Nonenzymatic modifications of amino sugars in vitro

Studies on the Formation of Maillard and Caramelization Products from Glucosamine Incubated at 37 °C

This experiment compared the in vitro degradation of glucosamine (GlcN), N-acetylglucosamine, and glucose in the presence of NH3 incubated at 37 °C in phosphate buffer from 0.5 to 12 days. The reactions were monitored with UV-vis absorption and fluorescence emission spectroscopies, and the main products of degradation, quinoxaline derivatives of α-dicarbonyl compounds and condensation products, were determined using UHPLC-UV and Orbitrap mass spectrometry. GlcN produced two major dicarbonyl compounds, glucosone and 3-deoxyglucosone, ranging from 709 to 3245 mg/kg GlcN and from 272 to 4535 mg/kg GlcN, respectively. 3,4-Dideoxyglucosone-3-ene, glyoxal, hydroxypyruvaldehyde, methylglyoxal, and diacetyl were also detected in lower amounts compared to glucosone and 3-deoxyglucosone. Several pyrazine condensation products resulting from the reaction between dicarbonyls and GlcN were also identified. This study determined that GlcN is a significantly unstable molecule producing a high level of degradation products at 37 °C.

Characterization of the in vitro binding and inhibition kinetics of primary amine oxidase/vascular adhesion protein-1 by glucosamine

BACKGROUND

Primary-amine oxidase (PrAO) catalyzes the oxidative deamination of endogenous and exogenous primary amines and also functions, in some tissues, as an inflammation-inducible endothelial factor, known as vascular adhesion protein-1. VAP-1 mediates the slow rolling and adhesion of lymphocytes to endothelial cells in a number of inflammatory conditions, including inflammation of the synovium.

METHODS

Glucosamine binding to the enzyme was assessed spectrofluorometrically and the kinetics of inhibition of PrAO were determined spectrophotometrically through the use of direct or coupled assays, in the presence of different substrates.

RESULTS

Glucosamine is not a substrate for PrAO, but acts as a time-dependent inhibitor of PrAO activity, displaying mixed inhibition kinetics. The observed inhibition and binding were augmented in the presence of H(2)O(2).

CONCLUSIONS

Significant in vitro effects on PrAO require glucosamine in the millimolar concentration range and it is not clear at this stage whether a low but persistent level of PrAO inhibition might contribute to the anti-arthritic response.

GENERAL SIGNIFICANCE

This work was aimed at characterizing the interactions of PrAO/VAP-1 with glucosamine, a widely used "over-the-counter" supplement for the treatment of osteoarthritis.

Altered utilization of N-acetyl-D-galactosamine by Escherichia coli O157:H7 from the 2006 spinach outbreak

In silico analyses of previously sequenced strains of Escherichia coli O157:H7, EDL933 and Sakai, localized the gene cluster for the utilization of N-acetyl-D-galactosamine (Aga) and D-galactosamine (Gam). This gene cluster encodes the Aga phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) and other catabolic enzymes responsible for transport and catabolism of Aga. As the complete coding sequences for enzyme IIA (EIIA)(Aga/Gam), EIIB(Aga), EIIC(Aga), and EIID(Aga) of the Aga PTS are present, E. coli O157:H7 strains normally are able to utilize Aga as a sole carbon source. The Gam PTS complex, in contrast, lacks EIIC(Gam), and consequently, E. coli O157:H7 strains cannot utilize Gam. Phenotypic analyses of 120 independent isolates of E. coli O157:H7 from our culture collection revealed that the overwhelming majority (118/120) displayed the expected Aga+ Gam- phenotype. Yet, when 194 individual isolates, derived from a 2006 spinach-associated E. coli O157:H7 outbreak, were analyzed, all (194/194) displayed an Aga- Gam- phenotype. Comparison of aga/gam sequences from two spinach isolates with those of EDL933 and Sakai revealed a single nucleotide change (G:C-->A:T) in the agaF gene in the spinach-associated isolates. The base substitution in agaF, which encodes EIIA(Aga/Gam) of the PTS, changes a conserved glycine residue to serine (Gly91Ser). Pyrosequencing of this region showed that all spinach-associated E. coli O157:H7 isolates harbored this same G:C-->A:T substitution. Notably, when agaF+ was cloned into an expression vector and transformed into six spinach isolates, all (6/6) were able to grow on Aga, thus demonstrating that the Gly91Ser substitution underlies the Aga- phenotype in these isolates.

Non-enzymatic interactions of glyoxylate with lysine, arginine, and glucosamine: a study of advanced non-enzymatic glycation like compounds

Glyoxylate is a 2 carbon aldo acid that is formed in hepatic tissue from glycolate. Once formed, the molecule can be converted to glycine by alanine-glyoxylate aminotransferase (AGAT). In defects of AGAT, glyoxylate is transformed to oxalate, resulting in high levels of oxalate in the body. The objective of this study was 2-fold. First, it was to determine, if akin to D-glucose, D-fructose or DL-glyceraldehyde, glyoxylate was susceptible to non-enzymatic attack by amino containing molecules such as lysine, arginine or glucosamine. Second, if by virtue of its molecular structure and size, glyoxylate was as reactive a reagent in non-enzymatic reactions as DL-glyceraldehyde; i.e., a glycose that we previously demonstrated to be a more effective glycating agent than D-glucose or D-fructose. Using capillary electrophoresis (CE), high performance liquid chromatography and UV and fluorescence spectroscopy, glyoxylate was found to be a highly reactive precursor of advanced glycation like end products (AGLEs) and a more effective promoter of non-enzymatic end products than D-glucose, D-fructose or DL-glyceraldehyde.

Capillary electrophoretic analysis of advanced glycation endproducts formed from the reaction of reducing sugars with the amino group of glucosamine

Glucosamine (GlcN) is an amino sugar sold over-the-counter and is widely used as a dietary supplement to relieve symptoms of osteoarthritis. It is not known whether it is the GlcN alone or one of its many possible nonenzymatic glycation products that is responsible for this effect. The current study demonstrates that reducing sugars form advanced glycation endproducts (AGEs) with GlcN and, as a result, decrease GlcN autocondensation by reducing the availability of the GlcN amino group. Capillary electrophoresis (CE) was used to analyze the in vitro Maillard reaction of GlcN with glyceraldehyde (GA), glucose (Glc), and fructose (Fru) as well as their inhibition of GlcN autocondensation under physiological conditions. Formation of AGEs was monitored by UV and fluorescence spectroscopy. Major components were separated by CE using a bare capillary and UV detection at 214 nm. AGE species were separated by HPLC and were complementary to the CE results. The effects of sugar concentration and incubation time on the AGE profile are also reported for each of the GlcN reducing sugar model systems. A simple and rapid CE method was developed to analyze the AGE formation in this initial report of the reaction of reducing sugars with the amino group of GlcN.

Monitoring the formation of Maillard reaction products of glucosamine with fibrinogen and human serum albumin using capillary electrophoresis

Formation of Maillard reaction products (MRP) of glucosamine (GlcN) with fibrinogen and human serum albumin (HSA), under simulated physiological conditions, was detected by fluorescence (excitation/emission: 340/420 nm) and UV/Vis (max. 275 nm) spectroscopy. The application of polyacrylamide gel electrophoresis demonstrated the generation of high-molecular-weight fibrinogen and HSA MRP by GlcN. A simple and rapid capillary electrophoresis method was developed to separate MRP formed by the reaction of GlcN with proteins from GlcN autocondensation products.

Relationship between the reduction of tetrazolium salt XTT and DNA strand breakage with aminosugars

Dihydropyrazine derivatives formed by the self-condensation reaction of D-glucosamine have the DNA breaking activity. To establish the monitoring method of the biological active dihydropyrazines, we investigated the relationship between the XTT (3'-[1-[(phenylamino)-carbonyl]-3, 4-tetrazolium]bis(4-methoxy-6-nitro)benzensulfonic acid hydrate) reducibility and the DNA breaking activity of aminosugars. Aminosugar in 50 mM sodium phosphate buffer (pH 7.4) was incubated at 37 degrees C. At a given time, the XTT reducibility and the DNA breaking activity of the incubated aminosugar were measured. Both XTT reducibility and DNA breaking activity showed a maximum value within 1-4 h after the incubation and then gradually decreased with the incubation time. Superoxide anion was suggested to involve in both of the DNA breaking activity and the XTT reducibility by the addition of the radical scavengers into those assay mixtures. The quantity of remaining covalently closed circular DNA and the XTT reducibility of all aminosugars showed a good correlation (r = 0.825, n = 26). This means that the XTT assay is applicable for the monitoring of those biologically active products derived from aminosugars when the participation of superoxide anion in DNA scission is recognized.

Poly(vinylbenzyl chloride) microsphere synthesis and their chemical modifications

Vinylbenzyl chloride (VBC) was dispersion polymerized to give monodisperse microspheres in the presence of poly(vinylpyrrolidone) (PVP) as a steric stabilizer. The effect of PVP concentration on the size and on microsphere stability during the polymerization process was investigated. Microsphere size was examined when co-stabilizer molecules were employed with PVP during the polymerization reaction. The built-in reactive chloromethyl groups of the microspheres were the sites of the nucleophilic reaction of two amino-group model molecules, glucosamine (G), a hexosamine implicated in processes of molecular recognition, and also bovine serum albumin (BSA). Elemental analyses and Fourier transform infrared spectroscopy (FTIR) spectra showed that poly(vinylpyrrolidone) was associated with the microsphere network. Elemental analyses, attenuated total reflection infrared spectroscopy (ATR-FTIR), and zeta potential measurements confirmed G and BSA links at the microsphere surface.

Involvement of oxidative DNA damage and apoptosis in antitumor actions of aminosugars

We investigated the mechanisms of apoptosis and DNA damage induced by aminosugars in relation to their antitumor actions. The order of cytotoxic effects of aminosugars was D-mannosamine (ManN) >> D-galactosamine (GalN) > D-glucosamine (GlcN). A comparison of the frequency of apoptotic cells showed the same order. DNA ladders were formed by only ManN and the formation of DNA ladders was inhibited by a caspase inhibitor. Pulsed-field gel electrophoresis showed that ManN caused cellular DNA cleavage at a lower concentration than those causing apoptosis. Cellular DNA cleavage was inhibited by catalase and enhanced by a catalase inhibitor. Flow cytometry showed that ManN enhanced the production of intracellular peroxides. These results suggest that ManN-induced apoptosis is preceded by H2O2-mediated DNA damage. The order of the extent of damage to 32P-labeled DNA fragments by aminosugars plus Cu(II) was ManN >> GalN > GlcN. The DNA damage was inhibited by catalase and bathocuproine, suggesting that H2O2 reacts with Cu(I) to form the metal-peroxide complex capable of causing DNA damage. Two mechanisms of H2O2 generation from aminosugars were proposed: one is the major pathway to form a dioxo compound and NH4+; the other is the minor pathway to form a pyrazine derivative through the condensation of two molecules of an aminosugar. The order of reactivity to generate these products was ManN >> GalN > GlcN. On the basis of these results, it is concluded that aminosugars, especially ManN, produce H2O2 to cause DNA damage, which mediates apoptosis resulting in tumor growth inhibition.

The pimB gene of Mycobacterium tuberculosis encodes a mannosyltransferase involved in lipoarabinomannan biosynthesis

The biosynthesis of lipoarabinomannan (LAM), a key mycobacterial lipoglycan that has been implicated in numerous immunoregulatory functions, was examined utilizing D-mannosamine (ManN) as a tool to identify mannosyltransferase genes involved in LAM synthesis. Cell-free reactions utilizing cellular membranes of mycobacteria as the enzyme source indicated that ManN inhibited the synthesis of phosphatidylinositol mannosides, early precursors to LAM. A selection strategy was devised to screen a Mycobacterium tuberculosis genomic library in Mycobacterium smegmatis for clones conferring conditional resistance to ManN, with the rationale that overexpression of the gene(s) encoding a target of ManN would impart a ManN-resistant phenotype under these conditions. This strategy led to the identification of pimB, whose deduced amino acid sequence shows similarity to mannosyltransferases and other glycosyltransferases. Partially purified recombinant PimB protein from Escherichia coli or membranes from M. smegmatis overexpressing the pimB gene were used in cell-free assays to show that PimB catalyzes the formation of triacylphosphatidylinositol dimannoside from GDP-mannose and triacylphosphatidylinositol monomannoside.