Brain Distribution of Dual ABCB1/ABCG2 Substrates Is Unaltered in a Beta-Amyloidosis Mouse Model.

Background: ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein) are co-localized at the blood-brain barrier (BBB), where they restrict the brain distribution of many different drugs. Moreover, ABCB1 and possibly ABCG2 play a role in Alzheimer's disease (AD) by mediating the brain clearance of beta-amyloid (A beta) across the BBB. This study aimed to compare the abundance and activity of ABCG2 in a commonly used beta-amyloidosis mouse model (APP/PS1-21) with age-matched wild-type mice. Methods: The abundance of ABCG2 was assessed by semi-quantitative immunohistochemical analysis of brain slices of APP/PS1-21 and wild-type mice aged 6 months. Moreover, the brain distribution of two dual ABCB1/ABCG2 substrate radiotracers ([C-11]tariquidar and [C-11]erlotinib) was assessed in APP/PS1-21 and wild-type mice with positron emission tomography (PET). [C-11]Tariquidar PET scans were performed without and with partial inhibition of ABCG2 with Ko143, while [C-11]erlotinib PET scans were only performed under baseline conditions. Results: Immunohistochemical analysis revealed a significant reduction (by 29-37%) in the number of ABCG2-stained microvessels in the brains of APP/PS1-21 mice. Partial ABCG2 inhibition significantly increased the brain distribution of [C-11]tariquidar in APP/PS1-21 and wild-type mice, but the brain distribution of [C-11]tariquidar did not differ under both conditions between the two mouse strains. Similar results were obtained with [C-11]erlotinib. Conclusions: Despite a reduction in the abundance of cerebral ABCG2 and ABCB1 in APP/PS1-21 mice, the brain distribution of two dual ABCB1/ABCG2 substrates was unaltered. Our results suggest that the brain distribution of clinically used ABCB1/ABCG2 substrate drugs may not differ between AD patients and healthy people.