Vascular contributions to cognitive impairment and dementia including Alzheimer's disease

Scientific evidence continues to demonstrate the linkage of vascular contributions to cognitive impairment and dementia such as Alzheimer's disease. In December, 2013, the Alzheimer's Association, with scientific input from the National Institute of Neurological Disorders and Stroke and the National Heart, Lung and Blood Institute from the National Institutes of Health, convened scientific experts to discuss the research gaps in our understanding of how vascular factors contribute to Alzheimer's disease and related dementia. This manuscript summarizes the meeting and the resultant discussion, including an outline of next steps needed to move this area of research forward.

Alzheimer's Disease prevalence, costs, and prevention for military personnel and veterans

By 2050, more than 13 million Americans of all ages are estimated to be living with Alzheimer's disease (AD), and the aggregate costs of care will swell to approximately $1.2 trillion. The rapidly climbing number of those affected with AD includes a growing population of aging military veterans affected who may have an added risk for the disease as a consequence of traumatic brain injury, posttraumatic stress disorder, and/or service-related injuries. The increasing number of individuals, the long duration of disability, and the rising cost of care for AD and other dementia to our society are important public health challenges facing many older adults. These challenges are further compounded by a burgeoning military veteran population that is much younger, with an increased risk of AD and other dementia, and who may experience decades-long periods of disability and care. This outlook underscores the critical need for investments in research at the federal and international levels to accelerate the pace of progress in developing breakthrough discoveries that will change the trajectory of AD and related dementia.

The future is now: model-based clinical trial design for Alzheimer's disease

Failures in trials for Alzheimer's disease (AD) may be attributable to inadequate dosing, population selection, drug inefficacy, or insufficient design optimization. The Coalition Against Major Diseases (CAMD) was formed in 2008 to develop drug development tools (DDT) to expedite drug development for AD and Parkinson's disease. CAMD led a process that successfully advanced a clinical trial simulation (CTS) tool for AD through the formal regulatory review process at the US Food and Drug Administration (FDA) and European Medicines Agency (EMA).

Development of a unified clinical trial database for Alzheimer's disease

INTRODUCTION

Data obtained in completed Alzheimer's disease (AD) clinical trials can inform decision making for future trials. Recognizing the importance of sharing these data, the Coalition Against Major Diseases created an Online Data Repository for AD (CODR-AD) with the aim of supporting accelerated drug development. The aim of this study was to build an open access, standardized database from control arm data collected across many clinical trials.

METHODS

Comprehensive AD-specific data standards were developed to enable the pooling of data from different sources. Nine member organizations contributed patient-level data from 24 clinical trials of AD treatments.

RESULTS

CODR-AD consists of control arm pooled and standardized data from 24 trials currently numbered at 6500 subjects; Alzheimer's Disease Assessment Scale-cognitive subscale 11 is the main outcome and specific covariates are also included.

DISCUSSION

CODR-AD represents a unique integrated standardized clinical trials database available to qualified researchers. The pooling of data across studies facilitates a more comprehensive understanding of disease heterogeneity.

Arsenic inhibits hedgehog signaling during P19 cell differentiation

Arsenic is a toxicant found in ground water around the world, and human exposure mainly comes from drinking water or from crops grown in areas containing arsenic in soils or water. Epidemiological studies have shown that arsenic exposure during development decreased intellectual function, reduced birth weight, and altered locomotor activity, while in vitro studies have shown that arsenite decreased muscle and neuronal cell differentiation. The sonic hedgehog (Shh) signaling pathway plays an important role during the differentiation of both neurons and skeletal muscle. The purpose of this study was to investigate whether arsenic can disrupt Shh signaling in P19 mouse embryonic stem cells, leading to changes muscle and neuronal cell differentiation. P19 embryonic stem cells were exposed to 0, 0.25, or 0.5 μM of sodium arsenite for up to 9 days during cell differentiation. We found that arsenite exposure significantly reduced transcript levels of genes in the Shh pathway in both a time and dose-dependent manner. This included the Shh ligand, which was decreased 2- to 3-fold, the Gli2 transcription factor, which was decreased 2- to 3-fold, and its downstream target gene Ascl1, which was decreased 5-fold. GLI2 protein levels and transcriptional activity were also reduced. However, arsenic did not alter GLI2 primary cilium accumulation or nuclear translocation. Moreover, additional extracellular SHH rescued the inhibitory effects of arsenic on cellular differentiation due to an increase in GLI binding activity. Taken together, we conclude that arsenic exposure affected Shh signaling, ultimately decreasing the expression of the Gli2 transcription factor. These results suggest a mechanism by which arsenic disrupts cell differentiation.

Developing novel blood-based biomarkers for Alzheimer's disease

Alzheimer's disease is the public health crisis of the 21st century. There is a clear need for a widely available, inexpensive and reliable method to diagnosis Alzheimer's disease in the earliest stages, track disease progression, and accelerate clinical development of new therapeutics. One avenue of research being explored is blood based biomarkers. In April 2012, the Alzheimer's Association and the Alzheimer's Drug Discovery Foundation convened top scientists from around the world to discuss the state of blood based biomarker development. This manuscript summarizes the meeting and the resultant discussion, including potential next steps to move this area of research forward.

Embryonic arsenic exposure reduces the number of muscle fibers in killifish (Fundulus heteroclitus)

Arsenic is a contaminant of drinking water and has been correlated with adverse developmental outcomes such as low birth weight, reduced weight gain, and altered locomotor activity. Previous research has shown that killifish (Fundulus heteroclitus) exposed to high arsenic levels during embryogenesis had smaller muscle fiber diameters. The current study was designed to determine whether changes in muscle fibers persisted, were exacerbated, or resolved over time. Killifish embryos were exposed to 0-5 ppm arsenite and, upon hatching, were transferred into either clean water or continued receiving the same exposure to arsenic for up to 16 weeks. Arsenic significantly decreased the weight of both embryonic-only exposed juveniles and continuously exposed juveniles between 4 and 16 weeks of development at concentrations as low as 0.8 ppm. Although arsenite exposure increased the percentage of small diameter fibers during the early weeks, fiber diameters returned to control levels in the embryonic-only exposed fish. However, muscle fiber density was still reduced to 85.7%, 80.3%, and 73.8% of control for the 0.8, 2, and 5 ppm embryonic-only exposure groups, respectively, even after 16 weeks of development. These results indicate that while continuous exposure to arsenic may alter the size of muscle fibers, embryonic-only exposure to arsenic has lasting effects on the number of muscle fibers formed.

Beyond amyloid: getting real about nonamyloid targets in Alzheimer's disease

For decades, researchers have focused primarily on a pathway initiated by amyloid beta aggregation, amyloid deposition, and accumulation in the brain as the key mechanism underlying the disease and the most important treatment target. However, evidence increasingly suggests that amyloid is deposited early during the course of disease, even prior to the onset of clinical symptoms. Thus, targeting amyloid in patients with mild to moderate Alzheimer's disease (AD), as past failed clinical trials have done, may be insufficient to halt further disease progression. Scientists are investigating other molecular and cellular pathways and processes that contribute to AD pathogenesis. Thus, the Alzheimer's Association's Research Roundtable convened a meeting in April 2012 to move beyond amyloid and explore AD as a complex multifactorial disease, with the goal of using a more inclusive perspective to identify novel treatment strategies.

Worldwide Alzheimer's disease neuroimaging initiative

The Alzheimer's Disease Neuroimaging Initiative (ADNI) was launched in 2003 to speed drug development by validating imaging and blood/cerebrospinal fluid biomarkers for Alzheimer's disease clinical treatment trials. ADNI is a naturalistic (nontreatment) multisite longitudinal study. A true public-private partnership, the first phase of ADNI (ADNI 1) set a new standard for data sharing without embargo. In addition, it has been extended to 2017 by additional funding (North American-ADNI Grand Opportunities and ADNI 2) as well as multiple projects around the world, collectively known as Worldwide ADNI (WW-ADNI). The goal of WW-ADNI is to harmonize projects and results across different geographical sites and to encourage and harmonize data management and availability to investigators around the world. WW-ADNI projects are currently underway in North America, Europe, Japan, Australia, Korea, Taiwan, and Argentina, with a nascent program in China and a possible future program in Brazil.

Arsenic exposure inhibits myogenesis and neurogenesis in P19 stem cells through repression of the β-catenin signaling pathway

Epidemiological studies have correlated embryonic arsenic exposure with adverse developmental outcomes such as stillbirths, neonatal mortality, and low birth weight. Additionally, arsenic exposure reduces neuronal cell migration and maturation, and reduces skeletal muscle cell formation, alters muscle fiber subtype, and changes locomotor activity. This study used P19 mouse embryonic stem cells to examine whether arsenic exposure could alter their differentiation into skeletal muscles and neurons. When P19 cells were exposed to 0.1, 0.5, or 1.0 μM sodium arsenite, embryoid body (EB) formation was not altered. However, arsenic suppressed their differentiation into muscles and neurons, as evidenced by morphological changes accompanied by a significant reduction in myosin heavy chain and Tuj1 expression. Real-time PCR, immunofluorescence, and immunoblotting were used to confirm that the altered differentiation was due to the repression of muscle- and neuron-specific transcription factors such as Pax3, Myf5, MyoD, myogenin, neurogenin 1, neurogenin 2, and NeuroD in the arsenite-exposed cells. The reductions in transcription factors expression appear to be caused by repressed Wnt/β-catenin signaling pathways in early embryogenesis, as evidenced by decreased β-catenin expression in the arsenic-exposed EBs on differentiation days 2 and 5. Interestingly, the expression of Nanog, a transcription factor that maintains the pluripotency of stem cells, was increased after arsenite exposure, indicating that arsenite inhibits their differentiation but not proliferation. This study demonstrates that arsenic can perturb the embryonic differentiation process by repressing the Wnt/β-catenin signaling pathway. More importantly, this study may provide insight into how arsenic exposure affects skeletal and neuronal differentiation during embryogenesis.

LOSS of Mrp1 alters detoxification enzyme expression in a tissue- and hormonal-status-specific manner

The multidrug resistance-associated protein1 (MRP1/ABCC1) is a member of the ABCC transporter subfamily that mediates the efflux of pharmaceuticals, xenobiotics and steroid hormones, typically as glutathione, glucuronide or sulfate conjugates. Since loss of one transporter can be compensated by increasing the expression of other transporters and conjugation enzymes, we sought to examine compensatory changes in phase I, II and III enzyme expression in extrahepatic tissues, including the kidney, lungs and small intestine of intact or castrated Mrp1(-/-) male mice. In the kidney, the expression of several P450s, sulfotransferase 1a1 (Sult), glucuronosyltransferases (Ugt) and Mrps2-4, were significantly changed owing to castration alone. The only time genotype mattered was between the castrated FVB and Mrp1 knockout mice. In contrast, expression of the Ugts, Sult 1a1 and Mrp3 in the lungs was significantly downregulated in the Mrp1 knockout mice, so based exclusively on genotype. In the small intestine, there were interactions between steroid hormone levels and genotype, as the expression differences were only found in mice lacking Mrp1, and were changed between intact and castrated animals. The mechanism behind this pattern of expression may be to due to Nrf2 regulation, as its expression mirrors that of the phase II and phase III enzymes. These results indicate that compensatory responses owing to the loss of Mrp1 vary dramatically, depending on the particular tissue. This information will aid in the understanding of how drug uptake, disposition and elimination can be influenced by both hormone status and the presence and magnitude of transporter expression.

Countrywide strategic plans on Alzheimer's disease: developing the framework for the international battle against Alzheimer's disease

As the world's population ages, countries must prepare for the significant impact Alzheimer's disease will have on their health systems, their economies, and their citizens. In anticipation of major global demographic changes, many countries in the G-20 since 2000 have begun to develop and enact plans to address Alzheimer's disease as a national priority. However, even with nearly half of these participating countries having plans in place, there has been little research done to quantify the value of enacting a countrywide plan on this disease. In this review, we summarize recent national plans (from the year 2000 and beyond) and any results stemming from their respective recommendations and activities.

Arsenic exposure to killifish during embryogenesis alters muscle development

Epidemiological studies have correlated arsenic exposure in drinking water with adverse developmental outcomes such as stillbirths, spontaneous abortions, neonatal mortality, low birth weight, delays in the use of musculature, and altered locomotor activity. Killifish (Fundulus heteroclitus) were used as a model to help to determine the mechanisms by which arsenic could impact development. Killifish embryos were exposed to three different sodium arsenite concentrations and were collected at 32 h post-fertilization (hpf), 42 hpf, 168 hpf, or < 24 h post-hatch. A killifish oligo microarray was developed and used to examine gene expression changes between control and 25-ppm arsenic-exposed hatchlings. With artificial neural network analysis of the transcriptomic data, accurate prediction of each group (control vs. arsenic-exposed embryos) was obtained using a small subset of only 332 genes. The genes differentially expressed include those involved in cell cycle, development, ubiquitination, and the musculature. Several of the genes involved in cell cycle regulation and muscle formation, such as fetuin B, cyclin D-binding protein 1, and CapZ, were differentially expressed in the embryos in a time- and dose-dependent manner. Examining muscle structure in the hatchlings showed that arsenic exposure during embryogenesis significantly reduces the average muscle fiber size, which is coupled with a significant 2.1- and 1.6-fold upregulation of skeletal myosin light and heavy chains, respectively. These findings collectively indicate that arsenic exposure during embryogenesis can initiate molecular changes that appear to lead to aberrant muscle formation.

Developing a global strategy to prevent Alzheimer's disease: Leon Thal Symposium 2010

The fourth Leon Thal Symposium (LTS2010) was convened in Toulouse, France, on November 3, 2010. This symposium reviewed design parameters that are necessary to develop comprehensive national databases on healthy aging. Such datasets offer the potential to serve as the foundation for a systems-approach to solve the dual public health problems of: (1) early detection of people who are at elevated risk for Alzheimer's disease, and (2) the development of interventions to delay onset of, or prevent, late-life dementia. The symposium considered three interrelated components of a National Database for Longitudinal Studies on Healthy Aging as follows: (a) a registry of healthy aging adults; (b) refined computer-based assessments for data gathering, including assessments of behavioral/memory changes associated with aging that are appropriate for broad use in nonexpert settings; and (c) high performance computing/supercomputer-based approaches for health data modeling and mining.

Impact of metals on macroinvertebrate assemblages in the Forgotten Stretch of the Rio Grande

The objective of this study was to examine how changes in the benthic macroinvertebrate community structure and a variety of abiotic variables, such as conductivity and sediment metal concentrations, are modified along the Forgotten River stretch of the Rio Grande. This stretch receives industrial effluent, raw sewage, and agricultural return flow from the El Paso (TX, USA)-Ciudad Juárez (CHI, Mexico) metroplex and then flows relatively undisturbed for 320 km before its next significant input. The high degree of use, followed by the 320-km undisturbed stretch, makes the Forgotten River a unique study site to examine downstream attenuation of contaminants and other abiotic variables to determine their potential effects on macroinvertebrates. Five different sites along the Forgotten Stretch were sampled over a 2-year period. Metal concentrations were low throughout the stretch and were predominantly correlated to percent sediment organic matter rather than explained spatially. Several sensitive invertebrate species, such as Leptophlebiidae, increased in relative abundance downstream, whereas the percentage of tolerant invertebrates decreased. Nonmetric multidimensional scaling separated the macroinvertebrate communities upstream from those downstream, with the more sensitive species being found predominantly downstream and more tolerant taxa associated upstream. Additionally, there was a distinct seasonal gradient to the community. The most important drivers of the community assemblage appear to be distance downstream and seasonality, as well as water conductivity and concentrations of sediment cadmium, which was the only metal that exceeded protective criteria. This study did not provide evidence of the downstream attenuation of heavy metals in the sediments in the Forgotten Stretch; however, downstream changes in macroinvertebrates toward more sensitive taxa suggests that other, unmeasured contaminants might be affecting biological communities in this isolated stretch of an international waterway.

Sodium arsenite delays the differentiation of C2C12 mouse myoblast cells and alters methylation patterns on the transcription factor myogenin

Epidemiological studies have correlated arsenic exposure with cancer, skin diseases, and adverse developmental outcomes such as spontaneous abortions, neonatal mortality, low birth weight, and delays in the use of musculature. The current study used C2C12 mouse myoblast cells to examine whether low concentrations of arsenic could alter their differentiation into myotubes, indicating that arsenic can act as a developmental toxicant. Myoblast cells were exposed to 20 nM sodium arsenite, allowed to differentiate into myotubes, and expression of the muscle-specific transcription factor myogenin, along with the expression of tropomyosin, suppressor of cytokine signaling 3 (Socs3), prostaglandin I2 synthesis (Ptgis), and myocyte enhancer 2 (Mef2), was investigated using QPCR and immunofluorescence. Exposing C2C12 cells to 20 nM sodium arsenite delayed the differentiation process, as evidenced by a significant reduction in the number of multinucleated myotubes, a decrease in myogenin mRNA expression, and a decrease in the total number of nuclei expressing myogenin protein. The expression of mRNA involved in myotube formation, such as Ptgis and Mef2 mRNA, was also significantly reduced by 1.6-fold and 4-fold during differentiation. This was confirmed by immunofluorescence for Mef2, which showed a 2.6-fold reduction in nuclear translocation. Changes in methylation patterns in the promoter region of myogenin (-473 to +90) were examined by methylation-specific PCR and bisulfite genomic sequencing. Hypermethylated CpGs were found at -236 and -126 bp, whereas hypomethylated CpGs were found at -207 bp in arsenic-exposed cells. This study indicates that 20 nM sodium arsenite can alter myoblast differentiation by reducing the expression of the transcription factors myogenin and Mef2c, which is likely due to changes in promoter methylation patterns. The delay in muscle differentiation may lead to developmental abnormalities.

Dose-responsive gene expression changes in juvenile and adult mummichogs (Fundulus heteroclitus) after arsenic exposure

The present study investigated arsenic's effects on mummichogs (Fundulus heteroclitus), while also examining what role that gender or exposure age might play. Adult male and female mummichogs were exposed to 172 ppb, 575 ppb, or 1720 ppb arsenic as sodium arsenite for 10 days immediately prior to spawning. No differences were noted in the number or viability of eggs between the groups, but there was a significant increase in deformities in 1720 ppb arsenic exposure group. Total RNA from adult livers or 6-week old juveniles was used to probe custom macroarrays for changes in gene expression. In females, 3% of the genes were commonly differentially expressed in the 172 and 575 ppb exposure groups compared to controls. In the males, between 1.1 and 3% of the differentially expressed genes were in common between the exposure groups. Several genes, including apolipoprotein and serum amyloid precursor were commonly expressed in either a dose-responsive manner or were dose-specific, but consistent across genders. These patterns of regulation were confirmed by QPCR. These findings will provide us with a better understanding of the effects of dose, gender, and exposure age on the response to arsenic.

Developing a national strategy to prevent dementia: Leon Thal Symposium 2009

Among the major impediments to the design of clinical trials for the prevention of Alzheimer's disease (AD), the most critical is the lack of validated biomarkers, assessment tools, and algorithms that would facilitate identification of asymptomatic individuals with elevated risk who might be recruited as study volunteers. Thus, the Leon Thal Symposium 2009 (LTS'09), on October 27-28, 2009 in Las Vegas, Nevada, was convened to explore strategies to surmount the barriers in designing a multisite, comparative study to evaluate and validate various approaches for detecting and selecting asymptomatic people at risk for cognitive disorders/dementia. The deliberations of LTS'09 included presentations and reviews of different approaches (algorithms, biomarkers, or measures) for identifying asymptomatic individuals at elevated risk for AD who would be candidates for longitudinal or prevention studies. The key nested recommendations of LTS'09 included: (1) establishment of a National Database for Longitudinal Studies as a shared research core resource; (2) launch of a large collaborative study that will compare multiple screening approaches and biomarkers to determine the best method for identifying asymptomatic people at risk for AD; (3) initiation of a Global Database that extends the concept of the National Database for Longitudinal Studies for longitudinal studies beyond the United States; and (4) development of an educational campaign that will address public misconceptions about AD and promote healthy brain aging.