*Article* **New Evidence for P-gp-Mediated Export of Amyloid-**β **Peptides in Molecular, Blood-Brain Barrier and Neuronal Models**

**Amanda B. Chai 1 , Anika M. S. Hartz 2,3 , Xuexin Gao 4 , Alryel Yang 1 , Richard Callaghan 4, \* and Ingrid C. Gelissen 1, \***


**Abstract:** Defective clearance mechanisms lead to the accumulation of amyloid-beta (Aβ) peptides in the Alzheimer's brain. Though predominantly generated in neurons, little is known about how these hydrophobic, aggregation-prone, and tightly membrane-associated peptides exit into the extracellular space where they deposit and propagate neurotoxicity. The ability for P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter, to export Aβ across the blood-brain barrier (BBB) has previously been reported. However, controversies surrounding the P-gp–Aβ interaction persist. Here, molecular data affirm that both Aβ<sup>40</sup> and Aβ<sup>42</sup> peptide isoforms directly interact with and are substrates of P-gp. This was reinforced ex vivo by the inhibition of Aβ<sup>42</sup> transport in brain capillaries from P-gp-knockout mice. Moreover, we explored whether P-gp could exert the same role in neurons. Comparison between non-neuronal CHO-APP and human neuroblastoma SK-N-SH cells revealed that P-gp is expressed and active in both cell types. Inhibiting P-gp activity using verapamil and nicardipine impaired Aβ<sup>40</sup> and Aβ<sup>42</sup> secretion from both cell types, as determined by ELISA. Collectively, these findings implicate P-gp in Aβ export from neurons, as well as across the BBB endothelium, and suggest that restoring or enhancing P-gp function could be a viable therapeutic approach for removing excess Aβ out of the brain in Alzheimer's disease.

**Keywords:** P-glycoprotein; ABCB1; amyloid-beta; neuron; SK-N-SH; Alzheimer's disease
