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Y Xu

Publications and source records attributed to Y Xu.

At least 775 records · Page 43Linked to original sources
PubMed1997

Detection of 13C-labeled metabolites in the in vivo canine heart by B1 insensitive heteronuclear coherent polarization transfer and comparison of signal enhancement with NOE.

A recently developed adiabatic coherent polarization transfer enhancement technique [H. Merkle, H. Wei, M. Garwood, K. Uğurbil. J. Magn. Reson, 99, 480-494 (1992)] was employed to perform 13C spectroscopy in the intact canine heart in vivo during [2-13C]-acetate infusion into the left descending coronary artery, the results were compared with 13C spectra obtained with conventionally employed nuclear Overhauser enhancement. The results demonstrate that both methods can be performed by using surface coils to obtain in vivo 13C spectra and that coherent polarization transfer provides better enhancement than NOE for [2-13C]-acetate but not for short T2 compounds.

Acetates↗
PubMed1997

Easy fabrication of a tunable high-pass birdcage resonator.

A practical design for a high-pass birdcage resonator is presented. Precision seamless telescoping tubes were used for easy tuning of resonant frequency by adjusting the length of the coils. Three probes, of 4.4, 5.0, and 25.0 cm in diameter, respectively, were constructed and tested. An empirical formula is given that can be used to calculate the capacitance needed for a given frequency when the desired physical dimension and the number of elements of the coll are specified. A simple three-step procedure is suggested for easy fabrication of resonators that are routinely tunable over tens of megahertz.

Magnetic Resonance Imaging↗
PubMed1997

Prospective study of early detection for primary liver cancer.

PURPOSE: To determine whether repeated screening can lead to early detection of primary liver cancer (PLC) and in turn to an improved clinical result. METHODS: In this randomized controlled study, Shanghai urban residents aged 35-55 years and with serum evidence of HBV infection or chronic liver disease were eligible for recruitment. Using cluster sampling, these subjects were allocated into two groups-the screening group and the control group: there were 8109 subjects in the screening group and 9711 in the control group. Subjects in the screening group were tested with serum AFP and real-time ultrasound every 6 months. One to four rounds of screening were completed. Liver cancer was treated according to stage at diagnosis. RESULTS: All subjects enrolled were followed up and classed at the end-point as alive without liver cancer, alive with liver cancer, dead from liver cancer, or dead from another cause. The mean follow-up was 1.2 years; total follow-up was 12,038 person-years in the screening group and 9,573 person-years in the control group. We detected 38 patients with PLC in the screening group and 18 patients with PLC in the control group. In the patients in the screening group 76.8% of patients were at a subclinical stage, and 70.6% of them underwent resection, the 1- and 2-year survival rates being 88.1% and 77.5%, respectively. However, in the control group, none of the patients was at a subclinical stage when diagnosed, none of them underwent resection, and none of them survived over 1 year. The lead time was estimated at 0.45 years. The cost of detecting PLC at an early stage was RMB 12,600 (US$1,500). CONCLUSION: The study proved that screening the high-risk population for PLC with a serum AFP test and real-time ultrasound examination can detect patients in the early stages, increase the resection rate and prolong the survival time. It is therefore recommended that screening for PLC be advocated in any high-risk area.

Adult↗
PubMed1997

Meniscal injury in children: long-term results after meniscectomy.

Twenty-four children who underwent open total meniscectomy were reviewed and followed-up for an average of 16.1 years (range 6-33 years). There were 7 boys and 17 girls aged between 7 and 16 years (average 12.5 years). Excellent and good results were noted in 62.5% of the patients. Eighty-seven of the children showed radiographic degeneration of the knee joint. This study in a Chinese population indicates that meniscectomy is not a benign procedure in children, and total meniscectomy should be avoided as far as possible.

Adolescent↗
PubMed1997

Different distribution of fluorinated anesthetics and nonanesthetics in model membrane: a 19F NMR study.

Despite their structural resemblance, a pair of cyclic halogenated compounds, 1-chloro-1,2,2-trifluorocyclobutane (F3) and 1,2-dichlorohexafluorocyclobutane (F6), exhibit completely different anesthetic properties. Whereas the former is a potent general anesthetic, the latter produces no anesthesia. Two linear compounds, isoflurane and 2,3-dichlorooctofluorobutane (F8), although not a structural pair, also show the same anesthetic discrepancy. Using 19F nuclear magnetic spectroscopy, we investigated the time-averaged submolecular distribution of these compounds in a vesicle suspension of phosphatidylcholine lipids. A two-site exchange model was used to interpret the observed changes in resonance frequencies as a function of the solubilization of these compounds in membrane and in water. At clinically relevant concentrations, the anesthetics F3 and isoflurane distributed preferentially to regions of the membrane that permit easy contact with water. The frequency changes of these two anesthetics can be well characterized by the two-site exchange model. In contrast, the nonanesthetics F6 and F8 solubilized deeply into the lipid core, and their frequency change significantly deviated from the prediction of the model. It is concluded that although anesthetics and nonanesthetics may show similar hydrophobicity in bulk solvents such as olive oil, their distributions in various regions in biomembranes, and hence their effective concentrations at different submolecular sites, may differ significantly.

Anesthetics↗
PubMed1997

Right ventricular dysfunction persists following brief right ventricular pressure overload.

OBJECTIVE: Acute pulmonary hypertension may cause right ventricular (RV) contractile failure. While it has been assumed that restoration of normal loading conditions after acute pulmonary hypertension is sufficient for complete recovery of RV function, this has not been rigorously examined. The purpose of this study was to test the hypothesis that acute RV pressure overload produces RV contractile dysfunction that persists following restoration of control loading conditions. METHODS: We subjected 18 autonomically-blocked, chloralose-anesthetized, open-chest pigs to 1 h of pulmonary artery constriction to increase RV systolic pressure from 35 +/- 1 to 55 +/- 1 mmHg, followed by 2 h of measurements after pulmonary artery constriction release. We determined regional RV free wall function from pressure-segment length loops and preload recruitable stroke work relations, and global RV function from stroke work vs. end-diastolic pressure relations. RESULTS: As expected, RV free wall systolic shortening diminished during pulmonary artery constriction, but the endo/epi blood flow ratio, lactate uptake, and coronary venous pH were not significantly changed. Following release of pulmonary artery constriction, RV systolic and diastolic pressure returned to control values. Nonetheless, contractile dysfunction persisted, with depressed RV free wall systolic shortening (70 +/- 22% of control), RV regional external work (59 +/- 11% of control at control end-diastolic length), and global RV stroke work (56 +/- 14% of control at control end-diastolic pressure). Depressed regional work was due to a parallel, rightward shift of the preload recruitable stroke work relation. Five pigs identically instrumented but not subjected to pulmonary artery constriction showed no significant over 3 h. CONCLUSIONS: Acute pulmonary hypertension causes RV contractile dysfunction that persists at least 2 h after restoration of control loading conditions. Contractile dysfunction is not attributable to RV ischemia during pressure overload.

Acute Disease↗
PubMed1997

Endothelial and macrophage upregulation of urokinase receptor expression in human renal cell carcinoma.

The binding of urokinase-type plasminogen activator (u-PA) to a specific cell surface receptor (uPA-R) has been shown to enhance plasminogen activation, a process involved in extracellular matrix degradation and cell migration during angiogenesis and tumor growth. We investigated the expression of u-PA and uPA-R in renal cell carcinomas (n = 11). By immunohistochemistry using monoclonal and polyclonal anti-uPA-R antibodies, we found that tumoral capillary endothelial cells (von Willebrand factor and CD31 positive cells) overexpressed uPA-R, whereas vascular endothelial cells of the normal human kidney do not. In addition, tumor-associated macrophages (CD68-positive cells) strongly expressed uPA-R. In contrast, few tumoral cells and stromal fibroblasts expressed uPA-R. By in situ hybridization using a cDNA S35-labeled probe specific for uPA-R, we confirmed the local expression of uPA-R messenger RNA. We also detected the induction of u-PA in tumoral capillary endothelial cells and in tumor-associated macrophages. In two cases, tumoral cells themselves were also stained by anti-u-PA antibodies in focal areas. Finally tissue-type plasminogen activator (t-PA) was also overexpressed by tumoral capillary endothelial cells as compared with endothelial cells of normal human kidney vessels. These findings indicate an active invasive phenotype of endothelial cells in renal cell carcinoma and suggest a role for the plasminogen activation system in tumoral angiogenesis and invasion.

Carcinoma↗
PubMed1997

Modulation of p53, WAF1/p21 and BCL-2 expression during retinoic acid-induced differentiation of NB4 promyelocytic cells.

The NB4 cell line, established from a patient with APL, carries the t(15; 17) and undergoes differentiation along the granulocytic pathway when exposed to retinoic acid (RA). The NB4 cell line was used as a model for exploring the expression of genes and proteins implicated in growth regulation, differentiation and apoptosis during treatment with RA. NB4 cells undergo a series of cytological and molecular alterations during RA treatment--Day 1: cell differentiation marked by an increase in CD11b is evident. Day 2: WAF1/p21 mRNA and then protein rise, though they drop 2 days later. Day 3: the percentage of cells in S phase begins to decrease and G1 arrest begins. Day 4: p53 mRNA level and then protein levels fall. Day 5: CD11b/BCL-2 double staining cells are markedly reduced. No signs of apoptosis were observed after up to 8 days of treatment with RA. These results demonstrate that NB4 cells treated with RA rapidly differentiate and arrest at G1 phase concurrent with p53-independent WAF1/p21 induction; in addition, phenotypic differentiation appears to commence before changes in cell cycle progression. An explanation for the decrease in p53 as well as the lack of apoptosis immediately after BCL-2 downregulation will require further study.

Antigens, CD↗
PubMed1997

Experimental confirmation of recombination upstream of the S1 hypervariable region of infectious bronchitis virus.

Chimeric infectious bronchitis virus (IBV) genomes with cross-over sites in the S1 gene were generated by co-infection with two distinct IBV strains. Recombinant viruses were collected from chicken embryos, embryonic cultured cells and chickens co-infected with Ark99 and Mass41 strains and purified by differential centrifugation. The recombinant S1 genes were identified by reverse transcription polymerase chain reaction (RTPCR) using heterologous primers and confirmed by nucleotide sequencing. The recombinants with Ark99 5' and Mass41 3' sequences were identified following the in vitro, in ovo and in vivo co-infections. Mixed RNA extracted from Ark99 and Mass41 did not produce RTPCR products with these primers at the PCR conditions used. Cross-over sites within the amplified 580 (Mass41) or 604 (Ark99) bases of the 5' S1 gene could only be detected between nucleotides 50 and 155. While this region, lying upstream of the S1 hypervariable region, corresponded with sites commonly identified in naturally occurring isolates, recombination sites identified in these studies could not be detected within the HVR of S1 of the genomes of chimeric viruses.

Animals↗
PubMed1997

Tyrosinase mRNA is expressed in human substantia nigra.

Dopamine acts, under appropriate conditions, as a selective neurotoxin. This toxicity is attributed to the autoxidation of the neurotransmitter into a reactive quinone that covalently modifies cellular macromolecules (i.e. proteins and nucleic acids). The oxidation of the catecholamine to a quinone is greatly accelerated by the enzyme tyrosinase. There is controversy, however, as to whether or not tyrosinase is expressed in human brain. In the present study, RT-PCR was utilized to demonstrate the presence of tyrosinase mRNA in post-mortem human brain tissues. Using gene-specific amplification primers, specific tyrosinase amplicons were detected following analysis of RNA from substantia nigra of four individuals. Analysis of cerebellar RNA from the same individuals produced no amplification products. Control reactions performed in the absence of reverse transcriptase failed to generate PCR products for any tissue tested. Three amplicons were subjected to direct DNA sequencing and all proved to be identical with tyrosinase sequences, thus obviating the possibility of amplification of a related gene. It is clear, therefore, that the tyrosinase gene is expressed in the human substantia nigra, lending support to previous studies describing tyrosinase-like activity and immunoreactive protein in the brain. This enzyme could be central to dopamine neurotoxicity as well as contribute to the neurodegeneration associated with Parkinson's disease.

Aged↗
PubMed1997

Recognition of RNA by triplex formation: divergent effects of pyrimidine C-5 methylation.

In DNA triple helices, methylation at C-5 of thymine or cytosine is reported to have similar stabilizing effects for both bases. Here we show, however, that methylation of the same positions in RNA triplexes has distinctly different effects than in DNA. We have previously described the use of circular triplex-forming RNA oligonucleotides to recognize RNA sequences. Here it is shown that addition of C-5 methyl groups to uracils in these compounds very significantly increases not only affinity but also sequence selectivity in binding a purine-rich RNA target, as measured by thermal denaturation with various target RNAs. Surprisingly, however, addition of C-5 methyl groups to cytosines actually decreases affinity in binding RNA, while the same substitution in DNA is thermally stabilizing. Possible sources of this divergent behavior are discussed. A synthesis of 5-methylcytidine ribonucleoside 2'-O-silyl-3'-O-phosphoramidite is also described.

Base Sequence↗
PubMed1997

Mineral induced phosphorylation of glycolate ion--a metaphor in chemical evolution.

Bilateral surface-active minerals with excess positive charge concentrate glycolate and trimetaphosphate ion from l0(-3) m aqueous solution to half-saturation of the internal surface sites, and induce phosphorylation of glycolate ion in the mineral with trimetaphosphate, sorbed from l0(-2) m solution. By utilizing reactants from dilute solution at near-neutral pH, and eliminating the need for participating organic nitrogen compounds, the reaction comprises several elements considered necessary for geochemical realism in models for molecular evolution.

Aluminum Hydroxide↗
PubMed1997

Endothelial cells of the kidney vasa recta express the urea transporter HUT11.

The cell specific expression of the human urea transporter HUT11 in human and rat kidneys was investigated by immunochemistry and in situ hybridization. Using specific rabbit polyclonal antibodies directed against the N-terminal part and the C-terminal part of HUT11, we found that endothelial cells of medullary vasa recta (outer and inner medulla) express HUT11. In addition, an HUT11-related protein expressed by smooth muscle cells of cortical arterioles can be detected by the anti-HUT11 N-terminal peptide antibody but not the anti-HUT11 C-terminal peptide antibody. The endothelial expression of HUT11 was confirmed by double labeling with anti-CD31 and anti-von Willebrand factor antibodies. No HUT11-positive cells expressed alpha smooth muscle actin, Tamm Horsfall protein, cytokeratin 18, or CAM-L1, a marker of the principal cells of collecting ducts. Medullary vasa recta of developing and mature rat kidneys were also stained with the anti-HUT11 C-terminal peptide antibody. By in situ hybridization using a specific HUT11 35S-cDNA probe on human kidney sections, medullary vasa recta but not other renal structures were found to express HUT11 mRNA. We conclude that endothelial cells of medullary vasa recta express HUT11, a specific urea transporter, which may play a role in urea recycling within the kidney and in the mechanisms of urinary concentration and urea excretion.

Animals↗
PubMed1997

Effect of glyoxylate on the function of the calcitriol receptor and vitamin D metabolism.

The biological action of calcitriol is mostly mediated through the interaction of the calcitriol receptor (VDR) with vitamin D response elements (VDREs) of target genes. These interactions produce special proteins that carry out the biological activities of calcitriol. Recently, we showed that the interaction of VDRs with VDREs is inhibited by uremic toxins. We hypothesize that uremic toxins that contain aldehyde or ketone groups potentially could form Schiff bases with lysine residues of the VDR DNA binding domain and inhibit VDR interaction with VDREs. We therefore chose glyoxylate, a compound which has an aldehyde group, to test this hypothesis. In vitro glyoxylate inhibited VDR binding to the osteocalcin and osteopontin VDREs as assessed by electrophoretic mobility shift assay and the inhibition was reversed when glyoxylate was preincubated with lysine. Further, this chemical compound also blocked the induction of chloramphenicol acetyltransferase (CAT) enzyme induced by calcitriol in cells transfected with a calcitriol responsive CAT reporter gene. Since induction of 24-hydroxylase synthesis is a VDR regulated process, we also studied the effect of glyoxylate on the activity of intestinal 24-hydroxylase in rats. This enzyme activity was suppressed in rats infused with glyoxylate. Taken together, our study suggests that glyoxylate could inhibit the interaction of VDR with VDREs and alter the biological action of calcitriol.

Animals↗
PubMed1997

Effect of glucose on the function of the calcitriol receptor and vitamin D metabolism.

The genomic action of calcitriol is mediated through the interaction of the calcitriol receptor (VDR) with vitamin D response elements (VDREs) of the target genes. It has been proposed that chemicals capable of Schiff base formation with the VDR potentially could alter the physiological function of VDR and calcitriol metabolism. Since glucose has been shown to form Schiff bases with proteins, we tested the hypothesis that glucose could influence the function of VDR and thereby alter calcitriol metabolism. Glucose 6-phosphate inhibited VDR binding to the osteocalcin VDRE and chemically modified the DNA binding domain or the dimerization domain of the VDR in vitro. Further, glucose also blocked the production of chloramphenicol acetyltransferase (CAT) enzyme induced by calcitriol in cells transfected with a constructed VDRE attached to a CAT reporter gene. Hyperglycemia induced by glucose infusion or by streptozotocin in normal rats significantly reduced intestinal 1 alpha, 25-dihydroxyvitamin D-24-hydroxylase activity. Taken together, these findings are consistent with the hypothesis that glucose could interact with the VDR to impair its DNA binding and function within cells.

Animals↗
PubMed1997

ATM and RPA in meiotic chromosome synapsis and recombination.

ATM is a member of the phosphatidylinositol 3-kinase (PIK)-like kinases, some of which are active in regulating DNA damage-induced mitotic cell-cycle checkpoints. ATM also plays a role in meiosis. Spermatogenesis in Atm-/- male mice is disrupted, with chromosome fragmentation leading to meiotic arrest; in human patients with ataxia-telangiectasia (A-T), gonadal atrophy is common. Immuno-localization studies indicate that ATM is associated with sites along the synaptonemal complex (SC), the specialized structure along which meiotic recombination occurs. Recombination, preceded by pairing of homologous chromosomes, is thought to require heteroduplex formation between homologous DNA, followed by strand exchange. These early meiotic steps (entailing the formation and processing of meiotic recombination intermediates with DNA-strand interruptions) require ssDNA-binding proteins such as replication protein A (RPA; refs 5-7). In somatic cells, DNA damage induces ATM-dependent phosphorylation of RPA. We demonstrate here that ATM and RPA co-localize along synapsed meiotic chromosomes and at sites where interactions between ectopic homologous chromosome regions appear to initiate. In Atm-/- meiotic prophase spermatocytes, immuno-localization shows that RPA is present along synapsing chromosomes and at sites of fragmentation of the SC. These results suggest that RPA and ATM co-localize at sites where interhomologous-DNA interactions occur during meiotic prophase and where breaks associated with meiotic recombination take place after synapsis, implying a possible functional interaction between these two proteins.

Animals↗
PubMed1997

Transforming growth factor-beta 1 in chronic hepatitis C.

Transforming growth factor-beta 1 (TGF-beta 1) has been implicated in mediating hepatic fibrogenesis and is known to have negative regulatory effects on the immune system. To analyse the effects of TGF-beta 1 in chronic HCV, serum samples were prospectively collected from 88 chronic hepatitis C virus (HCV) patients and 34 healthy controls. Total and biologically active TGF-beta 1, interleukin (IL)-4 and IL-10 were measured by enzyme-linked immunosorbent assay (ELISA). HCV RNA levels were quantified by branched DNA signal amplification pathway (bDNA), and HCV genotypes were determined by restriction fragment length polymorphism (RFLP) based on the 5'-untranslated region (UTR). Histological diagnosis was available in 87 patients, and liver sections from 80 other HCV patients were evaluated for hepatic expression of TGF-beta 1 using immunohistochemistry. Patients with chronic HCV infection had a higher level of TGF-beta 1, both total (817 +/- 464 ng ml-1) and biologically active forms (520 +/- 370 pg ml-1), compared with controls (total TGF-beta 1 183 +/- 105 ng ml-1, P < 0.001; active TGF-beta 1 290 +/- 140 pg ml-1, P < 0.01). There was no correlation between either total or biologically active TGF-beta 1 and clinical variables (age, gender, duration), liver biochemistry (serum alanine aminotransferase) or virological (HCV RNA level, genotype) parameters but there was a correlation between total TGF-beta 1 and Knodell scores (P = 0.03, n = 54). However, when individual histological parameters were analysed, only the fibrosis score showed significant correlation (P = 0.04, n = 54). Immunohistochemistry revealed that 62% of HCV patients had TGF-beta 1 present in sinusoidal cells. No correlation existed between hepatic expression of TGF-beta 1 and any histological parameters. A trend existed towards a correlation between total TGF-beta 1 and IL-4 (P = 0.059, n = 74) but not with IL-10. Therefore, the TGF-beta 1 system is activated in chronic HCV infection and may contribute towards hepatic fibrogenesis; in addition, the TGF-beta 1 system may interact with IL-4.

Adult↗