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Biomedical subjects

B Q Li

Publications and source records attributed to B Q Li.

At least 19 recordsLinked to original sources
PubMed2006

Combination of antagonistic yeasts with two food additives for control of brown rot caused by Monilinia fructicola on sweet cherry fruit.

AIMS: To evaluate beneficial effect of two food additives, ammonium molybdate (NH4-Mo) and sodium bicarbonate (NaBi), on antagonistic yeasts for control of brown rot caused by Monilinia fructicola in sweet cherry fruit under various storage conditions. The mechanisms of action by which food additives enhance the efficacy of antagonistic yeasts were also evaluated. METHODS AND RESULTS: Biocontrol activity of Pichia membranefaciens and Cryptococcus laurentii against brown rot in sweet cherry fruit was improved by addition of 5 mmol l(-1) NH4-Mo or 2% NaBi when stored in air at 20 and 0 degrees C, and in controlled atmosphere (CA) storage with 10% O2 + 10% CO2 at 0 degrees C. Population dynamics of P. membranefaciens in the wounds of fruit were inhibited by NH4-Mo at 20 degrees C after 1 day of incubation and growth of C. laurentii was inhibited by NH4-Mo at 0 degrees C in CA storage after 60 days. In contrast, NaBi did not significantly influence growth of the two yeasts in fruit wounds under various storage conditions except that the growth of P. membranefaciens was stimulated after storage for 45 days at 0 degrees C in CA storage. When used alone, the two additives showed effective control of brown rot in sweet cherry fruit and the efficacy was closely correlated with the concentrations used. The result of in vitro indicated that growth of M. fructicola was significantly inhibited by NH4-Mo and NaBi. CONCLUSION: Application of additives improved biocontrol of brown rot on sweet cherry fruit under various storage conditions. It is postulated that the enhancement of disease control is directly because of the inhibitory effects of additives on pathogen growth, and indirectly because of the relatively little influence of additives on the growth of antagonistic yeasts. SIGNIFICANCE AND IMPACT OF THE STUDY: The results obtained in this study suggest that an integration of NH4-Mo or NaBi with biocontrol agents has great potential in commercial management of postharvest diseases of fruit.

Ascomycota↗
PubMed2006

Effects of trehalose on stress tolerance and biocontrol efficacy of Cryptococcus laurentii.

AIMS: To investigate the effects of internal trehalose on viability and biocontrol efficacy of antagonistic yeast Cryptococcus laurentii under stresses of low temperature (LT), controlled atmosphere (CA) and freeze drying. METHODS AND RESULTS: The content of trehalose in C. laurentii was increased by culturing the yeast in trehalose-containing medium. Compared with yeast cells with low trehalose level, the yeast cells with high level of internal trehalose not only obtained higher viability, but also showed higher population and better biocontrol efficacy against Penicillium expansum on apple fruit both at 1 degrees C and in CA condition (5% O(2), 5% CO(2), 1 degrees C). After freeze drying, survival of the yeast with high trehalose level was markedly increased when stored at 25 degrees C for 0, 15 and 30 days. Meanwhile, high integrity of plasma membrane was detected in the freeze-dried yeast with high trehalose level by propidium iodide staining. CONCLUSIONS: Induced accumulation of internal trehalose could improve viability and biocontrol efficacy of C. laurentii under stresses of LT and CA. Moreover, survival of the yeast was also increased as internal trehalose accumulation after freeze drying, and one of the reasons might be that trehalose gave an effective protection to plasma membrane. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this experiment show a promising way to improve the biocontrol performance of antagonistic yeasts under the commercial conditions.

Atmosphere↗
PubMed2004

Coherent nano-area electron diffraction.

We describe the new coherent nano-area electron diffraction (NED) and its application for structure determination of individual nanostructures. The study is motivated by the challenge and the general lack of analytical techniques for characterizing nanometer-sized, heterogeneous phases. We show that by focusing electrons on the focal plane of the pre-objective lens using a 3rd condenser lens and a small condense aperture, it is possible to achieve a nanometer-sized highly parallel illumination or probe. The high angular resolution of diffraction pattern from the parallel illumination allows over-sampling and consequently the solution of phase problem based on the recently developed ab initio phase retrieval technique. From this, a high-contrast and high-resolution image can be reconstructed at resolution beyond the performance limit of the image-forming objective lens. The significance of NED for nanostructure characterization will be exemplified by single-wall carbon nanotubes and small metallic clusters. Imaging from diffraction patterns, or diffractive imaging, will be demonstrated using double-wall carbon nanotubes.

Computer Simulation↗
PubMed2004

Integrated modeling of microwave food processing and comparison with experimental measurements.

This paper presents an integrated electromagnetic and thermal model for the microwave processing offood packages. The model is developed by combining the edge finite element formulation of the 3-D vector electromagnetic field in the frequency domain and the node finite element solution of the thermal conduction equation. Both mutual and one-way coupling solution algorithms are discussed. Mutual coupling entails the iterative solution of the electromagnetic field and the thermal field, because the physical properties are temperature-dependent. The one-way coupling is applicable when the properties are temperature independent or this dependence is weak. Mesh sensitivity and shape regularity for the edge element based formulation for computational electromagnetics are discussed in light of available analytical solutions for a simple wave guide. The integrated model has been used to study the electromagnetic and thermal phenomena in a pilot scale microwave applicator with and without the food package immersed in water. The calculated results are compared with the experimentally measured data for the thermal fields generated by the microwave heating occurring in a whey protein gel package, and reasonably good agreement between the two is obtained.

Computer Simulation↗
PubMed2003

Size- and shape-dependent energetics of nanocrystal interfaces: experiment and simulation.

We study the interface energetics of Ag nanocrystals on a H-passivated Si(111) surface by a transmission electron microscopy experiment and molecular dynamics simulations. The annealed nanocrystals are oriented with Ag(111)||Si(111). Azimuthally, epitaxy is preferred for nanocrystals with an interface larger than a coincident-site-lattice (CSL) cell. The equilibrium orientation, or interface energy minimum, depends on the interface size and shape. For interfaces approaching a CSL cell in size ( approximately 2 nm nanocrystals), fluctuations of a single atom at an interface can lead to large variations in nanocrystal orientations.

Journal Article↗
PubMed2002

Nanostructure evolution during cluster growth: Ag on H-terminated Si(111) surfaces.

The size of small clusters has a large effect on cluster growth and structure. Using Ag clusters of sizes from approximately 1 to 10 nm grown on H-Si(111), we found that the cluster structure evolves in stages showing (1) irregular shapes at coverage <or=1 ML (monolayer), (2) mostly single crystal of faceted-hut-like shapes from 2 to 5 ML, and (3) defective disklike islands above 5 ML. We show that the rapid coalescence of small clusters drives the nanostructure transition and leads to a steplike growth of nanoclusters that is different from the predictions of scaling theory.

Journal Article↗
PubMed2001

The flavonoid baicalin inhibits superantigen-induced inflammatory cytokines and chemokines.

Excessive release of proinflammatory cytokines mediates the toxic effect of superantigenic staphylococcal exotoxins (SE). Baicalin, a flavone isolated from the Chinese herb Scutellaria baicalensis Georgi and used in China to treat infectious diseases, inhibited SE-stimulated T-cell proliferation (by 98%) and production of interleukin 1beta, interleukin 6, tumor necrosis factor, interferon gamma, monocyte chemotactic protein 1, macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta mRNA and protein by human peripheral blood mononuclear cells. These data suggest that baicalin may be therapeutically useful for mitigating the pathogenic effects of SE by inhibiting the signaling pathways activated by superantigens.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

The synthetic peptide WKYMVm attenuates the function of the chemokine receptors CCR5 and CXCR4 through activation of formyl peptide receptor-like 1.

The G protein-coupled 7 transmembrane (STM) chemoattractant receptors can be inactivated by heterologous desensitization. Earlier work showed that formly peptide receptor-like 1 (FPRL1), an STM receptor with low affinity for the bacterial chemotactic peptide formyl-methionyl-leucyl-phenylalamine (fMLF), is activated by peptide domains derived from the human immunodeficiency virus (HIV)-1 envelope glycoprotein gp120 and its activation results in desensitization and down-regulation of the chemokine receptors CCR5 and CXCR4 from monocyte surfaces. This study investigated the possibility of interfering with the function of CCR5 or CXCR4 as HIV-1 coreceptors by activating FPRL1. Cell lines were established expressing FPRL1 in combination with CD4/CXCR4 or CD4/CCR5 and the effect of a synthetic peptide, WKYMVm, a potent activator of formyl peptide receptors with preference for FPRL1 was determined. Both CXCR4 and CCR5 were desensitized by activation of the cells with WKYMVm via a staurosporine-sensitive pathway. This desensitization of CXCR4 and CCR5 also attenuated their capacity as the fusion cofactors for HIV-1 envelope glycoprotein and resulted in a significant inhibition of p24 production by cell lines infected with HIV-1 that use CCR5 or CXCR4 as coreceptors. Furthermore, WKYMVm inhibited the infection of human peripheral monocyte-derived macrophages and CD4(+) T lymphocytes by R5 or X4 strains of HIV-1, respectively. These results indicate that heterologous desensitization of CCR5 and CXCR4 by an FPRL1 agonist attenuates their major biologic functions and suggest an approach to the development of additional anti-HIV-1 agents. (Blood. 2001;97:2941-2947)

Antiviral Agents↗
PubMed2001

Stability of modulated-gravity-induced thermal convection in magnetic fields.

A stability analysis is presented of modulated-gravity-induced thermal convection in a heated fluid layer subject to an applied magnetic field. The nearest correction to the critical Rayleigh number for both single and multiple frequency oscillating-gravity components is obtained by solving the linearized magnetohydrodynamic equations using the small parameter perturbation technique. The correction depends on both the applied magnetic field and the oscillating frequency. In the absence of an applied magnetic field, the correction depends on the Prandtl number only when the exciting frequency is small. However, it asymptotically approaches zero as the frequency increases, with or without the presence of a magnetic field. The heated fluid layer is more stable with gravity modulation than with any type of wall temperature modulation. The difference becomes smaller with decreasing Prandtl number Pr. This finding is of critical importance in that ground-based experiments with appropriate wall temperature modulations may be conducted to simulate the oscillating-gravity effects on the onset of thermal convection in lower-Prandtl-number fluids. For conducting melts considered for microgravity applications, it is possible to apply an external magnetic field to further inhibit the onset of modulated-gravity-induced thermal convection. This effectiveness increases with the Hartmann number Ha. For large Ha, the nearest correction term R02 approximately Ha2 as the magnetic Prandtl number Pm<<1. However, R02 approximately Ha(4/3) for Ha>>1 and Pm>>1, provided that Ha<0.5pi(Pm/Pr(3/2)), which is satisfied by a majority of space melt experiments. Thus, under normal laboratory conditions applied magnetic fields are more effective in stabilizing a conducting fluid subject to an oscillating-gravity field than one subject to a constant field. If Ha>0.5pi(Pm/Pr(3/2)), R02 approximately -Ha2 for Ha>>1 and Pm>>1 and the magnetic field becomes less effective in stabilizing thermal convection driven by oscillating gravity than that driven by the constant gravity. This is in contrast with the existing studies on thermal convection stability in a magnetic field, which show that marginal stability is independent of Pm and always increases with increasing applied field.

Journal Article↗
PubMed2000

Flavonoid baicalin inhibits HIV-1 infection at the level of viral entry.

Baicalin (BA) is a flavonoid compound purified from medicinal plant Scutellaria baicalensis Georgi and has been shown to possess anti-inflammatory and anti-HIV-1 activities. In an effort to elucidate the mechanism of the anti-inflammatory effect of BA, we recently found that this flavonoid compound was able to form complexes with selected chemokines and attenuated their capacity to bind and activate receptors on the cell surface. These observations prompted us to investigate whether BA could inhibit HIV-1 infection by interfering with viral entry, a process known to involve interaction between HIV-1 envelope proteins and the cellular CD4 and chemokine receptors. We found that BA at the noncytotoxic concentrations, inhibited both T cell tropic (X4) and monocyte tropic (R5) HIV-1 Env protein mediated fusion with cells expressing CD4/CXCR4 or CD4/CCR5. Furthermore, presence of BA at the initial stage of HIV-1 viral adsorption blocked the replication of HIV-1 early strong stop DNA in cells. Since BA did not inhibit binding of HIV-1 gp120 to CD4, we propose that BA may interfere with the interaction of HIV-1 Env with chemokine coreceptors and block HIV-1 entry of target cells. Therefore, BA can be used as a basis for developing novel anti-HIV-1 agents.

Antiviral Agents↗
PubMed2000

The flavonoid baicalin exhibits anti-inflammatory activity by binding to chemokines.

Baicalin (BA) is a flavonoid compound purified from the medicinal plant Scutellaria baicalensis Georgi and has been reported to possess anti-inflammatory and anti-viral activities. In order to elucidate the mechanism(s) of action of BA, we tested whether BA could interfere with chemokines or chemokine receptors, which are critical mediators of inflammation and infection. We observed that BA inhibited the binding of a number of chemokines to human leukocytes or cells transfected to express specific chemokine receptors. This was associated with a reduced capacity of the chemokines to induce cell migration. Co-injection of BA with CXC chemokine interleukin-8 (IL-8) into rat skin significantly inhibited IL-8 elicited neutrophil infiltration. BA did not directly compete with chemokines for binding to receptors, but rather acted through its selective binding to chemokine ligands. This conclusion was supported by the fact that BA cross-linked to oxime resin bound chemokines of the CXC (stromal cell-derived factor (SDF)-1alpha, IL-8), CC (macrophage inflammatory protein (MIP)-1beta, monocyte chemotactic protein (MCP)-2), and C (lymphotactin (Ltn)) subfamilies. BA did not interact with CX3C chemokine fractalkine/neurotactin or other cytokines, such as TNF-alpha and IFN-gamma, indicating that its action is selective. These results suggest that one possible anti-inflammatory mechanism of BA is to bind a variety of chemokines and limit their biological function.

Animals↗
PubMed1999

Isoform-specific insertion near the Grb2-binding domain modulates the intrinsic guanine nucleotide exchange activity of hSos1.

Two human hSos1 isoforms (Isf I and Isf II; Rojas et al., Oncogene 12, 2291-2300, 1996) defined by the presence of a distinct 15 amino acid stretch in one of them, were compared biologically and biochemically using representative NIH3T3 transfectants overexpressing either one. We showed that hSos1-Isf II is significantly more effective than hSos1-Isf I to induce proliferation or malignant transformation of rodent fibroblasts when transfected alone or in conjunction with normal H-Ras (Gly12). The hSos1-Isf II-Ras cotransfectants consistently exhibited higher saturation density, lower cell-doubling times, increased focus-forming activity and higher ability to grow on semisolid medium and at low serum concentration than their hSos1-Isf I-Ras counterparts. Furthermore, the ratio of GTP/GDP bound to cellular p21ras was consistently higher in the hSos1-Isf II-transfected clones, both under basal and stimulated conditions. However, no significant differences were detected in vivo between Isf I- and Isf II-transfected clones regarding the amount, stability and subcellular localization of Sos1-Grb2 complex, or the level of hSos1 phosphorylation upon cellular stimulation. Interestingly, direct Ras guanine nucleotide exchange activity assays in cellular lysates showed that Isf II transfectants consistently exhibited about threefold higher activity than Isf I transfectants under basal, unstimulated conditions. Microinjection into Xenopus oocytes of purified peptides corresponding to the C-terminal region of both isoforms (encompassing the 15 amino acid insertion area and the first Grb2-binding motif) showed that only the Isf II peptide, but not its corresponding Isf I peptide, was able to induce measurable rates of meiotic maturation, and synergyzed with insulin, but not progesterone, in induction of GVBD. Our results suggest that the increased biological potency displayed by hSos1-Isf II is due to higher intrinsic guanine nucleotide exchange activity conferred upon this isoform by the 15 a.a. insertion located in proximity to its Grb2 binding region.

3T3 Cells↗
PubMed1998

Characterization of the p125 subunit of human DNA polymerase delta and its deletion mutants. Interaction with cyclin-dependent kinase-cyclins.

The catalytic subunit of human DNA polymerase (pol) delta was overexpressed in an active, soluble form by the use of a baculovirus system in insect cells. The recombinant enzyme was separated from endogenous DNA polymerases by phosphocellulose, Mono Q-Sepharose, and single-stranded DNA-cellulose chromatography. Recombinant DNA pol delta was also purified by immunoaffinity chromatography. The enzymatic properties of the purified catalytic subunit were characterized. The enzyme was active and possessed both DNA polymerase and associated 3' to 5' exonuclease activities. NH2-terminal deletion mutants retained polymerase activity, whereas the core and COOH-terminal deletion mutants were devoid of any measurable activities. Coinfection of Sf9 cells with recombinant baculovirus vectors for pol delta and cyclin-dependent kinase (cdk)-cyclins followed by metabolic labeling with 32Pi showed that the recombinant catalytic subunit of pol delta could be hyperphosphorylated by G1 phase-specific cdk-cyclins. When cdk2 was coexpressed with pol delta in Sf9 cells, pol delta was found to coimmunoprecipitate with antibodies against cdk2. Experiments with deletion mutants of pol delta showed that the NH2-terminal region was essential for this interaction. Coimmunoprecipitation and Western blot experiments in Molt 4 cells confirmed the interaction in vivo. Preliminary experiments showed that phosphorylation of the catalytic subunit of pol delta by cdk2-cyclins had little or no effect on the specific activity of the enzyme.

Animals↗
PubMed1997

Expression and characterization of the small subunit of human DNA polymerase delta.

DNA polymerase delta is a heterodimer consisting of a catalytic subunit of 125 kDa and a small subunit of 50 kDa (p50). We have overexpressed p50 in Escherichia coli and have characterized the recombinant protein. p50 was readily overexpressed using the pET vector as an insoluble protein. A procedure was developed for its purification and renaturation. Examination of the physicochemical properties of renatured p50 showed that it is a monomeric protein with an apparent molecular weight of 60,000, a Stokes radius of 34 A, and a sedimentation coefficient of 4.1 S. Its physical properties were indistinguishable from p50 expressed as a soluble protein using the pTACTAC vector. Examination of the effects of recombinant p50 on the activity of DNA polymerase delta showed that p50 is able to slightly stimulate (about 2-fold) the activity of the recombinant 125-kDa catalytic subunit using poly(dA).oligo(dT) as a template in the absence of proliferating cell nuclear antigen. In the presence of proliferating cell nulear antigen, activity is stimulated about 5-fold. Seven stable hybridoma cell lines were established that produced monoclonal antibodies against p50. One of these antibodies (13D5) inhibited the activity of calf thymus DNA polymerase delta. This antibody, when coupled to a solid support, also was found to provide a method for the immunoafffinity purification of recombinant p50 and of DNA polymerase delta from calf thymus or HeLa extracts. Immunoprecipitation and enzyme-linked immunosorbent assays also confirmed that p50 interacts with the catalytic subunit of DNA polymerase delta.

DNA Polymerase III↗
PubMed1995

Macrophage-stimulating protein activates Ras by both activation and translocation of SOS nucleotide exchange factor.

Macrophage-stimulating protein (MSP) is a chemotactic factor that activates the receptor tyrosine kinase RON. The involvement of Ras in MSP-induced signal transduction was investigated. Here we demonstrate that, in RON-transfected MDCK cells, an active GTP-bound form of Ras was rapidly accumulated by MSP treatment and the Ras-guanine nucleotide exchange activity in SOS immunoprecipitates was concomitantly increased. GAP activity was not changed under the same conditions used. Furthermore, the SH2 domain of adaptor protein GRB2, but not Shc, associated with the activated RON-beta chain, and GRB2-SOS complexes translocated from the cytosol to the membrane upon MSP treatment. These results strongly suggest that MSP activates Ras through RON, and that MSP-induced activation of Ras might be controlled by both the enhancement of catalytic exchange activity of SOS and its translocation to the membrane where its target Ras is localized.

Adaptor Proteins, Signal Transducing↗
PubMed1994

[Abnormal partograph in primipara with vertex presentation].

A prospective study on partograph (cross X type) was carried out in primipara with vertex presentation. There were 50 cases of dystocia in the study group and 50 cases of normal delivery in the control group. The results showed that the latent phase and active period of labor course in study group was significantly longer than the control group (P < 0.001). The speed of cervical dilation and descent of fetal presentation in the study group was marked slower than the control group (P < 0.001). The rate of postpartum hemorrhage, total time of labor, operative delivery rate and neonatal asphyxia rate in the study group were significantly higher than the control group (P < 0.001). After active management 38 cases in the abnormal group were delivered vaginally. It suggested that the use of partography is very important in revealing abnormal labor course and detection of dystocia, guiding the management of labor.

Adult↗