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Biomedical subjects

C Chen

Publications and source records attributed to C Chen.

At least 757 records · Page 42Linked to original sources
PubMed1996

Predictive value of prosthetic valve area index for early and late clinical results after valve replacement with the St Jude Medical valve prosthesis.

BACKGROUND: Previous studies indicate that a minimal prosthetic valve area index (VAI) of > or = 0.9 cm2/m2 for aortic and > or = 1.3 cm2/m2 for mitral valves minimizes postoperative pressure gradients. METHODS AND RESULTS: To determine VAI as an independent risk factor for postoperative events, 607 isolated aortic valve replacement (AVR) and 482 isolated mitral valve replacement (MVR) operations with the St Jude Medical valve were studied. End points included hospital deaths, NYHA functional class, late death and late valve-related death, major thromboembolism, anticoagulant-related hemorrhage, and reoperation. VAI was calculated from the ratio of prosthetic valve area to body surface area for each patient, and a range and mean were obtained for each valve size. Follow-up ranged from 1 to 120 months, totaled 2964 patient-years, and was 98% complete. Mean and range of VAI (cm2/m2) were 1.31 (0.74 to 2.86) in the aortic and 2.5 (1.4 to 6.32) in the mitral group. There were 33 AVR (5.4%) and 38 MVR (7.9%) hospital deaths. VAI was not a risk factor for NYHA class, early death, late death, or other postoperative events. The actuarial survival rates, 84% for AVR and 80% for MVR at 5 years, were not affected by VAI. CONCLUSIONS: Within the ranges measured, VAI did not influence the end points of the study.

Adolescent↗
PubMed1996

Down-regulation of gadd153 by c-myc in rat fibroblasts and its effect on cell growth and radiation-induced apoptosis.

Using differential display reverse transcription PCR (DDRT - PCR), we found that a 360 bp cDNA fragment was absent in several c-myc transfected rat fibroblasts: REC:myc, REC:myc + ras and rat1-myc. These cells also showed enhanced sensitivity to gamma ray-induced apoptosis. This cDNA fragment was present in the parental REC (Rat Embryo Cells) and rat1 cells, and in c-Ha-ras transfected REC (REC:ras), all of which were relatively resistant to gamma ray-induced apoptosis. The cDNA fragment was subsequently cloned and used as a probe to screen a rat1 cDNA library, and identified as one of the growth arrest and DNA damaging-inducible genes, gadd153. In addition to the down-regulation of rat gadd153 in all the c-myc transfectants, methyl methanesulfonate (MMS)-induced transcription of the gadd153 was attenuated. The rat1-myc cells, when successfully transfected with and stably expressing the rat gadd153, showed a significantly longer doubling time compared to the parental cells. However, overexpression of gadd153 in rat1-myc cells did not affect gamma ray-induced apoptosis. Thus, the suppression of gadd153 appears to be inversely correlated with that of myc, but not involved in the myc-dependent apoptotic pathway.

Animals↗
PubMed1996

Recombinant mitotoxin basic fibroblast growth factor-saporin reduces venous anastomotic intimal hyperplasia in the arteriovenous graft.

BACKGROUND: The plant cytotoxin saporin (SAP) is a potent ribosome-inactivating protein. When conjugated to basic fibroblast growth factor (FGF2), it selectively kills proliferating cells that have upregulated FGF receptors. In this study, we evaluated the effect of the recombinant chimeric mitotoxin rFGF2-SAP on venous anastomotic intimal hyperplasia, a major cause of failure of arteriovenous (AV) grafts. METHODS AND RESULTS: Recently designed expanded polytet-rafluoroethylene-based local infusion devices were implanted bilaterally as femoral AV conduits in six dogs. The venous anastomoses were the sites of continuous delivery of rFGF2-SAP (2.7 micrograms.kg-1.d-1) to one side and vehicle (4.6 microL.kg-1.d-1) as control to the contralateral side for 14 days. All animals survived, and all grafts were patent. Liver enzyme levels and histological analyses of liver, kidneys, and brain were normal, indicating the absence of systemic toxicity. Morphometric measurements and measurements of cell proliferation by bromodeoxyuridine index analysis were performed at both arterial and venous anastomoses. There were no significant differences between the treated grafts and the control grafts in intimal hyperplasia and intimal cell proliferation at the arterial anastomoses. In contrast, rFGF2-SAP reduced intimal thickness by 32%, intimal area by 40%, and cell proliferation index by 33% at the treated venous anastomoses compared with the control venous anastomoses (P < .05). CONCLUSIONS: These data demonstrate that local infusion of rFGF2-SAP significantly reduces venous anastomotic intimal hyperplasia and cell proliferation without systemic toxicity. This study suggests a new strategy for reducing intimal hyperplasia by the selective killing of proliferating smooth muscle cells with a potent chimeric mitotoxin through a novel local infusion device.

Anastomosis, Surgical↗
PubMed1996

Differences in cholinergic responses from outer hair cells of rat and guinea pig.

A cholinergic receptor on outer hair cells (OHC) in guinea pig cochlea induces a K+ current when it is activated by acetylcholine and suberyldicholine but not by nicotine or muscarine (Bobbin, 1995). This unusual receptor may contain an alpha 9-subunit. However, the pharmacology of the alpha 9-subunit cloned from rat and expressed in Xenopus oocytes does not completely match that obtained for the ACh receptor in guinea pig OHCs. The response to 1,1-dimethyl-4-phenylpiperazinium (DMPP) is large in guinea pig OHCs and small in oocytes containing receptors of the alpha 9-subunit. Therefore, we compared the effects of cholinergic receptor agonists in rat and guinea pig OHCs using the whole-cell variant of the patch-clamp technique. ACh caused the largest outward K+ current in OHCs from both rat and guinea pig. Carbachol- and suberyldicholine-induced responses were similar in magnitude in OHCs of rat and guinea pig. However, DMPP produced a small response in OHCs from rat and a large response in OHCs from guinea pig. At a concentration of 100 microM, muscarine, oxotremorine M, nicotine and cytisine induced little response in guinea pig OHCs and none in rat OHCs. Results suggest that the ACh receptor on rat OHCs is similar to the alpha 9-subunit-containing receptor expressed in oocytes but different from the ACh receptor on guinea pig OHCs.

Acetylcholine↗
PubMed1996

Determination of the amino acid residue involved in [3H]beta-funaltrexamine covalent binding in the cloned rat mu-opioid receptor.

We previously demonstrated that [3H]beta-funaltrexamine ([3H]beta-FNA) labeled the rat mu opioid receptor expressed in Chinese hamster ovary cells with high specificity, and [3H]beta-FNA-labeled receptors migrated as one broad band with a mass of 80 kDa. In this study, we determined the region and then the amino acid residue of the mu receptor involved in the covalent binding of [3H]beta-FNA. [3H]beta-FNA-labeled receptors were solubilized and purified to approximately 10% purity by immunoaffinity chromatography with antibodies against a C-terminal domain peptide. The site of covalent bond formation was determined to be within Ala206-Met243 by CNBr cleavage of partially purified labeled mu receptors and determinations of sizes of labeled receptor fragments. The amino acid residue of beta-FNA covalent incorporation was then determined by site-directed mutagenesis studies within this region. Mutation of Lys233 to Ala, Arg, His, and Leu completely eliminated covalent binding of [3H]beta-FNA, although these mutants bound beta-FNA with high affinity. Mutations of other amino acid residues did not affect covalent binding of [3H]beta-FNA. These results indicate that [3H]beta-FNA binds covalently to Lys233. Since [3H]beta-FNA is a rigid molecule, the information will be very useful for molecular modeling of interaction between morphinans and the mu receptor.

Amino Acid Sequence↗
PubMed1996

Requirement for Ku80 in growth and immunoglobulin V(D)J recombination.

The DNA-dependent protein kinase (DNA-PK) is a mammalian serine/threonine kinase that is implicated in the repair of DNA double-strand breaks, DNA replication, transcription, and V(D)J recombination. To determine the role of the DNA-binding subunit of DNA-PK in vivo, we targeted Ku80 in mice. In mutant mice, T and B lymphocyte development is arrested at early progenitor stages and there is a profound deficiency in V(D)J rearrangement. Although Ku80-/- mice are viable and reproduce, they are 40-60% of the size of littermate controls. Consistent with this growth defect, fibroblasts derived from Ku80-/- embryos showed an early loss of proliferating cells, a prolonged doubling time, and intact cell-cycle checkpoints that prevented cells with damaged DNA from entering the cell-cycle. The unexpected growth phenotype suggests a new and important link between Ku80 and growth control.

Animals↗
PubMed1996

Immunolabeling of Mu opioid receptors in the rat nucleus of the solitary tract: extrasynaptic plasmalemmal localization and association with Leu5-enkephalin.

Activation of the mu opioid receptor (MOR) by morphine within the caudal nucleus of the solitary tract (NTS) is known to mediate both cardiorespiratory and gastrointestinal responses. Leu5-enkephalin (LE), a potential endogenous ligand for MOR, is also present within neurons in this region. To determine the cellular sites for the visceral effects of MOR ligands, including LE, we used immunogold-silver and immunoperoxidase methods for light and electron microscopic localization of antisera against MOR (carboxyl terminal domain) and LE in the caudal NTS of rat brain. Light microscopy of coronal sections through the NTS at the level of the area postrema showed MOR-like immunoreactivity (MOR-LI) and LE labeling in punctate processes located within the subpostremal, dorsomedial and medial subnuclei. Electron microscopy of sections through the medial NTS at this level showed gold-silver particles identifying MOR-LI prominently distributed to the cytoplasmic side of the plasma membranes of axons and terminals. MOR labeled terminals formed mostly symmetric (inhibitory-type) synapses but sometimes showed multiple asymmetric junctions, characteristic of excitatory visceral afferents. MOR-LI was also present along extrasynaptic plasma membranes of dendrites receiving afferent input from unlabeled and LE-labeled terminals. We conclude that MOR ligands, possibly including LE, can act at extrasynaptic MORs on the plasma membranes of axons and dendrites in the caudal NTS to modulate the presynaptic release and postsynaptic responses of neurons. These are likely to include local inhibitory neurons and both gastric and cardiorespiratory afferents known to terminate in the subnuclei with the most intense MOR-LI.

Amino Acid Sequence↗
PubMed1996

Functional and structural alterations with 24-hour myocardial hibernation and recovery after reperfusion. A pig model of myocardial hibernation.

BACKGROUND: Short-term myocardial hibernation of 3 hours resulting from a moderate resting coronary flow reduction has been reproduced in pigs. This study was designed to determine whether any structural changes accompany short-term hibernation caused by a moderate flow reduction maintained for 24 hours and whether any such structural alterations are reversible after reperfusion. METHODS AND RESULTS: A severe left anterior descending coronary artery (LAD) stenosis was created with a reduction of resting flow to approximately 60% of baseline and maintained for 24 hours. Regional coronary flow was measured by a flowmeter; wall thickening was determined by echocardiography, and local metabolic changes were measured. Of 17 pigs, 11 completed the study protocol of 24 hours. The LAD flow was reduced from 0.91 +/- 0.11 to 0.52 +/- 0.13 mL.min-1.g-1, a 43% mean decrease, at 15 minutes after the LAD stenosis and was maintained at 0.56 +/- 0.11 mL.min-1.g-1 at 24 hours. The reduction of regional coronary flow initially produced acute myocardial ischemia, as evidenced by reduced regional wall thickening (from 37.2 +/- 6.9% at baseline to 11.5 +/- 6.8%), regional lactate production (-0.34 +/- 0.28 mumol.g-1.min-1), and a decrease in regional coronary venous pH (from 7.41 +/- 0.035 at baseline to 7.30 +/- 0.030). At 24 hours, the reductions in coronary flow and wall thickening were maintained relatively constant and the rate-pressure product was relatively unchanged, but lactate production ceased and regional H+ concentration normalized, with a tendency toward a further reduction in regional oxygen consumption, from 3.10 +/- 0.90 mL.min-1.100 g-1 at 15 minutes after stenosis to 2.52 +/- 0.95 mL.min-1.100 g-1 at 24 hours (P = .06), indicating metabolic adaptation of the hypoperfused regions. Of 11 pigs, 6 were free of myocardial infarction; 3 had patchy necrosis involving 4%, 5%, and 6% of the area at risk; and 2 other pigs had a few scattered myocytes with necrosis, detected only by light and electron microscopy. Ultrastructural changes consisted of a partial loss of myofibrils and an increase in mitochondria and glycogen deposition. Regional wall thickening recovered 1 week after reperfusion in most pigs, and the ultrastructural changes reverted to normal. CONCLUSIONS: In this pig model, moderately ischemic myocardium undergoes metabolic and structural adaptations but preserves the capacity to recover both functionally and ultrastructurally after reperfusion.

Actin Cytoskeleton↗
PubMed1996

Characterization of the structure and function of a new mitogen-activated protein kinase (p38beta).

Mitogen-activated protein (MAP) kinase cascades represent one of the major signal systems used by eukaryotic cells to transduce extracellular signals into cellular responses. Four MAP kinase subgroups have been identified in humans: ERK, JNK (SAPK), ERK5 (BMK), and p38. Here we characterize a new MAP kinase, p38beta. p38beta is a 372-amino acid protein most closely related to p38. It contains a TGY dual phosphorylation site, which is required for its kinase activity. Like p38, p38beta is activated by proinflammatory cytokines and environmental stress. A comparison of events associated with the activation of p38beta and p38 revealed differences, most notably in the preferred activation of p38beta by MAP kinase kinase 6 (MKK6), whereas p38 was activated nearly equally by MKK3, MKK4, and MKK6. Moreover, in vitro and in vivo experiments showed a strong substrate preference by p38beta for activating transcription factor 2 (ATF2). Enhancement of ATF2-dependent gene expression by p38beta was approximately20-fold greater than that of p38 and other MAP kinases tested. The data reported here suggest that while closely related, p38beta and p38 may be regulated by differing mechanisms and may exert their actions on separate downstream targets.

Activating Transcription Factor 2↗
PubMed1996

Dissection of functional domains of the human DNA replication protein complex replication protein A.

Replication protein A (RPA) is a mammalian single-stranded DNA binding factor essential for DNA replication, repair, and recombination. It is composed of three subunits of 70, 34, and 13 kDa (Rpa1, Rpa2, and Rpa3, respectively). Deletion mapping of the Rpa2 subunit identified the domain required for interaction with Rpa1 and Rpa3 which does not include the N-terminal domain that is phosphorylated during S phase. Deletion mapping of Rpa1 defined three domains. The C-terminal third of the Rpa1 polypeptide binds Rpa2 which itself forms a bridge between Rpa1 and Rpa3. The N-terminal third of Rpa1 bound single-stranded DNA under low stringency conditions only (0.1 M NaCl), while a central domain binds to single-stranded DNA under both low and high stringency conditions (0.5 M NaCl). Binding to p53 requires the N-terminal third of Rpa1 with some contribution from the C-terminal third. The evolutionarily conserved putative zinc finger near the C terminus of Rpa1 was not required for binding to single-stranded DNA, Rpa2, or p53. However, all three subdomains of Rpa1 and the zinc finger were essential for supporting DNA replication in vitro. These experiments are a first step toward defining peptide components responsible for the many functions of the RPA protein complex.

Animals↗
PubMed1996

Development of a capillary zone electrophoresis assay to examine the disposition of [D-pen2,5]enkephalin in rats.

A novel capillary zone electrophoresis (CZE) assay method was developed to evaluate the systemic disposition of [D-pen2,5]enkephalin (DPDPE) in rats. DPDPE was recovered from serum samples (200 microliters) by solid-phase extraction. Complete resolution of DPDPE and the internal standard ([D-ser2]leucine-enkephalin; DSLET) from other serum components was achieved within 15 min on a 50-microns I.D. capillary column with borate buffer (25 mM, pH 8.3). The peak-height ratio (DPDPE to DSLET) was linear through 100 micrograms/ml, with a detection limit of 250 ng/ml in serum, when absorbance of the column eluent was monitored at 210 nm. Serum samples obtained from rats after a 10 mg/kg intravenous bolus dose of DPDPE were analyzed with the present CZE method. The results suggest that CZE is a useful technique for quantitating therapeutic peptides in biological matrices.

Acetonitriles↗
PubMed1996

Tolerance of single, but not multiple, amino acid replacements in antibody VH CDR 2: a means of minimizing B cell wastage from somatic hypermutation?

Mutations in the heavy chain complementarity determining region 2 (CDR2) of the phosphocholine-specific T15 Ab can have a dramatic effect on the ability of the Ab to bind Ag. A panel of multisite mutants that had lost detectable binding to phosphocholine-containing Ags was previously created by saturation mutagenesis of the CDR2 region of T15. Based on the predicted importance of amino acid changes represented in the multisite mutants, we have created single-site mutations, yielding a panel of Abs with which to test 17 of the 19 CDR2 residues. Of the 17 positions examined, only one, Arg52, is intolerant to change, yielding a nonbinder phenotype even with conservative amino acid replacement. Mutation at two other sites, Ala50 and Tyr55, can yield a nonbinder phenotype depending on the amino acid replacement. Single-site mutations of the remaining 14 positions allowed retention of binding ability. Thus, except for positions 50, 52, and 55, multiple mutations must be introduced into the CDR2 region to create a nonbinder phenotype. We provide a newly refined model of T15, illustrating the structure and the interactions of the CDR2 region. Our results imply that introduction of point mutations would not normally delete Ag-binding ability until two or more mutations had accumulated. This would minimize potentially harmful effects of somatic mutation on Ig V region genes and improve the chance of survival for an Ab such as T15, which in its unmutated form is already well suited to bind Ag.

Amino Acid Sequence↗