Combined use of 1H-NMR and GC-MS for metabolite monitoring and in vivo 1H-NMR assignments

Thirty-three metabolites were observed in perchloric acid extracts of four different tissues by in vitro 1H-NMR, GC-MS and alcohol dehydrogenase assay, and the information was used to interpret an in vivo two-dimensional nuclear Overhauser effect 1H-NMR spectrum. The metabolite profiles of the different tissues indicate a number of potential tissue-specific markers: N-acetylaspartate and gamma-aminobutyric acid for rat brain, glutamine/glutamic acid ratio for dog heart, arginine and sucrose for carrot, and t-aconitate, sucrose, asparagine/aspartic acid concentration ratios for corn roots. gamma-Aminobutyric acid and malate can be regarded as metabolic indicators for stressed corn roots. Concentrations of threonine and valine in corn roots were constant under hypoxic and salt stress, and can serve as internal standards for both in vivo and in vitro NMR studies. The in vitro information was further used to identify 12 compounds from the in vivo 1H-NMR spectra (including the two-dimensional nuclear Overhauser effect spectrum) of a carrot cylinder by correlating the chemical shift and nuclear Overhauser effect information. Thus, our choice of methods with a capability for structural determination allows the characterization of complex tissue extracts with minimum sample preparation, and supports, as well as complements, in vivo 1H-NMR investigations of metabolism.     

Determination of flux through different metabolite pathways in Saccharomyces cerevisiae by 1H-NMR and 13C-NMR spectroscopy.

We propose an experimental approach combining 1H-NMR and 13C-NMR spectroscopy to investigate metabolite flux in cells under physiological conditions and present a mathematical model giving the relationships between the following different parameters. 13C fractional enrichment, fluxes in competing pathways, metabolite concentration and experimental time. This model has been used for determining the absolute and/or relative values of five fluxes involving pyruvate, ethanol, acetyl-CoA and glutamate via the Krebs cycle in glucose-grown repressed Saccharomyces cerevisiae cells fed with [1-13C]glucose and/or unlabeled ethanol. The glucose consumption and the production of various compounds such as ethanol, glycerol, trehalose etc. were studied qualitatively and/or quantitatively as a function of time. The 13C fractional enrichment of [2-13C]ethanol was determined by observing the proton resonance of the methyl group. Addition of 25 mM unlabeled ethanol shows no significant effect on the glucose consumption or the production of any metabolites. However unlabeled ethanol exerts a strong influence on the enrichment of glutamate C4, but only induces an insignificant change on glutamate C2 and C3. Apart from the fact that ethanol is a potential precursor of acetyl-CoA as expected, these results indicate that (a) the probability for citrate and 2-oxoglutarate to make one turn or more in the Krebs cycle is negligible and (b) the scrambling between C4 and C3 via the glyoxylate shunt is virtually absent. The flux of ethanol formation from pyruvate is about three-times and nine-times greater than that of ethanol consumption and acetyl-CoA formation, respectively, from pyruvate via pyruvate dehydrogenase. Without addition of unlabeled ethanol, the ratio of the integrated resonance of glutamate (C2 + C3)/C4 reflecting the activity of pyruvate carboxylase relative to that of citrate synthase, is about 1.1. By comparing the absolute values of the different fluxes, it was found that 88% of the glucose was used to synthetize ethanol but the observed concentration of ethanol in the supernatant represents only 58% of the glucose consumption. The validity of the present model was supported by the data obtained from similar experiments using unlabeled ethanol and non-NMR techniques.     

Characterization of lipid composition in stimulated human lymphocytes by 1H-NMR

Recent in vivo NMR studies have raised interest in the structural changes of cellular lipids during proliferative activity. We investigated the changes in plasma membrane lipid and total cell lipid during mitogenically-stimulated proliferation of human peripheral blood lymphocytes by extraction of lipids and assay by 500 MHz 1H-NMR. Resonances were assigned using one- and two-dimensional spectroscopic techniques, and signals unique to certain species of lipid were identified. Choline and ethanolamine-containing lipids, glycerophospholipid backbones, sphingolipids, cholesterol, plasmalogens and triacylglycerols were readily detected. Resolution of a number of lipid species was not possible, despite the use of high-resolution techniques. NMR values for proliferation-induced changes in the most easily determined parameters, namely the total cholesterol to total phospholipid molar ratio, and phosphatidylcholine, phosphatidylethanolamine and sphingolipid composition, were found to agree with traditional methods. Differences in phospholipid and fatty acid profiles were found between plasma membranes and total cell lipid for resting values and for response to mitogen.     

1H-NMR metabolite profiles of different strains of Plasmodium falciparum

Although efforts to understand the basis for inter-strain phenotypic variation in the most virulent malaria species, Plasmodium falciparum, have benefited from advances in genomic technologies, there have to date been few metabolomic studies of this parasite. Using ¹H-NMR spectroscopy, we have compared the metabolite profiles of red blood cells infected with different P. falciparum strains. These included both chloroquine-sensitive and chloroquine-resistant strains, as well as transfectant lines engineered to express different isoforms of the chloroquine-resistance-conferring pfcrt (P. falciparum chloroquine resistance transporter). Our analyses revealed strain-specific differences in a range of metabolites. There was marked variation in the levels of the membrane precursors choline and phosphocholine, with some strains having >30-fold higher choline levels and >5-fold higher phosphocholine levels than others. Chloroquine-resistant strains showed elevated levels of a number of amino acids relative to chloroquine-sensitive strains, including an approximately 2-fold increase in aspartate levels. The elevation in amino acid levels was attributable to mutations in pfcrt. Pfcrt-linked differences in amino acid abundance were confirmed using alternate extraction and detection (HPLC) methods. Mutations acquired to withstand chloroquine exposure therefore give rise to significant biochemical alterations in the parasite.     

1H-NMR studies of lipid extracts of rat liver mitochondria

Lipid extracts of rat liver mitochondria were studied by 1H-NMR at 200 MHz. Each spectrum, obtained in 6 min with routine acquisition parameters, allowed the estimation of the phosphatidylcholine/phosphatidylethanolamine ratio, the cholesterol/total lipid molar ratio, the average fatty acid length, the unsaturation ratio and the oxidation state of the ubiquinone/ubiquinol couple. 1H-NMR spectroscopy was also used to analyze structural changes of the lipids following peroxidation. In model liposomes subjected to enzymatic peroxidation the appearance of hydroperoxides and conjugated double bonds were detected, whereas in mitochondria no such changes were seen even after a period of relatively high oxidative stress. This suggests that the systems for protection against oxidative damage in mitochondria are able to keep the amount of peroxidation products below the detection limit of the technique.     

1H NMR metabolite fingerprinting and metabolomic analysis of perchloric acid extracts from plant tissues

Metabolite fingerprinting provides a powerful method for discriminating between biological samples on the basis of differences in metabolism caused by such factors as growth conditions, developmental stage or genotype. This protocol describes a technique for acquiring metabolite fingerprints from samples of plant origin. The preferred method involves freezing the tissue rapidly to stop metabolism, extracting soluble metabolites using perchloric acid (HClO4) and then obtaining a fingerprint of the metabolic composition of the sample using 1D 1H NMR spectroscopy. The spectral fingerprints of multiple samples may be analyzed using either unsupervised or supervised multivariate statistical methods, and these approaches are illustrated with data obtained from the developing seeds of two genotypes of sunflower (Helianthus annuus). Preparation of plant extracts for analysis takes 2-3 d, but multiple samples can be processed in parallel and subsequent acquisition of NMR spectra takes approximately 30 min per sample, allowing 24-48 samples to be analyzed in a week.     

Induction of apoptosis in proliferating lymphocytes by tricyclic antidepressants

We have previously found that tricyclic antidepressants (TCAs) induce apoptosis in quiescent human lymphocytes. The aim of the present study was to evaluate if TCAs induce apoptosis in proliferating human lymphocytes and in established blastoid lymphocytes also. The development of conA-induced lymphoblast populations was followed by measuring the CD25 membrane expression. Three TCA compounds were run with the following concentrations: imipramine (10, 20, 30, 40, 60 M), clomipramine (1, 10, 20, 30, 40 M) and citalopram (40, 60, 80, 100, 180 M). They all induced a dose-dependent apoptosis both in continuously transformed, as well as in established lymphoblasts. Preincubation of the TCA up to 48 h did not significantly increase induction of apoptosis. The three drugs tested were found to be potent inducers of apoptosis in proliferating lymphocytes. Furthermore, we found that the apoptotic populations in proliferating and in established blastoid lymphocytes were of f airly the same magnitude than in the corresponding population in TCA-incubated resting lymphocytes. In conclusion, we demonstrate that TCAs induce apoptosis in proliferating lymphocytes, as they do in quiescent lymphocytes. Furthermore, the exent of apoptosis was even more pronounced in TCA-incubated lymphoblasts compared to TCA-treated resting lymphocytes.     

1H-NMR spectroscopy of the cell membranes of thymus lymphocytes in AKR mice

360 MHz 1H NMR was used to monitor the changes of AKR mice thymus lymphocytes in cases of spontaneous and transplantable leukemia and vincristine administration. A comparison of relative signal intensities of methyl and methylene fatty acid chains protons and phosphatidylcholine headgroups protons enables to monitor leukemia development and vincristine effect. Spin-lattice relaxation curves of the same protons of leukemic thymi lymphocytes are well fitted by biexponential functions, bringing evidence for two regions with different lipid mobility.     

Stereospecific synthesis and two-dimensional 1H-NMR investigation of isoursocholic acid.

This report describes the chemical synthesis of isoursocholic acid (3 beta, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) from its corresponding 3 alpha-analog. The method consists of refluxing a mixture of ursocholic acid, triphenylphosphine, and diethyl azodicarboxylate in benzene solution with an acid such as formic acid. The sterically pure ester (3 beta-formate) so formed after saponification with LiOH-aqueous methanol then allowed an easy access to the epimer of the starting acid. Large scale preparative separation and purification of the final product and synthetic intermediates were accomplished by flash column chromatography of their methyl ester derivatives. Structural assignment of the isourscholic acid molecule was confirmed by complete analysis of proton NMR spectra using 2-D NMR correlation experiments which rigorously established the (3 beta/3 alpha) and (7 beta/7 alpha) hydroxyl configurations in the isoursocholic and ursocholic acids. It is suggested that the isoursocholic acid will be useful as a reference compound and as a substrate in studies dealing with the hepatic inversion of the 3 beta-hydroxy group.     

Demonstration of a very short post-mitotic G1 period in proliferating PHA-stimulated lymphocytes

Evidence indicating a very short duration of the post-mitotic G1 phase of PHA-stimulated lymphocytes was obtained in experiments where proliferating lymphocytes were pulsed for 1 h with ³H-TdR and then, following different periods of incubation in ‘cold’ medium, again pulsed for 1 h with ¹⁴C-TdR. Cells labelled with ³H-and (³H + ¹⁴C)-TdR were counted in double layer autoradiograms. Cells labelled with ³H-TdR should gradually leave the S phase when incubated in ‘cold’ medium and would consequently not incorporate ¹⁴C-TdR. Thus, the quotient

$\text{\%(}{}^3\text{H}\text{+}{}^{14}\text{C}\text{)}\text{cells}\text{\%}{}^3\text{H}\text{+ \%(}{}^3\text{H}\text{+}{}^{14}\text{C}\text{)}\text{cells}$

should decrease with time in ‘cold’ medium and should be zero after an incubation time corresponding to the length of the S phase. If, however, the sum of the G2 + M + G1 phases is shorter than the length of the S phase, the zero value will not be obtained. This was actually the case, and the quotients obtained agreed well with those that could be calculated on basis of the G1 period being 0 h, whereas they did not agree with those calculated on basis of G1 being 4–6 h.     

1H-NMR studies on nucleotide binding to the catalytic sites of bovine mitochondrial F1-ATPase

The conformation of adenine nucleotides bound to bovine mitochondrial F1-ATPase was investigated using transfer nuclear Overhauser enhancement measurements. It is shown that all nucleotides investigated adopt a predominantly anti conformation when bound to the catalytic sites. Furthermore, the experiment suggests that 8-azido-ADP and 8-azido-ATP, which are predominantly in the syn conformation in solution, are in the anti conformation when bound to F1 catalytic sites.     

Probing perturbation of bovine lung surfactant extracts by albumin using DSC and 2H-NMR

Lung surfactant (LS), a lipid-protein mixture, forms films at the lung air-water interface and prevents alveolar collapse at end expiration. In lung disease and injury, the surface activity of LS is inhibited by leakage of serum proteins such as albumin into the alveolar hypophase. Multilamellar vesicular dispersions of a clinically used replacement, bovine lipid extract surfactant (BLES), to which (2% by weight) chain-perdeuterated dipalmitoylphosphatidycholine (DPPG mixtures-d(62)) had been added, were studied using deuterium-NMR spectroscopy ((2)H-NMR) and differential scanning calorimetry (DSC). DSC scans of BLES showed a broad gel to liquid-crystalline phase transition between 10-35 degrees C, with a temperature of maximum heat flow (T(max)) around 27 degrees C. Incorporation of the DPPC-d(62) into BLES-reconstituted vesicles did not alter the T(max) or the transition range as observed by DSC or the hydrocarbon stretching modes of the lipids observed using infrared spectroscopy. Transition enthalpy change and (2)H-NMR order parameter profiles were not significantly altered by addition of calcium and cholesterol to BLES. (2)H-NMR spectra of the DPPC-d(62) probes in these samples were characteristic of a single average lipid environment at all temperatures. This suggested either continuous ordering of the bilayer through the transition during cooling or averaging of the DPPC-d(62) environment by rapid diffusion between small domains on a short timescale relative to that characteristic of the (2)H-NMR experiment. Addition of 10% by weight of soluble bovine serum albumin (1:0.1, BLES/albumin, dry wt/wt) broadened the transition slightly and resulted in the superposition of (2)H-NMR spectral features characteristic of coexisting fluid and ordered phases. This suggests the persistence of phase-separated domains throughout the transition regime (5-35 degrees C) of BLES with albumin. The study suggests albumin can cause segregation of protein bound-lipid domains in surfactant at NMR timescales (10(-5) s). Persistent phase separation at physiological temperature may provide for a basis for loss of surface activity of surfactant in dysfunction and disease.     

Quantitative determination of cyclic diguanosine monophosphate concentrations in nucleotide extracts of bacteria by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry

The physiological response to small molecules (secondary messengers) is the outcome of a delicate equilibrium between biosynthesis and degradation of the signal. Cyclic diguanosine monophosphate (c-di-GMP) is a novel secondary messenger present in many bacteria. It has a complex cellular metabolism whereby usually more than one enzyme synthesizing and degrading c-di-GMP is encoded by a bacterial genome. To assess the in vivo conditions of c-di-GMP signaling, we developed a high-performance liquid chromatography (HPLC)-mass spectrometry-based method to detect c-di-GMP with high sensitivity and to quantify the c-di-GMP concentration in the bacterial cell as described here in detail. We successfully used the methodology to determine and compare the c-di-GMP concentrations in bacterial species such as Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa, and Vibrio cholerae. We describe the use of the methodology to assess the change in c-di-GMP concentration during the growth phase and the contribution of a point mutation in S. typhimurium to the overall cellular c-di-GMP concentration.     

Pharmacokinetic assessment of teratologically effective concentrations of an endogenous retinoic acid metabolite

Retinoic acid is a natural vitamin A derivative that undergoes oxidative metabolism in the body to yield several metabolites, which apparently represent the products of a detoxification pathway. To assess if such metabolic conversions diminished teratogenic potency, one of the major metabolites (4-oxo-all-trans-retinoic acid) was tested for its teratogenic activity in pregnant ICR mice and further investigated for its pharmacokinetic features to determine if it accumulated in the embryo in concentrations sufficient to elicit a teratogenic response. Administration of single oral doses (10, 25, 50, or 100 mg/kg) of the compound to ICR mice on day 11 of gestation (plug day = day 0) produced dose-dependent frequencies of serious fetal anomalies of the type usually associated with the use of retinoic acid and other retinoids. The metabolite was equivalent in teratogenic potency to retinoic acid, and, in the instance of cleft palate frequency, it was even more active. Concentrations of 4-oxo-all-trans-retinoic acid and its 13-cis isomer were measured in the maternal plasma and whole embryos at 30 min to 10 hr after administration of the lowest (10 mg/kg) and the highest (100 mg/kg) teratogenic dose of 4-oxo-all-trans-retinoic acid by means of high-performance liquid chromatography methodology. Distribution of the compound in the maternal system and transfer to the embryo occurred rapidly with either dose. Peak concentration in the maternal plasma and the embryo persisted for 3-4 hr after the higher dose but not with the lower dose; however, elimination kinetics for the two dose levels were similar.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determination of mycophenolic acid and its phenol glucuronide metabolite in human plasma and urine by high-performance liquid chromatography

Simultaneous determination of mycophenolic acid (MPA) and mycophenolate phenol glucuronide (MPAG) in plasma and urine was accomplished by isocratic HPLC with UV detection. Plasma was simply deproteinated with acetonitrile and concentrated, whereas urine was diluted prior to analysis. Linearity was observed from 0.2 to 50 μg/ml for both MPA and MPAG in plasma and from 1 to 50 μg/ml of MPA and 5 to 2000 μg/ml MPAG in urine with extraction recovery from plasma greater than 70%. Detection limits using 0.25 ml plasma were 0.080 and 0.20 μg/ml for MPA and MPAG, respectively. The method is more rapid and simple than previous assays for MPA and MPAG in biological fluids from patients.     

Effect of ergotamine on plasma metabolite and insulin-like growth factor-1 concentrations in cows

Bovine plasma was assayed to determine if ergotamine affected plasma metabolite and insulin-like growth factor-1 (IGF-1) concentrations. In Experiment 1, four cows received a single bolus intravenous injection of ergotamine tartrate (19 microg/kg body wt.) or saline vehicle in a crossover design 2 days after prostaglandin-induced luteolysis. Treatmentxtime affected plasma glucose, triglyceride, total cholesterol and IGF-1 concentrations. Glucose and cholesterol were increased after ergotamine. Triglycerides were elevated within 1 h after ergotamine, but were decreased 3 h after ergotamine treatment. Plasma IGF-1 decreased in response to ergotamine. Blood constituents were unchanged after treatment with saline. In Experiment 2, six cows received a single bolus intravenous injection of ergotamine (20 microg/kg body wt.) or saline vehicle in a crossover design 10 days after receiving norgestomet (6 mg) via subcutaneous ear implant. Treatmentxtime affected glucose, triglycerides, total cholesterol and IGF-1 concentrations. Glucose and cholesterol were increased after ergotamine. Triglycerides were elevated 1 h after ergotamine and decreased 3-7 h after ergotamine. Plasma IGF-1 decreased after ergotamine treatment. Blood constituents were unresponsive to the saline vehicle. Results indicated ergotamine altered plasma metabolite and IGF-1 concentrations in cows.