Evaluation of the mechanism of the brain transport of nobiletin via passive and P-glycoprotein-mediated transport

Abstract

Background: Nobiletin, a polymethoxyflavonoid found in citrus fruits, exhibits neuroprotective potential in disorders of the central nervous system. However, the precise mechanism governing its passage across the blood-brain barrier (BBB) remains unclear. 

Objective: This study aimed to elucidate the mechanism of the brain transport of nobiletin by determining its passive transport ability, P-glycoprotein (P-gp) substrate recognition, and the effect of P-gp on its brain transport. 

Methods: The ability of nobiletin to traverse the BBB was assessed using an artificial lipid membrane (PAMPA-BBB) to determine passive diffusion parameters. Its interaction with P-gp was examined through ATPase activation assays and bidirectional transport studies in P-gp-overexpressing cell lines (LLC-GA5-COL300) compared with control cells (LLC-PK1). The in vivo distribution of nobiletin in mouse brain and plasma was further quantified following oral administration, with and without P-gp inhibition by elacridar. 

Results: Nobiletin exhibited high passive transport in artificial lipid membrane permeation assay. It increased ATPase activity in P-gp-overexpressing membranes. Significant increases in basolateral-to-apical transport were observed in P-gp-expressing cells, indicating that P-gp transports nobiletin as a substrate, similar to verapamil, but not as effectively as quinidine. When orally administered to mice, the plasma and brain concentrations of nobiletin increased simultaneously and peaked at 30 min, indicating rapid distribution between the blood and brain. The brain/plasma concentration ratio at 30 min was not significantly increased upon P-gp inhibition, indicating that P-gp does not affect the brain transport of nobiletin. 

Novelty: This study provides the first quantitative in vivo evidence that P-gp does not functionally restrict the brain distribution of nobiletin, establishing passive diffusion as the predominant BBB transport mechanism of nobiletin.

Conclusions: These results demonstrate that nobiletin efficiently crosses the BBB primarily via passive diffusion, with minimal modulation by P-gp. These findings clarify its brain transport kinetics and reinforce its potential as a neuroprotective bioactive compound for dietary and pharmaceutical development. 

Keywords: Nobiletin; Blood–brain barrier; P-glycoprotein; Passive transport; Brain distribution.