Metabolism and Effects on Endogenous Metabolism of Paracetamol (Acetaminophen) in a Porcine Model of Liver Failure

The metabolic fate, toxicity, and effects on endogenous metabolism of paracetamol (acetaminophen, APAP) in 22 female Landrace cross large white pigs were evaluated in a model of acute liver failure (ALF). Anesthetized pigs were initially dosed at 250 mg/kg via an oroduodenal tube with APAP serum concentrations maintained above 300 mg/l using maintenance doses of 0.5–4 g/h until ALF. Studies were undertaken to determine both the metabolic fate of APAP and its effects on the endogenous metabolic phenotype of ALF in using ¹H NMR spectroscopy. Increased concentrations of citrate combined with pre-ALF increases in circulating lactate, pyruvate, and alanine in plasma suggest mitochondrial dysfunction and a switch in hepatic energy metabolism to glycolysis in response to APAP treatment. A specific liquid chromatography-tandem mass spectrometry assay was used to quantify APAP and metabolites. The major circulating and urinary metabolite of APAP was the phenolic glucuronide (APAP-G), followed by p-aminophenol glucuronide (PAP-G) formed from N-deacetylated APAP. The PAP produced by N-deacetylation was the likely cause of the methemoglobinemia and kidney toxicity observed in this, and previous, studies in the pig. The phenolic sulfate of APAP, and the glutathione-derived metabolites of the drug were only found as minor components (with the cysteinyl conjugate detected but not the mercapturate). Given its low sulfation, combined with significant capacity for N-deacetylation the pig may represent a poor translational model for toxicology studies for compounds undergoing significant metabolism by sulfation, or which contain amide bonds which when hydrolyzed to unmask an aniline lead to toxicity. However, the pig may provide a useful model where extensive amide hydrolysis is seen for drugs or environmental chemicals in humans, but not in, eg, the rat and dog which are the preclinical species normally employed for safety assessment.

Alterations in endo-lysosomal function induce similar hepatic lipid profiles in rodent models of drug-induced phospholipidosis and Sandhoff disease

Drug-induced phospholipidosis (DIPL) is characterized by an increase in the phospholipid content of the cell and the accumulation of drugs and lipids inside the lysosomes of affected tissues, including in the liver. Although of uncertain pathological significance for patients, the condition remains a major impediment for the clinical development of new drugs. Human Sandhoff disease (SD) is caused by inherited defects of the β subunit of lysosomal β-hexosaminidases (Hex) A and B, leading to a large array of symptoms, including neurodegeneration and ultimately death by the age of 4 in its most common form. The substrates of Hex A and B, gangliosides GM2 and GA2, accumulate inside the lysosomes of the CNS and in peripheral organs. Given that both DIPL and SD are associated with lysosomes and lipid metabolism in general, we measured the hepatic lipid profiles in rodent models of these two conditions using untargeted LC/MS to examine potential commonalities. Both model systems shared a number of perturbed lipid pathways, notably those involving metabolism of cholesteryl esters, lysophosphatidylcholines, bis(monoacylglycero)phosphates, and ceramides. We report here profound alterations in lipid metabolism in the SD liver. In addition, DIPL induced a wide range of lipid changes not previously observed in the liver, highlighting similarities with those detected in the model of SD and raising concerns that these lipid changes may be associated with underlying pathology associated with lysosomal storage disorders.

PPAR-pan activation induces hepatic oxidative stress and lipidomic remodelling

The peroxisome proliferator-activated receptors (PPARs) are ligand activated nuclear receptors that regulate cellular homoeostasis and metabolism. PPARs control the expression of genes involved in fatty-acid and lipid metabolism. Despite evidence showing beneficial effects of their activation in the treatment of metabolic diseases, particularly dyslipidaemias and type 2 diabetes, PPAR agonists have also been associated with a variety of side effects and adverse pathological changes. Agonists have been developed that simultaneously activate the three PPAR receptors (PPARα, γ and δ) in the hope that the beneficial effects can be harnessed while avoiding some of the negative side effects. In this study, the hepatic effects of a discontinued PPAR-pan agonist (a triple agonist of PPAR-α, -γ, and -δ), was investigated after dietary treatment of male Sprague-Dawley (SD) rats. The agonist induced liver enlargement in conjunction with metabolomic and lipidomic remodelling. Increased concentrations of several metabolites related to processes of oxidation, such as oxo-methionine, methyl-cytosine and adenosyl-methionine indicated increased stress and immune status. These changes are reflected in lipidomic changes, and increased energy demands as determined by free fatty acid (decreased 18:3 n-3, 20:5 n-3 and increased ratios of n-6/n-3 fatty acids) triacylglycerol, phospholipid (decreased and increased bulk changes respectively) and eicosanoid content (increases in PGB2 and 15-deoxy PGJ2). We conclude that the investigated PPAR agonist, GW625019, induces liver enlargement, accompanied by lipidomic remodelling, oxidative stress and increases in several pro-inflammatory eicosanoids. This suggests that such pathways should be monitored in the drug development process and also outline how PPAR agonists induce liver proliferation.

Systems toxicology: modelling biomarkers of glutathione homeostasis and paracetamol metabolism

One aim of systems toxicology is to deliver mechanistic, mathematically rigorous, models integrating biochemical and pharmacological processes that result in toxicity to enhance the assessment of the risk posed to humans by drugs and other xenobiotics. The benefits of such 'in silico' models would be in enabling the rapid and robust prediction of the effects of compounds over a range of exposures, improving in vitro-in vivo correlations and the translation from preclinical species to humans. Systems toxicology models of organ toxicities that result in high attrition rates during drug discovery and development, or post-marketing withdrawals (e.g., drug-induced liver injury (DILI)) should facilitate the discovery of safe new drugs. Here, systems toxicology as applied to the effects of paracetamol (acetaminophen, N-acetyl-para-aminophenol (APAP)) is used to exemplify the potential of the approach.

Molecular phenotyping of a UK population: defining the human serum metabolome

Phenotyping of 1,200 'healthy' adults from the UK has been performed through the investigation of diverse classes of hydrophilic and lipophilic metabolites present in serum by applying a series of chromatography-mass spectrometry platforms. These data were made robust to instrumental drift by numerical correction; this was prerequisite to allow detection of subtle metabolic differences. The variation in observed metabolite relative concentrations between the 1,200 subjects ranged from less than 5 % to more than 200 %. Variations in metabolites could be related to differences in gender, age, BMI, blood pressure, and smoking. Investigations suggest that a sample size of 600 subjects is both necessary and sufficient for robust analysis of these data. Overall, this is a large scale and non-targeted chromatographic MS-based metabolomics study, using samples from over 1,000 individuals, to provide a comprehensive measurement of their serum metabolomes. This work provides an important baseline or reference dataset for understanding the 'normal' relative concentrations and variation in the human serum metabolome. These may be related to our increasing knowledge of the human metabolic network map. Information on the Husermet study is available at http://www.husermet.org/. Importantly, all of the data are made freely available at MetaboLights (http://www.ebi.ac.uk/metabolights/).

Novel gut-based pharmacology of metformin in patients with type 2 diabetes mellitus

Metformin, a biguanide derivate, has pleiotropic effects beyond glucose reduction, including improvement of lipid profiles and lowering microvascular and macrovascular complications associated with type 2 diabetes mellitus (T2DM). These effects have been ascribed to adenosine monophosphate-activated protein kinase (AMPK) activation in the liver and skeletal muscle. However, metformin effects are not attenuated when AMPK is knocked out and intravenous metformin is less effective than oral medication, raising the possibility of important gut pharmacology. We hypothesized that the pharmacology of metformin includes alteration of bile acid recirculation and gut microbiota resulting in enhanced enteroendocrine hormone secretion. In this study we evaluated T2DM subjects on and off metformin monotherapy to characterize the gut-based mechanisms of metformin. Subjects were studied at 4 time points: (i) at baseline on metformin, (ii) 7 days after stopping metformin, (iii) when fasting blood glucose (FBG) had risen by 25% after stopping metformin, and (iv) when FBG returned to baseline levels after restarting the metformin. At these timepoints we profiled glucose, insulin, gut hormones (glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY) and glucose-dependent insulinotropic peptide (GIP) and bile acids in blood, as well as duodenal and faecal bile acids and gut microbiota. We found that metformin withdrawal was associated with a reduction of active and total GLP-1 and elevation of serum bile acids, especially cholic acid and its conjugates. These effects reversed when metformin was restarted. Effects on circulating PYY were more modest, while GIP changes were negligible. Microbiota abundance of the phylum Firmicutes was positively correlated with changes in cholic acid and conjugates, while Bacteroidetes abundance was negatively correlated. Firmicutes and Bacteroidetes representation were also correlated with levels of serum PYY. Our study suggests that metformin has complex effects due to gut-based pharmacology which might provide insights into novel therapeutic approaches to treat T2DM and associated metabolic diseases.

TRIAL REGISTRATION

www.ClinicalTrials.gov NCT01357876.

Genome-wide association study of metabolic traits reveals novel gene-metabolite-disease links

Metabolic traits are molecular phenotypes that can drive clinical phenotypes and may predict disease progression. Here, we report results from a metabolome- and genome-wide association study on (1)H-NMR urine metabolic profiles. The study was conducted within an untargeted approach, employing a novel method for compound identification. From our discovery cohort of 835 Caucasian individuals who participated in the CoLaus study, we identified 139 suggestively significant (P<5×10(-8)) and independent associations between single nucleotide polymorphisms (SNP) and metabolome features. Fifty-six of these associations replicated in the TasteSensomics cohort, comprising 601 individuals from São Paulo of vastly diverse ethnic background. They correspond to eleven gene-metabolite associations, six of which had been previously identified in the urine metabolome and three in the serum metabolome. Our key novel findings are the associations of two SNPs with NMR spectral signatures pointing to fucose (rs492602, P = 6.9×10(-44)) and lysine (rs8101881, P = 1.2×10(-33)), respectively. Fine-mapping of the first locus pinpointed the FUT2 gene, which encodes a fucosyltransferase enzyme and has previously been associated with Crohn's disease. This implicates fucose as a potential prognostic disease marker, for which there is already published evidence from a mouse model. The second SNP lies within the SLC7A9 gene, rare mutations of which have been linked to severe kidney damage. The replication of previous associations and our new discoveries demonstrate the potential of untargeted metabolomics GWAS to robustly identify molecular disease markers.

Intrinsic electron beam emittance from metal photocathodes: the effect of the electron effective mass

A theoretical development of prior analyses, together with our solenoid scan measurements on eight planar metal photocathodes (Ag, Be, Cr, Cu, Mo, Sn, Ta, and W) and previous data on Mg [X. J. Wang, M. Babzien, R. Malone, and Z. Wu, in Proceedings of LINAC2002, Gyeongju, Korea, 2002 (Pohang Accelerator Laboratory, Pohang, Korea, 2002), pp. 142-144.] indicate that the transverse momentum (and hence intrinsic emittance) of an electron beam is fundamentally dependent on the electron effective mass in the metal.

The contrasting roles of PPARδ and PPARγ in regulating the metabolic switch between oxidation and storage of fats in white adipose tissue

BACKGROUND

The nuclear receptors peroxisome proliferator-activated receptor γ (PPARγ) and peroxisome proliferator-activated receptor δ (PPARδ) play central roles in regulating metabolism in adipose tissue, as well as being targets for the treatment of insulin resistance. While the role of PPARγ in regulating insulin sensitivity has been well defined, research into PPARδ has been limited until recently due to a scarcity of selective PPARδ agonists.

RESULTS

The metabolic effects of PPARγ and PPARδ activation have been examined in vivo in white adipose tissue from ob/ob mice and in vitro in cultured 3T3-L1 adipocytes using (1)H nuclear magnetic resonance spectroscopy and mass spectrometry metabolomics to understand the receptors' contrasting roles. These steady state measurements were supplemented with (13)C-stable isotope substrate labeling to assess fluxes, in addition to respirometry and transcriptomic microarray analysis. The metabolic effects of the receptors were readily distinguished, with PPARγ activation characterized by increased fat storage, synthesis and elongation, while PPARδ activation caused increased fatty acid β-oxidation, tricarboxylic acid cycle rate and oxidation of extracellular branch chain amino acids. Stimulated glycolysis and increased fatty acid desaturation were common pathways for the agonists.

CONCLUSIONS

PPARγ and PPARδ restore insulin sensitivity through varying mechanisms. PPARδ activation increases total oxidative metabolism in white adipose tissue, a tissue not traditionally thought of as oxidative. However, the increased metabolism of branch chain amino acids may provide a mechanism for muscle atrophy, which has been linked to activation of this nuclear receptor. PPARδ has a role as an anti-obesity target and as an anti-diabetic, and hence may target both the cause and consequences of dyslipidemia.

H NMR spectroscopy-based metabolomic assessment of uremic toxicity, with toxicological outcomes, in male rats following an acute, mid-life insult from ochratoxin a

Overt response to a single 6.25 mg dose of ochratoxin A (OTA) by oral gavage to 15 months male rats was progressive loss of weight during the following four days. Lost weight was restored within one month and animals had a normal life-span without OTA-related terminal disease. Decline in plasma OTA concentration only commenced four days after dosing, while urinary excretion of OTA and ochratoxin alpha was ongoing. During a temporary period of acute polyuria, a linear relationship between urine output and creatinine concentration persisted. Elimination of other common urinary solutes relative to creatinine was generally maintained during the polyuria phase, except that phosphate excretion increased temporarily. ¹H NMR metabolomic analysis of urine revealed a progressive cyclic shift in the group principal components data cluster from before dosing, throughout the acute insult phase, and returning almost completely to normality when tested six months later. Renal insult by OTA was detected by ¹H NMR within a day of dosing, as the most sensitive early indicator. Notable biomarkers were trimethylamine N-oxide and an aromatic urinary profile dominated by phenylacetylglycine. Tolerance of such a large acute insult by OTA, assessed by rat natural lifetime outcomes, adds a new dimension to toxicology of this xenobiotic.

Increased hepatic oxidative metabolism distinguishes the action of Peroxisome proliferator-activated receptor delta from Peroxisome proliferator-activated receptor gamma in the ob/ob mouse

BACKGROUND

The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors and members of the nuclear receptor superfamily. The PPAR family consists of three members: PPARalpha, PPARgamma, and PPARdelta. PPARdelta controls the transcription of genes involved in multiple physiological pathways, including cellular differentiation, lipid metabolism and energy homeostasis. The receptor is expressed almost ubiquitously, with high expression in liver and skeletal muscle. Although the physiological ligands of PPARdelta remain undefined, a number of high affinity synthetic ligands have been developed for the receptor as a therapeutic target for type 2 diabetes mellitus, dyslipidemia and the metabolic syndrome.

METHODS

In this study, the metabolic role of PPARdelta activation has been investigated in liver, skeletal muscle, blood serum and white adipose tissue from ob/ob mice using a high affinity synthetic ligand and contrasted with PPARgamma activation. To maximize the analytical coverage of the metabolome, (1)H-nuclear magnetic resonance ((1)H-NMR) spectroscopy, gas chromatography-mass spectrometry (GC-MS) and ultra performance liquid chromatography-mass spectrometry (UPLC-MS) were used to examine metabolites from tissue extracts.

RESULTS

Analysis by multivariate statistics demonstrated that PPARdelta activation profoundly affected glycolysis, gluconeogenesis, the TCA cycle and linoleic acid and alpha-linolenic acid essential fatty acid pathways.

CONCLUSIONS

Although activation of both PPARdelta and PPARgamma lead to increased insulin sensitivity and glucose tolerance, PPARdelta activation was functionally distinct from PPARgamma activation, and was characterized by increased hepatic and peripheral fatty acid oxidative metabolism, demonstrating the distinctive catabolic role of this receptor compared with PPARgamma.

Metabolic phenotyping of a model of adipocyte differentiation

The 3T3-L1 murine cell line is a robust and widely used model for the study of adipogenesis and processes occurring in mature adipocytes. The fibroblastic like cells can be induced by hormones to differentiate into mature adipocytes. In this study, the metabolic phenotype associated with differentiation of the 3T3-L1 cell line has been studied using gas chromatography-mass spectrometry, (1)H nuclear magnetic resonance spectroscopy, liquid chromatography-mass spectrometry, direct infusion-mass spectrometry, and 13C substrate labeling in conjunction with multivariate statistics. The changes in metabolite concentrations at distinct periods during differentiation have been defined including alterations in the TCA cycle, glycolysis, the production of odd chain fatty acids by alpha-oxidation, fatty acid synthesis, fatty acid desaturation, polyamine biosynthesis, and trans-esterification to produce complex lipids. The metabolic changes induced during differentiation of the 3T3-L1 cell line were then compared with the metabolic differences between pre- and postdifferentiation primary adipocytes. These metabolic alterations reflect the changing role of the 3T3-L1 cells during differentiation, as well as possibly providing metabolic triggers to stimulate the processes which occur during differentiation.

Identification of phenacetin metabolites in human urine after administration of phenacetin-C2H3: measurement of futile metabolic deacetylation via HPLC/MS-SPE-NMR and HPLC-ToF MS

The metabolism of acetyl-labelled phenacetin-C2H3 was investigated in man following a single (150 mg) oral dose. Urine samples were collected at predose, 0-2 h and >2-4 h post-dose, and samples from each time-point were then analysed directly using 1H-nuclear magnetic resonance (NMR) spectroscopy. The phenacetin metabolites acetaminophen (paracetamol) glucuronide, sulphate and the N-acetyl-L-cysteinyl conjugate were identified by this method, and all showed clear evidence of the loss of the original 2H3-acetyl label and its replacement with 1H3 (futile deacetylation). The observed percentage futile deacetylation by 1H-NMR spectroscopy was measured as approximately 20% in each metabolite (about 2% of the recovered dose). After sample preparation by solid-phase extraction on a C18 solid-phase extraction (SPE) cartridge, further profiling was performed using high-performance liquid chromatography/mass spectrometry-solid-phase extraction-nuclear magnetic resonance (HPLC/MS-SPE-NMR) confirming futile deacetylation had taken place as indicated by NMR spectroscopy on both the isolated acetaminophen glucuronide and L-cysteinyl-metabolites. Additional analysis by high-performance liquid chromatography-time-of-flight mass spectrometry (HPLC-ToF MS) identified further phenacetin metabolites, and from these data the mean percentage of futile deacetylation was measured as 31% +/- 2% for the acetylated phenacetin metabolites. A number of non-acetylated metabolites were also detected in the sample via HPLC-ToF MS. The results showed that phenacetin underwent a transient formation via a number of toxic intermediates to a much greater extent than had been observed in similar studies on acetaminophen. These results may contribute to the understanding of the analgesic nephropathy reported following chronic phenacetin consumption.

Proposed minimum reporting standards for chemical analysis Chemical Analysis Working Group (CAWG) Metabolomics Standards Initiative (MSI)

There is a general consensus that supports the need for standardized reporting of metadata or information describing large-scale metabolomics and other functional genomics data sets. Reporting of standard metadata provides a biological and empirical context for the data, facilitates experimental replication, and enables the re-interrogation and comparison of data by others. Accordingly, the Metabolomics Standards Initiative is building a general consensus concerning the minimum reporting standards for metabolomics experiments of which the Chemical Analysis Working Group (CAWG) is a member of this community effort. This article proposes the minimum reporting standards related to the chemical analysis aspects of metabolomics experiments including: sample preparation, experimental analysis, quality control, metabolite identification, and data pre-processing. These minimum standards currently focus mostly upon mass spectrometry and nuclear magnetic resonance spectroscopy due to the popularity of these techniques in metabolomics. However, additional input concerning other techniques is welcomed and can be provided via the CAWG on-line discussion forum at http://msi-workgroups.sourceforge.net/ or http://Msi-workgroups-feedback@lists.sourceforge.net. Further, community input related to this document can also be provided via this electronic forum.

Metabolomics as a functional genomic tool for understanding lipid dysfunction in diabetes, obesity and related disorders

With the rise of systems biology, a number of approaches have been developed to globally profile a tier of organization in a cell, tissue or organism. Metabolomics is an approach that attempts to profile all the metabolites in a biological matrix. One of the major challenges of this approach, as with other 'omic' technologies, is that the metabolome is context-dependent and will vary with pathology, developmental stage and environmental factors. Thus, the possibility of globally profiling the metabolome of an organism is a genuine analytical challenge, as by definition this must also take into consideration all relevant factors that influence metabolism. Despite these challenges, the approach has already been applied to understand the metabolism in a range of animal models, and has more recently started to be projected into the clinical situation. In this review, the technologies currently being used in metabolomics will be assessed prior to examining their use to study diseases related to the metabolic syndrome, including Type II diabetes, obesity, cardiovascular disease and fatty liver disease.

Comparative metabonomics of differential hydrazine toxicity in the rat and mouse

Interspecies variation between rats and mice has been studied for hydrazine toxicity using a novel metabonomics approach. Hydrazine hydrochloride was administered to male Sprague-Dawley rats (30 mg/kg, n = 10 and 90 mg/kg, n = 10) and male B6C3F mice (100 mg/kg, n = 8 and 250 mg/kg, n = 8) by oral gavage. In each species, the high dose was selected to produce the major histopathologic effect, hepatocellular lipid accumulation. Urine samples were collected at sequential time points up to 168 h post dose and analyzed by 1H NMR spectroscopy. The metabolites of hydrazine, namely diacetyl hydrazine and 1,4,5,6-tetrahydro-6-oxo-3-pyridazine carboxylic acid (THOPC), were detected in both the rat and mouse urine samples. Monoacetyl hydrazine was detected only in urine samples from the rat and its absence in the urine of the mouse was attributed to a higher activity of N-acetyl transferases in the mouse compared with the rat. Differential metabolic effects observed between the two species included elevated urinary beta-alanine, 3-D-hydroxybutyrate, citrulline, N-acetylcitrulline, and reduced trimethylamine-N-oxide excretion unique to the rat. Metabolic principal component (PC) trajectories highlighted the greater degree of toxic response in the rat. A data scaling method, scaled to maximum aligned and reduced trajectories (SMART) analysis, was used to remove the differences between the metabolic starting positions of the rat and mouse and varying magnitudes of effect, to facilitate comparison of the response geometries between the rat and mouse. Mice followed "biphasic" open PC trajectories, with incomplete recovery 7 days after dosing, whereas rats followed closed "hairpin" time profiles, indicating functional reversibility. The greater magnitude of metabolic effects observed in the rat was supported by the more pronounced effect on liver pathology in the rat when compared with the mouse.

NMR spectroscopic-based metabonomic studies of urinary metabolite variation in acclimatizing germ-free rats

Understanding metabolic variation in "normal" animals is critical to the evaluation of drug-induced metabolic perturbation related to toxicity or pharmacology. NMR spectroscopic-based metabonomic methods were used to evaluate the acclimatization pathways of germ-free (axenic) rats to standard laboratory conditions concomitant with the associated development of gut microfloral communities. Urine samples from male Fischer 344 germ-free rats were collected over 21 days following introduction to a standard laboratory environment and analyzed using NMR spectroscopy. NMR spectra were data-reduced and analyzed using principal component analysis to visualize the changes in the host metabolic trajectory over the course of the study. At days 2 and 6 of the acclimatization process, there were marked episodes of glycosuria. In comparison to the concentrations in the 0-6 h samples, there was a reduction in the level of the tricarboxylic acid cycle intermediates (citrate, 2-oxoglutarate, and succinate) from 6 h to day 6, after which there was a sustained increase until the end of the study. The concentrations of hippurate and trimethylamine N-oxide increased over the course of the study in comparison to the levels at 0-6 h, with the most pronounced increase in the former between days 17 and 21. Phenylacetylglycine levels increased after 6 h whereas 3-hydroxypropionic acid was observed at day 12 and increased up to day 17. By day 21, the urinary metabolic profile was within the control range when compared to historical data, implying the establishment of a stable gut microflora. Although the metabolic alterations caused by the microbial alterations were not as substantial as those from metabolic dysfunction, their presence does have an effect on the interpretation of the profiles, the state of the animal, and the mechanism for the cause of such alterations. Furthermore, the use of oral drug delivery will have an effect on the microbial state, not only as a direct influence of the drug but also from it's associated vehicle. Such effects are likely to be observed particularly in the area of preclinical investigation where the data from these studies are of particular relevance.

Integrated Metabonomic Analysis of the Multiorgan Effects of Hydrazine Toxicity in the Rat

Hydrazine is a model toxin that induces both hepatotoxic and neurotoxic effects in experimental animals. The direct biochemical effects of hydrazine in kidney, liver, and brain tissue were assessed in male Sprague-Dawley rats using magic angle spinning nuclear magnetic resonance (NMR) spectroscopy. A single dose of hydrazine (90 mg/kg) resulted in changes to the biochemical composition of the liver after 24 h including an increase in triglycerides and beta-alanine, together with a decrease in hepatic glycogen, glucose, choline, taurine, and trimethylamine-N-oxide (TMAO). From histopathology measurements of liver tissue, minimal to mild hepatocyte alteration was observed in all animals at 24 h. The NMR spectra of the renal cortex at 24 h after dosing were dominated by a marked increase in the tissue concentration of 2-aminoadipate (2-AA) and beta-alanine, concomitant with depletions in TMAO, myo-inositol, choline, taurine, glutamate, and lysine. No alteration to the NMR spectral profile of the substantia nigra was observed after hydrazine administration, but perturbations to the relative concentrations of creatine, aspartate, myo-inositol, and N-acetyl aspartate were apparent in the hippocampus of hydrazine-treated animals at 24 h postdose. No overt signs of histopathological toxicity were observed in either the kidney or the brain regions examined. Elevated alanine levels were observed in all tissues indicative of a general inhibition of alanine transaminase activity. By 168 h postdose, NMR spectral profiles of treated rats appeared similar to those of matched controls for all tissue types indicative of recovery from toxic insult.

Automatic alignment of individual peaks in large high-resolution spectral data sets

Pattern recognition techniques are effective tools for reducing the information contained in large spectral data sets to a much smaller number of significant features which can then be used to make interpretations about the chemical or biochemical system under study. Often the effectiveness of such approaches is impeded by experimental and instrument induced variations in the position, phase, and line width of the spectral peaks. Although characterizing the cause and magnitude of these fluctuations could be important in its own right (pH-induced NMR chemical shift changes, for example) in general they obscure the process of pattern discovery. One major area of application is the use of large databases of (1)H NMR spectra of biofluids such as urine for investigating perturbations in metabolic profiles caused by drugs or disease, a process now termed metabonomics. Frequency shifts of individual peaks are the dominant source of such unwanted variations in this type of data. In this paper, an automatic procedure for aligning the individual peaks in the data set is described and evaluated. The proposed method will be vital for the efficient and automatic analysis of large metabonomic data sets and should also be applicable to other types of data.

Use of Metabonomics to Identify Impaired Fatty Acid Metabolism as the Mechanism of a Drug-Induced Toxicity

An increased diversity of therapeutic targets in the pharmaceutical industry in recent years has led to a greater diversity of toxicological effects. This, and the increased pace of drug discovery, leads to a need for new technologies for the rapid elucidation of toxicological mechanisms. As part of an evaluation of the utility of metabonomics in drug safety assessment, 1H NMR spectra were acquired on urine and liver tissue samples obtained from rats administered vehicle or a development compound (MrkA) previously shown to induce hepatotoxicity in several animal species. Multivariate statistical analysis of the urinary NMR data clearly discriminated drug-treated from control animals, due to a depletion in tricarboxylic acid cycle intermediates, and the appearance of medium chain dicarboxylic acids. High-resolution magic angle spinning NMR data acquired on liver samples exhibited elevated triglyceride levels that were correlated with changes in the urinary NMR data. Urinary dicarboxylic aciduria is associated with defective metabolism of fatty acids; subsequent in vitro experiments confirmed that MrkA impairs fatty acid metabolism. The successful application of metabonomics to characterize an otherwise ill-defined mechanism of drug-induced toxicity supports the practicality of this approach for resolving toxicity issues for drugs in discovery and development.

Metabolic profiling of rodent biological fluids via 1H NMR spectroscopy using a 1 mm microlitre probe

The application of a 1 mm TXI (1H/13C/15N) microlitre NMR probe with z-gradient for metabolic profiling of biofluids is described. The probe was used to provide spectral profiles for rat blood plasma using only approximately 2 microl of fluid with a range of solvent suppression techniques. Using a similar amount of fluid, spectra were obtained from rat and mouse cerebrospinal fluid, demonstrating that the probe could be used to profile rodents metabolically via biofluids previously inaccessible to NMR analysis without the need for termination.

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.

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.

Directly-coupled HPLC-NMR spectroscopic studies of metabolism and futile deacetylation of phenacetin in the rat

The metabolism and futile deacetylation of phenacetin has been investigated in the rat via 1H NMR spectroscopic analysis of urine. Animals were dosed with either phenacetin or phenacetin-C2H3 and urine samples were collected for -24-0 (pre-dosing), 0-8. 8-24, and 24-48 h post-dosing. Drug metabolites of the two compounds were concentrated from the urine using solid-phase extraction prior to the use of directly-coupled HPLC-1H NMR spectroscopy for separation and identification. Following dosing of phenacetin, the metabolites identified were paracetamol glucuronide, paracetamol and N-hydroxyparacetamol, whilst paracetamol and N-hydroxyparacetamol sulphate were identified following dosing of phenacetin-C2H3. Quantitatively the percentage futile deacetylation of phenacetin-C2H3 metabolites was found to be 32% in both paracetamol and N-hydroxyparacetamol sulphate. This study further indicated the importance of futile deacetylation in simple analgesics and the value of directly-coupled HPLC-NMR spectroscopy for the study of this process.

Development of a model for classification of toxin-induced lesions using 1H NMR spectroscopy of urine combined with pattern recognition

Pattern recognition approaches were developed and applied to the classification of 600 MHz 1H NMR spectra of urine from rats dosed with compounds that induced organ-specific damage in either the liver or kidney. Male rats were separated into groups (n = 5) and each treated with one of the following compounds; adriamycin, allyl alcohol, 2-bromoethanamine hydrobromide, hexachlorobutadiene, hydrazine, lead acetate, mercury II chloride, puromycin aminonucleoside, sodium chromate, thioacetamide, 1,1,2-trichloro-3,3,3-trifluoro-1-propene or dose vehicle. Urine samples were collected over a 7 day time-course and analysed using 600 MHz 1H NMR spectroscopy. Each NMR spectrum was data-reduced to provide 256 intensity-related descriptors of the spectra. Data corresponding to the periods 8-24 h, 24-32 h and 32-56 h post-dose were first analysed using principal components analysis (PCA). In addition, samples obtained 120-144 h following the administration of adriamycin and puromycin were included in the analysis in order to compensate for the late onset of glomerular toxicity. Having established that toxin-related clustering behaviour could be detected in the first three principal components (PCs), three-quarters of the data were used to construct a soft independent modelling of class analogy (SIMCA) model. The remainder of the data were used as a test set of the model. Only three out of 61 samples in the test set were misclassified. Finally as a further test of the model, data from the 1H NMR spectra of urine from rats that had been treated with uranyl nitrate were used. Successful prediction of the toxicity type of the compound was achieved based on NMR urinalysis data confirming the robust nature of the derived model.

Nuclear magnetic resonance spectroscopic and principal components analysis investigations into biochemical effects of three model hepatotoxins

1H NMR spectroscopy of urine combined with pattern recognition (PR) methods of data analysis has been used to investigate the time-related biochemical changes induced in Sprague-Dawley rats by three model hepatotoxins: alpha-naphthyl isothiocyanate (ANIT), d-(+)-galactosamine (GalN), and butylated hydroxytoluene (BHT). The development of hepatic lesions was monitored by conventional plasma analysis and liver histopathology. Urine was collected continuously postdosing up to 144 h and analyzed by 600-MHz 1H NMR spectroscopy. NMR spectra of the urine samples showed a number of time-dependent perturbations of endogenous metabolite levels that were characteristic for each hepatotoxin. Biochemical changes common to all three hepatotoxins included a reduction in the urinary excretion of citrate and 2-oxoglutarate and an increased excretion of taurine and creatine. Increased urinary excretion of betaine, urocanic acid, tyrosine, threonine, and glutamate was characteristic of GalN toxicity. Both GalN and ANIT caused increased urinary excretion of bile acids, while glycosuria was evident in BHT- and ANIT-treated rats. Data reduction of the NMR spectra into 256 integrated regions was used to further analyze the data. Mean values of each integrated region were analyzed by principal components analysis (PCA). Each toxin gave a unique time-related metabolic trajectory that could be visualized in two-dimensional PCA maps and in which the maximum distance from the control point corresponded to the time of greatest cellular injury (confirmed by conventional toxicological tests). Thereafter, the metabolic trajectories changed direction and moved back toward the control region of the PR map during the postdose recovery phase. The combination of urinary metabolites which were significantly altered at various time points allowed for differentiation between biliary and parenchymal injury. This NMR-PR approach to the noninvasive detection of liver lesions will be of value in furthering the understanding of hepatotoxic mechanisms and assisting in the discovery of novel biomarkers of hepatotoxicity.

NMR spectroscopic studies on the metabolism and futile deacetylation of phenacetin in the rat

1. 1H-NMR spectroscopy of urine was used to determine the % deacetylation and re-acetylation of 2H-labelled (in the acetyl) phenacetin metabolites in the rat. 2. Male Sprague-Dawley rats were each dosed with either phenacetin or phenacetin-C2H3 at 50 mg kg-1. The total urinary recoveries for phenacetin and phenacetin-C2H3 were 47.6 +/- 16.7 and 50.1 +/- 16.2% respectively (not significantly different, p > 0.05). Paracetamol sulphate and glucuronide are the major urinary metabolites of both protio and deuteriophenacetin. 3. The futile deacetylation given by the urinary recovery of protio-acetyl metabolites of phenacetin-C2H3 was 29.6 +/- 0.9% for paracetamol sulphate and 36.6 +/- 3.1% for paracetamol glucuronide. These observations demonstrate a high level of futile deacetylation in the paracetamol conjugates formed by metabolism of phenacetin-C2H3 and this may indicate a high metabolic flux through the nephrotoxic intermediate 4-aminophenol. 4. The level of futile deacetylation for phenacetin was significantly higher than that found previously in studies of labelled paracetamol in rat or man, and may be important in understanding the higher nephrotoxicity of phenacetin as compared with paracetamol.

Direct observation of resolved intracellular and extracellular water signals in intact human red blood cells using 1H MAS NMR spectroscopy

High resolution 400 MHz 1H NMR spectra of red blood cell suspensions when measured using magic angle spinning (MAS) show two water resonances separated by 15 Hz. Based on addition of a paramagnetic Mn-EDTA complex, measurement of relaxation times and variation of extracellular H2O/D2O ratios, these have been assigned as intracellular (linewidth 17.5 Hz) and extracellular water (linewidth 4.6 Hz). This is the first direct observation of intracellular water using NMR spectroscopy and the 1H MAS NMR spectroscopic approach offers the possibility of studying directly the compartmentation of substances in cells and kinetics of molecular transport.

NMR and HPLC-NMR spectroscopic studies of futile deacetylation in paracetamol metabolites in rat and man

HPLC-NMR spectroscopy has been used to investigate the level of deacetylation followed by reacetylation (futile deacetylation) of metabolites of paracetamol detected in human and rat urine. This has been achieved through the synthesis and administration of paracetamol isotopically labeled at the acetyl group with C2H3, 13CH3 and 13CO-13CH3. Using paracetamol-C2H3 it had been shown that in the rat the sulphate metabolite present in the urine shows 10-13% futile deacetylation depending on the dose, whereas for paracetamol-13CO-13CH3 the corresponding value was about 8%. After solid phase extraction, it was also possible to determine the level of futile deacetylation in the glucuronide metabolite using directly-coupled HPLC-NMR. This approach was facilitated by the use of acetonitrile-d3 as an HPLC eluent and the HPLC-NMR analyses showed that the level of futile deacetylation in the sulphate and glucuronide metabolites were equal at about 9%. The glucuronide of paracetamol-C2H3 was the predominant metabolite in man and following separation using HPLC-NMR, the level of futile deacetylation was shown to be 1% for the glucuronide and 2% for the sulphate, these values being equal within experimental error. This work demonstrates the utility of NMR and HPLC-NMR spectroscopy for isotope exchange studies.

NMR spectroscopic and theoretical chemistry studies on the internal acyl migration reactions of the 1-O-acyl-beta-D-glucopyranuronate conjugates of 2-, 3-, and 4-(trifluoromethyl) benzoic acids

High resolution 19F NMR spectroscopy has been used to investigate the kinetics of internal acyl migration and hydrolysis of the synthetic beta -1-O-acyl-D-glucopyranuronates of 2-, 3-, and 4-(trifluoromethyl) benzoic acids (TFMBAs) in phosphate buffer solutions at 30 degrees C as models of drug ester glucuronides. Apparent first-order degradation of the 1-O-acyl glucuronide and the sequential appearance of 2-, 3-, and 4-O-acyl isomers as both alpha- and beta-anomeric forms were observed for each TFMBA isomer. The overall degradation rate constants of the 2-, 3-, and 4-TFMBA 1-O-acyl isomers were 0.065 h-1, 0.25 h-1, and 0.52 h-1. In order to probe the reasons for these differences in reactivity, theoretical structural and electronic parameters for the beta-anomers of the 1-O-acyl glucuronides, their beta-2-O-acyl isomers, and both structures of the postulated ortho-acid ester intermediate were computed using semiempirical molecular orbital (AM1 and PM3) methods. The distinction between the slowly reacting 2-TFMBA glucuronide and the much faster reacting 3- and 4-TFMBA glucuronides could be observed by calculation of the relative bond order of the C-O bonds in the ortho-acid ester intermediates. The slow internal acyl migration rate of the 2-TFMBA isomer was also partly attributed to the high degree of steric hindrance of the trifluoromethyl group obstructing attack by the glucuronic acid 2-hydroxy group on the carbonyl carbon to form the ortho-acid ester intermediate. Some calculated molecular orbital properties, namely, dipole moment, energy of the lowest unoccupied molecular orbital (LUMO), LUMO density, and nucleophilic frontier density on the carbonyl carbon, were also shown to be related to the measured half-lives. This work gives insight into the molecular physicochemical properties that influence the acyl migration kinetics of simple model drug glucuronides and is of potential importance in understanding more complex drug glucuronide acyl migration reactions of toxicological interest.

Development of a simple liquid chromatographic method for the separation of mixtures of positional isomers and anomers of synthetic 2-, 3- and 4-fluorobenzoic acid glucuronides formed via acyl migration reactions

Many drugs containing carboxylate groups form beta-1-O-acyl glucuronides as their major phase II metabolites in vivo. These ester glucuronides are potentially reactive due to the susceptibility of the acyl group to nucleophilic reactions resulting in hydrolysis, acyl migration or covalent adduct formation. In the present study, a number of synthetic fluorobenzoic acid glucuronide conjugates were chosen as models for chromatographic studies. A high-performance liquid chromatography method is presented for the simultaneous determination of the 1-, 2-, 3- and 4-positional isomers of the acyl glucuronides, and their alpha- and beta-anomers for the 2-, 3- and 4-fluorobenzoic acids as well as each aglycone formed as a result of hydrolysis. The same elution order was found for the acyl migrated glucuronide isomers of the three fluorobenzoic acids in their equilibrium mixtures. The alpha-4-O-acyl isomer eluted first followed by the beta-4-O-acyl isomer, then the beta-1-O-acyl, the beta-3-O-acyl, the alpha-3-O-acyl, the alpha-2-O-acyl and finally the beta-2-O-acyl isomer eluted. The method was used to determine the overall degradation rates, the acyl migration rates and the hydrolysis rates of 1-O-(2-fluorobenzoyl)-beta-D-glucopyranuronic acid 1-O-(3-fluorobenzoyl)-beta-D-glucopyranuronic acid and 1-O-(4-flurobenzoyl)-beta-D-glucopyranuronic acid in a buffer system pH 7.4 at 25 degrees C. It was found that the order of beta-1-glucuronide acyl migration rates was 2-fluorobenzoyl > 3-fluorobenzoyl > 4-fluorobenzoyl. Both the acyl migration rates and the elution order were interpreted in terms of electronic effect of the fluorine substituent on the carbonyl carbon.

Assignment of the 750 MHz 1H NMR resonances from a mixture of transacylated ester glucuronic acid conjugates with the aid of oversampling and digital filtering during acquisition

Many drugs containing carboxylic acid functional groups are metabolised in vivo to ester glucuronides (1-O-acyl-beta-D-glucopyranuronates) and, of these, a number show a propensity to undergo internal isomerisation via a transacylation process, causing the carboxylic acid moiety to migrate successively to the 2-, 3- and 4-positions of the glucuronic acid. These products may be responsible, through reactions with plasma proteins, for some of the allergenic side effects in a number of non-steroidal anti-inflammatory drugs. It is important to understand those properties of the drug molecules which facilitate this reaction, and to this end we have studied the transacylation product formation and reaction kinetics in a series of aryl carboxylic acid glucuronides using NMR spectroscopy. However, the resulting 1H NMR spectra are very complex with much resonance overlap, and recourse to spectral simplification processes is necessary. Here, improvement in spectral resolution by oversampling and digital filtering to restrict the detection range of the spectrometer, thus yielding improved digital resolution, is demonstrated. The approach has been applied to the assignment of a mixture of transacylated ester glucuronides of 2-trifluoromethylbenzoic acid through the use of a two-dimensional 1H-1H TOCSY experiment.

High resolution NMR spectroscopic studies on the metabolism and futile deacetylation of 4-hydroxyacetanilide (paracetamol) in the rat

Paracetamol (4-hydroxyacetanilide, acetaminophen) was synthesized with the acetyl group labelled with C2H3 (paracetamol-C2H3), and dosed to rats i.p. at 25 mg/kg (N = 5) and 40 mg/kg (N = 3) body weight. Paracetamol, with a 13CH3 in the acetyl group (paracetamol-13CH3) was also synthesized and dosed to rats i.p. at 40 mg/kg (N = 3). The metabolism and excretion of the 2H-labelled compound was followed in the rat using 600 MHz 1H and 92.1 MHz 2H NMR spectroscopy of urine collected 0-8, 8-24, 24-32 and 32-48 hr post-dosing. The metabolism of paracetamol-13CH3 was also monitored using 600 MHz 1H NMR spectroscopy of urine collected 0-8, 8-24 and 24-48 hr post-dosing. For paracetamol-C2H3 the total recovery of the sulphate, glucuronide and N-acetyl cysteinyl metabolites via the urine accounted for 61.2 +/- 14.1% of the 25 mg/kg dose and 61.4 +/- 8.8% of the 40 mg/kg dose. For paracetamol-13CH3 the recovery was 102.7 +/- 3.7% indicating that the low % urinary recovery with the C2H3-labelled drug is the result of isotope effects on the disposition of paracetamol. In the case of the paracetamol-C2H3, quantitative 1H NMR analysis of urine showed that 13.3 +/- 0.5 and 10.0 +/- 1.2 mole % (25 and 40 mg/kg, respectively) of the urinary paracetamol sulphate recovered following dosing of the deuterium labelled drug had the C2H3 acetyl groups replaced by C1H3 acetyl groups from endogenous sources. In the case of the paracetamol-13CH3 8.9 +/- 0.7 mole % of the sulphate conjugate had also been transacetylated to paracetamol-12CH3. There was no significant difference between the level of futile deacetylation observed for the deuterated and 13C-labelled drug. Overall these data indicate a high level of deacetylation followed by reacetylation (i.e. futile deacetylation) prior to excretion of paracetamol via the nephrotoxic intermediate 4-aminophenol. The level of deacetylation is much higher than has previously been thought which may cast new light on the role of 4-aminophenol in the development of paracetamol induced nephrotoxicity.

High-field deuterium nuclear magnetic resonance spectroscopic monitoring of the pharmacokinetics of selectively deuterated benzoic acid in man

The stable isotope tracer technique using 13C labeling of substrates followed by NMR spectroscopy of biofluids has been widely used in metabolic investigations, whereas the use of 2H labeling and 2H NMR spectroscopy has been extremely limited. The applicability of the high-field 2H NMR spectroscopy (14.1 T, 92 MHz 2H frequency) in a simple pharmacokinetic problem has now been investigated using selectively deuterated benzoic acid (BA) as a model. [7-13C,2,6-2H2]BA was synthesized for use as a tracer to compare the efficiency and sensitivity of 2H and 13C labeling. The urinary excretion of [7-13C,2,6-2H2]hippuric acid (HA) formed from orally administered [7-13C,2,6-2H2]BA (250 mg) was followed by 92-MHz 2H and 150-MHz 13C NMR spectroscopy (only 10 min accumulation time) following concentration of urine by a factor of 10, using a standard for quantitation. The heights of resonances for 13C7 and 2H2,6 were used to calculate the [7-13C,2,6-2H2]HA concentration. The lower limit of detection using this 2H NMR approach was approximately 60 nmol/ml and was found to be comparable with that of the 13C NMR approach where the quaternary carbon (C7) was labeled. The administered [7-13C,2,6-2H2]BA was found to be quantitatively biotransformed to HA and excreted in urine within 4 h by both NMR approaches. The 2H NMR approach using a high-field NMR spectrometer is potentially useful and practical for pharmacokinetic research on small molecules whose 2H resonances are relatively sharp since the procedures are very simple and convenient.