New Nuclear Medicine Tracer Will Help Study the Aging Brain

By Sondra Forsyth

A new PET imaging radiotracer could help researchers understand neurodegenerative disease and the aging brain. The study was featured in the October 2018 issue of The Journal of Nuclear Medicine.

A release from the Society of Nuclear Medicine and Molecular Imaging explains that past studies have shown a reduced density of the α4β2 nicotinic acetylcholine receptor (α4β2-nAChR) in the cortex and hippocampus of the brain in aging patients and those with neurodegenerative disease. The α4β2-nAChR is partly responsible for learning, and even a small loss of activity in this receptor can have wide-ranging effects on neurotransmission across neural circuits. However, fast and high-performing α4β2-nAChR-targeting radiotracers are scarce for imaging outside the thalamus, where the receptor is less densely expressed.

A team at Johns Hopkins University assessed the pharmacokinetic behavior of ¹⁸F-XTRA, a new PET imaging radiotracer for the α4β2-nAChR. The researchers tested the new radiotracer on a group of 17 adults and focused on extrathalamic regions of the brain. The research team found that ¹⁸F-XTRA rapidly entered the brain and distributed quickly.

The release quotes Martin Pomper, MD, PhD. As saying, “We present data using a new radiotracer with PET to characterize the distribution of the α4β2-nAChR in the human brain. The observed high uptake into the brain, fast pharmacokinetics, and ability to estimate binding in extrathalamic regions within a 90-minute scan supports further use of ¹⁸F-XTRA in clinical research populations. We also report the finding of lower ¹⁸F-XTRA binding in the hippocampus with healthy aging, which marks a potentially important finding from biological and methodological perspectives.”

The team said their findings will be important for future studies, especially in cases relating to neurodegeneration and aging, to monitor and assess changes in the human brain.

“Together, our results suggest that ¹⁸F-XTRA PET may be sufficiently sensitive to measure the hypothesized loss of α4β2-nAChR availability over aging, particularly in the hippocampus,” Dr. Pomper said. “This is a promising tool for the future study of changed cholinergic signaling in the brain over healthy aging that may be linked to changes in memory over the lifespan.”

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Authors of “18F-XTRA PET for Enhanced Imaging of the Extrathalamic α4β2 Nicotinic Acetylcholine Receptor” include Jennifer Coughlin, Stephanie Slania, Yong Du, Hailey Rosenthal, Wojciech Lesniak, Il Minn, Gwenn Smith, Robert Dannals, Hiroto Kuwabara, Dean Wong, Yuchuan Wang, Andrew Horti and Martin Pomper, Johns Hopkins Medical Institutions, Baltimore, Maryland.