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Transport of fluorescein in MDCKII-MRP1 transfected cells and mrp1-knockout mice
H Sun1, D R Johnson, R A Finch
1Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA.
Abstract:
The multidrug resistant-associated protein 1 (MRP1) is a membrane-bound transport protein that is involved in the efflux of organic anions and has been implicated in multidrug resistance in cancer. MRP1 has also been reported to be ubiquitously expressed in normal tissues, including the brain. The presence of functional organic anion transporters in the blood-brain and blood-CSF barriers that influence the distribution of various compounds to the brain has long been known. The purpose of this study was to examine the role of MRP1 in the brain distribution of a model organic anion, fluorescein. The substrate specificity of MRP1 for fluorescein was initially determined by examining the accumulation of fluorescein in MDCKII MRP1-transfected cells. The distribution of fluorescein in the brain was then examined in wild-type and mrp1 gene knockout mice. The results show that in MDCKII MRP1-transfected cells, the accumulation of fluorescein was significantly lower (about 40% lower) than that in wild-type MDCKII cells. MRP1 inhibitors such as probenecid, MK-571, and LY402913 enhanced fluorescein accumulation in MDCKII MRP1-transfected cells to a greater extent than in wild-type MDCKII cells. In an in vivo study, after intravenous injection of fluorescein, the fluorescein brain-to-plasma concentration ratio in mrp1 knockout mice was not significantly different than that in wild-type mice. However, when probenecid was co-administered with fluorescein in wild-type mice, the fluorescein brain-to-plasma ratio was significantly increased (1.5-fold). These findings suggest that fluorescein is a substrate for MRP1. Furthermore, the in vivo study also suggests that MRP1 has a limited role in the transport and distribution of fluorescein in the brain. Therefore, other organic anion transport proteins, including the various isoforms of the MRP family, may be responsible for the accumulation and transport of organic anions in the brain.
Insights
Multidrug resistant-associated protein 1 (MRP1) transports organic anions. While MRP1 transports fluorescein in cells, it plays a limited role in brain distribution, suggesting other transporters are involved.
Area of Science:
- Pharmacology
- Neuroscience
- Molecular Biology
Background:
- Multidrug resistant-associated protein 1 (MRP1) is a key efflux transporter for organic anions.
- MRP1 is expressed in normal tissues, including the brain, and influences compound distribution across barriers.
- Organic anion transporters at the blood-brain and blood-cerebrospinal fluid barriers are critical for brain penetration.
Purpose of the Study:
- To investigate the role of MRP1 in the brain distribution of fluorescein, a model organic anion.
- To determine if fluorescein is a substrate for MRP1.
- To assess MRP1's contribution to fluorescein transport across the blood-brain barrier.
Main Methods:
- In vitro assessment of fluorescein accumulation in MRP1-transfected cells and wild-type cells.
- Evaluation of MRP1 inhibitor effects on fluorescein uptake in cells.
- In vivo study of fluorescein brain-to-plasma distribution in wild-type and MRP1 knockout mice.
- Assessment of probenecid's effect on fluorescein brain distribution in wild-type mice.
Main Results:
- Fluorescein accumulation was significantly lower (40%) in MRP1-transfected cells compared to wild-type cells, indicating MRP1 efflux.
- MRP1 inhibitors (probenecid, MK-571, LY402913) increased fluorescein accumulation in MRP1-transfected cells more than in wild-type cells.
- In vivo, MRP1 knockout mice showed no significant difference in fluorescein brain-to-plasma ratio compared to wild-type mice.
- Co-administration of probenecid with fluorescein in wild-type mice significantly increased the brain-to-plasma ratio (1.5-fold).
Conclusions:
- Fluorescein is confirmed as a substrate for MRP1.
- MRP1 plays a limited role in the in vivo transport and distribution of fluorescein in the brain.
- Other organic anion transporters, potentially including other MRP family members, likely mediate brain accumulation and transport of organic anions.
