Association between Kidney Tubular Secretory Clearance with Cognitive Function among Adults with CKD in the Systolic Blood Pressure Intervention Trial.

BACKGROUND: Persons with CKD are disproportionally affected with cognitive impairment, yet the pathophysiology linking the two conditions is unclear. Because kidney tubule secretion is essential for clearance of medications, uremic toxins, and metabolites, we hypothesized that worse tubular secretion would be associated with reduced cognitive function in CKD. METHODS: The Systolic Blood Pressure Intervention Trial tested a systolic blood pressure target <120 mmHg vs. <140 mmHg in hypertensive individuals at high cardiovascular risk. In paired blood and urine specimens from 1,937 participants with eGFR <60 ml/min/1.73m2, we measured 10 endogenous tubule-secreted metabolites and calculated a urine/plasma ratio for each, then averaged these to generate a summary secretion score. We used unadjusted and multivariable-adjusted linear regression and mixed models to evaluate cross-sectional and longitudinal associations of the secretion score with the Montreal Cognitive Assessment, Digit Symbol Coding, and Logical Memory immediate and delayed tests-measured at baseline and months 24 and 48 of follow-up. Multivariable Cox regression evaluated associations with incident probable dementia and mild cognitive impairment, adjudicated by prespecified criteria. RESULTS: Mean age was 73 ± 9 years, 41% were women, mean eGFR was 48.2 ± 11.4 ml/min/1.73m2, median albuminuria was 14.8 [7.1-48.6] mg/g. Lower secretion score was associated with a 0.06 higher adjusted logical memory delayed score (95% CI: 0.02, 0.11) but not with other cognitive tests at baseline or longitudinal cognitive decline. After a median 4.1 years of follow-up, 118 developed probable dementia and 187 developed mild cognitive impairment. Each 1-SD lower secretion score was associated with lower risk of probable dementia (HR 0.78, 95% CI: 0.63, 0.98) but not mild cognitive impairment. CONCLUSIONS: Among Systolic Blood Pressure Intervention Trial participants with CKD, lower estimated tubular secretion was not associated with worse cognition at baseline or during longitudinal follow-up.