids and accumulation of alpha 2u-globulin to renal tubular necrosis in male rats requires further study.

Beta-oxidation of 2-ethyl-5-carboxypentyl phthalate in rodent liver

[7-14C]-2-Ethyl-5-carboxypentyl phthalate was isolated and purified from urine of rats given [7-14C]-di-(2-ethylhexyl) phthalate. This metabolite was shown to serve as a precursor for 2-ethyl-3-carboxypropyl phthalate in vivo. 2-Ethyl-5-carboxypentyl phthalate was oxidized to 2-ethyl-3-carboxypropyl phthalate in liver slices from control or, much more rapidly, from clofibrate-pretreated rats. Inhibition by KCN in liver slices from untreated rats, and strong inhibition by acrylate, suggested that formation of 2-ethyl-3-carboxypropyl phthalate involved mitochondrial beta-oxidation. The strong enhancement of the production of this compound by clofibrate (a very weak inducer for mitochondrial dehydrogenases), and strong inhibition by chlorpromazine suggested that peroxisomes may also be able to oxidize 2-ethyl-5-carboxypentyl phthalate. We were able to detect beta-oxidation of 2-ethyl-5-carboxypentyl phthalate to 2-ethyl-3-carboxypropyl phthalate using purified mitochondria, but strong phthalate monoester hydrolase activity observed during incubation of the former compound with purified peroxisomes made it impossible to determine whether 2-ethyl-3-carboxypropyl phthalate could be produced in the latter organelle or not. 2-Ethyl-5-carboxypentyl phthalate was such an inefficient substrate for beta-oxidation compared to palmitic acid that it is unlikely that it contributes significantly to the production of H2O2 in rats chronically exposed to di-(2-ethylhexyl) phthalate. Normal fatty acids are most likely to serve as the dominant substrates for peroxisomal beta-oxidase.

Image analysis of hepatocyte nuclei in assessing di(2-ethylhexyl)phthalate effects eluding detection by conventional microscopy

The effect of di(2-ethylhexyl)phthalate (DEHP) administered in single intraperitoneal doses of 30, 300 and 3000 mg/kg in Syrian golden hamsters was studied by means of routine pathologic investigations, electron microscopy and image analysis. The morphological evaluations did not show apparent differences between the control and treated animals. Such differences, however, were recognized by using image analysis. They concerned morphology of the hepatocyte nuclei and were defined by quantitative parameters reflecting geometrical, optical and structural properties. Of importance for differentiating dose/effect relationships were features of chromatin structure. In order to describe those features we developed special algorithms capable of identifying and characterizing regions of condensed chromatin as subimages. These were distinguished by their size, shape and optical density and showed typical distributions within the nucleus. As our results demonstrate, image analysis methods permit detection of DEHP related pathology in animals which, as far as is evident from routine morphologic evaluations, belong to the no-effect experimental group.

Comparative pharmacokinetics and subacute toxicity of di(2-ethylhexyl) phthalate (DEHP) in rats and marmosets: extrapolation of effects in rodents to man

Certain phthalate esters and hypolipidemic agents are known to induce morphological and biochemical changes in the liver of rodents, which have been associated with an increased incidence of hepatocellular tumors in these species. There is evidence that hypolipidemic agents do not induce these effects in either subhuman primates or man. The oral and intraperitoneal administration of di(2-ethylhexyl) phthalate (DEHP) to the marmoset monkey at doses up to 5 mmole DEHP/kg body weight/day for 14 days did not induce morphological or biochemical changes in the liver or testis comparable with those obtained in rats given the same amount of DEHP. In the marmoset, the excretion profile of [14C]-DEHP following oral, IP, and IV administration and the lower tissue levels of radioactivity demonstrated a considerably reduced absorption in this species compared to the rat. The urinary metabolite pattern in the marmoset was in many respects qualitatively similar to but quantitatively different from that in the rat; the marmoset excreted principally conjugated metabolites derived from omega- 1 oxidation. The pharmacokinetic differences between these two species indicate that the tissues of the marmoset are exposed to a level of DEHP metabolites equivalent to the complete absorption of a dose of Ca. 0.1 to 0.25 mmole DEHP/kg body weight/day without significant toxicological effects. These exposure levels are at least 100-fold greater than the worst estimates of incidental human exposure (ca. 0.0015 mmole/kg/day). They are comparable with the human therapeutic dose of many hypolipidemic drugs (ca. 0.15 mmole/kg/day), a dose at which it is claimed that there is an absence of morphological or biochemical changes to human or subhuman primate liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-linearities in the pharmacokinetics of di-(2-ethylhexyl) phthalate and metabolites in male rats

The disposition of the plasticizer di-(2-ethylhexyl) phthalate (DEHP) and four of its major metabolites was studied in male rats given single infusions of a DEHP emulsion in doses of 5, 50 or 500 mg DEHP/kg body weight. Plasma concentrations of DEHP and metabolites were followed for 24 h after the start of the infusion. The kinetics of the primary metabolite mono-(2-ethylhexyl) phthalate (MEHP) was studied separately. The concentrations of DEHP in plasma were at all times considerably higher than those of MEHP, and the concentrations of MEHP were much higher than those of the other investigated metabolites. In animals given 500 mg DEHP/kg, the areas under the plasma concentration-time curves (AUCs) of the other investigated metabolites were at most 15% of that of MEHP. Parallel decreases in the plasma concentrations of DEHP, MEHP and the omega- and (omega-1) oxidized metabolites indicated that the elimination of DEHP was the rate-limiting step in the disposition of the metabolites. This was partly supported by the observation that the clearance of MEHP was higher than that of DEHP. Nonlinear increases in the AUCs of DEHP and MEHP indicated saturation in the formation as well as the elimination of the potentially toxic metabolite MEHP.

The metabolism of di(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) in rats: in vivo and in vitro dose and time dependency of metabolism

This study investigated the in vivo metabolism of di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP) in rats after multiple dosing, the metabolism of MEHP in primary rat hepatocyte cultures for periods of up to 3 days, and the biotransformation of some major metabolites of MEHP. Rats were orally administered [14C]DEHP or [14C]MEHP at doses of 50 and 500 mg/kg body wt for three consecutive days. Urine was collected at 24-hr intervals, and metabolite profiles were determined. After a single dose of either compound, urinary metabolite profiles were similar to those previously reported. However, after multiple administration of both DEHP and MEHP at 500 mg/kg, increases in omega-/beta-oxidation products [metabolites I and V, mono(3-carboxy-2-ethylpropyl) phthalate and mono(5-carboxy-2-ethylpentyl) phthalate, respectively] and decreases in omega - 1-oxidation products [metabolites VI and IX, mono(2-ethyl-5-oxohexyl) phthalate and mono(2-ethyl-5-hydroxyhexyl) phthalate, respectively] were seen. At the low dose of 50 mg/kg little or no alteration in urinary metabolite profiles was observed. At 500 mg/kg of MEHP a 4-fold stimulation of CN- -insensitive palmitoyl-CoA oxidation (a peroxisomal beta-oxidation marker) was seen after three consecutive daily doses. At the low dose of 50 mg/kg only a 1.8-fold increase was noted. Similar observations were made with rat hepatocyte cultures. MEHP at concentrations of 50 and 500 microM was extensively metabolized in the rat hepatocyte cultures. Similar metabolic profiles to those seen after in vivo administration of MEHP were observed. At the high (500 microM) concentration of MEHP, changes in the relative proportions of omega- and omega- 1-oxidized metabolites were seen. Over the 3-day experimental period, omega-/beta-oxidation products increased in a time-dependent manner at the expense of omega - 1-oxidation products. At a concentration of 500 microM MEHP, a 12-fold increase of CN- -insensitive palmitoyl CoA oxidation (a peroxisomal beta-oxidation marker) was observed. At the low concentration of MEHP (50 microM) only a 3-fold increase in CN- -insensitive palmitoyl-CoA oxidation was noted and little alteration in the metabolite profile of MEHP was observed with time. Biotransformation studies of the metabolites of MEHP confirmed the postulated metabolic pathways. Metabolites I and VI appeared to be endpoints of metabolism, while metabolite V was converted to metabolite I, and metabolite IX to metabolite VI. It was also possible to reduce the transformation of metabolite X [mono(2-ethyl-6-hydroxyhexyl) phthalate] to metabolite V.(ABSTRACT TRUNCATED AT 400 WORDS)

Circulating concentrations of di(2-ethylhexyl) phthalate and its de-esterified phthalic acid products following plasticizer exposure in patients receiving hemodialysis

The degree of exposure to the plasticizer di(2-ethylhexyl) phthalate (DEHP) was assessed in 11 patients undergoing maintenance hemodialysis for the treatment of renal failure. The amount of DEHP leached from the dialyzer during a 4-hr dialysis session was estimated by monitoring the DEHP blood concentration gradient across the dialyzer. Circulating concentrations of the biologically active products of DEHP de-esterification, viz., mono(2-ethylhexyl) phthalate (MEHP) and phthalic acid, were also determined during the dialysis session. On the average, an estimated 105 mg of DEHP was extracted from the dialyzer during a single dialysis session, with a range of 23.8 to 360 mg. The rate of extraction of DEHP from the dialyzer was correlated with serum lipid content as expressed by the sum of serum cholesterol and triglyceride concentrations (r = +0.65, p less than 0.05). Time-averaged circulating concentrations of MEHP during dialysis (1.33 +/- 0.58 micrograms/ml) were similar to those of DEHP (1.91 +/- 2.11 micrograms/ml). Blood concentrations of phthalic acid (5.22 +/- 3.94 micrograms/ml) were higher than those of the esters. The length of time patients had been receiving regular dialysis treatment was not a determinant of circulating concentrations of DEHP or MEHP. In contrast, time-averaged circulating concentrations of phthalic acid correlated strongly with the duration (in years) of dialysis treatment (r = +0.92, p less than 0.001). The results indicated substantial exposure to DEHP during hemodialysis and that the de-esterified products of DEHP are present in significant concentrations in the systemic circulation. Further study is needed to assess the contribution of these metabolites to the biological actions of DEHP in man.

Effects of route of administration and repetitive dosing on the disposition kinetics of di(2-ethylhexyl) phthalate and its mono-de-esterified metabolite in rats

The disposition kinetics of the plasticizer di(2-ethylhexyl) phthalate (DEHP) and its biologically active metabolite mono(2-ethylhexyl) phthalate (MEHP) were studied in rats following single or multiple administration of DEHP by various routes. Following a single intraarterial (ia) injection, a large apparent volume of distribution (5390 ml/kg) and a high rate of clearance (21.5 ml/min/kg) were observed for DEHP. The systemic availability of DEHP was low following both single po (13.6%) and ip (5.2%) administration. A marked route-dependency in the formation of MEHP from DEHP was observed. The circulating concentrations of MEHP were substantially higher than those of DEHP (i.e., area under the blood concentration-time curve (AUC) ratio of approximately 7) after po administration, whereas concentrations of the mono-de-esterified metabolite were much lower relative to the parent diester concentration after ia or ip administration (i.e., AUC ratio less than 0.4). Pharmacokinetic calculations revealed that approximately 80% of a po dose of DEHP undergoes mono-de-esterification, as compared to only about 1% of the dose following either ia or ip administration. Hence, the low po systemic availability of DEHP may be largely attributed to presystemic hydrolysis of DEHP to MEHP in the gut, whereas slow and/or incomplete absorption is the likely cause of the poor bioavailability of DEHP after ip administration. No significant accumulation in the circulating concentrations of DEHP or derived MEHP were observed following 7 days of repetitive administration of DEHP. However, multiple ip injections resulted in an apparent decrease in the rate and/or extent of DEHP absorption from the peritoneal cavity, while no significant change in the po absorption of the diester was observed. The striking difference in the MEHP to DEHP AUC ratio between po and ip routes was still evident after multiple dosing. These data suggest that previously reported differences in the biologic effects of DEHP in rodents following different routes of administration may be due to route dependency in the mono-de-esterification of the diester.

Bacterial mutagenicity testing of urine from rats dosed with 2-ethylhexanol derived plasticizers

Di-(2-ethylhexyl)phthalate (DEHP) produced hepatocellular carcinomas in rodents at high doses in a NTP/NCI bioassay. DEHP has not shown evidence of genotoxic activity in in vitro mutagenicity tests. We extended these studies by examining the mutagenicity of urine from rats dosed with DEHP, 2-ethylhexanol (2-EH), and several other 2-EH derived plasticizers, i.e. di-(2-ethylhexyl)adipate (DEHA), di-(2-ethylhexyl)terephthalate (DEHT) and tri-(2-ethylhexyl)trimellitate (TEHT). A modified Ames Salmonella/microsome assay was used to determine mutagenicity. Urine was pooled from male Sprague--Dawley rats dosed daily for 15 days with 2000 mg/kg of each test substance with the exception of 2-EH which was given at 1000 mg/kg. Direct plating procedures were used to determine the presence of mutagens in urine. Urine from rats dosed with 8-hydroxyquinoline was used as a positive control. There was no evidence that mutagenic substances were excreted in the urine by rats dosed with either DEHP, DEHA, DEHT, TEHT or 2-EH as determined in the presence or absence of rat liver microsomes, and with or without treatment with beta-glucuronidase/aryl sulfatase. Our findings indicate that the above test compounds were not converted to urinary metabolites that were mutagenic. These observations provide no evidence for a genotoxic mechanism for DEHP carcinogenicity in rodents.

Methods for measuring mutagenicity in urine of rats dosed with [14C]di(2-ethylhexyl)phthalate

Di(2-ethylhexyl)phthalate (DEHP) is extensively used as a plasticizer for vinyl plastic articles. It has been found to be positive in an NCI rodent bioassay but has generally given negative results in in vitro genotoxicity tests. We therefore decided to test the urine of rats fed [14C]DEHP for mutagenic activity in the Ames Salmonella test. The recovery of radioactivity from the urine of rats dosed with [14C]DEHP was examined by solvent extraction and XAD-2 resin absorption procedures. Both of these procedures were inadequate for quantitative recovery of urinary metabolites required for subsequent mutagenicity testing using the Ames Salmonella/microsome procedure. Recoveries of less than 5% were observed using standard solvent extraction techniques whereas the XAD-2 adsorption technique gave about 67% at high resin/urine ratios. Treatment of the urine with beta-glucuronidase/aryl sulfatase did not affect these recoveries. The direct urine plating procedure represents a viable alternative to the above concentration procedures for this phthalate ester. The effects of L-histidine and the beta-glucuronidase/aryl sulfatase preparation on the background reversion frequencies of the Ames tester strains is discussed.

Excretion and metabolism of di(2-ethylhexyl)phthalate in man

Di-(2-ethylhexyl)phthalate (DEHP) taken orally by two volunteers (30 mg each) was excreted in the urine to the extent of 11 and 15% of dose. After enzymic hydrolysis the urinary metabolites (derivatives of mono (2-ethylhexyl)phthalate) were methylated and identified by g.l.c.-mass spectrometry (C.I.), and the quantitative distribution of conjugated and free metabolites determined. DEHP taken by the same volunteers over a period of four days at doses of 10 mg daily gave no evidence of accumulation; 15 and 25% of the total dose was recovered in the urine.

Kinetics of di-(2-ethylhexyl) phthalate in immature and mature rats and effect on testis

The testicular response of di-(2-ethylhexyl) phthalate (DEHP), as well as the kinetics of DEHP and its primary metabolite mono-(2-ethylhexyl) phthalate (MEHP), were studied in immature and mature rats. After 14 daily oral doses of 1.0 g DEHP/kg body weight to 25, 40 and 60-day-old rats, testicular damage was observed in the youngest age group only. DEHP was not found to any significant extent in the peripheral plasma after an oral dose of 1.0 g DEHP/kg body weight. High plasma levels of MEHP were found, with maximal plasma concentrations ranging from 48 to 152 micrograms/ml. The in vitro plasma protein binding of MEHP was extensive, approximately 98%, in all age groups and no age-related difference in the elimination half-life was observed. The amount of DEHP-derived material excreted in urine was twice as high in 25 as in 60-day-old rats. The mean area under the plasma concentration-time curve of MEHP was also significantly larger in 25 than in 40 and 60-day-old rats. These observations suggest that the extent of absorption, and hence total exposure to MEHP and its metabolites, is higher in young than in more mature rats after oral administration of DEHP. It seems probable that this finding is relevant to the age-related difference in the toxic effects on the testis.

Urinary metabolites of orally administered di-(5-hexenyl) phthalate and di-(9-decenyl) phthalate in the rat

Di-(5-hexenyl)- and di-(9-decenyl) phthalates were administered to male CD rats by gavage. The urinary metabolites retaining the phthalate moiety were identified by chromatographic and mass-spectrometric techniques. Di-(5-hexenyl) phthalate gave rise to epoxide and vicinal diol metabolites not previously seen with phthalic acid esters of saturated alcohols. Neither epoxide nor diol were detected when di-(9-decenyl) phthalate was fed. The distributions of carboxyl-terminated metabolites suggested that somewhat different pathways were followed for the two test compounds. The formation of epoxides from these unsaturated phthalate esters may have relevance to their potential toxicities. Like the metabolites of di-n-butyl phthalate, the metabolites of di-(5-hexenyl) phthalate included glucuronide conjugates; like the metabolites of di-(2-ethylhexyl) phthalate, those of di-(9-decenyl) phthalate did not.

Comparative studies on di-(2-ethylhexyl) phthalate-induced hepatic peroxisome proliferation in the rat and hamster

Young male Sprague-Dawley rats and Syrian hamsters were treated with 25-1000 mg/kg/day di-(2-ethylhexyl) phthalate (DEHP) orally for 14 days. Liver enlargement was observed in both species, the magnitude being greater in the rat than in the hamster. In the rat there was a marked dose-dependent induction of the peroxisomal marker cyanide-insensitive palmitoyl-CoA oxidation and also of carnitine acetyltransferase. Little effect was observed on the mitochondrial markers carnitine palmitoyltransferase and succinate dehydrogenase. Whereas in the rat, increased peroxisomal enzyme activities were observed after treatment with 100 and 250 mg/kg/day DEHP, much less effect was observed in the hamster even after 1000 mg/kg/day DEHP. Parallel morphological investigations demonstrated a greater increase in hepatic peroxisome numbers in the rat than in the hamster. 14C-labeled DEHP was found to be more rapidly hydrolyzed by rat than hamster hepatic and small intestinal mucosal cell preparations and differences were also observed in the absorption and excretion of oral doses of [14C]DEHP. Studies with mono-(2-ethylhexyl) phthalate (MEHP), a primary metabolite of DEHP, and a hypolipidemic drug clofibrate also resulted in a greater increase in hepatic peroxisomal enzymes in the rat compared to the hamster. The results demonstrate that while DEHP, MEHP, and clofibrate induced hepatic peroxisome proliferation in both species, there was a marked species difference in response. Comparative long-term studies in these species may thus help to clarify the role of peroxisome proliferation in the hepatocarcinogenicity of DEHP.

Polar metabolites of di-(2-ethylhexyl)phthalate in the rat

Di-(2-ethylhexyl)phthalate (DEHP) is an important industrial chemical widely used as a plasticizer for vinyl and other plastics. DEHP is extensively metabolized by mammals, different species showing dramatic differences in metabolite distributions. Previous studies of the metabolism in rats led to the suggestion that the enzymatic processes normally associated with omega-, omega-1, alpha-, and beta-oxidation of fatty acids could account for the known metabolites of DEHP found in the urine. Several additional metabolites of DEHP have been identified in the present study. Their formation requires that the initial hydroxylation process be less specific than fatty acid omega- and omega-1 oxidation are thought to be. Furthermore, it is necessary to postulate either that the aliphatic chain of mono-(2-ethylhexyl)phthalate can be oxidized at two sites simultaneously, or that oxidation products can be recycled for a second hydroxylation prior to excretion.

The carcinogenicity of di(2-ethylhexyl) phthalate (DEHP) in perspective

The commonly used plasticizer di(2-ethylhexyl) phthalate (DEHP) was recently tested for chronic toxic potential by incorporation into the diet of rats and mice for approximately 2 yr. Upon reviewing the test results, the sponsoring organization concluded that DEHP was carcinogenic to the rats and mice, as indicated by increased occurrences of liver tumors in the DEHP-exposed animals in comparison to controls. Another group has disagreed with this conclusion, however, citing perceived methodological deficiencies and improper interpretations in the study, and has also suggested that rodents may not be adequate models of human response to DEHP. This communication compares the conduct of the DEHP bioassay favorably with state-of-the-art procedures in animal carcinogenicity testing and documents approval of the study interpretations by several independent peer review groups. The carcinogenic potential of DEHP is placed in perspective by evaluating the evidence for DEHP-induced tumors in rodent species in light of dose response relationships, other biochemical and toxicological effects of DEHP, and its comparative metabolism and disposition in rodent and primate species. A composite analysis of the currently available information indicates that DEHP has been shown to be carcinogenic to rodents in a valid chronic test, indicating that it should be considered as a potential carcinogen in humans, as well. Further experimental inquiry will be required, however, to accurately assess the potential health risks posed to humans by exposure to small amounts of this plasticizer.

Incorporation of radioactivity from labeled Di-(2-ethylhexyl)phthalate into DNA of rat liver in vivo

Di-(2-ethylhexyl)phthalate (DEHP), when fed at high levels in the diet for two years, is reportedly an hepatocarcinogen to rats and mice. Radioactivity from ethylhexyl-labeled, but not from phthalate-labeled, [14C]-DEHP is associated with highly purified DNA from the livers of treated rats and this radioactivity is not accounted for by assumptions of adsorption, intercalation, attachment to RNA or histones, an impurity in the labeled DEHP, or artifactual binding during sample workup. Spontaneous binding of radioactivity to DNA from either ethylhexyl-labeled DEHP or its total urinary metabolites could not be detected. Although rat liver slices generated all of the known metabolites of DEHP in vitro, no binding to DNA occurred. Administration of dual 3H/14C-labeled DEHP to rats yielded liver DNA whose 3H/14C ratio was inconsistent with the attachment of any reasonable multi-carbon fragment from the ethylhexyl portion to the DNA. The observation that roughly 100 times as high a percentage of the 14C administered was found in urea as in total DNA suggests that the 14C entered DNA through carbamyl phosphate, a precursor of both urea and pyrimidine bases. If this is the case, the association of C-1 from the ethylhexyl portion of DEHP with DNA may not involve alteration of the DNA or genetic damage.