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Biomedical subjects

P Xu

Publications and source records attributed to P Xu.

At least 127 records · Page 7Linked to original sources
PubMed1995

Association between increased estrogen status and increased fibrinolytic potential in the Framingham Offspring Study.

BACKGROUND: Although extensive evidence indicates that estrogen is responsible for the markedly decreased cardiovascular risk of premenopausal women, the mechanism through which estrogen might exert its protective effect has not been adequately explained. Since thrombosis is now recognized to play an important role in the onset of cardiovascular disease, we investigated the relation between estrogen status and fibrinolytic potential, a determinant of thrombotic risk. METHODS AND RESULTS: We determined levels of plasminogen activator inhibitor (PAI-1) antigen and tissue plasminogen activator (TPA) antigen in 1431 subjects from the Framingham Offspring Study. Fibrinolytic potential was compared between subjects with high estrogen status (premenopausal women and postmenopausal women receiving hormone replacement therapy) and low estrogen status (men and postmenopausal women not receiving hormone replacement therapy). In all comparisons, subjects with high estrogen status had greater fibrinolytic potential (lower PAI-1 levels) than subjects with low estrogen status. First, postmenopausal women receiving estrogen replacement therapy had lower levels of PAI-1 than those not receiving therapy (13.0 +/- 0.5 versus 19.5 +/- 1.0 ng/mL, P < .001). Second, premenopausal women had lower levels of PAI-1 than men of a similar age (14.8 +/- 0.6 versus 20.3 +/- 0.8 ng/mL, P < .001); this sex difference diminished when postmenopausal women not receiving hormone replacement therapy were compared with men of a similar age (19.6 +/- 0.7 versus 21.1 +/- 0.7 ng/mL, P = .089). Third, premenopausal women had markedly lower levels of PAI-1 antigen than postmenopausal women not receiving estrogen therapy (14.8 +/- 0.6 versus 19.5 +/- 1.0 ng/mL, P < .001). The between-group differences observed for TPA antigen were similar to those for PAI-1 antigen. CONCLUSIONS: Each of these comparisons indicates that the cardioprotective effect of estrogen may be mediated, in part, by an increase in fibrinolytic potential. These findings might provide at least a partial explanation for the protection against cardiovascular disease experienced by premenopausal women, and the loss of that protection following menopause.

Coronary Disease↗
PubMed1995

Study of aging of silicone rubber biomaterials with NMR.

Multinuclear nuclear magnetic resonance (NMR) spectroscopy (29Si, 13C, 1H) is used to characterize the aging process of silicone rubber-based biomaterials in a rat model. 1H NMR relaxation measurements (spin-lattice, T1, and spin-spin, T2, relaxation times) were performed to better understand the molecular dynamics of polysiloxane chains in implants. After 1 year of implantation in animals, changes in the 1H T2 relaxation times and the NMR spectra were observed in polydimethylsiloxane, Silastic sheets and chin implants, while these measurements remain unchanged in finger joints. Very small amounts of fat were detected in all types of silicone rubber implants at the end of the implantation period. This work shows that free silicone migrates from the implants to adjacent tissues and distant sites, such as spleen or liver, and is chemically modified.

Animals↗
PubMed1995

Improvement of tracheal autograft survival with transplantation into the greater omentum.

BACKGROUND: Reconstruction of tracheal defects with tracheal grafts is not practicable clinically because the problem of tracheal graft revascularization has not been solved successfully. We conducted experiments to investigate efficacy of implanting tracheal graft into the greater omentum for revascularization and possibility of adopting staged transplantation procedure for repair of tracheal defect. METHODS: Twenty-four mongrel dogs were randomly and equally divided into groups I and II. Six-ring cervical tracheal segments were harvested as autografts. The grafts were wrapped with the omentum and placed into the peritoneal cavity in group I, and reimplanted with omentopexy in group II. Four grafts were examined macroscopically, microscopically, and 35S-autoradiographically on postoperative days 3, 7, and 14, respectively. RESULTS: Epithelium loss was evident in the mucosas of the grafts except the 4 from group I. Percentages of viable chondrocytes assessed with 35S-autoradiography were significantly higher in tracheal grafts from group I than group II. All tracheal grafts with their own omental pedicles could be brought to any portions of the trachea. CONCLUSIONS: We conclude that prior implantation of tracheal graft in the omentum is beneficial for preservation of its structure, and reconstruction of a tracheal defect with a tracheal graft implanted first into the omentum is feasible.

Animals↗
PubMed1995

Modulation of skeletal muscle sodium channels by human myotonin protein kinase.

In myotonic muscular dystrophy, abnormal muscle Na currents underlie myotonic discharges. Since the myotonic muscular dystrophy gene encodes a product, human myotonin protein kinase, with structural similarity to protein kinases, we tested the idea that human myotonin protein kinase modulates skeletal muscle Na channels. Coexpression of human myotonin protein kinase with rat skeletal muscle Na channels in Xenopus oocytes reduced the amplitude of Na currents and accelerated current decay. The effect required the presence of a potential phosphorylation site in the inactivation mechanism of the channel. The mutation responsible for human disease, trinucleotide repeats in the 3' untranslated region, did not prevent the effect. The consequence of an abnormal amount of the kinase would be altered muscle cell excitability, consistent with the clinical finding of myotonia in myotonic dystrophy.

Animals↗
PubMed1995

High-concentration ethanol production from cooked corn starch by using medium-temperature cooking process.

An improved process for high-concentration ethanol production from cooked corn starch by Saccharomyces sp. W4 has been well developed. Simultaneous cooking and liquefaction of corn starch were performed by using thermophilic alpha-amylase at 95 degrees to 105 degrees C. The mash was then saccharified at 60 degrees C by using high-efficiency glucoamylase. Saccharomyces sp. W4 could produce 18.3% (v/v) ethanol at 30 degrees C within 60 hrs, with 1.2% reducing sugar and 4.1% total sugar remaining in the fermented mash. It was found that ammonium sulfate could accelerate the fermentation rate. When 0.9 g of ammonium sulfate was added to 280 mL of the fermentation media, 18.9% (v/v) ethanol could be reached in the mash after 50 hrs of fermentation, leaving 0.27% reducing sugar and 3.1% total sugar in the fermented media.

Ammonium Sulfate↗
PubMed1995

[Synthesis of substituted benzeneseleninic acid and its antineoplastic activity].

In view of the negative relationship between selenium and cancer, we designed and synthesized eleven substituted benzeneselenic acids (IVa-k) The antineoplastic activity of the title compounds was evaluated via the tests of inhibition of acetylcholinesterase, HL-60 and K562 in vitro, and Ehrlich carcinoma in mice. The result showed that the compounds IVa and IVb had distinct antineoplastic activity. The life span increase rate of IVb on mice bearing Ehrlich carcinoma was 20.30% (20mg/kg), which was higher than the increase rate of sodium selenite (10.65%, 0.5mg/kg).

Animals↗
PubMed1994

Assignment of human xanthine dehydrogenase gene to chromosome 2p22.

Xanthine dehydrogenase (XDH, EC 1.1.1.204) oxidizes a variety of purines, pterins, and other heterogenic nitrogen compounds, serving as a rate-limiting enzyme in nucleic acid degradation. The genetic defect of XDH results in hereditary xanthinuria and other disorders in purine metabolism. Based on the cloning and sequencing results of human XDH cDNA in our laboratory, we studied the localization and sublocalization of the XDH gene. A Version 3.0 human-hamster somatic cell hybrid PCRable DNA panel and specific PCR primers derived from human XDH cDNA for amplification were used to assign the XDH gene to human chromosome 2. The fidelity of the PCR product was confirmed by nucleotide sequencing the PCR product. The assignment of the XDH gene to chromosome 2 at band p22 was established by fluorescence in situ hybridization on human metaphase chromosomes using a clone from a pWE 15 cosmid library containing the XDH gene. The results should be useful for further studies of the molecular basis for hereditary xanthinuria and other genetic disorders related to abnormal XDH activity.

Animals↗
PubMed1994

Heterologous expression of cDNAs encoding barley (Hordeum vulgare) (1-->3)-beta-glucanase isoenzyme GV.

Two cDNAs have been isolated from libraries generated from poly(A)+RNA of young barley roots and leaves, using a cDNA encoding barley (1-->3)-beta-glucanase isoenzyme GII as a probe. Nucleotide sequence analyses and ribonuclease protection assays show that the two cDNAs differ only in the length of their 3'-untranslated regions; the corresponding mRNAs are likely to originate from a single gene by tissue-specific processing at separate polyadenylation sites. When the coding region of the cDNA is expressed in E. coli, the resultant protein catalyses the hydrolysis of (1-->3)-beta-glucan with an action pattern characteristic of a (1-->3)-beta-glucan endohydrolase (EC 3.2.1.39). The enzyme has been designated isoenzyme GV of the barley (1-->3)-beta-glucanase family).

Amino Acid Sequence↗
PubMed1994

Molecular cloning, tissue expression of human xanthine dehydrogenase.

Xanthine dehydrogenase (XDH, EC 1.1.1.204) is a molybdenum iron-sulphur flavin hydroxylase which oxidizes a variety of purines, pterins and other heterogenic nitrogen compounds, serving as a rate-limiting enzyme in nucleic acid degradation. In this work, we have isolated and sequenced cDNA clones of human liver XDH. The obtained cDNA covers 4577 bases of human liver XDH mRNA with a 63 bp 5'-end untranslated region and a 515 bp 3'-end untranslated region. A termination codon TGA and a polyadenylation signal AATAAA were identified. An open reading frame encodes 1333 amino acid residues. The assignment of the N-terminal was confirmed by directly sequencing that region of purified human milk XDH. Northern blot analysis shows that the human XDH gene is widely expressed in human tissues.

Amino Acid Sequence↗
PubMed1994

Na-independent Cl(-)-HCO3- exchange mediates recovery of pHi from alkalosis in guinea pig ventricular myocytes.

The pH-sensitive fluorescent indicator, carboxy-seminaphthorhodafluor 1 (SNARF 1) was used to assess the contribution of forward Na-independent Cl(-)-HCO3- exchange (1 external Cl- exchanged for 1 internal HCO3-) to intracellular pH (pHi) recovery from alkalosis in adult ventricular myocytes (guinea pig). Intracellular alkalosis was elicited by external application of the weak base, trimethylamine. In the absence of CO2-HCO3- (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solution) the initial rate of pHi recovery from alkalosis (pHi = 7.25-7.75) was slow and independent of pHi, yielding an apparent net HCO3- efflux of 0.36 +/- 0.11 mM/min. In CO2-HCO3(-)-buffered solution, the initial rate of pHi recovery and net HCO3- efflux were much faster and markedly increased by raising pHi. At pHi approximately 7.25, net HCO3- efflux was approximately 2 mM/min and rose to 9 mM/min at pHi approximately 7.6. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (0.4 mM) decreased net HCO3- efflux by 78.1 +/- 8.9% in CO2-HCO3(-)-buffered solution. Reduction in extracellular Cl- concentration from 135 to 20 mM markedly slowed the rate of pHi recovery from alkalosis and reduced net HCO3- efflux. pHi recovery from alkalosis was unaffected by removal of external sodium or exposure to 1 mM amiloride. These results indicate that forward Na-independent Cl(-)-HCO3- exchange mediates pHi recovery from alkalosis in guinea pig ventricular myocytes.

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

[Immunohistochemical study on fibrin in brain traumas].

The fibrin formation in brain traumas was studied by immunohistochemical method. Eleven cases of brain trauma were examined. The fibrin was demonstrated not only in the areas of brain contusion and the neuronal cytoplasm of hypothalamus, thalamus, brainstem, and cerebellum, but also on the membrane of endothelial cells and red blood cells within some capillaries. The fibrin was also found around capillaries and the areas far from the brain trauma. It was suggested that injuries to the brain occurred not only in the local areas of the brain subjected to the violence, but also in the areas far from the local injury. It meant that the brain injuries were not local, but diffuse. The fibrin observed in the neuronal cytoplasm, and on the membrane of endothelial cells and red blood cells within some capillaries was a sign of ante mortem brain traumas. The combined HE staining and immunohistochemical staining of the fibrin is useful in the demonstration of simple brainstem traumas.

Brain Chemistry↗
PubMed1994

[Synthesis of terephthalic acid derivatives and their activity on human promyelocytic leukaemia cells HL-60].

There were 13 derivatives of terephthalic acid were synthesized, in which 9 compounds were not found in literature. The 9 compounds were evaluated for their differentiation-inducing activities on human promyelocytic leukaemia cells HL-60. Compounds N1 and N4 possessed potential activity. Their percentage of differentiating effect was 55% (5 x 10(-6) mol/L), but it was less than that of retinoic acid (79%, 10(-7) mol/L).

Cell Transformation, Neoplastic↗
PubMed1994

[Synthesis of p-substituted benzoylaminobenzoic acid (methyl esters) and its differentiation induction in activities of human promyelocytic leukemia cells HL-60].

Sixteen p-substituted benzoylaminobenzoic acids and their methyl esters were synthesized, of which nine were not found in literature. All of the topic compounds were evaluated for their differentiation induction in activities of human promyelotic leukemia cells HL-60. Compounds III1, III2, III4, and III5 possessed potential activities. The differentiation rate, of III4 and III5 was 70% respectively. But it was less than that of retinoic acid (97%).

Antineoplastic Agents↗
PubMed1993

Conformational backbone dynamics of the cyclic decapeptide antamanide. Application of a new multiconformational search algorithm based on NMR data.

A general procedure for the analysis of biomolecular structures by NMR in the presence of rapid conformational dynamics has been applied to the study of the cyclic decapeptide antamanide. Two-dimensional experiments, relaxation measurements in the rotating frame, and homo- and heteronuclear coupling constant determinations have been used to characterize the dynamic properties of the molecule, in combination with a novel search algorithm for investigating multiconformational equilibria. Direct evidence for the presence of a conformational exchange process with an activation energy of approximately 20 kJ mol-1 and an exchange lifetime of approximately 25 microseconds at 320 K has been obtained from rotating frame relaxation measurements. This evidence is combined with the information derived from the multiconformational search algorithm MEDUSA to propose sets of structures that coexist in a dynamic exchange equilibrium.

Algorithms↗