The canine as a model of human cognitive aging: recent developments

1. Aged dogs display many of the cognitive impairments associated with aging and dementia. 2. Aged dogs, like humans, display a wide range of individual variability in cognitive functioning (i.e., different cognitive functions decline at different rates in aged dogs). 3. Different categories of aged canines can be identified on the basis of neuropsychological test performance, and these categories can be used to model different subgroups of aged humans (i.e., dementia, mild cognitive impairment and successful aging). 4. Additional research is required to further validate the dog as a model of human cognitive aging and dementia.     

Further evidence for the cholinergic hypothesis of aging and dementia from the canine model of aging

Memory decline in human aging and dementia is linked to dysfunction of the cholinergic system. Aging dogs demonstrate cognitive impairments and neuropathology that models human aging and dementia. This paper reviews recent evidence suggesting cholinergic involvement in canine cognitive aging based on studies with the anti-cholinergic drug, scopolamine, and a novel acetylcholinesterase inhibitor, phenserine. In particular, we examine: (1) the cognitive specificity of scopolamine's impairment in dogs, (2) the effect of age on scopolamine impairment and (3) the effect of phenserine on cognitive performance in dogs. Our findings indicate that working memory performance is disrupted by scopolamine at doses that do not disrupt non-cognitive behavior or long-term, semantic-like, memory, as indicated by performance of previously learned discriminations. This pattern of deficits is also seen in human and canine aging. We demonstrate that aged dogs are more sensitive to the impairing effects of scopolamine than young dogs, suggesting a decrease in cholinergic tone with increasing age. Dogs receiving phenserine demonstrate improved learning and memory compared to placebo controls. Our findings suggest that cholinergic decline could result in memory impairment, but that the memory impairment may be secondary to deficits in attention and/or encoding of new information. Together, these results suggest that the canine cholinergic system declines with age and that the aged dog is a unique model for screening therapeutics and for examining the relationship between amyloid pathology and cholinergic dysfunction in age-dependent cognitive decline.     

Lessons learned from failed and discontinued clinical trials for the treatment of Alzheimer's disease: future directions

While advances have been made in understanding the neurobiological processes underlying Alzheimer's disease (AD), few treatment options currently exist. Numerous potential therapeutic and/or preventive agents have been tested in clinical trials, yet most have failed to show a clear therapeutic benefit. The lack of effective medical therapies coupled with the incipient projected dramatic increase in the number of persons with AD in the coming decades has put medical research in a crisis to urgently find effective treatment and prevention strategies. Researchers and funding agencies have been rethinking investigative approaches in order to accelerate scientific discovery in AD therapeutics, including methodological issues in the design and implementation of clinical trials. This review discusses lessons learned from discontinued and failed clinical trials for the treatment and prevention of AD with an emphasis on future directions of AD clinical trials. In particular, attention is given to choice of study outcome measures, participant selection and retention, and clinical trial design. While there are few treatments available for AD currently, the potential for discovery over the next decade is promising.     

Current concepts in mild cognitive impairment.

The field of aging and dementia is focusing on the characterization of the earliest stages of cognitive impairment. Recent research has identified a transitional state between the cognitive changes of normal aging and Alzheimer's disease (AD), known as mild cognitive impairment (MCI). Mild cognitive impairment refers to the clinical condition between normal aging and AD in which persons experience memory loss to a greater extent than one would expect for age, yet they do not meet currently accepted criteria for clinically probable AD. When these persons are observed longitudinally, they progress to clinically probable AD at a considerably accelerated rate compared with healthy age-matched individuals. Consequently, this condition has been recognized as suitable for possible therapeutic intervention, and several multicenter international treatment trials are under way. Because this is a topic of intense interest, a group of experts on aging and MCI from around the world in the fields of neurology, psychiatry, geriatrics, neuropsychology, neuroimaging, neuropathology, clinical trials, and ethics was convened to summarize the current state of the field of MCI. Participants reviewed the world scientific literature on aging and MCI and summarized the various topics with respect to available evidence on MCI. Diagnostic criteria and clinical outcomes of these subjects are available in the literature. Mild cognitive impairment is believed to be a high-risk condition for the development of clinically probable AD. Heterogeneity in the use of the term was recognized, and subclassifications were suggested. While no treatments are recommended for MCI currently, clinical trials regarding potential therapies are under way. Recommendations concerning ethical issues in the diagnosis and the management of subjects with MCI were made.     

Clinical amyloid imaging in Alzheimer's disease

BACKGROUND: The hypothesis that amyloid deposition is the leading cause of Alzheimer's disease (AD) is supported by findings in transgenic animal models and forms the basis of clinical trials of anti-amyloid agents. According to this theory, amyloid deposition causes severe damage to neurons many years before onset of dementia via a cascade of several downstream effects. This hypothesis has, however, not yet been directly tested in human beings because of the very limited possibility of diagnosing amyloid deposition in vivo, which until recently required either brain biopsy or PET imaging with an on-site cyclotron and radiochemistry laboratory. Moreover, a clinical diagnosis of AD requires that patients have dementia, at which stage any effective treatment aimed at reducing amyloid deposition will probably be too late. RECENT DEVELOPMENTS: The amyloid imaging tracers flutemetamol, florbetapir, and florbetaben labelled with (18)F have been developed for PET; they can be produced commercially at central cyclotron sites and subsequently delivered to clinical PET scanning facilities. These tracers are currently undergoing formal clinical trials to establish whether they can be used to accurately image fibrillary amyloid and to distinguish patients with AD from normal controls and those with other diseases that cause dementia. They might also be used as biomarkers to predict development of AD before onset of dementia and to assess the effect of anti-amyloid therapy. Negative amyloid scans indicate absence of AD with a high level of accuracy, but healthy elderly volunteers might have positive amyloid scans, so their predictive value in isolation is less clear. Close association of in-vivo amyloid imaging results with post-mortem histopathological findings was shown with florbetapir in a phase 3 study. WHERE NEXT?: Therapeutic studies of anti-amyloid agents that include amyloid tracers as biomarkers are expected to be useful for drug development and to clarify the relation between amyloid removal and clinical effects. Once the (18)F tracers become available for diagnostic use, large-scale longitudinal studies will be needed to clarify their prognostic and diagnostic power in relation to age, risk factors, and AD subtypes. Ultimately, these tracers will hopefully clarify the pathophysiological role of amyloid in AD and contribute to development of new treatments.     

Longitudinal plasma amyloid beta as a biomarker of Alzheimer’s disease

Alzheimer's disease (AD) affects more than twenty-five million people worldwide and is the most common form of dementia. Symptomatic treatments have been developed, but effective intervention to alter disease progression is needed. Targets have been identified for disease-modifying drugs, but the results of clinical trials have been disappointing. Peripheral biomarkers of disease state may improve clinical trial design and analysis, increasing the likelihood of successful drug development. Amyloid-related measures, presumably reflecting principal pathology of AD, are among the leading cerebrospinal fluid and neuroimaging biomarkers, and measurement of plasma levels of amyloid peptides has been the focus of much investigation. In this review, we discuss recent data on plasma β-amyloid (Aβ) and examine the issues that have arisen in establishing it as a reliable biomarker of AD.     

Alzheimer's disease drug development in 2008 and beyond: problems and opportunities

Recently, a number of Alzheimer's disease (AD) multi-center clinical trials (CT) have failed to provide statistically significant evidence of drug efficacy. To test for possible design or execution flaws we analyzed in detail CTs for two failed drugs that were strongly supported by preclinical evidence and by proven CT AD efficacy for other drugs in their class. Studies of the failed commercial trials suggest that methodological flaws may contribute to the failures and that these flaws lurk within current drug development practices ready to impact other AD drug development [1]. To identify and counter risks we considered the relevance to AD drug development of the following factors: (1) effective dosing of the drug product, (2) reliable evaluations of research subjects, (3) effective implementation of quality controls over data at research sites, (4) resources for practitioners to effectively use CT results in patient care, (5) effective disease modeling, (6) effective research designs. New drugs currently under development for AD address a variety of specific mechanistic targets. Mechanistic targets provide AD drug development opportunities to escape from many of the factors that currently undermine AD clinical pharmacology, especially the problems of inaccuracy and imprecision associated with using rated outcomes. In this paper we conclude that many of the current problems encountered in AD drug development can be avoided by changing practices. Current problems with human errors in clinical trials make it difficult to differentiate drugs that fail to evidence efficacy from apparent failures due to Type II errors. This uncertainty and the lack of publication of negative data impede researchers' abilities to improve methodologies in clinical pharmacology and to develop a sound body of knowledge about drug actions. We consider the identification of molecular targets as offering further opportunities for overcoming current failures in drug development.     

AD and its comorbidities: An obstacle to develop a clinically efficient treatment?

Whilst the development of new drugs designed for the treatment of Alzheimer's disease (AD) has been widely publicised, we do not yet have treatments that are proven to slow the progression of AD. The decision taken by the US Food and Drug Administration (FDA) to grant a licence for the use of aducanumab, based on the premise that β-amyloid removal would result in downstream benefits rather than demonstration of cognitive efficacy per se contrasts with that made by the European Medicines Agency (EMA), who declined to grant a licence, citing lack of evidence of clinical improvement, and a failure to demonstrate that the treatment was sufficiently safe. Multiple factors have complicated the search for new and effective treatments for the management of AD. It is a complex neurodegenerative condition in which multiple comorbidities are common in the affected population. However, such conditions are commonly exclusion criteria in clinical trials for new treatments. Here we discuss how some of these comorbidities impact the development of clinically efficient treatments for AD. Firstly, we will examine what is meant by AD, and how definitions of this condition have changed and continue to evolve. Secondly, we describe some of the most important comorbid conditions accompanying and in some cases mimicking AD. Finally, we will examine how the inclusion, or exclusion, of these conditions from AD research may have had an effect on treatment trials, the implications of co-morbidities on “real-life” use of novel therapeutics especially when these have been trialled in patients with relatively pure disease, and how clinical trials may need to adapt to account for comorbidities in the future.     

Large animal ischemic stroke models: replicating human stroke pathophysiology

The high morbidity and mortality rate of ischemic stroke in humans has led to the development of numerous animal models that replicate human stroke to further understand the underlying pathophysiology and to explore potential therapeutic interventions.Although promising therapeutics have been identified using these animal models,with most undergoing significant testing in rodent models,the vast majority of these interventions have failed in human clinical trials.This failure of preclinical translation highlights the critical need for better therapeutic assessment in more clinically relevant ischemic stroke animal models.Large animal models such as non-human primates,sheep,pigs,and dogs are likely more predictive of human responses and outcomes due to brain anatomy and physiology that are more similar to humans-potentially making large animal testing a key step in the stroke therapy translational pipeline.The objective of this review is to highlight key characteristics that potentially make these gyrencephalic,large animal ischemic stroke models more predictive by comparing pathophysiological responses,tissue-level changes,and model limitations.     

Nursing home placement is related to dementia progression: experience from a clinical trial. Alzheimer's Disease Cooperative Study

OBJECTIVES: To examine the relationship between nursing home placement (NHP) and measures of change in other well-established clinical disease assessments in a longitudinal study of patients with probable AD. BACKGROUND: NHP is a common, major milestone in the natural history of AD. NHP is a readily identified event that can be accurately dated. NHP can be used in survival analyses, which are an efficient means of determining efficacy in clinical trials. NHP usually occurs in the setting of severe AD, but in cross-sectional studies, the strength of the association with disease severity has been controversial. DESIGN/METHODS: We used data from 341 AD patients who were enrolled in a recently published clinical trial of selegiline and tocopherol. At entry, all were rated as Clinical Dementia Rating (CDR) stage 2, were community-dwelling, and had an identified caregiver. Patients were followed at 3-month intervals for 2 years. We examined the relationship between four measures of dementia severity and a measure of behavioral dysfunction and NHP. The measures included changes in CDR status, changes in activities of daily living performance, changes from baseline to last measurement in dependence level, changes from baseline to last measurement on the Blessed Dementia Rating Scale (BDRS) score, and changes from baseline to last measurement on the total score and subscales of the Behavior Rating Scale for Dementia (BRSD). Statistical models were used to assess the strength of the associations. RESULTS: At the end of the 2-year period, 33% of patients had been institutionalized. The NHP patients did not differ at baseline from the not-NHP patients in gender, age, caregiver status, duration of illness, CDR sum of boxes, BDRS, or dependence level. The NHP patients had a lower baseline Mini-Mental State Examination score and a slightly worse BRSD total score. Patients reaching CDR3 were eight times more likely to be institutionalized than those who remained at CDR2. The change scores on all four dementia severity measures were strongly associated with NHP; the change score on the BRSD and its subscales were not. On the other hand, adverse events that included a behavioral disturbance, especially agitation, were associated with NHP. CONCLUSION: These data show that NHP closely reflects dementia progression in the context of a clinical trial. Coupled with the high face validity of NHP as a milestone of severe dementia, NHP is a valid primary outcome measure for AD clinical trials.     

Clinical trials in mild cognitive impairment: lessons for the future

Mild cognitive impairment (MCI) is an operational definition for a cognitive decline in individuals with a greater risk of developing dementia. The amnestic subtype of MCI is of particular interest because these individuals most likely progress to Alzheimer's disease (AD). Currently hypothesised therapeutic approaches in MCI are mainly based on AD treatment strategies. Long term secondary prevention randomised clinical trials have been completed in amnestic MCI populations, encompassing agents with various mechanisms of action: acetylcholinesterase inhibitors (donepezil, rivastigmine, galantamine), antioxidants (vitamin E), anti-inflammatories (rofecoxib), and nootropics (piracetam). The design of clinical trials in MCI is influenced by study objectives and definition of primary end points: time to clinical diagnosis of dementia, and AD in particular, or symptom progression. As none of the drugs previously shown to have clinical efficacy in AD trials or benefit in everyday practice have met the primary objectives of the respective trials, design of future clinical trials in MCI should be further developed particularly as regards the selection of more homogeneous samples at entry, optimal treatment duration, and multidimensional and reliable outcomes.     

A clinical perspective: anti tau's treatment in Alzheimer's disease

Alzheimer?s Disease (AD) physiopathology is not yet totally established. Nevertheless it is known that a metabolism dysfunction of the amyloid beta precursor protein (APP) and the abnormal tau protein phosphorylation lead to the formation of neuritic plaques and neurofibrillary tangles, respectively. These events finally drive to the clinical expression of dementia. Formally approved during the past decade, treatments for AD are lacking of an updating, being essentially symptomatic. Anticholinesterase agents have failed in providing a substantial improvement in the mental health condition of AD patients. On the other hand, antiamyloid strategies, have failed in their efficacy or security on their last development phases. In this context, tau represents a potential therapeutic target, by the action of drugs that diminish its aggregation, or acting by altering its phosphorylation or filaments formation. There is also anti-tau miscellaneous strategies such as normal microtubule-stabilizing agents. Thus, it might be possible that in a near future the neurodegenerative process could be stopped.     

The hexose transporter of human erythrocytes in aging and Alzheimer dementia

The hexose transporter protein of human erythrocyte membranes was investigated in aging and in demented patients with Alzheimer disease (AD) and Parkinson disease (PD) by assessing the D-glucose-displaceable binding of the ligand cytochalasin-B. We found no alteration in the hexose transporter of erythrocyte membranes in aging or in dementia of AD and PD. These findings indicate that the marked decrease in the density of hexose transporter that we previously reported in the cerebral cortex and brain microvessels in AD do not occur in erythrocyte membranes that have the highest density of the hexose transporter protein.     

Primary prevention and delay of onset of AD/dementia

Prevention in Alzheimer's disease and other dementias (AD/dementia) is defined on the basis of clinical states and their expressed symptoms. Primary prevention refers to delaying the development of the full-blown state of clinically expressed disease in normal individuals. Current primary prevention research is driven by evidence of AD/dementia protective factors that have emerged from epidemiological studies. The first randomized controlled trials (RCTs) of primary AD/dementia prevention have been designed to test the efficacy and safety of NSAIDs, hormonal therapy, antihypertensive drugs and antioxidants. The experience of these trials has indicated safety concerns as a key issue and highlighted significant design challenges in this type of research. These trials have required large sample sizes and unsustainable costs. There should be consideration given in future trials to enriching study samples with risk factors to increase progression rates to AD/dementia. Innovative strategies will also be needed to recruit and retain subjects given the long follow-up periods, modest perceived benefit and the potential for the risk-benefit ratio to change during the trial. It is foreseeable that regulatory authorities will be presented with primary prevention RCTs for approval and labelling, and that criteria to evaluate such evidence still need to be developed.     

Effectiveness of the Takeda Three Colors Combination Test as a screening test for dementia

Background:  The aged population is increasing worldwide and it is expected that dementia, for which aging is a risk factor, will increase as well. A critical issue then becomes a community's capacity for the early detection of dementia among its senior citizens. In the present paper, we report on the development and potential use of a screening test for dementia that can be administered and assessed easily in a short period of time by non-specialist clinicians and represents no burden for those undergoing the screening.
Methods:  Three hundred and sixty senior citizens, over 60 years of age, participated in the study. Of these, 126 had Alzheimer's disease (AD), 60 had vascular dementia (VaD), 41 had mild cognitive impairment (MCI), and 133 were healthy volunteers (control group). A screening test for dementia, which consisted of a colored cards configuration memory task (the Takeda Three Colors Combination Test; TTCC) was examined for sensitivity, specificity, reliability and criterion-related validity.
Results:  Sufficient sensitivity and specificity were demonstrated for each clinical group (AD, VaD) and the control group. The sensitivity of the TTCC was 0.94, 0.82, and 0.71 for the AD, VaD, and MCI groups, respectively; specificity was 0.83. In addition, sufficient reliability and validity were established. Administration of the TTCCand assessment procedures required only 1 or 2 min.
Conclusion:  Satisfactory sensitivity and specificity were indicated for both the AD and VaD groups, with sufficient reliability and validity also indicated. Thus, the TTCC is an effective dementia screening test.     

Anticonvulsant efficacy of the low-affinity partial benzodiazepine receptor agonist ELB 138 in a dog seizure model and in epileptic dogs with spontaneously recurrent seizures

PURPOSE: Ataxia, sedation, amnesia, ethanol and barbiturate potentiation, loss of efficacy (tolerance), development of dependence, and the potential for drug abuse limit the clinical use of benzodiazepines (BZDs) for long-term treatment of epilepsy or anxiety. BZD ligands that are in current use act as full allosteric modulators of gamma-aminobutyric acid (GABA)-gated chloride channels and, on long-term administration, trigger a functional uncoupling between the GABAA and BZD recognition sites. Partial allosteric modulators, which have a low intrinsic activity at the BZD recognition site of the GABAA receptor, might eventually overcome the limitations of full agonists such as diazepam (DZP). METHODS: In the present study, the new low-affinity partial BZD-receptor agonist ELB 138 [former name AWD 131-138; 1-(4-chlorophenyl)-4-morpholino-imidazolin-2-one] was evaluated in a dog seizure model and in epileptic dogs with spontaneously recurrent seizures. RESULTS: ELB 138 was shown to increase potently the pentylenetetrazole (PTZ) seizure threshold in dogs. Prolonged oral administration with twice-daily dosing of ELB 138 with either 5 or 40 mg/kg over a 5-week period was not associated with loss of anticonvulsant efficacy in the PTZ dog model. To study whether physical dependence developed during long-term treatment, the BZD antagonist flumazenil was injected after 5 weeks of treatment with ELB 138. Compared with prolonged treatment with DZP, only relatively mild abstinence symptoms were precipitated in dogs treated with ELB 138, particularly at the lower dosage (5 mg/kg, b.i.d.). In a prospective trial in dogs with newly diagnosed epilepsy, ELB 138 markedly reduced seizure frequency and severity without significant difference to standard treatments (phenobarbital or primidone) but was much better tolerated than the standard drugs. In dogs with chronic epilepsy, most dogs exhibited a reduction in seizure frequency and severity during add-on treatment with ELB 138. CONCLUSIONS: The data demonstrate that the partial BZD receptor agonist ELB 138 exerts significant anticonvulsant efficacy without tolerance in a dog seizure model as well as in epileptic dogs with spontaneously recurrent seizures. These data thus substantiate that partial agonism at the BZD site of GABAA receptors offers advantages versus full agonism and constitutes a valuable approach for treatment of seizures.     

Designing drug trials for Alzheimer’s disease: What we have learned from the release of the phase III antibody trials: A report from the EU/US/CTAD Task Force

An international task force of investigators from academia, industry, nonprofit foundations, and regulatory agencies met in Monte Carlo, Monaco, on October 31, 2012, to review lessons learned from the recent bapineuzumab and solanezumab trials, and to incorporate insights gained from these trials into future clinical studies. Although there is broad consensus that Alzheimer’s disease (AD) should be treated during its earliest stages, the concept of secondary prevention has evolved to be described more accurately as treatment of preclinical, presymptomatic, or early AD. There continues to be a strong emphasis on biomarkers and a need for new biomarkers; however, there has also been a realization, based on completed trials, that the most reliable indicator of clinical efficacy across the entire spectrum of disease from asymptomatic to AD dementia is likely a measure of cognition. The task force made many recommendations that should improve the likelihood of success in future trials, including larger phase 2 or combined phase 2/phase 3 studies, clear evidence of target engagement in the central nervous system, evidence of downstream effects on biomarkers before initiating phase 3 studies, consideration of adaptive and targeted trial designs, and use of sensitive measures of cognition as the most robust indicator of treatment benefit.     

Alzheimer's therapeutics: translation of preclinical science to clinical drug development

Over the past three decades, significant progress has been made in understanding the neurobiology of Alzheimer's disease. In recent years, the first attempts to implement novel mechanism-based treatments brought rather disappointing results, with low, if any, drug efficacy and significant side effects. A discrepancy between our expectations based on preclinical models and the results of clinical trials calls for a revision of our theoretical views and questions every stage of translation-from how we model the disease to how we run clinical trials. In the following sections, we will use some specific examples of the therapeutics from acetylcholinesterase inhibitors to recent anti-Aβ immunization and γ-secretase inhibition to discuss whether preclinical studies could predict the limitations in efficacy and side effects that we were so disappointed to observe in recent clinical trials. We discuss ways to improve both the predictive validity of mouse models and the translation of knowledge between preclinical and clinical stages of drug development.     

Application of Resource Utilization in Dementia (RUD) instrument in a global setting

BackgroundThe Resource Utilization in Dementia (RUD) questionnaire is the most widely used instrument for resource use data collection in dementia, enabling comparison of costs of care across countries with differing health care provisions. Recent feedback from payers questioned its face validity given that health care provisions have changed since the initial development of the RUD in 1998. The aim of this study was to update the RUD to improve its face validity in Alzheimer’s disease (AD) clinical research and its utility for health care resource allocation.MethodsAn extensive PubMed review was conducted of current relevant resource items in AD in 15 countries. The findings were complemented by interviews with local care providers and experts in dementia care and health economics. Their proposed revisions were discussed with five leading dementia experts in North and South America, northern and southern Europe, and Asia. A new version of the RUD was developed based on their recommendations.ResultsRUD users identified a need for more information relevant to coverage decisions. Proposed revisions included changes to existing questions (e.g., to capture more accurately the number and type of health care visits) and the addition of new questions (e.g., on informal caregiver hours and the primary caregiver’s hours of sleep).ConclusionSeveral minor changes were made to the RUD instrument to improve the accuracy and precision of the data while maintaining comparability with the original version and reflecting current medical practice. The RUD Complete Version 4.0 is now available for use in future AD clinical trials.     

Adult Changes in Thought study: dementia is an individually varying convergent syndrome with prevalent clinically silent diseases that may be modified by some commonly used therapeutics

The Adult Changes in Thought (ACT) study is a longitudinal population-based prospective cohort study of brain aging and incident dementia in the Seattle metropolitan area. Observational studies using autopsies from ACT indicate that dementia is a convergent syndrome that commonly derives from Alzheimer's disease (AD), microvascular brain injury (mVBI), and Lewy body disease (LBD), and that these diseases have prevalent subclinical forms that also are commonly co-morbid. The existence of subclinical diseases highlights potential opportunities to intervene before the development of clinically apparent impairments. Our observations suggest that some such interventions already may exist to suppress processes of AD (statin therapy) or mVBI (treatment of hypertension). Reduced burden of LBD is associated with cigarette smoking; although smoking is not recommended as an intervention, these exposure data may provide clues to alternative neuroprotective mechanisms. Self reported anti-oxidant supplementation was without apparent effect in this cohort on indices of AD, mVBI, or LBD. Continued observational studies of brain aging will provide further insight into the convergent complexity of the dementia syndrome and its subclinical forms as well as highlight potential interventions that will require validation in clinical trials.