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Biomedical subjects

X Y Li

Publications and source records attributed to X Y Li.

At least 55 records · Page 3Linked to original sources
PubMed2000

Influence of some operational variables on the radial keratotomy operation.

AIMS: To assess the contribution of the four major operational variables in the radial keratotomy operation (RK) to the correction of myopic eyes. To study the deformation of the cornea after the operation and provide some valuable references for clinical practice. METHODS: The expression of the correction ratio has been deduced, which can be directly represent as the deformation ratio of the corneal radius after the operation. This allows for the numerical simulation of the RK operation. On the basis of the known biomechanical property of the cornea, by means of the finite element method, a series of computerised geometric and biomechanical models for the simulation of refractive surgery have been established. Some operational variables in the RK operation were analysed, and their influence on the operational outcome has been computed and systematically analysed. RESULTS AND CONCLUSION: All of the four variables have a positive effect on the operational outcome. The greater the four variables are the more correction effects of myopia can be obtained. Because the four variables are interinfluential, the operational variables can be optimised to get the best result in order to meet patients' differing requirements.

Biomechanical Phenomena↗
PubMed2000

c-Jun-dependent inhibition of cutaneous procollagen transcription following ultraviolet irradiation is reversed by all-trans retinoic acid.

The aged appearance of skin following repeated exposure to solar ultraviolet (UV) irradiation stems largely from damage to cutaneous connective tissue, which is composed primarily of type I and type III collagens. We report here that a single exposure to UV irradiation causes significant loss of procollagen synthesis in human skin. Expression of type I and type III procollagens is substantially reduced within 24 hours after a single UV exposure, even at UV doses that cause only minimal skin reddening. Daily UV exposures over 4 days result in sustained reductions of both type I and type III procollagen protein levels for at least 24 hours after the final UV exposure. UV inhibition of type I procollagen synthesis is mediated in part by c-Jun, which is induced by UV irradiation and interferes with procollagen transcription. Pretreatment of human skin in vivo with all-trans retinoic acid inhibits UV induction of c-Jun and protects skin against loss of procollagen synthesis. We have reported previously that UV irradiation induces matrix-degrading metalloproteinases in human skin and that pretreatment of skin with all-trans retinoic acid inhibits this induction. UV irradiation, therefore, damages human skin connective tissue by simultaneously inhibiting procollagen synthesis and stimulating collagen breakdown. All-trans retinoic acid protects against both of these deleterious effects and may thereby retard premature skin aging.

Dose-Response Relationship, Radiation↗
PubMed2000

Pain as a mutual experience for patients, nurses and families: a perspective from Shanghai, China.

The author of this article visited China for the purpose of helping the faculty of the School of Nursing learn research skills by participating in research--a kind of learn by doing. Both investigators had conducted quantitative studies in the US--one with children and one with adults--that were adapted for use in China. Seeking to also include a qualitative study, the investigators explored several possible research areas. Because pain is a universal phenomena, it was chosen as the subject for the study using the qualitative methodology reported in the first part of this article.

Adult↗
PubMed2000

Effect of ginsenoside on IL-1 beta and IL-6 mRNA expression in hippocampal neurons in chronic inflammation model of aged rats.

AIM: To study the effects of ginseng root saponins (GRS) on interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) expression in hippocampal neurons in chronic inflammation model of aged rats. METHODS: Chronic inflammation was induced by consecutive intraperitioneal injections of bacterial lipopolysaccharides (LPS) in aged rats. The semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was used for determination of IL-1 beta and IL-6 mRNA in hippocampal neurons of aged rats. RESULTS: No marked expression of IL-1 beta and IL-6 mRNA was found in hippocampal neurons of young rats (3 months). In adult rats (9 months) the levels of IL-1 beta and IL-6 expressed were 1.54 +/- 0.21 and 1.63 +/- 0.21, respectively; in aged rats (24 months) treated with LPS the levels were 1.98 +/- 0.21 and 1.91 +/- 0.11 respectively, significantly higher than those of adult rats. After treatment with GRS (10, 20, 40 mg/kg), the IL-1 beta and IL-6 mRNA content in aged rats decreased markedly. CONCLUSION: The levels of IL-1 beta and IL-6 mRNA in hippocampal neurons increased with aging. GRS exerted inhibitory effects on IL-1 beta and IL-6 gene expression in chronic inflammation model of aged rats.

Aging↗
PubMed2000

Chemical characterization and immunological activities of an acidic polysaccharide isolated from the seeds of Cuscuta chinensis Lam.

AIM: To study chemical characterization and immunological activities of an acidic polysaccharide, CHC-1, isolated and purified from the seeds of Cuscuta chinensis Lam. METHODS: Both chemical and spectral methods were used to investigate the chemical characterization of CHC-1. Effect of CHC-1 on the proliferation rates of T- and B-lymphocytes both in vivo and in vitro, and antibody production in vivo was measured at various concentrations of CHC-1. RESULTS: The molecular weight of CHC-1 was estimated to be more than 1.0 x 10(6). The analytical results of sugar components indicated that CHC-1 was composed of Rha, Ara, Gal, and GalA in a molar ratio of 0.8:1.0:1.5:0.3. Methylation analysis and 1H, 13C NMR further identified the linkages of the residues of CHC-1. CHC-1 0.1 g/L promoted remarkably the proliferation of T-cells and B-cells in vitro. CHC-1 25 mg/kg, 50 mg/kg caused an evident increase in spleen weight, lymphocyte proliferation, antibody production, etc. But its effect on IgG levels was not significant. CONCLUSION: CHC-1 is a highly branched heteropolysaccharide and possessed immune enhancement activities.

Animals↗
PubMed2000

Effects of acute exposure to mild or moderate hypoxia on human psychomotor performance and visual-reaction time.

Objective. The aim of this study was to determine whether psychomotor performance and visual reaction time were affected by acute exposure to mild or moderate hypoxia. Method. Eighteen healthy male volunteers performed finger tapping, simple reaction time (SRT) and 4-choice reaction time (CRT) tests at simulated altitude of 300 m (control), 2800 m, 3600 m and 4400 m for 1 h in a hypobaric chamber. Result. SaO2 decreased from 98% (control) to 90%, 82% and 74% respectively at the various altitudes. All the performance parameters showed no significant change after exposure to 2800 m for 1 h relative to ground level (P>0.05). However the mean reaction time of 4-CRT under 3600 m prolonged and performance decreased as compared with baseline value (P<0.05), and the performance decreased further under 4400 m (P<0.01). No significant difference was found in finger tapping and SRT even under exposure to 4400 m for 1 h. Furthermore, no decrease in correct rate were observed at any altitude (P>0.05). Conclusion. The results from this study demonstrated that there were no measurable impairment of visual reaction time and psychomotor performance under exposure to an altitude of 2800 m for 1 h. However, adverse effects on psychomotor performance were observed under 3600 m and over.

Adolescent↗
PubMed2000

Effects of acute mild and moderate hypoxia on human mood state.

OBJECTIVE: To explore the effects of acute mild and moderate hypoxia on human mood state. METHOD: The mood states of 18 healthy male volunteers were evaluated by self-assessment questionnaires, profile of mood state (POMS) and state anxiety inventory (S-AI) after random exposure to simulated altitude of 300 m (control), 2800 m, 3600 m and 4400 m for 1 h in a hypobaric chamber. RESULT: The data at 300 m level were taken as the baseline control. The negative mood state factor points (tension, fatigue etc.) increased gradually as the altitude level increased while V (vigor-activity) points had a tendency to decrease (P<0.05 or P<0.01). No significant difference was found in the points of (D, A) even under exposure to 4400 m (P>0.05). At the early period of 2800 m exposure the tension points of POMS and S-AI scores were higher than those of control level (P<0.05) then dropped to baseline level when exposure to this altitude for 1 h. CONCLUSION: Exposure to acute mild hypobaric hypoxia at 2800 m for 1 h has adverse effect on mood state of healthy person and the negative effect was further aggravated with the increment of altitude level.

Adolescent↗
PubMed2000

[The effect of heat shock before rat partial hepatectomy on HSC70/HSP68 expression and phosphatase activities].

The contribution and content of the continuous heat shock protein 70/induced heat shock protein 68 (HSC70/HSP68), the contribution, variety and activity of acid phosphatases (ACP) and alkaline phosphatases (AKP) had been analysed qualitatively and quantitatively during the liver regeneration after 2/3 hepatectomy (PH) and HS (heat shock at 46 degrees C for 30 min, recovery for 8 h), which were compared with the results only by HS and only by PH. It was shown that the three kinds of treatment all can increase the activity of ACP, AKP and the expression of HSC70/HSP68, but with different change pattern. A further analysis show that after HS-PH the enhanced activity of ACP is related with that of 140 kD phosphatases, the enhanced activity of AKP is associated with that of 140 kD and 160-180 kD phosphatases. It can be reckoned from the results that ACP, AKP and HSC70/HSP68 all act on the heat shock response of hepatocyte and liver regeneration, and may take part in signal transduction in these processes, but ACP may play a dominant role in the start of hepatocyte multiplication, AKP and HSC70/HSP68 may play a dominant role in cytokineses.

Acid Phosphatase↗
PubMed2000

[Isolation of a gene related to trichosanthin-induced apoptosis (GRETA)].

Disturbance of the apoptosis-related signaling pathway is regarded as one of the critical factors for tumorigenesis. Isolation of the genes involved in the process of apoptosis would be thereby helpful to explore the mechanism of tumor transformation and to develop novel therapeutic approaches. Here we report a gene fragment GRETA, the gene related to trichosanthin-induced apoptosis, isolated from a leukemia cell line U937 undergoing apoptosis induced by a plant protein Trichosanhin (TCS). A 293bp segment of GRETA was revealed to be 78.3% homologous to Bruton's tyrosine kinase at nucleic acid level. And Northern blot analysis showed that three messengers of RNA with the size of about 0.8-kb, 2.0-kb and 7.0-kb, respectively, were detected in TCS-untreated U937 cells when probed with GRETA, but there were only 0.8-kb and 2.0-kb transcripts appeared in apoptotic U937 cells. In addition, the abundance of each transcript changed apparently. The 0.8-kb transcript, for example, was the main band in Northern analysis in apoptotic U937 cells while was only detected marginally in TCS-untreated cells. These data suggested a possible relationship between the alternative splicing patterns of GRETA and the apoptosis.

Apoptosis↗
PubMed2000

[Immune response in Pneumocystis carinii pneumonia in rats].

OBJECTIVE: To study the inflammatory immune response to Pneumocystis canii pneumonia(PCP) in rats induced by glucocorticoid(GC). METHODS: The model of PCP was set up by injecting GC subcutanously to SD rats. Lymphocyte proportion in peripheral blood, CD4+/CD8+ T cell ratio of PBL and lymphocyte proportion in the BALF were measured. The levels of sIL-2R and TNF-alpha in the BALF were detected. RESULTS: 1. After the rats were immunospressed, the lymphocyte proportion in the peripheral blood and CD4+/CD8+ ratio of PBL, and the lymphocyte proportion in the BALF were decreased, and the levels of sIL-2R, TNF-alpha in BALF were reduced. 2. The lowest levels of TNF-alpha in BALF and CD4+/CD8+ T cells of PBL were observed in PCP group; 3. The lymphocyte proportion in the BALF was significantly higher in PCP group than in PC negative group. CONCLUSION: The reduction in the level of TNF-alpha and CD4+/CD8+ T cell ratio in rats treated with GC might result in PCP infection under immunosuppressive condition.

Animals↗
PubMed1999

Site-directed mutagenesis of the conserved residues in component I of Bacillus subtilis heptaprenyl diphosphate synthase.

Heptaprenyl diphosphate synthase of Bacillus subtilis is composed of two dissociable heteromeric subunits, component I and component II. Component II has highly conserved regions typical of (E)-prenyl diphosphate synthases, but it shows no prenyltransferase activity alone unless it is combined with component I. Alignment of amino acid sequences for component I and the corresponding subunits of Bacillus stearothermophilus heptaprenyl diphosphate synthase and Micrococcus luteus B-P 26 hexaprenyl diphosphate synthase shows three regions of high similarity. To elucidate the role of these regions of component I during catalysis, 13 of the conserved amino acid residues in these regions were selected for substitution by site-directed mutagenesis. Kinetic studies indicated that substitutions of Val-93 with Gly, Leu-94 with Ser, and Tyr-104 with Ser resulted in 3-10-fold increases of K(m) values for the allylic substrate and 5-15-fold decreases of V(max) values compared to those of the wild-type enzyme. The three mutated enzymes, V93G, L94S, and Y104S, showed little binding affinity to the allylic substrate in the membrane filter assay. Furthermore, product analyses showed that D97A yielded shorter chain prenyl diphosphates as the main product, while Y103S gave the final product with a C(40) prenyl chain length. These results suggest that some of the conserved residues in region B of component I are involved in the binding of allylic substrate as well as determining the chain length of the enzymatic reaction product.

Alkyl and Aryl Transferases↗
PubMed1999

A versatile preparation of alpha,beta-unsaturated lactones from homoallylic alcohols.

[formula: see text] A new method for the synthesis of alpha,beta-unsaturated lactones from beta-acetoxy aldehydes by reaction with the lithium enolate of methyl acetate was developed. The reaction is relatively insensitive to structural changes in the aldehyde substrates. The process was extended to the synthesis of five-ring lactones from alpha-acetoxy aldehydes. Experimental evidence regarding the mechanism of this one-pot transformation was obtained. The observations are consistent with a pathway involving an initial aldol condensation with subsequent acyl migration, lactonization, and beta-elimination and not an enolate equilibration-aldol mechanism.

Alcohols↗
PubMed1999

Enhancement of TBP binding by activators and general transcription factors.

Eukaryotic transcriptional activators function, at least in part, by promoting assembly of the preinitiation complex, which comprises RNA polymerase II and its general transcription factors (GTFs). Activator-mediated stimulation of the assembly of the preinitiation complex has been studied in vitro but has been relatively refractory to in vivo analysis. Here we use a DNA-crosslinking/immunoprecipitation assay to study in living cells the first step in the assembly of the preinitiation complex, the interaction between the TATA-box-binding protein (TBP) and its binding site, the TATA box. Analysis of a variety of endogenous yeast genes, and of a series of activators of differing strength, reveals a general correlation between TBP binding and transcriptional activity. Using mutant yeast strains, we show that Mot1 prevents the binding of TBP to inactive promoters and that activator-mediated stimulation of TBP binding requires additional GTFs, including TFIIB and Srb4. Taken together, our results indicate that TBP binding in vivo is stringently controlled, and that the ability of activators to stimulate this step in the assembly of the preinitiation complex is a highly cooperative process involving multiple transcription factors.

Adenosine Triphosphatases↗
PubMed1999

Release of glycosylphosphatidylinositol-anchored carboxypeptidase M by phosphatidylinositol-specific phospholipase C upregulates enzyme synthesis.

Carboxypeptidase M (CPM), a glycosylphosphatidylinositol (GPI)-anchored membrane protein, remained at a constant level in confluent Madin Darby canine kidney (MDCK) cells but was continually released into the medium in soluble form. The released CPM contained ethanolamine, indicating liberation by a phospholipase. Treatment of MDCK cells with 0.01 U/ml phosphatidylinositol-specific phospholipase C for 6 h led to a 5.5-fold increase in soluble CPM, yet the activity in cells remained constant, resulting in a 30% increase in total activity. The increase was due to new protein synthesis as evidenced by inhibition with 0.2 microM cycloheximide and a 63% increase in [35S]methionine incorporation into newly synthesized CPM. MDCK cells treated with 1-alkyl-2-acyl-glycerol, the diglyceride component of mammalian glycosylphosphatidylinositol anchors, exhibited a 36% increase in CPM activity, but diacylglycerols or phorbol esters were ineffective. Thus, release of GPI-anchored CPM can generate a diglyceride signal to replenish and maintain constant levels on the cell surface.

Animals↗
PubMed1999

Increased nitric oxide concentrations in posterior hypothalamus and central sympathetic function on nitrate tolerance following subcutaneous nitroglycerin.

The present study was to examine the distributions of nitric oxide (NO) in the brain regions and peripheral vessels following subcutaneously administered nitroglycerin (NTG) and determine the noradrenergic activity and the role of central sympathetic function in acute nitrate tolerance. Tolerance to NTG was produced by subcutaneous (sc) administration of 4.0 mg NTG as four separate hourly pulse injections of 1.0 mg each in male (5-8 months) Sprague-Dawley rats. Rats in sham-treated group received sc injections of saline. Rats were killed by sodium pentobarbital (150 mg/kg, ip) at 10 min after last sc injection. The brain, gracilis muscle, aorta, superior mesenteric artery, coronary artery, and pulmonary vessels were quickly removed. Concentrations of nitrite (NO2-), nitrate (NO3-), and total NO2- plus NO3- (NOx-) were quantified in the micropunches of the anterior hypothalamus, the posterior hypothalamus (PH), the nucleus tractus solitarius, the lateral reticular nucleus, and the vessels in a blinded fashion. The central actions of acute tolerance to NTG were also determined using blockades of sympathetic functions in conscious rats. Four separate hourly pulse sc injections of 1.0 mg NTG produced a marked shift of the dose-response curve for arterial pressure depression induced by intravenous injection of the challenge doses of NTG. The same doses of sc NTG caused increases in NOx- [92+/-16% (mean +/- SE)] and NO3- productions (77+/-15%) in the PH, but did not significantly change in other brain regions (n = 6). NOx- and NO3- productions were significantly enhanced in the superior mesenteric artery, aorta, coronary artery, and pulmonary vessels following sc NTG, but were not altered in gracilis muscle by the treatment. The tolerance responses to arterial pressure depression were attenuated by intravenous administration of either prazosin (300 microg/kg), an alpha1-adrenoceptor antagonist, or chlorisondamine (10 mg/kg), a sympathetic ganglion blockading agent (n = 5-6). The results suggest that acute NTG tolerance predominately increases NO production in the PH. NO production was also markedly enhanced in the large and middle vessels but not in small vessels during acute NTG tolerance. The arterial pressure tolerance to NTG was reversed by blockade of central sympathetic function. We conclude that NO formation is increased in the PH following systemically administered NTG and NO in the PH may facilitate central sympathetic functions which contribute to nitrate tolerance.

Animals↗
PubMed1999

Inhibitory effects of indomethacin on interleukin-1 and nitric oxide production in rat microglia in vitro.

Indomethacin, as a nonsteroidal antiinflammatory drug, is reported to be effective in some degree in the prevention and treatment of Alzheimer's disease (AD). Effects of indomethacin on proinflammatory cytokines interleukin-1 (IL-1), tumor necrosis factor alpha and nitric oxide (NO) on rat microglia in vitro were investigated. The biological activities of IL-1 were assayed by thymocyte proliferation assay and the activities of TNG-alpha, by L929 cytotoxicity assay. NO concentration was represented by nitrite and determined by Griess reaction. Indomethacin inhibited IL-1 and NO production by rat microglia stimulated at the concentration of 0.1-10 micromol/l. However, it did not show any inhibitory effect on TNF-alpha production by resting and LPS-stimulated rat microglia. The results suggest that the mechanism by which indomethacin might be beneficial in treatment of AD might be due to the inhibition IL-1 and NO production from microglia.

Animals↗
PubMed1999

Short-term inflammatory responses following intratracheal instillation of fine and ultrafine carbon black in rats.

Ultrafine carbon black (ufCB) 14 nm in diameter and fine carbon black (CB) 260 nm in diameter were instilled intratracheally in rats at mass of 125 microg, and the bronchoalveolar lavage (BAL) profile at 6 h was assessed. UfCB generated a 50% neutrophil alveolitis 6 h after intratracheal instillation compared to CB, which showed similar activity to the phosphate-buffered saline (PBS) vehicle control. UfCB instillation also produced a marked increase in lactate dehydrogenase (LDH) levels in BAL fluid, which was associated with increased epithelial permeability measured as total protein. In contrast, CB had much less of an effect in increasing BAL protein. Although both particle types caused a decrease in glutathione (GSH) in lung tissue compared to control, the greatest depletion was seen in ufCB-treated animals. To investigate time response, bronchoalveolar lavage was carried out at 6 h, 24 h, and 7 days after a single 125-microg instillation of ufCB. Neutrophil influx was relatively persistent and was still maintained 7 days later. Tumor necrosis factor (TNF) production by BAL leukocytes increased gradually postinstillation, whereas NO production became significantly higher at 24 h after instillation and remained at raised levels up to 7 days. Higher doses of CB caused more inflammation than the ufCB. Thus, in the instillation model, a localized dose of particle over a certain level causes the particle mass to dominate the response, rather than the surface area. In contrast to the effect of CB, which showed a dose-related increasing inflammatory response, ufCB at the highest dose caused less of a neutrophil influx than at the lower dose. Six hours after intratracheal instillation, the threshold dose for neutrophil influx occurred at 50 microg. Calculation of surface area of particles instilled suggested that this was likely to be an overload-inducing dose of particles, as gauged from recent experiments with inhaled particles. In summary, this study provides evidence in a rat instillation model that ufCB has greater ability than CB to produce lung inflammation and oxidant stress at a relatively low dose of 125 microg. At high doses, however, BAL is not a reliable indicator of pulmonary response, since the overall response seems to scale to mass or volume of instilled particulate without an influence of surface area.

Animals↗