Treatment for MCI

High-Frequency rTMS Improves Visual Working Memory in Patients With aMCI: A Cognitive Neural Mechanism Study

BACKGROUND

Visual working memory (VWM), which is an essential component of higher cognitive processes, declines with age and is associated with the progression from amnestic mild cognitive impairment (aMCI) to Alzheimer's disease (AD). Cognitive impairment, particularly in VWM, is prominent in aMCI and may indicate disease progression. This study investigates the cognitive neural mechanisms responsible for VWM impairment in aMCI, with a focus on identifying the VWM processing stages affected. The study targets the dorsolateral prefrontal cortex (DLPFC) for repetitive transcranial magnetic stimulation (rTMS) to investigate its influence on VWM in aMCI patients. The role of the DLPFC in the top-down control of VWM processing is central to understanding rTMS effects on the stages of information processing in aMCI-related VWM impairments.

METHODS

A 7-day rTMS intervention was performed in 25 aMCI patients and 15 healthy elderly controls to investigate its effects on VWM and cognitive functions. Tasks included VWM change detection, digital symbol transformation, and the Stroop task for attention and executive functions. EEG analyses consisting of ERP, ERSP, and functional connectivity (wPLI) were integrated. The first part of the study addressed the cognitive neural mechanism of VWM impairment in aMCI and differentiated the processing stages using EEG. The second part investigated the effects of rTMS on EEG processing at different VWM stages and revealed cognitive neural mechanisms that improve visual working memory in aMCI.

RESULTS

The results indicated a significant deterioration of VWM tasks in aMCI, especially in accuracy and memory capacity, with prolonged reaction time and increased duration of the Stroop task. In the VWM memory encoding phase, N2pc amplitude, α-oscillation in the parieto-occipital region, and θ-band synchronization in the frontoparietal connectivity decreased. Conversely, rTMS improved N2pc amplitude, α-oscillation, and θ-band synchronization, which correlated with improved frontoparietal connectivity, parieto-occipital α-oscillation, and attentional capacity.

CONCLUSIONS

Patients with aMCI experience significant deterioration in VWM function, particularly during the encoding phase. This deterioration manifests in reduced accuracy and capacity of memory performance, accompanied by a significant decrease in N2pc amplitude, alpha oscillations, and theta-band connectivity in frontoparietal and fronto-occipital brain regions. rTMS proves to be a promising intervention that improves VWM, attention, and executive functions. In particular, it supports attention during target selection by increasing N2pc amplitude during encoding, enhancing alpha oscillations for better suppression of irrelevant information, and increasing synchronization in frontoparietal and occipital functional connectivity, which ultimately improves visual working memory.

Comparative efficacy of intermittent theta burst stimulation and high-frequency repetitive transcranial magnetic stimulation in amnestic mild cognitive impairment patients

Intermittent theta burst stimulation, a derivative of repetitive transcranial magnetic stimulation, has been applied to improve cognitive deficits. However, its efficacy and mechanisms in enhancing cognitive function in patients with amnestic mild cognitive impairment compared with traditional repetitive transcranial magnetic stimulation paradigms remain unclear. This study recruited 48 amnestic mild cognitive impairment patients, assigning them to intermittent theta burst stimulation, repetitive transcranial magnetic stimulation, and sham groups (5 times/wk for 4 wk). Neuropsychological assessments and functional magnetic resonance imaging data were collected pre- and post-treatment. Regarding efficacy, both angular gyrus intermittent theta burst stimulation and repetitive transcranial magnetic stimulation significantly improved general cognitive function and memory compared to the sham group, with no significant difference between the 2 treatment groups. Mechanistically, significant changes in brain activity within the temporoparietal network were observed in both the intermittent theta burst stimulation and repetitive transcranial magnetic stimulation groups, and these changes correlated with improvements in general cognitive and memory functions. Additionally, intermittent theta burst stimulation showed stronger modulation of functional connectivity between the hippocampus, parahippocampal gyrus, and temporal regions compared to repetitive transcranial magnetic stimulation. The intermittent theta burst stimulation and repetitive transcranial magnetic stimulation can improve cognitive function in amnestic mild cognitive impairment patients, but intermittent theta burst stimulation may offer higher efficiency. Intermittent theta burst stimulation and repetitive transcranial magnetic stimulation likely enhance cognitive function, especially memory function, by modulating the temporoparietal network.

Cognitive Intervention Using Information and Communication Technology for Older Adults with Mild Cognitive Impairment: A Systematic Review and Meta-Analysis

Background: Outside activities have decreased due to the spread of the COVID-19 since 2019; therefore, the need for education using information and communication technology (ICT) for older adults with mild cognitive impairment (MCI) has increased. This study systematically evaluated the effects of cognitive enhancement interventions using ICT on older adults with MCI. Methods: Six electronic databases (CINAHL, Cochrane CENTRAL, EMBASE, PubMed, RISS, and KISS) were searched for relevant articles published from 25 January to 10 February, 2021. Results: As a result of the systematic literature review, 12 research papers were finally selected as the literature for quality evaluation, and 11 final papers were selected, excluding one in the quality evaluation. From the synthesis in this study, it was found that cognitive intervention using ICT showed a statistically significant positive effect on cognitive function when compared with various control groups (SMD = 0.4547; p < 0.001; 95% CI: 0.1980–0.7113). Conclusions: Through this study, cognitive intervention using ICT showed a small effect size for older adults with mild cognitive impairment, and statistically significant results were found.

Cognitive reserve and the effects of virtual reality-based cognitive training on elderly individuals with mild cognitive impairment and normal cognition

BACKGROUND

Cognitive reserve (CR) is a concept proposed to account for discrepancies between the extent of brain pathology and clinical manifestations of that pathology. This study aimed to explore the associations between CR and the effects of cognitive training using fully immersive virtual reality (VR).

METHODS

A total of 44 older adults (22 cognitively normal, 22 with mild cognitive impairment) underwent eight cognitive training sessions using VR for a period of 4 weeks. CR was assessed using the Cognitive Reserve Index questionnaire (CRIq). To evaluate baseline cognitive function and the effects of VR training, the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuropsychological battery was administered to all participants before and after the training.

RESULTS

Greater improvement in the total CERAD score was seen for cognitively normal participants with higher versus lower scores on the Education subdomain of the CRIq. Among patients with mild cognitive impairment, none of the CRIq subdomain scores (Education, Working Activity, Leisure Time) were related to a change in CERAD total scores. The CRIq total score did not predict the improvement of global cognition in either group.

CONCLUSIONS

This study revealed different impacts of CR on cognitive training according to the participants' cognitive status. It also suggests that employing three proxies of CR rather than using a composite score would provide a more accurate understanding of one's CR.

Cognitive Frailty and Its Association with All-Cause Mortality Among Community-Dwelling Older Adults in Taiwan: Results from I-Lan Longitudinal Aging Study

The definition of cognitive frailty and its prediction for adverse outcome of community-living older adults remains controversial. This study aims to evaluate the association between cognitive frailty and all-cause mortality among community-living older adults. Data of the I-Lan Longitudinal Aging Study (ILAS) were retrieved for study. Frailty was defined by Fried's criteria, and a series of neuropsychological assessments, including the Mini-Mental State Examination, Center for Epidemiology Studies-Depression, the delayed free recall in the Chinese Version Verbal Learning Test, the Boston Naming Test, the category (animal) Verbal Fluency Test, the Taylor Complex Figure Test, the digital backward, and the Clock Drawing Test were performed. All participants received blood sampling after 10-hour overnight fast for various biochemical markers. Cognitive frailty was defined as the concomitant presence of dynapenia and cognitive declines in any domains. Overall, data of 678 participants aged 65 years and older (mean age: 73.3 ± 5.3 years) were obtained for the study. The prevalence of cognitive frailty in this study was 13.3%. People with cognitive frailty were significantly older, having higher multimorbidity burden, more likely to be women, and had less skeletal muscle mass. Adjusted for age and gender, both dynapenia without cognitive impairment (hazard ratio [HR]: 5.402; 95% confidence interval [CI]: 1.463-19.954; p = 0.011) and cognitive frailty (HR: 6.682; 95% CI: 1.803-26.116; p = 0.005) were significantly associated with all-cause mortality. The prevalence of cognitive frailty was 13.3% in Taiwan and was predictive for all-cause mortality. Further study is needed to explore the pathophysiology and reversibility of cognitive frailty.

Calf Circumference as a Screening Tool for Cognitive Frailty in Community-Dwelling Older Adults: The Korean Frailty and Aging Cohort Study (KFACS)

The aim of this study was to examine calf circumference in relation to cognitive frailty in community-dwelling older adults. Cross-sectional analysis was performed on the first-year baseline data of 1559 adults aged 70–84 years enrolled in the Korean Frailty and Aging Cohort Study. The final analysis included 1221 adults who were non-dependent in terms of instrumental activities of daily living, who underwent frailty and cognitive function assessments. Physical frailty was defined using the Fried Frailty Index. Cognitive impairment was defined as a score 1.5 standard deviations below the age-, sex- and education-matched norms on any of four cognitive-function tests. The prevalence of cognitive frailty was 2.8% for men and 3.8% for women. After adjusting for potential confounders, in comparison to the “physically robust without cognitive impairment” group, the estimates of increased odds ratios (ORs) for low calf circumference (<32 cm) were much greater in the prefrail with cognitive impairment (OR 4.62, 95% confidence interval (CI): 2.02–10.61) and frail with cognitive impairment (OR 10.94, 95% CI: 2.87–41.68) groups in men but not in women. Low calf circumference was strongly related to cognitive frailty in men only, suggesting calf circumference can be used as an indicator of these outcomes.

Cognitive frailty predicting all-cause mortality among community-living older adults in Taiwan: A 4-year nationwide population-based cohort study

BACKGROUND

Cognitive frailty (CF) featured as frailty plus cognitive impairment was deemed to be a novel target for dementia and disable prevention. The study was intended to investigate the epidemiology of CF and the association between CF and all-cause mortality.

METHODS

The national representative cohort study was comprised of 1,103 community-living middle-aged and older adults. CF was defined as the co-existence of dynapenia (weakness and/or slowness) and cognitive impairment (1.5 standard deviations below the age-, sex- and education-matched norms in cognitive tests) without known neurodegenerative diseases. Dynapenia was defined by the Asian Working Group for Sarcopenia and cognitive function was assessed by the Short Portable Mental Status Questionnaire.

RESULTS

The prevalence of CF was 8.6% in this study. Subjects with CF were older, more likely to be women, having less regular exercise, fewer educational years, more depressive symptoms and greater multimorbidity. Compared to robust individuals, CF was significantly associated with all-cause mortality (HR: 3.1, 95% CI:1.3-7.7, p = 0.012).

CONCLUSION

Dynapenia and cognitive impairment synergistically contribute to the mortality risk for the participants in this study. Further study is needed to explore the underlying pathophysiology and the reversibility of CF.

Cognitive frailty, a novel target for the prevention of elderly dependency

Frailty is a complex and heterogeneous clinical syndrome. Cognitive frailty has been considered as a subtype of frailty. In this study, we refine the definition of cognitive frailty based on existing reports about frailty and the latest progress in cognition research. We obtain evidence from the literature regarding the role of pre-physical frailty in pathological aging. We propose that cognitive impairment of cognitive frailty results from physical or pre-physical frailty and comprises two subtypes: the reversible and the potentially reversible. Reversible cognitive impairment is indicated by subjective cognitive decline (SCD) and/or positive fluid and imaging biomarkers of amyloid-β accumulation and neurodegeneration. Potentially reversible cognitive impairment is MCI (CDR=0.5). Based on the severity of cognitive impairment, it is possible to determine the primary and secondary preventative measures for cognitive frailty. We further determine whether SCD is a component of pre-clinical AD or the early stage of other neurodegenerative diseases, which is required for guiding personal clinical intervention.

Effect of handball training on cognitive ability in elderly with mild cognitive impairment

The aim was to examine the effect of handball training on cognitive ability in elderly with mild cognitive impairment. A total of 60 elderly were randomly divided into training group (n=30) and control group (n=30). The mini-mental state examination (MMSE) score and abilities of daily living scale (ADL) score before, after 3-month, and after 6-month intervention period was measured. The results showed that MMSE score was increased and ADL score was decreased in training group after 3-month and 6-month intervention (P<0.05), while there were no significant changes in MMSE or ADL in control group (P£3/40.05). These preliminary results indicated that handball training can improve cognitive ability in elderly with MCI.

Cognitive interventions targeting subjective cognitive complaints

Subjective cognitive complaints (SCCs) are being increasingly recognized as a preclinical phase of dementia. Thus, SCCs may represent a "promising" stage for planning and implementing preventive interventions aimed at reducing the incidence of cognitive disorders. The aim of the present study is to present and discuss the available evidence coming from clinical trials adopting cognitive interventions in individuals with SCCs. A systematic review of literature was conducted to evaluate the available trials testing nonpharmacological cognitive interventions for the prevention of dementia in subjects with SCCs. Six studies were included in the present study. Overall, most interventions showed to objectively improve cognitive performance in subjects with SCCs. A relevant heterogeneity was found concerning their characteristics and feasibility. Conversely, there is a current lack of evidence in the literature about the efficacy of nonpharmacological cognitive interventions for preventing dementia or cognitive impairment.

Cognitive frailty: rational and definition from an (I.A.N.A./I.A.G.G.) international consensus group

The frailty syndrome has recently attracted attention of the scientific community and public health organizations as precursor and contributor of age-related conditions (particularly disability) in older persons. In parallel, dementia and cognitive disorders also represent major healthcare and social priorities. Although physical frailty and cognitive impairment have shown to be related in epidemiological studies, their pathophysiological mechanisms have been usually studied separately. An International Consensus Group on "Cognitive Frailty" was organized by the International Academy on Nutrition and Aging (I.A.N.A) and the International Association of Gerontology and Geriatrics (I.A.G.G) on April 16th, 2013 in Toulouse (France). The present report describes the results of the Consensus Group and provides the first definition of a "Cognitive Frailty" condition in older adults. Specific aim of this approach was to facilitate the design of future personalized preventive interventions in older persons. Finally, the Group discussed the use of multidomain interventions focused on the physical, nutritional, cognitive and psychological domains for improving the well-being and quality of life in the elderly. The consensus panel proposed the identification of the so-called "cognitive frailty" as an heterogeneous clinical manifestation characterized by the simultaneous presence of both physical frailty and cognitive impairment. In particular, the key factors defining such a condition include: 1) presence of physical frailty and cognitive impairment (CDR=0.5); and 2) exclusion of concurrent AD dementia or other dementias. Under different circumstances, cognitive frailty may represent a precursor of neurodegenerative processes. A potential for reversibility may also characterize this entity. A psychological component of the condition is evident and concurs at increasing the vulnerability of the individual to stressors.

Therapy Techniques for Mild Cognitive Impairment

There is increasing concern among people in late middle age about cognitive changes they experience for everyday memory tasks. They are especially fearful that these memory lapses signal the beginning stages of Alzheimer’s disease (AD). For some, the diagnosis of mild cognitive impairment (MCI) represents a transitional state between normal aging and early dementia that precipitates a search for therapies to prevent conversion to AD. The purpose of this article is to describe a continuum of therapeutic approaches for the cognitive challenges experienced by persons with MCI, discuss the growing evidence for promising techniques to address these challenges, and outline a university-based memory strategies intervention program that incorporates several effective strategies.

Benefits of training working memory in amnestic mild cognitive impairment: specific and transfer effects

BACKGROUND

A growing number of studies are attempting to understand how effective cognitive interventions may be for patients with amnestic mild cognitive impairment (aMCI), particularly in relation to their memory problems.

METHODS

The present study aimed to explore the benefits of a working memory (WM) training program in aMCI patients. Patients (N = 20) were randomly assigned to two training programs: the experimental group practiced with a verbal WM task, while the active control group conducted educational activities on memory.

RESULTS

Results showed that the aMCI patients completing the WM training obtained specific gains in the task trained with some transfer effects on other WM measures (visuospatial WM) and on processes involved in or related to WM, e.g. fluid intelligence (the Cattell test) and long-term memory. This was not the case for the aMCI control group, who experienced only a very limited improvement.

CONCLUSION

This pilot study suggests that WM training could be a valuable method for improving cognitive performance in aMCI patients, possibly delaying the onset of Alzheimer's disease.

Cognitive intervention in amnestic Mild Cognitive Impairment: a systematic review

Mild Cognitive Impairment (MCI) represents a transitional state between normal aging and early dementia and is commonly associated with memory impairment (amnestic or A-MCI). Several studies have investigated therapeutic approaches to A-MCI, including cholinestherase inhibitors (I-ChEs), although this practice is still controversial. Thus, there is a current need to determine the effects of cognitive interventions either in combination with I-ChEs or alone. To assess the efficacy of such treatments, neuropsychological instruments and self-evaluated scoring of memory, mood, daily life activities and quality of life are employed. Recently, some studies have used functional magnetic resonance imaging (fMRI) in order to understand the neurobiological effects of these interventions. The aim of this systematic review is to investigate the effectiveness of cognitive interventions on the enhancement of learning abilities as well as their impacts on cognitive measurements of mood, everyday functioning and functional neuroimaging. This review also focused on the methodological aspects of such studies and attempted to introduce new perspectives on cognitive interventions in this population. The authors concluded that a-MCI patients are capable to learn new information and memory strategies. Although findings in standardized neuropsychological tests are limited, non-standardized cognitive measures and subjective measures show significant changes. Furthermore, fMRI reveals changes in the patterns of brain activation and increase of connectivity.

Cognitive intervention for persons with mild cognitive impairment: A meta-analysis

Cognitive training for persons with mild cognitive impairment (MCI) has become a hot topic. However to date it remains controversial whether persons with MCI can really benefit from cognitive intervention. We aim to further investigate this by using meta-analysis of seventeen clinical studies of cognitive intervention for MCI. The results demonstrate that after training, patients with MCI improve significantly both in overall cognition and overall self-ratings. Specifically, persons with MCI obtain moderate benefits in language, self-rated anxiety and functional ability, and receive mild benefits in episodic memory, semantic memory, executive functioning/working memory, visuo-spatial ability, attention/processing speed, MMSE, self-rated memory problem, quality of life, activities of daily life and self-rated depression. The results also suggest that persons with MCI benefit from the cognitive intervention in the follow-up data. The present meta-analysis demonstrates that cognitive intervention can be a potential efficient method to enhance cognitive and functional abilities in persons with MCI, although the improvements may be domain-specific.

The fate of the 0.5s: predictors of 2-year outcome in mild cognitive impairment

Impairments in executive cognition (EC) may be predictive of incident dementia in patients with mild cognitive impairment (MCI). The present study examined whether specific EC tests could predict which MCI individuals progress from a Clinical Dementia Rating (CDR) score of 0.5 to a score ≥1 over a 2-year period. Eighteen clinical and experimental EC measures were administered at baseline to 104 MCI patients (amnestic and non-amnestic, single- and multiple-domain) recruited from clinical and research settings. Demographic characteristics, screening cognitive measures and measures of everyday functioning at baseline were also considered as potential predictors. Over the 2-year period, 18% of the MCI individuals progressed to CDR ≥ 1, 73.1% remained stable (CDR = 0.5), and 4.5% reverted to normal (CDR = 0). Multiple-domain MCI participants had higher rates of progression to dementia than single-domain, but amnestic and non-amnestic MCIs had similar rates of conversion. Only three EC measures were predictive of subsequent cognitive and functional decline at the univariate level, but they failed to independently predict progression to dementia after adjusting for demographic, other cognitive characteristics, and measures of everyday functioning. Decline over 2 years was best predicted by informant ratings of subtle functional impairments and lower baseline scores on memory, category fluency, and constructional praxis.

Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial

Background

An increased rate of brain atrophy is often observed in older subjects, in particular those who suffer from cognitive decline. Homocysteine is a risk factor for brain atrophy, cognitive impairment and dementia. Plasma concentrations of homocysteine can be lowered by dietary administration of B vitamins.

Objective

To determine whether supplementation with B vitamins that lower levels of plasma total homocysteine can slow the rate of brain atrophy in subjects with mild cognitive impairment in a randomised controlled trial (VITACOG, ISRCTN 94410159).

Methods and Findings

Single-center, randomized, double-blind controlled trial of high-dose folic acid, vitamins B₆ and B₁₂ in 271 individuals (of 646 screened) over 70 y old with mild cognitive impairment. A subset (187) volunteered to have cranial MRI scans at the start and finish of the study. Participants were randomly assigned to two groups of equal size, one treated with folic acid (0.8 mg/d), vitamin B₁₂ (0.5 mg/d) and vitamin B₆ (20 mg/d), the other with placebo; treatment was for 24 months. The main outcome measure was the change in the rate of atrophy of the whole brain assessed by serial volumetric MRI scans.

Results

A total of 168 participants (85 in active treatment group; 83 receiving placebo) completed the MRI section of the trial. The mean rate of brain atrophy per year was 0.76% [95% CI, 0.63–0.90] in the active treatment group and 1.08% [0.94–1.22] in the placebo group (P = 0.001). The treatment response was related to baseline homocysteine levels: the rate of atrophy in participants with homocysteine >13 µmol/L was 53% lower in the active treatment group (P = 0.001). A greater rate of atrophy was associated with a lower final cognitive test scores. There was no difference in serious adverse events according to treatment category.

Conclusions and Significance

The accelerated rate of brain atrophy in elderly with mild cognitive impairment can be slowed by treatment with homocysteine-lowering B vitamins. Sixteen percent of those over 70 y old have mild cognitive impairment and half of these develop Alzheimer's disease. Since accelerated brain atrophy is a characteristic of subjects with mild cognitive impairment who convert to Alzheimer's disease, trials are needed to see if the same treatment will delay the development of Alzheimer's disease.

Trial Registration

Controlled-Trials.com ISRCTN94410159

Disease-modifying approach to the treatment of Alzheimer's disease: from alpha-secretase activators to gamma-secretase inhibitors and modulators

In the last decade, advances in understanding the neurobiology of Alzheimer's disease (AD) have translated into an increase in clinical trials assessing various potential AD treatments. At present, drugs used for the treatment of AD only slightly delay the inevitable symptomatic progression of the disease and do not affect the main neuropathological hallmarks of the disease, i.e. senile plaques and neurofibrillary tangles. Brain accumulation of oligomeric species of beta-amyloid (A beta) peptides, the principal components of senile plaques, is believed to play a crucial role in the development of AD. Based on this hypothesis, huge efforts are being made to identify drugs able to interfere with proteases regulating A beta formation from amyloid precursor protein (APP). Compounds that stimulate alpha-secretase, the enzyme responsible for non-amyloidogenic metabolism of APP, are being developed and one of these, EHT-0202, has recently commenced evaluation in a phase II study. The discovery of inhibitors of beta-secretase (memapsin-2, beta-amyloid cleaving enzyme-1 [BACE-1]), the enzyme that regulates the first step of amyloidogenic APP metabolism, has proved to be particularly difficult because of inherent medicinal chemistry issues and only one compound (CTS-21166) has proceeded to clinical testing. Conversely, several compounds that inhibit gamma-secretase, the pivotal enzyme that generates A beta, have been identified, the most advanced being LY-450139 (semagacestat), presently in phase III clinical development. There has been considerable disappointment over the failure of a phase III study of tarenflurbil, a compound believed to modulate the activity of gamma-secretase, after encouraging phase II findings. Nevertheless, other promising gamma-secretase modulators are being developed and are approaching clinical testing. All these therapeutic approaches increase the hope of slowing the rate of decline in patients with AD and modifying the natural history of this devastating disease within the next 5 years.

Beyond the neurotransmitter-focused approach in treating Alzheimer's disease: drugs targeting beta-amyloid and tau protein

Drugs currently used to treat Alzheimer's Disease (AD) have limited therapeutic value and do not affect the main neuropathological hallmarks of the disease, i.e., senile plaques and neurofibrillar tangles. Senile plaques are mainly formed of beta-amyloid (Abeta), a 42-aminoacid peptide. Neurofibrillar tangles are composed of paired helical filaments of hyperphosphorylated tau protein. New, potentially disease-modifying, therapeutic approaches are targeting Abeta and tau protein. Drugs directed against Abeta include active and passive immunization, that have been found to accelerate Abeta clearance from the brain. The most developmentally advanced monoclonal antibody directly targeting Abeta is bapineuzumab, now being studied in a large Phase III clinical trial. Compounds that interfere with proteases regulating Abeta formation from amyloid precursor protein (APP) are also actively pursued. The discovery of inhibitors of beta-secretase, the enzyme that regulates the first step of the amyloidogenic metabolism of APP, has been revealed to be particularly difficult due to inherent medicinal chemistry problems, and only one compound (CTS-21166) has reached clinical testing. Conversely, several compounds that inhibit gamma-secretase, the pivotal enzyme that generates Abeta, have been identified, the most advanced being LY-450139 (semagacestat), now in Phase III clinical development. Compounds that stimulate alpha-secretase, the enzyme responsible for the non-amyloidogenic metabolism of APP, are also being developed, and one of them, EHT-0202, has recently entered Phase II testing. Potent inhibitors of Abeta aggregation have also been identified, and one of such compounds, PBT-2, has provided encouraging neuropsychological results in a recently completed Phase II study. Therapeutic approaches directed against tau protein include inhibitors of glycogen synthase kinase- 3 (GSK-3), the enzyme responsible for tau phosphorylation and tau protein aggregation inhibitors. NP-12, a promising GSK-3 inhibitor, is being tested in a Phase II study, and methylthioninium chloride, a tau protein aggregation inhibitor, has given initial encouraging results in a 50-week study. With all these approaches on their way, the hope for disease-modifying therapy in this devastating disease may become a reality in the next 5 years.

Amyloid-based therapeutics: findings translated into novel treatments

For decades following the 1906 identification of Alzheimer’s disease (AD), it was believed that the disorder was untreatable. Only in the late 1970s, with the introduction of the cholinergic hypothesis of the underlying mechanisms of AD, were treatment options considered possible. The first positive treatment study was conducted in 1985. In 1993, tacrine, a cholinesterase inhibitor, was approved for the treatment of AD; three similar drugs soon followed. Memantine, an NMDA receptor antagonist, was approved in 2003, representing a second therapeutic class for AD.

Cholinesterase inhibitors were the first therapeutic options successfully employed, and there is strong evidence these agents confer benefits. The addition of memantine to the standard course of therapy can be beneficial as well, particularly at the moderate stages of the disorder (Mini-Mental State Exam score of ≤14). For patients without cardiovascular disease, diabetes, or statin use, 1,000 IU vitamin E BID is a consideration to mitigate the effects of AD. However, there is presently concern over the risks involved in vitamin E therapy. Unfortunately, there are no established treatments for mild cognitive impairment (MCI). Vitamin E is ineffective in treating MCI, and cholinesterase inhibitors, while possibly risky, are only minimally effective. The need for effective treatment remains expansive. The benefits of the available agents are modest, and there are currently no treatments for individuals with memory impairment who do not yet meet the diagnostic criteria for AD.