Biomedical subjects

X Pan

Publications and source records attributed to X Pan.

At least 19 recordsLinked to original sources

PubMed2006

Transforming growth factor-beta1 induces epithelial-to-mesenchymal transition and apoptosis via a cell cycle-dependent mechanism.

Apoptosis and epithelial-to-mesenchymal transition (EMT) have been implicated in a variety of biological processes, such as embryonic development, fibrosis and tumor progression. Transforming growth factor-beta (TGF-beta) can induce simultaneously both EMT and apoptotic response of epithelial cells. However, the underlying mechanism of these biological events remains not well understood. In the present study, we show that TGF-beta1 induces apoptosis and EMT in AML-12 cells in a cell cycle-related manner, in which apoptosis and EMT took place at G2/M and G1/S phases, respectively. TGF-beta1-induced apoptosis was correlated with different extent of caspase activation at different cell cycle phases. Interestingly, increased phosphorylation of protein kinase D (PKD) can be observed in G1/S phase in response to TGF-beta1, and inhibition of PKD by inhibitor or by small interference RNA blocked EMT but not apoptosis. Our data suggest a previously unrecognized role of cell cycle state in the regulation of TGF-beta-induced EMT and apoptosis, and demonstrate that PKD is involved in the TGF-beta1-induced EMT.

Apoptosis↗

PubMed2006

Breast composition measurements using retrospective standard mammogram form (SMF).

The standard mammogram form (SMF) representation of an x-ray mammogram is a standardized, quantitative representation of the breast from which the volume of non-fat tissue and breast density can be easily estimated, both of which are of significant interest in determining breast cancer risk. Previous theoretical analysis of SMF had suggested that a complete and substantial set of calibration data (such as mAs and kVp) would be needed to generate realistic breast composition measures and yet there are many interesting trials that have retrospectively collected images with no calibration data. The main contribution of this paper is to revisit our previous theoretical analysis of SMF with respect to errors in the calibration data and to show how and why that theoretical analysis did not match the results from the practical implementations of SMF. In particular, we show how by estimating breast thickness for every image we are, effectively, compensating for any errors in the calibration data. To illustrate our findings, the current implementation of SMF (version 2.2beta) was run over 4028 digitized film-screen mammograms taken from six sites over the years 1988-2002 with and without using the known calibration data. Results show that the SMF implementation running without any calibration data at all generates results which display a strong relationship with when running with a complete set of calibration data, and, most importantly, to an expert's visual assessment of breast composition using established techniques. SMF shows considerable promise in being of major use in large epidemiological studies related to breast cancer which require the automated analysis of large numbers of films from many years previously where little or no calibration data is available.

Algorithms↗

PubMed2006

Hospital and community surveys reveal the severe public health problem and socio-economic impact of human echinococcosis in Ningxia Hui Autonomous Region, China.

A comprehensive study of human echinococcosis (caused by Echinococcus granulosus or E. multilocularis), including assessment of hospital records, community surveys and patient follow-up, was conducted in Ningxia Hui Autonomous Region (NHAR), China. In contrast to hospital records that showed 96% of echinococcosis cases were caused by cystic echinococcosis (CE), 56% of cases detected in active community surveys were caused by alveolar echinococcosis (AE). The AE and CE cases co-existed frequently in the same village, even occurring in the same patient. A serious public health problem caused by echinococcosis was evident in southern NHAR, typified by: a long diagnostic history for both AE and CE (7.5 years) compared with a shorter treatment history (4.7 years); a significant mortality rate (39%) caused by AE in one surveyed village, where patients had no previous access to treatment; family aggregation of CE and AE cases; a high proportion of both AE (62.5%) and CE (58%) in females; a high rate of recurrent surgery (30%) for CE demonstrated by surgical records; and frequent symptomatic recurrences (51%) because of discontinuous or sporadic access to chemotherapy for AE. The disease burden for both human AE and CE is thus very severe among these rural communities in NHAR, and this study provides the first attempt to determine the costs of morbidity and surgical intervention of human CE and AE cases both at the hospital and community level in this setting. This information may be useful for assessing the cost effectiveness of designing effective public health programs to control echinococcosis in this and other endemic areas in China and elsewhere.

Adolescent↗

PubMed2005

Mechanism and site of attack for direct damage to DNA by low-energy electrons.

We report results on the desorption of OH- induced by 0-19 eV electrons incident on self-assembled monolayer films made of single and double DNA strands of different orientations with respect to a gold substrate. Such measurements make it possible to deduce the mechanism and site of OH- formation within a biomolecule as complex as DNA. This type of damage is attributed to dissociative electron attachment to the phosphate group of DNA, when it contains the counterion H+.

DNA↗

PubMed2005

The spatiotemporal learning rule and its efficiency in separating spatiotemporal patterns.

The hippocampus plays an important role in the course of establishing long-term memory, i.e., to make short-term memory of spatially and temporally associated input information. In 1996 (Tsukada et al. 1996), the spatiotemporal learning rule was proposed based on differences observed in hippocampal long-term potentiation (LTP) induced by various spatiotemporal pattern stimuli. One essential point of this learning rule is that the change of synaptic weight depends on both spatial coincidence and the temporal summation of input pulses. We applied this rule to a single-layered neural network and compared its ability to separate spatiotemporal patterns with that of other rules, including the Hebbian learning rule and its extended rules. The simulated results showed that the spatiotemporal learning rule had the highest efficiency in discriminating spatiotemporal pattern sequences, while the Hebbian learning rule (including its extended rules) was sensitive to differences in spatial patterns.

Animals↗

PubMed2003

Dissociative electron attachment to DNA.

Electron-stimulated desorption of anions from thin films of linear and supercoiled DNA is investigated in the range 3-20 eV. Resonant structures are observed with maxima at 9.4+/-0.3, 9.2+/-0.3, and 9.2+/-0.3 eV, respectively, in the yield dependence of H-, O-, and OH- on the incident electron energy. Their formation is attributed to dissociative electron attachment.

Anions↗

PubMed2003

Development of a fluorescence detection system using optical parametric oscillator (OPO) laser excitation for in vivo diagnosis.

In this work, the development and applications of a fluorescence detection system using optical parametric oscillator (OPO) laser excitation for in vivo disease diagnosis including oral carcinoma are described. The optical diagnosis system was based on an OPO laser for multi-wavelength excitation and time-resolved detection. The pulsed Nd-YAG-pumped OPO laser system (6 ns, 20 Hz) is compact and has a rapid, broad, and uniform tuning range. Time-gated detection of intensified charge-coupled device (ICCD) making use of external triggering was used to effectively eliminate the laser scattering and contribute to the highly sensitive in vivo measurements. Artificial tissue-simulating phantoms consisting of polystyrene microspheres and tissue fluorophores were tested to optimize the gating parameters. 51-ns gate width and 39-ns gate delays were determined to be the optimal parameters for sensitive detection. In vivo measurements with the optical diagnosis system were applied to esophagus, stomach, and small intestine using an endoscope in canine animal studies. The rapid tuning capability of the optical diagnosis system contributed greatly to the optimization of wavelength for the observation of porphyrin in the small intestine. When the small intestine was thoroughly washed with water, the emission band which corresponds to porphyrin disappeared. Based on this observation, it was concluded that the detected signal was yielded by porphyrin-containing bile secretion. Also, multispectral analyses using multiple excitations from 415 to 480 nm at 5 nm intervals confirmed the porphyrin detection in the small intestine. The optical diagnosis system was also applied to the detection of human xenograft of oral carcinoma in mice using 5-aminolevulinic acid (5-ALA) which is a photodynamic therapy (PDT) drug. Significant differences in protoporphyrin IX fluorescence intensity between normal and tumor tissue could be obtained 2 hours after the injection of 5-ALA into mice due to the preferential accumulation of 5-ALA in tumors. Results reported herein demonstrate potential capabilities of the LIF-OPO system for in vivo disease diagnosis.

Animals↗

PubMed2001

Conformational and functional significance of residue proline 17 in chicken muscle adenylate kinase.

The effect of mutation proline 17 on the multiple conformations and catalytic function in chicken muscle adenylate kinase (AK) has been studied. The substitution of proline 17 with glycine or valine altered the distribution of multiple conformations. Compared with the wild-type enzyme, the P17G and P17V mutants contained decreased fraction of minor conformer from 18% to 9% and 11%, respectively. Due to the mutation, the enzyme showed lower secondary structural content, poorer affinity to substrates or substrate analogues, and reduced catalytic efficiency. The results revealed the significance of proline 17 in the conformation and function of AK.

Adenosine Diphosphate↗

PubMed2001

Microwave-assisted extraction of tanshinones from Salvia miltiorrhiza bunge with analysis by high-performance liquid chromatography.

A novel microwave-assisted extraction (MAE) method has been developed for the extraction and determination of tanshinones (tanshinone IIA, cryptotanshinone and tanshinone I) from the root of Salvia miltiorrhiza bunge with analysis by HPLC. Various experimental conditions were investigated to optimize the percentage extraction. Under appropriate MAE conditions, such as ethanol concentrations of 95% (v/v), MAE for 2 min, liquid/solid ratio of 10:1 (ml/g), the percentage extraction can reach high in a short time. The percentage extraction (tanshinone IIA: 0.29%; cryptotanshinone: 0.23%; tanshinone I: 0.11%) by MAE was the same or even higher than conventional extraction methods. MAE only needs 2 min, but extraction at room temperature, heat reflux extraction, ultrasonic extraction and Soxhlet extraction need 24 h, 45 min, 75 min and 90 min, respectively. MAE was also available in pilot plant form for larger scale extraction.

Abietanes↗

PubMed2001

Microwave-enhanced dehydration and solvent washing purification of penicillin G sulfoxide.

In the present study, a new microwave-enhanced dehydration and solvent washing purification of penicillin G sulfoxide technique has been developed. The results show that microwave irradiation can dehydrate penicillin G sulfoxide from a water content of 14-26 to below 0.5% in 40-60 min in N2 or air. After washing with ethyl acetate to remove impurities and residual water, the penicillin G sulfoxide can be used to synthesize cephalosporanic acid. The recovery of cephalosporanic acid was equal to and the purity of cephalosporanic acid was higher by 2% than that of the current dehydration technique. FTIR spectroscopy was used to study the process of microwave-enhanced dehydration and solvent washing purification of penicillin G sulfoxide.

Chemistry, Pharmaceutical↗

PubMed2001

Distribution of streptococcal inhibitor of complement variants in pharyngitis and invasive isolates in an epidemic of serotype M1 group A Streptococcus infection.

Streptococcal inhibitor of complement (Sic) is a highly polymorphic extracellular protein made predominantly by serotype M1 group A Streptococcus (GAS). New variants of the Sic protein frequently appear in M1 epidemics as a result of positive natural selection. To gain further understanding of the molecular basis of M1 epidemics, the sic gene was sequenced from 471 pharyngitis and 127 pyogenic and blood isolates recovered from 598 patients living in metropolitan Helsinki, Finland, during a 37-month population-based surveillance study. Most M1 GAS subclones recovered from pyogenic infections and blood were abundantly represented in the pool of subclones causing pharyngitis. Alleles shared among the pharyngitis, pyogenic, and blood samples were identified in throat isolates a mean of 9.8 months before their recovery from pyogenic infections and blood, which indicates that selection of most sic variants occurs on mucosal surfaces. In contrast, no variation was identified in the emm and covR/covS genes.

Alleles↗

PubMed2001

Identification of up-regulated Ras-like GTPase, Rap1b, by suppression subtractive hybridization.

BACKGROUND: Diabetic nephropathy accounts for over 30% of the end-stage renal disease (ESRD). A number of defined mechanisms and molecules that are involved in its pathogenesis are known, while others remain to be identified. METHODS: Suppression subtraction hybridization (SSH)-polymerase chain reaction (PCR) was employed to search for new genes that may be relevant to the pathogenesis of diabetic nephropathy during embryonic development, the time when the kidney is most susceptible to various forms of stress. A diabetic state was induced in pregnant mice at day-13 of gestation by administration of streptozotocin. The kidneys of newborn mice with blood glucose level> 200 mg/dL were harvested, mRNA isolated and subjected to SSH-PCR. Several differentially expressed cDNA fragments with up-regulated expression were isolated. One of the cDNA fragments had homology with human Ras-like guanine 5'-triphosphate (GTPase), Rap1b gene. By utilizing the lambdaZAP II mouse cDNA library and SMART RACE amplification, a full-length Rap1b cDNA was isolated. A recombinant protein was generated in pET15b bacterial expression system. An anti-Rap1b antibody was raised in rabbits by immunizing them with the fusion protein, and its specificity was confirmed by Western blot analysis. RESULTS: Rap1b cDNA had an open reading frame of 552 bp with a predicted putative protein size of approximately 21 kD. In vitro translation verified the authentication of the Rap1b cDNA clone. Northern blot analyses revealed a single approximately 2.3 kb Rap1b mRNA transcript. Its expression was up-regulated in several tissues, including the kidney of newborn diabetic mice. The degree of up-regulation of Rap1b mRNA expression was proportional to the blood glucose levels. Western blot analyses confirmed the hyperglycemia-induced up-regulation of the Rap1b expression. In situ hybridization and immunofluorescence studies revealed that Rap1b was expressed in the inner medullary collecting tubules. During hyperglycemia, its expression was accentuated and extended into the outer medullary and cortical collecting tubules. Similar up-regulation of Rap1b was observed when embryonic kidneys, harvested at day-13 of gestation, were exposed to high glucose ambience. CONCLUSION: The data suggest that Rap1b, a GTP-binding protein that plays a critical role in various signaling intracellular events, is another molecule that may be relevant to the pathobiology of diabetic nephropathy.

Amino Acid Sequence↗

PubMed2001

Aerogenous spread of primary lung adenocarcinoma induces ultrastructural remodeling of the alveolar capillary endothelium.

To determine whether pulmonary alveolar capillaries manifest ultrastructural remodeling at areas of neoplastic invasion of primary lung adenocarcinomas, we examined 17 well-differentiated adenocarcinomas of lung (2 bronchioloalveolar and 15 papillary adenocarcinomas) by electron microscopy. The expression of vascular endothelial growth factor (VEGF) and proliferating cell nuclear antigen (PCNA) was demonstrated by immunohistochemical stainings. VEGF messenger RNA (mRNA) isoforms were detected by reverse-transcription polymerase chain reaction (RT-PCR) in alveolar walls microdissected from normal and tumor-associated tissues. Cytoplasm of neoplastic cells expressed VEGF protein in all patients. Endothelial cell nuclei of alveolar capillaries showed positive reaction for PCNA. Alveolar capillary lumina were distended like venules, and some intercellular junctions remained open. The cytoplasm of the capillary endothelial cells was enlarged and developed numerous organelles such as Weibel-Palade bodies and vesiculovacuolar organelles, in contrast to marked attenuation in their normal counterpart. Capillary sprouting occurred from proper alveolar capillaries in 2 patients. Cytoplasmic segments became extremely attenuated and developed diaphragm-like fenestrae in 65% of the patients. A relatively higher expression of diffusable isoforms of VEGF mRNA was seen in the tumor-bearing alveolar walls than in normal walls. Expression of KDR (one of the VEGF receptors) mRNA in tumor exceeded that in normal tissues. These results suggest that diffusable isoforms of VEGF mRNA released from the neoplastic cells are deeply involved in the induction of growth activity of alveolar capillary endothelial cells as much as in the characterization of tumor-associated microvessels in primary lung adenocarcinomas.

Adenocarcinoma, Bronchiolo-Alveolar↗

PubMed2001

The TOR signal transduction cascade controls cellular differentiation in response to nutrients.

Rapamycin binds and inhibits the Tor protein kinases, which function in a nutrient-sensing signal transduction pathway that has been conserved from the yeast Saccharomyces cerevisiae to humans. In yeast cells, the Tor pathway has been implicated in regulating cellular responses to nutrients, including proliferation, translation, transcription, autophagy, and ribosome biogenesis. We report here that rapamycin inhibits pseudohyphal filamentous differentiation of S. cerevisiae in response to nitrogen limitation. Overexpression of Tap42, a protein phosphatase regulatory subunit, restored pseudohyphal growth in cells exposed to rapamycin. The tap42-11 mutation compromised pseudohyphal differentiation and rendered it resistant to rapamycin. Cells lacking the Tap42-regulated protein phosphatase Sit4 exhibited a pseudohyphal growth defect and were markedly hypersensitive to rapamycin. Mutations in other Tap42-regulated phosphatases had no effect on pseudohyphal differentiation. Our findings support a model in which pseudohyphal differentiation is controlled by a nutrient-sensing pathway involving the Tor protein kinases and the Tap42-Sit4 protein phosphatase. Activation of the MAP kinase or cAMP pathways, or mutation of the Sok2 repressor, restored filamentation in rapamycin treated cells, supporting models in which the Tor pathway acts in parallel with these known pathways. Filamentous differentiation of diverse fungi was also blocked by rapamycin, demonstrating that the Tor signaling cascade plays a conserved role in regulating filamentous differentiation in response to nutrients.

Actin Cytoskeleton↗

PubMed2001

Comments on the filtered backprojection algorithm, range conditions, and the pseudoinverse solution.

The filtered backprojection (FBP) algorithm is widely used in computed tomography for inverting the two-dimensional Radon transform. In this paper, we analyze the processing of an inconsistent data function by the FBP algorithm (in its continuous form). Specifically, we demonstrate that an image reconstructed using the FBP algorithm can be represented as the sum of a pseudoinverse solution and a residual image generated from an inconsistent component of the measured data. This reveals that, when the original data function is in the range of the Radon transform, the image reconstructed using the FBP algorithm corresponds to the pseudoinverse solution. When the data function is inconsistent, we demonstrate that the FBP algorithm makes use of a nonorthogonal projection of the data function to the range of the Radon transform.

Algorithms↗

PubMed2001

Fourier-based approach to interpolation in single-slice helical computed tomography.

It has recently been shown that longitudinal aliasing can be a significant and detrimental presence in reconstructed single-slice helical computed tomography (CT) volumes. This aliasing arises because the directly measured data in helical CT are generally undersampled by a factor of at least 2 in the longitudinal direction and because the exploitation of the redundancy of fanbeam data acquired over 360 degrees to generate additional longitudinal samples does not automatically eliminate the aliasing. In this paper we demonstrate that for pitches near 1 or lower, the redundant fanbeam data, when used properly, can provide sufficient information to satisfy a generalized sampling theorem and thus to eliminate aliasing. We develop and evaluate a Fourier-based algorithm, called 180FT, that accomplishes this. As background we present a second Fourier-based approach, called 360FT, that makes use only of the directly measured data. Both Fourier-based approaches exploit the fast Fourier transform and the Fourier shift theorem to generate from the helical projection data a set of fanbeam sinograms corresponding to equispaced transverse slices. Slice-by-slice reconstruction is then performed by use of two-dimensional fanbeam algorithms. The proposed approaches are compared to their counterparts based on the use of linear interpolation-the 360LI and 180LI approaches. The aliasing suppression property of the 180FT approach is a clear advantage of the approach and represents a step toward the desirable goal of achieving uniform longitudinal resolution properties in reconstructed helical CT volumes.

Algorithms↗

PubMed2001

Transmission dynamics and molecular characterization of Mycobacterium tuberculosis isolates with low copy numbers of IS6110.

Population-based analysis of Mycobacterium tuberculosis transmission in Houston, Tex., over 5 years identified 377 patients infected with an isolate containing one to four copies of IS6110. The isolates were analyzed by spoligotyping and assigned to one of three major genetic groups based on nucleotide polymorphisms in codons katG 463 and gyrA 95. Prospectively obtained patient interviews were reviewed to assess epidemiologic links between apparently clustered patients. A total of 13 groups of isolates with the same IS6110 profile were identified, representing 326 of the 377 patients (86.5%; range 2 to 113 patients). In contrast, 28 groups of isolates containing 334 patients (88.6%) had the same spoligotype (range, 2 to 143 patients). Combination of IS6110 profile and spoligotype data identified 31 clusters with 300 patients (79.6%; range, 2 to 82 patients). All 377 isolates belonged to major genetic group 1 (77 patients) or genetic group 2 (300 patients); no major genetic group 3 isolates were identified. Among the 228 patients interviewed, 33 patients (14.5%) were directly linked to another patient in the same cluster. Possible epidemiologic links were also found among 11 patients. Moreover, many clusters consisted of individuals with the same ethnicity. In conclusion, we confirmed that IS6110 profiling and spoligotyping together provide enhanced molecular discrimination of M. tuberculosis isolates with low copy numbers of IS6110. Identification of epidemiologic links among some of the patients verified that the combination of these two methods reliably indexes tuberculosis transmission.

Bacterial Typing Techniques↗

PubMed2001

Insulin deprivation leads to deficiency of Sp1 transcription factor in H-411E hepatoma cells and in streptozotocin-induced diabetic ketoacidosis in the rat.

Members of the family of Sp transcription factors include Sp1, Sp3, and Sp4 and are important regulators of eukaryotic gene expression. We previously reported that Sp1 mediated stimulation of rat calmodulin I gene expression in response to insulin. To test whether other members of the Sp family are direct targets of insulin action, we compared the levels of Sp1 and Sp3 proteins from nuclear extracts obtained from both insulin-treated and untreated rat hepatoma (H-411E) cells. We demonstrated by Western blot analysis that levels of Sp1 and Sp3 proteins were increased more than 2-fold in the insulin-treated group. Additionally, the up-regulation of both Sp1 and Sp3 transcription factors by insulin was antagonized by tumor necrosis factor-alpha, a known inhibitor of insulin action. Immunohistochemical analysis demonstrated that H-411E cells treated with insulin (10,000 microU/ml) had a marked increase in demonstrable Sp1 in the nucleus compared with cells incubated in insulin-free medium. We extended these in vitro observations to in vivo studies in the streptozotocin-diabetic rat model. We demonstrated in rat liver tissue by both Western blot and immunohistochemical staining with anti-Sp1 antibody that 1) livers of fully diabetic streptozotocin rats have low levels of Sp1 transcription factor; and 2) insulin treatment of the diabetic rat rapidly reversed this process by markedly stimulating accumulation of Sp1 in rat liver. Studies of the signal transduction mechanisms involved in insulin's effect on Sp1 demonstrate a facilitating role for phosphoinositol 3-kinase and an inhibitory role for cyclic nucleotides. In summary, insulin stimulates Sp1 protein, a transcription factor that is shown to regulate calmodulin gene expression and most likely other, as yet untested, genes.

Animals↗