Studies of urinary metabolites of 2-(4-isobutylphenyl) propionic acid by gas-liquid chromatography-mass spectrometry

MASS SPECTROMETRIC FRAGMENTATION OF TRIMETHYLSILYL AND RELATED ALKYLSILYL DERIVATIVES

This review describes the mass spectral fragmentation of trimethylsilyl (TMS) and related alkylsilyl derivatives used for preparing samples for analysis, mainly by combined gas chromatography and mass spectrometry (GC/MS). The review is divided into three sections. The first section is concerned with the TMS derivatives themselves and describes fragmentation of derivatized alcohols, thiols, amines, ketones, carboxylic acids and bifunctional compounds such as hydroxy- and amino-acids, halo acids and hydroxy ethers. More complex compounds such as glycerides, sphingolipids, carbohydrates, organic phosphates, phosphonates, steroids, vitamin D, cannabinoids, and prostaglandins are discussed next. The second section describes intermolecular reactions of siliconium ions such as the TMS cation and the third section discusses other alkylsilyl derivatives. Among these latter compounds are di- and trialkyl-silyl derivatives, various substituted-alkyldimethylsilyl derivatives such as the tert-butyldimethylsilyl ethers, cyclic silyl derivatives, alkoxysilyl derivatives, and 3-pyridylmethyldimethylsilyl esters used for double bond location in fatty acid spectra. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 0000:1-107, 2019.

Hypersensitivity reactions to nonsteroidal anti-inflammatory drugs: from phenotyping to genotyping

PURPOSE OF REVIEW

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most frequent drugs involved in hypersensitivity drugs reactions. Both immunological and nonimmunological mechanisms can be involved. We describe the different phenotypes as well as analyze the genetic basis for NSAIDs hypersensitivity.

RECENT FINDINGS

Five major clinical entities are currently accepted in the classification of hypersensitivity reactions to NSAIDs. Three are mediated by nonspecific immunological mechanisms: NSAIDs-exacerbated respiratory disease, NSAIDs-exacerbated cutaneous disease and NSAIDs-induced urticaria/angioedema. Two are mediated by specific immunological mechanisms: single-NSAID-induced urticaria/angioedema or anaphylaxis and single-NSAID-induced delayed hypersensitivity reactions. The classification becomes more complex if we consider that in an important number of cases skin and airway involvement can occur, as well as the participation of other organs.

SUMMARY

Hypersensitivity reactions to NSAIDs are more complex than for other drugs like betalactams in terms of the number and types of reactions elicited, and mechanisms involved. As NSAIDs are the most frequent cause of drug hypersensitivity, it is feasible to gather a sufficient number of cases for undertaking pharmacogenetic studies.

Identification and dose dependency of ibuprofen biliary metabolites in rainbow trout

The biotransformation of the anti-inflammatory drug ibuprofen (IBF) was studied by exposing rainbow trout (Oncorhynchus mykiss) to IBF via intraperitoneal (i.p.) injection, and via water at four (0.17, 1.9, 13 and 145 μg L(-1)) exposure levels for 4d. Following exposure, the bile was collected and analyzed by LC-MS/MS methods. The identification of the formed metabolites in i.p. injected fish bile was based on the exact mass determinations by a time-of-flight mass analyzer (Q-TOF-MS) and on the studies of fragments and fragmentation patterns of precursor ions by ion trap mass analyzer (IT-MS). In addition to unmetabolized IBF, several phase I and phase II metabolites were found in the bile. The main metabolites were acyl glucuronides and taurine conjugates of IBF and of hydroxylated IBFs. The bioconcentration factors (BCFbile), defined as the ratio of the sum of IBF and its metabolites in fish bile to the concentration of IBF in water, was determined following enzymatic deconjugation and was found to range from 14000 to 49000. The highest BCFbile was found at the lowest exposure concentration (0.17 μg L(-1)). The results show that rainbow trout has a high capacity for biotransformation of IBF, and the exposure of fish to sub μg L(-1) concentrations of IBF can be determined by the analyses of the biliary metabolites of the compound.

1H NMR and UPLC-MS(E) statistical heterospectroscopy: characterization of drug metabolites (xenometabolome) in epidemiological studies

Statistical HeterospectroscopY (SHY) is a statistical strategy for the coanalysis of multiple spectroscopic data sets acquired in parallel on the same samples. This method operates through the analysis of the intrinsic covariance between signal intensities in the same and related molecular fingerprints measured by multiple spectroscopic techniques across cohorts of samples. Here, the method is applied to 600-MHz (1)H NMR and UPLC-TOF-MS (E) data obtained from human urine samples ( n = 86) from a subset of an epidemiological population unselected for any relevant phenotype or disease factor. We show that direct cross-correlation of spectral parameters, viz. chemical shifts from NMR and m/ z data from MS, together with fragment analysis from MS (E) scans, leads not only to the detection of numerous endogenous urinary metabolites but also the identification of drug metabolites that are part of the latent use of drugs by the population. We show previously unreported positive mode ions of ibuprofen metabolites with their NMR correlates and suggest the detection of new metabolites of disopyramide in the population samples. This approach is of great potential value in the description of population xenometabolomes and in population pharmacology studies, and indeed for drug metabolism studies in general.

High-temperature ultra-performance liquid chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry applied to ibuprofen metabolites in human urine

The application of sub-2 microm porous particle liquid chromatography (LC) operated at elevated temperatures, coupled with time-of-flight mass spectrometry (MS), to the separation and identification of metabolites of ibuprofen present in human urine following oral administrations is illustrated. The LC/MS system generated a high-resolution analytical separation that, with an analysis time of 20 min, provided a peak capacity in the order of ca. 350. Using this system a total of nine glucuronides of the drug and its metabolites were detected, including a number of isomeric acyl glucuronides of ibuprofen itself, a side-chain-oxidized carboxylic acid acyl glucuronide and a number of acyl glucuronides of various hydroxylated metabolites. The identities of the metabolites were confirmed by their accurate mass values and the presence of the common fragment ions from ibuprofen.

Direct assay of nonopioid analgesics and their metabolites in human urine by capillary electrophoresis and capillary electrophoresis-mass spectrometry

Capillary electrophoresis (CE) was used for the analysis of nonopioid analgesics and their metabolites directly in urine samples. A simple, reliable screening method was developed that allows identification of the drug and/or its metabolites in urine after oral application of paracetamol, acetylsalicylic acid, antipyrine, ibuprofen, naproxen, ketoprofen and propyphenazone by their migration in CE and by their UV spectra recorded with a diode-array detector in a common CE-UV system with 50 mM borax pH 9.4 as separation buffer. For the CE-electrospray (ESI)-MS coupling a volatile 50 mM ammonium acetate buffer at pH 9.8 was used. In order to analyze the metabolic pattern in more detail different methods were developed for each drug. The separation of the metabolites of acetylsalicylic acid could be improved by injection of the urine sample at the cathodic side of the capillary. In order to identify antipyrine as neutral compound as well as its neutral metabolites-a micellar electrokinetic chromatography (MEKC) method was developed.

Separatory determination of diastereomeric ibuprofen glucuronides in human urine by liquid chromatography/electrospray ionization-mass spectrometry

A method for the separatory determination of diastereomeric isomers of glucuronic acid conjugates of ibuprofen having a carboxyl group at the chiral center by liquid chromatography (LC)/electrospray ionization (ESI)-mass spectrometry (MS) has been developed. The authentic specimens of acyl glucuronides of R(-)- and S(+)-ibuprofen were chemically synthesized by the Mitsunobu reaction. In the ESI mode, the glucuronides were characterized by an abundant quasi-molecular ion [M-H]-, and the formation of the negative ion was markedly influenced by a drift voltage. The resolution of diastereomeric isomers was achieved on a Develosil ODS-HG-5 column with 20 mM ammonium acetate (pH 5.0):acetonitrile (5:2, v/v) as a mobile phase where diastereomers were monitored with a corresponding quasi-molecular ion. After oral administration of racemic ibuprofen, a preferential excretion of (S)-ibuprofen glucuronide into the urine was observed.

Regioselective and stereoselective metabolism of ibuprofen by human cytochrome P450 2C

The cytochrome P450s responsible for the regio- and stereoselectivity in the 2- and 3-hydroxylation of the chiral non-steroidal antiinflammatory drug ibuprofen were characterized in human liver microsomes. The rates of formation of both the 2- and 3-hydroxy metabolites exhibited monophasic (N = 2; N is the number of microsomal preparations) and biphasic (N = 2) substrate concentration dependence for both enantiomers of ibuprofen. The high affinity enzyme class parameters for S-ibuprofen (N = 4) were: 2-hydroxylation, Vmax = 566 +/- 213 pmol/min/mg, Km = 38 +/- 13 microM; 3-hydroxylation, Vmax = 892 +/- 630 pmol/min/mg, Km = 21 +/- 6 microM. For R-ibuprofen, the corresponding parameters were: 2-hydroxylation, Vmax = 510 +/- 117 pmol/min/mg, Km = 47 +/- 20 microM; 3-hydroxylation, Vmax = 593 +/- 113 pmol/min/mg, Km = 29 +/- 8 microM. cDNA-expressed CYP2C9 (Arg 144 and Cys 144) favored S-2- and S-3-hydroxyibuprofen formation, but CYP2C8 favored R-2-hydroxyibuprofen formation. Sulfaphenazole, retinol, and arachidonic acid competitively inhibited the rate of formation of all hydroxyibuprofens; Ki values (N = 3) for sulfaphenazole on the 2- and 3-hydroxylations of S-ibuprofen were 0.12 +/- 0.05 and 0.07 +/- 0.04 and of R-ibuprofen were 0.11 +/- 0.07 and 0.06 +/- 0.03 microM, respectively. Sulfaphenazole also competitively inhibited ibuprofen hydroxylation by cDNA-expressed CYP2C9 (Arg 144 and Cys 144) with Ki values in the range of 0.05 to 0.18 microM and CYP2C8 in the range of 0.36 to 0.55 microM. In a bank of 14 human liver microsome samples, significant correlations (r = 0.72 to 0.90; P < 0.01) were observed between the rates of formation of all four hydroxyibuprofens, and for each hydroxyibuprofen and prototypical CYP2C8/9 biotransformations. The regio- and stereoselectivities observed in vitro were consistent with those noted in vivo. The relative levels of both CYP2C8 and CYP2C9 and the expression of the corresponding variants may influence the disposition of ibuprofen in vivo.

Methods of analysis of chiral non-steroidal anti-inflammatory drugs

Although the analysis of the enantiomers of chiral non-steroidal anti-inflammatory drugs (NSAIDs) has been carried out for over 20 years, there often remains a deficit within the pharmaceutical and medical sciences to address this issue. Hence, despite world-wide therapeutic use of chiral NSAIDs the importance of stereoselectivity in pharmacokinetic, pharmacodynamic and pharmacological activity and disposition has often been ignored. This review presents both the general principles that allow separation of chiral NSAID enantiomers, and discusses both the advantages and disadvantages of the available chromatographic assay methods and procedures used to separately quantify NSAID enantiomers in biological matrices.

Changes in the liver, kidney and heart fatty acid composition following administration of ibuprofen to mice

Crl:NMRI-BR male mice received 0.6 mg/day of ibuprofen (animal model for human dose 1200 mg/day) in the diet for a period of 6 weeks. This treatment resulted in increased body mass, liver mass, and total lipid content in the liver tissue. Changes in the fatty acid composition in the individual lipid classes were most important in kidney tissue; levels of polyunsaturated fatty acids were increased in phospholipids and decreased in neutral lipids. These changes were compensated for by opposite changes in the levels of saturated and monoenoic acids. Similar changes were also observed in liver and heart lipids. An increased level of an unusual component was observed in heart tissue, which was identified as isopropyl myristate by GC-MS and verified by comparing the mass spectra and retention times with those of synthetic standards.

Metabolism of isobutylnaphthyl acetic acid in rats: determination of the chemical structures of metabolites

After oral and intravenous administration of radiolabelled isobutylnaphthyl acetic acid (INAA) to rats two metabolites were isolated from urine and plasma by HPLC. Field desorption, high resolution electron impact mass spectrometry as well as GC-MS after derivatization were used for structure elucidation and identification of the metabolites. The main biotransformation product in rat urine was found to be 5-(2'-hydroxy-2'-methyl-propyl)-1-naphthyl acetic acid (M1). The main metabolite in plasma was derived and was found to be 5-(2'-carboxypropyl)-1-naphthyl acetic acid (M2).

Determination of ibuprofen and its major metabolites in human urine by high-performance liquid chromatography

A sensitive and selective high-performance liquid chromatographic assay for free and total ibuprofen and its major metabolites in human urine is described. Urine is acidified, drug and metabolites are extracted into hexane-propanol, back-extracted into sodium bicarbonate, neutralized and chromatographed. Ibufenac (4-isobutylphenylacetic acid) and 2-phenylpropionic acid were employed as internal standards. The extraction efficiencies were 94-100% for all compounds. The two metabolites and their internal standard were separated using an isocratic chromatographic system, followed by an abrupt step gradient to a second eluent for separation of ibuprofen and its internal standard with a total run time of 18 min. Detection was by a fixed-wavelength detector (214 nm). Sample-to-sample and day-to-day reproducibility studies yielded coefficients of variability of less than 9% for all compounds. The sensitivity was sufficient to determine 2.5 micrograms/ml free ibuprofen in 100 microliters urine.

Method to determine the enantiomers of ibuprofen from human urine by high-performance liquid chromatography

By means of ethyl chloroformate, ibuprofen enantiomers were coupled to 4-methoxyaniline. The resulting amides were resolved from each other and from urinary constituents on a Pirkle column using an isocratic mobile phase with ultraviolet detection at 254 nm. Applicability of this method for the determination of inter-individual differences in urinary metabolic profiles of ibuprofen enantiomers is demonstrated. The chromatographic behavior of the corresponding amide derivatives of two ibuprofen metabolites is also described.

Development of capillary gas chromatographic-mass spectrometric methodology for the simultaneous determination of ibuprofen and [ar-2H4]ibuprofen in serum: demonstration of kinetic equivalence in the beagle

A capillary gas chromatographic-mass spectrometric method for the determination of ibuprofen and tetra-deuterated ibuprofen in serum is described. Ibuprofen, [ar-2H4]ibuprofen and the internal standard, [ar-2H4,3,3,3-2H3]ibuprofen, are extracted (after acidification) from serum onto a cross-linked styrene divinyl benzene resin by an automated sample processor. After elution and evaporation of the organic phase, samples are reconstituted with solvent and analyzed without derivatization by capillary gas chromatography-mass spectrometry. This methodology was used to evaluate possible kinetic isotope effects after the coadministration of an equimolar mixture of ibuprofen and the deuterium-labeled covariant in the beagle. No significant differences in absorption or elimination were observed.

Gas chromatographic separation of optically active anti-inflammatory 2-arylpropionic acids using (+)- or (-)-amphetamine as derivatizing reagent

A method is described for the derivatization of several non-steroidal anti-inflammatory arylalkanoic acids (ibuprofen, ketoprofen, naproxen, fenoprofen, flurbiprofen, pirprofen, cicloprofen, tiaprofenic acid, etodolic acid) with optically active amphetamine. The usefulness of this reagent compared to alpha-methylbenzylamine is described. The enantiomers are separated as diastereoisomers using capillary gas chromatography with nitrogen-phosphorus detection. The procedure is readily applied to the quantification of the enantiomers in urine and plasma samples.

The influence of hemodialysis on the pharmacokinetics of ibuprofen and its major metabolites

The pharmacokinetics of ibuprofen and its two major metabolites, the hydroxy and carboxy derivatives, were studied in seven functionally anephric subjects undergoing hemodialysis therapy. Subjects received ibuprofen 800 mg tid for 14 days. Hemodialysis was performed three times weekly during this period. Arterial and venous blood samples were collected before dialysis and along with dialysate, and during the final dosing interval and dialysis session. No accumulation of ibuprofen plasma concentrations and an absence of intact ibuprofen in dialysate indicated clearance through metabolic pathways. The metabolites did accumulate significantly (mean plasma levels, carboxy 249 micrograms/mL and hydroxy 57 mu/mL); however, both were detected in dialysate. Mean extraction efficiencies were 0.16 (hydroxy) and 0.15 (carboxy). Dialysis clearance calculated by arterial-venous difference was found to agree with actual recovery in dialysate for both metabolites. Side effects were not observed in any subject.

Ibuprofen disposition in obese individuals

Eleven obese subjects (weight 114 +/- 11 kg, mean +/- SE) and 11 age-matched subjects with normal body weight (61 +/- 3 kg) were given 600 mg of ibuprofen orally after an overnight fast. Peak ibuprofen concentration was significantly decreased in obese subjects (P less than 0.02), although the time from administration to peak concentration was not different. Ibuprofen volume of distribution was increased in obese subjects, and this increased distribution correlated positively with body weight (r = 0.82; P less than 0.001). Volume of distribution corrected for body weight was decreased in obese subjects, and this decrease correlated negatively with body weight. Ibuprofen clearance was also increased in obese subjects; the increase correlated positively with body weight (r = 0.81; P less than 0.001). Since the independent variables, volume of distribution and clearance, were increased in parallel in the obese subjects, the dependent variable, elimination half-life, was unchanged. Using mean values of distribution calculated from the 2 groups, ibuprofen distribution into body weight in excess of ideal body weight was found to be approximately 0.44 times as extensive as the distribution into ideal body weight. Furthermore, ibuprofen clearance increased in parallel with the volume of distribution and total body weight. Clinically, these data indicate that in obese patients, the ibuprofen dose may be increased without changing the dose interval, in order to achieve necessary plasma concentrations.

Disposition of ibuprofen in nephrectomized dogs

The pharmacokinetics of ibuprofen were studied in four nephrectomized and three normal dogs after administration of 214.3-227.6 mg iv of ibuprofen. Blood samples were collected at various time intervals for up to 10 h and serum concentrations of ibuprofen were assayed by an HPLC method. The elimination of serum ibuprofen followed first-order kinetics, with mean half-lives of 2.51 +/- 1.10 and 2.81 +/- 0.72 h in normal and nephrectomized dogs, respectively. Mean serum clearance of ibuprofen in nephrectomized dogs, 31.0 +/- 5.2 mL/h/kg, was higher than that in normal dogs, 12.2 +/- 8.6 mL/h/kg, (p less than 0.02). The difference may be attributed to the greater volume of distribution for ibuprofen in nephrectomized dogs, 125.2 +/- 39.0 (88.8-160.4) mL/kg as compared with 53.4 +/- 57.8 (26.0-119.9) mL/kg in the normal group (p less than 0.2).

The identification of ibuprofen and analogues in urine by pyrolysis gas chromatography mass spectrometry

The pyrolysis gas chromatography mass spectrometry of Ibuprofen, Fenoprofen, Naproxen and Ketoprofen, a series of anti-inflammatory propionic acid derivatives, is shown to proceed via decarboxylation and elimination to yield characteristic ethyl and vinyl fragments. The pyrogram enables the identification of the drug to be achieved as the pure compound, in a formulated dosage form or excreted in urine. The presence of metabolites derived from Ibuprofen causes four new fragments to be observed in the urine pyrogram. The identification of 16 components of the control urine pyrogram is presented.

Urinary metabolites of 2-ethyl-2-methylsuccinimide (ethosuximide) studied by combined gas chromatography mass spectrometry

Metabolites of 2-ethyl-2-methylsuccinimide (ethosuximide) have been studied by combined gas chromatography mass spectrometry in a urine sample from a patient treated for petit mal epilepsy with ethosuximide. A new metabolite, 2-carboxymethyl-2-methylsuccinimide, was identified in the urine. It is presumably formed by omega 1-hydroxylation of the ethyl sidechain of the drug followed by a further oxidation of the primary alcohol to a carboxyl group. A previously identified metabolite, 2-ethyl-3-hydroxy-2-methylsuccinimide, was shown in the present study to yield two gas chromatographic peaks (as the N-methylated compound), indicating the existence of a diastereoisomeric pair. Thus, the enzyme responsible for the ring hydroxylation is probably not stereospecific, or alternatively two enzymes with different stereospecificity may exist.

Urinary metabolites of 4-isobutylphenylacetic acid studied by combined gas chromatography mass spectrometry

After ingestion of 4-isobutylphenylacetic acid three metabolites were identified in the urine, viz. 4-(2-carboxypropyl)phenylacetic acid, 4-(2-hydroxy-2-methylpropyl)phenylacetic acid and 4-(1-hydroxy-2-methylpropyl)phenylacetic acid. These metabolites were identified by gas chromatography and mass spectrometry. In the in vivo formation of the metabolites the isobutyl sidechain of the drug is attacked by omega1-hydroxylation, followed by further oxidation of the primary alcohol to a carboxyl group, by omega2-hydroxylation and by omega3-hydroxylation, respectively. It has been shown previously that two other drugs with an isobutyl sidechain, viz. 2-p-methoxybenzenesulphonamido-5-isobutyl-1,3,4-thiadiazole and 2,4'-isobutylphenylpropionic acid, are metabolized in an analogous way.

Electron-capture GLC determination of ibuprofen in serum

To evaluate drug-protein binding, a sensitive method for the determination of ibuprofen in submilliliter amounts of serum was required. A specific and highly sensitive procedure, based on benzene extraction of the acidified specimen. TLC of the benzene extract residue, fomation of the pentafluorobenzyl esters of the materials eluted from the thin-layer chromatogram, and quantification of the pentafluorobenzyl esters by GLC, was developed. Utilizing electron-capture detection, the method is sensitive to 0.1 microgram of ibuprofen/0.1 ml of serum. Statistical analyses indicated an average recovery of 97.7% with a standard deviation of +/- 7.3%. Mass spectrometric analysis, in conjunction with GLC, confirmed the specificity of the method for the intact drug. The procedure was applied successfully to drug absorption and drug-protein binding studies in humans.

A novel metabolic pathway in the metabolism of 5-(4'-chloro-n-butyl)picolinic acid

The metabolism of 5-(4'-chloro-n-butyl)picolinic acid, which inhibits dopamine beta-hydroxylase and exhibits an antihypertensive effect, has been studied by gas chromatography mass spectrometry, utilising characteristic reaction products after derivatization. In rat urine five metabolities were identified by mass spectral analysis. It is found that four were elongated by a C2 unit in the carboxyl group at the 2-position on the pyridine ring and accounted for approximately 50% of the radioactivity in the 24 hour urine. The facts show that the metabolic pathway corresponding to the chain elongation of fatty acids is the major route of metabolism for this drug in the rat. Furthermore, this pathway would be confirmed in man, rabbit, guinea pig and mouse.