Estrogen Receptors (ERα, ERβ, GPER): BPB binds to and activates estrogen receptors. EC50 values for hERα transactivation range from 0.07-5 μM. Binds to human GPER with relative binding affinity 8.8% compared to estradiol. [1]
Androgen Receptor (AR): BPB binds to AR and exhibits antagonistic activity. IC50 values for AR antagonism range from 0.93-64.24 μM. [1]
Steroidogenic Enzymes: BPB modulates expression and activity of enzymes involved in steroidogenesis including aromatase (cyp19a1a/b), 17β-hydroxysteroid dehydrogenase, and cytochrome P450 enzymes. [1]

Estrogen Receptor Binding: BPB competitively binds to estrogen receptors of human, rat, and mouse. In hERα transactivation assays, EC50 values ranged from 0.59-5 μM in yeast-based assays and 0.07-0.3 μM in vertebrate reporter cell lines. [1]
GPER Activation: BPB bound to human G-protein coupled estrogen receptor with higher relative binding affinity (8.8% vs. estradiol) than to ER (<1%). In SKBR3 cells, 10 nM BPB significantly increased calcium mobilization and cAMP production, and promoted cell migration. These effects were blocked by the GPER-selective inhibitor G15. [1]
Estrogen-Regulated Gene Expression: In MCF-7 breast cancer cells, BPB induced ER-regulated gene expression including pS2 and progesterone receptor. [1]
Cell Proliferation: BPB induced proliferation of ER-positive human breast cancer cell lines (MCF-7, T47D) with AC50 values of 0.24-0.28 μM. [1]
Androgen Receptor Antagonism: BPB bound to AR of human, rat, and chimpanzee with IC50 values from 2.2-36.65 μM. In transactivation assays, BPB showed AR antagonistic activity in most vertebrate and yeast reporter gene assays with IC50 values ranging from 0.93-64.24 μM. No agonist activity was observed. [1]
Steroidogenesis (H295R Cells): In H295R steroidogenesis assays, BPB exposure decreased androstenedione, testosterone, and cortisol levels, while increasing estrogen levels. Testosterone IC50 = 18.8 μM; Androstenedione IC50 = 16 μM; Estradiol EC50 = 13.6 μM. [1]
Human Testis Explants: In adult human testis explants exposed to BPB for 24-48 hours, inconsistent lower testosterone secretions were observed at 0.1 μM, though results showed high variability. [1]
Comparison with BPA: In most in vitro assays, BPB showed similar or greater potency than BPA. The median estrogenic potency of BPB was 4-fold higher than BPA. BPA/BPB potency ratios ranged from 0.7 to >100. [1]

Rat 28-Day Oral Study (Ullah 2018a): Male Sprague-Dawley rats (70-80 days old) were orally exposed to BPB at 0, 5, 25, 50 mg/kg BW/d for 28 days (n=7/group). Effects: statistically significant lower height of seminiferous epithelium (19% reduction at 50 mg/kg); qualitative histological evaluation showed fewer spermatids and sperm in tubule lumen; at 50 mg/kg, very few tubules with no elongated spermatids. [1]
Rat 48-Week Drinking Water Study (Ullah 2018b): Male Sprague-Dawley rats (PND 23) received BPB in drinking water at 0, 5, 25, 50 μg/L for 48 weeks (estimated intake 0, 0.3, 1.5, 3 μg/kg BW/d). At 50 μg/L: significantly lower relative weights of testis, epididymis, and seminal vesicles; dose-dependent lower daily sperm production (9% reduction at 50 μg/L); lower sperm number in caput (from 25 μg/L) and cauda epididymis (at 50 μg/L); lower motile sperm percentage (at 50 μg/L); lower height of seminal epithelium (16% reduction at 50 μg/L); fewer spermatogonia, spermatocytes, and spermatids; 22% lower plasma testosterone; higher plasma estradiol, LH, and FSH. [1]
Zebrafish 21-Day Reproductive Study (Yang 2017): 4-month-old zebrafish exposed to BPB at 0, 0.001, 0.01, 0.1, 1 mg/L for 21 days (n=6/sex/group). At 1 mg/L: 50% reduction in egg laying; lower hatching rate and embryo survival; higher hepato-somatic index; lower gonado-somatic index; testicular disorganization with acellular areas and fewer mature spermatids; in females, one fish lacked post-vitellogenic oocytes at 1 mg/L. Dose-dependent lower body testosterone (significant from 0.1 mg/L in males, 1 mg/L in females); higher estradiol levels (from 0.01 mg/L). [1]
Uterotrophic Assay (Yamasaki 2002): Immature female rats treated subcutaneously with 200 mg/kg BW/d BPB from PND 20-22 had more watery uterine content and greater blotted uterine weight, indicating estrogenic activity. [1]
Medaka Study (Yamaguchi 2015): Male medaka exposed to BPB at 0.5, 5, 50 μM for 8 hours showed significantly higher expression of hepatic estrogen-responsive genes (vtg1, chgL, ERα) from 5 μM. LOEC for BPB (5 μM) was lower than for BPA (50 μM). [1]
Hershberger Assay (Yamasaki 2003): Castrated male rats exposed to BPB (50-600 mg/kg/d) for 10 days showed no androgenic activity. Anti-androgenic effect observed in one of five androgen-dependent organs. Co-exposure with testosterone propionate resulted in higher ventral prostate weight from 200 mg/kg and higher weight of all androgen-dependent targets at 600 mg/kg. [1]

ER Transactivation Assays: Various cell lines (yeast, HeLa, MCF-7, T47D, U2OS, BG1-luc4E2) were used to measure ERα and ERβ agonist/antagonist activity using reporter gene constructs. Cells were exposed to BPB for 4-48 hours, and luminescence or fluorescence was measured. EC50/IC50 values were calculated. [1]
ER Binding Assays: Competitive binding assays using uterine cytosol or recombinant ER proteins with radiolabeled estradiol. [1]
GPER Signaling Assays: SKBR3 cells were treated with BPB, and calcium mobilization (measured by fluorescence), cAMP production (by ELISA), and cell migration (by Transwell assay) were assessed. The GPER antagonist G15 was used to confirm specificity. [1]
Cell Proliferation Assays: MCF-7 and T47D cells were exposed to BPB for 80-144 hours, and proliferation was measured by various methods (e.g., cell counting, metabolic activity). AC50 values were calculated. [1]
Steroidogenesis Assay (H295R): H295R human adrenocortical carcinoma cells were exposed to BPB for 48 hours. Hormone levels in media (testosterone, androstenedione, estradiol, cortisol, etc.) were measured by ELISA or LC-MS/MS. [1]
Human Testis Explant Culture: Adult human testicular explants were cultured with BPB for 24-48 hours. Testosterone secretion was measured in media. [1]

Rat 28-Day Oral Study:** Male Sprague-Dawley rats (70-80 days old, n=7/group) were orally administered BPB at 0, 5, 25, 50 mg/kg BW/d for 28 days. Testis histology and hormone levels were assessed. [1]
* **Rat 48-Week Drinking Water Study:** Male Sprague-Dawley rats (PND 23, n=7/group) received BPB in drinking water at 0, 5, 25, 50 μg/L for 48 weeks. Water intake was monitored, and estimated daily intake calculated (0, 0.3, 1.5, 3 μg/kg/d). Reproductive organ weights, sperm parameters, testis histology, and hormone levels were assessed. [1]
* **Zebrafish 21-Day Reproductive Study:** 4-month-old zebrafish (n=6/sex/group) were exposed to BPB at 0, 0.001, 0.01, 0.1, 1 mg/L in water for 21 days. Reproductive output (egg number), hatching rate, embryo survival, gonado-somatic index, hepato-somatic index, histology, hormone levels, and gene expression were assessed. [1]
* **Uterotrophic Assay:** Immature female rats (PND 20, n=6-8/group) received subcutaneous injections of BPB at 200 mg/kg/d for 3 days. Uterine weight and morphology were assessed. [1]
* **Hershberger Assay:** Castrated male rats received BPB (50-600 mg/kg/d) alone or with testosterone propionate for 10 days. Weights of androgen-dependent tissues were measured. [1]
* **Medaka Study:** Male medaka were exposed to BPB at 0.5, 5, 50 μM for 8 hours. Hepatic gene expression was analyzed by qPCR. [1]

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Rat 28-Day Oral Study: Male Sprague-Dawley rats (70-80 days old, n=7/group) were orally administered BPB at 0, 5, 25, 50 mg/kg BW/d for 28 days. Testis histology and hormone levels were assessed. [1]
Rat 48-Week Drinking Water Study: Male Sprague-Dawley rats (PND 23, n=7/group) received BPB in drinking water at 0, 5, 25, 50 μg/L for 48 weeks. Water intake was monitored, and estimated daily intake calculated (0, 0.3, 1.5, 3 μg/kg/d). Reproductive organ weights, sperm parameters, testis histology, and hormone levels were assessed. [1]
Zebrafish 21-Day Reproductive Study: 4-month-old zebrafish (n=6/sex/group) were exposed to BPB at 0, 0.001, 0.01, 0.1, 1 mg/L in water for 21 days. Reproductive output (egg number), hatching rate, embryo survival, gonado-somatic index, hepato-somatic index, histology, hormone levels, and gene expression were assessed. [1]
Uterotrophic Assay: Immature female rats (PND 20, n=6-8/group) received subcutaneous injections of BPB at 200 mg/kg/d for 3 days. Uterine weight and morphology were assessed. [1]
Hershberger Assay: Castrated male rats received BPB (50-600 mg/kg/d) alone or with testosterone propionate for 10 days. Weights of androgen-dependent tissues were measured. [1]
Medaka Study: Male medaka were exposed to BPB at 0.5, 5, 50 μM for 8 hours. Hepatic gene expression was analyzed by qPCR. [1]

Metabolism / Metabolites
Researchers have previously demonstrated that bisphenol A [BPA; 2,2-bis(4-hydroxyphenyl)propane] or bisphenol B [BPB; 2,2-bis(4-hydroxyphenyl)butane] significantly enhances estrogenic activity upon incubation with rat liver S9 fraction. This metabolic activation requires the participation of microsomal and cytoplasmic components and has been observed not only in rat liver but also in human, monkey, and mouse liver S9 fractions. To identify the active metabolites of BPA and BPB, researchers analyzed the structures of the isolated active metabolites using negative ion mode liquid chromatography-tandem mass spectrometry (LC/MS/MS) and gas chromatography-mass spectrometry (GC/MS). The active metabolite of BPA showed a negative ion peak at [MH](-) 267 in LC/MS analysis and a single daughter ion peak at m/z 133 in MS/MS analysis, suggesting an isopropenylphenol dimer structure. Finally, multiple instrumental analyses confirmed that the active metabolite was identical to the standard 4-methyl-2,4-bis(p-hydroxyphenyl)pent-1-ene (MBP). The corresponding peaks of the BPB metabolite were [MH](-) 295 and m/z 147, indicating that it possesses an isobutylenylphenol dimer structure. Furthermore, co-incubation of BPA and BPB with rat liver S9 produced another active metabolite, which showed a negative ion peak at [MH](-) 281 and two daughter ion peaks at m/z 133 and m/z 147 in MS/MS analysis. These results strongly suggest that the active metabolites of BPA or BPB may be formed by the recombination of free radical fragments, which are single-electron oxidation products of carbon-phenyl bond cleavage. Notably, in multiple assays, the estrogenic activity of MBP, the active metabolite of BPA, was significantly stronger than that of maternal BPA, including two reporter gene assays using recombinant yeast expressing human estrogen receptor α and firefly luciferase plasmid transfected with MCF-7.

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Exposure Estimates: In a 48-week rat study, BPB was administered in drinking water at 5-50 μg/L, with estimated daily intake of 0.3-3 μg/kg BW/d. [1]
Environmental Detection: BPB has been detected in European food products (canned foods, milk) and in human urine and serum samples at concentrations comparable to BPA. [1]

Reproductive Toxicity (Male Rats): BPB exposure caused dose-dependent adverse effects on male reproductive system including reduced testis/epididymis weight, impaired spermatogenesis, reduced sperm count and motility, and lower testosterone levels. [1]
Reproductive Toxicity (Zebrafish): BPB exposure reduced fecundity, hatching rate, and embryo survival, and caused gonadal histological changes. [1]
Endocrine-Related Toxicity: Effects are mediated through estrogenic, anti-androgenic, and steroidogenesis-disrupting mechanisms. [1]

[1]. Evidence for Bisphenol B Endocrine Properties: Scientific and Regulatory Perspectives. Environ Health Perspect. 2019 Oct;127(10):106001.

[2]. Bisphenol A and its analogs bisphenol B, bisphenol F, and bisphenol S: Comparative in vitro and in vivo studies on the sperms and testicular tissues of rats. Chemosphere. 2018 Oct;209:508-516.

Bisphenol B is a type of bisphenol.

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Background: Bisphenol B is a structural analog of bisphenol A, differing only by an additional methyl group on the central carbon. It is used as an indirect food additive in the US (FDA registered) but not registered in the EU under REACH (<1 ton/year). It has been detected in various European food products and human biomonitoring samples. [1]
Regulatory Status: Based on this evidence, the authors conclude that BPB meets the WHO definition of an endocrine disrupting chemical. It shows adverse effects on reproductive function in rats and fish, clear endocrine activity (estrogenic, anti-androgenic, steroidogenesis disruption), and plausible mechanistic links between these observations. [1]
Comparison with BPA: BPB generally shows similar or greater potency than BPA in most assays. The median estrogenic potency is 4-fold higher. Effects on male reproduction in rats are similar or slightly more pronounced than BPA at comparable doses. [1]
Mechanism of Action: The primary mechanisms involve: (1) direct activation of estrogen receptors (ERα, ERβ, GPER); (2) antagonism of androgen receptors; (3) disruption of steroidogenesis (reducing testosterone production, increasing estradiol levels). These endocrine activities collectively contribute to impaired reproductive function. [1]
Regulatory Concern: As a potential BPA substitute, BPB may pose similar or greater health and environmental risks. The authors recommend considering the available evidence sufficient for regulating BPB for its endocrine properties to protect human health and wildlife. [1]

C16H18O2

242.3129

242.13

77-40-7

66166

White to off-white solid powder

1.1±0.1 g/cm3

412.2±25.0 °C at 760 mmHg

126°C

195.5±17.8 °C

0.0±1.0 mmHg at 25°C

1.589

3.96

2

2

3

18

226

0

O([H])C1C([H])=C([H])C(=C([H])C=1[H])C(C([H])([H])[H])(C1C([H])=C([H])C(=C([H])C=1[H])O[H])C([H])([H])C([H])([H])[H]

HTVITOHKHWFJKO-UHFFFAOYSA-N

InChI=1S/C16H18O2/c1-3-16(2,12-4-8-14(17)9-5-12)13-6-10-15(18)11-7-13/h4-11,17-18H,3H2,1-2H3

4-[2-(4-hydroxyphenyl)butan-2-yl]phenol

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~100 mg/mL (~412.69 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (10.32 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (10.32 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (10.32 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)