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Biomedical subjects

A Wang

Publications and source records attributed to A Wang.

At least 19 recordsLinked to original sources
PubMed1996

Heparin inhibits mitogen-activated protein kinase-dependent and -independent c-fos induction in mesangial cells.

Heparin suppresses mitogenic responses in renal mesangial cells, and when quiescent mesangial cells are stimulated with serum, heparin blocks the induction of c-fos seen at 15 min. Because heparin is taken up by cells over a much longer time course, we addressed mechanisms whereby extracellular heparin might suppress c-fos induction at such early times. Quiescent cells were treated with serum, 12-O-tetradecanoylphorbol-13-acetate, or low concentrations of Ca2+ ionophores that produced increases in intracellular Ca2+ concentration ([Ca2+]i) in the physiological range. Each treatment caused an increase in c-fos mRNA, but they did so by different mechanisms. Serum activated mitogen-activated protein kinase (MAPK) and increased [Ca2+]i without affecting protein kinase C. Activation of protein kinase C with phorbol ester activated MAPK without much effect on [Ca2+]i. Ionophores increased [Ca2+]i without affecting basal levels of protein kinase C or MAPK. Heparin (1 microg/ml) suppressed the induction of c-fos initiated by all three treatments. It did not affect the activity of protein kinase C, but inhibited activation of MAPK by either serum or phorbol ester, suggesting a common site of action at or below the probable convergence of the induced signals at Ras/Raf-1 activation. Heparin also inhibited the serum-stimulated entry of extracellular Ca2+ to the same extent as verapamil, consistent with the ability of verapamil to block L-type Ca2+ channels and the known presence of these channels in mesangial cells. However, this effect does not appear to be related to heparin's ability to inhibit induction of c-fos. First, verapamil had no effect on induction of c-fos by serum. Second, heparin had no effect on changes in [Ca2+]i achieved by ionophores. We conclude that heparin suppresses induction of c-fos in mesangial cells by blocking at least two different points in signal transduction cascades, one upstream of MAPK and the other independent of MAPK, but dependent on intracellular Ca2+.

Amino Acid Sequence↗
PubMed1996

Conformational trapping in a membrane environment: a regulatory mechanism for protein activity?

Functional regulation of proteins is central to living organisms. Here it is shown that a nonfunctional conformational state of a polypeptide can be kinetically trapped in a lipid bilayer environment. This state is a metastable structure that is stable for weeks just above the phase transition temperature of the lipid. When the samples are incubated for several days at 68 degrees C, 50% of the trapped conformation converts to the minimum-energy functional state. This result suggests the possibility that another mechanism for functional regulation of protein activity may be available for membrane proteins: that cells may insert proteins into membranes in inactive states pending the biological demand for protein function.

Magnetic Resonance Spectroscopy↗
PubMed1996

Substitution of basic amino acids in the basic region stabilizes DNA binding by E12 homodimers.

The E2A gene encodes two alternatively spliced products, E12 and E47. The two proteins differ in their basic helix-loop-helix motifs (bHLH), responsible for DNA binding and dimerization. Although both E12 and E47 can bind to DNA as heterodimers with tissue-specific bHLH proteins, E12 binds to DNA poorly as homodimers. An inhibitory domain in E12 has previously been found to prevent E12 homodimers from binding to DNA. By measuring the dissociation rates using filter binding and electrophoretic mobility shift assays, we have shown here that the inhibitory domain interferes with DNA binding by destabilizing the DNA-protein complexes. Furthermore, we have demonstrated that substitution of basic amino acids (not other amino acids) in the DNA-binding domain of E12 can increase the intrinsic DNA-binding activity of E12 and stabilize the binding complexes, thus alleviating the repression from the inhibitory domain. This ability of basic amino acids to stabilize DNA-binding complexes may be of biological significance in the case of myogenic bHLH proteins, which all possess two more basic amino acids in their DNA binding domain than E12. To function as heterodimers with E12, the myogenic bHLH proteins may need stronger DNA binding domains.

Alternative Splicing↗
PubMed1996

Asymmetric syntheses, opioid receptor affinities, and antinociceptive effects of 8-amino-5,9-methanobenzocyclooctenes, a new class of structural analogues of the morphine alkaloids.

Several 8-amino-5,9-methanobenzocyclooctenes have been prepared by asymmetric organic synthesis techniques. Opioid receptor affinity studies have revealed the virtual absence of enantioselectivity for receptor binding, particularly at the mu-receptor, for the (+)-3a-f and the (-)-3a-f series. It is noteworthy that inversion of configuration at the nitrogen-bearing carbon atom [5S,8S,9S)-8-amino-3-hydroxy-5, 9-methano-9-(methoxymethyl)-5-methylbenzocyclooctene, (+)-3a vs (5S,8S,9R)-8-amino-3-hydroxy-5, 9-methano-9-(methoxymethyl)-5-methylbenzocyclooctene, (dl)-22] resulted in a > 10-fold increase in kappa-receptor affinity. Antinociceptive studies demonstrated that (dl)-22 was a full kappa-agonist while (+)-3a and (-)-3a did not possess kappa-activity. Although both (dl)-22 and (+)-3a/(-)-3a had high affinity for the mu-receptor, these compounds did not act as high-affinity agonists or antagonists at this receptor.

Alkaloids↗
PubMed1996

Soluble tumor necrosis factor receptors inhibit phorbol myristate acetate and cytokine-induced HIV-1 expression chronically infected U1 cells.

Recombinant human tumor necrosis factor (TNF) binding protein-1 (r-h TBP-1) and recombinant human soluble dimeric TNF receptor (rhu TNFR:Fc) were used to determine the relative contributions of TNF to phorbol myristate acetate (PMA) and cytokine-induced human immunodeficiency virus type 1 (HIV-1) replication in chronically infected cell lines. Treatment of HIV-1-infected promonocytic U1 cells with r-h-TBP-1 or rhu TNFR:Fc reduced PMA-induced HIV-1 p24 antigen production in a concentration-dependent manner, with a maximal inhibition of approximately 90%. Maximal inhibition of p24 antigen production in T-lymphocytic ACH-2 cells was 47% with r-hTBP-1 and 42% with rhu TNFR:Fc. r-hTBP-1 and rhu TNFR:Fc also decreased p24 antigen synthesized by U1 cells in response to other stimuli, including phytohemagglutinin (PHA)-induced supernatant, granulocyte-macrophage colony-stimulating factor, interleukin-6, and TNF. Addition of r-hTBP-1 to U1 cells during the last 4 h of a 24 h incubation with PMA still inhibited p24 antigen production by 15%. U1 cells stimulated with 10(-7) M PMA released approximately 1 ng/ml endogenous TBP-1 with an initial peak observed at 1 h and a second peak at 24 h after PMA stimulation. r-hTBP-1 also partially reversed inhibition of U1 cellular proliferation caused by PMA. Both r-hTBP-1 and rhu TNFR:Fc blocked PMA induction of nuclear factor (NK)- kappa B DNA-binding activity in U1 cells in association with decreases in HIV-1 replication. We conclude that soluble TNF receptors can inhibit stimuli-induced HIV-1 expression and NK- kappa B DNA-binding activity in chronically infected U1 cells.

Base Sequence↗
PubMed1996

A reversible posterior leukoencephalopathy syndrome.

BACKGROUND AND METHODS: In some patients who are hospitalized for acute illness, we have noted a reversible syndrome of headache, altered mental functioning, seizures, and loss of vision associated with findings indicating predominantly posterior leukoencephalopathy on imaging studies. To elucidate this syndrome, we searched the log books listing computed tomographic (CT) and magnetic resonance imaging (MRI) studies performed at the New England Medical Center in Boston and Hôpital Sainte Anne in Paris; we found 15 such patients who were evaluated from 1988 through 1994. RESULTS: Of the 15 patients, 7 were receiving immunosuppressive therapy after transplantation or as treatment for aplastic anemia, 1 was receiving interferon for melanoma, 3 had eclampsia, and 4 had acute hypertensive encephalopathy associated with renal disease (2 with lupus nephritis, 1 with acute glomerulonephritis, and 1 with acetaminophen-induced hepatorenal failure). Altogether, 12 patients had abrupt increases in blood pressure, and 8 had some impairment of renal function. The clinical findings included headaches, vomiting, confusion, seizures, cortical blindness and other visual abnormalities, and motor signs. CT and MRI studies showed extensive bilateral white-matter abnormalities suggestive of edema in the posterior regions of the cerebral hemispheres, but the changes often involved other cerebral areas, the brain stem, or the cerebellum. The patients were treated with antihypertensive medications, and immunosuppressive therapy was withdrawn or the dose was reduced. In all 15 patients, the neurologic deficits resolved within two weeks. CONCLUSIONS: Reversible, predominantly posterior leukoencephalopathy may develop in patients who have renal insufficiency or hypertension or who are immunosuppressed. The findings on neuroimaging are characteristic of subcortical edema without infarction.

Adolescent↗
PubMed1996

Inhibition of fibroblast proliferation by human iris pigment epithelial cells in vitro: preliminary results.

BACKGROUND: The interaction between different cells plays an important role in many physiological and pathological processes. Since the proliferation of fibroblasts is very much involved in the pathogenesis of eye diseases such as proliferative vitreoretinopathy, the failure of filtration in glaucoma surgery, etc., we attempted to ascertain whether iris pigment epithelial cells (IPE) have some modulating effect on fibroblast proliferation. METHODS: Human IPE were explanted and the third-passage culture was transferred into serum-free RPMI-1640 medium. After 48 h of further incubation, the medium was collected and submitted to centrifugation; the supernatant was used as the conditioned medium of IPE (IPE-CM). Cultured fibroblasts from Tenon's capsule were seeded in a 96-well plate and incubated with IPE-CM in different concentrations. The proliferation of fibroblasts was estimated by thymidine incorporation and cell counting. RESULTS: The incorporation of tritiated thymidine by fibroblasts was reduced to 56.68% of baseline with 1:16 diluted IPE-CM and to 13.63% and 8.20%, respectively, with 1:8 and 1:2 diluted IPE-CM. These findings were in good accordance with the results of cell counting, performed in parallel. SDS-PAGE of IPE-CM revealed two specific bands with molecular weight 65 kDa and 40 kDa. CONCLUSION: IPE-CM showed an obvious dose-dependent inhibitory effect on fibroblast proliferation and was presumed to contain some active factors contributing to this effect.

Cell Count↗
PubMed1996

Different expression patterns of cyclins A, D1 and E in human colorectal cancer.

The expressions of cyclins A, D1 and E at the protein level were investigated by Western blotting in human colorectal carcinomas and in adjacent non-neoplastic colorectal mucosas. Cyclin E was higher in the cancer tissue than in the non-neoplastic mucosa in 92% patients (35 out of 38 cases). However, the cyclin A expression of the mucosa was higher than that of the cancer tissue in 63% (25 out of 40 cases) cases, and only 4 (10%) cancers had higher cyclin A expression. Eleven cancers (27%) demonstrated expression equivalent to that in the mucosa. Equal expression of cyclin D1 in cancer and mucosal tissues was found in 51% cases (20/39), lower expression of cyclin D1 by cancer tissues was demonstrated in 41% cases (16/39) and only three cancers showed higher expression than the mucosa. Proliferating-cell nuclear antigen immunohistochemistry revealed that the labeling index of the cancer tissue was 43.5 +/- 8.3% while that of the mucosa was only 14.8 +/- 5.1%. These results proved that colorectal cancers express high levels of cyclin E, consistent with a high rate of cell proliferation, whereas most of such cancer lose control of cyclin A and cyclin D1 expression.

Adult↗
PubMed1996

Comparison of the size and morphology of UHMWPE wear debris produced by a hip joint simulator under serum and water lubricated conditions.

This paper investigates the effect of lubricant on the size and morphology of ultra-high molecular weight polyethylene (UHMWPE) wear debris produced by a hip joint simulator. Bovine serum and water were chosen as the lubricants for comparison. When bovine serum was used as lubricant, the majority of the wear debris produced was submicron sized and equiaxed or elongated in shape; no transfer film was found on the femoral heads. When water was used as lubricant, large pieces of thin UHMWPE flakes about 2-3 mm across were produced and patches of transfer films were observed on the femoral heads. These large flakes were comprised of numerous smaller thin flakes compacted together. While the size and shape of the wear debris produced with serum lubrication are similar to those reported from clinical studies in total hip replacement, the debris produced with water lubrication bears no resemblance to what has been seen clinically.

Animals↗
PubMed1995

Effects of a naturally occurring compatible osmolyte on the internal dynamics of ribonuclease A.

Osmolytes are small organic solutes accumulated intracellularly by many organisms as they adapt to environmental stresses. Compatible osmolytes, a functional class of osmolytes, increase protein stability while having little or no effect on protein function. To investigate the interrelationships between protein stability, function, and internal dynamics, a hydrogen exchange (HX) quench method was established and used to study the effects of sucrose (a typical compatible osmolyte) on the structural fluctuations of ribonuclease A. It was found that the HX rates of the amide protons with intermediate rates are not affected by 1 M sucrose, but the slow-exchanging amide protons exchange even slower in 1 M sucrose. The protection factors of the slow-exchanging protons fall into a comparatively narrow range while those of the intermediate-exchanging protons vary widely. In agreement with the two-process model [Woodward, C.K., & Hilton, B. D. (1980) Biophys. J. 32, 561-575], we conclude that for those slow-exchanging amide protons, the exchange occurs mainly from the compact unfolded state ensemble of the protein. The internal dynamics leading to slow exchange involve exposure of large protein surface areas, similar to that which occurs upon the unfolding of protein. Because sucrose opposes such an increase in protein surface area exposure, both the slow HX rates and the protein stability are affected by sucrose. For those amide protons with fast and intermediate HX rates, the exchange occurs mainly from the native state ensemble of the protein. The internal dynamics involved in the exchange are localized without much surface area change, and functionally important structural fluctuations are likely to occur within this dynamic range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Effect of fluvastatin on lipoprotein profiles in treating renal transplant recipients with dyslipoproteinemia.

A single, blinded placebo-drug trial was conducted to study the efficacy and safety of fluvastatin, a new 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor, in treating dyslipoproteinemia in 16 renal transplant recipients who had been on an immunosuppressive regimen that included cyclosporine (CsA). They were studied for 32 consecutive weeks, with 4 weeks of baseline treatment, 4 weeks of placebo, 12 weeks of treatment with fluvastatin 20 mg daily, and 12 weeks of fluvastatin 40 mg daily. Blood samples were obtained every 4 weeks for measurement of the lipoprotein profiles, which included total cholesterol (TC), triglyceride, low density lipoprotein (LDL)-, high density lipoprotein (HDL)-, HDL2-, HDL3- and very low density lipoprotein-cholesterol (C), apolipoprotein (Apo) A-1, Apo B, and lipoprotein(a). Fifteen patients completed the trial. After 12 weeks of treatment, fluvastatin 20 mg significantly reduced TC by 13.4% (from 6.7 +/- 0.5 [mean +/- SEM] to 5.8 +/- 0.2 mmol/L), LDL-C by 22% (from 4.1 +/- 0.3 to 3.2 +/- 0.2 mmol/L), and Apo B by 13.2% (from 159.6 +/- 8.8 to 138.6 +/- 9.2 mg/dl) (P < 0.005). The subsequent 12-week treatment of fluvastatin 40 mg significantly reduced TC by 16.4% to 5.6 +/- 0.3 mmol/L, LDL-C by 29.3% to 2.9 +/- 0.2 mmol/L, and Apo B by 18.2% to 130.6 +/- 5.5 mg/dl (P < 0.00005). There was no significant change in levels of other lipoproteins, including lipoprotein (a). There were no significant changes in the whole blood trough CsA concentrations, renal and liver function tests, and serum creatine phosphokinase level during treatment when compared with baseline and placebo. No patient complained of myalgia or failed to complete the study due to side effects of the drug. Fluvastatin appears to be safe and effective in treating dyslipoproteinemia in renal transplant recipients who are maintained on CsA.

Adult↗
PubMed1995

Basic fibroblast growth factor mediates its effects on committed myeloid progenitors by direct action and has no effect on hematopoietic stem cells.

Basic fibroblast growth factor or fibroblast growth factor-2 (FGF) has been shown to affect myeloid cell proliferation and hypothesized to stimulate primitive hematopoietic cells. We sought to evaluate the effect of FGF on hematopoietic stem cells and to determine if FGF mediated its effects on progenitor cells directly or through the induction of other cytokines. To address the direct effects of FGF, we investigated whether FGF induced production of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, IL-6, granulocyte colony-stimulating factor, or granulocyte-macrophage colony-stimulating factor by two types of accessory cells, bone marrow (BM) fibroblasts and macrophages. We further evaluated whether antibodies to FGF-induced cytokines affected colony formation. To determine if FGF was capable of stimulating multipotent progenitors, we assessed the output of different colony types after stimulation of BM mononuclear cells (BMMC) or CD34+ BMMC and compared the effects of FGF with the stem cell active cytokine, kit ligand (KL). In addition, a subset of CD34+ BMMC with characteristics of hematopoietic stem cells was isolated by functional selection and their response to FGF was evaluated using proliferation, colony-forming, and single-cell polymerase chain reaction (PCR) assays. We determined that FGF had a stimulatory effect on the production of a single cytokine, IL-6, but that the effects of FGF on colony formation were not attributable to that induction. FGF was more restricted in its in vitro effects on BM progenitors than KL was, having no effect on erythroid colony formation. FGF did not stimulate stem cells and FGF receptors were not detected on stem cells as evaluated by single-cell reverse transcription PCR. In contrast, FGF receptor gene expression was detected in myeloid progenitor populations. These data support a directly mediated effect for FGF that appears to be restricted to lineage-committed myeloid progenitor cells. FGF does not appear to modulate the human hematopoietic stem cell.

Adipose Tissue↗
PubMed1995

Functional isolation and characterization of human hematopoietic stem cells.

Hematopoietic cells differentiate in steps marked by the acquisition or loss of specific phenotypic characteristics. Human bone marrow cells that were responsive to the early-acting cytokines Kit ligand and interleukin-3 were forced to a metabolic death. The subfraction remaining represented 1 in 10(5) bone marrow mononuclear cells, were determined to be quiescent by cell cycle analysis, and had a stem cell immunophenotype. The cells were highly enriched for long-term culture-initiating cells, were capable of secondary colony formation, and produced both myeloid and lymphoid progeny. Thus, this technically simple strategy led to the efficient purification of cells with characteristics of hematopoietic stem cells.

Antigens, CD↗
PubMed1995

Expression of the integrin subunit alpha 9 in the murine embryo.

The alpha 9 integrin subunit is expressed in adult skeletal muscle, visceral smooth muscle, hepatocytes, squamous epithelium, and airway epithelium. The in vivo function of this protein is unknown. Thus far, only a single alpha 9-containing integrin has been identified (alpha 9 beta 1) and only a single ligand (tenascin) has been found for this integrin. In order to gain insight into the potential function of alpha 9 integrin(s), we examined the spatiotemporal distribution of the alpha 9 subunit and tenascin during murine embryogenesis. In all tissues where alpha 9 was expressed, its appearance was associated with other evidence of cell differentiation. In developing airway, visceral, and vascular smooth muscles, the onset of alpha 9 expression either coincided with or immediately followed the expression of alpha-SM actin. Expression of alpha 9 in epithelia was restricted to the choroid plexus and the basal cell layer of squamous epithelia where its appearance coincided with the development of stratification. alpha 9 immunostaining was first detected in developing skeletal musculature when skeletal myotubes formed. Tenascin expression was detected in many, but not all tissues found to express alpha 9. For example, the hair germs of maturing hair follicles exhibited high levels of alpha 9 staining, but no tenascin immunoreactivity was detected either within the hair germ themselves or in the adjacent dermis. In some tissues where tenascin expression colocalized with alpha 9, expression patterns were not synchronous. Although alpha 9 expression was associated with the onset of tissue differentiation, its expression was not limited to terminally differentiated cells. In fact, in the skin, alpha 9 expression appeared restricted to cells known to retain the capacity to proliferate, i.e., basal cells and hair germs. Thus, alpha 9 integrin(s) are not likely to contribute to the early steps in organ formation, but probably play a role in the maturation and/or maintenance of a variety of differentiated tissues. The expression of alpha 9 without its only known ligand, tenascin, suggests the existence of additional ligands.

Animals↗
PubMed1995

Role of cyclic plastic deformation in the wear of UHMWPE acetabular cups.

The mechanisms of wear in ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups were investigated on both laboratory simulator-tested cups and a clinically retrieved component. Two different levels of wear process were identified: one characterized by the formation and detachment of platelet-like flakes from initial machining marks, and the other by the formation of fine ripple and fibrils by repeated passes of microscopic asperities on the femoral head. Both wear processes could be described by a criterion of critical plastic strain. A theoretical model was developed to account for the generation of the microscopic wear particles based on such a critical strain criterion. Its predictions of the dependence of the UHMWPE wear rate on surface roughness and applied load were in excellent agreement with previously published experimental correlations.

Acetabulum↗
PubMed1995

No involvement of Ki-ras or p53 gene mutations in colitis-associated rat colon tumors induced by 1-hydroxyanthraquinone and methylazoxymethanol acetate.

1-Hydroxyanthraquinone (1-HA), which is present in some herbs, and methylazoxymethanol (MAM) acetate, a metabolite of azoxymethane, show synergistic carcinogenicity in rat colon, and 1-HA induces ulcerative changes with simultaneous severe inflammation of the entire colon. In this study, mutations in Ki-ras (exons 1 and 2) and p53 (exons 4-7) were studied by polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP) analysis. Of 18 adenomas and 38 adenocarcinomas induced in male F344 rats (52 tumors induced by 1-HA plus MAM acetate, three by 1-HA alone, and one by MAM acetate alone), no mutations in Ki-ras or p53 were detected under two conditions of PCR-SSCP analysis. Because human colon carcinomas from patients with ulcerative colitis have a very low incidence of Ki-ras mutation, this experimental system would be a good animal model of human colon carcinomas with ulcerative colitis and of human colon carcinomas without Ki-ras or p53 mutations.

Animals↗
PubMed1995

Infusion of bile from methylene dianiline-treated rats into the common bile duct injures biliary epithelial cells of recipient rats.

Methylene dianiline (4,4'-diaminodiphenylmethane, DAPM) rapidly causes cholestasis and injury to biliary epithelial cells (BEC) in the liver and common bile duct of rats. Our objective was to determine if the proximate toxicant(s) was present in bile. Bile from DAPM-treated or control rats was infused through the common bile duct of untreated rats via inflow and outflow cannulas for 4 h. Cholestasis, increases in serum constituents, and intrahepatic BEC injury in the livers of DAPM-treated donor rats at 4 h were comparable to previous studies (Kanz et al., Toxicol. Appl. Pharmacol. 117 (1992) 88-97). BEC injury in the common bile duct of rats receiving DAPM bile or control bile was assessed by point counting. Percent necrosis was > 28% in the common bile duct of rats receiving DAPM bile compared to < 5% in rats receiving control bile. These results indicate that bile is a major route of BEC exposure to DAPM proximate toxicant(s) and demonstrate the utility of a new method for investigating mechanisms of biliary toxicants.

Aniline Compounds↗