Organic Cation Transporters are Involved in Fluoxetine Transport Across the Blood-Brain Barrier In Vivo and In Vitro

Background: The research and development of drugs for the treatment of central ner-vous system diseases faces many challenges at present. One of the most important questions to be answered is, how does the drug cross the blood-brain barrier to get to the target site for pharmaco-logical action. Fluoxetine is widely used in clinical antidepressant therapy. However, the mech-anism by which fluoxetine passes through the BBB also remains unclear. Under physiological pH conditions, fluoxetine is an organic cation with a relatively small molecular weight (<500), which is in line with the substrate characteristics of organic cation transporters (OCTs). Therefore, this study aimed to investigate the interaction of fluoxetine with OCTs at the BBB and BBB-associated efflux transporters. This is of great significance for fluoxetine to better treat depression. Moreover, it can provide a theoretical basis for clinical drug combination. Methods: In vitro BBB model was developed using human brain microvascular endothelial cells (hCMEC/D3), and the cellular accumulation was tested in the presence or absence of transporter in-hibitors. In addition, an in vivo trial was performed in rats to investigate the effect of OCTs on the distribution of fluoxetine in the brain tissue. Fluoxetine concentration was determined by a validat-ed UPLC-MS/MS method. Results: The results showed that amantadine (an OCT1/2 inhibitor) and prazosin (an OCT1/3 in-hibitor) significantly decreased the cellular accumulation of fluoxetine P( <.001). Moreover, we found that N-methylnicotinamide (an OCT2 inhibitor) significantly inhibited the cellular uptake of 100 and 500 ng/mL fluoxetine (P <.01 and P <.05 respectively). In contrast, corticosterone (an OC-T3 inhibitor) only significantly inhibited the cellular uptake of 1000 ng/mL fluoxetine P( <.05). The P-glycoprotein (P-gp) inhibitor, verapamil, and the multidrug resistance associated proteins (MRPs) inhibitor, MK571, significantly decreased the cellular uptake of fluoxetine. However, intra-cellular accumulation of fluoxetine was not significantly changed when fluoxetine was incubated with the breast cancer resistance protein (BCRP) inhibitor Ko143. Furthermore,in vivo experi-ments proved that corticosterone and prazosin significantly inhibited the brain-plasma ratio of flu-oxetine at 5.5 h and 12 h, respectively. Conclusion: OCTs might play a significant role in the transport of fluoxetine across the BBB. In addition, P-gp, BCRP, and MRPs seemed not to mediate the efflux transport of fluoxetine.