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S Xu

Publications and source records attributed to S Xu.

At least 343 records · Page 19Linked to original sources
PubMed1997

Comparative effects of topical ocular anti-allergy drugs on human conjunctival mast cells.

BACKGROUND: The concept of mast cell heterogeneity is well established. Recent data indicate that human conjunctival tissue mast cells and human connective tissue mast cells respond to various secretagogues in similar fashion. It is now recognized that different mast cell populations respond differently to anti-allergic drugs. OBJECTIVE: The purpose of the study is to compare the effects of three new ocular anti-allergic drugs (nedocromil, olopatadine, and pemirolast) on mediator release from the target human conjunctival mast cell population with those of cromolyn sodium. The affinity of the compounds for the histamine H1 receptor was also compared. METHODS: A monodispersed suspension of partially purified human conjunctival mast cells was prepared from cadaver conjunctival tissue. Mast cells (5 x 10(3)) were challenged with anti-human IgE in the presence or absence of test drugs, and histamine content of the cell supernatants was determined using a specific radioimmunoassay. H1 receptor binding activity was assessed using a radioligand binding assay. RESULTS: Cromolyn and pemirolast (100 nM to 1 mM) failed to significantly inhibit histamine release from human conjunctival mast cells using exposure times of 1 and 15 minutes prior to challenge. Using identical nedocromil concentrations and exposure times, statistically significant (P < .05) inhibition (28%) of histamine release was observed at only the 100 microM concentration and 1-minute exposure time. In contrast, olopatadine inhibited histamine release in a concentration-dependent fashion (r = 0.891, n = 59, IC50 = 653 microM). Only olopatadine exhibited significant H1 receptor binding activity at relevant concentrations (Ki = 36 nM, n = 13). CONCLUSIONS: These data indicate that olopatadine possesses anti-allergic activity in the appropriate targets for topical ocular anti-allergic drug therapy, human conjunctival mast cells. Coupled with the compound's antihistaminic activity, this suggests that olopatadine will have efficacy advantages in allergic conjunctivitis patients over the other drugs tested.

Administration, Topical↗
PubMed1997

Intracellular calcium ion responses to somatostatin in cells from human somatotroph adenomas.

OBJECTIVE: Various GH secretory responses to long-acting somatostatin (SRIH) analogues have been observed during the treatment of acromegalic patients. The effects of SRIH on intracellular Ca2+ homeostasis in human somatotroph adenoma cells has not been examined in detail, and the underlying mechanisms therefore remain to be determined. Using isolated cells from human somatotroph adenomas, we have investigated the SRIH-induced intracellular Ca2+ responses at a single-cell level with computerized real time intracellular calcium ion (Ca2+i) imaging. PATIENTS: Adenoma specimens were obtained from 4 male and 11 female acromagalic patients (mean age 56, range 26-72 years) undergoing transsphenoidal hypophysectomy. METHODS: The identity of the biopsy material obtained was confirmed by Immunocytochemistry for hGH and in situ hybridization histochemistry using a 35S end-labelled hGH oligodeoxynucleotide probe and probes complementary to proopiomelanocortin and prolactin. Genomic DNA coding for somatostatin receptor (SSTR2) from each adenoma was PCR amplified and sequenced. Cells cultured from these adenoma were subject to computerized real time intracellular Ca2+i imaging at a single cell level. RESULTS: In cells from 11 of the 15 adenomas, SRIH produced a reversible, dose-independent reduction in [Ca2+]i from the mean of 167 +/- 11 to 43 +/- 3 nM within 51 +/- 1.8 s, and blocked the growth hormone releasing hormone (GRH)-induced increase in [Ca2+]i as expected. In the same adenomas, withdrawal of SRIH after a 30 second exposure produced a small but significant increase in resting [Ca2+]i. Pretreatment with pertussis toxin abolished the SRIH-Induced inhibition of [Ca2+]i and prevented the SRIH-induced inhibition of the effect of GRH on [Ca2+]i. One of the remaining 4 adenomas was completely unresponsive to SRIH despite responding vigorously to other ligands and Immunostaining strongly for GH. Surprisingly, cells from 3 adenomas showed a paradoxical increase in [Ca2+]i in response to SRIH in some or, in one case, all of the cells examined. In all adenomas the sequence of SSTR2 corresponded to wild-type. CONCLUSIONS: In the majority of cells derived from human somatotrophic adenomas, SRIH caused a reduction in baseline [Ca2+]i and inhibition of GRH-induced [Ca2+]i increase, as observed in somatotrophs of other species. In addition, SRIH was found either to induce a paradoxical increase in [Ca2+]i or to have no effect on [Ca2+]i in a small proportion of somatotroph adenomas examined. This finding corroborates the clinical observation that the response to SRIH analogues varies markedly between somatotroph adenoma patients. There was no evidence of SSTR2 mutations in any of the adenomas examined.

Acromegaly↗
PubMed1997

Scanning (atomic) force microscopy imaging of earthworm haemoglobin calibrated with spherical colloidal gold particles.

Scanning (atomic) force microscopy (SFM) permits high-resolution imaging of a biological specimen in physiological solutions. Untreated extracellular haemoglobin molecules of the common North American earthworm. Lumbricus terrestris, were imaged in NH4Ac solution using calibrated SFM. Individual molecules and their top and side views were clearly identified and were comparable with the images of the same molecule obtained by scanning transmission electron microscopy (STEM). A central depression, the presumed mouth of the hole, was detected. We analysed 75 individual molecules for their lateral dimensions. Compression varied for different molecules, presumably because of the variation of the interaction between the SFM tip and the protein molecule. Two effective heights which correspond to the heights of the points of the haemoglobin molecules first and last touched by the tip, h1 and h2, respectively, were measured for each protein and ranged between 1.58 and 16.2 nm for h1 and 1.23 and 13.6 nm for h2. The apparent diameter was measured and ranged from 44.9 to 86.6 nm (63.2 +/- 10.5 nm, n = 75), which is about twice the diameter of the molecule reported by STEM for the top view orientation. The higher the measured effective heights, the worse was the tip convolution effect. In order to determine the tip parameters (semivertical angle, curvature of radius and the cut-off height) and to calibrate images of earthworm haemoglobin molecules, spherical gold particles were scanned as standards. The tip sectional radii at distances of h1 and h2 above the tip apex were subtracted from the apparent diameter of the protein. The calibrated lateral dimension was 29.1 +/- 3.85 nm, which is close to the reported scanning transmission electron microscopy data 30.0 +/- 0.8 nm. The results presented here demonstrate that the calibration approach of imaging gold particles is practical and relatively accurate. Calibrated SFM imaging can be applied to the study of other biomacromolecules.

Animals↗
PubMed1997

Neutralization of a clade B primary isolate by sera from human immunodeficiency virus-uninfected recipients of candidate AIDS vaccines.

The inability of antibodies induced by experimental human immunodeficiency virus type 1 (HIV-1) vaccines to neutralize HIV-1 primary isolates may be due to a failure to elicit such antibodies, antigenic differences between the vaccine and the strains tested, insensitivity of the assays used, or to a combination of factors. New neutralization assays were used to determine the ability of candidate AIDS vaccines to generate neutralizing antibodies for clade B primary isolate BZ167, which is closely related in portions of its envelope to the immunizing strains. Sera from HIV-uninfected volunteers in vaccine trials were tested, and neutralizing activity was found in recipients of recombinant (r) gp120MN or of rgp160MN-containing canarypox boosted with rgp120SF-2. Detection of antibodies that neutralize primary isolate BZ167 correlated with neutralizing activity for homologous vaccine strains. These data demonstrate that certain candidate AIDS vaccines can elicit antibodies that neutralize a primary isolate of HIV-1.

AIDS Vaccines↗
PubMed1997

Distinct requirements for somatic and germline expression of a generally expressed Caernorhabditis elegans gene.

In screening for embryonic-lethal mutations in Caenorhabditis elegans, we defined an essential gene (let-858) that encodes a nuclear protein rich in acidic and basic residues. We have named this product nucampholin. Closely homologous sequences in yeast, plants, and mammals demonstrate strong evolutionary conservation in eukaryotes. Nucampholin resides in all nuclei of C. elegans and is essential in early development and in differentiating tissue. Antisense-mediated depletion of LET-858 activity in early embryos causes a lethal phenotype similar to characterized treatments blocking embryonic gene expression. Using transgene-rescue, we demonstrated the additional requirement for let-858 in the larval germline. The broad requirements allowed investigation of soma-germline differences in gene expression. When introduced into standard transgene arrays, let-858 (like many other C. elegans genes) functions well in soma but poorly in germline. We observed incremental silencing of simple let-858 arrays in the first few generations following transformation and hypothesized that silencing might reflect recognition of arrays as repetitive or heterochromatin-like. To give the transgene a more physiological context, we included an excess of random genomic fragments with the injected DNA. The resulting transgenes show robust expression in both germline and soma. Our results suggest the possibility of concerted mechanisms for silencing unwanted germiline expression of repetitive sequences.

Amino Acid Sequence↗
PubMed1997

Altering developmental trajectories in mice by restricted index selection.

A restricted index selection experiment on mice was carried out for 1-4 generations on rate of early postnatal development (growth rate from birth to 10 days of age) vs. rate of development much later in ontogeny (growth rate from 28 to 56 days of age). Early rate of development (E) approximates hyperplasia (changes in cell number) and later rate (L) reflects hypertropy (changes in cell size). The selection criteria were as follows; E+LO was selected to increase early body weight gain while holding late body weight gain constant; E-LO was selected to decrease early body gain while holding late gain constant; EOL+ was selected to increase late gain holding early gain constant; and EOL- was selected to decrease late gain holding early gain constant. After 14 generations of selection, significant divergence among lines has occurred and the changes in the growth trajectories are very close to expectation. The genetic and developmental bases of complex traits are discussed as well as the concept of developmental homoplasy.

Animals↗
PubMed1997

Neutralization of HIV-1 primary isolates by polyclonal and monoclonal human antibodies.

To examine antibody-mediated neutralization of HIV-1 primary isolates in vitro, we tested sera and plasma from infected individuals against four clade B primary isolates. These isolates were analyzed further for neutralization by a panel of several human anti-HIV-1 mAb in order to identify the neutralizing epitopes of these viruses. Each of the HIV-1+ serum and plasma specimens tested had neutralizing activities against one or more of the four primary isolates. Of the three individual sera, one (FDA-2) neutralized all of the four isolates, while the other two sera were effective against only one virus. The pooled plasma and serum samples reacted broadly with these isolates. Based on the neutralizing activities of the mAb panel, each virus isolate exhibited a distinct pattern of reactivity, suggesting antigenic diversity among clade B viruses. Neutralizing epitopes were found in the V3 loop and CD4-binding domain of gp120, as well as near the transmembrane region (cluster II epitope) of gp41. A mAb directed to the cluster I epitope of gp41 near the immunodominant disulfide loop weakly neutralized one primary isolate. None of the mAb in the panel affected one primary isolate, US4, although this virus was sensitive to neutralization by some of the polyclonal antibody specimens. This isolate was also resistant to neutralization by a cocktail of 10 mAb, most of which individually inhibited at least one of the other three viruses tested. These results suggest that neutralizing activity for this latter virus is present in certain HIV-1+ sera/plasma, but is not exhibited by the mAb in the panel. Thus, effective neutralizing antibodies against primary isolates can be generated by humans upon exposure to HIV-1, but not all of these antigenic specificities are represented in a large panel of human anti-HIV-1 mAb.

Antibodies, Monoclonal↗
PubMed1997

Scavenger receptor BI--a cell surface receptor for high density lipoprotein.

The receptor-mediated transfer of lipids between cells and lipoproteins plays an important role in lipoprotein metabolism and cardiovascular disease. Although there have been many valuable studies of HDL binding to tissues, cells and membranes, and of the potential role of such binding in the transport of lipids between HDL and cells, much less is known about HDL receptors than about receptors for other lipoproteins (e.g. LDL, chylomicrons, vitellogenin). Here we review recent studies of the class B, type I scavenger receptor, which appears to be a physiologically relevant, cell surface HDL receptor that mediates the selective uptake of lipids by cells.

Animals↗
PubMed1997

A differential hybridization scheme to identify photoreceptor-specific genes.

Identification of genes expressed preferentially or exclusively in photoreceptors will facilitate the understanding of photoreceptor biology as well as provide candidate genes for inherited retinal degenerations. To achieve this goal we performed a differential hybridization screen of 3717 well-isolated phage clones from a human retinal cDNA library. Clones were selected for further study if they hybridized exclusively or strongly preferentially to a probe derived from RNA isolated from the cone-predominant retina of 13-line ground squirrels as compared to a probe derived from human fibroblast RNA. Twenty percent of clones (9/45) identified by this screen were derived from photoreceptor-specific genes and an additional 24.4% (11/45) were from neural-specific genes, demonstrating the utility of this strategy in identifying genes important for retinal biology.

Base Sequence↗
PubMed1997

Scleroderma fibroblasts show increased responsiveness to endothelial cell-derived IL-1 and bFGF.

Fibroblasts cultured from lesional skin in scleroderma (systemic sclerosis) demonstrate an activated phenotype that may be important in pathogenesis. Endothelial cell-derived cytokines can modulate fibroblast properties, and endothelial cell changes occur early in scleroderma. Thus, endothelial cell and fibroblast dysfunction may be linked through the paracrine activity of soluble endothelial cell products. We have explored endothelial cell-fibroblast interactions in vitro by investigating the modulation of scleroderma and control fibroblast properties by endothelial cell-conditioned medium (EC-CM). EC-CM caused a concentration-dependent stimulation of fibroblast DNA and protein synthesis and upregulation of cell surface ICAM-1 expression. Scleroderma fibroblasts showed consistently greater responses than control cells. Medium conditioned by mechanically wounded endothelial cells had a greater effect than that from resting endothelial cells. Pre-incubation of EC-CM with anti-bFGF significantly reduced the promotion of fibroblast thymidine incorporation but did not affect endothelial cell-induced leucine incorporation. Conversely, anti-IL-1 antibodies abrogated EC-CM-induced leucine incorporation and ICAM-1 expression but did not diminish thymidine incorporation. Recombinant bFGF or IL-1 modulated fibroblast properties similarly. These data demonstrate that endothelial cell-derived IL-1 and bFGF modulate fibroblast properties independently and that lesional scleroderma strains are more responsive than control fibroblasts to endothelial cell-induced modulation, which supports the hypothesis that altered endothelial cell-fibroblast communication may be involved in the pathogenesis of scleroderma.

Cell Count↗
PubMed1997

Proteolysis of insulin-like growth factor-binding protein-3 by human skin keratinocytes in culture in comparison to that in skin interstitial fluid: the role and regulation of components of the plasmin system.

Proteolysis of insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) is an important determinant of IGF action on cells. We have investigated this in a human skin keratinocyte cell line HaCaT. Although these cells did not normally produce an active IGFBP-3 protease, addition of plasminogen resulted in a dose-dependent proteolysis of endogenous and exogenous IGFBP-3, producing fragments similar to those cleaved by skin interstitial fluid, but different from those generated by plasmin. Protease inhibitor profiles suggested the enzyme in the conditioned medium to be a calcium-dependent serine protease. Exogenous IGFBP-3 either inhibited or slightly stimulated IGF-I-induced cell proliferation when it was coincubated or preincubated with the cells, respectively. Both effects were attenuated in the presence of plasminogen. Preincubation of cells with IGF-I or long R3 IGF-I divergently changed plasminogen activator inhibitor-1 and -2 secretion, but only IGF-I blocked IGFBP-3 proteolysis. Such inhibition was also observed in a cell-free protease assay. IGF-I, however, had no effect on plasmin-induced IGFBP-3 degradation. Together, these data indicate that an IGFBP-3 protease similar to that in skin interstitial fluid is generated in plasminogen-treated HaCaT cells, and it attenuates the effects of IGFBP-3 on IGF action. IGF-I, probably by coupling with IGFBP-3, can protect it from the action of this protease.

Cell Division↗
PubMed1997

Differential regulation of mitogen-activated protein/ERK kinase (MEK)1 and MEK2 and activation by a Ras-independent mechanism.

Mitogen-activated protein (MAP)/ERK kinase (MEK)1 and MEK2 are the upstream activators of the MAP kinases, ERK1 and ERK2. MEK1 and MEK2 are approximately 85% identical in sequence but have unique inserts in their C-terminal domains. MEK isoform-specific antibodies were used to examine expression and regulation of each enzyme. MEK1 and MEK2 were expressed in approximately equal amounts in several cell lines; in some, MEK1 was present in slight excess. Activation of tyrosine kinase-containing receptors, heterotrimeric G proteins, and protein kinase C enhanced the activities of both MEK isoforms in 293 and PC12 cells. AIF4-stimulated both MEK1 and MEK2 in PC12 cells expressing a dominant interfering Ras mutant that prevents nerve growth factor-dependent activation of the cascade. Carbachol also stimulated the pathway in these cells. Thus, in addition to their ability to activate Ras/Raf and the downstream ERK pathway, heterotrimeric G proteins also appear to trigger a Ras-independent mechanism to regulate this kinase cascade. In U373, Chinese hamster ovary (CHO), and INS-1 cells, MEK1 was activated by regulators of ERKs, while MEK2 was not. These data suggest that, like the MAP kinases ERK1 and ERK2, in some cell settings the two similar MEK isoforms are differentially regulated.

3T3 Cells↗
PubMed1997

[Models for describing ultrasound scattering in blood].

The acoustic scattering properties of blood, which are of fundamental importance for the diagnostic utilization of ultrasonic signals backscattered by blood in Doppler-based procedures, have now been investigated using three different scattering models: the particle model, the continuum model and the hybrid model. The analysis shows the limitations of the approaches so far described in the literature, and also permits a modification of the hybrid model to produce an appreciably more accurate description of the true scattering properties of the blood. This is verified by a comparison of theoretical and experimental results obtained for a large range of haematocrits.

Blood↗
PubMed1997

Effect of whole cottonseed, gossypol, and ruminally protected lysine supplementation on milk yield and composition.

To determine whether the gossypol content of the diet affected availability of dietary Lys, 4 cows with ruminal and duodenal cannulas and 16 intact cows in early lactation were assigned to diets containing either glanded cottonseed, glanded cottonseed plus 15 g/d of ruminally protected Lys, glandless cottonseed, or glandless cottonseed plus 15 g/d of ruminally protected Lys. The experimental design was a 4 x 4 Latin square design with 3-wk experimental periods. Gossypol concentrations in plasma were lower when cows were fed glandless cottonseed. Lysine supplementation increased the flow and percentage of Lys in duodenal digesta and increased the concentration of Lys in plasma. Neither type of cottonseed nor Lys supplementation affected dry matter intake. Yields of milk and fat-corrected milk from cannulated cows were not affected by diet, but yields from intact cows were increased by Lys supplementation. For both cannulated and intact cows, Lys supplementation increased the percentage of milk protein, and milk protein yield was increased by Lys in intact cows. Dietary gossypol did not affect the response to Lys, indicating that dietary gossypol had little or no effect on the availability of Lys for dairy cows.

Amino Acids↗
PubMed1997

[Effects of endothelin-1 on the progesterone production of rat preovulatory ovarian granulosa cells].

The effect of endothelin-1 (ET) on progesterone production of isolated rat granulosa cells and its mechanism were investigated. ET could inhibit the hCG-stimulated progesterone production significantly at the concentration of 10(-8) mol/L (P < 0.05, n = 6) and highly significantly at the concentration of 10(-7) mol/L (P < 0.05, n = 6), but ET did not inhibit the basal progesterone production at various concentrations (10(-10)-10(-7) mol/L). Further experiments showed that the inhibitory effect of ET on the hCG-stimulated progesterone production could be reversed by rabbit antiserum to ET (ET-A, 1:1000) or cAMP (10(5) mol/L). ET could decrease the binding sites and the affinity constant (ka) of LH/hCG receptor on granulosa cells. All these findings suggest that ET may be an intraovarian regulatory factor which may inhibit progesterone production stimulated by hCG from rat granulosa cells through inerfering LH/hCG receptor function and cAMP formation.

Animals↗
PubMed1997

[Mutual regulation of proliferation between pulmonary artery endothelial cells and pulmonary smooth muscle cells in vitro].

Vascular endothelial cell are closely related to vascular smooth muscle cells in structure and function. The interactions between them may play important roles in the modulation of function and structure of vascular wall. In the present study, the mitogenic regulations between cultured new bovine pulmonary arterial endothelial cell (PAEC) and pulmonary arterial smooth muscle (PASM) were investigated. When PAECs and PASMs were mixcultured, 3H-TdR incorporation into the mixed cells decreased significantly (P < 0.001 vs control). When PAECs and PASMs were cultured in conditioned medium from PASMs and PAECs respectively or they were cocultured, the proliferation of PAECs was inhibited while that of PASM was stimulated significantly (P < 0.05 vs control). It was also found that the concentration of cAMP increased but cGMP decreased in cocultured PASMs (P < 0.01 vs control), while the concentration of both cAMP and cGMP decreased significantly in cocultured PAECs (P < 0.01 vs control). These findings suggest that PAECs and PASMs may regulate their proliferation each other through the second messenger system.

Animals↗
PubMed1997

[The effects of hypoxia on angiotensin II secretion by cultured pulmonary artery endothelial cells].

The alterations of paracrine function of pulmonary arterial endothelial cells (PAEC) might play an important role in the development of hypoxic artery hypertension (HPAH). To test this hypothesis, the effects of hypoxia on angiotensin II (AT II) secretion by new born bovine PAEC were investigated. AT II secretion increased significantly when PAECs were incubated under 2.5% O2 hypoxic condition for 1.5 h (P < 0.01 vs control). But it decreased from 1.5 h to 12 h incubation and increased from 12 h to 48 h incubation under 0% O2 hypoxic condition, with significance compared with control group (P < 0.01). NO donor SIN-1 inhibited but endogenous NO inhibitor L-nitro-arginine promoted AT II secretion significantly under both normorxic and hypoxic conditions. It was also found that the concentration of cyclic guanine monophosphate in PAEC decreased significantly at 24 h incubation in 0% O2. The above results suggest that changes of AT II in PAEC may participate in the development of HPAH.

Angiotensin II↗