July 29, 2008
Markers in Blood and Spinal Fluid, and a New Imaging Agent, Show Promise for Early Detection of Alzheimer’s
To: NATIONAL EDITORS
Contact: Alzheimers Association media line: +1-312-335-4078, [email protected]; ICAD 2008 press room, July 27-31: +1-312-949-3253
CHICAGO, July 29/PRNewswire-USNewswire/ -- With the continued aging of the population and the growing epidemic of Alzheimers, early detection of the disease is crucial for risk assessment, testing new therapies, and eventual early intervention with better drugs, once they are developed. Four studies reported today at the Alzheimers Associations 2008 International Conference on Alzheimers Disease (ICAD 2008) in Chicago bring us closer to that goal of early detection by describing advances in biomarkers.
A biomarker is a substance or characteristic that can be objectively measured and evaluated as an indicator of normal body processes, disease processes, or the bodys response(s) to a therapeutic intervention.
It is widely believed that Alzheimers disease brain changes, including amyloid plaques and neurofibrillary tangles, begin many years before symptoms are evident or there is significant death of brain cells. It is critical to identify affected individuals while they are still cognitively normal so that future disease modifying therapies can preserve normal function. The testing and eventual use of such therapies requires identification of affected and at risk individuals in order to steer them to clinical trials, and to direct and monitor therapy.
Discovery of measurable markers that track with the presence of Alzheimers pathology and that predict the development of cognitive decline in people who are still cognitively normal, known as antecedent biomarkers, are especially needed, said William Thies, PhD, vice president of Medical and Scientific Relations at the Alzheimers Association. It is greatly preferable that these markers be easy to obtain, such as in samples of blood or urine, or through readily available imaging technologies, such as MRI and PET.
Blood Test on White Blood Cells May Be Useful for Early Detection of Alzheimers
Healthy brain cells do not go through the process of division and replication (known as the cell cycle) that is common in other cells in the body. However, in Alzheimers disease, brain cells have demonstrated an abnormal tendency to prepare to re-enter this cell cycle, which may increase their likelihood of dying or directly cause their death.
The equivalent cell cycle defect is found in lymphocytes of people with Alzheimers. Lymphocytes are white blood cells in the immune system that can easily be collected for testing by a simple blood draw. Professor Thomas Arendt, Director of the Paul Flechsig Institute, University of Leipzig, Germany, thought that this suggested a vehicle for detecting Alzheimers.
In a study performed in the U.S. by GW Medical, the licensor of Arendts technology, Arendt and colleagues measured the expression of CD-69 (a protein involved in white blood cell growth and production) on multiple cell lines in people with probable Alzheimers (n=32), healthy controls (n=30) and other dementias, chiefly Parkinsons disease dementia, (n=26).
Variations in levels of CD-69 enabled the researcher to clearly differentiate between Alzheimers subjects and demented Parkinsons subjects. It was accurate 91 percent of the time when the diagnosis was Alzheimers and 92 percent of the time when it was Parkinsons dementia. The assay correctly differentiated people with Alzheimers from cognitively normal subjects 88 percent of the time when the diagnosis was Alzheimers and 82 percent of the time when the person was cognitively normal.
In addition, Arendt found that the test results did not vary with dementia severity as measured by the Mini Mental State Exam.
The lack of variation suggests that this test may be useful in the early stages of Alzheimers, Arendt said. A larger trial is underway with results expected by late summer 2008. If confirmed, it will give primary care physicians a better, more accurate and non- invasive test for Alzheimers disease.
Spinal Fluid Marker Tracks Brain Amyloid, May Identify Alzheimers Before Symptoms
Some researchers believe that flaws in processes governing production, accumulation, or disposal of amyloid protein in the brain are the primary cause of Alzheimers. AB42 is a particularly sticky variety of amyloid protein fragment that is more likely to aggregate into small clusters and eventually into the plaques that are considered one hallmark of the Alzheimer brain.
Anne M. Fagan, PhD, of the Washington University School of Medicine, St. Louis, MO, and colleagues previously demonstrated in a small group (n=24) that a low level of AB42 in cerebrospinal fluid (CSF) is an effective marker for determining the presence of amyloid in the brain as assessed by PET scans using a marker called Pittsburgh Compound B (PIB).
In a new study presented at ICAD 2008, Fagan reported on a much larger cohort (n=132; age 45-88 years, mean 65.7). This group included individuals who were non-demented plus those with very mild or mild dementia. Consistent with the prior study, the researchers observed a striking inverse relation between presence of amyloid in the brain and levels of AB42 in CSF.
Overall, those people with high amounts of brain amyloid (as indicated by PET scan images showing positive PIB-binding) had low CSF AB42 (36/37, 97%). Those with low levels of brain amyloid (negative PIB-binding) had high CSF AB42 (80/95, 84%). This was true regardless of cognitive status, indicating excellent sensitivity of CSF AB42 for identifying the presence of brain amyloid, according to the researchers.
In addition, they observed that three non-demented, low CSF AB42, PIB-positive study participants have subsequently received an Alzheimers diagnosis suggesting that positive PIB and low CSF AB42 may be useful as markers of preclinical Alzheimers (that is, Alzheimers prior to visible symptoms).
We found that CSF AB42 is an excellent marker for identifying the presence of amyloid in the brain, regardless of the persons cognitive status, Fagan said. Our analyses also suggest that a decline in CSF AB42 may effectively identify non-demented individuals who are in the preclinical stage of Alzheimers, even before they are PIB positive.
Brain Enzyme May Improve Alzheimers Risk Assessment and Early Detection
Researchers have previously found elevated B-secretase (BACE1) activity in the brains of patients with Alzheimers compared to healthy individuals. BACE1 is one of two enzymes involved in the pathological processing of amyloid precursor protein (APP) and the production of toxic AB (beta amyloid, the main constituent of amyloid plaques in the brains of people with Alzheimer's).
Professor Harald Hampel, of Trinity College Dublin, Ireland and the University of Munich, Germany, Professor Yong Shen, of Sun Health Research Institute, USA, and colleagues investigated whether BACE1 assessed in cerebrospinal fluid (CSF) may be a feasible biomarker candidate for predicting Alzheimers in people with mild cognitive impairment (MCI). MCI is a transition stage between the cognitive changes of normal aging and the more serious problems caused by Alzheimer's.
The research had two parts. In the first part, the scientists measured BACE1 levels in CSF in 80 people with Alzheimers, 59 people with MCI, and 69 healthy elderly controls (HC) at two independent, international research centers. MCI subjects showed highly increased levels of BACE1 activity when compared to HC and people with Alzheimers. BACE1 activity was significantly correlated with AB level. A subsequent validation study replicated these initial findings in a new and independent set of 41 people with Alzheimers, 46 with amnestic MCI and elderly HC.
In the second part, 47 MCI subjects were clinically followed up over two years to assess the predictive value of BACE1 in combination with other biomarker candidates for predicting the conversion from MCI to Alzheimers. The additional candidates were abnormal brain proteins total tau and phosphorylated tau measured in CSF, and baseline performance on a large neuropsychological testing battery. Fifteen (15) MCI subjects converted to Alzheimers after a mean follow-up interval of 2.3 years. Analysis showed that BACE1 protein levels and ApoE genotype (a genetic risk factor for Alzheimers) were the strongest predictors of conversion to Alzheimers, after controlling for age and gender. The classification accuracy was 78%, the sensitivity was 80%, and the specificity was 77% for the combined model.
These important findings pave the way for further rigorous assessment of BACE1 as an effective and accurate clinical diagnostic tool, which could significantly improve risk assessment and early detection of Alzheimers, Hampel said. We believe that BACE1 will be an excellent outcome biomarker to look at in ongoing clinical trials of anti-amyloid, disease modifying therapies. Furthermore, we are working on a blood-based diagnostic test for BACE1 as well.
Improved Amyloid Imaging Agents for PET in Development
A major recent advance in Alzheimers is the ability to create images of amyloid in the brains of living people using positron emission tomography (PET) scanners. With PET, a radioactive compound, or tracer, is injected into the person to be scanned. The tracer attaches to a target substance in the body, in this case amyloid, which then lights up on the image captured by the scanner.
In research reported at ICAD 2008, Michael J. Pontecorvo, PhD, of Avid Radiopharmaceuticals, Philadelphia, PA, and colleagues reported the development of a novel 18F-labeled PET amyloid imaging agent, 18F-AV-45, that may eventually provide a practical approach for routine brain imaging for Alzheimers
PET scanners are relatively common - they are available in most hospitals - yet one of the challenges to more widespread use of PET imaging in Alzheimers is that the radioactivity of the first amyloid- imaging tracer, called 11C-PIB or Pittsburgh Compound B, is relatively short-lived. With this agent, based on radioactive carbon, half of the radioactivity is lost every 20 minutes. This means that it must be manufactured onsite, a process that requires a cyclotron (a type of particle accelerator), which is rarely found in community hospitals. This limitation has prompted a search for longer-lived tracers, such as 18F-labeled agents, based on radioactive fluorine, which would be suitable for regional production and wider community use.
In the study, three 18F-labeled compounds were evaluated in 42 cognitively healthy elderly volunteers and 39 individuals with Alzheimers. Each participant received a single intravenous injection of one of the compounds followed by PET imaging.
People with Alzheimers showed retention of all three tracers in brain areas expected to be high in amyloid. In contrast, cognitively healthy volunteers showed rapid removal of the tracers, with minimal retention in the brain. Two individuals diagnosed with Alzheimers had a pattern of tracer uptake similar to healthy volunteers. Chart notes for both suggested unusual presentations - prominent Parkinsonism in one case and slowly progressive dementia in the other.
While the three compounds were similar in pattern and amount of tracer retention, they differed in how they were processed by the body in ways that favored one compound, 18F-AV-45. For example, 18F- AV-45 showed rapid uptake and steady levels were maintained in the brain between 50 and 90 minutes post injection. This allowed high quality images to be obtained from PET imaging beginning 50 minutes after 18F-AV-45 administration, with minimal inconvenience or delay for the patient or the imaging center, according to the researchers.
18F-AV-45 is being used as a research tool today, but it has the potential to aid in the diagnosis and early detection of Alzheimers in a community setting and may be a useful biomarker for the development and monitoring of novel amyloid reducing therapies, Pontecorvo said. On the basis of the findings we reported today, Phase II trials with 18F-AV-45 have been initiated.
About the Alzheimers Association
The Alzheimers Association is the leading voluntary health organization in Alzheimers research, care and support. Our mission is to eliminate Alzheimers disease through the advancement of research, provide and enhance care and support for all affected, and reduce the risk of dementia through the promotion of brain health. Our vision is a world without Alzheimers. For more information, visit www.alz.org.
The Alzheimers Association 2008 International Conference on Alzheimer's Disease (ICAD 2008) is the largest gathering of Alzheimer researchers in history. At ICAD 2008, more than 5,000 researchers will share groundbreaking information and resources on the cause, diagnosis, treatment and prevention of Alzheimers and related disorders. As a part of the Associations research program, ICAD serves as a catalyst for generating new knowledge about dementia and fostering a vital, collegial research community.
-- Thomas Arendt. Diagnosis Of Alzheimers Disease Using Peripheral Blood Lymphocyte Expression Of CD-69 Following A Mitogenic Stimulus. (Funders: National Institutes of Health, GW Medical, Provista Life Sciences)
-- Anne M. Fagan. Update on the relationship between in vivo amyloid imaging with 11C-PIB and CSF AB42. (Funders: : National Institute on Aging, Dana Foundation, Anonymous Foundation, Charles and Joanne Knight Alzheimers Initiative)
-- Harald Hampel. Alteration of beta secretase (BACE1) functional candidate biomarkers in subjects with mild cognitive impairment and Alzheimer's disease. (Funders: Science Foundation Ireland, Federal Ministry of Education and Research (Germany), Alzheimers Association)
-- Michael J. Pontecorvo. Development of 18F-AV-45, a novel 18F- labeled A amyloid imaging agent. (Funders: Avid Radiopharmaceuticals)
SOURCE Alzheimer's Association
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