Difference between pharmacokinetics of mycophenolic acid (MPA) in rats and that in humans is caused by different affinities of MRP2 to a glucuronized form.
OBJECTIVE
Mycophenolic acid (MPA), an immunosuppressant, is excreted as its glucuronized form, MPAG. In humans, MPAG is mostly excreted into urine, whereas more than 80% of the dose is excreted into bile in rats. The aim of this study was to clarify the cause of the species difference. We investigated whether MPAG is a substrate of human organic anion transporters (hOATs), and we compared the affinities of multi-drug resistance-associated protein 2 (MRP2) for MPAG in rats and humans.


METHODS
The inhibitory effects of MPAG on the uptake of typical substrates via hOAT1 and hOAT3 were determined using HeLa cells heterologously expressing hOAT1 and Xenopus laevis oocytes heterologously expressing hOAT3. MPAG transport activity via hOAT1 and hOAT3 was determined by the two-microelectrode voltage-clamp technique using Xenopus laevis oocytes expressing hOAT1 and hOAT3. The affinities of MPAG for hMRP2 and rMrp2 were determined by the inhibitory effects of MPAG on p-aminohippuric acid (a typical substrate) uptake using membrane vesicles expressing hMRP2 or rMrp2.


RESULTS
MPAG inhibited the uptake of PAH via hOAT1 and hOAT3, and calculated IC50 values were 222.6+/-26.6 microM and 41.5+/-11.5 microM, respectively. However, MPAG was not transported by hOAT1 and hOAT3. MPAG strongly inhibited the uptake of PAH via both rMrp2 and hMRP2. However, the magnitudes of inhibitory effects were different. The calculated IC50 values were 286.2+/-157.3 microM and 1036.8+/-330.5 microM, respectively.


CONCLUSIONS
MPAG is not a substrate but is an inhibitor of hOAT1 and hOAT3. The affinity of rMRP2 to MPAG was about 3.6 times as high as that of hMRP2. Therefore, the difference of affinity between hMRP2 and rMrp2 is a possible mechanism of the difference of excretion ratio of MPAG between rats and human.
Takekuma
Yoh
Y
Laboratory of Pharmcotherapeutic Information, Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan. y-kuma@pharm.hokudai.ac.jp
Kakiuchi
Haruka
H
Yamazaki
Koujiro
K
Miyauchi
Seiji
S
Kikukawa
Takashi
T
Kamo
Naoki
N
Ganapathy
Vadivel
V
Sugawara
Mitsuru
M
D000818:Animals; D001646:Bile / Q000378:metabolism; D020719:Glucuronides / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007166:Immunosuppressive Agents / Q000493:pharmacokinetics*; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism*; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D009173:Mycophenolic Acid / Q000493:pharmacokinetics*; D027362:Organic Anion Transport Protein 1 / Q000502:physiology; D029362:Organic Anion Transporters, Sodium-Independent / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013045:Species Specificity; D014982:Xenopus laevis; D010130:p-Aminohippuric Acid / Q000493:pharmacokinetics
D020719:Glucuronides; D007166:Immunosuppressive Agents; D026901:Membrane Transport Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009173:Mycophenolic Acid; D027362:Organic Anion Transport Protein 1; D029362:Organic Anion Transporters, Sodium-Independent; D010130:p-Aminohippuric Acid; C000715087:ABCC2 protein, human; C114338:organic anion transport protein 3