The effect of creatinine level on amyloid-β and tau plasma concentrations in a cohort of Alzheimer's disease patients without kidney disease.

Background: Alzheimer's disease (AD) is pathologically characterized by the deposition of beta-amyloid and tau-protein. Blood biomarkers (BBM) might be employed for detecting these abnormal proteins in vivo. As the kidney is an important excretory organ, a decreased renal function might affect the clearance of BBM. In this study we aimed to assess the relationship between kidney function, the levels of BBM and cognitive impairment in a cohort of patients with a biological AD diagnosis without chronic kidney disease (CKD).

Methods: This is a retrospective cohort study on AD patients. Data regarding medical history at diagnosis (T0) were retrieved, together with the Mini-Mental State Examination (MMSE) score at T0 and after 6 months (T1). Cerebrospinal fluid and blood samples were collected and concentrations of Aβ42, Aβ40, t-Tau, and p-Tau181 were determined using commercially available kits. Kidney function was estimated through the 2021-CKD-EPI equation. To assess the effects of creatinine on our parameters of interest, we grouped patients into two groups -creatinine level <0.8 mg/dl (LOW) or ≥0.8 mg/dl (HIGH).

Results: The median MMSE score decreased significantly between the two timepoints. When we assessed for differences in the parameters of interest between subgroups, we found that only Aβ42 plasma level was significantly different in the HIGH vs LOW group.

Conclusion: We found out that only Aβ42 plasma levels are influenced by kidney function, while the other AD biomarkers are not affected by creatinine levels or eGFR. Our findings are consistent with the hypothesis of renal clearance of Aβ isoforms.