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In a cross-sectional study of adults with and those without cognitive impairment, chronic kidney disease was associated with increased plasma concentrations of phosphorylated tau (p-tau) 217 and 181.
However, there were no associations between chronic kidney disease and the ratio of p-tau217 to unphosphorylated tau 217 (pT217/T217), and the associations with p-tau181 to unphosphorylated tau 181 (pT181/T181) were attenuated in patients with cognitive impairment.
“These novel findings suggest that plasma measures of the phosphorylated to unphosphorylated tau ratios are more accurate than p-tau forms alone as they correlate less with individual difference in glomerular filtration rate or impaired kidney function,” reported an investigative team led by Oskar Hansson, MD, PhD, with Lund University in Sweden.
“Thus, to mitigate the effects of non-Alzheimer’s–related comorbidities like chronic kidney disease on the performance of plasma Alzheimer’s disease biomarkers, certain tau ratios, and specifically pT217/T217, should be considered for implementation in clinical practice and drug trials,” they added.
The study was published online in JAMA Neurology to coincide with a presentation at the International Conference on Alzheimer’s and Parkinson’s Diseases in Gothenburg, Sweden.
Skewed tau levels
Plasma biomarkers of amyloid-beta (Abeta) and tau pathologies, and in particular variants in p-tau217 and p-tau181, have shown promise for use in Alzheimer’s disease diagnosis and prognosis. However, previous reports have suggested that chronic kidney disease might influence plasma p-tau217 and p-tau181 concentrations, potentially decreasing their usefulness in the diagnostic workup of dementia.
Researchers investigated associations of chronic kidney disease with plasma ratios of p-tau217 and p-tau181 to the corresponding unphosphorylated peptides in Alzheimer’s disease.
The data came from 473 older adults, with and without cognitive impairment, from the Swedish BioFinder-2 study who had plasma tau assessments and chronic kidney disease status established within 6 months of plasma collection.
The researchers found that lower estimated glomerular filtration rate levels (indicative of kidney dysfunction) were associated with higher plasma concentrations of phosphorylated and unphosphorylated tau peptides measured simultaneously using the tau immunoprecipitation mass spectrometry assay.
However, the correlations with estimated glomerular filtration rate were nonsignificant for the pT217/T217 ratio in individuals with cognitive impairment and were significantly attenuated for pT217/T217 in cognitively unimpaired individuals and for pT181/T181 in both cognitively unimpaired and impaired individuals.
“Importantly, we demonstrate that there were no significant associations between chronic kidney disease and the pT217/T217 ratio and changes in plasma pT181/T181 associated with chronic kidney disease were small or nonsignificant,” the researchers noted.
“Our results indicate that by using p-tau/tau ratios we may be able to reduce the variability in plasma p-tau levels driven by impaired kidney function and consequently such ratios are more robust measures of brain p-tau pathology in individuals with both early- and later-stage Alzheimer’s disease,” they added.
The researchers believe this is likely true for the ratios of other related proteins – a view that is supported by findings of attenuated associations of chronic kidney disease with Abeta42/40, compared with Abeta42 and Abeta40 in the current study and in previous studies.