Approaches to mixture risk assessment of PFASs in the European population based on human hazard and biomonitoring data

Per- and polyfluoroalkyl substances (PFASs) are a highly persistent, mobile, and bioaccumulative class of chemicals, of which emissions into the environment result in long-lasting contamination with high probability for causing adverse effects to human health and the environment. Within the European Biomonitoring Initiative HBM4EU, samples and data were collected in a harmonized way from human biomonitoring (HBM) studies in Europe to derive current exposure data across a geographic spread. We performed mixture risk assessments based on recent internal exposure data of PFASs in European teenagers generated in the HBM4EU Aligned Studies (dataset with N = 1957, sampling years 2014-2021). Mixture risk assessments were performed based on three hazard-based approaches: the Hazard Index (HI) approach, the sum value approach as used by the European Food Safety Authority (EFSA) and the Relative Potency Factor (RPF) approach. The HI approach resulted in the highest risk estimates, followed by the RPF approach and the sum value approach. The assessments indicate that PFAS exposure may result in a health risk in a considerable fraction of individuals in the HBM4EU teenager study sample, thereby confirming the conclusion drawn in the recent EFSA scientific opinion. This study underlines that HBM data are of added value in assessing the health risks of aggregate and cumulative exposure to PFASs, as such data are able to reflect exposure from different sources and via different routes.

Bisphenols B, E, F, and S and 4-cumylphenol induce lipid accumulation in mouse adipocytes similarly to bisphenol A

Bisphenol A (BPA) has been widely reported to exert endocrine disrupting effects, including the induction of adipogenesis in cultured preadipocytes and intact animals. Because of the potential harm to human health, BPA is being substituted by structurally related bisphenols. Whether or not such BPA analogues are safe substitutes, however, remains largely unknown. Here, we investigated the potential of bisphenol B (BPB), bisphenol E (BPE), bisphenol F (BPF), bisphenol S (BPS), and 4-cumylphenol (4-CP) to affect lipid and hormone levels in 3 T3-L1 cells. We found that BPB, BPE, BPF, BPS, and 4-CP all affected lipid accumulation and leptin levels to the same extent and potencies as BPA. Based on these and other results, we conclude that these BPA analogues and 4-CP most likely will elicit similar effects on adipocytes as BPA. Using them to substitute BPA in products should be done with caution.

Workshop on the validation and regulatory acceptance of innovative 3R approaches in regulatory toxicology - Evolution versus revolution

At a joint workshop organized by RIVM and BfR, international experts from governmental institutes, regulatory agencies, industry, academia and animal welfare organizations discussed and provided recommendations for the development, validation and implementation of innovative 3R approaches in regulatory toxicology. In particular, an evolutionary improvement of our current approach of test method validation in the context of defined approaches or integrated testing strategies was discussed together with a revolutionary approach based on a comprehensive description of the physiological responses of the human body to chemical exposure and the subsequent definition of relevant and predictive in vitro, in chemico or in silico methods. A more comprehensive evaluation of biological relevance, scientific validity and regulatory purpose of new test methods and assessment strategies together with case studies that provide practical experience with new approaches were discussed as essential steps to build up the necessary confidence to facilitate regulatory acceptance.

Prenatal exposure to persistent organochlorine pollutants is associated with high insulin levels in 5-year-old girls

BACKGROUND

Several persistent organochlorine pollutants (POPs) possess endocrine disrupting abilities, thereby potentially leading to an increased risk of obesity and metabolic diseases, especially if the exposure occurs during prenatal life. We have previously found associations between prenatal POP exposures and increased BMI, waist circumference and change in BMI from 5 to 7 years of age, though only among girls with overweight mothers.

OBJECTIVES

In the same birth cohort, we investigated whether prenatal POP exposure was associated with serum concentrations of insulin and leptin among 5-year-old children, thus possibly mediating the association with overweight and obesity at 7 years of age.

METHODS

The analyses were based on a prospective Faroese Birth Cohort (n=656), recruited between 1997 and 2000. Major POPs, polychlorinated biphenyls (PCBs), p,p'-dichlorodiphenyldichloroethylene (DDE) and hexachlorobenzene (HCB), were measured in maternal pregnancy serum and breast milk. Children were followed-up at the age of 5 years where a non-fasting blood sample was drawn; 520 children (273 boys and 247 girls) had adequate serum amounts available for biomarker analyses by Luminex® technology. Insulin and leptin concentrations were transformed from continuous to binary variables, using the 75th percentile as a cut-off point. Multiple logistic regression was used to investigate associations between prenatal POP exposures and non-fasting serum concentrations of insulin and leptin at age 5 while taking into account confounders.

RESULTS

Girls with highest prenatal POP exposure were more likely to have high non-fasting insulin levels (PCBs 4th quartile: OR=3.71; 95% CI: 1.36, 10.01. DDE 4th quartile: OR=2.75; 95% CI: 1.09, 6.90. HCB 4th quartile: OR=1.98; 95% CI: 1.06, 3.69) compared to girls in the lowest quartile. No significant associations were observed with leptin, or among boys. A mediating effect of insulin or leptin on later obesity was not observed.

CONCLUSION

These findings suggest, that for girls, prenatal exposure to POPs may play a role for later development of metabolic diseases by affecting the level of insulin.

Effect of in utero-administered coumestrol, equol, and organic selenium on biomarkers for phase 2 enzyme capacity and redox status

The aim of the present study was to investigate the effect of in utero administration of coumestrol, equol, and selenium-enriched yeast on selected hepatic phase 2 enzymes, plasma hormone levels, and markers for redox status in plasma and red blood cells (RBCs). The test compounds were administered via the diet to pregnant Sprague-Dawley rats throughout gestation. Within 24 h following delivery dams and offspring were sacrificed, and blood, liver, and reproductive organs were sampled. Coumestrol, equol, and selenium-enriched yeast did not significantly affect hepatic glutathione S-transferase (GST), quinone reductase (QR), or RBC glutathione peroxidase (GPx) in the offspring, whereas significant increases in GST, QR, and GPx activities in dams were observed following administration of selenium-enriched yeast. The level of 17beta-estradiol in offspring from coumestrol-exposed dams was significantly increased compared with the control. The present results indicate that selenium-enriched yeast, coumestrol, and equol affect selected hepatic phase 2 enzymes and GPx in RBC in dams, whereas the offspring in general were refractive to the employed treatments. Further studies are warranted to investigate whether the observed in utero effects imposed by the selected plant compounds confer permanent alterations on the health status of the animal resulting in an altered resistance to cancer.

Effects of dietary antioxidants and 2-amino-3-methylimidazo[4,5-f]- quinoline (IQ) on preneoplastic lesions and on oxidative damage, hormonal status, and detoxification capacity in the rat

The potential beneficial or adverse affect of prolonged dietary administration of moderate to high doses (1-100 mg/kg diet) of the antioxidants, lycopene, quercetin and resveratrol or a mixture of lycopene and quercetin was investigated in male F344 rats. Selected markers for toxicity and defense mechanisms were assayed in blood, liver and colon and the impact of the antioxidant administrations on putative preneoplastic changes in liver and colon was assessed. The dietary carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) (200 mg/kg diet) served as a pro-oxidant, genotoxicity and general toxicity control. IQ increased the levels of protein and DNA oxidation products in plasma, the area of glutathione S-transferase-placental form positive (GST-P) foci in the liver as well as the number of colonic aberrant crypt foci (ACF). All antioxidants and the antioxidant combination significantly increased the level of lymphocytic DNA damage, to an extent comparable with the effect induced by IQ. In contrast to the control group where no GST-P foci were detected, GST-P foci were detected in animals exposed to quercetin, lycopene and the combination of the two. However, the increase in the volume of GST-P foci did not reach statistical significance. The present results indicate that moderate to high doses of common dietary antioxidants can damage lymphocyte DNA and induce low levels of preneoplastic liver lesions in experimental animals. Long-term exposure to moderate to high doses of antioxidants may thus via pro-oxidative mechanisms and non-oxidative mechanisms modulate carcinogenesis.

Applicability of the CALUX bioassay for screening of dioxin levels in human milk samples

The CALUX (chemically activated luciferase expression) bioassay based on rat hepatoma (H4IIE) cells is a sensitive assay for the detection of Ah receptor agonists like 2,3,7,8-substituted chlorinated dibenzo-p-dioxins and dibenzofurans and related PCBs. In this paper, the assay was optimized and applied for monitoring levels of dioxins in human milk samples. Combination effects of dioxin-like compounds were evaluated by testing potential mechanisms of interaction between seven of the major dioxin-like compounds in human milk using the isobole method. Results showed that the compounds acted additively, indicating that the usual assumption of additivity in the risk assessment process is valid. In general the relative potencies (REPs) of the single agents were in accordance with their TEFs assigned by the World Health Organisation, except for the mono-ortho-substituted PCB118 that had a 40-fold lower REP in CALUX. The total dioxin-like activity was determined in 16 Danish human milk samples and was in the range 20.5-55.8 pg TEQ g(-1) fat. These values were compared with TEQs obtained from GC/MS analysis (range 14.8-43.6 pg TEQ-g(-1) fat) that overall were a little lower than CALUX TEQs. The results obtained with the bioassay when testing milk extracts fractionated into dioxins/furans, non-ortho PCB and mono/di-ortho PCB fractions indicated that the correlation between the bioassay and the chemical analyses depends primarily on the Ah receptor activity observed in the mono/di-ortho PCB fraction.

Toxicity testing and chemical analyses of recycled fibre-based paper for food contact

Food-contact materials, including paper, have to comply with a basic set of criteria concerning safety. This means that paper for food contact should not give rise to migration of components, which can endanger human health. The objectives of this pilot study were, first, to compare paper of different qualities as food-contact materials and to perform a preliminary evaluation of their suitability, from a safety point of view, and, second, to evaluate the use of different in vitro toxicity tests for screening of paper and board. Paper produced from three different categories of recycled fibres (B-D) and a raw material produced from virgin fibres (A) were obtained from industry, and extracts were examined by chemical analyses and diverse in vitro toxicity test systems. The products tested were either based on different raw materials or different treatments were applied. Paper category B was made from 40% virgin fibres, 40% unprinted cuttings from newspapers, and 20% de-inked newspapers and magazines. Paper categories C and D were based on newspapers and magazines. However, paper D was de-inked, whereas C was not. To identify constituents of the papers with a potential to migrate into foodstuff, samples of the paper products were extracted with either 99% ethanol or water. Potential migrants in the extracts were identified and semiquantified by GC-IR-MS or GC-HRMS. In parallel to the chemical analyses, a battery of four different in vitro toxicity tests with different endpoints were applied to the same extracts. (1) a cytotoxicity test using normal human skin fibroblasts. The test was based on measurements of the reduction of resazurin to resorufin by cellular redox processes and used as a screening test for acute or general toxicity; (2) a Salmonella/microsome assay (Ames test) as a screening test for mutagenic and potentially carcinogenic compounds; (3) a recombinant yeast cell bioassay as a screening test for compounds with oestrogenic activity; (4) an aryl hydrocarbon (Ah)-receptor assay (CALUX assay) as a screening test for compounds with dioxin-like activity. In addition, the papers were testedfor microbial content and, in general, the microbiological load was quite low. The following microorganisms were counted and identified on both surface and homogenized pulp samples: the total number of aerobic bacteria, the number of aerobic and anaerobic spore formers, the number of Bacillus cereus/thuringiensis, and the number of yeast and moulds. The chemical analyses showed a significantly higher amount and different composition pattern of chemicals extracted with ethanol compared with water. Analyses of the ethanol extracts showed a distinctly smaller number and lower concentrations of chemicals in extracts prepared from sample A compared with extracts of samples B-D. The compounds identified in B-D were similar, but the amounts were lower in B compared with C and D. In accordance with the chemical analyses, the water extracts were less cytotoxic than the ethanol extracts. The extract prepared from virgin fibres was less cytotoxic than the extracts prepared from paper made from recycled fibres, and extracts prepared from C was the most cytotoxic. None of the extracts showed mutagenic activity. No conclusion about the oestrogenic activity could be made, because all extracts were cytotoxic to the test organism (yeast cells). Ethanol extracts of A and B showed a negligible positive response in the Ah-receptor assay at the highest nontoxic concentration, whereas C and D showed a more pronounced effect with C being the most potent. A comparable weak effect of water extracts of samples B-D was observed, too. However, the active compound(s) was not identified by chemical analyses.

In utero reproductive study in rats exposed to nonylphenol

Alkylphenol ethoxylates are widely used non-ionic surfactants. Nonylphenol ethoxylate constitutes 82% of the production of all alkylphenol ethoxylates and the breakdown product of nonylphenol ethoxylate, nonylphenol (NP) has been shown to be estrogenic in both in vitro and in vivo screening assays. To determine the potential reproductive toxicity of NP, a one-generation in utero study was conducted. Rats were dosed from gestation day 11 through 18 with NP at 3, 15, or 75 mg/kg/day or diethylstilbestrol (DES) at 30 microg/kg/day. DES was used as a positive control. Both substances were given orally by gavage. Male offspring were sacrificed at postnatal day (PND) 11, 21, or 110 and reproductive parameters were evaluated. Pup birth weight and body weight and percent motile sperm at age of 110 day were significantly reduced by DES. The absolute weight of the right epididymis was significantly reduced in the DES group. The absolute weight of the right epididymis were also significantly decreased in the animals exposed to 75 or 15 mg/kg/day NP, effects which disappeared when organ weight was related to body weight. This study showed a dose-dependent effect of nonylphenol on male reproductive development at doses of 75 and 15 mg/kg bw/day based on absolute epididymal weight.

Quantification of antiandrogen effect determined by Lightcycler technology

During the last decade, the possible effects of xenobiotics on male reproductive health have resulted in great concern. More recently, evidence of antiandrogen effect in vivo by certain chemicals has been reported. The classical Hershberger in vivo assay determining organ weight changes can be improved by measuring hormone levels as well as determining changes in gene expression of androgen-responsive genes. A real-time RT-PCR method using LightCycler technology (Roche) suitable for quantitative determination of gene expression is described. The technique combines rapid thermocycling with online fluorescence detection of PCR product formation. In this study, investigation of expression of prostate specific binding protein polypeptide C3 (PBP C3) and testosterone-repressed prostatic message 2 (TRPM-2) in the ventral prostate was performed in 60-days-old castrated Wistar rats treated daily with testosterone with or without addition of flutamide or vinclozolin for 7 days in total. We show that we can quantify the level of gene expression by use of LightCycler technology, supported by changes in reproductive organ weights as well as in hormone levels, and that analysis of gene expression levels is an even more sensitive endpoint.

Effect of highly bioaccumulated polychlorinated biphenyl congeners on estrogen and androgen receptor activity

Polychlorinated biphenyls (PCBs) are ubiquitous environmental persistent contaminants giving rise to potential health hazard. Some PCBs exert dioxin-like activities mediated through the aryl hydrocarbon receptor. Although reports on interaction with other nuclear receptors are sparce, some congeners are hypothesized to possess endocrine disruptive potential. Here we present evidence that the three PCBs most abundant in biological extracts, 2,2',3'4,4',5-hexachlorobiphenyl (PCB#138), 2,2',4,4',5,5'-hexachlorobiphenyl (PCB#153), and 2,2',3,4,4',5,5'-heptachlorobiphenyl (PCB#180) have pleiotropic effects on the estrogen- and androgen-receptor. In MCF-7 cells a slightly increased cell proliferation was observed at low concentrations (1-10 nM) in cells co-treated with 0.01 nM 17beta-Estradiol, whereas the compounds inhibited cell growth significantly at 1 and 10 microM. In reporter gene (ERE-tk-CAT) analysis the three congeners exhibited a significantly estrogen receptor-ligand mediated decrease of the chloramphenicol transferase activity in both control and 10 nM 17beta-estradiol induced MCF-7 cells. In addition, PCB#138 elicited a dose-dependent antagonistic effect on androgen receptor activity in transiently co-transfected Chinese Hamster Ovary cells with an IC(50), of 6.2 microM. In summary, this study indicate that the di-ortho, multiple-chloro substituted biphenyls, PCB#138, PCB#153 and PCB#180, can compete with the binding of the natural ligand to two nuclear receptors and thus possess the ability to interfere with sexual hormone regulated processes.

Identification and quantification of estrogenic compounds in recycled and virgin paper for household use as determined by an in vitro yeast estrogen screen and chemical analysis

The use of recycled paper for the manufacture of food contact materials is widespread, but very little is known about the presence of potential contaminants in the paper. The purpose of this study was to assess the worst-case migration of estrogenic active compounds using extracts of paper for household use. Twenty different brands of kitchen rolls, nine of which were made from recycled paper and the remainder from virgin paper, were obtained from retail shops. Paper extracts were subjected to (a) determination of the total estrogenic activity by using an in vitro estrogen screen based on yeast cells stably transfected with the human estrogen receptor alpha and (b) chemical analysis and quantification by GC/MS, GC/FTIR/MS, and GC/FID for detection of a variety of estrogenic compounds. A marked estrogenic response was observed in nine of the extracts, seven of which were made from recycled paper and two from virgin paper. The chemical analysis revealed that extracts made from recycled paper contained levels of bisphenol A ranging from 0.6 to 24 mg/kg of kitchen roll, whereas extracts from virgin paper contained no bisphenol A or only negligible amounts. In contrast, 4-tert-octylphenol, 4-nonylphenols, and di-n-butyl and diisobutyl phthalate were present to a varying degree in both recycled and virgin paper with no apparent preferable distribution between the two paper types. The estrogenic response of the two extracts made from virgin paper appeared to be due partly to the presence of the preservative propyl paraben. Diisopropylnaphthalene, which turned out to be weakly estrogenic active in vitro (EC(50) = 53 microM), was detected in minor amounts in most of the extracts with the major part, ranging from 0.3 to 4.7 mg/kg of paper, found in recycled paper. Our findings that recycled kitchen rolls contain bisphenol A and other xenoestrogens may apply to other types of recycled paper used for food packaging and emphasize the importance of identifying this and other contaminants in recycled paper in general. These data indicate that bisphenol A may be useful as a purity indicator for recycled paper.

Screening of selected pesticides for inhibition of CYP19 aromatase activity in vitro

Many pesticides are able to block or activate the steroid hormone receptors and/or to affect the levels of sex hormones, thereby potentially affecting the development or expression of the male and female reproductive system or both. This emphasizes the relevance of screening pesticides for a wide range of hormone-mimicking effects. Twenty-two pesticides were tested for their ability to affect CYP19 aromatase activity in human placental microsomes using the classical [(3)H](2)O method. Prochloraz, imazalil, propioconazole, fenarimol, triadimenol, triadimefon (all fungicides), and dicofol (an acaricide) gave rise to a statistically significant inhibition of aromatase activity. The IC(50)s of prochloraz, imazalil, propioconazole fenarimol, triadimenol, and triadimefon were calculated from dose-response curves to be 0.04, 0.34, 6.5, 10, 21 and 32 microM, respectively. The IC(50) of dicofol was greater than 50 microM. The positive control 4-hydroxyandrostendione (1 microM) caused an inhibition of aromatase activity by 74%. The compounds, which did not affect the aromatase activity, were bromopropylate, chlorfenvinphos, chlorobenzilate, chlorpyrifos, diuron, heptachlor, iprodion, linuron, pentachlorphenol, procymidon, propyzamide, quintozen, tetrachlorvinphos and tetradifon. With the purpose of comparing the results for fenarimol obtained with the microsomal system with data from an intact cell system, an aromatase assay based on JEG-3 cells was established. 4-Hydroxyandrostendione (1 microM) inhibited the aromatase activity in JEG-3 cells by 94%. The IC(50) for fenarimol in this system was 2 microM, slightly lower than that observed in the microsomal system. For the first time, fenarimol has been demonstrated to inhibit aromatase activity in human tissues and, furthermore, propioconazole, triadimefon, and triadimenol were identified as weak aromatase inhibitors. In conclusion, seven out of 22 tested pesticides turned out to be weak to moderate aromatase inhibitors in vitro, indicating the relevance of elucidating the endocrine effects in vivo of these- compounds.

Environmental polycyclic aromatic hydrocarbons affect androgen receptor activation in vitro

Nine structurally different polycyclic aromatic hydrocarbons (PAHs) were tested for their ability to either agonize or antagonize the human androgen receptor (hAR) in a sensitive reporter gene assay based on CHO cells transiently cotransfected with a hAR vector and an MMTV-LUC vector. Benz[a]anthracene (B[a]A), benzo[a]pyrene (B[a]P), fluoranthene, chrysene and 7,12-dimethylbenz[a]anthracene (DMBA) were acting as antiandrogens in vitro, resulting in IC(50) values of 3.2, 3.9, 4.6, 10.3 and 10.4 microM, respectively. Only at the highest concentration tested (10 microM), a slight inhibitory effect by pyrene, phenanthrene, and anthracene was observed. In contrast, dibenzo[a,h]anthracene (DB[a,h]A) gave rise to an agonistic effect, which was added upon the effect of the androgen receptor agonist R1881 (0.1 nM). The antiandrogenic responses by PAHs (10 microM) were found to be fully reversible, determined in the presence of increasing concentrations of R1881. No cytotoxic effects of the tested compounds were observed as determined either by metabolic reduction using AlamarBlue (up to 20 microM) or determined in cells transfected with a constitutively active hAR (up to 10 microM). The well-known ability of certain PAHs to activate the Ah receptor was assessed in H4IIE liver cancer cells, stably transfected with a luciferase reporter gene system. The positive control 2,3,7,8-tetrachlorodibenzodioxin (TCDD) caused a 13-14-fold induction of luciferase activity reaching maximum activity at 0.1 nM. DB[a,h]A, B[a]P, Chrysene, B[a]A and DMBA gave rise to a 4.5-fold induction of luciferase activity at 0.03, 0.4, 0.89, 3.06, and 9.27 microM, respectively, whereas fluoranthene, pyrene, phenanthrene and anthracene were without effect. In conclusion, no clear correlation between the antiandrogenic effects and the Ah receptor activation in vitro was seen. However, the Ah receptor agonists containing four or five aromatic rings (i.e. B [a] A, B [a] P, chrysene, DMBA) appeared to be the most potent antiandrogens (with the exception of DB [a, h] A), whereas those not able to activate the Ah receptor containing three or four aromatic rings (i.e. pyrene, phenanthrene, anthracene) displayed either very weak or no antiandrogenic effect at concentrations up to 10 microM (with the exception of fluoranthene which blocked the hAR at lower concentrations, but did not activate the Ah receptor).

Screening of selected pesticides for oestrogen receptor activation in vitro

Twenty pesticides were tested for their ability to activate the oestrogen receptor in vitro using an MCF7 cell proliferation assay and a Yeast Oestrogen Screen. The fungicides fenarimol, triadimefon, and triadimenol were identified as weak oestrogen receptor agonists, which at 10 microM induces a 2.0, 2.4, and 1.9-fold increase in proliferation of human MCF7 breast cancer cells (E3 clone). The relative proliferation efficiency (RPE) was 43-69%, indicating partial agonism at the oestrogen receptor. Several pesticides did not have any effect on the proliferation response after 6 days of exposure, including: chlorpyrifos, diuron, iprodion, linuron, pentachlorphenol, prochloraz, propioconazol, propyzamine, quintozen, tetrachorvinphos and tetradifon. Some pesticides resulted in a negligible proliferation response, which was not statistically significant under the present experimental conditions. These were: bromopropylate, chlorfenvinphos, chlorobenzilate, dicofol, heptachlor, and imazalil. Fenarimol and dicofol also gave rise to a positive oestrogenic response in yeast cells transfected with the oestrogen receptor alpha, whereas the remaining compounds resulted in a negative response due either to biological inactivity or cytotoxocity to the yeast cells. The EC50 for fenarimol was estimated to be 13 microM in the yeast cells, compared with an EC50 of 3 microM in the MCF7 cells, indicating higher sensitivity of the latter assay. No in vivo data for fenarimol, triadimefon or triadimenol have previously been published that support oestrogenic activity in the intact animal. Thus, from the present results we suggest that oestrogen receptor activation may not be an important mode of action for these compounds. The need to include at least two bioassays in a screening procedure and for combining in vitro and in vivo data is emphasized.

The subcellular localization of phospholipase D activities in rat Leydig cells

Rat Leydig cells contain a phospholipase D (PLD), which can be activated by vasopressin and phorbol ester. In order to clarify which Leydig cell organelles that express PLD activity, the subcellular localization of two differently regulated PLD activities was investigated by subcellular fractionation on a 40% (v/v) self-generating Percoll gradient. PLD activities in broken cells were estimated using radiolabeled didecanoylphosphatidylcholine as a substrate. Initial experiments revealed the presence of an oleate Mg2+ -activated PLD and a phosphatidylinositol 4,5-bisphosphate-activated PLD (PIP2-PLD) in the microsomal fraction of Leydig cells. The latter activity could be further stimulated by recombinant nonmyristoylated ADP ribosylating factor 1 (ARF1) plus GTPgammaS. The peak of oleate Mg2+ -PLD activity colocalized with the plasma membrane marker, whereas the highest specific activity of the PIP2-PLD activity was found in fractions with a slightly lower density than those containing the plasma membrane and trans-Golgi marker enzymes. In order to localize phorbol ester-stimulated PLD activity in intact Leydig cells, the cells were prelabeled with [14C]-palmitate and then stimulated for 15 min with 100 nM 4-beta-phorbol-12-myristate-13-acetate (PMA) in the presence of ethanol or butanol. The PLD product [14C]-phosphatidylethanol, expressed as the percentage of total labeled phospholipids in the fraction, was slightly increased in all Percoll fractions and showed a prominent peak in the fractions containing plasma membrane, trans-Golgi, and fractions of slightly lower density. The PMA-induced formation of [14C]-phosphatidylbutanol could be inhibited dose-dependently with brefeldin A suggesting that the activation of PLD by the phorbol ester was mediated by ARF.

Rapid and sensitive reporter gene assays for detection of antiandrogenic and estrogenic effects of environmental chemicals

Reports on increasing incidences in developmental abnormalities of the human male reproductive tract and the recent identifications of environmental chemicals with antiandrogenic activity necessitate the screening of a larger number of compounds in order to get an overview of potential antiandrogenic chemicals present in our environment. Thus, there is a great need for an effective in vitro screening method for (anti)androgenic chemicals. We have developed a rapid, sensitive, and reproducible reporter gene assay for detection of antiandrogenic chemicals. Chinese Hamster Ovary cells were cotransfected with the human androgen receptor expression vector and the mouse mammary tumour virus (MMTV)2-luciferase vector using the new nonliposomal transfection reagent FuGene. Stimulation of the cells for 24 h with the synthetic androgen receptor agonist, R1881 (10 nM), resulted in a 30- to 60-fold induction of luciferase activity. The classical antiandrogenic compounds hydroxy-flutamide, bicalutamide, spironolactone, and cyproterone acetate together with the pesticide(metabolite)s, vinclozolin, p,p'-DDE, and procymidone all potently inhibited the response to 0.1 nM R1881. Compared to the traditional calcium phosphate transfection method, this method has the advantage of being more feasible, as the assay can be scaled down to the microtiter plate format. Furthermore, the transfection reagent is noncytotoxic, allowing its addition together with the test compounds thereby reducing the hands-on laboratory time. This assay is a powerful tool for the efficient and accurate determination and quantification of the effects of antiandrogens on reporter gene transcription. To extend the application of FuGene, the reagent was shown to be superior compared to Lipofectin for transfecting MCF7 human breast cancer cells with an estrogen response element-luciferase vector. Thus, FuGene may prove to be valuable in diverse reporter gene assays involving transient transfections for screening of potential endocrine disruptors for (anti)androgenic and (anti)estrogenic properties.

Characterization of glutamate-induced formation of N-acylphosphatidylethanolamine and N-acylethanolamine in cultured neocortical neurons

Glutamate-induced formation of N-acylethanolamine (NAE) and N-acylphosphatidylethanolamine (NAPE) was studied in primary cultures of mouse neocortical neurons prelabeled with [14C] ethanolamine. The formation of these two lipids was dependent on the maturity of the cell culture; i.e., no glutamate-induced formation was seen in 2-day-old cultures, whereas glutamate induced a pronounced formation in 6-day-old cultures. The calcium ionophore A23187 (2 microM) stimulated, within 2 h, formation of NAPE in 2-day-old cultures (fourfold) as well as in 6-day-old cultures (eightfold). Glutamate exerted its effect via NMDA receptors as seen by the inhibitory action of the NMDA-selective receptor antagonists D-(-)-2-amino-5-phosphonovalerate and N-(1-(2-thienyl)cyclohexyl)piperidine and the lack of effect of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate-receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In 6-day-old cultures, exposure to NMDA (100 microM for 24 h) induced a linear increase in the formation of NAPE and NAE as well as a 40-50% neuronal death, as measured by a decrease in cellular formazan formation [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay]. The increase in NAPE and NAE could be detected earlier than the neuronal death. Neither cyclic AMP, cyclic GMP, nitric oxide, protein kinase C, nor peroxidation appears to be involved in the formation of NAPE and NAE, as assessed by the use of different pharmacological agents. Exposure to 5 mM NaN3 for 8 h resulted in a >80% decrease in the cellular MTT staining and a pronounced linear increase in the formation of NAE and NAPE (reaching 25-30% of total labeling). [14C]Anandamide was also formed in [14C]arachidonic acid-labeled neurons exposed to NaN3. No NAPE formation was detected in A23187-stimulated mouse astrocytes, rat Leydig cells and cardiomyocytes, and several other cells. These results suggest that the glutamate-induced formation of NAPE and NAE was mediated by the NMDA receptor and the formation of these lipids may be associated with neuronal death.

Arf and RhoA regulate both the cytosolic and the membrane-bound phospholipase D from human placenta

In this paper we demonstrate for the first time that human placenta contains a cytosolic phospholipase D (PLD) activity. This activity had a pH optimum of 7.0 and was stimulated by PIP2 and inhibited by oleate. Furthermore, cytosolic PLD was stimulated by 30 microM GTP gamma S (6-14-fold) and by the small G proteins 1 microM mArf3 (2-fold) and 0.37 nM RhoA (2-fold). This is the first report to show RhoA activation of a cytosolic PLD. The activation by mArf3 was maintained after partial purification on DEAE Sepharose of the enzyme. We have previously reported the existence of a membrane-bound PLD from human placenta, which is stimulated by PIP2, but not by oleate (Vinggaard, A. M. & Hansen, H. S. (1995) Biochim. Biophys. Acta 1258, 169-176). Here we show that oleic acid and alpha-linolenic acid both dose-dependently inhibited solubilized membrane PLD (65% inhibition at 4 mM), whereas stearic acid (4 mM) had no effect. Thus, the presence of double bonds in the fatty acid is important for the inhibitory effect. Furthermore, placental membrane PLD was activated by 30 microM GTP gamma S (4-fold) and by mArf3 (1 microM) and RhoA (0.37 nM) by a factor of 3 and 2, respectively. The solubilized membrane phospholipase D was partially purified to a basal specific activity of 25-37 nmol/min/mg. This preparation was devoid of endogenous RhoA and Arf and could not be stimulated by GTP gamma S. However, mArf3 (1 microM) still activated this partially purified membrane PLD, whereas RhoA (0.37 nM) was not able to activate this PLD fraction. In conclusion, our results suggest that the human placenta contains a PLD that is located both in the cytosol and the membranes, and that is activated by PIP2, mArf3 and RhoA but inhibited by oleate.

Didecanoyl phosphatidylcholine is a superior substrate for assaying mammalian phospholipase D

Phospholipase D (PLD) activity in crude or solubilized membranes from mammalian tissues is difficult to detect with the current assay techniques, unless a high radioactive concentration of substrate and/or long incubation times are employed. Generally, the enzyme has to be extracted and partially purified on one column before easy detection of activity. Furthermore, PLD activity in cultured cells can only be detected by the available assay techniques in the presence of guanosine 5'-[gamma-thio]-triphosphate (GTP[S]) and a cytosolic factor [usually ADP-ribosylation factor (Arf)]. In this paper we report that the use of didecanoyl phosphatidylcholine (C10-PC) in mammalian PLD assays considerably increases the detection limit. C10-PC was compared with the commonly used dipalmitoyl phosphatidylcholine (C16-PC) as a substrate for PLD activity from membranes of human neutrophils, human placenta and pig brain, and from placental cytosol. C10-PC was superior to C16-PC by a factor of 2-28 depending on assay conditions and tissue, and it allowed the detection of GTP[S]-and Arf-stimulated PLD activity without addition of phosphatidylinositol 4,5-bisphosphate.

Characterization and partial purification of phospholipase D from human placenta

We report the existence in the human placenta of a phosphatidylcholine-hydrolyzing phospholipase D (PLD) activity, which has been characterized and partially purified. Triton X-100 effectively solubilized PLD from the particulate fraction of human placenta in a dose-dependent manner. However, Triton X-100 caused decreasing enzyme activities. Maximum transphosphatidylation was obtained with 2% ethanol. The enzyme was found to have a pH optimum of 7.0-7.5 and an apparent Km of 33 mol% (or 0.8 mM). Ca2+ and Mg2+ was not required for the enzyme activity. Addition of phosphatidyl-4,5-bisphosphate, but not phosphatidylethanolamine, to the substrate mixture gave rise to a pronounced dose-dependent increase in PLD activity (EC50 = 0.3 mol%), suggesting a regulatory role of this phospholipid in PLD action. The enzyme was inhibited by sodium oleate when partly or fully substituting for octylglucoside in the substrate mixture. The PLD activity was enriched 15-fold by solubilization and purification on a DEAE-Sepharose column. N-Ethylmaleimide (10 mM) markedly inhibited the purified enzyme, indicating the presence of free thiol groups on PLD. Sphingosine (20 microM) and (+/-) propranolol (53 microM) had no direct effect on PLD activity. The present results form the basis for further purification of a PLD from human tissue.

Agents that increase phosphatidic acid inhibit the LH-induced testosterone production

The results of the present study point to phosphatidic acid (PtdOH) as a possible intracellular messenger, which might be involved in local modulation of testicular testosterone production in vivo. Propranolol (27-266 microM) induced an increased level of [3H]PtdOH in isolated rat Leydig cells, prelabeled with [3H]myristate, and at the same time a strong dose-dependent inhibition of the acute testosterone production stimulated by luteinizing hormone (LH). The inhibition was not bypassed by the addition of dibutyryl-cAMP but was overcome, when 22(R)-hydroxycholesterol was added as a direct substrate for cytochrome P-450 side chain cleavage enzyme. Thus, the inhibition appears to be exerted at a point distal to cAMP-generation but before the first enzyme in the testosterone synthetic pathway. Treatment with other agents (4 beta-phorbol 12-myristate 13-acetate (PMA), A23187, and sphingosine) giving rise to increases in the PtdOH-level resulted in the inhibition of the LH-induced testosterone formation as well, thus indicating a connection between the two effects. Furthermore, we were able to demonstrate a highly significant correlation between the PtdOH-increase and the inhibition of the LH-stimulated testosterone production. This may suggest a causal relationship between these two parameters.

Ventilation, CO2 production, and CO2 exposure effects in conscious, restrained CF-1 mice

Respiratory rate (f), tidal volume (VT) and carbon dioxide production (VECO2) were measured in restrained, conscious CF-1 mice. Mean f +/- S.D. and mean VT +/- S.D. were 270 +/- 8 breaths/min. and 0.123 +/- 0.024 ml (STPD) for male, and 274 +/- 15 breaths/min. and 0.115 +/- 0.023 ml (STPD) for female mice, respectively. VECO2 was obtained from a rebreathing (closed loop) system. The maximum VECO2 (STPD) amounted to 95.5 +/- 15.4 ml/(kg min.) in males and to 72.7 +/- 4.2 ml/(kg min.) in females. The CO2 concentration in the closed loop system increased slowly during a 30 min. rebreathing period and reached a concentration of about 2.7%. No effect was seen on f and on VT. Dynamic (abrupt) exposure up to 10.3% CO2 had no effect on f in male mice, whereas VT increased from 112% (2.3% CO2) to 181% (10.3% CO2). The estimated O2 concentrations decreased from 20.5% to 18.7% with increasing CO2 exposure. The equivalent CO2 experiments with O2 kept at 16% by N2 administration showed that the lower O2 concentration added an additional drive on the respiratory centre.

Bradykinin and vasopressin activate phospholipase D in rat Leydig cells by a protein kinase C-dependent mechanism

In the present study we report that bradykinin stimulated phospholipase D activity in rat Leydig cells. Bradykinin added for 8 min stimulated choline formation in a dose-dependent manner and, in the presence of ethanol, bradykinin (100 nmol/l) stimulated transphosphatidylation by phospholipase D resulting in the formation of phosphatidylethanol. This stimulation was abolished after down-regulation of protein kinase C by long-term pretreatment for 22 h with phorbol 12-myristate 13-acetate (PMA). The stimulation of phospholipase D by the simultaneous addition for 8 min of maximum concentrations of PMA and vasopressin (AVP), PMA and bradykinin, or AVP and bradykinin produced no additive phosphatidylethanol or choline response, suggesting that AVP, bradykinin and PMA stimulated phospholipase D-catalysed phosphatidylcholine hydrolysis by a similar protein kinase C-dependent mechanism. Furthermore, LH (10 ng/ml), insulin (500 nmol/l), GH (100 ng/ml), interleukin-1 beta (5 U/ml) and platelet-activating factor (200 nmol/l) were found not to activate phospholipase D, whereas the Ca2+ ionophore A23187 (10 mumol/l) stimulated phosphatidylethanol formation, suggesting that Ca2+ might be a regulator of phospholipase D in Leydig cells.

Regulation by dexamethasone of the 3 beta-hydroxysteroid dehydrogenase activity in adult rat Leydig cells

The effect of long-term in vitro treatment with dexamethasone, insulin and/or LH on the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity and the testosterone level was examined in cultures of Leydig cells from adult rats. A rapid and simple method for measuring the 3 beta-HSD activity has been developed, in which the NADH, generated by 3 beta-HSD, reduced nitroblue tetrazolium to a product with absorption maximum at 560 nm. Km for the reaction was 8.1 microM and Vmax was 12.7 nmol/min x mg protein. Addition of 0.1 or 1 microM dexamethasone for 44 h decreased the 3 beta-HSD activity to 83% and the basal testosterone level to 64% of control value after 22 and 44 h of culture. Addition of 1 nM insulin inhibited the 3 beta-HSD activity to 90% after 44 h of culture, whereas the testosterone level was increased after 3 h. Addition of 0.1 ng/ml LH did not affect the 3 beta-HSD activity in Leydig cells from adult rats. Concomitant treatment of the cells with dexamethasone and insulin inhibited the 3 beta-HSD activity to 74%, indicating an additive effect, whereas no additive effect on the testosterone level was observed. The results demonstrate that the 3 beta-HSD activity can be measured in a rapid and reliable way by measuring the reduction of nitroblue tetrazolium. Furthermore, the results suggest that dexamethasone acts on 3 beta-HSD through a mechanism different from that of insulin, as an additive effect was observed.

Phorbol ester and vasopressin activate phospholipase D in Leydig cells

In the present study evidence is provided for the existence of phospholipase D (PLD) activity in rat Leydig cells. Leydig cells were cultured and labelled with [3H]myristic acid. In the presence of ethanol, phorbol 12-myristate 13-acetate (PMA) stimulated the formation of [3H]phosphatidylethanol ([3H]PEt) in a dose-dependent manner at the expense of [3H]phosphatidic acid ([3H]PA). In cells prelabelled with [3H]choline, PMA caused a rapid increase in intracellular free [3H]choline. The time course of [3H]PEt formation was similar to the time course of intracellular [3H]choline formation. The data taken together support the notion that PMA stimulates phosphatidylcholine (PC) hydrolysis by a mechanism, which principally involves PLD. Activation of PLD by PMA was inhibited by long-term pretreatment of cells with PMA to downregulate protein kinase C (PKC) and by pretreatment with staurosporine. These data support the notion that activation of PLD by PMA is dependent on PKC. Arginine vasopressin (AVP) caused a rapid stimulation of PLD activity in the cells. This activation was inhibited after down-regulation of PKC, indicating that the agonist acts by a mechanism similar to that of PMA.

Sensory and pulmonary irritation of inhaled n-butylamine in CF-1 and NMRI mice

Sensory and pulmonary irritation of butylamine was investigated in CF-1 and NMRI mice according to the American standard test method (ASTM E981-84). The method is based on the reflexively induced reduction of the respiratory rate of mice, when exposed to chemical irritants. Sensory irritation was investigated in normal mice, yielding RD50 values (concentration which reduces the respiratory rate by 50%) of 121 and 246 ppm for CF-1 and NMRI mice, respectively. The concentration-effect curves were parallel, but had significantly different elevations, indicating a lower sensitivity of NMRI mice. Pulmonary irritation was investigated in mice, inhaling through a tracheal cannula, yielding RD50 values of 300 and 362 ppm for CF-1 and NMRI mice, respectively. No statistically significant difference between either the slopes or the elevations of the concentration-effect curves was found, indicating the same level of sensitivity of CF-1 and NMRI mice regarding pulmonary irritation. It can be concluded that the 2 mice stocks gave qualitatively comparable responses, but regarding sensory irritation they responded differently quantitatively. Thus for sensory irritation investigations the RD50 values obtained with NMRI mice should be multiplied by 0.49 to obtain comparable values to those, expected in the recommended stock given by E981-84.

Sensory irritation and pulmonary irritation of C3-C7 n-alkylamines: mechanisms of receptor activation

Sensory irritation due to inhalation of a series of alkylamines was estimated from the decrease in respiratory rate in normal (non-cannulated) mice (American standard method E 981-84, 1984). The irritation effects rapidly reached stable levels. The concentration-response relationships followed Michaëlis-Menten equations. The maximum response decreased with increasing chain length. The concentrations depressing the respiratory rate by 50% (RD-50) were 184, 121, 97, 51, and 27 p.p.m. for n-propylamine, n-butylamine, n-pentylamine, n-hexylamine, and n-heptylamine, respectively. It is suggested that the receptor is activated partly by the amines and partly by hydroxide ions. The nose has a scrubbing effect, which partly protects the lungs against water soluble irritants. Pulmonary irritation was estimated from the decrease in respiratory rate in tracheally cannulated mice. The plateau-level of the response was reached slowly. The respective concentrations depressing the respiratory rate by 50% (tRD-50) were 416, 300, 128, 66, and 36 p.p.m. for the C3-C7 n-amines. It is suggested that the pulmonary receptor environment is lipophilic and the receptor, probably the J-receptor, is activated chemically by the amines. The sensory and pulmonary irritation data were used to estimate workplace exposure limits (TLV's) which protect against these effects.

The effects of n-butanol vapour on respiratory rate and tidal volume

Exposure to n-butanol vapour gave rise to a sensory irritation response which was measured by the reflexively induced decrease in respiratory rate in mice according to the American standard method (E981-84). The response reached maximum within the 1st min of exposure. In this period the expected threshold response (RD-0) and the concentration expected to depress the respiratory rate by 50% (RD-50) were extrapolated to be 233 ppm and 11,696 ppm, respectively. The response followed the dynamics of a bimolecular reaction between butanol and the sensory irritant receptor. For concentrations below 3000 ppm, the response faded due to desensitization. However, concentrations above 3000 ppm gave rise to a new decrease in respiratory rate due to activation of lung receptors. Two types of lung receptors, probably J-receptors and stretch receptors, were involved. The sensory irritation response measured by the standard method gave a threshold response which was comparable to that found by electrophysiological experiments in rats. The irritation response in man as well as the maximum allowable concentration in the working environment were adequately predicted from the sensory irritation response in mice.