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

Low-dose exposure to di-(2-ethylhexyl) phthalate (DEHP) increases susceptibility to testicular autoimmunity in mice

Exposure to di-(2-ethylhexyl) phthalate (DEHP) induces spermatogenic disturbance (SD) through oxidative stress, and affects the immune system by acting as an adjuvant. Recently, we reported that in mice, a low dose of DEHP, which did not affect spermatogenesis, was able to alter the testicular immune microenvironment. Experimental autoimmune orchitis (EAO) can be induced by repeated immunization with testicular antigens, and its pathology is characterized by production of autoantibodies and SD. In the present study, we investigated the effect of a low-dose DEHP on the susceptibility of mice to EAO. The exposure to DEHP-containing feed (0.01%) caused a modest functional damage to the blood-testis barrier (BTB) with an increase in testicular number of interferon gamma (IFN-γ)-positive cells and resulted in the production of autoantibodies targeting haploid cells, but did not affect spermatogenesis. While only single immunization with testicular antigens caused very mild EAO, the concurrent DEHP exposure induced severe EAO with significant increases in number of interferon gamma-positive cells and macrophages, as well as lymphocytic infiltration and serum autoantibody titer accompanied by severe SD. To summarize, the exposure of mice to the low-dose DEHP does not induce significant SD, but it may cause an increase in IFN-γ positive cells and modest functional damage to the BTB in the testis. These changes lead to an autoimmune response against haploid cell autoantigens, resulting in increased susceptibility to EAO.

Beneficial role of celery oil in lowering the di(2-ethylhexyl) phthalate-induced testicular damage

Di(2-ethylhexyl) phthalate (DEHP), the most abundant phthalate in the environment, is known to be a reproductive toxicant. Considering the therapeutic significance of medicinal plants, this study was conducted to evaluate the effects of administration of celery oil on DEHP-induced testicular toxicity. The experiment was carried out for 8 weeks on 36 male rats that were divided equally into six groups. Group 1 was kept as normal control (given vehicle), while rats of group 2 were administered orally 200 mg/kg/day of celery oil. Groups 3 and 5 were orally given 500 and 1000 mg DEHP/kg/day, respectively. Groups 4 and 6 were treated with similar doses of DEHP as in groups 3 and 5 plus celery oil (200 mg/kg/day). Body and testicular weights, sperm parameters, serum hormones (testosterone, follicle-stimulating hormone, luteinizing hormone and estradiol), antioxidant enzymes (superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT)) and expression of cytochrome P450 aromatase (CYP19) messenger RNA (mRNA) were investigated at the end of 8th week. Treatment with DEHP alone resulted in a significant decrease in body and testicular weights, sperm parameters and serum hormone levels when compared with control. On the other hand, testicular antioxidant enzymes showed a significant dose-dependent increase. The expression of CYP19 mRNA was significantly reduced by increasing the doses of DEHP. Administration of celery oil along with DEHP partially prevented the decrease in body and testicular weights and enhanced epididymal sperm count, serum hormone levels and the expression of CYP19 mRNA along with diminution in the activities of SOD, GPx and CAT enzymes. The obtained results showed that the celery improved the testicular alterations induced by DEHP in albino rats.

Use of the rat postimplantation embryo culture to assess the embryotoxic potency within a chemical category and to identify toxic metabolites

The implementation of in vitro alternatives in the safety evaluation of chemicals in the animal intensive area of reproductive toxicity testing is highly desirable, but has been limited by issues around predictivity and applicability domains. The validation of alternatives may gain from a category approach, in which, rather than validating a test for the universe of chemicals, its predictive value is assessed for each class of chemicals for which the test represents relevant end point(s). We studied the embryotoxicity in rodent postimplantation whole embryo culture (WEC) of a series of phthalates and their metabolites. Phthalate diesters are widely applied industrial chemicals, their monoester derivatives being considered as their embryotoxic metabolites. The relative in vitro potency of three out of four monophthalates was found to mimick that of corresponding diphthalates tested in vivo. The phthalate that deviated from this ranking, monoethylhexylphthalate (MEHP), showed a relatively high in vitro toxicity as compared to in vivo data. This deviation could be explained through kinetic differences among phthalates, as shown between MEHP and monobutylphthalate. In addition, in vitro testing of specific secondary MEHP metabolites showed that they were all less potent than MEHP. This finding confirmed that MEHP in vitro embryotoxicity is most likely the best correlate to DEHP in vivo embryotoxicity. This study shows that a category approach in the assessment of the validation of in vitro alternatives is feasible, and can be improved when kinetic considerations are taken into account.

Short-term effects of di-(2-ethylhexyl) phthalate on testes, liver, kidneys and pancreas in mice

AIM

To determine the biochemical effect of di-(2-ethylhexyl) phthalate (DEHP) on testes, liver, kidneys and pancreas on day 10 in the process of degeneration of the seminiferous epithelium.

METHODS

Diets containing 2% DEHP were given to male Crlj:CD1(ICR) mice for 10 days. The dose of DEHP was 0.90 +/- 0.52 mg/mouse/day. Their testes, livers, kidneys and pancreata were examined for detection of mono-(2-ethylhexyl) phthalate (MEHP), nitrogen oxides (NOx) produced by peroxidation of nitric oxide (NO) with free radicals, and lipid peroxidation induced by the chain reaction of free radicals.

RESULTS

Histological observation and serum analysis showed the presence of severe spermatogenic disturbance, Leydig cell dysfunction, liver dysfunction and dehydration. Unexpectedly, the concentration of MEHP in the testes was extremely low compared with that in the liver. However, the concentration of the NOx in the testes was as high as the hepatic concentration. Furthermore, free radical-induced lipid peroxidation was histochemically detected in the testes but not in the liver.

CONCLUSION

The results indicate that DEHP-induced aspermatogenesis is caused by the high sensitivity of the testicular tissues to MEHP rather than the specific accumulation or uptake of circulating MEHP into the testes.

Male reproductive toxicity of four bisphenol antioxidants in mice and rats and their estrogenic effect

Male mice and rats were fed a diet containing four bisphenol antioxidants, 2,2'-methylenebis(4-ethyl-6-tert-butylphenol) (ME), 2,2'-methylenebis(4-methyl -6-tert-butylphenol) (MM), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol) (BM), or 4,4'-thiobis(3-methyl-6-tert-butylphenol) (TM) at levels of 0.06-0.25% for 2 months. BM and TM decreased epididymal, seminal vesicular, prostate and preputial weights, and injured seminiferous tubules in mice in a dose-dependent fashion. BM and TM also reduced sex accessory organ weights and sperm production capacity in rats, but MM and ME were more toxic to rats than BM and TM. ME and MM did not bind ERalpha up to 10(-3) M, while BM and TM competitively bound ERalpha against beta-estradiol (E2). Fifty percent inhibitory concentrations (IC50 s) of BM, TM, and bisphenol A (positive control) against E2-binding were 7.3 x 10(-6) M, 1.8 x 10(-5) M, and 1.4 x 10(-5) M, respectively. When ovariectomized (OVX) mice were sc administered TM at doses of 60 and 300 mg/kg/day for 4 days, or when OVX mice were fed BM in the diet at a level of 0.25% for 2 months, uterine weight was significantly increased. These results suggest that BM and TM are weakly toxic, possibly through an estrogenic mechanism to male reproductive organs in mice as well as rats, while MM and ME may be the direct testicular toxins in rats but not mice.

Di-(2-ethylhexyl) phthalate induces severe aspermatogenesis in mice, however, subsequent antioxidant vitamins supplementation accelerates regeneration of the seminiferous epithelium

Di-(2-ethylhexyl) phthalate (DEHP), now regarded as an endocrine disruptor, can experimentally induce spermatogenic disturbance in laboratory animals. Our previous study demonstrated that antioxidant vitamins (vitamins C and E) supplementation during DEHP-treatment significantly protected the rat seminiferous epithelium from DEHP-gonadotoxicity. In the present study, we gave these antioxidant vitamins to mice already having fully developed aspermatogenesis because of DEHP to determine whether or not the vitamins can cure the injured seminiferous epithelium. CD-1 male mice were fed on a DEHP-containing diet for 15 days and then fed on the DEHP-free normal diet with or without supplementation of vitamins C and E in drinking water for another 50 days. The results showed that severe aspermatogenesis was induced by the DEHP-treatment but that the damaged seminiferous epithelium spontaneously recovered whether the vitamins were provided or not. This indicates that the DEHP-induced aspermatogenesis was reversible. However, the supplementation of antioxidant vitamins significantly accelerated regeneration of the injured seminiferous epithelium, suggesting that the vitamins have a therapeutic effect on DEHP-induced aspermatogenesis.

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.

Role of oxidative stress in germ cell apoptosis induced by di(2-ethylhexyl)phthalate

Phthalate esters have been used extensively as plasticizers of synthetic polymers. Recent studies have revealed that these esters induce atrophy of the testis, although its pathogenesis remains unknown. The present study describes the possible involvement of oxidative stress in the pathogenesis of atrophy of the rat testis induced by di(2-ethylhexyl)phthalate (DEHP). Biochemical and immunohistochemical analysis revealed that oral administration of DEHP increased the generation of reactive oxygen species, with concomitant decrease in the concentration of glutathione and ascorbic acid in the testis, and selectively induced apoptosis of spermatocytes, thereby causing atrophy of this organ. Oxidative stress was selectively induced in germ cells, but not in Sertoli cells, treated with mono(2-ethylhexyl)phthalate (MEHP), a hydrolysed metabolite of DEHP. Furthermore, MEHP selectively induced the release of cytochrome c from mitochondria of the testis. These results indicate that oxidative stress elicited by MEHP principally injured mitochondrial function and induced the release of cytochrome c, thereby inducing apoptosis of spermatocytes and causing atrophy of the testis.

Comparative effects of phthalate monoesters on gap junctional intercellular communication and peroxisome proliferation in rodent and primate hepatocytes

Several phthalate esters, compounds used as plasticizers in a variety of commercial products, have been shown to induce hepatic tumors in rodents. In this study, the comparative effects of phthalate monoesters on inhibition of gap junctional intercellular communication and induction of peroxisomal beta-oxidation were assessed in primary cultured hepatocytes from rats, mice, hamsters, cynomolgus monkeys, and humans. A human liver cell line was also utilized. Eight monoesters examined included mono-2-ethylhexyl phthalate (MEHP), mono-n-octyl phthalate (MNOP), mono-isononyl phthalate (MINP, 3 types, -1, -2, and -3), mono-isoheptyl phthalate (MIHP), mono-isodecyl phthalate (MIDP), and mono-(heptyl, nonyl, undecyl) phthalate (M711P). Gap junctional intercellular communication was measured 4 and 24 h after treatment by lucifer yellow dye coupling. Gap junctional intercellular communication was inhibited in rat and mouse hepatocytes by all eight monoesters in a concentration-dependent manner. In most cases, gap junctional intercellular communication was significantly reduced at the lowest concentrations tested (50 pM). Inhibition of gap junctional intercellular communication in rodent cells was substantially reversed within 24 h of monoester removal. In contrast, cell-to-cell communication was not inhibited in hamster, cynomolgus, or human hepatocytes or in a human liver cell line at any concentration examined. In rat hepatocytes, peroxisomal beta-oxidation was elevated after treatment with MEHP, MINP, MIHP, and MIDP but not MNOP or M711P, and with all but MIHP in mouse hepatocytes. The eight phthalates produced no marked change on peroxisomal beta-oxidation in hepatocytes from other species. These data provide additional evidence that the toxicological effects of phthalate esters are species specific.

The mammalian testis accumulates lower levels of organochlorine chemicals compared with other tissues

Tissues were obtained from three separate experiments in order to quantify the tissue distribution of organochlorine chemicals that are thought to be potential reproductive toxicants in males: 1) Sprague Dawley rats received 1 microCi of 14C-Aldrin or 14C-Dieldrin (20.6 microCi/micromole) i.p. once a week for three weeks. One week and four weeks after the last injection, tissues were harvested and stored at -80 degrees C. Tissue 14C levels were quantified by scintillation spectrometry. 2) Cis- or trans-nonachlor (0, 0.25, 2.5, 25 mg/kg body weight) were administered daily in corn oil to male rats by gavage for 28 days. Tissues were harvested and frozen at -80 degrees C on the 29th day. Organochlorine residues were extracted and quantified by gas chromatography with electron capture detection. 3) Technical grade toxaphene (0, 0.1, 0.4 or 0.8 mg/kg body weight) was ingested daily by female cynomolgus monkeys of reproductive age for 18 months prior to being mated with control males. Dosing continued during pregnancy and lactation. Their infants received toxaphene via breast milk, and upon weaning, they ingested the same dose as their mothers for 48 to 49 weeks until, at 77 to 80 weeks of age, tissues were harvested and stored at -80 degrees C. Organochlorine residues were extracted and quantified as previously stated. In all three experiments, organochlorine residues in the testis were lower than in most of the other reproductive tract and nonreproductive tract tissues we examined. For example, testicular aldrin and dieldrin levels were <5% the epididymal content; testicular cis- and trans-nonachlor were <25% the epididymal content and, testicular toxaphene levels were <15% of the epididymal content. The reasons for the low degree of accumulation by the testis in comparison with other tissues are unknown. However, the lower testicular content may afford germ cells some protection from the potentially toxic effects of these chemicals.

Spermatogenic disturbance induced by di-(2-ethylhexyl) phthalate is significantly prevented by treatment with antioxidant vitamins in the rat

Phthalate esters, now regarded as endocrine disruptors, are widely used in the plastics industry. In particular, di-(2-ethylhexyl) phthalate (DEHP) is produced in large quantities, and is used in blood storage bags, catheters and haemodialysis instruments. Previous studies have demonstrated that treatment of rats with DEHP induces testicular atrophy with liver enlargement, although the precise nature and mechanism of the action of DEHP on these organs remains unclear. In the present study, we produced an experimental model of DEHP-induced spermatogenic disturbance in rats by feeding them a DEHP-containing diet. Liver enlargement occurred in rats fed either a 1 or 2% DEHP-containing diet. However, testicular atrophy accompanied by aspermatogenesis was induced by feeding with the 2% but not with the 1% DEHP-containing diet. This suggests that the critical DEHP dose for gonadotoxicity is higher than that for hepatotoxicity. Using the 2% DEHP-dose, the effect of simultaneous administration of antioxidant vitamins (= vitamins C and E) was next examined. It was found that the vitamin supplementation significantly prevented the testicular injury. The results suggest that antioxidant vitamins can protect the testes from DEHP-toxicity.

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.

Prevention of di(2-ethylhexyl)phthalate-induced testicular atrophy in rats by co-administration of the vitamin B12 derivative adenosylcobalamin

The administration of 2g/kg of di(2-ethylhexyl)-phthalate (DEHP)-induced severe testicular atrophy coincident with the reduction of testicular specific lactate dehydrogenase (LDH-X) activity, zinc, magnesium, and potassium concentrations in rats. Co-administration of DEHP and adenosyl cobalamin (AdoCbl), one of the active vitamin B12s, prevented these testicular specific changes including fluctuations in testicular weight. On the other hand, co-administration of DEHP and methylcobalamin (MeCbl), the other active vitamin B12, did not prevent the testicular atrophy induced by DEHP under the present experimental conditions. In the liver, DEHP administration caused hypertrophy with changes in several metal concentrations and serum biochemical parameters. Co-administration of DEHP and AdoCbl or MeCbl did not prevent these hepatic changes, but aggravated hypolipidemia. The results demonstrated that the preventive effect of AdoCbl was a testicular specific action, and this effect may be stimulated solely by AdoCbl in vitamin B12 groups.

Effects of phthalic acid esters on testicular mitochondrial functions in the rat

Although it is well established that high dose administration of di(2-ethylhexyl) phthalate (DEHP) and its monoester metabolite (MEHP) induces severe testicular atrophy in rats, the mechanisms of this testicular injury is not clear. The present experiment was undertaken to examine the effects of DEHP and MEHP on mitochondrial functions of rat testis. DEHP and di-n-octyl phthalate (DOP), a DEHP isomer which causes less severe testicular injury, did not inhibit the state 3 oxygen consumption up to 0.65 mumole/ml in vitro. On the other hand, MEHP and mono-n-octyl phthalate (MOP), a metabolite of DOP, inhibited the state 3 oxygen consumption down to a concentration of 0.065 mumole/ml. Testicular mitochondrial respiratory functions of rats administered 2 g/kg DEHP were lower than those of control or DOP-treated rats. These differences were verified by characteristics of pharmacokinetic parameters and testicular concentrations of MEHP and MOP. It may be suggested that a possible mechanism of testicular atrophy induced by DEHP may be due to direct inhibition by MEHP (and partially DEHP) of the respiratory functions of Sertoli cell mitochondria in rat testis.