Biomedical subjects

S Y Yoon

Publications and source records attributed to S Y Yoon.

At least 19 recordsLinked to original sources

PubMed2006

Continuously varying exponents in A+B-->0 reaction with long-ranged attractive interaction.

We investigate kinetics of A+B-->0 reaction with long-range attractive interaction V(r) approximately -r(-2sigma) between A and B or with drift velocity v approximately r(-sigma) in one dimension, where r is the closest distance between A and B . It is analytically shown that dynamical exponents for density of particles (rho) and size of domains (l) continuously vary with sigma when sigma < sigma(c) = 1/2 , while that for the distance between adjacent opposite species (l(AB)) varies when sigma < sigma(c)AB = 7/6 . For sigma > sigma(c)AB diffusive motions dominate the kinetics. These anomalous behaviors with the two crossover values of sigma are supported by numerical simulations.

Journal Article↗

PubMed2006

Anomalous kinetics of attractive A + B-->0 reactions.

We investigate the kinetics of the A + B-->0 reaction with the attractive interaction between opposite species in one spatial dimension. The attractive interaction leads to isotropic diffusions inside segregated single species domains, and accelerates the reactions of opposite species at the domain boundaries. At equal initial densities of and , we analytically and numerically show that the density of particles (rho), the size of domains (l), the distance between the closest neighbor of same species (lAA), and the distance between adjacent opposite species (lAB) scale in time as rho approximately t(-1/3), lAA approximately t(1/3), and l approximately lAB approximately lAB(2/3), respectively. These dynamical exponents define critical behavior distinguished from the class of uniformly driven systems of hard-core particles.

Journal Article↗

PubMed2006

Mycophenolic acid induces islet apoptosis by regulating mitogen-activated protein kinase activation.

Mycophenolic acid (MPA), an inosine monophosphate dehydrogenase inhibitor, is widely used as an immunosuppressive drug after transplantations including those of pancreas islet cells. However, recent reports have indicated that MPA has apoptotic effects on islet cells in vitro. To study the effect of MPA on islet cells and determine its mechanism, we used an insulin secreting cell-line, HIT-T15. We examined mitogen-activated protein kinase (MAPK) activation after MPA treatment, and determining cell death levels using methylthiazdetetrazolium assays. The activations of extracellular signal-regulated protein kinase (ERK), c-jun N-terminal kinase (JNK), and p38 MAPK and caspase-3 cleavage were measured by Western blotting. MPA (1, 10, 30 micromol/L) increased cell death and caspase-3 cleavage within 24 hours. Exogenous 500 micromol/L guanosine reversed the MPA-induced islet cell death, but exogenous adenosine did not. MPA 10 micromol/L induced cell apoptosis and increased the activations of JNK, ERK, and p38 MAPK. Furthermore, exogenous guanosine, but not exogenous adenosine, reversed these effects induced by MPA. This study demonstrated that MPA may induce islet apoptosis in HIT-T15 cells by increasing activations of JNK, ERK, and p38 MAPK in a guanosine-dependent manner.

Apoptosis↗

PubMed2006

New insight of amino acid-based dialysis solutions.

Malnutrition is a major complication of peritoneal dialysis (PD) and is associated with increased morbidity and mortality. Daily losses of proteins and amino acids (AAs) into dialysate contribute to this problem. Previous metabolic balance study demonstrated that treatment with 1.1% AA-based dialysis solution is safe and may improve protein malnutrition in continuous ambulatory peritoneal dialysis (CAPD) patients ingesting low protein intake. Other prospective studies also showed that AA solution can provide nutritional benefit for malnourished PD patients resulting in a significant improvement in some biochemical and/or anthropometric nutritional parameters. However, there are other studies showing no particular improvement in nutritional parameters after long-term use of AA solution. This may be related to the differences in the study design, sample size, methods used to assess nutritional status, and other factors such as dietary intake and comorbidities of study subjects. Published data will be reviewed to further emphasize the nutritional benefit of long-term use of AA solution in malnourished PD patients along with a brief discussion on the various reasons that may partly explain the different study results. We will also present the results of a longitudinal observational study evaluating changes in nutritional parameters following use of one exchange of 1.1% AA solution in malnourished Korean PD patients. A significant improvement of somatic protein status such as lean body mass (LBM) and hand grip strength was observed. No significant change in serum albumin level was noted. Patients with a positive estimated coefficient for LBM in the fitted regression model to the repeated observations over 1 year were classified as responders and patients with neutral or negative coefficient were considered as non-responders. Thirty-one out of 43 malnourished patients (72%) showed nutritional benefit based on the change of LBM. Hand grip strength and back lift strength were significantly higher in responders at baseline. Other baseline parameters did not differ between the two groups.

Amino Acids↗

PubMed2005

Roughness of two-dimensional surfaces with global constraints.

We study dynamical scaling properties of the two-dimensional surface growth models with global constraints. These include the growth model from a partition function Z = sigma{(h(r)Pi(h = h)(min) (h(max)) 1/2 (1 + z (n(h))), multiparticle-correlated surface growth models and dissociative Q-mer growth models. The equilibrium surfaces of all the models except the dimer model show the same dynamical scaling behavior W2 (L,t) = (1/2piK(G)) ln [L g (t/L(z(W)))] with z(W) = 2.5 and K(G) = 0.916 , whereas the surface in the dimer model has a correction to the scaling. The growing (eroding) surfaces have two phases. The models with z > or = 0 show the normal Kardar-Parisi-Zhang scaling behavior. In contrast the models with -1 < or = z < 0 and multiparticle-correlated growth model manifest grooved surface structures with alpha = 1. The growing surfaces of Q -mer models form rather complex facets.

Journal Article↗

PubMed2005

Docetaxel (Taxotere), cisplatin, UFT, and leucovorin combination chemotherapy in advanced gastric cancer.

We conducted this study to ascertain the efficacy and toxicity of docetaxel and cisplatin combined with oral UFT and leucovorin as a first-line treatment for patients with advanced gastric cancer. In all, 52 patients received courses of docetaxel 60 mg m(-2) intravenously (i.v.) for 1 h and then cisplatin 75 mg m(-2) i.v. for 2 h on day 1. Oral UFT at 400-600 mg day(-1), as determined by body surface area, and leucovorin at 75 mg day(-1) were administered for 21 consecutive days from day 1, and this was followed by a 7-day drug-free interval. A total of 225 courses were administered, and the median number of courses per patient was four. Four complete responses (7.7%) and 22 partial responses (42.3%) were achieved, giving an overall response rate of 50% (95% Confidence Interval: 36.4-63.6%). The major toxicity was neutropenia, which reached grade 3/4 in 36 patients (69.3%). Grade 3/4 nausea and vomiting was observed in 12 patients (23.1%). Median time to progression was 22 weeks (4 to 156+ weeks), median survival duration was 48 weeks (4 to 156+ weeks), and median response duration was 24 weeks (6-152 weeks). We conclude that docetaxel, cisplatin, oral UFT, and leucovorin combination chemotherapy is effective and tolerable for the treatment of advanced gastric cancer.

Adenocarcinoma↗

PubMed2005

Acinic cell carcinoma on the lower lip resembling a mucocele.

A 64-year-old woman presented with a 2-week history of an asymptomatic mass involving the lower lip. Histopathological examination showed a well-circumscribed tumour composed of many lobules separated by thin, fibrous connective tissue. Individual lobules were composed of round or polyhedral tumour cells, which had a characteristic finely granular and vacuolated cytoplasm and eccentric hyperchromatic nuclei. Positive staining was observed with Periodic acid-Shiff, and immunohistochemistry for cytokeratin, alpha-1 antitrypsin, and S-100 protein resulting in a final diagnosis of acinic cell carcinoma. Acinic cell carcinoma represents a well-established, although uncommon, entity in the classification of neoplasms of salivary gland origin. The parotid salivary gland is the most frequent site of acinic cell carcinoma, whereas the lip is a particularly unusual site. The unusual presentation of this tumour may lead to confusion with a mucocele. Given these findings, we suggest that acinic cell carcinoma should be considered in the differential diagnosis of any mucocele-like mass on the lower lip.

Biomarkers, Tumor↗

PubMed2004

Scaling properties of self-expanding surfaces.

Scaling properties of self-expanding surfaces are studied with a comparison to those of self-flattening surfaces [Phys. Rev. E 66, 040602(R) (2002)]. The evolution of self-expanding surfaces is described by a restricted solid-on-solid type monomer deposition-evaporation model in which both deposition at the globally lowest site and evaporation at the globally highest site are suppressed. We find numerically that equilibrium surface fluctuation has a scaling behavior with a roughness exponent alpha approximately 1 in one dimension (1D). In contrast, 2D equilibrium surfaces show the same dynamical scaling behavior with alpha=0 (log) and dynamic exponent z approximately 5/2 as 2D self-flattening surfaces. Stationary roughness can be understood analytically by relating the self-expanding growth model to self-repelling random walks. In the case of nonequilibrium growing/eroding surfaces, self-expanding dynamics cause the fluctuation of surfaces to be characterized by alpha approximately 1 in both 1D and 2D.

Models, Statistical↗

PubMed2003

Surface growth models with a random-walk-like nonlocality.

To understand the effects of a random-walk-like nonlocality on the dynamical scaling properties of surface growths, a stochastic growth model in which the height difference triangle up h((i,i+1))=|h(i)-h(i+1)| of a chosen nearest neighbor column pair (i,i+1) is decreased by one unit is introduced and studied by simulations. The probability P((i,i+1)) of choosing a column pair (i,i+1) on a one-dimensional substrate is assigned as P((i,i+1))=e(kappa triangle up h((i,i+1)))/ summation operator (L)(j=1)e(kappa triangle up h((j,j+1))). On a substrate of given size L, the dynamical scaling property satisfies a normal scaling behavior as W=L(alpha)f(t/L(z)), when kappa is very small. If kappa becomes moderately large, the scaling property with the dynamic exponent z=1 as in diffusion-limited erosion appears. If kappa becomes very large, no surface roughening is found.

Journal Article↗

PubMed2003

Partition functions and metropolis-type evolution rules for surface growth models with constraints.

We study dynamical scaling properties of the surface growth model with the Metropolis-type evolution rule from a partition function Z= sum ([h(r)])II (h(max))(h=h(min))1/2(1+z(n(h))), where z is a fugacity-like quantity and n(h) is the number of sites with height h in a surface configuration [h(r)]. The partition function describes a 2-particle correlated growth model when z=-1 and a self-flattening growth model when z=0. For one-dimensional equilibrium surfaces, the scaling properties for z>or=-1 except z=1 are all one phase with roughness exponent alpha=1/3 and growth exponent beta approximately equal 0.22. For the growing (eroding) surfaces, there exists a phase transition at z=0 from the grooved phase (alpha=1) for -1 0.

Journal Article↗

PubMed2003

Time-reversed dielectric-breakdown model for erosion phenomena.

A time-reversed dielectric-breakdown model in which the annihilating probability of a particle on the surface site (x,h) depends on Laplacian field phi(x,h,t) as P(x,h,t)=| inverted Delta phi(x,h,t)|(kappa)/ Sigma(x,h)| inverted Delta phi(x,h,t)|(kappa) is suggested. This model is shown to be a theoretical model that covers a variety of eroding surfaces from the linear phenomena with dynamic exponent z=1 to those showing nonlinear behavior. phi(x,t) is defined to satisfy the Laplace equation inverted Delta (2)phi=0 with the boundary condition phi=0 on the material and phi=1 far from the material. The model with 0.5 < or = kappa < or = 2 is found to follow the linear growth equation with z=1 as the diffusion-limited erosion, which is also a time-reversed version of diffusion-limited deposition. For small kappa, the dynamical scaling property of the eroding surface belongs to the Kardar-Parisi-Zhang universal class as the time-reversed Eden model. The model with kappa >2.5 does not show any surface roughening behavior.

Journal Article↗

PubMed2003

Upregulation of c-Kit receptor and stem cell factor in cerebellar inhibitory synapses in response to kainic acid.

Neuronal stimulation was induced in rats by systemic administration of kainic acid (KA) to determine if such stimulation is responsible for changes in the expression patterns of c-Kit and stem cell factor (SCF) in cerebellar synapses between inhibitory interneurons and Purkinje cells. Using immunocytochemistry and immunoblotting analyses, we demonstrate that c-Kit receptor tyrosine kinase and its ligand SCF are present on the pre- and postsynaptic sides of inhibitory synapses on Purkinje cells. These proteins are upregulated during the first 48 hr after KA treatment, whereas their levels fall below that of the control by 1 week and remain as such thereafter. Expression of both c-Kit and SCF are significantly elevated in the Purkinje cell layer 24 hr after KA administration, and the Purkinje cell layer exhibits a loss of calbindin D-28K immunoreactivity. Expression of c-Kit in basket cell axon terminals is activated until 48 hr after KA treatment, suggesting the transient participation of c-Kit receptor tyrosine kinase in the maintenance of these axonal terminals. Also during the first 48 hr after KA treatment, SCF levels increase in axonal processes of Purkinje cells, and these SCF-positive axons correlate with c-Kit-positive pinceau structures. The increased expression of c-Kit and SCF in response to KA-induced neuronal stimulation may indicate that c-Kit receptor tyrosine kinase and its ligand SCF function in the inhibitory synapse between cerebellar interneurons and Purkinje cells, and that this role is most pronounced during the first 48 hr after KA treatment.

Animals↗

PubMed2002

Fluctuations of self-flattening surfaces.

We study the scaling properties of self-flattening surfaces under global suppression on surface fluctuations. Evolution of self-flattening surfaces is described by restricted solid-on-solid type monomer deposition-evaporation model with reduced deposition (evaporation) at the globally highest (lowest) site. We find numerically that equilibrium surface fluctuations are anomalous with roughness exponent alpha approximately equal to 1/3 and dynamic exponent z(W) approximately equal to 3/2 in one dimension (1D) and alpha=0 (log) and z(W) approximately 5/2 in 2D. Stationary roughness can be understood analytically by relating our model to the static self-attracting random walk model and the dissociative dimer-type deposition-evaporation model. In case of nonequilibrium growing-eroding surfaces, self-flattening dynamics turns out to be irrelevant and the normal Kardar-Parisi-Zhang universality is recovered in all dimensions.

Journal Article↗

PubMed2002

Effects of biased diffusions on dynamical surface structures for the A+B-->0 reaction.

The dynamical scaling property of surface eroded by a chemical reaction A+B-->0 is studied by the simulation. To consider the effect of interactions between an A particle and the material which consists of B particles, the A particle is assumed to undergo a drifted-diffusive motion or a biased random walk before it touches the material. The surface of the material is eroded by the chemical reaction with a B particle which the A particle first encounters. In dimension d=2, we found three regimes in the dynamical surface structure. When there is attractive bias to the material, the dynamical scaling property belongs to the universality class with the dynamic exponent z=2. When there is no bias or relatively small repulsive bias, the scaling property belongs to the class with z=1. The surface roughening behavior disappears when repulsive bias becomes quite large. We also discuss the properties of the crossover between the existing regimes.

Journal Article↗

PubMed2002

Relaxation of particles in the sloped region in a conserved growth model.

The dynamical scaling properties of conserved growth models, in which the downward (upward) movement of a particle dropped only on the sloped region occurs with a probability p (1-p), are investigated by simulations in the substrate dimension d=1. By direct analysis of the surface fluctuation W, the models with p>1/2 are clearly and cleanly shown to have crossover behavior from Mullins-Herring (MH) universality to Edwards-Wilkinson (EW) universality. In contrast, the models with p<1/2 are shown to have an instability eventually, even though they initially follow the MH equation. The model with p=1/2 is shown to belong to the MH universality class and to be the critical model that splits the models with EW behavior from those with the instability. From these results we explain the physical reason for the very slow crossover in models like the Wolf-Villain model.

Journal Article↗

PubMed2002

Distribution of nociceptin-like immunoreactivity in the central nervous system of the Mongolian gerbil: an immunohistochemical study.

This study is designed to demonstrate the distribution of nociceptin, endogenous ORL1 receptor ligand, in the central nervous system of the Mongolian gerbil. To intensify the nociceptin-like immunoreactivity (NOC-LI), colchicine was administered into the lateral ventricle, at 48 h prior to the transcardiac perfusion. In the group without colchicine treatment, NOC-LI was observed in the fibres of the spinal dorsal horn, specifically in the superficial layers. However, the NOC-LI in the superficial layers disappeared after the administration of colchicine. In the brain, NOC-LI was prominent in the hypothalamus, hippocampus, cerebral peduncle, substantia nigra, dorsal raphe, periaqueductal grey, locus coeruleus and trapezoid nucleus. Colchicine treatment markedly intensified the NOC-LI in the somata of the central nervous system, whereas the untreated sections were too weak to observe and analyse. The distribution of NOC-LI provides informative data for studies of the neuronal circuit that nociceptin may be involved in.

Animals↗

PubMed2001

MPP(+) downregulates mitochondrially encoded gene transcripts and their activities in dopaminergic neuronal cells: protective role of Bcl-2.

The effects of neurotoxins on levels of mitochondrially encoded gene transcripts in a dopaminergic neuronal cell line, MN9D, were examined following treatment with 200 microM N-methyl-4-phenylpyridinium (MPP(+)) or 6-hydroxydopamine (6-OHDA). As confirmed by a Northern blot analysis, levels of cytochrome c oxidase subunit 3 (COX III) and ATPase subunit 6 (ATPase 6) transcript were decreased in a time-dependent manner following treatment with MPP(+) but not with 6-OHDA. Accordingly, enzymatic activity of cytochrome c oxidase (COX) and the intracellular ATP content were also decreased in MPP(+)-treated cells while these remained unaltered in 6-OHDA-treated cells. In the cell death paradigm induced by MPP(+), overexpression of Bcl-2 in MN9D cells (MN9D/Bcl-2) significantly blocked MPP(+)-induced downregulation of COX III and ATPase 6 transcripts. In MN9D/Bcl-2 cells, MPP(+)-induced downregulation of COX activity and the intracellular level of ATP was also blocked. Treatment with a pan-caspase inhibitor, however, neither prevented MPP(+)-induced downregulation of COX activity nor affected intracellular level of ATP in MN9D cells. Taken together, our present data suggest that Bcl-2 may play a regulatory role in energy metabolism by preventing downregulation of mitochondrially encoded gene(s) at a point distinct from its known anticaspase activity in MPP(+)-induced dopaminergic neuronal death.

1-Methyl-4-phenylpyridinium↗

PubMed2001

Phase II trial of epirubicin, cisplatin, oral uracil and tegafur, and leucovorin in patients with advanced gastric carcinoma.

BACKGROUND: The results of chemotherapy for patients with gastric carcinoma generally have been modest, although regimens developed more recently have produced higher response rates. One such regimen is epirubicin, cisplatin, and protracted infusion of 5-fluorouracil (ECF). The advantage of a long-term oral administration of uracil and tegafur (UFT) is that this treatment may be used to mimic the protracted infusion of 5-fluorouracil (5-FU). In addition, UFT treatment combined with leucovorin had a favorable activity and tolerable toxicity in patients with advanced gastric carcinoma. Instead of the inconvenience of an infusion pump and intravenous catheter for the protracted infusion of 5-FU, the authors administered UFT plus leucovorin in an ECF regimen for the treatment of patients with advanced gastric carcinoma. METHODS: Fifty-two patients with advanced gastric carcinoma received epirubicin, cisplatin, and oral UFT plus leucovorin. Epirubicin 50 mg/m(2) and cisplatin 60 mg/m(2) were administered on Day 1 by intravenous injection. Tegafur and uracil 360 mg/m(2)/day orally was administered in conjunction with leucovorin administered at a fixed dose of 45 mg/day orally in divided daily doses for 21 days followed by a 7-day rest period. These courses were repeated every 4 weeks. The median age of the patients was 59 years with a median World Health Organization performance status of 1. Patients received a median of five courses of treatment (range, 1-10). RESULTS: Among the 47 patients evaluated, three patients achieved complete response, and 24 patients had partial responses, for an overall response rate of 57.5% (95% confidence interval, 71.5-43.3%). Stable disease was reported in 11 patients (23.4%), and another 9 patients (19.1%) showed disease progression. The median duration of survival was 15 months (range, 2-33+). The main toxicity was nausea/vomiting and neutropenia. Significant toxicity (modified National Cancer Institute common toxicity Grade 3 or 4) included neutropenia in 22 patients (42%), nausea in 14(27%), vomiting in 9 (18%), oral mucositis in 3 (6%), and diarrhea in 3 (6%) patients. CONCLUSIONS: The authors conclude that epirubicin, cisplatin, and oral UFT plus leucovorin, a convenient regimen, has a significant activity and tolerable toxicities in patients with gastric carcinoma.

Administration, Oral↗