TY - JOUR
T1 - Involvement of reduced folate carrier 1 in the inner blood-retinal barrier transport of methyltetrahydrofolate
AU - Hosoya, Ken Ichi
AU - Fujita, Keiko
AU - Tachikawa, Masanori
N1 - Funding Information:
Received; May 8, 2007; Accepted; June 17, 2008 *To whom correspondence should be addressed: Ken-ichi HOSOYA, Ph.D., Department of Pharmaceutics, University of Toyama, 2630, Sugitani, Toyama, 930–0194, Japan. Voice: ＋81-76-434-7505, FAX: ＋81-76-434-5172, E-mail: hosoyak＠pha.u-toyama.ac.jp This study was supported, in part, by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science.
PY - 2008
Y1 - 2008
N2 - The purpose of this study was to elucidate the mechanism of methyltetrahydrofolate (MTF) transport at the inner blood-retinal barrier (inner BRB). The characteristics and function of MTF transport at the inner BRB were examined using a conditionally immortalized rat retinal capillary endothelial cell line (TRiBRB2) as an in vitro model of the inner BRB. The [3H]MTF uptake by TR-iBRB2 cells increased with lowering extracellular pH and was Na+- and Cl+-independent. The [3H]MTF uptake was concentration-dependent with a Km of 5.1 μM. This process was inhibited by reduced folate carrier 1 (RFC1) substrates, such as methotrexate and formyltetrahydrofolate, in a concentration-dependent manner with an IC50 of 8.7 and 2.8 μM, respectively, suggesting that RFC1 mediates MTF uptake in TR-iBRB2 cells. Although both RFC1 and proton-coupled folate transporter (PCFT) mRNA, which are pH-sensitive folate transporters, are expressed in TR-iBRB2 cells and isolated rat retinal vascular endothelial cells, the expression level of RFC1 mRNA was 83- and 49-fold greater than that of PCFT, respectively. Taken together, the above findings are consistent with the involvement of RFC1 in the inner BRB transport of MTF.
AB - The purpose of this study was to elucidate the mechanism of methyltetrahydrofolate (MTF) transport at the inner blood-retinal barrier (inner BRB). The characteristics and function of MTF transport at the inner BRB were examined using a conditionally immortalized rat retinal capillary endothelial cell line (TRiBRB2) as an in vitro model of the inner BRB. The [3H]MTF uptake by TR-iBRB2 cells increased with lowering extracellular pH and was Na+- and Cl+-independent. The [3H]MTF uptake was concentration-dependent with a Km of 5.1 μM. This process was inhibited by reduced folate carrier 1 (RFC1) substrates, such as methotrexate and formyltetrahydrofolate, in a concentration-dependent manner with an IC50 of 8.7 and 2.8 μM, respectively, suggesting that RFC1 mediates MTF uptake in TR-iBRB2 cells. Although both RFC1 and proton-coupled folate transporter (PCFT) mRNA, which are pH-sensitive folate transporters, are expressed in TR-iBRB2 cells and isolated rat retinal vascular endothelial cells, the expression level of RFC1 mRNA was 83- and 49-fold greater than that of PCFT, respectively. Taken together, the above findings are consistent with the involvement of RFC1 in the inner BRB transport of MTF.
KW - Carrier-mediated transport
KW - Inner blood-retinal barrier
KW - Methyltetrahydrofolate (MTF)
KW - Reduced folate carrier 1 (RFC1)
UR - http://www.scopus.com/inward/record.url?scp=56149123012&partnerID=8YFLogxK
U2 - 10.2133/dmpk.23.285
DO - 10.2133/dmpk.23.285
M3 - 学術論文
C2 - 18762716
AN - SCOPUS:56149123012
SN - 1347-4367
VL - 23
SP - 285
EP - 292
JO - Drug Metabolism and Pharmacokinetics
JF - Drug Metabolism and Pharmacokinetics
IS - 4
ER -