Estrogen as a treatment for Alzheimer disease

Management of postmenopausal women: Collège National des Gynécologues et Obstétriciens Français (CNGOF) and Groupe d'Etude sur la Ménopause et le Vieillissement (GEMVi) Clinical Practice Guidelines

AIM

The aim of these recommendations is to set forth an individualized approach to the management of early postmenopausal women (i.e., within the first 10 years after natural menopause) covering all aspects of lifestyle and therapeutic management, with or without menopause hormone therapy (MHT).

MATERIALS AND METHODS

Literature review and consensus of French expert opinion. Recommendations were graded according to the HAS methodology and levels of evidence derived from the international literature, except when there was no good-quality evidence.

SUMMARY RECOMMENDATIONS

The beginning of menopause is an ideal time for each woman to evaluate her health status by assessing her bone, cardiovascular, and cancer-related risk factors that may be amplified by postmenopausal estrogen deficiency and by reviewing her lifestyle habits. Improving lifestyle, including nutrition and physical activity, and avoiding risk factors (notably smoking), should be recommended to all women. MHT remains the most effective treatment for vasomotor symptoms but it could be also recommended as first-line treatment for the prevention of osteoporosis in early postmenopausal women at low to moderate risk for fracture. The risks of MHT differ depending on its type, dose, duration of use, route of administration, timing of initiation, and whether a progestogen is used. There is reasonable evidence that using transdermal estradiol in association with micronized progesterone or dydrogesterone may limit both the venous thromboembolic risk associated with oral estrogens and the risk of breast cancer associated with synthetic progestins. Treatment should be individualized to each woman, by using the best available evidence to maximize benefits and minimize risks, with periodic reevaluation of its benefit-risk balance. For bothersome genitourinary syndrome of menopause (GSM) symptoms, vaginal treatment with lubricants and moisturizers is recommended as first-line treatment together with low-dose vaginal estrogen therapy, depending on the clinical course. No recommendation of an optimal duration of MHT can be made, but it must take into consideration the initial indication for MHT as well as each woman's benefit-risk balance. Management of gynecological side-effects of MHT is also examined. These recommendations are endorsed by the Groupe d'Etude sur la Ménopause et le Vieillissement hormonal (GEMVI) and the Collège National des Gynécologues-Obstétriciens Français (CNGOF).

[Menopause hormone therapy and cognition. Postmenopausal women management: CNGOF and GEMVi clinical practice guidelines]

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.

Estrogen receptors and sex hormone binding globulin in neuronal cells and tissue

Estrogens exert a critical influence on neuronal tissues and cells. As demonstrated in many clinical studies, estrogens are neuroprotective to the extent that they improve prognosis for women with neurodegenerative diseases. Unfortunately, we still do not know exactly how these effects are mediated. Fifty years ago the first estrogen receptor was found, but since then many other new pathways of estrogen action have been identified. This review describes several of these pathways of estrogen effects and provides some conclusions and correlations about these as determined by recent studies with nerve growth factor differentiated rat pheochromocytoma cell line.

Sex-related differences in oxidative stress and neurodegeneration

Oxidative stress has been implicated in a number of neurodegenerative diseases spanning various fields of research. Reactive oxygen species can be beneficial or harmful, depending on their concentration. High levels of reactive oxygen species can lead to oxidative stress, which is an imbalance between free radicals and antioxidants. Increased oxidative stress can result in cell loss. Interestingly, sex differences have been observed in oxidative stress generation, which may underlie sex differences observed in neurodegenerative disorders. An enhanced knowledge of the role of sex hormones on oxidative stress signaling and cell loss can yield valuable information, leading to sex-based mechanistic approaches to neurodegeneration.

Epidemiology of estrogen and dementia in women with Down syndrome

Several lines of investigation have shown a protective role for estrogen in Alzheimer's disease through a number of biological actions. This review examines studies of the role of estrogen-related factors in age at onset and risk for Alzheimer's disease in women with Down syndrome, a population at high risk for early onset of dementia. The studies are consistent in showing that early age at menopause and that low levels of endogenous bioavailable estradiol in postmenopausal women with Down syndrome are associated with earlier age at onset and overall risk for dementia. Polymorphisms in genes associated with estrogen receptor activity and in genes for estrogen biosynthesis affecting endogenous estrogen are related to age at onset and cumulative incidence of dementia, and may serve as biomarkers of risk. To date, no clinical trials of estrogen or hormone replacement therapy (ERT/HRT) have been published for women with Down syndrome. While findings from clinical trials of ERT or HRT for dementia have generally been negative among women in the neurotypical population, the short interval between menopause and onset of cognitive decline, together with a more positive balance between potential benefits and risks, suggests an opportunity to evaluate the efficacy of ERT/HRT for delaying or preventing dementia in this high risk population, although questions concerning the optimal formulation and timing of the hormone therapy are not yet resolved.

Neurobiological Consequences of Long-Term Estrogen Therapy

Postmenopausal women demonstrate an increased incidence of Alzheimer's disease (AD). Epidemiological evidence suggests that estrogen replacement therapy (ERT) may reduce the risk or delay the onset of AD, yet recent clinical trials found no cognitive benefits of ERT in women with mild to moderate AD. This review suggests that the timing of estrogen administration may explain these conflicting results. Chronic administration has neurobiological consequences that can affect neural and immune function, but a therapy designed to mimic the natural cycle of fluctuating hormones may more effectively slow the progression of AD in postmenopausal women.

Menopause and mitochondria: windows into estrogen effects on Alzheimer's disease risk and therapy

Metabolic derangements and oxidative stress are early events in Alzheimer's disease pathogenesis. Multi-faceted effects of estrogens include improved cerebral metabolic profile and reduced oxidative stress through actions on mitochondria, suggesting that a woman's endogenous and exogenous estrogen exposures during midlife and in the late post-menopause might favourably influence Alzheimer risk and symptoms. This prediction finds partial support in the clinical literature. As expected, early menopause induced by oophorectomy may increase cognitive vulnerability; however, there is no clear link between age at menopause and Alzheimer risk in other settings, or between natural menopause and memory loss. Further, among older post-menopausal women, initiating estrogen-containing hormone therapy increases dementia risk and probably does not improve Alzheimer's disease symptoms. As suggested by the 'critical window' or 'healthy cell' hypothesis, better outcomes might be expected from earlier estrogen exposures. Some observational results imply that effects of hormone therapy on Alzheimer risk are indeed modified by age at initiation, temporal proximity to menopause, or a woman's health. However, potential methodological biases warrant caution in interpreting observational findings. Anticipated results from large, ongoing clinical trials [Early Versus Late Intervention Trial with Estradiol (ELITE), Kronos Early Estrogen Prevention Study (KEEPS)] will help settle whether midlife estrogen therapy improves midlife cognitive skills but not whether midlife estrogen exposures modify late-life Alzheimer risk. Estrogen effects on mitochondria adumbrate the potential relevance of estrogens to Alzheimer's disease. However, laboratory models are inexact embodiments of Alzheimer pathogenesis and progression, making it difficult to surmise net effects of estrogen exposures. Research needs include better predictors of adverse cognitive outcomes, biomarkers for risks associated with hormone therapy, and tools for monitoring brain function and disease progression.

Frontiers proposal. National Institute on Aging "bench to bedside: estrogen as a case study"

On 28-29 September 2004, the National Institute on Aging (NIA) convened scientists for a workshop on the aging female brain focused on translating into clinical practice discoveries concerning estrogens and progestogens. Workshop objectives were to examine effects of estrogen and progestogen on brain and cognitive function in relation to aging, to examine consistencies and apparent discrepancies between Women's Health Initiative Memory Study findings and other research on cognitive function, to determine whether additional hormone interventions could be developed in this area, and to offer advice on design of clinical trials for other interventions that might ameliorate cognitive aging. Following the workshop, participants joined by other interested scientists organized into regional work groups to continue the dialogue begun in Bethesda and to propose recommendations for NIA. The resulting recommendations, referred to as the "Frontiers Proposal for Estrogen and Cognitive Aging", acknowledge the persistence of critical gaps in our understanding of how decline in ovarian steroid secretion during reproductive aging and use of ovarian steroid hormone therapy affect normal brain function and risk for late-life neurodegenerative disorders such as Alzheimer's disease. There is a pressing need for preclinical, human, and integrated studies on the relationship between the menopausal transition and midlife exposures to estrogens, progestogens and related compounds, and risks for age-associated cognitive disorders. Research is also needed on better predictors of adverse cognitive outcomes, valid biomarkers for risks associated with hormone therapy use, enhanced tools for monitoring brain function and disease progression, and novel forms of therapy for improving long-term cognitive outcomes.

Postmenopausal hormone therapy and regional brain volumes: the WHIMS-MRI Study

OBJECTIVES

To determine whether menopausal hormone therapy (HT) affects regional brain volumes, including hippocampal and frontal regions.

METHODS

Brain MRI scans were obtained in a subset of 1,403 women aged 71-89 years who participated in the Women's Health Initiative Memory Study (WHIMS). WHIMS was an ancillary study to the Women's Health Initiative, which consisted of two randomized, placebo-controlled trials: 0.625 mg conjugated equine estrogens (CEE) with or without 2.5 mg medroxyprogesterone acetate (MPA) in one daily tablet. Scans were performed, on average, 3.0 years post-trial for the CEE + MPA trial and 1.4 years post-trial for the CEE-Alone trial; average on-trial follow-up intervals were 4.0 years for CEE + MPA and 5.6 years for CEE-Alone. Total brain, ventricular, hippocampal, and frontal lobe volumes, adjusted for age, clinic site, estimated intracranial volume, and dementia risk factors, were the main outcome variables.

RESULTS

Compared with placebo, covariate-adjusted mean frontal lobe volume was 2.37 cm(3) lower among women assigned to HT (p = 0.004), mean hippocampal volume was slightly (0.10 cm(3)) lower (p = 0.05), and differences in total brain volume approached significance (p = 0.07). Results were similar for CEE + MPA and CEE-Alone. HT-associated reductions in hippocampal volumes were greatest in women with the lowest baseline Modified Mini-Mental State Examination scores (scores <90).

CONCLUSIONS

Conjugated equine estrogens with or without MPA are associated with greater brain atrophy among women aged 65 years and older; however, the adverse effects are most evident in women experiencing cognitive deficits before initiating hormone therapy.

Hormone replacement therapy to maintain cognitive function in women with dementia

BACKGROUND

As estrogens have been shown to have several potentially beneficial effects on the central nervous system, it is biologically plausible that maintaining high levels of estrogens in postmenopausal women by means of estrogen replacement therapy (ERT) could be protective against cognitive decline in women with Alzheimer's disease (AD) or other dementia syndromes.

OBJECTIVES

To investigate the effects of ERT (estrogens only) or HRT (estrogens combined with a progestagen) compared with placebo in randomized controlled trials (RCTs) on cognitive function of postmenopausal women with dementia.

SEARCH STRATEGY

The Cochrane Dementia and Cognitive Improvement Group Specialized Register, which contains records from many medical databases, The Cochrane Library, EMBASE, MEDLINE, CINAHL, PsycINFO and LILACS were searched on 7 November 2007 using the terms ORT, PORT, ERT, HRT, estrogen*, oestrogen* and progesterone*.

SELECTION CRITERIA

All double-blind randomized controlled trials (RCTs) into the effect of ERT or HRT for cognitive function with a treatment period of at least two weeks in postmenopausal women with AD or other types of dementia.

DATA COLLECTION AND ANALYSIS

Abstracts of the references retrieved by the searches were read by two reviewers (EH and KY) independently in order to discard those that were clearly not eligible for inclusion. The two reviewers studied the full text of the remaining references and independently selected studies for inclusion. Any disparity in the ensuing lists was resolved by discussion with all reviewers in order to arrive at the final list of included studies. The selection criteria ensured that the blinding and randomization of the included studies was adequate. The two reviewers also assessed the quality of other aspects of the included trials. One reviewer (EH) extracted the data from the studies, but was aided and checked by JB from Cochrane.

MAIN RESULTS

A total of seven trials including 351 women with AD were analysed. Because different drugs were used at different studies it was not possible to combine more than two studies in any analysis.On a clinical global rating, clinicians scored patients taking CEE as significantly worse compared with the placebo group on the Clinical Dementia Rating scale after 12 months (overall WMD = 0.35, 95% CI = 0.01 to 0.69, z = 1.99, P < 0.05).Patients taking CEE had a worse performance on the delayed recall of the Paragraph Test (overall WMD = -0.45, 95% CI = -0.79 to -0.11, z = 2.60, P < 0.01) after one month than those taking placebo. They had a worse performance on Finger Tapping after 12 months (WMD = -3.90, 95% CI = -7.85 to 0.05, z = 1.93, P < 0.05).Limited positive effects were found for the lower dosage of CEE (0.625 mg/day) which showed a significant improvement in MMSE score only when assessed at two months, and disappeared after correction for multiple testing. No significant effects for MMSE were found at longer end points (3, 6 and 12 months of treatment). With a dosage of 1.25 mg/d CEE, short-term significant effects were found for Trial-Making test B at one month and Digit Span backward at four months. After two months of transdermal diestradiol (E2) treatment, a highly significant effect was observed for the word recall test (WMD = 6.50, 95% CI = 4.04 to 8.96, z = 5.19, P < 0.0001). No other significant effects were found for other outcomes measured.

AUTHORS' CONCLUSIONS

Currently, HRT or ERT for cognitive improvement or maintenance is not indicated for women with AD.

Hormone-dependent aging problems in women

One of the major social issues nowadays is the aging society. Korea is already an aging society, and 63 cities and districts are ultra-aged societies where the rate of people older than 65 yr exceeds 20%. Among them, more than 67% are women. These statistics reveal the importance of healthcare for older women. Disease and disability of older women are very closely related to the loss of female sex hormones after menopause. Major hormone-dependent aging problems in women such as osteoporosis, Alzheimer's disease (AD), urinary incontinence, and coronary atherosclerosis were surveyed in this review, and the key role of hormones in those diseases and hormone replacement therapy (HRT) were summarized. We expect that this review would provide some understanding of factors that must be considered to give optimal care to older women for healthy lives.

Menopause, estrogen, and gonadotropins in Alzheimer's disease

For decades, Alzheimer's disease (AD) has been linked to aging, gender, and menopause. Not surprisingly, this led most investigators to focus on the role of estrogen. While undoubtedly important, estrogen is unlikely the key determinant of disease pathogenesis. Rather, it appears that estrogen may work in conjunction with a novel determinant of disease pathogenesis, namely gonadotropins. The fact that gonadotropins, specifically luteinizing hormone, play a pivotal role in disease is apparent from significant etiological, epidemiological, and pathological evidences. Moreover, targeting gonadotropins appears to have beneficial actions as a therapeutic regimen.

Estradiol-17beta-induced human neural progenitor cell proliferation is mediated by an estrogen receptor beta-phosphorylated extracellularly regulated kinase pathway

Estradiol-17beta (E(2)) induces rodent hippocampal neural progenitor cell (NPC) proliferation in vitro, in vivo, and after brain injury. The purpose of the present investigation was to determine whether E(2)-induced proliferation observed in rodent model systems generalized to cells of human neural origin and the signaling pathway by which E(2) promotes mitosis of human NPCs (hNPCs). Results of these analyses indicate that E(2) induced a significant increase in hNPC proliferation in a time- and dose-dependent manner. E(2)-induced hNPC DNA replication was paralleled by elevated cell cycle protein expression and centrosome amplification, which was associated with augmentation of total cell number. To determine whether estrogen receptor (ER) and which ER subtype were required for E(2)-induced hNPC proliferation, ER expression was first determined by real-time RT-PCR, followed by Western blot analysis, and subsequently verified pharmacologically using ERalpha or beta-selective ligands. Results of these analyses indicated that ERbeta expression was predominant relative to ERalpha, which was barely detectable in hNPCs. Activation of ERbeta by the ERbeta-selective ligand, diarylpropionitrile, led to an increase in phosphorylated extracellular signal-regulated kinase, and subsequent centrosome amplification and hNPC proliferation, which were blocked by the MEKK antagonist, UO126, but not its inactive analog, UO124. These findings, for the first time, demonstrate the molecular cascade and related cell biology events involved in E(2)-induced hNPC proliferation in vitro. Therapeutic implications of these findings relevant to hormone therapy and prevention of neurodegenerative disease are discussed.

Estrogen replacement regimen and brain infusion of lipopolysaccharide differentially alter steroid receptor expression in the uterus and hypothalamus

The regimen of estrogen replacement can alter the consequences of estrogen therapy and stressors. To determine the long-term effects and interaction of these systems on the brain and periphery, adult female rats were infused with lipopolysaccharide (LPS) into the fourth ventricle of the brain for 4 weeks, and ovariectomized rats were administered either constant or pulsed regimens of estrogen replacement (17beta-estradiol) until sacrifice at 8 weeks. Constant, but not pulsed, estrogen replacement reduced ERalpha and increased HSP90, HSP70, and PR(B) uterine protein levels. Both estrogen regimens increased ERbeta, HSP27, and PR(A) uterine proteins. Both regimens reduced hypothalamic levels of ERalpha, but not ERbeta, HSP, or PR. No changes were observed in the hippocampus. Long-term brain infusion of LPS activated microglia and reduced body weight, but did not alter corticosterone or nitrotyrosine levels. LPS infusion into intact rats suppressed uterine weight, increased ERalpha and decreased HSP90 in the uterus. LPS did not alter uterine weight in ovariectomized rats treated with constant or pulsed estrogen. Together, these data suggest the timing of estrogen replacement and neuroinflammatory stressors can profoundly affect uterine and hypothalamic steroid receptor expression and may be important parameters to consider in the post-menopausal intervention with estrogen.

Geniposide, a novel agonist for GLP-1 receptor, prevents PC12 cells from oxidative damage via MAP kinase pathway

Alzheimer's disease (AD) is the most common form of dementia. Glucagon-like peptide-1 (GLP-1) gives a new genre in therapeutic targets for intervention in AD with its neurotrophic and neuroprotective functions. In previous work, we identified that geniposide is a novel agonist for GLP-1 receptor, which shows neurotrophic characteristics to induce the neuronal differentiation of PC12 cells. The aim of this study is to determine whether geniposide prevents neurons from oxidative damage, and to explore its signaling pathways. The results demonstrated that geniposide increased the expression of anti-apoptotic proteins, including Bcl-2 and heme oxygenase-1 (HO-1), to antagonize the oxidative damage in PC12 cells induced by hydrogen peroxide. LY294002 (a PI3K inhibitor) inhibited the effect of geniposide increasing of Bcl-2 level by activation of MAPK, MEK and c-Raf phosphorylation in hydrogen peroxide treated PC12 cells. U0126 (a selective inhibitor of MEK) also attenuated the enhancement of geniposide on Bcl-2 level by inhibiting the phosphorylation of p90RSK in the hydrogen peroxide treated PC12 cells. All these data demonstrate that geniposide, an agonist for GLP-1 receptor, regulates expression of anti-oxidative proteins including HO-1 and Bcl-2 by activating the transcriptor of p90RSK via MAPK signaling pathway in PC12 cells.

Increases in luteinizing hormone are associated with declines in cognitive performance

Questions surrounding estrogen therapy for post-menopausal cognitive decline and dementia led us to examine the role of luteinizing hormone that becomes elevated after menopause. We examined hippocampal-associated cognitive performance, as measured with the Y-maze task, in two strains of transgenic mice, one (Tg-LHbeta) which over-expresses luteinizing hormone and another (LHRKO), which has increased circulating luteinizing hormone levels, but its receptors are silenced. Our results demonstrate that Tg-LHbeta, but not LHRKO mice, show decreased Y-maze performance when compared to aged-matched wild-type animals. These findings indicate that increased luteinizing hormone levels, in the presence of functional receptors may, at least in part, be responsible for cognitive decline after menopause. As such, modulation of luteinizing hormone or its receptor levels may prove to be useful therapeutic strategies for cognitive decline associated with aging and age-related neurodegenerative diseases such as Alzheimer disease.

Dose and temporal pattern of estrogen exposure determines neuroprotective outcome in hippocampal neurons: therapeutic implications

To address controversies of estrogen therapy, in vitro models of perimenopause and prevention vs. treatment modes of 17beta-estradiol (E(2)) exposure were developed and used to assess the neuroprotective efficacy of E(2) against beta-amyloid-1-42 (Abeta(1-42))-induced neurodegeneration in rat primary hippocampal neurons. Low E(2) (10 ng/ml) exposure exerted neuroprotection in each of the perimenopausal temporal patterns, acute, continuous, and intermittent. In contrast, high E(2) (200 ng/ml) was ineffective at inducing neuroprotection regardless of temporal pattern of exposure. Although high E(2) alone was not toxic, neurons treated with high-dose E(2) resulted in greater Abeta(1-42)-induced neurodegeneration. In prevention vs. treatment simulations, E(2) was most effective when present before and during Abeta(1-42) insult. In contrast, E(2) treatment after Abeta(1-42) exposure was ineffective in reversing Abeta-induced degeneration, and exacerbated Abeta(1-42)-induced cell death when administered after Abeta(1-42) insult. We sought to determine the mechanism by which high E(2) exacerbated Abeta(1-42)-induced neurodegeneration by investigating the impact of low vs. high E(2) on Abeta(1-42)-induced dysregulation of calcium homeostasis. Results of these analyses indicated that low E(2) significantly prevented Abeta(1-42)-induced rise in intracellular calcium, whereas high E(2) significantly increased intracellular calcium and did not prevent Abeta(1-42)-induced calcium dysregulation. Therapeutic benefit resulted only from low-dose E(2) exposure before, but not after, Abeta(1-42)-induced neurodegeneration. These data are relevant to impact of perimenopausal E(2) exposure on protection against neurodegenerative insults and the use of estrogen therapy to prevent vs. treat Alzheimer's disease. Furthermore, these data are consistent with a healthy cell bias of estrogen benefit.

The estrogen myth: potential use of gonadotropin-releasing hormone agonists for the treatment of Alzheimer's disease

Estrogen and other sex hormones have received a great deal of attention for their speculative role in Alzheimer's disease (AD), but at present a direct connection between estrogen and the pathogenesis of AD remains elusive and somewhat contradictory. For example, on one hand there is a large body of evidence suggesting that estrogen is neuroprotective and improves cognition, and that hormone replacement therapy (HRT) at the onset of menopause reduces the risk of developing AD decades later. However, on the other hand, studies such as the Women's Health Initiative demonstrate that HRT initiated in elderly women increases the risk of dementia. While estrogen continues to be investigated, the disparity of findings involving HRT has led many researchers to examine other hormones of the hypothalamic-pituitary-gonadal axis such as luteinising hormone (LH) and follicle-stimulating hormone. In this review, we propose that LH, rather than estrogen, is the paramount player in the pathogenesis of AD. Notably, both men and women experience a 3- to 4-fold increase in LH with aging, and LH receptors are found throughout the brain following a regional pattern remarkably similar to those neuron populations affected in AD. With respect to disease, serum LH level is increased in women with AD relative to non-diseased controls, and levels of LH in the brain are also elevated in AD. Mechanistically, we propose that elevated levels of LH may be a fundamental instigator responsible for the aberrant reactivation of the cell cycle that is seen in AD. Based on these aforementioned aspects, clinical trials underway with leuprolide acetate, a gonadotropin-releasing hormone agonist that ablates serum LH levels, hold great promise as a ready means of treatment in individuals afflicted with AD.

Investigative models for determining hormone therapy-induced outcomes in brain: evidence in support of a healthy cell bias of estrogen action

The profound disparities between the largely positive basic science findings of gonadal steroid action in brain and the adverse outcomes of recent hormone therapy clinical trials in women who are either aged postmenopausal or postmenopausal with Alzheimer's disease have led to an intense reassessment of gonadal hormone action and the model systems used in basic and clinical science. The power of model systems is their predictive validity for a target population--in this case, menopausal women considering the health benefits and risks of hormone therapy. Analysis of the model systems used across the basic to clinical research continuum separate into two broad classes: those that use prevention interventions in healthy organisms and those that use hormone interventions in organisms with compromised neurological function. Basic science analyses that led to elucidation of the neurotrophic and neuroprotective effects of estrogen and the underlying mechanisms of action typically used a prevention-based experimental paradigm. This paradigm relies on healthy neurons/brains/animals/humans as the starting foundation followed by exposure to estrogen/hormone followed by exposure to neurodegenerative insult. The prevention paradigm in basic science analyses parallels the analyses of Sherwin and colleagues (Psychoneuroendocrinology 13: 345-357, 1988), who investigated the cognitive impact of estrogen therapy in women with surgical- or pharmacological-induced menopause. Observational retrospective and prospective studies are also consistent with the healthy cell bias of estrogen action and a prevention paradigm of estrogen or hormone therapy intervention. For the most part, the epidemiological observational data indicate reduction in the risk of Alzheimer's disease in women who began estrogen or hormone therapy at the time of the menopause. In contrast, studies that fall within the second class, hormone intervention in organisms with compromised neurological function--that is, a treatment paradigm--exhibit a mixed profile. In a randomized double-blind clinical trial of estrogen therapy in a cohort of women aged 72 or more years and diagnosed with Alzheimer's disease, estrogen therapy resulted in a modest benefit in the short term (2 months) and adverse progression of disease in the long term (12 months). In the Women's Health Initiative Memory Study (WHIMS) cohort of women 65 or more years of age, with no indicators of neurological disease but with variable health status, estrogen and hormone therapy for 5 years increased the risk of developing Alzheimer's disease. These data would suggest that as the continuum of neurological health progresses from healthy to unhealthy, so too do the benefits of estrogen or hormone therapy. If neurons are healthy at the time of estrogen exposure, their response to estrogen is beneficial for both neurological function and survival. In contrast, if neurological health is compromised, estrogen exposure over time exacerbates neurological demise. Based on these and other data, a hypothesis of a healthy cell bias of gonadal hormone action is put forth. The healthy cell bias of estrogen action hypothesis provides a lens through which to assess the disparities in outcomes across the domains of scientific inquiry and to access future applications of estrogen and hormone therapeutic interventions.

Estrogens and the pathophysiology of the biliary tree

The scientific framework concerning estrogen effects on different tissues has expanded enormously during the last decades, when estrogen receptor (ER) subtypes were identified. Estrogens are not only essential for the female reproductive system, but they also control fundamental functions in other tissues including the cardiovascular system, bone, brain and liver. Recently, estrogens have been shown to target the biliary tree, where they modulate the proliferative and secretory activities of cholangiocytes, the epithelial cells lining bile ducts. By acting on both estrogen receptors (ER-α) and (ER-β) subtypes, and by activating either genomic or non-genomic pathways, estrogens play a key role in the complex loop of growth factors and cytokines, which modulates the proliferative response of cholangiocytes to damage. Specifically, estrogens activate intracellular signalling cascades [ERK1/2 (extracellular regulated kinases 1/2, PI3- kinase/AKT (phosphatidylinositol-3’ kinase/AKT)] typical of growth factors such as insulin like growth factor (IGF1), nerve growth factor (NGF) and vascular endothelial growth factor (VEGF), thus potentiating their action. In addition, estrogens stimulate the secretion of different growth factors in proliferating cholangiocytes. This review specifically deals with the recent advances related to the role and mechanisms by which estrogens modulate cholangiocyte functions in normal and pathological conditions.

Estrogen-containing hormone therapy and Alzheimer’s disease risk: Understanding discrepant inferences from observational and experimental research

Estrogen has the potential to influence brain processes implicated in Alzheimer's disease pathogenesis. With the loss of ovarian estrogen production after menopause, estrogen-containing hormone therapy might be expected to influence the risk of Alzheimer's disease. Observational data link use of hormone therapy to reductions in Alzheimer risk, but experimental evidence from the Women's Health Initiative Memory Study trial demonstrates that oral estrogen, with or without a progestin, increases the incidence of dementia for postmenopausal women age 65 years or older. Mechanisms of harm in this setting are unknown. Bias and unrecognized confounding in observational research are leading candidates for discrepant results between observational studies and the Women's Health Initiative Memory Study trial. Studies are also distinguished by differences in outcome measures, hormone therapy formulations, prevalence of menopausal symptoms among study participants, and participant age. Finally, Women's Health Initiative Memory Study findings may not generalize to estrogen use by relatively young women during the menopausal transition or early postmenopause, a class of women who were ineligible for the Women's Health Initiative Memory Study trial. In observational studies, hormone therapy exposure often included use by younger women for menopausal vasomotor symptoms. Although there is no clinical trial evidence that hormone therapy at any age protects against Alzheimer's disease, it remains to be determined whether the age at which hormone exposure occurs or the timing of hormone therapy initiation in relation to the menopause (the critical window hypothesis) modifies treatment outcomes on dementia risk.

Gender differences in Alzheimer disease: the role of luteinizing hormone in disease pathogenesis

Epidemiological data reporting the predisposition of women to Alzheimer disease has provided researchers with an important clue as to the identity of the driving pathogenic force and lead many to question the potential role of sex steroids, namely estrogen, in disease pathogenesis. However, while estrogen has become the primary focus of research in the field, inconclusive data regarding estrogen replacement therapy has lead some researchers to begin investigating the effects of the other hormones of the hypothalamic-pituitary-gonadal (HPG) axis on the aging brain. Certain hormones of the HPG axis, namely the gonadotropins (luteinizing hormone and follicle-stimulating hormone), are not only involved in regulating reproductive function via a complex feedback loop but are also known to cross the blood-brain barrier. Recently, we proposed that an increase in gonadotropin concentrations, not the decrease in steroid hormone (eg, estrogen) production following menopause/andropause, is a potentially primary causative factor for the development of Alzheimer disease. In this review, we examine how the gonadotropins may play a central and determining role in modulating the susceptibility to, and progression of, Alzheimer disease. Based on this, we suggest that therapeutic interventions targeted at gonadotropins may both prevent disease in those patients currently asymptomatic or may halt, and even reverse, disease in those currently afflicted.

Estradiol or estradiol/progesterone treatment in older women: no strong effects on cognition

The relevance of estrogens for cognition in older women is still debated. In this double-blind experiment hysterectomized women (age 58-75 years) received placebo (n = 13), estradiol (n = 12) or estradiol/progesterone (n = 10) treatment. Cognitive testing (nine different tests) took place at baseline, after 4 and 24 weeks of treatment. Strong hormone increases occurred in both active treatment groups. However, no beneficial effects in any of the cognitive tests could be detected. This study, therefore, does not support the notion that treatment with sex hormones has beneficial effects on cognition in older hysterectomized women. The human brain might loose its responsiveness to gonadal steroids with aging or prolonged hormone depletion.

No changes in event-related potentials with estrogen or estrogen plus progesterone treatment in healthy older hysterectomized women: results from a double-blind, placebo-controlled study

RATIONALE

The potential to improve cognition in older women with estrogen or estrogen/progesterone therapy is currently a matter of intense debate. Only a few studies conducted so far have used electrophysiological indicators of cognitive information processing as outcome measures in randomised placebo controlled studies.

OBJECTIVES

This study was undertaken to measure changes in event-related potentials (ERPs) after short (4 weeks) or prolonged (24 weeks) hormone treatment in older women.

METHODS

A randomised, double-blind, placebo-controlled study in hysterectomized older women (aged 58-75 years) was performed (n = 51). The participants received orally estradiol (2 mg estradiol valerate), estradiol plus progesterone (100 mg micronized progesterone) or placebo for 24 weeks. Using four different paradigms, early and late ERPs were assessed at baseline and after 4 and 24 weeks of treatment.

RESULTS

Strong hormone increases were observed in the two active treatment groups. However, no significant effects on any of the assessed ERPs were observed in either of the two treatment groups. Similar non-significant findings were obtained for reaction time and error rate.

CONCLUSIONS

Estradiol or estradiol/progesterone treatment appears to have no strong effects on several ERP markers of information processing in older hysterectomized women. The current negative findings might suggest a reduced sensitivity of the aged brain to gonadal steroids.

Trolox and 17β-Estradiol Protect against Amyloid β-Peptide Neurotoxicity by a Mechanism That Involves Modulation of the Wnt Signaling Pathway

Oxidative stress is a key mechanism in amyloid beta-peptide (A beta)-mediated neurotoxicity; therefore, the protective roles of 17beta-estradiol (E2) and antioxidants (Trolox and vitamin C) were assayed on hippocampal neurons. Our results show the following: 1) E2 and Trolox attenuated the neurotoxicity mediated by A beta and H2O2 as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assays, quantification of apoptotic cells, and morphological studies of the integrity of the neurite network. 2) Vitamin C failed to protect neurons from A beta toxicity. 3) A beta-mediated endoperoxide production, reported to induce cell damage, was decreased in the presence of E2 and Trolox. 4) Two key Wnt signaling components were affected by E2 and Trolox; in fact, the enzyme glycogen synthase kinase 3beta was inhibited by both E2 and Trolox, and both compounds were able to stabilize cytoplasmic beta-catenin. 5) E2 activated the expression of the Wnt-5a and Wnt-7a ligands, and at the same time, E2, through the alpha-estrogen receptor, was able to prevent the excitotoxic A beta-induced rise in bulk-free Ca2+ as an alternative pathway to increase cell viability. 6) Finally, the Wnt-7a ligand protected against cytoplasmic calcium disturbances induced by A beta treatment. Our results suggest that control of oxidative stress, regulation of cytoplasmic calcium, and activation of Wnt signaling may prevent A beta neurotoxicity.

Dysregulation of the Hypothalamic-Pituitary-Gonadal Axis with Menopause and Andropause Promotes Neurodegenerative Senescence

Senescence is characterized neurologically by a decline in cognitive function, which we propose is the result of degenerative processes initiated by the dysregulation of the hypothalamic-pituitary-gonadal (HPG) axis with menopause and andropause. Compelling epidemiologic evidence to support this assertion includes the increased prevalence of Alzheimer disease (AD) in women, the correlation of serum HPG hormones with disease and the decreased incidence, and delay in the onset of AD following hormone replacement therapy. Dysregulation of the axis at this time leads to alterations in the concentrations of all serum HPG hormones (decreased neuronal sex steroid signaling, but increased neuronal gonadotropin releasing hormone, luteinizing hormone, and activin signaling). Hormones of the HPG axis, receptors for which are present in the adult brain, are important regulators of cell proliferation and differentiation during growth and development. Based on this, we propose that dysregulated HPG hormone signaling with menopause/andropause leads to the abortive reentry of differentiated neurons into the cell cycle via a process we term "dyosis." Interestingly, the major biochemical and neuropathologic changes reported for the AD brain also are intimately associated with neuron division: altered AbetaPP metabolism, Abeta deposition, tau phosphorylation, mitochondrial alterations, chromosomal replication, synapse loss, and death of differentiated neurons. Recent evidence supports the premise that AD-related biochemical changes are likely the combined result of increased mitotic signaling by gonadotropins and GnRH, decreased differentiative and neuroprotective signaling via sex steroids, and increased differentiative signaling via activins. This results in a hormonal milieu that is permissive of cell cycle reentry but does not allow completion of metaphase. Partial resetting of the axis following administration of normal endogenous sex steroids delays the onset and decreases the incidence of AD. Ideally, supplementation with HPG hormones should mimic closely the serum concentrations of all HPG hormones in reproductive men and cycling women to prevent dyotic signaling and attempted neuron division.

Obesity enhances verbal memory in postmenopausal women with Down syndrome

Several lines of evidence suggest that the loss of estrogen after menopause may play a role in cognitive declines associated with Alzheimer's disease (AD). In postmenopausal women, the principal source of estrogen is estrone, which is influenced by body mass index (BMI). Increased BMI in postmenopausal women is associated with higher levels of serum estradiol and estrone. We hypothesized that obesity could have a beneficial effect on cognition with advancing age. We compared the performance of healthy nondemented obese and non-obese women with Down syndrome (DS) on a broad spectrum of cognitive tests. Estrone levels were 66.9% higher in obese than in non-obese postmenopausal women, and 136% higher in obese than in non-obese premenopausal women. Obese postmenopausal women performed significantly better than non-obese women on measures of verbal memory and on an omnibus test of neuropsychological function, but did not differ significantly in verbal fluency, language, praxis or visuospatial functioning. Among premenopausal women, there was no difference in cognitive function between obese and non-obese women. Our results support the hypothesis that higher endogenous estrogen levels after menopause are associated with better performance on verbal memory.

Anesthetic considerations in patients with Alzheimer's disease

Alzheimer's disease is a form of dementia that is estimated to affect approximately 3 to 4 million Americans. Given the substantial number of people affected with this disease, it is likely that anesthesiologists will encounter many patients with Alzheimer's disease. Questions as to potential problems including informed consent, drug interactions, and preoperative progression of the disease may arise. This review describes anesthetic considerations, including pharmacologic and physiologic issues, in this growing population.

Estrogen receptor-alpha distribution in the human hypothalamus in relation to sex and endocrine status

The present study reports the first systematic rostrocaudal distribution of estrogen receptor-alpha immunoreactivity (ERalpha-ir) in the human hypothalamus and its adjacent areas in young adults. Postmortem material taken from 10 subjects (five male and five female), between 20 and 39 years of age, was investigated. In addition, three age-matched subjects with abnormal levels of estrogens were studied: a castrated, estrogen-treated 50-year-old male-to-female transsexual (T1), a 31-year-old man with an estrogen-producing tumor (S2), and an ovariectomized 46-year-old woman (S8). A strong sex difference, with more nuclear ERalpha-ir in women, was observed rostrally in the diagonal band of Broca and caudally in the medial mamillary nucleus. Less robust sex differences were observed in other brain areas, with more intense nuclear ERalpha-ir in men, e.g., in the sexually dimorphic nucleus of the medial preoptic area, paraventricular nucleus, and lateral hypothalamic area, whereas women had more nuclear ERalpha-ir in the suprachiasmatic nucleus and ventromedial nucleus. No nuclear sex differences in ERalpha were found, e.g., in the central part of the bed nucleus of the stria terminalis. In addition to nuclear staining, ERalpha-ir appeared to be sex-dependently present in the cytoplasm of neurons and was observed in astrocytes, plexus choroideus, and other non-neuronal cells. ERalpha-ir in T1, S2, and S8 suggested that most of the observed sex differences in ERalpha-ir are "activational" (e.g., ventromedial nucleus/medial mamillary nucleus) rather than "organizational." Species similarities and differences in ERalpha-ir distribution and possible functional implications are discussed.

Elevated luteinizing hormone expression colocalizes with neurons vulnerable to Alzheimer's disease pathology

In individuals with Alzheimer's disease (AD), there is a two-fold elevation in the serum concentrations of the gonadotropins, luteinizing hormone (LH), and follicle stimulating hormone compared to age-matched controls. Whether this plays a role in disease pathogenesis is unclear. Nonetheless, gonadotropins are known to cross the blood brain barrier and the highest density of gonadotropin receptors in the brain are found within the hippocampus. We report for the first time the localization of LH in the cytoplasm of pyramidal neurons. In addition, we find a significant increase in LH in the cytoplasm of pyramidal neurons and neurofibrillary tangles of AD brain compared to age-matched control brain. Whereas the functional consequences of increased neuronal LH are unknown, it is notable that LH is primarily localized to those neurons that are known to be vulnerable to Alzheimer's disease-related neurodegeneration. Elevated serum and cortical neuron levels of LH, coupled with the decline in sex steroid production, could play important roles in the pathogenesis of AD.

Long-term estrogen therapy worsens the behavioral and neuropathological consequences of chronic brain inflammation

Alzheimer's disease (AD) is accompanied by chronic neuroinflammation and occurs with greater incidence in postmenopausal women. The increased incidence may be delayed by estrogen replacement therapy (ERT). The authors investigated the interaction of chronic ERT and lipopolysaccharide (LPS)-induced neuroinflammation in the female rat. Ovariectomy did not impair water maze performance; however, addition of chronic ERT or neuroinflammation resulted in an impairment that became exacerbated by the simultaneous occurrence of both conditions. Chronic LPS activated microglia, which was not reduced by ERT. Intact females receiving LPS infusion were not impaired in the water maze and had significantly fewer activated microglia. Results suggest that chronic ERT in postmenopausal women may exacerbate the memory impairment induced by the chronic neuroinflammation associated with AD.

Oestrogen has neuroprotective effects and may reduce the risk of Alzheimer's disease

Evidence from both animals and humans supports a neuroprotective role of oestrogen. Epidemiological studies showing that oestrogen improves cognitive performance in postmenopausal women, clinical trials showing effects of oestrogen on cognition and data suggesting that oestrogen reduces the risk of Alzheimer's disease (AD) led to the proposal that oestrogen may be effective for improving symptoms or slowing decline in women with AD. Studies evaluating oestrogen as a treatment for AD have been performed with mixed findings. While a few studies have found modest improvements, the results have largely been disappointing. However, many of the studies suffer from substantial methodological problems that leave the findings in question. The role of oestrogen for the prevention or treatment of AD is not yet clear, but large, well-controlled, ongoing trials should provide definitive answers to many questions in the near future.

Mood, cognition and Alzheimer's disease

There is good evidence for sex differences in brain disease, and that oestrogen modulates brain development and ageing. For example, females are significantly more likely to suffer from Alzheimer's disease, depression and late-onset psychosis than are men. Moreover, hormone replacement therapy may reduce the rate of cognitive decline in post-menopausal women and reduce their risk of developing Alzheimer's disease (as compared to post-menopausal women who do not take hormone replacement therapy). The neurobiological basis of these differences in brain disease and ageing was unknown until relatively recently. In this chapter we discuss results of studies demonstrating that sex steroids (i) are crucial for development and ageing of brain regions affected in Alzheimer's disease; (ii) interact with neuronal networks and chemical systems at many different levels in brain, and (iii) affect mood and cognitive function in elderly women without Alzheimer's disease. The current literature supports the hypothesis that sex steroids can modulate brain ageing and provides a number of potential neurobiological explanations for the cognitive effects of hormone replacement therapy. There is only limited evidence that hormone replacement therapy is effective in women already suffering from Alzheimer's disease. Nonetheless, recent work may lead to new prevention strategies for age-related cognitive decline and brain diseases such as Alzheimer's disease.

Hormone replacement therapy for cognitive function in postmenopausal women

BACKGROUND

As estrogens have been found in animal models to be associated with the maintenance and protection of brain structures, it is biologically plausible that maintaining high levels of estrogens in postmenopausal women by medication could be protective against cognitive decline.

OBJECTIVES

To investigate the effect of ERT (estrogens only) or HRT (estrogens combined with a progestagen) in comparison with placebo in randomized controlled trials (RCTs) on cognitive function in postmenopausal women.

SEARCH STRATEGY

The CDCIG Specialized Register was searched using the terms ORT, PORT, ERT, HRT, estrogen*, oestrogen*, progesteron* on 16 May 2002. In addition MEDLINE (1966-2002/01); EMBASE (1985-2000/11); PsycINFO (1967-2002/01) and CINAHL (1982-2001/12) were searched as the CDCIG Register does not contain all trials with healthy volunteers.

SELECTION CRITERIA

All double-blind randomized controlled trials of the effect of ERT or HRT on cognitive function over a treatment period of at least two weeks in postmenopausal women.

DATA COLLECTION AND ANALYSIS

Abstracts of the references retrieved by the searches were read by two reviewers in order to discard those that were clearly not eligible for inclusion. The two reviewers studied the full text of the remaining references and independently selected studies for inclusion. Any disparity in the resulting lists was resolved by discussion with all reviewers in order to arrive at the final list of included studies. The selection criteria ensured that the blinding and randomization of the included studies was adequate. Two reviewers (EH and KY) assessed the quality of other aspects including design and assessment of outcomes. One reviewer (EH) extracted the data from the studies.

MAIN RESULTS

In total, 15 trials involving 566 postmenopausal women were included, but 6 studies did not have adequate data for analysis. Meta-analyses showed a positive effect of 10 mg of estradiol (E2) bolus injections intramuscularly monthly in relatively young surgically menopausal women on the Paired Associate learning test immediate recall (z=2.40, p<0.05, chi-square test=1.12, p=0.29, SMD=1.02, 95% C.I.=0.19-1.85), on a test of abstract reasoning (z=10.45, p<0.0001, WMD=6.80, 95% C.I.=5.52-8.08) and a test of speed and accuracy (z=9.16, p<0.0001 WMD=6.00, 95% C.I.=4.72-7.28). However, most studies showed no evidence of an effect on verbal or visuospatial memory, mental rotations, speed or accuracy measures. There was little evidence that Premarin, the most widely prescribed estrogen for postmenopausal use, had positive effects on cognitive function. The one effect of 9 months of treatment with Premarin (and a progestagen) on a measure of complex speed of information processing (the TMT-B) was probably explained by baseline differences, as it was not reported by the authors.

REVIEWER'S CONCLUSIONS

There was little evidence regarding the effect HRT or ERT on overall cognitive function in healthy postmenopausal women. There was an effect on some verbal memory functions (immediate recall), on a test of abstract reasoning and a test of speed and accuracy in relatively young (47 years of age) surgically menopausal women who had been given a bolus intramuscular injection of 10 mg E2 every month for 3 months. These effects were from small studies from a single research group. It remains to be determined whether factors such as an older age (> 69 years of age), type of menopause (surgical or natural) and type of treatment (E2 with or without a progestagen), mode of delivery (transdermal, oral or intramuscular), dosage and duration (> 3 months) could alter the effect on memory functions to a clinically relevant level. In addition, whether the absence or presence of menopausal symptoms can modify treatment effects should be investigated in more detail. Longitudinal RCTs currently underway in the U.S.A., U.K. and Canada will be able to test these hypotheses by the year 2010.

Hormone replacement therapy to maintain cognitive function in women with dementia

BACKGROUND

As estrogens have been shown to have several potentially beneficial effects on the central nervous system, it is biologically plausible that maintaining high levels of estrogens in postmenopausal women by means of estrogen replacement therapy (ERT) could be protective against cognitive decline and the development of Alzheimer's disease (AD) or other dementia syndromes.

OBJECTIVES

To investigate the effects of ERT (estrogens only) or HRT (estrogens combined with a progestagen) compared with placebo in randomized controlled trials (RCTs) on cognitive function of postmenopausal women with dementia.

SEARCH STRATEGY

The CDCIG Specialized Register, which contains up-to-date records from many medical databases was searched using the terms ORT, PORT, ERT, HRT, estrogen*, oestrogen*, progesteron* and Alzheim* on 16th of May 2002. In addition, MEDLINE (1966-2002/01); EMBASE (1985-2002/01); and PsyINFO (1967-2002/01) were searched.

SELECTION CRITERIA

All double-blind randomized controlled trials (RCTs) into the effect of ERT or HRT for cognitive function with a treatment period of at least two weeks in postmenopausal women with AD or other types of dementia.

DATA COLLECTION AND ANALYSIS

Abstracts of the references retrieved by the searches were read by two reviewers (EH and KY) independently in order to discard those that were clearly not eligible for inclusion. The two reviewers studied the full text of the remaining references and independently selected studies for inclusion. Any disparity in the ensuing lists was resolved by discussion with all reviewers in order to arrive at the final list of included studies. The selection criteria ensured that the blinding and randomization of the included studies was adequate. The two reviewers also assessed the quality of other aspects of the included trials. One reviewer (EH) extracted the data from the studies, but was aided and checked by JB from Cochrane.

MAIN RESULTS

A total of five trials including 210 women with AD were analysed. Meta-analyses showed that there was a limited positive effect from low dosage of conjugated equine estrogens (CEE, 0.625 mg once a day) but not from higher dosage (1.25 mg of CEE once a day) on the Mini-Mental Status Examination after 2 months (WMD=1.28, 95% C.I.=0.26 to 2.30, z=2.45, p<0.01) and the effect disappeared after 3, 6 and 12 months of treatment. This effect was small and not clinically relevant as there was only a difference of 1 point on average in comparison with the placebo users (the scale range is 0-30). There were also short-term effects of 1.25 mg of CEE on tests of concentration and executive function, namely the Trail Making Test-B (WMD=-40.90, 95% C.I.-79.29 to -2.51, z=2.09, p<0.05) and Digit Span backward (WMD=0.67, 95% C.I.=-0.01 to 1.34, z=1.94, p<0.05). With regard to memory, only cued delayed recall of a word list was positively affected by 2 months of transdermal diestradiol (E2) (WMD=6.50, 95% C.I.=4.04 to 8.96, z=5.19, p<0.0001). No HRT effects were seen on other word lists, Paragraph Recall or Paired Associate Learning. In addition, no effects were seen on visual memory, language functions, most speeded tests, clinical rating scales or depression. Controls had better performance on the delayed recall of the Paragraph Test (overall WMD=-0.45, 95% C.I.=-0.79 to -0.11, z=2.60, p<0.01) after 1 month and on Finger Tapping after 12 months (WMD=-3.90, 95% C.I.=-7.85 to 0.05, z=1.93, p<0.05). Clinicians also gave controls a better score on a dementia rating scale (CDR, overall WMD=0.35, 95% C.I.=0.01 to 0.69, z=1.99, p<0.05). Positive findings in favour of treatment or placebo could have been random effects caused by multiple analyses. After correction for multiple testing, only the short-term positive treatment effect of E2 on memory remained.

REVIEWER'S CONCLUSIONS

Currently, HRT or ERT for cognitive improvement or maintenance is not indicated for women with AD. As we did not have data on women with other types of dementia (e.g. vascular dementia) this remains to be investigated. As most studies only used CEE and our earlier review in healthy women found effects only after a bolus injection of E2, it remains possible that different preparations or types of ERT or HRT could have a different effects. Several questions are raised in this review, including whether factors such as age, dementia onset (early AD), or the use of a particular preparation for a longer duration of treatment could have different effects. Perhaps the most important question is whether ERT or HRT can delay the time of onset of dementia. For answers to these questions, we have to await the results of the large RCTs currently in progress in the UK, USA, and Canada.

Effects of hormone replacement therapy on cognitive and brain aging

Recent reports suggest that hormone therapy may be associated with a reduced risk for Alzheimer's disease and may offer some protection against age-associated declines in specific cognitive functions. The majority of these reports are based on observational studies, which are confounded by the "healthy user" bias--the tendency for women receiving hormone therapy to be younger, better educated, and have fewer medical problems. In one attempt to address these limitations, we conducted a series of studies examining effects of hormone therapy on cognitive and brain functioning in nondemented postmenopausal women in the Baltimore Longitudinal Study of Aging (BLSA). In this sample, women receiving hormone therapy and women who never received hormone therapy were comparable with respect to educational attainment, general medical health, and performance on a test of verbal knowledge. Despite these similarities, women receiving hormone therapy performed better on tests of verbal and visual memory compared to never-treated women. The two groups also differed in the patterns of regional brain activation evoked during performance of delayed verbal and figural memory tasks. Furthermore, longitudinal comparisons revealed greater relative blood flow increases over two years in women receiving hormone therapy for the hippocampus and other mesial temporal lobe structures that subserve memory. These observational findings from our studies in the BLSA have led to the development of a large-scale randomized clinical trial of hormone therapy and cognitive aging, the ancillary Women's Health Initiative Study of Cognitive Aging (WHISCA), and have important implications for studies of the effects of SERM's on cognitive and brain functioning.

Estrogen replacement therapy for the potential treatment or prevention of Alzheimer's disease

Alzheimer's disease (AD) is an irreversible, progressive brain disorder that occurs gradually and results in memory loss, behavior and personality changes, and a decline in cognitive abilities. Although basic biological data suggest that estrogen may have neuroprotective and neuroenhancing functions, a number of studies have produced conflicting findings on the use of estrogen for maintaining cognitive function in older people. This review summarizes clinical studies that have examined the effects of estrogen in women with AD.

Effects of estrogen on patterns of brain activity at rest and during cognitive activity: a review of neuroimaging studies

Animal and human studies provide evidence of systematic effects of estrogen on cerebral activity and cognitive function. In this article, we review studies of the activational effects of estrogen on cerebral activity during rest and during the performance of cognitive tasks in pre- and postmenopausal women. The goal is twofold--to better understand evidence suggesting that estrogen influences brain functioning and argue for the importance of considering hormone effects when designing neuroimaging studies. Hormone-related increases in blood flow during the resting state have been documented in healthy elderly women, elderly women with cerebrovascular disease, and middle-aged postmenopausal women with early menopause. There is no reliable influence of estrogen on blood flow during the resting state in women with Alzheimer's disease. Hormone therapy has been associated with changes in brain activation patterns in middle-aged and elderly postmenopausal women during performance of verbal and figural memory tasks, providing critical biological support for the view that estrogen might protect against age-associated changes in cognition and lower the risk of Alzheimer's disease. There is a paucity of studies examining changes in brain activation patterns across the menstrual cycle and a need for randomized studies of hormone therapy in postmenopausal women to confirm findings from observational studies. General procedural guidelines for controlling and investigating hormone effects in neuroimaging studies are discussed.

Testosterone-mediated neuroprotection through the androgen receptor in human primary neurons

Estrogen is an active neuroprotectant and is presently investigated as a potential therapy against Alzheimer's disease for women. To determine if male hormones could also be neuroprotective, we investigated the effect of testosterone, methyltestosterone, and epitestosterone at physiological concentrations on primary cultures of human neurons induced to undergo apoptosis by serum deprivation. Serum deprivation significantly induces neuronal apoptosis in a protracted fashion. As expected, physiological concentrations of 17-beta-estradiol and transcriptionally inactive 17-alpha-estradiol protect neurons against apoptosis. Similar to 17-beta-estradiol, physiological concentrations of testosterone are also neuroprotective. Androgen receptors are present at 8 +/- 2 fmol/mg protein in the neuron cultures. The non-aromatizable androgen, mibolerone, is also neuroprotective and aromatase inhibitor, 4-androsten-4-OL-3,17-dione, does not prevent testosterone-mediated neuroprotection. In contrast, anti-androgen, flutamide, eliminates testosterone-mediated neuroprotection. Testosterone analog, methyltestosterone, showed androgen receptor-dependent neuroprotection that was delayed in time indicating that a metabolite may be the active agent. The endogenous anti-androgen, epitestosterone, also showed a slight neuroprotective effect but not through the androgen receptor. These results indicate that androgens induce neuroprotection directly through the androgen receptor. These data suggest that androgens may also be of therapeutic value against Alzheimer's disease in aging males.

The nature of the effect of female gonadal hormone replacement therapy on cognitive function in post-menopausal women: a meta-analysis

We reviewed epidemiological and experimental studies of female gonadal hormone replacement therapy (HRT) on cognitive function in post-menopausal women and carried out meta-analyses. In healthy ageing women, HRT has small and inconsistent effects that include enhancement of verbal memory, abstract reasoning and information processing. Epidemiological studies show larger effects than experimental studies, which is not related to sample size. Important confounds may be that women who start using HRT are healthier than women who do not. Also, controlling for socio-economic status diminishes the effect of HRT. The effects of HRT may depend on the age and type of menopause and the therapeutic intervention used, with the most widely used drug, Premarin, having least effect. However, the effects are independent of mood and climacteric symptom alleviation. There is a paucity of experimental studies that include healthy elderly women. The evidence for an estrogen deficiency in women with dementia and cognitive dysfunction is inconsistent. Nevertheless, epidemiological studies suggest that HRT protects against the development of clinically diagnosed Alzheimer's disease. However, poor recall of HRT use by patients and altered physician behaviour may have confounded the effects. Surprisingly, both healthy and demented women with low education seem to benefit most from HRT. Three recent controlled experimental studies using Premarin showed no effects of HRT in preventing further cognitive decline in women who already have Alzheimer's disease. Duration of treatment seems to play an important role, with beneficial effects declining-and even reversing-with longer treatment in women with Alzheimer's disease.Future research should further investigate the cognitive effect of different HRT preparations, serum estrogen levels, and the interactions of HRT with age, menopausal status and existing protective (e.g. education) and risk factors (e.g. smoking and apolipoprotein E genotype) for cognitive decline and Alzheimer's disease.