Intrauterine exposure to low-dose DBP in the mice induces obesity in offspring via suppression of UCP1 mediated ER stress

Dibutyl phthalate (DBP) is recognized as an environmental endocrine disruptor that has been detected in fetal and postnatal samples. Recent evidence found that in utero DBP exposure was associated with an increase of adipose tissue weight and serum lipids in offspring, but the precise mechanism is unknown. Here we aimed to study the effects of in utero DBP exposure on obesity in offspring and examine possible mechanisms. SPF C57BL/6J pregnant mice were gavaged with either DBP (5 mg /kg/day) or corn oil, from gestational day 12 until postnatal day 7. After the offspring were weaned, the mice were fed a standard diet for 21 weeks, and in the last 2 weeks 20 mice were selected for TUDCA treatment. Intrauterine exposure to low-dose DBP promoted obesity in offspring, with evidence of glucose and lipid metabolic disorders and a decreased metabolic rate. Compared to controls, the DBP exposed mice had lower expression of UCP1 and significantly higher expression of Bip and Chop, known markers of endoplasmic reticulum (ER) stress. However, TUDCA treatment of DBP exposed mice returned these parameters nearly to the levels of the controls, with increased expression of UCP1, lower expression of Bip and Chop and ameliorated obesity. Intrauterine exposure of mice to low-dose DBP appears to promote obesity in offspring by inhibiting UCP1 via ER stress, a process that was largely reversed by treatment with TUDCA.

Oxidative Damage and Genetic Toxicity Induced by DBP in Earthworms (Eisenia fetida)

Di-n-butyl phthalate (DBP) is one of the most ubiquitous plasticizers used worldwide. However, it has negatives effects on the soil, water, atmosphere, and other environmental media and can cause serious pollution. According to the artificial soil test and previous studies, this study was conducted to evaluate the toxicity of earthworms induced by DBP at different concentrations (0, 0.1, 1.0, 10, and 50 mg kg^-1) on the 7th, 14th, 21st, and 28th days of exposure. The variations in the antioxidant activities of enzymes, such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and glutathione-S-transferase (GST), in the amounts of malondialdehyde (MDA) and reactive oxygen species (ROS) and in the amount of DNA damage were measured to evaluate the toxic impact of DBP in earthworms. Upon exposure to DBP, the SOD, CAT, POD, and GST activities were significantly increased, with the exception of the 0.1 mg kg^-1 treatment dose. High concentrations of DBP (10 and 50 mg kg^-1) induced superfluous ROS to be produced and caused the MDA content to increase significantly. Therefore, we proposed that DBP led to DNA damage in earthworm coelomocytes in a dose-dependent manner, which means that DBP is a source of oxidative damage and genetic toxicity in earthworms.

In Utero Exposure to Di( n-butyl)phthalate Induces Morphological and Biochemical Changes in Rats Postpuberty

Pregnant Sprague-Dawley rats were orally administered di( n-butyl)phthalate (DBP; 100 mg/kg/day) on gestation days (GD) 12 to 21. We investigated the male offspring and probed morphological alterations in Sertoli cells at 7, 9, 14, and 17 weeks of age. Parameters assessed in this study included offspring number, sex ratios, body weights, testis weights, seminiferous tubule (ST) profile numbers and diameters, number of vimentin-labeled Sertoli cells, and both testosterone and follicle-stimulating hormone (FSH) levels. Testicular weight/body weight ratios and the numbers and diameters of ST in maximum transverse testicular sections were statistically similar at weeks 7 and 9; however, at weeks 14 and 17, they were statistically different and displayed higher BrdU-positive Sertoli cells/Sertoli cell ratios in the DBP treatment group. Noteworthily, the serum FSH levels were higher and testicular testosterone levels were lower in the DBP treatment group. To our knowledge, the present study is the first to report that in utero DBP exposure significantly increased Sertoli cell numbers and their cellular proliferation from postpuberty to adulthood, with a significant decrease in testicular testosterone and an increase in FSH.

Prenatal exposure to di-n-butyl phthalate disrupts the development of adult Leydig cells in male rats during puberty

Fetal exposure to di-n-butyl phthalate (DBP) causes the adult disease such as lower testosterone production and infertility. However, the mechanism is still unknown. The objective of the present study is to determine how DBP affects the involution of fetal Leydig cells during the neonatal period and how this event causes the delayed development of the adult Leydig cells during puberty. The pregnant Sprague Dawley dams were randomly divided into 3 groups and were gavaged with 0 (corn oil, the vehicle control), 100 or 500mg/kg DBP from gestational day 12 (G12) to G21. The blood and testes were collected from male pups on postnatal day 4 (P4), P7, P14, P21, P28, and P56. Serum testosterone concentrations were assessed and the mRNA levels of Leydig cell- or gonadotroph cell-specific genes were measured. Prenatal exposure to DBP caused the aggregation of fetal Leydig cells, which slowly disappeared when compared to the control. This effect was associated with the reduction of testicular testosterone secretion and down-regulation of the mRNA levels of Leydig cell biomarkers including Scarb1, Star, Cyp11a1, Hsd3b1, Hsd11b1, and Hsd17b3 as well as the gonadotroph biomarkers including Lhb and Gnrhr. In conclusion, we demonstrated that the increased aggregation of fetal Leydig cells by DBP delayed fetal Leydig cell involution, thus leading to the disrupted development of the adult Leydig cells.

A crossover-crossback prospective study of dibutyl-phthalate exposure from mesalamine medications and semen quality in men with inflammatory bowel disease

BACKGROUND

Phthalates are widely used chemicals with ubiquitous exposure. Dibutyl-phthalate (DBP), a male reproductive toxicant in animals, is understudied in humans. Some mesalamine medications used to treat inflammatory bowel disease (IBD) have DBP in their coating, whereas other mesalamine formulations do not.

OBJECTIVES

Taking advantage of differences in mesalamine formulations, we investigated whether high-DBP exposure from mesalamine medications was associated with decreased semen parameters.

METHODS

73 men with IBD taking mesalamine participated in a crossover-crossback prospective study. Men taking non-DBP containing mesalamine at baseline i.e., background exposure, crossed-over for four months to high-DBP mesalamine and then crossed-back for four months to their non-DBP mesalamine (B1HB2-arm;Background1-High-Background2) and vice versa for men taking high-DBP mesalamine at baseline (H1BH2-arm;High1-Background-High2). Men provided up to six semen samples (2: baseline, 2: crossover and 2: crossback).

RESULTS

We estimated crossover, crossback and carryover effects using linear mixed models adjusted for abstinence time, age, season and duration on high-DBP mesalamine at baseline. Semen parameters in B1HB2-arm (26 men, 133 samples) decreased after high-DBP mesalamine exposure (crossover versus baseline), especially motility parameters, and continued to decrease further even after crossback to non-DBP mesalamine (crossback versus crossover). The cumulative carryover effect of high-DBP (crossback versus baseline) was a decrease of % total sperm motility by 7.61(CI:-13.1, -2.15), % progressive sperm motility by 4.23(CI:-8.05, -0.4) and motile sperm count by 26.0% (CI:-46.2%, 1.7%). However, H1BH2-arm (47 men, 199 samples) had no significant change during crossover or crossback.

CONCLUSIONS

Men newly exposed to high-DBP mesalamine for four months had a cumulative reduction in several semen parameters, primarily sperm motility, that was more pronounced and statistically significant even after exposure ended for four months.

Male Reproductive Tract Lesions at 6, 12, and 18 Months of Age Following in Utero Exposure to Di(n-butyl) Phthalate

In utero exposure of male rats to the antiandrogen di( n-butyl) phthalate (DBP) leads to decreased anogenital distance (AGD) on postnatal day (PND) 1, increased areolae retention on PND 13, malformations in the male reproductive tract, and histologic testicular lesions including marked seminiferous epithelial degeneration and a low incidence of Leydig cell (LC) adenomas on PND 90. One objective of this study was to determine the incidence and persistence of decreased AGD, increased areolae retention, and LC adenomas in adult rats following in utero DBP exposure. A second objective was to determine whether AGD and areolae retention during the early postnatal period are associated with lesions in the male reproductive tract. Pregnant Crl:CD(SD)BR rats were gavaged with corn oil or DBP at 100 or 500 mg/kg/day, 10 dams per group. Three replicates of rats (n = 30 rats per replicate) were exposed from gestation day 12 to 21 and the male offspring allowed to mature to 6, 12, or 18 months of age. Gross malformations in the male reproductive tract and histologic lesions in the testes were similar to those previously described. However, testicular dysgenesis, a lesion of proliferating LCs and aberrant tubules that has not been previously described in DBP-exposed testes, was diagnosed. The incidence of this lesion was approximately 20% unilateral and 7—18% bilateral in the high-dose group and was similar among all ages examined, implicating a developmental alteration rather than an age-related change. AGD and areolae retention were found to be permanent changes following in utero exposure to 500 mg/kg/day of DBP. Decreased AGD was a sensitive predictor of lesions in the male reproductive tract, relatively small changes in AGD were associated with a significant incidence of male reproductive malformations. In utero DBP exposure induced proliferative developmental lesions, some of which would have been diagnosed as LC adenomas by the morphological criteria set forth by the Society of Toxicologic Pathology. However, these lesions were dissimilar to traditional LC adenomas as the LCs were poorly differentiated and the lesions contained aberrant seminiferous tubules. While the morphology and incidence of this DBP-induced testicular developmental lesion has been fully characterized by this study, the detailed pathogenesis warrants further investigation.

Sublethal concentrations of di-n-butyl phthalate promote biochemical changes and DNA damage in juvenile Nile tilapia (Oreochromis niloticus)

Increase in consumption of consumer items such as plasticizers have resulted in a sharp rise in the presence of xenobiotics like phthalic acid esters (PEs) in freshwater and marine environments due to contaminated runoff and improper release of effluents. The sublethal toxicity of Di-n-butyl phthalate (DBP) was investigated in juvenile Nile tilapia, Oreochromis niloticus, in an attempt to determine the biological effect of exposure to 1/2 and 1/3 median lethal concentration (96-h LC50) which, in our study was experimentally determined to be 11.8 mg/l. Following four days of exposure, indices of the oxidative potential [Malondialdehyde content (MDA)], antioxidant parameters [superoxide dismutase activity (SOD) and reduced glutathione level (GSH)] and DNA damage were evaluated by single-cell gel electrophoresis (Comet assay). Hepato-renal markers [alanine aminotransferase activity (ALT), creatinine and urea level] and cortisol levels were also quantified in serum. Additionally, histopathological investigations of liver, kidney and gill tissues were conducted. Comparative results between the 1/2 96-h LC50 group and the 1/3 96-h LC50 group clearly showed that there was a significant elevation in MDA levels and a marked increase in DNA damage in addition to inhibition of antioxidant barriers as represented by attenuation of SOD activity and GSH level in the group that was exposed to higher concentration of DBP (1/2 96-h LC50). The hepatorenal markers and cortisol levels were also observed to be elevated. Histopathological examination of the liver, kidney and gills showed pathological alterations that could be correlated with changes in the biochemical profile of the exposed fish. Additionally, anomalous clinical signs were noted. Based on these findings, we conclude from our study that exposure of juvenile O. niloticus to DBP has the potential to induce biochemical as well as tissue morphological alterations associated with oxidative injury and DNA damage.

The effects on steroidogenesis and histopathology of adult male Japanese quails (Coturnix coturnix japonica) testis following pre-pubertal exposure to di(n-butyl) phthalate (DBP)

In the present study, we have investigated the effects of 30-day dietary (pre-pubertal) exposure to different doses (0 (control), 1, 10, 50, 200 and 400 mg/kg bodyweight/day) of di(n-butyl) phthalate (DBP) on Leydig cells of adult male Japanese quails by quantifying the transcript levels for P450 side-chain cleavage (p450scc), P450c17 (CYP17), and 3β- and 17β-hydroxysteroid dehydrogenase (hsd) using quantitative (real-time) polymerase chain reaction (qRT-PCR). In addition, the plasma testosterone levels were analysed using radioimmunoassay (RIA) and testis was examined for evidence of gross pathology and histopathology. Our data showed that pre-pubertal exposure to DBP produced alterations in testicular architecture as evident by poorly developed or mis-shaped testis, and altered spermatogenesis due to tubular degeneration and atrophy of seminiferous tubules especially in the high DBP dose (200 and 400 mg/kg) treated groups. In addition, DBP altered several key enzymes involved in testicular steroidogenesis pathways in an apparent dose-dependent manner. For example, biphasic effects of DBP were observed for P450scc and 3β-hsd mRNA, that were generally increasing at low dose 10 mg/kg, and thereafter, an apparent dose-dependent decrease between 50 and 400mg/kg. The steroidogenic acute regulatory (StAR) protein was at the lowest detectable limits and therefore not quantifiable. These effects did not parallel the non-significant changes observed for plasma testosterone levels. The present data is consistent with previous reports showing that DBP modulates Leydig cell steroidogenesis in several species, with a potential negative effect on reproduction in those avian species that are vulnerable to endocrine disrupting chemicals.

Estimated daily intake and hazard quotients and indices of phthtalate diesters for young danish men

Because of wide exposure to phthalates, we investigated whether simultaneous exposure to several phthalates reached levels that might cause adverse antiandrogenic effects. Thirty three healthy young Danish men each delivered three 24-h urine samples during a three months period. The daily intakes of the sum of di-n-butyl and di-iso-butyl phthalate, di(2-ethylhexyl) phthalate, di-iso-nonyl phthalate, and butylbenzyl phthalate were estimated based on urinary excretion of the metabolites. Based on a hazard quotient (HQ) of the individual phthalate (i.e., the ratio between the daily intake and an acceptable level of exposure), a hazard index (HI) for each man was calculated as the sum of HQs for the individual phthalates. All men were exposed to all phthalates during the urine collection periods. Median HIs were all below 1 (i.e., below an acceptable cumulative threshold) ranging from 0.11 to 0.17 over the three different sample collections. Of the 33 men, 2 men had HIs above 1 in one of their three samples, indicating that occasionally the combined exposure to the investigated phthalates reached a level that may not be considered safe. Besides the phthalates investigated here, humans are exposed to numerous other chemicals that also may contribute to a cumulative antiandrogenic exposure.

Prepubertal mouse testis growth and maturation and androgen production are acutely sensitive to di-n-butyl phthalate

Phthalates are plasticizers with widespread industrial, domestic, and medical applications. Epidemiological data indicating increased incidence of testicular dysgenesis in boys exposed to phthalates in utero are reinforced by studies demonstrating that phthalates impair fetal rodent testis development. Because humans are exposed to phthalates continuously from gestation through adulthood, it is imperative to understand what threat phthalates pose at other life stages. To determine the impact during prepuberty, we assessed the consequences of oral administration of 1 to 500 mg di-n-butyl phthalate (DBP)/kg/d in corn oil to wild-type (C57BL/6J) male mice from 4 to 14 days of age. Dose-dependent effects on testis growth correlated with reduced Sertoli cell proliferation. Histological and immunohistochemical analyses identified delayed spermatogenesis and impaired Sertoli cell maturation after exposure to 10 to 500 mg DBP/kg/d. Interference with the hypothalamic-pituitary-gonadal axis was indicated in mice fed 500 mg DBP/kg/d, which had elevated circulating inhibin but no change in serum FSH. Increased immunohistochemical staining for inhibin-α was apparent at doses of 10 to 500 mg DBP/kg/d. Serum testosterone and testicular androgen activity were lower in the 500 mg DBP/kg/d group; however, reduced anogenital distance in all DBP-treated mice suggested impaired androgen action at earlier time points. Long-term effects were evident, with smaller anogenital distance and indications of disrupted spermatogenesis in adult mice exposed prepubertally to doses from 1 mg DBP/kg/d. These data demonstrate the acute sensitivity of the prepubertal mouse testis to DBP at doses 50- to 500-fold lower than those used in rat and identify the upregulation of inhibin as a potential mechanism of DBP action.

Male Sprague-Dawley rats exposed to in utero di(n-butyl) phthalate: dose dependent and age-related morphological changes in Leydig cell smooth endoplasmic reticulum

When 100 mg/kg/day of di(n-butyl) phthalate (DBP) was intragastrically administered to pregnant Sprague-Dawley rats throughout gestation days 12 to 21, the male pups had similar body weights with no apparent physical differences (e.g., litter size, sex ratio) compared to that of the vehicle group. However, prominent age-related morphological alterations in the smooth endoplasmic reticulum (sER) of testicular Leydig cells (LCs) were observed once these animals reached puberty. At weeks 5 to 7, the abundant sER with non-dilated cisternae was distributed in LCs. Subsequently, although the number of LCs significantly increased, the amount of sER was significantly decreased at 9 to 14 weeks of age and had disappeared at 17 weeks. In contrast, the number of LCs and the amount of sER in LCs of the lower dose groups (10, 30, and 50 mg/kg/day) were similar to those of the vehicle group. Further, serum testosterone levels in the 100 mg/kg dose group were significantly lower during 5 to 17 weeks of age. While their luteinizing hormone (LH) level was significantly lower at 5 to 7 weeks of age, it became significantly higher during 9 to 17 weeks. The amount of sER in LCs decreased with age with the increase in LCs proliferation and serum LH levels in rat exposed in utero to DBP in a dose-dependent manner.

Pharmacokinetics of dibutyl phthalate (DBP) in the rat determined by UPLC-MS/MS

Dibutyl phthalate (DBP) is commonly used to increase the flexibility of plastics in industrial products. However, several plasticizers have been illegally used as clouding agents to increase dispersion of aqueous matrix in beverages. This study thus develops a rapid and validated analytical method by ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) for the evaluation of pharmacokinetics of DBP in free moving rats. The UPLC-MS/MS system equipped with positive electrospray ionization (ESI) source in multiple reaction monitoring (MRM) mode was used to monitor m/z 279.25→148.93 transitions for DBP. The limit of quantification for DBP in rat plasma and feces was 0.05 μg/mL and 0.125 μg/g, respectively. The pharmacokinetic results demonstrate that DBP appeared to have a two-compartment model in the rats; the area under concentration versus time (AUC) was 57.8 ± 5.93 min μg/mL and the distribution and elimination half-life (t_1/2,α and t_1/2,β) were 5.77 ± 1.14 and 217 ± 131 min, respectively, after DBP administration (30 mg/kg, i.v.). About 0.18% of the administered dose was recovered from the feces within 48 h. The pharmacokinetic behavior demonstrated that DBP was quickly degraded within 2 h, suggesting a rapid metabolism low fecal cumulative excretion in the rat.

Two generations of fall armyworm (Lepidoptera: Noctuidae) contamination by di-n-butylphthalate

The effects of di-n-butylphthalate (DnBP) were investigated with respect to bioaccumulation and whether these effects occurred over a second generation in the fall armyworm Spodoptera frugiperda (J.E. Smith, 1797). The concentrations of DnBP in males and females of the second generation were higher than those in first one. However, frequency of mortality of exposed individuals in the second generation was approximately 57% less but the reduction in size and weight was more pronounced than in the first generation.

Combined subchronic toxicity of bisphenol A and dibutyl phthalate on male rats

OBJECTIVE

To evaluate the combined subchronic toxicity of bisphenol A (BPA) and dibutyl phthalate (DBP) in male Sprague Dawley (SD) rats.

METHODS

Forty 4-week-old male rats weighing 115-125 g were randomly divided into BPA-treated, DBP-treated group, BPA+DBP-treated and control groups and fed with a soy- and alfalfa-free diet containing 285.4 ppm BPA, 285.4 ppm DBP, 285.4 ppm BPA plus 285.4 ppm DBP, and a control diet, respectively, for 90 consecutive days. At the end of the study, the animals were sacrificed by exsanguination via the carotid artery under diethyl etherane aesthesia and weighed. Organs, including liver, kidneys, spleen, thymus, heart, brain, and testis underwent pathological examination. The androgen receptor (AR), gonadotropin-releasing hormone receptor (GNRHR), and progesterone hormone receptor (PR) genes from the hypothalamus were detected by real-time PCR. The biomedical parameters were analyzed.

RESULTS

No significant difference was found in food intake, body weight, tissue weight, organ/brain weight ratio, and biomedical parameters among the four groups (P>0.05). However, BPA and DBP up-regulated AR, PR and GNRHR expression levels in rats and showed a synergistic or an additive effect in the BPA+DBP group.

CONCLUSION

The combined subchronic toxicity of BPA and DBP is synergistic or additive in male SD rats.

[Effects of di-butyl phthalate on the reproductive system of adolescent male rats]

OBJECTIVE

To explore the effects of di-butyl phthalate (DBP) on the reproductive system of adolescent male rats.

METHODS

Sprague-Dawley (SD) rats aged 5 weeks were assigned to receive corn oil (vehicle control) or DBP orally at 10, 100 and 500 mg/(kg x d) for 30 days. After the exposure, the testis, epididymis, liver and pituitary of the rats were weighted and their ratios to the body weight obtained. Histopathological changes of the testis and epididymis were examined by Hematoxylin-eosin staining, the levels of testosterone (T), luteinizing hormone (LH) and follicle stimulating hormone (FSH) in the serum were measured by radioimmunoassay, and the relative mRNA expressions of the steroidogenesis acute regulatory protein (StAR), proliferating cell nuclear antigen (PCNA), cytochrome P450 cholesterol side chain cleavage enzyme (P450scc) and scavenger receptor (SR) were detected by real-time quantitative RT-PCR.

RESULTS

DBP induced significant histopathological changes in the testicular tissue at 100 and 500 mg/(kg x d), and decreased the testicular and epididymal weights, inhibited the mRNA expressions of StAR and PCNA, reduced the levels of T and LH, and elevated the level of FSH at 500 mg/(kg x d). At the dose of 10 mg/(kg x d), DBP increased serum LH and FSH and the mRNA expression of P450scc. While the SR mRNA expression showed no significant changes in all the groups.

CONCLUSION

High level of DBP has apparent toxic effect on reproductive system of male rats. Low - dose DBP can increase the level of serum gonadotropin LH and affect the mRNA expression of P450scc in the testis.

Toxicity and carcinogenicity of ozone in combination with 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone and dibutyl phthalate in B6C3F1 mice for 16 and 32 weeks

OBJECTIVE

To evaluate the toxic and carcinogenic potential of ozone alone or in combination with 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and/or dibutyl phthalate (DBP).

METHODS

Male and female B6C3F1 mice were exposed, through inhalation, intravenous administration and diet, to 0.5 ppm of ozone, 1.0 mg/kg of NNK and 5000 ppm of DBP, individually and in combination for 16 and 32 weeks.

RESULTS

No treatment-related death was seen, but significant differences in body and organ weights between control and treated mice were observed during the study. No incidence of lung tumor incidence was recorded in mice exposed to either ozone alone or combined treatment. Oviductal carcinomas were observed in female mice exposed to ozone or DBP alone for 16 weeks and ozone in combination with NNK and DBP for 32 weeks.

CONCLUSION

Although ozone alone and in conjunction with NNK and/or DBP does not induce lung cancer under our experimental conditions, they induce oviductal carcinomas in B6C3F1 mice.

Subungual Penetration of Dibutyl Phthalate in Human Fingernails

Dibutyl phthalate (DBP) has a wide variety of manufacturing applications and is used in both commercial and consumer products. Results of animal reproductive toxicity and teratogenicity animal studies have not been consistent in identifying DBP as a reproductive toxicant. Expert reviews for its use in consumer products have consistently concluded that it is not a reproductive risk to consumers. Results from a subungual penetration study of 100% fluid DBP applied to human fingernails showed levels of penetration at the limits of chemical detection. Even if DBP penetrated the human fingernail, its rapid metabolism by the human body would prevent its having any toxic reproductive effects. Furthermore, DBP functions as a plasticizer in consumer products such as cosmetic nail products (nail polish, basecoats, topcoats, nail hardeners), resulting in its becoming unavailable for subungual penetration seconds after application of the cosmetic nail product since it is then trapped in the rapidly forming coating.

In utero exposure to di(n-butyl) phthalate and testicular dysgenesis: comparison of fetal and adult end points and their dose sensitivity

BACKGROUND

Fetal exposure of male rats to di(n-butyl) phthalate (DBP) induces reproductive disorders similar to those in human testicular dysgenesis syndrome (TDS), including infertility, cryptorchidism, focal "dysgenetic areas," and Sertoli cell-only tubules in the adult testis. Humans are widely exposed to DBP, but at much lower levels than those causing adverse effects in rats.

OBJECTIVES

The objective of this study was to evaluate end points affected by DBP action in rats in fetal and adult life that are relevant to human TDS, and to compare their dose sensitivity.

METHODS

Pregnant rats were gavaged daily with corn oil (control) or with 4, 20, 100, or 500 mg/kg DBP. We examined adult end points of TDS (infertility, cryptorchidism) and indicators within the fetal testis of dysgenesis [abnormal Leydig cell (LC) aggregation, multinucleated gonocytes (MNGs)], as well as conditions that may result from these indicators in adulthood (occurrence of focal dysgenetic areas). Fetal testis weight and testicular testosterone levels were also evaluated.

RESULTS

The fetal end points analyzed (testicular testosterone levels, abnormal LC aggregation, occurrence of MNGs) were most sensitive to disruption by DBP, as all were significantly affected at a dose of 100 mg/kg/day DBP, with a trend toward effects occurring at 20 mg/kg/day DBP; adult end points were affected consistently only by 500 mg/kg/day DBP.

CONCLUSIONS

The fetal end points we evaluated can be objectively quantified and may prove helpful in evaluating the health risk of exposure to DBP and other phthalates, as well as identifying DBP-sensitive fetal events that have adult consequences/end points that are identifiable in human TDS.

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

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

Identification of differentially expressed genes in the testis of Sprague-Dawley rats treated with di(n-butyl) phthalate

The aim of this study was to identify the di(n-butyl) phthalate (DBP)-induced differentially expressed genes (DEGs) using a novel annealing control primer system in the testes of Sprague-Dawley male rats. Animals (4 weeks of age) were administered orally either corn oil only (vehicle control) or DBP (250, 500, or 750 mg/kg/day) for 30 days. Total RNA was isolated from the rat testes and GeneFishing PCR was used to determine the differential gene expression levels. Using this technique, a total of 59 DEG mRNA fragments were observed in the testes treated with DBP 750 mg/kg/day compared to vehicle control. Of these 59 genes, 31 genes were significantly altered after exposing rats to high dose DBP (750 mg/kg/day), and their sequences cloned. Based on the Basic Local Alignment Search Tool (BLAST), 4 expressed sequence tags (EST), 27 cloned genes (Insl3, pgrp, H1SHR, etc.) and 3 genes (LDHA, lactate dehydrogenase A; Spag4, sperm associated antigen 4 and PBR, peripheral-type benzodiazepine receptor) were found to be involved in spermatogenesis and steroidogenesis. In addition, the expression patterns of the steroidogenesis-related genes such as scavenger receptor class B-1 (SR-B1), steroidogenic acute regulated protein (StAR), P450 side chain cleavage (P450scc), CYP17, and CYP19 were further analyzed by RT-PCR. Significant increases in the mRNA levels of steroidogenesis-related genes (PBR, SR-B1, StAR, P450scc, and CYP17) were observed in the high dose DBP-treated rats. However, DBP significantly decreased the CYP19 mRNA levels compared with controls. DBP (750 mg/kg/day) significantly increased the TR-alpha1 and PPARgamma expression in testes, whereas the AR and ERbeta protein levels were significantly reduced in the same group. These data indicate that the steroidogenesis- or spermatogenesis-related genes identified in this study may provide insights into the molecular mechanisms underlying environmental pollutants-mediated male infertility.

Low concentrations mono-butyl phthalate stimulates steroidogenesis by facilitating steroidogenic acute regulatory protein expression in mouse Leydig tumor cells (MLTC-1)

Di-n-butyl phthalate (DBP) is one of the most dominant phthalate esters and is widely distributed environmental contaminant. Although previous studies have demonstrated that DBP led to a variety of male reproductive abnormalities similar to those caused by androgen receptor antagonists, DBP and its active metabolite, mono-butyl phthalate (MBP), have been demonstrated no affinity for the androgen receptor, but rather exert anti-androgenic effect by altering testosterone biosynthesis. Furthermore, all these results were obtained from very high administrations of DBP or MBP. The purpose of this study was to determine the onset and the site of action of relatively low concentration of MBP on steroidogenesis in vitro. The mouse Leydig tumor cells (MLTC-1) was employed as a cellular model to investigate the effect of MBP on steroidogenesis. Various concentrations of MBP (1, 10, 100 and 1000nmol/l) and its solvent dimethyl sulfoxide (DMSO) were added to the medium for 24h followed by stimulation of some compounds such as human chorionic gonadotrophin (hCG), cholera toxin (CT), forskolin, cAMP analog 8-Br-cAMP, 22(R)-hydroxycholesterol (22R-HC) and pregnenolone. Progesterone in the medium and amounts of intracellular cAMP were measured by RIA. Expression of steroidogenic acute regulatory protein (StAR) was monitored by real-time PCR and Western blotting. The results revealed that the increases of progesterone production in the presence of hCG, CT, forskolin and 8-Br-cAMP were augmented by MBP. In contrast, the levels of intracellular cAMP exhibited no statistical significance when MLTC-1 cells were treated as above. These results implied that the site in the steroid biosynthesis pathway affected by MBP occurs after PKA activation in MLTC-1 cells. Moreover, supplementing the medium with 22R-HC and pregnenolone as progesterone precursors for P450 side chain cleavage enzyme (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), respectively, resulted in no rise in progesterone production, making clear that MBP did not influence the P450scc and 3beta-HSD but on the rate-limiting step, cholesterol transportation into mitochondria. In fact, the above results were confirmed by the upgraded StAR expression in MBP-treated cells. These data support that MBP promotes steroid hormone production by facilitating StAR expression in MLTC-1 cells.

Cellular origins of testicular dysgenesis in rats exposed in utero to di(n-butyl) phthalate

Foetal exposure of male rats to di(n-butyl) phthalate (DBP) induces testicular changes similar to testicular dysgenesis syndrome in humans, including the formation of focal 'dysgenetic areas' within post-natal testes, surrounded by otherwise normal tubules exhibiting complete spermatogenesis. We hypothesize that these dysgenetic areas form when Sertoli (and other) cells are 'trapped' during the abnormal formation of large Leydig cell (LC) clusters in foetal life and by post-natal day (d) 4 these groups of intermingled cells attempt to form seminiferous tubules. It is likely that the malformed tubules resulting correspond to the dysgenetic areas evident in later life. This also provides a plausible explanation for the occurrence of LCs within seminiferous cords/tubules in or bordering the dysgenetic areas. In our previous studies intratubular LCs (ITLCs) were identified by immunostaining for 3beta-hydroxysteroid dehydrogenase (3beta-HSD), the definitive LC cytoplasmic marker. However, the possibility remained that the 'presumptive' ITLCs were in fact Sertoli cells that had aberrantly gained the ability to express 3beta-HSD. Therefore, the aim of the present study was to fully characterize the ITLCs induced by in utero DBP exposure in d25 rats using a number of LC- (3beta-HSD, P450 side-chain cleavage enzyme, insulin-like factor 3, oestrogen receptor alpha) and Sertoli cell- (vimentin, Wilm's tumour-1) specific markers. Our results show that ITLCs express all four LC-specific markers but do not express either of the Sertoli cell markers. It is therefore concluded that the ITLCs are bona fide LCs that are abnormally located within the seminiferous tubules of DBP-exposed rats in post-natal life.

Cellular origins of testicular dysgenesis in rats exposed in utero to di(n-butyl) phthalate

Foetal exposure of male rats to di(n-butyl) phthalate (DBP) induces testicular changes similar to testicular dysgenesis syndrome in humans, including the formation of focal 'dysgenetic areas' within post-natal testes, surrounded by otherwise normal tubules exhibiting complete spermatogenesis. We hypothesize that these dysgenetic areas form when Sertoli (and other) cells are 'trapped' during the abnormal formation of large Leydig cell (LC) clusters in foetal life and by post-natal day (d) 4 these groups of intermingled cells attempt to form seminiferous tubules. It is likely that the malformed tubules resulting correspond to the dysgenetic areas evident in later life. This also provides a plausible explanation for the occurrence of LCs within seminiferous cords/tubules in or bordering the dysgenetic areas. In our previous studies intratubular LCs (ITLCs) were identified by immunostaining for 3beta-hydroxysteroid dehydrogenase (3beta-HSD), the definitive LC cytoplasmic marker. However, the possibility remained that the 'presumptive' ITLCs were in fact Sertoli cells that had aberrantly gained the ability to express 3beta-HSD. Therefore, the aim of the present study was to fully characterize the ITLCs induced by in utero DBP exposure in d25 rats using a number of LC- (3beta-HSD, P450 side-chain cleavage enzyme, insulin-like factor 3, oestrogen receptor alpha) and Sertoli cell- (vimentin, Wilm's tumour-1) specific markers. Our results show that ITLCs express all four LC-specific markers but do not express either of the Sertoli cell markers. It is therefore concluded that the ITLCs are bona fide LCs that are abnormally located within the seminiferous tubules of DBP-exposed rats in post-natal life.

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.

[Effects of dibutyl phthalate on sertoli cells of rat testis]

OBJECTIVE

The present study was performed to examine functional and structural impairment of rat sertoli cells following dibutyl phthalate (DBP) exposure.

METHODS

The 6-week-old healthy male Sprague Dawley rats were randomly divided into 4 groups with 16 animals in each group. DBP dissolved in peanut oil was administered by gavage at doses of 0, 250, 500 and 1 000 mg/kg. After 2-week DBP treatment, half of the rats were sacrificed. The rest were killed following 4-week DBP exposure. Follicle stimulating hormone (FSH) was analysed by radioimmunoassay. The relative expression levels of androgen binding protein (ABP) mRNA and inhibin (INH)alpha mRNA were determined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The sertoli cell ultrastructures were observed by using transmission electron microscope (TEM).

RESULTS

FSH levels were increased after 4-week DBP exposure with significance at doses of 250 and 1 000 mg/kg. Sperm head count and daily sperm product were decreased significantly in 500 and 1 000 mg/kg groups. The expression levels of ABP mRNA were 0.89 +/- 0.15, 0.85 +/- 0.23, 0.54 +/- 0.17, 0.52 +/- 0.16 and 0.88 +/- 0.16, 0.61 +/- 0.12, 0.48 +/- 0.15, 0.47 +/- 0.11 for 0, 250, 500 and 1 000 mg/kg after 2- and 4-week DBP treatments respectively with significance at doses of 500 and 1 000 mg/kg (P < 0.01), while the levels of INHalpha mRNA were 0.88 +/- 0.16, 0.61 +/- 0.12, 0.48 +/- 0.15, 0.47 +/- 0.11 and 0.75 +/- 0.19, 0.56 +/- 0.16, 0.53 +/- 0.08, 0.45 +/- 0.10 with significance at all exposure groups (P < 0.01 or P < 0.05). In sertoli cells of rats exposed to 1 000 mg/kg DBP, TEM photos showed more lysosomes in cytoplasm, proliferated and expanded endoplasmic reticulum and nuclei malformation.

CONCLUSIONS

Sertoli cell should be one of the major toxic targets. Impairment of spermatogenesis caused by DBP should be partly due to the suppression of ABP and INHalpha biosynthesis.

Reproductive and developmental toxicity in F1 Sprague–Dawley male rats exposed to di-n-butyl phthalate in utero and during lactation and determination of its NOAEL

Di-n-butyl phthalate (DBP) is one of the commonly used plasticizers in China. DBP can enter the environment and organisms through various routes and then affect reproductive and developmental processes of the organism and its descendants (mainly affecting male offspring). It is known that animals are sensitive to exposure of DBP in utero and during lactation. In the present study, pregnant rats were treated with different doses of DBP (0, 50, 250, and 500 mg/kg body weight/day) by daily gavage from GD1 to PND21. The developmental condition of F1 rats and the reproductive system of mature F1 male rats were monitored. DBP had no obvious effect on pregnant rats; however, it reduced several parameters including birth weight, number of live pups per litter, body weight gain and male anogenital distance. Severe damage to the reproductive system of mature F1 male rats included testicular atrophy, underdeveloped or absent epididymis, undescended testes, obvious decline of epididymal sperm parameters, total sperm heads per g testis, decrease of organ/body weight ratio of epididymis and prostate, and was observed in the group treated with 250 mg/kg BW/day and higher. These results showed that the male reproductive system was the main target organ of DBP exposure. The NOAEL (no observable adverse effect level) for developmental toxicity of DBP was established based on pup body weight and male reproductive lesions at 50 mg/kg BW/day. Accordingly, the RfD for human exposure to DBP through oral intake was recommended as 500 mg/kg BW/day.

Quantitative changes in gene expression in fetal rat testes following exposure to di(n-butyl) phthalate

Di(n-butyl) phthalate (DBP) alters male reproductive development by decreasing testicular testosterone (T) production when fetuses are exposed on gestation days (GD) 12-21. Previous studies have shown altered gene expression for enzymes in the T biosynthetic pathway following exposure to DBP. The objectives of this study were to develop a more detailed understanding of the effect of DBP on steroidogenesis, using a robust study design with increased numbers of dams and fetuses, compared with previous studies, and to explore messenger RNA (mRNA) expression for other critical genes involved in androgen biosynthesis and signaling. Additionally, immunohistochemical localization of protein expression for several key genes was performed to further confirm mRNA changes. Fetal Leydig cell lipid levels were also examined histochemically, using oil red O. Six to seven pregnant Crl:CD(SD)BR rats per group were gavaged with corn oil or DBP at 500 mg/kg/day on GD 12-19. Testicular RNA isolated from three randomly selected GD 19 fetuses per litter was used for real-time RT-PCR for the following genes: scavenger receptor class B-1 (SRB1), steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase (3beta-HSD), P450c17, 17beta-hydroxysteroid dehydrogenase (17beta-HSD), androgen receptor (AR), luteinizing hormone receptor (LHR), follicle-stimulating hormone receptor (FSHR), stem cell factor tyrosine kinase receptor (c-kit), stem cell factor (SCF), proliferating cell nuclear antigen (PCNA), and testosterone-repressed prostate message-2 (TRPM-2). mRNA expression was downregulated for SRB1, StAR, P450scc, 3beta-HSD, P450c17, and c-kit following DBP exposure, and TRPM-2 was upregulated. 17beta-HSD, AR, LHR, FSHR, and PCNA were not significantly changed. Immunohistochemical staining for c-kit was seen in fetal Leydig cells, which has not been previously reported. Downregulation of most of the genes in the T biosynthetic pathway confirms and extends previous findings. Diminished Leydig cell lipid content and alteration of cholesterol transport genes also support altered cholesterol metabolism and transport as a potential mechanism for decreased T synthesis following exposure to DBP.

Effects of dibutyl phthalate in male rabbits following in utero, adolescent, or postpubertal exposure

We evaluated sequelae in male rabbits following exposure to dibutyl phthalate (DBP) at a dose level known to adversely affect testicular function in rodents without causing systemic toxicity. Because rabbits have a relatively long phase of reproductive development simulating better than rodents the reproductive development of humans, and because the use of rabbits facilitates multiple evaluations of mating ability and seminal quality, we used this animal model. Rabbits were exposed to 0 or 400 mg DBP/kg/day in utero (gestation days [GD] 15-29) or during adolescence (postnatal weeks [PNW] 4-12), and male offspring were examined at 6, 12, and 25 weeks of age. Another group was exposed after puberty (for 12 weeks) and examined at the conclusion of exposure. The most pronounced reproductive effects were in male rabbits exposed in utero. Male offspring in this group exhibited reduction in numbers of ejaculated sperm (down 43%; p < 0.01), in weights of testes (at 12 weeks, down 23%; p < 0.05) and in accessory sex glands (at 12 and 25 weeks, down 36%; p < 0.01 and down 27%; p < 0.05, respectively). Serum testosterone levels were down (at 6 weeks, 32%; p < 0.05); a slight increase in histological alterations of the testis (p < 0.05) and a doubling in the percentage (from 16 to 30%, p < 0.01) of abnormal sperm; and 1/17 males manifesting hypospadias, hypoplastic prostate, and cryptorchid testes with carcinoma in situ-like cells. In the DBP group exposed during adolescence, basal serum testosterone levels were reduced at 6 weeks (p < 0.01) while at 12 weeks, testosterone production in vivo failed to respond normally to a GnRH challenge (p < 0.01). In addition, weight of accessory sex glands was reduced at 12 weeks but not at 25 weeks after a recovery period; there was a slight increase in the percentage of abnormal sperm in the ejaculate; and 1/11 males was unilaterally cryptorchid. In both of these DBP-treated groups, daily sperm production, epididymal sperm counts, mating ability, and weights of body and nonreproductive organs were unaffected. Thus, DBP induces lesions in the reproductive system of the rabbit, with the intrauterine period being the most sensitive stage of life.

Adjuvant effect of di-n-butyl-, di-n-octyl-, di-iso-nonyl- and di-iso-decyl phthalate in a subcutaneous injection model using BALB/c mice

During the last decades, the prevalence of the allergic airway diseases, asthma and rhinitis, has increased world-wide. Introduction of environmental chemicals with adjuvant effect may play a role in this increase. In the present study, the adjuvant effects of di-n-butyl-, di-n-octyl-, di-iso-nonyl- and di-iso-decyl phthalate are studied in a screening model. Ovalbumin, used as the model antigen, was injected subcutaneously in the neck region of BALB/cJ mice with the selected phthalate in concentrations from 2-2000 microg/ml. Additionally, the mice were boosted once or twice with ovalbumin alone. Immunization with ovalbumin alone, the ovalbumin control group, served as the baseline for antibody production, whereas aluminium hydroxide served as the positive control. The levels of ovalbumin-specific IgE, IgG1 and IgG2a antibodies in sera were determined. Adjuvant effect was accepted to be present if a statistical increase in antibody production occurred in a test group as compared to an ovalbumin control group together with the fulfillment of dose-response relationships. Adjuvant effect varied strongly between the phthalates investigated. Phthalates with 8 or 9 carbon atoms in the alkyl side chains were the stronger adjuvants whereas phthalates with shorter or longer alkyl side chains possessed less adjuvant activity. Adjuvant effects were apparent either from the IgE or the IgG1 response or both, whereas no effect was seen on the IgG2a response. Additional studies with airborne exposure are required to establish whether the hazards also result in a significant risk for the development of allergy in man.

Oxidative DNA damage in male Wistar rats exposed to di-n-butyl phthalate

Dialkyl phthalate esters are used in the plastic industry and widely distributed in the environment. Previously, it has been shown that di-n-butyl phthalate (DBP) produces testicular atrophy and liver enlargement in rodents, and the mechanisms behind this could involve reactive oxygen species (ROS). In this study, oxidative DNA damage was measured in terms of the premutagenic modified nucleoside 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxodG) in nuclear DNA from liver, kidneys, and testes from rats exposed to DBP in the perinatal or preadult period. In one experiment, pregnant rats were administered 0 or 0.5 g DBP/kg/d by gavage from d 7 after conception to d 17 after delivery and organs from male offspring were analyzed. In a second experiment, 25-d-old rats were administered 0, 0.5, or 2 g DBP/kg/d by gavage for 10 d. After perinatal exposure, body and organ weights were unchanged. The 8-oxodG/10(6) dG ratio in liver DNA increased significantly in the exposed group. In contrast, the 8-oxodG/10(6) dG ratio was significantly decreased in kidney DNA, whereas it remained unchanged in the testis. After preadult exposure (postnatal d 25 to 34) the testes weight of the exposed animals were significantly decreased and severe atrophy of the seminiferous tubules was observed. The body weight of the animals in the high-dose group was significantly decreased compared to the control. The 8-oxodG levels in liver, kidney, and testis DNA remained unchanged. Although ROS has been suspected of being involved in the formation of testicular atrophy in phthalate-exposed rats, no apparent sign of oxidative DNA damage was found after phthalate exposure perinatally or during the preadult stage. With respect to phthalate-induced oxidative DNA damage in the liver, it appears that the developmental stage during exposure is important.

Increased conversion ratio of tryptophan to niacin by dietary di-n-butylphthalate

We reported that the growth promoting activity of di-n-butylphthalate (DBP) was observed when rats were fed with a niacin-free and tryptophan-limiting diet (Shibata et al.. 1982. J Nutr Sci Vitaminol 28, 173-177). The present experiment was performed to investigate whether this phenomenon is attributable to the increase in the conversion ratio of tryptophan to niacin. The weaning rats were fed with a 10% (low protein diet) or 20% protein (conventional protein diet) diet with or without adding 1% DBP. The conversion ratio of tryptophan to niacin was significantly higher in the DBP group than in the control group; for 10% casein diets, it increased two-fold and for 20% casein diet, about five-fold. From these results, the previous finding is possibly explained by DBP increasing the conversion ratio of tryptophan to niacin.

Migration of dermal cells expressing a macrophage C-type lectin during the sensitization phase of delayed-type hypersensitivity

Dermal cells expressing a macrophage C-type lectin (mMGL) were previously suggested to migrate to regional lymph nodes during the sensitization phase of delayed-type hypersensitivity (DTH). The migration seemed to be induced by the solvent used to dissolve the antigen, and the DTH response was significantly enhanced by the migration. In this study, immunohistochemical analysis of skin after epicutaneous application of one of such solvents, a mixture of acetone and dibutylphthalate (AD), revealed a transient decrease in the number of mMGL-positive cells in the dermis. A similar decrease in this cell population was also observed in an ex vivo assay with skin explants excised from AD-treated sites. Conditioned medium from organ culture of AD-treated skin induced a similar decrease of mMGL-positive cells in untreated dermis, indicating the involvement of soluble factors. mMGL-positive cells seemed to represent a unique subpopulation of F4/80-positive dermal cells.

Developmental effects of di-n-butyl phthalate after a single administration in rats

The objective of this study was to determine the susceptible day for the developmental toxicity of di-n-butyl phthalate (DBP). Pregnant rats were given a single dose of DBP by gastric intubation at 1500 mg kg(-1) on one of days 6-16 of pregnancy. A significant increase in the incidence of postimplantation loss was found in pregnant rats given DBP on one of days 6-16, except for days 7 and 11. Significant increases in the incidences of fetuses with skeletal malformations, of fetuses with skeletal and internal malformations and of fetuses with external and skeletal malformations were noted after a single dosing of DBP on day 8, on day 9 and on day 15, respectively. Deformity of the cervical vertebrae was frequently observed after administration of DBP on day 8. Deformity of the cervical and thoracic vertebrae and ribs and dilatation of the renal pelvis were predominantly found in fetuses of dams treated with DBP on day 9. Cleft palate and fusion of the sternebrae were exclusively detected after administration of DBP on day 15. It could be concluded that the manifestation of deviant development induced by DBP varies with the developmental stage at the time of administration and that DBP induces two discrete responses from embryos to teratogenicity on days 8 and 9 and on day 15 of pregnancy.

Absorption of sunscreens and other compounds through human skin in vivo: derivation of a method to predict maximum fluxes

PURPOSE

The goal of this study was to quantify the transdermally absorbed amounts of the sunscreens octyl dimethyl p-aminobenzoic acid, oxybenzone, 4-isopropyl-dibenzoylmethane, 3-(4-methylbenzylidene)-camphor, isoamyl-4-methoxycinnamate, the repellent and plasticizer dibutyl phthalate, the antioxidant 3.5-di-t-butyl-4-hydroxyanisol, and the antimicrobial compounds butyl-4-hydroxybenzoate, biphenyl-2-ol, and 2,4,4'-tri-chlor-2'-hydroxydiphenylether (triclosane). Permeabilities PB and maximum fluxes Jmax should be correlated with relevant physicochemical properties.

METHODS

Saturated solutions of the above-mentioned compounds in a propylene glycol/water mixture were applied to the skin using glass chambers which were fixed to the upper arms of volunteers. Maximum fluxes were calculated from concentration decreases in the vehicle.

RESULTS

A linear relationship between the logarithms of permeabilities PB of the penetrants (0.02-0.28 cm h-1) and the corresponding octanol/vehicle partition coefficients PCOct/V (166-186,208) was found. Consequently, the influence of aqueous boundary layers could be neglected. However, the slope of the resulting straight line of 0.38 is considerably smaller than unity indicating that PCOct/V does not represent the lipophilicity of the stratum corneum adequately. Maximum fluxes range from 0.5 to 130 micrograms cm-2 h-1. A general equation for the calculation of Jmax was derived based on experimental data taking into account the PCOct/V and the solubilities CsV of the respective penetrants in the vehicle.

Mechanism of testicular atrophy induced by di-n-butyl phthalate in rats. Part 5. Testicular iron depletion and levels of ferritin, haemoglobin and transferrin in the bone marrow, liver and spleen

This study reports changes in levels of ferritin, haemoglobin and transferrin in the bone marrow, liver and spleen as an attempt to determine the causes of testicular iron depletion. A single oral dose of di-n-butyl phthalate (DBP) to male rats caused a sloughing of the germ cells (at 6 h) prior to testicular atrophy. Before the sloughing it was observed that DBP induced decreases both in the iron levels in the blood, bone marrow and testis and in haemoglobin (Hb) levels in the blood, bone marrow and spleen. Decrease in transferrin (Tf) levels was observed in the liver. Significant increases in ferritin and haemosiderin (Hs) levels were observed in the spleen and in the liver and spleen, respectively. In vitro studies where mono-n-butyl phthalate (MBP) was incubated with liver homogenates, MBP caused both the decreases in Hb and Tf-bound iron levels and increases in Hs and Hs-iron levels. The present study proposes that the mechanism of testicular atrophy by DBP might be associated with both the iron release from Hb and/or Tf in the liver and spleen and the subsequent depletion of iron in the blood and testes.

Mechanism of testicular atrophy induced by di-n-butyl phthalate in rats. Part 4. Changes in the activity of succinate dehydrogenase and the levels of transferrin and ferritin in the Sertoli and germ cells

A single oral dose of di-n-butyl phthalate (DBP) to male rats caused a sloughing of the germ cells at 6 h both with a decrease in the activity of succinate dehydrogenase (SDH) in the Sertoli cells and in the Sertoli-germ connection and with an increase in the activity of lactate dehydrogenase (LDH) in the germ cells. Increases in transferrin (Tf) concentrations were observed in the Sertoli cells, Sertoli-germ connection, epididymis-ductus deferens and liver of rats. Decreases in Tf and ferritin (Ft) levels were observed in the seminal vesicle and seminiferous lumen, respectively. An increase in favin adenine dinucleotide (FAD) level was found in the interstitial cells.

Phthalate esters: effects of orally administered dibutylphthalate on cytochrome P-450 mediated metabolism in rat liver and lung

Dibutylphthalate (DBP) was administered to male Sprague Dawley rats in oral doses of 0.01, 0.1 and 1.0 mmol/kg for five days. The lower dose was considered relevant to human intake. Additional groups were given a recovery period of four weeks without DBP. DBP significantly increased the liver microsomal concentration of cytochrome P-450 (48%) at the lowest dose and NADPH-cytochrome-c-reductase activity (28-29%), at the two lower doses. The liver microsomal metabolism of n-hexane increased to about the same extent at all dosage levels. The main increase was found in the formation of the preneurotoxic metabolite 2-hexanol. The induction of cytochrome P-450 and NADPH-cytochrome-c-reductase in liver microsomes did not return to normal after the period of recovery, whereas the metabolism of n-hexane normalized during the same period of time, indicating that the majority of the induced forms of cytochrome P-450 were not related to n-hexane metabolism. No major changes were observed in the liver microsomal metabolism of B(a)P. The only effect found in cytochrome P-450 related metabolism in lung microsomes was a decrease of the B(a)P metabolism, especially in the formation of the 9,10- and 4,5-diol metabolites at lower dosage levels. It is suggested that DBP and its hydrolyzed products formed in the intestine after oral administration exert the same effect on some specific forms of cytochrome P-450 in liver and lung. It is concluded that DBP is a moderate to weak inducer of several minor forms of liver microsomal cytochrome P-450 enzymes in doses which may be relevant to human oral intake.