Involvement of recognition and interaction of carnitine transporter in the decrease of L-carnitine concentration induced by pivalic acid and valproic acid.
OBJECTIVE
Prodrugs with pivalic acid and valproic acid decrease L-carnitine concentration in plasma and tissues by urinary excretion of acylcarnitine as pivaloylcarnitine (PC) and valproylcarnitine (VC), respectively. We investigated the role of the Na+/L-carnitine cotransporter in the porcine kidney epithelial cell line, LLC-PK1 for the decrease of L-carnitine concentration.


METHODS
The uptake of L-[3H]carnitine, acetyl-L-[3H]carnitine (AC), L-[3H]PC and L-[3H]VC were investigated in LLC-PK1 cells seeded in a 6-well culture plate.


RESULTS
L-Carnitine and AC uptake in LLC-PK1 cells exhibited Na+ dependency. The Km values for L-carnitine and AC uptake were 11.0 and 8.18 microM, respectively. These results indicated expression of Na+/ L-carnitine cotransporter in LLC-PK1 cells. PC and VC inhibited Na+/L-carnitine cotransporter in the competitive (Ki = 90.4 microM) and noncompetitive (Ki = 41.6 microM) manners, respectively. PC and VC uptake by Na+/L-carnitine cotransporter were not observed in LLC-PK1 cells.


CONCLUSIONS
These data suggested that PC and VC formed in the body could not be reabsorbed in the kidney, resulting in the decrease of L-carnitine concentration. In addition, inhibition of L-carnitine reabsorption by VC with lower Ki value could induce the decrease of L-carnitine concentration. Collectively, the recognition and interaction of Na+/L-carnitine cotransporter are important factors for carnitine homeostasis.
Okamura
Noboru
N
Developmental Research Laboratories, Shionogi & Co., Ltd., 3-1-1, Futaba-cho, Toyonaka, Osaka, 561-0825, Japan.
Ohnishi
Shuichi
S
Shimaoka
Hiroyuki
H
Norikura
Ryo
R
Hasegawa
Hiroshi
H
D000108:Acetylcarnitine / Q000378:metabolism; D000465:Algorithms; D026923:Amino Acid Transport Systems, Basic / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002331:Carnitine / Q000031:analogs & derivatives / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018374:LLC-PK1 Cells; D010421:Pentanoic Acids / Q000494:pharmacology*; D013552:Swine; D014635:Valproic Acid / Q000494:pharmacology*
D026923:Amino Acid Transport Systems, Basic; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D010421:Pentanoic Acids; D014635:Valproic Acid; D000108:Acetylcarnitine; C005566:pivalic acid; C044923:valproylcarnitine; C054040:pivaloylcarnitine; D002331:Carnitine