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Biomedical subjects

A Song

Publications and source records attributed to A Song.

At least 37 records · Page 2Linked to original sources
PubMed1999

Naturally occurring anti-alpha-galactosyl antibodies: relationship to xenoreactive anti-alpha-galactosyl antibodies.

Antibodies produced by an individual without a known history of sensitization to the relevant antigen are called "natural" antibodies. Some natural antibodies, called xenoreactive antibodies, react with the cells of foreign species. Most xenoreactive antibodies in humans and higher primates bind to a nonreducing terminal galactose expressed by pigs and other lower mammals. Although human natural antibodies which bind to one or more of a variety of terminal alpha-galactosyl structures have been identified previously, the antigen recognized by anti-alpha-galactosyl antibodies on the cells of foreign species is thought to be exclusively Galalpha1-3Gal. Thus, anti-alpha-galactosyl antibodies which do not react with Galalpha1-3Gal are thought to be nonxenoreactive. Here, we identify natural antibodies in human serum which bind to Galalpha1-6Hexosepyrranosides but not Galalpha1-3Gal, indicating that these antibodies are not xenoreactive. Various lower mammals were found to have natural anti-Galalpha1-2Gal antibodies in their sera, suggesting that at least some anti-Galalpha1-2Gal antibodies might not be xenoreactive and indicating, surprisingly, that anti-alpha-galactosyl antibodies are much more phylogenetically disperse than previously known. Also surprising was the finding that some natural antibodies which bind to Galalpha1-3Gal in vitro do not bind to porcine xenografts. These studies show that naturally occurring anti-alpha-galactosyl antibodies in mammalian serum include antibodies with a greater variety of reactivities than previously thought, only some of which would bind to a porcine xenograft. Further, these studies show that the methods used to detect anti-alpha-galactosyl antibodies of relevance in xenotransplantation must be carefully evaluated to avoid detection of anti-alpha-galactosyl antibodies which would not bind to a porcine organ and which therefore are not involved in xenograft rejection.

Animals↗
PubMed1998

PLA2-independent induction of CSF-1 gene expression in growth-arrested fibroblasts.

At the site of a wound or an infection, localized production of colony-stimulating factor-1 (CSF-1) by resident macrophages is chemotactic for circulating monocytes. Several intracellular signaling pathways, including those initiated in response to activation of phospholipase A2 (PLA2) have been proposed to play a role in the regulation of CSF-1 gene expression. The goal of these studies was to determine whether PLA2 is required for the initial increase in CSF-1 gene expression in serum- or IL-1 alpha-stimulated growth-arrested fibroblasts. IL-1 alpha- or serum-stimulation of growth-arrested fibroblasts had no effect on PLA2 enzyme activity and inhibitors of cytosolic or Ca(2+)-independent PLA2 activity had no effect on IL-1 alpha- or serum-mediated increases in CSF-1 mRNA levels. High concentrations of the PLA2 inhibitors, 4-bromophenacyl lactone and quinacrine, resulted in a generalized decrease in cellular mRNA levels. Our results, obtained in fibroblasts, suggest treatment with 4-bromophenacyl lactone or quinacrine, instead of inhibiting PLA2 activity specifically, results in a generalized depression of cellular mRNA levels. These data demonstrate that the initial increase in CSF-1 gene expression in growth-arrested fibroblasts treated with serum or IL-1 alpha occurs through a PLA2-independent mechanism.

Animals↗
PubMed1998

Phosphorylation of nuclear MyoD is required for its rapid degradation.

MyoD is a basic helix-loop-helix transcription factor involved in the activation of genes encoding skeletal muscle-specific proteins. Independent of its ability to transactivate muscle-specific genes, MyoD can also act as a cell cycle inhibitor. MyoD activity is regulated by transcriptional and posttranscriptional mechanisms. While MyoD can be found phosphorylated, the functional significance of this posttranslation modification has not been established. MyoD contains several consensus cyclin-dependent kinase (CDK) phosphorylation sites. In these studies, we examined whether a link could be established between MyoD activity and phosphorylation at putative CDK sites. Site-directed mutagenesis of potential CDK phosphorylation sites in MyoD revealed that S200 is required for MyoD hyperphosphorylation as well as the normally short half-life of the MyoD protein. Additionally, we determined that turnover of the MyoD protein requires the proteasome and Cdc34 ubiquitin-conjugating enzyme activity. Results of these studies demonstrate that hyperphosphorylated MyoD is targeted for rapid degradation by the ubiquitin pathway. The targeted degradation of MyoD following CDK phosphorylation identifies a mechanism through which MyoD activity can be regulated coordinately with the cell cycle machinery (CDK2 and CDK4) and/or coordinately with the cellular transcriptional machinery (CDK7, CDK8, and CDK9).

Amino Acid Sequence↗
PubMed1998

Fate of antigen in xenotransplantation: implications for acute vascular rejection and accommodation.

Antigen down-modulation plays a critical role in xenotransplants involving humoral responses against the Forssman antigen and may play a role in the long-term survival of ABO-incompatible allografts. The present study investigates the fate of porcine antigens in pig-to-primate xenotransplantation. Human antibodies bound to the glycocalyx of cultured porcine aortic endothelial cells as judged by electron microscopy and were shed from the cell surface in a complex with fibronectin, a glycoprotein that is found in the apical membrane glycocalyx of cultured cells. Antibody was shed in a metabolically dependent process with a t(1/2) of 2 to 3 hours. However, the amount of antigen on the cell surface did not change appreciably within 24 hours, suggesting that antigen modulation did not occur. Over the ensuing days, antigen expression decreased, although the change was always less than 50% of baseline. Changes in antigen expression were due for the most part to changes in expression of alpha-galactosyl residues. Consistent with results obtained in vitro, antigen expression in porcine organ transplants remained at approximately the baseline level as determined by immunofluorescence analysis of IgM binding to graft endothelium. If, as these results suggest, antigen is not down-modulated in pig-to-primate xenotransplantation, then therapies aimed at prolonged xenograft survival must focus on antibody or genetic manipulation of antigen expression.

Animals↗
PubMed1997

High-performance fiber-optic pH microsensors for practical physiological measurements using a dual-emission sensitive dye.

A fast and durable ratiometric pH microoptode that is highly accurate, precise, sensitive, reversible, and reproducible over the physiological ranges of pH, ionic strength, and temperature has been developed. The sensing site consists of 5 (and 6)-carboxynaphthofluorescein (CNF) entrapped in a polyacrylamide gel matrix via photopolymerization at the silanized end of an optical fiber with a diameter of 2 (pulled) or 125 microns (unpulled). The optode's precision for the pH 6.3-8.4 range in rat embryos, sera, or physiological (Earle's and Tyrode's) buffers was found to be better than +/- 0.03 pH unit. The pulled and unpulled optodes have respective upper limit response times of 1 and 400 ms for 1-pH-unit change. Over a 7-week period, they retain sensitivity for 600 and 10,000 measurements, respectively. Ratiometric measurements are made using a pH-sensitive emission peak on each side of an isosbestic point. The CNF microoptode is most suitable for biological applications because of its essentially linear response over the pH 7-8 range, its high sensitivity (slope about 2), and its almost perfect correlation with a pH macroelectrode. Furthermore, errors introduced by photobleaching, leaching, quenching, optode movement, and excitation source fluctuations are minimal.

Animals↗
PubMed1997

Transcriptional regulation of the mouse CSF-1 gene.

Research in our laboratory is aimed at understanding the cellular and molecular mechanisms that govern colony stimulating factor-1 (CSF-1) gene expression. Our hypothesis is that a basal set of trans-acting factors is bound to the CSF-1 gene during fibroblast proliferation, resulting in constitutive CSF-1 gene expression. Modulation of CSF-1 gene transcription by growth-arrest (decrease) or stimulation of growth-arrested fibroblasts (re-initiate) is mediated by changes in the basal set of factors bound and/or by the addition of stimulus-specific factors. We have extended our hypothesis to include other cell types (monocytes) to determine if mechanisms used to control CSF-1 gene expression in fibroblasts are unique or represent common nontissue-specific regulatory mechanisms. Analysis of CSF-1-CAT reporter constructs in transiently transfected fibroblasts and monocytes was used to identify CSF-1 genomic sequences that affect transcriptional activity. DNase I protection, electrophoretic mobility shift, and methylation interference assays were used to identify the putative cis-acting elements. Results of our study suggest multiple trans-acting factors may regulate CSF-1 gene expression; some may be tissue specific, while others, such as AP1, CTF/NF1, Sp1, and Sp3, are shared in common.

Animals↗
PubMed1996

In vitro fibroplasia: matrix contraction, cell growth, and collagen production of fibroblasts cultured in fibrin gels.

Extracellular matrix (ECM) reorganization, cell growth, and collagen synthesis/deposition are key features of fibroplasia during tissue repair. An in vitro fibrin gel culture model system simulating fibroplasia of wound repair was characterized. In the model system, fibrin gels were stabilized on plastic culture plates as hemispheres. In this way, fibroblasts were able to reorganize fibrin fibrils, resulting in a measurable decrease in gel thickness with no change in gel diameter, thereby producing a matrix with tension relevant to that of a repairing tissue. Within the study period, human dermal fibroblasts exhibited dynamic activities in cell growth and in reorganization and remodeling of the fibrin matrix. In the first 2 days of culture, fibroblasts quickly reorganized the fibrin matrix to 10% of its original thickness. Fibroblast proliferation occurred at a much slower rate compared to monolayer cultures. Proliferation continued at the same rate throughout the study in contrast to monolayer cultures, which ceased proliferation at confluence. Collagen synthesis was detected as early as the second day in culture. Type I collagen was the major collagen synthesized by fibroblasts with small amounts of type V and type III collagen. Collagen from either monolayer or fibrin gel cultures appeared identical when analyzed by two-dimensional peptide mapping of their CNBr fragments. Although collagen was detected biochemically from Day 2, organized collagen fibrils were apparently only in the later stage of cultures in transmission electron micrographs. Also, at this time, fibrin fibrils were largely removed and the matrix was filled with collagen fibrils and other filamentous ECM. The growth factor TGF-beta stimulated both fibrin gel contraction and collagen synthesis by fibroblasts. Therefore, using the model system, we have demonstrated that fibroblasts can actively reorganize the fibrin matrix and subsequently remodel it into a collagen-containing scar-like tissue. The unique features of this model system allow for creative designs in studying the complex mechanisms underlying tissue repair.

Cell Culture Techniques↗
PubMed1995

Aurintricarboxylic acid prevents acute rethrombosis in a canine model of arterial thrombosis.

Acute rethrombosis following thrombolytic therapy occurs in 5% to 25% of patients. We evaluated the effect of aurintricarboxylic acid (ATA), a triphenyl dye that blocks von Willebrand factor (vWF) binding to platelet glycoprotein Ib, on arterial reperfusion and acute rethrombosis following fibrinolytic therapy. Primary thrombosis was induced in the femoral arteries of anesthetized dogs by application of anodal current and partial arterial constriction. Blood flow was monitored with an electromagnetic flow probe, and primary thrombosis was considered to have occurred when blood flow was reduced to and remained at zero. Reperfusion was induced by intravenous streptokinase 30 minutes after thrombosis. Streptokinase reduced plasma fibrinogen levels from an average of 144 mg/dL to < 5 mg/dL resulting in inhibition of ADP- and epinephrine-induced platelet aggregation ex vivo. Acute rethrombosis following reperfusion occurred within 37 +/- 18 (mean +/- SD) minutes in 89% (16/18) of animals receiving thrombolytic activator treatment. Histological examination of reoccluding thrombi revealed densely aggregated platelets and erythrocytes with no detectable fibrin. In the two other study groups, ATA was infused in conjunction with thrombolytic therapy (10 arteries) or at near completion of acute rethrombosis following fibrinolytic activator treatment (6 arteries). In each case ATA prevented rethrombosis. However, concomitant administration of ATA and thrombolytic therapy delayed restoration of blood flow. ATA had no direct effect on hemodynamics, thrombin time, platelet count, or platelet aggregation response to ADP, epinephrine, or collagen. These data indicate that inhibition of vWF-platelet glycoprotein Ib interaction is effective in preventing acute rethrombosis following thrombolytic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1993

Inhibition of colony-stimulating factor-1 promoter activity by the product of the Wilms' tumor locus.

Colony-stimulating factor-1 (CSF-1) is a member of the immediate early gene family, which is expressed in mitogen-stimulated quiescent fibroblasts. The biological effects of CSF-1 are multifaceted and include stimulation of the proliferation and differentiation of myeloid progenitors and activity of circulating monocytes and tissue-specific macrophages. Ablation of circulating levels of biologically active CSF-1 in mice leads to osteopetrosis and sterility, thus implicating a role for CSF-1 in bone remodeling and implantation. Identification of regulatory elements and cognate transcription factors that bind the csf-1 promoter and mediate such diverse expression patterns is of great interest. We identified a sequence element at -273 to -265 (relative to the transcription initiation site) in the murine csf-1 promoter, which contains overlapping consensus sequences for the Wilms' tumor protein (WT1), EGR-1, SP1, and SP3 proteins. WT1 and EGR-1 proteins produced in vitro bound to this sequence, and co-transfection of wt1 with a csf-1-cat reporter plasmid resulted in repression of promoter activity. Interestingly, nuclear extracts prepared from serum-stimulated C3H10T1/2 cells contained predominantly SP1 and SP3 binding activities, which recognized the -273 to -265 site. Thus repression of the csf-1 promoter by WT1 at this site may involve competition between SP1 family transcriptional activators and the WT1 repressor. Colony-stimulating factor-1 may be a physiologically relevant target gene for regulation by the WT1 transcription factor.

Animals↗
PubMed1993

Modulation of myogenic determination factor 1 expression by cell-cell contact.

Myogenic determination factor 1 (MyoD1) expression is modulated by a variety of agents including growth factors and activated cellular proto-oncogenes. However, little is known about the effect of cell-cell contact, which increases as myoblasts terminally differentiate, on the control of MyoD1 expression. Steady-state levels of MyoD1 transcripts decline over a 6-12 hour time period when myoblasts plated at a single cell density are incubated in media supplemented with 0.2% serum; by 48 hours MyoD1 mRNA levels have returned to the initial basal level. The decline in MyoD1 transcripts is diminished, but not prevented in myoblasts which maintain cell-cell contacts (at least 50% of cells with two or more sites of contact). MyoD1 transcript levels do not change if single cell cultures are maintained in 10% serum or are cocultured with fibroblasts. Analysis of conditioned media revealed that myoblasts plated at the single cell density or at a density which allowed multiple sites of cell-cell contact are not producing an activity(s) responsible for modulating MyoD1 mRNA levels. The changes in MyoD1 expression are mediated at the transcriptional level. Thus changes in the degree of cell-cell contact in cultures of myogenically determined cell lines effect changes in MyoD1 gene expression. Consequently when the influence of cytokines or other pharmacological agents on commitment to terminal myogenic differentiation is examined, the degree of cell-cell contact within the culture system may affect the response elicited.

Animals↗
PubMed1992

Interleukin 1 alpha mediated inhibition of myogenic terminal differentiation: increased sensitivity of Ha-ras transformed cultures.

The commitment of myogenically determined cells to terminal differentiation can be modulated by a variety of agents, including growth factors and activated oncogenes. We have examined the effect of interleukin 1 alpha (IL-1 alpha) on the terminal differentiation of a normal myogenically determined cell line and two myogenically determined, differentiation competent cell lines which contain either one or six copies of the activated c-Ha-ras oncogene. Treatment of all cell lines with IL-1 alpha decreased but did not totally inhibit terminal myogenic differentiation. Over the range of IL-1 alpha concentrations assayed (1-40 ng/ml), the c-Ha-ras transformed cell lines demonstrated a significantly greater sensitivity to the inhibitory effects of IL-1 alpha. The inhibition of differentiation was not the result of enhanced proliferation. Interestingly, transformation with activated c-Ha-ras resulted in a decrease in IL-1 alpha receptor number and affinity. The enhanced IL-1 alpha responsiveness of the ras transformants was not the result of increased proliferation or changes in either ras gene expression or protein kinase C activity. IL-1 alpha treatment decreased the steady-state levels of both MyoD1 and myogenin transcripts in the c-Ha-ras transformed but not the normal myogenic cell line. Further studies are required to determine the mechanism(s) responsible for the increased sensitivity of the c-Ha-ras transformed cultures to the inhibitory effects of IL-1 alpha.

Actins↗
PubMed1992

The structure basis of the poor fibrin specificity of urokinase (II)--The inhibition of urokinase A chain 149-157 on the fibrin stimulated activation of plasminogen by tissue type plasminogen activator.

In view of the similarity of the charge distribution between fibrin A alpha 148-161 and A chain 149-157 of urokinase, the latter might compete with fibrin A alpha 148-161 when single chain pro-urokinase is converted to double chain urokinase. To test this, the stretch of urokinase A chain 135-157 was separated from the low molecular weight urokinase, a competitive binding between this stretch and fibrin to tPA kringle-2 was shown by radio-binding assay. The inhibition of the stretch on the fibrin stimulated activation of plasminogen was demonstrated in the caseinolytic system. The synthesized novapeptide urokinase A chain 149-157 (R-peptide) showed a significant inhibition on the activation of plasminogen in the presence of fibrin. By contrasting finely with R-peptide, a synthesized novapeptide in which Arg154 and Arg156 were replaced by Asp (D-peptide) did not show any inhibition effect on the fibrin stimulated activation of plasminogen by tPA. These results suggest that the positively charged residues in the stretch 149-157 of urokinase are crucial for the inhibition of fibrin binding with the kringle domain of urokinase.

Amino Acid Sequence↗
PubMed1991

Effects of tetrahydroaminoacridine (THA) on functional recovery after sequential lesion of the entorhinal cortex.

Unilateral lesions of rat entorhinal cortex produce a transitory performance deficit on spatial learning tasks, such as reinforced alternation in a T-maze. Tetrahydroaminoacridine (THA), a cholinesterase inhibitor, was administered to determine its effects on behavioral recovery using a reinforced alternation task in a T-maze. Rate of recovery after unilateral entorhinal lesion was not affected by a low dose of THA (0.05 mg/kg), while a higher dose (5.0 mg/kg) impaired recovery. Behavioral recovery was subsequently evaluated in the same rats following lesions to the contralateral entorhinal cortex. Serial bilateral lesions of the entorhinal cortex are known to produce a prolonged performance deficit on the alternation task. The 0.05 mg/kg THA group exhibited an intermediate rate of recovery, between the undamaged control group and bilateral lesion-saline injected groups. The group receiving 5.0 mg/kg of THA after bilateral lesion did not differ from the bilateral lesion-saline group. The failure of THA to significantly improve functional recovery in rats with lesions of the entorhinal cortex indicates that the compound may have limited applicability in treating human neurodegenerative disorders such as Alzheimer's disease.

Acetylcholinesterase↗
PubMed1990

Serum lipid and apolipoprotein levels in a Tibetan population sample.

Serum lipid and apolipoprotein levels were measured in a Tibetan population sample. In both men and women serum cholesterol levels were markedly lower than in Western populations. In men HDL-cholesterol levels were higher compared to both Oriental and Western populations while in women the values were markedly higher than in other Oriental populations and similar to Western populations. Highly significant positive relationships were found between serum lipid levels and corresponding apolipoprotein levels. In men but not in women serum cholesterol was markedly higher in office workers than in factory workers.

Adult↗
PubMed1987

Comparison of the thrombolytic efficacy of defibrase and urokinase on canine coronary artery thrombosis and the mechanism of urokinase-induced hemorrhage.

The thrombolytic efficacy of defibrase (DF) and urokinase (UK) was evaluated and compared in a canine model in which left circumflex coronary artery (LCX) thrombus formation was initiated by electrical stimulation (150 UA, DC) of the arterial intimal surface via an implanted copper wire electrode. Forty-eight mongrel dogs were equally divided into 8 groups: six groups for both intravenous (iv) and intracoronary (ic) infusion of DF, UK and normal saline 30 min after complete obstruction by a LCX thrombus, the remaining two groups for iv infusion DF and UK 360 min after occlusion. Results showed that in the control groups no LCX recanalization after infusion occurred, but all the treated groups recanalized when drug infusion started 30 min after occlusion. Thrombus wet weight and infarct size were much higher in the control group. No significant differences were found between treated groups except that the recanalizing speed was fastest by ic UK with the highest occurrence rate of reperfusion arrhythmia. For 6-hour-old thrombi, DF was more effective than UK for recanalization. Thrombus wet weight and infarct size were lower in the recanalized dogs. Both agents reduced plasma plasminogen and fibrinogen significantly but serious incision bleeding was only found in the UK group. In order to study the mechanism underlying UK-induced hemorrhage, we observed the influences of UK and DF on blood coagulation factors in another 12 dogs. Results showed that DF only reduced factor 1 while UK additionally reduced coagulation factors 2, 7, 8 and 10, indicating that the non-selective depletive effect on coagulation factors may be one of the mechanisms of UK-induced hemorrhage. We conclude that both DF and UK can lyse fresh coronary thrombi, DF was more effective than UK on lysing older thrombi, considering its convenient use and less frequency of side effects, DF is therefore considered a more promising agent clinically.

Animals↗
PubMed1984

Protease inhibition of natural killer (NK) and antibody-dependent cell-mediated cytoxicity (ADCC) activities.

The ability of protease inhibitors to modulate NK and ADCC cell activities was studied. NK and ADCC cell activities were suppressed by 1,10 phenanthroline (PHE), N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), L-1-tosylamide-2-phenylethylchoromethyl ketone (TPCK), N-benzoyl-DL-tyrosine ethyl ester (BTEE), and phenylethylchoromethyl fluoride (PMSF). The effect of these protease inhibitors on ADCC was not mediated through the early phase of cytotoxicity involving Fc-receptor binding, since they failed to alter EoxA rosetting of effector cells. The results suggest that an activated esterase system might play a role in the later phase of the cytotoxic mechanism by ADCC cells and perhaps NK cells.

Animals↗
PubMed1984

Wisconsin Behavior Rating Scale: measure of adaptive behavior for the developmental levels of 0 to 3 years.

The development of the Wisconsin Behavior Rating Scale was examined. We hypothesized that the extensive content of the scale as well as its arrangement of items with progressive difficulty would be effective in discriminating a rather homogeneous group of individuals functioning between 0 and 4.0 years. The scale was standardized on a sample of 325 institutionalized mentally retarded persons and a sample of 184 nonretarded infants and young children. Highly acceptable levels of reliability and validity were established for both samples. With respect to factorial validity, cognitive and psychomotor abilities accounted for approximately 83% of the explained variance. The hypothesis was supported in terms of adequate results of high concurrent and construct validity of the scale.

Activities of Daily Living↗