Search PubMed⌕ Search

Biomedical subjects

L Guan

Publications and source records attributed to L Guan.

At least 73 records · Page 4Linked to original sources
PubMed1994

[Clinicopathological observations on 28 cases of cutaneous leishmaniasis in Karamay area].

Clinicopathological observations on 28 cases of cutaneous leishmaniasis with dermal lesions for 1-48 months were carried out. The cutaneous lesions detected in the patients might be categorized into four types. 1. Papular eruption or plaque. It was predominated by inflammatory reaction, including numerous leishmanias and macrophages and other inflammatory cells infiltrating in cutaneous tissue. 2. Soft node or abscess. It was composed of necrotic tissues, many degenerated and dead leishmanias as well as disintegrated inflammatory cells in the focal site. 3. Ulceration. It contained necrotic cutaneous tissue, a considerable number of dead leishmanias and granuloma formation. 4. Hard nodule. Tissue proliferation and healing were distinct, which was indicated by the increase of fibroblasts and fibrous tissue formation, round cells infiltration as well as the foreign body giant cell appearance; besides, a few leishmanias existed; occasionally, scar formation was visible in the superficial and deep layers of the derma. The paper presented for the first time the histopathological changes of cutaneous leishmaniasis in China. And, the description of cutaneous lesions will be of significance in the differential diagnosis between cutaneous leishmaniasis and post kala-azar dermal leishmaniasis.

Diagnosis, Differential↗
PubMed1994

[Chemical constituents of Pogostemon cablin (Blanco) Benth].

Nine compounds were isolated from the herb of Pogostemon cablin. They were identified as patchouli alcohol (1), pogostone (2), friedelin (3), epifriedelinol (4), pachypodol (5), retusine (6), oleanolic acid (7), beta-sitosterol (8) and daucosterol (9) on the basis of spectral data (1H-NMR, IR, MS and UV). Compound 3, 4, 6, 7, 8 and 9 were obtained from the species for the first time.

Drugs, Chinese Herbal↗
PubMed1993

High-resolution analysis of gro alpha mRNA poly(A) shortening: regulation by interleukin-1 beta.

We have previously shown that destabilization of gro alpha mRNA is associated with poly(A) shortening. In this study, we used high-resolution Northern blots to determine the rate and extent of gro alpha mRNA poly(A) shortening. gro alpha mRNA was found to undergo complete deadenylation within 2 h following withdrawal of IL-1. However, the process was not uniform: at 1 h following IL-1 withdrawal, gro alpha mRNA poly(A) lengths ranged from 0 to 180 nucleotides. There was an accumulation of deadenylated gro alpha mRNA which suggested that there may be another step before the mRNA is destroyed. Cycloheximide was found to block gro alpha mRNA degradation at the level of poly(A) shortening. Northern blots revealed a previously unrecognized periodic distribution of poly(A) lengths that was consistent with endonucleolytic cleavage between complexes of poly(A)-binding protein. The findings indicate that the degradation pathway of gro alpha mRNA is a slower version of the c-fos mRNA model, with the important additional feature that deadenylation and degradation are subject to physiologic regulation. This study provides a detailed picture of gro alpha mRNA poly(A) shortening and establishes a basis for further investigation of the mechanism by which IL-1 stabilizes specific mRNAs.

Base Sequence↗
PubMed1993

Characterization of the catalase antioxidant defense gene Cat1 of maize, and its developmentally regulated expression in transgenic tobacco.

A genomic clone containing the maize Cat1 gene has been isolated and its complete DNA sequence determined. The start of transcription has been mapped by primer extension. Six introns were identified in the Cat1 coding region. In order to determine the tissue-specific expression pattern of the Cat1 gene, promoter-reporter gene fusion constructs were made consisting of 2.5 kb and 0.8 kb of the 5' Cat1 sequence fused to the coding region of the beta-glucuronidase (GUS) gene. These fusion constructs were introduced into Nicotiana tabacum cv. Burley 21 and the expression of Cat1-GUS in various tissues was examined. In transgenic tobacco, the Cat1 promoter can drive GUS expression at relatively high levels in mature seeds. GUS activity starts to accumulate at about 10 days after flowering, reaching a maximum at about 22 days after flowering, and decreases thereafter, but persists until after seed desiccation through early germination. Low levels of GUS activity can be detected in pollen. This corresponds to the Cat1 expression pattern observed in maize.

Amino Acid Sequence↗
PubMed1993

Catalase-peroxidase gene sequences in isoniazid-sensitive and -resistant strains of Mycobacterium tuberculosis from New York City.

Isoniazid resistance in Mycobacterium tuberculosis is associated with lack of catalase-peroxidase activity. A recent study showed that some isoniazid-resistant M. tuberculosis strains have a complete deletion of the gene (katG) encoding this enzyme. To examine what proportion of clinical isolates of M. tuberculosis have katG deletion, katG sequences in 80 randomly selected isolates from New York City were analyzed. Polymerase chain reaction was used to amplify a 282-bp segment of M. tuberculosis katG and showed that 35 (90%) of 39 isoniazid-sensitive and 31 (76%) of 41 isoniazid-resistant strains contained katG sequences (P > .1). Ten multidrug and high-level isoniazid-resistant strains with identical restriction fragment length polymorphism patterns were also analyzed. All were found to have katG sequences. These findings suggest that mechanisms other than complete deletion of katG are involved in isoniazid resistance among most clinical isolates of M. tuberculosis from New York City.

Base Sequence↗
PubMed1993

[In vitro antibacterial activity and clinical significance of domestic fluoroquinolones combinations with other antimicrobial agents].

The minimal inhibitory concentration of norfloxacin, pefloxacin, ciprofloxacin and other ten antimicrobial agents for 143 strains of Gram-positive cocci and 267 strains of Gram-negative bacilli of recent clinical isolates from June 1990 to March 1991 was analyzed. The results showed that ciprofloxacin and norrancomycin were more active than other antimicrobial agents against most of the Gram-positive cocci, while ciprofloxacin and the third generation cephalosporins were more active than other antimicrobial agents against most of the Gram-negative bacilli. The reason for the resistance to antimicrobial agents may be associated with the fact that these bacteria were isolated from inpatients with chronic urinary tract infection or lower respiratory infection of preexisting chronic pulmonary diseases, who had been treated with many antimicrobial agents. Bacteria with resistance to pefloxacin and ciprofloxacin have been found, though these agents have never been used in Tianjin. Resistance of bacteria to ciprofloxacin and pefloxacin may be concerned with cross-resistance that resulted from prolonged and widespread use of norfloxacin in Tianjin. It was also found that norvancomycin resistance (MIC, > 16 mg/L) was encountered in 6 of 34 clinical isolates of oxacillin-resistant staphylococcus aureus.

Anti-Infective Agents↗
PubMed1992

Postantibiotic effect of CI-960, enoxacin and ciprofloxacin on Escherichia coli: effect on morphology and haemolysin activity.

The postantibiotic effect (PAE) has been classically defined as the suppression of bacterial growth that persists after limited exposure of organisms to antimicrobial agents. Morphology and haemolysin activity during the PAE of three quinolones on Escherichia coli were examined in this study. A one hour exposure to the quinolones, CI-960, enoxacin and ciprofloxacin, produced a PAE of 0.5-2.0 h. When determinated by Coulter counter, at 0.5 x MIC of enoxacin or CI-960 after 1 h exposure, 58% or 42% cells, respectively, of the treated cells were filamentous (cell length greater than 12 microns). After drug removal, the population of the filamentous cells decreased, however, after even 4 h, 12% and 2% of the cells were still filamentous after exposure to enoxacin or CI-960. Further morphological studies during the PAE showed that the first division of the filamentous cell was asymmetrical, and both bacterial cell division and septation were delayed after exposure to 0.5 MIC of CI-960. Following quinolone removal, the treated E. coli did not exhibit normal activity of haemolysin for at least 2 h. Internal haemolysin activity was adversely affected for 1 h. The results of this study suggest that any consideration of postantibiotic effects should include the residual antibiotic effects on bacterial morphology and virulence factors, in addition to the defined suppression of bacterial regrowth.

Anti-Infective Agents↗
PubMed1992

Analysis of macromolecular biosynthesis to define the quinolone-induced postantibiotic effect in Escherichia coli.

Quinolones inhibit DNA gyrase, and the major effects of this inhibition are on replication and transcription of DNA. The postantibiotic effect (PAE) refers to continued inhibition of cell division, in terms of the viable count, following transient exposure to an antibiotic. Previous work has shown that quinolone-treated cells have not fully recovered by the time the classically defined PAE has ended. We describe the PAE of the quinolones CI-960, enoxacin, and ciprofloxacin on macromolecular biosynthesis in the clinical isolate Escherichia coli J96 in an attempt to relate the PAE to the time that it actually takes for the cells to recover fully. DNA synthesis was inhibited immediately upon exposure to these quinolones at 0.5x or 0.75x the MIC. This inhibition continued for several hours following quinolone removal. The effects of these quinolones on RNA and protein synthesis varied; enoxacin treatment at 0.5x the MIC resulted in an increase of over 60% in both RNA and protein synthesis per unit of cell mass, while ciprofloxacin and CI-960 at that level had no significant effects on either RNA or protein synthesis. The effects of enoxacin and ciprofloxacin on bacterial protein profiles were also distinguishable, and these changes corresponded to their PAE on DNA synthesis. Throughout the study, all measures of the physiological status of the cells returned to normal by the time DNA synthesis per unit of cell mass did so. These results suggest that DNA synthesis per unit of cell mass provides an accurate measure of the time required for quinolone-treated cells to recover fully.

Anti-Infective Agents↗
PubMed1992

Diffusion of meropenem and imipenem through the outer membrane of Escherichia coli K-12 and correlation with their antibacterial activities.

The outer membrane permeability to meropenem and imipenem in Escherichia coli K-12 was investigated, and its porin-deficient mutants were transformed with a constructed vector carrying the carbapenem-hydrolyzing CphA metallo-beta-lactamase gene. By using the method of Zimmermann and Rosselet, meropenem was shown to penetrate through the outer membrane of E. coli K-12 five times faster than cephaloridine but twice as slowly as imipenem. Lack of one or both porins significantly reduced the penetration of both carbapenems. No evidence of specific porin pathways of the type described in Pseudomonas aeruginosa was found. Despite its slower penetration, meropenem was two to eight times more active than imipenem against both parent and porin-defective mutants, whether harbouring CphA beta-lactamase or not. Meropenem was also more active than imipenem against E. coli DC2, a strain with a breakdown in the outer membrane permeability which made periplasmic concentrations of beta-lactams similar to the external concentrations. In this strain, meropenem caused a more than 50% reduction in cell number increase at a concentration very close to the 50% inhibitory concentration for penicillin-binding protein type 2 (PBP 2), whereas imipenem, at the same concentration, did not significantly inhibit cell growth. This result was explained by the higher affinity of meropenem for PBP 3 compared with imipenem and supports the conclusion that synergistic inhibition of both PBPs was the main mechanism in the better antibacterial activity of meropenem.

Bacteria↗
PubMed1992

A case-control study of dietary factors in patients with lung cancer.

A case-control study was designed to investigate association of dietary factors with the risk of lung cancer in Sichuan, China. The cases consisted of 135 patients with preinvasive lung cancer which had been confirmed with histopathology, fiber bronchoscope, CT and X-ray film in three provincial hospitals in the recent one year. Controls were healthy subjects who went to one of these hospitals for health check-up; patients with pulmonary diseases was excluded. Controls were matched to cases for sex and age with a ratio of 1:1. Nutrient intakes, the eating habit and other relevant factors were investigated. The data analyzed with the conditional logistic regression model indicated that dietary beta-carotene intakes had a significantly inverse association with the risk of lung cancer. Vitamin C had a less significantly inverse association with the risk. Association of protein, fat, energy, retinol intakes or diet-balance index with the risk was not significant. Association of tea, alcohol, garlic or mushroom, respectively, with the risk was also not observed. Consumption of more processed foods and deep-fried foods were found to be risk factors. Smoking and air pollution from coal burning stoves were also observed as independent risk factors of lung cancer in the present study. The mental stress incidence in the case was significantly higher than that in the control.

Adenoma↗
PubMed1992

Initiation of polymerization with ultrasound in dental composite resin.

A single paste composite resin comprising methacrylate monomers, inorganic fillers, activators and an ultrasonic generator assembled by a piezoceramic transducer and a working tip was developed. The resin can polymerize and harden under irradiation with ultrasound having frequencies from 20 to 50 KHz and intensity from 12 to 40 W/cm2. The new technology is promising as a safe and effective method for restoration of tooth defects.

Composite Resins↗
PubMed1990

[A study on the dental adhesive containing phosphate diesters].

Although a lot of kinds of dental adhesives have been applied recently, all of them cannot meet clinical requirement completely. This paper reports a new dental adhesive containing partial phosphate diesters developed by us. We synthesized aryl phosphorodichloridates (APDC), nine kinds of phosphate diester (PDE) adhesive monomers, sodium p-toluenesulfinate (TSS) and p-toluenesulfinic acid (TSA) accelerators, polymethyl methacrylate (PMMA) powder and the other compounds. The chemical structures of PDE adhesive monomers were confirmed by IR, 1HNMR, 31PNMR, refractive index and elementary analysis etc. The results showed that the tensile bond strength (TBS) between PDE dental adhesive and human tooth was better than others reported in China and some others reported in literature.

Dental Cements↗
PubMed1989

Deblurring random time-varying blur.

The problem of restoring a constant image distorted by a system of random time-varying point-spread functions is studied. The restoration is based on a finite number of images that are observed in a finite period of time. Two features distinguish this problem. The first is that of the signal-noise dependency, and the second is the availability of large amounts of data. The Wiener criterion approach is used to solve the signal-noise-dependency problem. The problem of data size is also alleviated. For the case of time-space separability, a Karhunen-Loève transformation is used to reduce the computations to the size of a single-frame problem. For the case in which the noise is stationary in time and in space, a solution based on the direct form of the Wiener filter is presented. The amount of computations here is reduced considerably by the use of fast Fourier transforms and circulant matrix approximations whenever they are valid.

Algorithms↗