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Possible endocrine disrupting effects of parabens and their metabolites
Abstract
Parabens are preservatives used in a wide range of cosmetic products, including products for children, and some are permitted in foods. However, there is concern for endocrine disrupting effects. This paper critically discusses the conclusions of recent reviews and original research papers and provides an overview of studies on toxicokinetics. After dermal uptake, parabens are hydrolyzed and conjugated and excreted in urine. Despite high total dermal uptake of paraben and metabolites, little intact paraben can be recovered in blood and urine. Paraben metabolites may play a role in the endocrine disruption seen in experimental animals and studies are needed to determine human levels of parabens and metabolites. Overall, the estrogenic burden of parabens and their metabolites in blood may exceed the action of endogenous estradiol in childhood and the safety margin for propylparaben is very low when comparing worst-case exposure to NOAELs from experimental studies in rats and mice.
... Parabens are synthetic compounds that are derived from para-hydroxybenzoic acid. They are produced by esterification of para-hydroxybenzoic acid with an alcohol, typically methanol or ethyl alcohol [38]. Parabens are used as preservatives in certain processed foods to inhibit microbial growth and extend their shelf life. ...
... Parabens may be used in certain sauces and dressings to prevent spoilage and maintain product quality. They can be found in baked goods, pastries, and confectionery items to inhibit the growth of mold and other microorganisms and are used in certain beverages, such as fruit juices, soft drinks, and alcoholic beverages, to extend their shelf life by preventing microbial contamination [38]. ...
Processed foods, accounting for most consumable food categories today, contain considerable amounts of food additives. Food additives are substances added to food products to improve taste, consistency, appearance, or shelf life. Various food additives, such as phthalates, bisphenol A, tartrazine, erythrosine, artificial sweeteners, and parabens, have been identified as potential sources of endocrine-disrupting chemicals (EDCs) in processed foods. EDCs are substances that frequently interfere with the regular functioning of the endocrine system, creating an unusual environment in the biological system, which leads to adverse health effects such as the disruption of hormone synthesis, receptor binding, and signal transduction pathways, as well as energy metabolic homeostatic disorders which potentially increasing the risk of obesity, type-2 diabetes, cardiometabolic diseases and may also trigger allergic reactions. Consequently, they can also impact mammary gland development, and reproductive function, further leading to developmental abnormalities. This review aims to insights into the various food additives that act as potential endocrine-disrupting chemicals (EDCs) and to describe their applications in the food industry, as well as the failure of hormonal homeostatic mechanisms, which eventually result in hazardous health effects. It also outlines strategies to reduce the use of food additives and suggests alternative additives with minimal or no endocrine-disrupting properties, highlighting their importance for maintaining human health.
... The alkyl chain length of paraben esters can positively correlate with their antimicrobial property (Doron et al., 2001;Gao et al., 2016). Parabens can be absorbed through intact skin and hydrolyzed by carboxylesterases in subcutaneous fatty tissues (Boberg et al., 2010). Studies showed that parabens are rapidly absorbed from the gastrointestinal tract and blood, hydrolyzed to p-hydroxybenzoic acid, conjugated, and then excreted in the urine, but some elimination can also occur through the bile and feces (Boberg et al., 2010;Vale et al., 2022). ...
... Parabens can be absorbed through intact skin and hydrolyzed by carboxylesterases in subcutaneous fatty tissues (Boberg et al., 2010). Studies showed that parabens are rapidly absorbed from the gastrointestinal tract and blood, hydrolyzed to p-hydroxybenzoic acid, conjugated, and then excreted in the urine, but some elimination can also occur through the bile and feces (Boberg et al., 2010;Vale et al., 2022). ...
Parabens are the most prevalent ingredients in cosmetics and personal care products (PCPs). They are colorless and tasteless and exhibit good stability when combined with other components. Because of these unique physicochemical properties, they are extensively used as antimicrobial and antifungal agents. Their release into the aquatic ecosystem poses potential threats to aquatic organisms, including fish. We conducted an electronic search in PubMed ( http://www.ncbi.nlm.nih.gov/pubmed ) using the search term parabens and fish and sorted 93 articles consisting of methyl paraben (MTP), ethyl paraben (ETP), propyl paraben (PPP), butyl paraben (BTP), and benzyl paraben (BNP) in several fish species. Furthermore, we confined our search to six fish species (common carp, Cyprinus carpio ; fathead minnows, Pimephales promelas ; Japanese medaka, Oryzias latipes ; rainbow trout, Oncorhynchus mykiss ; Nile tilapia, Oreochromis niloticus ; and zebrafish, Danio rerio) and four common parabens (MTP, ETP, PPP, and BTP) and sorted 48 articles for review. Our search indicates that among all six fish, zebrafish was the most studied fish and the MTP was the most tested paraben in fish. Moreover, depending on the alkyl chain length and linearity, long-chained parabens were more toxic than the parabens with short chains. Parabens can be considered endocrine disruptors (EDs), targeting estrogen-androgen-thyroid-steroidogenesis (EATS) pathways, blocking the development and growth of gametes, and causing intergenerational toxicity to impact the viability of offspring/larvae. Paraben exposure can also induce behavioral changes and nervous system disorders in fish. Although the USEPA and EU limit the use of parabens in cosmetics and pharmaceuticals, their prolonged persistence in the environment may pose an additional health risk to humans.
... Estrogenic activity of paraben compounds has been reported by several authors. Lemini et al. (2003) examined the impact of PHBA on the uterus, reporting that the estrogen equivalent concentration strength in the bloodstream (EEQ in vivo = 12,000 pM) was found to be more than 2000 times higher than the estrogen levels in children (Boberg et al., 2010). In addition, Pugazhendhi et al. (2005) found that exposure to 10 -5 M of PHBA increased the growth of two types of human breast cancer cells, MCF7 and ZR-75-1. ...
... Assays involving humans, dogs, rabbits, and rats have indicated that PHBA affects the reproductive system, hormonal equilibrium, neurodevelopment, cognitive capacities, and behavior of the offspring (Boberg et al., 2010;Song et al., 2020). Given these findings, comparable estrogenic effects in birds could potentially disrupt their reproductive systems and hormonal balance. ...
Parabens are alkyl esters of p ‐hydroxybenzoic acid that are commonly used as preservatives in personal care products such as cosmetics. Recent studies have revealed the presence of parabens in surface and tap water because of their use as disinfection products; however, little is known about their occurrence in biological samples and their bioaccumulation potential, particularly in raptor birds known as sentinels for pollutant detection. We examined the occurrence and tissue distribution of parabens, their metabolites, and halogenated byproducts in the liver, kidney, brain, and muscle of birds of prey from Texas and North Carolina (USA). Methylparaben (MeP), propylparaben (PrP), and butylparaben (BuP) were detected in more than 50% of all tissues examined, with the kidney exhibiting the highest concentration of MeP (0.65–6.84 ng/g wet wt). Para‐hydroxybenzoic acid (PHBA), a primary metabolite, had the highest detection frequency (>50%) and a high accumulation range in the liver, of 4.64 to 12.55 ng/g. The chlorinated compounds chloromethylparaben and chloroethylparaben were found in over half of the tissues, of which dichloromethylparaben (2.20–3.99 ng/g) and dichloroethylparaben (1.01–5.95 ng/g) in the kidney exhibited the highest concentrations. The dibrominated derivatives dibromideethylparaben (Br2EtP) was detected in more than 50% of samples, particularly in muscle and brain. Concentrations in the range of 0.14 to 17.38 ng/g of Br2EtP were detected in the kidney. Dibromidepropylparaben (Br2PrP) was not frequently detected, but concentrations ranged from 0.09 to 21.70 ng/g in muscle. The accumulations of total amounts (sum) of parent parabens (∑P), metabolites (∑M), and halogenated byproducts (∑H) in different species were not significantly different, but their distribution in tissues differed among the species. Positive correlations were observed among MeP, PrP, BuP, and PHBA in the liver, suggesting similar origins and metabolic pathways. Environ Toxicol Chem 2024;00:1–12. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
... Studies in animals have reported that exposure to parabens may potentiate estrogenic and other hormonal effects, thereby modulating the outcomes of reproduction. 1,2 Several studies have shown that parabens may impair spermatogenesis, and sperm quality in male rats, 3,4 and mice, 5 by damaging various steps in spermatogenesis. Similar effects are increasingly being reported in humans. ...
... Several studies have reported that parabens may impair the quality of human spermatozoa 6,7 and inflict damage to sperm DNA in humans. 8 These effects have been attributed to the elicitation of oxidative stress, 9 endocrine disrupting effects, 2 and possibly to the disturbance of cellular mitochondria. 10 However, a study among Japanese men failed to demonstrate a significant difference in levels of urinary parabens in association with sperm parameters in men attending an infertility clinic. ...
Background
Parabens, which are chemicals used as preservatives in cosmetic and pharmaceutical products, have been reported to be associated with low sperm quality in animal and human models. Despite the high exposure of men to paraben-containing products in Nigeria, there are no known studies that investigate the association of parabens with sperm quality in the country.
Objective
To determine the association of urinary levels of metabolites of parabens with sperm count and quality.
Design/Setting
A multicenter case–control study among fertile and infertile men in five hospitals in southern Nigeria. A total of 136 men diagnosed with male infertility (cases) were compared with 154 controls with normal fertility. Urinary levels of parabens (ethyl-paraben, methylparaben, propylparaben, and butylparaben) were measured using liquid chromatography mass spectrometry, while semen analysis and hormone assays were carried out using World Health Organization standards and radioimmunoassay, respectively. Data were analyzed with non-parametric statistics and non-parametric linear regression.
Results
The results showed high levels of parabens in both cases and controls. However, there was no statistically significant difference in urinary levels of ethyl-paraben, methylparaben, propylparaben, and butylparaben between cases and controls. In contrast, propylparaben had a decreasing association with total motility in both groups, but the effect was only statistically significant in the case of male infertility. The results of the regression analysis showed that a unit increase in propylparaben significantly decreased total motility in the cases (infertile men). Similarly, a unit increase in propylparaben decreased morphology significantly in the unadjusted model for infertile men. Only serum testosterone showed an insignificant correlation with urinary parabens.
Conclusion
We conclude that urinary parabens are associated with features of poor sperm quality – motility, morphology, and volume. Measures to reduce exposure of men to agents containing parabens in Nigeria may reduce the prevalence of male infertility in the country.
... Moreso, Harley et al. (2019) found that the concentration of prenatal Mep was related to early menarche in girls from a longitudinal birth cohort study. Furthermore, studies have found that for every ten times increase in urinary Mep concentration in boys with asthma, the prevalence of reporting emergency visits increases (Boberg et al. 2010). However, among the studies on parabens exposure and health problems, research on the association between Mep and BMD still needs to be explored. ...
... One of the reasons was that the urinary Mep concentration of females was higher than that in males. Moreso, many animal experiments showed that Mep had estrogen activity (Boberg et al. 2010;Darbre and Harvey 2008;Karpuzoglu et al. 2013). While bone is an estrogen-dependent tissue, sex hormones, especially estrogen, can directly or indirectly affect bone. ...
Previous epidemiological study has explored a positive association between methylparaben (Mep) and bone mineral density (BMD) in adults. Evidence linking Mep and BMD in children and adolescents is very limited. This study examined the association between Mep and BMD in children and adolescents aged 8–19 years. In this cross-sectional study, 1830 children and adolescents aged 8–19 years from NHANES 2011–2016 were analyzed. Mep was ln-transformed for analysis of the skewed distribution. Multiple linear regression analyses were performed to evaluate Mep’s association with BMD (containing total BMD, trunk bone BMD, pelvis BMD, lumbar spine BMD, and thoracic spine BMD). Moreover, a generalized additive model (GAM) and a fitted smoothing curve (penalized spline method) were conducted to explore the exact shape of curve between them. In the fully adjusted model, ln-transformed Mep and BMD showed an independent and positive association (total BMD (β = 0.003, 95% CI (0.001, 0.005), P = 0.01), trunk bone BMD (β = 0.002, 95% CI (0.000, 0.005), P = 0.04), pelvis BMD (β = 0.004, 95% CI (0.001, 0.008), P = 0.02), lumbar spine BMD (β = 0.005, 95% CI (0.001, 0.008), P = 0.01), thoracic spine BMD (β = 0.003, 95% CI (0.001, 0.005), P = 0.02)) and a linear association. Subgroup analysis showed positive association between ln-transformed Mep and BMD. Furthermore, the positive association was significant in females and children aged 12–19 years (P for trend < 0.05). This study is the first study to find evidence demonstrating that exposure to Mep may be positively associated with BMD in children and adolescents aged 8–19 years. Validation of our findings will need further research.
... 4-hydroxybenzoic acid (4-HB) is widely recognized as the ultimate metabolite of PBs in living organisms (Abbas et al., 2010). Nevertheless, it is important to note that there are additional metabolites of PBs that have been identified, namely 3,4-dihydroxybenzoic acid (3,4-DHB), methyl protocatechuate (OH-MeP), and ethyl protocatechuate (OH-EtP) (Boberg et al., 2010). These metabolites are also classified as emerging endocrine-disrupting chemicals. ...
... In addition, the absorption of parabens is dependent on the length of the ester chain and the specific formulation. Moreover, the rate of absorption of parabens into the skin is observed to escalate as the chain length increases, as confirmed by the findings of this investigation (specifically, MeP > EtP > BuP) (Boberg et al., 2010). Furthermore, it was observed that compounds with elevated hydrophobicity demonstrated a propensity to augment absorption efficacy during the process of digestion while concurrently reducing their excretion into the organism's surrounding environment (Gobas et al., 1999;Kelly et al., 2008). ...
Parabens have emerged as the primary preservative of choice in numerous consumer goods, prompting growing apprehension regarding their potential for human exposure. The study employed the optimized QuEChERs sample extraction method and the UHPLC-Q-Orbitrap HRMS system to generate the initial contamination profiles of seven parabens and their four metabolites in a total of 114 fish samples found along the coastline of Vietnam. The findings of the study indicated that methylparaben was the predominant substance detected, exhibiting the highest concentration in the largehead hairtail (Trichiurus lepturus) species at 32.8 ng g−1 dry weight (dw). Additionally, the metabolites with the highest detectable concentrations in the largehead hairtail were found to be 4-HB and 3,4-DHB, with levels of 8822.0 ng g−1 dw and 3490.8 ng g−1 dw, respectively. Besides, the study reveals notable variations in paraben concentrations across three distinct regions in Vietnam, namely the Central, North, and South (Mann-Whitney U test, p < 0.05). The trophic magnification factors (TMF) for methylparaben, ethylparaben, ethyl protocatechuate, and 4-hydroxybenzoic acid exhibited values exceeding 1, indicating substantial biomagnification of these substances within the marine food web of Vietnam. Additionally, noteworthy positive associations have been observed between methylparaben and ethylparaben, as well as their respective metabolites. Based on the findings of the study, it can be concluded that there is no direct impact of seafood consumption on human health in Vietnam.
... inhibition of the regeneration ability [12], alteration of cellular responses in liver, kidney and gills [13], and endocrine disruption (ED) [5,[14][15][16]. ...
Pharmaceuticals and personal care products (PPCPs) are emerging contaminants (ECs), whose presence in the environment is of increasing concern due to their widespread use and possible detrimental effects on wildlife and humans. These chemicals may present multiple hazardous properties such as environmental persistence, toxicity, high mobility, and the potential for bioaccumulation. In this study, extended bibliographic research was conducted to characterize the removal efficiency (RE) of PPCPs in wastewater treatment plants (WWTPs) considering different technologies. Measured values of RE were collected from the literature or calculated for 251 compounds. The molecular structure of the 245 PPCPs were used as the input to generate predictions of multiple properties using several QSAR tools, such as the OECD Toolbox, OPERA, EPI Suite™, and QSAR-ME Profiler. These predictions were compared to regulatory thresholds to identify hazardous chemicals and to screen persistent, mobile and toxic (PMT) or persistent, bioaccumulative and toxic (PBT) substances. Finally, chemicals were prioritized by combining values of RE and QSAR predictions for multiple properties. A total of 16 out of the 245 molecules were prioritized as the most hazardous compounds to the aquatic environment and, among these, six were associated with potential risk due to their exposure concentrations reported in the literature.
... Short chain paraben compounds, mainly including methylparaben (MeP), ethylparaben (EtP), propylparaben (PrP), butylparaben (BuP), and pentylparaben (PeP), are widely used as preservatives in food, medicine, cosmetics, and personal care products due to their strong anti-bacterial strength, low cost, and stability [15,21,34,4,5], among which MeP and PrP are especially commonly added in cosmetics and personal care products [27]. As a consequence, parabens have been widely detected in the environment, including wastewater, sewage sludge, sediment, surface water, biota, and even human tissues [28,29,45,8]. ...
... It enters the human body mainly through the skin or mucosa, and is metabolized and detoxified by the liver to produce metabolites that are excreted in urine [26]. Studies have shown that environmental phenyl hydroxides have endocrine-disrupting effects, and long-term exposure to phenyl hydroxide can inhibit hormone biosynthesis, metabolism, and other functions in humans [27,28]. Moreover, Loffredo et al. reported that environmental phenyl hydroxides such as BPA, a known endocrine disruptor, may be associated with increased risks of arthritis and systemic inflammation [29], but the physiological mechanisms of this process remain to be elucidated. ...
Background
To determine the relationship between mixed exposure to three types of endocrine-disrupting chemicals (EDCs), namely phenyl hydroxides, polycyclic aromatic hydrocarbons (PAHs), and phthalates (PAEs), and risk of arthritis.
Methods
Participants were selected from National Health and Nutrition Examination Survey (NHANES). The relationships between the urinary concentrations of phenyl hydroxides, PAHs, and PAEs and the risk of arthritis were analyzed by generalized linear regression model. The mixed exposure to these EDCs and the risk of arthritis was analyzed by weighted quantile sums (WQSs) and Bayesian kernel machine regression (BKMR) model.
Results
Our analysis showed that participants with urinary benzophenone-3 and methylparaben concentrations in the highest quartile (Q4) had an increased risk of arthritis compared with those in Q1. For each one-unit increase in the natural logarithm-converted urinary concentrations of 1-hydroxynapthalene and 2-hydroxynapthalene, the risk of arthritis increased by 5% and 8%, respectively. Chemical mixing index coefficients were significantly associated with risk of arthritis in both WQS positive- and negative-constraint models. In the BKMR model, there was a significant positive correlation between mixed exposure and the risk of arthritis.
Conclusion
Mixed exposure to phenyl hydroxides, PAHs, and PAEs increased the risk of arthritis, with exposure to PAHs being the key factor.
... Kasprzyk-Hordern et al. [24] analizaron la existencia y la cantidad de drogas ilícitas en tres ríos en el Reino Unido (incluyendo fármacos para el cuidado personal que tuvieran parabenos). Los autores proponen la necesidad de tratar mejor las aguas residuales para evitar este tipo de contaminaciones, aunque se den en niveles bajos [25]. En conclusión, aunque existen estudios que apoyan la tesis de que los parabenos no son dañinos para la salud humana [26], también existen estudios que muestran lo contrario [27] generando una incertidumbre sobre el impacto de los parabenos en la salud. ...
Resumen Aunque los parabenos son disruptores endocrinos y son bioacumulables en el organismo, son altamente usados en la industria farmacéutica y la literatura científica alrededor de este tema está fragmentada y las revisiones actuales tienen un enfoque narrativo. El objetivo de este artículo es entender la evolución de las diferentes discusiones sobre parabenos. Se realizó una consulta en Scopus y se aplicó el algoritmo de Tree of Science. Los resultados se muestran en forma de raíz, tronco y ramas. Estás últimas identifican las tres temáticas más importantes, que fueron: técnicas químicas y analíticas de remoción de parabenos en diversas matrices, los cuerpos de agua y su relación con la presencia de parabenos catalogados como contaminantes emergentes. La última subárea es la identificación de parabenos utilizando técnicas cromatográficas y preparación de muestras miniaturizadas. En general, se presenta una discusión alrededor del impacto de los parabenos en la salud humana.
... From the Applicant: A few reviews exist in the literature relating generally to parabens that discuss the potential of the parent paraben substance to be endocrine active (Golden et al. 2005;Boberg et Nowak et al. 2018). A number of in vitro and in vivo studies have been performed to investigate endocrine activity specifically for Methylparaben. ...
OPINION on Methylparaben (CAS No. 99-76-3, EC No. 202-785-7)
U. Bernauer, L. Bodin, Q. Chaudhry, P.J. Coenraads, M. Dusinska, J. Ezendam, E. Gaffet, C. L. Galli, E. Panteri, V. Rogiers, Ch. Rousselle, M. Stepnik, T. Vanhaecke, S. Wijnhoven, E. Benfentati, N. Cabaton, E. Corsini, A. Koutsodimou, H. Louro, W. Uter, N. von Goetz
The SCCS adopted this document by written procedure on 14 December 2023 (95 pages)
Mise en ligne : 29th July 2024
Ed. Publications Office of the European Union, Luxembourg, Luxembourg
ISSN : 1831-4767
ISBN : 978-92-68-19390-7
DOI : 10.2875/86920
Catalog Number : EW-AQ-24-007-EN-N
https://op.europa.eu/en/publication-detail/-/publication/3de5d26b-4e1b-11ef-acbc-01aa75ed71a1/language-en/format-PDF/source-337153926
... As observed for BPA, parabens and BP-3 were associated with delayed gonadarche in boys, mostly in those with underweight/normal weight, despite the capacity of these chemicals to display weak estrogenic activities and bind with the estrogen receptors (Boberg et al., 2010;Okubo et al., 2001;Schlumpf et al., 2001). The only available human study relating pubertal development to prenatal exposure to these chemicals found no association between exposure biomarkers during pregnancy and gonadarche or pubarche timing in boys in the CHAMACOS cohort, although it described an association between peripubertal PrPB and earlier gonadarche (Harley et al., 2019). ...
... From the Applicant: A few reviews exist in the literature relating generally to parabens that discuss the potential of the parent paraben substance to be endocrine active (Golden et al. 2005;Boberg et Nowak et al. 2018). A number of in vitro and in vivo studies have been performed to investigate endocrine activity specifically for Methylparaben. ...
SCCS OPINION on Methylparaben (CAS No. 99-76-3, EC No. 202-785-7) - SCCS/1652/23– Final Opinion and Corrigendum
U. Bernauer, L. Bodin, Q. Chaudhry, P.J. Coenraads, M. Dusinska, J. Ezendam, E. Gaffet, C. L. Galli, E. Panteri, V. Rogiers, Ch. Rousselle, M. Stepnik, T. Vanhaecke, S. Wijnhoven, E. Benfentati, N. Cabaton, E. Corsini, A. Koutsodimou, H. Louro, W. Uter, N. von Goetz
The SCCS adopted this document by written procedure on 14 December 2023 (95 pages)
CORRIGENDUM adopted by written procedure on 28 February 2024
Mise en ligne : 5 Mars 2024
https://health.ec.europa.eu/publications/methylparaben-cas-no-99-76-3-ec-no-202-785-7_en
https://health.ec.europa.eu/document/download/eb3192aa-089c-4fcf-8cac-b34892dd0b3e_en?filename=sccs_o_276_final.pdf
... Although parabens are generally considered to be safe, some in vivo and in vitro studies have recently demonstrated their endocrine disrupting effects, even at low concentrations (Vale et al., 2022;Wei et al., 2021). Likewise, 4-hydroxybenzoic acid (4-HB), the main metabolite and hydrolysate of parabens, also exhibited endocrine disrupting properties (Boberg et al., 2010). The most widely produced and used parabens included methylparaben (MeP), ethylparaben (EtP), propylparaben (PrP), butylparaben (BuP), and benzylparaben (BzP) (Jeong et al., 2019). ...
... The indiscriminate use of these compounds in various products has aroused scientific interest in the effects of exposure to parabens. Since then, it has been shown that parabens have a potential estrogenic action capable of interfering with the body's homeostasis and thus could be classified as an EDC [72][73][74]. To regulate the use of parabens in Brazil, the Agência Nacional de Vigilância Sanitaria (ANVISA, Brazil) allows the use of up to 0.4% of individual parabens and up to 0.8% of conjugated parabens in personal care products, but there are no restrictions on the use of parabens in food products, except for propylparaben, which was banned [75]. ...
Parabens are classified as endocrine-disrupting chemicals (EDCs) capable of interfering with the normal functioning of the thyroid, affecting the proper regulation of the biosynthesis of thyroid hormones (THs), which is controlled by the hypothalamic–pituitary–thyroid axis (HPT). Given the crucial role of these hormones in health and the growing evidence of diseases related to thyroid dysfunction, this review looks at the effects of paraben exposure on the thyroid. In this study, we considered research carried out in vitro and in vivo and epidemiological studies published between 1951 and 2023, which demonstrated an association between exposure to parabens and dysfunctions of the HPT axis. In humans, exposure to parabens increases thyroid-stimulating hormone (TSH) levels, while exposure decreases TSH levels in rodents. The effects on THs levels are also poorly described, as well as peripheral metabolism. Regardless, recent studies have shown different actions between different subtypes of parabens on the HPT axis, which allows us to speculate that the mechanism of action of these parabens is different. Furthermore, studies of exposure to parabens are more evident in women than in men. Therefore, future studies are needed to clarify the effects of exposure to parabens and their mechanisms of action on this axis.
... Other research indicates that parabens, especially isobutyl paraben, can alter neuro/psychological behaviors (Kawaguchi et al., 2009b;Kawaguchi et al., 2010;Ali and Elgoly, 2013). These studies have intensified the regulatory debate regarding the use of parabens in foods and cosmetics, resulting in the banning of parabens in personal care products targeted to consumers under the age of three (Boberg et al., 2010;E.U. Commission, 2011). ...
... Other research indicates that parabens, especially isobutyl paraben, can alter neuro/psychological behaviors (Kawaguchi et al., 2009b;Kawaguchi et al., 2010;Ali and Elgoly, 2013). These studies have intensified the regulatory debate regarding the use of parabens in foods and cosmetics, resulting in the banning of parabens in personal care products targeted to consumers under the age of three (Boberg et al., 2010;E.U. Commission, 2011). ...
... Other research indicates that parabens, especially isobutyl paraben, can alter neuro/psychological behaviors (Kawaguchi et al., 2009b;Kawaguchi et al., 2010;Ali and Elgoly, 2013). These studies have intensified the regulatory debate regarding the use of parabens in foods and cosmetics, resulting in the banning of parabens in personal care products targeted to consumers under the age of three (Boberg et al., 2010;E.U. Commission, 2011). ...
... Other research indicates that parabens, especially isobutyl paraben, can alter neuro/psychological behaviors (Kawaguchi et al., 2009b;Kawaguchi et al., 2010;Ali and Elgoly, 2013). These studies have intensified the regulatory debate regarding the use of parabens in foods and cosmetics, resulting in the banning of parabens in personal care products targeted to consumers under the age of three (Boberg et al., 2010;E.U. Commission, 2011). ...
In machine learning, deep learning is the most popular topic having a wide range of applications such as computer vision, natural language processing, speech recognition, visual object detection, disease prediction, drug discovery, bioinformatics, biomedicine, etc. Of these applications, health care and medical science-related applications are dramatically on the rise. The tremendous big data growth, the Internet of Things (IoT), connected devices, and high-performance computers utilizing GPUs and TPUs are the main reasons why deep learning is so popular. Based on their specific tasks, medical IoT, digital images, electronic health record (EHR) data, genomic data, and central medical databases are the primary data sources for deep learning systems. Several potential issues such as privacy, QoS optimization, and deployment indicate the pivotal part of deep learning. In this paper, deep learning for IoT applications in health care systems is reviewed based on the Systematic Literature Review (SLR). This paper investigates the related researches, selected from among 44 published research papers, conducted within a period of ten years – 2010 to 2020. Firstly, theoretical concepts and ideas of deep learning and technical taxonomy are proposed. Afterwards, major deep learning applications for IoT in health care and medical sciences are presented through analyzing the related works. Later, the main idea, advantages, disadvantages, and limitations of each study are discussed, preceding suggestions for further research.
... Indeed, they are considered "pseudo-persistent" because they are continually released into the environment (Tong et al., 2022). Many studies have shown that continuous exposure to some of these compounds contributes to the dissemination of antibiotic resistance genes (ARG) in the environment (Tadić et al., 2021) and poses health risks to living organisms, including humans (Boberg et al., 2010;Cavus et al., 2008;Liang et al., 2017;Rosenfeld and Feng, 2011;Zhao et al., 2013). ...
Currently, water scarcity affects more than three billion people. Nevertheless, the volume of treated wastewater discharged into the environment is estimated to exceed 100 m3 per inhabitant/year. These water resources are regularly used in agriculture worldwide to overcome water shortages. Such a practice, however, entails the uptake of waterborne pollutants, such as pharmaceuticals and personal care products (PPCPs), by crops and their further access to the food web, constituting an additional route of human exposure to PPCPs, with potential health outcomes. In this study, the occurrence of 56 PPCPs in tomatoes, lettuce, and carrot, together with soil and irrigation water, was evaluated using a QuEChERS-based methodology for extraction and LC-MS/MS for analysis. The influence of the selected cultivation conditions on the plant uptake levels of PPCPs was assessed. Two irrigation water qualities (secondary and tertiary treatment effluents), two soil compositions (sandy and clayey), two irrigation systems (dripping and sprinkling), and three crop types (lettuce, tomato, and carrot) were tested. Carrots showed the highest load of PPCPs (7787 ng/g dw), followed by tomatoes (1692 ng/g dw) and lettuces (1248 ng/g dw). The most translocated PPCPs were norfluoxetine (fluoxetine antidepressant main metabolite) (521 ng/g dw), and the anti-inflammatory diclofenac (360 ng/g dw). Nine PPCPs, are reported to be accumulated in crops for the first time. Water quality was the most important factor for reducing PPCPs' plant uptake. Overall, the best conditions for reducing PPCP uptake by crops were irrigation with reclaimed water by sprinkling in soils with higher clay content. The risk assessment performed revealed that the crops' consumption posed no risk to human health. This study serves as the first comprehensive assessment of the relevance of diverse cultivation factors on PPCPs' plant uptake under field agricultural practices.
... The indiscriminate use of these compounds in various products has aroused scientific interest in the effects of exposure to parabens. Since then, it has been shown that parabens have a potential estrogenic action capable of interfering with the body's homeostasis, and thus could be classified as an EDC 72,73 . To regulate the use of parabens in Brazil, the Agencia Nacional de Vigilancia Sanitaria (ANVISA, Brazil) allows the use of up to 0.4% of individual parabens and up to 0.8% of conjugated parabens in personal care products, but there are no restrictions on the use of parabens in food products, with the exception of propylparaben which was banned 75 . ...
Parabens are classified as endocrine disrupting compounds (EDCs), capable of interfering with the normal functioning of the thyroid, affecting the proper regulation of the biosynthesis of thyroid hormones (TH) which is controlled by hypothalamic-pituitary-thyroid axis (HPT). Given the crucial role of these hormones in health and the growing evidence of diseases related to thyroid dysfunction, this review looks at the effects of paraben exposure on the thyroid. In this study, we considered research carried out in vitro, in vivo, and epidemiological studies published between 1951 and 2023, which demonstrated an association between exposure to parabens and dysfunctions of the HPT axis. In humans, exposure to parabens appears to increase thyroid-stimulating hormone (TSH) levels, while in rodents, exposure decreases TSH levels. The effects on HT levels are also poorly described, as well as peripheral metabolism. Regardless, recent studies have shown different actions between different subtypes of parabens on the HPT axis, which allows us to speculate that the mechanism of action of these parabens is different. Furthermore, studies of exposure to parabens are more evident in women than in men. Therefore, future studies are needed to clarify the effects of exposure to parabens and their mechanisms of action on this axis.
Since the 1960s, more than 350,000 new chemicals have been introduced into the lives of humans and domestic animals. Many of them have become part of modern life and some are affecting nature as pollutants. Yet, our comprehension of their potential health risks for both humans and animals remains partial. The “epithelial barrier theory” suggests that genetic predisposition and exposure to diverse factors damaging the epithelial barriers contribute to the emergence of allergic and autoimmune conditions. Impaired epithelial barriers, microbial dysbiosis, and tissue inflammation have been observed in a high number of mucosal inflammatory, autoimmune and neuropsychiatric diseases, many of which showed increased prevalence in the last decades. Pets, especially cats and dogs, share living spaces with humans and are exposed to household cleaners, personal care products, air pollutants, and microplastics. The utilisation of cosmetic products and food additives for pets is on the rise, unfortunately, accompanied by less rigorous safety regulations than those governing human products. In this review, we explore the implications of disruptions in epithelial barriers on the well‐being of companion animals, drawing comparisons with humans, and endeavour to elucidate the spectrum of diseases that afflict them. In addition, future research areas with the interconnectedness of human, animal, and environmental well‐being are highlighted in line with the “One Health” concept.
Background
Phthalates and other environmental contaminants, such as phenols and parabens, have been implicated in metabolic health disturbances. This study investigates the mediating effects of urinary phenols and parabens on the relationship between phthalate exposure and Metabolic Changes in adults. Methods: Data from the National Health and Nutrition Examination Survey (NHANES) 2009–2010 cycle were utilized, encompassing 1,669 adults. Phthalate exposure was measured via urinary Ethyl Paraben. BMI served as a proxy for metabolic health changes. The analysis employed mediation models to explore whether urinary phenols and parabens mediate the relationship between phthalate exposure and metabolic Changes, adjusting for covariates. Results: The median age of participants was 46 years, with nearly equal gender distribution (51% males and 49% females). The mediation analysis revealed significant mediation effects for Benzophenone-3 and Propyl Paraben. For Benzophenone-3, the Average Causal Mediation Effect (ACME) was − 0.000773 (95% CI: -0.001242 to 0.000, p < 2e-16), and the direct effect (ADE) was − 0.004198 (95% CI: -0.008295 to 0.000, p = 0.016). Similarly, Propyl Paraben presented significant mediation with an ACME of -0.00105 (95% CI: -0.00159 to 0.000, p = 0.020), and the direct effect (ADE) was − 0.00393 (95% CI: -0.00789 to 0.000, p = 0.036). Conclusion: This study provides robust evidence that specific urinary phenols and parabens significantly mediate the relationship between phthalate exposure and metabolic Changes, shedding light on the pathways through which environmental contaminants might influence metabolic health. The findings underscore the necessity for further research and regulatory measures to mitigate exposure to these chemicals and their impacts on metabolic health.
There is a growing regulatory and scientific interest in the studies of environmental substances that are capable of interfering with the reproductive system. Among them, parabens stand out due to their widespread use and frequent detection as contaminants in human tissues and biological fluids. Therefore, we evaluated the toxic effects of butylparaben on the viability and follicular staging of bovine ovarian follicles in vitro. Fragments of ovaries from five cyclic bovine females were cultured for 44 h in a minimal essential medium (MEM; control) or MEM supplemented with 50 µg/mL and 100 µg/mL of butylparaben (BP 50 and BP 100 groups, respectively). The ovarian fragments were subjected to follicular staging, morphological analysis, morphometric analysis, estradiol analysis and oxidative profiling. No significant changes were observed between the experimental groups in follicular staging, estradiol analysis and oxidative profile analysis. However, the BP 50 group showed a significant decrease in the number of intact ovarian follicles. Moreover, a decrease in the follicular and oocyte diameters was observed in the groups that were exposed to butylparaben. In conclusion, butylparaben impairs the integrity and size of ovarian follicles in an in vitro bovine model, but does not affect the oxidative profile and steroidogenesis.
Bacterial vaginosis (BV) is a microbial dysbiosis that shifts the paradigms of vaginal flora from lactobacilli to opportunistic pathogens. Globally, BV is treated with antibiotic therapy and recurrence rates are > 70% occurring within 6 months due to antibiotic resistance against pathogenic bacteria. An incorporation of lactobacilli orally or intravaginally for the recolonization of healthy microbes in vagina is the suggested course of treatment. Although Lactobacilli are suggested as a novel therapeutic for women’s BV, evaluation of safety and toxicity have not been well understood previously. Therefore, in this study, we aimed to evaluate the safety profile of Lactobacillus plantarum ATG-K2 in subacute intravaginal animal toxicity in Sprague–Dawley rats under OECD guidelines and GLP regulations. Toxicological assessments were performed in a single-dose toxicity study by intravaginal administration with local tolerance study, 1-week repeated-dose intravaginal toxicity dose range finding (DRF) study, and a 2-week repeated-dose intravaginal toxicity study with a 2-week recovery period. Studies were performed at dose 3—18 × 109 CFU/head/day. No toxicological changes in clinical signs, body weight, water and food consumption, urinalysis, hematology, clinical biochemistry, gross findings, or histopathological examination were observed in intravaginal repeated-dose toxicity. And Lactobacillus plantarum ATG-K2 did not show any local tolerance at the same doses as the intravaginal repeated-dose toxicity study. In conclusion, the no-observed-adverse-effect level (NOAEL) of Lactobacillus plantarum ATG-K2 was 12 × 109 CFU/head/day and no target organ was identified in female rats. Our findings are the first to suggest that Lactobacillus plantarum is safe for use as an intravaginal treatment with no adverse effects observed in toxicological testing and has potential for application as a therapeutic agent or for other biological uses.
In this study, an easily applicable and rapid switchable hydrophilicity solvent-based liquid–liquid microextraction method was developed for the extraction of parabens (ethyl, propyl, and butyl parabens) from cream samples prior to analysis by high-performance liquid chromatography–ultraviolet detection. Di-(2-ethylhexyl)phosphoric acid can be used as a switchable hydrophilic extraction solvent which is existed in hydrophilic form in alkaline solution and converted to the hydrophobic formula when the solution is acidified with a mineral acid. Some parameters affecting extraction such as sodium hydroxide volume, hydrochloric acid volume, di-(2-ethylhexyl)phosphoric acid volume, Fe3O4 amount, vortex mixing time, elution solvent type, elution solvent volume and elution mixing time were examined and their optimum values were determined. Under optimum conditions, the limit of detection and limit of quantification were determined to be 0.03–0.11 µg g−1 and 0.12–0.36 µg g−1, respectively. The calibration graphs exhibited coefficients of determination (R2) greater than 0.9991. The relative standard deviation value was calculated as 1.5–5.7% for intraday and 5.2–8.5% for interday. The developed method was successfully applied for the determination of ethyl, propyl and butyl paraben from four different cream samples and relative recovery of 80.5–102.3% were achieved with relative standard deviations of below 5.4.
Silkworm pupae as widely consumed insect products are good biosources of protein and micronutrients. Silkworm rearing throughout the year can be achieved by feeding them an artificial diet instead of native plants, facilitating extensive pupa production. However, artificial diets are prone to spoilage caused by bacterial contamination. Here, we evaluated the antiseptic effect of ethylparaben (EP, chemical preservative) and medium-chain fatty acids (MCFA, natural preservative) in a silkworm artificial diet. Results showed that both preservatives effectively inhibited pathogenic bacterial growth. Furthermore, the addition of EP or MCFA did not negatively impact the production capacity of silkworms and the homeostasis of gut microbiota. However, the expression of genes involved in detoxification such as Ugt2 , and immune response such as Cecropin B , were upregulated after EP consumption. Therefore, natural preservative MCFA emerges as a suitable option from a safety perspective. These findings highlight future directions for improving insect artificial diet formulation.
Parabens (PBs) are used as preservatives in various products. They pollute the environment and penetrate living organisms, showing endocrine disrupting activity. Till now studies on long-term exposure of farm animals to PBs have not been performed. Among matrices using in PBs biomonitoring hair samples are becoming more and more important. During this study concentration levels of methyl paraben (MeP), ethyl paraben (EtP), propyl paraben (PrP) butyl paraben (BuP) and benzyl paraben (BeP) were evaluated using liquid chromatography–mass spectrometry (LC–MS) in hair samples collected from dairy cows bred in the Kyrgyz Republic. MeP was noted in 93.8% of samples (with mean concentration levels 62.2 ± 61.8 pg/mg), PrP in 16.7% of samples (12.4 ± 6.5 pg/mg) and EtP in 8.3% of samples (21.4 ± 11.9 pg/mg). BuP was found only in one sample (2.1%) and BeP was not detected in any sample included in the study. Some differences in MeP concentration levels in the hair samples depending on district, where cows were bred were noted. This study has shown that among PBs, dairy cows are exposed mainly to MeP, and hair samples may be a suitable matrix for research on PBs levels in farm animals.
In this study, a dielectric barrier discharge reactor was designed for the rapid and efficient degradation of methylparaben (MeP), an organic pollutant in wastewater. The superiority of the degradation performance against MeP was jointly evaluated by degradation, voltage-current waveform plots, kinetic curves, energy efficiency and synergy factor. The single DBD discharge performance was investigated and it was determined that the coaxial electrode structure achieves an optimal energy consumption of 0.28 g/kWh at a dielectric tube thickness of 1 mm gas gap of 2 mm peak voltage of 21 kV.The degradation rate of MeP reached 70.1% after 15 min of treatment at discharge frequency of 7.8 kHz, aeration flow rate of 8 L/min, initial MeP concentration of 30 mg/L and pH=7. The DBD synergized persulfate (PS) system conforms to first-order kinetics, with a kinetic constant increase of 0.080 min ⁻¹ over single DBD. The highest synergy factor was 2.50 at a PS addition of 15 mM, and the highest energy efficiency was 0.99 g/kWh at an initial concentration of 90 mg/L of MeP. Common inorganic anions, CO2-3 promoted degradation, SO 2- 4 inhibited degradation, Cl ⁻ and HPO2-4 had little effect. •OH, •O-2, and SO-4• all participate in the reaction, with •O-2 contributing the most. H 2 O 2 and O 3 were equally involved in degradation.The actual intermediates of the degradation process were identified by LC-MS and combined with DFT calculations to predict the MeP degradation pathway, and toxicity analysis by QSAR model.
Parabens (PBs) are a class of preservatives commonly used in cosmetics and pharmaceuticals. Studies have shown that these compounds may act as endocrine disruptors, affecting thyroxine levels in humans. PBs with longer chain substituents, such as butylparaben (BuP), are less prone to complete biotransformation and are therefore more likely to accumulate in the body. In this study, the effect of high-dose exposure to BuP on thyroid microstructure, ultrastructure, and function was investigated in rats. 50 mg/kg bw per day of BuP was injected subcutaneously into the neck of rats for 4 weeks. Rat thyroid weight, microstructure, and ultrastructure were determined, and the levels of thyroid sodium/iodide symporter (NIS), serum thyroid hormones, and thyroid autoantibodies were measured. The human thyroid cell line was used to study the mechanism of BuP on thyroid epithelial cells. The weight of the thyroid gland of BuP-exposed rats was increased, the structure of the thyroid follicles was irregular and damaged, the mitochondria and rough endoplasmic reticulum were swollen and damaged, and the microvilli at the tip of the epithelium were reduced and disappeared. Serum total T3, total T4, free T3, and free T4 were decreased in BuP-exposed rats, and TSH, peroxidase antibody, and thyroglobulin antibody were increased. In vitro, BuP decreased the level of NIS in thyroid epithelial cells, inhibited proliferation and viability, and induced apoptosis in a dose-dependent manner. This study demonstrated that high-dose exposure to BuP induced structural, ultrastructural, and functional impairment to the thyroid gland of rats, which may be one of the factors leading to hypothyroidism.
Owing to a wide range of advantages, such as stability, non-invasiveness, and ease of sampling, hair has been used progressively for comprehensive biomonitoring of organic pollutants for the last three decades. This has led to the development of new analytical and multi-class analysis methods for the assessment of a broad range of organic pollutants in various population groups, ranging from small-scale studies to advanced studies with a large number of participants based on different exposure settings. This meta-analysis summarizes the existing literature on the assessment of organic pollutants in hair in terms of residue levels, the correlation of hair residue levels with those of other biological matrices and socio-demographic factors, the reliability of hair versus other biomatrices for exposure assessment, the use of segmental hair analysis for chronic exposure evaluation and the effect of external contamination on hair residue levels. Significantly high concentrations of organic pollutants such as pesticides, flame retardants, polychlorinated biphenyls and polycyclic aromatic hydrocarbon were reported in human hair samples from different regions and under different exposure settings. Similarly, high concentrations of pesticides (from agricultural activities), flame retardants (E-waste dismantling activities), dioxins and furans were observed in various occupational settings. Moreover, significant correlations (p < 0.05) for hair and blood concentrations were observed in majority of studies featuring pesticides and flame retardants. While among sociodemographic factors, gender and age significantly affected the hair concentrations in females and children in general exposure settings, whereas adult workers in occupational settings. Furthermore, the assessment of the hair burden of persistent organic pollutants in domestic and wild animals showed high concentrations for pesticides such as HCHs and DDTs whereas the laboratory-based studies using animals demonstrated strong correlations between exposure dose, exposure duration, and measured organic pollutant levels, mainly for chlorpyrifos, diazinon, terbuthylazine, aldrin, dieldrin and pyrethroid metabolites. Considering the critical analysis of the results obtained from literature review, hair is regarded as a reliable matrix for organic pollutant assessment; however, some limitations, as discussed in this review, need to be overcome to reinforce the status of hair as a suitable matrix for exposure assessment.
Parabens, a group of alkyl esters of p-hydroxybenzoic acid, have been found in aquatic systems in particular, leading to concerns about their potential impact on ecosystems. This study investigated the effects of three commonly used parabens, methylparaben (MeP), ethylparaben (EtP), and propylparaben (PrP), on the brackish water flea Diaphanosoma celebensis. The results showed that PrP had the most adverse impact on survival rates, followed by EtP and MeP, while MeP and EtP induced significant adverse effects on reproductive performance. A transcriptome analysis revealed significant differential gene expression patterns in response to paraben exposure, with MeP associated with the most significant effects. MeP and EtP exposure produced greater disruption in the microbiota of D. celebensis than did PrP compared with control groups, and we identified eight key microbiota, including Ruegeria and Roseovarius. Correlation analysis between transcriptome and microbiome data revealed key interactions between specific microbiota and host gene expression. Certain microbial taxa were associated with specific toxicological pathways, shedding light on the complex molecular response and in vivo toxicity effects of parabens. These findings contribute to a deeper understanding of the molecular mechanisms underlying paraben toxicity and highlight the importance of considering the ecological impact of chemical contaminants in aquatic ecosystems.
The effects of ethyl and butyl paraben on steroidogenesis were evaluated in rats exposed in utero. Pregnant Wistar rats were dosed from gestational day (GD) 7 to GD 21, followed by examination of the dams, and the fetuses. Additionally, both parabens were tested in vitro in the H295R steroidogenesis assay and in the T-screen assay, the later to test for their ability to act as thyroid hormone receptor agonist or antagonist. In the in utero exposure toxicity study, neither ethyl nor butyl paraben showed any treatment-related effects on testosterone production, anogenital distance, or testicular histopathology. However, butyl paraben caused a significant decrease in the mRNA expression level of estradiol receptor-beta in fetal ovaries, and also significantly decreased the mRNA expression of steroidogenic acute regulatory protein and peripheral benzodiazepine receptor in the adrenal glands. In vitro butyl paraben increased the proliferation of the GH3 cells in the T-Screen assay, thereby acting as a weak thyroid hormone receptor agonist. In the adrenal H295R steroidogenesis assay both ethyl and butyl paraben caused a significant increase in the progesterone formation. Overall, the results indicate that butyl paraben might have the ability to act as endocrine disruptor by interfering with the transport of cholesterol to the mitochondrion, thereby interfering with steroidogenesis, but also that the two tested parabens do not show clear endocrine disrupting capabilities in our short-term in vivo experiment.
We have utilized a validated (standardized) estrogen receptor (ER) competitive-binding assay to determine the ER affinity for a large, structurally diverse group of chemicals. Uteri from ovariectomized Sprague-Dawley rats were the ER source for the competitive-binding assay. Initially, test chemicals were screened at high concentrations to determine whether a chemical competed with [3H]-estradiol for the ER. Test chemicals that exhibited affinity for the ER in the first tier were subsequently assayed using a wide range of concentrations to characterize the binding curve and to determine each chemical's IC 50 and relative binding affinity (RBA) values. Overall, we assayed 188 chemicals, covering a 1 × 106-fold range of RBAs from several different chemical or use categories, including steroidal estrogens, synthetic estrogens, antiestrogens, other miscellaneous steroids, alkylphenols, diphenyl derivatives, organochlorines, pesticides, alkylhydroxybenzoate preservatives (parabens), phthalates, benzophenone compounds, and a number of other miscellaneous chemicals. Of the 188 chemicals tested, 100 bound to the ER while 88 were non-binders. Included in the 100 chemicals that bound to the ER were 4-benzyloxyphenol, 2,4-dihydroxybenzophenone, and 2,2′-methylenebis(4-chlorophenol), compounds that have not been shown previously to bind the ER. It was also evident that certain structural features, such as an overall ring structure, were important for ER binding. The current study provides the most structurally diverse ER RBA data set with the widest range of RBA values published to date.
Parabens are a group of antimicrobial preservatives widely used in cosmetics, pharmaceuticals, and in foods. Previous in vitro and in vivo studies have shown weak estrogenic effects of some parabens. Thus, especially, exposure of fetus and infants via the mother is a matter of concern. In order to obtain more knowledge about the distribution of ethyl paraben and butyl paraben in pregnant rats and pups after perinatal exposure, the presented study was designed. The data show response and distribution of ethyl paraben and butyl paraben in maternal rat plasma, pools of amniotic fluids, placenta, whole-body fetuses, and in fetal liver after dosing of dams with 100, 200, and 400 mg/kg body weight (bw)/day from gestational day 7 to 21. After cesarean section of dams, the fluids and tissues were collected, deconjugated, and purified by solid-phase extraction, and ethyl paraben and butyl paraben were analyzed by liquid chromatography-tandem mass spectrometry. Markedly higher levels of ethyl paraben compared to butyl paraben were found in all fluids and tissues. Both ethyl paraben and butyl paraben in maternal plasma, livers, and whole-body tissues from fetus seemed to be saturated after dosing with >or= 100 mg/kg bw/day, while both compounds were excreted into amniotic fluid in a dose-dependent manner. Significant difference was found between the level of ethyl paraben in maternal plasma and amniotic fluid after dosing with 200 mg/kg bw/day as well as between the levels of butyl paraben in maternal plasma and amniotic fluid after dosing with 100, 200, and 400 mg/kg bw/day.
Dermally absorbed chemicals can be locally metabolized in the skin during absorption but it is difficult to distinguish this metabolism from liver metabolism by biological monitoring in vivo. Studies with sub-cellular fractions have showed the presence of metabolizing enzymes in the skin but with loss of cellular localization. Studies in HaCat cells in culture maintain cellular localization and in skin, in short-term culture, the chemical can be applied to the skin surface and metabolism during absorption can be monitored. Flow though diffusion systems with tissue culture medium as receptor fluid have maintained the viability of skin and supported metabolism, but dilution of the metabolites in the receptor fluid has limited detection. This article uses data derived by a range of techniques from the Newcastle laboratory to discuss the importance of local metabolism in the skin of butoxyethanol to butoxyacetic acid and parabens to p-hydroxybenzoic acid during dermal absorption, following application to the skin surface.
We used a recombinant yeast estrogen assay to assess the activity of 73 phenolic additives that are used as sunscreens, preservatives, disinfectants, antioxidants, flavorings, or for perfumery. Thirty-two of these compounds displayed activity: 22 with potencies relative to 17beta-estradiol, ranging from 1/3,000 to < 1/3,000,000, and 10 compounds with an impaired response that could not be directly compared with 17beta-estradiol. Forty-one compounds were inactive. The major criteria for activity appear to be the presence of an unhindered phenolic OH group in a para position and a molecular weight of 140-250 Da.
Butyl p-hydroxybenzoic acid (butyl paraben, BP) is widely used as a preservative in food and cosmetic products. Routledge et al showed that BP is weakly estrogenic in both in vitro and in vivo (rat uterotrophic) analyses. We investigated whether maternal exposures to BP during gestation and lactation periods affected the development of the reproductive organs of the F1 offspring. Pregnant Sprague-Dawley rats were injected subcutaneously with 100 or 200 mg/kg of BP from gestation day (GD) 6 to postnatal day (PND) 20. In the group exposed to 200 mg/kg of BP, the proportion of pups born alive and the proportion of pups surviving to weaning were decreased. The body weights of female offspring were significantly decreased at PND 49. The weights of testes, seminal vesicles and prostate glands were significantly decreased in rats exposed to 100 mg/kg of BP on PND 49. In contrast, the weights of female reproductive organs were not affected by BP. The sperm count and the sperm motile activity in the epididymis were significantly decreased at doses of 100 and 200 mg/kg of BP. In accordance with the sperm count in the epididymis, the number of round spermatids and elongated spermatids in the seminiferous tubule (stage VII) were significantly decreased by BP. Testicular expression of estrogen receptor (ER)-alpha and ER-beta mRNA was significantly increased in 200 mg/kg of BP treated group at PND 90. Taken together, these results indicated that maternal exposure of BP might have adverse effects on the F1 male offspring.
The alkyl esters of p-hydroxybenzoic acid known as parabens (Pbens) are used as preservatives in food, pharmaceutical and cosmetic formulations. They have been reported as estrogenic. Here, we present evidence for the in vivo and in vitro bioactivities and receptor binding affinities of methylparaben (MePben), ethylparaben (EtPben), propylparaben (PrPben), and butylparaben (BuPben) compared with those of estradiol (E2). Estrogenicity was studied using the uterotrophic assay in immature (Im) and adult ovariectomized (Ovx) CD1 mice, and in immature female Wistar rats (IW). Animals were subcutaneously (sc) treated for three consecutive days with different molar equivalent doses ranging from 3.62 to 1086 micromol/kg body weight of Pbens, E2 (0.036 micromol/kg), or vehicle. Pbens increased uterine weight in Im and Ovx animals and their relative uterotrophic effect to E2 (100) (RUEE2) were from 34 to 91. The relative uterotrophic potencies related to E2 (100) (RUPE2) of these compounds were from 0.003 to 0.007. The E2 ED50 for CD1 animals able to increase the uterine weight was 7 microg/kg (0.9-55 confidence limits); and that of Pbens ranged from 18 to 74 mg/kg. In IW rats, the ED50 were from 33 to 338 mg/kg. All Pbens, except MePb, competed with [3H]E2 for the estrogen receptor binding sites. The uterotrophic effects of Pbens in Im mice have a positive correlation with the side-chain length of the ester group of these compounds. The E2 and Pbens relative binding affinities (RBA) and Ki values correlated to their estrogenic activity. The NOELs values for Pbens uterotrophic activity in Im were from 0.6 to 6.5 mg/kg per day; and Ovx from 6 to 55 mg/kg. The NOELs IW ranged from 16.5 to 70 mg/kg indicating that Im were more susceptible than Ovx and IW to these effects. The data shown here confirm the estrogenicity of Pbens.
It has been proposed that a global decline in sperm counts, semen quality, and several male reproductive disorders are associated with exposure to environmental chemicals. Thus, the present study examined the effects of two estrogenic chemicals, octylphenol (OP) and bisphenol A (BPA), on epididymal sperm counts and sperm motility, luteinizing hormone (LH)-releasing hormone (LHRH)-stimulated plasma LH and steroid hormones, insulin-like growth factor I (IGF-I), and accessory reproductive organs in pubertal male Wistar rats. Fifty-day-old rats in the OP group (n=11) and BPA group (n=11) received daily sc injections of the respective chemical at a dose of 3 mg/kg bw dissolved in 0.2 mL DMSO. Rats in the control group (DMSO group; n=10) received 0.2 mL DMSO alone. After 2 wk of treatment, a jugular blood sample was taken, and, on the next day, a second blood sample was taken 1 h after an sc injection of LHRH (250 ng). After 5 wk of treatment, rats were deeply anesthetized and heart blood was collected. Epididymal sperm motility and sperm head counts were determined. LHRH increased plasma LH to higher levels in all groups, but the increases were significant (pLHRH injection, the incremental responses of testosterone and progesterone in the OP and BPA groups were small compared to those in the DMSO group, which showed a small LH response. After 5 wk of treatment, plasma testosterone levels were significantly (pppIGF-I levels in the BPA (ppIGF-I, raising the possibility of a link between these chemicals and prostate diseases because IGF-I has been implicated in the pathogenesis of human prostate cancers.
The alkyl esters of p-hydroxybenzoic acid (PHBA) known as parabens (Pbens) are widely used as preservatives in food, pharmaceuticals, and cosmetics. Several in vivo and in vitro studies have shown these compounds to be estrogenic. Here, for the first time, we present evidence of their estrogenicity using a morphometric analysis of uteri from mice treated with the preservatives methylparaben (MePben), ethylparaben (EtPben), propylparaben (PrPben), and butylparaben (BuPben) compared with estradiol (E2). Different groups of adult ovariectomized (Ovx) CD1 mice were subcutaneously (sc) treated daily for three days with two different equimolar doses (362 and 1086 micromol/kg) of the Pbens: MePben (55 and 165 mg/kg), EtPben (60 and 180 mg/kg), PrPben (65 and 195 mg/kg), BuPben (70 and 210 mg/kg), E2 (10 microg/kg; 0.036 micromol/kg), and vehicle (propyleneglycol; V, 10 mL/kg). On the fourth day, uteri were dissected, blotted, weighed, and placed in a fixative solution for 24 h. The paraffin embeded uteri were cut to obtain 7 microm thick transversal sections. Luminal epithelium heights (LEH), glandular epithelium heights (GEH), and myometrium widths (MW) were measured. The highest Pbens dose was able to produce uterotrophic effects (38 to 76%) compared to E2 efects (100%). The relative uterotrophic potency to E2 (100) was from 0.02 to 0.009. Significant increases (P < 0.05) in LEH, GEH, and MW as compared with V were obtained: LEH from 87 to 113% (E2 153%), GEH from 10 to 40% (E2 60%), and MW from 35 to 43% (E2 88%). These results confirm that Pbens at the doses assayed here induce estrogenic histological changes in the uteri of Ovx mice.
Die bei 37,5° mit Sauerstoffgesättigter Tyrodelösung durchströmte Mäuseleber hydrolysierte mindestens 0,151 mg p-Oxybenzoesäureäthylester/g Leber/min zu p-Oxybenzoesäure.
Nach peroraler Aufnahme von 10–20 mg Ester/kg Körpergewicht lassen sich im Serum des Menschen in den folgenden 4 Std kein freier Ester, aber p-Oxybenzoesäure nachweisen.
Nach peroraler Verabreichung von 25, 100 und 500mg Ester/kg ist in den folgenden 8 Std im Serum des Hundes nur nach 500 mg/kg unveränderter Ester nachweisbar. Die p-Oxybenzoesäurekonzentrationen des Serums entsprechen den verabreichten Estermengen.
An androgen receptor (AR)-reporter gene assay for some chemicals was examined using two different types of stably transfected CHO-K1 cell lines (AR-EcoScreen cells for androgenic activity and c-luc cells for cell toxicity evaluation). One stably expresses luciferase with androgen induction. The other stably expresses it without the need for androgen induction. We studied the responsiveness of the luciferase of AR-EcoScreen to androgen agonists and androgen antagonists. The luciferase activity of AR-EcoScreen was highly induced by androgens such as 5α-dihydroxytestosterone and testosterone. Furthermore, the luciferase activity of AR-EcoScreen was very susceptible to androgen antagonists such as hydroxyflutamide and cyproproterone acetate compared with that of MDA-kb2, which stably expresses androgen and glucocorticoid-responsive luciferase and represents a tool for screening for androgenicity. We examined the AR-reporter gene assay of some chemicals containing alkylphenols and parabens using AR-EcoScreen and c-luc cells (AR-EcoScreen system). None of the tested chemicals had any androgenic activity. However, 4-t-octylphenol, 4-n-dodecylphenol, 4-n-nonylphenol, 4-n-hexylphenol, 4-n-pentylphenol, 4-n-octylphenol, and 4-n-propylphenol exerted antiandrogenicity. Isobutylparaben, n-butylparaben, isopropylparaben, and n-propylparaben also had antiandrogenic activity. The level at which these parabens effects were observed is a value that is lower than the upper limit of the acceptable daily intake (ADI, 10 mg/kg/day). 4-Ethylphenol, 4-methylphenol, ethylparaben, and methylparaben had no effect on the androgen-responsive luciferase activity. We propose that the AR-EcoScreen system is suitable for a battery of titer-1 tests to identify chemicals that affect the endocrine system, and that the ADI value of total parabens may have to be lowered in Japan.
In this note, we clarify a relation between block spaces and the Hardy space. We obtain that block spaces\(
B^{{0,\nu }}_{q} {\left( {S^{{n - 1}} } \right)} \subset H^{1} {\left( {S^{{n - 1}} } \right)} + L{\left( {\ln ^{ + } L} \right)}^{{1 + \nu }} {\left( {S^{{n - 1}} } \right)},\nu > - 1,q > 1.
\) Furthermore, if ν ≥ 0, q>1, we verify that block spaces \(
B^{{0,\nu }}_{q} {\left( {S^{{n - 1}} } \right)}
\) are proper subspaces of H
1(S
n−1).
In vitro and in vivo skin penetration of three drugs with different lipophilicities and the enhancing effects of l-geranylazacycloheptan-2-one (GACH) were studied in rats. In vivo drug absorption profiles obtained by deconvolution of urinary excretion profiles were compared to the corresponding in vitro data obtained with a diffusion experiment. In vivo skin penetration of lipophilic butylparaben was considerably greater than that observed in vitro, while hydrophilic mannitol and acyclovir showed low penetration in both systems without GACH pretreatment. On the other hand, GACH enhanced mannitol and acyclovir penetration, especially in the in vivo system. Analysis of absorption profiles, using a two-layer skin model with polar and nonpolar routes in the stratum corneum, suggested that the diffusion length of a viable layer (viable epidermis and dermis) was shorter in vivo than in vitro and the effective area of the polar route in the stratum corneum was larger in vitro without GACH pretreatment. GACH increased the partitioning of acyclovir into the nonpolar route to the same extent in both systems. In addition, GACH increased the effective area of the polar route in vivo, probably because of enhanced water permeability; however, this effect was smaller in vitro since the stratum corneum was already hydrated even without GACH pretreatment.
Phenolic acids, essentially hydroxycinnamic acids and hydroxybenzoic acids, are secondary plant products and commonly found in plant derived foodstuff. The antioxidant and anticarcinogenic properties of phenolic acids could be one of the facts to explain the inverse association between fruit and vegetable intake and the incidence of coronary heart disease and cancer, respectively, as found in epidemiologic studies. Phenolic acids are rarely listed in food composition tables and there are no dietary intake data available. Consequently, a data base containing the phenolic acid content of foods (literatur data) was built and 7-d dietary protocols of 63 women and 56 men of a Bavarian subpopulation (age 19–49 years) of the German National Food Consumption Survey (NVS) were evaluated.
The average phenolic acid intake of men and women is 222 mg/d within a large range. The dominating one within all the phenolic acids is clearly caffeic acid (206 mg/d); the intake of the other phenolic acids amounts to 0.2 (gentisic acid) up to 5.2 mg/d (ellagic acid). The sum of hydroxybenzoic acids and hydroxycinnamic acids amounts to 11 mg/d and 211 mg/d, respectively. Significant sex differences are found for some of the phenolic acids. Especially, the average intake of caffeic acid of women (229 mg/d) is higher than that of men (179 mg/d) caused by the high amount of coffee consumption. The age group “25–49 years” is consuming more coffee than the age group “19–24 years” and, therefore, reveals a significantly higher intake of caffeic acid. The major sources of phenolic acids are coffee with 92% of the caffeic acid intake and fruits (including fruit products and juices) with 75% of the salycilic acid and 59% of the p-coumaric acid intake.
Consequently, phenolic acids are consumed in considerable amounts with food. Since antioxidant and anticarcinogenic properties of phenolic acids are already proven in in vitro as well as in animal experiments, epidemiologic studies will show whether a high phenolic acid intake goes ahead with a reduced risk for coronary heart disease or cancer in humans.
We developed a method using on-line solid phase extraction (SPE) coupled to high performance liquid chromatography-isotope dilution tandem mass spectrometry (HPLC-MS/MS) to measure the serum concentrations of seven environmental phenols and five parabens: bisphenol A; ortho-phenylphenol; 2,4-dichlorophenol; 2,5-dichlorophenol; 2,4,5-trichlorophenol; benzophenone-3; triclosan; and methyl-, ethyl-, propyl-, butyl-, and benzyl-parabens. The phenols and parabens present in serum were retained and concentrated on a C18 reversed-phase size-exclusion SPE column, back-eluted from the SPE column while the eluate was diluted through a mixing Tee (analyte peak focusing), separated using a pair of monolithic HPLC columns, and detected by isotope dilution-MS/MS. Sample preparation did not require protein precipitation, only dilution of the serum with 0.1M formic acid. This method, which combines an on-line SPE with analyte peak focusing feature and the selective atmospheric pressure photoionization MS detection, resulted in limits of detection ranging from 0.1 to 0.5 ng/mL for most of the analytes. The high throughput and adequate sensitivity with yet a relative low serum volume used (100 microL) confirm that analytically it is possible to measure simultaneously these phenols and parabens with the precision and accuracy at sub-parts-per-billion levels required for biomonitoring. However, important additional factors, including validated sample collecting, handling, and storing protocols, as well as toxicokinetic data, are required if these measures are used for exposure assessment.
Four different equi-molar mixtures were investigated for additive endocrine disrupting effects in vitro using the concentration addition model. It was found that additive effects on the same molecular target (the androgen receptor; AR) can be predicted for both mixtures of compounds with effect on the AR (flutamide, procymidone and vinclozolin) and of compounds with and without effects on the AR [finasteride, mono-(2-ethylhexyl) phthalate, prochloraz and vinclozolin]. For a paraben mixture (methyl paraben, ethyl paraben, propyl paraben, butyl paraben and iso-butyl paraben) antagonistic effect on AR could not be predicted under assumption of additivity in our model system. For a mixture containing three azole fungicides (epoxiconazole, propiconazole and tebuconazole), the observed AR antagonistic effects were close to the predicted effect assuming additivity. Azole fungicides are known inhibitors of androgen biosynthesis and in the steroid synthesis assay using H295R cells, the inhibition of testosterone production was close to additive, whereas the inhibition of oestradiol production was over-estimated for the mixture of azole fungicides, when compared with the effect predicted when assuming additivity. Overall these and other studies show that weak endocrine disrupting compounds, like parabens and azole fungicides, give rise to combination effects when they occur in mixtures. These combination effects should be taken into account in regulatory risk assessment not to under-estimate the risks for adverse effects associated with exposure to disrupting chemicals.
The need to understand and estimate quantitatively the aggregate exposure to ingredients used broadly in a variety of product types continues to grow. Currently aggregate exposure is most commonly estimated by using a very simplistic approach of adding or summing the exposures from all the individual product types in which the chemical is used. However, the more broadly the ingredient is used in related consumer products, the more likely this summation will result in an unrealistic estimate of exposure because individuals in the population vary in their patterns of product use including co-use and non-use. Furthermore the ingredient may not be used in all products of a given type. An approach is described for refining this aggregate exposure using data on (1) co-use and non-use patterns of product use, (2) extent of products in which the ingredient is used and (3) dermal penetration and metabolism. This approach and the relative refinement in the aggregate exposure from incorporating these data is illustrated using methyl, n-propyl, n-butyl and ethyl parabens, the most widely used preservative system in personal care and cosmetic products. When these refining factors were used, the aggregate exposure compared to the simple addition approach was reduced by 51%, 58%, 90% and 92% for methyl, n-propyl, n-butyl and ethyl parabens, respectively. Since biomonitoring integrates all sources and routes of exposure, the estimates using this approach were compared to available paraben biomonitoring data. Comparison to the 95th percentile of these data showed that these refined estimates were still conservative by factors of 2-92. All of our refined estimates of aggregate exposure are less than the ADI of 10mg/kg/day for parabens.
In the present study, calbindin-D9k (CaBP-9k), a potent biomarker for screening estrogen-like environmental chemicals in vivo and in vitro, was adopted to examine the potential estrogen-like property of the following parabens: propyl-, isopropyl-, butyl-, and isobutylparaben. Immature female rats were administered for 3 days from postnatal day 14 to 16 with 17alpha-ethinylestradiol (EE, 1 mg/kg body weight [BW]/day) or parabens (62.5, 250, and 1000 mg/kg BW/day). In uterotrophic assays, significantly increased uterus weights were detected in the EE-treated group and in the groups treated with the highest dose of isopropyl-, butyl-, and isobutylparaben. In addition, these parabens induced uterine CaBP-9k messenger RNA (mRNA) and protein levels, whereas cotreatment of parabens and fulvestrant, a pure estrogen receptor (ER) antagonist, completely reversed the paraben-induced gene expression and increased uterine weights. To investigate the ER-mediated mechanism(s) by which parabens exert their effects, the expression level of ER-alpha and progesterone receptor (PR) was analyzed. Exposure to EE or parabens caused a dramatic decrease in expression of both ER-alpha mRNA and protein levels, whereas cotreatment with fulvestrant reversed these effects. These data showed the difference of CaBP-9k and ER-alpha expression, suggesting that CaBP-9k may not express via ER-alpha pathway. In the effect of parabens on CaBP-9k expression through PR mediation, a significantly increased expression of uterine PR gene, a well-known ER-regulating gene, at both transcriptional and translational levels was indicated in the highest dose of isopropyl- and butylparaben. These parabens-induced PR gene expression was completely blocked by fulvestrant. This result indicates that CaBP-9k expression may involve with PR mediates in the estrogenic effect of paraben in immature rat uteri. Taken together, parabens exhibited an estrogen-like property in vivo, which may be mediated by a PR and/or ER-alpha signaling pathway. In addition, our results expanded the current understanding of the potential adverse effects of parabens associated with their estrogen-like activities. Further investigation is needed to elucidate in greater detail the adverse effects of parabens in humans and wildlife.
Parabens, a class of preservatives routinely added to cosmetics, pharmaceuticals, and foods, have estrogenic properties. Given that intrauterine implantation of fertilized ova in inseminated females can be disrupted by minute levels of exogenous estrogens, we assessed the impact of parabens upon early gestation. In Experiment 1, butylparaben was administered subcutaneously in several doses ranging from 0.05 to 35 mg/animal/day to inseminated CF-1 mice on days 1-4 of pregnancy. Butylparaben exposure did not affect litter size, the number of pups born, postnatal day 3 litter weights, or the number of pups surviving to postnatal day 5. In contrast, administration of 500 ng/animal/day 17beta-estradiol terminated all pregnancies. In Experiment 2, propylparaben was subcutaneously administered to inseminated CF-1 mice on gestational days 1-4. Dams were sacrificed on gestation day 6 and the number of implantation sites was counted. Propylparaben had no impact on the number of implantation sites observed. Since Experiments 1 and 2 did not yield the anticipated results, an uterotrophic assay was conducted in Experiment 3 to re-evaluate the in vivo estrogenicity of parabens. Ovariectomized CF-1 and CD-1 mice were administered butylparaben in doses ranging from 0.735 to 35 mg per animal for three consecutive days. Mice were sacrificed on the fourth day, and uterine mass was recorded. There was no effect of butylparaben on uterine wet or dry mass at any dose in either strain. In contrast, administration of 17beta-estradiol consistently increased uterine mass in both strains. These data indicate that the estrogen-sensitive period of implantation is not vulnerable to paraben exposure, and that the in vivo estrogenicity of parabens may not be as potent as previously reported.
Parabens are widely used preservatives in topical products, and are estrogenic in numerous experimental models. The typical cutaneous metabolism model, rat skin, hydrolyzes parabens much faster than human skin. Chronic application and absorption of parabens, combined with low metabolism rates, may lead to prolonged estrogenic effects in the skin.
Parabens are widely used as preservatives in many foods, cosmetics, toiletries, and pharmaceuticals due to their relatively low toxicity profile and to a long history of safe use. Parabens are alkyl esters of p-hydroxybenzoic acid and typically include methylparaben, ethylparaben, propylparaben, butylparaben, isobutylparaben, isopropylparaben and benzylparaben. These compounds are known to have a null or very weak estrogenic activity in estrogen receptor assays in vitro. In recent years, an increasing concern has emerged regarding possible adverse effects of chemicals in food and in cosmetics on human reproduction outcomes. In developed countries about 15% of human couples are affected by infertility, almost half of these cases attributed to men, through low sperm motility or/and sperm count. It is known that a significant number of cases of male infertility results from exposure to xenobiotics, and also that testis mitochondria are particularly affected by drug-induced toxicity. The present review discusses evidence that parabens may not be as safe as initially thought, and suggests that the interaction between parabens and mitochondrial function in the testis may be key in explaining the contribution of parabens for a decrease in reproductive potential.
The biological fates of ethyl paraben and p-hydroxybenzoic acid in rat were investigated after intravenous and intraduodenal administrations at the dose of 2 mg/kg. The blood concentrations were measured in detail from 3 min after the administration at appropriate time intervals until 90 min. Areas under the blood concentration curves and clearances were calculated from these time course data. Ethyl paraben was little detected in blood after intraduodenal administration. It is suggested that the intestinal metabolism and the first pass effect in liver greatly contribute to the hydrolysis of ethyl paraben. Total radio activity after intraduodenal administration did not show the maximum peak and decreased rapidly. The maximum peak was not observed also in the time course of p-hydroxyhippuric acid after intravenous administration. It shows that not only the rate of hydrolysis but also absorption and conjugation are very rapid. The differences of the areas under the blood concentration curves of p-hydroxybenzoic acid or p-hydroxyhippuric acid was found between the routes or chemical forms of administration. The complex kinetic mechanisms were assumed in the biological fates of these compounds as follows: Conjugation to p-hydroxyhippuric acid is excellent in ethyl paraben administration than p-hydroxybenzoic acid, and in intraduodenal administration than intravenous administration. These phenomenon can not be explained by the conventional kinetic model which is constructed with the connected blood compartments in series. The kinetic models including the assumed routes conjugating directly ethyl paraben in blood or intestine to p-hydroxyhippuric acid were presented, and the least square curve fitting analyses were carried out on these kinetic models.
Effects of skin metabolism on percutaneous penetration of drugs with high lipophilicity were studied in vitro using rat skin pretreated with and without an esterase inhibitor, diisopropyl phosphorofluoridate [also known as diisopropyl fluorophosphate (DFP)]. Without DFP, about 96% of the total penetrated amount appeared as metabolized p-hydroxybenzoic acid in the receptor fluid after application of butylparaben, whereas about 30% penetrated as intact form after application of propylparaben. On the other hand, metabolized p-hydroxybenzoic acid was not defected in the receptor fluid under pretreatment with DFP. DFP significantly decreased (p < 0.05) the total amount that penetrated after application of butylparaben, but it did not significantly affect that of propylparaben. The results indicate that skin metabolism directly affects total amount that penetrated in the case of highly lipophilic drugs, and it was found that the higher metabolic rate to hydrophilic drugs is, the greater the amount that penetrated the skin would be. Thus, when optimal prodrugs are designed for the purpose of enhancing percutaneous penetration, we propose that the bioconversion rate to parent drugs as well as the lipophilicity of prodrugs becomes an important consideration.
Xenobiotic estrogens in the environment or diet have received much attention as a possible source of certain hormonal disease states in human and wildlife. Therefore, the detection of estrogenic activity of any substance, especially those related to the food industry, is important. The estrogenic activity of p-hydroxybenzoic acid (PHBA), a compound related to a commonly used group of preservatives in food, cosmetic, and pharmaceutical preparations, was evaluated with immature and adult ovariectomized female mice (CD1) using two well-known bioassays. Subcutaneous administrations (s.c.) of different doses of PHBA were compared with estradiol (E2), and their effects on vaginal cornification and uterotrophic activities were evaluated. Different groups of animals were treated s.c. daily for 3 days with vehicle (corn oil, 0.3 ml/100 g), E2 (1 microgram/100 g), and PHBA (0.5, 5, 50, and 500 micrograms/100 g). Four days after treatment, PHBA produced a dose-dependent response on vaginal cornification and uterotrophic activity in both immature and adult ovariectomized mice. The relative uterotrophic potency of PHBA (500 micrograms/100 g) to E2 (1 microgram/100 g) was 0.0011 in immature mice and 0.0018 in ovariectomized animals.
Phenolic acids, essentially hydroxycinnamic acids and hydroxybenzoic acids, are secondary plant products and commonly found in plant derived foodstuff. The antioxidant and anticarcinogenic properties of phenolic acids could be one of the facts to explain the inverse association between fruit and vegetable intake and the incidence of coronary heart disease and cancer, respectively, as found in epidemiologic studies. Phenolic acids are rarely listed in food composition tables and there are no dietary intake data available. Consequently, a data base containing the phenolic acid content of foods (literatur data) was built and 7-d dietary protocols of 63 women and 56 men of a Bavarian subpopulation (age 19-49 years) of the German National Food Consumption Survey (NVS) were evaluated. The average phenolic acid intake of men and women is 222 mg/d within a large range. The dominating one within all the phenolic acids is clearly caffeic acid (206 mg/d); the intake of the other phenolic acids amounts to 0.2 (gentisic acid) up to 5.2 mg/d (ellagic acid). The sum of hydroxybenzoic acids and hydroxycinnamic acids amounts to 11 mg/d and 211 mg/d, respectively. Significant sex differences are found for some of the phenolic acids. Especially, the average intake of caffeic acid of women (229 mg/d) is higher than that of men (179 mg/d) caused by the high amount of coffee consumption. The age group "25-49 years" is consuming more coffee than the age group "19-24 years" and, therefore, reveals a significantly higher intake of caffeic acid. The major sources of phenolic acids are coffee with 92% of the caffeic acid intake and fruits (including fruit products and juices) with 75% of the salycilic acid and 59% of the p-coumaric acid intake. Consequently, phenolic acids are consumed in considerable amounts with food. Since antioxidant and anticarcinogenic properties of phenolic acids are already proven in in vitro as well as in animal experiments, epidemiologic studies will show whether a high phenolic acid intake goes ahead with a reduced risk for coronary heart disease or cancer in humans.
The relationship between the metabolism and the cytotoxic effects of the alkyl esters of p-hydroxybenzoic acid (parabens) has been studied in freshly isolated rat hepatocytes. Incubation of hepatocytes with propyl-paraben (0.5 to 2.0 mM) elicited a concentration- and time-dependent cell death that was enhanced when enzymatic hydrolysis of propyl-paraben to p-hydroxybenzoic acid was inhibited by a carboxylesterase inhibitor, diazinon. The cytotoxicity was accompanied by losses of cellular ATP, total adenine nucleotide pools, and reduced glutathione, independently of lipid peroxidation and protein thiol oxidation. In the comparative toxic effects based on cell viability, ATP level, and rhodamine 123 retention, butyl- and isobutyl-parabens were more toxic than propyl- and isopropyl-parabens, and ethyl- and methyl-parabens and p-hydroxybenzoic acid were less toxic than propyl-paraben. The addition of propyl-paraben to isolated hepatic mitochondria reduced state 3 respiration with NAD+-linked substrates (pyruvate plus malate) and/or with an FAD-linked substrate (succinate plus rotenone), whereas state 3 respiration with ascorbate plus tetramethyl-p-phenylenediamine (cytochrome oxidase-linked respiration) was not affected significantly by propyl-paraben. Further, the addition of these parabens caused a concentration-dependent increase in the rate of state 4 oxygen consumption, indicating an uncoupling effect. The rate of state 3 oxygen consumption was inhibited by propyl-paraben, butyl-paraben, and their chain isomers. These results indicate that a) propyl-paraben-induced cytotoxicity is mediated by the parent compound rather than by its metabolite p-hydroxybenzoic acid; b) the toxicity is associated with ATP depletion via impairment of mitochondrial function related to membrane potential and/or oxidative phosphorylation; and c) the toxic potency of parabens to hepatocytes or mitochondria depends on the relative elongation of alkyl side-chains esterified to the carboxyl group of p-hydroxybenzoic acid.
The inadvertent estrogenicity of certain synthetic chemicals, and their subsequent effects on the endocrine system of humans and wildlife, is of concern. In this paper we report findings from in vitro and in vivo (uterotrophic) studies which confirm that a range of alkyl hydroxy benzoate preservatives (parabens) are weakly estrogenic. In a receptor-binding assay, butylparaben was able to compete with 3H-estradiol for binding to the rat estrogen receptor with an affinity approximately 5 orders of magnitude lower than that of diethylstilboestrol, and between 1 and 2 orders of magnitude less than nonylphenol. In an in vitro yeast-based estrogen assay, the four most widely used parabens (namely methyl-, ethyl-, propyl-, and butylparaben) were all found to be weakly estrogenic with the most potent (butylparaben) being 10,000-fold less potent than 17 beta-estradiol. The estrogenic activity of parabens was inhibited by 4-hydroxy tamoxifen in vitro, illustrating the requirement of these chemicals to interact with the estrogen receptor in order to activate the yeast. When administered orally to immature rats, the parabens were inactive. However, subcutaneous administration of butylparaben produced a positive uterotrophic response in vivo, although it was approximately 100,000 times less potent than 17 beta-estradiol. Given their use in a wide range of commercially available topical preparations, it is suggested that the safety in use of these chemicals should be reassessed, with particular attention being paid to estimation of the actual levels of systemic exposure of humans exposed to these chemicals. The acquisition of such data is a prerequisite to the derivation of reliable estimates of the possible human risk of exposure to parabens.
The effect of cutaneous metabolism on the skin penetration of drugs was analyzed based on a two-layer skin diffusion/metabolism model. In vitro permeation studies of propylparaben and butylparaben with or without an esterase inhibitor, diisopropyl fluorophosphate (DFP), were performed. Pretreatment of the skin with DFP prolonged the lag time for the penetration of intact parabens. Additionally, DFP significantly decreased the total flux of butylparaben, but not that of propylparaben. Model analysis of the penetration profiles revealed that DFP inhibits the cutaneous metabolism without affecting any other processes. To comprehensively understand the relationships among lipophilicity, metabolic rate, and skin permeation of drugs, simulation studies were performed with newly derived equations concerning the permeability coefficient and the lag time for the penetration of both intact and metabolite forms. The analysis revealed that the lag time for the penetration of both intact and metabolite forms becomes shorter with increasing metabolic rate. As the metabolic rate of the drug increases, skin penetration of the intact form decreases whereas that of the metabolite increases. The total flux of intact and metabolite forms increases with increasing metabolic rate, being more obvious for highly lipophilic drugs. This indicates that the permeation of lipophilic compounds such as butylparaben is more highly affected by cutaneous metabolism in the viable layer because these compounds easily penetrate the stratum corneum layer. Consequently, the balance between the permeability of drug across the stratum corneum and the dermis has been implicated to impose a significant influence on the percutaneous absorption of drugs subjected to cutaneous metabolism.
The relationship between mitochondrial membrane permeability transition (MPT) and the toxic effects of the alkyl esters of p-hydroxybenzoic acid (parabens) has been studied in mitochondria and hepatocytes isolated from rat liver. MPT has been proposed as a common final pathway in acute cell death through mitochondrial dysfunction. In isolated mitochondria, propyl-paraben (0.1 to 0.5 mM) in the presence of Ca2+ (50 microM) elicited a concentration-dependent induction of mitochondrial swelling dependent on MPT. This was prevented by pretreatment with a specific inhibitor of MPT, cyclosporin A (0.2 microM). For the other parabens tested, the induction of MPT depended on the relative elongation of alkyl side-chains in their molecular structure and was associated with the partition coefficients. In contrast, the induction caused by p-hydroxybenzoic acid was more potent than that of methyl- or ethyl-paraben. The pretreatment of freshly isolated hepatocytes with cyclosporin A (5 microM) and trifluoperazine (10 microM), which inhibit MPT in a synergistic manner, partially but not completely prevented propyl-paraben (1 mM; plus diazinon, 100 microM)-induced cell death, ATP loss, and decreased mitochondrial membrane potential. These results suggest that the onset of paraben-induced cytotoxicity is linked to mitochondrial failure dependent upon induction of MPT accompanied by the mitochondrial depolarization and depletion of cellular ATP through uncoupling of oxidative phosphorylation.
The oestrogenic activity of the parabens, methyl-, ethyl- and propyl p-hydroxybenzoate, widely used as antimicrobials in food, and butyl p-hydroxybenzoate, which is used in cosmetic products, and their shared main metabolite p-hydroxybenzoic acid was investigated in a mouse uterotrophic assay. Immature B6D2F1 mice were treated with oral or subcutaneous doses of the test compounds for three consecutive days. p-Hydroxybenzoic acid and butyl p-hydroxybenzoate were also tested by the subcutaneous route in a rat uterotrophic assay. A significant increase in the uterus weight at day 4 was considered an oestrogenic effect. In the mouse assay, none of the compounds tested produced any oestrogenic response at dose levels up to 100mg/kg body weight per day, for ethyl p-hydroxybenzoate even at a dose level of 1000mg/kg body weight per day. In immature Wistar rats, subcutaneous administration of butyl p-hydroxybenzoate produced a weak oestrogenic response at 600mg/kg body weight per day.
Characterization of p-hydroxy-hippuric acid as an inhibitor of Ca2+-ATPase in end-stage renal failure. In patients with end-stage renal failure (ESRF), disturbances of Ca2+ metabolism are common. Besides hormonal changes, inhibition of cellular Ca2+-ATPase was postulated to contribute to uremic toxicity. We purified a potent inhibitor of the Ca2+-ATPase from the ultrafiltrate of patients with ESRF by multiple steps of high-performance liquid chromatography to homogeneity, and identified the isolated inhibitor by mass spectrometric methods as p-hydroxy-hippuric acid. The enzyme used for the Ca2+-ATPase assay system was isolated from red blood cells by cross-flow filtration. The activity of the Ca2+-ATPase was measured spectrophotometrically as the difference in hydrolysis of adenosine 5'-triphosphate (ATP) in the presence and absence of Ca2+ with different concentrations of ATP and p-hydroxyhippuric acid. The Ca2+-ATPase was found to be inhibited by p-hydroxy-hippuric acid at a concentration above 11.7 micromol/L. p-Hydroxyhippuric acid inhibited the erythrocyte Ca2+-ATPase by reducing Vmax and increasing the Km value. The EC50 (log mol/L; mean +/- SEM) for p-hydroxy-hippuric acid was calculated as 4.82 +/- 0.14. In conclusion, p-hydroxy-hippuric acid may play a role in disturbed Ca2+ metabolism in end-stage renal failure.
Propyl paraben (CAS no. 94-13-3) is a stable, non-volatile compound used as an antimicrobial preservative in foods, drugs and cosmetics for over 50 years. It is an ester of p-hydroxybenzoate. Propyl paraben is readily absorbed via the gastrointestinal tract and dermis. It is hydrolyzed to p-hydroxybenzoic acid, conjugated and the conjugates are rapidly excreted in the urine. There is no evidence of accumulation. Acute toxicity studies in animals indicate that propyl paraben is relatively non-toxic by both oral and parenteral routes, although it is mildly irritating to the skin. Following chronic administration, no-observed-effect levels (NOEL) as high as 1200-4000 mg/kg have been reported and a no-observed-adverse-effect level (NOAEL) in the rat of 5500 mg/kg is posited. Propyl paraben is not carcinogenic, mutagenic or clastogenic. It is not cytogenic in vitro in the absence of carboxyesterase inhibitors. The mechanism of propyl paraben may be linked to mitochondrial failure dependent on induction of membrane permeability transition accompanied by the mitochondrial depolarization and depletion of cellular ATP through uncoupling of oxidative phosphorylation. Sensitization has occurred when medications containing parabens have been applied to damaged or broken skin. Parabens have been implicated in numerous cases of contact sensitivity associated with cutaneous exposure, but high concentrations of 5-15% in patch testing are needed to elicit reaction in susceptible individuals. Allergic reactions to ingested parabens have been reported, although rigorous evidence of the allergenicity of ingested paraben is lacking.
Estrogenic activities of the phenolic preservatives methylparaben, ethylparaben, propylparaben, butylparaben, isopropylparaben and isobutylparaben were examined by assaying estrogen-receptor (ER)-dependent proliferation of MCF-7 cells. All the compounds stimulated the proliferation to about the same level as the maximal cell yield attained with 3x10(-11) M 17beta-estradiol, but at a concentration in the order of 10(5) to 10(7) higher than 17beta-estradiol. The cell-proliferative effects of parabens were completely suppressed by anti-estrogen ICI 182,780. MCF-7 cells treated with butylparaben and isobutylparaben exhibited a decrease in gene expression of ERalpha and an increase in that of progesterone-receptor (PR), but the effects of these parabens were not as prominent as those of 17beta-estradiol. Western blot analysis indicated that these parabens caused a slight decrease in expression of ERalpha protein. Competitive binding to human ERalpha and ERbeta in vitro revealed that the parabens with longer side-chains showed greater affinity for estrogen receptors, and that they had similar relative binding affinity (RBA) values to both ERalpha and ERbeta. RBA values were much smaller than that of diethylstilbestrol. In conclusion, parabens have ER-dependent estrogenic activities, and their effects on the intracellular signaling pathway might be different from that of 17beta-estradiol.
Parabens (4-hydroxybenzoic acid esters) have been recently reported to have oestrogenic activity in yeast cells and animal models. Since the human population is exposed to parabens through their widespread use as preservatives in foods, pharmaceuticals and cosmetics, we have investigated here whether oestrogenic activity of these compounds can also be detected in oestrogen-sensitive human cells. We report on the oestrogenic effects of four parabens (methylparaben, ethylparaben, n-propylparaben, n-butylparaben) in oestrogen-dependent MCF7 human breast cancer cells. Competitive inhibition of [3H]oestradiol binding to MCF7 cell oestrogen receptors could be detected at 1,000,000-fold molar excess of n-butylparaben (86%), n-propylparaben (77%), ethyl-paraben (54%) and methylparaben (21%). At concentrations of 10(-6)M and above, parabens were are able to increase expression of both transfected (ERE-CAT reporter gene) and endogenous (pS2) oestrogen-regulated genes in these cells. They could also increase proliferation of the cells in monolayer culture, which could be inhibited by the antiestrogen ICI 182,780, indicating that the effects were mediated through the oestrogen receptor. However, no antagonist activity of parabens could be detected on regulation of cell proliferation by 17 beta-oestradiol at 10(-10)M. Molecular modelling has indicated the mode by which paraben molecules can bind into the ligand binding pocket of the crystal structure of the ligand binding domain (LBD) of the oestrogen receptor alpha (ERalpha) in place of 17beta-oestradiol; it has furthermore shown that two paraben molecules can bind simultaneously in a mode in which their phenolic hydroxyl groups bind similarly to those of the meso-hexoestrol molecule. Future work will need to address the extent to which parabens can accumulate in hormonally sensitive tissues and also the extent to which their weak oestrogenic activity can add to the more general environmental oestrogen problem.
Parabens are a group of compounds widely used as preservatives in foodstuffs, cosmetics, toiletries and pharmaceuticals. These compounds are known to exert a weak estrogenic activity, with butylparaben showing the most potent activity among methyl-, ethyl- and propyl esters in in vitro recombinant yeast assay and in in vivo uterotrophic assay. To account for potential reproductive effects in male animals, butylparaben was administered to 3-week-old Wistar rats divided in groups of eight subjects, at doses of 0.00%, 0.01%, 0.10% and 1.00% with the animal's diet. After 8 weeks, the rats were killed by decapitation and the weights of the testes, epididymides, prostates, seminal vesicles and preputial glands were recorded. The absolute and relative weights of epididymides were decreased in a dose-dependent manner and the decrease was statistically significant at 0.10% and above. The cauda epididymal sperm reserve of all treated groups was significantly decreased. The sperm count of the group receiving the highest dose was 58.2% of control values. The daily sperm production (DSP) in the testis was also significantly lower in all treated groups when compared to controls. Serum testosterone concentration was lowered dose-dependently and was significant at 0.1% or more. The daily intake of butylparaben that caused these disruptions is similar to the lower level of acceptable daily intake (ADI) for parabens in the European Community (EC) and in Japan. The results of the present experiments show for the first time that exposure of a postweaning mammal to butylparaben had an adverse effect on the secretion of testosterone and in the functions of the male reproductive system.
Parabens are alkyl ester compounds of p-hydroxybenzoic acid widely used as preservatives in foodstuffs, cosmetics, toiletries and pharmaceuticals. These compounds are known to exert a weak estrogenic activity in estrogen receptor assays in vitro and in uterotrophic assays in vivo. In this paper, we have shown that butyl paraben had an adverse effect on the male mouse reproductive system and that it damaged the late steps of spermatogenesis in the testis. Butyl paraben was administered to 4-week-old Crj:CD-1 mice assigned to groups of eight animals, at doses of 0.01%, 0.10%, and 1.00% in the diet for 10 weeks. The average butyl paraben intake from the calculated food consumption was 14.4+/-3.60, 146+/-35.9, and 1504+/-357 mg/kg per day for the 0.01%, 0.10%, and 1.00% dietary butyl paraben groups, respectively. There were no treatment-related effects of butyl paraben on the liver, ventral prostates, seminal vesicles, and preputial glands (both in terms of absolute weight and relative to body weight) in any of the study groups. Both the absolute and relative weights of the epididymides were significantly higher in 1.00% group when compared with controls. A dose-dependent decrease of both round and elongated spermatid counts in stages VII-VIII seminiferous tubules was observed, and the elongated spermatid counts were significantly lower in all of the treated groups. The numbers of spermatogonia and spermatocytes did not differ from control values. The serum testosterone concentration decreased in a dose-dependent fashion and was significant at 1.00%. These data demonstrated that butyl paraben can exert an adverse effect on the male reproductive system at doses that are well below those of the accepted daily intake (ADI) in Japan.
The alkyl esters of p-hydroxybenzoic acid (parabens) are used widely as preservatives in foods, pharmaceuticals and cosmetics to which the human population is exposed. Recent studies have reported that methylparaben, ethylparaben, n-propylparaben and n-butylparaben all possess oestrogenic activity in several in vitro assays and in animal models in vivo. This study reports on the oestrogenic activity of isobutylparaben in a panel of assays in vitro and in vivo. Isobutylparaben was able to displace [(3)H]oestradiol from cytosolic oestrogen receptor alpha of MCF7 human breast cancer cells by 81% at 100 000-fold molar excess. Using a clonal line of MCF7 cells containing a stably transfected oestrogen-responsive ERE-CAT reporter gene, CAT gene expression could be increased by isobutylparaben such that the magnitude of the response was the same at 10(-5) M isobutylparaben as with 10(-8) M 17beta-oestradiol. Isobutylparaben could also increase expression of the endogenous oestrogen-responsive pS2 gene in MCF7 cells and maximal expression at 10(-5) M isobutylparaben could be inhibited with the anti-oestrogen ICI 182 780. The proliferation of two oestrogen-dependent human breast cancer cell lines MCF7 and ZR-75-1 could be increased with isobutylparaben such that at concentrations of 10(-5) M the proliferation response was of the same magnitude as with 10(-8) M 17beta-oestradiol. Evidence for oestrogen receptor mediation of proliferation effects was provided by the inability of isobutylparaben to influence the growth of oestrogen-unresponsive MDA-MB-231 human breast cancer cells and by the ability of the anti-oestrogen ICI 182 780 to inhibit the isobutylparaben effects on MCF7 cell growth. The proliferation response to 10(-10) M 17beta-oestradiol was not antagonized with isobutylparaben at any concentration from 10(-9) M to 10(-4) M in either MCF7 or ZR-75-1 cells. Finally, subcutaneous administration of isobutylparaben was able to increase the uterine weight in the immature mouse after three daily doses of 1.2 or 12.0 mg per mouse. Previous work using linear-alkyl-chain parabens has shown that oestrogenic activity increases with alkyl chain length from methylparaben to n-butylparaben. The results here show that branching of the alkyl chain to isobutylparaben increases oestrogenic activity beyond that of the equivalent length linear alkyl chain in n-butylparaben.
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.
Previous work has demonstrated that the alkyl esters of p-hydroxybenzoic acid (parabens) possess oestrogenic activity, which increases with length of alkyl chain from methylparaben to n-butylparaben and with branching in the alkyl chain from n-butylparaben to isobutylparaben. This study reports on the oestrogenic activity of benzylparaben in a variety of assays in vitro and in vivo. Benzylparaben was able to displace [(3)H]oestradiol from cytosolic oestrogen receptor (ER) of MCF7 human breast cancer cells by 22% at 1000-fold molar excess, by 40% at 10,000-fold molar excess, by 57% at 100 000-fold molar excess and by 100% at 1,000,000-fold molar excess. It was able to increase expression of a stably transfected oestrogen responsive reporter gene (ERE-CAT) in MCF7 cells after 24 h at 10(-5)M/10(-4)M and after 7 days at 10(-6)M/10(-5)M/10(-4)M. Proliferation of MCF7 cells could be increased by 10(-6)M/10(-5)M benzylparaben and this could be inhibited by 10(-7)M pure anti-oestrogen ICI 182,780, indicating that growth effects were ER mediated. Further evidence for ER-mediation was provided from the ability of benzylparaben to increase the growth of a second oestrogen-dependent human breast cancer cell line ZR-75-1, but not the oestrogen-insensitive MDA-MB-231 cell line. When tested in the presence of 10(-10)M 17beta-oestradiol, benzylparaben gave no antagonist response on the growth of either MCF7 or ZR-75-1 cells. Finally, benzylparaben could increase uterine weight in the immature mouse following topical application of three daily doses of 33 mg to dorsal skin. These results demonstrate that the oestrogenicity of methylparaben can be increased by the addition of an aryl group as well as by lengthening or branching the alkyl grouping.
The ester-type glucuronide of p-hydroxybenzoic acid was isolated as two derivatives from the urine of rabbits receiving p-hydroxybenzoic acid and their structures were established as methyl (p-methoxybenzoyl 2, 3, 4-tri-O-acetyl-β-D-glucopyranosid) uronate and methyl (p-acetoxybenzoyl 2, 3, 4-tri-O-acetyl-β-D-glucopyranosid) uronate. When feeding p-hydroxybenzoic acid to rabbits, similarly as in using the methyl ester, the unchanged acid, p-hydroxyhippuric acid, the ether-type glucuronide, the estertype glucuronide, and p-carboxyphenyl sulfate were excreted as five metabolites in the urine.