The potential for estrogens in preventing Alzheimer's disease and vascular dementia

Effects of hormone therapy on cognition and mood

OBJECTIVE

Results of the Women's Health Initiative (WHI) and Women's Health Initiative Memory Study (WHIMS) suggested that hormone therapy (HT) may be detrimental to cognitive health. This article reviews clinical studies that address issues relevant to those results.

DESIGN

Literature review.

INTERVENTION(S)

A search of Pubmed and Web of Science was conducted using the search terms HT and cognition, HT and mood. Clinical and observational studies were selected if they were published after the year 2000. Theories of HT mechanisms of action, pharmacology, biology, and observational and clinical trials are discussed.

RESULT(S)

Although observational and clinical trials show conflicting findings, methodologic considerations must be acknowledged. HT formulation and dose, route of administration, timing of initiation, length of treatment, and health of participants all contribute to inconsistencies in results. Transdermal estradiol and micronized progesterone administered at time of menopause are generally associated with cognitive and affective benefit.

CONCLUSION(S)

At the present time, results from existing studies are equivocal regarding the benefits of HT on cognition and affect. Future studies, such as the Kronos Early Estrogen Prevention Study (KEEPS), should address methodologic inconsistencies to provide clearer answers to this important question.

Premature menopause and risk of neurological disease: basic mechanisms and clinical implications

Since basic scientific studies in the 1990s revealed dramatic gender differences in neurological damage from cerebral ischemia, significant evidence has accumulated for a neuroprotective role of ovarian-derived 17β-Estradiol (E2). Intriguingly, observational studies have further suggested that early and prolonged loss of ovarian E2 (premature menopause) leads to a doubled lifetime risk for dementia and a fivefold increased risk of mortality from neurological disorders, but some controversy remains. Here, we briefly summarize and analyze clinical cohort studies assessing the detrimental neurological outcomes of premature menopause. Furthermore, we discuss current basic science studies elucidating the molecular mechanisms underlying the enhanced risk of neurological disease in prematurely menopausal women and the "window of opportunity" for estrogen benefit. Finally, we highlight four critical issues in the field that require collaboration between basic scientists and clinicians for successful resolution, with the ultimate goal of maintaining optimal neurological health in prematurely menopausal women.

Prestroke dementia: characteristics and clinical features in consecutive series of patients

BACKGROUND/AIM

The prestroke level of cognitive function should be taken into account in order to predict the impact of stroke on the subsequent risk of dementia. The aim of the present study was to investigate the presence and correlates of prestroke dementia (PSD) as well as to identify its clinical features.

METHODS

Premorbid clinical and cognitive features of 158 consecutively recruited patients with a diagnosis of acute cerebrovascular pathology were assessed by interviewing the caregivers using multidimensional assessment. Patients were divided into two groups (PSD group and prestroke nondemented group). Baseline cognitive, functional and behavioral variables and neuroradiological hallmarks (medial temporal lobe atrophy, MTLA) were compared between these two groups.

RESULTS

In a logistic regression model, older age (OR 1.05), female gender (OR 2.3), Neuropsychiatric Inventory total score (OR 1.1) and MTLA (OR 1.2) were the variables independently associated with PSD.

CONCLUSIONS

These findings support the hypothesis that cognitive impairment in patients with stroke may not only be a direct consequence of the acute cerebrovascular event but also a consequence of underlying neurodegenerative pathology.

Long-term estrogen deprivation leads to elevation of Dickkopf-1 and dysregulation of Wnt/β-Catenin signaling in hippocampal CA1 neurons

Surgically menopausal women incur a 2- to 5-fold increased risk for dementia and mortality from neurological diseases, but the mechanisms underlying these increased risks remain unclear. Previously, we demonstrated that after global cerebral ischemia (GCI), 17β-estradiol (E2 or estrogen) suppresses hippocampal elevation of the Wnt antagonist Dickkopf-1 (Dkk1), a neurodegenerative factor. We, thus, hypothesized that prolonged loss of E2 may lead to dysregulation of neural Dkk1 and Wnt/β-Catenin signaling, which could contribute to an increased risk of neurodegeneration. To test this hypothesis, we examined the effect of short-term (1 week - STED) and long-term E2 deprivation (10 weeks - LTED) via ovariectomy upon basal and E2-regulated Dkk1 levels and Wnt/β-Catenin signaling in the hippocampal CA1 region following GCI. In STED rats, E2 exerted robust neuroprotection against GCI, suppressed post-ischemic elevation of Dkk1, and enhanced pro-survival Wnt/β-Catenin signaling, effects that were lost in LTED rats. Intriguingly, LTED rats displayed modest basal changes in Dkk1 and survivin expression. Further work showed that c-Jun N-terminal Kinase (JNK) mediated GCI-induced changes in Dkk1 and survivin, and JNK inhibition afforded neuroprotection in LTED rats. Finally, we extended our findings to natural aging, as 24-month-old, reproductively senescent female rats also displayed a modest increase in basal Dkk1 in the CA1, which consistently co-localized with the apoptotic marker TUNEL after GCI and coincided with a loss of E2 neuroprotection. As a whole, this study supports the "critical period hypothesis" and further suggests that perimenopausal estradiol replacement may prevent neurodegenerative changes in the hippocampus by maintaining favorable Wnt/β-Catenin signaling.

Oestrogen receptor α agonist improved long-term ovariectomy-induced spatial cognition deficit in young rats

Ovariectomy is known as 'surgical menopause' with decreased levels of oestrogen in female rodents and its reported risks and adverse effects include cognitive impairment. In the brain, oestrogen exerts effects through its receptors, oestrogen receptor α (ERα) and β (ERβ). However, the role of ERα or ERβ in ovariectomy-induced cognitive impairment needs further investigation. Here, we observed that bilaterally ovariectomized 3-month-old rats showed obvious spatial learning and memory deficits in the Morris water maze with significant loss of neurons and synapses in the hippocampus. In addition to the rapid decline in serum oestradiol levels, the expression of ERα, but not ERβ, was decreased in the hippocampus starting 1 wk after ovariectomy. Prompt 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT) treatment (1 mg/kg.d), an agonist of ERα, improved the spatial learning and memory ability of ovariectomized rats and rescued ovariectomy-induced neuron loss by up-regulating the level of BCLxl, an important anti-apoptosis protein. Furthermore, PPT treatment also improved ovariectomy-induced hippocampal synapse loss and up-regulated the levels of synaptic proteins (synapsin I, NR2A and GluR1) and the activates of CaMK Πα, ERK and Akt. Thus, these results demonstrated that ERα plays an important role in neuroprotection and that prompt ERα rescue is effective to improve hippocampal-dependent cognition deficit after long-term ovariectomy.

Neuroprotection with non-feminizing estrogen analogues: an overlooked possible therapeutic strategy

Although many of the effects of estrogens on the brain are mediated through estrogen receptors (ERs), there is evidence that neuroprotective activity of estrogens can be mediated by non-ER mechanisms. Herein, we review the substantial evidence that estrogens neuroprotection is in large part non-ER mediated and describe in vitro and in vivo studies that support this conclusion. Also, we described our drug discovery strategy for capitalizing on enhancement in neuroprotection while at the same time, reducing ER binding of a group of synthetic non-feminizing estrogens. Finally, we offer evidence that part of the neuroprotection of these non-feminizing estrogens is due to enhancement in redox potential of the synthesized compounds.

Impact of gender on platelet membrane functions of Alzheimer's disease patients

There are many evidences suggesting that oxidative stress is one of the earliest events in Alzheimer disease (AD) pathogenesis and plays a key role in the development of the AD pathology. The existence of substantial gender-related differences in the clinical features of AD has been recently confirmed (i.e. pathophysiologic features and epidemiologic trends). In addition, study results appear to indicate that the etiopathogenetic mechanisms of AD differ significantly in the 2 sexes. Based on previous results regarding changes in AD platelet plasma membrane, the purpose of the present study was to assess the impact of gender in the same model above reported. In particular we aimed at studying platelets from AD patients (M-AD and F-AD) and matched controls (M-C and F-C), divided into gender, by studying nitric oxide (NO) and peroxynitrite (ONOO(-)) production, the intracellular Ca(2+) concentration ([Ca(2+)]i), membrane Na(+)/K(+)-ATPase activity and fluidity. NO production was significantly elevated in platelets from both F-AD and M-AD compared to matched controls. M-AD showed NO production significantly higher than F-AD and it was the same between M-C and F-C. A similar trend was seen for ONOO(-). Platelets of both M-AD and F-AD had intracellular Ca(2+) concentrations significantly higher than F-C and M-C, while membrane Na(+)/K(+)-ATPase activity showed an opposite trend, but these differences are still significant. M-AD male subjects showed a significantly increased DPH fluorescence anisotropy (r) compared with controls, while for F-AD this discrepancy was not significant. The difference in DHP fluorescence anisotropy remained significant between M-AD and F-AD as well as between M-C and F-C. The TMA-DPH fluorescence anisotropy showed the same trend, but there were no significant differences between M-AD and F-AD, as well as between controls. The results of the current research support the conclusion that F-AD is not at greater risk than M-AD for oxidative stress injuries. Studies on gender differences could lead to a higher probability of improved health outcomes via better-targeted therapies.

A dominant negative ERβ splice variant determines the effectiveness of early or late estrogen therapy after ovariectomy in rats

The molecular mechanisms for the discrepancy in outcome of initiating estrogen therapy (ET) around peri-menopause or several years after menopause in women are unknown. We hypothesize that the level of expression of a dominant negative estrogen receptor (ER) β variant, ERβ2, may be a key factor determining the effectiveness of ET in post-menopausal women. We tested this hypothesis in ovariectomized nine month-old (an age when irregular estrous cycles occur) female Sprague Dawley rats. Estradiol treatment was initiated either 6 days (Early ET, analogous to 4 months post-menopause in humans), or 180 days (Late ET, analogous to 11 years post-menopause in humans) after ovariectomy. Although ERβ2 expression increased in all OVX rats, neurogenic and neuroprotective responses to estradiol differed in Early and Late ET. Early ET reduced ERβ2 expression in both hippocampus and white blood cells, increased the hippocampal cell proliferation as assessed by Ki-67 expression, and improved mobility in the forced swim test. Late ET resulted in either no or modest effects on these parameters. There was a close correlation between the degree of ERβ2 expression and the preservation of neural effects by ET after OVX in rats, supporting the hypothesis that persistent elevated levels of ERβ2 are a molecular basis for the diminished effectiveness of ET in late post-menopausal women. The correlation between the expression of ERβ2 in circulating white blood cells and brain cells suggests that ERβ2 expression in peripheral blood cells may be an easily accessible marker to predict the effective window for ET in the brain.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

To date many aspects of neurons and glia biology remain elusive, due in part to the cellular and molecular complexity of the brain. In recent decades, cell models from different brain areas have been established and proven invaluable toward understanding this complexity. In the field of steroid hormone neurobiology, an important question is: what is the profile of steroid hormone receptor expression in these specific cell lines? Currently, a clear summary of such receptor profiling is lacking. For this reason, we summarized in this review the expression of estrogen, progesterone, and androgen receptors in several widely used cell lines (glial and neuronal) derived from the forebrain and midbrain, based on our own data and that from the literature. Such information will aid in the selection of specific cell lines used to test hypotheses related to the biology of estrogens, progestins, and/or androgens.

Estrogen neuroprotection and the critical period hypothesis

17β-Estradiol (estradiol or E2) is implicated as a neuroprotective factor in a variety of neurodegenerative disorders. This review focuses on the mechanisms underlying E2 neuroprotection in cerebral ischemia, as well as emerging evidence from basic science and clinical studies, which suggests that there is a "critical period" for estradiol's beneficial effect in the brain. Potential mechanisms underlying the critical period are discussed, as are the neurological consequences of long-term E2 deprivation (LTED) in animals and in humans after natural menopause or surgical menopause. We also summarize the major clinical trials concerning postmenopausal hormone therapy (HT), comparing their outcomes with respect to cardiovascular and neurological disease and discussing their relevance to the critical period hypothesis. Finally, potential caveats, controversies and future directions for the field are highlighted and discussed throughout the review.