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Biomedical subjects

L Sun

Publications and source records attributed to L Sun.

At least 379 records · Page 21Linked to original sources
PubMed1996

NorA plasmid resistance to fluoroquinolones: role of copy number and norA frameshift mutations.

Staphylococcus aureus NorA protein is a transmembrane multidrug efflux pump that confers low-level resistance to hydrophilic fluoroquinolones. The norA gene promoter is active in Escherichia coli HB101. We have examined the genetic basis of norA-mediated resistance in E. coli by introducing a wild-type norA gene into HB101 in plasmid pCL1921, pBR322, or pUC18 exhibiting copy numbers that spanned a 22-fold range. Increased ciprofloxacin resistance correlated with norA transcript levels seen by Northern (RNA) analysis. Thus, contrary to some reports, a wild-type norA gene confers fluoroquinolone resistance in E. coli in a copy-number-dependent fashion and does not require mutational activation. Interestingly, a multicopy pUC19norA derivative gave transformants exhibiting a range of resistance phenotypes. The norA gene of one transformant carried a single base deletion (ATACAAT to AACAAT; the deleted base is underlined) in the putative--10 Pribnow box resulting in a promoter down-regulatory mutation; a second plasmid had acquired a frameshift producing a null mutation at codon 112. These mutations override the dual resistance-growth-inhibitory phenotype of high-copy-number norA plasmids. The results have implications for using the standard E. coli HB101 system to assess NorA function and potentially for plasmid-borne transmission of norA-mediated drug resistance.

Anti-Infective Agents↗
PubMed1996

The beta 1- and beta 2-adrenoceptor subtypes in cultured rat inner medullary collecting duct cells.

We investigated beta-adrenoceptor subtype(s) expressed in cultured rat inner medullary collecting duct (IMCD) cells. In radioligand binding assay, [125I]iodocyanopindolol bound to IMCD cell membranes, representing a single class of binding sites (dissociation constant = 96.1 pM, maximum binding capacity = 18.2 fmol/mg protein, n = 8). In competition studies, ICI-89406 (beta 1-antagonist) and ICI-118551 (beta 2-antagonist) bound with high affinity, fitting a two-site model. Isoproterenol increased intracellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation (half-maximal effective concentration = 200 nM). Propranolol completely inhibited isoproterenol-induced cAMP accumulation [half-maximal inhibitory concentration (IC50) = 270 nM]. ICI-89406 and ICI-118551 inhibited cAMP accumulation by 50% (IC50 = 1.5 microM and 1.7 microM, respectively). The combined addition of ICI-89406 and ICI-118551 resulted in a curve indistinguishable from that of propranolol. The beta 1- and beta 2-adrenoceptor mRNAs have been demonstrated using reverse transcription-polymerase chain reaction. In initial and terminal IMCD cells, propranolol (3 microM) inhibited isoproterenol-stimulated cAMP accumulation by 80%, whereas ICI-89406 (3 microM) and ICI-118551 (3 microM) resulted in only partial inhibition (50%). We conclude that both beta 1- and beta 2-adrenoceptors are expressed in initial and terminal IMCD cells in primary culture.

Adrenergic beta-Agonists↗
PubMed1996

Nafamostat mesilate, a broad spectrum protease inhibitor, modulates platelet, neutrophil and contact activation in simulated extracorporeal circulation.

Activation of humoral and cellular participants in inflammation enhances the risk of postoperative bleeding and multiple organ damage in cardiopulmonary bypass (CPB). We now compare the effects of heparin alone in combination with nafamostat mesilate (NM), a protease inhibitor with specificity of trypsin-like enzymes, in an extracorporeal circuit which simulates CPB. NM significantly inhibits the release of platelet beta-thromboglobulin (beta TG) at 60 and 120 min. Platelet counts do not differ. ADP-induced aggregation decreases in circuits with NM, which is due to a direct effect of NM on platelet function. NM prevents any significant release of neutrophil elastase; at 120 min, plasma elastase-alpha 1-antitrypsin complex is 0.16 micrograms/ml in the NM group and 1.24 micrograms/ml in the control group. NM completely inhibits formation of complexes of C1 inhibitor with kallikrein and FXIIa. NM does not alter markers of complement activation (C1-C1-inhibitor complex and C5b-9), or indicators of thrombin formation (F1.2). However, at 120 min, thrombin activity as measured by release of fibrinopeptide A is significantly decreased. The data indicate that complement activation during CPB correlates poorly with neutrophil activation and that either kallikrein or FXIIa or both may be more important agonists. The ability of NM to inhibit two important contact system proteins and platelet and neutrophil release raises the possibility of suppressing the inflammatory response during clinical CPB.

Anticoagulants↗
PubMed1996

[Construction of shuttle vector containing delta-endotoxin gene of Bacillus thuringiensis].

The Bacillus thuringiensis toxin gene CryIA(c) was inserted into the shuttle vector pBE-2 to construct pAMY for expressing the B.t. gene in both Gram-negative and -positive bacterial systems. pAMY was introduced into wild type Bacillus cereus, B.brevis and B.subtilis by electroporation. Transformants containing delta-endotoxin gene produced proteins reacted with B.t. crystal protein antibody. Upon biological toxicity tests, the transformants gave a mortality of 100% against Ostrinia furnacilis, 58.8% against Heliothis armigera and 100% against Heliothis assulta. The ability of promoting plant growth of the original strains is retained.

Bacillus cereus↗
PubMed1996

[Statistical models and their application in descriptive epidemiology of cancer].

There are some limitations or disadvantages of statistical methods traditionally used in descriptive epidemiology of cancer. It can not handle the true relationships of several variables under srudy, and the effectiveness of a variable may often be confounded by other variables. This paper describes two kinds of multivariable regression models frequently used in descriptive epidemiology of cancer, such as the age-period-cohort (APC) model for the analysis of cancer incidence or mortality rate and the relative survival (RSR) model for the analysis of cancer survival rate. Detailed statistical methods, model fitting, parameter estimation, etc., are presented and two examples are used for illustration using data sets of oesophageal and stomach cancers diagnosed in urban Shanghai. The advantages of multivariable regression models are able to adjust effectiveness of confounder factors, and give estimations and evaluations of adjusted relative risks for the population.

Adult↗
PubMed1996

[Factors influencing long-term survival in patients with nonoperable lung cancer: an analysis by Cox model].

This paper reports a prospective survey of 173 patients with nonoperable lung cancer between January. 1, 1983 to March. 1, 1985. The follow-up rate was 97.7% over five years. Fourteen factors including sex, age, course of disease before treatment, clinical stage, performance status, size of mass, metastatic status, hemoglobin before treatment, short-term response to treatment and so on which might influence long term survival were studied by univariate analysis (Kruskal-Wallis test for Kaplan-Meier survival curve) and by multivariate analysis (Cox's proportional hazad model and audio-visual chart test for goodness of fit). Multivariate analysis using Cox's model revealed 6 significant prognostic factors: performance status, short-term response to treatment, clinical stage, hemoglobin before treatment, smoking index and method of treatment. The survival prediction equation was chi 2 = 72.14, nu = 6, P < 0.0001. The results indicate that the performance status and the CR rate of the initial treatment, among other things, is the major factors affecting prognosis.

Adenocarcinoma↗
PubMed1996

[Radiographic findings in osteoarthrosis of temporomandibular joint in relation to its pathologic changes].

We analysed the results of the central standard lateral tomographic findings and the macroscopic/microscopic observations on the middle portion of the autopsy materials of 84 temporomandibular joints. It was not suitable to differentiate remodeling and osteoarthrosis of the temporomandibular joint only by whether the surface articular zone of the articular cartilage is intact or not. The early changes of osteoarthrosis could occur in the interface of the bone-cartilage except occuring in the articular zone, even though the surface articular zone was intact. Therefore, we suggest that the definition of osteoarthrosis should be wider. Histopathologic observations proved that the definte radiographic signs, such as sclerosis, erosion, pseudocyst, osteophyte and so on showed on the lateral tomographs were credible signs in the diagnosis of osteoarthrosis.

Aged↗
PubMed1996

[Immunological comparison of differently treated allografts of bone].

The immunnologic rejection induced by differently treated allografts of bone was compared. Methods Fresh bone (FB), autolyzed antigen-free bone (AAA), bone matrix gelatin (BMG), demineralized bone matrix (DBM) were implanted into the muscle pouch of mice, then, the immunological tests and alkaline phosphatase assay were conducted. Results Allogeneic FB induced the highest level of serum antibody in the host and stimulated lymphocytes proliferation remarkably in vitro; in contrast, AAA, BMG and DBM caused low titer of antibody and inhibited lymphocytes reproduction in vitro. Conclusions. Immunological rejection restrained osteogenesis of the bone implant, whereas the osteoinductive substance of bone suppressed immunological reaction.

Alkaline Phosphatase↗
PubMed1996

[Experience of banking osteoarticular and bone allografts].

Banking massive osteoarticular and other bone allografts were performed in our institute. For safeguarding recipients, the guidelines of donor selection were formulated and quality control was applied during procurement, preparation and storage of the grafts. Osteoarticular and bone grafts were harvested under aseptic or clean conditions, then, the bone and joint were cut into different shapes and sizes according to clinical needs, followed by removal of bone marrow and surface demineralization. In addition, sterilization with ethylene oxide or irradiation was carried out if necessary, at last the grafts were stored by freezing or freeze-drying. From October, 1991 to February, 1994, altogether 210 osteoarticular and bone grafts were used in 20 hospitals across the country, among them 120 grafts were implanted into 84 patients in our hospital with short-term satisfactory results.

Adult↗
PubMed1996

[Study on expression of nm23-H1 gene in laryngeal cancer tissues].

The nm23 gene is a metastasis suppressor gene. There are now two known isotypes of human nm23, namely nm23-H1 and nm23-H2. Several investigators have reported that reduced expression of nm23-H1 is associated with metastasis or disease progression in some of the tumor cases. In this study, the expression of nm23-H1 mRNA in the human laryngeal squamous cell carcinoma was investigated by Northern blot analysis. The levels of nm23-H1 mRNA were higher in cancers (n = 31) than in the adjacent normal tissues (n = 7), but the difference was not significant (P > 0.05). There was a significant decrease of nm23-H1 mRNA levels in tumors with lymph node metastasis (n = 11) as compared with those without (n = 20) (P < 0.01). Cancer tissues in clinical stages III-IV. (n = 23) also exhibited lower levels of nm23-H1 mRNA expression than those in stages I-II (n = 8) (P < 0.05). These results suggest that the nm23-H1 gene may play a role in the suppression of lymph node metastasis or disease progression in laryngeal cancer.

Adult↗
PubMed1995

Hyperplasia in the rabbit bladder urothelium following partial outlet obstruction. Autoradiographic evidence.

Previous experiments have shown that adult male rabbits subjected to partial outlet obstruction or overdistension and acutely labeled, 24 h later, in vivo or in vitro with 3H-Thymidine(3H-TdR) show high levels of incorporated radioactivity in bladder epithelium when they are visualized with autoradiography. To test the hypothesis that such labeling represents the onset of a wave of proliferation (that is, true hyperplasia), we injected 3H-TdR subcutaneously in two normal and three partially obstructed New Zealand White male rabbits on each of days One, Two or Three following obstruction. Bladders were excised on the seventh day(D) following obstruction or the sixth day after injection of normals. Under these conditions, cells labeled with 3H-TdR had the opportunity to proliferate, after labelling, for 6(OneD and Normals), 5(TwoD) or 4(ThreeD) days respectively. After processing tissues for autoradiography, normal bladders showed only trace levels of labeling. Animals exposed to 3H-TdR one day after obstruction, when large numbers of basal cells of the urothelium are known to incorporate 3HTdR (i.e., synthesize DNA), showed labeling in most layers of the urothelium seven days after injection, but levels of labeling in bladders injected TwoD or ThreeD were lower than those injected OneD after obstruction. The smaller numbers of urothelial cells labeled by 3H-TdR in TwoD bladders were found in clusters where one or two alternate or adjacent layers of cells were labeled. Obstructed animals injected ThreeD after surgery showed even less labeling. This evidence clearly supports the hypothesis that DNA synthesis that occurs in the urothelium within 24 h after obstruction is followed by proliferation, because by the seventh day, labeling can be found at all levels of the urothelium. The decline of labeling in TwoD and ThreeD animals suggests that the proliferative stimulus probably operates only during the first 24 h after insult. The data suggest that a substantial fraction of the urothelium enters one or more rounds of proliferation following obstruction and support the contention that hyperplasia does occur.

Animals↗
PubMed1995

Analytical magnetapheresis of ferritin-labeled lymphocytes.

Analytical magnetapheresis is a technique for analyzing magnetic particles in suspension. The magnetically susceptible particles form a deposition pattern from the suspending medium under carefully controlled flow and magnetic field conditions. This technique was used to determine the effective magnetic volumetric susceptibility, delta chi, of human lymphocytes labeled with an iron-rich protein, ferritin. Dynabeads M450, monodisperse polymeric beads doped with magnetite, of a diameter 4.5 microns, close to that of human lymphocytes, were used as a reference. The experiment showed an almost complete deposition of ferritin-labeled lymphocytes at an average flow velocity of 0.28 mm/s, a representative magnetic field of 1.67 T, and a magnetic field gradient of 2.57 T/mm. The calculated delta chi was (2.92 +/- 0.24) x 10(-6)[SI] (ferritin-labeled lymphocytes), and the corresponding number of ferritin molecules per lymphocyte was (1.75 +/- 0.44) x 10(7). In comparison, an almost complete deposition of the Dynabeads was observed at a much higher average flow velocity, 15 mm/s, a much lower field, 0.164 T, and a much lower field gradient, 0.025 T/mm. These results corresponded to a much higher delta chi = 0.245[SI] (Dynabeads M450). These results offer important guidelines in evaluating the use of ferritin as a soluble magnetic cell label.

Calibration↗
PubMed1995

Chromatography of proteins using polybutadiene-coated zirconia.

Polybutadiene-coated zirconia (PBD-ZrO2), when used as a stationary phase in conjunction with a mobile phase containing phosphates, constitutes a reversed-phase/cation-exchange mixed-mode chromatographic system. The separation of proteins on this phase can be achieved only through the use of mobile phases containing the correct combination of phosphoric acid, displacing salt, and organic cosolvent. We found that excessive Coulombic interactions between proteins and the stationary phase impair the system performance for the separation of proteins. The effects of mobile phase conditions on the separation of proteins using phosphate-adsorbed PBD-ZrO2 are studied in this work. Factors such as the presence of a multivalent cation, mobile phase pH, phosphate concentration, and salt concentration can be manipulated to reduce the net negative charge on the surface and thereby improve the performance of the system toward the separation of proteins.

Butadienes↗
PubMed1995

Demonstration that mutation of the type II transforming growth factor beta receptor inactivates its tumor suppressor activity in replication error-positive colon carcinoma cells.

Escape from negative growth regulation by transforming growth factor beta (TGF-beta) as a result of the loss of TGF-beta type II receptor (RII) expression has been found to be associated with the replication error (RER) colorectal cancer genotype, which is characteristic of hereditary nonpolyposis colorectal cancers. The RER-positive HCT 116 colon carcinoma cell line was examined for RII mutations. A 1-base deletion was found within a sequence of 10 repeating adenines (nucleotides 709-718), which resulted in a frameshift mutation. Although it is reasonable to predict that the loss of RII function would be an important determinant of malignancy, the large number of potential mutations in cells of this phenotype raises the possibility that an RII mutation may not be a key event in the tumorigenic phenotype of these cells. One way to test directly the importance of RII mutations in determining the malignant phenotype would be to restore its expression. If restoration of expression leads to diminished tumorigenicity, it would indicate that RII mutation is an important determinant of malignancy in the RER phenotype. To determine whether restoration of RII would lead to reversal of malignancy in RER colon cancers, an RII expression vector was transfected into the HCT 116 cell line. RII stable clones showed mRNA and protein expression of transfected RII. The fibronectin mRNA level was increased by exogenous TGF-beta 1 treatment in a dose-dependent manner in RII-positive clones, whereas the control cells remained insensitive. The RII transfectants showed reduced clonogenicity in both monolayer culture and soft agarose. They were growth arrested at a lower saturation density than control cells. TGF-beta 1-neutralizing antibody stimulated the proliferation of RII-transfected but not control cells, indicating that the alterations in the growth parameters of the transfected cells were due to the acquisition of autocrine-negative activity. Tumorigenicity in athymic mice was reduced and delayed in RII transfectants. These results indicate that reconstitution of TGF-beta autocrine activity by reexpression of RII can reverse malignancy in RER colon cancers, thus verifying that the malignancy of hereditary nonpolyposis colorectal cancer can be directly associated with the loss of RII expression.

Animals↗
PubMed1995

Mixed-mode retention of peptides on phosphate-modified polybutadiene-coated zirconia.

Zirconia HPLC packing materials were found to be potentially advantageous for large-scale protein separations due to their excellent pH stability and mechanical stability. However, Lewis acid sites on zirconia's surface cause irreversible adsorption of proteins due to their interactions with hard Lewis bases such as the carboxyl groups in proteins. Although the Lewis acid sites can be effectively blocked by adsorbing phosphate ions onto zirconia's surface, proteins and peptides cannot be eluted using a typical reversed-phase mobile phase. In this work, we found that the separation of peptides on a phosphate-modified polybutadiene-coated zirconia (PBD-ZrO2) can be brought about by using a mobile phase containing both an organic modifier and a high concentration of sodium perchlorate. The salt is needed to cancel the Coulombic interactions between the negatively charged stationary phase and the positively charged proteins. To understand the retention mechanism of proteins and peptides on phosphate-modified PBD-ZrO2, this work was aimed at the study of the surface characteristics of the phosphate-modified PBD-ZrO2. We found that the phosphate-modified PBD-ZrO2 phase has both reversed-phase and cation-exchange characteristics under the acidic mobile-phase conditions used for protein and peptide separations. The PBD coating provides hydrophobic moieties, and the phosphate ions adsorbed on zirconia's surface provide cation-exchange sites. Reversed-phase separation of a peptide standard mixture and cation-exchange separation of a cationic peptide standard mixture on the same phosphate-modified PBD-ZrO2 column shows excellent column resolution in both modes. Although mixed-mode stationary phases provide unique selectivity, the secondary equilibrium on phosphate-modified PBD-ZrO2 can cause peak broadening. Applications of the phosphate-modified PBD-ZrO2 to peptide separations are demonstrated here.

Amino Acid Sequence↗
PubMed1995

Autocrine transforming growth factor beta 1 modulates the expression of integrin alpha 5 beta 1 in human colon carcinoma FET cells.

Transforming growth factor beta (TGF-beta) has been extensively studied as an exogenous agent that stimulates the expression of extracellular matrix proteins and their cell-surface integrin receptors in a variety of cell types. However, the recent demonstration of autocrine TGF-beta growth effects in a number of cell types suggests that the steady-state expression of extracellular matrix and integrin proteins and their biological activity may also be under autocrine TGF-beta control. Previously, we reported that repression of autocrine TGF-beta 1 activity by constitutive expression of a full-length TGF-beta 1 antisense cDNA led to abrogation of autocrine negative TGF-beta and, as a result, increased tumorigenicity and anchorage-independent growth of a poorly tumorigenic, well-differentiated colon carcinoma cell line designated FET (Wu, S., Theodorescu, D., Kerbel, R. S., Willson, J. K. V., Mulder, K. M., Humphrey, L. E., and Brattain, M. G. (1992) J. Cell Biol. 116, 187-196). Consequently, we have used this model system to study the effects of repression of autocrine TGF-beta 1 activity on the expression of integrin alpha 5 beta 1 and integrin alpha 5 beta 1-mediated cell adhesion to fibronectin. The expression of the integrin alpha 5 subunit was reduced in TGF-beta 1 antisense transfected FET cells at both mRNA and protein levels as determined by RNase protection assays and immunoprecipitation, respectively. Autocrine TGF-beta 1 had no effect on the transcription of integrin alpha 5 and beta 1 subunits, indicating that autocrine TGF-beta 1 may regulate integrin alpha 5 beta 1 expression at the post-transcriptional level. The diminished expression of integrin alpha 5 beta 1 on the cell surface led to the reduced adhesion of TGF-beta 1 antisense transfected cells to fibronectin. This phenomenon could be reversed by treatment with exogenous TGF-beta 1.

Cell Adhesion↗