Current Alzheimer Research - Volume 11, Issue 5, 2014

Background: PF-04447943 is a potent, selective phosphodiesterase 9A (PDE9A) inhibitor that elevates guanoscine 3’,5’ – cyclic monophosphate (cGMP) in brain and cerebrospinal fluid. PDE9A inhibition enhances synaptic plasticity and improves memory in preclinical cognition models, and prevents decreases in dendritic spine density in transgenic mice that overexpress amyloid precursor protein (APP) leading to high levels of amyloid beta (Aβ) production (Tg2576). Objective: This Phase 2 multicenter study was designed to assess the efficacy, safety and pharmacokinetics of PF-04447943 compared with placebo in mild to moderate probable Alzheimer’s disease (AD). Methods: Subjects in overall good health with Mini Mental State Examination (MMSE) scores of 14-26 were randomized to 12 weeks treatment with PF-04447943 25 mg q12h (n=91) or placebo (n=100). Concomitant acetylcholinesterase inhibitor or memantine use was excluded. The primary outcome was the Alzheimer’s Disease Assessment Scale – cognitive subscale (ADAS-cog). The Neuropsychiatric Inventory (NPI), Clinical Global Impression-Improvement scale (CGI-I) and standard safety measures were secondary outcomes. Results: Completion rates were similar, 87% PF-04447943 vs 92% placebo. At week 12 the mean (SE) baseline adjusted decrease from baseline in ADAS cog for PF-04447943-treated patients was -1.91 (0.54). Placebo treated patients had a change of -1.60 (0.50). The difference between treatments was -0.31 (90% CI of -1.52, 0.90). Corresponding values for the NPI were -2.86 (0.72) vs -2.70 (0.67) with a treatment difference of -0.16 (90% CI of -1.78, 1.48). Neither these changes nor the distribution of CGI-I scores were statistically significantly different between groups. The incidence of serious adverse events (AEs) was similar between groups with 2 deaths in the placebo group. The PF-04447943 group reported more gastrointestinal AEs including diarrhea (5.5% vs 3%) and nausea (5.5% vs 1%) and had a higher rate of discontinuation due to AEs (6.6% vs 2%). Conclusions: Although generally safe and well-tolerated, 12 weeks PF-04447943 treatment did not improve cognition, behavior, and global change compared with placebo.

The currently available experimental data supports the hypothesis that the neuroprotective effect of dimebon is related to the protection of the brain-mitochondria from neurodegeneration. In this study, the influence of dimebon on mitochondria was investigated to gain a better understanding of the neuroprotective effects of this drug. Here, we demonstrate that dimebon enhances the resistance of the isolated rat brain and liver mitochondria to the induction of mitochondrial permeability transition (MPT) by calcium ions even in the presence of atractyloside, a MPT pore (MPTP) opener, but is ineffective against atractyloside-induced mitochondria swelling. Unlike cyclosporine A (CsA), a MPTP inhibitor, Dimebon does not influence the adenine nucleotide translocase (ANT) conformational changes and is not able to prevent the MPT of de-energized mitochondria. Using three different assays, and using amyloid-β peptide for inducing mitochondrial toxicity, we show that the influence of dimebon on the calcium retention capacity (CRC) of mitochondria depends on the mode of calcium addition. No obvious influence of dimebon on CRC was observed under the conditions of calcium infusion in the pump mode but the increase of CRC of rat brain mitochondria was observed when calcium was added in the bolus mode; the addition of calcium in the single pulse mode led to the increase of the lag period of calcium efflux from mitochondria. From these studies it is shown that dimebon is effective against amyloid-β (Aβ) potentiated mitochondrial swelling and decrease of calcium retention capacity (CRC) of the brain mitochondria.

The neuroinflammation induced by amyloid-β (Aβ) is one of the key events in Alzheimer’s disease (AD) progress in which microglia are the main cells involved. Receptor for advanced glycation end products (RAGE) mediates and enhances Aβ-induced microglial activation and leads to induction of proinflammatory mediators, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Geniposide, a pharmacologically active component purified from gardenia fruit, exhibits a broad spectrum anti-inflammatory effect as well as neurotrophic and neuroprotective properties. However, the effects of geniposide on Aβ-mediated microglial pathways have not been fully discovered. Here, we demonstrate that geniposide treatment significantly blocks Aβ-induced RAGE-dependent signaling (activation of ERK and NF-κB) along with the production of TNF-α and IL-1β in cultured BV2 microglia cells. Notably, based on the data from coimmunoprecipitation assay, we infer that geniposide exerts protective effects on Aβ-induced inflammatroy response through blocking Aβ binding to RAGE and suppressing the RAGE-mediated signaling pathway. Taken together, these findings indicate that geniposide is a potent suppressor of neuroflammation through inhibiting RAGE-dependent signaling pathway. Thus, geniposide may be a potential therapeutic agent for the treatment of neuroinflammation that is involved in neurological diseases such as AD.

As the most common neurodegenerative disease, therapeutic avenues for the treatment and prevention of Alzheimer’s Disease are highly sought after. The aspartic protease BACE1 is the initiator enzyme for the formation of Aβ, a major constituent of amyloid plaques that represent one of the hallmark pathological features of this disorder. Thus, targeting BACE1 for disease-modifying AD therapies represents a rationale approach. The collective knowledge acquired from investigations of BACE1 deletion mutants and characterization of BACE1 substrates has downstream significance not only for the discovery of AD drug therapies but also for predicting side effects of BACE1 inhibition. Here we discuss the identification and validation of BACE1 as the β-secretase implicated in AD, in addition to information regarding BACE1 cell biology, localization, substrates and potential physiological functions derived from BACE1 knockout models.

Brain glucose hypometabolism has been observed in Alzheimer’s disease (AD) patients, and is detected with 18F radiolabelled glucose, using positron emission tomography. A pathological hallmark of AD is deposition of brain β- amyloid plaques that may influence cerebral glucose metabolism. The five times familial AD (5XFAD) mouse is a model of brain amyloidosis exhibiting AD-like phenotypes. This study examines brain β-amyloid plaque deposition and 18FDG uptake, to search for an early biomarker distinguishing 5XFAD from wild-type mice. Thus, brain 18FDG uptake and plaque deposition was studied in these mice at age 2, 5 and 13 months. The 5XFAD mice demonstrated significantly reduced brain 18FDG uptake at 13 months relative to wild-type controls but not in younger mice, despite substantial β- amyloid plaque deposition. However, by comparing the ratio of uptake values for glucose in different regions in the same brain, 5XFAD mice could be distinguished from controls at age 2 months. This method of measuring altered glucose metabolism may represent an early biomarker for the progression of amyloid deposition in the brain. We conclude that brain 18FDG uptake can be a sensitive biomarker for early detection of abnormal metabolism in the 5XFAD mouse when alternative relative uptake values are utilized.

Apolipoprotein E (APOE) genetic variation and aging are the two most noted risk factors associated with the development of Alzheimer’s disease (AD) related dementia. However, the relationship between these two pathological factors is not understood. Formaldehyde (FA) is an age related factor that has been found to be elevated in AD patients and is known to have protein cross-linking properties. FA forms cross-links with larger arginine, lysine and tryptophan residues but also has thiol reactivity. This study investigated the formation of protein aggregates between amyloid-beta (1-40) peptide (Aβ), the main component of amyloid plaques in AD, with APOE isoforms in vitro. APOE4 protein, the isoform with arginines at residue 112 and 158, was found to form aggregates with more Aβ (P < 0.001) and APOE (P < 0.05) protein content in 10 mM FA than aggregates formed with either APOE3 or APOE2 protein. This aggregation pattern reflected the trend of vulnerability conferred by the APOE genetic variation (APOE4 > APOE3 > APOE2) and suggested that FA may have a role in the differential pattern of amyloid plaque formation in people with differing APOE genetic backgrounds. All told, this finding adds to a growing body of evidence that FA has a role in AD progression as well as provides a novel link between aging and APOE risk factors; the cornerstones of one of the world’s largest mental health concerns.

Multiple modalities of cognitive stimulation (CS) have been designed and tested in samples of patients with probable Alzheimer’s disease (AD). Despite the substantial inter-study variability, an overall positive impact of CS is reported. This impact has been especially observed in general measures of cognition. The mechanisms by which cognitive exercises would be beneficial for high-order cortical functions are still largely undetermined, however. When CS has been applied to patients with mild cognitive impairment (who are at the prodromal stage of AD) more stringent methodological criteria and designs were used and studies have been of greater clinical and research relevance. At this disease stage, a positive impact of CS has been reported in a range of different cognitive domains, and even at a neuro-computational level by the measurement of test-retest modifications of brain function. The effects of CS in healthy adults have also been studied. This population allows researchers to explore and test specific neural mechanisms possibly underlying the effect of pen-and-paper or computerised exercises. The evidence from these studies and those contributing to a better understanding of the pathophysiology of AD has led to devising forms of CS as preventive and therapeutical measures for neurodegenerative diseases based on novel frameworks of brain structure, function and connectivity. An extensive review of the literature was carried out to clarify whether CS is effective in AD and mild cognitive impairment and, together with the evidence from studies in healthy participants, to identify the relevant mechanisms that might sustain this effectiveness.

Objective: To investigate effects and functional mechanism of compound Congrongyizhi Capsule (CCRC), a Chinese medicine, on cognitive functions against amnestic mild cognitive impairment (aMCI) patients with functional magnetic resonance imaging (fMRI) based on n-back task. Methods: Forty-one aMCI participants from hospital and local communities in Beijing and randomly divided into treatment (16 patients with CCRC capsule treatment), placebo (12 patients with placebo capsules) and control group (13 patients with no treatment). The duration of intervention lasted for 3 months. Neuropsychological tests and fMRI were applied to assess cognitive ability and brain activation changes after three months treatment. Results: Drug group (n=16) presented increased significance in the MMSE (P=0.008) and digit span (P<0.001) tests, while other scores of neuropsychological tests showed no statistical significance. fMRI results showed an increased brain negative activation in drug group during performing the n-back working-memory task in posterior cingulate (PCC), inferior frontal gyrus and lingual gyrus regions after 3 months; placebo and control group did not show the same effect. Meanwhile, there were negative correlations between left PCC activation levels and changed values of MMSE and digit span separately since increased negative activation was associated with better performance on the scores of MMSE and Digit Span tests. Conclusions: CCRC can increase negative activation degree of PCC under performing working memory tasks while this modulation are associated with better performance on the MMSE and Digit Span.

Background: With age, performance of motor tasks becomes more reliant on cognitive resources to compensate for the structural and functional declines in the motor control regions in the brain. We hypothesized that participants with amnestic mild cognitive impairment (aMCI) are more prone to motor dysfunctions than cognitively normal older adults under dual-task conditions where competitive demands challenge cognitive functions while performing a motor task simultaneously. Methods: Sixteen aMCI participants (females=9, age=64±5yrs, clinical dementia rating score=0.5) and 10 age- and education-matched cognitively normal adults (females=5, age=62±6yrs) participated. Using a 10-meter-walk test (10MW), gait velocity was recorded at baseline and under 4 different dual-task (DT) conditions designed to challenge working memory, executive function, and episodic memory. Specifically, DT1: verbal fluency; DT2: 5-digit backward span; DT3: serial-7 subtraction; and DT4: 3-item delayed recall. Physical function was measured by Timed Up-and-Go (TUG), simple reaction time (RT) to a free-falling yardstick, and functional reach (FR). Results: No difference was found in physical functions, aerobic fitness, and exercise cardiopulmonary responses between aMCI participants and controls. However, aMCI participants showed more pronounced gait slowing from baseline when compared to the controls (p<0.05; p=0.001; p<0.001; p<0.001, respectively). Conclusions: Our finding supports the theory of shared resource of motor and cognitive control. Participants with aMCI manifested more gait slowing than cognitively-normal older adults under DT conditions, with the largest differences during tests of working and episodic memory. The outcome of dual-task assessment shows promise as a potential marker for detection of aMCI and early Alzheimer disease.

Different kinds of challenge can alter cognitive process and electroencephalographic (EEG) rhythms in humans. This can provide an alternative paradigms to evaluate treatment effects in drug discovery. Here, we report recent findings on the effects of challenges represented by sleep deprivation (SD), transient hypoxia, and transcranial magnetic stimulation (TMS) in healthy volunteers on cognitive processes and EEG rhythms to build a knowledge platform for novel research for drug discovery in AD Alzheimer's disease (AD). Sleep pressure enhanced frontal delta rhythms (< 4 Hz) during the night, while SD increased slow rhythms in the theta range (4-7 Hz), and reduced resting state alpha rhythms (8-12 Hz) after the following day. Furthermore, SD transiently affected cognitive performance. In contrast, transient experimental hypoxia induced abnormal posterior resting state delta and alpha rhythms in healthy volunteers that resemble the abnormal EEG rhythms typically recorded in AD patients. However, the relationship between the cognitive and EEG effects of such challenges is poorly understood. TMS reversibly interfered with higher brain functions during EEG recordings, but few studies have investigated the relationship between the cognitive and EEG effects of TMS. In conclusion, SD is the most mature challenge model for testing new drugs for AD. Future investigation is needed to better understand the opportunities offered by TMS and hypoxia challenges.