Determination of monosaccharides and sugar alcohols in tissues from diabetic rats by high-performance liquid chromatography with pulsed amperometric detection

Quantitative determination of free glycerol and myo-inositol from plasma and tissue by high-performance liquid chromatography

A high-performance liquid chromatographic method that accurately measures glycerol and myo-inositol from plasma and tissue is described. The method incorporates a pre-column derivatization reaction using aqueous extracts with benzoyl chloride as a modifying agent. The benzoylated derivatives are isolated by HPLC using reversed-phase gradient chromatography and quantified via absorbance detection at 231 nm. The benzoylated derivatives of glycerol and myo-inositol are well resolved from other known carbohydrates, internal standard and other contaminants encountered within samples and during incubation. The benzoylation of these analytes reach a maximum between 3.5 and 6 h of incubation and are stable for at least 24 days at 4 degrees C. The limit of quantization (LOQ) of glycerol was equal to 2.5 nmol/ml plasma and 6.4 nmol/g tissue and the LOQ of myo-inositol was 1.8 nmol/ml plasma and 3.6 nmol/g tissue. Incubation of known standards and samples with benzoyl chloride at 40 degrees C for 4 h showed fully benzoylated products as determined by mass spectral analysis. Calibration curves were linear between 2.7 and 174 nmol for glycerol and 1.4-89 nmol for myo-inositol. Comparison of tissue and plasma concentrations of glycerol and myo-inositol found using this method are in good agreement with other reported values using other techniques.

Glucose homeostasis across human airway epithelial cell monolayers: role of diffusion, transport and metabolism

Glucose in airway surface liquid (ASL) is maintained at low concentrations compared to blood glucose. Using radiolabelled [(3)H]-D: -glucose and [(14)C]-L: -glucose, detection of D: - and L: -glucose by high-performance liquid chromatography and metabolites by nuclear magnetic resonance, we found that glucose applied to the basolateral side of H441 human airway epithelial cell monolayers at a physiological concentration (5 mM) crossed to the apical side by paracellular diffusion. Transepithelial resistance of the monolayer was inversely correlated with paracellular diffusion. Appearance of glucose in the apical compartment was reduced by uptake of glucose into the cell by basolateral and apical phloretin-sensitive GLUT transporters. Glucose taken up into the cell was metabolised to lactate which was then released, at least in part, across the apical membrane. We suggest that glucose transport through GLUT transporters and its subsequent metabolism in lung epithelial cells help to maintain low glucose concentrations in human ASL which is important for protecting the lung against infection.

Sugar microanalysis by HPLC with benzoylation: Improvement via introduction of a C-8 cartridge and a high efficiency ODS column

An HPLC protocol for sugar microanalysis based on the formation of ultraviolet-absorbing benzoyl chloride derivatives was improved. Here, samples were prepared with a C-8 cartridge and analyzed with a high efficiency ODS column, in which porous spherical silica particles 3 microm in diameter were packed. These devices allowed us to simultaneously quantify multiple sugars and sugar alcohols up to 10 ng/ml and to provide satisfactory separations of some sugars, such as fructose and myo-inositol and sorbitol and mannitol. This protocol, which does not require special apparatuses, should become a powerful tool in sugar research.

Comparing N-glycan processing in mammalian cell lines to native and engineered lepidopteran insect cell lines

In the past decades, a large number of studies in mammalian cells have revealed that processing of glycoproteins is compartmentalized into several subcellular organelles that process N-glycans to generate complex-type oligosaccharides with terminal N -acetlyneuraminic acid. Recent studies also suggested that processing of N-glycans in insect cells appear to follow a similar initial pathway but diverge at subsequent processing steps. N-glycans from insect cell lines are not usually processed to terminally sialylated complex-type structures but are instead modified to paucimannosidic or oligomannose structures. These differences in processing between insect cells and mammalian cells are due to insufficient expression of multiple processing enzymes including glycosyltransferases responsible for generating complex-type structures and metabolic enzymes involved in generating appropriate sugar nucleotides. Recent genomics studies suggest that insects themselves may include many of these complex transferases and metabolic enzymes at certain developmental stages but expression is lost or limited in most lines derived for cell culture. In addition, insect cells include an N -acetylglucosaminidase that removes a terminal N -acetylglucosamine from the N-glycan. The innermost N -acetylglucosamine residue attached to asparagine residue is also modified with alpha(1,3)-linked fucose, a potential allergenic epitope, in some insect cells. In spite of these limitations in N-glycosylation, insect cells have been widely used to express various recombinant proteins with the baculovirus expression vector system, taking advantage of their safety, ease of use, and high productivity. Recently, genetic engineering techniques have been applied successfully to insect cells in order to enable them to produce glycoproteins which include complex-type N-glycans. Modifications to insect N-glycan processing include the expression of missing glycosyltransferases and inclusion of the metabolic enzymes responsible for generating the essential donor sugar nucleotide, CMP- N -acetylneuraminic acid, required for sialylation. Inhibition of N -acetylglucosaminidase has also been applied to alter N-glycan processing in insect cells. This review summarizes current knowledge on N-glycan processing in lepidopteran insect cell lines, and recent progress in glycoengineering lepidopteran insect cells to produce glycoproteins containing complex N-glycans.

HPLC simultaneous determination of glycerol and mannitol in human tissues for forensic analysis

A method for simultaneous determination of glycerol and mannitol in various human tissues was devised and for this we used high-performance liquid chromatography (HPLC). Specimens were homogenized in a mixture of chloroform and methanol, phosphate buffer (pH 7.0) and pentaerythritol (IS) solution. After centrifugation, an aliquot of the aqueous layer was evaporated to dryness and derivatized with p-nitrobenzoyl chloride at 50 degrees C for 1h, then applied to HPLC with analytical conditions of: column, CAPCELL PAK C18 MG (250 mm x 3.0 mm i.d., 5 microm, Shiseido Co. Ltd., Tokyo, Japan); column temperature, 1-2 degrees C; mobile phase, 75% acetonitrile-distilled water containing 0.05% trifluoroacetic acid, 0.05% heptafluoro-n-butyric acid and 0.1% triethylamine; flow rate, 0.5 ml/min; wavelength, 260 nm. Calibration curves for both substances were linear in concentration ranges from 1 to 500 microg/0.1g and correlation coefficients exceeded 0.99. The relative standard deviation (R.S.D.) of the method was evaluated at concentrations of 10 and 100 microg/0.1g, and ranged from 0.84 to 10.6%. Using this method, we determined the regional distribution levels of glycerol and mannitol in various tissues from an autopsied brain dead man.

Quantification of intracellular metabolites in Escherichia coli K12 using liquid chromatographic-electrospray ionization tandem mass spectrometric techniques

The quantitative comprehension of microbial metabolic networks is a prerequisite for an efficient rational strain improvement ("metabolic engineering"). It is therefore necessary to accurately determine the concentration of a large number of reactants (i.e., metabolites, nucleotides, cofactors) in order to understand "in vivo" reaction kinetics. Quantification of intracellular concentrations of glycolytic intermediates and nucleotides in Escherichia coli K12 using a perchloric acid extraction and an LC-ESI-MS method was achieved. Intracellular metabolites (e.g., glucose 6-phosphate, fructose 1,6-bisphosphate, 6-phospho gluconate, acetyl-CoA, adenine nucleotides) were quantified under defined (glucose-limited steady-state) growth conditions. The method was verified by comparing the intracellular metabolite concentrations measured via LC-ESI-MS with enzymatic determinations. It is thus possible to identify and quantify more than 15 intracellular metabolites in parallel with a minimal amount of sample volume.

Sensitive and simple determination of mannitol in human brain tissues by gas chromatography-mass spectrometry

A simple, reliable and sensitive gas chromatographic-mass spectrometric method was devised to determine the level of mannitol in various human brain tissues obtained at autopsy. Mannitol was extracted with 10% trichloroacetic acid solution which effectively precipitated brain tissues. The supernatant was washed with tert.-butyl methyl ether to remove other organic compounds and to neutralize the aqueous solution. Mannitol was then derivatized with 1-butaneboronic acid and subjected to GC-MS. Erythritol was used as an internal standard. For quantitation, selected ion monitoring with m/z 127 and 253 for mannitol and m/z 127 for internal standard were used. Calibration curves were linear in concentration range from 0.2 to 20 microg/0.1 g and correlation coefficients exceeded 0.99. The lower detection limit of mannitol in distilled water was 1 ng/0.1 g. Mannitol was detected in control brain tissues, as a biological compound, at a level of 50 ng/0.1 g. The precision of this method was examined with use of two different concentrations, 2 and 20 microg/0.1 g, and the relative standard deviation ranged from 0.8 to 8.3%. We used this method to determine mannitol in brain tissues from an autopsied individual who had been clinically diagnosed as being brain dead. Cardiac arrest occurred 4 days later.

Effect of aldose reductase inhibitors on glucose-induced changes in sorbitol and myo-inositol metabolism in human neutrophils

AIM

To investigate the influence of glucose and the efficacy of two different aldose reductase (AR) inhibitors, epalrestat and SNK-860, on the polyol pathway and myo-inositol metabolism in human neutrophils.

METHODS

We incubated neutrophils with various concentrations of glucose and AR inhibitors. The neutrophils from healthy volunteers were incubated in the media containing 5-40 mmol/l glucose with or without an AR inhibitor. The sorbitol and myo-inositol contents, and myo-inositol uptake were measured by high performance liquid chromatography and radio isotope technique with 2-[3H]-myo-inositol.

RESULTS

After 2 h incubation, the sorbitol content increased with rising extracellular glucose concentrations, while the myo-inositol content decreased. Both AR inhibitors reduced the sorbitol content in neutrophils exposed to 40 mmol/l glucose medium. A 70% fall in the myo-inositol content in neutrophils exposed to 40mmol/glucose medium was attenuated approximately 40% by the addition of AR inhibitors. myo-Inositol uptake into neutrophils was inhibited by high glucose. AR inhibitors significantly ameliorated the decrease in myo-inositol uptake, but did not completely normalize it.

CONCLUSIONS

Our present in vitro studies showed that the glucose-induced metabolic alterations in human neutrophils were similar to those in tissues prone to diabetic complications, and that AR inhibitors effectively corrected glucose-induced imbalances of the polyol pathway and myo-inositol uptake in neutrophils. In addition, our study suggests that glucose-induced metabolic alterations may result in the neutrophil dysfunction and that an AR inhibitor may be capable ameliorating it.

Improvements to in-line desalting of oligosaccharides separated by high-pH anion exchange chromatography with pulsed amperometric detection

High-pH anion exchange chromatography with pulsed amperometric detection (HPAEC/PAD) (1) is routinely used to separate neutral and charged oligosaccharides differing by branch, linkage, and positional isomerism. Oligosaccharides are eluted in 0.1 M NaOH with gradients of sodium acetate (up to 0.25 M). Analyses of HPAEC/PAD-purified oligosaccharides generally require neutralization and removal of eluent salts. To facilitate the process, we designed and produced a cation-exchange system to remove sodium ions (Na+) from the eluent after oligosaccharide detection [the Carbohydrate Membrane Desalter (CMD), with a volatile regenerant]. Exchange of >99.5% of eluent Na+ for hydronium ions (H3O+) within the CMD generates dilute acetic acid (removable by vacuum evaporation). The exchange process desalts up to 0.35 M Na+ at 1.0 ml/min. Oligosaccharides collected after on-line desalting, evaporated and resuspended in their original volume of deionized water contained < or = 350 muM residual Na+ when the eluting sodium concentration was 300 mM. This represents a desalting efficiency of >99.8%. Recovery of neutral and sialylated oligosaccharides under these conditions ranged from 75 to 100%. With the CMD system and postcollection evaporation, HPAEC/PAD can purify oligosaccharides ready for further characterization. As a proof test, oligosaccharides from a human monoclonal antibody were separated by HPAEC/PAD, desalted with the CMD system, dried, and analyzed by matrix-assisted laser desorption-ionization, time-of-flight mass spectrometry.

Determination of blood sugars by high pressure liquid chromatography with fluorescent detection

In this study, a high pressure liquid chromatography method with fluorescent detector was developed to analyze blood galactose, lactose and glucose simultaneously. Plasma sugars were prepared as fluorescent derivatives to react with FMOC-hydrazine (9-fluorenyl methyl chloroformate). A C18 reversed phase column and a fluorescent detector were used and run in ambient. The resolution index of galactose and glucose derivatives in the analytical method was 1.15. The coefficients of variation of the analysis were less than 7.5%. The concentration of FMOC-hydrazine did not significantly influence the analytical results for determination of the concentration of galactose. However, the ratios of acetonitrile in the mobile phase significantly affected the analysis of the fluorescent derivatives of sugars. The sensitivity of this method for galactose detection was 5 micrograms ml-1, and the required plasma volume for testing was only 25 microliters each. This analytical method was successfully applied to study the pharmacokinetics of galactose in vivo in a rabbit model.

The permselectivity of glomerular basement membrane can be compromised by glycation or by exposure to low levels of hypochlorite

Earlier studies indicated that chemically crosslinking glomerular basement membrane (GBM) rendered it more permeable to water and to macromolecules. Here possible mechanisms for the introduction of crosslinks into GBM under pathological conditions were explored. Glycation with glucose and with fructose over periods of 2 wk (fructose) and 6 weeks (glucose) rendered the GBM more permeable to water and myoglobin as judged from in vitro ultrafiltration behaviour. The membranes were also made more permeable to serum following glycation. The permeation changes were shown to be dependent on glycoxidative reactions judging by their inhibition by EDTA and DTPA. Aminoguanidine also prevented glycation from altering the permeability of GBM. Fluorescence studies indicated the formation of bityrosine in glycated GBM. Studies with oxidants showed that while hydrogen peroxide superoxide and peroxynitrite had little effect on GBM, hypochlorite anion was capable of increasing GBM permeability to water, myoglobin, albumin and serum. Changes in permeation were induced by very low quantities of hypochlorite, well within the range of the amounts of hypochlorite formed by activated neutrophils. Thus glycoxidation, or oxidation by hypochlorite, are chemical mechanisms by which GBM permeability can be increased.

Quantitative analysis of neutral and acidic sugars in whole bacterial cell hydrolysates using high-performance anion-exchange liquid chromatography-electrospray ionization tandem mass spectrometry

A procedure for analysis of a mixture of neutral and acidic sugars in bacterial whole cell hydrolysates using high-performance anion-exchange liquid chromatography-electrospray ionization tandem mass spectrometry (HPAEC-ESI-MS-MS) is described. Certain bacteria (including bacilli), grown under phosphate-limited conditions, switch from producing a teichoic acid (containing ribitol) to a teichuronic acid (characterized by glucuronic acid content). Bacterial cells were hydrolyzed with sulfuric acid to release sugar monomers. The solution was neutralized by extraction with an organic base. Hydrophobic and cationic contaminants (including amino acids) were removed using C18 and SCX columns, respectively. HPAEC is well established as a high-resolution chromatographic technique, in conjunction with a pulsed amperometric detector. Alternatively, for more selective detection, sugars (as M-H- ions) were monitored using ESI-MS. In HPAEC, the mobile phase contains sodium hydroxide and sodium acetate, which are necessary for chromatographic separation of mixtures of neutral and acidic sugars. Elimination of this high ionic content prior to entry into the ESI ion source is vital to avoid compromising sensitivity. This was accomplished using an on-line suppressor and decreasing post-column flow-rates from 1 ml to 50 microliters/min. In the selected ion monitoring mode, background (from the complex sample matrix as well as the mobile phase) was eliminated, simplifying chromatograms. Sugar identification was achieved by MS-MS using collision-induced dissociation.

Polyol pathway, 2,3-diphosphoglycerate in erythrocytes and diabetic neuropathy in rats

The relationship between the 2,3-diphosphoglycerate concentration in red blood cells as a biological indicator of tissue hypoxia and diabetic neuropathy, and the effect of a potent aldose reductase inhibitor, (2S,4S)-6-fluoro-2'5'-dioxospiro [chroman-4,4'-imidazolidine]-2-carboxamide (SNK-860), on both were investigated in streptozotocin-induced diabetic rats. Diabetic rats demonstrated significantly delayed motor nerve conduction velocity and reduced sciatic nerve blood flow. Altered biochemical features in the sciatic nerves, including a marked accumulation of sorbitol and fructose, myo-inositol depletion and decreased Na+/K(+)-ATPase activity were also detected in diabetic rats. These defects were accompanied by a decrease in the red blood cell 2,3-diphosphoglycerate concentration. Treatment with SNK-860 partially or completely ameliorated these abnormalities. These observations suggest that a decrease in the red blood cell 2,3-diphosphoglycerate concentration is one of the factors contributing to tissue hypoxia, which results in diabetic neuropathy, and that this decrease is mediated through an aldose reductase inhibitor-sensitive pathway.

In vitro glycation of glomerular basement membrane alters its permeability: a possible mechanism in diabetic complications

The permeability of glomerular basement membrane (GBM) was assessed in vitro by the filtration of solutions of proteins across films formed from isolated pig GBM. Incubation of the films with fructose or glucose increased their permeability to water and serum albumin. The effect of fructose was similar to that previously noted for films crosslinked with glutaraldehyde. The metal chelator DTPA abolished the effects of glycation; EDTA was partially effective in this respect. Transition metal catalysed formation of glycoxidation induced crosslinks may explain the increased permeability of glycated GBM.