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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 613 records · Page 34Linked to original sources
PubMed1999

[Implantation of the molteno tube for refractory glaucoma following penetrating keratoplasty].

PURPOSE: To assess the surgical effectiveness of the molteno tube implantation in glaucoma secondary to penetrating keratoplasty. METHODS: 9 eyes in critical condition with glaucoma secondary to corneal graft surgery, whose intraocular pressures (IOP) have previously failed to respond to glaucoma medication, were undergone Molteno tube implantation. RESULTS: IOPs ranged from 0.8-2.8 kPa (1 kPa = 7.5 mmHg) were obtained in 7 eyes, the success rate accounted for 7/9, 2 eyes still required installation of beta-blocker, the graft rejection occurred in one eye and was remedied with medical treatment, the graft remained half-transparent in one eye. Visual acuity improved in 4 eyes, stayed the same in 4 eyes and was worse in one eye. The best corrected visual acuity over 0.05 was recorded in 4 eyes. CONCLUSION: Moltemo tube implantation is a rational and effective method for preserving a certain level of visual acuity in patients with glaucoma following penetrating keratoplasty.

Adult↗
PubMed1999

CD28/B7-mediated costimulation is required for parathyroid gland allograft rejection in rats.

The activation of T cells to differentiate and to proliferate is an essential step in the immune response to antigen, especially in cell mediated acute allograft rejection. Besides the interaction of CD3/TCR complex with Ag/MHC complex presented on antigen-presenting cells, a complete T-cell activation and proliferation requires a second costimulatory signal. The interaction of CD28/CTLA-4 and B7 is a major costimulatory pathway for T Cell activation. Inhibition of this pathway results in development of antigen-specific unresponsiveness and clonal anergy. In present study, the biologic function of anti-CD28 monoclonal antibody and its Fab fragment were investigated in vitro and in vivo. The results indicate that mAbCD28 and its Fab fragments could promote the functional recovery of allografts and prolong the graft survival, but could not reverse the acute rejection or induce transplantation tolerance in the rat PTG allograft model. We also found that peripheral TNF-alpha level and NK-cell activity were suppressed in the presence of mAbCD28 and its Fab fragments for a relatively long time after PTG transplantation.

Animals↗
PubMed1999

[Effect of the number of splinted abutments on stress distribution of support tissue]

OBJECTIVE:This study applied an SJ-1 bolt attachment partial denture to restorate distal extension edentulous areas.Finite element analysis (FEA) was used to monitor induced around abutment supporting tissues under the different number of splinted abutments.METHODS:Finite element analysis. RESULTS:The result demonstrate that the reduction of the number of splinted unit from three to two resulted in an insignificant increase of stress records,whereas reduction of the number from two to one resulted in a significant increase of stress nine times greater than the three unit splint values.CONCLUSION:Hence,at least two teeth on each side should be splinted when SJ 1 bolt(extracoronal) distal extension attachment prostheses are used.

Journal Article↗
PubMed1999

[Effect of the abutments with reduced periodontal support on stress distribution of support tissue]

OBJECTIVE:This study applied finite element analysis (FEA) compared stress distribution characteristics of mandible,bilateral,SJ-1 bolt(extracoronal) distal extension attachment prostheses when the abutments were subject to eight different loss of periodontal support.METHODS:Finite element analysis.RESULTS:It was shown that periodontal support loss results in increased stress of the terminal abutment tooth without sudden changes.CONCLUSION:Compared favorable stress distribution result from splinted compromised abutment,and the first premolar periodontal support loss less than that of the second premolar and this loss below 30%.

Journal Article↗
PubMed1999

[Study on the ternary complex of CPFX, copper (II) and DNA by the method of fluorescence].

Using the method of fluorescence spectrometry, the formation of binary complexes of CPFX-Cu(II) and CPFX-eucaryote DNA, and ternary complexes of CPFX-Cu(II)-eucaryote DNA was studied. The results show that the fluorescent intensity of CPFX can be quenched in the presence of Cu(II ) or DNA in CPFX system. In the presence of Cu (II), the fuorescence quenching action of DNA on CPFX was enhanced strongly. Based on the fluorescent intensity, the formation constants of CPFX-Cu (II) and CPFX-DNA in either the presence or absence were calculated,and the mechanism of interaction among CPFX,Cu(II) and DNA was presented.

Animals↗
PubMed1999

[Fluorescence studies on amoxicillin].

The effects of pH, various organic solvents such as acetone, methanol, ethanol, surface-active agent on amoxicillin have been studied in detail. Put in pH=8 buffer solution, amoxicillin has strong fluorescence emission, excitaion wavelength of 277 nm, and emission wavelength of 303 nm. Calibration curve of amoxicillin was linear between 2 x 10(-5) and 2 x 10(-4) mol/L, with a regression coefficient of 0.9996. CTAB can enhance its fluorescence intensity. The results of fluorescence spectra of amoxicillin added with metal ions (Mg2+, Ca2+, Al3+, Ga3+) at pH=12 showed that there are interactions between amoxicillin and metal ions.

Amoxicillin↗
PubMed1999

[Fluorescence study on phenothiazine and its halogenate derivatives].

The fluorescence spectra of 3-bromine-N-ethyl-phenothiazine with various acid degrees and different polarity surfactants in aqueous solutions were studied in detail. The reasons why fluorescence spectra of Br-Pwere very sensitive to environmental polar and acid changes were discussed based on Lewis acid-base theory. Meanwhile the spectrum of Br-P under ultraviolet ray illumination showed that Br-P had kinetic fluorescence. The method is not only simple but also sensitive with low limit of detection. The calibration curves were linear between 1 x 10(-7) and 1 x 10(-4) mol/L, with a regression coefficient of 0.9995 and RSD<2.8%.

English Abstract↗
PubMed1999

[Improving spectral property of light source to increase signal-to-noise ratio of optical multichannel analyzer in measurement of absorbances].

In the present paper we report that the spectral property of light radiation was improved by using the method of increasing intensity of short wave radiation for increasing signal-to-noise ratio (S/N) of CCD-OMA in measurement of sample's absorbance in visible light-region especially short wave region. The signal-to-noise ratio resulting from the recording of short wave region for improved light source was increased by 8 times as high as that of a general Wlamp. As demonstrated by the experiment, absorbance spectrum with high S/N ratio can be obtained in the entire visible light region by using the improved light source in the measurement of absorbance.

English Abstract↗
PubMed1999

[The thermodynamic molar absorptivity of coordination color reaction of indium(III) with 4,5-dihydroxybenzene-1,3-disufornic acid].

The thermodynamic molar absorptivity of complex formed by 1:1 coordination color reaction of tiron with highly charged cation In3+ has been measured spectrophotometrically at 20.0+/-0.1 degrees C, using NaClO4 as supporting electrolyte. The influence of å on linear relation between molar absorptivity and ionic strength has been investigated. At å = 6.5, the thermodynamic molar absorptivity lg epsilon(o) was found to be 3.69.

English Abstract↗
PubMed1999

Human salivary tea catechin levels and catechin esterase activities: implication in human cancer prevention studies.

Because of the possible application of tea in the prevention of oral and esophageal cancers, the salivary levels of tea catechins were determined in six human volunteers after drinking tea. Saliva samples were collected after thoroughly rinsing the mouth with water. After drinking green tea preparations equivalent to two to three cups of tea, peak saliva levels of (-)-epigallocatechin (EGC; 11.7-43.9 microg/ml), EGC-3-gallate (EGCG; 4.8-22 microg/ml), and (-)-epicatechin (EC; 1.8-7.5 microg/ml) were observed after a few minutes. These levels were 2 orders of magnitude higher than those in the plasma. The elimination half-life (t(1/2)) of the salivary catechins was 10-20 min, much shorter than that of the plasma. Holding a tea solution in the mouth for a few minutes without swallowing produced even higher salivary catechin levels, but taking tea solids in capsules resulted in no detectable salivary catechin level. Holding an EGCG solution in the mouth resulted in EGCG and EGC in the saliva and, subsequently, EGC in the urine. The results suggest that EGCG was converted to EGC in the oral cavity, and both catechins were absorbed through the oral mucosa. A catechin esterase activity that converts EGCG to EGC was found in the saliva. The enzyme was likely of human origin, but the activity was not inhibited by common human esterase inhibitor. The present results suggest that slowly drinking tea is a very effective way of delivering rather high concentrations of catechins to the oral cavity and then the esophagus.

Absorption↗
PubMed1998

Affinity purification and partial characterization of a yeast multiprotein complex for nucleotide excision repair using histidine-tagged Rad14 protein.

The nucleotide excision repair (NER) pathway of eukaryotes involves approximately 30 polypeptides. Reconstitution of this pathway with purified components is consistent with the sequential assembly of NER proteins at the DNA lesion. However, recent studies have suggested that NER proteins may be pre-assembled in a high molecular weight complex in the absence of DNA damage. To examine this model further, we have constructed a histidine-tagged version of the yeast DNA damage recognition protein Rad14. Affinity purification of this protein from yeast nuclear extracts resulted in the co-purification of Rad1, Rad7, Rad10, Rad16, Rad23, RPA, RPB1, and TFIIH proteins, whereas none of these proteins bound to the affinity resin in the absence of recombinant Rad14. Furthermore, many of the co-purifying proteins were present in approximately equimolar amounts. Co-elution of these proteins was also observed when the nuclear extract was fractionated by gel filtration, indicating that the NER proteins were associated in a complex with a molecular mass of >1000 kDa prior to affinity chromatography. The affinity purified NER complex catalyzed the incision of UV-irradiated DNA in an ATP-dependent reaction. We conclude that active high molecular weight complexes of NER proteins exist in undamaged yeast cells.

Chromatography, Affinity↗
PubMed1998

A targeted disruption of the murine Brca1 gene causes gamma-irradiation hypersensitivity and genetic instability.

Germline mutations of the Brcal gene are responsible for most cases of familial breast and ovarian cancers, but somatic mutations are rarely detected in sporadic events. Moreover, mouse embryos deficient for Brca1 have been shown to die during early embryogenesis due to a proliferation defect. These findings seem incompatible with the tumor suppress function assigned to this gene and raise questions about the mechanism by which Brca1 mutations cause tumorigenesis. We now directly demonstrate that BRCA1 is responsible for the integrity of the genome. Murine embryos carrying a Brca1 null mutation are developmentally retarded and hypersensitive to gamma-irradiation, suggesting a failure in DNA damage repair. This notion is supported by spectral karyotyping (SKY) of metaphase chromosomes, which display numerical and structural aberrations. However, massive chromosomal abnormalities are only observed when a p53-/- background is introduced. Thus, a p53 dependent cell cycle checkpoint arrests the mutant embryos and prevents the accumulation of damaged DNA. Brca1-/- fibroblasts are not viable, nor are Brca1-/-:p53-/- fibroblasts. However, proliferative foci arise from Brca1-/-: p53-/- cells, probably due to additional mutations that are a consequence of the accumulating DNA damage. We believe that the increased incidence of such additional mutations accounts for the mechanism of tumorigenesis associated with Brca1 mutations in humans.

Animals↗
PubMed1998

NK1.1 cells express 4-1BB (CDw137) costimulatory molecule and are required for tumor immunity elicited by anti-4-1BB monoclonal antibodies.

The 4-1BB (CDw137) T-cell molecule is a member of the TNF receptor family and triggering by either 4-1BB ligand or antibody ligation induces T-cell activation and growth. We have recently demonstrated that administration of anti-4-1BB monoclonal antibodies (mAb) induced the regression of established large tumors in several mouse models by activation of T-cell-mediated immunity. Herein we report that selective depletion of natural killer (NK) cells in mice by the anti-AsialoGM1 or anti-NK1.1 antibodies completely abrogated the antitumor effect of anti-4-1BB mAb. However, it is unlikely that NK1. 1 cells are the effectors of the response because P815 cells are resistant to lysis by NK1.1 cells in vitro. Despite the fact that activated NK1.1 cells express 4-1BB on their surface, redirection of NK1.1 cells by anti-4-1BB mAb or by transfection into P815 cells of the 4-1BB natural ligand did not trigger cytolysis. Our results thus gain further insight into the cellular mechanisms of the antitumor effects of anti-4-1BB mAb and implicate an immunoregulatory rather than effector function of 4-1BB molecule on NK1.1 cells.

Animals↗
PubMed1998

Adenovirus vector-based purging of multiple myeloma cells.

Adenoviruses are efficient gene delivery agents for a variety of neoplasms. In the present study, we have investigated the use of adenoviruses for the delivery of the thymidine kinase (tk) gene into multiple myeloma (MM) cells. We first demonstrated that MM cell lines and MM patient cells express both adenovirus receptors as well as the DF3/MUC1 protein, thus providing a rationale for using adenoviruses to selectively deliver genes under the control of the DF3 promoter. By using an adenoviral construct containing beta-galactosidase (beta-gal) gene driven by the DF3 promoter (Ad. DF3-betagal), we demonstrate greater than 80% transduction efficiency in OCI-My5 and RPMI 8226 MM cell lines at a multiplicity of infection of 1 to 100. Importantly, transduction with the tk gene driven by the DF3 promoter (Ad.DF3-tk) followed by treatment with 50 micromol/L ganciclovir (GCV) purged >/=6 log of contaminating OCI-My5 and RPMI 8226 MM cells within bone marrow mononuclear cells. In contrast, normal human hematopoietic progenitor cell number was unaffected under these conditions. Selectivity of DF3/MUC1 promoter was further confirmed, because Ad.DF3-betagal or Ad.DF3-tk did not transduce MUC1-negative HeLa cervical carcinoma cells. In addition, GCV treatment of Ad.DF3-tk-transduced RPMI 8226 MM cells did not induce a significant bystander effect. These findings demonstrate that transduction with Ad vectors using a tumor-selective promoter provides a highly efficient and selective approach for the ex vivo purging of MM cells.

Adenoviridae↗
PubMed1998

P-CIP1, a novel protein that interacts with the cytosolic domain of peptidylglycine alpha-amidating monooxygenase, is associated with endosomes.

The cytosolic domain of the peptide processing enzyme peptidylglycine alpha-amidating monooxygenase (PAM) contains signals that direct its trafficking in the secretory and endosomal pathways. Using the yeast two-hybrid system, Alam et al. (Alam, M. R., Caldwell, B. D., Johnson, R. C., Darlington, D. N., Mains, R. E., and Eipper, B. A. (1996) J. Biol. Chem. 271, 28636) identified three proteins that interact with a fragment of the PAM cytosolic domain containing these targeting signals. We cloned the rat and human cDNAs encoding PAM COOH-terminal interactor protein-1 (P-CIP1). Both cDNAs contain an open reading frame that encodes a novel protein of 435 amino acids. The P-CIP1 protein is highly conserved from rat to human (85% identity) but does not display significant homology to proteins in the GenBank data base. In vitro, P-CIP1 interacts with the cytosolic domain of wild type PAM-1, but does not interact with mutant PAM-1 proteins that fail to target correctly when expressed in endocrine cells. P-CIP1 contains multiple consensus serine/threonine phosphorylation sites and a region predicted to form a coiled-coil at the COOH terminus. When expressed in endocrine cells or fibroblasts, P-CIP1 is distributed in a punctate pattern in the perinuclear area but does not significantly overlap the distribution of transfected wild type PAM-1. The distribution of P-CIP1 displays significant overlap with the distribution of the secretory carrier membrane proteins, internalized Texas Red-conjugated transferrin, and Rab11. The data suggest that P-CIP1 associates with vesicles in the recycling endosomal pathway, and may play a role in regulating the trafficking of integral membrane PAM.

Amino Acid Sequence↗
PubMed1998

Excitotoxic effect of kainic acid on chicken cochlear afferent neurons.

The excitotoxic effects of kainic acid, a glutamate analog, on the auditory neurons in the chicken cochlea were assessed by light and transmission electron microscopy. Kainic acid was directly applied onto the round window of adult chickens and their cochleas were harvested 3 h after application. Transverse microscopic sections of the basilar papilla revealed swelling of afferent dendrites without any morphological changes in efferent endings. The regions of the basilar papilla damaged by kainic acid were localized in the apical 80% and primarily on the neural side where tall hair cells are located. The basal, abneural short hair cell region was devoid of damage. These results imply that glutamate is a primary neurotransmitter in chicken auditory afferent neurons that synapse on tall hair cells.

Animals↗