Comparative effects of diethylhexyl phthalate or monoethylhexyl phthalate on male mouse and rat reproductive organs

A systematic review on the adverse health effects of di-2-ethylhexyl phthalate

Di (ethylhexyl) phthalate (DEHP) is a global environmental pollutant. This study aims to systematically review the literature on health effects of exposure to DEHP including effects on reproductive health, carcinogenesis, pregnancy outcome, and respiratory system. The literature search was done through Scopus, ISI Web of Science, Google Scholar, PubMed, Medline, and the reference lists of previous review articles to identify relevant articles published to June 2016 in each subject area. The inclusion criteria were as follows: original research, cross-sectional studies, case-control studies, cohort studies, interventional studies, and review articles. Both human and animal studies were included. The search was limited to English language papers. Conference papers, editorials, and letters were not included. The systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Overall, 152 of the 407 papers met the inclusion criteria. We provided an up-to-date comprehensive and critical assessment of both human and animal studies undertaken to explore the effects of DEHP. It revealed that in experimental studies, exposure to DEHP mainly targeted the reproductive, neurodevelopment, and respiratory systems. Human studies reported that exposure to this contaminant had carcinogenic effects and influenced neurodevelopment in early life. This systematic review underscored the adverse health effects of DEHP for pregnant women and the pediatric age group. It summarizes different response of humans and experimental animals to DEHP exposure, and some suggested underlying mechanisms.

Effects of mono-(2-ethylhexyl) phthalate (MEHP) on chicken germ cells cultured in vitro

In recent decades, many toxicological tests based on in vivo or in vitro models, mainly from mammalian (rat-mouse) and fish species, were used to assess the risks raised by contact or ingestion of molecules of pharmaceutical, agricultural, or natural origin. But no, or few, in vitro tests using other non-mammalian models such as bird have been explored despite their advantages: the embryonic gonads of birds have a high plasticity of development sensitive to estrogen, and sperm production is nearly two times faster than in rodents. Hence, we have established an in vitro culture of germ cells and somatic cells from chicken post-natal testis, and we have evaluated the sensitivity against the endocrine disruptor compound mono-(2-ethylhexyl) phthalate (MEHP) in comparison to previous studies using rodent and human models. After 96 h of exposure in presence of 10 μM MEHP, chicken seminiferous tubules cultures present a structural alteration, a reduction in cell proliferation and in germ cells population. Apoptosis of germ and somatic cells increases in presence of 1 μM MEHP. Furthermore, MEHP does not affect inhibin B and lactate production by Sertoli cells. These results are in accordance with previous studies using rat, mice, or human culture of testicular cells and in similar range of exposures or even better sensitivity for some "end-points" (biological parameters). In conclusion, the establishment of this postnatal testicular cells culture could be considered as an alternative method to in vivo experiments frequently used for evaluating the impact on the terrestrial wildlife species. This method could be also complementary to mammal model due to the limiting number of animals used and its elevated sensitivity.

Fetal mouse phthalate exposure shows that Gonocyte multinucleation is not associated with decreased testicular testosterone

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

The Toxicology of Ligands for Peroxisome Proliferator-Activated Receptors (PPAR)

Peroxisome proliferator-activated receptors (PPARs) are ligand activated transcription factors that modulate target gene expression in response to endogenous and exogenous ligands. Ligands for the PPARs have been widely developed for the treatment of various diseases including dyslipidemias and diabetes. While targeting selective receptor activation is an established therapeutic approach for the treatment of various diseases, a variety of toxicities are known to occur in response to ligand administration. Whether PPAR ligands produce toxicity via a receptor-dependent and/or off-target-mediated mechanism(s) is not always known. Extrapolation of data derived from animal models and/or in vitro models, to humans, is also questionable. The different toxicities and mechanisms associated with administration of ligands for the three PPARs will be discussed, and important data gaps that could increase our current understanding of how PPAR ligands lead to toxicity will be highlighted.

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

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

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.

Testicular toxicity and reduced Sertoli cell numbers in neonatal rats by di(2-ethylhexyl)phthalate and the recovery of fertility as adults

Neonatal and adult rats (1, 2, 3, 6, and 12 weeks of age) were given five daily oral doses of di(2-ethylhexyl) phthalate (DEHP) (0, 10, 100, 1000, 2000 mg/kg) and histological changes in the testes were examined 24 hr after the last dose. Relative testis weights were reduced at doses of 1000 mg/kg in 1, 2, 3, and 6-week-old but not in 12-week-old rats, while doses of 2000 mg/kg were fatal to suckling rats and caused decreased relative testis weight but not death in 6- and 12-week-old rats. In neonatal rats (1 week old), DEHP (1000 mg/kg) caused a 35% decrease in Sertoli cell numbers while 2- and 3-week-old rats showed losses of spermatocytes but not of Sertoli cells. The 6- and 12-week-old rats showed loss of both spermatids and spermatocytes at 1000 and/or 2000 mg/kg. Total testicular zinc concentrations were decreased in 12-week-old but not in suckling (3-week) or weaned (6-week) rats. The results support the hypothesis that the Sertoli cell is the primary testicular target of phthalate ester toxicity since effects were observed at an age when only Sertoli cells were present. Fertility was assessed in mating trials in adult male rats after neonatal exposure to DEHP on Days 6-10. Although Sertoli cell number was reduced 24 hr after the last dose, the numbers were normal at 6 and 13 weeks of age. However, at 6 weeks there was a dose-related decrease in maturation of the spermatids in the tubules. There were no consistent changes in fertility, implantation rate, or numbers of live fetuses in untreated females mated with the DEHP-treated males. However, there were decreases in testis weight and testicular spermatid numbers at 13 and 19 weeks but not at 11, 12, 16, or 23 weeks of age. Therefore, a loss of Sertoli cells due to DEHP exposure neonatally did not affect the fertility of the rats as adults, but may have caused subtle effects on sperm production.

Di-(2-ethylhexyl)-phthalate as plasticizer in PVC respiratory tubing systems: indications of hazardous effects on pulmonary function in mechanically ventilated, preterm infants

Several PVC medical devices contain the plasticizer Di-(2-ethylhexyl)-phthalate (DEHP) in high concentration. Taken systematically DEHP only has minor toxic effects in the human organism. In three preterm infants artificially ventilated with PVC respiratory tubes unusual lung disorders resembling those observed in hyaline membrane disease, verified both clinically and radiologically, were observed during the fourth week of life. It was assumed that these lung disorders were causally related to the exposure to high doses of DEHP, which was released from the walls of the respiratory tubes. DEHP was found in the lung tissue of one patient who died of pneumothorax soon after birth after being artificially ventilated. It is strongly recommended that for disposable PVC respiratory devices the plasticizer DEHP should be used with more restrictions.

A review of the subchronic toxicity of butyl benzyl phthalate

This review compares the subchronic toxicity of butyl benzyl phthalate (BBP) across several species. Data from the published literature as well as previously unpublished studies sponsored by Monsanto are presented. BBP-induced toxicity occurs only at relatively high levels of exposure and is dependent on the species, age and strain of test animals used. These factors should be considered in extrapolating findings from animal toxicology studies to humans when assessing the safety of BBP.

Influence of dietary zinc on di(2-ethylhexyl)phthalate-induced testicular atrophy and zinc depletion in adult rats

Groups of 48 adult male F344 rats were maintained on synthetic diets containing 20 ppm (normal), 2 ppm (low), or 200 ppm (high) zinc. After 1 week of acclimation to the various diets, groups of 12 rats from each dietary regimen were gavaged for 13 consecutive days with 0.0 (vehicle), 0.33, 1.0, or 3.0 g/kg di(2-ethylhexyl)phthalate (DEHP). These were selected as relatively nontoxic, mildly toxic, and moderately toxic doses for producing testicular injury in adult male rats. At termination on the 14th day, body weight gain was reduced by 3.0 g/kg DEHP dose in the normal and low-zinc diet groups but not in the high-zinc diet group. The low-zinc diet alone reduced body weight gain, independent of DEHP treatment. DEHP had no perceptible effects on the weights of testis, seminal vesicle, prostate, or epididymis from rats maintained on normal- or high-zinc diets, but reduced the weights of all of these organs from animals on the low-zinc diet in a dose-dependent manner. Lactate dehydrogenase activity, total and free sulfhydryl contents, and zinc concentrations in testes were also reduced, and testicular degeneration was induced by DEHP in the low-zinc diet groups. In contrast, dose-dependent liver enlargement and hypolipidemia (reduction of serum cholesterol and triglyceride concentrations) were produced by equivalent doses of DEHP in all of the three zinc groups. The selectively enhanced susceptibility of adult male F344 rats on a zinc deficient diet to the gonadotoxic effects of DEHP supports the hypothesis that testicular zinc depletion is causally related to the ensuing testicular and accessory sex organ atrophies. Other biological effects of DEHP (e.g., hypolipidemia, hepatomegaly) appear to occur independent of zinc homeostasis.

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

The disposition 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 micrograms/ml DEHP and 63.2 +/- 8.7 micrograms/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 14C-DEHP 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 micrograms/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.

Adverse effects of butyl benzyl phthalate on the reproductive and hematopoietic systems of male rats

A 14-day dietary study was conducted in adult, male, Fischer 344 rats at levels of 0.0, 0.625, 1.25, 2.5 and 5.0% butyl benzyl phthalate (BBP) to evaluate potential effects of this plasticizer on the male reproductive and hematopoietic systems. Total body, thymus, testis, epididymis, prostate and seminal vesicle weights were reduced in the 2.5% and 5% BBP dose groups, while pituitary weight was unaffected. Histological evaluations revealed dose-dependent atrophy of the testis, prostate and seminal vesicles at 2.5% and 5%, atrophy of the thymus and epididymis at 5%, and the presence of immature sperm cells in the tubular lumens and necrosis of the tubular epithelium in the epididymis at 2.5% and 5% BBP. Plasma testosterone concentration was decreased at 5%, while follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were increased at 2.5% and 5.0% BBP. The circulating components of blood, and clotting times (prothrombin time, activated partial thromboplastin time), were unaffected although bone marrow cellularity was reduced at 2.5% and 5%. Changes in non-reproductive organs included enlargement of liver and kidneys, thymic atrophy and associated morphological abnormalities in these organs. These data indicate a direct toxic effect of BBP on the testis with secondary effects on other reproductive organs. Pituitary and hypothalamic responses did not appear to be affected. The reduced bone marrow cellularities suggest that prolonged exposures to BBP could affect circulating blood components or compromise clotting ability.

Biological effects of di-(2-ethylhexyl) phthalate and other phthalic acid esters

Esters of o-phthalic acid are widely distributed in the ecosystem. The phthalate acid esters (PAE's) are used as plasticizers in the manufacture of polyvinylchlorides. They are also used as solvents in certain industrial processes and as vehicles for pesticides. The PAE's are used in enormous quantities for a variety of industrial uses in the formulation of plastics. While there are a number of important PAE's, di-ethylhexyl phthalate has perhaps been used the most extensively in the formulation of plastics used in medical devices and blood bag assemblies. The metabolism, biodistribution and excretion varies to some extent among the various PAE's. There are species differences with respect to the metabolism of the PAE's. The route of administration, and the level and length of exposure, are known to affect the toxicological profile of the various PAE's. There is little evidence of bioaccumulation of the various PAE's, and only at very large doses have there been reports of overt toxicity. Evidence for the carcinogenicity of certain PAE's apparently is related to prolonged exposure to high levels.

Comment on the carcinogenic potential of di(2-ethylhexyl) phthalate

Analysis of the carcinogen bioassay of di(2-ethylhexyl) phthalate (DEHP) has shown that the designated maximum tolerated dose was exceeded in the low- and high-dose groups of male rats, in the high-dose group of female rats, and in the low- and high-dose groups of female mice. Significant differences in tumor incidence among small populations of laboratory animals within the testing facility further confounded interpretation of the bioassay. Critical data on food consumption, nutritional status, clinical signs, clinical pathology, and intestinal microorganisms are lacking. This review concludes that because of major deficiencies in the available data, the studies cannot be interpreted as showing a carcinogenic effect due to DEHP alone. Epigenetic mechanisms to explain the biologic effects are examined.