**2. Direct actions of BPA in the ovary**

The cycling ovary comprises follicles and the CL. During steroidogenesis, antral follicles

ing the expression of steroid hormone receptors. The ovarian steroid hormone receptors

ing hormone (LH) and follicle‐stimulating hormone (FSH). The endocrine system is dis‐ rupted when a hormone can no longer bind its receptor due to a disruption in hormone synthesis or receptor binding (**Figure 1**). Additionally, a disruption in folliculogenesis or CL formation can lead to reproductive disturbances, such as aneuploidy, anovulation, decreased fertility, polycystic ovary syndrome (PCOS) and premature ovarian failure (POF). The overall damage to the ovary and its effects on fertility depends on the type of

Hormonal disturbances also underlie ovarian carcinogenesis and oestrogens, androgens, P<sup>4</sup>

LH and FSH have been proposed to promote ovarian cancer development [3]. Depending on the cellular origin of the tumour, ovarian cancer can be classified as epithelial, stromal or germinal, with each tumour possessing different histopathological features and clinical outcomes (**Figure 2**). Epithelial cell tumours account for ∼80–90% of ovarian malignancies, whereas stromal tumours account for ∼8%. The most frequently diagnosed type of stromal

Previous studies show correlations between women working in graphics and printing indus‐ tries and increased risk of ovarian cancer [4], as well as between women working in similar industries and ovarian cancer mortality [5]. The increased incidence of ovarian cancers cannot be explained by genetic factors. We believe that environmental factors, such as toxic chemi‐

**Figure 1.** Ovarian steroidogenic enzymes and steroid hormone receptors are targets of endocrine disruption. Oestrogen receptor (ER), androgen receptor (AR) and progesterone receptor (PR), luteinising hormone receptor (LHR) and follicle‐

stimulating hormone receptor (FSHR) and dehydroepiandrosterone (DHEA).

cals, can cause ovarian cancer, but it is very difficult to prove cause and effect.

)] from androgens [androstenedione

(PR), as well as those for luteinis‐

). This balance can

or by affect‐

,

produce oestrogens [principally 17β‐oestradiol (E<sup>2</sup>

include those for oestrogen (ER), androgen (AR) and P<sup>4</sup>

tumour is the granulosa cell tumour (GCT).

follicles affected [2].

58 Bisphenol A Exposure and Health Risks

(A4) and testosterone (T)], whereas the CL produces progesterone (P<sup>4</sup>

be disrupted by altering the concentrations of oestrogen, androgen and/or P<sup>4</sup>

BPA accumulates in reproductive organs and disrupts the endocrine system. In the general population, BPA has been detected in follicular fluid at concentrations of ∼1–2 ng/ml [6]. Several epidemiological studies identified correlations between BPA and various abnormali‐ ties in the ovary of foetuses and adults. Moreover, the effects of BPA in the ovary, which goes through different stages such as folliculogenesis, ovulation and luteinisation, depend on the time of exposure.

#### **2.1. BPA action on the foetal and neonatal ovary**

BPA affects oogenesis and follicle formation during foetal and early postnatal periods. For example, BPA disrupts chromosome segregation during the first meiotic division in the foetal rhesus monkey ovary. During follicle formation, BPA increases the number of multiple oocyte follicles (MOFs), which occurs when more than one oocyte is surrounded by a single layer of granulosa cells [7]. BPA also disrupts meiosis and oogenesis in the foetal mouse ovary, thereby increasing the risks of synaptic abnormalities and aneuploidy [8]. BPA also inhibits germ cell nest breakdown in the foetal mouse ovary by altering the expression of apoptotic proteins, which can lead to various fertility problems and higher percentage of dead pups [9].

Exposure of rats to BPA during the early postnatal period decreases the primordial follicle reserve and increases the incidence of MOFs [10, 11]. In the neonatal mouse ovary, BPA pro‐ motes the transition of primordial follicles to primary follicles and suppresses the meiotic maturation of oocytes due to abnormal spindle assembly during meiosis I [12]. Additionally, exposure of rats to BPA during gestational and neonatal periods induces the development of PCOS‐like syndrome during adulthood [13–15]. PCOS is the most common endocrinological pathology in women of reproductive age. It is characterised by hyperandrogenism, insulin resistance and chronic anovulation.

## **2.2. BPA action on the adult ovary**

Oocyte abnormalities were noted in adult mice exposed to BPA, possibly due to changes in the structural integrity of microtubules that constitute meiotic spindles [16]. BPA also disrupts meiotic maturation, spindle organisation and chromosome alignment and increases oocyte degeneration in human oocytes [17].

BPA affects ovarian steroidogenesis by modulating the expression of key steroidogenic enzymes. For example, BPA decreases aromatase (*CYP19A1*) expression and E<sup>2</sup> production in human granulosa cells [18]. In mice, BPA inhibits P<sup>4</sup> , testosterone (T) and E<sup>2</sup> synthesis by decreasing the expression of steroidogenic acute regulatory protein (*Star*), 3β‐hydroxysteroid dehydrogenase (*Hsd3b1*) and 17α‐hydroxylase (*Cyp17a1*) [19]. In rats, however, BPA increases P4 and T synthesis, as well as the expression of *Star*, cholesterol side‐chain cleavage enzyme (*Cyp11a1*) and *Cyp17a1*, but decreases E<sup>2</sup> synthesis and *Cyp19a1* expression [20]. In pigs, BPA increases basal and FSH‐induced P<sup>4</sup> synthesis, whereas it decreases FSH‐induced E<sup>2</sup> synthesis [21] (**Figure 3**).

In vitro studies demonstrated that BPA affects fertility by disrupting E<sup>2</sup> signalling, which is evolutionarily conserved among mammals and indispensable for fertility. E<sup>2</sup> function is mainly mediated by the classical nuclear oestrogen receptors ERα and ERβ. BPA can bind both ERα and ERβ (its affinity is higher for ERβ than ERα) [22], although its binding affinity for both receptors is greater than 1000–10000‐fold lower than that for E<sup>2</sup> [23]. Furthermore, BPA can also induce oestrogen‐like effects, because BPA elicits rapid responses through non‐ classical oestrogen signalling that involves the oestrogen‐related receptor γ (ERRγ), [24, 25] as well as membrane‐associated G protein‐coupled receptor (GPR30) [26] (**Figure 3**).

Therefore, we suggest that BPA seems to be uniquely estrogenic in its receptor binding and androgenic in its hormone profile/steroidogenesis influences.

#### **2.3. BPA and ovarian carcinogenesis**

The correlation between BPA exposure and ovarian cancer is supported by little evidence. BPA exposure might increase the incidence of ovarian cysts, because women with PCOS pos‐ sess higher serum BPA levels than healthy women [27]. Furthermore, women with PCOS have approximately twofold to threefold increased risk of endometrial and ovarian cancers [28, 29]. BPA might also increase the incidence of other ovarian pathologies that ultimately lead to cancer.

The balance between cell proliferation and apoptotic resistance is closely linked to cancer, and it is generally accepted as one of the major contributing factors to cancer development. BPA increases the proliferation of human epithelial ovarian cancer BG‐1 [30] and OVCAR‐3 [31] cells. The mitogenic effects of BPA are mainly mediated by the upregulation of genes

PCOS‐like syndrome during adulthood [13–15]. PCOS is the most common endocrinological pathology in women of reproductive age. It is characterised by hyperandrogenism, insulin

Oocyte abnormalities were noted in adult mice exposed to BPA, possibly due to changes in the structural integrity of microtubules that constitute meiotic spindles [16]. BPA also disrupts meiotic maturation, spindle organisation and chromosome alignment and increases oocyte

BPA affects ovarian steroidogenesis by modulating the expression of key steroidogenic

decreasing the expression of steroidogenic acute regulatory protein (*Star*), 3β‐hydroxysteroid dehydrogenase (*Hsd3b1*) and 17α‐hydroxylase (*Cyp17a1*) [19]. In rats, however, BPA increases

and T synthesis, as well as the expression of *Star*, cholesterol side‐chain cleavage enzyme

mainly mediated by the classical nuclear oestrogen receptors ERα and ERβ. BPA can bind both ERα and ERβ (its affinity is higher for ERβ than ERα) [22], although its binding affinity

BPA can also induce oestrogen‐like effects, because BPA elicits rapid responses through non‐ classical oestrogen signalling that involves the oestrogen‐related receptor γ (ERRγ), [24, 25] as

Therefore, we suggest that BPA seems to be uniquely estrogenic in its receptor binding and

The correlation between BPA exposure and ovarian cancer is supported by little evidence. BPA exposure might increase the incidence of ovarian cysts, because women with PCOS pos‐ sess higher serum BPA levels than healthy women [27]. Furthermore, women with PCOS have approximately twofold to threefold increased risk of endometrial and ovarian cancers [28, 29]. BPA might also increase the incidence of other ovarian pathologies that ultimately

The balance between cell proliferation and apoptotic resistance is closely linked to cancer, and it is generally accepted as one of the major contributing factors to cancer development. BPA increases the proliferation of human epithelial ovarian cancer BG‐1 [30] and OVCAR‐3 [31] cells. The mitogenic effects of BPA are mainly mediated by the upregulation of genes

production

synthesis by

synthesis

function is

signalling, which

[23]. Furthermore,

, testosterone (T) and E<sup>2</sup>

synthesis and *Cyp19a1* expression [20]. In pigs, BPA

synthesis, whereas it decreases FSH‐induced E<sup>2</sup>

enzymes. For example, BPA decreases aromatase (*CYP19A1*) expression and E<sup>2</sup>

In vitro studies demonstrated that BPA affects fertility by disrupting E<sup>2</sup>

for both receptors is greater than 1000–10000‐fold lower than that for E<sup>2</sup>

androgenic in its hormone profile/steroidogenesis influences.

is evolutionarily conserved among mammals and indispensable for fertility. E<sup>2</sup>

well as membrane‐associated G protein‐coupled receptor (GPR30) [26] (**Figure 3**).

resistance and chronic anovulation.

60 Bisphenol A Exposure and Health Risks

**2.2. BPA action on the adult ovary**

degeneration in human oocytes [17].

(*Cyp11a1*) and *Cyp17a1*, but decreases E<sup>2</sup>

increases basal and FSH‐induced P<sup>4</sup>

**2.3. BPA and ovarian carcinogenesis**

P4

[21] (**Figure 3**).

lead to cancer.

in human granulosa cells [18]. In mice, BPA inhibits P<sup>4</sup>

**Figure 3.** BPA action on ovarian steroidogenesis. Stars indicate the sites of action. Steroidogenic acute regulatory protein (Star), cholesterol side‐chain cleavage enzyme (Cyp11a1), 17α‐hydroxylase (Cyp17a1), 3β‐hydroxysteroid dehydrogenase (Hsd3b1), aromatase (CYP19a1), oestrogen receptor (ER), androgen receptor (AR) and progesterone receptor (PR), luteinising hormone receptor (LHR) and follicle‐stimulating hormone receptor (FSHR), dehydroepiandrosterone (DHEA) and membrane‐associated G protein‐coupled receptor (GPR30).

that induce cell proliferation (i.e., cyclin D1, cyclin A, CDK4, PCNA, E2F1 and E2F3) and the downregulation of genes that inhibit cell proliferation (i.e., p21, Weel‐1 and GADD45α) in OVCAR‐3 cells [31]. These findings are intriguing because decreased p21/WAF1 expression in ovarian cancer patients is an indicator of poor prognosis [32]. Furthermore, downregula‐ tion or inactivation of CDK inhibitors, such as p21Waf1/Cip1, p27Kip1 and p16Ink4a, which renders cells susceptible to extracellular signals that control proliferation, is often observed in various tumours [33]. BPA‐induced cell proliferation triggers a rapid biological response involving the phosphorylation of extracellular signal‐regulated kinases (ERK1/2), signal transducer and activator of transcription 3 (STAT3) and protein kinase B (AKT) in BG‐1 and OVCAR‐3 cells [30, 34]. BPA also inhibits OVCAR‐3 cell apoptosis by activating ERK1/2 sig‐ nalling [35] (**Figure 4**).

During tumourigenesis, cells can separate from the primary tumour to invade distant organs. Metastatic cancer cells undergo an epithelial‐to‐mesenchymal transition (EMT), which is

**Figure 4.** BPA action on epithelial ovarian cancer progression. Stars indicate the sites of BPA action. The arrow facing up indicates a stimulation, and the arrow facing down indicates an inhibition by BPA. Matrix metalloproteinase‐2 (MMP‐2), matrix metalloproteinase‐9 (MMP‐9), vascular endothelial growth factor‐A (VEGF‐A), vascular endothelial growth factor receptor 2 (VEGF‐R2), extracellular signal‐regulated kinases (ERK1/2), signal transducer and activator of transcription 3 (STAT3) and protein kinase B (Akt).

characterised by the upregulation of mesenchymal proteins such as N‐cadherin, downregu‐ lation of epithelial cell‐associated proteins such as E‐cadherin and overexpression of matrix metalloproteinases (MMPs). MMP‐2 and MMP‐9 are the key enzymes required for the ini‐ tial steps of ovarian cancer metastasis [36, 37]. In OVCAR‐3 cells, BPA upregulates MMP‐2, MMP‐9 and N‐cadherin expression by activating ERK1/2 and AKT signalling, which pro‐ motes cell migration [38] (**Figure 4**).

Vascular endothelial growth factor‐A (VEGF‐A), which is upregulated in most solid tumours, including ovarian cancers, correlates with tumour progression and poor prognosis [39, 40]. Several studies show that the serum VEGF‐A level is higher in patients with ovarian cancer than in healthy individuals [41–43]. In addition, the expression of VEGF‐A and its receptor (VEGF‐R2) is higher in cancerous ovarian tissues than in benign or normal ovarian tissue [44]. BPA upregulates VEGF‐A expression in reproductive organs, such as the uterus and vagina in the rat [45] and the ovary in the pig [46]. Moreover, BPA markedly increases VEGF‐A and VEGF‐R2 expression in OVCAR‐3 and SKOV‐3 cells [47], indicating a possible intensification of pro‐angiogenic activity in ovarian cancer cells (**Figure 4**).

These findings indicate that BPA promotes the progression of epithelial ovarian cancer by stimulating epithelial cell proliferation and migration and inhibiting apoptosis. However, there is no evidence to indicate that BPA affects stromal‐ and germinal‐derived ovarian cancers.
