Search PubMed⌕ Search

Biomedical subjects

X Chen

Publications and source records attributed to X Chen.

At least 397 records · Page 22Linked to original sources
PubMed2001

[Studies on ultrastructure and histochemistry of Trichomonas vaginalis adhering to vaginal mucosa of rats].

OBJECTIVE: To study interaction between Trichomonas vaginalis and epithelium of genital tract of host as well as the pathogenesis of T. vaginalis. METHODS: Immunohistochemical technique was used to observe the adhering process of T. vaginalis to vaginal mucosa in rats by transmission and scanning microscopy. RESULTS: T. vaginalis were shown to be PAS positive and clusters of T. vaginalis were found to adhere to columnar epithelium rich in mucopolysaccharide on the surface of vaginal mucosa as viewed in sections of the middle and upper parts of the orgen. T. vaginalis was positive for cathepsin. And the membrane of epithelial cells was often damaged by the released hydrolase. The parasite was also positive for actin; the microfilament bundles were arranged in reticular form in ameboid T. vaginalis. The latter would penetrate between epithelial cells, and its filiform pseudopodia would invade the interspace of microvilli of the epithelium, to encircle and gradually phagocytize microvilli. Digitiform pseudopodia would insert between epithelial cells and encircle part of them. A few T. vaginalis were found to adhere to the keratinized epithelium between mucosal folds as shown in the sections of the lower part of vagina. CONCLUSION: T. vaginalis is inclined to parasitise vaginal fornix because the superficial epithelial cells there are rich in mucinogen granules and abundant microvilli exist. After adhering, T. vaginalis releases hydrolase to digest and phagocytize epithelium which may directly damage the epithelium of the genital canal. Moreover, T. vaginalis would take in mucopolysaccharide to affect the normal clearance process of vagina, resulting in inflammation of parasitized tissue. The cytoskeleton, cell coat, polymorphism of pseudopodia and lysosome of T. vaginalis play an important role in the courses of movement, adhesion, encirclement, phagocytosis and digestion.

Actins↗
PubMed2001

[K. pneumoniea endotoxin induced mice beta-defensin-4 mRNA expression and its signaling transduction].

OBJECTIVE: To investigate the in vivo effects of Klebsiella pneumoniae endotoxin(LPS) on beta-defensin expression and the relevant signaling transduction pathway. METHODS: A LPS tolerant mouse C3H/HeJ with a point mutation at Toll-like receptor-4 (TLR4) gene and its wild type strain C3H/HeN were used in this study. C3H/HeJ and C3H/HeN were injected with 4 mg/kg of LPS intraperitoneally. The tracheas, lungs and kidneys of the C3H/HeJ and C3H/HeN were collected respectively at different LPS-treated time points, and the total RNA of each sample was extracted. The expression of mice beta-defensin-3 and/or beta-defensin-4 mRNA in these tissues was determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The sequence of cDNA amplified from the lung of C3H/HeN treated by LPS for 24 h was analyzed. By using western blot, p-I kappa B alpha (phosphorylated I kappa B alpha) and I kappa B alpha of in the lungs of C3H/HeJ and C3H/HeN were detected at different time points after treatment with LPS or without LPS. RESULTS: 1. beta-defensin-4 mRNA was detected in the lungs of C3H/HeN after 24 h treatment with LPS. In contrast, no signal was determined in C3H/HeJ mice with LPS treatment and the C3H/HeN mice without LPS treatment. 2. Compared with the control, increas of the p-I kappa B alpha was observed in the lungs of C3H/HeN at 4 h after treatment with LPS, while both the p-I kappa B alpha and I kappa B alpha contents showed a tendency to go down at 8 h after treatment and dramatically decreased at 24 h. But there were no changes in the of p-I kappa B alpha and I kappa B alpha content the lungs of C3H/HeJ under the same conditions. CONCLUSION: K. pneumoniea endotoxin could induce the expression of beta-defensin-4 mRNA in the lung of C3H/HeN, and TLR4-mediated NF-kappa B activation signaling pathway may be responsible for this event.

Amino Acid Sequence↗
PubMed2001

[Bonding and mechanical interlocking of three kinds of luting cements in retention of complete metal crowns].

OBJECTIVE: To evaluate the effects of bonding and mechanical interlocking of three kinds of luting cements in the retention of complete metal crowns. METHODS: Zinc phosphate cement (ZP), glass ionomer cement (GI) and polycarboxylate cement (PC) are in common use for clinical treatment. In this study, these cements were selected to bond the complete crowns to molars in vitro. The retention capacities of the complete crowns were tested and compared. And apart from mechanical interlocking, the effect of bonding was tested. On this basis the interlocking capacity of the cement was calculated. RESULTS: 1. The retention capacities of complete metal crowns from the highest to least were: GI > ZP > PC. 2. The proportions of mechanical interlocking of ZP, GI and PC in the retention of complete metal crowns were 62.6%, 48.3% and 20.1% and the ratios of bonding of ZP, GI and PC were 37.4%, 51.7% and 79.9%, respectively. CONCLUSION: The effects varied with different cements in the retention of complete metal crowns because of the discrepancy in bonding and mechanical interlocking properties. Mechanical interlocking plays a prominent role when ZP or GI is used, and the role of bonding is apparent in PC.

Adhesives↗
PubMed2001

[Correlation of tumor microvessel density with prognosis in laryngopharyngeal malignant melanoma].

OBJECTIVE: To investigate the relationship between microvessel density and clinicopathology, as well as the prognosis in pharyngo-laryngeal malignant melanoma. METHODS: Specific endothelial cell markers with immunohistochemistry and microvessel density with morphometry in 28 cases of laryngopharyngeal malignant melanoma. RESULTS: There was no correlation between the microvessel density (MVD) and the tumor size, Clark grade, as well as Breslow grade; however, significant correlation was found between the MVD and the AJC's grade, as well as the proliferating cell nuclear antigen (PCNA) labelling index. Microvessel counts were associated with overall survival by Kaplan-Meier analysis. An average vessel count of less than 36.5 (x 200) suggested a better survival, but a higher vessel count of more than 36.5 (x 200) showed a trend to worse the overall survival. CONCLUSION: The results suggest a significant relationship between MVD and prognosis; moreover, MVD may be a useful prognostic indicator in laryngopharyngeal malignant melanoma.

Adult↗
PubMed2001

[Pharyngeal passage tube treatment for obstructive apnea syndrome].

OBJECTIVE: To investigate the therapeutical effect of pharyngeal passage tube for OSAS. METHODS: Fifty-seven patients were treated during May 1995 to August 1999. All patients were examined by GKD-405 A polysomnography for apnea index (AI), hypnea index (HI), AHI (AI + HI) at cetera 7 items index before and after pharyngeal passage tube treatment. RESULTS: After treatment, the longest time of apnea shortened from (54.82 +/- 20.83) s to (25.74 +/- 9.50) s, the AHI lessened from 70.82 +/- 18.06 to 30.00 +/- 10.10, the oxygen desaturation increased from (62.36 +/- 11.53)% to (78.68 +/- 12.09)%. After treatment, the recorded parameters showed obvious therapeutical effect (P < 0.05-0.001, t values is from 2.20 to 15.29, the snore loudness of all patients dropped from (84.32 +/- 18.51) dB to (32.64 +/- 10.16) dB. The therapeutical successful rate was 87.72%. The long-term use rate (over 6 months) was 72.73%. CONCLUSION: The pharyngeal passage tube has obvious effect for patients suffering from severe OSAS. It is recommended for the treatment of OSAS as a conservative method.

Adult↗
PubMed2001

[Clinical study of juvenile-onset recurrent respiratory papillomatosis].

OBJECTIVE: To study the clinical behavior of juvenile-onset recurrent respiratory papillomatosis in order to find some factors correlated to the development of this disease, and to sum up the significance and experience of CO2 laser surgery. METHOD: Sixty patients with juvenile-onset recurrent respiratory papillomatosis from September 1995 to December 1998 were retrospectively analyzed. RESULTS: The age of onset in 50 cases (83.3%) was below 4 years, and the peak-age was 2 years. The rates of recurrence were 72.0% and 45.7% (chi 2 = 4.71, P < 0.05) below and over 2 years, respectively. The rates of aggressive disease were 88.0% and 54.3% (chi 2 = 7.66, P < 0.01) below and over 2 years, respectively. The predominant sites of the disease were the vocal cords, the false vocal cords, the laryngeal ventricle, the laryngeal surface of the epiglottis and the subglottic region. Tracheostomy induced the development of tracheal papilloma, therefore should be avoided as possible. Laryngeal papilloma might be divided into four types on the basis of the growth manner and surface form corresponding to clinical behaviors. Five patients were followed-up for 1.5 years without recurrence, 18 patients had fewer recurrences following treatment, 33 patients were under treatment, and 3 patients died. Nineteen patients lost follow-up. The major complications included laryngeal and tracheal stenosis. CONCLUSION: Clinical behaviors of juvenile-onset recurrent respiratory papillomatosis were relevant to the age, growth form and tracheotomy. CO2 laser was an ideal instrument for ablation of the laryngeal papillomas with the following advantages: simple management, less bleeding, preservation of laryngeal structure and avoidance of tracheostomy.

Age Factors↗
PubMed2001

[Upconversion luminescent dynamics of HoP5O14 noncrystallite excited by DCM dye laser].

The dynamics processes of 370-580 nm upconversion luminescence of HoP5O14 noncrystalline excited by DCM dye laser is reported in this paper. It is found that both mechanisms of energy transfer upconversion among ions and step-wise multiphoton absorption of single ion are involved in the upconversion luminescence, the upconversion dynamics would change greatly when the frequency of pumping laser has a little variation.

Crystallization↗
PubMed2001

[Optical parameters of Tm3+ in oxyfluoride glass ceramic].

Optical-absorption spectrum of Tm3+ ions in oxyfluoride glass ceramic was measured, from which the measured oscillator strengths were obtained. The Judd-Ofelt intensity parameters omega t (t = 2, 4, 6) were determined by a best fit of the calculated and measured oscillator strengths, the rms deviation was 3.9 x 10(-7). Some predicted spectroscopic parameters of the excited states, like the spontaneous radiative transition rate, radiative lifetime, branching ratio and integrated emission cross section were given using the intensity parameters. The spectroscopic parameters were comparable with some laser materials, and some of them were better.

Ceramics↗
PubMed2001

[Studies on non-protected fluid room temperature phosphorescence of phenanthrine].

A strong and stable room temperature phosphorescence (RTP) signal of phenanthrine aqueous solution in the absence of a protecting medium can be induced only by using Na2SO3 as deoxygenator and KI as heavy atom pertuber. The maximum phosphorescence intensity wavelengths are lambda ex/lambda em = 283/482,504 nm. It is also found that the kind and amount of organic solvent added to the luminescent system effects obviously the RTP properties. Under the present of 1% acetonitrile the RTP intensity is linear to phenanthrine concentration in the rage of 8.0 x 10(-7)-6.0 x 10(-6) mol.L-1 and 6.0 x 10(-6) mol.L(-1)-4.0 x 10(-5) mol.L-1, respectively. The detection limit is 2.6 x 10(-8) mol.L-1.

Acetonitriles↗
PubMed2001

[The upconversion "characteristic saturation phenomenon" of ErYb:ZBLAN glass excited by 966 nm diode laser].

This paper researches the upconversion luminescence of Er:ZBLAN and ErYb:ZBLAN glasses excited by 966 nm diode laser. It is found that there is a new kind of "characteristic saturation phenomenon". It is that the log-log plot's slope of upconversion luminescence intensity upon laser power of ErYb:ZBLAN glass is decreased clearly than that of Er:ZBLAN, and both of their log-log plots are rather good straight line. This upconversion mechanism is a new kind of "diffusion-transfer" mechanism, that is energy diffusion among Yb3+ ions sequential followed by energy transfer between Er(3+)-Yb3+ ions. The "characteristic saturation phenomenon" is just resulted from energy diffusion.

English Abstract↗
PubMed2001

[Measurement of waveguide depth in proton-exchanged LiNbO3 by infrared absorption spectroscopy].

A novel method for determining proton-exchanged LiNbO3 waveguide depth by infrared absorption spectroscopy was proposed. The method overcomes the shortcoming that the conventional prism-coupling + IWKB technique is only applicable to the multimode waveguides. For the commonly used single-mode waveguides, however, it is helpless. The experimental results indicated that this method has good accuracy.

Absorptiometry, Photon↗
PubMed2000

Regulation of the DPP1-encoded diacylglycerol pyrophosphate (DGPP) phosphatase by inositol and growth phase. Inhibition of DGPP phosphatase activity by CDP-diacylglyceron and activation of phosphatidylserine synthase activity by DGPP.

The regulation of the Saccharomyces cerevisiae DPP1-encoded diacylglycerol pyrophosphate (DGPP) phosphatase by inositol supplementation and growth phase was examined. Addition of inositol to the growth medium resulted in a dose-dependent increase in the level of DGPP phosphatase activity in both exponential and stationary phase cells. Activity was greater in stationary phase cells when compared with exponential phase cells, and the inositol- and growth phase-dependent regulations of DGPP phosphatase were additive. Analyses of DGPP phosphatase mRNA and protein levels, and expression of beta-galactosidase activity driven by a P(DPP1)-lacZ reporter gene, indicated that a transcriptional mechanism was responsible for this regulation. Regulation of DGPP phosphatase by inositol and growth phase occurred in a manner that was opposite that of many phospholipid biosynthetic enzymes. Regulation of DGPP phosphatase expression by inositol supplementation, but not growth phase, was altered in opi1Delta, ino2Delta, and ino4Delta phospholipid synthesis regulatory mutants. CDP-diacylglycerol, a phospholipid pathway intermediate used for the synthesis of phosphatidylserine and phosphatidylinositol, inhibited DGPP phosphatase activity by a mixed mechanism that caused an increase in K(m) and a decrease in V(max). DGPP stimulated the activity of pure phosphatidylserine synthase by a mechanism that increased the affinity of the enzyme for its substrate CDP-diacylglycerol. Phospholipid composition analysis of a dpp1Delta mutant showed that DGPP phosphatase played a role in the regulation of phospholipid metabolism by inositol, as well as regulating the cellular levels of phosphatidylinositol.

Amino Acid Sequence↗
PubMed2000

Definition of the p53 functional domains necessary for inducing apoptosis.

The p53 protein contains several functional domains necessary for inducing cell cycle arrest and apoptosis. The C-terminal basic domain within residues 364-393 and the proline-rich domain within residues 64-91 are required for apoptotic activity. In addition, activation domain 2 within residues 43-63 is necessary for apoptotic activity when the N-terminal activation domain 1 within residues 1-42 is deleted (DeltaAD1) or mutated (AD1(-)). Here we have discovered that an activation domain 2 mutation at residues 53-54 (AD2(-)) abrogates the apoptotic activity but has no significant effect on cell cycle arrest. We have also found that p53-(DeltaAD2), which lacks activation domain 2, is inert in inducing apoptosis. p53-(AD2(-)DeltaBD), which is defective in activation domain 2 and lacks the C-terminal basic domain, p53-(DeltaAD2DeltaBD), which lacks both activation domain 2 and the C-terminal basic domain, and p53-(DeltaPRDDeltaBD), which lacks both the proline-rich domain and the C-terminal basic domain, are also inert in inducing apoptosis. All four mutants are still capable of inducing cell cycle arrest, albeit to a lesser extent than wild-type p53. Interestingly, we have found that deletion of the N-terminal activation domain 1 alleviates the requirement of the C-terminal basic domain for apoptotic activity. Thus, we have generated a small but potent p53-(DeltaAD1DeltaBD) molecule. Furthermore, we have determined that at least two of the three domains (activation domain 1, activation domain 2, and the proline-rich domain), are required for inducing cell cycle arrest. Taken together, our results suggest that activation domain 2 and the proline-rich domain form an activation domain for inducing pro-apoptotic genes or inhibiting anti-apoptotic genes. The C-terminal basic domain is required for maintaining this activation domain competent for transactivation or transrepression.

Apoptosis↗
PubMed2000

Protection of normal proliferating cells against chemotherapy by staurosporine-mediated, selective, and reversible G(1) arrest.

BACKGROUND: A major limiting factor in human cancer chemotherapy is toxicity in normal tissues. Our goal was to determine whether normal proliferating cells could be protected from chemotherapeutic agents by taking advantage of the differential drug sensitivity of cell cycle G(1) checkpoint in normal and cancer cells. METHODS: Normal mammary epithelial cells and mammary cancer cells were initially treated with staurosporine at a cytostatic (i.e., nonlethal) concentration, which preferentially arrests normal cells in the G(0)/G(1) phase of the cell cycle without affecting the proliferation of tumor cells. After the selective arrest of normal cells in G(0)/G(1), both normal and tumor cells were treated with doxorubicin or camptothecin, two cytotoxic (i.e., lethal) chemotherapeutic agents. Cells were then allowed to recover in drug-free medium for 12 days. RESULTS: After pretreatment of both normal and tumor cells with staurosporine followed by treatment with doxorubicin or camptothecin, tumor cells were selectively killed by chemotherapeutic agents, whereas normal cells resumed proliferation after the drugs were removed. Pretreatment with staurosporine also protected normal circulating lymphocytes that had been induced to proliferate in vitro with phytohemagglutinin from chemotherapeutic agents. Staurosporine-induced arrest of normal cells in G(0)/G(1) phase was reversible, and arrested cells tolerated doses of camptothecin that were more than 100-fold higher than necessary to eradicate all tumor cells in culture. Staurosporine-mediated G(0)/G(1) arrest targets the retinoblastoma protein (pRb) pathway and was accompanied by a rapid decrease in cyclin-dependent kinase (CDK) 4 protein levels, increased binding of CDK inhibitors p21 and p27 to CDK2, and inhibition of CDK2 activity in normal cells. CONCLUSIONS: Breast cancer cells with defective checkpoints regulated by the pRb pathway can be targeted specifically with chemotherapeutic agents, following staurosporine-mediated, selective and reversible G(0)/G(1) arrest in normal cells.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2000

Altered gating of opiate receptor-modulated K+ channels on amygdala neurons of morphine-dependent rats.

The molecular mechanism of tolerance to opiate drugs is poorly understood. We have used single-channel patch-clamp recordings to study opiate receptor effects on dissociated neurons from rat amygdala, a limbic region implicated in addiction processes. A 130-pS inwardly rectifying K(+)-preferring cation channel was activated by mu opioid receptors in a membrane-delimited manner. After chronic treatment of the rats with morphine, channel gating changed markedly, with an approximately 100-fold decrease in open probability at a given morphine concentration. The change in channel gating correlated both in time course and in dose of morphine treatment with the development of functional opiate dependence and appeared to arise at a step after G-protein activation and before channel permeation by K(+). This decreased receptor-channel coupling appears to be large enough to account quantitatively for opiate tolerance and may represent one of the mechanisms through which tolerance occurs.

Amygdala↗
PubMed2000

Heterogeneity of HLA and EBER expression in Epstein-Barr virus-associated nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC) is an aggressive tumour of multifactorial aetiology that, although rare in most parts of the world, poses a significant mortality problem in its high incidence area of Southern China. Improved therapies are an urgent requirement and, towards this end, immunotherapeutic methods are being developed in several centres. Such strategies are dependent on the immune competence of the target tumour, in particular its expression of HLA class-I. We examined HLA class-I and -II expression in 27 primary NPC biopsies and found that 15% were extensively down-regulated for class-I expression with the majority of tumour cells appearing negative. Whilst HLA class-II was expressed at high levels in the majority of tumours, 37% showed substantial down-regulation. NPC is associated with Epstein-Barr virus (EBV). Expression of the virus-encoded EBER RNAs is accepted as a marker of EBV latency and is regarded as a valuable diagnostic criterion. EBER RNAs were expressed in all samples, but in some the level was remarkably heterogeneous, being barely detectable in many tumour cells. Our study reinforces the concept of extensive phenotypic variation in NPC. There are morphological differences between tumour cells. Some tumours express HLA class-I and/or -II, whilst others are down-regulated or negative. Individual tumours may or may not express the EBV-encoded LMP-1 protein, and individual tumour cells may express high levels of EBER, yet adjacent tumour cells express very little or none.

Adult↗
PubMed2000

Synthesis of alpha-Gal epitope derivatives with a galactosyltransferase-epimerase fusion enzyme.

Alpha-Gal epitopes are carbohydrate structures bearing an alpha-D-Galp-(1-->3)-beta-D-Galp terminus and are the main cause of antibody-mediated hyperacute rejection in xenotransplantation. Nine monosaccharides and ten disaccharides were evaluated as substrates for a fusion protein, which contains both alpha-(1-->3)-galactosyltransferase and uridine-5'-diphosphogalactose 4-epimerase. Four disaccharide and six trisaccharide alpha-Gal epitope derivatives were synthesized utilizing this novel fusion enzyme.

Animals↗