Biomedical subjects

X Chen

Publications and source records attributed to X Chen.

At least 253 records · Page 14Linked to original sources

PubMed2001

Research and prediction of coordination reactions between CPA-mA and some metal ions using artificial neural networks.

The complex relationship between maximum absorption wavelength (lambda(max)), molar absorptivity (epsilon) of the coordination compounds formed from m-acetyl-chlorophosphonazo (CPA-mA) and the metal ions, the acidity of coordination reaction, some properties of metal ions and the properties of more than 20 coordination compounds were studied using artificial neural networks with extended delta-bar-delta EDBD back learning algorithms in this paper. Six parameters: the pH of coordination reactions, metal ion radius (R), relative atomic weight (Wt), ionic electronic energy (E), metal ion standard Gibbs' free energy (deltaG0) and hard-soft acid-base dual scale (f) were used as input parameters, to predict the lambda(max) and epsilon of the coordination compounds. The structures of networks and the learning times were optimized. The best networks structure is 6-7-2. The optimum number of learning times is about 160,196. It is shown that the maximum relative error is no more than 6% in the testing set. The trained networks are used to simulate the complicated relations between the metal ion properties, coordination reaction conditions and the properties of coordination compounds. This optimized networks have been used for the prediction of the lembda(max) and epsilon of coordination compounds formed from Tb3+, Ho3+ with CPA-mA separately and with satisfactory results.

Journal Article↗

PubMed2001

Microcirculation patterns other than loops and networks in choroidal and ciliary body melanomas.

PURPOSE: To provide ophthalmologists and pathologists with expanded criteria for separating patients at high risk of metastatic melanoma from those at low risk on the basis of microcirculation patterns in choroidal and ciliary body melanomas. DESIGN: Tissue culture studies and observational case series. PARTICIPANTS: The pattern-forming ability of four uveal melanoma cell lines of varying degrees of aggressive behavior was studied in vitro. Histologic sections of 234 eyes removed for choroidal or ciliary body melanoma were studied for the presence of microcirculation patterns. METHODS: The study was divided into two phases: the study of histologic sections of eyes removed for choroidal and ciliary body melanomas and observations on the in vitro behavior of cultured melanoma cells of varying degrees of invasive behavior. The presence or absence of each of nine microcirculation patterns was recorded from tissue sections, and interrelationships between different patterns were explored statistically. In vitro reconstitution of patterns and a study of the interrelationships of patterns in histologic sections was carried out. In the in vitro studies, uveal melanoma cell lines of varying degrees of aggressive potential were cultured to observe the development of architectural patterns other than loops and networks. MAIN OUTCOME MEASURES: In histologic studies, the outcome measure was the conditional probability of detecting loops or networks given the presence or absence of other patterns positive for periodic acid-SCHIFF: For tissue culture studies, the outcome measure was either the development or lack of development of patterns of different shapes in vitro. RESULTS: Histologic studies disclosed that given the presence of arcs without or with branching in a tissue section, it is likely that loops or networks will be detected in the same section plane, suggesting that the production of these patterns by aggressive tumor cells reflects a spectrum of architectural potential. In vitro studies confirmed this hypothesis by revealing that highly aggressive and metastatic uveal melanoma cell lines, but not poorly aggressive tumor cell lines, generated parallel channels with and without crosslinking and arcs with and without branching as well as loops and networks. CONCLUSIONS: The criteria for separating patients into low- and high-risk categories for metastasis from uveal melanoma should be expanded to include patterns other than loops or networks. In both the pathology laboratory as well as in a clinical setting, the detection of arcs or arcs with branching and parallel channels should prompt a careful search for loops and networks and for crosslinking parallel channels, respectively.

Choroid Neoplasms↗

PubMed2001

On the relationship of P3a and the Novelty-P3.

Deviant stimuli give rise to a late positive ERP component with latencies from 250 to 400 ms. Target deviants elicit a P300 with maximum amplitude over parieto-central recording sites while the 'P300' elicited by deviant nontarget stimuli occurs somewhat earlier and shows a more frontally-oriented scalp distribution. Two varieties of frontal P300s have been described, elicited either by rare stimuli (target or nontarget) presented in a two-stimulus oddball task (P3a) or by infrequent, unrecognizable stimuli presented in the context of a three-stimulus oddball task (Novelty-P3). The Novelty-P3 has been observed in a number of subsequent studies; the P3a has not been extensively studied and both its significance and existence have been called into question. The present report describes a replication of two prototypical studies with 'frontal' P3s observed in each context. Application of factor analysis to the two sets of ERP waveforms does not support a distinction between these two components.

Adult↗

PubMed2001

Experimental imaging of the acoustic nonlinearity parameter B/A for biological tissues via a parametric array.

The acoustic nonlinearity parameter B/A is an important parameter in nonlinear acoustics and has been suggested to be a novel parameter for ultrasound tissue characterization. In this paper, the principle and experimental results for B/A imaging by using a parametric array are presented. As two primary waves with different frequencies are radiated simultaneously from a circular piston source, a secondary wave at the difference frequency is generated due to the nonlinear interaction of the two primary waves. The axial sound pressure amplitude curve for the generated difference frequency wave in the near field is measured and agrees well with the theoretical calculation. Unlike the second harmonic wave, the difference frequency component of the parametric array grows almost linearly with distance from the piston source and goes through fewer oscillations in the near field. It therefore provides a better source for acoustic nonlinearity parameter tomography. On the basis of the finite amplitude insert substitution method and the conventional CT technology, an experimental imaging system for acoustic nonlinearity parameter B/A via a parametric array is set up. B/A images for several biological specimens, including normal and pathological tissues, are obtained.

Acoustics↗

PubMed2001

Hyper-responsivity in a subset of C-fiber nociceptors in a model of painful diabetic neuropathy in the rat.

While clinical characteristics of diabetic painful neuropathy are well described, the underlying electrophysiological basis of the exaggerated painful response to stimuli, as well as the presence of spontaneous pain, are poorly understood. In order to elucidate peripheral contributions to painful diabetic neuropathy, we quantitatively evaluated the function of C-fibers in a rat model of painful diabetic neuropathy, diabetes induced by the pancreatic beta-cell toxin streptozotocin. While there was no significant effect of diabetes on conduction velocity, mechanical threshold or spontaneous activity, the number of action potentials in response to sustained threshold and suprathreshold mechanical stimuli was significantly increased in the diabetic rats. Moreover, there was a clustering of responses of C-fibers in diabetic rats; while two-thirds of C-fibers fired at the same mean frequency as C-fibers in control rats, one-third of C-fibers in diabetic rats were markedly hyper-responsive, demonstrating a threefold increase in firing frequency. The high-firing-frequency C-fibers in rats with diabetes also had faster conduction velocity than the low-firing-frequency C-fibers in rats with diabetes or in C-fibers in control rats. The hyper-responsiveness was characterized by a selective increase of the shortest interspike intervals (<100ms) in the burst component (first 10s) of the response to a sustained suprathreshold stimulus; in the plateau phase (last 50s) of the response to a 60-s suprathreshold stimulus, we found a selective increase of interspike intervals between 100 and 300ms in hyper-responsive C-fibers in rats with diabetes. The hyper-responsiveness did not correlate with mechanical threshold, presence of spontaneous activity or location of the fiber's receptive field. In summary, in an established model of painful diabetic neuropathy in the rat, a subset of C-fibers demonstrated a marked hyper-responsiveness to mechanical stimuli. The subset was also found to have a greater mean conduction velocity than the fibers not demonstrating this hyper-responsivity. The present findings suggest that study of individual neurons in vitro may allow elucidation of the ionic basis of enhanced nociception in diabetic neuropathy.

Action Potentials↗

PubMed2001

Role of protein kinase Cepsilon and protein kinase A in a model of paclitaxel-induced painful peripheral neuropathy in the rat.

The clinical use of the antineoplastic agent paclitaxel (Taxol) is significantly limited in its effectiveness by a dose-related painful peripheral neuropathy. To evaluate underlying mechanisms, we developed a model of Taxol-induced painful peripheral neuropathy in the rat and determined the involvement of two second messengers that contribute to enhanced nociception in other models of inflammatory and neuropathic pain, protein kinase Cepsilon and protein kinase A. Taxol administered acutely, or chronically over 12 days, produced a decrease in mechanical nociceptive threshold. Acutely, Taxol induced hyperalgesia that was significant within 1 h, maximal after 6 h and resolved completely by 24 h after a single treatment. Chronically, Taxol treatment resulted in a dose (0.1-1 mg/kg/day)-dependent decrease in nociceptive threshold, measured 24 h after administration, maximal within 5 days from the commencement of Taxol administration and resolving by 2 weeks after the last dose of Taxol. Chronic Taxol treatment also increased the number of action potentials evoked by sustained (60-s) threshold and suprathreshold (10-g) stimulation of a sub-population of C-fibers in rats with Taxol-induced hyperalgesia. Mechanical allodynia and thermal hyperalgesia were also present in Taxol-treated rats. Hyperalgesia, produced by both acute and chronic Taxol, was attenuated by intradermal injection of selective second messenger antagonists for protein kinase Cepsilon and protein kinase A. These findings provide insight into the mechanism of Taxol-induced painful peripheral neuropathy that may help control side effects of chemotherapy and improve its clinical efficacy.

Animals↗

PubMed2001

Quantifying amorphous content of lactose using parallel beam X-ray powder diffraction and whole pattern fitting.

The objective of this study was to demonstrate the applicability of parallel beam X-ray powder diffraction (XRPD) and a new method for whole pattern fitting to the quantification of the residual amount of amorphous content in a pharmaceutical solid using lactose as a model system. Lactose monohydrate, prepared by slurry conversion of anhydrous lactose, was mixed with different amounts of amorphous lactose produced by lyophilization. X-ray powder diffractograms of each mixture were recorded and analyzed by whole pattern fitting using Percentage Crystallinity Determination Software from Kratos Analytical Inc. The polycapillary X-ray optic, which provides a parallel beam of X-radiation, has advantages over Bragg-Brentano Optics with respect to sample height artifacts. Significant shifts in peak position with changes in sample height of lactose monohydrate were observed using Bragg-Brentano Optics while no change was detected for the polycapillary X-ray optic. A technique to normalize all diffractograms to have the same total integrated intensity was necessary to eliminate tube fluctuation effects. After normalization, the amorphous content of lactose in the range of 1-10% was reproducibly predicted (small standard deviation between samplings) using whole pattern fitting. The limit of detection was calculated to be 0.37% amorphous content. The results indicated that parallel beam XRPD and whole pattern fitting can provide accurate analysis of relatively small amounts of amorphous content in pharmaceuticals compared to typical XRPD analysis.

Lactose↗

PubMed2001

Adolescent smoking in Wuhan, China: baseline data from the Wuhan Smoking Prevention Trial.

BACKGROUND: This study reports the prevalence of adolescent smoking in the urban and rural areas of Wuhan, China, the capital of Hubei Province, on the Yangtze River in central China. METHODS: Smoking behavior was examined by age, gender, and urbanicity as part of the Wuhan Smoking Prevention Trial. Subjects included 6994 seventh- to ninth-grade students attending 22 randomly selected schools in urban and rural districts. Outcome measures included lifetime smoking, past-30-day smoking, established smoking (>100 cigarettes in lifetime), and susceptibility to smoking (absence of a firm commitment not to smoke). RESULTS: Lifetime smoking prevalence was 47% among boys and 18% among girls. Past-30-day smoking prevalence was 16% among boys and 4% among girls. Established smoking prevalence was 2% among boys and 0% among girls. The prevalence of susceptibility to smoking was 31% among boys and 10% among girls. Smoking increased significantly with age (p<.0005). Susceptibility was more prevalent in rural areas than in urban areas (p<.05), but there were no urban-rural differences in lifetime, past 30-day smoking, or established smoking. Trend analyses revealed that smoking increased with age more rapidly among boys than among girls (p<.05). Smoking was more prevalent among rural boys than among urban boys, but it was more prevalent among urban girls than among rural girls (p<.05). CONCLUSIONS: Adolescent smoking is a significant public health problem in China. Boys are at particularly high risk, as are girls living in urban areas. Effective smoking prevention programs for adolescents, as well as restrictions on tobacco industry marketing and youth access to tobacco, are needed to prevent tobacco-related morbidity and mortality in China.

Adolescent↗

PubMed2001

Factors affecting client response to HIV outreach efforts.

PURPOSE: This article describes 12 HIV Outreach Demonstration Projects funded by the Center for Substance Abuse Treatment in 1995, and the clients these projects served. The article also summarizes the findings of multivariate statistical analyses aimed at identifying important project and client characteristics that influenced project success in achieving two key outcomes: persuading at-risk clients to obtain HIV tests, and facilitating entry by substance-abusing clients into structured substance abuse treatment (SAT). METHODS: Hierarchical linear modeling (HLM) analysis was used to conduct the analyses. RESULTS: The findings support the hypothesis that HIV Outreach, as an integrated approach to addressing the multiple problems clients have due to substance abuse and related problems, can be an effective model for reaching clients who have not been reached through traditional means. IMPLICATIONS: By implementing a complement of comprehensive HIV Outreach interventions, many of the HIV Outreach projects were successful in addressing the various needs of their clients. However, as detailed in this article, some services and service delivery procedures, were more effective than others in achieving project objectives.

AIDS Serodiagnosis↗

PubMed2001

Characterization for didodecyldimethylammonium bromide liquid crystal film entrapping catalase with enhanced direct electron transfer rate.

Direct electrochemistry for catalase (CAT) embedded in the liquid crystal film of didodecyldimethylammonium bromide (DDAB) was investigated at pyrolytic graphite (PG) electrode by voltammetric methods. The reduction reaction involved the redox couple in CAT, i.e. FeIII/FeII couple. The electron transfer between the incorporated CAT and PG electrode was found to be greatly enhanced by DDAB. The heterogeneous electron transfer rate constant k(s) was fitted as 3.0 +/- 0.4 s(-1) using the nonlinear regression analysis of the square wave voltammograms at a series of pulse heights. The pH dependence of the formal potential for CAT in DDAB film was 57 mV/pH, which suggested one-proton-transfer together with a one-electron reaction. Visible absorption and reflectance-absorbance infrared (RAIR) spectra inferred the similar heme environment of CAT in DDAB film to its native status. Circular dichroism (CD) results indicated DDAB affected slightly on the second structure of CAT.

Animals↗

PubMed2001

Cr2, a candidate gene in the murine Sle1c lupus susceptibility locus, encodes a dysfunctional protein.

The major murine systemic lupus erythematosus (SLE) susceptibility locus, Sle1, corresponds to three loci independently affecting loss of tolerance to chromatin in the NZM2410 mouse. The congenic interval corresponding to Sle1c contains Cr2, which encodes complement receptors 1 and 2 (CR1/CR2, CD35/CD21). NZM2410/NZW Cr2 exhibits a single nucleotide polymorphism that introduces a novel glycosylation site, resulting in higher molecular weight proteins. This polymorphism, located in the C3d binding domain, reduces ligand binding and receptor-mediated cell signaling. Molecular modeling based on the recently solved CR2 structure in complex with C3d reveals that this glycosylation interferes with receptor dimerization. These data demonstrate a functionally significant phenotype for the NZM2410 Cr2 allele and strongly support its role as a lupus susceptibility gene.

Alleles↗

PubMed2001

Fluorescence characteristic study of the ternary complex of fluoroquinolone antibiotics and cobalt (II) with ATP.

The results from the measurement of the fluorescence spectra of fluoroquinolone antibiotics including ofloxacin (OF), norfloxacin (NOR) and ciprofloxacin (CIP) complexed with cobalt (II) and ATP give information concerning the antibiotics-nucleotide interactions. From the fluorescence spectral data, it appears that the fluoroquinolone antibiotic cannot directly complex with ATP but indirectly complex with cobalt (II), which is playing an intermediary role. The interaction of fluoroquinolone antibiotic with the nucleotide occurs mainly through the phosphate group. The conclusion offers a more complete mechanism, which is important for understanding the interaction of these drugs with DNA.

Adenosine Triphosphate↗

PubMed2001

Shikonin, a component of antiinflammatory Chinese herbal medicine, selectively blocks chemokine binding to CC chemokine receptor-1.

Shikonin is a chemically characterized component of traditional Chinese herbal medicine and has been shown to possess antiinflammatory activities. We ascertained that shikonin blocked radiolabelled Regulated on Activation, Normal T cell Expressed and Secreted (RANTES) and macrophage inflammatory protein-1 (MIP-1alpha) binding to human monocytes with IC50 values of 3.58 x 10(-6) and 2.57 x 10(-6) M, respectively. In contrast, up to 1.7 x 10(-5) M of shikonin failed to inhibit stromal cell-derived factor-1 (SDF-1alpha) binding to the cells. Additionally, shikonin blocked RANTES and MIP-1alpha binding to stable CC chemokine receptor-1 (CCR1) transfected human embryonic kidney (HEK)/293 cells with IC50 values of 2.63 x 10(-6) and 2.57 x 10(-6) M, respectively. However, shikonin inhibited neither RANTES nor MIP-1alpha binding to CCR5 transfected HEK/293 cells. Shikonin also did not inhibit monocyte chemoattractant protein-1 (MCP-1) binding to CCR2 cells, eotaxin binding to CCR3 cells, interferon-inducible T cell alpha-chemoattractant (I-TAC) binding to CXCR3 cells and SDF-1alpha binding to CXCR4 cells. Additionally, shikonin inhibited RANTES-induced CCR1 cell migration, but did not inhibit CCR1 cell migration induced by epidermal growth factor (EGF). Our study suggests shikonin may be a target for the future design of more potent, highly selective therapeutics that could be useful antiinflammatory agents for selectively blocking the binding of CCR1 ligands.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2001

Nucleotide sequence and transcriptional analysis of a putative basic DNA-binding protein of Helicoverpa armigera nucleopolyhedrovirus.

A putative basic DNA-binding protein (BDBP) gene was identified in the fragment EcoRI-K of the Helicoverpa armigera single-nucleocapsid nucleopolyhedrovirus (HearNPV) genome. The ORF is 330 nucleotides long encoding a basic protein of 109 amino acids with a molecular mass of 11.6 kDa. It is the first BDBP identified in single nucleocapsid NPVs and a homologue of Autographa californica MNPV (AcMNPV) P6.9. A consensus late transcription motif, ATAAG, was found at 57 nt upstream of the translational start codon and a polyadenylation signal was observed at 172 nt downstream of the stop codon. A major transcript of 620 nt was first observed in HearNPV-infected Hz2e5 cells 16 h post infection. Primer extension analysis revealed that this transcript initiated from the first residue of the consensus ATAAG late transcription start motif. Comparison with other baculoviral BDBPs showed that they all contained two conserved cAMP- and cGMP-dependent protein kinase phosphorylation motifs, R-R-R-S. The HearNPV P6.9 homologue is the longest BDBP found so far in baculoviruses.

Amino Acid Sequence↗

PubMed2001

Behavioral and electrophysiological responses of Arhopalus tristis to burnt pine and other stimuli.

The exotic longhorn beetle Arhopalus tristis is a pest of pines, particularly those damaged by fire, and a major export quarantine issue in New Zealand. Actinograph recordings of caged individuals showed that males and females were most active from dusk to midnight. Olfactometer experiments indicated that females moved upwind toward odors from burnt pine (80%, N = 75), compared to unburnt pine (20%). Oviposition choice tests showed that eggs were predominantly laid on burnt logs (79%, N = 20), compared to unburnt logs. Beetles were trapped by funnel traps baited with burnt (mean catch per trap 7.8) and unburnt (mean catch 4.1 per trap) pine bark from inside a screen cage (4 x 3 m), while unbaited traps had a mean catch 0.1 beetles (N = 8 replicates). The treatment of burnt pine bark with a 1:1:2 mixture of green leaf volatiles (E)-2-hexen-1-ol and (E)-2-hexenal) in mineral oil as a repellent reduced trap catch by fivefold in a similar experiment (mean catches of 1.2 beetles per trap to burnt pine bark plus repellent treatment and 6.2 beetles per trap to burnt pine bark alone). The treatment of burnt pine bark with this solution also reduced oviposition by 98.5% (mean eggs per log of 11.1 on burnt pine and 0.3 on burnt pine plus repellent), indicating that oviposition cues have the potential to be significantly disrupted. The electrophysiological responses of adult beetles were recorded to a range of odorants. Normalized responses to monoterpenes known to occur in Pinus radiata ranged from about 20 to about 150, with alpha-terpineol giving the greatest responses in both sexes. Green leaf volatiles also gave high responses. The potential exists to improve the management of this insect using chemical cues in various ways.

Animals↗

PubMed2001

Male-produced sex attractant pheromone of the green stink bug, Acrosternum hilare (Say).

Sexually mature virgin adult males of the green stink bug, Acrosternum hilare attracted sexually mature virgin adult females in laboratory bioassays using a vertical Y-tube. There was no indication that males attracted other males, or that females attracted either sex. These results suggested that A. hilare males produce a sex pheromone. Extracts of odors collected from sexually mature males contained compounds that were not present in extracts from females or sexually immature males. (4S)-Cis-(Z)-bisabolene epoxide ((4S)-cis-Z-BAE) was the major sex-specific component of the extract. The crude extract was attractive to female A. hilare, but when separated into four fractions, only the portion containing (4S)-cis-Z-BAE and the minor component (4S)-trans-Z-BAE was attractive to females. This fraction was as attractive as the crude extract, suggesting that the former contained all the pheromone components. Neither synthetic (4S)-cis-Z-BAE nor (4S)-trans-Z-BAE alone was attractive to females, but a 95:5 cis:trans blend, mimicing the ratio naturally produced by males, was attractive to females in Y-tube bioassays. Bioassays in a field cage showed that significantly more A. hilare females were attracted to cotton string lures treated with 1 mg of a 95:5 blend of (4S)-cis-Z-BAE and (4S)-trans-Z-BAE placed inside a bouquet of alfalfa than to an alfalfa bouquet containing a pentane-treated control. In field cage studies, attraction of females was greatest during the late afternoon and evening hours, and female A. hilare approached the synthetic pheromone source almost exclusively by walking.

Animals↗

PubMed2001

A convenient and rapid method for genetic transformation of E. coli with plasmids.

A convenient and rapid method for the genetic transformation of Escherichia coli with plasmids is proposed. By mixing the recipient cells and plasmid DNA and spreading them directly on selective medium plates containing Ca2+, the so-called 'plate transformation' could achieve almost the same transformation efficiency as the classical transformation method with calcium. The whole protocol takes only about 2 min, its simplicity compared favorably, not only to the usual protocol, but also to all other documented modifications.

Calcium Chloride↗

PubMed2001

Bilateral central retinal vein occlusions in a Chinese patient with HIV-infection.

PURPOSE: To report a case of bilateral nonischemic central retinal vein occlusions as the initial presentation in a Chinese patient with HIV-infection. METHODS: Complete ophthalmological examination and fundus fluorescein angiography were performed in the eyes of this patient. RESULTS: Ophthalmic examination and fundus fluorescein angiography revealed bilateral nonischemic central retinal vein occlusions and optic disc edema in a 22-year-old man who was HIV-positive. The findings of fundus examination and fluorescein angiography were similar in both eyes. CONCLUSION: This case provides additional evidence that central retinal vein occlusion is probably part of the spectrum of HIV retinopathy.

Adult↗