Corticotropin-releasing factor receptor-1 antagonism mitigates beta amyloid pathology and cognitive and synaptic deficits in a mouse model of Alzheimer's disease

INTRODUCTION

Stress and corticotropin-releasing factor (CRF) have been implicated as mechanistically involved in Alzheimer's disease (AD), but agents that impact CRF signaling have not been carefully tested for therapeutic efficacy or long-term safety in animal models.

METHODS

To test whether antagonism of the type-1 corticotropin-releasing factor receptor (CRFR1) could be used as a disease-modifying treatment for AD, we used a preclinical prevention paradigm and treated 30-day-old AD transgenic mice with the small-molecule, CRFR1-selective antagonist, R121919, for 5 months, and examined AD pathologic and behavioral end points.

RESULTS

R121919 significantly prevented the onset of cognitive impairment in female mice and reduced cellular and synaptic deficits and beta amyloid and C-terminal fragment-β levels in both genders. We observed no tolerability or toxicity issues in mice treated with R121919.

DISCUSSION

CRFR1 antagonism presents a viable disease-modifying therapy for AD, recommending its advancement to early-phase human safety trials.

Dissociation of Down syndrome and Alzheimer's disease effects with imaging

Introduction

Down Syndrome (DS) adults experience accumulation of Alzheimer's disease (AD)–like amyloid plaques and tangles and a high incidence of dementia and could provide an enriched population to study AD-targeted treatments. However, to evaluate effects of therapeutic intervention, it is necessary to dissociate the contributions of DS and AD from overall phenotype. Imaging biomarkers offer the potential to characterize and stratify patients who will worsen clinically but have yielded mixed findings in DS subjects.

Methods

We evaluated 18F fluorodeoxyglucose positron emission tomography (PET), florbetapir PET, and structural magnetic resonance (sMR) image data from 12 nondemented DS adults using advanced multivariate machine learning methods.

Results

Our results showed distinctive patterns of glucose metabolism and brain volume enabling dissociation of DS and AD effects. AD-like pattern expression corresponded to amyloid burden and clinical measures.

Discussion

These findings lay groundwork to enable AD clinical trials with characterization and disease-specific tracking of DS adults.

Impact of CRFR1 Ablation on Amyloid-β Production and Accumulation in a Mouse Model of Alzheimer's Disease

Stress exposure and the corticotropin-releasing factor (CRF) system have been implicated as mechanistically involved in both Alzheimer's disease (AD) and associated rodent models. In particular, the major stress receptor, CRF receptor type 1 (CRFR1), modulates cellular activity in many AD-relevant brain areas, and has been demonstrated to impact both tau phosphorylation and amyloid-β (Aβ) pathways. The overarching goal of our laboratory is to develop and characterize agents that impact the CRF signaling system as disease-modifying treatments for AD. In the present study, we developed a novel transgenic mouse to determine whether partial or complete ablation of CRFR1 was feasible in an AD transgenic model and whether this type of treatment could impact Aβ pathology. Double transgenic AD mice (PSAPP) were crossed to mice null for CRFR1; resultant CRFR1 heterozygous (PSAPP-R1(+/-)) and homozygous (PSAPP-R1(-/-)) female offspring were used at 12 months of age to examine the impact of CRFR1 disruption on the severity of AD Aβ levels and pathology. We found that both PSAPP-R1(+/-) and PSAPP-R1(-/-) had significantly reduced Aβ burden in the hippocampus, insular, rhinal, and retrosplenial cortices. Accordingly, we observed dramatic reductions in Aβ peptides and AβPP-CTFs, providing support for a direct relationship between CRFR1 and Aβ production pathways. In summary, our results suggest that interference of CRFR1 in an AD model is tolerable and is efficacious in impacting Aβ neuropathology.

Functional Impact of Corticotropin-Releasing Factor Exposure on Tau Phosphorylation and Axon Transport

Stress exposure or increased levels of corticotropin-releasing factor (CRF) induce hippocampal tau phosphorylation (tau-P) in rodent models, a process that is dependent on the type-1 CRF receptor (CRFR1). Although these preclinical studies on stress-induced tau-P provide mechanistic insight for epidemiological work that identifies stress as a risk factor for Alzheimer’s disease (AD), the actual impact of stress-induced tau-P on neuronal function remains unclear. To determine the functional consequences of stress-induced tau-P, we developed a novel mouse neuronal cell culture system to explore the impact of acute (0.5hr) and chronic (2hr) CRF treatment on tau-P and integral cell processes such as axon transport. Consistent with in vivo reports, we found that chronic CRF treatment increased tau-P levels and caused globular accumulations of phosphorylated tau in dendritic and axonal processes. Furthermore, while both acute and chronic CRF treatment led to significant reduction in CREB activation and axon transport of brain-derived neurotrophic factor (BDNF), this was not the case with mitochondrial transport. Acute CRF treatment caused increased mitochondrial velocity and distance traveled in neurons, while chronic CRF treatment modestly decreased mitochondrial velocity and greatly increased distance traveled. These results suggest that transport of cellular energetics may take priority over growth factors during stress. Tau-P was required for these changes, as co-treatment of CRF with a GSK kinase inhibitor prevented CRF-induced tau-P and all axon transport changes. Collectively, our results provide mechanistic insight into the consequences of stress peptide-induced tau-P and provide an explanation for how chronic stress via CRF may lead to neuronal vulnerability in AD.

Corticotropin-Releasing Factor Receptor-1 Antagonism Reduces Oxidative Damage in an Alzheimer’s Disease Transgenic Mouse Model

Reports from Alzheimer’s disease (AD) biomarker work have shown a strong link between oxidative stress and AD neuropathology. The nonenzymatic antioxidant, glutathione (GSH), plays a crucial role in defense against reactive oxygen species and maintenance of GSH redox homeostasis. In particular, our previous studies on GSH redox imbalance have implicated oxidative stress induced by excessive reactive oxygen species as a major mediator of AD-like events, with the presence of S- glutathionylated proteins (Pr-SSG) appearing prior to overt AD neuropathology. Furthermore, evidence suggests that oxidative stress may be associated with dysfunction of the hypothalamic-pituitary-adrenal axis, leading to activation of inflammatory pathways and increased production of corticotropin-releasing factor (CRF). Therefore, to investigate whether oxidative insults can be attenuated by reduction of central CRF signaling, we administered the type-1 CRF receptor (CRFR1) selective antagonist, R121919, to AD-transgenic mice beginning in the preclinical/prepathologic period (30-day-old) for 150 days, a time point where behavioral impairments and pathologic progression should be measureable. Our results indicate that R121919 treatment can significantly reduce Pr-SSG levels and increase glutathione peroxide activity, suggesting that interference of CRFR1 signaling may be useful as a preventative therapy for combating oxidative stress in AD.

Comparing biological markers of Alzheimer's disease across blood fraction and platforms: Comparing apples to oranges

Introduction

This study investigated the comparability of potential Alzheimer's disease (AD) biomarkers across blood fractions and assay platforms.

Methods

Nonfasting serum and plasma samples from 300 participants (150 AD patients and 150 controls) were analyzed. Proteomic markers were obtained via electrochemiluminescence or Luminex technology. Comparisons were conducted via Pearson correlations. The relative importance of proteins within an AD diagnostic profile was examined using random forest importance plots.

Results

On the Meso Scale Discovery multiplex platform, 10 of the 21 markers shared >50% of the variance across blood fractions (serum amyloid A R² = 0.99, interleukin (IL)10 R² = 0.95, fatty acid-binding protein (FABP) R² = 0.94, I309 R² = 0.94, IL-5 R² = 0.94, IL-6 R² = 0.94, eotaxin3 R² = 0.91, IL-18 R² = 0.87, soluble tumor necrosis factor receptor 1 R² = 0.85, and pancreatic polypeptide R² = 0.81). When examining protein concentrations across platforms, only five markers shared >50% of the variance (beta 2 microglobulin R² = 0.92, IL-18 R² = 0.80, factor VII R² = 0.78, CRP R² = 0.74, and FABP R² = 0.70).

Discussion

The current findings highlight the importance of considering blood fractions and assay platforms when searching for AD relevant biomarkers.

Reproductive Stage and Modulation of Stress-Induced Tau Phosphorylation in Female Rats

Chronic stress is implicated as a risk factor for Alzheimer's disease (AD) and other neurodegenerative disorders. Although the specific mechanisms linking stress exposure and AD vulnerability have yet to be fully determined, our laboratory and others have shown that acute and repeated restraint stress in rodents leads to an increase in hippocampal tau phosphorylation (tau-P) and tau insolubility, a critical component of tau pathology in AD. Although tau phosphorylation induced by acute psychological stress is dependent on intact signaling through the type 1 corticotropin-releasing factor receptor, how sex steroids or other modulators contribute to this effect is unknown. A naturally occurring attenuation of the stress response is observed in female rats at the end of pregnancy and throughout lactation. To test the hypothesis that decreased sensitivity to stress during lactation modulates stress-induced tau-P, cohorts of virgin, lactating and weaned female rats were subjected to 30 min of restraint stress or no stress (control) and were killed 20 min or 24 h after the episode. Exposure to restraint stress induced a significant decrease in tau-P in the hippocampus of lactating rats killed 20 min after stress compared to lactating controls and virgins subjected to stress treatment. Lactating rats killed 24 hr after restraint stress exposure showed significant elevation in tau-P compared to lactating cohorts killed 20 min after stress. Levels of tau-P in these latter cohorts did not differ signficantly from control animals. Furthermore, glycogen synthase kinase (GSK)3-α levels were significantly decreased in stressed lactating animals at both timepoints. This suggests a steep, yet transient stress-induced dephosphorylation of tau, influenced by GSK3, in the hippocampus of lactating rats.

A randomized, double-blind, placebo-controlled trial of resveratrol for Alzheimer disease

OBJECTIVE

A randomized, placebo-controlled, double-blind, multicenter 52-week phase 2 trial of resveratrol in individuals with mild to moderate Alzheimer disease (AD) examined its safety and tolerability and effects on biomarker (plasma Aβ40 and Aβ42, CSF Aβ40, Aβ42, tau, and phospho-tau 181) and volumetric MRI outcomes (primary outcomes) and clinical outcomes (secondary outcomes).

METHODS

Participants (n = 119) were randomized to placebo or resveratrol 500 mg orally once daily (with dose escalation by 500-mg increments every 13 weeks, ending with 1,000 mg twice daily). Brain MRI and CSF collection were performed at baseline and after completion of treatment. Detailed pharmacokinetics were performed on a subset (n = 15) at baseline and weeks 13, 26, 39, and 52.

RESULTS

Resveratrol and its major metabolites were measurable in plasma and CSF. The most common adverse events were nausea, diarrhea, and weight loss. CSF Aβ40 and plasma Aβ40 levels declined more in the placebo group than the resveratrol-treated group, resulting in a significant difference at week 52. Brain volume loss was increased by resveratrol treatment compared to placebo.

CONCLUSIONS

Resveratrol was safe and well-tolerated. Resveratrol and its major metabolites penetrated the blood-brain barrier to have CNS effects. Further studies are required to interpret the biomarker changes associated with resveratrol treatment.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that for patients with AD resveratrol is safe, well-tolerated, and alters some AD biomarker trajectories. The study is rated Class II because more than 2 primary outcomes were designated.

Characterization of ATP alternations in an Alzheimer's disease transgenic mouse model

Mitochondrial impairment as evidenced by decline in adenosine 5'-triphosphate (ATP) is associated with oxidative stress in Alzheimer's disease neuropathology and suggests that mitochondria may fail to maintain cellular energy, through reduced ATP production in neurons. To gain insights into the ATP characteristics of Alzheimer's disease transgenic (Tg) mice, we investigated ATP contents in the brain and whole blood of Tg mice at three ages (1-, 5-, and 24-months old). Overall, our results demonstrate that tissue ATP contents in Tg mice are significantly reduced, suggesting a decrease of tissue ATP production and mitochondrial dysfunction.

The down syndrome biomarker initiative (DSBI) pilot: proof of concept for deep phenotyping of Alzheimer's disease biomarkers in down syndrome

To gain further knowledge on the preclinical phase of Alzheimer’s disease (AD), we sought to characterize cognitive performance, neuroimaging and plasma-based AD biomarkers in a cohort of non-demented adults with down syndrome (DS). The goal of the down syndrome biomarker Initiative (DSBI) pilot is to test feasibility of this approach for future multicenter studies. We enrolled 12 non-demented participants with DS between the ages of 30–60 years old. Participants underwent extensive cognitive testing, volumetric MRI, amyloid positron emission tomography (PET; 18F-florbetapir), fluorodeoxyglucose (FDG) PET (18F-fluorodeoxyglucose) and retinal amyloid imaging. In addition, plasma beta-amyloid (Aβ) species were measured and Apolipoprotein E (ApoE) genotyping was performed. Results from our multimodal analysis suggest greater hippocampal atrophy with amyloid load. Additionally, we identified an inverse relationship between amyloid load and regional glucose metabolism. Cognitive and functional measures did not correlate with amyloid load in DS but did correlate with regional FDG PET measures. Biomarkers of AD can be readily studied in adults with DS as in other preclinical AD populations. Importantly, all subjects in this feasibility study were able to complete all test procedures. The data indicate that a large, multicenter longitudinal study is feasible to better understand the trajectories of AD biomarkers in this enriched population. This trial is registered with ClinicalTrials.gov, number NCT02141971.

Oral glucose tolerance testing to modulate plasma amyloid levels: A novel biomarker

INTRODUCTION

Plasma levels of amyloid-beta (Aβ) do not correlate well with different stages of Alzheimer's disease (AD) in cross-sectional studies. Measuring the changes in Aβ plasma levels with an acute intervention may be more sensitive to distinguishing individuals in earlier stages of AD (mild cognitive impairment; MCI) from normal controls.

METHODS

57 participants (18 with AD/MCI and 39 cognitively normal controls) underwent oral glucose tolerance testing (OGTT). Blood samples were obtained over a 2 hour time period. Changes in plasma Aβ40 and42 levels were measured from either baseline or 5 minutes to the 10 minute time point.

RESULTS

Compared to normal controls, subjects with AD/MCI had significantly less change (Δ) in plasma levels for both Aβ40(-3.13(40.93)pg/ml vs. 41.34(57.16)pg/ml;p=0.002) and Aβ42(-0.15(3.77)pg/ml vs. 5.64(10.65)pg/ml; p=0.004).

DISCUSSION

OGTT combined with measures of plasma Aβ40 and 42 is potentially useful in distinguishing aging individuals who are in different stages of AD.

Longitudinal plasma amyloid beta in Alzheimer's disease clinical trials

INTRODUCTION

Little is known about the utility of plasma amyloid beta (Aβ) in clinical trials of Alzheimer's disease (AD).

METHODS

We analyzed longitudinal plasma samples from two large multicenter clinical trials: (1) donezepil and vitamin E in mild cognitive impairment (n = 405, 24 months) and (2) simvastatin in mild to moderate AD (n = 225, 18 months).

RESULTS

Baseline plasma Aβ was not related to cognitive or clinical progression. We observed a decrease in plasma Aβ40 and 42 among apolipoprotein E epsilon 4 (APOE ε4) carriers relative to noncarriers in the mild cognitive impairment trial. Patients treated with simvastatin showed a significant increase in Aβ compared with placebo. We found significant storage time effects and considerable plate-to-plate variation.

DISCUSSION

We found no support for the utility of plasma Aβ as a prognostic factor or correlate of cognitive change. Analysis of stored specimens requires careful standardization and experimental design, but plasma Aβ may prove useful in pharmacodynamic studies of antiamyloid drugs.

Increased tau phosphorylation and aggregation in the hippocampus of mice overexpressing corticotropin-releasing factor

Clinical and basic science research suggests that stress and/or changes in central stress signaling intermediates may be involved in Alzheimer's disease (AD) pathogenesis. Although the links between stress and AD remain unsettled, data from our group and others have established that stress exposure in rodents may confer susceptibility to AD pathology by inducing hippocampal tau phosphorylation (tau-P). Work in our laboratory has shown that stress-induced tau-P requires activation of the type-1 corticotropin-releasing factor receptor (CRFR1). CRF overexpressing (CRF-OE) mice are a model of chronic stress that display cognitive impairment at 9-10 month of age. In this study we used 6-7 month old CRF-OE mice to examine whether sustained exposure to CRF and stress steroids would impact hippocampal tau-P and kinase activity in the presence or absence of the CRFR1-specific antagonist, R121919, given daily for 30 days. CRF-OE mice had significantly elevated tau-P compared to wild type (WT) mice at the AT8 (S202/T204), PHF-1 (S396/404), S262, and S422 sites. Treating CRF-OE mice with R121919 blocked phosphorylation at the AT8 (S202/T204) and PHF-1 (S396/404) sites, but not at the S262 and S422 sites and reduced phosphorylation of c-Jun N Terminal Kinase (JNK). Examination of hippocampal extracts from CRF-OE mice at the ultrastructural level revealed negatively stained round/globular aggregates that were positively labeled by PHF-1. These data suggest critical roles for CRF and CRFR1 in tau-P and aggregation and may have implications for the development of AD cognitive decline.

Elevated cerebrovascular resistance index is associated with cognitive dysfunction in the very-old

INTRODUCTION

Age-related vascular changes, including blood pressure elevation and cerebral blood flow (CBF) reduction, are associated with cognitive decline and Alzheimer's disease (AD). Evidence suggests that the relationship between blood pressure and dementia risk varies between younger and older samples within the elderly population.

METHODS

We examined the relationship between mean arterial pressure (MAP), CBF, and cognition in young-old (60 to 75 years of age) versus very-old (80+ years of age) adults. Fifty-eight non-demented older adults completed an arterial spin labeling MRI scan, and an index of cerebrovascular resistance (CVRi) was estimated for each participant by calculating the ratio of MAP and CBF.

RESULTS

Results demonstrated a similar negative relationship between MAP and CBF across both age groups. However, very-old participants exhibited elevated CVRi and reduced CBF compared to young-old participants in regions implicated in AD and cerebral small vessel disease. Furthermore, significant age by CVRi interactions revealed that elevated CVRi in the thalamus was inversely related to verbal fluency performance in the very-old group.

CONCLUSIONS

Findings support CVRi as a potential vascular biomarker and suggest that regionally-specific vascular changes may contribute to cognitive decline, particularly in the very-old.

Guidelines for the standardization of preanalytic variables for blood-based biomarker studies in Alzheimer's disease research

The lack of readily available biomarkers is a significant hindrance toward progressing to effective therapeutic and preventative strategies for Alzheimer's disease (AD). Blood-based biomarkers have potential to overcome access and cost barriers and greatly facilitate advanced neuroimaging and cerebrospinal fluid biomarker approaches. Despite the fact that preanalytical processing is the largest source of variability in laboratory testing, there are no currently available standardized preanalytical guidelines. The current international working group provides the initial starting point for such guidelines for standardized operating procedures (SOPs). It is anticipated that these guidelines will be updated as additional research findings become available. The statement provides (1) a synopsis of selected preanalytical methods utilized in many international AD cohort studies, (2) initial draft guidelines/SOPs for preanalytical methods, and (3) a list of required methodological information and protocols to be made available for publications in the field to foster cross-validation across cohorts and laboratories.

Cortical and subcortical cerebrovascular resistance index in mild cognitive impairment and Alzheimer's disease

BACKGROUND

Reduced regional cerebral blood flow (rCBF) is a well-established finding in Alzheimer's disease (AD), although fewer studies have examined the role of increased regional cerebrovascular resistance. By calculating the ratio of mean arterial pressure to rCBF, it is possible to estimate an index of regional cerebrovascular resistance (CVRi) that may be a sensitive measure of occult cerebrovascular disease.

OBJECTIVE

To compare probable AD patients to mild cognitive impairment (MCI) and normal control (NC) participants on CVRi, the ratio of mean arterial pressure to rCBF.

METHODS

Eighty-one participants (12 AD, 23 MCI, 46 NC) were compared on CVRi using voxel-wise analyses. Region-of-interest analyses examined correlations between subcortical CVRi and both cognition and white matter lesion (WML) volume.

RESULTS

Voxel-wise analyses revealed CVRi elevation in AD relative to NCs (subcortical, medial temporal, posterior cingulate, precuneus, inferior parietal, superior temporal) and MCI (subcortical, posterior cingulate). MCI participants exhibited intermediate CVRi values within cortical and medial temporal areas. Significant CVRi clusters were larger and more widespread than those of parallel CBF analyses. Among MCI and AD participants, subcortical CVRi elevation was associated with lower Dementia Rating Scale score (r = -0.52, p = 0.001, for both thalamus and caudate), and caudate CVRi correlated with WML volume (r = 0.45, p = 0.001).

CONCLUSIONS

Cortical and subcortical CVRi is elevated in AD, particularly within the caudate and thalamus, where it is associated with decreased cognitive performance and increased WMLs. Findings suggest CVRi may play a role in cognitive decline and cerebrovascular disease in MCI and AD.

Long-Term Electrophysiological and Behavioral Analysis on the Improvement of Visual Working Memory Load, Training Gains, and Transfer Benefits

Recent evidence demonstrates that with training, one can enhance visual working memory (VWM) capacity and attention over time in the near transfer tasks. Not only do these studies reveal the characteristics of VWM load and the influences of training, they may also provide insights into developing effective rehabilitation for patients with VWM deficiencies. However, few studies have investigated VWM over extended periods of time and evaluated transfer benefits on non-trained tasks. Here, we combined behavioral and electroencephalographical approaches to investigate VWM load, training gains, and transfer benefits. Our results reveal that VWM capacity is directly correlated to the difference of event-related potential waveforms. In particular, the “magic number 4” can be observed through the contralateral delay amplitude and the average capacity is 3.25-item over 15 participants. Furthermore, our findings indicate that VWM capacity can be improved through training; and after training exercises, participants from the training group are able to dramatically improve their performance. Likewise, the training effects on non-trained tasks can also be observed at the 12th week after training. Therefore, we conclude that participants can benefit from training gains, and augmented VWM capacity sustained over long periods of time on specific variety of tasks.

CSF biomarker variability in the Alzheimer's Association quality control program

BACKGROUND

The cerebrospinal fluid (CSF) biomarkers amyloid beta 1-42, total tau, and phosphorylated tau are used increasingly for Alzheimer's disease (AD) research and patient management. However, there are large variations in biomarker measurements among and within laboratories.

METHODS

Data from the first nine rounds of the Alzheimer's Association quality control program was used to define the extent and sources of analytical variability. In each round, three CSF samples prepared at the Clinical Neurochemistry Laboratory (Mölndal, Sweden) were analyzed by single-analyte enzyme-linked immunosorbent assay (ELISA), a multiplexing xMAP assay, or an immunoassay with electrochemoluminescence detection.

RESULTS

A total of 84 laboratories participated. Coefficients of variation (CVs) between laboratories were around 20% to 30%; within-run CVs, less than 5% to 10%; and longitudinal within-laboratory CVs, 5% to 19%. Interestingly, longitudinal within-laboratory CV differed between biomarkers at individual laboratories, suggesting that a component of it was assay dependent. Variability between kit lots and between laboratories both had a major influence on amyloid beta 1-42 measurements, but for total tau and phosphorylated tau, between-kit lot effects were much less than between-laboratory effects. Despite the measurement variability, the between-laboratory consistency in classification of samples (using prehoc-derived cutoffs for AD) was high (>90% in 15 of 18 samples for ELISA and in 12 of 18 samples for xMAP).

CONCLUSIONS

The overall variability remains too high to allow assignment of universal biomarker cutoff values for a specific intended use. Each laboratory must ensure longitudinal stability in its measurements and use internally qualified cutoff levels. Further standardization of laboratory procedures and improvement of kit performance will likely increase the usefulness of CSF AD biomarkers for researchers and clinicians.

Interaction of age and APOE genotype on cerebral blood flow at rest

We investigated the impact of APOE genotype on cerebral blood flow (CBF) in older and younger adults. Forty cognitively normal older adults (16 ε4 carriers, 24 non-ε4 carriers) and 30 younger adults (15 ε4 carriers, 15 non-ε4 carriers) completed a resting-state whole-brain pulsed arterial spin labeling magnetic resonance scan. Main effects of aging were demonstrated wherein older adults had decreased gray matter CBF corrected for partial volume effects compared to younger adults in widespread brain regions. Main effects of APOE genotype were also observed wherein ε4 carriers displayed greater CBF in the left lingual gyrus and precuneus than non-carriers. An interaction between age and APOE genotype in the left anterior cingulate cortex (ACC) was characterized by reduced CBF in older ε4 carriers and increased CBF in young ε4 carriers. Increased CBF in the left ACC resulting from the interaction of age group and APOE genotype was positively correlated with executive functioning in young ε4 adults (r = 0.61, p = 0.04). Results demonstrate APOE genotype differentially impacts cerebrovascular function across the lifespan and may modify the relationship between CBF and cognition. Findings may partially support suggestions that the gene exerts antagonistic pleiotropic effects.

Detection and quantification of 8-hydroxy-2'-deoxyguanosine in Alzheimer's transgenic mouse urine using capillary electrophoresis

8-Hydroxy-2'-deoxyguanosine (8-OHdG) is one of the major forms of oxidative DNA damage, and is commonly analyzed as an excellent marker of DNA lesions. The purpose of this study was to develop a sensitive method to accurately and rapidly quantify the 8-OHdG by using CE-LIF detection. The method involved the use of specific antibody to detect the DNA lesion (8-OHdG) and consecutive fluorescence labeling. Next, urinary 8-OHdG fluorescently labeled along with other constituents were resolved by capillary electrophoretic system and the lesion of interest was detected using a fluorescence detector. The limit of detection was 0.18 fmol, which proved sufficient sensitivity for detection and quantification of 8-OHdG in untreated urine samples. The relative standard deviation was found to be 11.32% for migration time and 5.52% for peak area. To demonstrate the utility of this method, the urinary concentration of 8-OHdG in an Alzheimer's transgenic mouse model was determined. Collectively, our results indicate that this methodology offers great advantages, such as high separation efficiency, good selectivity, low limit of detection, simplicity and low cost of analysis.

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.

Lipopolysaccharide-induced tau phosphorylation and kinase activity--modulation, but not mediation, by corticotropin-releasing factor receptors

Clinical studies suggest that exposure to stress can increase risk for Alzheimer's disease (AD). Although the precise links between stress and vulnerability to develop AD remain uncertain, recent animal work suggests that stress may promote susceptibility to AD pathology by activating tau kinases and inducing tau phosphorylation (tau-P). Our previous findings indicate the differential involvement of corticotropin-releasing factor receptor (CRFR) types 1 and 2 in regulating tau-P in the hippocampus induced by acute restraint, an emotional stressor. To assess the generality of CRFR involvement in stress-induced tau-P and tau kinase activity, the present study extends our investigation to a well-characterized physiological stressor, i.e. immune challenge induced by bacterial lipopolysaccharide (LPS). Acute systemic administration of LPS (100 μg/kg) robustly increased hippocampal (but not isocortical or cerebellar) tau-P, peaking at 40-120 min postinjection and abating thereafter. Assessments of the genotype dependence of this effect yielded results that were distinct from the restraint model. Treatment with LPS increased phosphorylation in wild-type, single and double CRFR knockouts with only subtle variation, which included a reliable exaggeration of tau-P responses in CRFR1-deficient mice. Parallel analyses implicated glycogen synthase kinase-3 and cyclin-dependent kinase-5 as likely cellular mediators of LPS-induced tau-P. Conversely, our data suggest that temperature-dependent fluctuations in tau protein phosphatase 2A (PP2A) may not play a role in this context. Thus, neither the strict CRFR1 dependence of restraint-induced tau-P nor the exaggeration of these responses in CRFR2 null mice generalize to the LPS model. CRFR mediation of stress-induced hippocampal tau-P may be limited to emotional stressors.