Atrophy predictor
Results showed that higher plasma p-tau181 levels at baseline were associated with more rapid progression of hypometabolism and atrophy in areas vulnerable to Alzheimer’s disease among cognitively impaired participants (FDG-PET standardized uptake value ratio change, r = –0.28; P < .001; gray-matter volume change, r = –0.28; P < .001).
The association with atrophy progression in cognitively impaired participants was stronger for p-tau181 than for NfL.
Plasma p-tau181 levels at baseline also predicted atrophy in temporoparietal regions vulnerable to Alzheimer’s disease among cognitively unimpaired participants (r = –0.11; P = .03). NfL, however, was associated with progressive atrophy in frontal regions among cognitively unimpaired participants.
At baseline, plasma p-tau181 levels were associated with prospective cognitive decline in both the cognitively unimpaired group (r = −0.12; P = .04) and the cognitively impaired group (r = 0.35; P < .001). However, plasma NfL was linked to cognitive decline only among those who were cognitively impaired (r = 0.26; P < .001).
Additional analyses showed that p-tau181, unlike NfL, was associated with hypometabolism and atrophy only in participants with amyloid-beta, regardless of cognitive status.
Between 25% and 45% of the association between baseline p-tau181 level and cognitive decline was mediated by baseline imaging markers of neurodegeneration. This finding suggests that another factor, such as regional tau pathology, might have an independent and direct effect on cognition, Dr. Schöll noted.
Furthermore, changes over time in p-tau181 levels were associated with cognitive decline in the cognitively unimpaired (r = –0.24; P < .001) and cognitively impaired (r = 0.34; P < .001) participants. Longitudinal changes in this biomarker also were associated with a prospective decrease in glucose metabolism in cognitively unimpaired (r = –0.05; P = .48) and cognitively impaired (r = –0.27; P < .001) participants, but the association was only significant in the latter group.
Changes over time in p-tau181 levels were linked to prospective decreases in gray-matter volume in brain regions highly characteristic of Alzheimer’s disease in those who were cognitively unimpaired (r = –0.19; P < .001) and those who were cognitively impaired (r = –0.31, P < .001). However, these associations were obtained only in patients with amyloid-beta.
Dr. Schöll noted that blood-based biomarkers that are sensitive to Alzheimer’s disease could greatly expand patients’ access to a diagnostic workup and could improve screening for clinical trials.
“While the final validation of the existence and the monitoring of potential changes of neuropathology in vivo is likely to be conducted using neuroimaging modalities such as PET, our results suggest that at least a part of these examinations could be replaced by regular blood tests,” Dr. Schöll said.
Lead author Alexis Moscoso, PhD, a postdoctoral researcher in psychiatry and neurochemistry at the University of Gothenburg, reported that the researchers will continue validating blood-based biomarkers, especially against established and well-validated neuroimaging methods. “We are also hoping to be able to compare existing and novel blood-based Alzheimer’s disease biomarkers head to head to establish the individual roles each of these play in the research and diagnosis of Alzheimer’s disease,” Dr. Moscoso said.
‘Outstanding study’
Commenting on the findings, David S. Knopman, MD, professor of neurology at Mayo Clinic, Rochester, Minn., said that this is “an outstanding study” because of its large number of participants and because the investigators are “world leaders in the technology of measuring plasma p-tau and NfL.”
Dr. Knopman, who was not involved with the research, noted that the study had no substantive weaknesses.
“The biggest advantages of a blood-based biomarker over CSF- and PET-based biomarkers of Alzheimer disease are the obvious ones of accessibility, cost, portability, and ease of repeatability,” he said.
“As CSF and PET exams are largely limited to major medical centers, valid blood-based biomarkers of Alzheimer disease that are reasonably specific make large-scale epidemiological studies that investigate dementia etiologies in rural or urban and diverse communities feasible,” he added.
Whereas p-tau181 appears to be specific for plaque and tangle disease, NfL is a nonspecific marker of neurodegeneration.
“Each has a role that could be valuable, depending on the circumstance,” said Dr. Knopman. “Plasma NfL has already proved itself useful in frontotemporal degeneration and chronic traumatic encephalopathy, for example.”
He noted that future studies should examine how closely p-tau181 and NfL align with more granular and direct measures of Alzheimer’s disease–related brain pathologies.
“There has got to be some loss of fidelity in detecting abnormality in going from brain tissue to blood, which might siphon off some time-related and severity-related information,” said Dr. Knopman.
“The exact role that plasma p-tau and NfL will play remains to be seen, because the diagnostic information that these biomarkers provide is contingent on the existence of interventions that require specific or nonspecific information about progressive neurodegeneration due to Alzheimer disease,” he added.
The study was funded by grants from the Spanish Instituto de Salud Carlos III, the Brightfocus Foundation, the Swedish Alzheimer Foundation, and the Swedish Brain Foundation. Dr. Schöll reported serving on a scientific advisory board for Servier on matters unrelated to this study. Dr. Moscoso and Dr. Knopman have reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.