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Biomedical subjects

D M Kim

Publications and source records attributed to D M Kim.

At least 19 recordsLinked to original sources
PubMed2006

Probing nanoscale ferroelectricity by ultraviolet Raman spectroscopy.

We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature (Tc) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO3 layers in BaTiO3/SrTiO3 superlattices are not only ferroelectric (with Tc as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. Tc was tuned by approximately 500 kelvin by varying the thicknesses of the BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.

Journal Article↗
PubMed2006

Electrical control of antiferromagnetic domains in multiferroic BiFeO3 films at room temperature.

Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. In this work, we demonstrate the first observation of electrical control of antiferromagnetic domain structure in a single-phase multiferroic material at room temperature. High-resolution images of both antiferromagnetic and ferroelectric domain structures of (001)-oriented multiferroic BiFeO3 films revealed a clear domain correlation, indicating a strong coupling between the two types of order. The ferroelectric structure was measured using piezo force microscopy, whereas X-ray photoemission electron microscopy as well as its temperature dependence was used to detect the antiferromagnetic configuration. Antiferromagnetic domain switching induced by ferroelectric polarization switching was observed, in agreement with theoretical predictions.

Journal Article↗
PubMed2006

Stabilization of monodomain polarization in ultrathin PbTiO3 films.

Using in situ high-resolution synchrotron x-ray scattering, the Curie temperature TC has been determined for ultrathin c-axis epitaxial PbTiO3 films on conducting substrates (SrRuO3 on SrTiO3), with surfaces exposed to a controlled vapor environment. The suppression of TC was relatively small, even for the thinnest film (1.2 nm). We observe that 180 degrees stripe domains do not form, indicating that the depolarizing field is compensated by free charge at both interfaces. This is confirmed by ab initio calculations that find polar ground states in the presence of ionic adsorbates.

Journal Article↗
PubMed2005

Prevalence of obesity in Korea.

During the past decade, obesity has substantially increased in Korea, and this is leading to dramatic increases in complications such as type 2 diabetes. In this review, we discuss the past and the current situation of obesity in Korea based on the national health and nutrition surveys of 1995, 1998, and 2001. Because Korea is geographically isolated with relatively few migrants and has a low level of genetic heterogeneity, this report demonstrates the impact of environmental factors on the development of obesity beyond epidemiological information about one of the Asian countries. The third national health and nutrition survey reported in 2001 announced that the overall prevalence of obesity [body mass index (BMI) > or = 25.0 kg m(-2)] in Korean adults is 30.6% (32.4% in men and 29.4% in women). The prevalence of obesity in adults and children has increased rapidly from 1990s through the beginning of the new millennium and is steadily increasing in parallel with our rapid socio-economic progress. In particular, special attention should be paid to two groups in hormonal transition: first, middle-aged men and women who experience a great increase in body weight, BMI and waist circumference because of andropause or menopause, and second, adolescents in middle to high school who are preparing for qualification or entrance examinations and are prone to overnutrition or nutritional imbalance and physical inactivity.

Adolescent↗
PubMed2004

Sibutramine improves fat distribution and insulin resistance, and increases serum adiponectin levels in Korean obese nondiabetic premenopausal women.

The aim of this study was to evaluate the effects of sibutramine on body composition and fat distribution, insulin resistance, and serum adiponectin levels in obese women. A total of 28 obese, premenopausal women (mean age, 34.5 +/- 13.7 years; BMI, 31.00 +/- 4.10 kg/m2) was studied before and after 12-week-course of sibutramine (10mg/day). Sibutramine treatment reduced body mass index (P < 0.05) and total body fat (P < 0.05). Abdominal subcutaneous and visceral fat areas (ASFA and AVFA) and mid-thigh low density muscle areas (LDMA) measured by computed-tomography decreased significantly (all, P < 0.05). Insulin resistance (IR) calculated from the homeostasis model assessment (HOMA) method decreased (P < 0.05) and serum adiponectin levels increased significantly (P < 0.05). In our sequential data, the changes of fasting serum insulin levels and the HOMA-IR scores, serum free fatty acids and triglyceride levels, serum adiponectin levels and the mid-thigh LDMA preceded significant changes of body weight, total body fat, and abdominal fat distribution, suggesting sibutramine might improve insulin sensitivity directly by alterations of fatty acid metabolism or secondarily by increasing serum adiponectin levels. Conclusively, sibutramine improved fat distribution and insulin resistance, and increased serum adiponectin levels in Korean obese nondiabetic premenopausal women.

Adiponectin↗
PubMed2004

An implication of hypertriglyceridemia in the progression of diabetic nephropathy in metabolically obese, normal weight patients with type 2 diabetes mellitus in Korea.

This study was undertaken to investigate diverse risk factors affecting the progression of diabetic nephropathy (DN) by observing the changes of 24 h urinary albumin excretion (24 h UAE) in 90 abdominally obese, normal weight, type 2 diabetic patients with normo- or micro-albuminuria. Patients were divided into three groups according to the 24h UAE; normo-, micro-, and macro-albuminuria group. After 4 years of follow-up, patients were divided into either progression or non-progression group according to the changes of 24 h UAE. About 37% of the normo-albuminuria group and 18% of the micro-albumiuria group were classified into the progression group. The initial serum creatinine levels and the initial and follow-up post-prandial plasma glucose levels were significantly higher in the progression group than in the non-progression group. Most remarkably, the initial and follow-up serum triglyceride (TG) levels (190 +/- 132 versus 132 +/- 49 mg/dl and 191 +/- 124 versus 133 +/- 41 mg/dl, P < 0.01 in both) were significantly higher in the progression group than in the non-progression group, suggesting hypertriglyceridemia might be included in the progression factors of DN. The increases in 24-hour UAE were positively associated with the initial and follow-up post-prandial plasma glucose levels (P < 0.05 in both), the initial and follow-up serum creatinine levels (P < 0.05 in both), and the initial serum TG levels (P < 0.05). Whereas, insulin users or patients with retinopathy at follow-up (P < 0.05 in both) showed more rapid progression of albuminuria, ACE inhibitors or acarbose (P < 0.05 in both) use turned out to protect against it.

Albuminuria↗
PubMed2004

Insulin sensitivity in physically fit and unfit children of parents with Type 2 diabetes.

AIMS: First-degree relatives of patients with Type 2 diabetes mellitus (T2DM) are often reported to be insulin resistant. We wanted to identify early metabolic abnormalities in this condition, and determine whether they are altered by regular physical training. METHODS: We measured insulin sensitivity using the euglycaemic glucose clamp technique and insulin response to oral glucose in 10 unfit (did not participate in routine physical exercise) offspring of T2DM parents and 10 unfit control subjects, and compared them with six fit (routinely swam for 3 h/day 5 days/week) offspring of T2DM parents and six fit controls with no family history of T2DM. RESULTS: Unfit offspring had a higher plasma glucose response than the other three groups. The mean area under the glucose curve was also significantly higher in unfit offspring than in the other three groups (12.6 +/- 0.6 vs. 10.4 +/- 0.4, 9.6 +/- 0.5, and 9.5 +/- 0.7 mmol/l per hour for the unfit controls, fit offspring and fit controls, respectively; P < 0.05). The corresponding insulin response of unfit offspring was significantly higher at 60 min in the oral glucose tolerance test (OGTT) that that of fit offspring or fit controls. In addition, the mean area under the insulin curve was significantly greater in unfit offspring than in either fit offspring or fit controls (868 +/- 172 vs. 294 +/- 71, 287 +/- 43 mmol/l per hour, respectively; P < 0.05). Moreover, the glucose disposal rate (GDR), measured using a euglycaemic clamp, was significantly lower in unfit and fit offspring than in unfit and fit controls (5.6 +/- 0.3 vs. 8.6 +/- 0.3 mg/kg per minute; P < 0.01 and 9.3 +/- 0.9 vs. 12.1 +/- 0.8 mg/kg per minute, respectively; P < 0.015), whereas the GDR was similar in unfit controls and fit offspring (8.6 +/- 0.4 vs. 9.3 +/- 0.9 mg/kg per minute; P > 0.05). CONCLUSION: These results support the concept that early metabolic abnormalities, as reflected by a decreased GDR (insulin sensitivity) in the offspring of T2DM patients, may be improved by increased physical fitness.

Administration, Oral↗
PubMed2003

Comparison of localised nerve fibre layer defects in normal tension glaucoma and primary open angle glaucoma.

AIM: To compare the pattern of localised nerve fibre layer (NFL) defects in normal tension glaucoma (NTG) and primary open angle glaucoma (POAG). METHODS: 50 NTG eyes and 36 POAG eyes, all with localised NFL defects, were enrolled. On retinal NFL photography, the proximity of the defect to the centre of the fovea (angle alpha) and the sum of the angular width of the defects (angle beta) were determined. Angle alpha was the angle made by a line from the centre of the fovea to the disc centre and a line from the disc centre to the disc margin, where the nearest border of the defect met. The patterns of localised NFL defects in NTG and POAG were compared with angles alpha and beta. Independent t test was used for statistical analysis. RESULTS: Angle alpha in NTG (35.1 (SD 20.0) degrees ) was significantly smaller than that of POAG (45.9 (21.9) degrees ) (p=0.02), while angle beta in NTG (49.0 (31.9) degrees ) was significantly larger than that of POAG (33.1 (23.9) degrees ) (p=0.01). CONCLUSIONS: The pattern of NFL defects in NTG was different from that in POAG. Localised NFL defects in NTG were closer to the fovea and wider in width than those in POAG.

Adult↗
PubMed2001

Regeneration of adenosine triphosphate from glycolytic intermediates for cell-free protein synthesis.

A new approach for adenosine triphosphate (ATP) regeneration in a cell-free protein synthesis system is described. We first show that pyruvate can be used as a secondary energy source to replace or supplement the conventional secondary energy source, phosphoenol pyruvate (PEP). We also report that glucose-6-phosphate, an earlier intermediate of the glycolytic pathway, can be used for ATP regeneration. These new methods provide more stable maintenance of ATP concentration during protein synthesis. Because pyruvate and glucose-6-phosphate are the first and last intermediates of the glycolytic pathway, respectively, the results also suggest the possibility of using any glycolytic intermediate, or even glucose, for ATP regeneration in a cell-free protein synthesis system. As a result, the methods described provide cell-free protein synthesis with greater flexibility and cost efficiency.

Adenosine Triphosphate↗
PubMed2001

Accuracy of predonation Hct sampling affects donor safety, eligibility, and deferral rates.

BACKGROUND: Safe blood donation depends upon reliable predonation Hct screening. Earstick (ES) capillary samples are frequently used, but they may not be accurate. STUDY DESIGN AND METHODS: Predonation ES and fingerstick (FS) and postdonation venous Hct results were compared in 1960 whole-blood and 210 apheresis donors. The validity of using postdonation venous samples to evaluate predonation ES and FS Hct was assessed in 20 whole-blood donors. The impact of Hct screening method on donor Hct deferrals was examined during periods when either ES or FS sampling was used exclusively. RESULTS: All donors were eligible to donate on the basis of a predonation capillary Hct of > or = 38 percent. In venous samples obtained immediately after donation, 36 percent of whole-blood donors had a Hct <38 percent. With correction for a decrease of approximately 2 Hct units during donation, 20 percent of these donors had a predonation Hct <38 percent. The lowest venous Hct was 23.1 percent. FS samples showed better correlation with venous Hct. Hct discrepancies were similar for apheresis donors. Hct deferrals were significantly higher with FS sampling, especially among women. CONCLUSION: Hct determinations from ES samples overestimate venous Hct. Fingerstick samples are more sensitive in detecting anemia. The accuracy of predonation Hct sampling has implications for donor safety, eligibility, and deferral rates.

Blood Component Removal↗
PubMed2000

Asp41-His48 region of streptokinase is important in binding to a substrate plasminogen.

Streptokinase is a plasminogen activator protein produced by several strains of beta-hemolytic streptococci. Random mutagenesis of streptokinase was carried out for the determination of critical amino acid residues in plasminogen activation. We selected and sequenced 14 streptokinase mutants with no plasminogen activation activity on skim milk-plasminogen overlay plate. Specific activities of the selected streptokinase mutants were determined with chromogenic assay. Eight mutants (V19F, V35E, E85D, L292R, D325P, D341E, I345N, and M369L) resulted in greatly decreased amidolytic activities. However, unexpectedly, six mutants (D41C, S44K, S44P, R45P, H48T, and D220G) showed substantial amidolytic activities comparable to that of wild type. Moreover, five-point mutations were concentrated on the Asp41-His48 region. These data indicate that the Asp41-His48 region in a streptokinase-plasminogen binary complex plays an important role in binding to a substrate plasminogen.

Amidohydrolases↗
PubMed2000

Elevated glutamate levels in the vitreous body of an in vivo model of optic nerve ischemia.

OBJECTIVE: To explore the possibility that an elevation of glutamate levels in the vitreous might be associated with the microvascular compromise of the optic nerve. MATERIALS AND METHODS: Endothelin-1, 0.1 microg/d (5 rabbits), or balanced salt solution (4 rabbits) was delivered to the perineural region of the anterior optic nerve by osmotically driven minipumps for 2 weeks. Vitreous specimens were obtained, and their amino acid contents were determined by high-performance liquid chromatography. RESULTS: There was a statistically significant elevation in the mean +/- SEM vitreous concentrations of glutamate (264% +/-41%; P = .04), aspartate (269% +/-31%; P = .04), and glycine (232% +/-26%; P = .04) in the eyes subjected to endothelin-1 when compared with the fellow control eyes. CONCLUSION: Administration of endothelin-1 to the microvasculature of the optic nerve leads to elevation of glutamate, aspartate, and glycine concentrations in the vitreous. CLINICAL RELEVANCE: The increase of excitatory amino acids in the vitreous might be associated with various ischemic processes of the optic nerve, including glaucomatous optic neuropathy, and may play a role in the neuronal damage that is seen in these diseases.

Animals↗
PubMed2000

Platelet adhesion onto segmented polyurethane film surfaces modified by addition and crosslinking of PEO-containing block copolymers.

Polyethylene oxide (PEO) surfaces were prepared by the addition of PEO-containing amphiphilic block copolymers as surface modifying additives and of dicumyl peroxide (DCP) as a crosslinking agent in segmented polyurethane (PU). PEO-polypropylene oxide-PEO triblock copolymers (Pluronics) with different PEO chain length (from 0 to 98) were used as the surface modifying additives. The PEO additives in the PU film were then crosslinked to be stably entrapped in the PU matrix. The crosslinking was done by free radicals produced from the decomposition of DCP in the film through heating (120 degrees C) or ultraviolet irradiation (254 nm). The surface properties of the PEO additive-entrapped PU films were investigated by the measurement of water contact angles and electron spectroscopy for chemical analysis. The bulk properties such as water absorption, long-term film stability, and tensile strength and elongation at break, were also investigated. It was observed that addition of a small amount (5 wt% based on PU) of the PEO additives resulted in a considerable change of surface characteristics. The PEO additives were stably entrapped in the PU films by crosslinking of them, without significant changes of bulk properties of the films. From the platelet adhesion test on the prepared PEO additive-containing film surfaces, it was observed that the platelet adhesion on the surfaces decreases with increase in PEO chain length of PEO additives. The film surface containing additive with long PEO chains (chain length of 98) was particularly effective in preventing platelet adhesion. The crosslinking of the PEO additives in PU films did not affect the behavior of platelet adhesion on the surfaces; the films with crosslinked PEO additives showed similar platelet adhesion on the surfaces to the films with uncrosslinked ones.

Biocompatible Materials↗
PubMed2000

Effects of heat processing and storage on flavanols and sensory qualities of green tea beverage.

This research was conducted to understand the effects of heat processing and storage on flavanols and sensory qualities of green tea extract. Fresh tea leaves were processed into steamed and roasted green teas by commercial methods and then extracted with hot water (80 degrees C) at 1:160 ratio (tea leaves/water by weight). Green tea extracts were heat processed at 121 degrees C for 1 min and then stored at 50 degrees C to accelerate chemical reactions. Changes in flavanol composition and sensory qualities of green tea extracts during processing and storage were measured. Eight major flavanols (catechin, epicatechin, gallocatechin, epigallocatechin, epicatechin gallate, catechin gallate, epigallocatechin gallate, and gallocatechin gallate) were identified in the processed tea extract. Among them, epigallocatechin gallate and epigallocatechin appeared to play the key role in the changes of sensory qualities of processed green tea beverage. The steamed tea leaves produced a more desirable quality of processed green tea beverage than the roasted ones.

Flavonoids↗
PubMed2000

Enhancement of secretion and extracellular stability of staphylokinase in Bacillus subtilis by wprA gene disruption.

Staphylokinase (SAK), a polypeptide secreted by Staphylococcus aureus, is a plasminogen activator with a therapeutic potential in thrombosis diseases. A Bacillus subtilis strain which is multiply deficient in exoproteases was transformed by an expression plasmid carrying a promoter and a signal sequence of subtilisin fused in frame with the sak open reading frame. However, the amount of SAK secretion was marginal (45 mg/liter). In contrast, disruption of the wprA gene, which encodes a subtilisin-type protease, strongly promoted the production of SAK in the stationary phase (181 mg/liter). In addition, the extracellular stability of mature SAK was dramatically enhanced. These data indicate a significant role of the wprA gene product in degrading foreign proteins, both during secretion and in the extracellular milieu.

Bacillus subtilis↗