Biomedical subjects

Z Li

Publications and source records attributed to Z Li.

At least 865 records · Page 48Linked to original sources

PubMed1998

[Studies on molecular teratogenic mechanism of methylmercury in early developing rat embryos].

The present study further revealed the teratogenic mechanism of methylmercury chloride (MMC) during rat neurulation by means of nonradioactive in situ hybridization (ISH), semiquantitative analysis of immunohistochemical staining and in vivo teratogenic test. The main aim was to teat the hypothesis that iNOS, HSP70, NT, TGF-beta and Bcl-2 genes contribute to MMC-induced day 9.5 embryonic damages. Results showed there were no obvious poisoning signs and death of pregnant female rats injected intraperitoncally with 0, 0.2, 0.4, 0.8, 1.6 and 3.2 mg/kg MMC. While the doses increased, the total morphological scores decreased gradually, and the rates of embryo deformity and development delay increased step by step to 34% and 76% respectively. The levels of iNOS mRNA and protein and HSP70 mRNA increased, and NT mRNA with its protein became down, all these changes were concentration dependent. In addition, MMC could inhibit the level of TGF-beta mRNA, but no obvious influence on the levels of Bcl-2 mRNA and Bcl-2 protein. On the basis of parallel findings from embryos, genes and proteins, abnormal expression of genes in transcriptional level might be related to MMC-induced teratogenic insult.

Animals↗

PubMed1998

[Effects of different zinc level diets and heat exposure on the contents of Zn, Cu and Fe in brains of rats].

Forty-eight SD male rats were randomly divided into group A, B and C. Rats in each group were also divided into 2 parts. One part was used for heat exposure and the other was used for room temperature control. On the basis of AIN-93 m diet composition, group A, B and C zinc diets were prepared by adding or reducing zinc carbonate. Zinc contents of group A, B and C zinc diet per kilogram were 92.2 mg, 45.61 mg and 21.70 mg respectively. 14 days later the rats were exposed to high temperature (Tdb 40 degrees C, Twb 30.8 degrees C) for 3 hours. The Contents of Zn, Cu and Fe in hippocampus, cerebral cortex and cerebellum of rats were determined by atomic absorption spectrophotometer. The results revealed that 1. hyperthermal exposure could increase Cu content in rat hippocampus significantly, 2. after heat exposure, Cu content in hippocampus was higher than in cerebral cortex and cerebellum. Cu contents in cerebellum of room temperature control rat were higher than cerebral cortex and hippocampus, 3. intakes of different zinc level diets chiefly influenced content of Cu rat cerebellum and slightly affected iron content in it, 4. high, middle level zinc diet intake could reduce Cu content in heat-stressed rat cerebellum.

Animals↗

PubMed1998

Solid-phase synthesis of potential protein tyrosine phosphatase inhibitors via the Ugi four-component condensation.

A library of 108 alpha,alpha-difluoromethylenephosphonic acids was prepared by Ugi four-component condensation using Rink-NH2 resin, 4-[(diethoxyphosphinyl) difluoromethyl]benzoic acid, and a set of 18 aldehydes and 6 isonitriles. Following resin cleavage, the diethylphosphonate esters were hydrolyzed with trimethylsilyl bromide to yield the free acids which were assayed for inhibition of PTP alpha, PTP beta and PTP epsilon.

Aldehydes↗

PubMed1998

MyoD, myogenin, and desmin-nls-lacZ transgene emphasize the distinct patterns of satellite cell activation in growth and regeneration.

Although satellite cell differentiation is involved in postnatal myogenesis from growth to posttrauma regeneration, the early stages of this process remain unclear. This study investigated pHuDes-nls-lacZ transgene activity, as revealed by X-gal staining and the accumulation of MyoD, myogenin, endogenous desmin, and myosin, in order to determine whether satellite cells share the same activation program during growth and regeneration. After birth, skeletal myonuclei in which myogenin expression was limited were briefly characterized by transgene activity. Satellite cells were only evidenced by MyoD and slow myosin accumulation, but failed to initiate transgene expression. After freeze trauma, satellite cell activation led to MyoD, myogenin, and desmin expression. Subsequently, when myosin expression occurred, transgene activation was apparent in regenerating structures, with more intense X-gal staining in mononucleated cells than regenerating myotubes. After the second week posttrauma, only desmin and myogenin expression were maintained in regenerating structures. In culture, the behavior of satellite cells showed that desmin expression was committed before transgene activation occurred, i.e., concurrently with MyoD, myogenin, myosin expression, and the first fusion events. Quantitative analysis confirmed the discrepancy between endogenous desmin and transgene expression and demonstrated the close correlation between transgene activation and the fusion index. Our results strongly suggest that satellite cells promote distinct pathways of myogenic response during growth and regeneration.

Animals↗

PubMed1998

Identification and analysis of PH domain-containing targets of phosphatidylinositol 3-kinase using a novel in vivo assay in yeast.

Phosphatidylinositol 3-kinase (PI3K) mediates a variety of cellular responses by generating PtdIns(3,4)P2 and PtdIns(3,4,5)P3. These 3-phosphoinositides then function directly as second messengers to activate downstream signaling molecules by binding pleckstrin homology (PH) domains in these signaling molecules. We have established a novel assay in the yeast Saccharomyces cerevisiae to identify proteins that bind PtdIns(3,4)P2 and PtdIns(3,4,5)P3 in vivo which we have called TOPIS (Targets of PI3K Identification System). The assay uses a plasma membrane-targeted Ras to complement a temperature-sensitive CDC25 Ras exchange factor in yeast. Coexpression of PI3K and a fusion protein of activated Ras joined to a PH domain known to bind PtdIns(3,4)P2 (AKT) or PtdIns(3,4,5)P3 (BTK) rescues yeast growth at the non-permissive temperature of 37 degreesC. Using this assay, we have identified several amino acids in the beta1-beta2 region of PH domains that are critical for high affinity binding to PtdIns(3,4)P2 and/or PtdIns(3,4,5)P3, and we have proposed a structural model for how these PH domains might bind PI3K products with high affinity. From these data, we derived a consensus sequence which predicts high-affinity binding to PtdIns(3, 4)P2 and/or PtdIns(3,4,5)P3, and we have identified several new PH domain-containing proteins that bind PI3K products, including Gab1, Dos, myosinX, and Sbf1. Use of this assay to screen for novel cDNAs which rescue yeast at the non-permissive temperature should provide a powerful approach for uncovering additional targets of PI3K.

Amino Acid Sequence↗

PubMed1998

Molecular and pharmacological characterization of recombinant rat/mice N-methyl-D-aspartate receptor subtypes in the yeast Saccharomyces cerevisiae.

The genes encoding the ionotropic N-methyl-D-aspartate (NMDA) receptor subunits NR1a, NR2B and NR2D were cloned in the multi-copy yeast-Escherichia coli shuttle vectors pMBO1 and pMB02. The protease-deficient yeast Saccharomyces cerevisiae c13-ABYS-86 (leu-, ura-, his-) was transformed with the recombinant plasmids pMBNR1a (leu+), pMBNR1a/pMBNR2D (ura+), pMBNR1a/pMBNR2D/ pMBNR2B (his+) or pMBNR1a/pMBNR2A/pMBNR2B, respectively, and was used to express the different NMDA receptor subunit genes. Western-blotting analysis with the specific NMDA receptor antibodies showed a clear but differently strong expression of the recombinant receptor proteins which were found to be only partially glycosylated in the cell membranes of the recombinant yeast strains. By immunofluorescence microscopy using the specific subunit antibodies and fluorescence-labeled secondary antibodies, the distinctly expressed NR1a and NR2D subunits could be located in the plasma membrane of the transformed yeast cells. Pharmacological characterization of crude membrane preparations of the recombinant yeast cells expressing 1-3 NMDA receptor subunits showed saturable binding of the glycine antagonist [3H]MDL105,519 with different Kd values of 56.88+/-5.38 nM (NR1a), 1365.11+/-76 nM (NR1a/NR2D), 22.97+/-3.37 nM for NR1a/NR2B/NR2D and 7.4+/-1.2 nM for NR1a/NR2A/NR2B. The bound capacities were 13.07+/-0.92 (NRla), 14.63+/-0.50 (NR1a/NR2D), 12.85+/-1.68 (NR1a/NR2B/NR2D) and 8.3+/-0.7 (NR1a/NR2A/NR2B) pmol/mg membrane protein. The [3H]MDL105,519 binding was inhibited by the glycine antagonist 5,7-dichlorokynurenate (DCKA), ethyl-2-carboxy-4.6-dichloro-3-indoleacetate (ECDI) and itself, but not by glycine, D-serine and 1-amino-cyclopropanecarboxylic acid (ACPC). Each of these recombinant receptor proteins consisting both of NR1 and NR2 subunits also showed a specific binding site for the NMDA agonist glutamate when using L-[3H]glutamate as a radioligand. Analysis of saturation experiments revealed that this ligand binds to a specific site with Kd values of 536+/-43, 688+/-60, and 856+/-48 nM for NR1a/NR2B, NR1a/NR2D, and NR1a/NR2B/NR2D respectively.

Animals↗

PubMed1998

Overexpression of the large subunit of the protein Ku suppresses metallothionein-I induction by heavy metals.

Metallothioneins (MT) are involved in the scavenging of the toxic heavy metals and protection of cells from reactive oxygen intermediates. To investigate the potential role of the protein Ku in the expression of MT, we measured the level of MT-I mRNA in the parental rat fibroblast cell line (Rat 1) and the cell lines that stably and constitutively overexpress the small subunit, the large subunit, and the heterodimer of Ku. Treatment with CdS04 or ZnS04 elevated the MT-I mRNA level 20- to 30-fold in the parental cells and the cells (Ku-70) that overproduce the small subunit or those (Ku-7080) overexpressing the heterodimer. By contrast, the cells (Ku-80) overexpressing the large subunit of Ku failed to induce MT-I. In vitro transcription assay showed that the MT-I promoter activity was suppressed selectively in the nuclear extracts from Ku-80 cells. The specificity of the repressor function was shown by the induction of hsp 70, another Cd-inducible gene, in Ku-80 cells. Addition of the nuclear extract from Ku-80 cells at the start of the transcription reaction abolished the MT-l promoter activity in the Rat 1 cell extract. The transcript once formed in Rat 1 nuclear extract was not degraded by further incubation with the extract from Ku-80 cells. The repressor was sensitive to heat. The DNA-binding activities of at least four transcription factors that control the MT-I promoter activity were not affected in Ku-80 cells. These observations have set the stage for further exploration of the mechanisms by which the Ku subunit mediates suppression of MT induction.

Animals↗

PubMed1998

Neutralizing antibodies administered before, but not after, virulent SHIV prevent infection in macaques.

By subcutaneous inoculation of SHIV(KU-2) in the hands of macaques, we developed a model of human immunodeficiency virus type-1 (HIV-1) occupational infection due to needle-stick injury and used the model to determine whether neutralizing serum to SHIV administered before or after virus inoculation could either prevent or abort infection, respectively. Six rhesus macaques were given 15 ml/kg pooled anti-SHIV plasma and challenged 24 hr later with approximately 300 animal infectious doses of SHIV(KU-2), subcutaneously. Three of the six macaques completely resisted infection with SHIV(KU-2). A fourth animal failed to yield infectious virus, but DNA extracted from its peripheral blood mononuclear cells (PBMC) and lymph nodes had viral sequences. Partial resistance was noted in the other two animals because virus recovery was delayed compared with the control animals. In contrast, six of six macaques given the same dose of anti-SHIV plasma 18 hr after exposure to virus became infected, as did two of two macaques given anti-SHIV plasma only 2 hr after exposure to virus. Our results suggest that neutralizing antibodies may have a prophylactic but not a therapeutic role in HIV-1 infections.

Animals↗

PubMed1998

Failure of SIVmac to be neutralized in macrophage cultures is unique to SIVmac and not observed with neutralization of SHIV or HIV-1.

Except during acutely lethal infection, macaques infected with SIVmac251 produce antibodies that neutralize the virus in CEMx174 cells, macaque PBMC and macrophage cultures. In a previous report, we had shown that whereas neutralization of the SIVmac251 was complete in lymphocyte cultures, "protected" macrophages had actually become latently infected, and remained viral DNA-positive, but the infection was nonproductive as long as antibodies were maintained in the medium. Removal of the antibodies as long as 1 week later, resulted in resurgence of virus replication. In the present study, we compared neutralization of SIVmac239 with that of neutralization of SHIV and HIV-1, and sought to determine whether the failure to prevent infection in macrophages was also typical of neutralization of SHIV and HIV-1 in macaque and human macrophage cultures, respectively. The results showed that similar to SIVmac251, neutralizing antibodies did not block SIVmac239 infection in macaque macrophages, although they blocked infection of the virus in T cells. The data from neutralization of SHIV using anti-SHIV antibodies and for neutralization of HIV-1 (89.6 and Bal) using anti-HIV IgG in both T cells and macrophages, however, can be summarized with a single statement: neutralization of SHIV and HIV-1 was complete in all of the cultures, with no evidence of establishment of latent infection in or resurgence of virus replication after antibodies were removed from macrophage cultures. The non-neutralizability of SIVmac (251 and 239) in macrophages is therefore unique to the SIVmac and not relevant to neutralization of HIV-1.

Animals↗

PubMed1998

Characterization of Structural and Surface Properties of Activated Carbon Fibers.

Nitrogen adsorption isotherms on activated carbon fibers (ACFs) were measured at 77.3 K in the relative pressure range from 10(-7) to 0.995. The low relative pressure data are examined in detail in order to characterize the microporosity and the surface heterogeneity of the samples studied. The pore structure of ACFs was studied by using the alphas plot and DFT methods. Adsorption potential and adsorption energy distributions were also calculated. The results showed that ACFs are highly microporous and in some cases contain small mesopores (2-4 nm). ACFs exhibit a significant structural and energetic heterogeneity. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

In vivo phosphorylation of cardiac troponin I by protein kinase Cbeta2 decreases cardiomyocyte calcium responsiveness and contractility in transgenic mouse hearts.

Recently, it has been reported that the protein kinase C (PKC) beta isoform plays a critical role in the development of hypertrophy and heart failure. The purpose of the present study was to clarify the mechanism by which activation of PKCbeta led to depressed cardiac function. Thus, we used a PKCbeta2 overexpressing mouse, an animal model of heart failure, to examine mechanical properties and Ca2+ signals of isolated left ventricular cardiomyocytes. The percentage of shortening, rate of shortening, and rate of relengthening of cardiomyocytes were markedly reduced in PKCbeta2 overexpression mice compared to wild-type control mice, although the baseline level and amplitude of Ca2+ signals were similar. These findings suggested a decreased myofilament responsiveness to Ca2+ in transgenic hearts. Therefore, the incorporation of [32P] inorganic phosphate into cardiac myofibrillar proteins was studied in Langendorff-perfused hearts. There was a significant increase in the degree of phosphorylation of troponin I in PKCbeta2-overexpressing transgenic mice. The depressed cardiomyocyte function improved after the superfusion of a PKCbeta selective inhibitor. These findings indicate that in vivo PKCbeta2-mediated phosphorylation of troponin I may decrease myofilament Ca2+ responsiveness, and thus causes cardiomyocyte dysfunction. Since chronic and excess activation of PKCbeta2 plays a direct and contributory role in the progression of cardiac dysfunction, the PKCbeta selective inhibitor may provide a new therapeutic modality in the setting of heart failure.

Animals↗

PubMed1998

The vacB gene required for virulence in Shigella flexneri and Escherichia coli encodes the exoribonuclease RNase R.

vacB, a gene previously shown to be required for expression of virulence in Shigella and enteroinvasive Escherichia coli, has been found to encode the 3'-5' exoribonuclease, RNase R. Thus, cloning of E. coli vacB led to overexpression of RNase R activity, and partial deletion or interruption of the cloned gene abolished this overexpression. Interruption of the chromosomal copy of vacB eliminated endogenous RNase R activity; however, the absence of RNase R by itself had no effect on cell growth. In contrast, cells lacking both RNase R and polynucleotide phosphorylase were found to be inviable. These data indicate that RNase R participates in an essential cell function in addition to its role in virulence. The identification of the vacB gene product as RNase R should aid in understanding how the virulence phenotype in enterobacteria is expressed and regulated. On the basis of this information we propose that vacB be renamed rnr.

Bacterial Proteins↗

PubMed1998

A neural model of contour integration in the primary visual cortex.

Experimental observations suggest that contour integration may take place in V1. However, there has yet to be a model of contour integration that uses only known V1 elements, operations, and connection patterns. This article introduces such a model, using orientation selective cells, local cortical circuits, and horizontal intracortical connections. The model is composed of recurrently connected excitatory neurons and inhibitory interneurons, receiving visual input via oriented receptive fields resembling those found in primary visual cortex. Intracortical interactions modify initial activity patterns from input, selectively amplifying the activities of edges that form smooth contours in the image. The neural activities produced by such interactions are oscillatory and edge segments within a contour oscillate in synchrony. It is shown analytically and empirically that the extent of contour enhancement and neural synchrony increases with the smoothness, length, and closure of contours, as observed in experiments on some of these phenomena. In addition, the model incorporates a feedback mechanism that allows higher visual centers selectively to enhance or suppress sensitivities to given contours, effectively segmenting one from another. The model makes the testable prediction that the horizontal cortical connections are more likely to target excitatory (or inhibitory) cells when the two linked cells have their preferred orientation aligned with (or orthogonal to) their relative receptive field center displacements.

Feedback↗

PubMed1998

Determination of the amino acid neurotransmitters in the dorsal root ganglion of the rat by capillary electrophoresis with a laser-induced fluorescence-charge coupled device.

A sensitive, rapid and accurate analysis of the amino acid neurotransmitters in dorsal root ganglion (DRG) of rat was accomplished by capillary electrophoresis with a laser-induced fluorescence-charged coupled device (LIF-CCD) and fluorescein isothiocyanate (FITC) derivatization. Since the CCD is an image detector with a matrix array of photoelements, the photogenerated charge generated from single photoelements was summed up by on-chip charge binning, and used to improve the detection sensitivity. A self-compiled data processing program was used to calculate digitally the summation of the multiwavelength data and transform three-dimensional electropherograms into two-dimensional electropherograms. Use of this program improved the detection sensitivity, the extraction of useful statistical data and the performance of the quantitative analysis. Owing to its excellent detectability and the unique characteristic of its two-dimensional format, which allows to perform analog and digital summation, high detection sensitivity with detection limits ranging from 1.2 to 17.2 nM was obtained for the amino acid neurotransmitters by LIF-CCD. This method was demonstrated to be a powerful tool for analyzing the complex biological samples through quantitative determination of the six amino acid neurotransmitters in the DRG of rat.

Animals↗

PubMed1998

[The detection and isolation of fetal nucleated erythrocytes from maternal blood using flow cytometry].

OBJECTIVE: To isolate fetal nucleated red blood cells (NRBCs) from maternal blood and to confirm its fetal origin. METHODS: Monoclonal antibody against the glycophorin A (GPA) was used to identify nucleated erythrocytes in the peripheral blood of pregnant women. Candidates fetal cells from 3 pregnancies at 16 to 24 weeks of gestation were isolated successfully. Sorted cells were also confirmed using Y-special probe (PY3.4) repeated sequences (SRY) in maternal blood from women carrying male fetuses were detected by polymerase chain reaction (PCR). RESULTS: The PY3.4 position hybridization rates were 31.5%, 0 and 38% respectively in sorted GPA positive cells (GPA+)of 3 samples by FISH, and the results of GPA+ cells of the 3 cases by PCR were positive, negative and positive respectively, which were manifested by the gender after aborticide. CONCLUSION: This study demonstrates that fetal NRBCs are present in the peripheral blood of pregnant women and it is possible to isolate and detect them.

Erythrocytes↗

PubMed1998

Optimized dose distribution of a high dose rate vaginal cylinder.

PURPOSE: To present a comparison of optimized dose distributions for a set of high-dose-rate (HDR) vaginal cylinders calculated by a commercial treatment-planning system with benchmark calculations using Monte-Carlo-calculated dosimetry data. METHODS AND MATERIALS: Optimized dose distributions using both an isotropic and an anisotropic dose calculation model were obtained for a set of HDR vaginal cylinders. Mathematical optimization techniques available in the computer treatment-planning system were used to calculate dwell times and positions. These dose distributions were compared with benchmark calculations with TG43 formalism and using Monte-Carlo-calculated data. The same dwell times and positions were used for a quantitative comparison of dose calculated with three dose models. RESULTS: The isotropic dose calculation model can result in discrepancies as high as 50%. The anisotropic dose calculation model compared better with benchmark calculations. The differences were more significant at the apex of the vaginal cylinder, which is typically used as the prescription point. CONCLUSION: Dose calculation models available in a computer treatment-planning system must be evaluated carefully to ensure their correct application. It should also be noted that when optimized dose distribution at a distance from the cylinder surface is calculated using an accurate dose calculation model, the vaginal mucosa dose becomes significantly higher, and therefore should be carefully monitored.

Brachytherapy↗

PubMed1998

Phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P3)/Tec kinase-dependent calcium signaling pathway: a target for SHIP-mediated inhibitory signals.

Tec family non-receptor tyrosine kinases have been implicated in signal transduction events initiated by cell surface receptors from a broad range of cell types, including an essential role in B-cell development. A unique feature of several Tec members among known tyrosine kinases is the presence of an N-terminal pleckstrin homology (PH) domain. We directly demonstrate that phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P3) interacting with the PH domain acts as an upstream activation signal for Tec kinases, resulting in Tec kinase-dependent phospholipase Cgamma (PLCgamma) tyrosine phosphorylation and inositol trisphosphate production. In addition, we show that this pathway is blocked when an SH2-containing inositol phosphatase (SHIP)-dependent inhibitory receptor is engaged. Together, our results suggest a general mechanism whereby PtdIns-3,4,5-P3 regulates receptor-dependent calcium signals through the function of Tec kinases.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed1998

Btk/Tec kinases regulate sustained increases in intracellular Ca2+ following B-cell receptor activation.

Bruton's tyrosine kinase (Btk) is essential for B-lineage development and represents an emerging family of non-receptor tyrosine kinases implicated in signal transduction events initiated by a range of cell surface receptors. Increased dosage of Btk in normal B cells resulted in a striking enhancement of extracellular calcium influx following B-cell antigen receptor (BCR) cross-linking. Ectopic expression of Btk, or related Btk/Tec family kinases, restored deficient extracellular Ca2+ influx in a series of novel Btk-deficient human B-cell lines. Btk and phospholipase Cgamma (PLCgamma) co-expression resulted in tyrosine phosphorylation of PLCgamma and required the same Btk domains as those for Btk-dependent calcium influx. Receptor-dependent Btk activation led to enhanced peak inositol trisphosphate (IP3) generation and depletion of thapsigargin (Tg)-sensitive intracellular calcium stores. These results suggest that Btk maintains increased intracellular calcium levels by controlling a Tg-sensitive, IP3-gated calcium store(s) that regulates store-operated calcium entry. Overexpression of dominant-negative Syk dramatically reduced the initial phase calcium response, demonstrating that Btk/Tec and Syk family kinases may exert distinct effects on calcium signaling. Finally, co-cross-linking of the BCR and the inhibitory receptor, FcgammaRIIb1, completely abrogated Btk-dependent IP3 production and calcium store depletion. Together, these data demonstrate that Btk functions at a critical crossroads in the events controlling calcium signaling by regulating peak IP3 levels and calcium store depletion.

Agammaglobulinaemia Tyrosine Kinase↗