[Competitive binding of some alkyl p-hydroxybenzoates to human estrogen receptor alpha and beta]

Repeated-dose toxicity and toxicokinetic study of isobutylparaben in rats subcutaneously treated for 13 weeks

Parabens have historically served as antimicrobial preservatives in a range of consumables such as food, beverages, medications, and personal care products due to their broad-spectrum antibacterial and antifungal properties. Traditionally, these compounds were believed to exhibit low toxicity, causing minimal irritation, and possessing limited sensitization potential. However, recent evidence suggests that parabens might function as endocrine-disrupting chemicals (EDCs). Consequently, extensive research is underway to elucidate potential human health implications arising from exposure to these substances. Among these parabens, particular concerns have been raised regarding the potential adverse effects of iso-butylparaben (IBP). Studies have specifically highlighted its potential for inducing hormonal disruption, significant ocular damage, and allergic skin reactions. This study aimed to evaluate the prolonged systemic toxicity, semen quality, and estrus cycle in relation to endocrine disruption endpoints, alongside assessing the toxicokinetic behavior of IBP in Sprague-Dawley rats following a 13-week repeated subcutaneous administration. The rats were administered either the vehicle (4% Tween 80) or IBP at dosage levels of 2, 10, and 50 mg/kg/day for 13 weeks. Blood collection for toxicokinetic study was conducted on three specified days: day 1 (1st), day 30 (2nd), and day 91 (3rd). Systemic toxicity assessment and potential endocrine effects were based on various parameters including mortality rates, clinical signs, body weights, food and water consumption, ophthalmological findings, urinalysis, hematological and clinical biochemistry tests, organ weights, necropsy and histopathological findings, estrus cycle regularity, semen quality, and toxicokinetic behavior. The findings revealed that IBP induced local irritation at the injection site in males at doses ≥ 10 mg/kg/day and in females at 50 mg/kg/day; however, systemic toxicity was not observed. Consequently, the no-observed-adverse-effect level (NOAEL) for IBP was determined to be 50 mg/kg/day in rats of both sexes, indicating no impact on the endocrine system. The toxicokinetics of IBP exhibited dose-dependent systemic exposure, reaching a maximum dose of 50 mg/kg/day, and repeated administration over 13 weeks showed no signs of accumulation.

Synergistic effects of parabens on the induction of calbindin-D9k gene expression act via a progesterone receptor-mediated pathway in GH3 cells

Although the endocrine-disrupting bioactivity of parabens is weakly estrogenic (parabens are xenoestrogens), their combined synergistic effect is unknown. The aim of this study was to investigate the effects of methyl paraben (MP), ethyl paraben (EP), propyl paraben (PP), isopropyl paraben (IPP), butyl paraben (BP), and isobutyl paraben (IBP), either alone or in combination (MP + EP + PP + BP; PP + IPP; and BP + IBP) on the induction of the estrogenic biomarker gene, calbindin-D9k( CaBP-9k), in rat pituitary lactosomatotrophic GH3 cells. The expression of CaBP-9k mRNA and protein was analyzed using real-time PCR and Western blot analysis, respectively. After 24 h of treatment, a significant increase in CaBP-9k expression was observed. This was dependent upon the length of the paraben alkyl chains (shortest in MP and longest in IBP). Interestingly, the synergistic effects of these paraben combinations were observed at a dose (10−5 M) of these parabens, which induced the highest expression of CaBP-9k mRNA and protein. To investigate the involvement of estrogen receptors (ERs) and progesterone receptors (PRs), through which parabens exert their effects, the expression levels of ERα and PR-B were also examined. The expression of ERα mRNA and protein fluctuated after paraben treatment in GH3 cells, which was not significant. However, the expression level of ERα gene was induced when cotreated with 17β-estradiol (E2) and ICI 182, 780 (estrogen receptor antagonist). The different combinations of parabens induced the expression of the PR-B gene, which was abolished by cotreatment with ICI 182,780. The expression patterns of CaBP-9k and PR-B genes appeared to be similar in response to paraben treatments. This implied that CaBP-9k expression in GH3 cells may be induced by parabens via a PR-mediated pathway. Taken together, these results suggest that exposure to multiple parabens at low concentrations may increase their synergistic estrogenic activities in GH3 cells through a PR-mediated pathway.

Exposure to endocrine disrupting compounds via the food chain: Is packaging a relevant source?

Contamination of foodstuffs by environmental pollutants (e.g. dioxins, metals) receives much attention. Until recently, food packaging as a source of xenobiotics, especially those with endocrine disrupting properties, has received little awareness despite its ubiquitous use. This article reviews the regulations and use of endocrine disrupting compounds (EDCs) in food packaging and discusses their presence within the context of new toxicology paradigms. I focused on substances known to be legally used in food packaging that have been shown to exhibit endocrine disruptive effects in biological systems. I compiled a list of 50 known or potential EDCs used in food contact materials and examined data of EDCs leaching from packaging into food, with a focus on nonylphenol. I included recent advances in toxicology: mixture effects, the developmental origins of adult disease hypothesis, low-dose effects, and epigenetics. I especially considered the case of bisphenol A. The core hypothesis of this review is that chemicals leaching from packaging into food contribute to human EDCs exposure and might lead to chronic disease in light of the current knowledge. Food contact materials are a major source of food contaminants. Many migrating compounds, possibly with endocrine disruptive properties, remain unidentified. There is a need for information on identity/quantity of chemicals leaching into food, human exposure, and long-term impact on health. Especially EDCs in food packaging are of concern. Even at low concentrations, chronic exposure to EDCs is toxicologically relevant. Concerns increase when humans are exposed to mixtures of similar acting EDCs and/or during sensitive windows of development. In particular, non-intentionally added substances (NIAS) migrating from food contact materials need toxicological characterization; the overall migrate of the finished packaging could be evaluated for biological effects using bioassays. The widespread legal use of EDCs in food packaging requires dedicated assessment and should be updated according to contemporary scientific knowledge.

The effects of in utero exposure to a migrant, 4,4'-butylidenebis(6-t-butyl-m-cresol), from nitrile-butadiene rubber gloves on monoamine neurotransmitter in rats

4,4'-Butylidenebis(6-t-butyl-m-cresol) (BBBC) can be eluted from disposable gloves made of nitrile-butadiene rubber and possibly also detected in food. We have reported that BBBC is an androgen and estrogen antagonist. In this report, BBBC (0.1, 1.0 mg/kg body weight (bw)/day) was subcutaneously administered to pregnant rats from gestation days 11 through 18 and the effects on male offspring (postnatal day (PND) 102) were examined. Body weight at lactation and brain weight at PND 102 were decreased in the 1.0 mg/kg bw BBBC-treated group. Altered levels and turnover of the monoamines dopamine (DA), serotonin (5-HT), and noradrenalin (NA) as well as their metabolites were detected. In the prefrontal cortex DA, 3,4-dihydroxyphenylacetic acid (DOPAC), 5-HT, 5-hydroxyindole-3-acetic acid (5-HIAA) levels were significantly increased, but homovanillic acid (HVA)/DA was decreased. In the striatum NA level, DOPAC/DA and HVA/DA were significantly increased, but 3-methoxy-4-hydrophenylglycol hemipiperazinium (MHPG) level and MHPG/NA were decreased. In hippocampus MHPG level was significantly decreased. In hypothalamus 5-HIAA level and 5-HIAA/5-HT were significantly increased. These results suggested that prenatal exposure to BBBC affects the central nervous system of male rat offspring, and BBBC may be an endocrine disrupting-chemical during the fetal periods.

Final Amended Report on the Safety Assessment of Methylparaben, Ethylparaben, Propylparaben, Isopropylparaben, Butylparaben, Isobutylparaben, and Benzylparaben as used in Cosmetic Products

Parabens is the name given to a group of p-hydroxybenzoic acid (PHBA) esters used in over 22,000 cosmetics as preservatives at concentrations up to 0.8% (mixtures of parabens) or up to 0.4% (single paraben). The group includes Methylparaben, Ethylparaben, Propylparaben, Isopropylparaben, Butylparaben, Isobutylparaben, and Benzylparaben. Industry estimates of the daily use of cosmetic products that may contain parabens were 17.76 g for adults and 378 mg for infants. Parabens in cosmetic formulations applied to skin penetrate the stratum corneum in inverse relation to the ester chain length. Carboxylesterases hydrolyze parabens in the skin. Parabens do not accumulate in the body. Serum concentrations of parabens, even after intravenous administration, quickly decline and remain low. Acute toxicity studies in animals indicate that parabens are not significantly toxic by various routes of administration. Subchronic and chronic oral studies indicate that parabens are practically nontoxic. Numerous genotoxicity studies, including Ames testing, dominant lethal assay, hostmediated assay, and cytogenic assays, indicate that the Parabens are generally nonmutagenic, although Ethylparaben and Methylparaben did increase chromosomal aberrations in a Chinese Hamster ovary cell assay. Ethylparaben, Propylparaben, and Butylparaben in the diet produced cell proliferation in the forestomach of rats, with the activity directly related to chain length of the alkyl chain, but Isobutylparaben and Butylparaben were noncarcinogenic in a mouse chronic feeding study. Methylparaben was noncarcinogenic when injected subcutaneously in mice or rats, or when administered intravaginally in rats, and was not cocarcinogenic when injected subcutaneously in mice. Propylparaben was noncarcinogenic in a study of transplacental carcinogenesis. Methylparaben was nonteratogenic in rabbits, rats, mice, and hamsters, and Ethylparaben was nonteratogenic in rats. Parabens, even at levels that produce maternal toxicity, do not produce fetal anomalies in animal studies. Parabens have been extensively studied to evaluate male reproductive toxicity. In one in vitro study, sperm were not viabile at concentrations as low as 6 mg/ml Methylparaben, 8 mg/ml Ethylparaben, 3 mg/ml Propylparaben, or 1 mg/ml Butylparaben, but an in vivo study of 0.1% or 1.0% Methylparaben or Ethylparaben in the diet of mice reported no spermatotoxic effects. Propylparaben did affect sperm counts at all levels from 0.01% to 1.0%. Epididymis and seminal vesicle weight decreases were reported in rats given a 1% oral Butylparaben dose; and decreased sperm number and motile activity in F1 offspring of rats maternally exposed to 100 mg/kg day–1 were reported. Decreased sperm numbers and activity were reported in F1 offspring of female rats given Butylparaben (in DMSO) by subcutaneous injection at 100 or 200 mg/kg day–1, but there were no abnormalities in the reproductive organs. Methylparaben was studied using rats at levels in the diet up to an estimated mean dose of 1141.1 mg/kg day–1 with no adverse testicular effects. Butylparaben was studied using rats at levels in the diet up to an estimated mean dose of 1087.6 mg/kg day–1 in a repeat of the study noted above, but using a larger number of animals and a staging analysis of testicular effects—no adverse reproductive effects were found. Butylparaben does bind to estrogen receptors in isolated rat uteri, but with an affinity orders of magnitude less than natural estradiol. Relative binding (diethylstilbesterol binding affinity set at 100) to the human estrogen receptors α and β increases as a function of chain length from not detectable for Methylparaben to 0.267 ± 0.027 for human estrogen receptor α and 0.340 ± 0.031 for human estrogen receptor β for Isobutylparaben. In a study of androgen receptor binding, Propylparaben exhibited weak competitive binding, but Methylparaben had no binding effect at all. PHBA at 5 mg/kg day–1 subcutaneously (s.c.) was reported to produce an estrogenic response in one uterotrophic assay using mice, but there was no response in another study using rats (s.c. up to 5 mg/kg day–1) and mice (s.c. up to 100 mg/kg day–1) and in a study using rats (s.c. up to 100 mg/kg day–1). Methylparaben failed to produce any effect in uterotrophic assays in two laboratories, but did produce an effect in other studies from another laboratory. The potency of Methylparaben was at least 1000 × less when compared to natural estradiol. The same pattern was reported for Ethylparaben, Propylparaben, and Butylparaben when potency was compared to natural estradiol. In two studies, Isobutylparaben did produce an estrogenic response in the uterotrophic assay, but the potency was at least 240,000 × less than estradiol. In one study, Benzylparaben produced an estrogenic response in the uterotrophic assay, but the potency was at least 330,000 × less than estradiol. Estrogenic activity of parabens and PHBA was increased in human breast cancer cells in vitro, but the increases were around 4 orders of magnitude less than that produced by estradiol. Parabens are practically nonirritating and nonsensitizing in the population with normal skin. Paraben sensitization has occurred and continues to be reported in the case literature, but principally when exposure involves damaged or broken skin. Even when patients with chronic dermatitis are patch-tested to a parabens mix, parabens generally induce sensitization in less than 4% of such individuals. Many patients sensitized to paraben-containing medications can wear cosmetics containing these ingredients with no adverse effects. Clinical patch testing data available over the past 20 years demonstrate no significant change in the overall portion of dermatitis patients that test positive for parabens. As reviewed by the Cosmetic Ingredient Review (CIR) Expert Panel, the available acute, subchronic, and chronic toxicity tests, using a range of exposure routes, demonstrate a low order of parabens' toxicity at concentrations that would be used in cosmetics. Parabens are rarely irritating or sensitizing to normal human skin at concentrations used in cosmetics. Although parabens do penetrate the stratum corneum, metabolism of parabens takes place within viable skin, which is likely to result in only 1% unmetabolized parabens available for absorption into the body. The Expert Panel did consider data in the category of endocrine disruption, including male reproductive toxicity and various estrogenic activity studies. The CIR Expert Panel compared exposures to parabens resulting from use of cosmetic products to a no observed adverse effect level (NOAEL) of 1000 mg/kg day–1 based on the most statistically powerful and well-conducted study of the effects of Butylparabens on the male reproductive system. The CIR Expert Panel considered exposures to cosmetic products containing a single parabens preservative (use level of 0.4%) separately from products containing multiple parabens (use level of 0.8%) and infant exposures separately from adult exposures in determining margins of safety (MOS). The MOS for infants ranged from ~6000 for single paraben products to ~3000 for multiple paraben products. The MOS for adults ranged from 1690 for single paraben products to 840 for multiple paraben products. The Expert Panel considers that these MOS determinations are conservative and likely represent an overestimate of the possibility of an adverse effect (e.g., use concentrations may be lower, penetration may be less) and support the safety of cosmetic products in which parabens preservatives are used.

Endocrine disruptive effects of chemicals eluted from nitrile-butadiene rubber gloves using reporter gene assay systems

Disposable gloves made of nitrile-butadiene rubber (NBR) are used for contact with foodstuffs rather than polyvinyl chloride gloves containing di(2-ethylhexyl)phthalate (DEHP), because endocrine-disruptive effects are suspected for phthalate diesters including DEHP. However, 4,4'-butylidenebis(6-t-butyl-m-cresol) (BBBC), 2,4-di-t-butylphenol, and 2,2,4-trimetyl-1,3-pentanediol diisobutyrate can be eluted from NBR gloves, and possibly also detected in food. In this study, we examined the endocrine-disrupting effects of these chemicals via androgen receptor (AR) and estrogen receptor (ER)-mediated pathways using stably transfected reporter gene cell lines expressing AR (AR-EcoScreen system) and ER (MVLN cells), respectively. We also examined the binding activities of these chemicals to AR and ER. The IC50 value of BBBC for antagonistic androgen was in the range of 10(-6)M. The strength of inhibition was about 5 times that of a known androgen antagonist, 1,1'-(2,2-dichloroethylidene)bis[4-chlorobenzene] (p,p'-DDE), and similar to that of bisphenol A. The IC50 value of BBBC for antagonistic estrogen was in the range of 10(-6)M. These results suggest that BBBC and its structural homologue, 4,4'-thiobis(6-t-butyl-m-cresol) are androgen and estrogen antagonists. It is therefore necessary to study these chemicals in vivo, and clarify their effect on the endocrine system.

A review of the endocrine activity of parabens and implications for potential risks to human health

Parabens are a group of the alkyl esters of p-hydroxybenzoic acid and typically include methylparaben, ethylparaben, propylparaben, butylparaben, isobutylparaben, isopropylparaben, and benzylparaben. Parabens (or their salts) are widely used as preservatives in cosmetics, toiletries, and pharmaceuticals due to their relatively low toxicity profile and a long history of safe use. Testing of parabens has revealed to varying degrees that individual paraben compounds have weakly estrogenic activity in some in vitro screening tests, such as ligand binding to the estrogen receptor, regulation of CAT gene expression, and proliferation of MCF-7 cells. Reported in vivo effects include increased uterine weight (i.e., butyl-, isobutyl-, and benzylparaben) and male reproductive-tract effects (i.e., butyl- and propylparaben). However, in relation to estrogen as a control during in vivo studies, the parabens with activity are many orders of magnitude less active than estrogen. While exposure to sufficient doses of exogenous estrogen can increase the risk of certain adverse effects, the presumption that similar risks might also result from exposure to endocrine-active chemicals (EACs) with far weaker activity is still speculative. In assessing the likelihood that exposure to weakly active EACs might be etiologically associated with adverse effects due to an endocrine-mediated mode of action, it is paramount to consider both the doses and the potency of such compounds in comparison with estrogen. In this review, a comparative approach involving both dose and potency is used to assess whether in utero or adult exposure to parabens might be associated with adverse effects mediated via an estrogen-modulating mode of action. In utilizing this approach, the paraben doses required to produce estrogenic effects in vivo are compared with the doses of either 17beta-estradiol or diethylstilbestrol (DES) that are well established in their ability to affect endocrine activity. Where possible and appropriate, emphasis is placed on direct comparisons with human data with either 17beta-estradiol or DES, since this does not require extrapolation from animal data with the uncertainties inherent in such comparisons. Based on these comparisons using worst-case assumptions pertaining to total daily exposures to parabens and dose/potency comparisons with both human and animal no-observed-effect levels (NOELs) and lowest-observed-effect levels (LOELs) for estrogen or DES, it is biologically implausible that parabens could increase the risk of any estrogen-mediated endpoint, including effects on the male reproductive tract or breast cancer. Additional analysis based on the concept of a hygiene-based margin of safety (HBMOS), a comparative approach for assessing the estrogen activities of weakly active EACs, demonstrates that worst-case daily exposure to parabens would present substantially less risk relative to exposure to naturally occurring EACs in the diet such as the phytoestrogen daidzein.

Estrogenic activity of cosmetic components in reporter cell lines: parabens, UV screens, and musks

In this work, the estrogenic effects of three classes of substances included in cosmetic formulations-parabens, ultraviolet (UV) screens, and musk fragrances-were studied. Their estrogenic activity was measured with the use of three reporter cell lines: HELN, HELN ERalpha, and HELN ERbeta. These three cell lines allowed for the measurement of estrogenic activity toward estrogen receptors alpha and beta (ERalpha and ERbeta, while taking nonspecific interactions into account. Eight of the 15 substances tested showed specific estrogenic activity with the following degree of potency on ERalpha butylparaben > propylparaben > homosalate = octyl-dimethyl-PABA = 4-methyl-benzylidenecamphor = octyl-methoxycinnamate > ethylparaben = galaxolide. Among these active substances, parabens activated ERalpha and ERbeta similarly, UV screens activated ERalpha moderately and had almost no effect on ERbeta, and fragrances did not activate ERbeta. Methylparaben, ethylparaben, musk moskene, celestolide, and cashmeran did not activate estrogenic responses up to 10(-5) M. Musk ketone and benzophenone-3 were not considered estrogenic at 10(-5) M.

Unequivocal estrogen receptor-binding affinity of phthalate esters featured with ring hydroxylation and proper alkyl chain size

The effect of plasticizers phthalate esters (PEs) on health is a controversial subject. PEs are likely to be estrogenic, but the results on the potency obtained by many investigators are still inconsistent and the endocrine disrupting mechanism remains to be clarified. Here, we show that PEs acquire unequivocal binding affinities for human estrogen receptors (ERs) through ring hydroxylation that is possible in the environment and through metabolism. Unexpectedly, the acquired affinities of hydroxylated PEs (PEs-OH) were enhanced by elongation and branching of the ester alkyl chains. PEs-OH with alkyl chains more than six carbons may grope for a new binding site, which is inaccessible to PEs-OH with short chains. The strongest ER-binding affinity among the tested PEs-OH was close to that of diethylstilbestrol, the most potent synthetic ER-binder. Ring hydroxylation would be a new clue to the clarification of the endocrine disruption mechanism of PEs.

Study on anti-androgenic effects of bisphenol a diglycidyl ether (BADGE), bisphenol F diglycidyl ether (BFDGE) and their derivatives using cells stably transfected with human androgen receptor, AR-EcoScreen

We studied in vitro hormonal activity of bisphenol A diglycidyl ether (BADGE) and bisphenol F diglycidyl ether (BFDGE), which are used as a material of interior coating for food cans. We also examined related compounds such as 2,2-bis[4-(3-chloro-2-hydroxypropoxy)phenyl]propane (BADGE.2HCl), and bis[4-(3-chloro-2-hydroxypropoxy)phenyl]methane (BFDGE.2HCl) etc. For this purpose, we constructed two stably transfected CHO-K1 cell lines (AR-EcoScreen for androgenic activity and c-luc for cell toxicity evaluation). One stably expresses luciferase with induction of androgen. The other stably expresses luciferase without androgen induction. Also, we have determined the androgenic and anti-androgenic effects of the test chemicals by reporter gene assay with these cell lines. None of the chemicals tested by this assay exhibited androgen agonistic activity. However, BADGE.2HCl and BFDGE.2HCl had the conspicuous antagonistic activity for androgen. These compounds had a high binding affinity for androgen receptor. Furthermore, these two compounds did not show the estrogenic activity in vitro assays. On the contrary, bisphenol A and bisphenol F exhibited anti-androgenic activity in vitro in addition to the estrogenic activity. These results suggest that these chlorohydroxy compounds of BADGE and BFDGE act as androgen antagonist through the process of binding to androgen receptor.

Effect of UV screens and preservatives on vitellogenin and choriogenin production in male medaka (Oryzias latipes)

Ultra violet (UV) screens and preservatives are widely and increasingly used in cosmetics and pharmaceuticals. In the present study, we examined the estrogenicity of 4-methyl-benzylidene camphor (4-MBC), octyl-methoxycinnamate (OMC), and propyl paraben (n-propyl-p-hydroxy-benzoate; PP), among UV screens and preservatives, using male medaka (Oryzias latipes), in regard to production of vitellogenin (VTG) and choriogenin (CHG) which are known to be estrogen-responsive gene products. First, using a VTG enzyme-linked immunosorbent assay (ELISA) system, we determined the increase in VTG plasma concentration in medaka due to exposure to 4-MBC, OMC, and PP, and compared this concentration to the non-treated control. Next, we found increases in mRNA expression levels of VTG subtypes VTG-1 and VTG-2, and CHG subtypes CHG-L and CHG-H, in liver due to exposure to 4-MBC, OMC, and PP compared to the non-treated control. In addition, we also found increased mRNA expression levels of estrogen receptor (ER) alpha, among sex hormone receptors in the liver, due to exposure to 4-MBC, OMC, and PP compared to the non-treated control. In this study, we showed that 4-MBC, OMC, and PP have estrogenic activity in fish.

Effects of propyl paraben on the male reproductive system

Parabens are p-hydroxybenzoic acid ester compounds widely used as preservatives in foods, cosmetics, toiletries and pharmaceuticals. These compounds exert a weak estrogenic activity as determined by in vitro estrogen receptor assay and in vivo uterotrophic assay. In a previous study, it was demonstrated by the present author that exposure of post-weaning mammals to butyl paraben adversely affects the secretion of testosterone and the function of the male reproductive system. In the present study, it is shown that propyl paraben also adversely affects the hormonal secretion and the male reproductive functions. Propyl paraben was administered to 3-week-old rats which were divided into four groups of eight animals each, at doses of 0.00, 0.01, 0.10 and 1.00% with the AIN93G modified diet. At the end of 4 weeks, the rats were sacrificed by decapitation and the weights of testes, epididymides, prostates, seminal vesicles and preputial glands were determined. There were no treatment-related effects of propyl paraben on the organ weights in any of the study groups. The cauda epididymal sperm reserves and concentrations decreased in a dose-dependent manner and the difference was significant at dose of 0.10% and above. Daily sperm production and its efficiency in the testis of all groups receiving propyl paraben significantly decreased. The serum testosterone concentration decreased in a dose-dependent manner and the decrease was significant in the group that received the highest dose. The exposure level at which this effect was observed is the same as the upper-limit acceptable daily intake (10 mg/kg body weight/day) of parabens in the European Community and Japan.