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Biomedical subjects

H Xiong

Publications and source records attributed to H Xiong.

At least 73 records · Page 4Linked to original sources
PubMed1996

Involvement of various combinations of endogenous inflammatory cytokines in Listeria monocytogenes-induced expression of inducible nitric oxide synthase in mice.

Using a in vitro infection of spleen cells with Listeria monocytogenes, the relationship between endogenous cytokines and the expression of inducible nitric oxide synthase (iNOS) was examined. When all interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 alpha, or the combination of IFN-gamma with either TNF-alpha or IL-1 alpha were neutralized by antibodies, there was a significant reduction of iNOS expression and nitrite production in culture. However, there was no reduction of iNOS expression and nitrite production when these cytokines were individually neutralized. After the depletion of natural killer cells, there was no change in the expression of Listeria-induced iNOS and nitrite production although the IFN-gamma production was abrogated. Neutralization of TNF-alpha and IL-1 alpha in natural killer cell-depleted culture resulted in the reduction of iNOS expression. Thus, various combinations of cytokines to play an important role in iNOS induction by L. monocytogenes.

Animals↗
PubMed1996

Brain-derived peptides inhibit synaptic transmission via presynaptic GABAB receptors in CA1 area of rat hippocampal slices.

GABAB receptors form the basis of a powerful and versatile inhibitory system in the mammalian brain. Presynaptic and postsynaptic actions of GABAB receptors have been described in various brain regions, including the hippocampus. We report here on a novel pharmacological agent, presumably a peptide, which inhibits synaptic transmission in the CA1 area of the rat hippocampus via GABAB receptors. The agent is a component of a nootropic drug, Cerebrolysin, obtained from pig's brain extract. In contrast to other, presently known agonists, such as baclofen or GABA, Cerebrolysin acts preferentially on presynaptic GABAB receptors and has no detectable postsynaptic inhibitory effects. Additional, postsynaptic depolarizing action of the drug resulting in increased excitability is pharmacologically distinct from the GABAB response and partially masked by the inhibition. The presynaptic GABAB agonist may add to clinical effects of Cerebrolysin in treatment of brain injuries. Moreover, it promises to be a useful experimental agent in further studies of many possible functional roles of GABAB receptors.

Animals↗
PubMed1996

Suppression of IFN-gamma production from Listeria monocytogenes-specific T cells by endogenously produced nitric oxide.

The induction of nitric oxide (NO) by IFN-gamma has been well documented in a variety of experimental settings, but so far there has been no report on whether the endogenously produced NO can suppress IFN-gamma production. In the present study, CD4+ T cells from Listeria monocytogenes-immune mice produced IFN-gamma upon stimulation with specific antigen and NO was generated in culture. When NG-monomethyl-L-arginine (NMMA) was added to the culture at a dose sufficient for the complete blockade of NO production, there was a significant level of enhancement of IFN-gamma production, which was also dose dependently correlated with addition of NMMA. RT-PCR revealed that IFN-gamma mRNA per given amount of total RNA remained the same irrespective of NO blockade by NMMA; however, total RNA recovery was significantly higher in the culture with NMMA. The endogenously produced NO suppressed T-cell proliferation which can be restored by the addition of NMMA. Sodium nitroprusside, a spontaneous NO generator, inhibited T-cell proliferation dose dependently and suppressed IFN-gamma production. Taken together, it may be concluded that NO down-regulates IFN-gamma production mainly by inhibiting T-cell proliferation.

Animals↗
PubMed1996

Induction of cytokine gene expression by listeriolysin O and roles of macrophages and NK cells.

To determine the role of listeriolysin O (LLO) of Listeria monocytogenes in the host response at the initial stage of infection, cytokine gene expression in mouse peritoneal exudate macrophages and spleen cells was examined by reverse transcription-PCR. Expression of various cytokine mRNAs, especially those of interleukin-1 (IL-1), tumor necrosis factor alpha, gamma interferon (IFN-gamma), and IL-12, was observed to occur in spleen cells after direct stimulation with an LLO preparation purified to a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Induction of mRNA expression by LLO was not blocked by cholesterol, which abrogated the hemolytic activity of LLO. After the depletion of NK cells in spleen cells by treatment with anti-asialo GM1 antibody plus complement, LLO-induced expression of IFN-gamma was decreased, indicating that NK cells were the main source of IFN-gamma. After depletion of macrophages by passing spleen cells over a Sephadex G-10 column, expression of macrophage-derived cytokines, including IL-1alpha, tumor necrosis factor alpha, and IL-12, was diminished. In addition, IFN-gamma mRNA expression was impaired, indicating that IFN-gamma mRNA expression from NK cells required signaling from macrophages. It is suggested that LLO is capable of inducing endogenous cytokines of mice, and both NK cells and macrophages are involved in the host cytokine response to LLO.

Animals↗
PubMed1996

The further metabolism of sorbitol-3-phosphate and fructose-3-phosphate in the mature rat lens.

Glucose and phosphorus metabolism in mature (8-month-old) rat lenses were examined with NMR spectroscopy. Nondiabetic mature lenses contained sorbitol-3-phosphate (S3P) and fructose-3-phosphate (F3P) which were absent from young (1- to 2-month-old) normal rat lenses. The concentrations of these two phosphates can be changed through (1) diabetes induction with streptozotocin - this results in a dramatic increase in both compounds; and (2) oral dosing with a drug known to prevent sorbitol production - both metabolites disappeared. When normal mature lenses were incubated in 35.5 mM 13C1-glucose, both 13C1-lactate and 13C3-lactate were produced. Preservation of the 13C label at C1 is likely through the formation of 13C1-S3P and -F3P, which were then split through an aldolase-like mechanism into two 3-carbon compounds, one an unlabeled glycerol and the other 13C1-alpha-glycerophosphate (from S3P) and 13C1-dihydroxyacetone phosphate (from F3P). These reactions can contribute to the increase in alpha-glycerophosphate observed in both the streptozotocin-induced diabetic lenses and lenses incubated in high glucose.

Aging↗
PubMed1995

Alanine-scanning mutagenesis of the epsilon subunit of the F1-F0 ATP synthase from Escherichia coli reveals two classes of mutants.

Alanine-scanning mutagenesis was applied to the epsilon subunit of the F1-F0 ATP synthase from E. coli. Nineteen amino acid residues were changed to alanine, either singly or in pairs, between residues 10 and 93. All mutants, when expressed in the epsilon deletion strain XH1, were able to grow on succinate minimal medium. Membranes were prepared from all mutants and assayed for ATP-driven proton translocation, ATP hydrolysis +/- lauryldiethylamine oxide, and sensitivity of ATPase activity to N,N'-dicyclohexylcarbodiimide (DCCD). Most of the mutants fell into 2 distinct classes. The first group had inhibited ATPase activity, with near normal levels of membrane-bound F1, but decreased sensitivity to DCCD. The second group had stimulated ATPase activity, with a reduced level of membrane-bound F1, but normal sensitivity to DCCD. Membranes from all mutants were further characterized by immunoblotting using 2 monoclonal antibodies. A model for the secondary structure of epsilon and its role in the function of the ATP synthase has been developed. Some residues are important for the binding of epsilon to F1 and therefore for inhibition. Other residues, from Glu-59 through Glu-70, are important for the release of inhibition by epsilon that is part of the normal enzyme cycle.

Adenosine Triphosphate↗
PubMed1995

Periodicity of polar and nonpolar amino acids is the major determinant of secondary structure in self-assembling oligomeric peptides.

The tendency of a polypeptide chain to form alpha-helical or beta-strand secondary structure depends upon local and nonlocal effects. Local effects reflect the intrinsic propensities of the amino acid residues for particular secondary structures, while nonlocal effects reflect the positioning of the individual residues in the context of the entire amino acid sequence. In particular, the periodicity of polar and nonpolar residues specifies whether a given sequence is consistent with amphiphilic alpha-helices or beta-strands. The importance of intrinsic propensities was compared to that of polar/nonpolar periodicity by a direct competition. Synthetic peptides were designed using residues with intrinsic propensities that favored one or the other type of secondary structure. The polar/nonpolar periodicities of the peptides were designed either to be consistent with the secondary structure favored by the intrinsic propensities of the component residues or in other cases to oppose these intrinsic propensities. Characterization of the synthetic peptides demonstrated that in all cases the observed secondary structure correlates with the periodicity of the peptide sequence--even when this secondary structure differs from that predicted from the intrinsic propensities of the component amino acids. The observed secondary structures are concentration dependent, indicating that oligomerization of the amphiphilic peptides is responsible for the observed secondary structures. Thus, for self-assembling oligomeric peptides, the polar/nonpolar periodicity can overwhelm the intrinsic propensities of the amino acid residues and serves as the major determinant of peptide secondary structure.

Amino Acid Sequence↗
PubMed1995

Phosphorylation of eukaryotic protein synthesis initiation factor 4E by insulin-stimulated protamine kinase.

Insulin-stimulated protamine kinase (cPK) and protein kinase C (PKC) phosphorylated eukaryotic protein synthesis initiation factor 4E (eIF-4E) on serine and threonine residues located on an identical tryptic fragment as judged by two-dimensional phosphopeptide mapping. With cPK and PKC, the apparent Km for eIF-4E was about 1.2 and 50 microM, respectively. Relative to recombinant human eIF-4E, cPK exhibited about 100% and < or = 5% activity with eIF-4ES209A and eIF-4ET210A, respectively, and eIF-4ES209A was phosphorylated exclusively on threonines. Bovine kidney eIF-4E enhanced up to 1.8-fold globin synthesis in m7GTP-Sepharose-treated reticulocyte lysates. In contrast, following incubation with cPK, these eIF-4E preparations stimulated globin synthesis up to 6-fold. Compared to the dephosphorylation of the cPK-modified serine on eIF-4E, reticulocyte lysates and highly purified protein phosphatase 2A exhibited marked preference for the cPK-modified threonine. The results indicate that cPK phosphorylates eIF-4E on Ser209 and Thr210, that the hydroxyl group or phosphorylation of Thr210 is necessary for cPK to act on Ser209, and that Ser209 phosphorylation activates reticulocyte globin synthesis. The results suggest that cPK could contribute to the insulin-stimulated phosphorylation of eIF-4E, but that protein phosphatase 2A may confer the site specificity of this response.

Animals↗
PubMed1995

Correlation between the presence of virulence-associated genes as determined by PCR and actual virulence to mice in various strains of Listeria spp.

Five chromosomal genes, prfA, plcA, hlyA, mpl and plcB, are implicated in the virulence of Listeria monocytogenes and some of these genes have been used for the identification of bacteria by polymerase chain reaction (PCR). Using 6 strains of L. monocytogenes and 3 L. innocua strains, the relationship was examined between the presence of five virulence-associated genes and actual virulence to mice in terms of 50% lethal dose (LD50), bacterial viability in the organ of infected mice and the intracellular growth in cultured macrophages. None of the five genes could be amplified by PCR in all the L. innocua strains and they were actually avirulent to mice. All L. monocytogenes strains were shown to be virulent and to have intact virulence-associated genes except for the strain ATCC15313. This particular strain was revealed to be avirulent and defective in hlyA and plcA in PCR amplification. It was suggested that PCR detection of genes prfA, mpl, or plcB may not be sufficient to detect virulent strains of L. monocytogenes. It appeared that the ability to produce listeriolysin O (LLO), which is encoded by hlyA, was critical for the expression of virulence regardless of the amount of LLO produced.

Animals↗
PubMed1995

Construction and plasmid-borne complementation of strains lacking the epsilon subunit of the Escherichia coli F1F0 ATP synthase.

Two strains of Escherichia coli that lack the epsilon subunit of the F1F0 ATP synthase have been constructed. They are shown to be viable but with very low growth yields (28%). These strains can be complemented by plasmids carrying wild-type uncC, but not when epsilon is overproduced. These results indicate that epsilon is not essential for growth on minimal glucose medium and that the level of its expression affects the assembly of the ATP synthase.

Base Sequence↗
PubMed1995

Brain tissue hydrolysate acts on presynaptic adenosine receptors in the rat hippocampus.

Adenosine is a potent inhibitory modulator in the brain. It suppresses glutamatergic synaptic transmission and possibly acts as a brain endogenous neuroprotective agent. In this study we have examined the effects of a clinically used porcine brain tissue hydrolysate, Cerebrolysin, on synaptic transmission in the CA1 area of rat hippocampal slices. A major effect of the drug at doses approximating those administered clinically to demented patients was a depression of synaptic transmission at the Schaffer collateral-commissural pathway in CA1. Detailed analysis showed that the inhibition is presynaptic and can be reduced by low doses of a specific blocker of adenosine A1 receptors, 8-cyclopentyltheophylline. Because Cerebrolysin does not contain a detectable amount of adenosine, the effect on adenosine A1 receptors must be indirect, perhaps by release of the endogenous agonist. This action of Cerebrolysin is consistent with a putative neuroprotective action underlying its clinical usage.

Adenosine↗
PubMed1995

[Characters and insecticidal polypeptide of a new strain of Bacillus thuringiensis subsp. kenyae in China].

A new strain of Bacillus thurinigiensis Bt with high toxicity against noctuidae larvae has been screened for many generations since isolated from larvae candle of Aphomia gularis in Yiyang County, Jiangxi Province, in China. By comparison and analysis of results of physiological and biochemical test, flagella antigen identification and esterase type, the strain is identified as H4a-4c Bt serovar. kenyae. Since its crystal protein type and plasmid type are different from those of Bt serovar. kenyae's type 023. The strain is assigned a novel strain: Btken-Ag. Btken-Ag's parasporal crystals are multi-morphorous: bipyramid, cube, small irregular sphere and embedded. After UMT dissolve, PAGE and SDS-PAGE separation preparation and analysis, it is found that its major insecticide component to Heliothis armigera is 61kD toxic protein. By ELISA homology analysis, it is found that this toxic protein has high homology with crystal protein of 023 and 7501 (H4a-4c), partly homology with that of HD-1(H3a-3b), but no homology with that of Bti(H14) and (Bacillus sphaericus) Ts-1 strain. In bioassay with larvae from Culex pipiens, Pseudaletia unipuncta and Heliothis armigera, together with other ten Bt strains, Btken-Ag is toxic to 3 star larvae of Culex pipiens; two isolates of Btken-Ag (b1-4 and H4-1) show higher toxicity than type strain 023 and HD-1 do to Pseudaletia unipuncta and Heliothis armigera.

Animals↗
PubMed1994

Autophosphorylation-activated protein kinase inactivates the protein tyrosine phosphatase activity of protein phosphatase 2A.

Phosphorylation of the catalytic subunit of protein phosphatase 2A (PP2A) on threonines with a distinct autophosphorylation-activated protein kinase [Guo and Damuni (1993) Proc. Natl. Acad. Sci. USA 90, 2500-2504] inactivated the phosphatase with 32P-labelled myelin basic protein prepared by incubation with the kinase domain of the epidermal growth factor receptor, the src-family protein kinases p56lck and p60c-src, myelin basic protein kinase-1, or protamine kinase. Phosphoamino acid analysis demonstrated that the kinase domain of the epidermal growth factor receptor, p56lck and p60c-src phosphorylated myelin basic protein on tyrosines, that the protamine kinase phosphorylated myelin basic protein on serines, and that myelin basic protein kinase-1 phosphorylated myelin basic protein on threonines. The results demonstrate that the autophosphorylation-activated protein kinase not only inactivates the protein serine/threonine phosphatase, but also the protein tyrosine phosphatase activity of PP2A. This autophosphorylation-activated protein kinase-mediated inactivation of PP2A may, in response to extracellular stimuli, not only contribute to the enhanced phosphorylation of cellular proteins on serines and threonines but also on tyrosines.

Adenosine Triphosphate↗
PubMed1994

Angiotensin II depresses glutamate depolarizations and excitatory postsynaptic potentials in locus coeruleus through angiotensin II subtype 2 receptors.

A previously reported depression of glutamate responses by angiotensin II was investigated to define the nature of this neuromodulatory effect. Studies were carried out in an vitro brain slice preparation containing the locus coeruleus, using intracellular recordings, and iontophoretic, micropressure and bath perfusion methods for application of drugs. The angiotensin action was found to be blocked by a non-peptide antagonist specific for the angiotensin type 2 receptor, and not by an antagonist selective for the type 1 receptor. Excitatory postsynaptic potentials mediated primarily by excitatory amino acids were also depressed by angiotensin II. The angiotensin II depressions of glutamate were shown to be strong and highly specific. The low effectiveness of bath-applied compared with iontophoretically or micropressure-applied angiotensin II was found to be at least partly explained by a rapid degradation by peptidases. Ammonium ions and hydrogen ions were also able to depress glutamate responses, but these effects were not specific for locus coeruleus neurons and were mediated independently of the angiotensin actions. Strong depression by angiotensin II of excitatory postsynaptic potentials as well as exogenously applied glutamate strengthens the strong possibility of a physiological role for this neuromodulatory mechanism. The identification of the type 2 angiotensin receptor subtype as the mediator of this effect indicates a novel functional role for this receptor, since previously recognized functions of angiotensin II in the brain, such as vascular and body fluid regulation, have been associated with the type 1 receptor.

Angiotensin II↗
PubMed1994

Enzyme-catalysed kinetic resolution of 4-endo-hydroxy-2-oxabicyclo[3.3.0]oct-7-en-3-one and employment of the pure enantiomers for the synthesis of anti-viral and hypocholestemic agents.

The endo-hydroxylactone (+/-)-(1) was resolved by enantioselective acetylation using Candida cylindracea lipase or preferentially Pseudomonas fluorescens lipase (pfl). Alternatively the corresponding butyrate (+/-)-(3) was hydrolysed with pfl to give the ester (+)-(1S,4R,5S)-(3) and the alcohol (-)-(1R,4S,5R)-(1). The latter compound was converted into carbovir (-)-(1R,4S)-(12) while the ester (+)-(3) was transformed into the delta-lactone (+)-(3R,5S)-(18). The exo-hydroxylactone (+/-)-(2) was resolved less efficiently by a trans-esterification process employing pfl and vinyl acetate.

Anticholesteremic Agents↗
PubMed1994

Detection of multiple virulence-associated genes of Listeria monocytogenes by PCR in artificially contaminated milk samples.

The inhibitory effect of milk in the PCR detection of Listeria monocytogenes could be overcome by washing the contaminated milk sample with phosphate-buffered saline and concentrating the bacteria to 1/10 of the original volume. In order to avoid a possible failure in the detection of virulent L. monocytogenes, a one-step procedure which enabled demonstration of three virulence-associated genes, prfA, hlyA, and plcB, simultaneously in a single PCR mixture was developed.

Animals↗
PubMed1994

Cytokine gene expression in mice at an early stage of infection with various strains of Listeria spp. differing in virulence.

By using reverse transcription-PCR, cytokine gene expression was examined in mice 24 h after infection with various strains of Listeria spp. differing in virulence as determined by in vivo growth and 50% lethal dose values. All the virulent strains of Listeria monocytogenes induced the expression of mRNAs specific for interleukin-1 alpha (IL-1 alpha), gamma interferon (IFN-gamma), and tumor necrosis factor alpha (TNF-alpha) in the spleen of mice, while an L. monocytogenes strain incapable of producing listeriolysin O and strains of Listeria innocua induced the expression of TNF-alpha mRNA only. The levels of expression of IL-1 alpha and IFN-gamma mRNAs were proportional to the levels of listeriolysin O produced by each strain. Those strains which induced the expression of IFN-gamma were capable of generating protective immunity in the infected host, suggesting that the virulence-related induction of some cytokine at the initial stage of infection plays a role in the induction of acquired cellular resistance to L. monocytogenes.

Animals↗