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Biomedical subjects

X Pan

Publications and source records attributed to X Pan.

At least 109 records · Page 6Linked to original sources
PubMed1998

Variability of velocity and duration of microembolic signals detected by bigated transcranial Doppler sonography in carotid endarterectomy.

OBJECTIVE: To differentiate between gaseous and particular microemboli in carotid surgery one clinical approach is the interpretation of the effective sample volume length (SVL). We investigated whether such a clinical interpretation is based on reproducible measurements. METHODS: Microembolic signals (MES) recorded during carotid endarterectomy by a bigated transcranial Doppler device were analyzed off-line. In the two sample volumes, the duration and the velocity of the MES were measured by two observers independently from each other twice within 2 weeks. The SVL of the MES were calculated by multiplying duration with velocity. RESULTS: In the anatomical proximal sample volume 215 MES were recorded of which 203 (94.5%) were also present in the distal. The SVL medians of the MES were 2.2-4.1 mm lower in the distal than in the proximal sample volume as a result of lower velocity and shorter duration of the MES in the distal sample volume. The median of the paired differences of the SVL was 0.2 mm (interquartile range: 0.0-1.2) in the proximal sample volume and 0.8 mm (0.2-1.8) in the distal sample volume for observer 1, and 0.6 mm (0.4-2.2) and 0.9 mm (0.5-1.6) for observer 2. The median of the paired differences of the SVL between the observers was 1.4 mm (1.2-2.9) in the proximal sample volume and 1.6 mm (1.3-3.0) in the distal. CONCLUSION: The intra- and interobserver agreement on calculating SVL is good. However, the depth of insonation influences some features of embolic signals.

Aged↗
PubMed1998

Genotypic characterization of drug-resistant Mycobacterium tuberculosis isolates from Peru.

SETTING: Twenty-nine epidemiological unrelated and mostly multidrug-resistant Mycobacterium tuberculosis (MDR-TB) strains from Peruvian patients. OBJECTIVE: To investigate the molecular genetics of MDR-TB strains recovered in a Latin American country. DESIGN: Antimicrobial agent susceptibility testing, major genetic group designation, IS6110 fingerprinting, spoligotyping, and automated deoxyribonucleic acid sequencing of regions of the katG, rpoB, embB, gyrA, and pncA genes with mutations commonly associated with drug resistance. RESULTS: Nineteen isolates were found to be multidrug-resistant by susceptibility testing. IS6110 typing showed that virtually all isolates were unique and therefore had independently acquired drug resistance. Seventy-nine percent of isoniazid-resistant strains had a Ser315Thr amino acid change in KatG. Ninety-five percent of rifampin-resistant isolates had amino acid replacements in the rifampin-resistance determining region of RpoB. Six of 11 ethambutol-resistant strains had EmbB alterations. Eleven pyrazinamide-resistant strains had distinct mutations in pncA. CONCLUSION: Virtually all organisms evolved drug resistance independently. The types of drug resistance-associated mutations identified were very similar to changes occurring in isolates from other areas of the world. Nucleotide sequence-based strategies for rapid detection of drug resistance-conferring mutants will be applicable to organisms recovered in Peru, and potentially other areas of Latin America.

Amidohydrolases↗
PubMed1998

Genetic diversity among Mycobacterium avium complex strains recovered from children with and without human immunodeficiency virus infection.

The genetic diversity and molecular epidemiology of Mycobacterium avium complex (MAC) infections in children with and without human immunodeficiency virus (HIV) infection were evaluated. Isolates recovered from 136 children were subtyped by sequence analysis of a 360-bp region of the gene (hsp65) encoding a 65-kDa heat-shock protein. Twenty-one distinct hsp65 alleles were identified. On the basis of hsp65 genotype, 6 isolates were not MAC organisms. Of the remaining 130 samples, 61% were M. avium, 37% were Mycobacterium intracellulare, and 2% were species nonspecific MAC. Eighty-eight percent of the isolates obtained from HIV-infected children were M. avium. In contrast, only 38% of the isolates obtained from children without HIV infection were M. avium (chi2 test, P < .001). M. avium isolates were further subtyped by Southern blot analysis with insertion element IS1245. Taken together, no evidence for a single clonal M. avium strain causing infection was detected.

AIDS-Related Opportunistic Infections↗
PubMed1998

Quasi-bandlimited properties of radon transforms and their implications for increasing angular sampling densities.

The n-dimensional (n-D) radon transform, which forms the mathematical basis for a broad variety of tomographic imaging applications, can be viewed as an n-D function in n-D sinogram space. Accurate reconstruction of continuous or discrete tomographic images requires full knowledge of the radon transform in the corresponding n-D sinogram space. In practice, however, one can have only a finite set of discrete samples of the radon transform in the sinogram space. One often derives the desired full knowledge of the radon transform from its discrete samples by invoking various interpolation algorithms. According to the Wittaker-Shannon sampling theorem, a necessary condition for a full and unique recovery of the radon transform from its discrete samples is that the radon transform itself be bandlimited. Therefore, it is necessary to analyze the bandlimited properties of the radon transform. In this work, we analyze explicitly the bandlimited properties of the radon transform and show that the radon transform is mathematically quasi-bandlimited [or essentially bandlimited] in two quantitative senses and can essentially be treated as bandlimited in practice. The quasi-bandlimited properties can be used for increasing the angular sampling density of the radon transform.

Image Processing, Computer-Assisted↗
PubMed1998

A general approach for multidimensional smoothing.

Smoothing is closely related to regression in statistics. It is frequently applied to data that contain statistical noise in attempts to discern and highlight patterns concealed in the data. In medical imaging applications, the acquired data are often N dimensional (where N > or = 2) and thus multidimensional smoothing approaches would best exploit the multidimensional correlations inherent in the data. Unfortunately, extensions of advanced (especially adaptive) one-dimensional smoothing approaches to multidimensional data are, in general, theoretically challenging and computationally prohibitive. In this work, we propose a novel approach that accomplishes effectively higher-dimensional smoothing by exploiting the Fourier transform properties of the data to reduce data dimensions, allowing for lower-dimensional smoothing. We present the theoretical basis for this approach and verify this approach by applying it to computer-simulated data as well as real data acquired in medical imaging studies.

Bone and Bones↗
PubMed1998

Image restoration and reconstruction with a Bayesian approach.

We have extended Johnson's Bayesian method for image restoration and reconstruction by introducing diagonal line sites, using symmetric neighborhood configurations, and employing an additional hyperparameter for estimation of line sites. A general formulation for arbitrary neighborhood configurations was derived. The major part of this paper deals with the conduct of computer simulations intended to examine the effect of the hyperparameters, the diagonal line sites, and the size of the neighborhood configuration on the performance of the proposed Bayesian method. We show that, for optimal performance, distinct hyperparameters should be used for the intensity sites and line sites. The results also suggest that a large neighborhood configuration should be used. By comparing the near-optimal restored images, we demonstrated that the use of diagonal line sites, along with the symmetric configurations thus made possible, can effectively remove the blocky edge artifacts and produce images of better quality. When the method was applied to positron emission tomography (PET) image reconstruction, our results showed that the quality of the reconstructed images was improved for both computer-simulated and real patient PET data.

Algorithms↗
PubMed1998

SR 141716A acts as an inverse agonist to increase neuronal voltage-dependent Ca2+ currents by reversal of tonic CB1 cannabinoid receptor activity.

The CB1 cannabinoid receptor antagonist SR 141716A abolished the inhibition of Ca2+ currents by the agonist WIN 55,212-2. However, SR 141716A alone increased Ca2+ currents, with an EC50 of 32 nM, in neurons that had been microinjected with CB1 cRNA. For an antagonist to elicit an effect, some receptors must be tonically active. Evidence for tonically active CB1 receptors was seen as enhanced tonic inhibition of Ca2+ currents. Preincubation with anandamide failed to enhance the effect of SR 141716A, indicating that anandamide did not cause receptor activity. Under Ca2+-free conditions designed to block the Ca2+-dependent formation of anandamide and sn-2-arachidonylglycerol, SR 141716A again increased the Ca2+ current. The Ca2+ current was tonically inhibited in neurons expressing the mutant K192A receptor, which has no affinity for anandamide, demonstrating that this receptor is also tonically active. SR 141716A had no effect on the Ca2+ current in these neurons, but SR 141716A could still antagonize the effect of WIN 55, 212-2. Thus, the K192 site is critical for the inverse agonist activity of SR 141716A. SR 141716A appeared to become a neutral antagonist at the K192A mutant receptor. Native cannabinoid receptors were studied in male rat major pelvic ganglion neurons, where it was found that WIN 55,212-2 inhibited and SR 141716A increased Ca2+ currents. Taken together, our results demonstrate that a population of native and cloned CB1 cannabinoid receptors can exist in a tonically active state that can be reversed by SR 141716A, which acts as an inverse agonist.

Animals↗
PubMed1998

NO decreases phosphorylation of focal adhesion proteins via reduction of Ca in rat aortic smooth muscle cells.

Our laboratory has previously reported that the antimitogenic effect of nitric oxide (NO) in primary cultures of rat aortic smooth muscle cells may be attributed to activation of protein tyrosine phosphatase and dephosphorylation of protein phosphotyrosine [G.S. Dhaunsi, C. Matthews, K. Kaur, and A. Hassid, Am, J. Physiol. 272 (Heart Circ. Physiol. 41): H1342-H1349, 1997]. The goal of the current study was to investigate the role of cytoplasmic Ca in this process and to identify protein substrates that are dephosphorylated by treatment with NO. Treatment of primary rat aortic smooth muscle cell cultures with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) decreased cytoplasmic Ca levels and elicited phosphotyrosine dephosphorylation. Both effects were mimicked by the extracellular and intracellular Ca chelators ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) and 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), respectively, and by the Ca channel blocker nifedipine. Conversely, elevation of cytoplasmic Ca via the use of the Ca ionophore A-23187 or high extracellular K+ prevented or attenuated SNAP-induced dephosphorylation. Both BAPTA and nifedipine also decreased DNA synthesis, providing further evidence to link dephosphorylation to antimitogenesis. Two of the proteins dephosphorylated by treatment of cells with NO or EGTA were identified as the focal adhesion proteins, cortactin and paxillin. These results indicate that NO-induced dephosphorylation of protein phosphotyrosine is mediated by reduction of cytoplasmic Ca and suggest that dephosphorylation of focal adhesion proteins may be of relevance to the antimitogenic effect of NO.

Animals↗
PubMed1998

YEB3/VAC8 encodes a myristylated armadillo protein of the Saccharomyces cerevisiae vacuolar membrane that functions in vacuole fusion and inheritance.

Armadillo (Arm) repeat proteins such as beta-catenin and alpha-karyopherin (importin) are thought to mediate the docking of cargo at membrane-associated cytoskeletal elements. YEB3 encodes an uncharacterized Saccharomyces cerevisiae protein that contains eleven tandem Arm repeats. While YEB3 is nonessential for growth, yeb3delta cells accumulated numerous small vacuoles and are defective in vacuolar inheritance. A functional Yeb3p-green fluorescent protein (GFP) chimera localized to vacuolar membranes. Confocal microscopy revealed that Yeb3p-GFP is localized over the surface of the vacuole, but is concentrated approximately 5- to 7-fold in bands located between clustered vacuoles. N-terminal myristylation of Yeb3p is required for vacuolar localization. The first 69 amino acids of Yeb3p were sufficient to target a GFP reporter protein to the vacuolar membrane; however, this fusion protein also localized to the plasma membrane, indicating that additional sequence is required for exclusive steady state vacuolar localization. By analogy to the function of beta-catenin in cell-cell adhesion, alpha-karyopherin in nuclear transport, and smgGDS in the control of ras-like GTPases, Yeb3p may provide a link between vacuoles and the actin cytoskeleton during vacuolar inheritance and fusion and perhaps mediate the assembly of a GTPase regulated docking complex.

Amino Acid Sequence↗
PubMed1998

Unified reconstruction theory for diffraction tomography, with consideration of noise control.

In diffraction tomography, the spatial distribution of the scattering object is reconstructed from the measured scattered data. For a scattering object that is illuminated with plane-wave radiation, under the condition of weak scattering one can invoke the Born (or the Rytov) approximation to linearize the equation for the scattered field (or the scattered phase) and derive a relationship between the scattered field (or the scattered phase) and the distribution of the scattering object. Reconstruction methods such as the Fourier domain interpolation methods and the filtered backpropagation method have been developed previously. However, the underlying relationship among and the noise properties of these methods are not evident. We introduce the concepts of ideal and modified sinograms. Analysis of the relationships between, and the noise properties of the two sinograms reveals infinite classes of methods for image reconstruction in diffraction tomography that include the previously proposed methods as special members. The methods in these classes are mathematically identical, but they respond to noise and numerical errors differently.

Artifacts↗
PubMed1998

A study on visual evoked potential to show the relationship between the eyes and the twelve regular channels.

The visual electrophysiologic method was used to investigate the relationship between the eyes and the 12 regular channels. The values of the latent period and the amplitude of P100 wave were calculated and compared statistically. The results show that: 1) The eyes and the 12 regular channels are closely related, no matter whether the channels are classically associated with the eyes or not, while the control (non-channel)/ point has no such relationship; 2) the degrees of relationship between the eyes and the 12 regular channels vary significantly; and 3) acupuncture at the 12 regular channels induces different effects on the visual evoked potential that the Urinary Bladder Channel presents a facilitation effect whereas all the other channels chiefly show an inhibitory effect.

Adolescent↗
PubMed1998

[Isolation of antibacterial polypeptides of human cervical mucus].

The acid-soluble extract of human cervical mucus was obtained by solving mucus with 5% acetic acid in the presence of protease inhibitor. The antibacterial activity of the acid-soluble extract was analyzed by gel overlay technique. The result showed that two protein bands which were designated human cervical protein-1 (Hcp-1), human cervical protein-2(Hcp-2) were potently antibacterial against E. coli 25922 and S. aureus 25923. Tricine-SDS-PAGE analysis indicated that Hcp-1, Hcp-2 actually contained three and four protein bands respectively. The molecular weights of Hcp-1 were 6.7 kd, 10 kd, 15.4 kd; these of Hcp-2 were 4.4 kd, 6.7 kd, 9 kd, 15.4 kd. Our studies suggested that human cervical mucosa might secrete some currently-unknown antibacterial polypeptides which play an important role in the cervical defense against infection.

Anti-Bacterial Agents↗
PubMed1998

[The effect of Epstein-Barr virus gene BHRF1 expression on the apoptotic resistance of nasopharyngeal carcinoma cells].

OBJECTIVE: To investigate the effect of EB virus gene BHRF1 expression on the apoptotic resistance of nasopharyngeal carcinoma cell. METHODS: Expression vector for BHRF1 was constructed and transfected into nsaopharyngeal carcinoma cell line, CNE2. The alteration of biologic behaviour of the transfected cells was tested after 60Co radiation. RESULTS: BHRF1 expression could inhibit the expression of proliferative cell nuclear antigen, redistribute cell cycle, decrease cell sensitivity to radiation, and enhance their survival ability. CONCLUSION: It is suggested that BHRF1 expression can increase the apoptotic resistance induced by radiation.

Animals↗
PubMed1998

A clinicopathological study of Alport syndrome and detection of type IV collagen chains in Alport patients.

OBJECTIVE: To summarize the clinical and pathological findings of Alport syndrome (AS), detect the distribution of type IV collagen within basement membrane of patients with AS and evaluate the diagnostic value of indirect immunofluorescence (iIF) study of type IV collagen in AS. METHODS: Fourteen patients belonging to 12 families were collected from January 1990 to June 1996. The clinical examinations include biochemical examination, audiometry and ocular examination. IIF technique was used to detect the location of chains of type IV collagen in 6 renal and 5 skin specimens from 8 Alport patients. RESULTS: Among fourteen patients, 11 were male and 3 female (mean age 29.4 years). Microscopic hematuria was found in 13 patients, and recurrent gross hematuria in 7. All had proteinuria. Three patients presented nephrotic syndrome. Slowly progressive renal failure occurred in 10 of 11 males (11-39 years) and 1 female (40 years). Sensorineural deafness was observed in 9 patients particularly high frequency sound. Anterior lenticonus were presented in 2. Five families transmitted as X-linked dominant (XD) trait and 3 autosomal dominant, 3 autosomal recessive inheritance. In 7 renal biopsies, the findings by light microscopy mostly revealed focal and segmental sclerosis glomerulonephritis (4/7). The results of IF were negative in 4. Ultrastructural studies showed variable thickening, thinning of glomerular basement membrane (GBM) in 7 specimens with lamellation and basket wearing of GBM in 1. Using the iIF technique, the alpha 3, 4, 5 (IV) chains were observed to be absent within both GBM and EBM of 4 male XD-AS patients. Six patients were treated with hemodialysis, 2/6 with transplantation. CONCLUSION: Alport syndrome (AS) is a heterogeneous hereditary disease characterized by progressive hematuric nephritis with or without sensorineural hearing loss and ocular defects. Ultrastructural alterations of GBM are helpful to the diagnosis of AS. IIF study suggests that type IV collagen in basement membrane of AS was abnormal and iIF study of type IV collagen chains distribution is useful for confirming the diagnosis of AS.

Adolescent↗
PubMed1998

[The study of radioresistance of BHRF1 gene].

In order to learn relationship between the expression of BHRF1 gene and radiative sensitivity of cells of nasopharyngeal carcinoma. High BHRF1 expressive vector was set up and transfected in the cell line of nasopharyngeal carcinoma, CNE2. Then the cells were radiated to test its ability of clone formation in nude mice. The results showed that the tumors formed by BHRF1-CNE2 cells were lighter before radiation and weighter after radiation (P < 0.01), and apoptotic index of BHRF1-CHE2 was less than control groups (P < 0.01). So, it suggests that the BHRF1 expression could prevent apoptosis by enhancing the resistibility of the tumor cells to radiation.

Animals↗
PubMed1998

[Study on the polyoxygenated cyclohexenes from Uvaria boniana].

Seven new polyoxygenated cyclohexenes, named uvaribonol A-G (1-7) have been isolated from the ethanol extract of the stems of Uvaria boniana Finet. (Annonaceae), and their structures, including the absolute configuration, were determined by spectral and chemical methods. In vitro cytotoxicity test against several human tumor cell lines indicated that all of the new natural compounds are inactive, but some of the derivatives showed obvious activities. Compound 2a is the most active, exhibiting significant cytotoxicities against KB and Bel7402 cells with IC50 < 1 microgram.ml-1, and against HCT-8 cell with IC50 < 0.1 microgram.ml-1.

Annonaceae↗
PubMed1998

[Study on the relationship between provenance, leaf type and quality in Magnolia officinalis].

An analysis of effective ingredients in 20 to 29 year old Magnolia officinalis of three different leaf types coming from various sources shows that the content of phenols differ extremely significantly in various leaf types which are a key to determination of quality of Magnolia officinalis also varies significantly among different sources which only have a significant effect on the content of magnolol. Varieties and types cultivated in different places are responsible for the variation in content of magnolol. The conclusions obtained from this study coincide with the traditional insight into quality of Magnolia officinalis.

Biphenyl Compounds↗