Uptake of cardiovascular drugs into the human heart: expression, regulation, and function of the carnitine transporter OCTN2 (SLC22A5).
BACKGROUND
To date, the uptake of drugs into the human heart by transport proteins is poorly understood. A candidate protein is the organic cation transporter novel type 2 (OCTN2) (SLC22A5), physiologically acting as a sodium-dependent transport protein for carnitine. We investigated expression and localization of OCTN2 in the human heart, uptake of drugs by OCTN2, and functional coupling of OCTN2 with the eliminating ATP-binding cassette (ABC) transporter ABCB1 (P-glycoprotein).


RESULTS
Messenger RNA levels of OCTN2 and ABCB1 were analyzed in heart samples by quantitative polymerase chain reaction. OCTN2 was expressed in all auricular samples that showed a pronounced interindividual variability (35 to 1352 copies per 20 ng of RNA). Although a single-nucleotide polymorphism in OCTN2 (G/C at position -207 of the promoter) had no influence on expression, administration of beta-blockers resulted in significantly increased expression. Localization of OCTN2 by in situ hybridization, laser microdissection, and immunofluorescence microscopy revealed expression of OCTN2 mainly in endothelial cells. For functional studies, OCTN2 was expressed in Madin-Darby canine kidney (MDCKII) cells. Using this system, verapamil, spironolactone, and mildronate were characterized both as inhibitors (EC50=25, 26, and 21 micromol/L, respectively) and as substrates. Like OCTN2, ABCB1 was expressed preferentially in endothelial cells. A significant correlation of OCTN2 and ABCB1 expression in the human heart was observed, which suggests functional coupling. Therefore, the interaction of OCTN2 with ABCB1 was tested with double transfectants. This approach resulted in a significantly higher transcellular transport of verapamil, a substrate for both OCTN2 and ABCB1.


CONCLUSIONS
OCTN2 is expressed in the human heart and can be modulated by drug administration. Moreover, OCTN2 can contribute to the cardiac uptake of cardiovascular drugs.
Peter Holtz Research Center of Pharmacology and Experimental Therapeutics, Department of Pharmacology, Ernst Moritz Arndt University, Greifswald, Germany.
Markus
M
Grube
Henriette E U
HE
Meyer zu Schwabedissen
Damaris
D
Präger
Jeanette
J
Haney
Klaus-Uwe
KU
Möritz
Konrad
K
Meissner
Dieter
D
Rosskopf
Lothar
L
Eckel
Michael
M
Böhm
Gabriele
G
Jedlitschky
Heyo K
HK
Kroemer
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D000368:Aged; D000818:Animals; D002317:Cardiovascular Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D002460:Cell Line; D004285:Dogs; D042783:Endothelial Cells / Q000737:chemistry; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008763:Methylhydrazines / Q000494:pharmacology; D008875:Middle Aged; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D027701:Organic Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D000074058:Solute Carrier Family 22 Member 5; D013148:Spironolactone / Q000494:pharmacology; D014162:Transfection; D014700:Verapamil / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002317:Cardiovascular Agents; D008763:Methylhydrazines; D027701:Organic Cation Transport Proteins; D012333:RNA, Messenger; C492020:SLC22A5 protein, human; D000074058:Solute Carrier Family 22 Member 5; D013148:Spironolactone; C050147:3-(2,2,2-trimethylhydrazine)propionate; D014700:Verapamil