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S Chen

Publications and source records attributed to S Chen.

At least 415 records · Page 23Linked to original sources
PubMed2000

Development of early melanocytic lesions in transgenic mice predisposed to melanoma.

We have previously described a line of transgenic mice (TG3) that spontaneously develops heritable malignant melanoma. Histological analysis of these animals during the first postnatal month is described here. In the TG3 line, the number of melanocytes is increased at all anatomical sites to which neural-crest-derived melanocytes normally migrate. Clonal expansion and morphological changes of these melanocytes can be detected as early as postnatal day (PND) 15. By PND 30, cells morphologically indistinguishable from the tumor cells of adult transgenic mice were detected in the ear, eye lid and perianal region. These cells are believed to be the precursors of the primary tumors in adult mice. The stepwise development of melanoma in the TG3 line is similar to the stepwise development of melanoma in humans.

Animals↗
PubMed2000

Serial learning by rhesus monkeys: II. Learning four-item lists by trial and error.

Three rhesus macaque monkeys were trained to produce novel 4-item lists (A-->B-->C-->D) on which all items were displayed from the start of training. Subjects were previously trained to produce 4-item lists by adding one item at a time (A, A-->B, A-->B-->C, and A-->B-->C-->D; lists K. B. Swartz et al., 1991). Those lists could be mastered by responding to each new item last. To learn lists on which all items were displayed from the start of training, subjects had to recall the consequences of errors and correct responses to each item. Errors ended the trial; correct responses to A, B, or C allowed the trial to continue. A correct response to D produced food reward. Although the probability of executing a 4-item list correctly by chance was .04, each subject mastered 4 novel 4-item lists by trial and error. The ability of monkeys to use a trial-and-error strategy to learn novel lists provides a basis for studying the development of serial expertise in animals.

Animals↗
PubMed2000

Interaction of endothelin-1 with vasoactive factors in mediating glucose-induced increased permeability in endothelial cells.

Alteration of endothelins (ET) and/or their receptors may be important in mediating vascular dysfunction in diabetes. We investigated mechanisms regulating ET-1 expression in human umbilical vein endothelial cells (HUVEC) in response to glucose and the functional significance of these mechanisms. Permeability across HUVEC, grown in medium containing either low (5 mmol/l) or high (25 mmol/l) D-glucose were investigated. L-glucose was used as a control. ET-1, ET(A), and ET(B) mRNA were assessed by semiquantitative RT-PCR. ET-1 immunoreactivity and F-actin microfilament assembly were investigated using confocal microscopy. Increased transendothelial permeability was noted in cells cultured in high glucose or when the cells grown in low (physiologic) glucose were incubated with ET-1, vascular endothelial growth factor (VEGF), or N (G) -nitro-L-arginine methyl ester but not when they were incubated with ET-3, N(G)-nitro-D-arginine methyl ester, or L-glucose. Increased permeability was associated with increased ET-1, ET(A), and ET(B) mRNA expression and augmented ET-1 immunoreactivity. High glucose induced increased permeability, increased ET-1, ET(A), and ET(B) mRNA expression. ET-1 immunoreactivity was blocked by the protein kinase C (PKC) inhibitor chelerythrine, the specific PKC isoform inhibitor 379196, VEGF-neutralizing antibody, or the ET(A) blocker TBC11251, but was not blocked by the specific ET(B) blocker BQ788 or by a VEGF-non-neutralizing antibody. Increased permeability was also associated with deranged F-actin assembly in the endothelial cells and by derangement of endothelial cell junctions as assessed by electron microscopy. Data from this study suggest that high glucose-induced increased permeability may be induced through increased ET-1 expression and disorganization of F-actin assembly. ET-1 expression and increased permeability may occur secondary to PKC isoform activation and may be modulated by VEGF and nitric oxide.

Base Sequence↗
PubMed2000

Treatment of BK virus-associated hemorrhagic cystitis and simultaneous CMV reactivation with cidofovir.

Hemorrhagic cystitis (HC) is a common complication following high-dose chemotherapy and bone marrow transplantation, and the treatment of virus-associated HC remains to be optimized. This is the first report on the successful use of cidofovir in a patient with HC and polyoma viruria concomitant with CMV reactivation after allogeneic BMT. Treatment led to a significant decrease in viruria and to sustained suppression of CMV reactivation. Administered with probenecid and hydration, cidofovir was well tolerated, and there were no side-effects.

Antiviral Agents↗
PubMed2000

Naturally occurring polyphenolic antioxidants modulate IgE-mediated mast cell activation.

Reactive oxygen species (ROS) are known to modulate activities of a host of kinases, phosphatases and transcription factors. Rutin and chlorogenic acid (CGA) are the major polyphenolic antioxidants present in the small molecular fraction of smokeless tobacco leaf extracts, as ascertained by reverse-phase high-pressure liquid chromatography (HPLC) and mass spectrometry. Levels of intracellular ROS in resting versus antigen-immunoglobulin E (IgE)-challenged murine mast cells were measured at 510 nm by fluorescence-activated cell sorting (FACS) using carboxy-dichlorofluorescein (DCFH-DA). Enhanced ROS production was observed in IgE-sensitized mast cells following antigenic challenge. Rutin and CGA reduced ROS levels in antigen-IgE-activated mast cells. Concomitantly, they also profoundly inhibited histamine release by these activated mast cells. In contrast, rutin and CGA augmented the inducible cytokine messages, i.e. interleukin (IL)-10, IL-13, interferon-gamma (IFN-gamma), IL-6 and tumour necrosis factor-alpha (TNF-alpha) in IgE-sensitized mast cells following antigen challenge. This study indicates that tobacco polyphenolic antioxidants that quench intracellular ROS, differentially affect two effector functions of antigen-IgE-activated mast cells. This model system may be employed to determine the molecular target of polyphenols. The potential role of these polyphenolic antioxidants on IgE-mediated allergy in vivo depends on a balance of their differential effects on mast cell activation.

Animals↗
PubMed2000

Growth hormone-releasing hormone decreases voltage-gated potassium currents in GH4C1 cells.

The electrophysiological properties of anterior pituitary somatotropes integrally involve the function of voltage-gated K+ currents. In this study, we have used GH4C1 cell lines to investigate the effect of human GHRH on voltage-gated K+ currents. Because of a clear 'rundown' of the K+ current with classic whole cell recording (WCR) without ATP in pipette solution, nystatin-perforated WCR was the major recording configuration used. Using a low Ca2+ (0.5 mM) bath solution containing Co2+ (1 mM) and TTX (1 microM), GH4 cells predominantly exhibited an outward delayed rectifier K+ current (IK). Local application of growth hormone releasing hormone (GHRH) (100 nM) reversibly reduced the amplitude of the K+ currents (to 83% of control). There was no effect of GHRH on the activation curve of the K+ current and no difference observed using 2.5 mM Ca2+ or low Ca2+ (0.5 mM Ca2++1 mM Co2+) bath solutions. Under the condition of low Ca2+ bath solution, the application of apamin (1 microM) or charybdotoxin (1 microM), two specific blockers of the Ca2+-activated K+ current, did not alter the K+ current or the response to GHRH. This reduction in the K+ current by GHRH was also observed with classic WCR with a pipette solution containing ATP (2 mM). The GHRH-induced reduction in the K+ current was completely abolished by the presence of GDP-beta-s (500 microM) in the pipette solution or by addition of PKC inhibitors, calphostin C (100 nM) and chelerythrine (1 microM), in bath solution. Inhibitor for cAMP-PKA system (Rp-cAMP and H89) did not affect the K+ current response to GHRH. These results suggest that GHRH reduces the voltage-gated K+ current in GH4C1 cells, a response that is mediated by G-proteins and PKC system but not by cAMP-PKA system. The reduction in the K+ current may partially contribute to the GHRH-stimulated growth hormone (GH) secretion.

Apamin↗
PubMed2000

Catalytic differences between porcine blastocyst and placental aromatase isozymes.

Two isozymes of porcine aromatase, the placental and the blastocyst forms, were expressed in CHO cells using the mammalian cell transfection method. Using an 'in-cell' assay (a 3H-water release method), catalytic parameters of the porcine placental aromatase were found to be very similar to those of the human enzyme; however, the activity of the blastocyst isozyme was found to be one-thirtieth that of the placental isozyme. Product isolation assay (using testosterone as the substrate) revealed that the major steroid products were 17beta-estradiol and 19-nortestosterone. The product ratio of estradiol/19-nortestosterone was found to be 94 : 6 for the porcine placental form, 6 : 94 for the porcine blastocyst form, and 92 : 8 for the human wild-type aromatase. Therefore, the porcine blastocyst aromatase isozyme catalyzes mainly androgen 19-desmethylation rather than aromatization. In addition, inhibition profile analyses on the placental and blastocyst isozymes were performed using three steroidal inhibitors [4-hydroxyandro-stenedione (4-OHA), 7alpha-(4'-amino)phenylthio-1, 4-androstandiene-3,17-dione (7alpha-APTADD), and bridge (2, 19-methyleneoxy) androstene-3,17-dione (MDL 101,003)], and four nonsteroidal inhibitors [aminoglutethimide (AG), CGS 20267, ICI D1033, and vorozole (R83842)]. While the two isozymes of porcine aromatase share 93% amino-acid sequence identity, our results indicate that the two porcine aromatase isozymes have distinct responses to various aromatase inhibitors.

Animals↗
PubMed2000

Non-steroidal anti-inflammatory drug toxicity in the upper gastrointestinal tract.

Non-steroidal anti-inflammatory drug (NSAID) toxicity in the upper gastrointestinal tract is the most common serious drug-induced toxicity reported to drug regulatory authorities. In the last two decades, the rediscovery of H. pylori, development of potent ulcer-healing drugs and specific Cox-II inhibitors have opened new horizons in the management of NSAID toxicity. A Working Party composed of gastroenterologists and rheumatologists in the Asia-Pacific region met in Cairns, Australia, in 1999 to review the literature and develop appropriate guidelines. Recommendations were made based on the latest existing evidence. The importance of clinical events as study endpoints was emphasized. While differences exist between NSAIDs and aspirin, most studies have shown that advanced age, history of peptic ulcer disease, serious concomitant illnesses and coprescription of NSAID/aspirin with anticoagulants and steroids are high risk factors. These patients should be considered for prophylactic anti-ulcer therapy. Helicobacter pylori infection may aggravate the toxicity of NSAIDs and, in selected cases, should be treated before NSAID/aspirin is prescribed. Proton pump inhibitors and misoprostol are the most promising agents in preventing gastric and duodenal ulcers. When NSAID/aspirin needs to be continued in patients who develop an NSAID-related ulcer, proton pump inhibitors offer the best healing effect. With the discovery of cyclo-oxygenase isoforms (Cox-I and Cox-II), preferential and specific Cox-II inhibitors have been developed. While early clinical data have suggested promising antiinflammatory effects and improved safety profile in the gastrointestinal tract, several key issues on long-term safety remain unresolved. The use of potent anti-ulcer therapy, treatment of H. pylori infection and the development of Cox-II inhibitor will change the scenario of NSAID/aspirin-related gastrointestinal toxicity in the next millennium.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Amadori-glycated albumin in diabetic nephropathy: pathophysiologic connections.

Amadori-glycated albumin in diabetic nephropathy: Pathophysiologic connections. Nonenzymatic glycation of proteins represents a major mechanism by which hyperglycemia leads to diabetic renal disease. Recent research has shown that Amadori-modified albumin, the principal glycated protein in plasma, elicits pathobiologic effects in cultured renal cells that are identical to those of high ambient glucose. When added to the incubation media of glomerular mesangial and endothelial cells, glycated albumin stimulates protein kinase C (PKC) activity, increases transforming growth factor-beta (TGF-beta) bioactivity, and induces gene overexpression and enhanced production of extracellular matrix proteins. These cellular events, whereby PKC-mediated TGF-beta activation leads to increased matrix expression, are inextricably linked, and they form the central tenets of a pathophysiologic connection between glycated proteins and diabetic nephropathy. In vivo studies further corroborate the role of glycated proteins in the pathogenesis of diabetic nephropathy. Reduction or neutralization of glycated albumin in the db/db mouse model of type 2 diabetes significantly ameliorates the proteinuria, renal insufficiency, mesangial expansion, and overexpression of matrix proteins. In human type 1 diabetes, the plasma-glycated albumin concentration is independently associated with the presence of nephropathy. Abrogating the biologic effects of increased glycated albumin has novel therapeutic potential in the management of renal complications in diabetes.

Animals↗
PubMed2000

Polyorchism.

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Child, Preschool↗
PubMed2000

Optimization of the size distribution and myocardial contrast effect of perfluorocarbon-filled albumin microbubbles by lyophilization under continuous negative pressure.

This study was undertaken to evaluate the effect of lyophilization under continuous negative pressure on perfluoropropane-filled albumin microbubble size distribution and myocardial contrast effect. Three different microbubble preparations were studied: (1) 1% albumin solution without a sugar (Optison), (2) 1% albumin and 5% dextrose (PESDA), and (3) 1% albumin and 5% fructose (PESFA). The 2 preparations containing sugar were also subjected to lyophilization under continuous negative pressure. Microbubble size distribution was measured with a Coulter Multisizer II (Beckman Coulter, Inc, Fullerton, Calif). The microbubbles were injected intravenously into a rat during intravital microscopy of the mesenteric microcirculation. Finally, the different albumin microbubbles were injected intravenously into 10 dogs, and myocardial contrast effect was assessed by videodensitometry. Results of the Coulter counter studies showed lyophilized PESFA to have a smaller size distribution with 99.9% + or - 0.1% of microbubbles <10 microm in diameter and 88.5% + or - 1.4% <4 microm in diameter (P <.05 compared with Optison or PESDA). On intravital microscopy, PESFA microbubbles behaved as intravascular tracers without microvascular plugging or coalescence. Finally, myocardial peak gray scale and area under the curve were significantly higher for PESFA than for PESDA or Optison, respectively. In conclusion, lyophilization of perfluoropropane-filled albumin microbubbles results in smaller microbubbles with a more uniform size distribution and brighter myocardial contrast. In addition, the substitution of fructose for dextrose improves size distribution and contrast effect. These findings have important implications regarding the use of novel imaging technologies that take advantage of microbubble destruction to image myocardial perfusion.

Albumins↗
PubMed2000

Ligneous conjunctivitis: a local manifestation of a systemic disorder?

Ligneous conjunctivitis is a descriptive term. It refers to the "woody" consistency of the pseudomembrane that usually forms on the palpebral conjunctiva of those affected. It is rare and probably only one manifestation of a multiorgan, pseudomembranous disease. (1-4) We report a case of ligneous conjunctivitis in which investigation revealed a plasminogen deficiency in the heterozygous range (previously reported only in association with a homozygous plasminogen deficiency). We suggest a strategy for investigating known and new cases of ligneous conjunctivitis and/or pseudomembranous disease.

Biopsy↗
PubMed2000

Effects of a neutral endoprotease enzyme inhibitor, thiorphan, on hemodynamics and renal excretory function in four models of experimental hypertension.

Thiorphan, a neutral endoprotease (NEP) enzyme inhibitor, has been shown to enhance the effects of atrial natriuretic peptide (ANP) in vivo. In this study, we examined the effects of an intravenous (iv) infusion of thiorphan on cardiovascular hemodynamics and excretion of urine volume (UV), sodium (U(Na)V) and potassium (UKV) in four different models of experimental hypertension, namely: 1) SHR, 2) two-kidney, one clip (2K1C),3) one-kidney, 1 clip (1K1C) and. 4) 70% reduced renal mass-salt (RRM-S) hypertensive rats. SHR has normal plasma renin activity, 2K1C is renin dependent, and 1K1C and RRM-S are low renin volume dependent models of hypertension. Rats were divided into experimental and control groups. Under inactin (120 mg/kg, body weight) anesthesia, rats were instrumented to record blood pressure and dP/dt (Millar catheter) and urine was collected through a suprapubic urinary bladder catheter. Experimental animals received an iv infusion of thiorphan, 0.5 mg/kg/min for 120 minutes. Control animals received vehicle only. In some animals, vascular smooth muscle cell membrane potentials (Em) was measured in vivo. In another series of experiments, using the identical protocol, cardiac output was recorded. The thiorphan infusion produced a similar progressive decrease in blood pressure in all models of hypertension. Cardiac output did not change relative to vehicle infused control animals. Thus pressure decreased because of a decrease in total peripheral resistance. The contractility index (dP/dt/P, where P = left ventricular pressure) did not change but vascular smooth muscle cells in tail arteries hyperpolarized in all four models. In spite of a significant decrease in blood pressure, thiorphan infusion either increased or produced no change in urinary volume (UV) and sodium (U(Na)V) excretion. These data show that thiorphan, an NEP inhibitor, decreases the blood pressure of hypertensive rats due to a decrease in total peripheral resistance, perhaps by hyperpolarizing vascular smooth muscle cells. These effects are independent of the mechanism of the hypertension. Increased UV and U(Na)V in the face of decreased pressure suggests a direct renal effect.

Animals↗
PubMed2000

Collaborative multidisciplinary workshop report: clinical antimicrobial trials for primary and secondary prevention of atherosclerotic cardiovascular disease.

The task assigned to the working group on Clinical Antimicrobial Trials for Primary and/or Secondary Prevention of Atherosclerotic Cardiovascular Disease was to evaluate the need for additional clinical antibiotic trials of a primary or secondary nature for the treatment of atherosclerotic heart disease and to suggest possible designs for future trials. In addition, the working group was to define the role of collaboration in answering research questions.

Anti-Bacterial Agents↗
PubMed2000

Inhibition of human cancer cell growth by inducible expression of human ribonucleotide reductase antisense cDNA.

Ribonucleotide reductase (RR) is a rate-limiting enzyme in DNA synthesis and repair. The enzyme consists of two dissimilar subunits, M1 and M2. It is known that the M2 subunit plays a role in tumorgenicity and metastasis. In this study, we transfected human oropharyngeal KB cancer cells with human RR M1 and M2 antisense cDNA expressed by an inducible vector system. The transfectants were double-selected with hygromycin and G418. The clones, designated KB-M1AS, KB-M2AS and KB-CAT, represented transfectant clones that contained M1 antisense cDNA, M2 antisense cDNA, and a CAT reporter gene, respectively. In a colony-forming assay, colony formation for the KB-M2AS clone decreased approximately 50% when M2 antisense mRNA expression was induced by isopropylthiogalactose (IPTG). However, the KB-M1AS clone revealed no significant inhibition under IPTG induction. RR enzyme activity, as measured by 14CDP reduction assay, revealed a 30% decrease in the IPTG-induced KB-M2AS clone relative to non-IPTG-induced samples at 144 hours. As shown by Northern blot, expression of the M2 antisense mRNA showed peaks at 48 hours and 144 hours after induction by IPTG. M2 antisense mRNA expression induced by IPTG was 33-fold greater than the uninduced control at 144 hours. Western blot analysis showed that the M2 subunit protein level decreased in the KB-M2AS clone beginning at 72 hours after induction and continued to decrease to 50% of the uninduced control at 144 hours, then showed a slight recovery at 168 hours. In conclusion, M2 antisense mRNA expression by an inducible system can effectively decrease RR M2 protein expression, reduce enzyme activity, and inhibit growth. Furthermore, this approach can be employed in future antisense investigations.

Blotting, Western↗
PubMed2000

Proteasomal proteomics: identification of nucleotide-sensitive proteasome-interacting proteins by mass spectrometric analysis of affinity-purified proteasomes.

Ubiquitin-dependent proteolysis is catalyzed by the 26S proteasome, a dynamic complex of 32 different proteins whose mode of assembly and mechanism of action are poorly understood, in part due to the difficulties encountered in purifying the intact complex. Here we describe a one-step affinity method for purifying intact 26S proteasomes, 19S regulatory caps, and 20S core particles from budding yeast cells. Affinity-purified 26S proteasomes hydrolyze both model peptides and the ubiquitinated Cdk inhibitor Sic1. Affinity purifications performed in the absence of ATP or presence of the poorly hydrolyzable analog ATP-gamma-S unexpectedly revealed that a large number of proteins, including subunits of the skp1-cullin-F-box protein ligase (SCF) and anaphase-promoting complex (APC) ubiquitin ligases, copurify with the 19S cap. To identify these proteasome-interacting proteins, we used a recently developed method that enables the direct analysis of the composition of large protein complexes (DALPC) by mass spectrometry. Using DALPC, we identified more than 24 putative proteasome-interacting proteins, including Ylr421c (Daq1), which we demonstrate to be a new subunit of the budding yeast 19S cap, and Ygr232w (Nas6), which is homologous to a subunit of the mammalian 19S cap (PA700 complex). Additional PIPs include the heat shock proteins Hsp70 and Hsp82, the deubiquitinating enzyme Ubp6, and proteins involved in transcriptional control, mitosis, tubulin assembly, RNA metabolism, and signal transduction. Our data demonstrate that nucleotide hydrolysis modulates the association of many proteins with the 26S proteasome, and validate DALPC as a powerful tool for rapidly identifying stoichiometric and substoichiometric components of large protein assemblies.

Adenosine Triphosphate↗
PubMed2000

Prospective randomized trial to evaluate the efficacy of a vaginal ring releasing progesterone for IVF and oocyte donation.

A polysyloxane vaginal ring containing 1g of natural progesterone was developed as luteal supplementation for women treated with IVF-embryo transfer and for agonadal women participating in an oocyte donation programme. The ring provides continuous release of progesterone (10-20 nmol/l) for 90 days. The efficacy of this form of progesterone supplementation was evaluated in two multicentre prospective randomized trials. IVF-embryo transfer trial: After oocyte aspiration, 505 women were randomly allocated to progesterone supplementation with vaginal ring or i.m. progesterone (50 mg/day). The clinical pregnancy rate was 36.6% in both groups. Implantation rate was 15.9% in the vaginal ring and 16.0% in i.m. progesterone. Oocyte donation trial: After endometrial proliferation with micronized oestradiol, 153 women were allocated to progesterone replacement with a vaginal ring or i.m. progesterone (100 mg/day). Clinical pregnancy rate was 39.8 and 28.6% respectively. Implantation rate was significantly higher with the vaginal ring compared with i.m. progesterone (19.9 and 11.6% respectively, P = 0.006). The vaginal ring is a novel development which provides continuous release of progesterone for 90 days. In IVF-embryo transfer, its effectiveness is similar to daily i.m. injections. In oocyte donation the ring provides a progestative milieu which improves the implantation rate and eliminates the discomfort of daily i.m. injections.

Adult↗