Biomedical subjects

Z Xu

Publications and source records attributed to Z Xu.

At least 307 records · Page 17Linked to original sources

PubMed1998

The spatial and temporal expression of HNK-1 by myogenic and skeletogenic cells in the embryonic rat.

The existence of phenotypic differences within a population of cells provides evidence for discrete stages in cellular differentiation and/or identifies subsets of cells with unique functional properties. The monoclonal antibody HNK-1 has been widely shown to identify subpopulations of cells in the developing nervous system. In this paper we focus on the developmental expression of HNK-1 immunoreactivity by derivatives of somitic (paraxial) mesoderm. We show that between embryonic day 12 and 14 (E12-E14) the HNK-1 epitope is transiently expressed by postmitotic myotomal cells. In E14-E17 developing vertebral columns (which are derived from somitic sclerotomal cells), HNK-1 immunolabeling was expressed by subpopulations of skeletogenic cells, including perinotochordal cells associated with the forming annulus fibrosus and cells within or adjacent to the perichondrium. Chondrocytes within forming centra and vertebral arches did not exhibit HNK-1 immunoreactivity. These results, taken together, show that the expression of the HNK-1 epitope can be used to identify subsets of myogenic and skeletogenic cells both spatially and temporally in the developing rat.

Animals↗

PubMed1998

Neuropeptide Y: some viewpoints on a multifaceted peptide in the normal and diseased nervous system.

Using immunohistochemical and in situ hybridization methodologies the localization of neuropeptide tyrosine (NPY) and two of its receptors, the Y1- and the Y2-receptor (R), has been analysed in various tissues in normal animals and animals subjected to different experimental procedures as well as animals with a genetic and an acquired disease. (1) Dorsal root ganglion (DRG) neurons are discussed with special focus on the effect of peripheral nerve injury. In normal DRG neurons NPY cannot be detected, whereas Y1-R mRNA and Y1-R-like immunoreactivity (LI) are strongly expressed. The Y1-Rs decorate the membrane of the cell soma and are not transported peripherally into the axonal branches. Y2-R mRNA levels are low. After axotomy there is a marked increase in NPY, a decrease in Y1-Rs and an increase in Y2-Rs. The Y2-R is transported centrifugally. These findings suggest that NPY-ergic mechanisms participate in the adaptive changes of sensory neurons in response to injury. (2) Using specific antibodies the cellular and subcellular localization of the Y1-R protein have been analysed in cerebral blood vessels. The results demonstrate high concentrations of receptors in smooth muscle cells around pial arterioles with lower numbers in large vessels on the basal surface of the brain. In many regions the receptors 'disappear' after the arterioles have entered the brain tissue. At the ultrastructural level the receptors are found both on the endothelial and peripheral side of the muscle cells as well as laterally, where muscle cells oppose each other. The receptor protein is often associated with small vesicles. No NPY-positive nerve fibers were found around the Y1-R-rich arterioles, but they were only seen around the arteries with low Y1-R levels. The Y1-R-rich arterioles were, however, seen close to numerous NPY-positive fibers originating from central interneurons. These findings raise the possibility that centrally originating NPY can influence cerebral blood flow, possibly by stimulating NPY-Rs on the peripheral side of the muscle cells. However, also blood borne NPY, released under special conditions, such as stress from sympathetic nerves and the adrenal medulla and transported with blood, may stimulate receptors on the endothelial side of the smooth muscle cells. (3) In the arcuate nucleus Y1- and Y2-Rs are found, whereby the Y1-Rs are located in its ventro-medial portion and co-localized with POMC peptides, and the Y2-R in its ventromedial part, partly co-localized with NPY. NPY nerve endings makes synaptic contact with the POMC/Y1-R-positive neurons. In a mouse model for genetic anorexia very high levels of NPY were observed in arcuate neurons as compared to control mice. However, NPY mRNA levels were not different between the two groups. Taken together these findings are in good agreement with the view that NPY in the arcuate nucleus plays an important role in regulating feeding behaviour. (4) After intracerebral prion inoculation in mice an upregulation of NPY mRNA levels was observed in CA3 pyramidal neurons, and this effect was seen at a time point just before the first behavioural symptoms were manifested. At approximately the same time there was a dramatic decrease in Y2-R binding in strata oriens and radiatum of the CA1 region of the hippocampus, whereas in other regions no changes or much smaller changes were observed. Also, there was only a very slight decrease in Y2-R mRNA levels in CA3 neurons. It thus appears as if the prion disease prevents ligand binding to the Y2-R, perhaps by influencing traffic of receptor proteins, possibly at the level of cell membrane-associated caveolae, which have been implicated in the conversion of normal protein to scrapie protein. It is possible that these changes in NPY-ergic mechanisms may underlie some of the central symptoms associated with the prion disease. (ABSTRACT TRUNCATED)

Animals↗

PubMed1998

Oxygen sites in the zeolite stilbite: a comparison of static, MAS, VAS, DAS and triple quantum MAS NMR techniques.

Static, magic angle spinning (MAS), variable angle spinning (VAS), dynamic angle spinning (DAS) and triple quantum magic angle spinning (3QMAS) NMR techniques were applied to separate and quantify oxygen signals from Al-O-Si and Si-O-Si sites of 17O-enriched samples of the mineral stilbite, a natural zeolite. DAS experiments showed that there was a distribution of quadrupolar coupling constants, asymmetry parameters and isotropic chemical shifts. Two methods were used to study the quantification problem of DAS and 3QMAS. Our results showed that DAS was quantitative. In 3QMAS, signal intensity from sites with larger quadrupolar coupling constants was reduced because of less efficient excitation. All techniques have shown a clear difference in rates of exchange between the two types of sites with interchannel H2O molecules.

Humans↗

PubMed1998

Elevated "hydroxyl radical" generation in vivo in an animal model of amyotrophic lateral sclerosis.

Mutations in the enzyme copper/zinc superoxide dismutase-1 (SOD1) are associated with familial amyotrophic lateral sclerosis (FALS). The means by which the mutations cause FALS appears to be due to an adverse property of the mutant SOD1 protein that may involve increased generation of free radicals. We used in vivo microdialysis to measure the conversion of 4-hydroxybenzoic acid to 3,4-dihydroxybenzoic acid (3,4-DHBA) as a measure of "hydroxyl radical-like" production in transgenic amyotrophic lateral sclerosis (ALS) mice with the G93A mutation as well as littermate controls. The conversion of 4-hydroxybenzoic acid to 3,4-DHBA was significantly increased in the striatum of transgenic ALS mice at baseline but not in mice overexpressing wild-type human SOD1. Following administration of 3-nitropropionic acid 3,4-DHBA generation was significantly increased as compared with baseline, and the increase in the transgenic ALS mice was significantly greater than those in controls, whereas the increase in mice overexpressing wild-type human SOD1 was significantly attenuated. The present results provide in vivo evidence that expression of mutations in SOD1 can lead to increased generation of "hydroxyl radical-like" activity, which further implicates oxidative damage in the pathogenesis of ALS.

Amyotrophic Lateral Sclerosis↗

PubMed1998

Genomic features of human PKR: alternative splicing and a polymorphic CGG repeat in the 5'-untranslated region.

The double-stranded RNA-dependent protein kinase (PKR) is a serine/threonine kinase that plays an important role in the antiviral activities of interferon (IFN). To determine the organization and regulation of the PKR locus, lambda phage and bacterial artificial chromosome (BAC) clones containing the human PKR gene were isolated. Characterization of these clones revealed that PKR has 17 exons and 16 introns dispersed in a genomic region of 50 kb. Sequence analysis of the PKR 5'-flanking region identified a canonical IFN-stimulated response element (ISRE), GAAAACGAAACT. Transient transfection of PKR promoter constructs linked to a luciferase reporter gene into human T98G cells indicated that this 5'-flanking region is capable of functioning as a basal promoter that is also inducible by IFN-alpha and IFN-beta but not IFN-gamma. Interestingly, the PKR gene contains a polymorphic CGG trinucleotide repeat in exon 1. In addition, four PKR alleles, varying in repeat number from 7 to 10, were detected in 30 individual chromosomes. The PKR gene undergoes alternative splicing of exon 2, which gives rise to two forms of 5'-untranslated exons of different length. Although the human and murine PKR proteins have high homology, comparison of their gene structures reveals divergence in 5'-flanking regions, suggesting distinct regulation at the genomic level.

5' Untranslated Regions↗

PubMed1998

The SFP1 gene product of Saccharomyces cerevisiae regulates G2/M transitions during the mitotic cell cycle and DNA-damage response.

In eukaryotic cells, checkpoint pathways arrest cell-cycle progression if a particular event has failed to complete appropriately or if an important intracellular structure is defective or damaged. Saccharomyces cerevisiae strains that lack the SFP1 gene fail to arrest at the G2 DNA-damage checkpoint in response to genomic injury, but maintain their ability to arrest at the replication and spindle-assembly checkpoints. sfp1Delta mutants are characterized by a premature entrance into mitosis during a normal (undamaged) cell cycle, while strains that overexpress Sfp1p exhibit delays in G2. Sfp1p therefore acts as a repressor of the G2/M transition, both in the normal cell cycle and in the G2 checkpoint pathway. Sfp1 is a nuclear protein with two Cys2His2 zinc-finger domains commonly found in transcription factors. We propose that Sfp1p regulates the expression of gene products involved in the G2/M transition during the mitotic cell cycle and the DNA-damage response. In support of this model, overexpression of Sfp1p induces the expression of the PDS1 gene, which is known to encode a protein that regulates the G2 checkpoint.

Amino Acid Sequence↗

PubMed1998

Targeted replacement of normal and mutant CFTR sequences in human airway epithelial cells using DNA fragments.

Recent studies have reported that mutant genomic cystic fibrosis (CF) transmembrane conductance regulator ( CFTR ) sequences can be corrected in transformed CF airway epithelial cell lines by targeted replacement with small fragments of DNA with wild-type sequence. To determine if the observed genotype modification following small fragment homologous replacement (SFHR) was limited to transformed CF cell lines, further studies were carried out in both transformed and non-transformed primary normal airway epithelial cells. The endogenous genotype of these normal cell lines was modified following liposome or dendrimer transfection using DNA fragments with DeltaF508 CFTR sequence (488 nt, complementary single strands) designed to also contain a unique restriction enzyme cleavage site (Xho I). Replacement at the appropriate genomic locus by exogenous DeltaF508 CFTR DNA and its expression as mRNA was demonstrated by PCR amplification of genomic DNA and mRNA-derived cDNA as well as Xho I digestion of the PCR products. These studies show that SFHR occurs in both transformed and non-transformed primary human airway epithelial cells and indicate that single base substitution (the silent mutation giving rise to the Xho I site) and deletion or insertion of at least three consecutive bases can be achieved in both normal and CF epithelial cells. Furthermore, these studies reiterate the potential of SFHR as a strategy for a number of gene targeting applications, such as site-specific mutagenesis, development of transgenic animals, development of isogenic cell lines and for gene therapy.

Binding Sites↗

PubMed1998

In vitro culture retards spontaneous activation of cell cycle progression and cortical granule exocytosis that normally occur in in vivo unfertilized mouse eggs.

We have previously demonstrated that metaphase II-arrested eggs recovered from oviducts at increasing times after hCG administration display a time-dependent spontaneous entry into anaphase, as well as release of cortical granules (CGs) and the associated modifications of the zona pellucida (ZP), a decrease in histone H1 and mitogen-activated protein kinase activities, and the recruitment of maternal mRNAs [Xu et al., Biol Reprod 1997; 57:743-750). These changes are correlated with the time-dependent increase in susceptibility of these eggs to undergo parthenogenetic activation. We report here the effect of culture of ovulated eggs, retrieved 13 or 16 h post-hCG administration and cultured in vitro for various periods of time, on the aforementioned parameters of egg activation and cell cycle resumption. In contrast to extended residence of the eggs in the oviduct, culture in vitro retarded cell cycle events associated with completion of the second meiotic reduction and inhibited CG release and the associated modifications of the ZP, as well as the recruitment of maternal mRNAs. The retardation or inhibition of these changes during in vitro culture resulted in eggs that were less susceptible to parthenogenetic activation than eggs that resided in the oviduct for comparable time periods. Results of these experiments indicate that egg culture in vitro (which likely occurs under suboptimal conditions) inhibits, rather than accelerates, the progression into the interphase-like state as compared to that seen in eggs residing in the oviduct for increasing periods of time. These results also suggest that, for studies focused on in vitro fertilization or egg activation, the ovulated eggs should be placed under appropriate in vitro conditions as soon as possible.

Animals↗

PubMed1998

The use of improved radiochromic film for in vivo quality assurance of high dose rate brachytherapy.

GAFChromic film has become increasingly popular for radiation dosimetry. In this study we explore the use of GAFChromic film as an in vivo dosimeter for quality assurance (QA) of fractionated high dose rate 192Ir treatments. Accuracy of dose distribution is explored for the simple vaginal cylinder geometry for which the dose can be easily calculated for comparison. Source dwell times for several patients were optimized to deliver 500 cGy at 0.5 cm from the surface of the vaginal cylinder applicator using a commercial treatment planning system. GAFChromic film was taped to the vaginal cylinder applicator and was enclosed in a leak proof rubber sleeve prior to its insertion. Optical densities were measured along the film at 2 mm spacing, using a densitometer with filtered red light. Density corrections for transient film darkening effects were made and optical densities were converted to absorbed dose in cGy. In vivo patient dose distribution measured for different patients and different fractions were compared with the calculated values along the applicator surface. The variation between the calculated and measured dose was +/- 10%. the reproducibility of dose measurement for different fraction was within +/- 5%. This study demonstrates the potential usefulness of the film as an in vivo for brachytherapy QA.

Administration, Intravaginal↗

PubMed1998

A new genetic algorithm technique in optimization of permanent 125I prostate implants.

Real time optimized treatment planning at the time of the implant is desirable for ultrasound-guided transperineal 125I permanent prostate implants. Currently available optimization algorithms are too slow to be used in the operating room. The goal of this work is to develop a robust optimization algorithm, which is suitable for such application. Three different genetic algorithms (sGA, sureGA and securGA) were developed and compared in terms of the number of function evaluations and the corresponding fitness. The optimized dose distribution was achieved by searching the best seed distribution through the minimization of a cost function. The cost function included constraints on the periphery dose of the planned target volume, the dose uniformity within the target volume, and the dose to the critical structure. Adjustment between the peripheral dose, the dose uniformity and critical structure dose can be achieved by varying the weighting factors in the cost function. All plans were evaluated in terms of the dose nonuniformity ratio, the conformation number and the dose volume histograms. Among these three GA algorithms, the securGA provided the best performance. Within 2500 function evaluations, the near optimum results were obtained. For a large target volume (5 cm x 4 cm x 4.5 cm) including urethra with 20 needles, the computer time needed for the optimization was less than 5 min on a HP735 workstation. The results showed that once the best set of parameters was found, they were applicable for all sizes of prostate volume. For a fixed needle geometry, the optimized plan showed much better dose distribution than that of nonoptimized plan. If the critical structure was considered in the optimization, the dose to the critical structure could be minimized. In the cases of irregular and skewed needle geometry, the optimized treatment plans were almost as good as ideal needle geometry. It is concluded that this new genetic algorithm (securGA) allows for an efficient and rapid optimization of dose distribution, which is suitable for real time treatment planning optimization for ultrasound-guided prostate implant.

Algorithms↗

PubMed1998

Structure and function in GroEL-mediated protein folding.

Recent structural and biochemical investigations have come together to allow a better understanding of the mechanism of chaperonin (GroEL, Hsp60)-mediated protein folding, the final step in the accurate expression of genetic information. Major, asymmetric conformational changes in the GroEL double toroid accompany binding of ATP and the cochaperonin GroES. When a nonnative polypeptide, bound to one of the GroEL rings, is encapsulated by GroES to form a cis ternary complex, these changes drive the polypeptide into the sequestered cavity and initiate its folding. ATP hydrolysis in the cis ring primes release of the products, and ATP binding in the trans ring then disrupts the cis complex. This process allows the polypeptide to achieve its final native state, if folding was completed, or to recycle to another chaperonin molecule, if the folding process did not result in a form committed to the native state.

Adenosine Triphosphate↗

PubMed1998

K+ current inhibition by amphiphilic fatty acid metabolites in rat ventricular myocytes.

Fatty acid metabolites accumulate in the heart under pathophysiological conditions that affect beta-oxidation and can elicit marked electrophysiological changes that are arrhythmogenic. The purpose of the present study was to determine the impact of amphiphilic fatty acid metabolites on K+ currents that control cardiac refractoriness and excitability. Transient outward (Ito) and inward rectifier (IK1) K+ currents were recorded by the whole cell voltage-clamp technique in rat ventricular myocytes, and the effects of two major fatty acid metabolites were examined: palmitoylcarnitine and palmitoyl-coenzyme A (palmitoyl-CoA). Palmitoylcarnitine (0.5-10 microM) caused a concentration-dependent decrease in Ito density in myocytes internally dialyzed with the amphiphile; 10 microM reduced mean Ito density at +60 mV by 62% compared with control (P < 0.05). In contrast, external palmitoylcarnitine at the same concentrations had no effect, nor did internal dialysis significantly alter IK1. Dialysis with palmitoyl-CoA (1-10 microM) produced a smaller decrease in Ito density compared with that produced by palmitoylcarnitine; 10 microM reduced mean Ito density at +60 mV by 37% compared with control (P < 0.05). Both metabolites delayed recovery of Ito from inactivation but did not affect voltage-dependent properties. Moreover, the effects of palmitoylcarnitine were relatively specific, as neither palmitate (10 microM) nor carnitine (10 microM) alone significantly influenced Ito when added to the pipette solution. These data therefore suggest that amphiphilic fatty acid metabolites downregulate Ito channels by a mechanism confined to the cytoplasmic side of the membrane. This decrease in cardiac K+ channel activity may delay repolarization under pathophysiological conditions in which amphiphile accumulation is postulated to occur, such as diabetes mellitus or myocardial infarction.

Animals↗

PubMed1998

Altered K+ current of ventricular myocytes in rats with chronic myocardial infarction.

The aim of the present study was to define the cellular mechanisms underlying changes in K+ channel function in the failing heart after myocardial infarction. Rats with left coronary artery ligation were prepared and allowed to recover for 16 wk before study. Animals with chronic infarction exhibited marked cardiac hypertrophy and signs of heart failure, as indicated by a nearly twofold increase in heart weight- and lung weight-to-body weight ratios, respectively, compared with time-matched controls. Cardiac hypertrophy was also evident by a 49% increase in whole cell capacitance of isolated left ventricular myocytes (P < 0.05). Voltage-clamp experiments revealed that the maximum density of the Ca(2+)-independent, transient outward current (I.t.o.), measured at +60 mV, was 42% less in myocytes from infarcted hearts than in myocytes from control hearts (P < 0.05), whereas the inward rectifier current (IK1) density was not different between groups. The reduced Ito density in the infarcted group was reversed, however, in 4-5 h by treatment with exogenous dichloroacetate or pyruvate, both activators of pyruvate dehydrogenase. Moreover, control myocytes incubated for 6 h in the presence of an inhibitor of pyruvate dehydrogenase, 3-bromopyruvate, exhibited a concentration-dependent decrease in Ito density compared with untreated cells. The present data demonstrate that Ito density is reversibly decreased in surviving myocytes from infarcted hearts and suggest that mechanisms related to glucose metabolism via pyruvate dehydrogenase may be involved. These postinfarction changes in myocyte Ito channel function may relate to impaired contractility and arrhythmogenesis, which are characteristic of the intact, failing heart.

Animals↗

PubMed1998

Fos expression in rat brain during depletion-induced thirst and salt appetite.

The expression of Fos protein (Fos immunoreactivity, Fos-ir) was mapped in the brain of rats subjected to an angiotensin-dependent model of thirst and salt appetite. The physiological state associated with water and sodium ingestion was produced by the concurrent subcutaneous administration of the diuretic furosemide (10 mg/kg) and a low dose of the angiotensin-converting enzyme (ACE) inhibitor captopril (5 mg/kg; Furo/Cap treatment). The animals were killed 2 h posttreatment, and the brains were processed for Fos-ir to assess neural activation. Furo/Cap treatment significantly increased Fos-ir density above baseline levels both in structures of the lamina terminalis and hypothalamus known to mediate the actions of ANG II and in hindbrain regions associated with blood volume and pressure regulation. Furo/Cap treatment also typically increased Fos-ir density in these structures above levels observed after administration of furosemide or captopril separately. Fos-ir was reduced to a greater extent in forebrain than in hindbrain areas by a dose of captopril (100 mg/kg sc) known to block the actions of ACE in the brain. The present work provides further evidence that areas of lamina terminalis subserve angiotensin-dependent thirst and salt appetite.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1998

[Epidemiology and cost-effectiveness analysis of hepatitis A vaccination in Liuzhou City].

The changes of annual incidence rates were predicted for 7 cohorts of different ages either with or without vaccination. Cost-effectiveness ratio (CER) was estimated by the annual differences of HA incidence of the two scenarios at 15 years after inoculation, the medical costs and quality of life impact (QALY) for conditions related to the vaccination and disease. The estimated age specific HA incidence rates of the cohorts without vaccination fitted the observed age specific HA incidence rates quite well, indicating the correctness of our calculation models. Under the basecase assumptions, vaccination in general population would entail medical costs. The average CER was 153,277.6 Yuan/QALY, 11 times more than the average per-capita GNP in 1994. The basecase CERs varied from 113,369.3 Yuan/QALY in 10-19 years of age to 292,138.3 Yuan/QALY in age group 50-years. However, much better CERs are found when vaccination is directed toward a high risk population. In this case, widespread use of HAV vaccine in general population with intermediate epidemicity would not be cost-effective while it should be only focused on the high risk population. Sensitivity analysis showed that none of the basic variables might change this conclusion.

Adolescent↗

PubMed1998

[Studies on re-immunization with live attenuated hepatitis A vaccine].

OBJECTIVE: The possibility of re-immunization with a booster dose of live attenuated hepatitis A (HA) vaccine was studied. METHODS: Children randomly sampled were divided into three groups with re-immunization, primary immunization and immunity via natural infection. Antibodies against hepatitis A virus (anti-HAV) were detected qualitatively and quantitatively with modified Abbott enzyme immunoassay (EIA). RESULTS: Proportion of children with positive anti-HAV and its mean geometric titer (GMT) increased within two weeks after re-immunization, and as compared, those increased slowly and GMT reached the peak three months after primary immunization. Response to the live attenuated vaccine differed between the groups of re-immunization and immunity via natural infection, and should be taken into consideration in studying immune persistence of the vaccine. Proportion of children, who converted negative of their anti-HAV after primary immunization, with positive anti-HAV after re-immunization was 83.3% (10/12), significantly higher than that in those who failed in primary immunization and then were vaccinated again (50%, with 17/34), and that in both of them were higher than in primary immunization (29.6%). CONCLUSION: Reminiscence could be induced by re-immunization, and the effects of it depended on primary immunization. Detection of anti-HAV with modified Abbott EIA still underestimated primary immune reaction. A more sensitive and specific method for detecting anti-HAV after vaccination should be used.

Child↗

PubMed1998

[Antagonistic action of organic selenium on lead poisoning].

Ninety white rats were treated with liquid lead acetate. When the concentration of lead in urine was more than (0.81 +/- 0.26) mg/L and blood lead was more than (4.8 +/- 0.33) mg/L, the rats were divided into three groups randomly. The oxygenic damage indicators in serum showed SOD activity decreased and MDA content increased. In one group of lead rats fed with an organic selenium compound (code FCQY) the SOD activities were high and the lipid peroxidation was inhibited compared with controls without selenium supplementation. The lead contents of bone, kidney and liver were measured. The results suggested that the organic selenium compound could interfere with the absorption and accumulation of lead.

Animals↗

PubMed1998

[Distribution of morphine in acute morphine-treated rats].

The distribution of morphine in acute morphine-treated rats was studied by immunohistochemistry (PAP). Samples were examined for morphine distribution and localization in internal organs at 10-160 min after intraperitoneal injection of morphine. The results showed that morphine was distributed in the heart, hepatocytes, epithelial cells of the bile canalicular cells in liver, spleen, kidney, adrenal glands, stomach parietal cells, small intestinal villus, pancreas islet, sublingual glands and submandibular glands. Morphine was found in the cardiac tissue, liver, spleen, pancreas islet, small intestinal villus at 10 min after injection and in the cardiac tissue, stomach parietal cells at 160 min after injection. The cause of the postmortem the distribution of morphine in internal organs at different times after injection was discussed. The results of this study may be used as a basis for the choice of samples for the forensic toxicological analysis.

Animals↗