Transport of fluorescent chenodeoxycholic acid via the human organic anion transporters OATP1B1 and OATP1B3

Hiroaki Yamaguchi,Masahiro Okada,Shou Akitaya,Hiroshi Ohara,Tsuyoshi Mikkaichi,Haruna Ishikawa,Mayumi Sato,Masaki Matsuura,Toshihide Saga,Michiaki Unno,Takaaki Abe,Nariyasu Mano,Takanori Hishinuma,Junichi Goto

doi:10.1194/jlr.m500532-jlr200

Abstract

This study sought to clarify the contributions of organic anion-transporting polypeptide (OATP) 1B1 and 1B3 to the liver uptake of chenodeoxycholic acid (CDCA). We synthesized a fluorescent version of CDCA, chenodeoxychilyl-(Nepsilon-NBD)-lysine (CDCA-NBD), to characterize transporter-mediated uptake. CDCA-NBD is efficiently transported by OATP1B1 and OATP1B3 with high affinities. The Michaelis-Menten constants for CDCA-NBD uptake by OATP1B1 and OATP1B3 were 1.45 +/- 0.39 microM and 0.54 +/- 0.09 microM, respectively. By confocal laser scanning microscopy, CDCA-NBD, which is taken up by OATP1B1 and OATP1B3, was observed to localize to the cytosol. We also examined the transport of newly synthesized fluorescent bile acids. NBD-labeled bile acids, including cholic acid, deoxycholic acid, lithocholic acid, and ursodeoxycholic acid, were all transported by OATP1B1 and OATP1B3. CDCA-NBD exhibited the highest rate of transport of the five NBD-labeled bile acids examined in OATP1B1- and OATP1B3-expressing cells. Our results suggest that OATP1B1 and OATP1B3 play important roles in CDCA uptake into the liver. Fluorescent bile acids are useful tools to characterize the uptake properties of membrane transporters.

Highlights

Organic anion-transporting polypeptides (OATPs) are sodium-independent organic anion transporters found in a variety of tissues, including liver, kidney, intestine, and brain
We examined the contribution of the Na1-independent hepatic transporters OATP1B1 and OATP1B3 to the liver uptake of chenodeoxycholic acid (CDCA) using fluorescent bile acids
CDCA-NBD was efficiently transported by both OATP1B1 and OATP1B3; both transporters exhibited high affinities for this bile acid [Km values of 1.45 6 0.39 mM and 0.54 6 0.09 mM for OATP1B1 and OATP1B3, respectively] (Figs. 2, 3)

Summary

Introduction

Organic anion-transporting polypeptides (OATPs) are sodium-independent organic anion transporters found in a variety of tissues, including liver, kidney, intestine, and brain. OATPs contribute to the transport of bile acids, thyroid hormones, steroid conjugates, anionic oligopeptides, eicosanoids, various drugs, and other xenobiotic compounds across membranes [1,2,3]. OATP1B1 (LST-1/ OATP2) and OATP1B3 (LST-2/OATP8) are members of the liver-specific subfamily of OATPs, which are localized to the basolateral membrane of hepatocytes [4,5,6,7,8]. OATP1B3 shares 80% amino acid identity with OATP1B1, the substrate specificity differs slightly between these two transporters. In addition to the liver, OATP1B3 is expressed in solid digestive organ cancers [9]. The development of a specific substrate of OATP1B3 may be useful in cancer treatment

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