ABCB1 and Alzheimer disease: Both ABCB1 and ABCG2 have been identified as Aβ transporters [5,6,7,8,9,22,23,24] and the abundance and activity of cerebral ABCB1 were found to be decreased in AD [10,11,12,13,14], which may be caused by an Aβ-induced ubiquitination, internalization and proteasomal degradation of ABCB1 [38].