Hormone replacement therapy to maintain cognitive function in women with dementia

Role of Sex Hormones on Brain Mitochondrial Function, with Special Reference to Aging and Neurodegenerative Diseases

The mitochondria have a fundamental role in both cellular energy supply and oxidative stress regulation and are target of the effects of sex steroids, particularly the neuroprotective ones. Aging is associated with a decline in the levels of different steroid hormones, and this decrease may underline some neural dysfunctions. Besides, modifications in mitochondrial functions associated with aging processes are also well documented. In this review, we will discuss studies that describe the modifications of brain mitochondrial function and of steroid levels associated with physiological aging and with neurodegenerative diseases. A special emphasis will be placed on describing and discussing our recent findings concerning the concomitant study of mitochondrial function (oxidative phosphorylation, oxidative stress) and brain steroid levels in both young (3-month-old) and aged (20-month-old) male and female mice.

Progesterone, compared to medroxyprogesterone acetate, to C57BL/6, but not 5α-reductase mutant, mice enhances object recognition and placement memory and is associated with higher BDNF levels in the hippocampus and cortex

Progesterone (P4) may influence cognition in part through actions of its 5α-reduced metabolite, allopregnanolone. Ovariectomized mice that were C57BL/6 wildtype (WT), or deficient in the 5α-reductase Type 1 enzyme (5α-reductase knockout; 5αRKO), were administered vehicle, P4, allopregnanolone, or medroxyprogesterone acetate (MPA) after training in the object recognition or placement tasks. WT mice administered P4 or allopregnanolone performed significantly better in the object recognition and placement tasks than did WT mice administered vehicle or MPA. 5αRKO mice administered allopregnanolone, but not P4, MPA, or vehicle showed enhanced performance in the object recognition and placement tasks. Levels of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex and hippocampus were lowest among mice administered MPA. Thus, some of P4s effects to enhance cognitive performance may be incumbent upon its 5α-reduction.

Pharmacological Treatment of Alzheimer's Disease: Is it Progressing Adequately?

INTRODUCTION

Between 1993 and 2000 four acetylcholinesterase inhibitors were marketed as a symptomatic treatment for Alzheimer's disease (AD), as well as memantine in 2003. Current research is focused on finding drugs that favorably modify the course of the disease. However, their entrance into the market does not seem to be imminent.

RESEARCH DEVELOPMENT

The aim of AD research is to find substances that inhibit certain elements of the AD pathogenic chain (beta- and gamma-secretase inhibitors, alpha-secretase stimulants, beta-amyloid aggregability reducers or disaggregation and elimination inductors, as well as tau-hyperphosphorylation, glutamate excitotoxicity, oxidative stress and mitochondrial damage reducers, among other action mechanisms). Demonstrating a disease's retarding effect demands longer trials than those necessary to ascertain symptomatic improvement. Besides, a high number of patients (thousands of them) is necessary, all of which turns out to be difficult and costly. Furthermore, it would be necessary to count on diagnosis and progression markers in the disease's pre-clinical stage, markers for specific phenotypes, as well as high-selectivity molecules acting only where necessary. In order to compensate these difficulties, drugs acting on several defects of the pathogenic chain or showing both symptomatic and neuroprotective action simultaneously are being researched.

CONCLUSIONS

There are multiple molecules used in research to modify AD progression. Although it turns out to be difficult to obtain drugs with sufficient efficacy so that their marketing is approved, if they were achieved they would lead to a reduction of AD prevalence.

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.

Present and prospective clinical therapeutic regimens for Alzheimer's disease

Alzheimer's disease (AD) is an incurable neurodegenerative disorder that produces cognitive impairments that increase in severity as the disease progresses. The clinical symptoms are related to the presence of neuritic plaques and neurofibrillary tangles in the cerebral cortex which represent the pathophysiological hallmarks of AD. The debilitating nature of the disease can result in clinical burden for the patient, emotional strain for those that care for patients with Alzheimer's, and significant financial burden to society. The goals of current treatments, such as cholinesterase inhibitors and N-methyl-D-aspartate receptor antagonist, are to reduce the severity or slow the progression of cognitive symptoms. Although these treatments have demonstrated modest clinical benefit, they are unable to prevent, prohibit, or reverse the underlying pathophysiology of AD. Considerable progress has been made toward the development of disease-modifying treatments. Treatments currently under development mainly target the production, aggregation, and removal of existing amyloid beta-peptide aggregates which are believed to instigate the overall development of the neuropathology. Additional strategies that target tau pathology are being studied to promote neural protection against AD pathology. The current research has continued to expand our knowledge toward the development of disease modifying Alzheimer's therapies; however, no specific treatment strategy capable of demonstrating empirical efficacy and safety has yet to emerge.

Hormonal treatment, mild cognitive impairment and Alzheimer's disease

A plethora of in vitro and in vivo studies have supported the neuroprotective role of estrogens and their impact on the neurotransmitter systems implicated in cognition. Recent hormonal replacement therapy (HRT) trials in non-demented postmenopausal women suggest a temporary positive effect (notably on verbal memory), and four meta-analyses converge to suggest a possible protective effect in relation to Alzheimer's disease (reducing risk by 29 to 44%). However, data from the only large randomized controlled trial published to date, the Women's Health Initiative Memory Study, did not confirm these observations and have even suggested an increase in dementia risk for women using HRT compared to controls. Apart from methodological differences, one key shortcoming of this trial has probably been the focus on late-onset (postmenopausal) hormonal changes, i.e. at a time when the neurodegenerative process has already begun and without taking into account individual lifetime exposure to hormone variability. Multifactorial models based on an exhaustive view of all hormonal events throughout the reproductive life (rather than on a specific exposure to a given steroid) together with other risk factors (notably genetic risk factors related to estrogen receptor polymorphisms) should be explored to clarify the role of hormonal risk factors, or protective factors for cognitive dysfunction and dementia.

Increased glucose levels are associated with episodic memory in nondiabetic women

OBJECTIVE

Patients with type 2 diabetes have an increased risk of a reduction in cognitive function. We investigated the hypothesis that plasma glucose is associated with a reduction in episodic and/or semantic memory already in nondiabetic subjects.

RESEARCH DESIGN AND METHODS

We linked two large population-based datasets in Sweden: the Betula study, in which a random sample from the population aged 35-85 years was investigated for cognitive function, including episodic and semantic memory; and the Västerbotten Intervention Program, a health survey with subjects aged 40, 50, and 60 years, that includes measuring of fasting and 2-h plasma glucose, along with other risk factors for diabetes and cardiovascular disease. We identified 411 (179 men and 232 women, mean age 50.6 +/- 8.0 years) nondiabetic subjects, free from dementia, who had participated in the two surveys within 6 months.

RESULTS

Women had better episodic (score 7.37 +/- 1.42) and semantic memory (score 16.05 +/- 2.76) than men (score 6.59 +/- 1.29 and 15.15 +/- 2.92, respectively, P < 0.001 for both). In an adjusted multivariate model, fasting plasma glucose (fPG) and 2-h plasma glucose (2hPG) were significantly negatively associated with episodic memory (fPG: B -0.198, SE 0.068, beta -0.209, P = 0.004; and 2hPG: B -0.061, SE 0.031, beta -0.148, P = 0.048, respectively) in women but not in men. The association was not found in relation to semantic memory.

CONCLUSIONS

We conclude that an increase in plasma glucose is associated with impairment in episodic memory in women. This could be explained by a negative effect on the hippocampus caused by raised plasma glucose levels.

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 RCTs on cognitive function in postmenopausal women.

SEARCH STRATEGY

The CDCIG Specialized Register was searched 7 March 2006. Additional searches were made of MEDLINE (1966-2006/02); EMBASE (1985-2006/02); PsycINFO (1967-2006/02) and CINAHL (1982-2006/01).

SELECTION CRITERIA

All double-blind RCTs 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

Selection of studies, assessment of quality and extraction of data were undertaken independently by three reviewers with disagreements resolved by discussion.

MAIN RESULTS

In total, 24 trials were included, but only 16 (10,114 women) had analysable data. Meta-analyses showed no effects of either ERT or HRT on prevention of cognitive impairment after five and four years of treatment, respectively (odds ratio 1.34, 95% CI 0.95 to 1.9; odds ratio 1.05, 95% CI 0.72 to 1.54 respectively) (trend favouring control in both instances). Analyses assessing the effects of treatment over time found that both ERT and HRT did not maintain or improve cognitive function and may even adversely affect this outcome (WMD = -0.45, 95% CI -0.99 to 0.09; WMD = -0.16, 95% CI -0.58 to 0.26, respectively at maximum follow up). Negative effects were found for ERT after one year and HRT after three and four years of therapy. Results from smaller trials assessing effects on individual cognitive domains mostly reported no evidence of benefit.

AUTHORS' CONCLUSIONS

There is good evidence that both ERT and HRT do not prevent cognitive decline in older postmenopausal women when given as short term or longer term (up to five years) therapy. It is not known whether either specific types of ERT or HRT have specific effects in subgroups of women, although there was evidence that combined hormone therapy in similarly aged women was associated with a decrement in a number of verbal memory tests and a small improvement in a test of figural memory. There is insufficient evidence to determine whether subgroups of women using specific types of hormone therapy could benefit from treatment. It remains to be determined whether factors such as younger age (< 60 years of age), type of menopause (surgical or natural) and type of treatment (type of estrogen with or without a progestagen), mode of delivery (transdermal, oral or intramuscular) and dosage have positive effects at a clinically relevant level. In addition, whether the absence or presence of menopausal symptoms can modify treatment effects should be investigated in more detail. Large RCTs currently underway in the USA may be able to provide answers to these uncertainties by the year 2010. In the meantime, based on the available evidence, ERT or HRT cannot be recommended for overall cognitive improvement or maintenance in older postmenopausal women without cognitive impairment.

Dementia syndromes: evaluation and treatment

As our population ages, diseases affecting memory and daily functioning will affect an increasing number of individuals, their families and the healthcare system. The social, financial and economic impacts will be profound. This article provides an overview of current dementia syndromes to assist clinicians in evaluating, educating and treating these patients.

Combination therapy in Alzheimer's disease: a review of current evidence

Treating dementia has become a major challenge in clinical practice. Presently, acetylcholinesterase inhibitors are the first-line drugs in the treatment of Alzheimer's disease (AD). These options are now complemented by memantine, which is approved for the treatment of moderate-to-severe AD. Altogether, a minimum of six agent classes already exist, all of which are approved for clinical use and are either already being tested or ready for phase III clinical trials for the treatment of AD. These include cholinesterase inhibitors, blockers of the NMDA receptor, antioxidants or blockers of oxidative deamination (including Gingko biloba), anti-inflammatory agents, neurotrophic factors (including hormone replacement therapy and drugs acting on insulin signal transduction) and antiamyloid agents (including cholesterol-lowering therapy). These approaches hold promise for disease modification and have a potential to be used as combination therapy for cognitive enhancement. Presently, only nine clinical studies have been published that have investigated the effects of a combination regimen on cognitive performance or AD. Among those, one study was conducted in elderly cognitively intact persons; the others involved patients with AD. Only five of the treatment studies followed a randomised, controlled design. Not all studies favoured the superior efficacy of combination therapy over monotherapy. Some studies, however, showed some evidence for synergistic combination effects of symptomatic therapy, including delay or prevention of disease progression in AD patients. In addition, six studies investigated the effects of AChE inhibitor in combination with antipsychotic or antidepressant therapy on behavioural aspects of AD symptomatology. In four of those studies there were indications that combination therapy had greater efficacy over monotherapy. The treatment of AD patients requires optimised options for all stages of illness based on the available drugs. There is a great need for further well designed studies on combination therapy in AD.

Estrogen enhances potassium-stimulated acetylcholine release in the rat hippocampus

Short-term estrogen replacement has been shown to enhance basal forebrain cholinergic function. Whether or not long-term estrogen replacement can enhance basal forebrain cholinergic function has been questioned in light of recent studies showing that several cholinergic measures which are increased following short-term treatment are not increased following longer-term (>30 days) treatment. In the present study, in vivo microdialysis was used to assess the effects of continuous estradiol replacement on basal forebrain cholinergic function. Our data show that 6-7 weeks of continuous estradiol replacement significantly enhanced potassium-stimulated acetylcholine release in the hippocampus of ovariectomized rats, and that this effect was reversed following discontinuation of the estrogen treatment. These data are consistent with the hypothesis that estrogen-mediated effects on cholinergic neurons can contribute to the effects of long-term estrogen replacement on cognitive performance recently described.