SILK Blood Test Can Catch Alzheimer’s Sooner

The Stable Isotope Labeling Kinetics (SILK™) blood test can catch Alzheimer’s years before signs appear. Learn about this important advance for prevention, treatment and research.

Biomarkers in the blood, indicating Alzheimer’s, may appear 15 years before there are signs of trouble. If researchers could just use those biomarkers to catch Alzheimer’s earlier, they would have a much better shot at finding ways to prevent and treat it.

New technologies are trying to achieve this goal. Leading the pack is the Stable Isotope Labeling Kinetics (SILK™) platform pioneered at Washington University School of Medicine (WUSM) in St. Louis and already marketed by C2N. It includes new technologies that enable a novel approach to measure the metabolism of brain-derived proteins implicated in Alzheimer’s disease (AD) and mild cognitive impairment (MCI).

Biomarkers are chemicals in our bodies that are markers for an illness, such as Alzheimer’s. Until now, doctors looking for Alzheimer’s biomarkers would go through the delicate process of taking cerebrospinal fluid from patients. For the first time, instead of analyzing Alzheimer’s proteins in cerebrospinal fluid, it is now possible to detect the same metabolic markers in patients’ blood samples.

This capability has implications for the advancement of new treatments, early prevention, and personal wellness. Alzheimer’s is now one of the major global healthcare concerns. Approximately 44 million people currently have clinical Alzheimer’s disease (AD). Millions more have MCI that places them at high risk for progression to clinical AD. The number of cases of AD and MCI are expected to increase sharply in the years ahead due to the aging baby boomer population.

Pharmaceutical companies developing new drugs targeting AD increasingly recognize that early intervention provides the greatest chance of halting or reversing disease progression. Biomarkers are needed to detect this early pathology, which can begin at least 15 years before the onset of any clinical symptoms. At the same time, dynamic biomarkers, like those offered by the SILK™ platform, may also track treatment responses during the pre-symptomatic stages of disease.

Since 2008, C2N has applied the SILK-Aβ® test to measure the kinetics of beta-amyloid in cerebrospinal fluid. The test has served as a primary endpoint in clinical drug studies to demonstrate target engagement and guide dose selection. The SILK-Aβ® isoforms test is also highly sensitive to identifying people with brain amyloidosis (one of the earliest indicators of Alzheimer’s), even before amyloid deposits are seen with brain imaging. Still, the more invasive nature of cerebrospinal fluid sampling has impeded the full potential of the SILK-Aβ® method.

“With a simplified SILK-Aβ® test available through blood sampling, we now have an opportunity to validate a unique therapeutic and diagnostic marker,” stated Dr. Joel B. Braunstein, CEO of C2N. “We plan to achieve this validation by collaborating with pharmaceutical companies that are testing their compounds in phase 2 and phase 3 clinical studies, as well as by participating in natural history studies tracking the progression of AD. If successful, we expect to be able to offer a reliable and informative screening test that is also convenient for patients.”

Alzheimer’s Disease & Mild Cognitive Impairment

Currently AD is diagnosed based on clinical assessment by skilled neurologists or based on an amyloid imaging brain scan: there are no approved blood based biomarkers for this disease. Early detection of AD is a major research focus since early detection would pave the way for early intervention. Mild cognitive impairment (MCI) is often a precursor of clinical AD. The disorder is associated with cognition changes that are serious enough to be noticed by the individuals experiencing them or to other people, but the changes are not severe enough to interfere with activities of daily living. Individuals with MCI have a significantly increased risk of eventually developing AD, with approximately 50% of such individuals converting to AD within three years.

SILK-Aβ® Technology

Dr. Randall Bateman and Dr. David Holtzman originally developed the SILK™ technology at WUSM. Scientific American recognized the SILK-Aβ® assay as one of the top 50 new innovative technologies of the year. Similar to a pulse chase assay, the SILK-Aβ® assay relies on in vivo labeling of human subjects with a stable isotope labeled amino acid. The stable isotope labeled amino acid is non-radioactive, safe to the environment and to humans, and is incorporated into newly generated proteins. Using a highly sensitive mass spectrometer, we can measure the incorporation of the stable isotope into Aβ and thereby assess the metabolism of Aβ. This ability is particularly useful for early detection of brain amyloidosis or when assessing the pharmacodynamic effect of drugs that are hypothesized to alter the metabolism of Aβ in humans. With these new developments, we have expanded the use of the assay to measuring Aβ metabolism in plasma.