Saag

Publications (15)0 Total impact

• Article: Phytoestrogen-mediated inhibition of proliferation of the human T47D breast cancer cells depends on the ER /ER ratio

  A.M. Sotoca Covaleda, D. Ratman, Saag, A Ström, J A Gustafsson, J.J.M. Vervoort
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  ABSTRACT: This study investigates the importance of the intracellular ratio of the two estrogen receptors ER¿ and ERß for the ultimate potential of the phytoestrogens genistein and quercetin to stimulate or inhibit cancer cell proliferation. This is of importance because (i) ERß has been postulated to play a role in modulating ER¿-mediated cell proliferation, (ii) genistein and quercetin may be agonists for both receptor types and (iii) the ratio of ER¿ to ERß is known to vary between tissues. Using human osteosarcoma (U2OS) ER¿ or ERß reporter cells it was shown that compared to estradiol (E2), genistein and quercetin have not only a relatively greater preference for ERß but also a higher maximal potential for activating ERß-mediated gene expression. Using the human T47D breast cancer cell line with tetracycline-dependent ERß expression (T47D-ERß), the effect of a varying intracellular ER¿/ERß ratio on E2- or pythoestrogen-induced cell proliferation was characterised. E2-induced proliferation of cells in which ERß expression was inhibited was similar to that of the T47D wild type cells, whereas this E2-induced cell proliferation was no longer observed when ERß expression was increased. With increased expression of ERß the phytoestrogen-induced cell proliferation was also reduced. These results point at the importance of the cellular ER¿/ERß ratio for the ultimate effect of (phyto)estrogens on cell proliferation.
  Journal of Steroid Biochemistry and Molecular Biology 112 (2008) 4-5.
• Article: Influence of cellular ER alpha/ER beta ratio on the ER alpha-agonist induced proliferation of human T47D breast cancer cells

  A.M. Sotoca Covaleda, Berg, van den, J.J.M. Vervoort, Saag, A. Strom, J A Gustafsson, I.M.C.M. Rietjens, A.J. Murk
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  ABSTRACT: Breast cancer cells show overexpression of estrogen receptor (ER) relative to ERß compared to normal breast tissues. This observation has lead to the hypothesis that ERß may modulate the proliferative effect of ER. This study investigated how variable cellular expression ratios of the ER and ERß modulate the effects on cell proliferation induced by ER or ERß agonists, respectively. Using human osteosarcoma (U2OS) ER or ERß reporter cells, propyl-pyrazole-triol (PPT) was shown to be a selective ER and diarylpropionitrile (DPN) a preferential ERß modulator. The effects of these selective estrogen receptor modulators (SERMs) and of the model compound E2 on the proliferation of T47D human breast cancer cells with tetracycline-dependent expression of ERß (T47D-ERß) were characterized. E2-induced cell proliferation of cells in which ERß expression was inhibited was similar to that of the T47D wild-type cells, whereas this E2-induced cell proliferation was no longer observed when ERß expression in the T47D-ERß cells was increased. In the T47D-ERß cell line, DPN also appeared to be able to suppress cell proliferation when levels of ERß expression were high. In the T47D-ERß cell line, PPT was unable to suppress cell proliferation at all ratios of ER/ERß expression, reflecting its ability to activate only ER and not ERß. It is concluded that effects of estrogen-like compounds on cell proliferation are dependent on the actual ER/ERß expression levels in these cells or tissues and the potential of the estrogen agonists to activate ER and/or ERß.
  Toxicological sciences 105 (2008) 2.
• Article: Interference between progesterone and dioxin signal transduction pathways: different mechanisms are involved in repression by the progesterone receptor A and B isoforms.

  C W Kuil, A. Brouwer, Saag, P.T, Burg
  J. Biol. Chem. 273 (1998) 8829-8834.
• Article: Selective estrogenicity in orally exposed transgenic male mice of compounds known to be estrogenic in vitro

  Veld, M.G.R, ter, Saag, P.T, I.M.C.M. Rietjens, A.J. Murk
• Article: Xeno-estrogens: impact on the fetus and test system development

  J G Lemmen, J. Legler, A.J. Murk, A. Brouwer, J.L.M. Broekhof, Brink, C.E, van den, J A Gustafsson, G.G.J.M. Kuiper, Saag, P.T, Burg
  In: Endocrine Disrupting Compounds : Wildlife and human health risks, The Hague. - The Hague : [s.n.], 2000.
• Article: Role of retinoids in spermatogonial proliferation and differentiation and the meiotic prophase.

  Rooij, D.G, Pelt, A.M.M, Kant, H.J.G, Saag, P.T, A.H.F.M. Peters, C. Heijting, Boer
  In: Function of somatic cells in the testis, A. Bartke (ed.). Springer Verlag New York/Berlin (1994) 345-361.
• Article: Food-associated estrogenic compounds induce estrogen receptor-mediated luciferase gene expression in transgenic male mice

  Veld, M.G.R, ter, E. Zawadzka, Berg, J.H.J, van den, Saag, P.T, I.M.C.M. Rietjens, A.J. Murk
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  ABSTRACT: The present paper aims at clarifying to what extent seven food-associated compounds, shown before to be estrogenic in vitro, can induce estrogenic effects in male mice with an estrogen receptor (ER)-mediated luciferase (luc) reporter gene system. The luc induction was determined in different tissues 8 h after dosing the ER-luc male mice intraperitoneally (IP) or 14 h after oral dosing. Estradiol-propionate (EP) was used as a positive control at 0.3 and 1 mg/kg bodyweight (bw), DMSO as solvent control. The food-associated estrogenic compounds tested at non-toxic doses were bisphenol A (BPA) and nonylphenol (NP) (both at 10 and 50 mg/kg bw), dichlorodiphenyldichloroethylene (p,p¿-DDE; at 5 and 25 mg/kg bw), quercetin (at 1.66 and 16.6 mg/kg bw), di-isoheptyl phthalate (DIHP), di-(2-ethylhexyl) phthalate (DEHP) and di-(2-ethylhexyl) adipate (DEHA) all at 30 and 100 mg/kg bw. In general IP dosing resulted in higher luc inductions than oral dosing. EP induced luc activity in the liver in a statistically significant dose-related way with the highest induction of all compounds tested which was 20,000 times higher than the induction by the DMSO-control. NP, DDE, DEHA and DIHP did not induce luc activity in any of the tissues tested. BPA induced luc in the liver up to 420 times via both exposure routes. BPA, DEHP and quercetin induced luc activity in the liver after oral exposure. BPA (50 mg/kg bw IP) also induced luc activity in the testis, kidneys and tibia. The current study reveals that biomarker-responses in ER-luc male mice occur after a single oral exposure to food-associated estrogenic model compounds at exposure levels 10 to 104 times higher than the established TDI's for some of these compounds. Given the facts that (i) the present study did not include chronic exposure and that (ii) simultaneous exposure to multiple estrogenic compounds may be a realistic exposure scenario, it remains to be seen whether this margin is sufficiently high
  Chemico-Biological Interactions 174 (2008) 2.
• Article: The stimulation of cell proliferation by quercetin is mediated by the estrogen receptor

  Woude, Veld, M.G.R, ter, N. Jacobs, Saag, P.T, A.J. Murk, I.M.C.M. Rietjens
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  ABSTRACT: Quercetin causes biphasic modulation of the proliferation of specific colon and mammary cancer cells. In this study, the possible involvement of the estrogen receptor (ER) in the stimulation of cell proliferation by quercetin was investigated. For this purpose, the effect of quercetin on cell proliferation was tested in ER-positive MCF-7 and T47D cells, and in ER-negative HCC-38 and MDA-MB231 cells. Quercetin stimulated proliferation of ER-positive cells only, suggesting this effect to be ER-dependent. In support of these results, quercetin induced ER-ERE-mediated gene expression in a reporter gene assay using U2-OS cells transfected with either ER or ER, with 105-106 times lower affinity than 17-estradiol (E2) and 102-103 times lower affinity than genistein. Quercetin activated the ER to a 4.5-fold higher level than E2, whereas the maximum induction level of ER by quercetin was only 1.7 fold that of E2. These results point at the relatively high capacity of quercetin to stimulate supposed beneficial ER responses as compared to the stimulation of ER, the receptor possibly involved in adverse cell proliferative effects. Altogether, the results of this study reveal that physiologically relevant concentrations of quercetin can exert phytoestrogen-like activity similar to that observed for the isoflavonoid genistein.
  Molecular Nutrition & Food Research 49 (2005) 8.
• Article: Development of a stably transfected estrogen receptor-mediated luciferase reporter gene assay in the human T47D breast cancer cell line

  J. Legler, Brink, van den, A. Brouwer, A.J. Murk, Saag, P.T, A.D. Vethaak, Berg
  Toxicological Sciences 48 (1999).
• Article: In vitro and in vivo assessment of potential (anti-)estrogenic compounds using stably transfected cell lines and transgenic zebrafish

  J. Legler, Brink, C.E, van den, J. Broekhof, A. Brouwer, A.J. Murk, Saag, A.D. Vethaak, Burg
  In:Congress Proceedings / Keystone Symposia on molecular en cellular biology : Endocrine Disruptors. Lake Tahoe, California,January 1999 / Kenneth S.Korach and George M.Stancel (eds).
• Article: In vitro and in vivo assessment of potential (anti-)estrogenic compounds with a stably transfected cell line and transgenic zebrafish

  J. Legler, Brink, C.E, van den, J. Broekhof, A. Brouwer, A.J. Murk, Saag, A.D. Vethaak, Burg
  In: Congress Proceedings, Environmental Endocrine Disrupting Chemicals, Ascona, Zwitzerland, March 1999 / Walter Giger, KarlFent, Urs Friederich (eds).
• Article: Measurement of (anti-)oestrogenic potency in complex mixtures using a novel stably transfected luciferase reporter gene assay in the human T47D breast cancer cell

  J. Legler, Brink, van den, A. Brouwer, Saag, A.D. Vethaak, A.J. Murk, Burg
  In: Endocrine Disrupting Compounds : Wildlife and human health risks, The Hague 1998. - The Hague : [s.n.], 2000.
• Article: Development of an in vivo assay for oestrogenic potency using transgenic zebrafish

  J. Legler, J. Broekhof, A. Brouwer, A.J. Murk, Saag, A.D. Vethaak, Burg
  In: Endocrine Disrupting Compounds : Wildlife and human health risks, The Hague 1998. - The Hague : [s.n.], 2000.
• Article: Estrogenic potency of food-packaging-associated plasticizers and antioxidants as detected in ERa and ERb reporter gene cell lines

  Veld, M.G.R, ter, B. Schouten, J. Louisse, Es, D.S, Saag, P.T, I.M.C.M. Rietjens, A.J. Murk
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  ABSTRACT: This study presents the estrogenic potency of 21 food-packaging-associated compounds determined for the first time, using two transfected U2-OS (human osteoblasts devoid of endogenous estrogen receptors) estrogen receptor (ER) alpha and beta cell lines. Six plasticizers and three antioxidants were slightly estrogenic in the ER cells. The model compounds bisphenol A and nonylphenol, one plasticizer [tris(2-ethylhexyl)trimellitate (TEHTM)], and two antioxidants (propyl gallate and butylated hydroxyanisole) were estrogenic in both ER and ER cells. Compared to estradiol (E2), these compounds appeared to be relatively more estrogenic in the ER cells than in the ER cells. Three sorbitol-based plasticizers activated neither ER nor ER and may be good replacements of existing plasticizers. All responses were additive with the response of E2. This indicates that they may contribute to the total effects of the pool of estrogenic compounds humans are exposed to. The estrogenic potencies of these compounds, together with the suggested beneficial effect of ER-mediated responses and adverse ER-mediated effects, support the importance of detecting characteristics for ER and ER response separately in independent models, as done in the present study
  Journal of Agricultural and Food Chemistry 54 (2006) 12.
• Source

  Available from: AlberTinka Murk

  Article: A novel in vivo bioassay for (xeno-)estrogens using transgenic zebrafish

  J. Legler, J.L.M. Broekhof, A. Brouwer, P.H. Lanser, A.J. Murk, Saag, P.T, A.D. Vethaak, P. Wester, D Zivkovic, Burg
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  ABSTRACT: Adverse trends in the reproductive health of male fish, including testis abnormalities and intersex gonads, have been increasingly reported over recent years. These effects have been associated with the exposure of fish to natural, synthetic, and xenobiotic estrogens present in the aquatic environment. A novel in vivo test system using transgenic zebrafish has been developed to rapidly determine the effects of estrogenic chemicals on critical life stages and sensitive target organs in the fish. In the transgenic zebrafish, an estrogen binding sequence linked to a TATA box and luciferase reporter gene was stably introduced. Binding of a substance to endogenous estrogen receptors (ER) and the subsequent transactivation of the ER result in luciferase gene induction that is easily measured in tissue lysates. Exposure to estradiol (E2) during juvenile stages of the transgenic zebrafish revealed the period of gonad differentiation to be the most responsive early life stage. In adult male transgenic zebrafish, the testis was the most sensitive and responsive target tissue to estrogens. Partial sequences of zebrafish estrogen receptor subtypes and were cloned for the first time and were found to be differentially expressed in developing fish and tissues of adult male zebrafish. The transgenic zebrafish assay is a promising new tool to rapidly determine the estrogenic potency of chemicals in vivo.
  Environmental Science and Technology 34 (2000).