Does short-term estrogen therapy produce lasting benefits in brain?

Treatments for Breast Cancer That Affect Cognitive Function in Postmenopausal Women

About one of every eight women will develop breast cancer during her lifetime. Approximately a quarter of a million new cancer cases are expected in 2017. Of those breast cancers, 60% to 75% will have characteristics suggesting that estrogens are likely to promote growth of those tumors. Consequently, inhibiting estrogen synthesis is one of the main treatments of choice. Therefore, women must understand the potential adverse effects of those treatments on quality of life. This review discusses (a) the role of estrogens locally synthesized in the brain in laboratory animals and women, (b) the effects of estrogens and blockers of estrogen synthesis on cognitive function, and (c) the limitations in experiments on women taking inhibitors. This article aims to provide women and oncologists with information that will encourage them to consider side effects of aromatase inhibitors (AIs) treatment on the brain.

Effect of Ovarian Hormone Therapy on Cognition in the Aged Female Rhesus Macaque

Studies of the effect of hormone therapy on cognitive function in menopausal women have been equivocal, in part due to differences in the type and timing of hormone treatment. Here we cognitively tested aged female rhesus macaques on (1) the delayed response task of spatial working memory, (2) a visuospatial attention task that measured spatially and temporally cued reaction times, and (3) a simple reaction time task as a control for motor speed. After task acquisition, animals were ovariectomized (OVX). Their performance was compared with intact controls for 2 months, at which time no group differences were found. The OVX animals were then assigned to treatment with either a subcutaneous sham implant (OVX), 17-β estradiol (E) implant (OVX+E) or E implant plus cyclic oral progesterone (OVX+EP). All groups were then tested repeatedly over 12 months. The OVX+E animals performed significantly better on the delayed response task than all of the other groups for much of the 12 month testing period. The OVX+EP animals also showed improved performance in the delayed response task, but only at 30 s delays and with performance levels below that of OVX+E animals. The OVX+E animals also performed significantly better in the visuospatial attention task, particularly in the most challenging invalid cue condition; this difference also was maintained across the 12 month testing period. Simple reaction time was not affected by hormonal manipulation. These data demonstrate that chronic, continuous administration of E can exert multiple beneficial cognitive effects in aged, OVX rhesus macaque females.

SIGNIFICANCE STATEMENT

Hormone therapy after menopause is controversial. We tested the effects of hormone replacement in aged rhesus macaques, soon after surgically-induced menopause [ovariectomy (OVX)], on tests of memory and attention. Untreated ovarian-intact and OVX animals were compared with OVX animals receiving estradiol (E) alone or E with progesterone (P). E was administered in a continuous fashion via subcutaneous implant, whereas P was administered orally in a cyclic fashion. On both tests, E-treated animals performed better than the other 3 experimental groups across 1 year of treatment. Thus, in this monkey model, chronic E administered soon after the loss of ovarian hormones had long-term benefits for cognitive function.

Enhanced striatal β1-adrenergic receptor expression following hormone loss in adulthood is programmed by both early sexual differentiation and puberty: a study of humans and rats

After reproductive senescence or gonadectomy, changes occur in neural gene expression, ultimately altering brain function. The endocrine mechanisms underlying these changes in gene expression beyond immediate hormone loss are poorly understood. To investigate this, we measured changes in gene expression the dorsal striatum, where 17β-estradiol modulates catecholamine signaling. In human caudate, quantitative PCR determined a significant elevation in β1-adrenergic receptor (β1AR) expression in menopausal females when compared with similarly aged males. No differences were detected in β2-adrenergic and D1- and D2-dopamine receptor expression. Consistent with humans, adult ovariectomized female rats exhibited a similar increase in β1AR expression when compared with gonadectomized males. No sex difference in β1AR expression was detected between intact adults, prepubertal juveniles, or adults gonadectomized before puberty, indicating the necessity of pubertal development and adult ovariectomy. Additionally, increased β1AR expression in adult ovariectomized females was not observed if animals were masculinized/defeminized with testosterone injections as neonates. To generate a model system for assessing functional impact, increased β1AR expression was induced in female-derived cultured striatal neurons via exposure to and then removal of hormone-containing serum. Increased β1AR action on cAMP formation, cAMP response element-binding protein phosphorylation and gene expression was observed. This up-regulation of β1AR action was eliminated with 17β-estradiol addition to the media, directly implicating this hormone as a regulator of β1AR expression. Beyond having implications for the known sex differences in striatal function and pathologies, these data collectively demonstrate that critical periods early in life and at puberty program adult gene responsiveness to hormone loss after gonadectomy and potentially reproductive senescence.

Assessing and treating forgetfulness and cognitive problems in adults with HIV

In addition to the immune system, HIV affects the nervous system and the brain, producing neurological sequelae, often resulting in forgetfulness and cognitive problems. These problems can compromise medication adherence, interfere with instrumental activities of daily living such as driving and managing finances, increase dependency, and decrease quality of life. Cognitive problems emerge due to a variety of reasons; likewise, several evidence-based methods to mitigate causes and compensate for cognitive problems can be used alone or in combination. This article focuses on nonpathological, nondementia forgetfulness and cognitive problems. However, dementia must be considered and assessed as measured by marked cognitive decline over time. Methods for assessing and measuring forgetfulness and cognitive problems are provided. In addition, methods of treating nonpathological cognitive problems are provided, ranging from Recommended for Practice to Not Recommended for Practice. A case study is presented to demonstrate how to implement recommended treatment options.

Effects of estrogen on beta-amyloid-induced cholinergic cell death in the nucleus basalis magnocellularis

Alzheimer disease is characterized by accumulation of β-amyloid (Aβ) and cognitive dysfunctions linked to early loss of cholinergic neurons. As estrogen-based hormone replacement therapy has beneficial effects on cognition of demented patients, and it may prevent memory impairments, we investigated the effect of estrogen-pretreatment on Aβ-induced cholinergic neurodegeneration in the nucleus basalis magnocellularis (NBM). We tested which Aβ species induces the more pronounced cholinotoxic effect in vivo. We injected different Aβ assemblies in the NBM of mice, and measured cholinergic cell and cortical fiber loss. Spherical Aβ oligomers had the most toxic effect. Pretreatment of ovariectomized mice with estrogen before Aβ injection decreased cholinergic neuron loss and partly prevented fiber degeneration. By using proteomics, we searched for proteins involved in estrogen-mediated protection and in Aβ toxicity 24 h following injection. The change in expression of, e.g., DJ-1, NADH ubiquinone oxidoreductase, ATP synthase, phosphatidylethanolamine-binding protein 1, protein phosphatase 2A and dimethylarginine dimethylaminohydrolase 1 support our hypothesis that Aβ induces mitochondrial dysfunction, decreases MAPK signaling, and increases NOS activation in NBM. On the other hand, altered expression of, e.g., MAP kinase kinase 1 and 2, protein phosphatase 1 and 2A by Aβ might increase MAPK suppression and NOS signaling in the cortical target area. Estrogen pretreatment reversed most of the changes in the proteome in both areas. Our experiments suggest that regulation of the MAPK pathway, mitochondrial pH and NO production may all contribute to Aβ toxicity, and their regulation can be prevented partly by estrogen pretreatment.

What can development teach us about menopause?

Development and aging are often mirror image processes and this may be equally true in the effects of estradiol, a potent endogenous steroid regulating brain development as well as a therapeutic used to relieve the negative components of perimenopause. Both the developing and perimenopausal brain are characterized by a sensitive period of hormone responsiveness, and in both cases, the neurotransmitters GABA and glutamate, as well as synaptogenesis and cell proliferation are major hormone targets. This review compares and contrasts the effects of estradiol on the developing and aging brain and highlights new avenues of exploration and therapeutic development.

Duration of estrogen deprivation, not chronological age, prevents estrogen's ability to enhance hippocampal synaptic physiology

Whether estrogen replacement is beneficial to cognitive health is controversial. Some studies have shown that estrogen replacement therapy (ERT) relieves memory impairment associated with menopause in women, whereas others suggest that estrogen not only is incapable of providing a benefit, but actually can be detrimental. One possible explanation for this discrepancy in study findings could be the varying time after menopause at which ERT is initiated. It has been proposed that a critical period exists during which ERT must be administered to enhance cognitive function. This idea has yet to be tested directly using functional synaptic studies, however. Here we investigated whether prolonged hormone deprivation caused by ovariectomy (OVX) in young adult rats prevents the ability of estrogen replacement to increase synaptic function in the hippocampus to a degree necessary for estrogen-induced improvement in learning and memory. Remarkably, estrogen replacement was found to increase long-term potentiation, the current mediated by NR2B-containing NMDA receptors, and the dendritic spine density at CA3-CA1 synapses up to 15 months post-OVX. However, by 19 months post-OVX, the same estrogen replacement was unable to induce these changes. Importantly, this loss of estrogen's effectiveness was seen to be a consequence of the duration of deprivation. In female rats aged with their ovaries intact and examined at the same chronological age as the 19-month post-OVX group, estrogen replacement significantly increased synaptic function and spine density. These data clearly demonstrate that a critical period exists during which ERT must be administered, and that once this period passes, the beneficial effects are lost.

LIM kinase mediates estrogen action on the actin depolymerization factor Cofilin

The ovarian hormone estrogen increases the axospinous synapse density in the hippocampal CA1 region of young female rats but fails to do so in aged rats. This estrogen-mediated alteration of spine synapse structures suggests the coincident requirement for the structural reorganization of the underlying actin cytoskeleton network. Actin reorganization is known to require the deactivation of Cofilin, an actin depolymerization factor. Cofilin is deactivated by LIM kinase (LIMK), and LIMK activity is modulated by the phosphorylation of specific residues. We have previously demonstrated that estrogen is able to increase phosphorylated LIMK (pLIMK) immunoreactivity (IR) in the hippocampus in vivo and that this estrogen-stimulated pLIMK-IR is decreased in the aged brain. Because Cofilin phosphorylation allows for actin filament elongation and spine synapse growth, we sought to determine if estrogen acts through Cofilin and if such estrogen action requires the observed LIMK activity. Using both hippocampal neurons and the NG108-15 neuroblastoma cell line, we demonstrate here that estrogen stimulates the phosphorylation of Cofilin in vitro. Furthermore, this estrogen action on Cofilin requires LIMK. Lastly, while initiating the phosphorylation of LIMK and Cofilin, estrogen can also stimulate the formation of filopodial extensions, an early step in the formation of nascent spines, demonstrating that estrogen can alter the actin-dependent neuronal morphology. This linkage of estrogen communication to Cofilin via LIMK provides the functionality to the age-sensitive pLIMK-IR that we have observed in vivo.