Search PubMed⌕ Search

Biomedical subjects

L Tang

Publications and source records attributed to L Tang.

At least 73 records · Page 4Linked to original sources
PubMed2000

Identification of neural progenitors in the adult mammalian eye.

We have shown that the embryonic mammalian retina contains neural progenitors which display stem cell properties in vitro. Here we report the characterization of neural progenitors isolated from the adult mammalian eye. These quiescent cells, located in the pigmented ciliary bodies, proliferate in the presence of FGF2 and express the neuroectodermal marker nestin. The proliferating cells give rise to neural spheres and are multipotential; they express cell type-specific markers corresponding to neurons and glia. In addition, neural progenitors can generate secondary neural spheres, thus displaying potential to self-renew. The ciliary body-derived neural progenitors display retina-specific properties; the undifferentiated cells express Chx10, a retinal progenitor marker, and upon differentiation express markers corresponding to specific retinal cell types. Therefore, the pigmented ciliary body in the adult mammalian eye harbors neural progenitors that display stem cell properties and have the capacity to give rise to retinal neurons in vitro.

Animals↗
PubMed2000

Biphasic actions of prostaglandin E(2) on the renal afferent arteriole : role of EP(3) and EP(4) receptors.

Prostaglandin (PG) E(2) is an important modulator of the actions of angiotensin (Ang) II. In the present study, we investigated the renal microvascular actions of PGE(2) and the EP receptor subtypes involved. Ibuprofen potentiated Ang II-induced vasoconstriction in in vitro perfused normal rat kidneys and augmented afferent arteriolar, but not efferent arteriolar, responses in the hydronephrotic rat kidney model. This preglomerular effect of endogenous prostanoids was mimicked by exogenous PGE(2), which reversed Ang II-induced afferent arteriolar vasoconstriction at concentrations of 0.1 to 10 nmol/L without affecting the efferent arteriole. The PGE(2)-induced vasodilation was potentiated by the phosphodiesterase inhibitor Ro 20-1724 and was mimicked by 11-deoxy-PGE(1) (0.01 to 1 nmol/L). Butaprost, which acts preferentially at EP(2) receptors, was relatively ineffective. Whereas 0.1 to 10 nmol/L PGE(2) elicited vasodilation, higher concentrations (1 to 10 micromol/L) restored Ang II-induced afferent arteriolar vasoconstriction. This response was blocked by pertussis toxin (200 microg/mL) and was mimicked by the EP(1)/EP(3) agonist sulprostone (1 to 300 nmol/L). Reverse transcription-polymerase chain reaction of individually isolated afferent arterioles revealed the presence of message for EP(4) and all 3 EP(3) splice variants (alpha, beta, and gamma) but not EP(1) or EP(2). Our findings thus indicate that PGE(2) elicits both vasodilatory and vasoconstrictor actions on the afferent arteriole. The vasodilation is mediated by EP(4) receptors coupled to cAMP, presumably via G(alphas). The vasoconstriction is mediated by an EP(3) receptor coupled to G(alphai) and appears to reflect a functional antagonism of the EP(4)-induced vasodilation.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed2000

Determining the DNA bending angle induced by non-specific high mobility group-1 (HMG-1) proteins: a novel method.

To study the DNA bending induced by non-sequence-specific HMG-1 domain proteins, we have engineered a fusion protein linking the yeast NHP6A with a sequence-specific DNA binding domain, the DNA binding domain of the Hin recombinase, Hin-DBD. A series of biochemical experiments were carried out to characterize the DNA binding property of this fusion protein. Our data showed that the fusion protein not only specifically recognizes a DNA fragment containing the Hin-DBD binding site, but also binds DNA with a higher affinity in comparison with either domain alone. Both domains of the fusion protein are bound to the DNA in juxtaposition. Permutation assays showed that the fusion protein induced a DNA bending at the site of NHP6A binding by an estimated value of 63 degrees. We believe that this experimental design provides an effective vehicle to determine the DNA bending induced by nonspecific HMG-1 proteins.

Biosensing Techniques↗
PubMed2000

Cloning and heterologous expression of the epothilone gene cluster.

The polyketide epothilone is a potential anticancer agent that stabilizes microtubules in a similar manner to Taxol. The gene cluster responsible for epothilone biosynthesis in the myxobacterium Sorangium cellulosum was cloned and completely sequenced. It encodes six multifunctional proteins composed of a loading module, one nonribosomal peptide synthetase module, eight polyketide synthase modules, and a P450 epoxidase that converts desoxyepothilone into epothilone. Concomitant expression of these genes in the actinomycete Streptomyces coelicolor produced epothilones A and B. Streptomyces coelicolor is more amenable to strain improvement and grows about 10-fold as rapidly as the natural producer, so this heterologous expression system portends a plentiful supply of this important agent.

Bacterial Proteins↗
PubMed2000

Removal of hydrogen peroxide by a 1-cysteine peroxiredoxin enzyme of the filarial parasite Dirofilaria immitis.

Prior studies have shown that filarial nematodes can effectively metabolize hydrogen peroxide in excess of that generated by activated host cells. However, the mechanisms of H2O2 removal by the filarial parasites are unclear. Herein we report the results of studies carried out on the biochemical activity and on immunolocalization of a recombinant peroxiredoxin (Prx) enzyme from the dog filarial parasite Dirofilaria immitis. A full-length cDNA encoding a 1-Cys Prx enzyme from the dog heartworm D. immitis was expressed in Escherichia coli as a recombinant polyhistidine fusion protein (rDiPrx-1). rDiPrx-1 was capable of reducing H2O2 in the presence of dithiothreitol. The apparent kinetic constants determined for DiPrx-1 using H2O2 as a substrate were a Michaelis constant (Km) of 16.28 mM and a maximal velocity (Vmax) of 16 micromol/min(-1). Consistent with the enzyme activity, D. immitis adult worms could detoxify exogenously added H2O2 in vitro. Antibodies to rDiPrx-1 identified a 27-kDa native antigen in parasite extracts and larval and adult excretory-secretory products. The antibodies were used to localize the native antigen to the lateral hypodermal chords of both male and female worms by immunohistochemistry. In addition, labeling was seen in the afibrillar muscle cells in male worms and in some areas of the uterine wall in female worms. Thus, DiPrx-1 is the first parasite Prx to be shown to detoxify exogenously added H2O2 in an in vitro system.

Animals↗
PubMed2000

Nitrosyl adducts of FixL as probes of heme environment.

This report presents a spectroscopic investigation of the nitrosyl adducts of FixL, the sensor in the signal transduction system responsible for regulating nitrogen fixation in Rhizobium meliloti. Variable-temperature resonance Raman (RR), electron spin resonance (ESR), and variable-temperature UV-visible absorption data are presented for the ferrous NO adducts of two FixL deletion derivatives, FixLN (the heme-containing domain) and FixL* (a functional heme-kinase). A temperature-dependent equilibrium is observed between the five-coordinate (5-c) and six-coordinate (6-c) ferrous nitrosyl adducts, with lower temperatures favoring formation of the 6-c nitrosyl adduct. This equilibrium is perturbed as the solution freezes, and the amount of 5-c FixL-NO increases sharply until a nearly constant ratio of 6-c to 5-c adducts is obtained. Complexation between the heme domain of FixL and its response regulator, FixJ, is revealed through specfic FixJ-induced increase in the energy separation between 5-c and 6-c FixL-NO. Ferric nitrosyl adducts of FixL* and FixLN autoreduce to their corresponding ferrous nitrosyl adducts. The kinetic behavior of this reduction is monophasic for FixL*-NO, while the reaction for ferric FixLN-NO is biphasic. These results suggest conformational inhomogeneity in the heme pocket of FixLN and conformational homogeneity in that of FixL*. Hence the kinase domain plays a role in distal pocket conformational stability. Implications for the signal transduction mechanism are discussed.

Bacterial Proteins↗
PubMed2000

Analysis of small amines in pharmaceuticals by capillary ion electrophoresis with conductivity detection.

Capillary ion electrophoresis (CIE) with direct conductivity detection is a simple, fast, and versatile method for analysis of ions. In this study CIE with conductivity detection was used to analyze for hydroxylamine which is often used in the synthesis of pharmaceutical intermediates and drug substances. The conductivity response of hydroxylamine was investigated by using different buffer types and buffer concentrations. Other small amines were also studied with this method and were correlated with the molecular weight of the amines. The response of hydroxylamine increased significantly with MES glycylglycine buffer as compared to MES-histidine buffer (LOD from 10 to 1 ppm). The detection of trace level of hydroxylamine in a drug substance proved to be possible with this method. The developed method was also tested for the linearity range, reproducibility, and selectivity with several small amines. The method developed in this study was demonstrated as a sensitive and reliable method for detection and quantification of small amines in pharmaceutical substances.

Amines↗
PubMed2000

Formation of functional heterologous complexes using subunits from the picromycin, erythromycin and oleandomycin polyketide synthases.

BACKGROUND: Recently developed tools for the genetic manipulation of modular polyketide synthases (PKSs) have advanced the development of combinatorial biosynthesis technologies for drug discovery. Although many of the current techniques involve engineering individual domains or modules of the PKS, few experiments have addressed the ability to combine entire protein subunits from different modular PKSs to create hybrid polyketide pathways. We investigated this possibility by in vivo assembly of heterologous PKS complexes using natural and altered subunits from related macrolide PKSs. RESULTS: The pikAI and pikAII genes encoding subunits 1 and 2 (modules 1-4) of the picromycin PKS (PikPKS) and the eryAIII gene encoding subunit 3 (modules 5-6) of the 6-deoxyerythronolide B synthase (DEBS) were cloned in two compatible Streptomyces expression vectors. A strain of Streptomyces lividans co-transformed with the two vectors produced the hybrid macrolactone 3-hydroxynarbonolide. Co-expression of the same pik genes with the gene for subunit 3 of the oleandomycin PKS (OlePKS) was also successful. A series of hybrid polyketide pathways was then constructed by combining PikPKS subunits 1 and 2 with modified DEBS3 subunits containing engineered domains in modules 5 or 6. We also report the effect of junction location in a set of DEBS-PikPKS fusions. CONCLUSIONS: We show that natural as well as engineered protein subunits from heterologous modular PKSs can be functionally assembled to create hybrid polyketide pathways. This work represents a new strategy that complements earlier domain engineering approaches for combinatorial biosynthesis in which complete modules or PKS protein subunits, in addition to individual enzymatic domains, are used as building blocks for PKS engineering.

Anti-Bacterial Agents↗
PubMed2000

Within-subject comparison of maxillary long-bar implant-retained prostheses with and without palatal coverage: patient-based outcomes.

Although maxillary implant overdentures are used in oral rehabilitation, different designs have not been compared previously in clinical trials. This crossover trial was designed to measure differences in patient satisfaction with maxillary long-bar implant overdentures with and without palatal coverage opposed by a fixed mandibular implant-supported prosthesis. Data were also gathered on new conventional dentures and on maxillary conventional dentures opposed by mandibular fixed prostheses. Sixteen participants were selected from a population wearing conventional dentures. Fifteen received new upper and lower dentures (1 drop-out). Four implants were placed in the maxilla and mandible (2 drop-outs). A mandibular fixed prosthesis was inserted in 13 participants, who were then divided into 2 groups. One group (n = 7) received long-bar overdentures with palate, then long-bar overdentures without palate. The other group (n = 6) received the same treatments in the reverse order. Mastication tests and psychometric evaluations using Visual Analog Scales and Categorical Scales were performed throughout the study. General satisfaction was very high with both maxillary implant-supported prostheses, as were ratings of almost all psychosocial and functional variables. There were no significant differences between treatments, suggesting that patients are equally satisfied with long-bar overdentures with and without palate when these are opposed by mandibular fixed prostheses. However, the ratings given to the maxillary implant prostheses were not significantly higher than for new conventional maxillary prostheses. This suggests that maxillary implant prostheses should not be considered as a general treatment of choice in patients with good bony support for maxillary conventional prostheses.

Adult↗
PubMed2000

A kinetic study of the synthesis of ascorbate fatty acid esters catalysed by immobilized lipase in organic media.

The kinetics of the synthesis of L-ascorbyl laurate and L-ascorbyl palmitate catalysed by immobilized lipase from L-ascorbic acid and an acyl donor (lauric acid, palmic acid and their methyl and ethyl esters) in 2-methylbutan-2-ol have been investigated. The factors affecting the reaction rate (shaking speed, temperature, water activity, enzyme concentration as well as substrate concentration) are discussed. The reaction conditions have been optimized as follows: shaking speed 200 rev./min, temperature 55 degrees C, enzyme 17-20% (w/w of substrate) for these substrates. The most suitable substrate concentration for all of these substrates was 300 mmol/l. The reactions were modelled. For lauric acid, methyl laurate and ethyl laurate: K(m)=74.3, 48.97 and 55.8 mmol/l, respectively; and V(max)=0.010764, 0.0114, 0.01116 mmol.min(-1).g(-1), respectively. The most suitable substrate was methyl laurate. For palmic acid, methyl palmitate and ethyl palmitate: K(m)=102, 94.9 and 104 mmol/l, respectively; and V(max)=0.0417, 0.0424 and 0.0435 mmol.min(-1).g(-1), respectively. The most suitable substrate was methyl palmitate.

Ascorbic Acid↗
PubMed2000

Drug release from film-coated chlorpheniramine maleate nonpareil beads: effect of water-soluble polymer, coating level, and soluble core material.

The purpose of this research was to use a new drug release model to study the effects of formulation parameters on drug release from a film-coated chlorpheniramine (CPM) nonpareil system. The film-coated CPM nonpareils were prepared by using a fluid bed apparatus. A hydroxylpropylmethylcellulose (HPMC) solution was blended with an aqueous ethylcellulose dispersion (Surelease) to adjust the permeability of the film. The apparent permeability of samples was obtained from dissolution data using a previously reported drug release equation. The apparent permeability was plotted versus the film coating level or the HPMC concentration in the film. When the natural logarithm of the apparent permeability versus coating level was graphed, a biphasic plot was observed in the group without HPMC in the film, showing the occurrence of a critical coating level. It was suggested that a mechanically formed porous film (due to an incomplete coating) could change to a nonporous film after the bead was completely coated. However, in the group that contained 12% HPMC in the film, the critical coating level was not observed. A porous film, formed by the leaching out of the water-soluble polymer, would not change to a nonporous film even after the bead is completely coated. Through a mathematical derivation, the decrease of apparent permeability versus coating level was related to the reduction of the total hole area. The apparent permeability was found to increase with the HPMC concentration. After a critical concentration was reached, the further addition of HPMC into the film caused a rapid increase in apparent permeability. The critical HPMC concentration was related to a minimum domain formation concentration (MDFC). A rapid increase of the drug release was observed when the dissolution profile of a sample made from a regular sugar nonpareil core (soluble) was compared with the sample made from a precoated nonpareil core (insoluble), which suggests that the drug release can be enhanced by the dissolution of the core. A minimum concentration of the HPMC was required to effectively modify permeability of the film. The critical coating level and critical concentration of HPMC can be determined from the apparent permeability plot using a previously published equation. The dissolution of a soluble core can greatly enhance the release of the drug from the nonpareil system.

Anti-Allergic Agents↗
PubMed2000

Cloning, characterization and heterologous expression of a polyketide synthase and P-450 oxidase involved in the biosynthesis of the antibiotic oleandomycin.

The gene cluster encoding the deoxyoleandolide polyketide synthase (OlePKS) was isolated from the oleandomycin producing strain Streptomnyces antibioticus. Sequencing of the first two genes encoding OlePKS, together with the previously identified third gene revealed an overall genetic and protein architecture similar to that of the erythromycin gene cluster encoding the 6-deoxyerythronolide B synthase (DEBS) from Saccharopolyspora erythraea. When the entire OlePKS (10,487 amino acids) was expressed in the heterologous host Streptomyces lividans, it produced 8,8a-deoxyoleandolide, an aglycone precursor of oleandomycin. The role of the P-450 monooxygenase, OleP, in oleandomycin biosynthesis was also examined in vivo by co-expression with DEBS in S. lividans. The production of 8,8a-dihydroxy-6-deoxyerythronolide B and other derivatives indicates that OleP is involved in the epoxidation pathway of oleandomycin biosynthesis. Since there are currently no genetic systems available for manipulation of the natural oleandomycin producing strain, the heterologous expression system reported here provides a useful tool for studying this important macrolide antibiotic.

Anti-Bacterial Agents↗
PubMed2000

A comparative study of factors affecting chiral separations under reversed-phase conditions using cellulosic and Pirkle-type chiral selectors.

Limited studies have been conducted in reversed-phase chiral chromatography despite the relevance to water soluble chiral analytes. Systematic investigation and interpretation of factors affecting chiral separation in reversed-phase LC is crucial to efficient chiral method development. Two of the most useful chiral stationary phases (CSPs), a cellulosic (Chiralcel OJ-R) and a Pirkle-type (Chirex 3005), were chosen as the chiral selectors in this study to systematically investigate the factors affecting chiral separation of a series of Fmoc-amino acids. The effects of temperature, pH, buffer concentration, buffer type and organic modifiers on retention and chiral selectivity were compared between the cellulosic and the Pirkle-type selectors. Temperature affected retention and selectivity, as predicted by thermodynamics, using both types of chiral selectors. On the cellulosic CSP, buffer pH was the only factor which caused a significant change in chiral selectivity, while several factors, including buffer concentration and organic modifier type, affected chiral selectivity on the Pirkle-type CSP. The results also indicated that the cellulosic CSP had a retention mechanism analogous to conventional reversed-phase LC, however, the Pirkle-type selector appeared to show a mixed mode retention mechanism for these analytes.

Journal Article↗
PubMed2000

Progress in malaria control in China.

PURPOSE: To summarize the main achievements of the control of malaria in the People's Republic of China. DATA SOURCES: The data are from national case reporting system (1955-1998), and bibliographic reviews of textbooks and review articles. STUDY SELECTION: Successes in control and research of malaria were identified and selected to address the stated purpose. DATA EXTRACTION: In the past 50 years, large-scale malaria control activities were conducted in the country, relying on primary health care networks and community participation. The control of malaria was implemented according to the time- and locality-oriented approaches. As a result, remarkable success has been achieved. By the end of 1998, there were 31.3 thousand malaria cases in China, with a morbidity of 0.25 per ten thousand, which dropped by 99% in comparison with that in the 1950s. RESULTS: Most of the original hyper-endemic areas became meso- or hypo-endemic and for most of the previously meso- or hypo-endemic areas, the disease became sporadic. Malaria distribution and epidemic pattern also demonstrated great changes. CONCLUSIONS: Malaria control in China has been considerably successful in the past 50 years, which coincides with the target of the World Health Organization's "Health for all by the year 2000".

China↗
PubMed2000

[Ultrastructure study on extraocular muscle of infiltrative exophthalmos].

OBJECTIVE: To investigate histopathologic and ultrastructural changes of extraocular muscles (EOMs) in infiltrative exophthalmos in order to collect some evidences of pathogenesis. METHODS: Ten EOM samples in infiltrative exophthalmos were obtained after operation. Each of them was cut into two pieces. One of them was stained with HE and observed by light microscope. Another one was sectioned with ultrathin method and observed by transmission electron microscope. RESULTS: Under the light microscope, the extraocular muscular cells had no significant abnormality at the early stage, while at the middle and late stage, sarcoplasm coagulation, granular degeneration, vacuolization and necrosis were found in the cells. Under the electron microscope, there were disturbance and disappearance of the Z line in part of muscular fibers in early cases; at the middle and late stage, various degrees of sarcoplasmic reticulum dilatation, myofilament lysis and destruction with formation of vacuoles, secondary lysosome and remnant bodies were seen. In severe cases, the muscular cells could be completely destroyed and phagocytosed by macrophages, fibrosis occurred and myofibroblasts were found in some cases. CONCLUSIONS: The EOMs in infiltrative exophthalmos are destroyed in various degrees, and the muscular cells may be the target cells in Graves' ophthalmopathy.

Adult↗
PubMed2000

[Preventive effects of three kinds of inactive vaccines against epidemic hemorrhagic fever (EHF) after 5 years of vaccination].

OBJECTIVE: To observe the safety and the preventive effects of three kinds of vaccines as Mongolian gerbils kidney vaccine, mouse brains vaccine and hamster kidney vaccine inoculated 5 years ago. METHODS: Field study and laboratory tests were carried out by random grouping and IFAT, MCPENT, ELISA, HI tests. RESULTS: The antibody-dependent enhancement did not appear in all individuals who received vaccines after four or five years. The seroconversion rates of MCPENT were 8.97%, 11.76% and 18.75% while the seroconversion rates of IFAT were 20.73%, 30.22% and 23.40% respectively for Mongolian gerbils kidney vaccine, mouse brains vaccine and hamster kidney vaccine. The protection rates were 100% for all three kinds of inactive vaccines which showed good epidemiological efficacy. CONCLUSION: The vaccines can protect clinical infection of EHF effectively after four or five years of the initial vaccination.

Animals↗
PubMed2000

[Report on epidemic hemorrhagic fever (EHF) surveillance in 1999].

OBJECTIVE: To understand the epidemic tread of epidemic hemorrhagic fever (EHF) in 1999 and to develop programs for its control and prevention. METHODS: Epidemiological, zoo-epidemiologic, serologic and viral diagnostics were used to analyse the information of monthly and annual reports from surveillance spots. RESULTS: Twelve thousand nine hundred and thirty cases of EHF in all surveillance spots were reported with 135 cases of death in 1999. The morbidity and mortality were 5.37/100,000, and 1.04% respectively, which had a 1.47% decrease and 9.47% increase, comparing to that of 1998. The accordance of serological and clinical diagnosis was 67.25%, with rate of misreporting 1.28%. In animal surveillance, the density of mouse was 7.46% with predominant species Apodemus agrarius. In residential areas, the density of mouse was 6.21%, with predominant species Rattus norvegicus. For Apodemus agrarius in fields and Rattus norvegicus in residential areas, the indexes of HV carrier were 0.032 and 0.031 respectively in 1999. In spring and autumn, the indexes of HV carrier in Rattus norvegicus were apparently higher than that of Apodemus agrarius as the indexes of HV carrier in Rattus norvegicus were 0.028 and 0.036 comparing with 0.026 and 0.020 in Apodemus agrarius. CONCLUSION: It is suggested that more attention should be paid to the surveillance in low and medium-sized epidemic areas because northern China is dry with short rainy season while the epidemic situation in the serious epidemic areas had been under control to some degree.

Animals↗