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Title: Sexually dimorphic gene regulation in brain as a target for endocrine disrupters: Developmental exposure of rats to 4-methylbenzylidene camphor

Abstract

The developing neuroendocrine brain represents a potential target for endocrine active chemicals. The UV filter 4-methylbenzylidene camphor (4-MBC) exhibits estrogenic activity, but also interferes with the thyroid axis. We investigated effects of pre- and postnatal exposure to 4-MBC in the same rat offspring at brain and reproductive organ levels. 4-MBC (7, 24, 47 mg/kg/day) was administered in chow to the parent generation before mating, during gestation and lactation, and to the offspring until adulthood. mRNA of estrogen target genes involved in control of sexual behavior and gonadal functions was measured by real-time RT-PCR in ventromedial hypothalamic nucleus (VMH) and medial preoptic area (MPO) of adult offspring. 4-MBC exposure affected mRNA levels of ER alpha, progesterone receptor (PR), preproenkephalin (PPE) and insulin-like growth factor-I (IGF-I) in a sex- and region-specific manner. In order to assess possible changes in sensitivity of target genes to estrogens, offspring were gonadectomized on day 70, injected with estradiol (E2, 10 or 50 {mu}g/kg s.c.) or vehicle on day 84, and sacrificed 6 h later. The acute induction of PR mRNA, and repression (at 6 h) of PPE mRNA by E2 was enhanced by 4-MBC in male and female VMH and female MPO, whereas male MPO exhibitedmore » reduced responsiveness of both genes. Steroid receptor coactivator SRC-1 mRNA levels were increased in female VMH and MPO. The data indicate profound sex- and region-specific alterations in the regulation of estrogen target genes at brain level. Effect patterns in baseline and E2-induced gene expression differ from those in uterus and prostate.« less

Authors:
 [1];  [1];  [1];  [1];  [2]
  1. Institute of Pharmacology and Toxicology and GREEN Tox, University of Zurich, CH-8057 Zurich (Switzerland)
  2. Institute of Pharmacology and Toxicology and GREEN Tox, University of Zurich, CH-8057 Zurich (Switzerland). E-mail: Walter.Lichtensteiger@access.unizh.ch
Publication Date:
OSTI Identifier:
20976849
Resource Type:
Journal Article
Resource Relation:
Journal Name: Toxicology and Applied Pharmacology; Journal Volume: 218; Journal Issue: 2; Other Information: DOI: 10.1016/j.taap.2006.10.026; PII: S0041-008X(06)00406-6; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; BRAIN; CAMPHOR; ESTRADIOL; GENE REGULATION; GENES; GROWTH FACTORS; INSULIN; LACTATION; POLYMERASE CHAIN REACTION; PROGENY; PROGESTERONE; PROSTATE; RATS; RECEPTORS; SENSITIVITY; SEX; THYROID; UTERUS

Citation Formats

Maerkel, Kirsten, Durrer, Stefan, Henseler, Manuel, Schlumpf, Margret, and Lichtensteiger, Walter. Sexually dimorphic gene regulation in brain as a target for endocrine disrupters: Developmental exposure of rats to 4-methylbenzylidene camphor. United States: N. p., 2007. Web. doi:10.1016/j.taap.2006.10.026.
Maerkel, Kirsten, Durrer, Stefan, Henseler, Manuel, Schlumpf, Margret, & Lichtensteiger, Walter. Sexually dimorphic gene regulation in brain as a target for endocrine disrupters: Developmental exposure of rats to 4-methylbenzylidene camphor. United States. doi:10.1016/j.taap.2006.10.026.
Maerkel, Kirsten, Durrer, Stefan, Henseler, Manuel, Schlumpf, Margret, and Lichtensteiger, Walter. Mon . "Sexually dimorphic gene regulation in brain as a target for endocrine disrupters: Developmental exposure of rats to 4-methylbenzylidene camphor". United States. doi:10.1016/j.taap.2006.10.026.
@article{osti_20976849,
title = {Sexually dimorphic gene regulation in brain as a target for endocrine disrupters: Developmental exposure of rats to 4-methylbenzylidene camphor},
author = {Maerkel, Kirsten and Durrer, Stefan and Henseler, Manuel and Schlumpf, Margret and Lichtensteiger, Walter},
abstractNote = {The developing neuroendocrine brain represents a potential target for endocrine active chemicals. The UV filter 4-methylbenzylidene camphor (4-MBC) exhibits estrogenic activity, but also interferes with the thyroid axis. We investigated effects of pre- and postnatal exposure to 4-MBC in the same rat offspring at brain and reproductive organ levels. 4-MBC (7, 24, 47 mg/kg/day) was administered in chow to the parent generation before mating, during gestation and lactation, and to the offspring until adulthood. mRNA of estrogen target genes involved in control of sexual behavior and gonadal functions was measured by real-time RT-PCR in ventromedial hypothalamic nucleus (VMH) and medial preoptic area (MPO) of adult offspring. 4-MBC exposure affected mRNA levels of ER alpha, progesterone receptor (PR), preproenkephalin (PPE) and insulin-like growth factor-I (IGF-I) in a sex- and region-specific manner. In order to assess possible changes in sensitivity of target genes to estrogens, offspring were gonadectomized on day 70, injected with estradiol (E2, 10 or 50 {mu}g/kg s.c.) or vehicle on day 84, and sacrificed 6 h later. The acute induction of PR mRNA, and repression (at 6 h) of PPE mRNA by E2 was enhanced by 4-MBC in male and female VMH and female MPO, whereas male MPO exhibited reduced responsiveness of both genes. Steroid receptor coactivator SRC-1 mRNA levels were increased in female VMH and MPO. The data indicate profound sex- and region-specific alterations in the regulation of estrogen target genes at brain level. Effect patterns in baseline and E2-induced gene expression differ from those in uterus and prostate.},
doi = {10.1016/j.taap.2006.10.026},
journal = {Toxicology and Applied Pharmacology},
number = 2,
volume = 218,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • 3-(4-Methylbenzylidene)camphor (4-MBC) is an UV-filter frequently used in sunscreens and cosmetics. Equivocal findings in some screening tests for hormonal activity initiated a discussion on a possible weak estrogenicity of 4-MBC. In this study, the toxicokinetics and biotransformation of 4-MBC were characterized in rats after oral administration. Male and female Sprague-Dawley rats (n = 3 per group) were administered single oral doses of 25 or 250 mg/kg bw of 4-MBC in corn oil. Metabolites formed were characterized and the kinetics of elimination for 4-MBC and its metabolites from blood and with urine were determined. Metabolites of 4-MBC were characterized by {supmore » 1}H NMR and LC-MS/MS as 3-(4-carboxybenzylidene)camphor and as four isomers of 3-(4-carboxybenzylidene)hydroxycamphor containing the hydroxyl group located in the camphor ring system with 3-(4-carboxybenzylidene)-6-hydroxycamphor as the major metabolite. After oral administration of 4-MBC, only very low concentrations of 4-MBC were present in blood and the peak concentrations of 3-(4-carboxybenzylidene)camphor were approximately 500-fold above those of 4-MBC; blood concentrations of 3-(4-carboxybenzylidene)-6-hydroxycamphor were below the limit of detection. Blood concentration of 4-MBC and 3-(4-carboxybenzylidene)camphor peaked within 10 h after 4-MBC administration and then decreased with half-lives of approximately 15 h. No major differences in peak blood levels between male and female rats were seen. In urine, one isomer of 3-(4-carboxybenzylidene)hydroxycamphor was the predominant metabolite [3-(4-carboxybenzylidene)-6-hydroxycamphor], the other isomers and 3-(4-carboxybenzylidene)camphor were only minor metabolites excreted with urine. However, urinary excretion of 4-MBC-metabolites represents only a minor pathway of elimination for 4-MBC, since most of the applied dose was recovered in feces as 3-(4-carboxybenzylidene)camphor and, to a smaller extent, as 3-(4-carboxybenzylidene)-6-hydroxycamphor. Glucuronides of both metabolites were also present in feces, but partly decomposed during sample workup and were thus not quantified. The results show that absorbed 4-MBC undergoes extensive first-pass biotransformation in rat liver resulting in very low blood levels of the parent 4-MBC. Enterohepatic circulation of glucuronides derived from the two major 4-MBC metabolites may explain the slow excretion of 4-MBC metabolites with urine and the small percentage of the administered doses recovered in urine.« less
  • The toxicokinetics of 4-MBC after dermal administration were investigated in human subjects and in rats. Humans (3 male and 3 female subjects) were exposed to 4-MBC by topical application of a commercial sunscreen formulation containing 4% 4-MBC (w/w), covering 90% of the body surface and resulting in a mean dermal 4-MBC dose of 22 mg/kg bw. In rats, dermal 4-MBC doses of 400 and 2000 mg/kg bw were applied in a formulation using an occlusive patch for 24 h. Concentrations of 4-MBC and its metabolites were monitored over 96 h in plasma (rats and humans) and urine (humans). In humanmore » subjects, plasma levels of 4-MBC peaked at 200 pmol/ml in males and 100 pmol/ml in females 6 h after application and then decreased to reach the limit of detection after 24 h (females), respectively, 36 h (males). After dermal application of 4-MBC, peak plasma concentrations of 3-(4-carboxybenzylidene)-6-hydroxycamphor were 50-80 pmol/ml at 12 h and of 3-(4-carboxybenzylidene)camphor were 100-200 pmol/ml at 24 h. In male and female rats, peak plasma levels of 4-MBC were 200 (dose of 400 mg/kg bw) and 1 200 pmol/ml (dose of 2000 mg/kg bw). These levels remained constant for up to 24-48 h after dermal application. Peak plasma concentrations of 3-(4-carboxybenzylidene)-6-hydroxycamphor were 18,000 pmol/ml (males) and of 3-(4-carboxybenzylidene)camphor were 55,000 pmol/ml (females) between 48 and 72 h after application of the high dose of 4-MBC. In human subjects, only a small percentage of the dermally applied dose of 4-MBC was recovered in the form of metabolites in urine, partly as glucuronides. The obtained results suggest a more intensive biotransformation of 4-MBC in rats as compared to humans after dermal application and a poor absorption of 4-MBC through human skin.« less
  • OMC and 4MBC are 2 absorbers of ultraviolet light which are used in unknown quantities in sunscreens, cosmetics and plastic products to protect against UV light-induced damage of the skin or of fragrances or plastic material. From there, they were shown to reach surface water and/or by direct contamination or ingestion the human. Under various conditions in mice and rats, both substances were shown to be estrogenic. Therefore, we compared in vitro and in vivo the effects of chronic application of these compounds at 2 doses with those of E2, all administered via food. No signs of toxicity were observedmore » under application of 0.6 mg E2, 57.5 or 275 mg of OMC, 57.5 or 250 mg of 4MBC; these amounts were ingested with 21 g of control food, 17.8 g E2 food, 20.6 g or 22.3 g OMC food and 23.7 or 22.8 g 4MBC food. In the uterus, vagina and bone, E2 exerted the expected stimulatory effects which were minimally shared by OMC and 4MBC in the uterus and vagina as assessed by histology and determination of a variety of estrogen-regulated genes such as insulin-like growth factor-1, progesterone receptor and estrogen receptor {beta}. In the bone, OMC had no effect, while 4MBC shared the antiosteoporotic effects of E2 as measured by quantitative computer tomography in the metaphysis of the tibia. The mechanism of action of 4MBC, however, appears to be different as E2 reduced serum osteocalcin and the C-terminal breakdown products of collagen-1{alpha}1 which were both increased by 4MBC. Taken together, these data indicate a very weak estrogenic effect of OMC and 4MBC in the uterus and in the vagina but not in the bone where 4MBC exerted antiosteoporotic effects by a different mechanism than E2.« less
  • Octylmethoxycinnamate (OMC) and 4-methylbenzylidene camphor (4MBC) are commercially used absorbers of ultraviolet (UV) light. In rats, they were shown to exert endocrine disrupting including uterotrophic, i.e. estrogenic effects. Estrogens have also metabolic effects, therefore the impact of oral application of the two UV absorbers at 2 doses for 3 months on lipids and hormones were compared with those of estradiol-17{beta} (E2). E2, OMC and 4MBC reduced weight gain, the size of fat depots and serum leptin, a lipocyte-derived hormone, when compared to the ovariectomized control animals. Serum triglycerides were also reduced by the UV screens but not by E2. Onmore » the other hand, E2 and OMC reduced serum cholesterol, low density lipoproteins and high density lipoproteins; this effect was not shared by 4MBC. While E2 inhibited, OMC and 4MBC stimulated serum LH levels. In the uterus, both UV filters had mild stimulatory effects. 4MBC inhibited serum T4 resulting in increased serum TSH levels. It is concluded that OMC and 4MBC have effects on several metabolic parameters such as fat and lipid homeostasis as well as on thyroid hormone production. Many of these effects are not shared by E2. Hence, other than estrogen-receptive mechanisms may be responsible for these effects.« less
  • Methoxychlor (MXC) is an organochlorine pesticide with estrogenic, anti-estrogenic, and anti-androgenic properties. To investigate whether transient developmental exposure to MXC could cause adult ovarian dysfunction, we exposed Fischer rats to 20 {mu}g/kg/day (low dose; environmentally relevant dose) or 100 mg/kg/day (high dose) MXC between 19 days post coitum and postnatal day 7. Multiple reproductive parameters, serum hormone levels, and ovarian morphology and molecular markers were examined from prepubertal through adult stages. High dose MXC accelerated pubertal onset and first estrus, reduced litter size, and increased irregular cyclicity (P < 0.05). MXC reduced superovulatory response to exogenous gonadotropins in prepubertal femalesmore » (P < 0.05). Rats exposed to high dose MXC had increasing irregular estrous cyclicity beginning at 4 months of age, with all animals showing abnormal cycles by 6 months. High dose MXC reduced serum progesterone, but increased luteinizing hormone (LH). Follicular composition analysis revealed an increase in the percentage of preantral and early antral follicles and a reduction in the percentage of corpora lutea in high dose MXC-treated ovaries (P < 0.05). Immunohistochemical staining and quantification of the staining intensity showed that estrogen receptor {beta} was reduced by high dose MXC while anti-Mullerian hormone was upregulated by both low- and high dose MXC in preantral and early antral follicles (P < 0.05). High dose MXC significantly reduced LH receptor expression in large antral follicles (P < 0.01), and down-regulated cytochrome P450 side-chain cleavage. These results demonstrated that developmental MXC exposure results in reduced ovulation and fertility and premature aging, possibly by altering ovarian gene expression and folliculogenesis.« less