Camilla Taxvig

Possible endocrine disrupting effects of parabens and their metabolites

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.

Are Structural Analogues to Bisphenol A Safe Alternatives

BACKGROUND Bisphenol A (BPA) is a chemical with widespread human exposure suspected of causing low-dose effects. Thus, a need for developing alternatives to BPA exists. Structural analogues of BPA have already been detected in foods and humans. Due to the structural analogy of the alternatives, there is a risk of effects similar to BPA. OBJECTIVES The aim was to elucidate and compare the hazards of bisphenol B (BPB), bisphenol E (BPE), bisphenol F (BPF), bisphenol S (BPS) and 4-cumylphenol (HPP) to BPA. METHODS In vitro studies on steroidogenesis, receptor activity, and biomarkers of effect, as well as Quantitative Structure-Activity Relationship (QSAR) modeling. RESULTS All test compounds caused the same qualitative effects on estrogen receptor and androgen receptor activities, and most of the alternatives exhibited potencies within the same range as BPA. Hormone profiles for the compounds indicated a specific mechanism of action on steroidogenesis which generally lead to decreased androgen, and increased estrogen and progestagen levels. Differential effects on corticosteroid synthesis were observed suggesting a compound-specific mechanism. Overall, BPS was less estrogenic and antiandrogenic than BPA, but BPS showed the largest efficacy on 17α-hydroxyprogesterone (17α-OH progesterone). Finally, there were indications of DNA damage, carcinogenicity, oxidative stress, effects on metabolism, and skin sensitization of one or more of the test compounds. CONCLUSIONS Interference with the endocrine system was the predominant effect of the test compounds. A substitution of BPA with these structural analogues should be carried out with caution.

Endocrine disrupting effects in vitro of conazole antifungals used as pesticides and pharmaceuticals.

Widely used conazole antifungals were tested for endocrine disruptive effects using a panel of in vitro assays. They all showed endocrine disrupting potential and ability to act via several different mechanisms. Overall the imidazoles (econazole, ketoconazole, miconazole, prochloraz) were more potent than the triazoles (epoxiconazole, propiconazole, tebuconazole). The critical mechanism seems to be disturbance of steroid biosynthesis. In the H295R cell assay, the conazoles decreased the formation of estradiol and testosterone, and increased the concentration of progesterone, indicating inhibition of enzymes involved in the conversion of progesterone to testosterone. Prochloraz was most potent followed by econazole~miconazole>ketoconazole>tebuconazole>epoxiconazole>propiconazole. In the MCF-7 cell proliferation assay, the conazoles showed anti-estrogenic effect, including aromatase inhibition, since they inhibited the response induced by both 17β-estradiol (miconazole>econazole~ketoconazole>prochloraz>tebuconazole>epoxiconazole>propiconazole) and testosterone (econazole>miconazole>prochloraz>ketoconazole>tebuconazole>epoxiconazole>propiconazole). The triazoles were anti-androgenic in an androgen receptor reporter gene assay (epoxiconazole∼tebuconazole>propiconazole). This effect could not be evaluated for the pharmaceutical imidazoles due to cytotoxicity.

Effects of prenatal exposure to diesel exhaust particles on postnatal development, behavior, genotoxicity and inflammation in mice

BackgroundResults from epidemiological studies indicate that particulate air pollution constitutes a hazard for human health. Recent studies suggest that diesel exhaust possesses endocrine activity and therefore may affect reproductive outcome. This study in mice aimed to investigate whether exposure to diesel exhaust particles (DEP; NIST 2975) would affect gestation, postnatal development, activity, learning and memory, and biomarkers of transplacental toxicity. Pregnant mice (C57BL/6; BomTac) were exposed to 19 mg/m3 DEP (~1·106 particles/cm3; mass median diameter ≅ 240 nm) on gestational days 9–19, for 1 h/day.ResultsGestational parameters were similar in control and diesel groups. Shortly after birth, body weights of DEP offspring were slightly lower than in controls. This difference increased during lactation, so by weaning the DEP exposed offspring weighed significantly less than the control progeny. Only slight effects of exposure were observed on cognitive function in female DEP offspring and on biomarkers of exposure to particles or genotoxic substances.ConclusionIn utero exposure to DEP decreased weight gain during lactation. Cognitive function and levels of biomarkers of exposure to particles or to genotoxic substances were generally similar in exposed and control offspring. The particle size and chemical composition of the DEP and differences in exposure methods (fresh, whole exhaust versus aged, resuspended DEP) may play a significant role on the biological effects observed in this compared to other studies.

Do Parabens Have the Ability to Interfere with Steroidogenesis

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.

Differential effects of environmental chemicals and food contaminants on adipogenesis, biomarker release and PPARγ activation

Eleven environmental relevant chemicals were investigated for their ability to affect adipogenesis in vitro, biomarker release from adipocytes and PPARα and γ activation. We found that butylparaben stimulated adipogenesis in 3T3-L1 adipocytes and increased release of leptin, adiponectin and resistin from the cells. Butylparaben activated PPARγ as well, which may be a mediator of the adipogenic effect. Polychlorinated biphenyl (PCB)153 also stimulate adipogenesis and biomarker release, but did not affect PPARs. The data indicates that PPARγ activating chemicals often stimulate adipocyte differentiation although PPARγ activation is neither a requirement nor a guarantee for stimulation. Four out of the eleven chemicals (bisphenol A, mono-ethylhexyl phthalate, butylparaben, PCB 153) caused increased adipogenesis. The release of adipocyte-secreted hormones was sometimes but not always correlated with the effect on adipocyte differentiation. Eight chemicals were able to cause increased leptin release. These findings strengthen the hypothesis that chemicals can interfere with pathways related to obesity development.

Mixture effects of endocrine disrupting compounds in vitro

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.

Adverse effects on sexual development in rat offspring after low dose exposure to a mixture of endocrine disrupting pesticides.

The present study investigated whether a mixture of low doses of five environmentally relevant endocrine disrupting pesticides, epoxiconazole, mancozeb, prochloraz, tebuconazole and procymidone, would cause adverse developmental toxicity effects in rats. In rat dams, a significant increase in gestation length was seen, while in male offspring increased nipple retention and increased incidence and severity of genital malformations were observed. Severe mixture effects on gestation length, nipple retention and genital malformations were seen at dose levels where the individual pesticides caused no or smaller effects when given alone. Generally, the mixture effect predictions based on dose-additivity were in good agreement with the observed effects. The results indicate that there is a need for modification of risk assessment procedures for pesticides, in order to take account of the mixture effects and cumulative intake, because of the potentially serious impact of mixed exposure on development and reproduction in humans.

Endocrine potency of wastewater: Contents of endocrine disrupting chemicals and effects measured by in vivo and in vitro assays

Industrial and municipal effluents are important sources of endocrine disrupting compounds (EDCs) discharged into the aquatic environment. This study investigated the endocrine potency of wastewater and the cleaning efficiency of two typical urban Danish sewage treatment plants (STPs), using chemical analysis and a battery of bioassays. Influent samples, collected at the first STP grate, and effluent samples, collected after the sewage treatment, were extracted using solid phase extraction. Extracts were analyzed for the content of a range of industrial chemicals with endocrine disrupting properties: phthalate metabolites, parabens, industrial phenols, ultraviolet screens, and natural and synthetic steroid estrogens. The endocrine disrupting bioactivity and toxicity of the extracts were analyzed in cell culture assay for the potency to affect the function of the estrogen, androgen, aryl hydrocarbon, and thyroid receptors as well as the steroid hormone synthesis. The early-life stage (ELS) development was tested in a marine copepod. The concentrations of all analyzed chemicals were reduced in effluents compared with influents, and for some to below the detection limit. Influent as well as effluent samples from both STPs were found to interact with all four receptors and to interfere with the steroid hormone synthesis showing the presence of measured EDCs. Both influent samples and one of the effluent samples inhibited the development of the copepod Acartia tonsa. In conclusion, the presence of EDCs was reduced in the STPs but not eliminated, as verified by the applied bioassays that all responded to the extracts of effluent samples. Our data suggest that the wastewater treatment processes are not efficient enough to prevent contamination of environmental surface waters.

Concentration Addition, Independent Action and Generalized Concentration Addition Models for Mixture Effect Prediction of Sex Hormone Synthesis In Vitro

Humans are concomitantly exposed to numerous chemicals. An infinite number of combinations and doses thereof can be imagined. For toxicological risk assessment the mathematical prediction of mixture effects, using knowledge on single chemicals, is therefore desirable. We investigated pros and cons of the concentration addition (CA), independent action (IA) and generalized concentration addition (GCA) models. First we measured effects of single chemicals and mixtures thereof on steroid synthesis in H295R cells. Then single chemical data were applied to the models; predictions of mixture effects were calculated and compared to the experimental mixture data. Mixture 1 contained environmental chemicals adjusted in ratio according to human exposure levels. Mixture 2 was a potency adjusted mixture containing five pesticides. Prediction of testosterone effects coincided with the experimental Mixture 1 data. In contrast, antagonism was observed for effects of Mixture 2 on this hormone. The mixtures contained chemicals exerting only limited maximal effects. This hampered prediction by the CA and IA models, whereas the GCA model could be used to predict a full dose response curve. Regarding effects on progesterone and estradiol, some chemicals were having stimulatory effects whereas others had inhibitory effects. The three models were not applicable in this situation and no predictions could be performed. Finally, the expected contributions of single chemicals to the mixture effects were calculated. Prochloraz was the predominant but not sole driver of the mixtures, suggesting that one chemical alone was not responsible for the mixture effects. In conclusion, the GCA model seemed to be superior to the CA and IA models for the prediction of testosterone effects. A situation with chemicals exerting opposing effects, for which the models could not be applied, was identified. In addition, the data indicate that in non-potency adjusted mixtures the effects cannot always be accounted for by single chemicals.