Biomedical subjects

C H Yan

Publications and source records attributed to C H Yan.

At least 19 recordsLinked to original sources

PubMed2006

Heterogeneous meshing and biomechanical modeling of human spine.

We aim to develop a patient-specific biomechanical model of human spine for the purpose of surgical training and planning. In this paper, we describe the development of a finite-element model of the spine from the VHD Male Data. The finite-element spine model comprises volumetric elements suitable for deformation and other finite-element analysis using ABAQUS. The mesh generation solution accepts segmented radiological slices as input, and outputs three-dimensional (3D) volumetric finite element meshes that are ABAQUS compliant. The proposed mesh generation method first uses a grid plane to divide the contours of the anatomical boundaries and its inclusions into discrete meshes. A grid frame is then built to connect the grid planes between any two adjacent planes using a novel scheme. The meshes produced consist of brick elements in the interior of the contours and with tetrahedral and wedge elements at the boundaries. The nodal points are classified according to their materials and hence, elements can be assigned different properties. The resultant spine model comprises a detailed model of the 7 cervical vertebrae, 12 thoracic vertebrae, 5 lumbar vertebrae, and S1. Each of the vertebrae and intervertebral disc has between 1200 and 6000 elements, and approximately 1200 elements, respectively. The accuracy of the resultant VHD finite element spine model was good based on visual comparison of volume-rendered images of the original CT data, and has been used in a computational analysis involving needle insertion and static deformation. We also compared the mesh generated using our method against two automatically generated models; one consists of purely tetrahedral elements and the other hexahedral elements.

Adult↗

PubMed2006

The effects of all-trans-retinoic acid on cell cycle and alkaline phosphatase activity in pancreatic cancer cells.

Pancreatic cancer is one of the tumors with the highest mortality, poorly responding to available chemotherapeutic agents. The objective of this study was to study the anticancer effects of all-trans retinoid acid, a functional form of vitamin A, on pancreatic cancer cells. Human pancreatic cancer MiaPaCa-2 cells were treated with 1, 5, 10, 20, 30, 40 and 50 microM ATRA for 1, 2, 3, 4, 5 or 6 d, respectively. Cell growth was determined by MTT viability assay. The cell cycle distribution and the alkaline phosphatase (ALP) activity were analyzed by flow cytometry and chemical analyzer, respectively. The results show that ATRA significantly inhibited the growth of MiaPaCa-2 cells at 40 and 50 microM. ATRA arrested pancreatic cancer cells at G0/G1 phase. The sub-G1 peak and DNA fragmentation were observed. There were time and dose dependent increases in alkaline phosphatase activity (ALP), an indicator of cell differentiation, upon treatment with ATRA when compared to controls. In conclusion, ATRA has an inhibitory effect on the cell growth of MiaPaCa-2, and its tumor suppressive effect is by means of cell cycle arrest and apoptosis induction.

Alkaline Phosphatase↗

PubMed2005

Computational biomechanical modelling of the lumbar spine using marching-cubes surface smoothened finite element voxel meshing.

There is a need for the development of finite element (FE) models based on medical datasets, such as magnetic resonance imaging and computerized tomography in computation biomechanics. Direct conversion of graphic voxels to FE elements is a commonly used method for the generation of FE models. However, conventional voxel-based methods tend to produce models with jagged surfaces. This is a consequence of the inherent characteristics of voxel elements; such a model is unable to capture the geometries of anatomical structures satisfactorily. We have developed a robust technique for the automatic generation of voxel-based patient-specific FE models. Our approach features a novel tetrahedronization scheme that incorporates marching-cubes surface smoothing together with a smooth-distortion factor (SDF). The models conform to the actual geometries of anatomical structures of a lumbar spine segment (L3). The resultant finite element analysis (FEA) at the surfaces is more accurate compared to the use of conventional voxel-based generated FE models. In general, models produced by our method were superior compared to that obtained using the commercial software ScanFE.

Biomechanical Phenomena↗

PubMed2002

The X-ray attenuation characteristics and density of human calcaneal marrow do not change significantly during adulthood.

Changes in the material characteristics of bone marrow with aging can be a significant source of error in measurements of bone density when using X-ray and ultrasound imaging modalities. In the context of computed tomography, dual-energy computed techniques have been used to correct for changes in marrow composition. However, dual-energy quantitative computed tomography (DE-QCT) protocols, while increasing the accuracy of the measurement, reduce the precision and increase the radiation dose to the patient in comparison to single-energy quantitative computed tomography (SE-QCT) protocols. If the attenuation properties of the marrow for a particular bone can be shown to be relatively constant with age, it should be possible to use single-energy techniques without experiencing errors caused by unknown marrow composition. Marrow was extracted by centrifugation from 10 mm thick frontal sections of 34 adult cadaver calcanei (28 males, 6 females, ages 17-65 years). The density and energy-dependent linear X-ray attenuation coefficient of each marrow sample were determined. For purposes of comparing our results, we then computed an effective CT number at two GE CT/i scan voltages (80 and 120 kVp) for each specimen. The coefficients of variation for the density, CT number at 80 kVp and CT number at 120 kVp were each less than 1%, and the parameters did not change significantly with age (p > 0.2, r2 < 0.02, power > 0.8 where the minimum acceptable r2 = 0.216). We could demonstrate no significant gender-associated differences in these relationships. These data suggest that calcaneal bone marrow X-ray attenuation properties and marrow density are essentially constant from the third through sixth decades of life.

Adolescent↗

PubMed2001

Zinc diphosphonates templated by organic amines: syntheses and characterizations of [NH3(CH2)2NH3]Zn(hedpH2)22H2O and [NH3(CH2)nNH3(CH2)nNH3]Zn2(hedpH)22H2O (n=4,5,6) (hedp=1-hydroxyethylidenediphophonate).

Four new zinc diphosphonate compounds with formulas [NH(3)(CH(2))(2)NH(3)]Zn(hedpH(2))(2).2H(2)O, 1, [NH(3)(CH(2))(n)()NH(3)]Zn(2)(hedpH)(2).2H(2)O, (n = 4, 2; n = 5, 3; n = 6, 4) (hedp = 1-hydroxyethylidenediphosphonate) have been synthesized under hydrothermal conditions at 110 degrees C and in the presence of alkylenediamines NH(2)(CH(2))(n)()NH(2) (n = 2, 4, 5, 6). Crystallographic data for 1: monoclinic, space group C2/c, a = 24.7422(15), b = 5.2889(2), c = 16.0338(2) A, beta = 117.903(1) degrees, V = 1856.17(18) A(3), Z = 4; 2: monoclinic, space group P2(1)/n, a = 5.4970(3), b = 12.1041(6), c = 16.2814(12) A, beta = 98.619(5) degrees, V = 1071.07(11) A(3), Z = 2; 3: monoclinic, space group P2(1)/n, a = 5.5251(2), b = 12.5968(3), c = 16.1705(5) A, beta = 99.182(1) degrees, V = 1111.02(6) A(3), Z = 2; 4: triclinic, space group P-1, a = 5.4785(2), b = 14.1940(5), c = 16.0682(6) A, alpha = 81.982(2) degrees, beta = 89.435(2) degrees, gamma = 79.679(2) degrees, V = 1217.11(8) A(3), Z = 2. In compound 1, two of the phosphonate oxygens are protonated. The metal ions are bridged by the hedpH(2)(2-) groups through three of the remaining four phosphonate oxygens, forming a one-dimensional infinite chain. The protonated ethylenediamines locate between the chains in the lattice. In compounds 2-4, only one phosphonate oxygen is protonated. Compounds 2 and 3 have a similar three-dimensional open-network structure composed of [Zn(2)(hedpH)(2)](n) double chains with strong hydrogen bonding interactions between them, thus generating channels along the [100] direction. The protonated diamines and water molecules reside in the channels. Compound 4 contains two types of [Zn(2)(hedpH)(2)](n) double chains which are held together by strong hydrogen bonds, forming a two-dimensional network. The interlayer spaces are occupied by the [NH(3)(CH(2))(6)NH(3)](2+) cations and water molecules. The significant difference between structures 2-4 is also featured by the coordination geometries of the zinc atoms. The geometries of those in 2 can be described as distorted octahedral, and those in 3 as distorted square pyramidal. In 4, two independent zinc atoms are found, each with a distorted octahedral and a tetrahedral geometry, respectively.

Journal Article↗

PubMed2001

Delta-aminolevulinate dehydratase polymorphism and blood lead levels in Chinese children.

This study investigated the relationship between the delta-aminolevulinate dehydratase (ALAD) isozymes and the blood lead levels of Chinese children. The purpose of this study was to determine the precise ALAD genotyping in Chinese children and identify the contribution of the ALAD genotype to the body lead burden. Blood samples were obtained from 109 boys and 120 girls. These children were 6-10 years old and from a single primary school. Both the school and their homes were within a community in which a large smelter was located. An environmental questionnaire was obtained for each subject, and blood lead levels and ALAD isozyme phenotype were analyzed in a double-blinded fashion. The blood lead levels of 229 children ranged from 4.5 to 26.4 microg/dl; the mean was 10.3 microg/dl and the standard deviation was 3.3 microg/dl. The gene distribution of the ALAD isozyme phenotypes in these environmentally exposed children was ALAD 1-1 (92%), ALAD 1-2, (8%), and ALAD 2-2 (0%). The mean blood level of the environmentally exposed children, who were homozygous for the ALAD1 allele, was 9.7 microg/dl; the mean for those who were heterozygous for the ALAD2 allele was 11.7 microg/dl. Using the t test, the means of the groups were different at the level of t=2.2058, P<0.05. Step-wise regression and multiple analyses of covariance were employed to control the confounders to measuring the independent contribution of the ALAD genotype on blood lead levels. After controlling the confounders, the contribution of the ALAD genotype to the blood lead level was greater and still statistically significant (F=7.3201, P<0.01). These results indicate that individuals carrying the ALAD2 allele are more likely to have sustained increases in blood lead levels when exposed to a lead-contaminated environment.

Alleles↗

PubMed2001

Structural components of the nuclear body in nuclei of Allium cepa cells.

Nuclear bodies have long been noted in interphase nuclei of plant cells, but their structural component, origin and function are still unclear by now. The present work showed in onion cells the nuclear bodies appeared as a spherical structure about 0.3 to 0.8 microm in diameter. They possibly were formed in nucleolus and subsequently released, and entered into nucleoplasm. Observation through cytochemical staining method at the ultrastructural level confirmed that nuclear bodies consisted of ribonucleoproteins (RNPs) and silver-stainable proteins. Immunocytochemical results revealed that nuclear bodies contained no DNA and ribosomal gene transcription factor (UBF). Based on these data, we suggested that nuclear bodies are not related to the ribosome or other gene transcription activities, instead they may act as subnuclear structures for RNPs transport from nucleolus to cytoplasm, and may also be involved in splicing of pre-mRNAs.

Cell Nucleolus↗

PubMed2001

Cancer chemopreventive activities of S-3-1, a synthetic derivative of danshinone.

Salvia miltiorrhiza is a traditional Chinese medicine which has been well documented for its anti-cancer effects. Based on the structure of danshinone, one of the active compounds derived from Salvia miltiorrhiza, we synthesized a simplified phenolic analog, S-3-1, and tried to explore its possible actions in preventing the development of cancer. With the Ames test, S-3-1 was found to efficiently suppress the mutagenicity of benzo[alpha]pyrene. This result is consistent with the inhibitory effect of S-3-1 on the activation of benzo[alpha]pyrene by hepatic microsomal enzymes. Besides the anti-initiation effects, S-3-1 could significantly inhibit the croton oil-induced increase of mouse skin epithermal ornithine decarboxylase activity. Moreover, S-3-1 quenched both superoxide and hydroxyl free radicals whereas it inhibited lipid peroxidation in the in vitro model. These results suggest that S-3-1 might act as anti-initiation and anti-promotion agents through reversing the biochemical alterations induced by carcinogen during carcinogenesis. Therefore, we further investigated the effects of S-3-1 on carcinogenesis. In vitro, S-3-1 inhibited the benzo[alpha]pyrene-induced transformation of V79 Chinese hamster lung fibroblasts. At 10-40 mg/kg, S-3-1 was found to inhibit the development of DMBA/croton oil-induced skin papilloma in mice through decreasing the incidence of papilloma, prolonging the latent period of tumor occurrence and reducing tumor number per mouse in a dose-dependent manner. We concluded from this study that S-3-1 might be developed as a new chemopreventive drug.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2001

[Genescan analysis of the loss of heterozygosity on the long arm of chromosome 6 in non-small cell lung cancer].

To investigate if there are microsatellite loci in the long arm of chromosome 6 that have close relationship with non-small cell lung cancer, Multiple PCR approach was used to analyze the 36 loci in the long arm of chromosome 6. The PCR products were analyzed in PAGE and then the electrophoresis maps were analyzed with Genescan and Genotyper. There is different LOH frequency in different loci. The total frequency of LOH in 41 lung cancers was 78%(32/41), with the highest frequency of LOH was detected on the locus D6S302(75%). There are 14 loci which have LOH frequency more than 20% and the loci are mainly located in 2 regions: 6q16.3-q21 [6 loci D6S458 (21.43%), D6S1694 (26.92%), D6S1717 (35.71%), D6S1565 (40%), D6S302 (75%), D6S1706 (36.36%) and 6q26-q27 (5 loci D6S1550 (38.46%), D6S264 (20%), D6S1585 (25%), D6S446 (33.33%), D6S281 (30.77%)], There may be tumor suppressor genes located in the two regions, which have a close relationship with non-small cell lung cancer.

Carcinoma, Non-Small-Cell Lung↗

PubMed2001

[Energy transfer between electric polymer PVK and terbium complex and its transmission electronmicroscope (TME) study].

A chloroform-soluble terbium complex, which is confirmed to be Tb(aspirin)3 phen using element analysis and FT-IR spectroscopy, was synthesized. Photoluminescent investigation on the terbium complex and PVK-terbium complex composite was conducted. Förster energy transfer occurred between the terbium complex and the PVK matrix. There are no overlap between UV spectrum of the complex and the emission spectrum of PVK, however, overlap is observed between the excitation spectrum of the complex and the emission spectrum of PVK. Therefore, we suggest that the necessary condition of Förster energy transfer should be overlap between the excitation (not UV) spectrum of one complex and the emission spectrum of polymer matrix. Further investigation indicates that the emission of PVK can be suppressed at different extents by doping various amount of Tb(aspirin)3 phen into PVK films. The ratio of Tb(aspirin)3 phen: PVK = 1:2 (wt%) are regarded as an optimized ratio for limiting the emission of PVK. TEM images of PVK/Tb(aspirin)3 phen films reveal that nanoparticles of the Tb complex are dispersed in the PVK matrix. The size of the aggregated complex in PVK matrix is 20-30 nm. The film is not homogeneous as dark regions co-exist with light region in the TEM images. This phenomenon may be related to the short lifetime of electroluminescent devices.

Chelating Agents↗

PubMed2000

Involvement of poly(ADP-ribose) polymerase and activation of caspase-3-like protease in heat shock-induced apoptosis in tobacco suspension cells.

The cleavage of poly(ADP-ribose) polymerase (PARP) by caspase (casp)-3 is an essential link in the apoptotic pathway in animal cells. In plant cells, however, there is no authentic evidence for the similar role that PARP may play during apoptosis. Using a heat shock (HS)-induced apoptosis system of tobacco cells, we found that immediately after a 4 h heat treatment, PARP was cleaved to form an 89 kDa signature fragment, while DNA laddering appeared only after a 20 h recovery following the HS. An activation of casp-3-like protease was also observed. The results suggest that apoptosis in plants and animals may share common mechanisms. On the other hand, when cells were preincubated with 4 mM 3-aminobenzamide or 2-8 mM nicotinamide, the specific inhibitors of PARP, before HS treatment, apoptotic cell death was reduced significantly. Our results thus imply that PARP may also be involved in apoptosis in a different way from the casp-related events.

Apoptosis↗

PubMed2000

Reconstruction algorithm for polychromatic CT imaging: application to beam hardening correction.

This paper presents a new reconstruction algorithm for both single- and dual-energy computed tomography (CT) imaging. By incorporating the polychromatic characteristics of the X-ray beam into the reconstruction process, the algorithm is capable of eliminating beam hardening artifacts. The single energy version of the algorithm assumes that each voxel in the scan field can be expressed as a mixture of two known substances, for example, a mixture of trabecular bone and marrow, or a mixture of fat and flesh. These assumptions are easily satisfied in a quantitative computed tomography (QCT) setting. We have compared our algorithm to three commonly used single-energy correction techniques. Experimental results show that our algorithm is much more robust and accurate. We have also shown that QCT measurements obtained using our algorithm are five times more accurate than that from current QCT systems (using calibration). The dual-energy mode does not require any prior knowledge of the object in the scan field, and can be used to estimate the attenuation coefficient function of unknown materials. We have tested the dual-energy setup to obtain an accurate estimate for the attenuation coefficient function of K2 HPO4 solution.

Algorithms↗

PubMed1999

The in vitro antiapoptotic effect of dehydroepiandrosterone sulfate in mouse thymocytes and its relation to caspase-3/caspase-6.

The effects of dehydroepiandrosterone sulfate (DHEAS) on thymocyte apoptosis induced by dexamethasone (DEX) were investigated. Apoptosis was measured by using agarose gel electrophoresis of DNA, the terminal deoxynucleotidyltransferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay and flow cytometry. Our results showed that preincubation with 1 x 10(-4) M DHEAS protected thymocytes from DEX-induced apoptosis in vitro. Moreover, we found no blocking effect on the DEX-induced activation of caspase-3 and caspase-6 by the preincubation of thymocytes with DHEAS. This may be interpreted to mean that the antagonism of DHEAS to DEX-induced apoptosis is not related to the activation of these down-stream caspases which play a critical role in the execution of apoptosis.

Animals↗

PubMed1999

Effects of genistein, a soybean-derived isoflavone, on proliferation and differentiation of B16-BL6 mouse melanoma cells.

Genistein, a soybean-derived isoflavone, may contribute to the lower cancer incidence in South Asian countries. In this study, the effects and molecular mechanisms of genistein on growth and differentiation of B16-BL6 mouse melanoma cells were investigated. Genistein suppressed the growth of these melanoma cells. The IC50 value is 15.5 microM. On the other hand, genistein induced the changes of cell shape and cytoskeletal network. The cytoskeletal filaments were induced to form a bundle along the direction of elongation of the cells. Moreover, tyrosine phosphorylation levels of cytoskeleton-associated proteins decreased after the cells were exposed to 20 or 30 microM of genistein for 3 days. All these morphological and molecular changes were accompanied by appearance of the differentiated phenotypes. Genistein induced the increase of cellular melanin content, enhancement of tyrosinase activity, and decrease of colonization potentials in soft agar in a time-dependent and dose-dependent manner. The effective concentration was no more than 10 microM after 3 days' exposure. The tumorigenic potentials of B16-BL6 cells in C57BL/6 mouse also decreased after exposure to 20 or 30 microM of genistein for 3 days. When expressions of tumor-related genes were investigated in the differentiation-induced cells, the content of P53 dramatically increased while that of c-Myc protein decreased. Therefore, due to its ability to induce cellular and molecular changes, genistein suppressed the growth and induced differentiated phenotypes in B16-BL6 melanoma cells.

Animals↗

PubMed1999

Longitudinal sampling and aliasing in spiral CT.

Although analyses of in-plane aliasing have been done for conventional computed tomography (CT) images, longitudinal aliasing in spiral CT has not been properly investigated. We propose a mathematical model of the three-dimensional (3-D) sampling scheme in spiral CT and analyze its effects on longitudinal aliasing. We investigated longitudinal aliasing as a function of the helical-interpolation algorithm, pitch, and reconstruction interval using CT simulations and actual phantom scans. Our model predicts, and we verified, that for a radially uniform object at the isocenter, the spiral sampling scheme results in spatially varying cancellation of the aliased spectral islands which, in turn, results in spatially varying longitudinal aliasing. The aliasing is minimal at the scanner isocenter, but worsens with distance from it and rapidly becomes significant. Our results agree with published results observed at the isocenter of the scanner and further provide new insight into the aliasing conditions at off-isocenter locations with respect to the pitch, interpolation algorithm, and reconstruction interval. We conclude that longitudinal aliasing at off-isocenter locations can be significant, and that its magnitude and effects cannot be predicted by measurements made only at the scanner isocenter.

Algorithms↗

PubMed1999

Modeling of polychromatic attenuation using computed tomography reconstructed images.

This paper presents a procedure for estimating an accurate model of the CT imaging process including spectral effects. As raw projection data are typically unavailable to the end-user, we adopt a post-processing approach that utilizes the reconstructed images themselves. This approach includes errors from x-ray scatter and the nonidealities of the built-in soft tissue correction into the beam characteristics, which is crucial to beam hardening correction algorithms that are designed to be applied directly to CT reconstructed images. We formulate this approach as a quadratic programming problem and propose two different methods, dimension reduction and regularization, to overcome ill conditioning in the model. For the regularization method we use a statistical procedure, Cross Validation, to select the regularization parameter. We have constructed step-wedge phantoms to estimate the effective beam spectrum of a GE CT-I scanner. Using the derived spectrum, we computed the attenuation ratios for the wedge phantoms and found that the worst case modeling error is less than 3% of the corresponding attenuation ratio. We have also built two test (hybrid) phantoms to evaluate the effective spectrum. Based on these test phantoms, we have shown that the effective beam spectrum provides an accurate model for the CT imaging process. Last, we used a simple beam hardening correction experiment to demonstrate the effectiveness of the estimated beam profile for removing beam hardening artifacts. We hope that this estimation procedure will encourage more independent research on beam hardening corrections and will lead to the development of application-specific beam hardening correction algorithms.

Algorithms↗

PubMed1999

[Induction of programmed cell death by menadione in suspension culture of carrot cells].

Menadione (VK3), a quinone that undergoes redox cycles leading to the formation of superoxide radicals, was found to induce cell death in suspension culture of carrot cells. The effect of menadione was in a dose-dependent manner. 100-800 mumol/L menadione caused 10-33 percent cell death. When concentration of menadione reached 1 mmol/L, 100 percent of cell death was observed. DNA cleavage, a hallmark of apoptosis was further studied. DNA ladders were observed in cells treated with 600 and 800 mumol/L menadione but not with lower concentration treatments where only very low percentage of cell death was found. There was no DNA ladders in the cells treated with 1 mmol/L menadion indicating that necrosis may occur. In situ detection of nuclear DNA fragmentation by TUNEL reaction revealed fragmented nuclear DNA in cells treated with 100-800 mumol/L menadion but not in cells treated with 1 mmol/L menadione.

Apoptosis↗

PubMed1998

Low-level prenatal lead exposure and neurobehavioral development of children in the first year of life: a prospective study in Shanghai.

We used a prospective study design to assess the effects of prenatal low-level lead exposure on the development of urban, inner-city children in Shanghai. Umbilical cord blood samples wee consecutively collected from 605 live newborns. Two hundred and fifty-seven samples were excluded from the study due to clotting. Lead levels were determined on 348 cord blood samples. The geometric mean was 9.2 micrograms/dl. Based on their cord blood lead levels, infants were classified into two exposure groups: 104 in a relatively low lead group (lead levels < or = 30 percentile), and 104 in a relatively high lead group (lead levels > or = 70 percentile). Seventy-five subjects failed to complete the study, and 133 babies were included in the final cohort: 69 babies in the high lead group and 64 in the low lead group. At 3, 6, and 12 months, the Bayley Scales of Infant Development were administered and capillary blood lead levels were measured. Detailed information was obtained on a wide range of variables relevant to infant development. At all three ages, the Mental Development index (MDI) scores, adjusted for confounders, were inversely related to the infants' cord blood lead levels. The difference of the mean adjusted MDI scores between low and high lead groups was 3.4 at 3 months, 6.3 at 6 months, and 5.2 at 12 months of age. These differences were statistically significant at all time points. No significant association between cord blood lead levels and the Psychomotor Development Index (PDI) scores was detected at all three visits after adjustment for confounders. Postnatal lead levels were unrelated to concurrent developmental status. We conclude that prenatal low-level lead exposure, which is relatively common in Shanghai, is associated with an adverse developmental impact on children through the first year of life.

Child Development↗