An adenoviral vector deleted for all viral coding sequences results in enhanced safety and extended expression of a leptin transgene

Adenoviral (Ad)-mediated in vivo gene transfer and expression are limited in part by cellular immune responses to viral-encoded proteins and/or transgene immunogenicity. In an attempt to diminish the former responses, we have previously developed and described helper-dependent (HD) Ad vectors in which the viral protein coding sequences are completely eliminated. These HD vectors have up to 37 kb insert capacity, are easily propagated in a Cre recombinase-based system, and can be produced to high concentration and purity (>99.9% helper-free vector). In this study, we compared safety and efficacy of leptin gene delivery mediated by an HD vector (HD-leptin) and a first-generation E1-deleted Ad vector (Ad-leptin) in normal lean and ob/ob (leptin-deficient) mice. In contrast to evidence of liver toxicity, inflammation, and cellular infiltration observed with Ad-leptin delivery in mice, HD-leptin delivery was associated with a significant improvement in associated safety/toxicity and resulted in efficient gene delivery, prolonged elevation of serum leptin levels, and associated weight loss. The greater safety, efficient gene delivery, and increased insert capacity of HD vectors are significant improvements over current Ad vectors and represent favorable features especially for clinical gene therapy applications.

Mechanism of action of the immunosuppressant rapamycin

Rapamycin has potent immunosuppressive properties reflecting its ability to disrupt cytokine signaling that promotes lymphocyte growth and differentiation. In IL-2-stimulated T cells, rapamycin impedes progression through the G1/S transition of the proliferation cycle, resulting in a mid-to-late G1 arrest. Two major biochemical alterations underlie this mode of action. The first one affects the phosphorylation/activation of the p70 S6 kinase (p70s6k), an early event of cytokine-induced mitogenic response. By inhibiting this enzyme, whose major substrate is the 40S ribosomal subunit S6 protein, rapamycin reduces the translation of certain mRNA encoding for ribosomal proteins and elongation factors, thereby decreasing protein synthesis. A second, later effect of rapamycin in IL-2-stimulated T cells is an inhibition of the enzymatic activity of the cyclin-dependent kinase cdk2-cyclin E complex, which functions as a crucial regulator of G1/S transition. This inhibition results from a prevention of the decline of the p27 cdk inhibitor, that normally follows IL-2 stimulation. To mediate these biochemical alterations, rapamycin needs to bind to intracellular proteins, termed FKBP, thereby forming a unique effector molecular complex. However, neither(p70s6k) inhibition, nor p27-induced cdk2-cyclin E inhibition are directly caused by the FKBP-rapamycin complex. Instead, this complex physically interacts with a novel protein, designated "mammalian target of rapamycin" (mTOR), which has sequence homology with the catalytic domain of phosphatidylinositol kinases and may therefore be itself a kinase. mTOR may act upstream of (p70s6K) and cdk2-cyclin E in a linear or bifurcated pathway of growth regulation. Molecular dissection of this pathway should further unravel cytokine-mediated signaling processes and help devise new immunosuppressants.

Role of viral antigens in destructive cellular immune responses to adenovirus vector-transduced cells in mouse lungs

Adenoviruses missing E1 have been used as gene delivery vectors to the lungs for the treatment of cystic fibrosis. Transient expression of the recombinant gene and the development of inflammation have been two major limitations to the application of first-generation recombinant adenoviruses for gene therapy. Studies with mouse models of liver- and lung-directed gene therapy suggested that CD8+ cytotoxic T lymphocytes (CTLs) are effectors that contribute to extinction of transgene expression. The precise antigens responsible for activation of CTLs have not been identified. In this study, we examine the relative contributions of viral proteins versus the transgene product to the activation of CTLs which eliminate transgene-containing cells in mouse lungs. Instillation of a lacZ-expressing virus into the lungs of C57BL/6 mice elicited CTL responses to both viral proteins and the transgene product, beta-galactosidase, which collectively contribute to loss of trans-gene expression in mouse airways. Similar results were obtained in two experimental models in which the animals should be tolerant to the transgene, i.e., lacZ virus delivered to an animal transgenic for lacZ and a virus expressing the liver-specific enzyme ornithine transcarbamylase administered to the lungs of various strains of immune-competent mice. These data confirm the hypothesis that CTLs specific for viral antigens contribute to the problem of transgene instability in mouse lungs and indicate that CTLs specific for transgene product alone cannot account for the observed problem.

Expression of hepatitis B virus X protein in HBV-infected human livers and hepatocellular carcinomas

Transactivation of cellular genes and functional inactivation of p53 by the hepatitis B virus (HBV) X gene-encoded protein (HBx) are proposed as alternative mechanisms for induction of hepatocellular carcinomas (HCCs) in chronic HBV infection. Using an immunohistochemical approach, we studied the expression of HBx in 39 explanted livers with HBV-associated disease. Because the data reported previously have been inconsistent, possibly due to the application of different antibodies, we compared results with 5 polyclonal and 6 monoclonal anti-HBx antibodies from five laboratories. Ten of the 11 antibodies reacted with recombinant HBx by Western blotting, but only 1 polyclonal and 2 monoclonal antibodies reacted specifically with HBx in tissue, and were thus suitable for immunohistochemistry. Three other polyclonal antibodies reacted with tissue components in addition to HBx. One polyclonal and 4 monoclonal antibodies did not recognize the HBx in the tissue. HBx was demonstrated in 16 of 30 (53.3%) cirrhotic livers and 10 of 18 (58.8%) HCCs by all specific antibodies. The expression of HBx, among three HBV antigens examined, was found to be preferentially maintained in HCC and the surrounding liver parenchyma, including focal or nodular preneoplastic lesions. However, the immunoreactivity was always limited to the cytoplasm of a small number of parenchymal and neoplastic cells. The role of X gene expression in HBV-associated human hepatocarcinogenesis remains to be established.

Transient subversion of CD40 ligand function diminishes immune responses to adenovirus vectors in mouse liver and lung tissues

First-generation adenovirus vectors will have limited application in gene therapy for chronic diseases because of destructive host immune responses. Important immune effectors include CD8+ T cells, which mediate target cell destruction and ablate transgene expression, and B cells, which produce neutralizing antibodies that block effective readministration of vector. Previous studies indicated that activation of CD4+ T cells by virus capsid proteins is necessary for full realization of effector function of CD8+ T cells and B cells. In this paper, we present a strategy for preventing CD4+ T-cell activation by an adenovirus vector delivered to mouse liver and lung tissues which is based on interfering with T-cell priming via CD40 ligand-CD40 interactions. Adenovirus transgene expression was stabilized in mice genetically deficient in CD40 ligand (CD40L), and neutralizing antibody to adenovirus did not develop, allowing efficient readministration of vector. A transient blockade of T-cell activation with an antibody to CD40L infused into the animal at the time of adenovirus vector-mediated gene transfer led to stabilization of transgene expression and diminished production of neutralizing antibody, allowing readministration of vector. In vitro T-cell assays suggested that a block in the primary activation of CD4+ T cells was responsible for the lack of B-cell- and cytotoxic-T-cell-dependent responses. This suggests a strategy for improving the potential of adenovirus vectors based on administration of an antibody to CD40L at the time of vector administration.

Postglacial recolonization and cpDNA variation of silver birch, Betula pendula

Chloroplast PCR-RFLP markers were used to reconstruct the history of the silver birch, Betula pendula Roth, in Europe since the last glacial maximum (LGM). In birch, fossil pollen maps do not reveal a clear chronological sequence of postglacial spread. If anything, the pollen record suggests that most of Europe was recolonized by birches as early as 10000 bp, probably from populations that remained close to the ice sheets during the LGM. The geographical distribution of haplotypes supports a scenario of early colonization. Two of the 13 haplotypes that were observed are common, representing 35% and 49% of the total sample, respectively. Although one of the common haplotypes is predominant in the NW and the other in the SE, both are present throughout most of the investigated geographical area. Rare haplotypes are geographically restricted. The distribution of the haplotypes reveals five genetic boundaries between groups of haplotypes and allows us to infer patterns of postglacial recolonization. Europe was re-occupied by two main waves of recolonization: one eastern and one western, with origins at intermediate latitudes. Populations in the Iberian Peninsula and in Italy did not take part in the postglacial recolonization of Europe.

Selective solid-phase extraction using molecularly imprinted polymer for the analysis of polar organophosphorus pesticides in water and soil samples

An analytical methodology for the analysis of four polar organophophorus pesticides (monocrotophos, mevinphos, phosphamidon, omethoate) in water and soil samples incorporating a molecularly imprinted solid-phase extraction (MISPE) process using a monocrotophos-imprinted polymer was developed. Binding study demonstrated that the polymer showed excellent affinity and high selectivity to monocrotophos. The MISPE procedure including the clean-up step to remove any interferences was optimized. The accuracy and selectivity of the MISPE process developed were verified using a non-imprinted (blank) polymer and a classical ENVI-18 cartridge as the SPE matrix during control experiments. The use of MISPE improved the accuracy and precision of the GC method and lowered the limit of detection. The recoveries of four polar organophosphorus pesticides (OPPs) extracted from 1 L of river water at a 100 ng/L spike level were in the range of 77.5-99.1%. The recoveries of organophosphorus pesticides extracted from a 5-g soil sample at the 100 microg/kg level were in the range of 79.3-93.5%. The limit of detection varied from 10 to 32 ng/L in water and from 12 to 34 microg/kg in soil samples. The molecularly imprinted polymer (MIP) enabled the selective extraction of four organophosphorus pesticides successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.

Immunology of gene therapy with adenoviral vectors in mouse skeletal muscle

Skeletal muscle is an attractive target for somatic gene transfer of both acquired and inherited disorders. Direct injection of adenoviral vectors in the skeletal muscle leads to recombinant gene expression in a large number of muscle fibers. Transgene expression has been transient in most organs and associated with substantial inflammation when experiments are performed in adult immune competent mice. In this report, we utilize a variety of in vivo and in vitro models of T and B cell function to characterize the nature of the immune response to adenoviral vectors injected into murine skeletal muscle. Cellular immunity dependent on CD4+ and CD8+ T cells contributes to the loss of recombinant gene expression and the development of localized inflammation. Antigen specific activation of T cells occurs to both viral proteins and the reporter gene beta-galactosidase. Systemic levels of neutralizing antibody to the capsid proteins of the vector are also generated. Destructive immune responses responsible for loss of transgene expression are largely directed against beta-galactosidase in that transgene expression was stable when beta-galactosidase was eliminated as a neoantigen in mice transgenic for lacZ. A strategy to prevent the cellular and humoral immunity to this therapy was developed based on transiently ablating CD4+ T cell activation at the time of vector delivery. Encouraging results were obtained when vector was administered with one of several immune modulating agents including cyclophosphamide, mAb to CD4+ cells, and mAb to CD40 ligand. These studies indicate that cellular and humoral immune responses are elicited in the context of gene therapy directed to skeletal muscle with adenoviral vectors. Transient ablation of CD4+ T cell activation prevents the effects responses of the CD8+ T and B cells.

Extensive sharing of chloroplast haplotypes among European birches indicates hybridization among Betula pendula, B. pubescens and B. nana

Extensive sharing of chloroplast haplotypes among the silver birch, Betula pendula Roth., the downy birch, B. pubescens Ehrh., and the dwarf birch, B. nana L., was discovered using polymerase chain reaction-restriction fragment length polymporphism markers. The geographical component of the genetic variation was stronger than the species component: the species were not significantly different while 11% of the variation could be attributed to differentiation between the two main regions studied, Scandinavia and western Russia. All haplotypes occurring in more than 2% of the individuals were shared among the species and the introgression ratios were quite large: 0.79 between B. pubescens and B. pendula and 0.67 between B. pubescens and B. nana. The data also indicate that B. pendula individuals are more similar to sympatric B. pubescens than to B. pendula individuals from nearby forests. However, this trend is not as pronounced when B. pubescens is considered, suggesting that introgression is not symmetrical. The haplotype sharing among the three Betula species is most likely caused by hybridization and subsequent cytoplasmic introgression.

Films coated with molecular imprinted polymers for the selective stir bar sorption extraction of monocrotophos

The flexibility and simplicity of stir bar sorption extraction (SBSE) have been combined with the selectivity of molecularly imprinted polymers (MIP). Stir bars were coated reproducible with a 180 microm film formed from a formic acid solution of nylon-6 polymer either nonimprinted or imprinted with monocrotophos. Time sorption profiles were measured for the extraction of monocrotophos from dichloromethane at the concentration of 10-200 micromol/L levels with both types of films in order to compare extraction characteristics. The results indicated that the MIP coated layer showed remarkable high affinity toward monocrotophos and equilibrium adsorption was attained rapidly (60 min) in contrast to free standing molecularly imprinted polymer in which equilibrium adsorption was normally attained after several hours. The stir bars coated with MIP films were capable of extracting four structural analogues of monocrotophos from dichloromethane solution, which suggests that both the amino group and PO part of these molecules is responsible for interaction with the imprinted polymer. Evidence was also presented by FT-IR analysis that the amide-hydrogen-bonding interaction between the MIP-coated films and monocrotophos was originated for monocrotophos recognition. To achieve selective extraction of monocrotophos from sample, stir bars coated with MIP films were washed with 10% (v/v) acetic acid/methanol and methanol. Clean extracts and yields of 95% were obtained, demonstrating the suitability of stir bar coated with MIP films for the analysis of environmental and biological samples. Compared with traditional MIP and SBSE, the MIP-coated film showed not only the high selectivity but also the rapid equilibrium adsorption.

Probing the mechanism of proton coupled electron transfer to dioxygen: the oxidative half-reaction of bovine serum amine oxidase

Bovine serum amine oxidase (BSAO) catalyzes the oxidative deamination of primary amines, concomitant with the reduction of molecular oxygen to hydrogen peroxide via a ping-pong mechanism. A protocol has been developed for an analysis of chemical and kinetic mechanisms in the conversion of dioxygen to hydrogen peroxide. Steady-state kinetics show that two groups need to be deprotonated to facilitate the oxidative half-reaction. The pH dependence of Vmax/Km(O2) reveals pKa's of 6.2 +/- 0.3 and 7.0 +/- 0.2, respectively. A pKa of 7.2 +/- 0.1 has been obtained from a titration of anaerobically reduced BSAO using UV-vis spectrophotometry. The near identity of the pKa obtained from the reduced enzyme titration with the second pKa from steady-state kinetics suggests that this second pKa arises from the reduced cofactor. The assignment of pKa is supported by the observed pH dependence for formation of the cofactor semiquinone signal, detected by EPR spectroscopy under anaerobic conditions. To address the nature of rate-limiting steps in the oxidative half-reaction, the solvent isotope effect, viscosity effect, and O-18 isotope effect on Vmax/Km(O2) have been determined. The solvent isotope effect is indistinguishable from unity, ruling out a proton transfer as a rate-determining step. Use of glucose as a solvent viscosogen shows no viscosity effect, indicating that binding of oxygen is not in the rate-determining step. The O-18 kinetic isotope effect is independent of pH with an average value of 18(V/K) = 1.0097 +/- 0. 0010. This has been compared to calculated equilibrium O-18 isotope effects for various dioxygen intermediate species [Tian and Klinman (1993) J. Am. Chem. Soc. 115, 8891], leading to the conclusion that either the first electron transfer to dioxygen or the desorption of product peroxide from a Cu(II)-OOH complex could be the rate-limiting step. The distribution of steady-state enzyme species was, therefore, analyzed through a combination of stopped-flow experiments and analysis of DV and D(V/K) for benzylamine oxidation. We conclude that the major species accumulating in the steady state are the oxidized cofactor-substrate Schiff base complex and the reduced, aminoquinol form of cofactor. These data rule out a slow release of product hydroperoxide from the aminoquinone form of enzyme, leading to the conclusion that the first electron transfer from substrate-reduced cofactor to dioxygen is the rate-determining step in the oxidative half-reaction. This step is also estimated to be 40% rate-limiting in kcat. An important mechanistic conclusion from this study is that dioxygen binding is a separate step from the rate-limiting electron-transfer step to form superoxide. On the basis of a recently determined X-ray structure for the active form of a yeast amine oxidase from Hansenula polymorpha [Li et al. (1998) Structure 6, 293], a hydrophobic space has been identified near the O-2 position of reduced cofactor as the putative dioxygen binding site. Movement of superoxide from this site onto the Cu(II) at the active site may occur prior to further electron transfer from cofactor to superoxide.

Expression of insulin-like growth factor II in hepatitis B, cirrhosis and hepatocellular carcinoma: its relationship with hepatitis B virus antigen expression

Expression of insulin-like growth factor II in two human hepatocellular carcinoma cell lines and in hepatitis B, cirrhosis and hepatocellular carcinoma in 419 cases were investigated, and its relationship with the expression of hepatitis B virus X gene was studied by means of immunohistochemical and electron microscopic techniques. The results demonstrated that hepatocellular carcinoma cells (SMMC 7721 and QGY 7703) in culture could express insulin-like growth factor II. Expression seemed to be regulated by cell density, which was suggested as the molecular basis of the contact inhibition of cell proliferation. In tissue sections, cells with high expression of insulin-like growth factor II were observed not only in hepatocellular carcinoma (93%) but also in 95% of the pericancerous liver tissues, 72% of cirrhotic livers, 64% of chronic active hepatitis and 37% of chronic persistent hepatitis. In most cases of hepatocellular carcinoma, insulin-like growth factor II was localized in the cytoplasm of the cancer cells. In the benign liver disorders, four types of cells that highly expressed insulin-like growth factor II were observed: (a) a kind of small liver cell we named the small polygonal liver cell; (b) multinuclear giant hepatocytes; (c) hepatocytes in most of hyperplastic and neoplastic nodules, small hepatocyte nodules and some of regenerative nodules; and (d) some proliferating ductular cells. Even more interestingly, insulin-like growth factor II expression was shown to be closely related to the expression of hepatitis B virus X gene product. We suggest that the activation of insulin-like growth factor II gene and its overexpression may be a crucial step in the processes of hepatitis B virus-associated hepatocarcinogenesis and that the X gene product may activate the insulin-like growth factor II gene through a transactivation mechanism. In addition, we studied the characteristics of small polygonal liver cells, and the roles they may play in the regeneration and carcinogenesis of hepatitis B virus-infected liver are discussed.

SNAP-29: a general SNARE protein that inhibits SNARE disassembly and is implicated in synaptic transmission

Using the yeast two-hybrid system with syntaxin-1A as bait, we isolated soluble NSF attachment protein (SNAP)-29 from a human brain cDNA library. Synaptosomal fractionation and immunocytochemical staining of hippocampal neurons in culture showed that SNAP-29 is present at synapses and is predominantly associated with synaptic vesicles. The interaction of SNAP-29 with syntaxin-1 was further confirmed with immunoprecipitation analysis. Binding competition studies with SNAP-29 demonstrated that it could compete with alpha-SNAP for binding to synaptic SNAP receptors (SNAREs) and consequently inhibit disassembly of the SNARE complex. Introduction of SNAP-29 into presynaptic superior cervical ganglion neurons in culture significantly inhibited synaptic transmission in an activity-dependent manner. Although SNAP-29 has been suggested to be a general SNARE component in membrane trafficking, our findings suggest that it may function as a regulator of SNARE complex disassembly and modulate the process of postfusion recycling of the SNARE components.

POR C of Arabidopsis thaliana: a third light- and NADPH-dependent protochlorophyllide oxidoreductase that is differentially regulated by light

During the sequencing of the genome of Arabidopsis thaliana a gene has been identified that encodes a novel NADPH-protochlorophyllide oxidoreductase (POR)-like protein (accession number AC 002560). This protein has been named POR C. We have expressed the POR C protein in Escherichia coli and have determined its in vitro activity. POR C shows the characteristics of a light-dependent and NADPH-requiring POR similar to POR A and POR B. The expression of the POR C gene differs markedly from that of the POR A and POR B genes. In contrast to the POR A and POR B mRNAs, the POR C mRNA has been shown previously to accumulate only after the beginning of illumination. In light-adapted mature plants only POR B and POR C mRNAs were detectable. The amounts of both mRNAs show pronounced diurnal rhythmic fluctuations. While the oscillations of POR B mRNA are under the control of the circadian clock, those of POR C mRNA are not. Another difference between POR B and POR C was found in seedlings that were grown under continuous white light. The concentration of POR C mRNA rapidly declined and soon dropped beyond the limit of detection, after these seedlings were transferred to the dark. On the other hand. POR B mRNA was unaffected by this light/dark shift. When seedlings were exposed to different light intensities, the amounts of POR B mRNA remained the same, while POR A and POR C mRNAs were modulated in an inverse way by these light intensity changes. POR A mRNA was still detectable in seedlings grown under low light intensities but disappeared at higher light intensities, while the mRNA concentration of POR C rose with increasing light intensities. These different responses to light suggest that the functions of the three PORs of Arabidopsis are not completely redundant, but may allow the plant to adapt its needs for chlorophyll biosynthesis more selectively by using preferentially one of the three enzymes under a given light regime.

Extraction of Mass Spectra and Chromatographic Profiles from Overlapping GC/MS Signal with Background

An adaptive immune algorithm (AIA) was proposed for resolution of the overlapping GC/MS signal with background. By using AIA, the chromatographic profiles corresponding to the independent components (ICs) in the overlapping signal are calculated with the mass spectra extracted by means of independent component analysis (ICA). The number of the ICs in the overlapping signal is determined by the difference between the reconstructed and the original data. Both simulated and experimental data are investigated with the proposed AIA approach. It was found that the mass spectra and chromatographic profiles of the components in an overlapping multicomponent GC/MS signal can be accurately resolved with the existence of background, and the results are better than that by using an interactive self-modeling mixture analysis (SIMPLISMA) method. The AIA approach may be a promising tool for the resolution of overlapping GC/MS signal.

Syntaphilin: a syntaxin-1 clamp that controls SNARE assembly

Syntaxin-1 is a key component of the synaptic vesicle docking/fusion machinery that forms the SNARE complex with VAMP/synaptobrevin and SNAP-25. Identifying proteins that modulate SNARE complex formation is critical for understanding the molecular mechanisms underlying neurotransmitter release and its modulation. We have cloned and characterized a protein called syntaphilin that is selectively expressed in brain. Syntaphilin competes with SNAP-25 for binding to syntaxin-1 and inhibits SNARE complex formation by absorbing free syntaxin-1. Transient overexpression of syntaphilin in cultured hippocampal neurons significantly reduces neurotransmitter release. Furthermore, introduction of syntaphilin into presynaptic superior cervical ganglion neurons in culture inhibits synaptic transmission. These findings suggest that syntaphilin may function as a molecular clamp that controls free syntaxin-1 availability for the assembly of the SNARE complex, and thereby regulates synaptic vesicle exocytosis.

Gut microbes in correlation with mood: case study in a closed experimental human life support system

BACKGROUND

Gut microbial community, which may influence our mood, can be shaped by modulating the gut ecosystem through dietary strategies. Understanding the gut-brain correlationship in healthy people is important for maintenance of mental health and prevention of mental illnesses.

METHODS

A case study on the correlation between gut microbial alternation and mood swing of healthy adults was conducted in a closed human life support system during a 105-day experiment. Gut microbial community structures were analyzed using high-throughput sequencing every 2 weeks. A profile of mood states questionnaire was used to record the mood swings. Correlation between gut microbes and mood were identified with partial least squares discrimination analysis.

KEY RESULTS

Microbial community structures in the three healthy adults were strongly correlated with mood states. Bacterial genera Roseburia, Phascolarctobacterium, Lachnospira, and Prevotella had potential positive correlation with positive mood, while genera Faecalibacterium, Bifidobacterium, Bacteroides, Parabacteroides, and Anaerostipes were correlated with negative mood. Among which, Faecalibacterium spp. had the highest abundance, and showed a significant negative correlation with mood.

CONCLUSIONS & INFERENCES

Our results indicated that the composition of microbial community could play a role in emotional change in mentally physically healthy adults.

Nature of oxygen activation in glucose oxidase from Aspergillus niger: the importance of electrostatic stabilization in superoxide formation

Glucose oxidase catalyzes the oxidation of glucose by molecular dioxygen, forming gluconolactone and hydrogen peroxide. A series of probes have been applied to investigate the activation of dioxygen in the oxidative half-reaction, including pH dependence, viscosity effects, 18O isotope effects, and solvent isotope effects on the kinetic parameter Vmax/Km(O2). The pH profile of Vmax/Km(O2) exhibits a pKa of 7.9 +/- 0.1, with the protonated enzyme form more reactive by 2 orders of magnitude. The effect of viscosogen on Vmax/Km(O2) reveals the surprising fact that the faster reaction at low pH (1.6 x 10(6) M-1 s-1) is actually less diffusion-controlled than the slow reaction at high pH (1.4 x 10(4) M-1 s-1); dioxygen reduction is almost fully diffusion-controlled at pH 9.8, while the extent of diffusion control decreases to 88% at pH 9.0 and 32% at pH 5.0, suggesting a transition of the first irreversible step from dioxygen binding at high pH to a later step at low pH. The puzzle is resolved by 18O isotope effects. 18(Vmax/Km) has been determined to be 1.028 +/- 0.002 at pH 5.0 and 1.027 +/- 0.001 at pH 9.0, indicating that a significant O-O bond order decrease accompanies the steps from dioxygen binding up to the first irreversible step at either pH. The results at high pH lead to an unequivocal mechanism; the rate-limiting step in Vmax/Km(O2) for the deprotonated enzyme is the first electron transfer from the reduced flavin to dioxygen, and this step accompanies binding of molecular dioxygen to the active site. In combination with the published structural data, a model is presented in which a protonated active site histidine at low pH accelerates the second-order rate constant for one electron transfer to dioxygen through electrostatic stabilization of the superoxide anion intermediate. Consistent with the proposed mechanisms for both high and low pH, solvent isotope effects indicate that proton transfer steps occur after the rate-limiting step(s). Kinetic simulations show that the model that is presented, although apparently in conflict with previous models for glucose oxidase, is in good agreement with previously published kinetic data for glucose oxidase. A role for electrostatic stabilization of the superoxide anion intermediate, as a general catalytic strategy in dioxygen-utilizing enzymes, is discussed.

Advanced glycation end-products induce injury to pancreatic beta cells through oxidative stress

AIM

This study evaluated the direct effects of advanced glycation end-products (AGEs) on pancreatic β cells, including cellular viability, generation of reactive oxygen species (ROS) and insulin secretion, and also looked for the main source of ROS in INS-1 cells and the possible molecular mechanism(s) of cell injury by AGEs.

METHODS

INS-1 cells were cultured with 100, 200 and 500 mg/L of AGEs for specific periods of time. Cell apoptosis was determined by ELISA and real-time PCR assays. ROS were detected by DCFH-DA and MitoSOX Red probes with a flow cytometer, NADPH oxidase activity was measured by lucigenin chemiluminescence and MAPK phosphorylation was measured by Western blot tests.

RESULTS

Both cell apoptosis and ROS generation increased in AGE-treated cells in a dose-dependent way, and both the mitochondrial electron transport chain and NADPH oxidase pathway participated in ROS generation, although the role of the mitochondrial pathway was earlier and more important. AGEs exerted a toxic effect on insulin secretion that could be largely reversed by inhibiting ROS.

CONCLUSION

AGEs injured INS-1 cells by oxidative stress mainly through the mitochondrial pathway, although the JNK and p38 MAPK signaling pathways were also key modulators in ROS-mediated β-cell death.