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Biomedical subjects

K Park

Publications and source records attributed to K Park.

At least 163 records · Page 9Linked to original sources
PubMed2000

Enhanced effect of sulfonylurea (SU) in copolymer comprising a sugar moiety and SU derivative as double ligands on insulin secretion from MIN6 cells.

Copolymers composed of sulfonylurea (SU) as an antagonist of ATP-sensitive K+ channel and sugar moieties as double ligands were synthesized. Insulin secretion from MIN6 cells (insulinoma cell line) in contact with the copolymers was evaluated. MIN6 cells attached to the poly(N-p-vinylbenzyl-D-maltonamide-co-SU) [P(VMA-co-SU)]-coated dishes were in the more aggregated form as compared to other polymer-coated surfaces. By introducing SU into the sugar bearing homopolymer, an enhanced effect on insulin secretion from MIN6 cells was observed due to the specific interaction between SU ligands and SU receptors on the beta-cell membrane. P(VMA-co-SU) composed of SU and non-reducing glucose moieties demonstrated enhanced insulin secretion from MIN6 cells and faster proliferation of MIN6 cells as compared to poly(N-p-vinylbenzyl-D-lactonamide-co-SU) [P(VLA-co-SU)] probably owing to the glucose transporters presence on the MIN6 cell membrane. Insulin secretion from MIN6 cells pretreated with diazoxide as an agonist of ATP-sensitive K+ channel was suppressed.

Adenosine Triphosphate↗
PubMed2000

In vitro and in vivo studies of PEO-grafted blood-contacting cardiovascular prostheses.

The initial step of thrombus formation on blood-contacting biomaterials is known to be adsorption of blood proteins followed by platelet adhesion. Poly(ethylene oxide) (PEO) has been frequently used to modify biomaterial surfaces to minimize or prevent protein adsorption and cell adhesion. PEO was grafted onto a number of biomaterials in our laboratory. Nitinol stents and glass tubes were grafted with PEO by priming the metal surface with trichlorovinylsilane (TCVS) followed by adsorption of Pluronic and y-irradiation. Nitinol stents were also coated with Carbothane for PEO grafting. Chemically inert polymeric biomaterials, such as Carbothane, polyethylene, silicone rubber, and expanded polytetrafluoroethylene (e-PTFE), were first adsorbed with PEO-polybutadiene-PEO (PEO-PB-PEO) triblock copolymers and then exposed to gamma-irradiation for covalent grafting. For PEO grafting to Dacron (polyethylene terephthalate), the surface was sequentially treated with PEO-PB-PEO and Pluronics followed by gamma-irradiation. In vitro studies showed substantial reduction in fibrinogen adsorption and platelet adhesion to the PEO-grafted surfaces compared with control surfaces. Fibrinogen adsorption was reduced by 70-95% by PEO grafting on all surfaces, except for e-PTFE. The platelet adhesion corresponded to the fibrinogen adsorption. When the PEO-grafted surfaces were tested ex vivo/in vivo, however, the expected beneficial effect of PEO grafting was inconsistent. The beneficial effect of the PEO grafting was most pronounced on the PEO-grafted nitinol stents. Thrombus formation was reduced by more than 85% by PEO grafting on metallic stents. Only moderate improvement (i.e. 35% decrease in platelet deposition) was observed with PEO-grafted tubes of polyethylene, silicone rubber, and glass. For PEO-grafted heart valves made of Dacron, however, no effect of PEO grafting was observed at all. It appears that the extent of thrombus formation on PEO-grafted biomaterials was directly related to the extent of tissue damage during implantation surgery. Platelets can be activated and form aggregates in the bulk blood, and the formed platelet aggregates may be able to deposit on the PEO monolayer overcoming its repulsive property. Our studies indicate that the testing of in vitro platelet adhesion should include adhesion of large platelet aggregates, in addition to adhesion of individual platelets. Furthermore, the surface modification methods should be improved over the current monolayer grafting concept so that the repulsive force by the grafted PEO layers is large enough to prevent adhesion of platelet aggregates formed in the bulk blood before arriving at the biomaterial surface.

Adsorption↗
PubMed2000

pH-sensitivity of fast responsive superporous hydrogels.

Stimuli-sensitive hydrogels (or smart hydrogels) are hydrogels that swell or shrink in response to small changes in environmental conditions in which they are placed. While the extent of swelling or shrinking may be large, the kinetics of such changes is slow, since the diffusion of water into and out of the hydrogel is a slow process. To obtain fast responses, we have prepared superporous hydrogels (SPHs) that can swell or shrink extremely fast regardless of their dimensions. The swelling and shrinking are orders of magnitude faster than expected for a nonporous hydrogel of the same dimensions. Water molecules are taken up into the SPHs by capillary forces, and this makes water uptake much faster than diffusion. The swelling ratio of the poly(acrylamide-co-acrylic acid) (p(AM-co-AA)) SPHs was dependent on the pH and ionic strength of the medium. The effect of pH was most pronounced and the effect of ionic strength was observed at all pH values. SPHs made at pH around 5 showed transient maximum swelling when exposed to pH 1.2 medium due to the transient low hydrogen ion concentration inside the swelling SPHs. The p(AM-co-AA) SPHs showed repeated swelling and shrinking by alternating the medium pH between 1.2 and 7.5, and the changes in swelling ratio was quite fast occurring in a matter of a minute. This fast sensitivity may make the stimuli sensitive hydrogels useful in many applications not previously possible. These materials can be used for applications where a single-piece hydrogel is more advantageous than hydrogel microparticulates.

Acrylamides↗
PubMed2000

Distribution of obstructive intimal lesions and their cellular phenotypes in chronic pulmonary hypertension. A morphometric and immunohistochemical study.

We investigated the distribution of pulmonary arteriopathy in chronic pulmonary hypertension (PH) in a quantitative histopathologic study, using computer-assisted image analysis. We also examined the histologic manifestations and cellular phenotypes of various obstructive intimal lesions in PH with an immunohistochemical method. A total of 53 lungs removed at autopsy or explantation were obtained for the study from 51 documented cases of moderate to severe PH (15 cases of primary pulmonary hypertension [PPH], eight cases of Eisenmenger's syndrome [EISEN], 22 cases of chronic major-vessel thromboembolic disease [CTED], and three cases of PH associated with other known causes), and two unused donor lungs served as normal controls. Intimal thickening in PPH was most prominent in small pulmonary arteries and arterioles less than 200 micrometer in diameter. Plexiform lesions in PPH were associated with significantly smaller arteries than in EISEN. Arteries larger than 400 micrometer showed a significant intimal thickening only in CTED. Obstructive intimal lesions in PH comprised a morphologic spectrum with frequent intermediate forms between plexiform and thrombotic lesions. Most cells within various intimal lesions showed an immunoprofile of myofibroblasts that were positive for vimentin and alpha-smooth muscle actin, but negative for desmin and endothelial markers including Factor VIII, clonal designator (CD)31, and CD34. Endothelial markers were positive only in the single layer of cells lining slitlike lumens, when the latter were present. In conclusion, major types of PH had characteristic distribution patterns of obstructive intimal lesions, showing mainly a myofibroblastic phenotype and variable endothelial/vascular differentiation.

Adult↗
PubMed2000

Surgical treatment of intractable epilepsy accompanying cortical dysplasia.

OBJECT: Surgical treatment of cortical dysplasia (CD) together with intractable seizures is challenging because both visualization and localization of the lesion are difficult, correlation with seizure foci requires comprehensive study, and the surgical outcomes reported thus far are unsatisfactory. The authors report their experience in the surgical treatment of CD classified according to a surgical point of view. METHODS: The definition of CD used in this study was a dysplastic lesion visible on magnetic resonance (MR) images or a lesion that, although not visible on MR images, was diagnosed as moderate-to-severe dysplasia by using pathological analysis. During the last 4.5 years, the authors treated 36 patients with intractable epilepsy accompanied by CD. They divided the 36 cases of CD into four characteristic groups: Group A, diffuse bilateral hemispheric dysplasia; Group B, diffuse lobar dysplasia; Group C, focal dysplasia; and Group D, a moderate to severe degree of CD with a normal appearance on MR images. All but one patient in Group C were monitored in the epilepsy monitoring unit by using subdural electrodes for seizure localization and functional mapping. The incidence of CD among a cohort of 291 patients who had undergone epilepsy surgery at the authors' center during the study period was 12.4%. The mean age of the 36 patients was 21.3 years and the mean age at seizure onset was 8.5 years. The mean follow-up period was 26 months. Twenty-six patients (72.2%) belonged to Engel Class I or II (20 and six, respectively). There were five cases in Group A, nine in Group B, nine in Group C, and 13 in Group D. Patients in Groups A and B were significantly younger at seizure onset and had significantly poorer surgical outcomes compared with patients in Groups C and D (p < 0.05). If outcome is compared on the basis of the extent of removal of CD, patients in whom CD was completely removed had significantly better outcomes than those in whom CD was only partially removed (p < 0.001). CONCLUSIONS: The authors conclude that intractable epilepsy accompanied by CD can be treated surgically using comprehensive preoperative approaches. Deliberate resective procedures aimed at complete removal of dysplastic tissue ensure excellent seizure control without permanent neurological deficit.

Adolescent↗
PubMed2000

Incidence of presbycusis of Korean populations in Seoul, Kyunggi and Kangwon provinces.

Presbycusis, a bilateral sensorineural hearing loss caused by changes in the inner ear, is related to multiple factors such as noise exposure and otologic disease. In institute-based studies, we tried to determine the incidence of presbycusis in Korean populations living in Seoul, Kyunggi and Kangwon provinces by gender and age groups. The subjects were people who had visited health promotion centers. Pure tone audiometry was done over 20 years on 6,028 subjects. In a community-based study, the subjects were elderly residents of Kanghwa-do area. There were no obvious factors that could cause hearing impairment in the subjects. For the pure tone audiometry, hearing threshold was obtained by using the six-dimension method. The incidence of presbycusis for subjects aged 65 years and older was 37.8% and 8.3% for > or = 27 dB HL criterion and > or = 41 dB HL criterion, respectively. The incidence increased with age. A statistically significant difference in the hearing threshold was found between men and women aged 65 years or older. No differences were found between the community-based study and the institute- based studies. There was a high incidence (about 40%) of presbycusis among Koreans aged 65 years or older (for > or = 27 dB HL criterion). With an aging population, we anticipate that this report could be used to provide a basic data for the study of presbycusis.

Adult↗
PubMed2000

Changes in gallbladder motility in gastrectomized patients.

OBJECTIVES: Gastric resection may predispose gallstone formation. However, the mechanism has not been clearly understood. To evaluate the relationship between gastric resection and gallstone formation, we compared gallbladder(GB) motility in gastrectomized patients and control subjects. METHODS: We compared the GB volume and ejection fraction of the 46 gastrectomized patients with 37 healthy controls using real time ultrasonography. RESULTS: GB volume increased significantly in the gastrectomized group in fasting (30.2 +/- 13.9 ml). The GB volume after a fatty meal was greater in the gastrectomized group (12.6 +/- 6.4 ml) than in the control group (4.3 +/- 3.3 ml) (p < 0.01). A significant reduction of ejection fraction was found in gastrectomized patients (56.9 +/- 13.0%) in comparison with the control group (75.5 +/- 16.1%) (p < 0.01). The GB ejection fraction had a poor correlation to the postoperative period (r = 0.232). CONCLUSION: A gastrectomy appears to be a risk factor of GB dysmotility, which may play a major role in gallstone formation in gastrectomized patients.

Adult↗
PubMed2000

Demographic, clinical, and neurocognitive correlates of everyday functional impairment in severe mental illness.

Although cognitive deficits often accompany severe mental illness, their implications for everyday functioning remain poorly understood. In this study, an occupational therapist (OT) rated the everyday functioning of 105 adult psychiatric patients. Using demographic, clinical, and cognitive variables, the authors tested alternative models to account for the observed variability in OT ratings. Although age, education, and the presence of schizophrenia each contributed to a model that accounted for 27% of the variation in functional independence, adding terms for auditory divided attention and verbal learning increased the proportion of explained variance to 45% and decreased the beta weights for age and education--but not schizophrenia--to nonsignificant levels. These findings demonstrate the relevance of cognitive performance to everyday functioning in severe mental illness. They are discussed with respect to hypothesized determinants of psychiatric disability.

Activities of Daily Living↗
PubMed2000

Theophylline, pentostatin (Nipent), and chlorambucil: a dose-escalation study targeting intrinsic biologic resistance mechanisms in patients with relapsed lymphoproliferative disorders.

In spite of the chemosensitivity seen with the initial treatment of malignant lymphoid disorders, relapse is common and death most often occurs as a result of disease progression. This is related to a multitude of resistance mechanisms associated with the various lymphoproliferative disorders. As a result, therapies targeting intrinsic drug-resistance mechanisms are evolving and have become an active area of research. In vitro studies of human chronic lymphocytic leukemia cells incubated with theophylline, a phosphodiesterase inhibitor, resulted in downregulation of bcl-2 concomitant with induction of apoptosis. We describe the preclinical basis for a novel combination therapy involving pentostatin (Nipent; SuperGen, San Ramon, CA), chlorambucil, and theophylline in the treatment of patients with relapsed chronic lymphoproliferative disorders. An ongoing study based on such justification, which is currently accruing patients, is also described. Results from this trial appear promising, and a phase II study is now being planned.

Antibiotics, Antineoplastic↗
PubMed2000

Deletion of one adenine base within the polyadenine tract of transforming growth factor-beta receptor type II in human MDA-MB-231 breast cancer cell line.

Microsatellite mutation of the polyadenine tract (10 adenine repeat) within the TbetaR-II [transforming growth factor-beta (TGF-beta) receptor type II] coding region have been found in a variety of human cancers, particularly in association with microsatellite instability (MSI). Since breast cancers have been reported to carry MSI, although its frequencies were quite variable, we examined whether microsatellite mutation of the polyadenine tract occurs in the human breast cancer MDA-MB-231 cell line. TbetaR-II expression in MDA-MB-231 was found to be low on our Northern and Western analyses. Sequencing analysis for the polyadenine tract of TbetaR-II cDNA obtained from MDA-MB-231 cells indicated heterozygous deletion of one adenine base. Subsequently, sensitivity to TGF-beta induced growth-inhibitory effects of control and TbetaR-II transfected MDA-MB-231 cells was compared. The sensitivity of TbetaR-II transfectants to exogenous as well as endogenous TGF-beta1 was increased distinctly compared with control transfectant. These results suggest that heterozygous deletion of one adenine base within the polyadenine tract in MDA-MB-231 cells might lead to reduced TbetaR-II expression and sensitivity to TGF-beta.

Adenine↗
PubMed2000

A review of the literature for whole-body FDG PET in the management of patients with melanoma.

BACKGROUND: A review and meta-analysis of the literature on the use of 2-[18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in the detection of recurrent melanoma was conducted. The goals were to evaluate the quality of data reporting and to determine the overall values for the sensitivity and specificity of whole body FDG PET and management changes. METHODS: Guidelines to evaluate reporting within articles were formulated based on the United States medical payer source criteria for assessing studies reporting information on the utilization of new medical technology. A meta-analysis was conducted using methodology described in the peer reviewed literature. RESULTS: Our MEDLINE PLUS search resulted in a universe of 89 total articles. Within these 89, 19 were categorized in our targeted content area of which 13 were selected for analysis in our targeted subset, with the remaining 70 covering 24 different related content areas. Five of 13 (38%) articles in the target subset reported data which was adequate for incorporation into modeling objectives based on PET sensitivity and specificity values, with 1 of 13 (8%) in the same target subset reporting data adequate for modeling based on change-in-management data. Through a meta-analysis of the 13 target articles we determined, within a 95% confidence level, an overall sensitivity of 92% (95% confidence level 88.41%-95.82%) and an overall specificity of 90% (95% confidence level 83.26%-96.05%) as calculated by number of lesions, for FDG PET detecting recurrent melanoma throughout the whole body. Furthermore, limited data available for change-in-management suggests an overall FDG PET directed change-in-management value of 22%. CONCLUSIONS: Our review suggests that improvements can be made to more effectively report the results of these FDG PET studies. The overall values determined through the meta-analysis indicate the potential benefits of using FDG PET as a diagnostic/management tool. Furthermore, these values should prove useful to assessing the cost effectiveness of utilizing FDG PET in the management of recurrent melanoma.

Confidence Intervals↗
PubMed2000

The effect of carbonated beverages on colorimetric end-tidal CO(2) determination

Esophageal intubation is a significant complication of attempted airway control. Colorimetric end-tidal CO(2) monitors are highly sensitive and specific for detecting the presence of CO(2). There are reports of false-positive end-tidal CO(2) readings from esophageal intubations in patients who had ingested carbonated beverages. OBJECTIVE: To determine whether carbonated gastric contents can affect colorimetric end-tidal CO(2) readings. METHODS: End-tidal CO(2) was measured in sacrificed piglets at measured time intervals after instillation of 5-, 10-, 15-, and 20-mL aliquots of Diet Coke were placed into the stomach via a 28-French orogastric tube followed by esophageal intubation. The stomach was completely evacuated prior to each instillation and rechecked for baseline CO(2). RESULTS: Compiled data from three piglets (20-30 kg). Piglets were not ventilated or moved and determinations were measured at 20 degrees while supine. All data collected within 2 hours postmortem (table 24-1). CONCLUSIONS: The colorimetric end-tidal CO(2) turned "yellow" and did not change to blue with extended insufflations. The CO(2) of a small quantity of carbonated beverage in the stomach could be "blown off" by multiple insufflations. We conclude that esophageal intubation in the setting of recent ingestion of a carbonated beverage may result in a false-positive end-tidal CO(2) determination.

Journal Article↗
PubMed1999

Z-curve: a computer program calculating DNA helical axis coordinates for three-dimensional graphic presentation of curvature.

In order to predict curvature of DNA fragments, we previously developed a computer program for simply calculating a vectorial sum of all individual roll, tilt and twist wedge angles between the nearest base pairs for a given DNA fragment [Lee et al., (1991)]. Now, a new program, called Z-curve, was developed to calculate three-dimensional coordinates of the helical center of each base pair along the DNA, using helical axis deviations from B-form DNA by wedge angles. The output file of the new program was designed to become an input file for a graphics program, Insight II. Thus, we were able to obtain three-dimensional graphic presentations of DNA helical axis curvatures of any length. It visualized spatial details of the DNA curvature, where and how much it curves, and to which direction. It also allowed calculation of the three-dimensional distance between two ends of a DNA fragment, which could provide a measure of its curvature. Here, three DNA fragments, both curved and straight, were subjected to the Z-curve and Insight II programs. The results showed that their curvature details could be visualized to the level of the base pair, whether the DNA fragments contained an oligo(A) track or not. Their estimated curvatures were consistent with the experimental results of permutation gel mobility assay.

Algorithms↗