Evaluation of endocrine disrupting activity of plasticizers in polyvinyl chloride tubes by estrogen receptor alpha binding assay

Polyvinyl chloride (PVC) tubing is an indispensable medical material for extracorporeal circulation therapy. However, di(2-ethylhexyl)phthalate (DEHP), a suspected endocrine disruptor, can be eluted from PVC, suggesting that an alternative material that does not contain DEHP is needed for clinical applications. First, we evaluated the endocrine disrupting risks of the plasticizers contained in PVC tubes by investigating their binding affinities for the human estrogen receptor alpha (ERα). Our results revealed that, while DEHP has some binding affinity for ERα, neither epoxidized soybean oil nor tris(2-ethylhexyl)trimellitate (an alternative to DEHP) has any affinity for ERα. Second, we evaluated the endocrine disrupting risks of a tube made of newly developed plasticizer-free (PF) materials. We confirmed the presence of DEHP and detected several unidentified substances in plasma stored within the PVC tube. This plasma's competitive binding affinity for ERα was significantly higher than that of control plasma (P < 0.01). In contrast, the profile of plasma stored in the PF tube was similar to that of the control, both in terms of high-performance liquid chromatography chromatograms and competitive binding capacity for ERα, suggesting that the PF tube is biocompatible and is useful for reducing the elution of substances capable of binding to ERα. Presented in part at the 42nd Congress of the Japanese Society for Artificial Organs, October 5–7, 2004, Tokyo, Japan     

Participation of the Fas-Signaling System in the Initiation of Germ Cell Apoptosis in Young Rat Testes after Exposure to Mono-(2-Ethylhexyl) Phthalate

The Fas-signaling system is composed of the interacting proteins Fas (CD95/APO-1) and Fas ligand (FasL, CD95L, APO-1L) and is proposed to act in the testis as a paracrine signaling mechanism by which FasL-expressing Sertoli cells initiate apoptosis of Fas-bearing germ cells. Here we describe alterations in the expression of Fas and FasL in the testis after the intimate physical association between Sertoli cells and germ cells is disrupted by exposure to the Sertoli cell toxicant mono-2-(ethylhexyl) phthalate (MEHP). Young, 28-day-old Fisher rats were treated with MEHP (2 g/kg po) and killed 0, 3, 6, and 12 h after exposure. Immunohistochemical analyses revealed a significant increase in the numbers of Fas-positive germ cells as well as increases in the expression of Sertoli cell FasL. Western blot analysis demonstrated a time-dependent increase in the production of the soluble form of FasL after MEHP exposure and suggests that it may participate in triggering apoptosis in germ cells that have lost their intimate association with the Sertoli cells. Measurement of Fas in cytosolic and membrane fractions of testis homogenates by Western blot analysis revealed a significant shift of Fas expression into the membrane fraction after MEHP exposure. Taken together, these observations indicate that the Fas-mediated paracrine signaling mechanism participates in triggering apoptosis of germ cells despite the loss of their close physical association with Sertoli cells. A working model is presented to explain the involvement of the Fas-system in stimulating germ cell apoptosis after MEHP exposure.     

Effects of Diethyl Phthalate and Other Plasticizers on Laurate Hydroxylation in Rat Liver Microsomes

Diethyl phthalate (DEP) is used in pharmaceutical coatings, cosmetics, and plastic films to wrap foods. There is a health concern associated with the exposure to certain phthalate esters because they belong to a class of compounds referred to as peroxisome proliferators which have been shown to increase the incidence of liver tumors when administered to rats. In this study, we have compared DEP to four other commonly used plasticizers, 2-diethylhexyl phthalate (DEHP), dibutyl phthalate (DBP), 2-diethylhexyl adipate (DEHA), and acetyltributyl citrate (ATBC), for their ability to induce the cytochrome P450-mediated fatty acid -hydroxylation system, which is one of the initial cellular responses when animals are treated with peroxisome proliferators. The administration of DEHP, DBP, and DEHA to rats increased the specific activity of laurate 12-hydroxylase from 2.8 ± 1.1 in control rats to 30.3 ± 11.6, 14.5 ± 4.1, and 9.7 ± 1.9 nmol 12-hydroxylaurate formed/min/nmol P450, respectively. In contrast, laurate 12-hydroxylase activity in DEP-and ATBC-treated rats were 4.4 ± 1.2 and 4.4 ± 1.0 nmol 12-hydroxylaurate formed/min/nmol P450, respectively. In addition, whereas DEHP increased peroxisomal palmitoyl-CoA oxidation 6-fold, DEP increased this activity only 1.3-fold. Two protein bands, at 51 and 52 kDa, were found to increase 6- to 12-fold in microsomes of DEHP-, DBP-, and DEHA-treated rats, but these bands were increased only 2-fold in DEP- or ATBC-treated rats.     

Altered gene expression during rat Wolffian duct development following di(n-butyl) phthalate exposure.

Di(n-butyl) phthalate (DBP) is a common plasticizer and solvent that disrupts androgen-dependent male reproductive development in rats. In utero exposure to 500 mg/kg/day DBP on gestation days (GD) 12 to 21 decreases androgen biosynthetic enzymes, resulting in decreased fetal testicular testosterone levels. One consequence of prenatal DBP exposure is malformed epididymides in adult rats. Reduced fetal testosterone levels may be responsible for the malformation, since testosterone is required for Wolffian duct stabilization and their development into epididymides. Currently, little is understood about the molecular mechanisms of Wolffian duct differentiation. The objective of this study was to identify changes in gene expression associated with altered morphology of the proximal Wolffian duct following in utero exposure to DBP. Pregnant Crl:CD(R) (SD) rats were gavaged with corn oil vehicle or 500 mg/kg/day DBP from GD 12 to GD 19 or 21. There were only small morphological differences between control and DBP-exposed Wolffian ducts on GD 19. On GD 21, 89% of male fetuses in the DBP dose group showed marked underdevelopment of Wolffian ducts, characterized by decreased coiling. RNA was isolated from Wolffian ducts on GD 19 and 21. Together with empirical information, cDNA microarrays were used to help identify candidate genes that could be associated with the morphological changes observed on GD 21. These candidate genes were analyzed by real-time RT-PCR. Changes in mRNA expression were observed in genes within the insulin-like growth factor (IGF) pathway, the matrix metalloproteinase (MMP) family, the extracellular matrix, and in other developmentally conserved signaling pathways. On GD 19, immunolocalization of IGF-1 receptor protein demonstrated an increase in cytoplasmic expression in the mesenchymal and epithelial cells. There was also a variable decrease in androgen receptor protein in ductal epithelial cells on GD 19. This study provides insight into the effects of antiandrogens on the molecular mechanisms involved in Wolffian duct development. The altered morphology and changes in gene expression following DBP exposure are suggestive of altered paracrine interactions between ductal epithelial cells and the surrounding mesenchyme during Wolffian duct differentiation due to lowered testosterone production.     

邻苯二甲酸二丁酯对雌性果蝇生殖能力的双重作用

目的:研究邻苯二甲酸二丁酯(DBP)对雌性果蝇生殖能力的影响。方法:将未交配雌性果蝇随机分为5组,分别给予含DBP0.1%(A组)、0.4%(B组)、1.6%(C组)和6.4%(D组)的培养基喂饲,并以0浓度为对照组(E组),在染毒10d和20d时,分别取存活的实验雌蝇进行交配试验和生育试验。结果:各染毒组雌蝇1h交配率随DBP浓度升高而降低,D组雌蝇的1h交配率和生育率明显低于E组(P<0.05或P<0.01);染毒10d后C组的平均生育数和平均产卵期均明显高于E组(P<0.05),且在连续产卵10d后仍保持较高的生育水平;染毒20d后D组的平均生育数和平均产卵期均明显低于E组(P<0.01)。结论:DBP对雌蝇生殖能力有双重作用,较低浓度可提高雌性果蝇生育力,而较高浓度可使其生育能力降低。     

Effects of di(2‐ethylhexyl)phthalate on testicular oxidant/antioxidant status in selenium‐deficient and selenium‐supplemented rats

Di(ethylhexyl)phthalate (DEHP), the most widely used plasticizer, was investigated to determine whether an oxidative stress process was one of the underlying mechanisms for its testicular toxicity potential. To evaluate the effects of selenium (Se), status on the toxicity of DEHP was further objective of this study, as Se is known to play a critical role in testis and in the modulation of intracellular redox equilibrium. Se deficiency was produced in 3‐weeks‐old Sprague–Dawley rats feeding them ≤0.05 mg Se /kg diet for 5 weeks, and Se‐supplementation group was on 1 mg Se/kg diet. DEHP‐treated groups received 1000 mg/kg dose by gavage during the last 10 days of the feeding period. Activities of antioxidant selenoenzymes [glutathione peroxidase 1 (GPx1), glutathione peroxidase 4 (GPx4), thioredoxin reductase (TrxR)], catalase (CAT), superoxide dismutase (SOD), and glutathione S‐transferase (GST); concentrations of reduced glutathione (GSH), oxidized glutathione (GSSG), and thus the GSH/GSSG redox ratio; and thiobarbituric acid reactive substance (TBARS) levels were measured. DEHP was found to induce oxidative stress in rat testis, as evidenced by significant decrease in GSH/GSSG redox ratio (>10‐fold) and marked increase in TBARS levels, and its effects were more pronounced in Se‐deficient rats with ～18.5‐fold decrease in GSH/GSSG redox ratio and a significant decrease in GPx4 activity, whereas Se supplementation was protective by providing substantial elevation of redox ratio and reducing the lipid peroxidation. These findings emphasized the critical role of Se as an effective redox regulator and the importance of Se status in protecting testicular tissue from the oxidant stressor activity of DEHP. © 2011 Wiley Periodicals, Inc. Environ Toxicol 29: 98–107, 2014.     

邻苯二甲酸二丁酯暴露对青春期雌性大鼠卵巢P450scc基因表达的影响

目的:探讨邻苯二甲酸二丁酯(DBP)对青春期雌性大鼠的生殖毒性作用及作用机制.方法:21d龄SPF级雌性SD大鼠,随机分为DBP250 mg/kg、500 mg/kg、1 000 mg/kg3个染毒组和溶剂对照组(玉米油),连续8周灌胃染毒.染毒结束后,在动情前期对大鼠实施处死,取动脉血,利用放射免疫荧光法检测血清中孕酮(P)水平;取卵巢组织提取mRNA,实时荧光定量RT-PCR检测大鼠卵巢组织细胞色素P450胆固醇侧链裂解酶(P450scc)mRNA表达水平.结果:各处理组间大鼠血清P水平有统计学差异(F=4.306,P=0.014),与对照组比较,DBP 1 000 mg/kg剂量组大鼠血清P水平降低(P＜0.05),与对照组比较,250mg/kg及500mg/kg剂量大鼠血清P水平无统计学差异.各处理组间大鼠卵巢P450scc mRNA表达水平有统计学差异(H=15.591,P＜0.01),与对照组比较,DBP 250 mg/kg、500 mg/kg、1 000 mg/kg剂量组大鼠卵巢P450scc mRNA表达水平降低(P＜0.01),各剂量组间卵巢P450scc mRNA表达水平比较无统计学差异(P＞0.05).结论:DBP可使青春期雌性大鼠卵巢P450scc表达降低,提示DBP对雌性大鼠产生生殖毒性.     

增塑剂DEHP对青春期前小鼠学习记忆和氧化应激的影响

目的:研究邻苯二甲酸二乙基已酯(di-2-ethylhexyl phthalate,DEHP)对青春期前小鼠学习记忆和脑组织氧化应激的影响。方法:将初断乳雄性昆明小鼠随机分成0、10、100、1 000mg.kg-1.d-1DEHP剂量组,连续灌胃染毒30d。期间通过行为学实验测试小鼠学习记忆功能的变化,染毒结束后断头处死小鼠,取全脑,检测脑组织中活性氧(ROS)水平、丙二醛(MDA)含量及超氧化物歧化酶(SOD)活性。结果:行为学实验结果显示10、100、1 000mg/kg DEHP对小鼠学习记忆均产生明显损伤作用。随着DEHP染毒剂量的升高,小鼠脑组织中ROS水平和MDA含量逐渐上升,SOD活性下降,并且均在100mg/kg和1 000mg/kg浓度时与对照组相比差异有统计学意义(P<0.05～0.01)。结论:青春期前DEHP暴露对小鼠的学习记忆产生明显损伤作用,其机制可能与脑组织脂质过氧化反应有关。     

邻苯二甲酸二丁酯（DBP）与2型糖尿病的研究进展

邻苯二甲酸二丁酯(di-n-butyl phthalate,DBP)属于邻苯二甲酸脂类,是塑化剂的一种常见成分,也是一种我们普遍接触的到的低水平污染物。糖尿病的发病率在全世界范围内不断增加,如今已成为危害人类身体健康的主要疾病之一。国外研究证实DBP通过氧化应激以及损害过氧化物酶增殖物激活物(PPAR)信号旁路,参与葡萄糖代谢和糖尿病发展。该综述就DBP与2型糖尿病近几年的研究综述如下。     

Derivation of an oral reference dose (RfD) for the plasticizer,di-(2-propylheptyl)phthalate (Palatinol® 10-P)

Di-(2-propylheptyl) phthalate (DPHP) is a high molecular weight polyvinyl chloride plasticizer. Since increasing production volume and broad utility may result in human exposure, an oral reference dose (RfD) was derived from laboratory animal data due to the lack of human data. In addition to liver and kidney, target organs were the thyroid, pituitary and adrenal glands in rats, recognizing that reproductive performance was not altered in two successive generations of DPHP-exposed rats. DPHP caused a reduction in pup and maternal body weights but not developmental or testicular effects typical of “phthalate syndrome.” DPHP was not genotoxic. Due to the lack of carcinogenicity data, there is inadequate information to assess carcinogenic potential. The RfD of 0.1 mg/kg-day was derived from the human equivalent BMDL₁₀ of 10 mg/kg-day for thyroid hypertrophy/hyperplasia in male F₁ adults from the two-generation study. While in utero exposure did not alter sensitivity to thyroid lesions compared to subchronic exposures beginning at 6 weeks of age, F₁ adult males were the longest-term exposed population. The total uncertainty factor of 100x was comprised of intraspecies (10x), study duration (3x), and database (3x) factors but not an interspecies factor since rodents are more sensitive than humans to thyroid gland effects.