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.     

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.     

Quantitative evaluation of alternative mechanisms of blood and testes disposition of di(2-ethylhexyl) phthalate and mono(2-ethylhexyl) phthalate in rats.

Di(2-ethylhexyl) phthalate (DEHP), a commercially important plasticizer, induces testicular toxicity in laboratory animals at high doses. After oral exposure, most of the DEHP is rapidly metabolized in the gut to mono(2-ethylhexyl) phthalate (MEHP), which is the active metabolite for induction of testicular toxicity. To quantify the testes dose of MEHP with various routes of exposure and dose levels, we developed a physiologically based pharmacokinetic (PBPK) model for DEHP and MEHP in rats. Tissue:blood partition coefficients for DEHP were estimated from the n-octanol: water partition coefficient, while partition coefficients for MEHP were determined experimentally using a vial equilibration technique. All other parameters were either found in the literature or estimated from blood or tissue levels following oral or intravenous exposure to DEHP or MEHP. A flow-limited model failed to adequately simulate the available data. Alternative plausible mechanisms were explored, including diffusion-limited membrane transport, enterohepatic circulation, and MEHP ionization (pH-trapping model). In the pH-trapping model, only nonionized MEHP is free to become partitioned into the tissues, where it is equilibrated and trapped as ionized MEHP until it is deionized and released. All three alternative models significantly improved predictions of DEHP and MEHP blood concentrations over the flow-limited model predictions. The pH-trapping model gave the best predictions with the largest value of the log likelihood function. Predicted MEHP blood and testes concentrations were compared to measured concentrations in juvenile rats to validate the pH-trapping model. Thus, MEHP ionization may be an important mechanism of MEHP blood and testes disposition in rats.     

Toxicokinetic relationship between di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate in rats

The toxicokinetic relationship between di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP), a major metabolite of DEHP, was investigated in Sprague-Dawley rats orally treated with a single dose of 14C-DEHP. Urinary excretion of total 14C-DEHP and of its metabolites was followed by liquid scintillation counting (LSC). Concentrations of DEHP and MEHP were determined 6, 24, and 48 h after treatment in rat serum and 6, 12, 24, and 48 h after treatment in urine by high-performance liquid chromatography (HPLC). After 24 h, peak concentrations of MEHP in both urine and serum were observed in animals treated with 40, 200, or 1000 mg DEHP/kg. HPLC showed that general toxicokinetic parameters, such as Tmax (h), Cmax (microg/ml), Ke (1/h), and AUC (microg-h/ml/) were greater for MEHP than DEHP in both urine and serum. In contrast, the half-lives (t1/2 [h]) of DEHP were greater than those of MEHP. The AUC ratios between DEHP and MEHP were relatively smaller in serum than in urine, suggesting the important role of urinary DEHP data for exposure assessment of DEHP. The toxicokinetic relationship between DEHP and MEHP in rats suggests that DEHP exposure assessment should be based on DEHP and MEHP in urine and serum for risk assessment applications.     

Atropine inhibition of the cardiodepressive effect of mono(2-ethylhexyl)phthalate on human myocardium

Di(2-ethylhexyl)phthalate (DEHP) is a commonly used plasticizer in polyvinylchloride (PVC)-derived plastic. Mono(2-ethylhexyl)phthalate (MEHP), the major metabolite of DEHP, had a reversible, concentration-dependent (15-200 micrograms/ml) negative inotropic effect on a human in vitro atrial trabecular isometric preparation with an IC50 of 85 micrograms/ml. When atropine (22-32 micrograms/ml) was included in the atrial preparation the IC50 was shifted to greater than 120 micrograms/ml, suggesting that MEHP acts in part through the cholinergic receptors.     

Effect of sterilization process on the formation of mono(2-ethylhexyl)phthalate from di(2-ethylhexyl)phthalate

The risk assessment of di(2-ethylhexyl)phthalate (DEHP) migrating from polyvinyl chloride (PVC) medical devices is an important issue. Many studies have been conducted to determine the level of DEHP migration. A recent report has indicated that DEHP in blood bags is hydrolyzed by esterase into mono(2-ethylhexyl)phthalate (MEHP). However, MEHP is thought to be even more toxic than the parent compound. Therefore, a method for the simultaneous determination of DEHP and MEHP was developed. The limits of quantification (LOQs) of DEHP and MEHP were 2.5 and 0.75 ng/ml, respectively. In this study, the effect of sterilization process on the levels of DEHP and MEHP migration was investigated. The level of migration of DEHP from gamma(gamma)-ray sterilized PVC sheet was low compared with that of the unsterilized control. By contrast, the level of MEHP migration from the gamma-ray sterilized PVC sheet was high compared with that of the unsterilized control. In addition, a high content of MEHP was found in the gamma-ray sterilized PVC sheet.     

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.     

Distribution and elimination of di-2-ethylhexyl phthalate (DEHP) and mono-2-ethylhexyl phthalate (MEHP) after a single oral administration of DEHP in rats

The distribution and elimination of di-2-ethylhexyl phthalate (DEHP) and mono-2-ethylhexyl phthalate (MEHP) after a single oral administration of DEHP (25 mmol/kg) were studied. A gas-liquid Chromatographic method was used for the simultaneous determination of MEHP and DEHP. The compounds were extracted with methylene chloride and the monoester was alkylated to the hexyl derivative by solid-liquid phase transfer catalysis in methylethyl ketone. The coefficients of variation of this method for determination of DEHP and MEHP were 8.3% and 11.4% respectively. The concentration of DEHP and MEHP in blood and tissues increased to maximum within 6–24 h after dosing, while the highest levels observed in the heart and lungs occurred within 1 h. At 6 h after administration, the highest ratio of MEHP/DEHP (mol%) were recorded in testes (210%) while the other tissues exhibited less than 100%. MEHP disappeared exponentially with t _1/2 values ranging from 23 to 68 h; DEHP t _1/2 ranged from 8 to 156 h and the t _1/2 values of MEHP in several tissues were slightly longer than DEHP. The t _1/2 values in blood were 23.8 h and 18.6 h for MEHP and DEHP, respectively.     

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.     

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.     

Kinetics of orally administered di(2-ethylhexyl) phthalate and its metabolite,mono(2-ethylhexyl) phthalate,in male pigs

Di(2-ethylhexyl) phthalate (DEHP) is used as a plastic softener in the polymer industry and is widespread in medical devices. DEHP has been incriminated as an endocrine-disrupting chemical, and the effects of DEHP in various species have included disturbances in the reproductive system. The effects of the chemical have varied, depending upon exposure routes and species. This study was performed in order to characterise the kinetics of DEHP and its metabolite mono(2-ethylhexyl) phthalate (MEHP) in the young male pig, an omnivore model-species for research in reproductive toxicology. Eight pigs were given 1000 mg DEHP/kg bodyweight by oral gavage. The concentrations of DEHP and MEHP were then measured in the plasma and tissues of the pigs at different time points after administration. There was no consistent rise above contamination levels of concentrations of DEHP in the plasma of the pigs. However, the metabolite MEHP reached the systemic blood circulation. The half-life of MEHP in the systemic blood circulation was calculated to be 6.3 h. Absorption from the intestine was biphasic in six of the eight pigs and the mono-exponential elimination-phase started 16 h after the after the administration of DEHP. To conclude, MEHP consistently reaches the systemic circulation in the pig when DEHP is administered orally. The kinetic pattern of the parent substance on the other hand is more difficult to characterise.     

Assessment of the teratogenicity of di(2-ethylhexyl)phthalate and mono(2-ethylhexyl)phthalate in mice

Di(2-ethylhexyl)phthalate (DEHP) and mono(2-ethylhexyl)phthalate (MEHP) were administered PO or IP to pregnant ICR mice at varying doses on days 7, 8, and 9 of gestation. In groups given DEHP orally, resorptions and malformed fetuses increased significantly at 1,000 mg/kg. Fetal weights were also significantly suppressed. Anterior neural tube defects (anencephaly and exencephaly) were the malformations most commonly produced. No teratogenic effects were revealed by IP doses of DEHP and PO or IP doses of MEHP, although high doses were abortifacient and lethal to pregnant females. Thus DEHP is highly embryotoxic and teratogenic in mice when given PO but not IP. The difference in metabolism, disposition, or excretion by the route of administration may be responsible for the difference in DEHP teratogenicity. Although MEHP is a principal metabolite of DEHP and is several times more toxic than DEHP to adult mice, it seems that MEHP and its metabolites are not teratogenic in ICR mice.     

Induction of propranolol metabolism in isolated rats hepatocytes treated by di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP).

Blood lines of polyvinyl chloride (PVC) for hemodialysis usually contain di(2-ethylhexyl) phthalate (DEHP) as a plasticizer. Previous studies show that 1 mg/kg of this plasticizer can leach into the blood during one dialysis session. It is rapidly metabolized in the liver. Mono(2-ehtylhexyl) phthalate (MEHP), its main metabolite can be detected as well. After oral administration to rodents, both compounds caused a variety of adverse biological effects such as testicular atrophy, peroxisome proliferation and hepatic peroxisomal enzyme induction. Male wistar rats were treated intraperitoneally by DEHP and MEHP using twice the dose of that involved in human exposure during a dialysis session. Propranolol metabolism by hepatocytes was investigated after fresh isolation from treated and untreated rats by means of reverse phase HPLC. The choice of propranolol as a substrate was made because of its rather quick liver metabolisation. Phenobarbital was chosen in the study as a reference of enzymatic inducer to evaluate the inducing effect of DEHP and MEHP. Propranolol was metabolized by the hepatocytes of both treated and untreated rats. Hepatocytes isolated from rats treated by phenobarbital, MEHP and DEHP were shown to have a higher speed constant of metabolism indicating a rapid metabolism of propranolol. Under these conditions, in fact, propranolol metabolisation was found to be respectively 6, 2.7, 2 times faster than the propranolol metabolisation of untreated rats. The hypothesis that DEHP and MEHP are enzymatic inducers, particularly cytochrome P450 (CYP) inducers of the xenobiotics metabolism on the intact liver after IP administration has become been found to be valid. The results obtained in this study confirm the value of isolated hepatocytes as an in vivo drug metabolism predictive model.     

Mono(2-ethylhexyl)phthalate exhibits genotoxic effects in human lymphocytes and mucosal cells of the upper aerodigestive tract in the comet assay

Phthalic acid esters such as di(2-ethylhexyl)phthalate (DEHP) are widely used as plasticizers in PVC products manufactured for commercial, medical, and consumer purposes. Humans are exposed to phthalates originating, e.g., from blood storage bags, tubing materials, and from food-wrapping. While xenoestrogenic and chronic toxic effects of phthalates have been extensively discussed, there is little data on genotoxic effects in human cells. The alkaline comet assay was used to detect single-strand breaks and alkali labile sites of DNA after incubation of human nasal mucosal cells (n = 11) and peripheral lymphocytes (n = 11) with mono(2-ethylhexyl)phthalate (MEHP), the principal hydrolysis product of DEHP. MEHP showed a dose-dependent enhancement of DNA migration both in human mucosal cells and in lymphocytes. This effect indicates a genotoxic potential of MEHP in human mucosal cells. It confirms previous data obtained on the effect of MEHP on lymphocytes.     

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.     

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

The dispositon of di-(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) was studied in the rat. Three hours after a single oral dose of DEHP (2.8 g/kg), plasma concentrations of 8.8±1.7 g/ml DEHP and 63.2±8.7 g/ml MEHP were reached. MEHP levels declined with a half-life of 5.2±0.5 h. The ratio of the area under the plasma concentration-time curve of MEHP to that of DEHP was 16.1±6.1. When ¹⁴CDEHP was administered, 19.3±3.3% of the radioactivity was excreted in the urine within 72 h, the rest being excreted in the faeces. The urinary excretion rate of total radioactivity declined with a half-life of 7.9±0.5 h. Single administration of MEHP (0.4 g/kg) resulted in plasma concentrations of 84.1±14.9 g/ml 3 h after dosing; the half-life of MEHP was 5.5±1.1 h. Multiple dosing with DEHP (2.8 g/kg/day) for 7 consecutive days produced no accumulation of DEHP or MEHP in plasma.     

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 and (-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.     

Effects of di-(2-ethylhexyl) phthalate and five of its metabolites on rat testis in vivo and in in vitro

In an attempt to establish which compound or compounds are responsible for the testicular damage observed after administration of di-(2-ethylhexyl) phthalate (DEHP) in rats, the effects of the parent compound and five of its major metabolites (mono-(2-ethylhexyl) phthalate (MEHP), 2-ethylhexanol (2-EH), mono-(5-carboxy-2-ethylpentyl) phthalate, mono-(2-ethyl-5-oxohexyl) phthalate and mono-(2-ethyl-5-hydroxyhexyl) phthalate) were investigated in vivo and in vitro. The concentrations of MEHP and the three MEHP-derived metabolites in plasma were determined after single and multiple oral doses of DEHP. The plasma concentrations and areas under the plasma concentration-time curves (AUC's) of each of the MEHP-derived metabolites were considerably lower than those of MEHP both after single and after repeated administration of 2.7 mmol of DEHP/kg body weight. The mean elimination half-life of MEHP was significantly shorter in animals given repetitive doses than in those given a single dose, but there was no statistically significant difference between the mean AUC values. No testicular damage was observed in young rats given oral doses of 2.7 mmol of DEHP or 2-EH/kg body weight daily for five days. In animals which received corresponding doses of MEHP the number of degenerated spermatocytes and spermatids was increased, whereas no such effects were found in animals given the MEHP-derived metabolites. MEHP was also the only compound that enhanced germ cell detachment from mixed primary cultures of Sertoli and germ cells.     

Identification of the proximate peroxisome proliferator(s) derived from di(2-ethylhexyl) phthalate

A primary rat hepatocyte culture system was utilized to determine the proximate peroxisome proliferator(s) derived from di(2-ethylhexyl) phthalate (DEHP). DEHP was administered to rats and the urinary metabolites were identified and isolated. The major metabolites were those resulting from initial omega- or omega - 1-carbon oxidation of the mono(2-ethylhexyl) phthalate (MEHP) moiety. These metabolites, together with MEHP and 2-ethylhexanol, were added to primary rat hepatocyte cultures and the effect on peroxisomal enzyme activity was determined. The omega-carbon oxidation products [mono(3-carboxy-2-ethylpropyl) phthalate (I) and mono(5-carboxy-2-ethylpentyl) phthalate (V)] and 2-ethylhexanol produced little or no effect on CN- -insensitive palmitoyl-CoA oxidation (a peroxisomal marker). MEHP and the omega - 1-carbon oxidation products [mono-(2-ethyl-5-oxohexyl) phthalate (VI) and mono(2-ethyl-5-hydroxyhexyl) phthalate (IX)] produced a large (7- to 11-fold) induction of peroxisomal enzyme activity. Similar structure-activity relationships were observed for the induction of cytochrome P-450-mediated lauric acid hydroxylase and increase in cellular coenzyme A content. This identification of the proximate proliferators will aid in the elucidation of the mechanism by which DEHP causes proliferation of peroxisomes in the rodent liver. Oral administration of MEHP (150 or 250 mg/kg) to male guinea pigs did not produce hepatic peroxisome proliferation. Addition of MEHP (0 to 0.5 mM) or one of the "active" proliferators in the rat (metabolite IX, 0 to 0.5 mM) to primary guinea pig hepatocyte cultures also failed to produce an induction of peroxisomal beta-oxidation. Possible reasons for this species difference are discussed.     

High-throughput determination of mono- and di(2-ethylhexyl)phthalate migration from PVC tubing to drugs using liquid chromatography-tandem mass spectrometry

The risk assessment of di(2-ethylhexyl) phthalate (DEHP) that migrated from polyvinyl chloride (PVC) medical devices is an important issue for hospitalized patients. Many studies have been conducted to determine the level of DEHP migration. A recent report has indicated that DEHP in blood bags was hydrolyzed by esterase to mono(2-ethylhexyl) phthalate (MEHP). Therefore, a method for the simultaneous determination of DEHP and MEHP was developed. The migration of DEHP and MEHP from PVC tubing to drugs was examined. Although we detected MEHP in the drugs, we found no enzymatic activity involved in the migration process. Some reports have indicated that hydrolysis may have occurred during sterilization by autoclaving. However, we did not perform any heat treatment. It is speculated that the MEHP migrated directly from the PVC tubing. The simultaneous determination of DEHP and MEHP is required for risk assessment, as MEHP may be even more toxic than the parent compound.