Barcelona, Spain – August 14, 2013 – A study published today reported the identification of what may be the earliest known biomarker associated with the risk of developing Alzheimer's disease (AD). The results suggest that this novel potential biomarker is present in cerebral spinal fluid (CSF) at least a decade before signs of dementia manifest.
"If our initial findings can be replicated by other laboratories, the results will change the way we currently think about the causes of Alzheimer's disease," said Dr. Ramon Trullas, research professor at the CSIC Institute of Biomedical Research of Barcelona and lead author of the study that was published in Annals of Neurology. "This discovery may enable us to search for more effective treatments that can be administered during the preclinical stage."
Alzheimer's disease affects more than five million Americans and is the sixth leading cause of death in the United States. At present, the only way to accurately diagnose the disease is by post-mortem neuropathological analysis. The relationship of currently known biomarkers with the cause of the disease is unclear, making it nearly impossible to diagnose preclinical stages of the disease with any real certainty.
The CSIC researchers demonstrated that a decrease in the content of mitochondrial DNA (mtDNA) in CSF may be a preclinical indicator for Alzheimer's disease; furthermore, there may be a directly causative relationship. The hypothesis is that decreased mtDNA levels in CSF reflect the diminished ability of mitochondria to power the brain's neurons, triggering their death. The decrease in the concentration of mtDNA precedes the appearance of well-known biochemical Alzheimer's biomarkers (the Aβ1-42, t-tau, and p-tau proteins), suggesting that the pathophysiological process of Alzheimer's disease starts earlier than previously thought and that mtDNA depletion may be one of the earliest predictors for the disease.
In addition to enabling an investigation of the potential causal relationship of mtDNA and Alzheimer's progression, the use of mtDNA as an index of preclinical Alzheimer's disease provides an important advantage over previous biochemical markers: the detection of this novel nucleic acid biomarker is unhampered by the technical difficulties associated with protein detection. mtDNA can be readily quantified by real-time quantitative PCR (qPCR) or droplet digital PCR (ddPCR).
Quantitation of mtDNA
Prior to this study, researchers had not reported that circulating cell-free mtDNA could be detected in human CSF. But with this study, Dr. Trullas' team was able to both detect and reproducibly quantitate mtDNA using qPCR, carefully optimized by adhering to the MIQE guidelines.
To validate their qPCR findings, Dr. Trullas' team used Bio-Rad Laboratories' QX100™ Droplet Digital™ PCR system. Unlike qPCR assays, the QX100 system provides an absolute quantification of target DNA molecules without the need for a standard curve. In addition, an important factor for their CSF analysis was that the Droplet Digital PCR system did not require sample purification to remove PCR inhibitors, as is necessary for qPCR assays.
"Droplet Digital PCR allowed us to validate our initial qPCR measurements because it provides absolute quantitation at the single-molecule level without relying on a standard curve," said Dr. Trullas. "As the technology becomes more widely adopted, we anticipate that Droplet Digital PCR will be the future of detecting mtDNA in cerebral spinal fluid."
Dr. Trullas hopes that other laboratories and hospitals will successfully replicate his group's research results, confirming that reduced mtDNA levels should be investigated as a possible cause of Alzheimer's disease. By finding a way to block this degeneration, clinicians may be able to diagnose and treat Alzheimer's disease before symptoms appear.
This work was supported by the Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED) and by grants SAF2008-03514, SAF2011-23550 from the Government of Spain. Dr. Trullas is also affiliated with the Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS).
About Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas (CIBERNED)
CIBERNED is a public nonprofit organization of the Government of Spain for biomedical research on neurodegenerative diseases, such as Alzheimer's. CIBERNED is funded by the Health Institute Carlos III from the Ministry of Economy and Competitiveness. In addition to basic and clinical research, CIBERNED aims to involve society in reducing the negative impact of neurodegeneration. http://www.ciberned.es.
About Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS)
IDIBAPS is a consortium formed by three public nonprofit governmental research institutions from Catalonia and Spain: Hospital Clínic of Barcelona, University of Barcelona School of Medicine, and CSIC's Barcelona Biomedical Research Institute. IDIBAPS aims to translate basic research on current medical challenges into clinical treatments, and that the results obtained in laboratories can be effectively used to benefit patients. http://www.idibaps.org.
Bio-Rad Laboratories, Inc. (NYSE: BIO and BIOb) has been at the center of scientific discovery for 60 years, manufacturing and distributing a broad range of products for life science research and clinical diagnostic markets. The company is renowned for its commitment to quality and customer service among university and research institutions, hospitals, public health and commercial laboratories, as well as the biotechnology, pharmaceutical, and food safety industries. Founded in 1952, Bio-Rad is based in Hercules, California, and serves more than 100,000 research and industry customers through its global network of operations. The company employs approximately 7,600 people worldwide and had revenues exceeding $2 billion in 2012. Visit us at http://www.bio rad.com.
Annals of Neurology