Estrogens regulate important processes in reproductive, skeletal, cardiovascular, and central nervous systems that impact women\'s overall health. Understanding endogenous and exogenously administered estrogen metabolism is vital to determining therapeutic estrogen levels. The present review provides an overview of estrogen metabolites formed in non-pregnant and pregnant women, and those resulting from exogenous estrogen administration. There are four principal endogenous estrogens: estrone (E1), estradiol (E2), estriol (E3), and estetrol (E4). E4, which is produced only in pregnancy, has emerged recently as an estrogen with significant therapeutic potential. E1, E2, and E3 undergo extensive metabolism primarily through phase I (hydroxylation, oxidation, reduction) and phase II (primarily conjugation) reactions, whereas E4 undergoes only phase II reactions. Exogenous estrogens commonly used for menopausal treatment and/or contraception, including micronized E2, conjugated equine estrogens, and ethinyl estradiol, also undergo phase I and phase II reactions, but differ widely in the types of metabolites formed. The mechanisms by which estrogen metabolites are formed and their excretion in urine, bile, and feces, are still poorly understood. We highlight areas that require further research to foster a better understanding of how estrogen metabolism impacts dosing of oral estrogens for therapeutic use, as well as the physiological regulation of endogenous estrogens.

The results of the WHI, which reported a doubling of the risk of Alzheimer\'s disease (AD) and a decline in cognitive function in women who were given menopause hormone therapy (MHT), have raised concerns on the deleterious impact of MHT on the central nervous system. Such as for the cardiovascular system, the very late age of initiation of treatment and the nature of the molecules have led to conclusions that cannot be extended to women in their fifties, at the onset of their menopause which is the usual age of MHT initiation. The molecules, which are used in France, 17-beta estradiol and natural progesterone (or its isomer, dydrogesterone) are very different from the equine conjugated estrogens and medroxyprogesterone acetate used in the WHI. It can now be stated that if MHT is started within the window of opportunity (i.e. before the age of 60 or within the first 10years after the beginning of menopause) no deleterious effect on cognition is observed. Moreover, cognition remains relatively stable at the beginning of menopause since the cognitive reserve as well as the different compensation circuits allow compensation for estrogen deficiency. This does not in any way prejudge a possible positive effect of MHT on AD, which is very difficult to demonstrate, as the age of onset of this dementia is very late, 20 or 30years after the initiation of treatment.

The Kronos Early Estrogen Prevention Study (KEEPS) was a randomized, double-blind, placebo-controlled trial designed to determine the effects of hormone treatments (menopausal hormone treatments [MHTs]) on the progression of carotid intima-medial thickness (CIMT) in recently menopausal women. Participants less than 3 years from menopause and without a history of overt cardiovascular disease (CVD), defined as no clinical CVD events and coronary artery calcium < 50 Agatston units, received either oral conjugated equine estrogens (0.45 mg/day) or transdermal 17β-estradiol (50 µg/day), both with progesterone (200 mg/day for 12 days/month), or placebo pills and patches for 4 years. Although MHT did not decrease the age-related increase in CIMT, KEEPS provided other important insights about MHT effects. Both MHTs versus placebo reduced the severity of menopausal symptoms and maintained bone density, but differed in efficacy regarding mood/anxiety, sleep, sexual function, and deposition of β-amyloid in the brain. Additionally, genetic variants in enzymes for metabolism and uptake of estrogen affected the efficacy of MHT for some aspects of symptom relief. KEEPS provides important information for use of MHT in clinical practice, including type, dose, and mode of delivery of MHT recently after menopause, and how genetic variants in hormone metabolism may affect MHT efficacy on specific outcomes.

Numerous observational studies have suggested that hormone therapy (HT) might protect postmenopausal women against cognitive decline and Alzheimer\'s disease (AD). However, because of the significant disparity between results, especially those between observational and randomized controlled trials (RCT), this postulate remains unproven. A significant contributing factor to these inconsistencies is the loose use of the generic definitions of estrogens and progestogens with most studies not delineating the clear differences between non-endogenous and endogenously identical (bioidentical) hormones, their molecular binding affinities and actions, and resultant metabolites. This is highlighted by the generalized terminological use of HT, which is often used to encompass significantly disparate hormonal formulations without clear demarcation. This has impacted and continues to significantly influence interpretations of data, meta-analyses, observational studies, etc., relevant to AD. To progress forward and allow unbiased interpretation, it is no longer acceptable to group HT formulations together as a homogenous group. This will also allow differentiation between compounds that exhibit beneficial actions and those that do not and whether these effects are specific or generalized. The role of the endogenous hormones, 17 beta-oestradiol (E2) and progesterone (P4), in the development of sporadic AD in postmenopausal women is also examined.

Conjugated equine estrogens (CEEs), whose brand name is Premarin, are widely used as a hormone-replacement therapy (HRT) drug to manage postmenopausal symptoms in women. Extracted from pregnant mare urine, CEEs are composed of nearly a dozen estrogens existing in an inactive sulfated form. To determine whether the hepatic steroid sulfatase (STS) is a key contributor to the efficacy of CEEs in HRT, we performed estrogen-responsive element (ERE) reporter gene assay, real-time PCR, and UPLC-MS/MS to assess the STS-dependent and inflammation-responsive estrogenic activity of CEEs in HepG2 cells and human primary hepatocytes. Using liver-specific STS-expressing transgenic mice, we also evaluated the effect of STS on the estrogenic activity of CEEs in vivo We observed that CEEs induce activity of the ERE reporter gene in an STS-dependent manner and that genetic or pharmacological inhibition of STS attenuates CEE estrogenic activity. In hepatocytes, inflammation enhanced CEE estrogenic activity by inducing STS gene expression. The inflammation-responsive estrogenic activity of CEEs, in turn, attenuated inflammation through the anti-inflammatory activity of the active estrogens. In vivo, transgenic mice with liver-specific STS expression exhibited markedly increased sensitivity to CEE-induced estrogenic activity in the uterus resulting from increased levels of liver-derived and circulating estrogens. Our results reveal a critical role of hepatic STS in mediating the hormone-replacing activity of CEEs. We propose that caution needs to be applied when Premarin is used in patients with chronic inflammatory liver diseases because such patients may have heightened sensitivity to CEEs due to the inflammatory induction of STS activity.

The aim of this study was to determine the effects of different menopausal hormone therapy regimens on body composition in healthy postmenopausal Chinese women.
One hundred and twenty-three healthy postmenopausal Chinese women were randomly assigned to either group A (0.625 mg conjugated equine estrogens [CEE] plus 100 mg micronized progesterone [MP]), group B (0.3 mg CEE plus 100 mg MP), or group C (0.625 mg CEE plus 10 mg dydrogesterone). Body composition was assessed by dual-energy X-ray absorptiometry.
One hundred and two women completed the trial at 1 year. A small but significant gain in lean body mass (619 ± 1019 g, p = 0.002) and a decrease of fat mass in all separate regions was observed in group A. A significant shift from gynoid to android fat distribution was observed in group B and group C (android/gynoid fat percentage ratios increased by 0.06 ± 0.08, p = 0.000 and 0.03 ± 0.08, p = 0.018, respectively), whereas no significant change was observed in group A (0.02 ± 0.06, p = 0.103).
In healthy postmenopausal Chinese women, 0.625 mg of CEE combined with 100 mg of MP was associated with a more favorable fat distribution compared with 0.3 mg CEE plus 100 mg MP or 0.625 mg CEE plus 10 mg dydrogesterone.

Prior to 2002, hormone replacement therapy (HRT) was considered to be an important component of postmenopausal healthcare. This was based on a plethora of basic, epidemiological and clinical studies demonstrating the health benefits of supplementation with human sex steroids. However, adverse findings from the Women\'s Health Initiative (WHI) studies that examined the 2 major forms of HRT in use in the US at that time - Premarin (conjugated equine estrogens; CEE) and Prempro (CEE + medroxyprogesterone acetate; MPA), cast a shadow over the use of any form of HRT. Here we review the biochemical and physiological differences between the non-human WHI study hormones - CEE and MPA, and their respective human counterparts 17β-estradiol (E2) and progesterone (P4). Preclinical data from the last 30 years demonstrate clear differences between human and non-human sex steroids on numerous molecular, physiological and functional parameters in brain, heart and reproductive tissue. In contrast to CEE supplementation, which is not always detrimental although certainly not as optimal as E2 supplementation, MPA is clearly not equivalent to P4, having detrimental effects on cognitive, cardiac and reproductive function. Moreover, unlike P4, MPA is clearly antagonistic of the positive effects of E2 and CEE on tissue function. These data indicate that minor chemical changes to human sex steroids result in physiologically distinct actions that are not optimal for tissue health and functioning.

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.

The Women\'s Health Initiative studies reported that the menopausal hormone therapy (MHT) regimen containing conjugated equine estrogen (CEE) and medroxyprogesterone acetate increased, whereas CEE alone reduced breast cancer incidence. These observations suggest the possibility that CEE might exert unique actions on breast and also suggest the need to eliminate the progestogen from MHT regimens. A MHT regimen called a tissue selective estrogen complex (TSEC), containing CEE plus bazedoxifene (BZA), to avoid the need for a progestogen, was developed and FDA approved. Our study addressed two questions regarding this TSEC: (i) whether CEE exert effects on breast cancer which differ from those of estradiol (E2 ) and (ii) whether BZA antagonize the effects of E2 and CEE on breast cancer? Two rodent models (NMU and ACI) were used to compare the effect of CEE with E2 on mammary tumor formation, proliferation and apoptosis. In both the NMU and ACI models, E2 significantly increased tumor incidence and multiplicity whereas in striking contrast CEE did not, even though the estrogenic effects of CEE and E2 on uterine weight were identical. Mechanistically E2 blocked whereas CEE stimulated apoptosis (cleaved caspase-3) in ACI animals and only E2 stimulated proliferation (Ki67). BZA exerted highly potent anti-estrogenic effects on tumors by completely blocking palpable tumor formation. These data suggest that the CEE/BZA TSEC may be a safer, breast-antagonistic, MHT agent for women and might have potential to prevent breast cancer while relieving menopausal symptoms.

BACKGROUND: While benefits and risks of hormone therapy (HT) have been shown in rigorous randomized, controlled trials, clinical use and further study have discovered effects of age, time of HT initiation, and differential effects of various regimens and administration routes on its safety profile. Areas covered: The safety of HT with regard to cardiovascular disease, thrombosis, the endometrium, the breast, and cognition was reviewed. Differential safety effects of estradiol versus conjugated equine estrogens, and progesterone versus synthetic progestins are reported. Expert opinion: Perceived safety of HT has evolved based on data from observational studies, the Women\'s Health Initiative and its subsequent analyses, more recent randomized, controlled trials, and studies examining the differences between different estrogens and between different progestogens. Unexpected safety concerns with HT became apparent with release of the first results from WHI. Differences between estrogen-alone versus estrogen-progestogen therapies, estradiol versus conjugated equine estrogens, and progesterone versus progestins were found in subsequent WHI analyses and studies examining components of various regimens. The decision to use HT depends on balancing risks and benefits for each individual and determining the most appropriate choice of therapy, dosing, and route of administration, while also considering the safety evidence of different estrogens and progestogens.