The potential of 19F NMR spectroscopy for rapid screening of cell cultures for models of mammalian drug metabolism

The use of microbial cultures as a complementary model for mammalian drug metabolism has been well established previously. Here is a preliminary investigation into the potential of 19F NMR spectroscopy as a rapid screening tool to quantify the biotransformations of fluorine-containing model drugs. Biotransformations of three model drugs in 48 taxonomically diverse organisms were measured by acquiring 19F NMR spectra at 376 MHz. The presence of fluorine in the molecules allowed rapid, simultaneous detection of over 20 biotransformation products without sample pretreatment, chromatography, mass spectrometric techniques or the use of radiolabelled substrates. The detection limit at 376 MHz using 5 mm NMR tubes was ca. 0.3 microg ml(-1) using a typical analysis time of 20 min per sample. With the recent advent of flow injection NMR technology, analysis time of 5 min could be achieved with less sample. This approach may be used to develop fast small-scale microbial screens for the biosynthesis of metabolite standards and production of novel drug analogues, whilst also having a role in reducing animal experiments needed to identify animal and human metabolites of fluorinated xenobiotics.

A rapid and facile method for the dereplication of purified natural products

A new approach to the use of commercial databases for the dereplication of purified natural products has been developed. This is based on searching a text file that links each structure with its molecular weight and an exact count of the number of methyl, methylene, and methine groups it contains. Analysis of such a text file, constructed from a database containing more than 126,000 natural product structures, revealed that these data, readily measured using MS and NMR spectroscopy, are highly discriminating. The identification of an alkaloid and a sesquiterpene using this new approach is described.

Recovery of underwater resonances by magnetization transferred NMR spectroscopy (RECUR-NMR)

A method for detecting small molecule NMR resonances under a water peak in biological samples is presented. After high-efficiency solvent suppression using double WATERGATE, either a TOCSY- or ROESY-based coherence transfer sequence is applied to reestablish the resonances close to, or under, water through magnetization transfer using scalar or dipolar coupling, respectively. The use of the TOCSY and ROESY methods ensures an in-phase magnetization transfer, which makes the new approach readily extended for the measurement of transverse relaxation times, internuclear ROEs, and ROE buildup rates. An extension of the new approach for J-resolved spectroscopy is also presented and tested using a sample of human blood plasma.

Investigations into biochemical changes due to diurnal variation and estrus cycle in female rats using high-resolution (1)H NMR spectroscopy of urine and pattern recognition

Metabonomic methods utilizing (1)H NMR spectroscopy and pattern recognition analysis (NMR-PR) have been applied to investigate biochemical variation in a control population of female rats over time in relation to diurnal and estrus cycle fluctuations. Urine samples were collected twice daily (6 AM-6 PM and 6 PM-6 AM) from female rats (n = 10) for a period of 10 days. (1)H NMR spectroscopic analysis and PR were performed on each sample. Subtle differences in the endogenous metabolite excretion profiles of urine samples at the various stages of the estrus cycle were observed. The main inherent metabolic clustering in the principal components analysis (PCA) maps was related to interrat variation and was observed in the first two principal components (PCs), accounting for 66% of the variance in these data. Separation of urinary data according to time of sampling (day and night) was achieved in the lower PCs. Some of the differences in the urinary profiles of day and night samples causing this separation were attributed to the increase in metabolic activity of the rat during the night. Individual rat data were also mapped as a function of time, using PCA, to produce a metabolic trajectory, which in a number of cases facilitated separation of one or more stages of the estrus cycle. Several of the fluctuations observed between urine samples collected during the different stages of the estrus cycle may be related to hormone levels. Although variation in metabolite profiles relating to both diurnal and hormonal variation could be detected these perturbations were minor compared with the effects observed due to interrat variation. This is the first time that a hormonal cycle has been described for individuals based on NMR spectroscopic and multivariate analysis of metabolic data and shows the value of metabonomic methods in the investigation of physiological variation and rhythms.

Metabonomic investigations into hydrazine toxicity in the rat

The systemic biochemical effects of oral hydrazine administration (dosed at 75, 90, and 120 mg/kg) have been investigated in male Han Wistar rats using metabonomic analysis of (1)H NMR spectra of urine and plasma, conventional clinical chemistry, and liver histopathology. Plasma samples were collected both pre- and 24 h postdose, while urine was collected predose and daily over a 7 day postdose period. (1)H NMR spectra of the biofluids were analyzed visually and via pattern recognition using principal component analysis. The latter showed that there was a dose-dependent biochemical effect of hydrazine treatment on the levels of a range of low molecular weight compounds in urine and plasma, which was correlated with the severity of the hydrazine induced liver lesions. In plasma, increases in the levels of free glycine, alanine, isoleucine, valine, lysine, arginine, tyrosine, citrulline, 3-D-hydroxybutyrate, creatine, histidine, and threonine were observed. Urinary excretion of hippurate, citrate, succinate, 2-oxoglutarate, trimethylamine-N-oxide, fumarate and creatinine were decreased following hydrazine dosing, whereas taurine, creatine, threonine, N-methylnicotinic acid, tyrosine, beta-alanine, citrulline, Nalpha-acetylcitrulline and argininosuccinate excretion was increased. Moreover, the most notable effect was the appearance in urine and plasma of 2-aminoadipate, which has previously been shown to lead to neurological effects in rats. High urinary levels of 2-aminoadipate may explain the hitherto poorly understood neurological effects of hydrazine. Metabonomic analysis of high-resolution (1)H NMR spectra of biofluids has provided a means of monitoring the progression of toxicity and recovery, while also allowing the identification of novel biomarkers of development and regression of the lesion.

An NMR-based metabonomic approach to the investigation of coelomic fluid biochemistry in earthworms under toxic stress

The endogenous metabolites of the coelomic fluid of the earthworm Eisenia veneta were characterised using high-resolution one-dimensional and two-dimensional 1H nuclear magnetic resonance spectroscopy. Signals from common organic acids, such as acetate, fumarate, malonate, malate, formate, and succinate, were identified together with adenosine and nicotinamide mononucleotide. The potential use of this information as a baseline dataset for future toxicological or physiological studies was demonstrated by a metabonomic analysis: a series of earthworms were dosed with the model compound 3-fluoro-4-nitrophenol, and toxic effects followed by multivariate analysis of the spectral data of the coelomic fluid. Relative concentrations of acetate and malonate were decreased in the dosed worms compared to the controls.

Investigation of water environments in a C18 bonded silica phase using 1H magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy

High resolution 1H magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra have been obtained on typical C18 bonded silicas used in chromatographic solid-phase extraction separations. It has been shown for the first time that water molecules distributed in distinct physico-chemical environments within the chromatographic system can be detected directly using a simple 1H MAS NMR measurement. The resonances assigned to water protons in differing physico-chemical environments have distinct chemical shifts, line widths, relaxation times (T1 and T2) and also exhibit temperature dependent coalescence behaviour. This novel MAS approach may lead to a better understanding of the environments of other analytes in mixtures during such separations.

S-naproxen-beta-1-O-acyl glucuronide degradation kinetic studies by stopped-flow high-performance liquid chromatography-1H NMR and high-performance liquid chromatography-UV

Acyl-migrated isomers of drug beta-1-O-acyl glucuronides have been implicated in drug toxicity because they can bind to proteins. The acyl migration and hydrolysis of S-naproxen-beta-1-O-acyl glucuronide (S-nap-g) was followed by dynamic stopped-flow HPLC-1H NMR and HPLC methods. Nine first order rate constants in the chemical equilibrium between six species (S-nap-g, its alpha/beta-2-O-acyl, alpha/beta-3-O-acyl, alpha/beta-4-O-acyl, and alpha-1-O-acyl-migration isomers, and S-naproxen aglycone) were determined by HPLC-UV studies in 25 mM potassium phosphate buffer, pH 7.40, 25 mM potassium phosphate buffer in D2O pD 7.40, and 25 mM potassium phosphate buffer in D2O pD 7.40/MeCN 80:20 v/v (HPLC-1H NMR mobile phase). In the 25 mM potassium phosphate buffer (pH 7.40) the acyl-migration rate constants (h(-1)) were 0.18 (S-nap-g-alpha/beta-2-O-acyl isomer), 0.23 (alpha/beta-2-O-acyl-alpha-1-O-acyl), 2.6 (alpha-1-O-acyl-alpha/beta-2-O-acyl), 0.12 (alpha/beta-2-O-acyl-alpha/beta-3-O-acyl), 0.048 (alpha/beta-3-O-acyl-alpha/beta-2-O-acyl), 0.059 (alpha/beta-3-O-acyl-alpha/beta-4-O-acyl), and 0.085 (alpha/beta-4-O-acyl-alpha/beta-3-O-acyl). The hydrolysis rate constants (h(-1)) were 0.025 (hydrolysis of S-nap-g) and 0.0058 (hydrolysis of all acyl-migrated isomers). D2O and MeCN decreased the magnitude of all nine kinetic rate constants by up to 80%. The kinetic rate constants for the degradation of S-nap-g in the mobile phase used for HPLC-1H NMR determined using HPLC-UV could predict the results obtained by the dynamic stopped-flow HPLC-1H NMR experiments of the individual acyl-migrated isomers. It is therefore recommended that beta-1-O-acyl glucuronide degradation kinetics be investigated by HPLC-UV methods once the identification and elution order of the isomers have been established by HPLC-1H NMR.

Investigation of the metabolite variation in control rat urine using (1)H NMR spectroscopy

An exploratory statistical analysis has been undertaken of 640 (1)H NMR spectra of rat urine, obtained from predose and control animals during the course of eight separate toxicology studies. The aim was to determine the degree and type of variation between (1)H NMR spectra from such control animals and to investigate the variations in the spectral descriptors based on averaged peak intensities. The results showed that many of the spectral descriptors had skew and/or multimodal distributions, and that it was possible to distinguish between samples of urine collected at different times of day with a success rate of (89%) and to classify 90% of the predose spectra into their correct study group using principal component and linear discriminant analyses. The results show that successful classification can be achieved of NMR spectra of control rat urine, which exhibit more subtle changes than those previously reported when treated and control animals were compared. The results presented here suggest that it will be possible to identify very subtle toxicological changes if care is taken to standardize the experimental conditions used during toxicity screens.

High-performance liquid chromatography linked to inductively coupled plasma mass spectrometry and orthogonal acceleration time-of-flight mass spectrometry for the simultaneous detection and identification of metabolites of 2-bromo-4-trifluoromethyl

The use of HPLC coupled to inductively coupled plasma mass spectrometry (ICPMS) and orthogonal acceleration time-of-flight (oa-TOF) for the profiling, identification, and quantification of metabolites in rat urine following the administration of 2-bromo-4-trifluoromethylacetanilide is described. The metabolites present in the sample were separated by reversed-phase gradient chromatography with UV-diode array detection. The bulk of the eluent (90%) from the UV detector was directed to an ICPMS where bromine-containing metabolites were detected and quantified using ICPMS. The minor portion of the eluent (10%) was taken for oa-TOFMS for identification. By these means, the metabolites were identified as sulfate and glucuronide conjugates of a ring hydroxy-substituted metabolite, a N-sulfate, a N-hydroxylamine glucuronide, and N- and N-hydroxyglucuronides.

Application of directly coupled HPLC NMR to separation and characterization of lipoproteins from human serum

Disorders in lipoprotein metabolism are critical in the etiology of several disease states such as coronary heart disease and atherosclerosis. Thus, there is considerable interest in the development of novel methods for the analysis of lipoprotein complexes. We report here a simple chromatographic method for the separation of high-density lipoprotein, low-density lipoprotein, and very low-density lipoprotein from intact serum or plasma. The separation was achieved using a hydroxyapatite column and elution with pH 7.4 phosphate buffer with 100-microL injections of whole plasma. Coelution of HDL with plasma proteins such as albumin occurred, and this clearly limits quantitation of that species by HPLC peak integration. We also show, for the first time, the application of directly coupled HPLC 1H NMR spectroscopy to confirm the identification of the three major lipoproteins. The full chromatographic run time was 90 min with stopped-flow 600-MHz NMR spectra of each lipoprotein being collected using 128 scans, in 7 min. The 1H NMR chemical shifts of lipid signals were identical to conventional NMR spectra of freshly prepared lipoprotein standards, confirming that the lipoproteins were not degraded by the HPLC separation and that their gross supramolecular organization was intact.

Directly coupled HPLC-NMR and HPLC-MS approaches for the rapid characterisation of drug metabolites in urine: application to the human metabolism of naproxen

High resolution nuclear magnetic resonance (NMR) spectroscopy is a very powerful tool for the structural identification of xenobiotic metabolites in complex biological matrices such as plasma, urine and bile. However, these fluids are dominated by thousands of signals resulting from endogenous metabolites and it is advantageous when investigating drug metabolites in such matrices to simplify the spectra by including a separation step in the experiment by directly-coupling HPLC and NMR. Naproxen (6-methoxy-alpha-methyl-2-naphthyl acetic acid) is administered as the S-enantiomer and is metabolised in vivo to form its demethylated metabolite which is subsequently conjugated with beta-D-glucuronic acid as well as with sulfate. Naproxen is also metabolised by phase II metabolism directly to form a glycine conjugate as well as a glucuronic acid conjugate at the carboxyl group. In the present investigation, the metabolism of naproxen was investigated in urine samples with a very simple sample preparation using a combination of directly-coupled HPLC-1H NMR spectroscopy and HPLC-mass spectrometry (MS). A buffer system was developed which allows the same chromatographic method to be used for the HPLC-NMR as well as the HPLC-MS analysis. The combination of these methods is complementary in information content since the NMR spectra provide evidence to distinguish isomers such as the type of glucuronides formed, and the HPLC-MS data allow identification of molecules containing NMR-silent fragments such as occur in the sulfate ester.

LC-1H NMR used for determination of the elution order of S-naproxen glucuronide isomers in two isocratic reversed-phase LC-systems

The reactive metabolite S-naproxen-beta-1-O-acyl glucuronide was purified from human urine using solid phase extraction (SPE) and preparative HPLC. The structure was confirmed by 600 MHz 1H NMR. Directly coupled 600 MHz HPLC-1H NMR was used to assign the peaks in chromatograms obtained when analysing a sample containing S-naproxen aglycone and the 1-, 2-, 3-, and 4-isomers of S-naproxen-beta-1-O-acyl glucuronide in two simple isocratic reversed phase HPLC-systems. Using mobile phase 1 (50 mM formate buffer pH 5.75/acetonitrile 75:25 v/v) the elution order was: 4-O-acyl isomers, beta-1-O-acyl glucuronide, 3-O-acyl isomers, 2-O-acyl isomers, and S-naproxen aglycone. Using mobile phase II (25 mM potassium phosphate pH 7.40/acetonitrile 80:20 v/v) the elution order was: alpha/beta-4-O-acyl isomers, S-naproxen aglycone, beta-1-O-acyl glucuronide, 3-O-acyl isomers, and alpha/beta-2-O-acyl isomers. In both systems the elution order for the 2-, 3- and 4-O-acyl isomers corresponded with previously published results for 2-, 3-, and 4-fluorobenzoic acid glucuronide isomers determined by reversed phase HPLC-1H NMR (U.G. Sidelmann, S.H. Hansen, C. Gavaghan, A.W. Nicholls, H.A.J. Carless, J.C. Lindon, I.D. Wilson, J.K. Nicholson, J. Chromatogr. B Biomed. Appl. 685 (1996) 113-122]. The alpha-1-O-acyl isomer was found to be present at approximately 3% of the initial S-naproxen-beta-1-O-acyl glucuronide concentration in the glucuronide isomer mixture after 6 h of incubation at pH 7.40 and 37 degrees C. In both HPLC systems it eluted just before the beta-1-O-acyl glucuronide well separated from other isomers. Investigators should consider the possible formation of a alpha-1-O-acyl isomer when studying glucuronide reactivity and degradation.

The biochemical profile of rat testicular tissue as measured by magic angle spinning 1H NMR spectroscopy

The testis is the principal organ of male fertility, responsible for the production of spermatozoa and their maturation into sperm. However, the underlying biochemistry of the testis is relatively understudied. The fluidic and homogeneous nature of the testis makes it an ideal organ for high resolution magic angle spinning (MAS) 1H NMR spectroscopy. In this study we have catalogued the low molecular weight metabolites. The testis contains large amounts of creatine, of which a substantial proportion was shown to be extracellular using bipolar gradients to measure apparent diffusion coefficients. The tissue also contained relatively high amounts of uridine.

Directly coupled HPLC-NMR and HPLC-NMR-MS in pharmaceutical research and development

The methodology for the direct coupling of HPLC with NMR spectroscopy and the simultaneous double coupling of HPLC with NMR and mass spectrometry (MS) is described. Indications of the necessary technical developments to achieve this are given, and the applications of these new techniques to studies of pharmaceutical relevance are reviewed. These include studies of combinatorial chemistry libraries, synthetic chemical impurities, characterisation of drug mixtures, identification of natural products of possible pharmaceutical interest and identification of xenobiotic metabolites in human, animal and in vitro systems. In addition, HPLC-NMR has been used to investigate xenobiotic metabolite reactivity. Finally, the potential future directions of the techniques are discussed.

Mass directed peak selection, an efficient method of drug metabolite identification using directly coupled liquid chromatography-mass spectrometry-nuclear magnetic resonance spectroscopy

Mass spectrometry (both MS and MS-MS) has been used to determine which eluting chromatography peaks in an LC-MS-nuclear magnetic resonance (NMR) experiment should be selected for extended NMR spectroscopic measurement. This mass directed selection of chromatographic peaks has been applied to test mixtures and urine samples for identification of drug metabolites. It was used to simultaneously determine when drug-related material was eluting and provided molecular mass information on these components. Stop-flow LC-NMR was used to acquire data for structural characterisation of drug-related components. This work further serves to demonstrate the potential of coupling tandem mass spectrometry using an ion trap spectrometer with LC-NMR spectroscopy, to provide an extremely powerful tool in structural elucidation.

Use of directly coupled ion-exchange liquid chromatography-mass spectrometry and liquid chromatography-nuclear magnetic resonance spectroscopy as a strategy for polar metabolite identification

Ion-exchange LC-MS and LC-NMR have been successfully used to identify a novel N-acetyl metabolite of a highly polar drug candidate [2-(ethanimidoylamino)ethyl]sulfonyl alanine (GW273629) under development as a therapeutic agent. This has been achieved using a simple HPLC method without the need for complicated and time consuming pre- or post-column derivatisation. Ion-exchange chromatography using simple ionic strength buffer and organic solvent mobile phases, as applied here, should be suitable for the analysis of other charged polar species. Optimisation of the system described could result in the development of a rational generic HPLC approach specifically designed for the characterisation of polar drug molecules and their metabolites.

Application of directly coupled LC-NMR-MS to the structural elucidation of metabolites of the HIV-1 reverse-transcriptase inhibitor BW935U83

The human in vivo metabolism of the HIV-1 reverse transcriptase inhibitor 5-chloro-1-(2',3'-dideoxy-3'-fluoro-erythro-pentofuranosyl)uracil (BW935U83) was studied using 19F NMR spectroscopy, directly coupled LC-NMR and LC-NMR-MS. The number and relative proportions of the drug metabolites were obtained from 19F NMR spectra of whole human urine. The novel use of the continuous-flow 19F detected LC-NMR experiment yielded chromatographic retention times and 19F chemical shifts for the parent drug, the glucuronide conjugate of the parent and an early eluting polar metabolite. The parent drug and its glucuronide conjugate were easily characterised by directly coupled 1H LC-NMR spectroscopy and two-dimensional TOCSY experiments. The identification of the second metabolite was achieved using 19F NMR and directly coupled 1H LC-NMR-MS which furnished the molecular weight, and through the use of MS-MS techniques, information on the fragment ions. This species was identified as 3-fluoro-ribolactone.

High-resolution (1)H and (1)H-(13)C magic angle spinning NMR spectroscopy of rat liver

High-resolution magic angle spinning (MAS) (1)H NMR spectra of small samples (ca. 8 mg) of intact rat liver are reported for the first time. One dimensional spectra reveal a number of large well-resolved NMR signals mainly from low to medium molecular weight compounds (generally <1000 Daltons) from a variety of chemical classes. A range of 2D MAS-NMR experiments were performed, including (1)H J-resolved (JRES), (1)H-(1)H total correlation spectroscopy (TOCSY) and (1)H-(13)C heteronuclear multiple quantum coherence (HMQC) to enable detailed signal assignment. Resonances were assigned from alpha- and beta-glucose, glycerol, alanine, glutamate, glycine, dimethylglycine, lysine, and threonine, together with phosphocholine, choline, lactate, trimethylamine-N-oxide (TMAO), and certain fatty acids. Well-resolved (1)H NMR signals from glycogen (poly 1-4 alpha-glucose) were observed directly in intact liver using MAS-NMR spectroscopy. In addition, the resonances from the glycogen C(1)H proton in alpha(1-->4) linked glucose units with either alpha(1-->4) units adjacent or alpha(1-->6) linked branches could be resolved in a high-resolution (1)H NMR experiment giving direct in situ information on the ratio of alpha(1-->4) to alpha(1-->6) units. This indicates that despite the relatively high MW (>1,000,000 Daltons) there is considerable segmental motion in the glycogen molecules giving long (1)H T(2) relaxation times. Magn Reson Med 44:201-207, 2000.

Investigation of the metabolism of 14C/13C-practolol in rat using directly coupled radio-HPLC-NMR-MS

1. The metabolic fate of 14C/13C-practolol was investigated using on-line HPLC-NMR-MS following oral administration to rat. The major route of elimination for the radiolabel was via the urine with the principal biotransformation products confirmed as the 2-hydroxy- and 2-hydroxyglucronide metabolites. 2. In addition, futile deacetylation, determined by the replacement of 13C-labelled acetyl groups with endogenous 12C-acetyls accounted for approximately 7-10% of the urinary metabolites, corresponding to approximately 5% of the dose undergoing N-deacetylation. 3. Evidence for chiral metabolism was sought via NMR of isolated metabolites using beta-cyclodextrin as a chiral shift agent. Practolol was excreted as a racemate. However, some enantioselective metabolism/excretion had occurred as the hydroxy- and hydroxyglucuronide were not excreted as racemic mixtures. 4. Directly coupled radio-HPLC-NMR-MS is extremely effective for the identification of the metabolites of radiolabelled xenobiotics in urine samples.

High-resolution magic angle spinning (1)H NMR spectroscopy of intact liver and kidney: optimization of sample preparation procedures and biochemical stability of tissue during spectral acquisition

High-resolution magic angle spinning (MAS) (1)H NMR spectroscopy has been used to investigate the biochemical composition of whole rat renal cortex and liver tissue samples. The effects of a number of sample preparation procedures and experimental variables have been investigated systematically in order to optimize spectral quality and maximize information recovery. These variables include the effects of changing the sample volume in the MAS rotor, snap-freezing the samples, and the effect of organ perfusion with deuterated saline solution prior to MAS NMR analysis. Also, the overall biochemical stability of liver and kidney tissue MAS NMR spectra was investigated under different temperature conditions. We demonstrate improved resolution and line shape of MAS NMR spectra obtained from small spherical tissue volume (12 microl) rotor inserts compared to 65 microl cylindrical samples directly inserted into the MAS rotors. D(2)O saline perfusion of the in situ afferent vascular tree of the tissue immediately postmortem also improves line shape in MAS NMR spectra. Snap-freezing resulted in increased signal intensities from alpha-amino acids (e.g., valine) in tissue together with decreases in renal osmolytes, such as myo-inositol. A decrease in triglyceride levels was observed in renal cortex following stasis on ice and in the MAS rotor (303 K for 4 h). This work indicates that different tissues have differential metabolic stabilities in (1)H MAS NMR experiments and that careful attention to sample preparation is required to minimize artifacts and maintain spectral quality.

Chemometric models for toxicity classification based on NMR spectra of biofluids

1H NMR spectroscopic and pattern recognition (PR)-based methods were used to investigate the biochemical variability in urine obtained from control rats and from rats treated with a hydrazine (a model hepatotoxin) or HgCl(2) (a model renal cortical toxin). The 600 MHz (1)H NMR spectra of urine samples obtained from vehicle- or toxin-treated Han-Wistar (HW) and Sprague-Dawley (SD) rats were acquired, and principal components analysis (PCA) and soft independent modeling of class analogy (SIMCA) analysis were used to investigate the (1)H NMR spectral data. Variation and strain differences in the biochemical composition of control urine samples were assessed. Control urine (1)H NMR spectra obtained from the two rat strains appeared visually similar. However, chemometric analysis of the control urine spectra indicated that HW rat urine contained relatively higher concentrations of lactate, acetate, and taurine and lower concentrations of hippurate than SD rat urine. Having established the extent of biochemical variation in the two populations of control rats, PCA was used to evaluate the metabolic effects of hydrazine and HgCl(2) toxicity. Urinary biomarkers of each class of toxicity were elucidated from the PC loadings and included organic acids, amino acids, and sugars in the case of mercury, while levels of taurine, beta-alanine, creatine, and 2-aminoadipate were elevated after hydrazine treatment. SIMCA analysis of the data was used to build predictive models (from a training set of 416 samples) for the classification of toxicity type and strain of rat, and the models were tested using an independent set of urine samples (n = 124). Using models constructed from the first three PCs, 98% of the test samples were correctly classified as originating from control, hydrazine-treated, or HgCl(2)-treated rats. Furthermore, this method was sensitive enough to predict the correct strain of the control samples for 79% of the data, based upon the class of best fit. Incorporation of these chemometric methods into automated NMR-based metabonomics analysis will enable on-line toxicological assessment of biofluids and will provide a tool for probing the mechanistic basis of organ toxicity.

Distinction between normal and renal cell carcinoma kidney cortical biopsy samples using pattern recognition of (1)H magic angle spinning (MAS) NMR spectra

The technique of magic angle spinning (MAS) high resolution (1)H NMR spectroscopy applied to intact tissues provides excellent peak resolution and thus much biochemical information. The use of computer-based pattern recognition techniques to classify human renal cortex tissue samples as normal or tumour based on their (1)H MAS NMR spectra has been investigated. In this preliminary study of 22 paired control and tumour samples, exploratory data analysis using principal components based on NMR spectral intensities showed clear separation of the two classes. Furthermore, using the supervised method of linear discriminant analysis, based on individual data point intensities or on integrated spectral regions, it was possible to distinguish between the normal and tumour kidney cortex tissue with 100% accuracy, including a single example of a metastatic tumour from a primary lung carcinoma. A tumour sample from the collecting duct of the kidney showed a different NMR spectral profile, and pattern recognition indicated that this sample did not classify with the cortical tumours.

High-performance liquid chromatography and inductively coupled plasma mass spectrometry (HPLC-ICP-MS) for the analysis of xenobiotic metabolites in rat urine: application to the metabolites of 4-bromoaniline

The use of HPLC-ICP-MS for the profiling and quantification of the metabolites of 4-bromoaniline following reversed-phase gradient chromatography is demonstrated. In the 0-8 h post dose sample, which contained the highest concentrations of compound-related material, it was possible to detect at least 16 metabolites of the compound. The methodology described offers the possibility of obtaining metabolite profiles and quantification for drugs and other xenobiotics in biological fluids and excreta without the requirement for radiolabelled tracers.

Application of directly coupled HPLC-NMR-MS/MS to the identification of metabolites of 5-trifluoromethylpyridone (2-hydroxy-5-trifluoromethylpyridine) in hydroponically grown plants

Directly coupled HPLC-NMR-MS was used to characterize two major metabolites of 5-trifluoromethylpyridone (2-hydroxy-5-trifluoromethylpyridine), a model compound for herbicides, after it had been dosed into hydroponically grown maize plants. The combination of NMR and MS data allowed the identification of both of these metabolites, namely, the N-glucoside and O-malonylglucoside conjugates of the parent pyridone. This work demonstrates the efficiency and the potential application of HPLC-NMR-MS to the investigation of the metabolism of agrochemicals. The work also indicates that combination of the use of hydroponically grown plants and directly coupled HPLC-NMR-MS allows rapid identification of metabolites with little sample preparation.