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Biomedical subjects

B Xu

Publications and source records attributed to B Xu.

At least 307 records · Page 17Linked to original sources
PubMed1994

Expression of organophosphate hydrolase in the filamentous fungus Gliocladium virens.

The broad-spectrum organophosphate hydrolase (OPH; EC 3.1.8.1) encoded by the organophosphate-degrading gene (opd) from Pseudomonas diminuta MG and Flavobacterium sp. ATCC 27551 possesses capabilities of both P-O bond hydrolysis (e.g. paraoxon) and P-F bond hydrolysis [e.g. sarin and diisopropylfluorophosphate (DFP)]. In the present study a 9.4-kb plasmid, pCL1, was used to transform the saprophytic fungus Gliocladium virens. pCL1 was derived from pJS294 by placing the fungal promoter (prom1) from Cochliobolus heterostrophus upstream and the trpC terminator from Aspergillus nidulans down-stream of the opd gene. Southern analysis of restricted genomic DNA from various transformants indicated that integration occurred non-specifically at multiple sites. Western blot analysis of mycelial extracts from transformants confirmed the production of a processed form of the enzyme in the fungus. Maximal levels of OPH activity (rate of p-nitrophenol production from paraoxon) were observed after 168 h of culture and activity levels correlated with biomass production in mature vegetative growth.

Blotting, Southern↗
PubMed1994

Protein kinase A-regulated Cl- channel in ML-1 human hematopoietic myeloblasts.

Using the inside-out patch clamp technique, we identified a Cl- channel in patches from the membrane of cultured human hematopoietic myeloblastic leukemia ML-1 cells. The Cl- channel was not seen at negative membrane potentials in excised patches until the membrane potential was depolarized to greater than +40 mV. The channel was also activated by addition of cAMP-dependent protein kinase (PKA) catalytic subunit at physiological membrane potential (-40 mV). Biophysical studies of the Cl- channel revealed that the current-voltage (I-V) relationship of the Cl- channel was outwardly rectifying in symmetrical 142 mM Cl- solutions. Single channel conductances were 48 pS for the outward current measured at +60 mV and 27 pS for the inward current at -60 mV. The open time constant of the channel was dependent on the membrane potential and was significantly prolonged at positive membrane potentials. Channels activated by cAMP-dependent protein kinase spent a significantly longer time in the open state compared to those channels activated by depolarization pulses. Pharmacological properties of the Cl- channel were also studied. Two anion transport inhibitors, anthracene-9-carboxylic acid (9-AC) and 4,4-diisothiocyanatostilbene-2,2-disulfonic acid (DIDS) caused a flickering block of the channel. Half-inhibitory concentrations (IC50) for 9-AC and DIDS were 174 +/- 20 and 70 +/- 16 microM, respectively. Blockade of the Cl- channel by 9-AC or DIDS was completely reversible. Our findings suggest that outwardly rectifying Cl- channels (ORCC) are present in human hematopoietic myeloblasts. The function of ORCC may be involved in hormone-regulated cell growth, cell volume regulation and immune responses.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Concentrations of cadmium, lead, selenium, and zinc in human blood and seminal plasma.

The concentrations of cadmium, lead, selenium, and zinc in blood and seminal plasma were determined in 76 Singapore males. Except for zinc, the concentrations were generally higher in blood than in seminal plasma (cadmium, 1.31 micrograms/L vs 0.61 micrograms/L; lead, 82.6 micrograms/L vs 12.4 micrograms/L, and selenium, 163.6 micrograms/L vs 71.5 micrograms/L). The mean concentration of zinc in seminal plasma was more than 30 times higher than in blood (202 mg/L vs 6.2 mg/L). Significant positive correlations were found between the concentrations in blood and seminal plasma for the two essential trace elements: selenium (r = 0.45, p < 0.001) and zinc (r = 0.25, p < 0.05). However, no relationships were found between the concentrations in blood and seminal plasma for two toxic metals (cadmium and lead). Significant inverse correlations were observed between Cd and Zn (r = -0.40, p < 0.01), and Pb and Se (r = -0.32, p < 0.05) in blood, whereas significant positive correlations were noted between Cd and Se (r = 0.45, p < 0.01), Cd and Zn (r = 0.35, p < 0.05), and Se and Zn (r = 0.57, p < 0.001) in seminal plasma. The physiological significance of these relationships are also discussed in this paper.

Adult↗
PubMed1994

The forever young gene encodes an oxidoreductase required for proper development of the Arabidopsis vegetative shoot apex.

In plant development, leaf primordia are formed on the flanks of the shoot apical meristem in a highly predictable pattern. The cells that give rise to a primordium are sequestered from the apical meristem. Maintenance of the meristem requires that these cells be replaced by the addition of new cells. Despite the central role of these activities in development, the mechanism controlling and coordinating them is poorly understood. These processes have been characterized in the Arabidopsis mutant forever young (fey). The fey mutation results in a disruption of leaf positioning and meristem maintenance. The predicted FEY protein shares significant homology to a nodulin and limited homology to various reductases. It is proposed that FEY plays a role in communication in the shoot apex through the modification of a factor regulating meristem development.

Amino Acid Sequence↗
PubMed1994

Sex differences of infant and child mortality in China.

The purpose of this paper was to study the sex differences in infant mortality and mortality before the age of 5 in China, and the differences between urban and rural areas on the one hand and urban areas of mainland China and Hong Kong on the other. Published data from the 1982 and 1990 national censuses, the mortality survey of 1976, and UN's publications were used to calculate sex differences and sex ratios of mortality. Infant mortality of both sexes decreased notably from the 1970's onwards, the sex ratios of mortality being 1.15 in 1973-75, 1.06 in 1981 and 0.86 in 1990. A remarkable decline of mortality before the age of 5 was also seen in both sexes, but the sex ratios of mortality were not greatly altered, remaining less than 1 from the 1970's on. In rural areas female infants and young children had a higher mortality compared with males than in urban areas. In Hong Kong, the sex differences of infant and early child mortality were much smaller than in urban areas of mainland China.

Child, Preschool↗
PubMed1994

Role of galanin in stimulation of pituitary luteinizing hormone secretion as revealed by a specific receptor antagonist, galantide.

In this study, a specific galanin (GAL) receptor antagonist, galantide, was employed to evaluate the role of endogenous GAL in episodic basal and phasic LH release in rats. To assess the specificity of galantide, a series of experiments was performed. In the first experiment, we observed that administration of GAL (0.62 nm) intracerebroventricularly (icv) in ovarian steroid-primed ovariectomized (ovx) rats rapidly increased plasma LH levels between 10-30 min, and prior injection of galantide icv (5 nm) blocked the GAL-induced LH release. In the second experiment, galantide inhibited the GAL-evoked in vitro release of LHRH from the median eminence-arcuate nucleus (ME-ARC) of ovarian steroid-primed ovx rats. In addition, galantide on its own significantly decreased the basal efflux of LHRH from the ME-ARC of similarly treated rats, thereby suggesting that even the basal LHRH secretion may be a GAL-dependent event. In the third experiment, the effects of galantide on the phasic LH surge elicited by progesterone (P) in estradiol benzoate-primed ovx rats and that occurring spontaneously on proestrus were examined. Ovx rats bearing icv cannulae were primed with estradiol benzoate (30 micrograms/rat, sc) and 2 days later received a P (2 mg/rat, sc) injection at 1000 h to evoke a LH surge in the afternoon. Galantide (1 or 5 nm) in 3 microliters saline or saline was injected icv at 1300, 1400, and 1500 h. The results showed that the two dosages of galantide suppressed the LH surge in the afternoon. On the other hand, only a very high dose of galantide (15 nm) injected iv at 1300, 1400, and 1500 h blunted the P-induced LH hypersecretion. Central injections of galantide (1 or 5 nm) at 1300, 1400, and 1500 h on proestrus also inhibited the preovulatory LH surge and significantly reduced the numbers of rats ovulating the following day. In the final experiment, the role of GAL receptors in modulation of episodic LH release was analyzed in ovx rats. The results showed that an injection of galantide (5 nm, icv) significantly decreased both the mean LH levels and the amplitude of LH episodes during the 3-h observation period. Cumulatively, these results show that normally GAL stimulates LHRH release by activation of a specific receptor located in the ME-ARC, and that GAL may be a key excitatory signal in the hypothalamic neural circuitry involved in the regulation of basal episodic and phasic LHRH secretion in cycling female rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Functional expression of a mouse growth hormone receptor cDNA in transfected mouse L cells.

A cDNA encoding a full-length mouse (m) growth hormone receptor (GHR) derived from 3T3 F442A cells was amplified by RT-PCR and cloned into a mammalian expression vector. A mouse L cell line (mGHR1.6), which expresses high levels of full-length mGHR, was established. A mGHR-specific mRNA of approx 2.8 kb was found in these cells. Ligand binding studies showed that mGHR 1.6 cells were capable of binding 125I-hGH with a dissociation constant (Kd) of 2.9 +/- 0.13 nM. Scatchard analysis indicated that mGHR1.6 cells had only a single class of mGHR and possessed approx 128,000 GH specific binding sites per cell. Affinity crosslinking studies showed that the recombinant mGHR possessed an apparent molecular mass of 105 kDa. In addition, mGHR1.6 cells responded to growth hormones (GHs) from several species. Two proteins, pp92 and pp95, were found to be tyrosyl phosphorylated following GH treatment. An hGH antagonist, hGH-G120R, inhibited GH-induced phosphorylation of both pp92 and pp95 in a dose-dependent manner. This cell line may be used as an in vitro model in the studies of GH signal transduction and in the screening of GH analogs for biological activity.

3T3 Cells↗
PubMed1994

Gamma-IFN induced cell adhesion in chronic myelogenous leukemia cells.

Both gamma- and alpha-interferons (IFNs) have been shown to induce clinical responses in chronic myelogenous leukemia (CML). The mechanisms behind these effects are not known. In chronic phase CML, granulocytic progenitors normally found in the bone marrow only, are found extramedullary. A defect in the adhesion of CML cells, that may be responsible for this finding, has been described earlier. In this study, we have investigated whether IFN can restore the defect in CML cell adhesion. It was found that gamma-, but not alpha-IFN, strongly induced the adhesion of CML cells to other cells and to plastic in a majority of the patients. In parallel, an induction in the expression of the adhesion molecules ICAM-1 and LFA-1 was found, and blocking of these molecules by antibodies abolished the effect. The ability of gamma-IFN to restore the adhesive property of CML cells may add to the antitumor effects observed with gamma-IFN therapy in CML.

2',5'-Oligoadenylate Synthetase↗
PubMed1994

Malaria in Hubei Province, China: approaching eradication.

In the last six years, there has been a steady reduction of Plasmodium vivax malaria in Hubei Province with an API (annual parasite incidence) of 0.134 per thousand by 1992. This is especially so in the south, east, west and north-west parts of the province. Much of this reduction has been produced by a policy of repeated radical treatment in the non-malaria season. In the centre of Hubei, where Anopheles anthropophagus is the chief vector, malaria is still a problem. The key factors in destabilizing malaria are a sudden increase in the number of An. anthropophagus, introduction of non-immunes into the endemic area, and the village doctors' diminished interest in malaria surveillance activities. Impregnated bed nets are possibly the best strategy for reducing malaria, but where the prevalence is reduced to a sufficiently low level efficient case finding and detection are able to contain malaria and produce a continued reduction.

Animals↗
PubMed1994

Antitumor effect of alpha isomer of anordrin in vitro and cell cycle arrest at G1 phase.

Alpha isomer of anordrin (2 alpha, 17 alpha-diethyl-A-norandrostane-2 beta, 17 beta-diol dipropionate, alpha-Ano) inhibited mouse hepatoma (Hep A) and P388 cell growth in vitro. alpha-Ano (20 micrograms.ml-1) inhibited the incorporation of [3H]uridine and [3H]thymidine into RNA and DNA within 3 h, but the inhibition of L-[3H]lysine incorporating into protein was not obvious. alpha-Ano had no effect on the DNA-dependent RNA synthesis with purified nuclei of Hep A cells. It is suggested that the inhibition of RNA and DNA syntheses is the major cause of the cytostatic effect. alpha-Ano blocked the P388 cells at G1/G0 phase, and the delay in G1/G0 to S phase transition plays an important role in the inhibition of P388 cell growth.

Animals↗
PubMed1994

Interferon system defects in malignant T-cells.

Deletions of chromosome 9p21-22 occur in acute lymphocytic leukemia (ALL), melanoma and glioma. With some exceptions, these deletions include the alpha- and beta-interferon (IFN) genes. In this study, the frequency of alpha- and beta-IFN gene deletions was investigated in 17 T-cell lines, and losses of IFN genes were related to other aspects of the IFN system. Deletions of alpha-/beta-IFN genes were observed in 7/17 cell lines. In two cases the deletions were homozygous for both loci. In most cases aberrations of chromosome 9 were also apparent on cytogenetic analysis. An increased proportion (40% as compared to the expected 13%) of the remaining ten cell lines showed homozygosity for all five common polymorphic alpha-/beta-IFN markers, possibly implicating allelic deletion by loss of heterozygosity (LOH) in some of these clones. The cell lines showed a large variability in IFN production, IFN-alpha receptor number, susceptibility to IFN measured as induction of the enzyme 2',5' oligoadenylate synthetase and cell growth inhibition. No correlations between loss of IFN genes and IFN-producing capacity, or susceptibility to IFN, were found. Of the seven cell lines with a normal IFN-gene dosage and heterozygosity for the alpha- and beta-IFN genes, three had a deficiency in their IFN-producing capacity and one was also insensitive to growth inhibition by IFN. All IFN-producing cell lines predominantly produced beta-IFN.

2',5'-Oligoadenylate Synthetase↗
PubMed1994

[Isolation and identification of an oxygen-tolerant strain of Bifidobacterium from human feces].

This paper reports 136 strains suspected to be species of the genes Bifidobacterium isolated from adult human faeces. Through detection of the ability to tolerate molecular oxygen in cultural environments, we obtained an oxygen-resistant strain TQ21-2-2 according to the Bergy's manual. It was identified as Bifidobacterium longum. A limited number of drinking the beverage, the experiments also using this strain in milk as a starter revealed that this strain has been found useful for treating cases with constipation.

Bifidobacterium↗