Rapid and simple quantitative assay method for diastereomeric flurbiprofen glucuronides in the incubation mixture

Optimization to eliminate the interference of migration isomers for measuring 1-O-beta-acyl glucuronide without extensive chromatographic separation

A highly selected reaction monitoring (SRM) method has been investigated for the determination of muraglitazar 1-O-beta-acyl glucuronide in animal and human plasma without chromatographic separation of this naturally formed acyl glucuronide from its migration isomers. In the ion source or the collision cell, glucuronides are often prone to lose the dehydrated glucuronic acid (176 Da) and convert back into the parent drug (aglycone). The extent of loss of the glucuronide moiety can differ among glucuronides. For the naturally occurring muraglitazar 1-O-beta-acyl glucuronide, or its synthetic anomer 1-O-alpha-glucuronide, the loss of the glucuronide moiety was a major fragment ion. The loss of the glucuronide moiety was greater for the 1-O-beta-acyl glucuronide than the 1-O-alpha-anomer. In addition, the loss of the glucuronide moiety was insignificant (less than 0.01%) with the other glucuronide isomers (2-, 3- or 4-O, alpha or beta). Given the fact that the 1-O-alpha-anomer was a minor impurity in the muraglitazar 1-O-beta-acyl glucuronide reference standard, and not either a conversion product of 1-O-beta-acyl glucuronide or endogenously formed, the SRM transition corresponding to the loss of the glucuronide moiety was very specific for 1-O-beta-acyl glucuronide, and practically free from interference of the other isomers under optimized collision-cell conditions. As a result, extensive chromatographic separation of 1-O-beta-acyl glucuronide from its migration isomers was not required. The use of this specific SRM transition effectively reduced the separation time from 12.0 min of a long-column high-performance liquid chromatography (HPLC) method to 2.5 min by use of a shorter column. The standard curve performance and analysis results of 1-O-beta-acyl glucuronide incubation samples showed that the short-column method could produce equivalent results to the long-column method but with a 4.5-fold improvement in sample throughput. This approach may be useful for other 1-O-beta-acyl glucuronide measurements with proper tuning of collision energy. The generation of a breakdown curve (abundance vs. collision energy) helps to define whether appropriate conditions may be selected for specific MRM transitions.

Predominant Contribution of UDP-Glucuronosyltransferase 2B7 in the Glucuronidation of Racemic Flurbiprofen in the Human Liver

Flurbiprofen is a nonsteroidal anti-inflammatory drug used as a racemic mixture. Although glucuronidation is one of its elimination pathways, the role of UDP-glucuronosyltransferase (UGT) in this process remains to be investigated. Thus, the kinetics of the stereoselective glucuronidation of racemic (R,S)-flurbiprofen by recombinant UGT isozymes and human liver microsomes (HLMs) were investigated, and the major human UGT isozymes involved were identified. UGT1A1, 1A3, 1A9, 2B4, and 2B7 showed glucuronidation activity for both (R)- and (S)-glucuronide, with UGT2B7 possessing the highest activity. UGT2B7 formed the (R)-glucuronide at a rate 2.8-fold higher than that for (S)-glucuronide, whereas the other UGTs had similar formation rates. The glucuronidation of racemic flurbiprofen by HLMs also resulted in the formation of (R)-glucuronide as the dominant form, which occurred to a degree similar to that by recombinant UGT2B7 (2.1 versus 2.8). The formation of (R)-glucuronide correlated significantly with morphine 3-OH glucuronidation (r = 0.96, p < 0.0001), morphine 6-OH glucuronidation (r = 0.91, p < 0.0001), and 3'-azido-3'-deoxythymidine glucuronidation (r = 0.85, p < 0.0001), a reaction catalyzed mainly by UGT2B7, in individual HLMs. In addition, the formation of both glucuronides correlated significantly (r = 0.99, p < 0.0001). Mefenamic acid inhibited the formation of both (R)- and (S)-glucuronide in HLMs with similar IC(50) values (2.0 and 1.7 muM, respectively), which are close to those in recombinant UGT2B7. In conclusion, these findings suggest that the formation of (R)- and (S)-glucuronide from racemic flurbiprofen is catalyzed by the same UGT isozyme, namely UGT2B7.

Separation of a BMS drug candidate and acyl glucuronide from seven glucuronide positional isomers in rat plasma via high-performance liquid chromatography with tandem mass spectrometric detection

A high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed and validated for the determination of a BMS drug candidate and its acyl glucuronide (1-O-beta glucuronide) in rat plasma. A 50-microL aliquot of each plasma sample was fortified with acetonitrile containing the internal standard to precipitate proteins and extract the analytes of interest. After mixing and centrifugation, the supernatant from each sample was transferred to a 96-well plate and injected into an LC/MS/MS system. Chromatographic separation was achieved isocratically on a Phenomenex Luna C(18), 3 mm x 150 mm, 3 microm column. The mobile phase contained 0.075% formic acid in 70:30 (v/v) acetonitrile/water. Under the optimized chromatographic conditions, the BMS drug candidate and its acyl glucuronide were separated from its seven glucuronide positional isomers within 10 min. Resolution of the parent from all glucuronides and acyl glucuronide from its positional isomers was critical to avoid their interference with quantitation of parent or acyl glucuronide. Detection was by positive ion electrospray MS/MS on a Sciex API 4000. The standard curve, which ranged from 5 to 5000 ng/mL, was fitted to a 1/x(2) weighted quadratic regression model for both the BMS drug candidate and its acyl glucuronide. Whole blood and plasma stability experiments were conducted to establish the sample collection, storage, and processing conditions. The validation results demonstrated that this method was rugged and repeatable. The same methodology has also been used in mouse and human plasma for the determination of the BMS drug candidate and its acyl glucuronide.

Inhibition of the rat hepatic microsomal flurbiprofen acyl glucuronidation by bile acids

Glucuronidation of carboxylic acids, primarily catalyzed by hepatic UDP-glucuronosyltransferases, is an important phase II metabolic pathway functioning in detoxification. Acyl glucuronides of 2-aryl propionates, however, can form covalently bound protein adducts, which may generate hypersensitive reactions. We previously identified and quantified R- and S-flurbiprofen acyl glucuronides in human urine following the oral administration of flurbiprofen by liquid chromatography/electrospray ionization mass spectrometry. Recent studies also demonstrated the inhibitory effect of bile acids and their metabolites toward rat hepatic bile acid acyl glucuronidation, which may also be the target of the flurbiprofen isoenzyme. We therefore performed a kinetic analysis of rat hepatic flurbiprofen UDP-glucuronosyltransferase using bisubstrate kinetic analysis and inhibition studies. The results indicated that both bile acid and its metabolites clearly inhibited flurbiprofen acyl glucuronidation. The inhibitory effect on flurbiprofen was more efficient than the effect seen on bile acid acyl glucuronidation. Unconjugated, glycine- and taurine-conjugated chenodeoxycholic acids inhibited glucuronidation using a noncompetitive mechanism, whereas the inhibition by chenodeoxycholic acid 24-acyl glucuronide occurred according to a mixed type mechanism. The inhibition by bile acids and their metabolites may be responsible for the suppression of the toxicity of carboxy-linked glucuronides.

Separation and Determination of Diastereomeric Flurbiprofen Acyl Glucuronides in Human Urine by LC/ESI-MS with a Simple Column-Switching Technique

Endogenous and exogenous compounds having a carboxyl group, such as alpha-arylpropionic acid derivatives, undergo a phase II metabolic reaction to produce an amino acid conjugate through the acyl CoA thioester as well as the acyl glucuronide. It was previously shown that flurbiprofen, one of the nonsteroidal anti-inflammatory drugs, is not subjected to activation of the carboxyl group by the CoA thioester ligase, suggesting that acyl glucuronidation is the main phase II metabolic pathway. Recent observations, however, have demonstrated that the nonenzymatic formation of a covalently protein-bound drug, which is produced by the action of the acyl glucuronide, may cause hypersensitive reactions. Accordingly, a reliable method to measure diastereomeric flurbiprofen glucuronides in human biological fluids is required. In this study, we describe a liquid chromatographic/mass spectrometric method with a simple column switching technique to determine diastereomeric flurbiprofen acyl glucuronides in human urine specimens. The optimal conditions for the electrospray ionization were established based on the effects of orifice and ring lens voltages as well as mobile phase additives. The proposed method applied to urine specimens demonstrates high accuracy and reproducibility for the determination of flurbiprofen glucuronides in a quantitative range from 0.74 to 146.5 microg/mL, with a detection limit of 7.4 pg (17.6 fmol)/injection of S-flurbiprofen glucuronide, at a signal-to-noise ratio of 10 under the selected ion-monitoring mode. The urinary concentration of R-flurbiprofen glucuronides in healthy subjects determined by the proposed method were 6.8-29.4 microg/mL, and those values were slightly higher than that of S-flurbiprofen glucuronides (3.9-18.0 microg/mL).