Measuring the Kinetics of the Binding of Xenoestrogens and Estrogen Receptor Alpha by Fluorescence Polarization

Kwok Wing Yiu; Chi Kin Lee; Ka Cheung Kwok; Nai Ho Cheung

doi:10.1021/es503801c

Measuring the Kinetics of the Binding of Xenoestrogens and Estrogen Receptor Alpha by Fluorescence Polarization

Kwok Wing Yiu, Chi Kin Lee, Ka Cheung Kwok, Nai Ho Cheung^*

^*Corresponding author for this work

Department of Physics

Research output: Contribution to journal › Journal article › peer-review

6 Citations (Scopus)

Abstract

The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ERα with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (∼10^-4) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC₅₀ assays because of their low solubility. Third, we found that BPA had a surprisingly high k_on > 10⁴ M^-1 s^-1. While its RBA was 1500 times lower than that of 17β estradiol (E2), its k_on was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.

Original language	English
Pages (from-to)	11591-11599
Number of pages	9
Journal	Environmental Science and Technology
Volume	48
Issue number	19
DOIs	https://doi.org/10.1021/es503801c
Publication status	Published - 7 Oct 2014

Scopus Subject Areas

General Chemistry
Environmental Chemistry

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title = "Measuring the Kinetics of the Binding of Xenoestrogens and Estrogen Receptor Alpha by Fluorescence Polarization",

abstract = "The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ERα with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (∼10-4) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC50 assays because of their low solubility. Third, we found that BPA had a surprisingly high kon > 104 M-1 s-1. While its RBA was 1500 times lower than that of 17β estradiol (E2), its kon was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.",

author = "Yiu, {Kwok Wing} and Lee, {Chi Kin} and Kwok, {Ka Cheung} and Cheung, {Nai Ho}",

note = "Funding information: This work was supported by the General Research Fund of the Research Grants Council of Hong Kong under Grant No. HKBU 200508 and the Faculty Research Grants of Hong Kong Baptist University under Grant No. FRG1/12-13/020. Publisher copyright: {\textcopyright} 2014 American Chemical Society",

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AU - Yiu, Kwok Wing

AU - Lee, Chi Kin

AU - Kwok, Ka Cheung

AU - Cheung, Nai Ho

N1 - Funding information: This work was supported by the General Research Fund of the Research Grants Council of Hong Kong under Grant No. HKBU 200508 and the Faculty Research Grants of Hong Kong Baptist University under Grant No. FRG1/12-13/020. Publisher copyright: © 2014 American Chemical Society

PY - 2014/10/7

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N2 - The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ERα with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (∼10-4) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC50 assays because of their low solubility. Third, we found that BPA had a surprisingly high kon > 104 M-1 s-1. While its RBA was 1500 times lower than that of 17β estradiol (E2), its kon was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.

AB - The mechanism of endocrine disruption by environmental xenoestrogens is unclear. Bisphenol-A (BPA) is an example. Its concentration in human serum is low, and its binding with estrogen receptor (ER) is weak. Yet its effect on prostate and mammary gland development was observed. We investigated whether this effect could be explained in terms of binding kinetics. We used the method of fluorescence polarization anisotropy to measure the kinetic rate constants of the binding of ERα with 19 xenoestrogens. Relative binding affinities (RBA) were also deduced from the kinetics. We drew three observations. First, our RBAs were consistent with published values, thus establishing the validity of our results. Second, our method allowed the determination of low RBAs (∼10-4) of lipophilic ligands, such as dibutyl phthalate. They could not be measured by steady-state IC50 assays because of their low solubility. Third, we found that BPA had a surprisingly high kon > 104 M-1 s-1. While its RBA was 1500 times lower than that of 17β estradiol (E2), its kon was >1/90 that of E2. As a result, a 10 min surge of BPA from pM to nM could drive the fraction of BPA-activated ERα to a potent 0.1%. This might help to explain the observable estrogenic impacts of BPA.

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Measuring the Kinetics of the Binding of Xenoestrogens and Estrogen Receptor Alpha by Fluorescence Polarization

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