The failure to diagnose Alzheimer’s disease—the most common form of dementia in the elderly—at an early stage of molecular pathology is considered a major reason that treatments fail in clinical trials. Previous research to molecularly diagnose Alzheimer’s disease yielded “A/T/N” central biomarkers based on the measurements of proteins, β-amyloid (“A”) and tau (“T”), and “N” encompassing neurodegeneration. A/T/N can be measured in brain tissue, by in vivo brain imaging techniques, and by analysis of cerebrospinal fluid and plasma.

Alzheimer’s disease is thought to be triggered by combinations of genetic and environmental risk factors. Blood-based biomarkers such as plasma microRNAs (miRNAs)—molecules that regulate genome-environment interactions and control the expression of genes governing brain functions which deteriorate in Alzheimer’s—could offer advantages of cost-savings, accessibility and decreased invasiveness.

Two new papers by a team of researchers at Boston University, the Indiana University School of Medicine and the Alzheimer’s Disease Neuroimaging Initiative (ADNI), and the German Center for Neurodegenerative Diseases (DZNE) in Goettingen, Germany, published in Alzheimer’s & Dementia demonstrate that evaluating microRNAs in blood can be used not only to diagnose mild cognitive impairment (MCI), but also, critically, to predict the conversion from MCI to dementia due to Alzheimer’s disease. Moreover, the researchers uncovered microRNA candidate molecular biomarkers that associate with current amyloid, tau, and neurodegeneration (A/T/N) Alzheimer’s biomarkers.

“Our papers are the result of a successful collaboration that tied the technology developed by professor Andre Fischer in Germany’s DZNE to reliably measure the levels of microRNA in human plasma, and the power of blood samples obtained from hundreds of ADNI participants participating in a simulated clinical trial taking place at about 60 medical centers across the US and Canada,” said Ivana Delalle, MD, Ph.D., professor of pathology & laboratory medicine at Boston University Chobanian & Avedisian School of Medicine, and one of four senior authors.

Our discovery is important, because unlike the current A/T/N biomarkers, microRNAs may serve as blood molecular biomarkers years before Alzheimer’s disease manifests clinically, thus identifying the time window for effective prevention or early intervention to stop the progression of Alzheimer’s.”

The other senior authors are Andre Fischer, Ph.D., DZNE speaker and professor of epigenetics of neurodegenerative diseases at University Medical Center Goettingen, Germany; Kwangsik Nho, Ph.D., professor of radiology and imaging sciences at the IU School of Medicine; and Andrew J. Saykin, PsyD, Raymond C. Beeler Professor of Radiology and director of the Center for Neuroimaging and the Indiana Alzheimer’s Disease Research Center at the IU School of Medicine.

The researchers examined miRNA expression in the plasma samples of three diagnostic groups of participants—cognitively normal, mildly cognitively impaired and dementia due to Alzheimer’s disease patients. They found that when combined with neuropsychological testing, plasma microRNAome evaluation helps predict which aging individuals concerned about cognitive decline will progress to develop Alzheimer’s.

“These findings provide a path toward a better understanding of the molecular mechanisms driving plaques, tangles and atrophy, and may provide clues for the next generation of therapeutic targets,” Saykin said.

While these are exciting times with novel therapies for Alzheimer’s disease entering clinical care, the researchers note that those therapies will only work in a real-world setting if patients at risk are identified as early as possible.

“MicroRNAs are ideal biomarkers since they are not only very stable, but also control entire molecular pathways, thereby ensuring cellular homeostasis. As such, one microRNA can simultaneously control many proteins belonging to a certain pathway,” Fischer said.

“Therefore, the analysis of a few microRNAs can inform about complex pathological changes reflecting multiple pathways, such as neuroinflammation, metabolic changes, or synapse dysfunction. Thus, we need biomarkers that allow screening applicable in a point-of-care setting. Our studies are an important step in this direction.”

“We have laid the groundwork for further investigations into the role of microRNAs in Alzheimer’s disease pathogenesis,” Nho said. “We envision that once specific miRNA signatures are further confirmed, the analysis of blood miRNAs will be transferred to simple assay formats, enabling the adoption of blood miRNAome analysis in clinical practice.”

The researchers said improved tools for the early detection of Alzheimer’s are indispensable for developing prevention and treatment strategies for the disease that is causing enormous suffering and burdens on health care systems around the world.