Hormone therapy, estrogen metabolism, and risk of breast cancer in the Women's Health Initiative Hormone Therapy Trial

Effects of menopausal hormone therapy-based on the role of estrogens, progestogens, and their metabolites in proliferation of breast cancer cells

Menopausal hormone therapy (MHT) has been widely used for the clinical treatment of symptoms associated with menopause in women. However, the exact nature of the relationship between MHT and the increased risk of breast cancer has not been fully elucidated. The results of the Women's Health Initiative's randomized controlled clinical studies showed that estrogen monotherapy was associated with a lower incidence of breast cancer as compared to estrogen-progesterone combined therapy, with an elevated risk of breast cancer. The evidence currently available from randomized trials and observational studies is based on data from different populations, drug formulations, and routes of administration. Even though the risks of MHT and breast cancer have received a great deal of attention, information regarding the unpredictable toxicological risks of estrogen and progestogen metabolism needs to be further analyzed. Furthermore, the diversity and complexity of the metabolic pathways of estrogen and different progestogens as well as the association of the different estrogen and progestogen metabolites with the increased risk of breast cancer need to be adequately studied. Therefore, this review aimed to describe the biological effects of estrogen, progesterone, and their metabolites on the proliferation of breast cancer cells, based on relevant basic research and clinical trials, to improve our understanding of the biological functions of estrogen and progestogen as well as the safety of MHT.

17β-Estradiol Inhibits PCSK9-Mediated LDLR Degradation Through GPER/PLC Activation in HepG2 Cells

Plasma levels of PCSK9 are significantly higher in postmenopausal women. Pharmacologically increased estrogen levels have been shown to lower PCSK9 and LDL-C levels in animals and humans. The action of estrogen suggests that it has the ability to prevent PCSK9-mediated LDLR degradation in liver cells. However, little is known about how estrogen alters PCSK9-mediated LDLR degradation. Here, we report that 17β-estradiol (βE2) reduces PCSK9-mediated LDLR degradation by a mechanism that involves activation of the G protein-coupled estrogen receptor (GPER). In cultured HepG2 cells, βE2 prevented the internalization of PCSK9, which subsequently lead to PCSK9-mediated LDLR degradation. The altered LDLR levels also resulted in an increase in LDL uptake that was not observed in the absence of PCSK9. In addition, we showed that clathrin was rapidly increased in the presence of PCSK9, and this increase was blocked by βE2 incubation, suggesting rapid recruitment of clathrin in HepG2 cells. PLCγ activation and intracellular Ca²⁺ release were both increased due to the rapid effect of estrogen. By using a GPER antagonist G15, we demonstrated that the GPER mediates the action of estrogen. Together, the data from this in vitro study demonstrate that estrogen can regulate LDLR levels mainly through GPER activation, which prevents PCSK9-dependent LDLR degradation in HepG2 cells.

Estrogen metabolism in menopausal hormone users in the women's health initiative observational study: Does it differ between estrogen plus progestin and estrogen alone?

The WHI found an unexpected reduced breast cancer risk in women using CEE alone. We hypothesized CEE alone induces estrogen hydroxylation along the 2-pathway rather than the competing 16-pathway, a pattern linked to reduced postmenopausal breast cancer risk. One thousand eight hundred and sixty-four women in a WHIOS case-control study of estrogen metabolism and ovarian and endometrial cancer were studied of whom 609 were current E + P users (351 used CEE + MPA), while 272 used E alone (162 used CEE). Fifteen EM were measured, and analyses were conducted for each metabolite, hydroxylation pathway (2-, 4-, or 16-pathway) and ratios of pathway concentrations using inverse probability weighted linear regression. Compared to E + P users, all EM were higher in E alone users (significant for unconjugated estrone, total/conjugated estradiol, total/unconjugated 2-methoxyestrone, 4-methoxyestrone and unconjugated estriol). The relative concentrations of 2- and 4-pathway EM did not differ between the MHT users (2-pathway EM comprised 15% and 4-pathway EM <2% of the total), but 16-pathway EM were lower in E alone users (p = 0.036). Ratios of 2- and 4-pathway EM compared to 16-pathway EM were significantly higher in E alone compared to E + P users. Similar but not significant patterns were observed in CEE-alone and CEE + MPA users. Our data suggest that compared to E + P users, women using E alone have more extensive metabolism via the 2- vs. the competing 16-pathway. This is consistent with epidemiologic evidence of reduced postmenopausal breast cancer risk associated with this metabolic profile and may provide a clue to the breast cancer risk reduction in CEE alone users during the WHI.

Doxorubicin-induced cardiotoxicity is suppressed by estrous-staged treatment and exogenous 17β-estradiol in female tumor-bearing spontaneously hypertensive rats

Background

Doxorubicin (DOX), an anthracycline therapeutic, is widely used to treat a variety of cancer types and known to induce cardiomyopathy in a time and dose-dependent manner. Postmenopausal and hypertensive females are two high-risk groups for developing adverse effects following DOX treatment. This may suggest that endogenous reproductive hormones can in part suppress DOX-induced cardiotoxicity. Here, we investigated if the endogenous fluctuations in 17β-estradiol (E2) and progesterone (P4) can in part suppress DOX-induced cardiomyopathy in SST-2 tumor-bearing spontaneously hypersensitive rats (SHRs) and evaluate if exogenous administration of E2 and P4 can suppress DOX-induced cardiotoxicity in tumor-bearing ovariectomized SHRs (ovaSHRs).

Methods

Vaginal cytology was performed on all animals to identify the stage of the estrous cycle. Estrous-staged SHRs received a single injection of saline, DOX, dexrazoxane (DRZ), or DOX combined with DRZ. OvaSHRs were implanted with time-releasing pellets that contained a carrier matrix (control), E2, P4, Tamoxifen (Tam), and combinations of E2 with P4 and Tam. Hormone pellet-implanted ovaSHRs received a single injection of saline or DOX. Cardiac troponin I (cTnI), E2, and P4 serum concentrations were measured before and after treatment in all animals. Cardiac damage and function were further assessed by echocardiography and histopathology. Weight, tumor size, and uterine width were measured for all animals.

Results

In SHRs, estrous-staged DOX treatment altered acute estrous cycling that ultimately resulted in prolonged diestrus. Twelve days after DOX administration, all SHRs had comparable endogenous circulating E2. Thirteen days after DOX treatment, SHRs treated during proestrus had decreased cardiac output and increased cTnI as compared to animals treated during estrus and diestrus. DOX-induced tumor reduction was not affected by estrous-staged treatments. In ovaSHRs, exogenous administration of E2 suppressed DOX-induced cardiotoxicity, while P4-implanted ovaSHRs were partly resistant. However, ovaSHRs treated with E2 and P4 did not have cardioprotection against DOX-induced damage.

Conclusions

This study demonstrates that estrous-staged treatments can alter the extent of cardiac damage caused by DOX in female SHRs. The study also supports that exogenous E2 can suppress DOX-induced myocardial damage in ovaSHRs.

Electronic supplementary material

The online version of this article (10.1186/s13293-018-0183-9) contains supplementary material, which is available to authorized users.

Endogenous Estrogens, Estrogen Metabolites, and Breast Cancer Risk in Postmenopausal Chinese Women

BACKGROUND

The role of estrogen metabolism in determining breast cancer risk and differences in breast cancer rates between high-incidence and low-incidence nations is poorly understood.

METHODS

We measured urinary concentrations of estradiol and estrone (parent estrogens) and 13 estrogen metabolites formed by irreversible hydroxylation at the C-2, C-4, or C-16 positions of the steroid ring in a nested case-control study of 399 postmenopausal invasive breast cancer case participants and 399 matched control participants from the population-based Shanghai Women's Health Study cohort. Odds ratios (ORs) and 95% confidence intervals (CIs) of breast cancer by quartiles of metabolic pathway groups, pathway ratios, and individual estrogens/estrogen metabolites were estimated by multivariable conditional logistic regression. Urinary estrogen/estrogen metabolite measures were compared with those of postmenopausal non-hormone-using Asian Americans, a population with three-fold higher breast cancer incidence rates. All statistical tests were two-sided.

RESULTS

Urinary concentrations of parent estrogens were strongly associated with breast cancer risk (ORQ4vsQ1 = 1.94, 95% CI = 1.21 to 3.12, Ptrend = .01). Of the pathway ratios, the 2-pathway:total estrogens/estrogen metabolites and 2-pathway:parent estrogens were inversely associated with risk (ORQ4vsQ1 = 0.57, 95% CI = 0.35 to 0.91, Ptrend = .03, and ORQ4vsQ1 = 0.61, 95% CI = 0.37 to 0.99, Ptrend = .04, respectively). After adjusting for parent estrogens, these associations remained clearly inverse but lost statistical significance (ORQ4vsQ1 = 0.65, 95% CI = 0.39 to 1.06, Ptrend = .12 and ORQ4vsQ1 = 0.76, 95% CI = 0.44 to 1.32, Ptrend = .28). The urinary concentration of all estrogens/estrogen metabolites combined in Asian American women was triple that in Shanghai women.

CONCLUSIONS

Lower urinary parent estrogen concentrations and more extensive 2-hydroxylation were each associated with reduced postmenopausal breast cancer risk in a low-risk nation. Markedly higher total estrogen/estrogen metabolite concentrations in postmenopausal United States women (Asian Americans) than in Shanghai women may partly explain higher breast cancer rates in the United States.

Epidemiologic studies of estrogen metabolism and breast cancer

Early epidemiologic studies of estrogen metabolism measured only 2-hydroxyestrone and 16α-hydroxyestrone and relied on direct enzyme immunoassays without purification steps. Eight breast cancer studies have used these assays with prospectively collected blood or urine samples. Results were inconsistent, and generally not statistically significant; but the assays had limited specificity, especially at the low concentrations characteristic of postmenopausal women. To facilitate continued testing in population-based studies of the multiple laboratory-based hypotheses about the roles of estrogen metabolites, a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed to measure concurrently all 15 estrogens and estrogen metabolites in human serum and urine, as unconjugated and total (glucuronidated+sulfated+unconjugated) concentrations. The assay has high sensitivity (lower limit of quantitation ∼1-2 pmol/L), reproducibility (coefficients of variation generally ⩽5%), and accuracy. Three prospective studies utilizing this comprehensive assay have demonstrated that enhanced 2-hydroxylation of parent estrogens (estrone+estradiol) is associated with reduced risk of postmenopausal breast cancer. In the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) cohort, the serum ratio of 2-hydroxylation pathway metabolites to parent estrogens was associated with a 28% reduction in breast cancer risk across extreme deciles (p-trend=.05), after adjusting for unconjugated estradiol and breast cancer risk factors. Incorporating this ratio into a risk prediction model already including unconjugated estradiol improved absolute risk estimates substantially (by ⩾14%) in 36% of the women, an encouraging result that needs replication. Additional epidemiologic studies of the role of estrogen metabolism in the etiology of hormone-related diseases and continued improvement of estrogen metabolism assays are justified.

Circulating estrogen metabolites and risk of breast cancer in postmenopausal women

BACKGROUND

It has been hypothesized that predominance of the 2-hydroxylation estrogen metabolism pathway over the 16α-hydroxylation pathway may be inversely associated with breast cancer risk.

METHODS

We examined the associations of invasive breast cancer risk with circulating 2-hydroxyestrone (2-OHE1), 16α-hydroxyestrone (16α-OHE1), and the 2-OHE1:16α-OHE1 ratio in a case-control study of postmenopausal women nested within two prospective cohorts: the New York University Women's Health Study (NYUWHS) and the Northern Sweden Mammary Screening Cohort (NSMSC), with adjustment for circulating levels of estrone, and additional analyses by tumor estrogen receptor (ER) status. Levels of 2-OHE1 and 16α-OHE1 were measured using ESTRAMET 2/16 assay in stored serum or plasma samples from 499 incident breast cancer cases and 499 controls, who were matched on cohort, age, and date of blood donation.

RESULTS

Overall, no significant associations were observed between breast cancer risk and circulating levels of 2-OHE1, 16α-OHE1, or their ratio in either cohort and in combined analyses. For 2-OHE1, there was evidence of heterogeneity by ER status in models adjusting for estrone (P ≤ 0.03). We observed a protective association of 2-OHE1 with ER+ breast cancer [multivariate-adjusted OR for a doubling of 2-OHE1, 0.67 (95% confidence interval [CI], 0.48-0.94; P = 0.02)].

CONCLUSIONS

In this study, higher levels of 2-OHE1 were associated with reduced risk of ER+ breast cancer in postmenopausal women after adjustment for circulating estrone.

IMPACT

These results suggest that taking into account the levels of parent estrogens and ER status is important in studies of estrogen metabolites and breast cancer.

Menopausal hormone therapy and cardiovascular disease risk: utility of biomarkers and clinical factors for risk stratification

BACKGROUND

Menopausal hormone therapy (HT) continues to have a clinical role in symptom management, but identifying women for whom benefits will outweigh the risks remains a challenge. Although hormone therapy (HT) is the most effective strategy for ameliorating vasomotor and other symptoms, randomized clinical trials show an unfavorable balance of benefits and risks for many women. However, closer examination of data from these trials suggests that it may be possible to classify women as better or worse candidates for HT by using individual risk stratification.

CONTENT

Data from 2 landmark trials-the Women's Health Initiative (WHI) and the Heart and Estrogen/progestin Replacement Study (HERS)-suggest an important role for clinical characteristics, serum biomarkers, genomic markers, and gene-environment interactions in developing a personalized approach to the prediction of risk for cardiovascular disease (CVD) events for women while on HT. The available data suggest several characteristics of women who are optimal candidates for HT use: younger age (<60 years), recent onset of menopause (<10 years), favorable lipid profile (LDL cholesterol <130 mg/dL or LDL/HDL cholesterol ratio <2.5), absence of metabolic syndrome, and absence of factor V Leiden genotype. The identification of other characteristics is an area of active investigation. In addition, women at high risk for venous thromboembolism should avoid systemic HT or choose a transdermal rather than oral delivery route.

SUMMARY

Personalized medicine-i.e., the use of the specific biological profile of an individual to guide the choice of treatment-is highly relevant for clinical decision-making regarding HT and offers promise for improved treatment efficacy and safety.

Postmenopausal hormone therapy: risks and benefits

Postmenopausal hormone therapy (PMHT) is used for the relief of menopausal symptoms, but the dosage has varied greatly throughout its existence. By the end of the 1990s, PMHT was mainly used to prevent chronic diseases such as osteoporosis, coronary heart disease and dementia, and large prevention trials were undertaken in this context. Following the initial negative reports of these trials, use of PMHT dramatically decreased. These reports noted surprisingly increased risks, notably of coronary heart disease, stroke and breast cancer, in people who used PMHT. Nowadays, considering the currently available data, it seems that an important distinction should be made between the treatment of climacteric symptoms in young, generally healthy, postmenopausal women and the prevention of chronic diseases in elderly women. PMHT seems to be beneficial and safe for postmenopausal symptomatic women aged <60 years. Treatments with a high safety profile should be the preferred option, including low-dose PMHT, oestrogen-only therapy in women who have had a hysterectomy, and vaginal oestrogen therapy for women with atrophic vaginitis. Nonandrogenic progestin might have a reduced thrombotic and breast cancer risk, and transdermal oestrogen could have a reduced thrombotic risk. Nevertheless, PMHT should not be used for the prevention of chronic diseases in the elderly (>70 years old) owing to the increased risk of stroke and breast cancer in these patients.

Plant sterols as anticancer nutrients: evidence for their role in breast cancer

While many factors are involved in the etiology of cancer, it has been clearly established that diet significantly impacts one’s risk for this disease. More recently, specific food components have been identified which are uniquely beneficial in mitigating the risk of specific cancer subtypes. Plant sterols are well known for their effects on blood cholesterol levels, however research into their potential role in mitigating cancer risk remains in its infancy. As outlined in this review, the cholesterol modulating actions of plant sterols may overlap with their anti-cancer actions. Breast cancer is the most common malignancy affecting women and there remains a need for effective adjuvant therapies for this disease, for which plant sterols may play a distinctive role.