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

Investigation of intestinal elimination and biliary excretion of ibuprofen in hyperglycemic rats

An in vivo intestinal perfusion model was used to investigate how experimental hyperglycemia affects intestinal elimination and biliary excretion in the rat. Experimental diabetes was induced by administration of streptozotocin (65 mg/kg, i.v.). The intestinal perfusion medium contained 250 μM (±)-ibuprofen. An isocratic high-performance liquid chromatography method with UV-visible detection was developed to quantitate ibuprofen in the intestinal perfusate, while a gradient method was applied to quantitate ibuprofen and ibuprofen-β-d-glucuronide in the bile. The limit of quantitation of ibuprofen was found to be 0.51 μM in the perfusate of the small intestine. In the bile, the limit of quantitation of ibuprofen and ibuprofen-β-d-glucuronide was 4.42 and 10.3 μM, respectively. Unconjugated ibuprofen and ibuprofen-β-d-glucuronide were detected in the bile; however, no β-d-glucuronide of ibuprofen could be detected in the intestinal perfusate. The results indicate that experimental diabetes can cause a decrease in the disappearance of ibuprofen from the small intestine. Excretion of both ibuprofen and ibuprofen-β-d-glucuronide decreased to the bile in experimental diabetes. The results can be explained by the results of molecular biological studies indicating streptozotocin-initiated alterations in the intestinal and hepatic transport processes.

Measurement of DNA concentration as a normalization strategy for metabolomic data from adherent cell lines

Metabolomics is a rapidly advancing field, and much of our understanding of the subject has come from research on cell lines. However, the results and interpretation of such studies depend on appropriate normalization of the data; ineffective or poorly chosen normalization methods can lead to frankly erroneous conclusions. That is a recurrent challenge because robust, reliable methods for normalization of data from cells have not been established. In this study, we have compared several methods for normalization of metabolomic data from cell extracts. Total protein concentration, cell count, and DNA concentration exhibited strong linear correlations with seeded cell number, but DNA concentration was found to be the most generally useful method for the following reasons: (1) DNA concentration showed the greatest consistency across a range of cell numbers; (2) DNA concentration was the closest to proportional with cell number; (3) DNA samples could be collected from the same dish as the metabolites; and (4) cell lines that grew in clumps were difficult to count accurately. We therefore conclude that DNA concentration is a widely applicable method for normalizing metabolomic data from adherent cell lines.

Quantitative estimation of circulating metabolites without synthetic standards by ultra-high-performance liquid chromatography/high resolution accurate mass spectrometry in combination with UV correction

An early assessment of metabolite exposure in preclinical species can provide quantitative estimation on possible active or toxic metabolites. Frequently, synthetic metabolite standards are not available at the preclinical stage, precluding the quantitation of metabolites by means of calibration curves and quality control (QC) samples. We present here an approach to determine the extent of circulating metabolites using 'metabolite standards' generated by in vitro incubations in combination with the correction for mass spectrometry response based on UV response. The study was done by coupling ultra-high-performance liquid chromatography (UHPLC) to LTQ-Orbitrap high-resolution mass spectrometry, and the quantitation was based on full scan high-resolution accurate mass analysis in combination with retention time. First, we investigated the separation capacity of a 10.5 min UHPLC method and the quantitative capability of an LTQ-Orbitrap for full scan accurate mass quantitation by spiking chemical standards of buspirone and its six metabolites in blank plasma. Then we demonstrated the use of a UV correction approach to quantitatively estimate buspirone and its metabolites in plasma samples from a rat pharmacokinetics study. We compared the concentration versus time profiles of buspirone and its six metabolites in rat plasma samples obtained using three different approaches, including using UV correction, using individual standard curves for each metabolite prepared from the synthetic standard, and using a calibration curve of the parent compound buspirone. We demonstrated the estimated metabolite exposure of buspirone using this UV correction approach resulted in rank ordering of metabolite exposure within three-fold of the value obtained with metabolite standards, in contrast to eight-fold without UV correction. The approach presented in this paper provides a practical solution to an unmet bioanalytical need for quantitative information on metabolites without standards in preclinical in vivo studies.

A novel LC-MS approach for the detection of metabolites in DMPK studies

BACKGROUND

The profiling and quantification of drug metabolites in discovery and development bioanalysis studies is playing an increasingly important role in early candidate selection. Using a conventional tandem quadrupole mass spectrometer this activity normally requires several analytical runs to acquire the necessary analytical data.

RESULTS

In this article we present the use of a new tandem quadrupole mass spectrometer equipped with a novel collision cell design, which allows the rapid switching between multiple reaction monitoring and full-scan MS mode. This approach allowed for the collection of multiple reaction monitoring data and full-scan data with no loss in sensitivity, with analysis times in the 1-2 min range.

CONCLUSION

A modified approach of using the multiple reaction monitoring data to trigger the acquisition of full scan MS/MS data is described, where the data is collected on the trailing edge of the LC-MS peak, thus improving data quality and throughput.

Chromatography with higher pressure, smaller particles and higher temperature: a bioanalytical perspective

Recent years have seen widespread use of ultra-high-pressure liquid chromatography (UHPLC) in biological fluids. Most commonly the emphasis is on developing high throughput assay methods to reduce the analysis time and cost. Particle size and temperature are chromatographic parameters that can be changed to improve efficiency and obtain rapid separations. UHPLC and high-temperature liquid chromatography (HTLC) are two techniques that reduce the analysis time by decreasing the size of the column packing material and increasing the column temperature, respectively. Both of these techniques have advantages and limitations. In this article we have summarized the history, theoretical background of UHPLC and HTLC and the various advantages and limitations of sample preparation techniques and the detection systems (mass spectrometry and ultraviolet) used for the bioanalytical assays. In addition, selected bioanalytical applications of the two techniques have been reviewed and tabulated.

Xenobiotic metabolism: a view through the metabolometer

The combination of advanced ultraperformance liquid chromatography coupled with mass spectrometry, chemometrics, and genetically modified mice provide an attractive raft of technologies with which to examine the metabolism of xenobiotics. Here, a reexamination of the metabolism of the food mutagen PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine), the suspect carcinogen areca alkaloids (arecoline, arecaidine, and arecoline 1-oxide), the hormone supplement melatonin, and the metabolism of the experimental cancer therapeutic agent aminoflavone is presented. In all cases, the metabolic maps of the xenobiotics were considerably enlarged, providing new insights into their toxicology. The inclusion of transgenic mice permitted unequivocal attribution of individual and often novel metabolic pathways to particular enzymes. Last, a future perspective for xenobiotic metabolomics is discussed and its impact on the metabolome is described. The studies reviewed here are not specific to the mouse and can be adapted to study xenobiotic metabolism in any animal species, including humans. The view through the metabolometer is unique and visualizes a metabolic space that contains both established and unknown metabolites of a xenobiotic, thereby enhancing knowledge of their modes of toxic action.

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.