PGP and Alzheimer disease: To determine ubiquitinated P-gp levels, we performed immunoprecipitation experiments with brain capillaries from brain tissue of CNI and AD patients and observed that ubiquitination of P-gp was 2.8-fold higher in brain capillaries from patients with AD compared to CNI (n = 3; p = 0.05, Figure 1F; Supplementary Figures S1A,B).