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Biomedical subjects

G Xiao

Publications and source records attributed to G Xiao.

At least 73 records · Page 4Linked to original sources
PubMed1999

Effect of benzene, toluene, xylene on the semen quality of exposed workers.

OBJECTIVE: To examine the effects on semen and sperm quality of workers after a short and long term exposure to benzene, toluene, and xylene. METHODS: The semen and blood of 24 married workers exposed to benzene, toluene, and xylene from shoemaking, spray painting, or paint manufacturing factories were collected. The concentration of benzene, toluene, and xylene in the blood and semen was determined by using headspace chromatographic method. Routine sperm test was carried out and acrosin activity detected. RESULTS: The results showed that benzene, toluene, and xylene were found in the blood and semen of some ex-workers in a working environment where the air concentration of benzene, toluene, and xylene exceeded the maximum allowable concentration (MAC). This result was not found in workers of the control group. There were also some effects on the quality of semen in the exposed workers. For example, the percentage of semen with liquefaction time exceeding 30 minutes increased. The sperm vitality, motility and acrosin activity decreased. At the same time, there were a positive correlation between liquefaction time and the level of toluene in semen, and a negative correlation between sperm vitality, sperm activity or acrosin activity and working history. CONCLUSIONS: The results suggested that the mixture could affect the quality of semen and sperm, which might be the main reason of the abnormal pregnancy outcome among the wives of workers exposed to benzene, toluene, and xylene. Further studies are, however, required to confirm these findings.

Acrosin↗
PubMed1999

[The relationship between obstructive sleep apnea and gastroesophageal reflux and the effect of antireflux therapy].

OBJECTIVE: To evaluate the relationship between gastroesophageal reflux (GER) and obstructive sleep apnea (OSA) and the effect of combined therapy with cisapride and omeprazole. METHODS: 24-hour esophageal pH and manometric monitoring and polysomnography (PSG) were performed in 18 patients with snoring, daytime sleepiness and acid reflux, heartburn and regurgitation. Cisapride 10 mg qid and omeprazole 20 mg q12h were given to patients with GER and OSA. these tests were repeated on the 7th day. RESULTS: 7 of the 18 patients with OSA had severe GER. All except one had daytime GER as well as nocturnal GER. Nocturnal recordings were analyzed and it was found that esophageal pH below 4.0 was frequently followed by swallow action (58.6%, control = 20.6%, P < 0.05), gross body movement (18.6%, control = 4.8%, P < 0.05) and arousal (26.8%, control = 16.8%, P < 0.05). The mean lowest esophageal pressure [(-15.2 +/- 9.6) mmHg] before and [(-18.6 +/- 10.1) mmHg] after the drops of pH were significantly lower than that during control periods [(-10.6 +/- 8.1) mmHg, P < 0.005]. After antireflux therapy, there was dramatically improvement in total apnea time [from (52.7 +/- 27.1) to (21.6 +/- 21.2) minutes, P < 0.002)] and apnea hypopnea index (AHI) [from (38.9 +/- 17.6) to (15.2 +/- 12.3) No./h, P < 0.002]. CONCLUSION: GER is a predisposing factor for OSA, they may coexist and aggravate each other. Combined therapy with cisapride and omeprazole is a new, simple and effective method for GER with OSA.

Adult↗
PubMed1999

[Anaerobic infection and its rapid detection in surgical patients].

OBJECTIVE: To investigate anaerobic infection and its rapid detection in surgical patients. METHODS: 372 specimens were collected from surgical patients for anaerobe detection. To find a rapid detectable method, 110 specimens were collected for comparative studies by using indirect immunofluorescent antibody technique (IFA), enzyme labeled antibody technique (ELAT) and general cultural method (CM). RESULTS: The isolation rate of anaerobes was rather high in pyothorax (88.9%), abdominal abscess (86.7%), appendicitis (83.9%) and cerebral abscess (all five cases were positive). In burn wounds, the rate was about 23.6% especially in deep burn wounds. Among 212 strains detected, the predominant anaerobes were as follows B. melaninogenicus (28.8%), B. fragilis (25%), F. nucleatum (7.5%), C. perfringens (7.5%), and peptostreptococcus (5.7%); most of them (87.8%) were non-sporing anaerobes. Mixed infection with aerobes accounted for 64%. The survey of rapid detection was conducted in B. fragilis, B. melaninogenicus, C. perfringens, F. nucleatum and peptostreptococcus. The detectable rate was higher in IFA (79.1%) and ELAT (80.9%) than in CM (37.3%). CONCLUSION: IFA and ELAT might be rapid, specific, sensitive, and simple for detecting anaerobes.

Abdominal Abscess↗
PubMed1999

[Digital subtraction angiography of cerebrum for diagnosis of cavernous sinus fistula and its intravascular treatment].

OBJECTIVE: To evaluate the diagnosis of digital subtraction angiography (DSA) of cerebral arteries and the intravascular treatment for carotid artery-cavernous sinus fistula (CCF) mainly manifesting as pulsating exophthalmos. METHODS: Digital subtraction angiography (DSA) of cerebral arteries was carried out for 15 patients with pulsating exophthalmos. Of them, detectable balloon and tungsten filament microcoil were used for intravascular embolism treatment in 12 cases, and the 3 cases with CCF of the branch of external carotid artery were not treated. RESULTS: Of the 15 cases, 12 were fallen in the CCF of high flow type of unilateral internal carotid artery, and 3 in the CCF of low flow type of unilateral external carotid artery. The symptoms and signs of intravascular embolism disappeared after treatment in 11 cases. CONCLUSION: Cerebral artery DSA and intravascular therapy are the ideal methods for the diagnosis and treatment of CCF mainly manifesting as pulsating exophthalmos.

Adult↗
PubMed1999

[Development of continuous rat infusion device].

In order to perform better scientific researches on fluid resuscitation, total parenteral nutrition and continuous drug administration in rats, we developed a set of rat infusion device. The device, the characteristics of reasonable design, simple operation, low cost, good practicability, and making it by oneself or buying a whole set, can not only assure rats to run around, drink water, eat food freely, but also insure continuous infusion and drug administration during the experimental study of rats.

Animals↗
PubMed1998

Role of the alpha2-integrin in osteoblast-specific gene expression and activation of the Osf2 transcription factor.

Extracellular matrix molecules such as type I collagen are required for the adhesion, migration, proliferation, and differentiation of a number of cell types including osteoblasts. Matrix components often affect cell function by interacting with members of the integrin family of cell surface receptors. Previous work showed that collagen matrix synthesis, induced by addition of ascorbic acid to cells, precedes and is essential for the expression of osteoblast markers and induction of the osteocalcin promoter in murine MC3T3-E1 cells. This later response requires OSE2, the promoter element recognized by Osf2 (also called Cbfa1/AML3/PEBP2alphaA), a recently identified osteoblast-specific transcription factor. Osteoblasts express several integrins including alpha2beta1 which is a major receptor for type I collagen. This paper examines the role of the alpha2-integrin subunit in osteocalcin promoter activation and osteoblast differentiation. Disruption of alpha2-integrin-ECM interactions with a blocking antibody or DGEA peptide containing the cell-binding domain of type I collagen blocked activation of the mouse osteocalcin gene 2 promoter by ascorbic acid as well as induction of endogenous osteocalcin mRNA and mineralization. Furthermore, anti-alpha2-integrin blocking antibody or peptide reduced ascorbic acid-dependent binding of Osf2 to OSE2 without affecting levels of transcription factor mRNA. Time course studies revealed that ascorbic acid-dependent binding of Osf2 to OSE2 preceded increases in osteocalcin and bone sialoprotein expression and this increase in Osf2 binding was not accompanied by comparable changes in levels of transcription factor mRNA or protein. Taken together, these studies demonstrate that an alpha2-integrin-collagen interaction is required for activation of Osf2 and induction of osteoblast-specific gene expression. Furthermore, matrix signals may regulate Osf2 through a post-translational pathway or via an accessory factor.

3T3 Cells↗
PubMed1998

Functional hierarchy between two OSE2 elements in the control of osteocalcin gene expression in vivo.

Osteocalcin gene expression is initiated perinatally and is restricted to mature osteoblasts and odontoblasts. Because their pattern of expression is highly restricted, the osteocalcin genes are excellent tools to study osteoblast-specific gene expression. To define the mechanisms of osteocalcin cell-specific gene expression in vivo, we generated transgenic mice harboring deletion mutants of the promoter region of OG2, one of the mouse osteocalcin genes. We show here that only 647 base pairs of this promoter are sufficient to confer cell-specific and time-specific expression to a reporter gene in vivo. This promoter fragment contains two copies of OSE2. This osteoblast-specific cis-acting element binds Osf2, a recently characterized osteoblast-specific transcription factor (Ducy, P., Zhang, R., Geoffroy, V., Ridall, A. L., and Karsenty, G. (1997) Cell 89, 747-754). We also demonstrate that the proximal OSE2 element is critical to confer an osteoblast-specific, developmentally regulated pattern of expression to a reporter gene. The other OSE2 element, located more upstream and presenting a lower affinity for Osf2, affects only weakly OG2 promoter activity. These data demonstrate the crucial role of Osf2 in controlling osteocalcin gene expression. Since osteocalcin synthesis is a hallmark of the differentiated osteoblast phenotype, these results suggest that, beyond its developmental function, Osf2 is also required for the maintenance of the osteoblast phenotype postnatally.

Animals↗
PubMed1998

Conformational changes in the crystal structure of rat glutathione transferase M1-1 with global substitution of 3-fluorotyrosine for tyrosine.

The structure of the tetradeca-(3-fluorotyrosyl) M1-1 GSH transferase (3-FTyr GSH transferase), a protein in which tyrosine residues are globally substituted by 3-fluorotyrosines has been determined at 2.2 A resolution. This variant was produced to study the effect on the enzymatic mechanism and the structure was undertaken to assess how the presence of the 3-fluorotyrosyl residue influences the protein conformation and hence its function. Although fluorinated amino acid residues have frequently been used in biochemical and NMR investigations of proteins, no structure of a protein that has been globally substituted with a fluorinated amino acid has previously been reported. Thus, this structure represents the first crystal structure of such a protein containing a library of 14 (28 crystallographically distinct) microenvironments from which the nature of the interactions of fluorine atoms with the rest of the protein can be evaluated. Numerous conformational changes are observed in the protein structure as a result of substitution of 3-fluorotyrosine for tyrosine. The results of the comparison of the crystal structure of the fluorinated protein with the native enzyme reveal that conformational changes are observed for most of the 3-fluorotyrosines. The largest differences are seen for residues where the fluorine, the OH, or both are directly involved in interactions with other regions of the protein or with a symmetry-related molecule. The fluorine atoms of the 3-fluorotyrosine interact primarily through hydrogen bonds with other residues and water molecules. In several cases, the conformation of a 3-fluorotyrosine is different in one of the monomers of the enzyme from that observed in the other, including different hydrogen-bonding patterns. Altered conformations can be related to differences in the crystal packing interactions of the two monomers in the asymmetric unit. The fluorine atom on the active-site Tyr6 is located near the S atom of the thioether product (9R,10R)-9-(S-glutathionyl)-10-hydroxy-9,10-dihydrophenanthrene and creates a different pattern of interactions between 3-fluorotyrosine 6 and the S atom. Studies of these interactions help explain why 3-FTyr GSH transferase exhibits spectral and kinetic properties distinct from the native GSH transferase.

Animals↗
PubMed1998

NF-kappaB-inducing kinase and IkappaB kinase participate in human T-cell leukemia virus I Tax-mediated NF-kappaB activation.

The tax gene product of human T-cell leukemia virus I induces aberrant expression of various cellular genes, which contributes to transformation of host cells. Induction of many Tax target genes is mediated through transcription factor NF-kappaB. Here we show that Tax triggers activation of cellular protein kinases, IkappaB kinase alpha (IKKalpha) and IKKbeta, which phosphorylate the NF-kappaB inhibitory protein IkappaB alpha, resulting in its degradation and NF-kappaB activation. Constitutive IKK activation occurs in both Tax-transfected and human T-cell leukemia virus I-infected T cells. We further demonstrate that Tax-mediated NF-kappaB signaling also requires the NF-kappaB-inducing kinase (NIK). Consistently, inactive forms of either IKKs or NIK attenuate Tax-mediated NF-kappaB activation. Therefore, Tax activates NF-kappaB by targeting cellular signaling molecules, including both IKKs and NIK.

Catalysis↗
PubMed1998

Enzymes harboring unnatural amino acids: mechanistic and structural analysis of the enhanced catalytic activity of a glutathione transferase containing 5-fluorotryptophan.

The catalytic characteristics and structure of the M1-1 isoenzyme of rat glutathione (GSH) transferase in which all four tryptophan residues in each monomer are replaced with 5-fluorotryptophan are described. The fluorine-for-hydrogen substitution does not change the interaction of the enzyme with GSH even though two tryptophan residues (Trp7 and Trp45) are involved in direct hydrogen-bonding interactions with the substrate. The rate constants for association and dissociation of the peptide, measured by stopped-flow spectrometry, remain unchanged by the unnatural amino acid. The 5-FTrp-substituted enzyme exhibits a kcat of 73 s-1 as compared to 18 s-1 for the native enzyme toward 1-chloro-2,4-dinitrobenzene. That the increase in the turnover number is due to an enhanced rate of product release in the mutant is confirmed by the kinetics of the approach to equilibrium for binding of the product. The crystal structure of the 5-FTrp-containing enzyme was solved at a resolution of 2.0 A by difference Fourier techniques. The structure reveals local conformational changes in the structural elements that define the approach to the active site which are attributed to steric interactions of the fluorine atoms associated with 5-FTrp146 and 5-FTrp214 in domain II. These changes appear to result in the enhanced rate of product release. This structure represents the first of a protein substituted with 5-fluorotryptophan.

Animals↗
PubMed1998

Polymorphous crystallization and diffraction of threonine deaminase from Escherichia coli.

The biosynthetic threonine deaminase from Escherichia coli, an allosteric tetramer with key regulatory functions, has been crystallized in several crystal forms. Two distinct forms, both belonging to either space group P3121 or P3221, with different sized asymmetric units that both contain a tetramer, grow under identical conditions. Diffraction data sets to 2.8 A resolution (native) and 2. 9 A resolution (isomorphous uranyl derivative) have been collected from a third crystal form in space group I222.

Crystallization↗
PubMed1998

Structure and control of pyridoxal phosphate dependent allosteric threonine deaminase.

BACKGROUND: Feedback inhibition of biosynthetic threonine deaminase (TD) from Escherichia coli provided one of the earliest examples of protein-based metabolic regulation. Isoleucine, the pathway end-product, and valine, the product of a parallel pathway, serve as allosteric inhibitor and activator, respectively. This enzyme is thus a useful model system for studying the structural basis of allosteric control mechanisms. RESULTS: We report the crystal structure of TD at 2.8 A resolution. The tetramer has 222 symmetry, with C-terminal regulatory domains projecting out from a core of catalytic PLP-containing N-terminal domains. The subunits, and especially the regulatory domains, associate extensively to form dimers, which associate less extensively to form the tetramer. Within the dimer, each monomer twists approximately 150 degrees around a thin neck between the domains to place its catalytic domain adjacent to the regulatory domain of the other subunit. CONCLUSIONS: The structure of TD and its comparison with related structures and other data lead to the tentative identification of the regulatory binding site and revealed several implications for the allosteric mechanism. This work prepares the way for detailed structure/function studies of the complex allosteric behaviour of this enzyme.

Allosteric Regulation↗
PubMed1998

Comparison of structural stabilities of prostaglandin H synthase-1 and -2.

There are two known isoforms of prostaglandin H synthase (PGHS), a key enzyme in the conversion of arachidonic acid to bioactive prostanoids. The "constitutive" isoform, PGHS-1, is thought to have housekeeping functions, and the "inducible" isoform, PGHS-2, has been implicated in cellular responses to cytokines. The two isoforms have high sequence conservation in the cyclooxygenase active site and quite similar crystallographic structures, but differ markedly in their interactions with many cyclooxygenase substrates and inhibitors. We have evaluated the stability of the overall folding, and of the active sites of ovine PGHS-1 and human PGHS-2 using denaturation with guanidinium hydrochloride (GdmHCl). Changes in hydrodynamic and cross-linking properties indicated a dimer --> monomer transition for both isoforms between 0.5 and 2 M GdmHCl; the monomers unfolded at higher GdmHCl levels. Changes in overall secondary and tertiary structure, measured by tryptophan fluorescence and circular dichroism, occurred in two phases for each isoform, with the transition between the phases at 0.2-0.5 M GdmHCl. Disruption of active site functions (cyclooxygenase, peroxidase, and cyclooxygenase inhibitor binding activities) began at GdmHCl levels below 0.2 M. The structural and functional changes were completely reversible up to about 2 M GdmHCl, they were more pronounced at lower protein levels, and they required lower GdmHCl levels for PGHS-2 than for PGHS-1. The results are consistent with a four-state denaturation process for both isoforms: native dimers --> inactive dimers --> compact monomers --> unfolded monomers. The first two steps are reversible for both isoforms; PGHS-2 undergoes the first and last steps more readily than PGHS-1. Thus, the structural stability of PGHS-2, both in the active site regions and in the subunits overall, is distinctly less than that of PGHS-1. These differences in structural stability may contribute to the isoforms' active site ligand selectivity.

Binding Sites↗
PubMed1998

p53 binds to a constitutively nucleosome free region of the mdm2 gene.

The mdm2 oncogene is a p53 responsive gene which contains both a p53 independent and a p53 dependent promoter (P1 and P2 respectively). We have utilized ligation mediated PCR genomic footprinting in order to investigate the intra-nuclear binding of p53 to the mdm2 P2 promoter. The DNase I protection pattern in nuclei from murine cells lacking p53 has been compared to the protection pattern in cells containing a temperature sensitive p53-Val135. At 32 degrees C p53-Val135 assumes a wild-type conformation while at 37 degrees C this p53 is conformationally mutant. We observed clear wild-type p53 dependent protection of the putative p53 response elements (REs) as well as protection of the adjacent TATA box. Interestingly the protection pattern observed with purified wild-type p53 on naked DNA showed less nucleotide sequence protection than the protection observed to be p53 dependent in nuclei. Constitutive DNase I hypersensitivity at both the mdm2 P1 and P2 promoters was detected by indirect Southern blot analysis. DNase I hypersensitivity reflects altered chromatin conformations resulting, most likely, from the absence of nucleosomes. Taken together our findings suggest that the mdm2 P2 promoter is maintained in a nucleosome free state which is pre-primed for transcriptional activation by p53.

Animals↗
PubMed1998

Structural characterization of arachidonyl radicals formed by prostaglandin H synthase-2 and prostaglandin H synthase-1 reconstituted with mangano protoporphyrin IX.

A tyrosyl radical generated in the peroxidase cycle of prostaglandin H synthase-1 (PGHS-1) can serve as the initial oxidant for arachidonic acid (AA) in the cyclooxygenase reaction. Peroxides also induce radical formation in prostaglandin H synthase-2 (PGHS-2) and in PGHS-1 reconstituted with mangano protoporphyrin IX (MnPGHS-1), but the EPR spectra of these radicals are distinct from the initial tyrosyl radical in PGHS-1. We have examined the ability of the radicals in PGHS-2 and MnPGHS-1 to oxidize AA, using single-turnover EPR studies. One wide singlet tyrosyl radical with an overall EPR line width of 29-31 gauss (G) was generated by reaction of PGHS-2 with ethyl hydroperoxide. Anaerobic addition of AA to PGHS-2 immediately after formation of this radical led to its disappearance and emergence of an AA radical (AA.) with a 7-line EPR, substantiated by experiments using octadeuterated AA. Subsequent addition of oxygen resulted in regeneration of the tyrosyl radical. In contrast, the peroxide-generated radical (a 21G narrow singlet) in a Y371F PGHS-2 mutant lacking cyclooxygenase activity failed to react with AA. The peroxide-generated radical in MnPGHS-1 exhibited a line width of 36-38G, but was also able to convert AA to an AA. with an EPR spectrum similar to that found with PGHS-2. These results indicate that the peroxide-generated radicals in PGHS-2 and MnPGHS-1 can each serve as immediate oxidants of AA to form the same carbon-centered fatty acid radical that subsequently reacts with oxygen to form a hydroperoxide. The EPR data for the AA-derived radical formed by PGHS-2 and MnPGHS-1 could be accounted for by a planar pentadienyl radical with two strongly interacting beta-protons at C10 of AA. These results support a functional role for peroxide-generated radicals in cyclooxygenase catalysis by both PGHS isoforms and provide important structural characterization of the carbon-centered AA..

Arachidonic Acid↗
PubMed1998

2,5-bis[4-(N-alkylamidino)phenyl]furans as anti-Pneumocystis carinii agents.

The syntheses of 12 new 2,5-bis[4-(N-alkylamidino)phenyl]furans are reported. The interaction of these dicationic furans with poly(dA-dT) and with the duplex oligomer d(CGCGAATTCGCG)2 was determined by Tm measurements, and the effectiveness of these compounds against the immunosuppressed rat model of Pneumocystis carinii was evaluated. At the screening dose of 10 mumol/kg, 9 of the 14 N-alkylamidino furans described here are more active than the parent compound 1. Substitution of an alkyl group of the amidino nitrogen, except for in 9, 13, and 15, resulted in higher affinity for DNA than the parent compound as judged by the larger delta Tm values and suggests enhanced van der Waals interactions in the bis-amidine-DNA complex. Five of the compounds, 3, 5, 7, 10, and 12, yield cyst counts of less than 0.1% of control when administered at a dosage of 10 mumol/kg. Five compounds, 1, 6, 8, 10, and 12, show significant activity at a dosage of approximately 1 mumol/kg; 12 is the most active derivative, and it is approximately 100 times more effective than pentamidine in this animal model.

Animals↗