Determination of the acyl glucuronide metabolite of mycophenolic acid in human plasma by HPLC and Emit.
BACKGROUND
The acyl glucuronide (AcMPAG) of mycophenolic acid (MPA) has been found to possess pharmacologic and potentially proinflammatory activity in vitro. To establish its pharmacologic and toxicologic relevance in vivo, a reversed-phase HPLC method was modified to simultaneously determine MPA, the phenolic MPA-glucuronide (7-O-MPAG), and AcMPAG. In addition, cross-reactivity of AcMPAG in the Emit assay for MPA was investigated.


METHODS
The procedure used simple sample preparation, separation with a Zorbax Eclipse-XDB-C8 column, and gradient elution. AcMPAG was quantified as 7-O-MPAG-equivalents.


RESULTS
The assay was linear up to 50 mg/L for MPA, 250 mg/L for 7-O-MPAG, and 10 mg/L for AcMPAG (r >0.999). Detection limits were 0.01, 0.03, and 0.04 mg/L for MPA, 7-O-MPAG, and AcMPAG, respectively. The recoveries were 99-103% for MPA, 95-103% for 7-O-MPAG, and 104-107% for AcMPAG. The within-day imprecision was <5.0% for MPA (0.2-25 mg/L), <4.4% for 7-O-MPAG (10-250 mg/L), and < or =14% for AcMPAG (0.1-5 mg/L). The between-day imprecision was <6.2%, <4.5%, and < or =14% for MPA, 7-O-MPAG, and AcMPAG, respectively. When isolated from microsomes, purified AcMPAG (1-10 mg/L) revealed a concentration-dependent cross-reactivity in an Emit assay for the determination of MPA ranging from 135% to 185%. This is in accordance with the bias between HPLC and Emit calculated in 270 samples from kidney transplant recipients receiving mycophenolate mofetil therapy, which was greater (median, 151.2%) than the respective AcMPAG concentrations determined by HPLC. AcMPAG was found to undergo hydrolysis when samples were stored up to 24 h at room temperature or up to 30 days at 4 degrees C or -20 degrees C. Acidified samples (pH 2.5) were stable up to 30 days at -20 degrees C.


CONCLUSIONS
The HPLC and Emit methods for AcMPAG described here may allow investigation of its relevance for the immunosuppression and side effects associated with mycophenolate mofetil therapy.
Shipkova
M
M
Abteilung Klinische Chemie, Zentrum Innere Medizin, Georg-August-Universität Göttingen, Germany. ewieland@med.uni-goettingen.de
Schütz
E
E
Armstrong
V W
VW
Niedmann
P D
PD
Oellerich
M
M
Wieland
E
E
D002851:Chromatography, High Pressure Liquid; D003429:Cross Reactions; D004355:Drug Stability; D017248:Enzyme Multiplied Immunoassay Technique; D005965:Glucuronates / Q000097:blood*; D020719:Glucuronides; D006801:Humans; D007166:Immunosuppressive Agents / Q000097:blood*; D009173:Mycophenolic Acid / Q000031:analogs & derivatives* / Q000097:blood
D005965:Glucuronates; D020719:Glucuronides; D007166:Immunosuppressive Agents; C113145:mycophenolic acid glucuronide; D009173:Mycophenolic Acid